Development of a pelvic musculoskeletal model based on statistical shape modelling for estimating sacroiliac and pubic joint reaction forces in females.

The sacroiliac joints (SIJs) and pubic symphysis (PS) form a 'pelvic ring' that plays a critical role in load transfer between the spine and lower extremities. Direct in vivo measurement of pelvic joint loading remains challenging, and existing musculoskeletal models often simplify or exclude pubic joint contributions. This study developed a female pelvis musculoskeletal model incorporating both SIJs and PS, integrated with a personalisation framework including: (1) a pelvis shape-scaling workflow based on a female statistical shape model; and (2) an inertia estimation workflow using 3D full-body scans. Kinematic and kinetic data were collected from eight healthy female participants during bilateral standing, single-leg standing and walking. Compressive and superior-inferior shear loads at the SIJs and PS were estimated using inverse dynamics and static optimisation. The model produced physiologically plausible joint loads consistent with previous studies. During bilateral standing, pubic joint loads were minimal, and SIJ loads showed minor asymmetries. Single-leg standing induced SIJ tensile (1.9 N/kg), pubic compression (2.2 N/kg), and superior-inferior shearing at the support-side SIJ (4 N/kg). During walking, pubic joint loads were closely related to SIJ loading patterns and appeared to facilitate load transmission from the stance-side SIJ to the swing-side SIJ. This pelvis musculoskeletal model provides a feasible tool for investigating SIJ and PS reaction forces in females, enabling a more physiologically realistic assessment of pelvic joint biomechanics than previously available models. The proposed framework is adaptable to other populations and supports future research on pelvic pain mechanisms, pregnancy-related adaptations, and sex-specific musculoskeletal disorders.