Scaphoid non-union and malunion deformity correction using computer navigation

Scaphoid non-union and malunion following a fracture at its waist results in a typical humpback deformity and pronation of the distal fragment with a bone defect. Arthroscopic bone grafting relies on fluoroscopic and direct visual assessment of reduction. However, because of the bone defect and irregular geometry, it is difficult to determine the precise width of the bone gap and restore the original bone length, and to correct interfragmentary rotation. Correction of alignment can be performed by computer-assisted planning and intraoperative guidance. 

Objective 

We proposed a method of anatomical reconstruction in scaphoid deformity by computer-assisted preoperative planning combined with intraoperative computer navigation. This was combined with an arthroscopic bone grafting technique.   

Methods: 

A feasibility study using 2 cadaveric upper limbs was performed. A displaced scaphoid waist fracture was produced, and a navigation tracker was inserted into the radius shaft. A K-wire was used to transfix the radius and proximal scaphoid. 2 titanium K-wires were inserted into the distal scaphoid fragment. 3D images were acquired and matched to those from a high-resolution computed tomography (CT) scan. In an image processing software, the fracture was reduced and pin tracts were planned into the proximal fragment. In scaphoid malunions, the osteotomies were performed under navigation guidance. The K-wires were driven into the proximal fragment under computer navigation. A post-fixation CT was obtained to assess reduction.  

Five patients with scaphoid non-union or malunion deformity and dorsal intercalated segment instability were treated with this technique, combined with arthroscopic bone grafting. Post-operative outcomes were reviewed. 

Results and Discussion 

In the 2 cadaveric wrists, satisfactory alignment was obtained with part comparison showing a discrepancy of 0.5mm root-mean-square. All 5 patients had bony union of the scaphoids. DISI deformities were corrected. This study demonstrated that reduction of the scaphoid in non-unions and displaced fractures can be accurately performed by computer-assisted planning and navigation in a minimally invasive manner.