Transarticular versus Extraarticular Ankle Pin Fixation: A Biomechanical Study

Abstract

Transarticular pin fixation for ankle stabilization has drawbacks, including ankle joint arthrosis. An extraarticular technique could help avoid these problems. We compared stiffness under minimal dorsiflexion loading with transarticular versus extraarticular fixation. Cadaveric specimens from ten lower extremity matched pairs were randomized to receive transarticular or extraarticular fixation. For transarticular fixation, axial pins were passed retrograde through the plantar heel, calcaneus, subtalar joint, talar body, and ankle joint. For extraarticular fixation, the first pin was inserted antegrade from the anterior distal tibia to the posterolateral aspect of the calcaneus tuberosity. The second pin was inserted percutaneously antegrade from the distal medial tibial metaphysis to the dorsal navicular, passing anterior to the ankle and dorsal to the talonavicular joint. Each specimen was subjected to 1000 cycles at 5 mm/s to 100 N. After testing, the extraarticular specimens were dissected to establish the distance of the pin from the flexor hallucis longus (FHL) tendon. There was no significant difference in stiffness between the transarticular and the extraarticular group (mean+/-standard error of the mean) (17.93 N/mm+/-1.0 N/mm and 18.61 N/mm+/-1.07 N/mm, respectively). The lateral pin was 4.2+/-1.4 mm (range, 2.5 to 6.0 mm) from the FHL. Fixation stiffness with extraarticular crossed antegrade pins was not different from that of transarticular fixation and did not disrupt the ankle or the plantar skin. Extraarticular ankle fixation may help avoid the complications found with the joint, cartilage, and plantar skin disruption associated with transarticular fixation.