Intra-operative bleeding at the bone ending after the release of the tourniquet, is the most reliable indicator of vascularity, particularly of the proximal fragment [10]. Pre-operatively, however, the best imaging is provided by magnetic resonance (MRI). This has a high correlation with intra-operative findings, particularly if a contrast is used [11, 12].

A normal T1-weighted image represents viable bone. When there is loss of bone marrow signal in T1, blood flow is compromised (Fig. 6.3a). The use of gadolinium is mandatory to distinguish between avascular bone and marrow edema. T2 fat-saturated imaging may show an enhancement indicative of marrow edema (Fig. 6.3b) or no enhancement, which is synonymous with avascular bone (AVN, Fig. 6.4a, b). In a prospective series, including 88 patients, the concurrence between MRI and intra-operative bleeding points was high with a rate of over 90 % [11].

Unfortunately, there is still some confusion over the interpretation of MRI findings. MRI can give information about blood supply, but not histology. This means that the diagnosis of true avascular necrosis (AVN) cannot be made by MRI alone, in effect, simply based on the loss of bone marrow signal during T1 imaging. MRI scanning can, however, be used to distinguish between absent perfusion, which in effect means ischaemic bone, and disturbed blood supply with edema.

The precise definition of AVN is dead bone, with loss of the normal trabecular structure (Fig. 6.5). With this process, the bone tends to collapse and deform, in contrast to ischaemic bone, which appears dense on x-ray and sclerotic at the time of surgery. This dense bone does not collapse and can be stabilized by internal fixation, with the possibility of revascularization; this is not possible with true AVN. Most of the non-perfused scaphoid bones in cases of non-union still show some preserved bony architecture and, as such, are successfully amenable to surgery (Fig. 6.1). AVN, which means D4 according to the Herbert classification, also has destroyed bony architecture similar to that seen in Kienböck’s disease. For this pattern, a true reconstructive solution does not currently exist, even with vascularized bone graft. The term AVN, as established in the literature, tends to mean an ischaemic proximal fragment with no contrast enhancement on MRI and the loss of bleeding points intra-operatively on release of the tourniquet.

With regard to Herbert’s classification, D1 mostly represents viable bone in the proximal part, whereas D4 indicates avascular bone, as seen by contrast enhanced MRI. D2 and D3 mostly show compromised blood supply with edema or ischemia.

At the level of the scaphoid waist we either see a stable non-union with preserved carpal alignment, where presumably the blood supply is intact, or the pattern of a “hump backed” deformity with carpal mal-alignment; here the proximal fragment either shows signs of compromised blood supply or even an avascular fragment. With non-unions of the proximal pole, we find a fibrous non-union with preserved blood supply, or complete non-union of compromised or avascular necrosis, with disturbed blood architecture. In these cases formal reconstruction is no longer possible. Other variables include failed previous surgery and secondary degenerative arthritis. In the latter, only those early cases, with arthritis limited to the radial styloid, are suitable for reconstruction. In the rest, generally a salvage procedure using either a four corner fusion, total wrist fusion or proximal row carpectomy is employed [13].

It is not unreasonable to suggest that the different patterns of non-union need different surgical approaches. The ultimate goal of treatment, however, is to achieve bony union by resecting the pseudarthrosis until cancellous bone is seen, putting in a bone graft and restoring the original shape and length of the scaphoid and finally performing rigid stabilization. Stability and blood supply are the two most important factors for bone healing. Additional factors include smoking, age and delay between trauma and surgery.

With regard to a surgical approach, it is generally accepted that for the middle third a palmar approach is preferable and for the proximal third a dorsal approach. Rarely a “humped back” deformity is found in combination with a small proximal fragment. In these rare cases, a combined approach may be necessary [14]. With regard to the source of bone graft, generally a non-vascular graft taken from the iliac crest, distal radius or olecranon is satisfactory, as is a vascularized bone graft (VBG) pedicled on the distal radius. Finally, a free vascular bone graft taken from the medial femoral condyle (MFC) or the iliac crest can again be used. Obviously, however, these are more labour intensive.

Fibrous non-union (D1), where the carpal alignment is preserved, can be treated by resecting the pseudarthrosis through a small window created in the scaphoid bone and inserting cancellous bone graft from either the distal radius, or alternatively, from the olecranon, with additional screw fixation through either a palmar approach for the mid-third and/or a dorsal approach for the proximal third (Fig. 6.5).

Conversely, D2 and D3 type non-unions require rigid solid autologous bone graft, preferably harvested from the iliac crest. This is particularly necessary in cases of “hump backed” deformity, where restoration of the length of the scaphoid by a large bone graft is required to allow stable fixation with a straight screw. If the “hump back” or flexion deformity persists, the screw can only fix through a small dorsal portion of the proximal fragment, resulting in less stability and a higher risk for failure. We prefer to harvest the graft from the iliac crest with a special reamer [15], as it is more convenient and less painful than conventional techniques and it provides a solid fragment of compressed cancellous bone; which can be trimmed to fit the defect perfectly (Fig. 6.6). Added to this, we usually remove the cortical part, as this will accelerate bony union. Only when the graft does not seem stable would the anterior cortical part be left to support the restored scaphoid bone (Fig. 6.7).

In cases of longstanding “hump backed” deformity, where the distal fragment rotates palmarly, and the proximal fragment rotates dorsally with the lunate, it is usually helpful to initially correct the DISI deformity with a temporary K-wire, placed through the radius into the lunate with the lunate reduced. With this, mal-alignment is usually corrected and the proximal fragment is held in a stable position (Fig. 6.8).

Headless screws, which are mostly available in a cannulated, self tapping and self screwing mode, are the method of choice for fixation. For the small proximal fragment, mini types of these screws are preferred (Fig. 6.9c). They provide rigid fixation in contrast to the inlay graft technique of Russe, which was the previous method of choice and indeed requires a significant period of immobilization [10, 16, 17].

For failed surgery, where screw removal is necessary, revision will require a larger bone graft and possibly fixation with an external plate. This technique was used in the past by Ender, using a special condylar plate [18]. Nowadays, however, there are smaller, better shaped plates for this use. With this technique, again a higher degree of stability can be obtained (Fig. 6.10).