SLR - May 2017 - Kyung I. Seo

3-D Computer Modeling of Malunited Posterior Malleolar Fracture: Effect of Fragment Size and Offset on Ankle Stability, Contact Pressure and Pattern

Reference: Teresa Alonso-Rasgado, David Jimenez-Cruz, Michael Karski. 3-D Computer Modeling of Malunited Posterior Malleolar Fracture: Effect of Fragment Size and Offset on Ankle Stability, Contact Pressure and Pattern Journal of Foot and Ankle Research. 2017 Mar 11;10:13.

Reviewed By: Kyung I. Seo, DPM
Residency Program: Temple University Hospital, Philadelphia, PA

Podiatric Relevance: Current consensus is to reduce posterior malleolar fractures that involve more than 20 to 25 percent of tibial plafond. Nonreduced posterior malleolar fractures would cause posttraumatic osteoarthritis (OA) as a result of a reduction in the joint contact area and an increase in contact pressure at the ankle joint. Recently, several studies demonstrate that there are no significant changes in contact area and pressure following posterior malleolar fractures. This study reviews a total of 16 malunited posterior malleolar fracture scenarios using 3-D finite element analysis.

Methods: A 3-D finite element model was developed to investigate the effect of fragment size and offset of malunited posterior malleolus on the tibiotalar joint contact area, pressure/stress, motion of joint and ligament forces. Three positions of the joint, including neutral, 20-degree dorsiflexion and 30-degree plantarflexion of the ankle, were evaluated. A total of 16 malunited posterior malleolus fracture scenarios with different SL (section length) and SO (section offsets) were performed.

Results: Contact area and peak pressure of the normal (intact) ankle joint and ones with malunion of posterior malleolar fracture were evaluated. It was evaluated with three different ankle positions, including plantarflexion, dorsiflexion and neutral position. Tibia contact area increased in both dorsiflexion and plantarflexion compared to neutral position in a normal joint. Tibia contact area is increased with SL, but SO was relatively invariant in the neutral position in the fracture scenarios. Total joint contact area reduced as fragment size increased beyond 6 mm in ankle dorsiflexion in the fracture scenarios. Similar results occurred in the fracture scenario with the ankle in plantarflexion as was the case for dorsiflexion, but total joint contact area remained constant. When ankle repositioning/alteration was inspected after having malunion at the posterior malleolus, there was no alteration in the ankle in the neutral position; however, translation of the ankle joint was observed in the dorsiflexed and plantarflexed position. It is demonstrated that there was not a notable effect on joint ligaments except only in dorsiflexion, which even resulted in force increases in both anterior talofibular and anterior tibiofibular ligament.

Conclusions: This article states that there was no decreased contact area in the tibiotalar joint and no overall elevation of peak pressure following posterior malleolar fractures, which was thought to cause posttraumatic arthritis. This article also supports the idea that posttraumatic OA occurs not from the increased peak pressure and decreased joint area, but as a result of a change in joint contact pattern.

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