Aims. The survival of humeral hemiarthroplasties in patients with relatively intact glenoid cartilage could theoretically be extended by minimizing the associated postoperative glenoid erosion. Ceramic has gained attention as an alternative to metal as a material for hemiarthroplasties because of its superior tribological properties. The aim of this study was to assess the in vitro wear performance of ceramic and metal humeral hemiarthroplasties on natural glenoids. Methods. Intact right cadaveric shoulders from donors aged between 50 and 65 years were assigned to a ceramic group (n = 8, four male cadavers) and a metal group (n = 9, four male cadavers). A dedicated shoulder wear simulator was used to simulate daily activity by replicating the relevant joint motion and loading profiles. During testing, the joint was kept lubricated with diluted calf serum at room temperature. Each test of wear was performed for 500,000 cycles at 1.2 Hz. At intervals of 125,000 cycles, micro-CT scans of each glenoid were taken to characterize and quantify glenoid wear by calculating the change in the thickness of its articular cartilage. Results. At the completion of the wear test, the total thickness of the cartilage had significantly decreased in both the ceramic and metal groups, by 27% (p = 0.019) and 29% (p = 0.008), respectively. However, the differences between the two were not significant (p = 0.606) and the patterns of wear in the specimens were unpredictable. No significant correlation was found between cartilage wear and various factors, including age, sex, the size of the humeral head, joint mismatch, the thickness of the native cartilage, and the surface roughness (all p > 0.05). Conclusion. Although ceramic has better tribological properties than metal, we did not find evidence that its use in hemiarthroplasty of the shoulder in patients with healthy cartilage is a better alternative than conventional metal humeral heads. Cite this article: Bone Joint J 2024;106-B(11):1273–1283

Aims

The eccentric glenosphere was principally introduced into reverse shoulder arthroplasty to reduce the incidence of scapular notching. There is only limited information about the influence of its design on deltoid power and joint reaction forces.

The aim of our study was to investigate how the diameter and eccentricity of the glenosphere affect the biomechanics of the deltoid and the resultant joint reaction forces.

We measured the tension in the interosseous membrane in six cadaveric forearms using an in vitro forearm testing system with the native radial head, after excision of the radial head and after metallic radial head replacement. The tension almost doubled after excision of the radial head during simulated rotation of the forearm (p = 0.007). There was no significant difference in tension in the interosseous membrane between the native and radial head replacement states (p = 0.09). Maximal tension occurred in neutral rotation with both the native and the replaced radial head, but in pronation if the radial head was excised. Under an increasing axial load and with the forearm in a fixed position, the rate of increase in tension in the interosseous membrane was greater when the radial head was excised than for the native radial head or replacement states (p = 0.02). As there was no difference in tension between the native and radial head replacement states, a radial head replacement should provide a normal healing environment for the interosseous membrane after injury or following its reconstruction. Load sharing between the radius and ulna becomes normal after radial head Replacement. As excision of the radial head significantly increased the tension in the interosseous membrane it may potentially lead to its attritional failure over time.

Cite this article: Bone Joint J 2013;95-B:1383–7.