MRI-based classification of pes anserinus tendon variations and their clinical implications in non-traumatic knees

The pes anserinus (PA) is a morphologically variable structure whose in vivo tendon configurations remain incompletely characterized on routine MRI. This study aimed to define the typical tritendinous configuration of the PA, identify variant tendon patterns, and evaluate their association with concomitant intra-articular pathological findings.

A total of 125 non-traumatic knee MRIs were screened, and 119 met the inclusion criteria. PA morphology was classified using a three-digit numerical coding system into Group A (classic 1-1-1; n = 64) and Group B (variants; n = 55; B1-B4 subgroups). Morphological assessments were independently performed by a radiologist and an anatomist. Concomitant intra-articular pathologies were analyzed as secondary exploratory outcomes.

Eight distinct PA configurations were identified, with the classic 1-1-1 pattern being the most frequent (53.8%). Inter-observer agreement was almost perfect (κ = 0.924). No significant association was found between PA morphology and intra-articular pathologies. Exploratory analyses revealed age differences in selected subgroups; however, these findings did not remain significant after multiple-comparison correction.

PA morphology can be reliably classified on routine MRI, but tendon variation alone does not appear to be associated with intra-articular pathology in non-traumatic knees. MRI-based identification of PA configurations may support preoperative planning, particularly in cases with complex tendon patterns. These findings also support the use of PA tendons in ACL reconstruction regardless of morphological variation.