Ultrasound of horizontal instability of the acromioclavicular joint: Asimple and reliable test based on acadaveric study

BackgroundHorizontal instability influences the clinical outcome after acromioclavicular joint (ACJ) injuries and in joint degeneration. Astandardized, dynamic examination of the horizontal instability has not been described before. This current study presents asonographic method to analyze the dynamics between the clavicle and acromion in the horizontal plane.MethodsThe horizontal joint play, the ACJ space and the offset between clavicle and acromion were sonographically assessed by a45 degrees ventrally angulated longitudinal section. A total of four investigators with different experience in the field of musculoskeletal ultrasound examining 20ACJs in 10 human cadavers. Measurements in the absence of any pressure and under standardized anterior and posterior pressure onto the clavicle were carried out in different ligament status intact acromioclavicular (AC) and coracoclavicular (CC) ligaments as well as in aRockwood (RW) II and IIImodel. A two-sided t-test was used to examine the differences between joint positions and ligament status.ResultsThe horizontal joint play was 1.30.9mm with intact ligaments, 1.4 +/- 1.2mm by transecting the AC ligaments and 1.9 +/- 1.3mm after additionally transecting the CC ligament. The joint space was 3.3 +/- 1.1mm with intact ligaments, 4.1 +/- 1.8mm in an iatrogenic RW2 injury, and 5.3 +/- 3.3mm in an iatrogenic RW3 injury. Manipulating the clavicle by applying anterior or posterior pressure did not change the difference within one injury pattern. Interobserver reliability was 83.9%.ConclusionApart from evaluating the ligaments and the joint capsule, measurement of the dynamic horizontal instability is possible in ahuman cadaver model. The ultrasound-based measurement of horizontal instability dynamics avoids radiation exposure, is readily available and cost-efficient.