Dysplastic hip anatomy alters muscle moment arm lengths, lines of action, and contributions to joint reaction forces during gait

Abstract

Developmental dysplasia of the hip (DDH) is characterized by abnormal bony anatomy, which causes detrimental hip joint loading and leads to secondary osteoarthritis. Hip joint loading depends, in part, on muscle-induced joint reaction forces (JRFs), and therefore, is influenced by hip muscle moment arm lengths (MALs) and lines of action (LoAs). The current study used subject-specific musculoskeletal models and in-vivo motion analysis to quantify the effects of DDH bony anatomy on dynamic muscle MALs, LoAs, and their contributions to JRF peaks during early (~17%) and late-stance (~52%) of gait. Compared to healthy hips (N = 15, 16-39 y/o), the abductor muscles in patients with untreated DDH (N = 15, 16-39 y/o) had smaller abduction MALs (e.g. anterior gluteus medius, 35.3 vs. 41.6 mm in early stance, 45.4 vs. 52.6 mm late stance, p ≤ 0.01) and more medially-directed LoAs. Abduction-adduction and rotation MALs also differed for major hip flexors such as rectus femoris and iliacus. The altered MALs in DDH corresponded to higher hip abductor forces, medial JRFs (1.26 vs. 0.87 × BW early stance, p = 0.03), and resultant JRFs (5.71 vs. 4.97 × BW late stance, p = 0.05). DDH anatomy not only affected hip muscle force generation in the primary plane of function, but also their out-of-plane mechanics, which collectively elevated JRFs. Overall, hip muscle MALs and their contributions to JRFs were significantly altered by DDH bony anatomy. Therefore, to better understand the mechanisms of joint degeneration and improve the efficacy of treatments for DDH, the dynamic anatomy-force relationships and multi-planar functions of the whole hip musculature must be collectively considered.

Acetabular Edge Loading During Gait Is Elevated by the Anatomical Deformities of Hip Dysplasia

“…After Institutional Review Board approval and informed consent, 15 female patients with untreated DDH and 15 female healthy control subjects were included, as previously reported (Song et al, 2020 ). An a priori power analysis based on prior hip JRFs findings during gait (Harris et al, 2017 ) indicated 15 subjects per group could detect inter-group differences with a statistical power of 0.8.…”

“…With each DDH and control subject lying prone in a neutral hip position, magnetic resonance images were collected from the lumbar region to the knees using a 3T scanner (VIDA, Siemens AG; Munich, Germany) with T1-weighted VIBE gradient-echo sequences and SPAIR fat suppression (1 × 1 × 1 mm voxels) (Song et al, 2020 ). From the images, 3D bony anatomy of the whole pelvis and femurs was reconstructed using Amira software (v2019a; Thermo Fisher Scientific; Houston, TX), including detailed acetabular anatomy.…”

“…Subject-specific musculoskeletal models were created in the OpenSim software (Delp et al, 2007 ) as recently described (Song et al, 2020 ). Briefly, a generic OpenSim model (Lai et al, 2017 ) was modified by adding image-based pelvis and femur bony anatomy, including landmark-based 3D alignment of the pelvis tilt, obliquity, and rotation.…”

“…A reason for the lack of such studies could be that the generic anatomy used in most models does not closely represent the bony deformities of dysplastic hips (Song et al, 2019 ), and cannot be used to characterize hip joint loading beyond JRFs. Recently, we showed that image-based musculoskeletal models can delineate joint and muscle mechanical differences, including JRFs, between hips with and without DDH (Harris et al, 2017 ; Song et al, 2020 ). Still, because interpreting the clinical meanings of JRFs remains challenging, more precise ways to quantify joint loading and its associations with damage are needed.…”

Effects of Hip Abductor Strengthening on Musculoskeletal Loading in Hip Dysplasia Patients after Total Hip Replacement

“…Unfortunately, no similar studies are available on hip contact and muscle forces after THR in DDH patients, indeed this is the first study that analyzed the musculoskeletal loads during gait in DDH patients after THR. Previous research focused on dysplastic hips [32,33] or in patients operated on periacetabular osteotomy [34,35]. Sørensen et al [35] reported a normal hip muscle function during walking after 12 month periacetabular osteotomy, and found that joint force magnitude continued to be higher than normal, justifying this finding with the need for joint structures of a longer time to heal than muscles, with a residual pain alleviating strategy.…”