The wrist is a complex joint providing an extraordinary degree of mobility for positioning the hand for function. It has developed through evolution from a weight-bearing forelimb joint similar to the ankle, through a joint primarily allowing suspension from tree branches with increased mobility, to its present role in allowing the hand to be positioned for prehensile function. During this sequence of changes the wrist joint has become vulnerable to injury when its old action of weight-bearing is called into play again, for example in a fall onto the hand. The wrist relies on ligaments to restrain the various bones in the joint from excessive movement relative to each other. If too much force is applied, ligaments can give way, leading to instability of the wrist, poor function and pain.
The area of the wrist most often affected by ligament injury are the joints of the first row of bones beyond the wrist joint, called the proximal carpal row, and the particular joints affected are those between the scaphoid and lunate bones (scapholunate joint) and between the lunate and triquetral bones (lunotriquetral joint).
Scapholunate ligament injury allows the two bones to move apart, leaving a gap seen on x-ray. This is known as the Terry Thomas sign. The width of the gap is variable, but the most important effect of this injury is that the scaphoid is no longer properly controlled and falls into a flexed position (bent forwards). Smooth movement is no longer possible and the patient complains of clicking, pain and weakness. The instability can be progressive, with worsening symptoms and ultimately arthritic changes (called SLAC wrist, or scapholunate advanced collapse).
Diagnosis of scapholunate injury is by examination, x-ray, MRI scan (not always helpful) and arthroscopy. If the wrist has not developed arthritis, the diagnosis is clear, and the symptoms sufficient to warrant it, surgical repair of the scapholunate ligament is possible. Various techniques exist, involving the use of nearby tendon tissue to reconstruct ligaments between the two bones. This is supported with a temporary wire between the two bones to hold them together. The ligament repair takes 7-8 weeks to heal, then the wire is removed. It is usual that some movement (flexion and extension) is lost through operation, an inevitable price for the stability and strength regained. The operation is helpful in most cases, but not universally, and poor results can occur especially if the diagnosis is wrong or other injuries coexist.
Lunotriquetral ligament injury is less easy to diagnoses as the bones do not separate on x-ray. Arthroscopy is usually needed. There is often also some damage to the cartilage on the end of the ulna (TFCC or triangular fibrocartilage complex) The lunotriquetral joint can be stabilized in a similar way if the diagnosis is clear, in association with treatment of the TFCC if indicated, or even sometimes combined with scapholunate ligament repair.
A painful tear in the TFCC may be effectively treated by shortening the ulna bone, reducing the pressure on the torn cartilage. A small section of bone is removed, then the bone moved back together and held by a steel plate during healing.
If the TFCC is torn away from the ulna altogether there is instability of the joint between ulna and radius. This joint is vital for the most important movement in the forearm, pronation and supination, or rotation. Without this movement the repertoire of hand positioning is greatly limited. Reattachment of the TFCC to the ulna is possible. The diagnosis is largely on clinical examination, but x-ray or a CT scan are needed to assess the condition of the joint between the radius and ulna which is essential for smooth rotation. Although reattachment of the TFCC to the ulna can be carried out through the arthroscope (keyhole method), an open operation may allow strong more positive reattachment, and the drawback of having a longer scar is minimal. The operation is best done in supination (palm up position) and this can be achieved by placing the patient on the side with the arm on a rest above the body. In this position the part of the wrist needing surgery is accessible on top, yet the forearm is supinated. For anatomical reasons this places the part of the ulna to which the TFCC is attached in the right place. The forearm has to be immobilized in supination (palm up) using a splint extending above the elbow for about 7 weeks. Regaining pronation (palm down) requires hard work. Stability can usually be restored, but as with all operations of this nature failures do occur, either due to loosening of the repair, re-injury, stiffness, or the presence of previously undetected injuries.
Another problem that causes wrist pain is hypermobility (double jointedness). Such individuals are susceptible to pain when the joint is frequently pushed beyond its natural limit of movement. This occurs particularly in gymnasts and other sportsmen and women. Management is difficult and often under career pressure to continue the pain-inducing activity. Rest and splintage help but may be incompatible with that activity. Surgery is rarely indicated and involves tightening up ligaments, but the loss of movement range may again be a problem for the athlete.