March 1995
F.D.Burke
CARPAL BONE ABNORMALITIES
Kienbock's disease
Kienbock's disease remains a management dilemma for hand surgeons. It is known that one-third of the population have precarious end arterial circulation within the lunate , such that injury to one or two blood vessels may jeopardize circulation within the bone. Softening and collapse of the bone follows with fissuring often occurring sub-chondrally In most cases, the cause of the problem remains uncertain. Micro-fractures within the bone may produce vascular injury. It is felt these stresses may be maximal in situations where the lunate is partly supported on a firm radius but inadequately supported ulnarly on the triangular fibro-cartilage which covers a foreshortened ulna (an ulna minus variance). Early cases without collapse or arthritis would logically be treated by revascularization techniques. This may take the form of a direct arterial mobilization and insertion into bone, or with bone graft raised on an a vascular pedicle, either dorsally or volarly. Others pin their hopes on adjustment of radio-ulna length in those cases where there is felt to be a significant imbalance This may take the form of radial shortening or ulna lengthening; all these techniques can be justified by small moderately successful series, but a definitive long-term statement of the optimal procedure for early cases is not available to us.
Lunate collapse without arthritis can be treated by the same techniques in the hope of containing the situation, but the alignment of the carpal bones has been affected with overall foreshortening and carpal collapse. This has led some surgeons to consideration of distraction of the carpus using external fixation and bone grafting of the lunate in an attempt to regain carpal length.
Established arthritis around the Lunate alters the available options. Revascularization techniques or adjustment of radio-ulna length are no longer appropriate. On occasion, the arthritic process has seemed limited to the radio-lunate joint, indicating that a Chamay fusion may control the pain and preserve some wrist movement. Revascularization of the lunate will occur from the radius.
Proximal row carpectomy, excising the proximal carpal row so that the capitate articulates with the lunate fossa on the radius is rarely indicated, as the capitate and radial articulations are almost invariably damaged by the disease process in the lunate. However, the procedure can produce gratifying results in carefully selected cases of wrist arthritis where the two key articular surfaces are considered to be satisfactory on radiographic assessment. The proximal carpal bones are excised through a dorsal approach with dorsal capsular repair. The wrist is rested in a cast in neutral flexion/extension for 4-6 weeks and then mobilized. Power and movement are only slowly regained but the patient usually obtains 40-60' of flexion/extension range around the neural point with moderate grip strength one year after surgery. If the key articular surfaces were in satisfactory condition pre-operatively, reasonable pain relief is obtained.
Silastic lunate implants have been replaced by titanium models in recent years. Long-term follow-up of the technique remains uncertain, an important consideration as many patients with Kienbock's disease are in their teens and twenties and keen to use the upper limb as vigorously as discomfort, permits.
Well-established arthritis throughout the carpus indicates three other possible surgical options.
Denervation of the wrist. No attempt is made to treat the arthritis, simply the pain that it causes. The nerves that supply the carpus are classified into radial, median and ulnar groups, and serial nerve blocks will reveal to an extent the likely result of ablation of these various nerves. An extensive long-term study has shown it to be useful in reducing pain but retaining movement, apparently without the risk of a Charcot joint. Ninety per cent of Buck Gramcko's series were considered to have gained reasonable pain relief (60% pain-free and 30% improved).
Arthroplasty of the wrist. The most frequently used wrist implant in rheumatoid patients has been that developed by Swanson, a stemmed silicone elastomer spacer. A limited range of motion perhaps 40--60 is sought around the neutral position. Such a range permits most activities to be performed with ease. There is a tendency for the implant to gradually seat within the wrist with migration of the metacarpal bases proximally and progressive loss of motion over several years. However, the implant is usually well tolerated and patients greatly appreciate the limited range of motion the joint replacement permits.
Acceptance of the various formal joint replacements (metal polyethylene articulations cemented in radius and metacarpals) has been more cautious. This has been partly through the concern over the amount of bone stock excised and the difficulties in retrieving the situation if loosening or infection occurs. The implants are being used more frequently for both rheumatoid and osteoarthritic joints, although Meuli feels that the joint replacement should not be used for heavy manual activities, or in situations where crutches or walking sticks pass considerably forces across the wrist.
Arthrodesis of the wrist. Fusion of an osteoarthritic wrist is most commonly obtained by the use of a plate and screws to radius, carpus and third metacarpal, augmented with cancellous bone graft. Slight dorsal angulation potentiates grasp. The dorsal incision extends to the radius, retracting the extensor indicis proprius compartment radially and the digital extensor compartment ulnarly. The dorsal two-thirds of the articular surfaces of the wrist joint are rawed and the cavities packed with cancellous bone. Modern low profile plates and screws are not unduly prominent, and there is normally no need to remove the metal work unless discomfort is experienced. The stability of the fixation is such that the fingers and the thumb can be mobilized immediately. The dissection can largely avoid direct exposure of the extensor tendons, reducing the risk of tendon adhesions.