Sunday, July 17, 2016

Reverse total shoulder - the effect of implant design on external rotation range of motion

The Effect of Humeral Inclination on Range of Motion in Reverse Total Shoulder Arthroplasty: A Systematic Review.

These authors conducted a systematic review of studies evaluating reverse total shoulders (RTSA) that reported the type of prosthesis as well as active postoperative ROM at a minimum of 12 months after surgery. Preoperative range of motion, postoperative range of motion and the difference in range of motion was compared between RTSA humeral components with cup inclination 135° and 155°.

Sixty-five studies with 3302 patients (3434 shoulders; 1211 in the 135° group and 2223 in the 155° group) were included. 

Patients in the 135° group had significantly greater improvement in external rotation (P < .001) and significantly more overall external rotation compared to the 155° group. No significant difference were found between the 135° and 155° groups in range of motion improvements in forward elevation or abduction.

Comment: As the authors point out, the 135° neck shaft angle humeral prosthesis is usually used with a laterally offset glenosphere

whereas the 155° humeral prosthesis is usually used with a medialized glenosphere
So the effects of the humeral neck shaft angle may not be separable from the effects of the glenosphere design.

While the authors do not suggest why the 135° neck shaft angle humeral prosthesis is associated with more rotation, it is possible that the steeper angle and the lateral glenosphere offset reduce the risk of humeral abutment against the glenoid in external rotation as suggested by this axillary view.

Our approach to reverse total shoulder arthroplasty is shown in this link. Our goal, whenever possible, is a cementless impaction grafted humeral stem with a 135 degree angle and a laterally offset glenopshere securely fixed with screws in the high quality bone at the base of the subscapularis fossa with minimal inferior placement to avoid excess tension on the acromion and the brachial plexus. This combination may allow for a greater range of external rotation.


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