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The Scapho-lunate ligament rupture is the commonest ligament injury in the wrist. It connects the scaphoid and lunate bones together and stops them from being prised apart. If left untreated the wrist can deteriorate and become arthritic over the following 5-10 years. This is the so-called SLAC wrist (Scapho-Lunate-Advanced-Collapse)
The mechanism of injury is often a fall onto an outstretched hand and wrist.
Pain is well localised to the back of the wrist centrally. Patients often lose wrist extension (cock wrist back). Occasionally they will notice clunking and a feeling of giving way of the wrist.
Plain x-rays may show a gap between the scaphoid and lunate on the AP (front on) view. On the lateral (side on) x-ray view sometimes the lunate bone may be falling backwards called a DISI deformity (Dorsal Intercalated Segment Instability). In the x-ray below right the red arrow shows an increased gap between the scaphoid and lunate.
Often however the x-rays can be normal, but on stress grip views, the bones can move apart and be shown on the images. In such situations the patient is asked to grip a wooden bar as hard as a possible. This puts stress on the wrist and allows the bones to be prised apart and shown up on X-ray. this is described as a dynamic X-ray.
MRI scans show the bones, ligaments and the bone angles in respect of each other. An MRI arthrogram involves an injection dye into the wrist under x-ray control. An MRI is then performed. The MRI can see where the dye has tracked and any abnormal areas of dye collection can help identify the injuries sustained.
The gold standard for diagnosing scapho-lunate ligament injuries is the wrist arthroscopy. This is performed under general anaesthesia as a day case. Four or five small incisions are made in the wrist and a telescope is passed around the joint to directly visualise the bones and ligaments.
Surgery is performed in the acute injury. The two bones are held together with bone anchors and stabilised with fine temporary wires. The wires are removed at 6-8 weeks and the wrist mobilised. It takes approximately 3-4 months to return to normal activities
If there is a delay to diagnosis and there is no arthritis present, then a ligament reconstruction can be performed. My particular preferred technique is the Tri-ligament tenodesis using a slip of a tendon (flexor carpi radialis).
The back of the wrist is opened and the gap between the two bones is seen. A strip of a tendon on the front of the wrist is harvested and passed along a bone tunnel that has been drilled in the scaphoid. The tendon exits on the back of the scaphoid and is passed across the back of the wrist to bring the scaphoid and lunate together.
Surgery is performed under general anaesthetic . The patient is placed in a splint and allowed dart-throwing motion at 4-6 weeks. We have published our results in 2006 and my current series of this operation in professional athletes was presented at the recent British Society of Surgery of the Hand annual meeting in 2012.
The results that we have show a reliable return of wrist stability but there is some loss of flexion and extension but still retraining a very functional range.
If left untreated the wrist can become arthritic. In such cases the articular cartilage that normally coats the ends of the bones is worn away resulting in bone rubbing on bone. This causes stiffness and pain. In the diagram below the black arrow shows the narrowing of the joint space between the scaphoid and radius . The red arrow shows the gap between the scaphoid and lunate. Often salvage surgery is required when arthritis occurs and this includes partial or total wrist fusions or total wrist replacement.