Posterior tibial slope and its association with sex and age in a Jordanian hospital-based sample: a cross-sectional radiographic study

Abstract Background Posterior tibial slope (PTS) affects sagittal knee biomechanics and is relevant to ligament reconstruction, osteotomy and arthroplasty. Published values vary with population and measurement method, and data from Jordan are lacking. This study described radiographic PTS in a Jordanian hospital-based sample and examined its association with sex, age and side. Methods This retrospective cross-sectional study used lateral knee radiographs obtained at Jordan University Hospital in 2022 from patients aged 16 to 65 years. Knees with a true lateral projection and without osteoarthritis, open physes, fracture, tumour or previous surgery were included. PTS was measured against a proximal tibial anatomical axis defined by two circles. Associations with sex, age and side were estimated in a linear mixed-effects model with a random intercept for participant, which accounts for participants who contributed both knees. Inter-observer agreement was assessed with the intraclass correlation coefficient (ICC). Results We analysed 720 knees from 517 participants (363 women, 70.2%; mean age 48.7 ± 11.3 years). Mean PTS was 10.28° ± 2.09° in right knees and 10.38° ± 2.11° in left knees. PTS was 0.52° higher in women than in men (95% confidence interval [CI] 0.15 to 0.89; p = 0.006) and 0.21° lower per 10 years of age (95% CI 0.06 to 0.36; p = 0.007). Side was not associated with PTS (0.06°, 95% CI − 0.19 to 0.32), and the sex difference did not differ between sides (interaction p = 0.92). The sex estimate was unchanged when one knee per participant was analysed, whereas the age estimate weakened when the mean of the two observers was used (− 0.12° per 10 years, p = 0.097). Inter-observer agreement was moderate (ICC 0.50, 95% CI 0.42 to 0.58). Conclusions In this hospital-based sample, mean PTS was about 10°. Women had slightly steeper slopes than men, and slope was slightly lower in older participants. Both differences were smaller than 1°, which is below the precision of a single radiographic measurement, so their clinical relevance is uncertain. Confirmation in independent cohorts is needed to establish their generalizability to the wider Jordanian population.