Anterior knee pain and patellar instability are common conditions related to the knee. There have been numerous studies showing a variety of risk factors for patellar instability, such as femoral torsion and angular abnormalities as well as trochlear dysplasia. With regard to detecting trochlear dysplasia, radiographic characteristics have been described and commonly used, and magnetic resonance imaging (MRI) has also been employed to look at the depth and angle of the trochlea. Ultrasound, which is increasingly used in orthopaedic offices, represents another potential modality for the diagnosis of trochlear dysplasia. But normative data are lacking with regard to ultrasound evaluation of trochlear morphology in an asymptomatic, skeletally mature patient population.
In the current issue of JBJS, DeVries et al. report on a study in which they evaluated the prevalence of trochlear dysplasia as diagnosed using ultrasound (measurements of the sulcus angle and trochlear depth) in a skeletally mature general population. They also examined associations of trochlear dysplasia and a history of patellar instability or patellofemoral pain syndrome.
A total of 203 knees of skeletally mature adolescents and adults ≤50 years of age were included. The patients were recruited from orthopaedic fracture and sports clinics, for concerns other than knee symptoms; those presenting with knee pain or who had prior intra-articular fracture, total knee arthroplasty, or syndromic ligamentous laxity or neuromuscular disease were excluded. Participants were queried with regard to their history of patellar instability and anterior knee pain, and they also completed the short-form version of the Kujala Anterior Knee Pain Scale (AKPS). Bilateral ultrasound evaluation was performed, and after validating the ultrasound measurements, the authors found:
- The average sulcus angle was 144.1° ± 6.8°, and the average trochlear depth was 5.5 ± 1.4 mm. “High-grade” trochlear dysplasia was defined as a sulcus angle at or above the 95th percentile or trochlear depth at or below the 5th percentile.
- 11 knees (5.4%) had high-grade dysplasia based on a sulcus angle of ≥154°.
- 20 knees (9.9%) had high-grade dysplasia based on a trochlear depth of ≤4 mm for males and ≤3 mm for females.
- Male patients had a significantly deeper trochlea (5.9 ± 1.4 versus 5.3 ± 1.4 mm; p = 0.016).
- Five knees (2%) had a history of patellar instability and were 11 times more likely to have high-grade dysplasia based on the sulcus angle than those without patellar instability history (p = 0.013).
- A greater percentage of female patients than males patients described having anterior knee pain (40% vs 26%), but this finding was not significant (p = 0.096).
- From an additional 11 knees that underwent MRI and ultrasound, the investigators found no significant difference in the sulcus angle or trochlear depth between the 2 imaging modalities.
This study represents an early look into “viewing” the trochlea via ultrasound and helping to establish normative values. As the authors note, further research is needed to validate ultrasound in this area. However, in-office ultrasound may prove beneficial as an adjunct tool in helping to explain to patients the possible anatomic causes for experienced patellar instability.
Click here for a downloadable JBJS Infographic summarizing this study.
Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media