Deformation of the innominate bone and mobility of the pubic symphysis during asymmetric moment application to the pelvis

BACKGROUND: Angular motions of human joints are frequently accompanied by bony deformations. In the case of the pelvis it is unknown how much deformation within the innominate and movement within pelvic joints will occur during an asymmetrical loading. Deeper insight into this topic could help to increase the understanding of the biomechanics of the pelvis during e.g. locomotion and improve interpretation of clinical tests in which manual force is asymmetrically applied to the pelvic bones. OBJECTIVE: To test the occurrence of deformation within the innominate and movement within the pubic symphysis during asymmetric moment application to the pelvis. METHODS: In 15 embalmed specimens an incremental moment was applied to one innominate bone in the sagittal plane with respect to the fixated contralateral innominate. The three-dimensional (3D) deformation within the fixated innominate, as well as displacement of the pubic symphysis, were described during each increment of the moment. Maximal amount of deformation within the fixated innominate was compared with displacement in the pubic symphysis and tested for significant difference for all subjects and separately by gender. RESULTS: Mean range of 3D deformation of the innominate bone (3.39 ± 2.92 mm) is comparable to the range of symphysis motion (3.20 ± 2.58 mm; p > 0.05). Largest deformation within the innominate was present in the transverse plane (1.41 ± 3.1 mm). Significant differences (p < 0.01) occured in the mobility of the pubic symphysis between male and female specimens. No significant gender differences were present in the deformation of the innominate bone. CONCLUSIONS: During asymmetrical loading both movement within the pubic symphysis as well as deformation within the innominate occur simultaneously. Deformation of the innominate is the largest in the transverse plane