Musculoskeletal Ultrasound of the Patellar Tendon in Adolescent Athletes

BACKGROUND: Patellar tendinopathy is a common chronic condition caused by mechanical loading that leads to patellar tendon (PT) degeneration, with an estimated incidence of 13% across all sports in adolescents. Musculoskeletal ultrasound (MSK-US) evaluation is becoming more common in the diagnostic process, but normative data are extremely rare for the adolescent population. These normative data are needed to aid in proper interpretation of the MSK-US image. PURPOSE: The purpose of this study was to determine standard reference values for thickness, width, and cross-sectional area (CSA) of the PT using MSK-US in asymptomatic adolescent athletes. METHODS: IRB approval, parental consent, and athlete assent were obtained prior to data collection. Bilateral PT were scanned using a portable US unit with a 12-4MHz linear array transducer. Long axis images were captured at the apex and 1cm distal to the patella, 1 cm proximal to the insertion and at the PT insertion (Figure 1a & 1b). Short axis images were captured 1 cm proximal and distal to the attachments. PT thickness, width, and CSA were measured using ImageJ by a single evaluator. Additional exploratory analyses were also conducted. RESULTS: Seventy-one adolescent athletes (27 males, 44 females) between 11-18 years old (13.8 ±1.8 years) volunteered. Mean values for PT thickness, width, and CSA are found in Table 1. Significant differences in PT thickness and CSA between sex were identified at each measurement location (P<.05), with males ranging 4.0-9.9 mm thicker than females. PT width was not significantly different proximally or distally. The left proximal PT was significantly wider than right (P<.0001), but no other side differences were found. Lastly, significant weak positive correlations were present in distal tendon CSA with height (left PT: r((52))=.348, P=.014, right PT: r((49))=.369, P=.007) and weight (left PT: r((50 ))=.290, P=.041). There was no correlation with age. CONCLUSION: These data represent one of the largest healthy cohorts of adolescent athletes from which normative data have been collected. This preliminary analysis reveals some interesting trends, such as the thickness of the PT is greatest at the insertion and origin, while thinner at mid-tendon, with the insertion the thicker of the two. Age was not correlated with PT size, but distal PT CSA was larger with taller and heavier individuals. These data will contribute to the paucity of adolescent PT MSK-US data, which should aid clinicians in interpretation, diagnostic accuracy, and management of active adolescent patients with patellar tendinopathy.