This week's Article of the Week comes from the June 2020 issue of JSES.
The Article
Mehl J, Hedgecock J, Otto A, et al. Glenoid version is associated with different labrum tear patterns in shoulder instability Journal of Shoulder and Elbow Surgery. 29(8);1642-1649.
The authors retrospectively studied 123 patients with symptomatic shoulder instability (dislocation) who underwent surgical repair of their labrum from a single surgeon. Exclusion criteria were patients with concomitant rotator cuff pathologies, fractures of the shoulder girdle other than bony Bankart lesions, osteoarthritis of the glenohumeral or acromioclavicular joint, and chronic systematic musculoskeletal disease (eg, rheumatoid arthritis).
Measurements of the glenoid retroversion from preoperative MRI's were compared to the location of the patient's labral pathology as noted from the operative report. Retroversion refers to a posterior facing glenoid (see figure) that is often the result of genetics, trauma or osteoarthritis (especially in overhead athletes).
The Findings
Patients were categorized into 3 groups based on where their labrum tear began and ended. Statistically significant differences were found for all group comparisons:
Figure 1: (anterior tears) average glenoid version was 11.2 + 5.3 deg retroversion
Figure 2: (posterior tears) average glenoid version was 19.9 + 4.7 deg retroversion
Figure 3: (anterior & posterior tears) average glenoid version was 14.2 + 4.6 deg retroversion
"Combined anterior, inferior, and posterior labral defects showed a significantly increased retroversion as compared to isolated anterior labral defects, whereas isolated posterior labral defects showed even higher angles of glenoid retroversion."
The Application
Based on this study's findings, more retroversion (and essentially sloping toward the posterior aspect of the glenoid) was correlated with more posterior labral tears and posterior instability. This is particularly relevant in overhead athletes, such as baseball players and swimmers. As the scapular and postural stabilizers (don't forget the thoracic spine!) become fatigued through forceful, repetitive activity, their ability to produce force weakens and some muscular stiffness is lost to compensatory tension. All this means, is the position of the scapula slowly changes on the rib cage, further protracting, tilting anterior and into internal rotation. This positioning combined with repetitive activity contribute to greater wearing of the glenoid rim and labrum under the humeral head.
This posterior wear pattern has also been noted in cases of osteoarthritis (OA) in the shoulder; replacement surgery (arthroplasty) attempts to either restore or stabilize the glenoid retroversion. This is why we note a forward, rounded shoulder in an examination, or the presence of a "posteriorly displaced humeral head" on XRay. While it may not truly indicate if a patient will develop posterior labral pathology or OA, it's still something to keep in the back of your mind as we work to correct the resultant positioning.
One last interesting point is that researchers have noticed patterns in muscle activation and patients with posterior instability. Evidence is also pointing to patients with shoulder OA and B glenoids (retroverted) have correlating deactivation of the suprascapular nerve which feeds the infraspinatus- a major stabilizing force during overhead motions.
Moral of the story: yes, more glenoid retroversion can be a contributing factor to identifying those at risk for posterior instability. All the more reason to work to maintain our athletes' mobility and strength through a season in order to prevent surgery!
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