Reliability and Validity of an Ultrasound-Derived Measure for Axial Patellofemoral Alignment

Area of Science:

• Orthopedics
• Radiology
• Biomedical Engineering

Background:

• Patellofemoral instability (PFI) assessment often uses MRI, but ultrasound (US) offers a cost-effective alternative.
• Evaluating axial extensor mechanism alignment is crucial for diagnosing PFI.

Purpose of the Study:

• To develop and validate a novel musculoskeletal ultrasound (US) measure for patellofemoral joint extensor mechanism alignment.
• To assess the reliability and construct validity of this US measure by comparing patients with and without PFI.

Main Methods:

• A cohort study compared patients with PFI (n=24) and healthy controls (n=26).
• Musculoskeletal US measured the distance between the midpoint of the patellar tendon and the lateral trochlear ridge (MPT-LTR).
• Interrater and test-retest reliability were assessed using intraclass correlation coefficients (ICC).

Main Results:

• The US-based MPT-LTR measurement demonstrated good (ICC=0.785) to excellent (ICC=0.958) reliability.
• Patients with PFI showed a significantly smaller MPT-LTR distance compared to controls in both involved and uninvolved limbs (P < .001).
• This smaller distance indicates greater lateralization of the patellar tendon relative to the trochlea in PFI patients.

Conclusions:

• The ultrasound-derived MPT-LTR distance is a reliable measure for assessing extensor mechanism alignment.
• A smaller MPT-LTR distance, indicative of greater lateralization, is associated with patellofemoral instability.