The Association of Genetic Variants Within the Type XII Collagen and Tenascin C Genes with Knee Joint Laxity Measurements

Background/Objectives: Types I, V, and XI collagen gene variants have been reported to associate with measurements of knee joint laxity and/or absolute knee ligament length changes. Type XII collagen and tenascin C are also ligament structural proteins whose expression is regulated by mechanical loading. This study investigated whether COL12A1 and TNC variants are associated with knee laxity and/or ligament length changes. Methods: Genu recurvatum, anterior–posterior tibial translation, external–internal tibial rotation, and ligament length changes were measured in 128 healthy participants. They were genotyped for COL12A1 (rs970547) and TNC (rs1061494, rs2104772, rs1138545). Results: Both the COL12A1 AA and TNC rs1061494 TT genotypes were associated with decreased external (p = 0.007, p = 0.010) and internal (p = 0.025, p = 0.002) rotation, as well as slack (p = 0.033, p = 0.014), in the dominant leg. Both genotypes, together with sex, weight, and/or COL1A1 genotypes, explained 26% and 32% of the variance in external and internal rotation, respectively. The TNC genotype, sex, and BMI explained 23% of the variance in slack. The COL12A1 AA and the TNC rs1061494 TT genotypes were associated with smaller changes in the MCL (aMCL: COL12A1 p = 0.009, TNC p = 0.045; iMCL: COL12A1 p = 0.004, TNC p = 0.043; pMCL: COL12A1 p = 0.003, TNC p = 0.067; aDMCL: COL12A1 p = 0.007, TNC p = 0.020; pDMCL: COL12A1 p = 0.007, TNC p = 0.023) and/or LCL (COL12A1 p = 0.652, TNC p = 0.049) lengths within the dominant knee. The TNC rs1061494 CC genotype was associated with larger changes in the non-dominant anterior (p = 0.021) and posterior (p < 0.001) ACL bundle lengths. Conclusions: These findings suggest that COL12A1 and TNC variants are associated with internal–external tibial rotation and knee ligament length changes in healthy individuals.