02/12/2010
AO Technical Commission Approved

2.4 mm VA -Locking Intercarpal Fusion System

Longstanding scaphoid nonunion advance collapse (SNAC) or scapholunate advanced collapse (SLAC) can lead to a painful wrist with limited range of motion. Midcarpal fusion, so-called four-corner fusion, is a reliable procedure for treating painful SNAC and SLAC wrists, with preservation of functional wrist motion. In this procedure the scaphoid is excised in order to address the painful radioscaphoid osteoarthritis. The midcarpal joint then needs to be stabilized, because depending on the stage of SLAC/SNAC, it may also be arthritic and painful. Stabilization is performed by arthrodesis among the lunate, capitate, hamate, and triquetrum, thus fourcorner fusion. As the radiolunate joint is usually spared from arthritic changes, it allows for sufficient and pain-free residual motion between the lunate and the radius.

The 2.4 mm VA-locking intercarpal fusion system combines the 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. To avoid impingement, proper positioning of the fusion, placement, and recession of the implant are mandatory. Apart from the standard reaming guide , the new reduction reaming guide permits reduction, compression, and stabilization of the fusion site during the reaming procedure. Laser markings on the reamer support the surgeon by precisely controlling the depth of reaming for optimal countersinking of the plate.

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 bones to the plate, whereas locking screws enhance the holding power in the cancellous bone. This results in an extremely rigid construct that can withstand the strains of early postoperative mobilization. Midcarpal fusion provides a functional (useful) wrist motion achieving a minimum of 30 extension, 30 flexion, and 30 combined ulnar-radial deviation. This is the rule of the 30s that allows the performance of about 90% of daily living activities.

Two plate sizes are available: 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.

Overall, the VA-locking intercarpal fusion system presents a major technological and conceptual step forward in reconstructive wrist surgery.

Fig 1 VA-locking intercarpal fusion system.

Fig 2 Seven-hole circular plate. Note the 2.4 mm variable angle locking holes, as well as thin holes for temporary fixation using K-wires. The central, plain hole is used for cancellous bone graft placement at the junction of the four bones to be fused.

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.

Case 1: SNAC wrist stage 3. Operative procedure and technical details.

Case provided by Ladislav Nagy, Zrich, Switzerland, and Fiesky Nez, Valencia, Venezuela.

Fig 1ab Preoperative x-rays. Notice the midcarpal joint destruction and the DISI deformity of the lunate.

Fig 2ab Dorsal intercalated segment instability correction and K-wire fixation.

Fig 3ab Bone debridement. Guide positioning and fixation.

Fig 3c Bone debridement. Guide positioning and fixation.

Fig 4c Once the carpal junctions have been putting closer by the new reduction-compression guide, reaming is done.

Fig 5ab Plate positioning and fixation. The combined VA-locking-standard guide allows drilling in the appropriate direction.

Fig 5cd Plate positioning and fixation. The combined VA-locking-standard guide allows drilling in the appropriate direction.

Fig 6ab Final appearance of fixed plate.

Fig 7ab No impingement of the plate against the dorsal rim of the radius in extension.


Case 2: Early degenerative wrist stage 3 secondary to a necrotic and collapsed proximal pole nonunion.

Case provided by Ariane Scheller, Berlin, Germany

Fig 1ab Preoperative x-rays. Note the carpal collapse a a b nd DISI deformity.

 


Case 3: Painful SNAC wrist in a 42-year-old man.

Case provided by Juan Gonzlez del Pino, Madrid, Spain

Fig 1 X-ray shows SNAC wrist.

 

Midcarpal Fusion Plate: The AO Four Corner Fusion Plate

Presented by J. Gonzalez Del Pino & F. Nunez in 2011

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