This study was performed to investigate the dynamic effect of medial displacement calcaneal osteotomy (MCO) on the calcaneal inversion.

10 fresh-frozen, intact cadaver foot-ankle specimens were tested, using a custom loading apparatus at an orientation consistent with the early heel rise portion (40%) of the gait cycle. Calcaneal inversion was measured with identical ground reac-tion force and tendon force, before and after MCO.

Calcaneal inversion was 2.1±2.4° in the pre-osteotomy condition and 3.7±3.1° after MCO. Calcaneal plantar flexion was 7.1±0.7° in the pre-osteotomy condition and 8.8±1.8° after MCO. Increases of calcaneal inversion and flexion were significant (intact vs. MCO), (p< 0.05).

The inversion capability of the Achilles tendon was enhanced by lengthening its moment arm when its insertion was displaced medially following MCO. MCO, therefore, could compensate for the weaker inverting power of the transferred toe flexor, when treating stage II posterior tibial tendon insufficiency.