Dynamic ultrasound may quantitatively assess medial patellofemoral complex injury in multiple clinical settings

The use of imaging to diagnose patellofemoral instability is often limited by the inability to dynamically load the joint during assessment. Therefore, the diagnosis is typically based on physical examination using the glide test to assess and quantify lateral patellar translation. However, precise quantification with this technique remains difficult.

Bhimani Et al found in a Controlled laboratory study that it is possible to quantify patellar position using ultrasound imaging under dynamic loading conditions to distinguish between knees with and without medial patellofemoral complex (MPFC) injury. Investigation was performed at Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA

In 10 cadaveric knees, the medial patellofemoral distance was measured to quantify patellar position from 00 to 400 of knee flexion at 100 increments. Knees were evaluated at each flexion angle under unloaded conditions and with 20 N of laterally directed force on the patella to mimic the glide test. Patellar position measurements were made on ultrasound images obtained before and after MPFC transection and compared for significant differences.

To determine the ability of medial patellofemoral measurements to differentiate between MPFC-intact and MPFC-deficient states, area under the receiver operating characteristic (ROC) curve analysis and the Delong test were used.

The optimal cutoff value to distinguish between the deficient and intact states was determined using the Youden J statistic.

The results of the study were -

• A significant increase in medial patellofemoral distance was observed in the MPFC-deficient state as compared with the intact state at all flexion angles (P =.005 to P < .001).

• When compared with the intact state, MPFC deficiency increased medial patellofemoral distance by 32.8% (6 mm) at 200 of knee flexion under 20-N load.

• Based on ROC analysis and the J statistic, the optimal threshold for identifying MPFC injury was 19.2 mm of medial patellofemoral distance at 200 of flexion under dynamic loading conditions (area under the ROC curve = 0.93, sensitivity = 77.8%, specificity = 100%, accuracy = 88.9%).

The authors concluded that - Using dynamic ultrasound assessment, they found that medial patellofemoral distance significantly increases with disruption of the MPFC, and such measurements can be used to accurately detect the presence of complete MPFC injury. Dynamic ultrasound allows quantitative assessment of MPFC insufficiency in multiple clinical settings. Future clinical studies are recommended to assess the utility of measurement thresholds in diagnosing and treating patellar instability.

Further reading:

Utility of Diagnostic Ultrasound in the Assessment of Patellar Instability

Bhimani et al

The Orthopaedic Journal of Sports Medicine, 10(5), 23259671221098748

DOI: 10.1177/23259671221098748