Objectives A continuum of pathological ultrasound patellar tendon changes from normal tendons, followed by diffuse and then focal change in echogenicity has been proposed. The anteroposterior (AP) diameter of each pathological state and whether change in pathological state is accompanied by change in AP diameter are not known. The aims of this study were to (1) investigate the AP diameter of previously described patellar tendon ultrasound groups (normal, diffuse and focal change in echogenicity) and (2) investigate the change in AP diameter among active volleyball players during a season and whether this corresponds with change in ultrasound group.

Methods The grey-scale ultrasound pathological groups (normal, diffuse, focal) and AP diameter were measured among 102 volleyball players at the beginning of a season and 58 volleyball players at 6 one-monthly intervals during a 5-month indoor season.

Results There was a significant ordinal relationship (analysis of variance, Student–Neuman–Keuls post hoc test, p < 0.05) between AP diameter and normal tendons, diffuse and focally abnormal tendons among men (3.4 ± 0.4, 4.9 ± 0.4, 6.5 ± 1.8 mm) and women (3.2 ± 0.4, 4.2 ± 0.4, 4.6 ± 0.7 mm). Tendons that stayed in the same group tended to have a smaller mean change than tendons that changed group.

Conclusions These findings support the proposed continuum of tendon pathology. Mild patellar tendon thickening (>4.2 mm among men, >4 mm among women) may indicate pathology among active athletes.