Box 1 Capitate summary

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Classification [95]

Type 1. Transverse body

Type 2. Transverse proximal pole (waist)

(Fig. 1) Type 3. Coronal oblique Type 4. Parasagittal

Mechanisms

1. Hyperextension with capitate striking distal radius

2. Axial load

3. Direct blow

Treatment

- Nondisplaced: Short arm thumb spica cast x 6-8 weeks

- Displaced: CRIF vs ORIF (K-wires, headless compression screws)

Abbreviations: CRIF, closed reduction internal fixation; K-wire, Kirschner wire; ORIF, open reduction internal fixation.

ligament and the FCU tendon, and the origin of the abductor digiti minimi muscle [45]. The FCU tendon continues distally as the pisohamate and pisometacarpal ligaments. The pisiform is the last carpal bone to ossify between the ages of 8 and 12 years. There may be multiple centers of ossification, giving it a fragmented appearance before age 12 years [44]. This normal variant must be distinguished from a fracture [46].

The mechanism of injury is most commonly direct trauma to the hypothenar eminence or avulsion when the FCU resists forcible hyperextension of the wrist, resulting in an osteochondral or avulsion fracture [44,47,48]. This can also be achieved by straining to lift a heavy object. A third mechanism postulated is repetitive trauma causing vascular disruption, microfractures, and then a complete fracture line [49].

The diagnosis is often missed because the adjacent bones obscure clear radiographic imaging of the pisiform on standard views [44,49-52]. Lacey and Hodge [53] highlighted the importance of obtaining a reverse oblique wrist radiograph with the wrist in supination. The pisiform fracture was only seen on this view in the two cases they presented. Fleege and coworkers [44] reported on 10 pisiform fractures, only 5 of which could be diagnosed on PA radiographs. Sagittal and transverse pisiform fractures may be seen on the PA view. The carpal tunnel view may also be a useful adjuvant view to diagnose pisiform fractures (Fig. 2). It profiles the pisiform with or without the pisotriquetral joint [43]. Abbit and Riddervold [54] presented a case of pisiform fracture that was not recognized on standard wrist views, but was diagnosed on the carpal tunnel view. it must be borne in mind that the carpal tunnel view may be unattainable in the acute setting because dorsi-flexion is limited by pain. Because of difficulty with diagnosis, the true incidence of pisiform

Carpal Tunnel View Radiograph
Fig. 2. Pisiform sagittal fracture (arrow), carpal tunnel view radiograph. (Courtesy of Martin A. Posner, MD, New York, NY.)

fractures is probably higher than that reported in the literature.

When plain radiographs remain nondiagnostic in a patient clinically suspected of a pisiform fracture, CT scan of the wrist is the study of choice. The importance of early diagnosis was emphasized by Fleege and coworkers [44]. Missed or delayed treatment of pisiform fractures may result in malunion or nonunion. This may manifest as chronic pain, grip weakness, or limitation of movement [45]. Later sequelae are pisotriquetral chondromalacia, subluxation, and osteoarthritis if the articular surface is poorly aligned [47,55].

Associated ulnar nerve palsy

The pisiform forms the ulnar wall of the Guyon tunnel, which contains the ulnar nerve and artery. It is because of this proximity that ulnar nerve palsy can be associated with pisiform fracture. Matsu-naga and colleagues [56] described two patients who had pisiform fracture resulting in ulnar nerve palsy. Both patients had multiple injuries resulting in delayed diagnosis of the fracture and subsequent ulnar nerve palsy. Tenderness over the pisiform and normal dorsal sensibility of the ring and small fingers were diagnostic for an ulnar nerve injury at Guyon's canal. Both patients underwent excision of the entire pisiform; one had full recovery of ul-nar nerve function and one had partial recovery. Two other cases of associated ulnar nerve palsy reported by Howard in 1961 [57] and Israeli and co-workers in 1982 [49] spontaneously resolved; one following nonoperative treatment with cast immobilization and the other having no treatment.

Because of the rarity of acutely diagnosed pisiform fracture, there are no well-defined guidelines for optimal treatment. Most acute pisiform fractures are treated by immobilization with a cast [5]. Israeli and colleagues [49] recommended immobilization for 6 weeks. Lacey and Hodge [53] suggest immobilization in a spica cast for 1 month and excision for those patients failing this period of immobilization. Georgoulis and colleagues [58] reported on four cases of pisiform fracture and recommended that acute fractures be treated with immobilization for 4 weeks. They emphasized that excision of the pisiform is not indicated in an acute injury.

For comminuted pisiform fractures, some authors feel that successful union is essentially precluded, and that early excision facilitates an uncomplicated recovery [59]. Geissler [60] recommended early excision for comminuted pisiform fractures in athletes to promote an uncomplicated recovery and early return to sport. The authors' preferred method of treatment is immobilization in a short-arm cast for 4 to 6 weeks for acute non- to minimally displaced fractures. Treatment for widely displaced fractures greater than 2-3 mm with loss of flexor carpi ulnaris (FCU) continuity should be pisiform excision and FCU repair. Pisiform excision is the treatment for cases of chronic, symptomatic nonunion, or pisotriquetral arthritis. Carroll and Coyle [48] reported complete relief in 65 out of 67 patients treated by excision of pisiform for pisotriquetral joint arthritis. Although this series did not include pisiform fractures, it nonetheless is suggestive of the efficacy of pisiform excision for chronic cases. No significant adverse effect on wrist function has been shown by total pisiform excision [45,53,55,61].

The indication for ulnar nerve exploration at Guyon's canal in patients who have pisiform fracture has not been clearly defined. According to Israeli and coworkers [49], the damage to the ul-nar nerve is usually neurapraxia, and nerve palsy should improve within 6 weeks. Nerve exploration is indicated when nerve function does not improve or it deteriorates. Matsunaga and colleagues [56] recommended nerve exploration if sensory deficits persist for several months or if the ulnar nerve palsy is progressive. They suggested that resolution of the palsy without surgery is unlikely to occur inside Guyon's canal in the presence of a compressive lesion such as that caused by fractured fragments. The authors' approach is to observe if the fracture is nondisplaced. If there is no resolution after 8 to 12 weeks, we decompress Guyon's canal and perform a total pisiform excision. If symptoms worsen at any point, or if there are fracture fragments in Guyon's canal with ulnar nerve palsy, we prefer early exploration, decompression, and total pisiform excision.

Technique of pisiform excision

A palmar approach is used with a curvilinear or zigzag incision slightly radial to the palpable pisiform. The ulnar nerve is exposed and the pisohamate ligament divided to decompress Guy-on's canal. This maneuver reduces the development of secondary compression in Guyon's canal postoperatively. If the fracture is old and the FCU tendon is intact, a longitudinal incision is made in the tendon and periosteum and the pisiform is shelled out. The tendon and skin are then closed and a soft dressing applied. If the injury has resulted in a transverse fracture with a wide diastasis, the FCU will not be intact; in such cases the transverse rent in the tendon is used to visualize and shell out the two halves of the pisiform. The tendon is then repaired [62]. Box 2 provides diagnosis and treatment guidelines.

Fractures of the trapezium

Fractures of the trapezium account for 3% to 5% of all carpal fractures [63,64]. These fractures are significant injuries when displaced because they affect the important trapeziometacarpal joint of the thumb. Inadequate treatment can lead to permanent impairment based on the substantial forces experienced at the trapeziometacarpal joint in pinch and grip [65].

Isolated fractures of the trapezium are uncommon [66]. McGuigan and Culp [67] reported on three isolated fractures in a multicenter retrospective study of 11 patients who had intra-articular fractures of the trapezium. Two of these

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