The Sonographic Posterolateral Rotatory Stress Test for Elbow Instability: A Cadaveric Validation Study

Area of Science:

• Orthopedic Surgery
• Diagnostic Imaging
• Musculoskeletal Ultrasound

Background:

• Clinical tests are established for detecting elbow posterolateral rotatory instability (PLRI).
• The diagnostic utility of ultrasound for evaluating PLRI remains unassessed.

Purpose of the Study:

• To evaluate the accuracy of a sonographic posterolateral rotatory stress test.
• To determine if increasing stages of elbow posterolateral rotatory subluxation can be assessed using ultrasound.

Main Methods:

• A cadaveric laboratory study utilized ten unpaired upper limbs.
• Ultrasound measured posterolateral ulnohumeral distance at rest and during stress testing across four instability stages.
• Instability stages involved sequential release of the extensor carpi radialis brevis (ECRB), lateral collateral ligament complex (LCLC), and capsule.

Main Results:

• Mean ulnohumeral laxities were 1 mm (intact), 3 mm (ECRB release), 6 mm (ECRB + LCLC release), and 10 mm (ECRB + LCLC + capsule release) (P < .001).
• Significant differences in laxity were observed between the intact elbow and all stages of instability (P < .001).
• A minimum laxity of 4 mm distinguished the intact elbow from a clinically positive posterolateral rotatory drawer test (Stage 3).

Conclusions:

• The sonographic posterolateral rotatory stress test effectively detects increasing ulnohumeral laxity correlating with clinical PLRI.
• This ultrasound technique can serve as an adjunct to clinical assessment and static imaging for evaluating ulnohumeral laxity.
• Sonographic ulnohumeral laxity exceeding 4 mm warrants suspicion for underlying elbow instability.