New quantitative radiographic parameters for vertical and horizontal instability in acromioclavicular joint...

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanics

Background:

• Acromioclavicular joint (ACJ) separations present challenges in accurately assessing vertical and horizontal instability.
• Existing radiographic methods may lack reliability or be susceptible to projectional variations.
• Standardized and validated quantitative parameters are needed for precise diagnosis and management.

Purpose of the Study:

• To identify the most accurate and reliable quantitative radiographic parameters for assessing vertical and horizontal instability in ACJ separations across different Rockwood grades.
• To investigate the impact of projectional variations on these parameters using the lateral Alexander view.

Main Methods:

• A Sawbone model simulated Rockwood-classified ACJ dislocations with horizontal posterior displacement.
• Projectional variations were introduced by altering the model's orientation.
• Anterior-posterior Zanca and lateral Alexander views were obtained for each simulated injury and projection.
• Five new parameters, including coracoclavicular distance, were measured for reliability, validity, and projectional effect.

Main Results:

• All measured radiographic parameters demonstrated excellent intra- and interobserver reliability.
• The acromial centre line to dorsal clavicle (AC-DC) showed excellent validity for vertical displacement, and glenoid centre line to posterior clavicle (GC-PC) for horizontal displacement.
• AC-DC and GC-PC exhibited strong convergent and discriminant validity, differentiating ACJ dislocation grades.
• Projectional variations minimally affected AC-DC and GC-PC, with maximal deviation of 3 mm under specific malpositioning.

Conclusions:

• AC-DC and GC-PC are novel, reliable, and valid quantitative radiographic parameters for assessing vertical and horizontal instability in ACJ dislocations.
• These parameters show reasonable robustness against malpositioning, making them suitable for clinical use.
• The study recommends using AC-DC for vertical and GC-PC for horizontal displacement assessment in a single lateral Alexander view to guide ACJ dislocation management, particularly for lower Rockwood grades.