Biomechanical analysis of Maxwell-Brancheau arthroereisis implants.

The Maxwell-Brancheau arthroereisis (MBA) implant is currently used in treating flexible flatfoot deformities in children and adults. However, no guidelines have been established to determine the degree of correction with the five different MBA implant sizes (6-, 8-, 9-, 10-, and 12-mm diameters). A biomechanical analysis of these implants was performed in fresh-frozen cadaver limbs to quantitate the effects on subtalar joint (STJ) motion restriction and radiographic angles. This study found a restriction of subtalar joint range of motion that ranged from 32.0 +/- 5.4%, 44.8 +/- 7.7%, 59.0 +/- 7.2%, 65.5 +/- 8.7%, and 76.8 +/- 7.6% restriction with successively larger sized implants respectively (p < .001). Repeated measures analysis of variance (ANOVA) revealed alterations in the first intermetatarsal, lateral talo-first metatarsal, talar declination, calcaneal inclination, and first metatarsal declination angles with successively larger implant use. Analysis of the dorsal talo-first metatarsal, talo-second metatarsal, lateral talocalcaneal angles, and first to fifth metatarsal head splay showed no changes as implant size was altered. The study also attempted to assess the effects on the tendo Achillis when the subtalar joint was changed from a pronated to a supinated position. The observations showed a 6.33 +/- 1.40% (p = .001) increase in tendon length which suggests increased tension to the tendon. These findings can aid the surgeon in selection of the MBA implant size based on the desired amount of subtalar joint motion restriction. In turn, this may reduce errors in the correction of flexible flatfoot with the MBA implant.