LONG-TERM OUTCOME OF FIRST-GENERATION OMNIFIT/OMNIFLEX STEM WITH USE OF TRANSTROCHANTERIC APPROACH

Abstract

Long term outcome of cementless femoral stem with use of transtrochanteric approach was evaluated by clinical outcome and radiological change.

37 joints in 33 patients who underwent surgery in our department more than 15 years before (from 1986 to 1993) were studied. Used implants were Omnifit (Fit group, 19 joints: all joints were microstructured) and Ominiflex (Flex group, 18 joints: all joints were microstructured). The preoperative diagnosis was secondary osteoarthritis caused by dysplasia of hip (29 joints), osteonecrosis of femoral head (2 joints), rheumatoid arthritis (4 joints), and others (2 joints). Mean age at surgery was 51 years (Fit group, 54.2 years; Flex group, 50.2 years) and average postoperative follow-up period was 17.8 years (Fit group, 19 years; Flex group, 16.5 years). Clinical outcome was evaluated by Japanese Orthopedic Association hip score (JOA score) and absence or presence of thigh pain. In radiological evaluation, the fixation of implant was evaluated by Engh’s classification and the presence or absence of stress shielding, spot welds, radiolucent line, osteolysis, and sinking were studied.

JOA score for Fit and Flex group was significantly improved from 35 to 79.3 points and 37 to 76.9 points, respectively. Improvement of pain and gait ability was marked. Thigh pain was observed in 1 joint only, in the Flex group. Radiological examination for Fit and Flex group showed bone ingrowth 100% and 61% of patients, respectively, showing good fixation for both groups. Radiological sign of Fit and Flex group showed stress shielding in 91% and 84%, spot welds in 73% and 44%, radiolucent line in 12% and 19%, osteolysis in 5.2% and 5%, and sinking in 0% and 11% of patients, respectively. Revision caused by loosening of stem was in only 1 joint in Flex group.

For first generation of Omnifit/Omniflex stem, many cases of early loosening caused by surface structure characteristics had been reported. Long-term outcome in our department was relatively good compared to these earlier reports. Good initial placement of femoral component and sufficient canal fill ratio with use of transtrochanteric approach is one factor of this better result.