PURPOSE: This study examined the influence of varus alignment, posterolateral corner (PLC) insufficiency, and PLC reconstruction on forces acting on the anterior cruciate ligament (ACL). It was hypothesized that increasing varus would increase ACL force, PLC transection would amplify this increase, and reconstruction would restore force toward PLC-intact values.
METHODS: Eight cadaveric knees (mean age 62 ± 12 years) underwent dynamic testing at 0°, 10°, 20°, 30° and 40° flexion under 200 N axial load in a materials testing machine with a custom five-degree-of-freedom setup. The ACL was tibially detached and refixated with 80 N using a custom tensioner. Lateral opening-wedge distal femoral osteotomy with external fixation and three-dimensionally printed wedges established 0°, 3°, 5° and 8° varus. Three conditions were tested: (1) native, (2) PLC transection (lateral collateral ligament and popliteus tendon) and (3) PLC reconstruction in Arciero technique.
RESULTS: Axial loading caused ACL forces in PLC-intact knees ranging from 77.1 ± 7.3 N (neutral alignment in 20° flexion) to 109.9 ± 46.8 N (8° varus at 40° flexion). Significant increases in ACL forces were observed at 30° (p = 0.006) and 40° (p = 0.001) of flexion with 8° varus. Following PLC transection, significant increases in ACL forces occurred at 5° varus and higher from 10° of flexion onwards, with a notable increase from 80.0 ± 12.3 (neutral) to 153.2 ± 58.4 N (8° varus, 40° flexion, p < 0.001). After PLC reconstruction, no significant effects of varus alignment or flexion on ACL forces were observed (p > 0.05).
CONCLUSION: Under axial compression and simulated varus-thrust loading conditions, varus alignment of 5° or less did not significantly increase ACL forces in PLC-intact knees, whereas 8° varus resulted in significantly increased ACL loading at selected flexion angles. PLC deficiency was associated with greater increases in ACL force with increasing varus alignment.
LEVEL OF EVIDENCE: NA.
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