Eclypse: partial ulnar head replacement for the isolated distal radio-ulnar joint arthrosis

Eclypse is a pyrocarbon spacer that has been developed to substitute the articular portion of the damaged ulnar head in patients with an isolated distal radioulnar joint degenerative arthritis. The spacer can be inserted without significantly detaching the foveal insertion of the triangular fibrocartilage and preserving intact the extensor carpi ulnaris sheath. The goal of the implant is to maintain adequate separation of the 2 forearm bones throughout the entire range of pronosupination. After surgery, the joint stability is supported by the joint physiological stabilizers such as the triangular fibrocartilage and extensor carpi ulnaris muscle. To avoid dislocation of the implant at the extremes of forearm rotation, a titanium stem is implanted into the ulnar distal metaphysis with a distal peg inserted in a cylindrical hole in the center of the spacer. The loose fitting of the peg into the spacer allows some proximodistal translation and slight axial rotation of the implant, enough to adjust its position to the always-changing space between the distal ulna and the sigmoid notch concavity. Preliminary results in 3 patients are very encouraging, with minimal discomfort at the extremes of motion and a mean pronation of 65 degrees and supination of 70 degrees. At an average 11 months' follow-up, all patients were able to lift up to 4 kg of load throughout the entire range of forearm rotation without yielding.