Objectives: We set out to investigate the cause of persistently increased signal intensity (SI) in the posterior portion of the proximal patellar tendon (pPT) on T1-weighted images (T1WI).
Methods: MR imaging was performed in eight cadavers, followed by gross histological examination. In addition, 84 patients without trauma history or anterior knee pain were included to compare the SI of the PTs. The patients were divided according to their age, sex, and Kellgren-Lawrence (KL) grades. The length and thickness of the increased SI portion in the pPT and whole PT (wPT) on T1WI were recorded.
Results: Histological specimens demonstrated that the adipose tissue, vessels, and perivascular connective tissue invaginated into the posterior portion of the pPT. This histological anatomy corresponded to the pPT signal change on MR imaging. There was linear and interdigitating increased SI of the pPT in all of the 84 patients (100%). There were no differences in the lengths and thicknesses of the increased SI portion of pPTs and wPTs according to age, sex, and KL grade (all p > 0.05).
Conclusions: The increased SI of the pPT on T1WI and fluid-sensitive MR images results from invaginating fat, vessels, and perivascular connective tissue. It is not pathological, but a normal and common finding.
Key points: • Increased linear/interdigitated SIs of the pPT is a normal and common finding. • Invaginated adipose tissue, vessels, and connective tissue could contribute to increased SI. • The fibrocartilage has a minimal role in increased SI of the pPT. • Age, sex, and KL grade do not significantly influence the increased SI. • Knowledge of this increased SI should help clinicians to avoid unnecessary treatment.