A Radiological Sign in Chronic Collateral Ligament Injuries of the Thumb Metacarpophalangeal Joint

Abstract

Background
Differentiating chronic from acute injuries of the collateral ligament of the metacarpophalangeal joint (MCPJ) of the thumb can be difficult in the absence of a conclusive history and examination. We aimed to establish the presence of a radiological sign in patients with a chronic injury and the reliability of the sign in differentiating chronic from acute ligament injury.

Methods
Consecutive patients undergoing surgical treatment for chronic (n = 14) or acute (n = 8) ligament injury of the MCPJ of the thumb were identified retrospectively. Six upper limb orthopedic surgeons and four musculoskeletal radiologists were recruited from three regional centers. Observers judged the presence or absence of the sign, an exostosis at the level of the neck of the thumb metacarpal, on radiographs presented on a computer program. The radiographs were then observed in a different random order. The sensitivity, specificity, positive predictive value (PPV), and negative predictive values (NPV) of the radiological sign were evaluated for each observer and the intra- and interobserver error was calculated.

Results
The mean observer specificity and sensitivity for the sign were 84 and 54 %, respectively. The PPV and NPV were 89 and 52 %, respectively. The kappa statistic for intraobserver error was 0.69 and interobserver error 0.34.

Conclusions
A radiological sign associated with chronic collateral ligament injuries of the MCPJ of the thumb is established. The presence of the sign can increase the confidence of the clinician in differentiating chronic from acute collateral ligament injuries, when history and examination are inconclusive in this respect.

Full text

SURGERY ARTICLES
A radiological sign in chronic collateral ligament injuries
of the thumb metacarpophalangeal joint
Alistair R. Hunter &Rosamond J. Tansey &
Lindsay T. Muir
Published online: 30 November 2012
#American Association for Hand Surgery 2012
Abstract
Background Differentiating chronic from acute injuries of
the collateral ligament of the metacarpophalangeal joint
(MCPJ) of the thumb can be difficult in the absence of a
conclusive history and examination. We aimed to establish
the presence of a radiological sign in patients with a chronic
injury and the reliability of the sign in differentiating chron-
ic from acute ligament injury.
Methods Consecutive patients undergoing surgical treat-
ment for chronic (n014) or acute (n08) ligament injury of
the MCPJ of the thumb were identified retrospectively. Six
upper limb orthopedic surgeons and four musculoskeletal
radiologists were recruited from three regional centers.
Observers judged the presence or absence of the sign, an
exostosis at the level of the neck of the thumb metacarpal,
on radiographs presented on a computer program. The
radiographs were then observed in a different random order.
The sensitivity, specificity, positive predictive value (PPV),
and negative predictive values (NPV) of the radiological
sign were evaluated for each observer and the intra- and
interobserver error was calculated.
Results The mean observer specificity and sensitivity for the
sign were 84 and 54 %, respectively. The PPV and NPV
were 89 and 52 %, respectively. The kappa statistic for
intraobserver error was 0.69 and interobserver error 0.34.
Conclusions A radiological sign associated with chronic
collateral ligament injuries of the MCPJ of the thumb is
established. The presence of the sign can increase the
confidence of the clinician in differentiating chronic from
acute collateral ligament injuries, when history and exami-
nation are inconclusive in this respect.
Keywords Chronic .Metacarpophalangeal joint .Collateral
ligament .Thumb .Radiological sign
Background
Injury of the collateral ligament of the metacarpophalan-
geal joint (MCPJ) of the thumb is common, particularly
amongst skiers and ball-handling athletes [2], and can lead
to disabling joint instability. The mechanism of acute
injury to the ulnar collateral ligament is sudden forced
abduction, with injury to the radial collateral ligament
requiring forced adduction. Chronic injuries to either lig-
ament occur with repeated trauma causing chronic liga-
mentous laxity [1] or with delayed presentation of acute
injury. An injury to the collateral ligament in this study
refers to a complete tear of the proper collateral and/or the
accessory collateral ligament.
In most cases, clinical evaluation by history and exami-
nation allows differentiation of chronic from acute injury.
The history for patients with chronic injury can be more
difficult to identify, presenting with recurrent trauma, a
sense of instability of the thumb, pincer grip weakness, or
difficulty grasping objects [6]. The reference standard for
diagnosis of an injury is clinical stress examination in flex-
ionandextension[12,16]. Examination in acute injury
reveals bruising, swelling, and tenderness at the MCPJ;
these signs are unlikely in chronic injury. Routine investi-
gation includes anteroposterior (AP) and lateral thumb
radiographs to identify avulsion fractures and exclude other
fractures. If the diagnosis of instability is uncertain, stress
radiographs can be performed [16]. Ultrasound and
A. R. Hunter :R. J. Tansey :L. T. Muir
Upper Limb Unit, Department of Orthopedic Surgery,
Salford Royal NHS Foundation Trust, Stott Lane,
Salford M6 8HD, UK
A. R. Hunter (*)
Department of Orthopedics, Chase Farm Hospital,
The Ridgeway, Enfield,
Middlesex EN2 8JL, UK
e-mail: hunteralistair@hotmail.com
HAND (2013) 8:191–194
DOI 10.1007/s11552-012-9472-7

magnetic resonance imaging (MRI) have been used to dis-
criminate simple avulsions from Stener lesions [4,8,11].
For acute unstable injuries, an acute repair is advocated
[16], with bone anchors giving excellent results [3,17]. At
more than 3 weeks between injury and surgery, “chronic”
cases require reconstruction rather than repair [13,15], with
a tendon graft giving good results [5]. Optimal operative
planning prior to surgical treatment is more difficult in the
minority of patients whose history and examination are
inconclusive in relation to the chronicity of the injury. A
further means of helping distinguish chronic from acute
injury would be useful.
We have observed a radiological sign on plain radio-
graphs of the thumb in patients with chronic injuries of the
collateral ligament of the MCPJ. The aim of the study was to
establish the presence of this sign in patients with chronic
injury and the reliability of the sign in differentiating chron-
ic from acute ligament injury.
Materials and Methods
This was a prospective study on retrospectively collected
material (radiographs). Consecutive patients undergoing
surgical treatment for chronic (n014) or acute (n08) liga-
ment injury of the MCPJ of the thumb under the care of the
senior author between 2006 and 2008 were identified by
reviewing the operative logbook (Table 1). For the purposes
of this study, acute injuries were defined as presenting
within 4 weeks of injury and chronic injuries after this
period. Patients with acute injuries underwent repair, where-
as those with chronic injuries underwent reconstruction.
Only patients with a conclusive history and examination
(with respect to chronicity) and consistent intraoperative find-
ings were included. The diagnosis of injury had been estab-
lished preoperatively based on standard history and
examination including stress examination in flexion. All
patients had AP and lateral plain radiographs. In 10 cases,
plain radiograph stress views or ultrasound stress views were
performed for confirmation of instability and one case had an
MRI scan. Patients under the age of 16 years were excluded.
The AP and lateral thumb plain radiograph images for each
patient were obtained (Institutional Review Board approval
was not required by the institution). The authors examined the
patients' radiographs to determine which they considered to
have the radiological sign as described (Table 1). Six upper
limb orthopedic surgeons (five consultants and one hand
fellow) and four consultant musculoskeletal radiologists were
recruited as observers from three regional centers. A computer
slide show was designed to present the images to the clini-
cians. The 22 sets of radiographs of chronic and acute injuries
were arranged in random order determined by a computer
random number generator. The series was then repeated in a
second random order. The first page demonstrated an example
of the radiological sign found in chronic collateral ligament
injuries as shown in Fig. 1. The sign is described as a bony
exostosis at the thumb metacarpal neck in the distal radial or
ulnar aspect on the AP view and often on the dorsal cortex on
the lateral view. Each observer judged the presence or absence
of the radiological sign for each set of radiographs on the
computer slide show.
We compared observations for chronic collateral liga-
ment injuries with acute collateral ligament injuries. The
sensitivity, specificity, positive predictive value (PPV), and
negative predictive values (NPV) of the sign were evaluated
for each observer. The mean and standard deviation for
these values across the observers was calculated. Each ob-
server assessed the radiographs on two occasions, allowing
derivation of the intraobserver error. The intraobserver error
and the interobserver agreement were calculated using kap-
pa statistics. In addition, an intraoperative biopsy of the
exostosis in a patient undergoing a reconstruction for a
chronic collateral ligament reconstruction was obtained.
Results
There were a total of 440 possible responses by observers;
from these, four (0.9 %) were not completed. The character-
istics of the patients are shown in Table 1. The sensitivity,
specificity, PPV, and NPV for the radiological sign are
shown in Table 2, both for all cases (a) and for the subset
of chronic cases that were confirmed sign-positive by the
authors (b). The mean observer concordance for the radio-
logical sign was 86 %, giving an intraobserver error of
14 %. The kappa statistic compares the extent of agreement
observed against how much would be expected to occur by
chance alone. The kappa value for the intraobserver
Table 1 The chronic and acute ligament injuries to the MCPJ of the thumb
Injury NMean age Ulnar collateral
ligament injured
Radial collateral
ligament injured
Sign-positive
a
as determined
by the authors
Chronic 14 38 9 5 12
Acute 8 31 7 1 0
a
Denotes the number of patients with the radiological sign as determined by the authors after careful scrutiny of the plain radiographs
192 HAND (2013) 8:191–194

reliability was 0.69, interpreted as substantial intraobserver
reliability [9]. The kappa statistic for the interobserver reli-
ability was 0.34, interpreted as “fair”agreement between
observers [9]. The histology of the bony exostosis revealed
it was composed of woven bone.
Discussion
This study has established a radiological sign in patients with
chronic collateral ligament injuries of the MCPJ of the
thumb. In the context of distinguishing chronic from acute
injuries, the sign has good specificity, positive predictive
value, and intraobserver reliability and acceptable interob-
server reliability. When present, the sign can increase the
confidence of the clinician when the chronicity of injury is in
doubt. For example, a patient may present with a history of
recent injury and pain in the thumb MCPJ, but a clinical
examination more consistent with chronic ligament injury.
Identification of the sign can aid preoperative decisions
regarding the appropriate choice of surgical procedure and
help in the preoperative counseling of the patient. The sign
shows low sensitivity, which means that absence of the sign
cannot be used to exclude a chronic injury.
Exostoses of the thumb in response to injury have previ-
ously been described. Wissinger et al. [18] described a series
of 10 cases of turret exostoses in the dorsal aspect of the
phalanges of the hand as a rare complication of minor
trauma. A case of turret exostosis in the distal fifth metacar-
pal reported by Rubin and Steinburg [14] and of the volar
aspect of the distal phalanx of the thumb by Mohanna et al.
[10] after similarly minor trauma. The pathogenesis was
postulated to be the presence of a wound of the dorsal
periosteum followed by the formation of a subperiosteal
hematoma. The drainage of the periosteum is obstructed
and the maintenance of the osteogenic properties of the
periosteum overlying the hematoma results in hematoma
ossification over a period of months.
The woven bone seen on the histology of one patient's
lesion is consistent with previous histology of the turret
exostosis [18]. We postulate that the exostosis develops by
a similar mechanism of a contained subperiosteal hematoma
adjacent to the distal metacarpal after the collateral ligament
rupture. This then ossifies over time, becoming evident on
the radiographs of the chronic collateral injury group, but
not seen on radiographs of the acute collateral ligament
injuries. Of note, the presence of a small hematoma on
ultrasound is a strong confirmation of the presence of a
collateral ligament rupture and is usually found at the meta-
carpal side [7]. This would account for the presence of the
exostosis at the metacarpal neck as opposed to the most
common site of injury of the ligament, the phalangeal side.
The 12 patients identified by the authors as having the sign
Fig. 1 The radiological sign: an exostosis at the neck of the thumb
metacarpal. Anteroposterior and lateral radiographs of the thumb. The
sign is indicated by the arrow on the anteroposterior and lateral views
Table 2 The observations of the sign in chronic collateral ligament injuries versus acute collateral ligament injuries
Comparison Mean sensitivity% Mean specificity% Mean PPV% Mean NPV%
(SD) (SD) (SD) (SD)
(a) All chronic injuries versus acute injuries 54 84 89 52
(18) (20) (13) (9)
(b) Sign-positive chronic injuries versus acute injuries 61 82 65 85
(21) (15) (26) (6)
SD standard deviation, PPV positive predictive value, NPV negative predictive value
HAND (2013) 8:191–194 193

presented at least 2 months after their apparent injury, indi-
cating that the exostosis may take this period of time to
develop.
An interesting and unexpected finding in our cohort is
that in 6 of the 14 cases, the sign was found on the contra-
lateral side to the collateral ligament injury. This may sug-
gest that the exostosis can be formed from subperiosteal
hematoma formation due to the ligament rupture itself or
by a contrecoup injury mechanism from the proximal aspect
of the proximal phalanx. An alternative explanation for the
exostosis might have been that this was a simple osteophyte
secondary to degenerative changes. However, on radiologi-
cal and routine intraoperative review, no cases showed signs
of osteoarthritis. We are only able to draw limited conclu-
sions regarding laterality of the sign in this study, as we did
not ask observers to document the side on which the sign
was identified.
The study was limited by the relatively small number of
cases, though the 10 independent observers increased the
total number of observations. Contralateral thumb radio-
graphs were not taken, but would rule out the possibility
of an underlying symmetrical abnormality. The radiographs
were assessed by observers in the absence of their clinical
context, as was necessary to ensure blinding to the diagno-
sis. A study reviewing the use of this sign in clinical practice
and its laterality would be of benefit.
A radiological sign associated with chronic collateral
ligament injuries of the MCPJ of the thumb is presented.
The presence of this sign can help the clinician differentiate
between chronic and acute collateral ligament injuries in
patients in whom the history and examination are inconclu-
sive in this respect, contributing to the planning of appro-
priate surgical intervention.
Conflict of interest All named authors hereby declare that they have
no conflicts of interest to disclose.
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