In Vitro Evaluation of the Effect Lateral Process Talar Excision on Ankle and Subtalar Joint Stability

BACKGROUND: Recent literature reflects a substantial increase in interest surrounding lateral talar process fractures. Previous anatomic investigations discovered that excision of a 1 cm3 fracture fragment from the lateral talar process involves approximately 100% of the lateral talocalcaneal ligament origin and 10% to 15% of both the posterior and anterior talofibular ligament insertions. The objective of this study was to determine the effect that excision of this 1 cm3 fragment has on ankle and subtalar joint stability. METHODS: Ten fresh-frozen cadaver lower limbs were thawed before testing and placed in a clinical stress apparatus (Model SE 20, Telos, Marburg, Germany). Radiographs were taken before and after application of a 150 N of force. Three views (lateral, anteroposterior, 30-degree Bróden) were used to asses anterior tibiotalar translation (AT), talar tilt (TT), medial talocalcaneal motion (TCM), and talocalcaneal tilt (TCT) before and after excision of the 1 cm3 fragment the lateral talar process. RESULTS: The mean increases in AT, TT, TCM and TCT after excision of the 1 cm3 fragment were: AT=1.0 mm+/-0.94 mm (p=0.0085); TT=0.4+/-0.52 degrees (p=0.0368); TCM=1.0 mm+/-1.25 mm (p=0.0319); TCT=1.2+/-1.32 degrees (p=0.0181). CONCLUSIONS: Since it has been generally accepted that a 3 mm increase in AT, 3-degree increase in TT, 5-mm increase in TCM, more than 5-degree increase in TCT define instability of the ankle and subtalar joints, respectively. These results suggest that excision of a 1 cm3 fragment causes neither ankle nor subtalar instability as defined by radiographic stress examination.