Rupture of extensor tendon secondary to previously undiagnosed Kienböck disease.

We report three patients with an unusual pattern of rupture of the extensor tendon. All were found to have previously undiagnosed Kienböck disease. Radiographic study of the wrist is essential before treating any closed rupture of an extensor tendon. Lesions may be progressive and extend to adjacent tendons and should be treated urgently.