To The Editor:
I read with great interest the article "Posterolateral
Dislocation of the Elbow Joint. Relationship to Medial Instability" (82-A:
555-560, April 2000), by Eygendaal et al. I congratulate the authors on
a well-designed study with a clear purpose. On the basis of their
study design, I believe that they have adequately fulfilled their
purpose in showing how residual medial instability after an elbow
dislocation can correlate with a worse clinical and radiographic
result. However, I was less satisfied with their discussion, as
they missed the opportunity to clarify some important points concerning
the involvement of the medial collateral ligament in posterolateral rotatory
instability of the elbow and also the importance of the position
of the forearm during the test for valgus instability. Also, the
authors’ sometimes interchangeable use of the terms "medial
instability" and "valgus instability" was confusing.
The authors assessed "medial instability" with
use of a radiographic stress test with the elbow flexed 25 and the
forearm in "slight" supination. They found that "all
of the elbows that were shown to have a ruptured or avulsed medial
collateral ligament on imaging studies [magnetic resonance
imaging combined with arthrography] were unstable on dynamic
radiographs." What they failed to explain was why some
patients had "medial instability" according to
their radiographic stress test but a normal image of the medial
collateral ligament. These patients likely had posterolateral instability
of the elbow without medial collateral ligament insufficiency. In
a patient with posterolateral rotatory instability of the elbow
and an intact medial collateral ligament, valgus instability may
be found on exam when the forearm is not fully pronated and maximally
if supinated. In this situation, valgus instability occurs because
the ulnohumeral joint subluxes posterolaterally, pivoting on the
intact medial collateral ligament, thus giving an examiner the impression
of valgus instability. To maximize the stress on the medial collateral ligament,
the forearm should be placed in full pronation, which reduces the
posterolateral subluxation. The authors tested their patients in "slight" supination, and
they measured the change in distance between the medial epicondyle
and the coronoid. If they wished to evaluate the correlation between
the findings of the stress test and those of magnetic resonance
imaging of the medial collateral ligament, then the stress test
should also have been performed with the forearm in full pronation.
Increased distance from the coronoid to the medial epicondyle can
occur with either valgus instability due to medial collateral ligament
insufficiency or posterolateral rotatory instability. The authors
could have analyzed the change in the medial ulnohumeral joint-space opening,
which may have a more direct correlation with medial collateral
ligament insufficiency.
As the article stands, the term "medial instability" can
refer to patients with either (1) true medial collateral ligament
instability with or without posterolateral rotatory instability,
or (2) posterolateral rotatory instability without involvement of
the medial collateral ligament. The conclusions are sound in that patients
with this residual "medial instability" have a
worse outcome in this study group. However, the readers of this
article should be cautioned not to conclude that this residual instability
is necessarily due just to medial collateral ligament insufficiency.
D. Eygendaal, S.H.M. Verdegaal, W.R. Obermann, A.B. van Vugt,
R.G. Pöll, and P.M. Rozing reply:
We carefully read the letter from Dr. Caputo. We do not agree with
his comments for the following reasons.
First, the medial collateral ligament is the primary stabilizer
for valgus forces. Resection of the radial head has been proven
not to produce any valgus instability1.
Second, posterolateral rotatory instability, as described by O’Driscoll
et al.2, can be detected only
with the hand in maximal supination. In our study we positioned
the hand in only slight supination.
Olsen et al.3 have recently
shown, in a cadaveric study, that complete transection of the lateral
collateral ligaments results in "pseudo" valgus
instability only between 40º and 120º of flexion
in the elbow. However, in our study the elbow was flexed 25º,
a position in which posterolateral instability cannot result in
valgus instability.
The fact that some patients demonstrated instability with dynamic
radiography despite an apparently normal magnetic resonance image
can be explained by the fact that small or partial ruptures of the
medial collateral ligament are hard to detect with magnetic resonance
imaging technology.
In the international literature the terms "valgus instability" and "medial
instability" are used interchangeably. Valgus instability
induced by an insufficient lateral collateral ligament complex is
often described as "pseudo-valgus instability."