Hip abduction can prevent posterior edge loading of hip replacements

Abstract

Edge loading causes clinical problems for hard-on-hard hip replacements, and edge loading wear scars are present on the majority of retrieved components. We asked the question: are the lines of action of hip joint muscles such that edge loading can occur in a well-designed, well-positioned acetabular cup? A musculoskeletal model, based on cadaveric lower limb geometry, was used to calculate for each muscle, in every position within the complete range of motion, whether its contraction would safely pull the femoral head into the cup or contribute to edge loading. The results show that all the muscles that insert into the distal femur, patella, or tibia could cause edge loading of a well-positioned cup when the hip is in deep flexion. Patients frequently use distally inserting muscles for movements requiring deep hip flexion, such as sit-to-stand. Importantly, the results, which are supported by in vivo data and clinical findings, also show that risk of edge loading is dramatically reduced by combining deep hip flexion with hip abduction. Patients, including those with sub-optimally positioned cups, may be able to reduce the prevalence of edge loading by rising from chairs or stooping with the hip abducted. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1172–1179, 2013.

Gait alterations can reduce the risk of edge loading

“…Although the cup position has the largest effect on edge loading, kinematics can still affect the risk of edge loading after surgery. Whereas previous research showed that abduction can prevent posterior edge loading in large flexion angles, this study suggests that during gait, antero‐superior edge loading can be prevented by decreasing hip extension during terminal double support.…”

“…Cup positions representing the edges of Lewinnek's safe zone were used, as well as coverage angles representative for commonly used prosthesis cups. 7,29 For all eight conditions, HCF-edge angles at the timing of the first and second peak hip contact force in the reference simulation were reported. Also the minimal HCF-edge angle during the entire stance phase and the corresponding magnitude and timing of the hip contact force were reported.…”

“…The effect of four different cup positions (an inclination angle of 30° and 50° and anteversion angle of 5° and 25°) for two different coverage angles (180° and 168°) was evaluated. Cup positions representing the edges of Lewinnek's safe zone were used, as well as coverage angles representative for commonly used prosthesis cups . For all eight conditions, HCF‐edge angles at the timing of the first and second peak hip contact force in the reference simulation were reported.…”

“…When evaluating the risk of edge loading, it is important to consider gait, as it is one of the most frequently performed activities of daily living . Edge loading was reported at the antero‐superior and the posterior side of the cup (Fig. ).…”

Individual muscle contributions to ground reaction and to joint contact, ligament and bone forces during normal gait

“…Hip, tibiofemoral, patellofemoral and ankle joint kinematic models were all based on anatomical considerations (see Supplementary material). Muscular lever arms were computed using a muscular geometry derived from that proposed by Klein Horsman et al [24] and adjusted by van Arkel et al [25]. This geometry consisted of 129 muscular lines of action representing 38 muscles, divided into 55 units with up to 6 bundles.…”