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The variation in medial and lateral collateral ligament strain and tibiofemoral forces following changes in the flexion and extension gaps in total knee replacement: A LABORATORY EXPERIMENT USING CADAVER KNEES

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Achieving deep flexion after total knee replacement remains a challenge. In this study we compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior cruciate ligament-sacrificing total knee replacement, using equal flexion and extension gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive movement in five cadaver knees, and measurements of strain were made simultaneously in the collateral ligaments. The tibiofemoral force was measured using a customised mini-force plate in the tibial tray. Measurements of collateral ligament strain were not very sensitive to changes in the gap ratio, but tibiofemoral force measurements were. Tibiofemoral force was decreased by a mean of 40% (SD 10.7) after 90 degrees of knee flexion when the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the force only in full extension. Because increasing the range of flexion after total knee replacement beyond 110 degrees is a widely-held goal, small increases in the flexion gap warrant further investigation.
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1528 THE JOURNAL OF BONE AND JOINT SURGERY
The variation in medial and lateral collateral
ligament strain and tibiofemoral forces
following changes in the flexion and
extension gaps in total knee replacement
A LABORATORY EXPERIMENT USING CADAVER KNEES
B. Jeffcote,
R. Nicholls,
A. Schirm,
M. S. Kuster
From Fremantle
Hospital, Fremantle,
Australia
B. Jeffcote, BMBS,
FRACS(Orth), Orthopaedic
Surgeon
Department of Orthopaedic
Surgery
R. Nicholls, PhD, Research
Fellow
University of Western
Australia, Fremantle
Orthopaedic Unit, Fremantle
Hospital, Alma Street,
Fremantle, Western Australia.
A. Schirm, MD, Orthopaedic
Surgeon
M. S. Kuster, MD, PhD,
FRACS(Orth), Chairman,
Professor
Klinik für Orthopädische
Chirurgie, Kantonsspital 9007,
St. Gallen, Switzerland.
Correspondence should be sent
to Professor M. S. Kuster; e-mail:
Markus.Kuster@kssg.ch
©2007 British Editorial Society
of Bone and Joint Surgery
doi:10.1302/0301-620X.89B11.
18834 $2.00
J Bone Joint Surg [Br]
2007;89-B:1528-33.
Received 30 October 2006;
Accepted after revision 27 July
2007
Achieving deep flexion after total knee replacement remains a challenge. In this study we
compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior
cruciate ligament-sacrificing total knee replacement, using equal flexion and extension
gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive
movement in five cadaver knees, and measurements of strain were made simultaneously in
the collateral ligaments. The tibiofemoral force was measured using a customised mini-
force plate in the tibial tray. Measurements of collateral ligament strain were not very
sensitive to changes in the gap ratio, but tibiofemoral force measurements were.
Tibiofemoral force was decreased by a mean of 40% (SD 10.7) after 90˚ of knee flexion when
the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the
force only in full extension. Because increasing the range of flexion after total knee
replacement beyond 110˚ is a widely-held goal, small increases in the flexion gap warrant
further investigation.
Flexion often remains limited after total knee
replacement (TKR). There have been reports of
flexion 140˚ being achieved,1 but most stud-
ies describe ranges of 105˚ to 115˚ one year
after operation.2-5 This range is adequate for
most elderly patients in the Western world, but
is unlikely to satisfy younger patients, or those
for whom kneeling and squatting are impor-
tant activities.6-8 The main factors influencing
the post-operative range of flexion identified to
date are the pre-operative range, the body mass
index, correct sizing of components, patellar
tracking, the accuracy of gap balancing and
post-operative physiotherapy.9-11 This study
explores the influence the balance of the flex-
ion/extension gap has on soft-tissue tension in
deep flexion.
Insall and Scott12 first recommended balanc-
ing knee ligaments by creating equal and rect-
angular flexion and extension gaps. This
recommendation has been generally accepted
and several authors have attributed poor clini-
cal results to inadequate balance of these
gaps.10,11,13,14 The flexion gap may be mea-
sured by plain radiography; MR scans are not
required.15 In practice, the exact balance of the
gaps can be difficult to measure, and various
intra-operative spreaders or distraction devices
have been used to obtain equal gaps.16 To date
there has been little biomechanical analysis of
the influence the balance of the flexion/exten-
sion gap has on the forces generated within the
tibiofemoral joint or the strains on the peri-
articular soft tissues. The aim of this study was
to quantify the compressive tibiofemoral force
and strain patterns in the collateral ligaments
in a series of cadaver knees after TKR with
equal and unequal flexion and extension gaps.
Materials and Methods
Five fresh-frozen specimens of the human knee
were tested. All had mild to moderate osteo-
arthritic changes, predominantly in the medial
compartment. The femur and tibia were
resected 250 mm from the medial joint line,
and all soft tissue except the articular capsule,
ligaments, popliteus muscle, and quadriceps
tendon was removed.
A simple system was employed to determine
the strain in the medial and lateral collateral
ligaments (MCL and LCL, respectively). Kir-
schner (K)-wires with a 1.6 mm diameter were
inserted perpendicular to the attachments of
the MCL and LCL. The anterior fibres of the
MCL were selected for measurement, with the
distal K-wire located 3 mm behind the anterior
Research
THE VARIATION IN MEDIAL AND LATERAL COLLATERAL LIGAMENT STRAIN AND TIBIOFEMORAL FORCES 1529
VOL. 89-B, No. 11, NOVEMBER 2007
edge of the insertion of the ligament on the tibia. Strain (ε)
was calculated using the engineering strain formula17 (%):
ε = (l - l0),
l0
where l represents the instantaneous length of the liga-
ment (measured with digital calipers accurate to 0.01 mm),
and l0 the reference length, which was the length at full
extension for both ligaments prior to implantation of the
prosthesis, as previously reported.18
In a pilot study, differential variable reluctance trans-
ducer (DVRT) strain gauges (Microstrain Inc., Burlington,
New England) were used on soft-fixed and fresh-frozen
cadaver knees to measure ligament strain, as suggested by
Harfe et al.19 However, the trials showed inconsistent
results beyond 120˚ of flexion. We attribute this to the
twisting and buckling of the ligaments in deep flexion.
Whereas Harfe et al19 presented the strain in the mid-
flexion range, our study interest was beyond 120˚ of flex-
ion. Measurements using the K-wire technique were more
consistent than the DVRT’s throughout the whole range of
movement and had the additional advantage of measuring
the behaviour of the ligament as a whole, rather than indi-
vidual fibre bundles.
Each knee was mounted in a customised passive move-
ment rig (Fig. 1) designed to apply a passive flexion-
extension moment to the tibia with the femur fixed. The rig
also permitted the normal rotation of the tibia during
movement. It aimed to mimic the surgical environment
where the knee is passively flexed by the surgeon with the
patient anaesthetised. A spring sutured to the quadriceps
tendon was calibrated such that it exerted no force at full
extension but gradually came into play as the knee flexed,
reaching a maximum force of 40 N at 150˚ of flexion. The
purpose of the spring was to reproduce the passive stretch-
ing of the extensor mechanism which generates force across
the tibiofemoral articulation in flexion. As there is minimal
hamstring tension during knee flexion in the anaesthetised
patient, no hamstring force was simulated.
Each joint was pre-conditioned in the rig by the applica-
tion of ten cycles of flexion from full extension to 150˚ (at
30˚ per second). The angle of flexion of the joint was deter-
mined using a calibrated rotary-angle potentiometer
attached to the rig. In each specimen, measurements of the
length of the MCL and LCL were obtained at 15˚ incre-
ments between 0˚ and 150˚ flexion. These measurements
were then repeated with two further cycles of flexion.
The knee was then removed from the rig and a medial
parapatellar arthrotomy with osteotomy of the tibial tuber-
osity was performed to gain access to the knee joint. The
osteotomy was fixed with two small fragment screws, and
the arthrotomy closed with 1-vicryl sutures. The Low Con-
tact Stress rotating platform instrumentation (LCS, DePuy,
Warsaw, Indiana) was used to prepare the bone cuts. Both
cruciate ligaments were resected. The femur was divided
using an intramedullary guide in 5˚ of valgus. Tibial resec-
tion was performed with a 7˚ posterior slope referenced
from an intramedullary guide, as the ankle was not present.
There was no significant coronal bowing of any of the tib-
iae. The width of the flexion and extension gaps was mea-
sured using digital callipers while applying a 100 N
distraction force to the distal tibia in full extension and 90˚
of flexion.
In this study two femoral components were used. The first
was the standard LCS femoral trial, which was press-fitted to
the divided distal femur. This component was used to obtain
measurements of baseline force and ligament strain for a
standard implantation technique with balanced flexion and
extension gaps (balanced gap (BG) series). The second com-
ponent was a custom-designed LCS femoral component
mounted on an intramedullary rod (Fig. 2). The geometry of
the articular surface was identical to that of the trial
Fig. 1
Photograph of a cadaver knee joint mounted in a customised passive
movement rig.
Fig. 2
Photograph of the adjustable low contact stress femoral component
in situ.
1530 B. JEFFCOTE, R. NICHOLLS, A. SCHIRM, M. S. KUSTER
THE JOURNAL OF BONE AND JOINT SURGERY
prosthesis. This device allowed the articular surface to be
translated proximally or distally in known increments, thus
allowing accurate adjustment of the extension gap. The
adjustable femoral component was implanted aligning the
component with the previous femoral cuts. In order to
increase the extension gap (EG) by 2 mm (EG+2 series) the
adjustable femoral component was translated 2 mm proxi-
mally. In order to increase the flexion gap (FG) by 2 mm
(FG+2 series) the adjustable femoral component was trans-
lated 2 mm distally while the tibial component was also
simultaneously translated 2 mm distally, with the effect of
increasing the flexion gap by 2 mm relative to the extension
gap.
In place of the standard LCS tibial tray, a miniature force
platform was implanted (Fig. 3). This was designed, cali-
brated and validated in our laboratory, and was con-
structed to allow the trial LCS rotating platform insert to
rest on the platform and rotate a central hub. A brass base-
plate was constructed to house six load sensors arranged in
triangular arrays in the medial and lateral compartments.
These sensors allow the measurement of compressive loads
(tibiofemoral force) in each compartment individually. The
system was linked to a PC notebook computer via a
National Instruments SC-2345 connector block and 6024E
12-bit data acquisition card (National Instruments, Austin,
Texas). The force platform was implanted by mounting it
on an intramedullary rod which could be adjusted to trans-
late the platform proximally or distally. The rod was fixed
within the tibial shaft using three screws and a wire stirrup.
The force platform was stabilised on the cut tibial surface
using metal shims, small metal wedges 10 mm in length and
2 mm maximum height, manufactured at the Fremantle
Hospital Biomedical Services Department.
After implanting the components, an identical loading
regimen was undertaken for each condition (BG, EG+2,
FG+2). After pre-conditioning, two cycles of flexion were
performed with measurements of tibiofemoral force and
ligament strain obtained at 15˚ increments between 0˚ and
150˚ knee flexion.
Results
Tibiofemoral force. The mean tibiofemoral force measure-
ments obtained from the force platform for the three meas-
urement series are shown in Figure 4. The main variations
of force occurred in full extension and beyond 90˚ of knee
flexion.
The mean tibiofemoral force in the balanced gap group
was 50 N (SD 26.6 for five specimens) at full extension. This
was a starting point chosen to reproduce the force that
might be expected in a TKR during implantation. The mean
force between 15˚ and 75˚ of flexion in the BG series was
15.5 N (SD 9.6), before rising in an exponential manner to
a peak at a mean of 175 N (SD 104) at 150˚ of flexion.
For the FG+2 group the mean force at full extension was
slightly less at 37 N (SD 18.9) and remained less than 15 N
(SD 9.7) until 90˚ of flexion. Thereafter, the force again
rose exponentially but less steeply than in the BG series, peak-
ing at a mean of 107 N (SD 65.1) at full flexion. This amounted
to a mean force reduction of 40% beyond 90˚ of knee flexion.
The mean force at full extension was also lower for the
EG+2 group at 27 N (SD 18.6), but the force from 15˚ of
flexion to 150˚ of flexion was similar to the BG series.
Collateral ligament strain. The measurements of collateral
ligament length prior to implantation of a prosthesis were
used as a baseline. The mean strains in the anterior MCL
and LCL are shown in Figures 5 and 6.
The anterior portion of the MCL recorded very little
change in length throughout the flexion range in the intact
knee. The mean peak strain was 1.7% (SD 2.4) at 90˚ flex-
ion, with a mean minimum strain of -0.8% (SD 3.9) at 150˚.
The LCL showed a very different strain pattern, with little
change in length over the first 60˚ of flexion followed by
progressive loosening to a mean minimum strain of -15.3%
(SD 4.5) at 150˚.
Fig. 3
Photograph of a customised miniature force platform designed for
measurement of uniaxial compressive tibiofemoral force in vitro.
Fig. 4
Graph showing the mean values for tibiofemoral force during flexion for
the balanced gap (BG), extension gap +2 mm (EG + 2) and flexion gap +
2 mm (FG + 2). The error bars show the range of results at each flexion
angle across five specimens.
Force (N)
250
200
150
100
50
0
0153045607590105120 135 150
Flexion angle (o)
BG
EG+2
FG+2
THE VARIATION IN MEDIAL AND LATERAL COLLATERAL LIGAMENT STRAIN AND TIBIOFEMORAL FORCES 1531
VOL. 89-B, No. 11, NOVEMBER 2007
After implantation of the components with BG, the mean
anterior MCL strain at full extension and full flexion was
slightly increased compared with the measurements in the
intact knee (1.6% strain, SD 1.8). The LCL was slightly
looser than the pre-implantation measurements at full
extension with a mean of -1.5% (SD 2.1) strain, but as the
knee flexed the slackening of the LCL was delayed to 90˚ of
knee flexion and less marked than in the intact knee. The
mean minimum strain was -7.0% (SD 3.8) at full flexion
after implantation of the components.
In the FG+2 group, the ligament strains were very similar
to those in the BG group. In the EG+2 group the ligament
strains were approximately 2% lower near extension than
in the balanced knee. This was the comparison of the mean
strain at extension in the BG group compared with the
mean strain in the EG+2 group. Otherwise no obvious
differences were detected.
Discussion
We believe this is the first study to examine the tibio-
femoral forces and collateral ligament strain for variations
in flexion and extension gaps. The behaviour of the collat-
eral ligament strain was not greatly different with the var-
iations, but the changes in tibiofemoral force were. The
non-linear stress-strain behaviour and complex anatomy
of the knee ligaments, combined with the limitations of
the strain measuring device, made collateral ligament
strain measurement less sensitive than with force trans-
ducers to changes in soft-tissue tension. The force trans-
ducers were able to detect force generated not only from
the collaterals but also from tension in the extensor mech-
anism, retinaculum and capsule, allowing a more compre-
hensive measurement of the soft-tissue balance. The effect
of the mobile-bearing articulation on the collateral liga-
ment strain in this study is difficult to identify clearly, but
we believe that the relative insensitivity of the measure-
ments of ligament strain compared with the force trans-
ducers would apply equally to fixed- as well as mobile-
bearing prostheses.
Precise balancing of flexion and extension gaps is at
times difficult to achieve at operation.20 Surgeons may have
to accept slight discrepancies in balance and it is, therefore,
important to know the effects of small variations in gap
ratio on the soft-tissue tension.
The results of the balanced gap group show that the com-
prehensive force within the cadaver knees decreased in
early flexion, remained low throughout mid-flexion, and
then increased exponentially after 90˚. When the extension
gap was increased by 2 mm relative to the flexion gap, there
was a decrease in the tibiofemoral force in full extension
only. Beyond 15˚ of flexion the force and ligament strains
were essentially the same as in the balanced gap group.
When the flexion gap was increased by 2 mm relative to the
extension gap the results were markedly different. The
tibiofemoral force in full extension was hardly influenced
(mean 37 N vs 50 N), and during mid-flexion the tibio-
femoral force was similar to the other two groups. Beyond
90˚ of flexion, however, the force was reduced by a mean of
40%. This finding suggests that small variations in the flex-
ion or extension gaps have little effect on the soft-tissue ten-
sion between 15˚ and 100˚ of flexion, which is the range of
movement achieved by most patients after TKR. However
in deeper flexion, ligament tension is sensitive to changes in
the flexion gap. Increasing the flexion gap by as little as
2 mm may have benefits in terms of reduced generation of
tibiofemoral force beyond 90˚ of flexion.
0153045607590105120 135 150
Strain (%)
4
6
2
0
-2
-4
-6
Flexion angle (o)
Intact
BG
EG+2
FG+2
Fig. 5
Graph showing the mean values for medial collateral ligament strain dur-
ing passive flexion for three total knee replacements compared with the
baseline (intact knee strain) (BG, balanced gap; EG + 2, extension gap + 2
mm; FG + 2, flexion gap + 2 mm). The error bars show the range of results
at each flexion angle across five specimens.
0153045607590105120 135 150
Strain (%)
5
0
-5
-10
-15
-20
Flexion angle (o)
Intact
BG
EG+2
FG+2
Fig. 6
Graph showing the mean values for lateral collateral ligament strain dur-
ing passive flexion for the total knee replacements compared with the
baseline (intact knee strain) (BG, balanced gap; EG + 2, extension gap +
2 mm; FG + 2, flexion gap + 2 mm). The error bars show the range of
results at each flexion angle across five specimens.
1532 B. JEFFCOTE, R. NICHOLLS, A. SCHIRM, M. S. KUSTER
THE JOURNAL OF BONE AND JOINT SURGERY
Although the benefits of a balanced flexion and extension
gap are based on sound theory, there are no published bio-
mechanical data to confirm this recommendation. There
are good reasons to question this traditional approach.
Several studies, including this one, have shown a non-iso-
metric behaviour of the LCL,21 and to a lesser extent the
MCL.19,22 Hence, balancing the gaps at 0˚ and 90˚ of flex-
ion will not necessarily provide ideal soft-tissue tension in
deeper flexion. Indeed, inferring from the present data, an
increased flexion gap of 2 mm reduces soft-tissue tension by
approximately 40% in deep flexion. Although equal flexion
and extension gaps will obtain knee flexion up to approxi-
mately 110˚, it seems advantageous to increase the flexion
gap slightly when deep knee flexion is a goal. There is also
clinical evidence in the literature to support this hypothesis.
In a clinical trial with bilateral TKRs it was shown that
patients consistently preferred the laxer knee, which tended
to provide an increased range of movement.23 Several other
authors have suggested that an increased flexion gap might
improve the post-operative range of movement.24-26
Our study showed that a looser flexion gap does decrease
soft-tissue tension beyond 120˚ of knee flexion. This is in
contrast to the work of Bellemans et al,27 who emphasised
the importance of a sufficient posterior condylar offset.
Whereas reduced condylar offset can induce posterior
tibiofemoral impingement, an increased offset tightens the
flexion gap and increases soft-tissue tension in flexion. As
both mechanisms seem to restrict movement, a balance
between condylar offset and soft-tissue tension in flexion
must be achieved. Furthermore, femoral rollback during
flexion can reduce the influence of the posterior condylar
offset on tibiofemoral impingement. Indeed, in the study by
Bellemans et al27 the kinematic analysis demonstrated a
parodoxical roll forward of the femur in flexion. Hence, the
patients in their series depended on a high condylar offset
to avoid impingement, whereas patients with sufficient fem-
oral rollback are less reliant. In most current designs of
TKR the tibial insert is concave. In order to allow the femur
to roll back the ligaments must loosen in flexion to accom-
modate the necessary superior translation. This can be
obtained by an increased tibial slope and a slightly looser
flexion gap. Kinematic in vitro and in vivo analyses are
necessary to give further insight into the complex and at
times conflicting interactions between the amount of
condylar offset, tibial slope, soft-tissue tension, and their
influence on femoral rollback and tibiofemoral impinge-
ment. The lack of kinematic data is therefore a limitation of
the current study.
The potential disadvantage of increasing the flexion gap
is that of instability in flexion, which in some cases can
require revision surgery.14 However, we do not believe that
symptomatic instability in flexion is likely when increasing
the gap by 2 mm, but to consistently obtain a 2 mm
increased flexion gap and to avoid instability, optimal ten-
sion is needed.
We chose to use a mobile-bearing posterior cruciate liga-
ment (PCL) sacrificing prosthesis in this study. Although
this is not representative of all TKR designs, it is a com-
monly-used implant with a long and successful track
record.28 The effects of a relative increase in the flexion gap
are unlikely to be specific to this individual design of pros-
thesis. We anticipate that TKR designs with a concave tibial
insert, such as most PCL-sacrificing, PCL-substituting and
medial pivot designs, may demonstrate an increased range
of flexion with a looser flexion gap. The effect of an
increased flexion gap on PCL-retaining designs, which gen-
erally have flatter tibial inserts, is difficult to anticipate
from this study. A recent study showed results that support
a relatively loose flexion gap also for PCL-retaining
knees.29
This study was only able to evaluate compressive tibio-
femoral force generation in the unloaded cadaver knees. It
does not take account of the generation of shear forces
within the knee, which could be significant, especially in a
lax or unstable implantation. Also, the compressive forces
are low compared with the forces expected within the knee
during normal walking. However, the generation of tibio-
femoral force in deep flexion is a reflection of the soft-tissue
tension around the knee. This is likely to be a restriction to
flexion in the knee replacement in vivo. Given that increas-
ing the flexion range of TKRs is a widely-held goal, small
increases in the flexion gap relative to the extension gap
may be a method worth investigating further.
No benefits in any form have been received or will be received from a commer-
cial party related directly or indirectly to the subject of this article.
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... This suggests that the MCL lengthens with knee flexion, while the LCL is most taut in full knee extension. Furthermore, performing valgus testing by applying 25 N at the ankle created strains of 2%, 4%, and 5% in both directions for the MCL 0°, 45°, and 90° of knee flexion, respectively [322,323]. While the MCL had a peak strain to failure of 5.1%, during a simulated drop landing in a cadaveric model, ACL loading was significantly greater at 15.3%, underscoring the greater risk of injury and failure to the ACL during athletic tasks such as drop landings [299]. ...
... While the MCL had a peak strain to failure of 5.1%, during a simulated drop landing in a cadaveric model, ACL loading was significantly greater at 15.3%, underscoring the greater risk of injury and failure to the ACL during athletic tasks such as drop landings [299]. Peak collateral strain (%) MCL, peak strain to failure [299,307,321,403] 17.1 (799 N) MCL [323] 0°0 MCL [323] 45°1-2 MCL [323] 90°2 MCL valgus knee testing using 25-N load at the ankle [322] 0°2 MCL valgus knee testing using 25-N load at the ankle [322] 45°4 MCL valgus knee testing using 25-N load at the ankle [322] 90°5 MCL varus knee testing using 25-N load at the ankle [322] 0°− 1 MCL varus knee testing using 25-N load at the ankle [322] 45°− 1 MCL varus knee testing using 25-N load at the ankle [322] 90°2 LCL, peak strain to failure [321] (392 N) LCL [323] 0°0 LCL [323] 45°0 LCL [323] 90°− 3 to − 4 LCL valgus knee testing using 25-N load at the ankle [322] 0°− 2 LCL valgus knee testing using 25-N load at the ankle [322] 45°− 3 LCL valgus knee testing using 25-N load at the ankle [322] 90°− 3 LCL varus knee testing using 25-N load at the ankle [322] 0°1.6 LCL varus knee testing using 25-N load at the ankle [322] 45°3 LCL varus knee testing using 25-N load at the ankle [322] 90°3 ...
... While the MCL had a peak strain to failure of 5.1%, during a simulated drop landing in a cadaveric model, ACL loading was significantly greater at 15.3%, underscoring the greater risk of injury and failure to the ACL during athletic tasks such as drop landings [299]. Peak collateral strain (%) MCL, peak strain to failure [299,307,321,403] 17.1 (799 N) MCL [323] 0°0 MCL [323] 45°1-2 MCL [323] 90°2 MCL valgus knee testing using 25-N load at the ankle [322] 0°2 MCL valgus knee testing using 25-N load at the ankle [322] 45°4 MCL valgus knee testing using 25-N load at the ankle [322] 90°5 MCL varus knee testing using 25-N load at the ankle [322] 0°− 1 MCL varus knee testing using 25-N load at the ankle [322] 45°− 1 MCL varus knee testing using 25-N load at the ankle [322] 90°2 LCL, peak strain to failure [321] (392 N) LCL [323] 0°0 LCL [323] 45°0 LCL [323] 90°− 3 to − 4 LCL valgus knee testing using 25-N load at the ankle [322] 0°− 2 LCL valgus knee testing using 25-N load at the ankle [322] 45°− 3 LCL valgus knee testing using 25-N load at the ankle [322] 90°− 3 LCL varus knee testing using 25-N load at the ankle [322] 0°1.6 LCL varus knee testing using 25-N load at the ankle [322] 45°3 LCL varus knee testing using 25-N load at the ankle [322] 90°3 ...
Article
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Mechanical loading to the knee joint results in a differential response based on the local capacity of the tissues (ligament, tendon, meniscus, cartilage, and bone) and how those tissues subsequently adapt to that load at the molecular and cellular level. Participation in cutting, pivoting, and jumping sports predisposes the knee to the risk of injury. In this narrative review, we describe different mechanisms of loading that can result in excessive loads to the knee, leading to ligamentous, muscu-lotendinous, meniscal, and chondral injuries or maladaptations. Following injury (or surgery) to structures around the knee, the primary goal of rehabilitation is to maximize the patient's response to exercise at the current level of function, while minimizing the risk of re-injury to the healing tissue. Clinicians should have a clear understanding of the specific injured tissue(s), and rehabilitation should be driven by knowledge of tissue-healing constraints, knee complex and lower extremity biomechanics, neuromuscular physiology, task-specific activities involving weight-bearing and non-weight-bearing conditions , and training principles. We provide a practical application for prescribing loading progressions of exercises, functional activities, and mobility tasks based on their mechanical load profile to knee-specific structures during the rehabilitation process. Various loading interventions can be used by clinicians to produce physical stress to address body function, physical impairments, activity limitations, and participation restrictions. By modifying the mechanical load elements, clinicians can alter the tissue adaptations, facilitate motor learning, and resolve corresponding physical impairments. Providing different loads that create variable tensile, compressive, and shear deformation on the tissue through mechanotransduction and speci-ficity can promote the appropriate stress adaptations to increase tissue capacity and injury tolerance. Tools for monitoring rehabilitation training loads to the knee are proposed to assess the reactivity of the knee joint to mechanical loading to monitor excessive mechanical loads and facilitate optimal rehabilitation. Key Points Mechanical loads encountered during high-risk cutting, pivoting, and jumping sports predispose the structures of the knee to risk of injury. Individual tissues of the knee respond and adapt differently to various mechanical load stimuli. Appropriate selection of exercises, functional activities , and mobility tasks based on their mechanical load profile can be utilized during rehabilitation to systematically and progressively load the structure of the knee to promote tissue healing and repair.
... Function of the collateral ligaments has also gained increasing attention as it relates to total knee arthroplasty (TKA) 8,9 , in which partial release of the MCL is often performed to correct limb alignment and achieve tension balance between the MCL and the lateral collateral ligament (LCL) 10,11 . A thorough understanding of the biomechanics of the collateral ligaments is critical to inform selective release of the MCL fibers, optimize tension balance between the 2 ligaments, and avoid complications including soft-tissue overloading, joint instability, or stiffness 12,13 . ...
... Many surgeons perform intraoperative gap balancing with the aim of achieving tension balance between the MCL and LCL at 0°as well as at 90°of knee flexion 10,11 . However, maintaining this tension balance throughout the full range of knee flexion requires isometric behavior of the MCL and LCL, which was not observed in the current study or previous in vivo or in vitro studies 8,23,24 . The subjects in our study had neutral limb alignment (with <3°of varus/valgus), which is the general target for mechanically aligned TKA 51 . ...
Article
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Background: Tranexamic acid (TXA) is increasingly used to minimize blood loss during total joint arthroplasty (TJA). Although TXA has been shown to be highly effective in reducing operative blood loss, many surgeons believe that it places patients with coronary artery disease (CAD) or a history of coronary stents at an increased risk for myocardial infarction. The purpose of this study was to determine if TXA is safe to use in patients with a history of CAD or coronary stents. Methods: We performed a retrospective analysis at a single, tertiary academic medical center identifying consecutive total hip and knee arthroplasty cases over an 8-year period. From this cohort who received TXA intraoperatively, we identified patients with a history of CAD or coronary stents and determined the total myocardial infarction and venous thromboembolism (VTE) rates within a 90-day postoperative period. Chi-square analyses were used to identify differences in VTE rates between cohorts. A post hoc power analysis was also performed to determine whether our results were powered to detect a difference in VTE rates. Results: In the 26,808 identified at-risk patients, there were no postoperative myocardial infarctions. No significant differences were observed for VTE rates compared with the control cohort using either topical or intravenous TXA, with regard to CAD (0.29% compared with 0.76%; p = 0.09) or coronary stents (0% compared with 0.76%; p = 0.14). Moreover, there was no significant difference observed in VTE rates when administration was subcategorized into intravenous and topical methods with regard to CAD (0.13% compared with 0.72%; p = 0.12) or coronary stents (0% compared with 0%; p = 1.0). Conclusions: In our series, topical and intravenous TXA were equally safe when used in patients with a history of CAD and coronary stents in comparison with the control cohort. With equal efficacy and risk of adverse events, we recommend intravenous TXA, which may enable easier institutional implementation. Level of evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
... Function of the collateral ligaments has also gained increasing attention as it relates to total knee arthroplasty (TKA) 8,9 , in which partial release of the MCL is often performed to correct limb alignment and achieve tension balance between the MCL and the lateral collateral ligament (LCL) 10,11 . A thorough understanding of the biomechanics of the collateral ligaments is critical to inform selective release of the MCL fibers, optimize tension balance between the 2 ligaments, and avoid complications including soft-tissue overloading, joint instability, or stiffness 12,13 . ...
... Many surgeons perform intraoperative gap balancing with the aim of achieving tension balance between the MCL and LCL at 0°as well as at 90°of knee flexion 10,11 . However, maintaining this tension balance throughout the full range of knee flexion requires isometric behavior of the MCL and LCL, which was not observed in the current study or previous in vivo or in vitro studies 8,23,24 . The subjects in our study had neutral limb alignment (with <3°of varus/valgus), which is the general target for mechanically aligned TKA 51 . ...
Article
Full-text available
Background: Improved knowledge of in vivo function of the collateral ligaments is essential for enhancing rehabilitation and guiding surgical reconstruction as well as soft-tissue balancing in total knee arthroplasty. The aim of this study was to quantify in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities. Methods: Knee kinematics were measured using radiographic images captured with a mobile fluoroscope while healthy subjects performed level walking, downhill walking, and stair descent. The registered in vivo tibiofemoral kinematics were then used to drive subject-specific multibody knee models to track collateral ligament elongation. Results: The elongation patterns of the medial collateral ligament varied distinctly among its bundles, ranging from lengthening of the anterior fibers to shortening of the posterior bundle with increases in the knee flexion angle. The elongation patterns of the lateral collateral ligament varied considerably among subjects. It showed an average 4% shortening with increasing flexion until 60% to 70% of the gait cycle, and then recovered during the terminal-swing phase until reaching its reference length (defined at heel strike). Conclusions: The observed nonuniform elongation of the medial collateral ligament bundles suggests that single-bundle reconstruction techniques may not fully restore healthy ligament function. Moreover, the observed ligament elongation patterns indicate greater varus than valgus laxity in the loaded knee. Clinical relevance: Through providing key knowledge about the in vivo elongation patterns of the collateral ligaments throughout complete cycles of functional activities, this study offers in vivo evidence for benchmarking ligament reconstruction and soft-tissue balancing in total knee arthroplasty.
... The elongation patterns of the collateral ligaments during functional movements following TKA have important implications for post-operative knee stability, range of motion, and pain (Jeffcote et al., 2007;Babazadeh et al., 2009;Mihalko et al., 2009;Goudie and Deep, 2014). When ligaments are over-strained, cell death, plastic deformation, and micro-tears can occur (Provenzano et al., 2002). ...
... Assuming average lengths of 100 mm (Liu et al., 2010) and 60 mm (Meister et al., 2000) for iMCL and LCL, they measured 2% slackening of iMCL and 12% slackening of the LCL at 60 • knee flexion with an applied quadriceps force. Isometry of the iMCL after TKA was also reported by a similar cadaver study (Jeffcote et al., 2007). Interestingly, another in vitro investigation (Kowalczewski et al., 2015) found near isometry in the MCL and LCL during passive flexion, but during simulated squatting the LCL shortened and the MCL lengthened with increasing flexion. ...
Article
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The primary aim of this study was to assess the effects of total knee arthroplasty (TKA) implant design on collateral ligament elongation patterns that occur during level walking, downhill walking, and stair descent. Using a moving fluoroscope, tibiofemoral kinematics were captured in three groups of patients with different TKA implant designs, including posterior stabilized, medial stabilized, and ultra-congruent. The 3D in vivo joint kinematics were then fed into multibody models of the replaced knees and elongation patterns of virtual bundles connecting origin and insertion points of the medial and lateral collateral ligaments (MCL and LCL) were determined throughout complete cycles of all activities. Regardless of the implant design and activity type, non-isometric behavior of the collateral ligaments was observed. The LCL shortened with increasing knee flexion, while the MCL elongation demonstrated regional variability, ranging from lengthening of the anterior bundle to slackening of the posterior bundle. The implant component design did not demonstrate statistically significant effects on the collateral elongation patterns and this was consistent between the studied activities. This study revealed that post-TKA collateral ligament elongation is primarily determined by the knee flexion angle. The different anterior translation and internal rotation that were induced by three distinctive implant designs had minimal impact on the length change patterns of the collateral ligaments.
... The design is not a factor in these cases, because this complication occurs in all different designs, especially in the ones who retain the posterior cruciate ligament [2][3][4][5]. Even more, Jeffcote et al. and Nicholls et al. describe that except for the initial choice for the constraint, for example, a cruciate retaining design with an insufficient cruciate ligament, the design is not a factor anymore for dislocation, especially not in the newer posterior stabilized design [13,14]. Tibiofemoral dislocation after total knee replacement with disengagement of the polyethylene liner is a rare complication [4], first reported by Insall et al. in 1979 after total condylar knee replacement in four patients out of a series of 220 patients [15]. ...
Article
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Introduction: Dislocation of a total knee arthroplasty is a rare complication that has rarely been described, while the total knee arthroplasty is frequently performed. From literature, we know patient-related factors, like obesity, neuropsychiatric disease, and severe valgus or varus deformity, are associated with higher risk of dislocation. We show our cases for awareness of the risk factors for surgeons. Case Presentations. We present four patients with a dislocation after a total knee arthroplasty. We compare these case reports with previous literature and show the most important risk factors for these dislocations. In our cases, three of them suffered from obesity, which possibly has contributed to the dislocation. Three patients did have instability which emphasizes the importance of ligament balancing while performing a total knee replacement. In all cases, an exchange of the polyethylene liner was performed. Conclusion: Implant-related factors and surgical technique as well as patient-related factors can contribute to this uncommon complication. Obesity, neuropsychiatric disorders, and a severe valgus or varus deformity are important patient-related risk factors. Our cases show these risk factors too. Some of these risk factors were encountered as well as other comorbidity factors. Such risk factors must be taken into consideration when deciding whether to perform a total knee arthroplasty. This stresses the importance of patient education and shared decision-making before performing a total knee replacement.
... Until now, our current knowledge on collateral ligament function has been almost exclusively obtained from cadaveric studies. Here, in vitro investigations on natural and replaced knees have consistently reported the LCL to be tightest in full extension, and to relax as the knee flexes, 22,49 which is in agreement with the elongation patterns presented in our study. However, compared to the LCL, the biomechanics of the MCL is more complicated mainly due to its band-like geometry. ...
Article
Full-text available
This study aimed to quantify the elongation patterns of the collateral ligaments following TKA during functional activities of daily living. Using mobile video-fluoroscopy to capture radiographic images of the knee in a group of six patients, each with an ultra-congruent knee implant, tibiofemoral kinematics were reconstructed throughout complete cycles of level gait, downhill walking, stair descent, and squat activities. Kinematic data were then used to drive subject-specific multibody knee models to estimate length-change patterns of the LCL as well as three bundles of the MCL. In addition, a sensitivity analysis examined the role of the attachment site in the elongation patterns. Our data indicate a slackening of the LCL but non-uniform length-change patterns across the MCL bundles (ranging from lengthening of the anterior fibers to shortening of the posterior fibers) with increasing knee flexion angle. Near-isometric behavior of the intermediate fibers was observed throughout the entire cycle of the studied activities. These length-change patterns were found to be largely consistent across different activities. Importantly, length-change patterns were critically sensitive to the location of the femoral attachment points relative to the femoral component. Thus, in TKA with ultra-congruent implants, implantation of the femoral component may critically govern post-operative ligament function.
Article
Introduction Alternative alignment concepts have garnered great interest in an effort to improve patient satisfaction following primary TKA. The purpose of this study was to determine variation or deviation from an individual’s native joint line in primary TKA using neutral mechanical versus a restricted kinematic technique. Methods An IRB-approved prospective cohort study was performed evaluating the effect of neutral mechanical alignment (nMA) versus a restricted kinematic technique (rKA) on the native joint line in 100 consecutive patients undergoing primary TKA. Using preoperative CT and intraoperative 3-dimensional software, two virtual preoperative plans were created: nMA and rKA. Templated bone resections were recorded. Change in joint line was calculated using known implant planar thickness and planned bone resection. Results Neutral MA yielded significantly greater deviation from the patient’s native joint line along the lateral compartment of the knee (lateral distal femoral condyle, lateral posterior femoral condyle, lateral tibial resection). With nMA, the lateral distal femoral joint line was distalized by a mean 4.3 versus 2.6 mm using rKA technique (p<0.001). In rKA, >60% of knees had < 3 mm of deviation from the native lateral posterior femoral offset, whereas in nMA, >95% of knees had ≥ 3 mm change in the lateral posterior femoral condylar offset. Conclusion Neutral MA-TKA resulted in statistically larger joint line deviations as compared to rKA-TKA, most notably along the lateral distal femoral condyle joint line. Further analysis is needed to determine the clinical consequences of joint line deviation from the native anatomy using nMA as the target for primary TKA.
Article
PurposeKinematically aligned total knee arthroplasty (KA TKA) targets restoration of patient-specific alignment and soft tissue laxity. However, whether KA TKA reproduces native soft tissue strain remains unclear. This cadaveric study tested the hypothesis that KA TKA would better restore the quantitative strain and strain distribution of medial collateral ligament (MCL) to the native healthy knee compared to mechanically aligned (MA) TKA.Methods Twenty-four fresh-frozen cadaver knees (12 pairs) were mounted on a customized knee squatting simulator to measure MCL strain during flexion. For each pair, one knee was assigned to KA TKA and the other to MA TKA. During KA TKA, the amount of femur and tibia resected was equivalent to implant thickness without MCL release using the calipered measuring technique. MA TKA was performed using conventional measured resection techniques. MCL strain was measured using a video extensometer (Mercury® RT RealTime tracking system, Sobriety s.r.o, Czech Republic). MCL strain and strain distribution during knee flexion were measured, and the measurements compared between native and post-TKA conditions.ResultsMean and peak MCL strain were similar between KA TKA and native knees at all flexion angles (p > 0.1 at all flexion angles) while mean strain at all flexion angles and peak strain at ≥ 60º of MA TKA were approximately twice those of the native knees (p < 0.05 at ≥ 60º of flexion). In addition, greater MCL strain was observed in 4 of 12 regions of interest (ROI) after MA TKA (M1, M2, P1 and P2) compared to the native knee, whereas after KA TKA, MCL strain measurements were similar at all but 1 ROI (P2).ConclusionsKA TKA restored a more native amount and distribution of MCL strain compared to MA TKA. These findings provide clues for understanding why patients may experience better performance and more normal knee sensations after KA TKA compared to MA TKA.Level of evidenceTherapeutic study, Level I.
Article
Aims To compare patients undergoing total knee arthroplasty (TKA) with ≤ 80° range of movement (ROM) operated with a 2 mm increase in the flexion gap with matched non-stiff patients with at least 100° of preoperative ROM and balanced flexion and extension gaps. Methods In a retrospective cohort study, 98 TKAs (91 patients) with a preoperative ROM of ≤ 80° were examined. Mean follow-up time was 53 months (24 to 112). All TKAs in stiff knees were performed with a 2 mm increased flexion gap. Data were compared to a matched control group of 98 TKAs (86 patients) with a mean follow-up of 43 months (24 to 89). Knees in the control group had a preoperative ROM of at least 100° and balanced flexion and extension gaps. In all stiff and non-stiff knees posterior stabilized (PS) TKAs with patellar resurfacing in combination with adequate soft tissue balancing were used. Results Overall mean ROM in stiff knees increased preoperatively from 67° (0° to 80°) to 114° postoperatively (65° to 135°) (p < 0.001). Mean knee flexion improved from 82° (0° to 110°) to 115° (65° to 135°) and mean flexion contracture decreased from 14° (0° to 50°) to 1° (0° to 10°) (p < 0.001). The mean Knee Society Score (KSS) improved from 34 (0 to 71) to 88 (38 to 100) (p < 0.001) and the KSS Functional Score from 43 (0 to 70) to 86 (0 to 100). Seven knees (7%) required manipulations under anaesthesia (MUA) and none of the knees had flexion instability. The mean overall ROM in the control group improved from 117° (100° to 140°) to 123° (100° to 130°) (p < 0.001). Mean knee flexion improved from 119° (100° to 140°) to 123° (100° to 130°) (p < 0.001) and mean flexion contracture decreased from 2° (0° to 15°) to 0° (0° to 5°) (p < 0.001). None of the knees in the control group had flexion instability or required MUA. The mean KSS Knee Score improved from 48 (0 to 80) to 94 (79 to 100) (p < 0.001) and the KSS Functional Score from 52 (5 to 100) to 95 (60 to 100) (p < 0.001). Mean improvement in ROM (p < 0.001) and KSS Knee Score (p = 0.017) were greater in knees with preoperative stiffness compared with the control group, but the KSS Functional Score improvement was comparable (p = 0.885). Conclusion TKA with a 2 mm increased flexion gap provided a significant improvement of ROM in knees with preoperative stiffness. While the improvement in ROM was greater, the absolute postoperative ROM was less than in matched non-stiff knees. PS TKA with patellar resurfacing and a 2 mm increased flexion gap, in combination with adequate soft tissue balancing, provides excellent ROM and knee function when stiffness of the knee had been present preoperatively. Cite this article: Bone Joint J 2020;102-B(4):426–433.
Article
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We have investigated the ability to kneel after total knee replacement. We asked 75 patients (100 knees) at least six months after routine uncemented primary total knee replacement, to comment on and to demonstrate their ability to kneel. Differences between the perceived and actual ability to kneel were noted. In 32 knees patients stated that they could kneel without significant discomfort. In 54 knees patients avoided kneeling because of uncertainties or recommendations from third parties (doctors, nursing staff, friends, etc). A total of 64 patients was actually able to kneel without discomfort or with mild discomfort only and 12 of the remainder were unable to kneel because of problems which were not related to the knee. Twenty-four patients therefore were unable to kneel because of discomfort in the knee. There was no difference between the ‘kneelers’ and ‘non-kneelers’ with regard to overall knee score, range of movement and the presence of patellar resurfacing.
Article
The shape of the flexion gap in 20 normal knees was evaluated by axial radiography of the distal femur, and the results compared with those obtained in a previous study by MRI. The observed asymmetry was reduced by 29% using radiography, with a mean value of 3.6° (1.5° to 6.3°) compared with that obtained by MRI of 5.1° (2.6° to 9.5°), a mean discrepancy of 1.49°. The results obtained by radiography and MRI showed a strong correlation (r = 0.78). Axial radiography is acceptable for the evaluation of the flexion gap and is less expensive and more comfortable to perform than MRI. Additionally, no metallic artefact occurs when the radiological method is used for assessment after arthroplasty.
Our purpose was to determine the mechanism which allows the maximum knee flexion in vivo after a posterior-cruciate-ligament (PCL)-retaining total knee arthroplasty. Using three-dimensional computer-aided design videofluoroscopy of deep squatting in 29 patients, we determined that in 72% of knees, direct impingement of the tibial insert posteriorly against the back of the femur was the factor responsible for blocking further flexion. In view of this finding we defined a new parameter termed the 'posterior condylar offset'. In 150 consecutive arthroplasties of the knee, the magnitude of posterior condylar offset was found to correlate with the final range of flexion.
Article
Forty-seven patients who had been treated by 63 total knee arthroplasties were assessed at 12-84 months after the operation. The data were analyzed to determine if collateral ligament laxity had a detrimental effect on the clinical outcome. The Hospital for Special Surgery (HSS) score was used to make the clinical assessment and a modified HSS score, which excluded points awarded for laxity, was also used. Unidirectional (varus or valgus) and total (varus and valgus) laxity were used as a basis of analysis. None of the examined parameters produced results suggesting that lax knees were worse than stable knees. Indeed, knees with increasing laxity through the categories of mild and moderate showed better statistically significant results in HSS score and pain than those with lesser degrees of laxity. Seventy-five percent of the knees with unidirectional laxity were classified as excellent; only 38.5% of the stable knees were graded as excellent (p less than 0.01). Only 9% of the lax knees had complaints of pain; 38% of the stable knees were painful (p less than 0.05). No significant difference in functional score and walking ability was noted between the lax and the stable knees. Seventy-eight percent of the lax knees had a range of motion over 100 degrees; 62.5% of the stable knees achieved this range.
Article
A strain transducer was developed which employs a magnetic field sensing device to detect linear displacement. The transducer was attached to the medial collateral ligament (MCL) of human autopsy specimens, minimally influencing their physiologic behavior. A strain 'map' of the MCL as a function of knee flexion (full extension to 120 degrees) both with and without abduction force was obtained. Our investigation revealed consistent differences in the strain patterns between proximal, middle and distal segments of the anterior and posterior borders of the MCL. Anatomic variations in the pattern of collagen fibers within the MCL, interactions between posterior oblique capsular fibers and the MCL, and the skeletal configuration may account for these varied strain patterns.
Article
Between 1990 and 1995, 25 painful primary posterior cruciate ligament retaining total knee arthroplasties were revised for flexion instability. These patients shared typical clinical presentations that included a sense of instability without frank giving way, recurrent knee joint effusion, soft tissue tenderness involving the pes anserine tendons and the retinacular tissue, posterior instability of 2+ or 3+ with a posterior drawer or a posterior sag sign at 90 degrees flexion, and above average motion of their total knee arthroplasty. The primary total knee arthroplasty was performed for osteoarthritis in 23 patients and rheumatoid arthritis in two patients. There were 13 male and 12 female patients and their mean age was 65 years (range, 35-77 years). Before the revision operation, Knee Society knee scores averaged 45 points (range, 17-68 points) and function scores averaged 42 points (range, 0-60 points). Twenty-two of the knee replacements were revised to posterior stabilized implants and three underwent tibial polyethylene liner exchange only. Nineteen of the 22 knee replacements revised to a posterior stabilized implant were improved markedly after the revision surgery. Only one of three knee replacements that underwent tibial polyethylene exchange was improved. After the revision for flexion instability, Knee Society knee scores averaged 90 points (range, 82-99 points) and function scores averaged 75 points (range, 45-100 points) for the 20 knees with a successful outcome. This study suggests that flexion instability can be a cause of persistent pain and functional impairment after posterior cruciate ligament retaining total knee arthroplasty. A revision operation that focuses on balancing the flexion and extension spaces, in conjunction with a posterior stabilized knee implant, seems to be a reliable treatment for symptomatic flexion instability after posterior cruciate retaining total knee arthroplasty.
Article
The anatomy and kinematics of the lateral collateral ligament were studied in 10 unembalmed limbs and 20 isolated femurs and fibulas. The ligament's average overall length was 66 mm (range, 59 to 74) and the average greatest dimension of its thin middle portion was the anteroposterior dimension of 3.4 mm (range, 3 to 4). The center of the femoral attachment site was 3.7 mm posterior to the ridge of the lateral epicondyle, not at it apex. A potential radiographic technique for operatively locating the femoral attachment site to within 3 mm is described. During knee flexion in neutral rotation the distance between the femoral and fibular attachment sites of the lateral collateral ligament decreased to 88% of its value in full extension. With 6.5 N x m of applied external rotation force, beyond 30 degrees of flexion the attachment sites rapidly approximated. With the same internal rotation force, beyond 15 degrees of flexion the attachment sites separated. From 60 degrees to 105 degrees they were greater than 100% of the value in full extension, suggesting significant distraction between the attachment sites. These changes correlated well with the ligament's change from an 11 degrees posterior slope in extension to a 19 degrees anterior slope in flexion with no applied rotation.
Article
To the best of our knowledge, this is the first study to assess the accuracy of balancing of the flexion and extension gaps in total knee arthroplasty (TKA). Measurements of the heights of the flexion and extension gaps were obtained during 104 consecutive primary, posterior-stabilized TKAs in osteoarthritic patients. Clinically, all knees appeared to be well balanced intraoperatively. Rectangular flexion and extension gaps almost always were obtained within 1 mm (84%-89%). None of the knees was >3 mm from being perfectly rectangular. Equality of the flexion and extension gaps was more difficult to obtain (47%-57% were within 1 mm). With meticulous attention, perfect soft tissue balance is not always achieved in TKA.
Article
OBJECTIVE: To determine the responses of the medial and lateral collateral ligaments (MCL, LCL) of the human knee to externally applied stresses. DESIGN: Differential variable reluctance transducers were used to measure length changes along the long posterior parallel fibers of the MCL and the middle third of the LCL through a flexion range of 15-120 degrees and a variety of external stresses. BACKGROUND: There is a lack of consensus regarding the collateral ligament response to internal and external tibial rotation. In addition, there are very few studies that have investigated the effects of quadriceps and hamstrings muscle group loads on the strain in the collateral ligaments. METHODS: Three series of tests were performed. First, the passive behavior of the ligaments was obtained as well as the ligament response to 3 degrees of varus and valgus rotation. The next series tested the ligaments' response to 0-10 degrees of internal and external tibial axial rotation. Finally, isolated and co-contracted quadriceps and hamstrings muscle group loads were applied. RESULTS: The instrumented portions of both ligaments were more strained in extension than flexion. Varus rotations stretched the LCL, whereas valgus rotations elongated the MCL. The strain in the MCL was shown to increase during external rotation and decrease during internal rotation. The LCL did not exhibit a uniform response across specimens to internal or external tibial axial rotation, but was consistent between left and right knees from a single cadaver. Highly consistent trends of interactions between muscle loads and the strain in both the MCL and LCL were noted. CONCLUSIONS: The responses of the MCL and LCL to applied stresses are dependent upon the flexion angle of the knee, the influence of muscle loading and, to a lesser extent, anatomic variation in the ligaments themselves. Guidelines for rehabilitation of the collateral ligaments following injury are suggested.