DIAGNOSIS WRIST INJURIES

Movement Measure the active and passive range of movement in all directions. Do specific stress tests for scapho-lunate instability, luno-triquetral instability and distal radio-ulnar joint instability.

Fracture of the distal radius The distal radius is vulnerable in a

Figure 1: Radius and ulnar plate

fall on the outstretched hand. The type of fracture depends on age. In adolescents, before closure of the growth plates, a physeal injury of the distal radius is more likely to occur than a scaphoid fracture. In young and middle-aged adults, the distal radius fractures across the metaphysis. With increasing energy, the fracture becomes comminuted. Snowboarders and motocross riders are particularly prone to this. In the older, osteopenic patient, the fracture impacts and tilts dorsally (Colles’ fracture). Diagnosis is secured by X-ray.

Occasionally CT is needed to define the extent of comminution and plan surgical reconstruction.

Figure 2: Scaphoid non-union

Simple undisplaced fractures are managed in a cast for 5 weeks. Displaced fractures need manipulation and then stabilisation with metalwork – wires or plates (Fig. 1).

Fracture of the scaphoid This is a common fracture to miss, and there should be a high clinical suspicion after a fall on to an outstretched hand. Symptoms and signs include a swollen and tender anatomical snuffbox (although the unaffected side may also be tender). There may also be pain applying pressure over the scaphoid tuberosity and scapho-lunate interval. Investigations include scaphoid

X-rays. If these are negative and clinical suspicion is still high, further investigation with an MRI scan is indicated. This test is very sensitive for the presence of a fracture because of the dramatic signal changes. However, MRI does not define cortical margins well; if surgery is contemplated, then a CT scan provides much better definition of the fracture line. The main risk of missing this fracture is non-union (Fig. 2) due to its poor blood supply leading to chronic wrist pain and loss of grip strength. Ninety per cent of undisplaced

Figure 3: Scaphoid fixed with a screw and bone graft from the distal radius

Figure 4: Terry Thomas sign

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waist fractures heal in a promptly applied cast within 8–12 weeks. The union rate for proximal pole fractures and displaced fractures is much less reliable. These latter two configurations warrant early surgery. There is an increasing trend to fix undisplaced waist fractures immediately with a percutaneous cannulated compression screw in order to speed recovery and return to training (Fig. 3).

Scapho-lunate ligament tear The scapho-lunate ligament maintains the proximal pole of the scaphoid adjacent to the lunate (scapho-lunate gap) and stabilises the palmar rotation force of the scaphoid against the dorsal rotation force of the lunate. This structure is injured when the wrist hyperextension mechanism that might result in a scaphoid fracture instead disrupts the adjacent scapho- lunate ligament. This may occur as a partial tear with pain but no instability, best treated by rest and sometimes arthroscopic debridement. More complete injuries may result in dynamic scapho-lunate instability, with normal plain X-rays but pain with use and an increased radiological scapho-lunate gap with the fist clenched. Complete disruption of the scapho-lunate ligament results in an instability pattern visible on plain X-rays, with widening of the scapho-lunate gap (the “Terry Thomas sign”) (Fig. 4) and the lunate tilted backwards with the scaphoid flexed on the lateral view (dorsal intercalated segment instability, DISI). On examination, there is tenderness over the scapho-lunate ligament (just beyond the bony prominence on the back of the distal radius known as Lister’s tubercle). It may be possible to elicit a positive Watson’s test (not specific for the injury). The test involves applying pressure to the palmar portion of the scaphoid while moving the wrist into ulnar deviation. When the wrist is then moved into radial deviation, the scaphoid cannot flex as it is blocked by the examiner’s thumb. If the scapho- lunate ligament is torn, the scaphoid will move dorsally against the examiner’s finger, causing pain. When the scaphoid pressure is removed, the scaphoid then moves back into position with a clunk. MRI arthrography is helpful in

diagnosing this injury, with characteristic soft-tissue signal changes and contrast flowing through the space. Wrist arthroscopy is the definitive investigation. The tear can be identified and the severity of instability established. In later stages, associated arthritis can be assessed. Minor tears can be debrided.

Complete unstable scapho-lunate injuries should be repaired as soon as they are diagnosed. In the first few weeks, a direct repair is possible; thereafter, the tissue degrades and an

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