Fractures of the Pisiform Bone

Luc De Smet

7.1 Introduction

Fractures of the pisiform bone are not frequent, or at least are not frequently diagnosed or reported. In fact most publications are occasional case reports.

The pisiform bone is situated in the proximal carpal row. Some authors consider it as a sesamoid while others see it as a remnant of the seventh ray in the heptodactylous ancestors of modern animals.¹ It articulates with the triquetrum and this joint is a complex one. It is the only carpal bone on which a tendon (i.e., the flexor carpi ulnaris) inserts. This insertion forms two fibrous bands: the pisohamate and the pisometacarpal ligaments. The pisiform also forms the origin of the abductor digiti quinti. Last but not the least, the transverse carpal ligament (retinaculum flexorum) attaches on the palmar surface of the pisiform. The role of the pisiform in the kinematics of the carpus is not clear. The anatomy and biomechanics of the pisotriquetral joint have been well described.² The effect of pisiformectomy on the wrist function is minimal, although Beckers and Koebke³ found that the pisiform contributes to the stability of the ulnar column of the carpus and suggest that pisiformectomy should be reconsidered.

The ossification takes place between 8 and 12 years. Since multiple ossifications can be present, this can give a false image of a fracture in young persons.

7.2 Etiology

Despite its superficial location, and the frequent occurrence of direct trauma to the hypothenar region, pisiform bone fractures are rare. About 0.2% to 1% of all carpal bone fractures involve the pisiform. In a fall on the outstretched pronated hand or in a backward fall on the supinated wrist, the pisiform bone hits the floor and is at risk of fracture. Most pisiform bone fractures are in fact the consequence of direct trauma. Forceful contraction of the flexor carpi ulnaris (FCU) (resisting a forceful extension of the wrist or during the lifting of a heavy object) can also result in an osteochondral avulsion fracture. Repetitive trauma—as part of the hypothenar hammer syndrome—has been reported as a cause of fracture.

In sports the pisiform can be injured by direct falls such as in inline skating, despite the use of protective gloves.⁴ Chronic overuse has been reported in racket game players⁵ as well as in volleyball players.⁶

7.3 Diagnosis

Knowing the mechanisms of injury, the presentation of this fracture is obvious. The patient presents after a fall on the outstretched hand—more specifically on the hypothenar region—or a forceful extension of the wrist. Radiating pain in the territory of the ulnar nerve can be reported, even up to sensory loss in the fourth and fifth fingers or motor paralysis of the hypothenar muscles, the interosseous muscles, or the adductor pollicis. Although these fractures heal well, even without treatment, malunion is frequent. This can lead to pisotriquetral osteoarthritis with persisting pain and weakness of grip. Again, ulnar nerve compression can occur.

Plain radiographs usually do not reveal the fracture. Specific views are necessary: the carpal tunnel view and the reversed (supinated) oblique view.⁷

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