Review Question - QID 220107

This patient presents with posterior lateral rotatory instability (PLRI) after an open release and debridement of the extensor carpi radialis brevis (ECRB). The most likely cause of this instability is iatrogenic lateral ulnar collateral ligament injury due to excessive resection.

The lateral collateral ligament complex consists of the radial collateral ligament, accessory collateral ligament, annular ligament, and lateral ulnar collateral ligament (LUCL). The LUCL is the primary restraint to varus and external rotation stress during elbow motion. LUCL incompetence or injury can result in PLRI. With a combination of forearm supination, axial load, and valgus stress, the radial head will subluxate away from the capitellum. This combination of maneuvers can be recreated when a patient uses their hands to push off from chair handles when going from a seated to a standing position. LUCL iatrogenic injury can be prevented by staying anterior to the equator of the radial head.

Hackl et al. published an anatomical study of 81 human cadaveric upper extremities investigating the lateral collateral ligament of the elbow. They identified 3 distinct morphologies of LUCL insertion based on the annular ligament and supinator crest involvement. The authors report the LUCL can be considered as a posterior branch of the lateral radial collateral ligament. They recommend further clinical research to evaluate the efficacy of more precise anatomical reconstruction.

Coonrad et al. published a retrospective radiographic review of 10 simple and complete elbow dislocations and compared them to an adult series of 20 consecutive lateral elbow radiographs of uninjured patients. They reported an increase in the ulnar humeral distance of 4 mm or greater in 9/10 dislocated elbows on post-reduction elbow lateral films. Two of ten patients developed recurrent instability requiring surgical intervention. They label this as the drop sign and recommend careful evaluation of post reduction elbow X-rays in simple dislocations.

Figure A shows the elbow lateral ligament complex without identifiers. Illustration 1 shows the same image with identifiers.

Incorrect Answers:
Answers 1-4: Isolated injury of the annular ligament, radial collateral ligament, accessory collateral ligament, or articular capsule would not explain findings of PLRI.