Vascularized Second Metacarpal Bone Graft for the Treatment of Idiopathic Osteonecrosis of the Capitate

Abstract

Background: Idiopathic osteonecrosis of the capitate is rare condition with few reports of treatment using vascularized bone graft. Methods: A case of a 45-year-old woman with idiopathic necrosis of the capitate who underwent surgical treatment with a vascularized bone graft from the base of the second metacarpal bone is reported. Results: At 14 months postoperatively, the range of motion of her wrist was maintained, and localized wrist pain was relieved. Conclusions: This bone graft, which has a reliable pedicle with few anomalies, offers sufficient cancellous bone for the capitate, and can be harvested in the same operative field, is desirable for the treatment of osteonecrosis of the capitate.

Introduction

Osteonecrosis of the capitate is a rare condition that may be idiopathic or the result of posttraumatic avascular change, and there are a few reports of the outcomes of surgical treatment.^1-3 For treatment in the early stage of necrosis without bone or cartilage collapse, vascularized bone grafting has achieved reliable outcomes,^1,2,4-6 but there are several disadvantages of each donor site. The dorsal surface of the radius based on the fourth extensor compartment artery (4th ECA)^1,4 and the 2,3 intercompartmental supraretinacular artery (2,3 ICSRA)⁵ are reasonable donor sites, but these bone grafts need a long longitudinal incision for flap elevation. A relatively wide bone graft could be harvested from the iliac crest⁶ or the medial femoral condyle,² but these procedures require a microsurgical technique and an additional exposure for flap harvest.

Vascularized bone from the base of the second metacarpal bone with a dorsal approach (Figure 1) was reported for the treatment of Kienböck disease⁷ and of scaphoid nonunion,⁸ which could be elevated easily with a reliable vascular pedicle without arterial anomalies. A case of idiopathic osteonecrosis of the capitate that was treated with this vascularized second metacarpal bone transfer is presented.

Figure 1.

Schema of the vascularized bone graft from the base of the second metacarpal bone.

Case Report

A 45-year-old woman, working on light duty, presented with localized right wrist pain that developed gradually over 6 months. At the first visit, localized pain and tenderness on the dorsal aspect of the capitate were present, and the range of motion of the wrist (right/left) was flexion 40°/70°, extension 35°/90°, radial deviation 20°/25°, ulnar deviation 40°/40°, pronation 90°/90°, and supination 90°/90°. Grip strength in the right hand was 4 kg (left 16 kg), and the visual analog scale (VAS) score of the wrist pain was 73 (/100). At this point, the Mayo wrist score was 15 (/100). On the radiographs, no changes were seen in the carpal bones. However, magnetic resonance imaging (MRI) of her wrist showed a homogeneous low-density area occupying the entire capitate on T1-weighted imaging and a high-signal-intensity area occupying the proximal half of the capitate on fat-saturated T2-weighted imaging (Figure 2). These findings were consistent with idiopathic osteonecrosis of the capitate, type 1 (sclerotic change and fragmentation apparent in the proximal part of the capitate) of the Milliez classification.⁹ Surgical intervention was performed to improve the hypovascular change. The capitate was exposed through a dorsal transverse skin incision followed by capsular incision, and normal-looking cortical bone of the dorsal surface of the capitate was partially removed. Cancellous bone of the capitate was partially collapsed in the proximal half area, but that of the distal half area was intact. Thereafter, the first dorsal metacarpal artery was identified on the radial side of the tendon of the extensor carpi radialis longus (ECRL) muscle (Figure 3a). The pedicled bone with a size of 12 × 6 × 6 mm³ was harvested from the base of the second metacarpal bone (Figure 3b) and transferred to the defect of the capitate passing beneath the ECRL and the extensor carpi radialis brevis tendon. The transferred bone graft was fixed with suture and a single temporary Kirschner wire, followed by repair of the wrist capsule and extensor retinaculum. Four weeks after surgery, the short wrist cast and temporary wire were removed, and wrist joint exercise was started. On pathological examination, degenerative change in the form of mild necrosis was observed in the trabecular bone without infection or neoplastic change.

Figure 2.

Preoperative magnetic resonance images: (a) T1-weighted. (b) Fat-saturated T2-weighted.

Figure 3.

Flap dissection and elevation. (a) The first dorsal metacarpal artery is easily identified on the radial side of extensor carpi radialis longus (yellow arrow). (b) Harvested vascularized bone graft.

At 14 months after surgery, active range of motion of the right wrist was flexion 45°, extension 70°, radial deviation 25°, ulnar deviation 40°, pronation 90°, and supination 90°. Improved grip strength was seen, 16 kg, in the right hand, and the VAS score of wrist pain was 20 (/100) with extensive motion. The Mayo wrist score was improved to 80 (/100). On MRI findings, T1-weighted imaging demonstrated the grafted bone and improved signal intensity of the entire capitate (Figure 4a), and fat-saturated T2-weighted imaging showed disappearance of the high-signal-intensity area (Figure 4b).

Figure 4.

Magnetic resonance images 14 months after surgery: (a) T1-weighted. (b) Fat-saturated T2-weighted.

Discussion

The etiology of idiopathic osteonecrosis of the capitate has not been clearly demonstrated, but it is considered to be caused by poor vascularization in intraosseous anastomosis and retrograde flow within the capitate.¹ In addition, there is no consensus on treatment of avascular necrosis of the capitate, but it is recommended that it be based on the stage of ischemic change.³ Surgical treatment consists of arthrodesis, proximal capitate resection, interposition plasty, prosthesis, curettage and bone grafting, and denervation.^2,3,9 In the advanced stage that demonstrates collapse of the capitate on imaging, arthrodesis, partial resection, prosthesis, and denervation surgeries are appropriate for pain relief.³ However, in the early stage, as in the present case, without capitate collapse, in which osteonecrotic changes could only be identified on MRI, curettage followed by conventional or vascularized bone grafting is desirable from the perspective of preserving joint range of motion.^2,3,5 Indeed, among the past case reports, early-stage treatment by vascularized bone grafting following partial bone excision or curettage achieved excellent results without significant loss of range of motion.^1,2,6 To evaluate the process of osteonecrosis, imaging tests were usually used, but arthroscopy has recently been found to be useful for direct evaluation of the articular cartilage or chondral defect.⁹

Several donor sites have been described for vascularized bone grafting, but an ideal donor site has the following important conditions: adequate quantity of bone, sufficient length of the flap pedicle, constant pedicle anatomy without variations, low donor site morbidity, and harvest within the same operative field if possible. Vascularized bone from the base of second metacarpal bone has several advantages as a pedicled graft for the capitate: (1) it does not require a long pedicle; (2) the vascular pedicle of the first dorsal metacarpal artery could be identified constantly as a large bundle^5,10,11; (3) sufficient bone graft could be obtained for the capitate; (4) harvested bone could involve joint cartilage of the second carpometacarpal joint; and (5) this bone flap could be harvested in the same surgical transverse incision. In a cadaveric study,¹⁰ the first dorsal metacarpal artery was found in all dissections (30 hands), and its origin was directly from the radial artery. It also gave an average of 4 branches (2 to 8 branches) to second metacarpal bone on the radial side, which suggested that a second metacarpal bone graft is more reliable and easier to use than other metacarpal bone grafts.

A vascularized bone graft from the base of the metacarpal bone may be a convenient and reliable procedure for treating osteonecrosis of the capitate. More studies or reports are needed to establish the management of this rare condition.