Review Question - QID 220046

Scapholunate Ligament Injury & DISI Etiology Associated injuries QID: 220046 (SBQ24HW.78)

QID 220046 (Type "220046" in App Search)

A 28-year-old male reports to the orthopedic clinic with a 6-week history of left wrist pain. One and a half months prior, he crashed on his bike and caught himself with his hands. Injury and repeat films report no acute osseous abnormality. He endorses weakness and pain when gripping heavy objects. He is tender over the anatomic snuff box on physical exam. He also experiences pain when his wrist deviates from ulnar to radial with force applied to the scaphoid tubercle. A video of his wrist MRI is seen in Figure A. If his injury is not addressed, what carpal deformity will initially develop?

Type & Select Correct Answer

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Lunate flexion

32/813

Scaphoid flexion

61%

494/813

Volar intercalated segment instability

12%

96/813

Scaphoid humpback deformity

15%

124/813

Scapholunate arthritis

60/813

Select Answer to see Preferred Response

This patient presents with history, exam, and imaging findings consistent with a scapholunate ligament injury. Complete scapholunate ligament (SL) injury results in scaphoid flexion and lunate extension.

Carpal wrist kinematics are maintained in proper balance by complex interactions between the proximal and distal carpal rows. When the SL ligament is injured, the scaphoid and lunate begin to move in a disconnected fashion. The scaphoid is pulled into flexion by its distal connections to the trapezium, trapezoid, and capitate. The lunate experiences an extension moment from connections to the triquetrum, and with no scaphoid-induced flexion to balance, the lunate falls into extension. This combination of scaphoid flexion and lunate extension results in dorsal intercalated instability (DISI). This wrist instability leads to irregular contact pressures that first start at the scaphoid fossa, and then progress to the arthritic pattern seen in scaphoid ligament-associated collapse (SLAC).

Bednar et al. published a review article on carpal instability, with a focus on the resulting kinematic deformities. As the wrist moves from radial to ulnar deviation the proximal row should rotate from flexion to extension. SL instability leads to above mentioned DISI deformity. The authors recommended SL repair in both acute and subacute injuries.

Walsh et al. published a review article regarding the anatomy, kinematics, diagnosis, and treatment of SL injuries. The authors highlight that the dorsal portion of the SL is the most important for maintaining proper scaphoid and lunate motion. The scaphoid deformity is what first leads to arthritic changes in the wrist.

Figure A shows an MRI of the left wrist with widening at the scaphoid lunate interval and complete SL disruption.

Incorrect Answers:
Answer 1: The lunate falls into extension after an SL injury.
Answer 3: Volar intercalated segment instability (VISI) is secondary to lunotriquetral ligament injury. The loss of the extension moment from the triquetrum results in unopposed flexion on the lunate from the scaphoid.
Answer 4: Scaphoid humpback deformity is associated with scaphoid fracture malunion.
Answer 5: The scaphoid lunate joint is spared of arthritic changes until late in the SLAC disease course.