Hip Abduction Can Prevent Posterior Edge Loading of Hip Replacements

Medical Engineering, Department of Mechanical Engineering, Imperial College London, London, SW7 2AZ, United Kingdom.
Journal of Orthopaedic Research (Impact Factor: 2.99). 08/2013; 31(8). DOI: 10.1002/jor.22364
Source: PubMed


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.

Download full-text


Available from: Andrew T M Phillips, Jul 02, 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: To the Editor,We read with great interest the paper “Consistency Among Musculoskeletal Models: Caveat Utilitor” by Wagner et al.12 The paper compares eight musculoskeletal models by scaling them to the same dimensions in order to evaluate differences in the quadriceps moment arms, muscle forces and tibio-femoral contact forces for a standardized knee flexion task. We would like to comment on the methods and interpretation of results presented in the paper, particularly with regard to the London Lower Limb Model (LLLM).10 As the authors of that paper, we note that the muscle force distribution between the quadriceps muscles reported in Figure 4 of Wagner et al.12 for the LLLM and described as the result of “a potential modelling error” arises from an unintended use of the model. We have not assessed the results reported by Wagner et al. for other models used in their study and so only comment on the use of our model.The publicly available LLLM model was implemented in OpenSim,3 assessed ...
    No preview · Article · Nov 2014 · Annals of Biomedical Engineering
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study aimed to assess the level of co-activation of the superficial shoulder muscles during lifting movement. Boxes containing three different loads (6, 12, and 18kg) were lifted by fourteen subjects from the waist to shoulder or eye level. The 3D kinematics and electromyograms of the three deltoids, latissimus dorsi and pectoralis major were recorded. A musculoskeletal model was used to determine direction of the moment arm of these muscles. Finally an index of muscle co-activation named the muscle focus was used to evaluate the effects of lifting height, weight lifted and phase (pulling, lifting and dropping phases) on superficial shoulder muscle coactivation. The muscle focus was lower (more co-contraction) during the dropping phase compared to the two other phases (-13%, p<0.001). This was explained by greater muscle activations and by a change in the direction of the muscle moment arm as a function of glenohumeral joint position. Consequently, the function of the shoulder superficial muscles varied with respect to the glenohumeral joint position. To increase the superficial muscle coactivation during the dropping phase may be a solution to increase glenohumeral joint stiffness. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Full-text · Article · Nov 2014 · Journal of Electromyography and Kinesiology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Edge-loading in patients with metal-on-metal resurfaced hips can cause high serum metal ion levels, the development of soft-tissue reactions local to the joint called pseudotumours and ultimately, failure of the implant. Primary edge-loading is where contact between the femoral and acetabular components occurs at the edge/rim of the acetabular component whereas impingement of the femoral neck on the acetabular component's edge causes secondary or contrecoup edge-loading. Although the relationship between the orientation of the acetabular component and primary edge-loading has been identified, the contribution of acetabular component orientation to impingement and secondary edge-loading is less clear. Our aim was to estimate the optimal acetabular component orientation for 16 metal-on-metal hip resurfacing arthroplasty (MoMHRA) subjects with known serum metal ion levels. Data from motion analysis, subject-specific musculoskeletal modelling and Computed Tomography (CT) measurements were used to calculate the dynamic contact patch to rim (CPR) distance and impingement risk for 3416 different acetabular component orientations during gait, sit-to-stand, stair descent and static standing. For each subject, safe zones free from impingement and edge-loading (CPR <10%) were defined and, consequently, an optimal acetabular component orientation was determined (mean inclination 39.7° (SD 6.6°) mean anteversion 14.9° (SD 9.0°)). The results of this study suggest that the optimal acetabular component orientation can be determined from a patient's motion and anatomy. However, 'safe' zones of acetabular component orientation associated with reduced risk of dislocation and pseudotumour are also associated with a reduced risk of edge-loading and impingement. Copyright © 2014 Elsevier Ltd. All rights reserved.
    No preview · Article · Nov 2014 · Journal of Biomechanics
Show more