Sunday, December 30, 2012

Anatomy of the arthritic glenoid

Three-dimensional measurement method of arthritic glenoid cavity morphology: Feasibility and reproducibility

In their first sentence, these authors remind us that "Glenoid component loosening is the main complication of total shoulder arthroplasty". They suggest that better knowledge of the arthritic glenoid cavity anatomy can help in developing new implants and techniques. In this study they use a CT scan-based, 3D measurement method used to describe the arthritic glenoid cavity morphology.

While we are unsure that the described methodology will find practical use in preoperative planning, this study is of greatest interest with respect to their measurements of this variation in 41 patients with glenohumeral osteoarthritis.  The size, age or gender of these patients are not provided.

Version averaged -12±11 degrees (23 of anteversion to  29 of retroversion). 
The radius of curvature of the glenoid face averaged 35±9 (22-66)
These two results show the wide variation the the anatomy that a shoulder surgeon needs to be prepared to manage in reconstructing the joint. In our experience, anteverted glenoids are more common in women, which is fortuitous because we can allow more range of internal rotation without worrying about posterior instability. The retroverted glenoid, on the other hand, is more common in men and require more attention to the risk of posterior instability.
Tightly cupped glenoids (such as those with a radius of curvature of 22 mm) may require reaming of the periphery to fit the back of the glenoid prosthesis, whereas flat glenoids (such as those with a radius of curvature of 66 mm) may require central reaming to fit the back of the glenoid prosthesis.

Their other measurements included:
The superior-inferior dimension of the glenoid averaged 41±6mm (32 to 55).
The anterior-posterior dimension of the glenoid averaged 29±5mm (20 to 45)
The distance from the inferior glenoid at the maximum glenoid width averaged 20±3mm (15 to 28)
 The variation here indicates that even with multiple shapes of glenoid prostheses, the surgeon will have to choose either to leave some glenoid surface uncovered or to have some of the prosthesis overhanging the bone.