Sports-Related Muscle Injury
in the Lower Extremity
Derek R. Armfield, MDa,b,*, David Hyun-Min Kim, MDc,
Jeffrey D. Towers, MDa, James P. Bradley, MDd,
Douglas D. Robertson, MD, PhDa,b
aDepartment of Radiology, University of Pittsburgh Medical Center, 200 Lothrop Street,
Pittsburgh, PA 15213, USA
bJefferson Regional Medical Center, 565 Coal Velley Road, Pittsburgh, PA 15236, USA
cUniversity of Southern California, Department of Radiology, 1500 San Pablo Street,
Los Angeles, CA 90033, USA
dBurke and Bradley Orthopaedics and Department of Orthopaedic Surgery, University
of Pittsburgh Medical Center, 200 Lothrop Street, Pittsburgh, PA 15213, USA
30% of injuries with the quadriceps (32%), hamstring (28%), adductor (19%),
and gastrocnemius (12%) muscle injuries being the most common . Treat-
ment typically consists of rest, ice, compression, elevation, and stretching and
rehabilitation. Programs are designed to treat and prevent, as those with prior
injuries are prone to recurrence. This problem is particularly important in elite
athletes where decisions regarding return to play and player performance can
have significant financial or strategic consequences for the player and team.
This paper reviews the basic imaging techniques and the pertinent findings
associated with common muscle injuries of the lower extremity, and emphasizes
the imaging features, whichcan help guide treatmentandofferprognosis. A gen-
eral overview of muscle injury and imaging modalities is provided followed by
a more detailed analysis of injuries to specific muscle groups of the lower ex-
tremity including the hamstrings, quadriceps, adductors, and lower leg muscles.
uscle injuries are common and often occur during sport or training
with over 90% caused by excessive strain or contusion . A 5-year
study of European soccer players showed muscle strain represented
TYPES OF MUSCLE INJURY
There are many different sizes and shapes of muscle. Some are long like the
biceps femoris with tendon insertions on bone at both ends and cross two joints
(biarticular). Others are short with a single tendon insertion spanning a single
*Corresponding author. Department of Radiology, University of Pittsburgh Medical Center,
200 Lothrop Street, Pittsburgh, PA 15213.
E-mail address: email@example.com (D.R. Armfield).
0278-5919/06/$ – see front matter
ª 2006 Elsevier Inc. All rights reserved.
Clin Sports Med 25 (2006) 803–842
CLINICS IN SPORTS MEDICINE
joint like the popliteus. Some have long muscle bellies (sartorius) whereas others
have long tendons (plantaris). Some have muscle fibers aligned with tendons in
a colinear fashion (unipennate) whereas others have muscle fibers inserting at
an angle on an intramuscular tendon (bipennate), which increases muscle fiber
density and ultimately contractile forces (ie, hamstrings, rectus femoris).
What they have in common is a propensity for injury at the interface of two
different materials namely muscle and tendon typically referred to as the my-
otendinous junction [3,4]. The term musculotendinous junction has also been
used synonymously. It is important to note that the typical connotation of a my-
otendinous junction is that of a specific focal point at either the proximal or dis-
tal aspect of a muscle before tapering to the tendon insertion. However the
hamstring and quadriceps tendons have large intramuscular or central tendons
and injury often occurs along this interface [5,6].
Most sports-related muscle injuries involve strains, contusions, and uncom-
monly lacerations. Muscle strains or tears often affect muscles with primarily
fast-twitch type-2 muscle fibers, span two joints (biarticular), and undergo ec-
centric contraction . As mentioned earlier, strain injuries typically occur at
the myotendinous junction. However, strains have also been described involv-
ing the periphery of a muscle (instead of the myotendinous junction) extending
to the epimysium seen with ultrasound and MRI [8,9]. Based on the patient’s
age and the underlying condition of the tendon itself, injury can occur any-
where along the muscle-tendon-bone chain . For example those with degen-
erated tendon because of aging or chronic use may develop a tear of the tendon
itself. Those with strong tendons may experience an avulsion of the tendon
from the bone or myotendinous strain. In skeletally immature patients, an
apophyseal avulsion may occur, as this junction biomechanically represents
the weakest interface.
Strains are often diagnosed clinically on a three-point scale: 1 ¼ mild, 2 ¼
partial tear, 3 ¼ complete . Mild injuries have no discernable loss of
strength or motion restriction. Partial tears demonstrate some loss of strength
and motion that is not complete, unlike type 3 injuries . Strain injury is as-
sociated with inflammation, edema, and sometimes hemorrhage with prolifer-
ation of inflammatory cells and fibroblastic activity in the first 24 to 48 hours
. Histological animal models of muscle stretch injury have shown that my-
otendinous injury results in inflammation, bleeding, and muscle fiber necrosis
initially. This destructive phase is followed by a concomitant repair and remod-
eling phase involving recruitment of progenitor cells, scar formation, and re-
modeling of organized tissue .
Because of the common nature of these injuries, many muscle strains are
treated clinically. However the clinical scenario may be unclear and grading
of injury may be difficult. Imaging may help delineate the presence and extent
of muscle injury. The main modalities used for evaluation almost exclusively
include MRI and ultrasound.
804ARMFIELD, KIM, TOWERS, ET AL
Radiographs are useful for evaluating bony avulsion injuries in adolescents
particularly of the pelvis that can be missed with MR and ultrasound. Subtle
areas of soft tissue swelling and unexpected bone-related problems (tumor,
stress fracture, and so forth) might be detected with plain films. While cross-sec-
tional imaging findings of muscle strain were originally described with com-
puted tomography (CT), currently CT has little role for evaluating acute
muscle injury because of its relative lack of tissue contrast as compared with
MR . It is useful to evaluate osseous structures associated with avulsion in-
juries and complications like myositis ossificans.
At some institutions ultrasound may be the preferred primary modality for
evaluation of muscle injury because of its portability, ease of use, and decreased
cost. While ultrasound does have excellent spatial resolution, the contrast res-
olution is not as good as MR particularly in the subacute or chronic phases
when injury-related edema begins to resolve. Also, because sound waves dissi-
pate and do not reflect over long distances, evaluation of deep structures in ath-
letes with bulky musculature may be difficult. Evaluation of more superficial
structures such as the patellar tendon is easier with ultrasound. Another rela-
tive disadvantage is the significant reliance on operator skill and expertise
that can only be achieved with dedication and practice.
At our institution we prefer evaluation of muscle injuries with MR because
of its superior soft tissue contrast, excellent spatial resolution, and reproducibil-
ity. Our typical protocol uses a combination of T1- and T2-weighted sequences
to emphasize anatomy and pathologic edema. Fatty structures appear bright on
T1-weighted images (and some T2-weighted images, ie, fast spin echo) and
muscle has intermediate signal intensity allowing for excellent anatomic detail
of fat planes. In general, fluid-sensitive or T2-weighted images, allow easy visu-
alization of mobile water protons, which means that pathologic processes in-
volving edema, like muscle strains, are easily detected. Contrast resolution is
increased when fat signal is nullified on fast spin echo T2-weighted images
with specific chemical fat-saturation pulse (ie, fat saturation). Alternatively,
fluid sensitivity may be achieved when a more diffuse nullifying signal is em-
ployed that limits non-water signal (ie, inversion recovery [IR] or STIR se-
quences). Either sequence is considered fluid sensitive and essential for the
evaluation of muscle strain injury.
Anatomic coverage includes long and short axis imaging of the region or
muscle of interest. We generally use a body coil to include both thighs and
lower legs depending on the area of concern to allow for comparative analysis
of anatomy in the symptomatic and asymptomatic extremity. Others prefer
dedicated unilateral imaging of the injured extremity. Studies have shown
that hamstring injuries can occur at multiple sites and involve multiple muscles
and therefore thorough evaluation along the course of the muscle group is
needed not just the area of pain [9,13,14].
For the screening protocol of the thigh or lower leg we include coronal T1,
coronal IR, axial T1, and axial T2 fat-saturated images. Depending on the clin-
ical scenario we may add additional sagittal T1 or fluid-sensitive sequences
805LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
perhaps in the case of an ischial tuberosity avulsion. The important concept is
to include short and long axis imaging of the structures of interests with T1 and
fluid-sensitive sequences for each.
Intravenous gadolinium contrast is used very sparingly for routine cases of
clinically suspected muscle injury. Some have suggested that low-grade injuries
that appear normal on fluid-sensitive sequences may be seen with postintra-
venous contrast imaging although this report was only a case series of four
athletes with high clinical suspicions of injury . Others have found intrave-
nous contrast imaging useful for evaluating symptomatic proximal adductor
insertional injuries. These contrast-enhanced images revealed enhancing teno-
periosteal granulation tissue associated with symptoms and partial healing .
Contrast should be used when cases of infection, tumor, or myositis are within
the differential (Fig. 1).
MR appearance of myotendinous injury has been well described [10,17–20].
Type 1 injuries demonstrate bright signal on fluid-sensitive sequences repre-
senting fluid and hemorrhage around the myotendinous unit extending into
the adjacent muscle creating a feathery appearance. The myotendinous junc-
tion usually appears normal and there is typically less than 5% involvement
of muscle fibers (Fig. 2A). Type 2 injuries of the myotendinous junction are
more severe and may show a thin or irregular appearance of the myotendinous
junction itself along with edema and hemorrhage (increased T2 signal inten-
sity) that often tracks along the fascial plane. However, increased T2 signal in-
tensity changes in strain injury may not necessarily be related to hemorrhage.
One recent study evaluated hamstring strain injuries and included gradient se-
quences, which are highly sensitive for detecting blood products, and found
only 1 case of 37 had the typical blooming artifact associated with blood prod-
ucts . Another article has characterized hematoma as a pathognomonic find-
ing of type 2 injury  (Fig. 2B). Type 3 injuries reveal complete disruption
Fig. 1. (A) Enhanced axial T1-weighted image with fat saturation of the calf showing enhanc-
ing muscle with areas of nonenhancement compatible with necrosis in this patient found unre-
sponsive. (B) Peripheral enhancement of the calf muscles in a patient with dermatomysositis.
806ARMFIELD, KIM, TOWERS, ET AL
and discontinuity of muscle typically at the myotendinous junction with
complete replacement of organized collagen with fluid signal on fluid sensitive
sequences. There is often an associated wavy tendon morphology and retrac-
tion. Surrounding edema or hemorrhage is usually extensive (Fig. 2C). MR
findings usually correlate with the clinical grading scheme and can help differ-
entiate mild injury from partial tears and referred pain in clinically indetermi-
nate cases .
Epimyseal or peripheral injury not associated with myotendinous injury has
also been described in the hamstring and quadriceps muscles and manifests as
peripheral edema in the muscle extending to and around the epimysium [8,9].
Contusions of muscle are a result from direct trauma (ie, football helmet), and
may predispose to hematoma formation. Infiltrative focal edema is a typical
finding on fluid-sensitive sequences and may resemble muscle strain. MR ap-
pearance of contusion is typically that of increased size with intact muscle fibers
Fig. 2. Coronal fluid sensitive images of posterior thighs demonstrating (A) Type 1 muscle
strain injury with mild feathery edema along the intramuscular myotendinous junction of biceps
femoris in a professional football wide receiver; (B) Type 2 injury of the proximal myotendinous
junction of biceps femoris with intramuscular hematoma formation; and (C) Type 3 injury prox-
imal biceps femoris with retraction of the tendon (arrow) in a professional football cornerback.
807LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
and increased fluid signal that is diffuse or geographic with feathery margins
 (Fig. 3).
Hematoma may result from direct trauma associated with contusion or re-
lated to myotendinous injury and subsequent bleeding. MRI and ultrasound
helps assess size and location and determine if it is intermuscular or intramus-
cular in nature. Large hematomas may result in compartment syndrome or sig-
nificant pain and aspiration may be needed.
The MR appearance of hematomas can be variable depending on age and
magnetic field strength and T1- and T2-weighted images can help determine
the age and relative oxidative state of hemoglobin [22–24]. Acute hematomas
are usually isointense to muscle on T1-weighted images. T2-weighted images
show increased signal intensity possibly with central decreased signal related
to deoxyhemoglobin (Fig. 4A). Subacute hematomas (>48 hours) have in-
creased amounts of methemoglobin, which has increased T1 signal. Chronic
hematomas may have a peripheral dark rim related to hemosiderin. A seroma
may ultimately develop with resorption of blood products (Fig. 4B).
HAMSTRING MUSCLE COMPLEX
The hamstring complex is composed of three major muscles: biceps femoris
and semimembranosus and semitendinosus muscles. The biceps femoris is
composed of a long and short head. The long head arises on the medial aspect
of the posterior ischial tuberosity with a common tendon insertion with the
semitendinosus called the conjoined tendon  (Fig. 5A–D). Distally it inserts
on the fibular head. Depending on leg positioning and relationship to the
ground it can serve as a hip extensor, knee flexor, and external rotator of
the hip and knee (Fig. 5E,F).
The short head of the biceps tendon is not biarticular but has a proximal at-
tachment on the lateral aspect of the linea aspera below the gluteal tuberosity
and inserts distally on the fibular head . The short head of the biceps can be
absent, and unlike the long head that receives innervation via a tibial portion of
Fig. 3. Axial fluid sensitive image mid thigh shows increased fluid signal in rectus femoris con-
sistent with contusion. Note enlargement and diffuse edema in this soccer player that sustained
a direct blow to the thigh.
808 ARMFIELD, KIM, TOWERS, ET AL
the sciatic nerve, the short head receives innervation from the common pero-
neal nerve. This dual innervation has been hypothesized a source of potentially
discordant contraction which can lead to injury .
The semitendinosus is another biarticular muscle with a common origin of
the long head of the biceps femoris via the conjoined tendon (Fig. 5). Distally
it has a long tendon, which inserts on the proximal medial tibia posterior to the
sartorius. Its function is similar to that of the long head of biceps femoris al-
though because of its medial sided insertion distally it functions as an internal
rotator of the hip and knee. It has been classified as a digastric muscle owing to
a central raphe where the proximal fibers insert .
Semimembranosus is the third major muscle of the hamstring complex with
a proximal attachment on the ischial tuberosity anterior the conjoined tendon
(Fig. 5). The distal insertion is primarily on the medial posterior aspect of the
tibial plateau but has multiple slips extending to surrounding structures such as
the medial collateral ligament, and popliteus muscle . Its function is similar
to the semitendinosus.
The ischial tuberosity also has insertion sites of the sacrotuberous ligament
posteromedially in close proximity to the conjoined tendon insertion. The
Fig. 4. (A) Prominent acute intramuscular medial gastrocnemius hematoma. Note mixed in-
creased and decreased signal probably related to deoxyhemoglobin. (B) Intermuscular fluid
collection presumable a seroma from a resorbed gastrocnemius hematoma. Note dark rim
compatible with hemosiderin (arrow).
809LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
posterior head of the adductor magnus arises from the anterior inferior aspect
of the ischial tuberosity. This portion inserts distally on the adductor tubercle
and functions as a hip extensor, as well, but is not typically categorized with the
hamstring muscle complex.
Fig. 5. (A) Axial T1-weighted images of proximal thighs. Note how T1-weighted images al-
low good depiction of muscle fat planes. This image is proximal to the ischial tuberosity
and shows the sacrotuberous ligament (white arrow) insertion on the tuberosity. (B) Mid tuber-
osity level shows the anterior semimembranosus insertion (black arrow) and the posterior con-
joined tendon of biceps femoris and semitendinosus (white arrow). (C) Inferior aspect of ischial
tuberosity shows semimembranosus (black arrow) and conjoined tendon separating (white
arrow). Note origin of adductor magnus anteriorly (open arrow). (D) Continued separation
of the three tendons. (E) Distally the semitendinosus has a long tendon (arrow) and lies poste-
rior to the semimembranosus. sm, semimembranosus; s, sartorius; g, gracilis; bf, biceps femo-
ris. (F) Tendons of the posterior knee: semimembranosus (arrowhead), semitendinosus (white
arrow), gracilis (open arrow), biceps femoris (black arrow). lg, lateral gastrocnemius; mg,
810ARMFIELD, KIM, TOWERS, ET AL
Location of Injury and Imaging Prognosis
Intrinsic and extrinsic factors associated with recurrent hamstring injuries in-
clude inadequate warm-up, muscle fatigue, inadequate preseason training, mus-
cle strength imbalances, decreased flexibility, increasing age, and history of
prior injury . Some suggest that an injured muscle may heal with scarring
resulting in suboptimal muscle length that predisposes recurrent injury .
Because of the high risk of recurrent injury and variable convalescence pe-
riod, imaging may have a prognostic role in evaluating hamstring injuries, par-
ticular for the elite athlete where strategic and financial stakes can be high.
The first MR study that described findings with poor prognosis of muscle
injury evaluated 14 patients and found that muscle rupture and retraction,
hemorrhage, ganglion-like fluid collections, and greater than 50% cross-sec-
tional involvement were associated with convalescent periods of more than 6
A more recent study of 30 MRI-proven hamstring injuries in Australian
Rules football players showed high correlation with volume of involvement
(range 0.04 cm3to 175.6 cm3, median 16.8 cm3) and maximum cross-sectional
percentage (8 to 100, median 46%) with time lost from competition (13 to 48
days, median 27) . Linear fluid signal representing the length inter- and in-
tramuscular fluid and edema showed strong correlation but was not statistically
significant in this study. More injuries occurred distally (19 versus 11 defined as
above or below origin of biceps femoris short head) but there was no correla-
tion with location of injury and missed competition (Fig. 6).
One important concept to reiterate is the myotendinous junction was in-
volved in 28 of 30 cases with 24 of these cases involving the intramuscular ten-
don of the muscle and only 4 cases involving the conventional proximal or
distal myotendinous junctions. Five cases involved the intramuscular tendon
and then extended to the conventional myotendinous junction.
In terms of predicting recurrence and length of convalescence another study
imaged 31 Australian Rules footballers with clinical grade 1 injury. Forty-five
percent had a negative MR exam and returned to full team training in 6.6
days versus 20.2 days for the MR-positive group. In this study the length of
the injury had a stronger correlation coefficient than the cross-sectional areas
with the rehabilitation interval unlike the previously mentioned study. Six of
17 MR-positive cases developed recurrent strains with no correlation between
length or cross-sectional area as a predictor for recurrence .
Verrall and colleagues  also compared the clinical finding of posterior
thigh injury with MRI findings of hamstring strain. Again, not all clinically sus-
pected hamstring injuries had findings on MR for muscle strain. Of the 83
patients imaged, 68 (82%) had typical hyperintense signal on fluid-sensitive
images as interpreted by a musculoskeletal radiologist, compatible muscle
strain, whereas 12 (14%) had no signal change at all. The remaining three pa-
tients had MR evidence of muscle injury outside of the hamstring muscle com-
plex (lower gluteus maximus, vastus lateralis, and adductor magnus). Those
with MRI-detectable signal changes had more pain (5/10 versus 2/10), were
811LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
more likely to have acute onset, and missed more days from practice (27 versus
16 days) as compared with the group without MR findings of muscle strain.
The authors hypothesized that those without MR findings have a referred
pain syndrome or neuromeningeal cause of posterior thigh pain. Thus, MR
helps accurately define the extent and location of injury and helps define causes
of referred pain and types of injury that might heal more quickly.
fessional Americanfootballplayerexperience issomewhatdifferent asonestudy
showed that the majority of cases result in no loss from game competition .
The reported 13-year National Football League (NFL) experience from 1985
to 1998 found 431 hamstring injuries with 324 first-degree type and 107 second
and third-degree type injuries. The first-degree type injuries had no loss of prac-
tice or game time. Some of the more advanced cases with a focal palpable abnor-
mality(58 cases) atthe expected locationof the proximalmyotendinous junction
underwent intramuscular steroid injection within 72 hours. Average time loss
Fig. 6. Grade 1 strain of the distal semitendinosus muscle (A). Coronal T1 showing partial
tear of distal biceps femoris tendon in this professional football defensive back (B).
812 ARMFIELD, KIM, TOWERS, ET AL
until full practice was 7.6 days and the averagetrainingroom treatment time was
missed one game and one player missed two games. Those with more serious
injuries were not treated with injections.
Distribution of Injuries and Ultrasound versus MR
A review of 179 cases of injury to the hamstring muscle complex (HMC) using
ultrasound (102 cases) and MR (97 cases) showed there were 21 injuries in-
volving the proximal insertion on the ischial tuberosity with 16 tendon avul-
sions; 154 injuries of the muscle belly, and only 4 injuries of the distal
tendon or bone insertion site . Approximately 80% (124 cases) of injuries
involved the biceps femoris (54 proximal, 48 mid, and 22 distal); 61% involved
the myotendinous junction and 35% were considered epimyseal or involving
the periphery of the muscle. Multiple muscle involvement was only seen in
5% cases for these authors, others have shown using MR primarily that multi-
ple muscle injury occurs nearly 30% to 40% of the time [13,14,21].
MR correctly identified all of the proximal hamstring avulsion injuries (16/
16), whereas those patients who also underwent ultrasound evaluation had
the avulsion injury detected in slightly more than half of the patients (7/12)
(Fig. 7). The authors did find ultrasound useful for detecting distal superficial
injuries (fairly uncommon) involving the distal semitendinosus and semimem-
branosus tendons. Operator dependence and skill were noted to be a factor for
successful interpretation of muscle injury using ultrasound.
A more recent longitudinal study of hamstring muscle injures compares so-
nography with MR in 60 professional Australian Rules football players . All
players were imaged within 3 days, at 2 weeks, and 6 weeks with both modal-
ities. Sonography detected 45, 25, and 10 cases of injuries over the three time
frames and MR detected 42, 29, and 15 injuries respectively. All injuries ap-
peared larger (length and cross-section) on MRI at all time points. The length
of the tear measured on coronal images and the cross-sectional area on MRI
Fig. 7. Partial chronic tear of hamstring insertion seen on MRI coronal fluid sensitive images in
a former world-class female marathon runner.
813 LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
was thebestpredictorfortimeto returntocompetition. Tearsshowed decreased
cross-sectional involvement over time with both modalities. Ultrasonography
was found to be more useful for evaluating epimyseal injuries and MR better
for intramuscular tendon abnormalities. Distribution of injuries confirmed bi-
ceps femoris as being most commonly injured typically along the intramuscular
versus myotendinous junction injuries. This study also showed a relative infre-
quent association with multiple muscle injuries (about 5%). While ultrasound
was good, bulky musculature in athletes limited its use and overall, the authors
felt MR was the preferred modality for the elite athlete when there is concern for
optimizing rehabilitation and a need for follow-up imaging.
The quadriceps muscle group is composed of the rectus femoris and vastus
muscles (intermedius, lateralis and medialis) (Fig. 8). The primary mechanism
of action is knee flexion. Only the rectus femoris is biarticular. Proximally the
rectus femoris has a direct head insertion on the anterior inferior iliac spine and
an indirect head extending slightly laterally blending with the lateral aspect of
acetabulum and hip capsule . The direct head forms the anterior fascia of
the proximal third of the muscle whereas the indirect head continues centrally
located within the muscle and terminating at the distal aspect of the muscle
Proximal attachments of the vastus lateralis are multiple and include the in-
tertrochanteric line, anterior and inferior border of greater trochanter, lateral
gluteal tuberosity, upper linea aspera, and lateral intermuscular septum. Dis-
tally it inserts on the lateral border of the patella and patellar tendon.
Fig. 8. Axial T1-weighted imaging of the mid thigh showing muscle of the quadriceps group: l,
vastus lateralis; m, vastus medialis; i, vastus intermedius; q, rectus femoris.
814 ARMFIELD, KIM, TOWERS, ET AL
The proximal attachment of the vastus intermedius is the upper two thirds of
anterolateral surface of femur and distally attaches to the upper border of pa-
tella and patellar tendon.
Vastus medialis proximal attachments include the entire length of linea as-
pera and medial condyloid ridge with the distal attachment primarily involving
the medial half upper border of patella and the patellar tendon. The most distal
fibers referred as the vastus medialis oblique (VMO) due to its oblique orien-
tation of muscle fibers that are important of patellar stability in last 10 to 20
degrees of knee extension .
Intramuscular/Central Tendon Injury
The largest study of the imaging appearance of quadriceps muscle strains fol-
lowed 40 professional Australian Rules football players for 3 years and com-
pared the rehabilitation interval (time to return to full-time training) after
Fig. 9. Axial T2 fat-saturated images from unilateral right hip MR arthrogram (higher resolu-
tion technique) shows direct and indirect tendons of the rectus femoris at the myotendinous
junction (A), tendon (B), and tendon insertion (C) levels. The white arrow represents the indirect
head, which forms the central tendon. The direct head (black arrow) inserts on the anterior in-
ferior iliac spine.
815 LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
having completed a predefined rehabilitation regimen . Fifteen cases in-
volved the rectus femoris, six vastus intermedius, one vastus lateralis, and three
had normal MRI exam.
This study found central injuries around the central tendon had a statistically
significantly longer time to rehabilitation as compared with peripheral injuries or
epimyseal injuries that did not involve the central tendon (26.8 versus 9.2 days).
The vastus tears had an average rehabilitation interval of 4.4 days. The MR-
negative group had rehabilitation interval of 5.7 days. Injuries involving the
as well (16.2 versus 10.8 days) (Fig. 10). No distal injuries occurred in this study.
Thus, the most significant injuries were rectus femoris central tendon injures
greater than 13 cm in length or greater than 15% cross-sectional area resulting
in rehabilitation intervals of 32.7 to 35.3 days. These injuries were termed acute
bullseye lesions because of MR appearance. Peripheral injures less than 15% of
cross-sectional area had the smallest rehabilitation interval of zero days in three
cases. One hypothesis for longer rehabilitation times for healing central tendon
injuries is that scar tissue from the healing process predisposes to discordant
contraction of deep and superficial fibers resulting in chronic irritation and pro-
This central tendon injury pattern of the rectus femoris has also been de-
scribed with ultrasound with good MR correlation but the experienced authors
of this study suggested that low-grade injuries may be difficult to detect and
may be overlooked .
Proximal nonapophyseal avulsions of the rectus femoris tendon have been de-
scribed but considered rare, although with increasing awareness of intra-artic-
ular hip pathology and imaging of unilateral hips, recognition may increase. A
recent case report describes injury in two professional football kickers in the
NFL . Each had MR findings of retraction of the direct head (1 and 3.5
cm). Both were treated conservatively with the patient with the 1-cm retraction
injury ultimately returning to competition. Another case report describes a sur-
gically corrected chronic rupture of proximal myotendinous junction of the rec-
tus femoris in a soccer player with good clinical outcome  (Fig. 11).
Distally the quadriceps tendons merge together before inserting on the patella.
MR appearance of the quadriceps tendon is that of a layered structure usually
trilaminar (56%), although occasionally one (6%), two (30%), or four (8%)
layers are seen. The superficial layer represents the rectus femoris, the deep
layer the vastus intermedius, and the middle layer consists of variable contribu-
tions of the vastus lateralis and medialis  (Fig. 12).
Distal injury to the quadriceps is an unusual injury most commonly occur-
ring in individuals over 40 . Injury may occur as result of direct trauma
but usually related to forced eccentric contraction in a mildly flexed position
often in effort to regain balance during falls . Spontaneous ruptures and
816 ARMFIELD, KIM, TOWERS, ET AL
bilateral ruptures have been described in those with systemic metabolic disease
and anabolic steroid use [40–42]. Because of the large forces required to disrupt
the tendon proper, most injury involves the myotendinous junction or under-
lying weakened tendon .
Fig. 10. (A) Focal edema around the central tendon of the rectus femoris on axial fluid sen-
sitive image. The central location of injury suggests longer rehabilitation time. (B) Coronal IR
images in a different patient with a long segment (>13 cm) injury of the central tendon. (C)
Focal peripheral injury of the rectus femoris involving a large cross-sectional area of the mus-
cle. (D) Chronic central tendon lesion of rectus femoris that has healed. Note fibrous prolifer-
ative scar tissue and lack of adjacent edema (arrow).
817LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Imaging plays an important role as disruptions of extensor mechanism may
be surprisingly misdiagnosed ranging from 39% to 67% of cases . Radio-
graphs may show extensive soft tissue swelling and loss of quadriceps tendon
shadow, displaced calcifications, or patella baja . MR imaging is the pre-
ferred modality of evaluation because of excellent anatomic depiction particu-
larly in the setting of soft tissue swelling and hematoma, which allows accurate
treatment planning [45–49]. Partial tears can be differentiated between com-
plete tears as no intact fibers are seen with complete tears. Ultrasound may
also be effective but again operator experience is needed .
Because of the superficial location, contusion injury of the quadriceps may
occur. Typical clinical history of pain and swelling exists along either MRI
Fig. 12. Sagittal image of a normal quadriceps tendon with superficial (black arrow rectus
femoris), middle (white arrow, vastus lateralis and medialis) and deep fibers (open arrow,
vastus intermedius) (A). Different patient with partial tear of quadriceps tendon (black arrow)
and residual intact fibers of vastus intermedius (B).
Fig. 11. Edema surrounding rectus femoris tendon 2 cm from its proximal insertion compat-
ible with partial tear (arrow).
818 ARMFIELD, KIM, TOWERS, ET AL
findings of muscle swelling and interstitial edema and hemorrhage [51,52]
(Fig. 13). Contusions of the rectus femoris have been graded clinically into
mild, moderate, and severe based on knee flexion, swelling, and pain .
The degree of injury is associated with length of disability and likelihood of
myositis ossificans. Mild, moderate, and severe contusions resolved on average
of 6.5, 56, and 72 days, respectively. Moderate to severe injuries were more
likely to develop myositis ossificans. No corresponding MR criteria exists, al-
though anecdotally the greater the amount of edema and cross-sectional in-
volvement the longer the healing time.
Sometimes patients do not recall muscle injury and may present several months
later with a small painless mass in the anterior thigh. While consideration for
sarcoma may exist, MR may detect pseudotumors related to chronic rectus
femoris tear. In one case series with normal x-rays without soft tissue calcifica-
tion or periostitis, MR showed an irregular mass (usually less than 5 cm) with
edema and some enhancement compatible with pseudotumors . Short-term
follow-up imaging may be needed to help distinguish pseudotumor from soft
tissue malignancy .
While not a true muscle injury, shear injuries of the deep subcutaneous tissues
and muscle-fascial interface may occur resulting in fluid collections known as
Morel-Lavalle ´e lesion or degloving injuries, which can mimic tumors (originally
described as posttraumatic cysts) particularly when chronic [54,55] (Fig. 13).
The adductors are composed primarily of superficial (pectineus, gracilis, and
adductor longus), middle (adductor brevis), and deep (adductor magnus) mus-
cle structures  (Fig. 14A,C). The adductor magnus has anterior and
Fig. 13. Curvilinear fluid collection along the crural fascia consistent with degloving injury
819LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
posterior heads. The anterior head of the adductor magnus (as well as other
muscles in the adductor group) receives innervation by the obturator nerve.
The posterior head is innervated by branch of sciatic nerve like other ham-
strings and functionally resembles a hamstring muscle. The adductor head of
the magnus has a proximal attachment on the ischial ramus and inserts distally
along the entire linea aspera. The posterior head has proximal attachment on
the ischial tuberosity anteroinferiorly and distally attaches on the medial distal
femur on the adductor tubercle.
The adductor brevis proximally attaches to the anterior surface of inferior
pubic ramus and distally attaches to the proximal third of the line aspera.
The adductor longus arises from anterior surface of the body of pubis and in-
serts distally on the middle third of the linea aspera. The gracilis arises on the
anterior aspect of the lower body of the pubis and inferior ramus and inserts on
the tibia with the tendons of the pes anserine.
Proximal Adductor Injury
The imaging finding of myotendinous strain of the adductor muscle have char-
acteristics similar to muscle injury elsewhere in the body (Fig. 14B). Adductor
strains have been listed as one of the most commonly injured groups of muscles
Fig. 14. Axial T1-weighted images of proximal thighs in professional football player with
acute groin pain on the left. The annotated right side (A) shows normal anatomy of the adduc-
tor muscle group: al, adductor longus; ab, adductor brevis; am, adductor magnus. The black
arrows show the normal myotendinous junction of the adductor longus. The white arrows de-
pict adductor brevis myotendinous junction and the white arrowhead shows myotendinous
junction of the gracilis. (B) Edema of myotendinous strain of adductor longus on fluid-sensitive
axial images. (C) Additional anatomy more distally of mid thigh. s, sartorius; g, gracilis.
820ARMFIELD, KIM, TOWERS, ET AL
[12,18]. In a nonconsecutive series of adductor muscle injuries (13) all involved
the adductor longus . The adductor longus seems to be the most commonly
injured muscle but other adductors such as adductor brevis, pectineus, and gra-
cilis may be injured [56–58].
Routine myotendinous muscle strains of adductor complex should be differ-
entiated from acute or chronic bone-tendon interface injuries (ie, insertional
avulsion) or tenoperiosteal injuries (Figs. 15, 16). These latter type injuries
are probably sources of chronic pain that do not resolve and more likely asso-
ciated with chronic groin pain or athletic pubalgia .
Acute insertional tears are infrequently reported in the literature but are
probably more common. These injuries have been surgically repaired in pro-
fessional footballers (two cases) with full return to play and no manual loss
of strength. Repair was the chosen method as adductor tenotomy has shown
to result in loss of muscle strength and decreased activity [59,60]. Clinically,
many others treat these injuries conservatively and some partial entheseal tears
are lysed to alleviate symptoms.
MR has been used to identify adductor-related groin pain manifesting pri-
marily as increased T2 signal near the pubic insertion . In a study of 52 ath-
letes with chronic groin pain abnormal increased postcontrast enhancement
was seen with MR, and there was significant correlation with athlete’s side
of symptoms . The authors felt this finding was related to enhancing active
tenoperiosteal granulation tissue related to chronic injury and partial healing.
Anecdotally we have noticed that minor gray signal changes on unenhanced
short echo time sequences representing disorganized collagen of the adductor
insertion may predispose to subsequent injury as well. Other authors have de-
scribed a parasymphyseal cleft sign seen on conventional MRI (and confirmed
with fluoroscopic guided symphyseal cleft injection), which correlated well with
athletes’ symptomatic side. This finding had high sensitivity and specificity and
appears to be related to adductor insertional partial tears .
Fig. 15. Partial insertional or entheseal tear of the adductor longus on the left (white arrow)
on fluid-sensitive axial images. Note the loss of cross-sectional volume of the tendon insertion
and subjacent bone marrow edema. For anatomic purposes, p ¼ pectineus and oe ¼ obturator
externus. Black arrow shows normal insertion on the right.
821LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Ultrasound has also been used to assess tendon insertional abnormalities of
the groin . In a recent review article by a group of musculoskeletal radiol-
ogists with significant ultrasound experience, they anecdotally favored MRI in
this region because of the difficulty in differentiating the tendons at their origin
Distal Adductor injury
Distal insertional injury of the adductor may also occur as it inserts on the fe-
mur, known as adductor insertion avulsion syndrome and represents a traction
injury along the muscle insertion on the femur (similar to tibial shinsplints) as
a result of overuse often affecting athletes and military recruits [65–68]. MRI
findings vary from periosteal edema to intramedullary signal changes. Radio-
graphs may show periosteal reaction . Based on anatomy, proximal injuries
are associated with the adductor brevis, mid-femoral abnormalities are related
to adductor longus, and distal posteromedial findings associated with the ad-
ductor magnus. Ultrasound may demonstrate periosteal edema, and bone
scan may show increased uptake as well . Differential also includes tumor,
pseudotumor, and osteomyelitis but clinically thigh splints tend to resolve
quickly in response to rest over 1 to 2 months [67,69,70] (Fig. 17).
Groin pain can be disabling to the high-performance and recreational athlete. It
is often associated with sports requiring kicking and rapid change in directions,
such as soccer, rugby, hockey, and American football players . Injury data
from the National Hockey League reveals groin injury occurs at a rate of 13 to
20 injuries per 100 players per year .
The differential for chronic groin pain is broad and includes both musculo-
skeletal and genitourinary etiologies. Musculoskeletally, the top differential in-
cludes intra-articular hip pathology (labral tears), true palpable hernia,
nonpalpable posterior abdominal wall abnormalities (sports hernia and groin
Fig. 16. Coronal IR image showing complete acute avulsion of the left adductor longus inser-
tion on the pubic symphysis in a professional football defensive lineman (A). Football line-
backer with chronic injury of the right adductor tendon that has healed but develops
intermittent pain. Note irregularity and enlargement of the tendon without surrounding edema
(arrow) as compared with the opposite side (B).
822ARMFIELD, KIM, TOWERS, ET AL
disruption), rectus abdominus injury, osteitis pubis, and adductor-related mus-
cle and tendon injury.
The term athletic pubalgia has been used to describe inguinal pain with ex-
ertion without exam findings of a hernia, which can occur in recreational and
elite athletes . This clinical diagnosis is composed of two basic posterior ab-
dominal wall abnormalities, sports hernias and groin disruptions. These terms
are often used interchangeably but a sports hernia defect usually is the result of
occult direct or indirect hernias, whereas groin disruption involves injuries to
the adjacent transversalis fascia, oblique muscles and aponeurosis, conjoined
tendon, and rectus abdominus insertion . Many imaging studies have
been used over the years to diagnose this entity, including herniorrhaphy (in-
traperitoneal injection of contrast to see if it enters the inguinal canal) although
this technique is no longer widely performed . Ultrasound has been found
to be useful for posterior abdominal wall deformities .
We prefer MRI evaluation as a means of evaluating patients with athletic pu-
balgia not because of its poor ability to detect posterior abdominal wall injuries
but rather to identify other causes of pain such as bone stress reactions and ad-
ductor-related injury. Occasionally abdominal wall defects such as asymmetric
muscle wall attenuation, fat herniation into the inguinal canal, and parasym-
physeal bone marrow edema may be seen with cases of sports hernia 
Osteitis Pubis and Marrow Edema
Osteitis pubis (inflammation of the pubic symphysis) is generally associated
with mechanical shear stresses, although direct traumatic and infectious etiolo-
gies have been described. It affects many different types of athletes including
Fig. 17. Axial fluid-sensitive images showing abnormal edema and some cortical destruction
(arrow) in a recreational 26-year-old hockey player. The injury did not improve after 8 weeks
with rest and subsequently was proven to be lymphoma.
823LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
runners, soccer players, and hockey players . Since radiographic findings
such as sclerosis, irregular margins, small osteophytes, and subchondral cystic
changes may be seen in asymptomatic individuals, image-guided symphyseal
cleft injections may help diagnosis and provide symptom relief . Nuclear
medicine scintigraphy may also show increased uptake but this finding is
Some studies have found that bone marrow edema of pubis is seen on 56%
to 77% of athletes with groin pain [61,77]. One clinical study evaluated the MR
findings of pubic bone abnormalities and effect on missed training and games.
Fifty-two Australian Rules footballers were assessed in the preseason and fol-
lowed during the subsequent season. Marrow edema greater than 2 cm in
length was not associated with pain or missed training or games. Linear hyper-
intense signal parallel to pubic symphysis was associated with missed training
time but not missed games. This finding may be related to shear injury of pubic
symphysis. Only the clinical finding of pubic pain was associated with missed
HIP ROTATORS AND ABDUCTORS
Injury to the musculature of the hip is covered elsewhere but briefly, the glu-
teus maximus, given its location, is prone to contusion injury, and muscle
strains are uncommon in comparison to hamstring and quadriceps injury. In-
sertional tendon injuries of the gluteus medius and minimus on the greater tro-
chanter are often overlooked and more recently recognized as a source of pain
that mimics trochanteric bursitis [78–80]. Calcific tendonitis/tendinosis may
also be a source of lateral hip pain and has been associated with ‘‘trochanteric
bursitis’’ and has been mistaken for malignancy in some cases because of in-
flammatory changes and adjacent bone changes [81,82].
There are numerous short rotators of the hip and isolated injury is infre-
quent. A case report of quadratus femoris muscle strain was recently reported
that was diagnosed with MRI. This patient failed conventional rehabilitation
Fig. 18. Axial fluid-sensitive image showing asymmetric edema on the left in the inguinal re-
gion compatible with history of athletic pubalgia (A). Coronal IR image demonstrating edema
of pubic bones bilaterally (arrows), which came by an incidental finding but this professional
baseball catcher had the typical clinical findings of osteitis pubis (B).
824ARMFIELD, KIM, TOWERS, ET AL
for presumed hamstring injury but then subsequently improved after the reha-
bilitation program was adjusted based on the MRI findings [83,84] (Fig. 19).
PELVIC APOPHYSEAL AVULSIONS INJURY
Likely sites of pelvic avulsions in adolescents with incomplete skeletal matura-
tion include ischial tuberosity (hamstring insertion), anterior superior iliac spine
(sartorius), anterior inferior iliac spine (rectus femoris), pubic symphysis (ad-
ductors), and greater and lesser trochanter (gluteus muscles and iliopsoas)
and rarely iliac crest apophysis (abdominal wall insertion) . Chronic avul-
sive injuries can also be confused for malignant lesions or chronic infections
and often result from chronic overuse injuries in patients participating in orga-
nized sports . A review of over 200 cases of apophyseal avulsions showed
the most common areas of involvement were the ischial tuberosity, anterior in-
ferior iliac spine (ASIS), and anterior superior iliac spine (AIIS) with the highest
association among those participating in soccer, gymnastics, and track and
field/athletics  (Fig. 20).
Diagnosis of many avulsive injuries is generally made by history and mech-
anism of injury along with radiographs. Curvilinear or amorphous bone mate-
rial is generally seen adjacent to the insertion site of concern although discrete
bone fragments may not be seen with pubic symphyseal avulsion . MR usu-
ally detects injury as a result of surrounding inflammation but subtle cortical
bone fragments often manifest as dark signal voids and can be difficult to detect
(Fig. 21). MR in the acute setting reassures that the myotendinous unit or ten-
don insertions are intact. In the younger child without apophyseal calcifica-
tions, MR is useful for diagnosis as radiographs may be negative . Most
avulsive injuries are treated conservatively but it is important to comment on
a displaced avulsion greater than 2 cm, as the may need to undergo surgical
repair [88–90]. Also hamstring avulsion injuries are more prone to complica-
tion because of proximity to the sciatic nerve and can be evaluated with
Fig. 19. Focal edema in quadratus femoris consistent with mild strain (arrows).
825LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Avulsions in Adults
Complete hamstring proximal avulsions can occur in adults but are unusual
with small series reported often involving forceful flexion of hip when the
knee is extended during athletic activity, particularly waterskiing [92–96].
They can be treated with surgical intervention with good outcomes in the acute
and chronic setting although acute intervention may be preferred [94,97,98].
Fig. 20. Plain film of 16-year-old hurdler with bony irregularities and calcifications of the
ASIS (black arrow) and AIIS (white arrow) (A). The injuries where confirmed to be apophyseal
avulsions with MRI: ASIS (B) and AIIS (C). Note intact contralateral sides for comparison.
Fig. 21. Axial T1 MR showing thin cortical rim of dark signal slightly avulsed from the ischial
tuberosity (arrow) compatible with apophyseal avulsion in a 14 year old.
826 ARMFIELD, KIM, TOWERS, ET AL
Importantly, when avulsive injuries (particulary of the lesser trochanter) oc-
cur in older adults without history of significant trauma, one must consider un-
derlying malignant process until proven otherwise [99–101] (Fig. 22).
Injury to the gastrocnemius muscle is among the more common injuries to
occur in the lower leg. Like the hamstring and quadriceps muscles the gastroc-
nemius is prone to injury as it spans two joints and has a high proportion of
fast-twitch type 2 fibers . The medial and lateral heads of gastrocnemius
arise from separate proximal attachment sites on the posterior aspect of the
femoral condyles . Distally the heads form a flat aponeurosis at the distal
myotendinous junction before coalescing with the soleus aponeurosis to form
the Achilles tendon.
The medial head is injured more commonly than the lateral head as it has
been shown to be more active . In a series of 20 MRIs of the distal myo-
tendinous junction, the medial head was more commonly involved 19/22 ver-
sus lateral 3/22  (Fig. 23). It is important to have high clinical suspicion for
deep venous thrombosis (DVT) in patients with calf pain as patients may have
DVT mimicking muscle strain or a DVT may be associated with the muscle
strain injury. Thrombophlebitis is also within the differential for calf pain
 (Fig. 24).
sis or provide image guidance for needle aspiration of fluid collections [106,107].
The term ‘‘tennis leg’’ has been used to describe muscle injury and pain in the
calf. The term is attributed to the tennis serving motion of fully extending the
knee with sudden ankle dorsiflexion invoking maximal stretch on the calf.
Fig. 22. Sports-related traumatic avulsion of the lesser trochanter in a 15-year-old track ath-
lete (A). Avulsion of lesser trochanter in an adult without significant history of injury (B). MRI
in the same adult shows focal metastatic disease (C).
827LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Fig. 23. Axial image showing increased fluid signal in the proximal lateral gastrocnemius
consistent with a mild strain although the location is somewhat atypical (arrow).
Fig. 24. Axial T2 sequences of a calf showing diffuse mild edema of posterior muscles in a pa-
tient thought to have a muscle strain (A). Note filling defects of popliteal branch vessels as com-
pared with opposite side. White arrows demonstrate vicinity where one could look for black
dots representing clot in the veins. Patient eventually developed shortness of breath and was
found to have a pulmonary embolism filling defect (arrow shows thrombus in a pulmonary ar-
tery) seen on CT angiography treated successfully (B).
828 ARMFIELD, KIM, TOWERS, ET AL
However, this injury has been described in young athletes during periods of
heavy exercise (such as basketball, running, or severe stretching) and in
more elderly patients who may simply be stepping out of a car or getting
out of bed [104,108]. Patients will experience sudden onset of pain with focal
swelling and ecchymosis of the calf. Tennis leg typically refers to injury of
the distal myotendinous junction, although proximal myotendinous injury
may occur. In an ultrasound study of 141 patients with tennis leg 67% showed
partial tear of medial gastrocnemius, 1.4% were associated with plantaris
tendon rupture, and 21% had intermuscular fluid collection without muscle
tear of the medial gastrocnemius (Fig. 25). Importantly, 10% had DVT without
other findings and it was associated finding in another 5% .
Treatment of most gastrocnemius injuries is usually conservative. Occasion-
ally, surgery may be performed to evacuate a hematoma, to repair a grade III
injury or to perform surgical decompression in the case of compartment syn-
drome . One case report describes surgical release of the sural nerve in
a patient with sensory loss as the sural nerve was entrapped within scar tissue
beneath the deep fascia of the gastrocnemius from remote injury . Tennis
leg can be associated with acute compartment syndrome as well .
Injury to the proximal myotendinous junction of gastrocnemius posterior to the
knee can occur but is an unusual clinical entity and the imaging appearance is
rarely reported . The clinical significance of proximal injuries is also un-
clear aside from localization of pain to the knee instead of the mid calf, which
can alter the differential diagnosis. If no abnormality exits on MRI, one should
consider referred pain related to lower lumbar disc pathology (ie, L5 level). In
children and adolescents some types of ‘‘cortical desmoid’’ or metaphyseal cor-
tical defects in asymptomatic individual are seen at the gastrocnemius insertion
Fig. 25. Intermuscular fluid collection between medial gastrocnemius and soleus muscle on
ultrasound (arrows) in a patient clinically with tennis leg.
829LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
on MRI and are thought to be related to chronic avulsive injury and must be
distinguished from tumor .
Like the gastrocnemius muscle, the plantaris muscle spans both the knee and
the ankle joints. It has a proximal attachment at the lateral supracondylar
line of the femur just superior and medial to the lateral head of the gastrocne-
mius muscle. The distal attachment is via a long tendon that courses between
the medial head of the gastrocnemius and the soleus muscle as it inserts onto
the medial aspect of the calcaneus adjacent to the Achilles tendon. The planta-
ris tendon ranges from 7 to 13 cm in length with the myotendinous junction
occurring at the level of the origin of the soleus muscle at the proximal tibia.
The tendon may be absent in 7% to 20% of the population and is often har-
vested for reconstruction of tendons or ligaments [107,114].
Injury to the plantaris tendon can mimic injury to the medial head of the
gastrocnemius and distinguishing the two can be clinically difficult. Patients
will feel a sudden pop with pain and swelling in the posterior calf. Often, injury
to the plantaris muscle belly coexists with injury to the ACL and posterolateral
structures in the knee while tendon injuries tend to be isolated and related to
tennis leg. A partially or completely torn muscle at the level of the myotendinous
gastrocnemius and soleus muscles . More distally, ruptures of the plantaris
tendon are depicted on MRI as a fluid collection between the medial head of the
gastrocnemiusmuscle and soleus muscle with retraction of the muscle appearing
as a mass. Some authors believe that the presence of a hematoma in this location
favors the diagnosis of injury to the medial head of the gastrocnemius muscle
given the avascularity of the plantaris tendon [107,114]. Treatment is similar
to injuries of the gastrocnemius muscle (Fig. 26).
Fig. 26. Coronal IR images showing large intermuscular fluid collection between gastrocne-
mius and soleus muscle as a result of distal plantaris tendon rupture (arrow shows retracted
830 ARMFIELD, KIM, TOWERS, ET AL
Injury to the soleus is considered uncommon and is only rarely reported. It has
been postulated, however, that injury to this muscle may occur more fre-
quently than reported as soleus tears may be erroneously diagnosed as tears
of the gastrocnemius . The soleus muscle originates at the posterior aspect
of the proximal tibia and fibula and runs deep to the gastrocnemius muscle.
The soleus and gastrocnemius muscles gradually conjoin to form the Achilles
tendon 8 to 10 cm above its insertion onto the calcaneus .
With only a few case reports of soleus muscle injury, mechanism and descrip-
in 17% (4/23) of distal myotendinous injuries to the gastrocnemius .
The popliteus muscle originates at the posteromedial aspect of the proximal tib-
ial metaphysis and can have several attachments but primarily inserts on the
lateral aspect of femoral condyle. The popliteus muscle functions as an internal
rotator of the tibia on the femur and assists in flexion of the knee. It is an im-
portant stabilizer of the posterolateral corner of the knee and prevents forward
translation of the femur on the tibia .
The overwhelming majority of injuries to the popliteus muscle occur at the
muscle belly and myotendinous junction rather than the insertion, although
this can occur . The mechanism of injury is thought to be from a direct
blow to the anteromedial aspect of the proximal tibia as the knee is hyperex-
tended. Without contact, injury can occur with external rotation and hyperex-
tension. Most injuries to the popliteus are found in conjunction with injuries to
other structures in the knee, most commonly the ACL, with associated injuries
to the PCL, menisci, or collateral ligaments also reported . A small minor-
ity of popliteus injuries occurs in isolation [118,119].
Tears range from being partial interstitial to complete rupture. MRI will
reveal enlargement of the muscle with increased signal on T2-weighted images
(Fig. 27). With complete rupture, there will be retraction and clumping of the
muscle and possible formation of a hematoma in the proximal calf . In this
situation, hematoma can compress the neurovascular bundle in the proximal
calf, causing temporary compromise of the posterior tibial nerve . More
recently a case of popliteus strain with muscle edema and enlargement resulted
in a permanent partial deficit of the tibial nerve .
OTHER MUSCLE INJURIES AND COMPLICATIONS
The differential diagnosis for MR finding of muscle edema is broad. General-
ized muscle edema may occur as a result of exercise. Postexercise imaging of
muscle demonstrates increase in extracellular fluid and T2 signal and referred
to as exercise enhancement [10,121].
831 LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Delayed onset muscle soreness (DOMS) is a clinical entity of muscle sore-
ness and pain after intense exercise (often eccentric contractions) that is usually
self-limiting [18,122,123]. It has an MR appearance similar to low-grade muscle
strain although abnormal increased T2 signal may persist up to 80 days accord-
ing to one report . Because of its similar appearance to muscle strain it is
often diagnosed clinically. With severe DOMS, muscle necrosis may occur
with marked increased signal on fluid-sensitive sequences [18,125].
Muscle edema may also be related to denervation, although this is usually
not visualized until the subacute setting  (Fig. 28A). Fibrofatty atrophic
changes may be seen in the musculature in patients with chronic denervation
related to prior trauma or other muscle damaging process such as acquired
or congenital neuropathic disorders (Fig. 28B).
Compartment syndrome often involves the calf following blunt trauma or frac-
ture [21,22]. It may also result from muscle strain injury and associated swelling
and hematoma (Fig. 29). Compartment syndrome without muscle injury has
been described in the anterior compartment of the lower leg in soccer players
. Increased pressure within fascial compartments leads to capillary circula-
tory compromise with ischemia to the musculature and nerves, and progress to
tissue necrosis if left untreated. While typically a clinical diagnosis confirmed
with pressure measurements, MR may be used to evaluate the extent of in-
volvement but should not delay intervention in emergency cases. Findings in
the acute setting include increased T2 signal with muscle enlargement, edema,
or both .
Compartment syndrome can also be chronic, as a result of neoplasm or
associated with exercise (Fig. 30). MRI before and after exercise may demon-
strate increased T2 signal in the compartment of concern [128–131]. Although
a recent prospective study comparing the invasive gold standard of direct
Fig. 27. Axial image demonstrates increased fluid signal of myotendinous junction of popli-
teus consistent with muscle strain (arrow).
832ARMFIELD, KIM, TOWERS, ET AL
pressure measurement with near infrared spectroscopy (NIRS, a noninvasive
method detecting hemoglobin saturation), and MRI discovered that NRIS
was equivalent to direct pressure measurements and superior to MRI .
One of the more common injuries to occur in the lower leg is a muscle hernia.
A muscle hernia is a focal protrusion of a muscle through a small defect in the
Fig. 29. Axial T2 image showing large soleus hematoma and lower extremity enlargement
with muscle edema consistent with clinical finding of compartment syndrome (arrow).
Fig. 28. Proximal tibiofibular joint ganglion (white arrow) with mass effect on the anterior
branch of peroneal nerve resulting in muscle denervation and edema (black arrow) (A). Cor-
onal T1 image showing diffuse fatty infiltration of medial gastrocnemius muscle related to prior
trauma and loss of normal muscle architecture (arrow) (B).
833LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
fascial plane [133,134]. The anterior compartment is more commonly involved
particularly the tibialis anterior and, to a lesser extent, the extensor digitorum
longus, and the peroneus muscles . Hernias can be associated with trauma
or muscle hypertrophy and may be painful. . When there is a history of
trauma, it is usually from penetrating wounds or violent impact . The di-
agnosis of a muscle hernia is generally a clinical one, based on symptoms and
physical examination. A small superficial bump may be noted with the limb at
rest, which will become more prominent with contraction of the associated
muscle. If the clinical picture is not clear, an MRI may show a focal protrusion
of muscle through the fascial defect, however dynamic imaging muscle contrac-
tion can make the herniation more conspicuous. It is critical for the interpreting
radiologist to mark the area of concern with a vitamin E capsule or visually in-
spect the leg, as these findings may be subtle with MRI (Fig. 31). It is also im-
portant to exclude underlying true tumors.
Treatment of muscle herniations, especially when asymptomatic, is conser-
vative, although fasciotomy may be performed for cosmetic reasons. Fascial re-
pair is no longer performed as this may result in compartment syndrome .
Herniation may rarely result in muscle necrosis as a result of strangulation .
Myositis ossificans circumscripta is another well-known sequela of muscle in-
jury often affecting larger muscles in the extremities [10,18,23,24,135]. Myositis
ossificans presents diagnostic imaging difficulties because of variable imaging
appearance, which can be aggressive and overlap with neoplastic processes.
The cause is usually blunt trauma, although burns and paralysis have also
been implicated, but often no traumatic history is present. Acute to subacute
lesions are ill defined and isointense to muscle on T1-weighted images and het-
erogeneous on T2-weighted images. There is often a large area of surrounding
edema, and at this stage, the lesion may be difficult to distinguish from a neo-
plasm. More mature lesions are better defined with fat signal intensity from
Fig. 30. Patient with chronic compartment syndrome as a result of a large hemangioma seen
on these post contrast axial T1-weighted images (arrow).
834ARMFIELD, KIM, TOWERS, ET AL
ossification on both T1- and T2-weighted images and with little or no edema.
Clinical history and sequential imaging (radiographs and CT) are critical to
Calcific myonecrosis is a rare complication of muscle trauma that is associ-
ated with peripheral nerve injury and usually affects a single muscle 
(Fig. 32). It is best evaluated with CT or MR demonstrating plaque-like periph-
eral calcification of the muscle with central fluid .
Fig. 31. Axial T1-wieghted images reveal subtle contour defect of medial gastrocnemius on
the left (arrows) consistent with a small fascial herniation, which was much more evident on
Fig. 32. Radiograph of the pelvis with cylindrical peripheral calcifications associated with
calcific myonecrosis or old hematoma of the distal iliopsoas muscle on the right.
835 LOWER EXTREMITY SPORTS-RELATED MUSCLE INJURY
Muscle injury and strains are very common among athletes. MR is the pre-
ferred method of evaluation because of superior contrast resolution, reproduc-
ibility, and excellent anatomic detail. Ultrasound is also useful and advocated
by some as a front line diagnostic modality because of its lower costs and por-
tability particularly in experienced hands. It is important to remember that in-
jury usually occurs at the myotendinous junction, which may be intramuscular
in the hamstring and quadriceps muscles. The size of injury and relationship to
the myotendinous junction can provide prognostic information regarding
convalescent period, which can be extremely important for the elite athlete.
Literature on prognostication is limited and probably results from relative com-
monality and mild nature of most injuries but further studies are warranted as
injuries could affect different sporting population more than others.
Future developments regarding treatment will become more important and
analysis and classification of imaging finding may provide better prognostica-
tion. For example, some have identified the importance of the COX pathway
for muscle injury healing and possible deleterious effects of inhibitors (ie, non-
steroidal anti-inflammatory drugs) . Others have experimentally shown
the introduction of relaxin growth factor via gene therapy promotes muscle
healing [138,139]. With new treatments on the horizon it is important to
have supportive objective and accurate information regarding extent and types
of injury to help stratify treatment groups and improve patient care. Precise re-
porting of the location of muscle and tendon injuries is needed, as prognosis
may be different. Therefore continued evaluation and classification of muscle
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