DO LATERAL VERSUS STANDARD STEMS PERFORM DIFFERENTLY? MIGRATION MEASUREMENTS AND CLINICAL OUTCOME

Abstract

Introduction: The non-cemented CBC femoral stem has been used in total hip arthroplasty (THA) since 1997. This shaft exists in a standard and a lateralised version. The concept behind the design of the implant focuses on proximal anchoring and load introduction. Migration within the first two years after surgery is confirmed to be a good predictive value for early failure of the femoral component in THA. With respect to the different load transformation of the two stem types clinical outcome and migration were investigated.

Material and Methods: Prospective follow-up study of 170 patients (52% female) who received 172 non-cemented CBC femoral stems. THA was performed in eight European clinics between March 2001 and April 2005. 127 standard and 45 lateral CBC stems were implanted. 106 cases fulfilled the criteria having a series of four X-rays during a minimum period of two years. After a mean follow-up of 32.1 months in 106 patients migration was analysed using the EBRA system. The mean age at surgery was 66.9 years (range, 39.1–85.2 years). Mean body mass index was 27.8 kg/m2 (range, 16.3–42.6 kg/m2).

Results: The average subsidence is − 0.63 mm (− 0.36 mm lateral, − 0.75 mm standard group), 7.6% of the stems showed a subsidence of > 2 mm. None of the lateralised stems migrated > 3 mm, but there is no statistical significance between the groups. There is no evidence of association of high stem migration (> 2 mm) and lower scores. The HHS increased from a preoperative mean of 51 to 96 points after 5 years follow-up. At last follow-up patients with a standard stem had a flexion, external rotation and total ROM value of 105°, 29°, and 220°, respectively. Patients with a lateralised stem reached values of 115°, 36°, and 237°, respectively. Interestingly, 93% of patients with a lateral stem indicated putting on socks “easy”, compared to 81% in the standard group, although the BMI of patients with a lateralised stem was significantly (p=0.014) higher. No thigh pain was reported after 5 years follow-up. No revisions had taken place.

Conclusion: The prism-shaped geometry of the ribs promotes good osteointegration. The standard stems showed higher migration values compared to the lat-eralised stem, statistically not significant. Patients with a lateralised femoral component showed better results for ROM, flexion, external rotation, putting on socks. Putting on socks “easy” was positively correlated with a higher flexion angle. All patients undergoing THA showed significant improvements in postoperative functioning and activity level after the implantation of a CBC stem. None of the stems had to be revised.