A Lane In Headingley Leeds John Atkinson Grimshaw, oil on board 1881

Transcription

1 CARPAL DISLOCATIONS A Lane In Headingley Leeds John Atkinson Grimshaw, oil on board 1881

2 The half moon shows a face of plaintive sweetness Ready and poised to wax or wane; A fire of pale desire in incompleteness, Tending to pleasure or to pain:- Lo, while we gaze she rolleth on in fleetness To perfect loss or perfect gain. Half bitterness we know, we know half sweetness; This world is all on wax, on wane: When shall completeness round time s incompleteness, Fulfilling joy, fulfilling pain?- Lo, while we ask, life rolleth on in fleetness To finished loss or finished gain. The Half Moon Shows a Face of Plaintive Sweetness, Christina Rossetti 1893 In 1893 Christina Rossetti used the half moon as a metaphor for life. There are the good times and the bad times. Suddenly when things seem good life goes bad, similarly when all seems lost a ray of hope appears. Like the moon our fortunes in life will forever wax and wane. The lunate bone of the carpus was named for the half-moon which it closely resembles. This is most plainly seen in cases of lunate dislocations. It is in these circumstances however that there lies a balance, of fortune. The dislocated lunate may be missed on x- ray when mistaken for a normal pisiform. Should we recognise the lunate form and act accordingly the fate of the lunate will wax toward a perfect gain by its timely reduction. Should we on the other hand miss this sign; the fate of the lunate will wane toward an avascular necrotic perfect loss.

3 CARPAL DISLOCATIONS Introduction Carpal dislocations are relatively uncommon injuries but are important to recognize because of the potential for immediate median nerve injury and delayed avascular necrosis of carpal bones. Lunate dislocations are commonly missed on plain radiography. Classification Carpal (or wrist) dislocations can essentially be of 2 types. 1. Peri-proximal carpus dislocations: Here the distal row of the carpus (and sometimes part of the proximal row) dislocates backwards (relative to the remanning proximal carpal bones which remain in alignment with the radius) Occasionally one of the carpal bones will also fracture, with one part remaining in alignment whilst the other part displaces with the distal row of the carpus. The prefix peri is used to describe the displaced structures in relation to the non-displaced proximal bones. Examples within this group therefore include: Perilunate dislocation of the carpus, (1, in the diagram below) Periscapholunate dislocation of the carpus, (2, in the diagram below) Trans-scapho perilunate dislocation of the carpus, (3, in the diagram below) In this case the trans refers to the fact that the scaphoid has also fractured with one segment staying aligned with the radius and the other segment dislocating backwards with the distal carpal row. This is the second most common type of carpal dislocation. (Other injury patterns within this group, such as transcapitate or transtriquetral perilunate dislocations may occur but are very rare). 2. Proximal carpus dislocations:

4 Here the dislocated distal row itself realigns with the radius and part of the proximal row is extruded. Examples within this group therefore include: Scaphoid dislocation, (4, in the diagram below) Lunate dislocation, (5, in the diagram below) This is the commonest of all the carpal dislocations. 1 Scaphoid and lunate dislocation, (6, in the diagram below) Dislocation of the lunate and part of the scaphoid, (7, in the diagram below) N: Shows the normal alignment of the carpal bones. 1 Group 1: Shows Peri-proximal carpus dislocations Group 2: Shows Proximal carpus dislocations. Structures shown in faint outline are the displaced structures, (volar views). 1: Perilunate dislocation of the carpus. 2. Periscapholunate dislocation 3. Trans-scapho perilunate dislocation. 4. Scaphoid dislocation. 5. Lunate dislocation. 6. Scaphoid and lunate dislocation. 7. Dislocation of the lunate and part of the scaphoid.

5 Mechanism Carpal dislocations usually result from hyperextension injuries of the wrist joint secondary to a fall onto the outstretched hand. They are relatively uncommon injuries. Complications Complications include: 1. Median nerve injury. Prompt reduction usually results in no permanent damage. 2. Avascular necrosis of carpal bones: Scaphoid in particular when this is also fractured in the injury. Lunate when grossly displaced in lunate dislocations. 3. Secondary osteoarthritic changes in the longer term. 4. Reflex sympathetic dystrophy. Clinical Features 1. Pain and local tenderness are significant. 2. Swelling is seen and may be very marked. 3. Vascular compromise is uncommon, however median nerve involvement is not and its function should always be carefully assessed. 4. As with any fall on the outstretched hand, attention to the wrist should not overshadow a careful search for possible associated more proximal injuries involving the elbow, AC joint, shoulder complex and clavicle. Investigations Plain radiography: Carpal dislocations can usually be diagnosed on plain radiography, however the exact nature or the true extent of the injury is often difficult to appreciate and often a CT scan will also be required to fully evaluate the injury.

6 Lunate dislocations in particular are often missed due to a failure of interpretation of the lateral x-rays. When interpreting the lateral x-ray of the wrist it is important to recall the relationships of the bony structures. As shown in the diagram (N) above, the most proximal structure is the radius, which articulates with the lunate, which in turn articulates with the capitate, which in turn articulates with the third metacarpal bone. Left Panel: Perilunate dislocation: Here the lunate (blue arrow) can be seen with its normal articulation with the radius, however the concave cup of the lunate (where the capitate, red arrow, should be) is empty. The capitate is lying posterior to the lunate. Right Panel: Lunate dislocation: Here the lunate is seen clearly displaced forwards away from its articulation with the radius. The capitate now sits directly on the radius. The main reason lunate dislocations are missed is that they are mistaken for a normal pisiform bone.

7 The shape of the dislocated lunate is very different from the more ovoid/ quadrilateral shape of the pisiform. The concave surface in which the capitate normally sits is rotated anteriorly and the crescent moon shape of the lunate (and hence its name) is readily apparent, (also known as the spilled teacup ). On A-P the dislocated lunate appears more triangular in shape, rather than its normal quadrilateral shape. See appendix 1 below for normal A-P x-ray view of the carpus. CT scan: This will often be required to fully evaluate the exact nature and the full extent of injury as well as to help in the planning for cases requiring ORIF. It will also be required when plain radiography is equivocal or apparently normal, yet a high index of suspicion for injury remains. The index of suspicion for injury will depend on: The mechanism of injury. The severity of the patient s symptoms. The degree of clinical swelling observed. Management 1. RICE: Immediate first aid management involves the RICE principle: R: Rest. I: Ice packs. C: Compression bandage. E: Elevation. 2. Analgesia: Pain is usually severe and will require narcotic analgesia titrated to clinical affect. 3. Reduction and repair:

8 Most of these injuries will require referral to the orthopaedic unit for reduction under LAMP or GAMP as reduction can be very difficult. This is especially the case in delayed presentations. After one week closed reduction may not be possible, and open reduction may be necessary. Those with severe dislocations and/ or associated fractures will often require ORIF The urgency of reduction will depend on the degree of neurovascular compromise. Principles of reduction for the 2 commonest uncomplicated injury patterns: Perilunate dislocation: Reduction may be achieved by strong traction under sedation or regional anaesthesia. At the same time distal and volar force should be applied to the dorsal base of the capitate Lunate dislocation: Reduction may be achieved under sedation or regional anaesthesia.

9 Apply traction to the supinated wrist (1) Extend the wrist while maintaining traction (2) Apply direct pressure dorsally over the lunate (3) As soon as the lunate is felt to reduce flex the wrist (4) Follow-up Backslab and re-x-ray to confirm reduction Colles type plaster Refer to a follow-up fracture clinic. These injuries will require close specialist follow-up. Avascular necrosis of carpal bones needs to be looked for.

10 Appendix 1 A-P Radiograph of the Normal Carpus: Normal radiological anatomy of the carpal bones. References 1. Dislocation of the Carpus in McRae R. Practical Fracture Treatment. 3 rd ed 1994 p Dr J. Hayes Dr Peter Papadopoulos. Reviewed 2011.