CARPAL INSTABILITY

Question 1

Aetiology of carpal instability

Answer 1

Traumatic vs. atraumatic
Traumatic
1. Fracture = scaphoid fracture
2. Ligament injury = SL or LT ligament injury
3. Dislocation = perilunate/ lunate dislocation
Atraumatic = inflammatory (RA)

Question 2

Classification of carpal instability

Answer 2

Can be classified based on
1. Aetiology = traumatic vs. atraumatic
2. Location
CID
- intrinsic or intracarpal row instability
- within a carpal row
- DISI and VISI
CIND
- extrinsic or intercarpal row instability
- between carpal rows
- radiocarpal and midcarpal instability
CIC
- combination of intercarpal and intracarpal instability
- perilunate/ lunate dislocation
CIA
- instability associated with extrinsic malalignment
- classic is malunited DR fracture
3. Dobyn’s classification = divides carpal instability into 2 basic types based on location
- CID = intrinsic instability caused by dysfunction of intrinsic ligaments
- CIND = extrinsic instability caused by dysfunction of extrinsic ligaments

Question 3

McMurtry’s index

Answer 3

Used to assess for ulnar translocation of carpus
Carpal-ulnar distance = distance between centre of capitate head (COR of carpus) and axis of ulna
McMurtry’s index = ratio of carpal-ulnar distance and 3rd MC length
Normal = 0.30

Question 4

Normal and functional wrist motions

Answer 4

Wrist flexion = normal 65deg, functional 10deg
- more at midcarpal joint
Wrist extension = normal 55deg, functional 30deg
- more at radiocarpal joint
Radial deviation = normal 20deg, functional 10deg
- almost all at midcarpal joint
Ulnar deviation = normal 45deg, functional 10deg
- 50/50

Question 5

Space of Poirier

Answer 5

Weak area in floor of carpal tunnel
Volar capsule between capitate and lunate is not reinforced by ligaments
Lies between 2 V-shaped convergence of ligaments

Question 6

Main volar extrinsic ligaments of the wrist

Answer 6

Form 2 Vs converging on lunate and capitate
1. Ligaments converging on lunate:
Radial side
- Radioscaphoid ligament (radioscapholunate ligament of Testut is not a true ligament, acts as a NV conduit)
- Radiolunate ligament
Ulnar side
- Ulnolunate ligament
- Ulnotriquetral ligament
2. Ligaments converging on capitate:
Radial side = radioscaphocapitate ligament
Ulnar side = ulnocapitate ligament

Question 7

3 strongest volar extrinsic ligaments of the wrist

Answer 7

1. Radioscaphocapitate ligament
   - strongest = load to failure 150N
   - fulcrum around which scaphoid rotates
2. Long radiolunate (radiolunotriquetral) ligament
   - load to failure = 100N
3. Short RL ligament

Question 8

Main dorsal extrinsic ligament of the wrist

Answer 8

Dorsal ligaments converge on triquetrum
Dorsal radiocarpal (radiotriquetral) ligament

Question 9

3 main intrinsic ligaments of the wrist

Answer 9

1. SL interosseous ligament = dorsal component strongest
2. LT interosseous ligament = volar component strongest
3. Dorsal intercarpal ligament (DIC) = triquetrum to scaphoid, trapezium and trapezoid

Question 10

3 factors to consider with management of carpal instability

Answer 10

1. Acuity of injury
   - acute < 3wks
   - subacute 3-6wks
   - chronic > 6wks
2. Correctability of deformity = dynamic is correctable
3. Arthritis