[Rupture of the thumb ulnar collateral ligament of the metacarpophalangeal joint: is it possible to operate according to the position of sesamoides on dynamic Xray]. / Entorse grave du pouce: opérer selon la position des sésamoïdes lors des clichés en stress.

AIM: Acute complete ruptures of the ulnar collateral ligament should be treated with surgical repair of the ligament. But diagnosis using ultrasound, dynamic X ray and magnetic resonance imaging are unable to diagnose surely the complete rupture. According to Rotella and Urpi if the radiograph shows no parallelism between the sesamoid bones and the metacarpal head, the injury of ulnar collateral ligament is total and complete and requires surgical reparation. The aim of this work was to verify the finding of Rotella and Urpi and the relationship between the lost of parallelism and the Stener lesion (interposition of adductor aponeurosis between the ruptured ulnar collateral ligament and its site of insertion on the base of the proximal phalanx). MATERIAL AND METHODS: Embalmed anatomical specimens were used to systematically investigate and document the role played in joint stability by each of the anatomical elements. Each ligament was sectioned and instability documented. A retrospective radiological study was performed on 93 patients who had an history of injured ulnar collateral ligament of the thumb. RESULTS: The anatomical study confirmed the result of Rotella and Urpi in showing that the loss of parallelism between the sesamoid bones and the metacarpal head was associated with complete rupture of ulbnar collateral ligement The clinical study showed that the lost of parallelism was associated with a Stener lesion (N=23). CONCLUSION: The association between the lost of parallelism of sesamoid bones and Stener lesion confirm that the rupture of all elements of the ulnar collateral ligament. This anatomical and clinical findings have to be confirmed by a prospective clinical study.