Abstract
Glenoid loosening is a major problem in total shoulder arthroplasty. Failure of osteointegration, osteolysis and loosening are potential problems with concerning reports of these complications with earlier metal back designs. CT scans have been reported as more accurate than plain x-rays in examining fixation of components. This study examines the medium term osteointegration of the SMR (Lima) metal back glenoid component. 20 consecutive patients operated on by the same surgeon (KM) were evaluated at a mean of 3 years 9 months (range 3-5 years) using CT analysis. Films were read by a musculoskeletal radiologist (AS). 8 zones were described and the interface graded as ‘osteointergrated’, ‘lucent zone < 1mm’, ‘lucent zone 1-2mm’, ‘lucent zone > 2mm osteolysis’. Loosening was defined as lucent line on all zones > 1mm or migration of implant.
No components were loose. All components were osteointegrated around the central peg. Osteointegration was observed in 85% of zones. 4% of the zones were graded as osteolysis, all in the one patient. This patient had osteolysis 4 years post-surgery with superior subluxation of the humeral head and polyethlylene and metal wear. The glenoid component was not loose at revision surgery. Problems with this technique of assessment include radiation exposure and artefact. Small lucent zones often had a well contoured margin suggesting that the component did not seat perfectly on the bone surface in these areas.
These results confirm that reliable medium term osteointegration does occur with the SMR metal back glenoid in anatomical total shoulder replacement. Osteolysis can occur and longer term follow up is ongoing.
