Lower age increases the risk of revision for stemmed and resurfacing shoulder hemi arthroplasty.

Background and purpose - The number of patients where shoulder hemiarthroplasty (SHA) is an option is still substantial. Descriptive analyses performed by the Swedish Shoulder Arthroplasty Registry (SSAR) showed that while patients receiving SHA designs, i.e. resurfacing hemi (RH) and stemmed hemi (SH), reported similar shoulder functionality and quality of life, the revision rate for RH (12%) was larger than for SH (6.7%); this difference was studied. Patients and methods - All primary SHA (n = 1,140) for OA reported to SSAR between 1999 and 2009 were analyzed regarding risk factors for revision and PROM outcome, 950 shoulders with primary OA (POA), and 190 secondary OA (SOA). Mean age was 67.4 years (SD 10.8). PROM including WOOS and EQ-5D were collected at 5 years, until December 31, 2014. Results - 76/950 prostheses because of POA and 16/190 prosthesis because of SOA were revised. Age at primary surgery was the main factor that influenced the risk of revision, lower age increased the risk of revision, and was also the explanation for the difference between SH and RH. We also found that SH and RH had similar outcomes measured by PROM, but the POA group had higher scores than the SOA group with a clinically relevant difference of 10% in WOOS. Interpretation - The risk of revision for SH and RH is similar when adjusted for age and does not depend on primary diagnosis or sex. A lower age increases the risk of revision. Patients suffering from POA experience better shoulder functionality than SOA patients irrespective of implant type.

Measurement of migration of a humeral head resurfacing prosthesis using radiostereometry without implant marking: an experimental study.

INTRODUCTION: Standard radiostereometric analysis of prosthetic migration requires that tantalum beads are inserted into the implant. For manufacturing reasons, this is not possible for humeral head resurfacing implants. We therefore used marker-free radiostereometry, developed for metal-backed acetabular cups, on a dummy model to validate the method for a humeral head resurfacing prosthesis. MATERIAL AND METHODS: 3 hemispherical resurfacing prostheses of different sizes were marked with tantalum beads and mounted in a sawbone. Standard and marker-free radiostereometry was then done repeatedly with gradual shifts of position of the prosthesis between each analysis. The marker-free algorithm was then compared to the standard to determine the accuracy. RESULTS: The accuracy for marker-free radiostereometry was 0.22-0.47 mm for translations and 0.92-1.56 degrees for rotations. INTERPRETATION: Based on our results, marker-free radiostereometry can be used to measure migration of humeral head resurfacing prostheses. This indicates that implant marking is not required when doing radiostereometry on humeral head resurfacing in clinical trials.