Cementless Curved Short Stem Shoulder Prostheses with a Proximal Porous Coating: Ingrowth Properties at 2-5 Years Radiological Follow-up with Clinical Correlation

BACKGROUND Little is known about the way the newest generation of stems integrate into the proximal humerus and their effect on the surrounding bone. Factors that may influence ingrowth have not been investigated. METHODS A consecutive cohort study was conducted that examined 74 anatomical, reverse, or pyrocarbon hemiprostheses, using a curved modular short stem with a proximal porous coating 2-5 years postoperatively (mean 35 months). X-rays were reviewed by 2 examiners independently. Bone loss was scored with 1 point per zone with partial and 2 points per zone with complete resorption (10 zones). The Constant score was used for clinical correlation. Multiple linear regression was employed to investigate correlations between variables. RESULTS No subsidence or shift of the stems occurred. Two of 74 patients showed 1 zone of periprosthetic lucency of 1 mm. The filling ratio averaged 0.54 (range: 0.36-0.75). Thirty patients (40.5%) displayed bone resorption, first seen at 16.6 months (range: 3-40 months), commonly in zones 1 and 5. A total of 22 patients had ≥1 zone with partial resorption, and 8 (10.8%) developed full thickness resorption after 32 (range: 10-49) months.One new finding was that female sex and older age accounted for 51% of the variation of the filling ratio. A high filling ratio, especially when >0.55, correlated with bone resorption (P 0.55), is observed proximally around these stems. The development of sclerotic lines around the stem indicates oversizing. Other factors were not found to have a significant effect on stem ingrowth. The implantation of stems with a large filling ratio is more common in older females and in patients receiving reverse shoulder prosthesis. Autologous impaction bone grafting could downsize the required stem. If adequate hold is not afforded by a suitably small stem, cementation is advisable.