EFFECT OF FEMORAL NECK MODULARITY ON HIP RANGE OF MOTION

Abstract

Introduction: A femoral stem with a modular neck can optimize the range of motion (ROM). The hip’s maximal rotational ranges were evaluated with three different modular neck versions

Methods: This study included 52 primary implantations of a short cementless anatomical modular stem using navigation control. ROM was measured using the sagittal femoral and the anterior pelvic plane as references. Once the cup and stem were implanted, three different neck versions (retroverted: −7°, neutral: 0, and anteverted: +7°) were used. A dynamic test measured the maximal ROM for each patient and neck version. Simultaneously, the surgeon evaluated the stability and the absence of posterior impingement.

Results: The average rotational range in extension was 72° for a retroverted neck, 71° for a neutral neck and 76° for an anteverted neck. This difference was not clinically significant. The equilibrium of the rotational ranges appeared better with a retroverted neck (average center: −6°) than with a neutral neck (average center: −8°) or an anteverted neck (average center: −13°) (p< 0,001). The equilibrium of the rotational range correlated with the femoral stem anteversion (r=−0.70, p< 0.001) and with the combined anteversion (r=−0.74, p< 0.001). Finally, an anteverted neck was used in 3 cases, a neutral neck in 25 cases and a retroverted neck in 24 cases. The surgeon’s final neck version choice obtained the best equilibrium in 60% of cases.

Discussion/Conclusion: The study showed that balancing the hip rotational ranges may be a helpful operative test when choosing a modular neck without a navigation system.