Cementless lateralized stems in primary THA: Mid-term survival and risk factors for failure in 172 stems.

INTRODUCTION: Increasing the femoral offset when performing total hip arthroplasty (THA) theoretically increases the stresses and risks of the stem not integrating itself into bone. But this concept has not been validated for cementless stems; this led us to conduct a retrospective study to determine: (1) the risk factors for the occurrence of symptomatic femoral radiological abnormalities, (2) the incidence of these abnormal radiological findings, (3) the revision rate for aseptic non-integration of a cementless lateralized stem.

HYPOTHESIS: Young patients with significant femoral canal flare and a small cementless lateralized stem have a higher risk of abnormal osseointegration.

MATERIAL AND METHODS: We analyzed retrospectively 172 consecutive lateralized stems (KHO, Corail™ product line) implanted during primary THA between 2006 and 2012 in 157 patients (mean age 68years±12.6 (20-95), 89% men). Radiographs were used to evaluate osseointegration scores, offset restoration and the Noble index. Kaplan-Meier survival analysis was performed using "symptomatic femoral radiological abnormalities" and "revision for aseptic stem non-integration" as endpoints.

RESULTS: The mean follow-up was 5.9years±2.7 (range, 2-12.4years). Being more than 70years of age (HR=0.7, 95% CI: [0.3-0.9], P=0.004) and having a larger stem (HR=0.6, 95% CI: [0.4-0.9], P=0.03) were protective against symptomatic femoral radiological abnormalities, while increasing the postoperative femoral offset (HR=1.1, 95% CI: [1.01-1.2], P=0.02) was deleterious. The survival free of "symptomatic femoral radiological abnormalities" was 93% (95% CI: 89-97) at 5years and 84% (95% CI: 75-95) at 8years. The survival free of "revision for aseptic stem non-integration" was 98% (95% CI: 96.8-100) at 5years and 97% (95% CI: 95.2-100) at 8years.

DISCUSSION: In this study, the risk factors for symptomatic radiological abnormalities were being less than 70years of age, having a small lateralized stem and restoring a large femoral offset. Lateralized stems used in this study had a 10% rate of symptomatic radiological abnormalities and a 4% rate of revision for aseptic non-integration.

LEVEL OF EVIDENCE: IV, retrospective study.