gms | German Medical Science

Objective: Fixed cavovarus deformity can lead to anteromedial ankle arthrosis due to elevated medial joint contact stresses. Lateralizing calcaneal osteotomies and tibial osteotomies are commonly used to treat symptoms and redistribute joint contact forces. In a former study a significant lateral shift of the centre of force (COF) was observed for three different calcaneal osteotomies. The effect of supramalleolar tibia valgisation osteotomies in terms of redistributing contact stresses in the ankle joint are unknown. In a biomechanical study, the COF lateralisation in the ankle after a lateralizing calcaneal sliding and supramalleolar tibia valgisation osteotomies were compared in a cavovarus model.

Methods: A previously validated cavovarus model with fixed hindfoot varus was simulated in six cadaver specimen. Therefore the tarsometatarsal (TMT) joints 1-3 were opened dorsally and a 30° wedge was inserted in the first TMT joint. To allow forefoot adduction and hindfoot varisation the lateral talonavicular joint capsule was opened. Every foot was embedded in a specifically molded PMMA form to prevent collapse of the arch under loading.

Closing wedge valgus tibia osteotomies of 7° and 12° were performed 3cm above the ankle joint level. After restoring the tibial anatomy, lateralizing calcaneal sliding osteotomies with 5mm and 10mm displacement were performed. Using high-resolution TekScan pressure sensors the COF migration in the ankle were recorded at 300 N axial static load (half-body weight).

Results and conclusion: A significant lateral COF shift was observed for each osteotomy: 2.6 mm for the 7° (p = 0.027) and 3.4 mm for the 12° tibial valgus osteotomy (p = 0.026). There was no significant difference between the two extents of the tibial osteotomy (p = 0.463).

The 5 mm calcaneal osteotomy led to a lateral shift of 2.6 mm (p = 0.046) and the 10mm calcaneal osteotomy to a shift of 3.9 mm (p = 0.027). Again there was no significant difference between the two extents of the calcaneal osteotomy (p=0.172).

Comparing the two osteotomy sites with respect to the effect on COF lateralization the 7° tibial valgus osteotomy was not superior to the 5 mm or 10 mm calcaneal osteotomy (p = 0.116 and p = 0.749). The 12° tibial osteotomy again was not superior to the two calcaneal osteotomies (p = 0.916 and p= 0.753)

Regarding the anteroposterior COF shift no significant change could be found for any osteotomy.

In this cadaver study lateralizing calcaneal sliding osteotomies and lateral closing tibia valgus osteotomies substantially helped to normalize anteromedial elevated ankle contact stresses in the cavovarus model. To unload the medial ankle, supramalleolar osteotomy is recommend for varus alignment through the ankle joint and lateralizing calcaneal sliding osteotomies for neutral ankle alignment, whereas the unloading effect of both osteotomies is equivalent.