The Effect of Arch Drop on Tibial Rotation and Tibiofemoral Contact Stress in Postpartum Women.

BACKGROUND: Women are at greater risk for knee osteoarthritis and numerous other lower limb musculoskeletal disorders. Arch drop during pregnancy and the resultant excessive pronation of the feet may alter loading patterns and contribute to the greater prevalence of knee osteoarthritis in women.

OBJECTIVE: To determine the effect of arch drop on tibial rotation and tibiofemoral contact stress.

DESIGN: Interventional study with internal control.

SETTING: Biomechanics laboratory.

PARTICIPANTS: Eleven postpartum women (age 33.4 ± 5.3 years, body mass 76.1 ± 13.5 kg) who had lost arch height with pregnancy in a previous study.

METHODS: Subjects underwent standing computed tomography (SCT) with their knees in a 20° fixed-flexed position with and without semirigid arch supports to reconstitute prepregnancy arch height. Magnetic resonance imaging of the knee was acquired at a flexion angle equivalent to that of SCT. Bone and cartilage were manually segmented on the magnetic resonance images and segmented surfaces were registered to the 3-dimensional SCT image sets for the arch-supported and -unsupported conditions. These models were used to measure changes in tibial rotation, as well as to estimate contact stress in the medial and lateral tibiofemoral compartments, using computational methods.

MAIN OUTCOME MEASURES: Change in tibial rotation and tibiofemoral contact stress with arch drop.

RESULTS: Arch drop resulted in a mean tibial internal rotation of 0.75 ± 1.33° (P = .02). Changes in mean or peak contact stress were not detected.

CONCLUSIONS: Arch drop causes internal tibial rotation, resulting in a shift in the tibiofemoral articulation. An associated increase in contact stress was not detected. Internal rotation of the tibia increases stress on the anterior cruciate ligament and menisci, potentially explaining the greater prevalence of knee disorders in postpartum women.

LEVEL OF EVIDENCE: To be determined.