Midcarpal fusion involves excision of the scaphoid in order to address the painful radioscaphoid osteoarthritis. The midcarpal joint needs to be stabilized due to potential pain and arthritis depending on the stage of SLAC/SNAC. Stabilization is performed by arthrodesis of the lunate, capitate, hamate and triquetrum, subsequently named a 'four-corner fusion.' As the radiolunate joint is usually spared from arthritic changes, there is normally sufficient and pain-free residual motion between the lunate and the radius.

The 2.4 mm VA-locking intercarpal fusion system combines a circular plating technique with 2.4 mm variable angle locking technology and dedicated instrumentation . The circular plate design with a smooth surface and rounded edges minimizes soft-tissue irritation (Fig 2). To avoid impingement, proper positioning of the fusion as well as accurate placement and recession of the implant is mandatory. In addition to the standard reaming guide (Fig 3 in Instrument tab), the new reduction reaming guide permits reduction, compression and stabilization of the fusion site during the reaming procedure (Fig 4 in Instrument tab). Laser markings on the reamer support the surgeon by precisely controlling the depth of reaming for optimal countersinking of the plate (Fig 5 in Instrument tab).

The VA-locking plate holes accept both 2.4 mm cortex and VA locking screws. The use of cortex screws provides the option for compression by pulling the bone to the plate and locking screws enhance fixation in cancellous bone. The result is an extremely rigid construct that can withstand the strains of early postoperative mobilization. Midcarpal fusion provides a functional wrist motion achieving a minimum of 30° extension, 30° flexion, and 30° combined ulnar-radial deviation. This '30° rule' enables the patient to perform up to 90% of daily living activities.

The available two plate sizes include a 6-hole plate with a diameter of 15 mm, and a 7-hole plate with a diameter of 17 mm to fit different sized patients and applications.

Fig 3 Standard reaming guide with four pairs of K-wire fixation holes.

Fig 4a The reduction reaming guide also allows application of compression on the carpal bones.

Fig 4b The reduction reaming guide allows midcarpal distraction for bone graft packaging, and then application of compression at the carpal bones junctions.

Fig 5 The reamer has 6 cutting teeth for the improvement of cutting performance. The laser markings ensure a safe and precise reaming depth.