The Association of Lateral Knee Sagittal Radius of Curvature with ACL Injury: Gender or Geometry? (SS-67)

Christopher J. Wahl; Robert Westermann; Gregory Blaisdell; Amy M. Cizik

doi:10.1016/j.arthro.2011.03.071

Attributes of femoral condyle and tibial plateau geometry may play a role in the stability of the knee. We studied differences in lateral knee length and radial geometry in ACL-injured and uninjured cohorts. 185 age- and activity-matched uninjured and non-contact unilateral (uACL)- and bilateral (bACL)-injured groups were included. MRI measurements of the articular cartilage surfaces in the mid-weight-bearing sagittal plane of the lateral compartment evaluated tibial plateau radius of curvature (TPr) and distal femoral radius of curvature (Fr). The Fr was measured at the weight-bearing segment of a best fit logarithmic curve (Fibonacci sequence). Measurements were also made of the maximum distance from anterior to posterior femur perpendicular to the femoral shaft (FAP) and anteroposterior tibial articular length (TPAP). Calculations of Fr:TPr and FAP:TPAP were used to adjust for individual variations in anatomic size. Measurements were made by 3 observers blinded to gender and injury group. Interclass correlation coefficient was performed to assess inter-rater reliability. Two-sampled Student t-tests were used to compare quantitive variables. All data represented a normal distribution. Combined gender: The mean lateral plateau radius of curvature, femoral radius of curvature, and tibial plateau lengths were all significantly smaller in ACL-injured versus non-injured groups (33.6 vs. 37.4mm, p=0.003; 25.1 vs. 24.2mm, p=0.01; 31.4 vs. 33.2mm, p=0.004; respectively). Femoral length was not different between ACL-injured and uninjured groups (p=0.19). Adjusting for size differences, FAP:TPAP was significantly larger in injured versus controls, indicating that the length of the tibial plateau was significantly smaller relative to the femur in injury groups. Gender Groups (Table 1): No significant differences existed between ACL-injured females and uninjured females with respect to femoral length, tibial length, femoral radius, tibial plateau radius or FAP:TPAP. Conversely, compared to uninjured males, ACL-injured males demonstrated significantly smaller tibial plateau radius (41.1 vs. 35.3mm), femoral radius (26.7 vs. 25.5mm), and tibial plateau length (35.5 vs. 33.1mm). No differences existed between femoral length between injured and uninjured males. FAP:TPAP differences suggested that the length of the tibial plateau was significantly shorter relative to the femur in ACL-injured males (p<0.001). Furthermore, after adjusting for size differences, ACL-injured males demonstrated no significant differences than control or injured females with respect to the relative size of the plateau to distal femur (FAP:TPAP) or relative radii of the femur and tibia (Fr:TPr). Our data suggest that all females (injured or uninjured) and ACL-injured males share a common lateral knee geometry characterized by a shorter tibial plateau length relative to the femur and smaller (more convex) articulating surfaces of both the proximal tibia and distal femur. It is possible that the opposition of two highly-convex articulating surfaces may be inherently less stable to anterior tibial translation and rotation. These findings also may help to explain the apparent female predilection for ACL injury compared to males, but suggest that this may be as much driven by geometry as it is by gender.

The Association of Lateral Knee Sagittal Radius of Curvature with ACL Injury: Gender or Geometry? (SS-67)

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