A Radiographic Evaluation of Short Monolithic Femoral Hip Stem (SMF) for Dysplastic Osteoarthritis: Does Stem Alignment Influence on the Stability?

Abstract

Background: There have been a few reports of SMF TM stem for dysplastic hips. The aim of this study is to evaluate the influence of stem alignment in dysplastic femurs on the stability of the implants and on the bone reaction by means of consecutive radiographical analysis. Methods: The preoperative diagnosis is dysplastic osteoarthritis in all patients. Twenty-nine hips in 28 patients after MIS-THA were followed up for two or more years (3.5 years in average). The average age at the surgery was 60. Those who belonged to Crowe's classification I were 19 and those of II were 10 hips. The shape of the femur was classified as Dorr's Type A in 5, B in 21, and C in 3 hips. Results: The varus alignment of the stem was 21 hips and non-varus was 8 hips. Crowe's Grade did not have influence on the stem alignment. The ratio of non-varus alignment was more with Dorr's Type C than with others. Achieving rate of mediolateral fixation was significantly higher in the varus alignment than in non-varus. The significant subsidence occurred in 3 hips (10.3%) although all stems became stable within 6 months. No revision was necessary. Conclusion: The varus insertion of the stem seemed more secure also in dysplastic femurs, but even non-varus ones seemed acceptable as they brought about no severe problem. Comprehensively evaluating the result, careful selection of the patient is essential to take the advantage of and to overcome the disadvantage of this short stem for dysplastic hips.