Use of a locking stem for reverse shoulder arthroplasty is a rare but reliable option.

Introduction: RSA is widely used in the treatment of complex trauma or degenerative changes of the shoulder. Strong primary fixation of the stem is necessary to prevent any loosening of the stem and subsequent revision. Presently, cement fixation or press-fit fixation are two options for humeral fixation, though each has its own limitations and risks. The aim of the current study is to evaluate the effectiveness of an alternative option involving a distal screw interlocking system for fixation of the humeral stem from initial implantation.

Methods: We performed a retrospective multicenter study of patients implanted with the Humelock Reversed® stem RSA that can be locked with distal humeral screws in cases of operative poor press fit or to modulate the lengthening of the arm via prosthetic humeral height. Seventy-two patients with a minimum two year follow-up were included, 13 for acute trauma, 42 for degenerative changes, and 17 for revision surgery.

Results: No difference was seen in radiological or clinical results for patients with or without interlocking screw primary stabilization. For non-trauma patients, the mean raw Constant score improved significantly from 31 (± 12) to 71 (± 12). For trauma patients, the mean raw Constant score for trauma (63.4) was significantly lower than for non-trauma cases (72.1) (p < 0.001). Analysis of the filling ratio demonstrated that interlocking screws were not used for lower filling ratios and that midterm fixation of the stem is not negatively impacted by distal interlocking screw fixation.

Discussion: Even if use of a distal interlocking screw fixation system is rare, it can be useful for patients with poor quality fixation of stemmed RSA.

Conclusion: Use of an interlocking screw system to stabilize the stem in RSA provides good immediate and midterm stability of the implant allowing for clinical and radiological outcomes comparable to those obtained with press-fit fixation alone.