Improving Distal Fixation with Total Shoulder Arthroplasty in Cases of Severe Humeral Bone Loss

The usage of and indications for total shoulder arthroplasty have grown in recent years. Certain aspects of these arthroplasty procedures can be very complex, especially in revision and fracture cases, often leading to proximal humerus bone loss. For cases with significant bone loss, there is a need for improved devices with additional options to treat a wider range of deformities while also mitigating existing complications and rates, such as poor distal fixation, inadequate soft tissue reattachment options, and joint instability. To that end, a fatigue and torsional test was conducted on two different devices to assess the ability of each to survive an extreme fatigue and torsional load when assembled in worst-case configurations. Evaluation of the Equinoxe® humeral reconstruction prosthesis demonstrated superior fixation in both the fatigue loading scenario and also the torsional loading scenario as compared to the 8 mm x 215 mm cemented humeral long stem, where each had only 80 mm of cemented fixation. The results of the fatigue test demonstrated that despite the humeral reconstruction prosthesis being subjected to a 960 N force and 45 Nm bending moment (which was significantly more challenging than the 576 N force and 24.2 Nm bending moment subjected to the cemented humeral long stem), the humeral reconstruction prosthesis completed 1 M cycles without fracture or failure. Additionally, the Equinoxe® humeral reconstruction prosthesis was associated with a significantly greater torsional resistance in both the torque to initial slip (29.4 Nm versus 8.2 Nm; p = 0.0002) and also the maximum torque to failure (44.3 Nm versus 12.1 Nm; p < 0.0001). These significant improvements in fixation are at least partially attributed to the application of a novel distal fixation ring, which is press fit around the diaphysis of the humerus to supplement the cemented fixation of the distal stem. These fatigue and torsional test results paired with several novel features of fer the potential for the Equinoxe® humeral reconstruction prosthesis to be an improved treatment option for patients with proximal humeral bone loss, though clinical follow-up is necessary to confirm these positive biomechanical results.