Novel Hallux Valgus Cadaveric Model: Role of Ligament Damage and Tendon Pull in Recreating the Deformity

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: Hallux valgus (HV) is of uncertain origin, which explains the plethora of treatment options available. In the last few years it has been shown that it is not a one plane deformity, but a multiplanar one. It is the authors belief that Hallux Valgus originates from instabilities located at medial ray joints. To be able to further understand this frequent pathology, a cadaveric model should be developed. Through specific and limited medial column ligament damage, a model was developed trying to obtain similar deformities to the ones observed in real life, i.e. first ray varus and pronation. METHODS: 7 fresh frozen lower leg specimens were used without evident foot and ankle pathology. Tibio-talar and talo-navicular joints were fixed. Luminous markers were attached to the medial and middle foot ray bones, including talus. A constant tibial axial load of 25 kg was used. Cyclic tibial rotation (to simulate gait phases) and 5 kg pull on the extensor and flexor hallucis tendons (EHL and FHL) were applied to every specimen. Limited and sequential medial and middle column ligamentous sectioning were performed, including the naviculocuneiform, intercuneiform, metatarsocuneiform, metatarsophalangeal medial capsule and intermetatarsal ligaments. After each ligament damage, 3D bony alignment was registered using high speed high definition infrared cameras. RESULTS: After ligament sectioning, an increase in intermetatarsal angle was observed of 2.5 degrees (range 0.8-5) (p=0.001), with 1 degree (0-3) (p=0.02) of further increase when Hallucis tendons pull was applied. Intercuneiform angle increased 2.3 degrees (0- 6) (p=0.01), with no change with tendons pull. Regarding bone rotation, the metatarsal pronated in relation to the navicular (metatarso-navicular angle) 6.3 degrees (3-20) (p=0.015) and the cuneiform pronated in relation to the navicular (naviculo- cuneiform angle) 3.3 degrees (0.5-6) (p=0.005). At the metatarso-cuneiform joint, a non-significant rotation was identified (1 degree (p=0.39). Hallucis tendons pull did not significantly affect any rotation angle. An evident hallux valgus deformity could be created, which further deformed with hallucis tendons pull. CONCLUSION: After sequential medial and middle ray ligament sectioning, a progressive and simultaneous increase in medial column varus and pronation were observed. Hallucis tendons pull, increased the medial column varus, but appeared not to play a role in bone rotation. Bone rotation occurs along the medial column joints, not isolated to the tarsometatarsal joint. Progressive medial ray ligamentous sectioning was able to recreate a Hallux valgus deformity, including medial ray varus and pronation.