Review Question - QID 5585

The stout radioscaphocapitate ligament is the main restraint against ulnar translation of the carpus.

On a posteroanterior radiograph, carpal alignment is evaluated using the lunate position relative to the radius. The lunate should align with the ulnar column of the distal radius with a minimum of 2/3 of the lunate articulating with the radius. Radiocarpal fracture dislocations can be classified based on the presence of associated intercarpal dissociation (Moneim classification), or the extent of radial styloid involvement (Dumontier classification).

Ilyas et al. reviewed radiocarpal fracture dislocations. They advise suspecting a scapholunate injury when the radial styloid fracture exits at the junction between scaphoid and lunate fossae. They enumerate the steps for surgical treatment as: (1) provisional reduction, (2) neurovascular decompression, (3) joint de´bridement, (4) treatment of intercarpal injuries, and (5) fracture fixation and/or soft tissue repair.

Mudgal et al. retrospectively reviewed 12 patients with radiocarpal fracture dislocations. Open injuries and Moneim Type II injuries result in inferior outcomes compared with closed and Type I injuries. They opine that anatomical repair and stable fixation will lead to a satisfactory outcome in these injuries.

Figure A shows ulnar translation of the carpus. The lunate is now centered over the distal ulna instead of over the lunate fossa of the radius. Illustrations A and B are the Moneim and Dumontier classifications of radiocarpal fracture-dislocations respectively. Illustration C shows the volar extrinsic ligaments. The main ligaments seen are
the radioscaphocapitate (RSC), the radioscapholunate (RSL), long radiolunate (or radiolunotriquetral or volar radiolunate), and short radiolunate.

Incorrect Answers:
Answer 1: The short radiolunate ligament is likely disrupted. However, while it functions to add mechanical support to the lunate (and in turn, the rest of the carpus), it is not the main mechanical restraint to ulnar translation of the carpus.
Answer 2: The SLIL is an intrinsic ligament. Disruption leads to a widened SL interval and "Terry Thomas sign" on PA radiograph.
Answer 3: The radiotriquetral ligament is a dorsal extrinsic ligament. Disruption of this structure (together with lunotriquetral ligament rupture) leads to VISI deformity.
Answer 5: The radioscapholunate ligament (Ligament of Testut and Kuentz) is a neurovascular conduit and confers no mechanical strength.