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What is the mechanism of Pivot shift test in PLRI?

Asked by Tom 

PLRI or Posterolateral rotatory instability is caused by the incompetence of LUCL (Lateral ulnar collateral ligament). LUCL attaches on lateral epicondyle on humerus and supinator crest on ulna. It is the primary varus restraint throughout the elbow range of motion.

Lateral pivot shift test (O'Driscoll) reproduces instability with combination of supination, axial loading and valgus loading as elbow is brough from full extension to 40 degrees of flexion. During the test, apprehension is common, and either intra-articular local anesthetic must be given, or examination must be done under anesthesia to confirm the diagnosis.
  • Role of supination: Ulna rotates externally on trochlea and as the ulna rotates, radius moves along producing posterior radial head subluxation
  • Role of increasing flexion: Triceps becomes taut, and the radial head reduces with a palpable clunk