Hypermobility of the first ray

Abstract

Hypermobility of the first ray is one of the causative components in common foot problems (such as hallux valgus) with a large intermetatarsal angle and metatarsus primus varus. Although not always associated with hallux valgus, hypermobility is a predisposing factor for this deformity, especially in conjunction with extrinsic factors, such as disruption of the plantar first metatarsal cuneiform ligament and tendon-muscle imbalance. Hypermobility is also frequently found in adolescents with hallux valgus, especially when associated with a large intermetatarsal angle. Motion at the first metatarsocuneiform joint occurs in the sagittal and transverse planes. Most studies agree that greater than 4 degrees and greater than 8 degrees, respectively, constitutes excessive motion. Clinically, hypermobility is evaluated by determining sagittal motion (the grasping test) and transverse motion (the clinical squeeze test) and by identifying signs such as the presence of a dorsal bunion, intractable plantar keratosis beneath the second metatarsal head, and arthritis of the first and second metatarsocuneiform joint. Radiographically, hypermobility is evaluated by measurements from the modified Coleman block test (for sagittal motion) and the radiographic squeeze test (for transverse motion) and by the identification of signs, such as cortical hypertrophy along the medial border of the second metatarsal shaft, a cuneiform split, the presence of os intermetatarseum, and the round shape and increased medial slope of the first metatarsocuneiform joint. Usually, treatment for hypermobility of the first ray is operative, but surgery is contraindicated for patients less than 20 years of age (especially when the epiphysis is not closed) and for patients with generalized ligamentous laxity, short first metatarsal, and arthritis of the hallux MTP joint. The authors' surgical treatment of choice is arthrodesis of the tarsometatarsal joint (as part of the hallux valgus correction), exostectomy, capsulorraphy, and distal soft tissue release to correct and stabilize the first metatarsal at the apex of the deformity. The authors have found it unnecessary to include the base of the second metatarsal. The main complications associated with the Lapidus procedure and its modifications are nonunion, malunion, and dorsal elevation of the first metatarsal. Although radiographic nonunion is the most frequent complication, only 25% of the patients with this condition have associated clinical findings; the results have been defined as good or excellent in two series. These results closely equal those in rheumatoid or sedentary patients managed with newer, modified, less traumatic techniques that stabilize the first metatarsocuneiform joint with screws rather than with arthrodesis.