Patterns of proximal humeral bone resorption after total shoulder arthroplasty with an uncemented rectangular stem.

Background The aim of this study was to assess the timing and location of cortical bone resorption after total shoulder arthroplasty with an uncemented rectangular stem and investigate its effect on shoulder function up to 5 years after implantation. Methods Between June 2003 and September 2006, 183 consecutive total shoulder arthroplasties were performed, 133 of which received a cementless rectangular stem as indicated by primary or post-traumatic osteoarthritis (OA). The 5-year postoperative follow-up rate was 80%. Standardized radiographic controls and clinical assessments were performed at 6 weeks, 6 months, and 1, 2, and 5 years. Results Twenty-two patients (17%) showed full-thickness cortical bone resorption, 21 of whom were diagnosed with Sperling zone 2 resorption. The maximum craniocaudal distance of full resorption averaged 19.1 mm (range, 5.6-46.7 mm). The median distance progressed significantly from 9.6 mm to 13.8 mm between 6 and 12 months ( P  = .005). The risk of bone resorption was 3.1 times higher for post-traumatic OA patients than for those with primary OA. The occurrence of bone resorption increased significantly with increasing stem diameters relative to the humeral diameter. There was no significant effect of bone resorption on functional outcome. Conclusion Full-thickness cortical bone resorption in the proximal posterolateral humerus after receipt of a cementless rectangular stem has a prevalence of 17%, mostly occurring within the first year after surgery. Risk factors include age, post-traumatic conditions, and larger stem sizes relative to the humerus. This is a radiographic phenomenon without significant impairment of function or need for revision within 5 years after surgery.