Thursday, November 26, 2015

Shoulder arthritis - evaluating and managing the abnormal anatomy

A comparison of normal and osteoarthritic humeral head size and morphology

These authors evaluated 150 humeral heads included: (a) "normal" cadaveric specimens, (b) patients with OA and  symmetric glenoid erosion, and (c) patients with OA and asymmetric (type B2) glenoid erosion.

Measurements included sphere-fit diameter of the humeral head articular surface, circle-fit diameter of the humeral head articular surface in the superoinferior plane, circle-fit diameter of the humeral articular surface in the anteroposterior plane, humeral head height relative to the osteotomy plane, and superoinferior and anteroposterior chord distances of the osteotomy surface after excision of the humeral head. Some of the results are shown in the chart below.

The authors concluded that while OA humeral head morphology varies significantly from normal, it does not vary between shoulders with symmetric and asymmetric glenoid wear. 

Comment: Essentially this study shows that arthritic humeral heads are flattened in comparison to cadaveric humeral heads without obvious arthritis. While the normal diameters of curvature ranged from 37 to 55 mm, the arthritic heads ranged in diameter from 36 to 96 mm in the AP dimension!

This humeral head flattening is nicely shown by a case we treated two years ago

 The standardized axillary view (the 'truth' view) also shows the biconcave glenoid and posterior subluxation of the head on the glenoid face (no CT needed).

While some surgeons may treat this pathology using patient specific instrumentation, posterior glenoid bone graft, reaming the high side of the glenoid or a posteriorly augmented plastic glenoid component, in these situations we ream the glenoid conservatively with out attempting to change version, insert a standard glenoid component, and balance the soft tissues. This shoulder was clinically and radiographically stable at two years after surgery.

On the standardized axillary view, the humeral head center remained nicely aligned with the center line of the glenoid prosthesis.

In our practice of ream and run arthroplasty, the glenoid is almost always reamed to a 58 mm diameter of curvature mating with a 56 mm diameter of curvature humeral head component irrespective of the preoperative pathoanatomy or the estimated 'normal' anatomy of the shoulder.

Be sure to visit "Ream and Run - the state of the art"  regarding this radically conservative approach to shoulder arthritis at this link.


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