Surface and form alterations in retrieved shoulder hemiarthroplasty.

BACKGROUND: Shoulder hemiarthroplasty is a viable treatment for shoulder arthritis, particularly if the natural glenoid is still intact. One of the most common reasons for revision surgery is glenoid erosion, where the cartilage or bone is worn. The aim of the current study was to analyze whether the metallic articular surface of retrieved shoulder hemiarthroplasty is different from new implants. We hypothesized that the surface roughness would increase as a result of the articulation and that metallic wear would be detectable on the implants.

METHODS: Included were 13 retrieved and 3 new shoulder hemiarthroplasties. The surface roughness was measured on different sites of the surface (dome of the head and the rim). The implants were further measured using a coordinate measuring machine to gain information on volumetric wear and geometric alterations. The surface was analyzed with a scanning electron microscope to see marks of wear.

RESULTS: Compared with new implants, the surface roughness on the retrievals was significantly increased. The roughness parameters within the retrieval group were generally higher at the dome of the head than at the rim; however, this difference was not significant. Apart from shape deviations caused by deformation of the retrievals, no volumetric wear was detectable on the heads.

CONCLUSIONS: The current results indicate that the roughness of the surface of the implant and the shape changes occur in vivo and that the material incurs damaged caused by the articulation against the softer cartilage or bone. Increasing roughness of the humeral component may be one cause for glenoid erosion over time.