The Boat and the Moon

Author: BuMin Kong, MD; Susie Lee, BA

Peer-Reviewer: Mark Hopkins, MD

Final Editor:  Alex Tomesch, MD

25 year-old male presents to the ED with right wrist pain after falling on an outstretched hand. Pain is localized to the anatomical snuffbox, exacerbated by wrist dorsiflexion, and associated with swelling over the dorsal aspect of the wrist.

Image 1: Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 9894

1. What is your diagnosis?

2. What other images can aid in making your diagnosis in the ED?

3. What is your treatment in the ED?

4. What is your disposition?

-- see below for answers --

1. What is your diagnosis?

Scapholunate dissociation. 

In the PA view of the wrist, the scapholunate interval will be over 3mm wide (Terry Thomas or David Letterman sign) [1]. There may also be a ringed appearance of the distal scaphoid because of scaphoid misalignment (Cortical Ring sign).

Image 2: Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 9894. Annotation by authors

• Pearl: This injury occurs due to tearing of the scapholunate interosseous ligaments and is caused by a FOOSH in young patients or degenerative tears in the elderly.

2. What other images can aid in making your diagnosis in the ED?

Clenched fist and PA views of the wrist with ulnar deviation can exaggerate the scapholunate interval and assist in making your diagnosis [1].

Image 3: Clenched fist view with right scapholunate dissociation. Note the difference between the scapholunate intervals. Case courtesy of Andrew Murphy, Radiopaedia.org, rID: 47035. Annotation by authors

Image 4: PA view of a normal right wrist in ulnar deviation. S: Scaphoid. L: Lunate. Tr: Triquetrum. P: Pisiform. Tm: Trapezium. Td: Trapezoid. C: Capitate.  H: Hamate. Case courtesy of Assoc Prof Craig Hacking, Radiopaedia.org, rID: 37482. Annotation by authors.

3. What is your treatment in the ED?

Short course of NSAIDS and immobilization with radial gutter or forearm volar splint.

 

4. What is your disposition?

Follow up outpatient with orthopedics in 1-2 weeks.

• Pearl: Serial exams are important because malunion can lead to a progressive pattern of wrist arthritis called Scapholunate Advanced Collapse (SLAC) [2].

Additional reading on Scapholunate dislocation can be found at WikiSM

Reference

1. Konopka G, Chim H. Optimal management of scapholunate ligament injuries. Orthop Res Rev. 2018 Aug 6;10:41-54. doi: 10.2147/ORR.S129620. PMID: 30774459; PMCID: PMC6209348.

2. Linscheid RL, Dobyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist. Diagnosis, classification, and pathomechanics. J Bone Joint Surg Am. 1972 Dec;54(8):1612-32. PMID: 4653642.

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