Scapho-luno-capitate fusion with proximal lunate articular surface preservation for management of grade IIIA Kienböck’s disease: a prospective case series

Kienböck’s disease is a rare disease that was first described about a century ago [23]. The optimal treatment option for Kienböck’s disease with lunate collapse without osteoarthritis (Lichtman stage III) is debatable [14]. Lunate collapse and fragmentation are believed to occur as a consequence of excessive forces across the lunate. Limited carpal fusion aims to unload the lunate, provide an adequate painless wrist function, and delay the development of radio-carpal and middle carpal arthritis [24, 25]. Lunate excision and SC or STT arthrodesis are the most used form of limited carpal fusion for treating the disease [13, 18].

Biomechanical studies have shown that SC fusion reduces the load across the radio-lunate and luno-capitate joints while increasing the load across the radio-scaphoid joint [26, 27].

In this study, we evaluated the outcomes of treating stage IIIA Kienböck’s disease by a novel technique of limited carpal fusion, including SLC fusion. We did partial lunate excision with preservation of the proximal lunate surface to preserve the radio-lunate joint, which could balance axial load transmission through radio-lunate and radio-scaphoid joints. At the last follow-up, this technique resulted in significant improvement in range of motion, grip strength, and Mayo Wrist Score, with a significant reduction in VAS score. Also, no carpal collapse was observed. Only one patient had delayed union until 20 weeks, but at the end of the follow-up period, all patients achieved union.

With the same principle of balancing axial load transmission through radio-lunate and radio-scaphoid joints, the Graner II procedure included complete lunate excision and its replacement with the head of the capitate through capitate lengthening so that the articular surface of the head of the capitate articulated with the lunate surface of the radius. To prevent intercarpal instability following the lunate excision, intercarpal fusion between all carpal bones except the trapezium and pisiform was done [28, 29]. However, this procedure had several reported complications, including osteonecrosis and nonunion of the head of the capitate, and long-term arthritis [29,30,31,32].

In our study, at the final follow-up period, the mean hand grip strength was 88.3 ± 12.4% of the contralateral side, which was better than that of Collon et al. [14] with 76% and Charee et al. [18] with 74% strength of the contralateral side. These studies evaluated the outcomes of lunate excision and SC fusion for the management of Lichtman stage III Kienböck’s disease [14, 18].

In our study, all patients had complete SLC fusion at the last follow-up, while the rate of nonunion was 23% in Collon et al. [14], 6% in Charee et al. [18], and 10% in Luegmair et al. [33]. The achievement of full union in our study was attributed to abundant cancellous iliac crest bone grafting and the increased fusion mass between the three bones.

The disease is more likely to develop in patients with negative ulnar variance [24]. In our study, 60% of patients had negative ulnar variance.

Joint leveling surgeries could relieve the symptoms when ulnar variance is negative [34]. However, in stage IIIA, the lunate begins to collapse, and the condition would progress to proximal migration of the capitate and scaphoid rotational instability in stage IIIB. Therefore, limited wrist arthrodesis is recommended once the patient presents with stage III [14, 34].

Limited carpal fusion prevents scaphoid rotatory instability and maintains wrist stability [2]. Various types of limited carpal fusion, including SC, STT, and CH have been described [11]. SC and STT arthrodesis shifts loads from the radio-lunate joint to the radio-scaphoid joint, in addition to reducing force transmission at the luno-capitate joint [35].

During normal power grip, the scaphoid receives approximately 50% of the total load, followed by the lunate at 35%, and the triquetrum at 15% [36]. Lunate loads are then transmitted partly to the radius and partly to the triangular fibrocartilage complex (TFCC) [36]. In our study, we aimed to preserve the proximal surface of the lunate which, theoretically, can maintain balanced axial load transmission through the radio-lunate and radio-scaphoid joints instead of the whole load being transmitted through the radio-scaphoid joint.

Limited carpal fusion is traditionally accompanied by lunate excision, and a few reports in the literature describe SC fusion without lunate excision [14, 37]. It is still questionable whether lunate excision improves wrist function, and whether it is mandatory [14]. Sennwald et al. [37] reported that SC arthrodesis without lunate excision in 11 patients resulted in complete pain relief in 10 patients. Rhee et al. [38] stated that lunate excision might predispose to evolving carpal collapse and ulnar translocation of carpal bones. At present, there is no evidence to support excising the lunate during limited carpal fusion, and it makes the procedure more challenging without improving the results [14].

This study has some limitations, including the relatively small number of patients, the relatively short follow-up period, and the absence of a comparative control group. Future randomized clinical trials comparing our technique with other types of limited carpal fusion, with long-term follow-up, are needed to properly evaluate the functional and radiological outcomes. Moreover, a biomechanical study is needed to estimate the load transmission through the radio-lunate and radio-scaphoid joints following SLC fusion.

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