BackgroundThe aim of this magnetic resonance imaging (MRI) study was to investigate controversial sexual dimorphism of the posterior condylar offset of the femur (the offset) and the posterior slope of the tibia (the slope) in non-arthritic knees of Egyptian adults.MethodsOn 100 male and 100 female MRIs of non-arthritic knees, linear measurements of the distal part of the femur (the offset) and the angular measurements of the proximal part of the tibia (the slope) were performed and compared regarding sex and ethnicity. The intraclass correlation coefficient (ICC) was used to test the interrater agreement.ResultsBoth offsets and the lateral offset ratio were larger in males (p< 0.001), the medial offset ratio, and the medial slope in females (pfrom < 0.001 to 0.007), whereas the lateral slope was sex-free (p= 0.41). Irrespective of sex, however, the medial offset with its ratio, and the medial slope were larger than their counterparts (p< 0.001). Our means of the offsets, their ratios, and the slopes mostly differed from those of other ethnicities (pfrom ≤ 0.001 to 0.004). ICCs > 0.8 proved MRI’s precision was high.ConclusionThere was a sexual dimorphism of both the offset and the medial slope in non-arthritic knees of Egyptian adults. We believe future designs of knee implants should consider these differences in order to improve postoperative range of motion and patients’ satisfaction after total knee arthroplasty.Level of evidenceLevel III Retrospective Cohort Study.Trial registrationClinicalTrials.govidentifier: NCT03622034, registered on July 28, 2018.