Capsuloligamentous Constraint.
Last updated Thursday, February 10, 2005
Common functional positions Shoulders were stressed to the clinical end point The amount of translation was highly reproducible This group of normal shoulders demonstrated substantial translations on these clinical laxity tests The magnitudes of the passive glenohumeral translations measured in the unstable shoulders were remarkably similar to those measured in the normal subjects Capsular laxityWhat is laxity in the glenohumeral joint? The capsule and its associated ligaments are lax in most of the common functional positions of the glenohumeral joint.
To see this compare the common functional positions with the
envelope of motion in which there is no capsular tension (see figures).
This laxity is necessary for the joint to achieve its large range of
positions. Because of this midrange laxity, the capsule cannot
stabilize the joint in many important functional positions. Instead,
centering of the humeral head in the glenoid fossa must depend on other
mechanisms, such as concavity compression.
To demonstrate the degree of laxity present in eight normal
shoulders, electromagnetic sensors were pinned to the humerus and
scapula to allow accurate measurement of the magnitude of translation
on standard clinical tests of glenohumeral laxity: the anterior and
posterior drawer tests, the sulcus test, and the push-pull test. The
anterior and posterior drawer tests were performed by stabilizing the
scapula and clavicle with one hand while grasping the proximal humerus
with the other hand. The arm was placed in a relaxed position at the
subject's side. The humeral head was pushed forward to assess maximal
anterior translation and then pushed posteriorly to assess maximal
posterior translation. In the sulcus test, downward traction was
applied to the subject's arm while the shoulder girdle was stabilized
with the other hand.
The push-pull test was performed with the subject supine and the arm
elevated 90 degrees in the plus 20 degrees thoracic plane. The examiner
pushed down on the proximal humerus with one hand while pulling up on
the subject's wrist with the other.
The shoulders were stressed to the clinical end point. Even though
the force applied was not quantified, the amount of translation was
highly reproducible. The results of these tests indicate that this
group of normal shoulders demonstrated substantial translations on
these clinical laxity tests. These data indicate that, in the positions
tested, the capsule and ligaments were lax and were not contributing to
the centering of the humeral head in the glenoid fossa. We conclude
that in these midrange positions, the head is centered by stabilizing
mechanisms other than the capsule and ligaments.
Because laxity is a feature of stable shoulders, it is of interest
to ask whether unstable shoulders have more laxity than stable
shoulders. Of greater clinical relevance are the questions: Are laxity
tests useful in discriminating stable from unstable shoulders? Do
laxity tests reveal the primary pathology in glenohumeral instability?
As a step toward answering these questions, we measured the laxity of
16 patients requiring surgery because of symptomatic recurrent
instability that was refractory to non-operative management. We then
compared these results with those of normal shoulders presented
earlier. Eight of these patients had classic anterior traumatic
instability and eight had classic atraumatic instability. Each patient
was studied under anesthesia just prior to surgical repair, with our
electromagnetic position sensors rigidly attached to the humerus and
scapula. The laxity tests were carried out exactly as described earlier
for the normal subjects. The magnitudes of the passive glenohumeral
translations measured in the unstable shoulders were remarkably similar
to those measured in the normal subjects.
These results suggest that glenohumeral laxity is not the
preponderant factor in determining the clinical stability of the
shoulder. Shoulders that are quite lax may be completely stable, while
those without major laxity may be clinically unstable. These data
further serve to caution against using the magnitude of translation on
these laxity tests to distinguish between clinically stable and
unstable shoulders. As we will see, the diagnosis of instability must
rest on a careful history and physical examination which endeavor to
define the problem that is symptomatic for the patient.
In conclusion, substantial translational laxity is allowed by the
normal glenohumeral joint capsule, especially in midrange positions.
The wide variance in translation among normal shoulders precludes the
definition of a "normal" amount of translation on laxity tests.
Translation on clinical laxity tests is not an indication of
instability. Stability of the glenohumeral joint, especially in
midrange positions, must be due to factors other than tension in the
capsular structures.
Movies
Disclaimer
This resource has been provided by the University of Washington Department of Orthopaedics and Sports Medicine as general information only. This information may not apply to a specific patient. Additional information may be found at http://www.orthop.washington.edu or by contacting the UW Department of Orthopaedics and Sports Medicine.
How useful was this page or article?
|
|