Predicted effects of hip distraction on knee ligament mechanics following total knee arthroplasty: A finite element...

Hip distraction is essential for hip arthroscopy and other orthopaedic surgeries, but high traction forces often lead to complications like nerve injury and soft tissue impairment. Patients with total knee arthroplasties (TKAs) may face increased risk due to altered joint mechanics; however, the impact of specific TKA configurations on knee behavior during distraction is poorly understood.

A validated finite element model of the pelvis and lower extremity was developed from patient CT and MRI data. Three configurations were modeled: bi-cruciate retaining (BCR), posterior-cruciate retaining (PCR; lacking ACL), and posterior-stabilized (PS; lacking both cruciates). Hip distraction was simulated with axial traction forces (100-500 N) applied to the distal tibia/fibula with the pelvis fixed proximally. Knee and hip joint displacement and ligament strains were evaluated.

The BCR model demonstrated the highest knee stiffness. ACL removal (PCR) reduced stiffness more compared to PCL removal. While the amount of hip distraction was consistent across models, PCR and PS knees experienced excessive knee distraction (>12 mm) and ligament strains exceeding 20% before achieving 10 mm of hip distraction. Conversely, the BCR model remained under 10 mm of knee distraction and 15% strain at equivalent hip distraction levels.

Finite element analysis revealed that PCR and PS configurations exhibit knee instability, exceeding soft tissue injury thresholds (>20% strain) within standard clinical traction ranges (250-350 N). The ACL contributed greater to knee complex stiffness in axial traction compared to the PCL. Standard traction forces may pose an iatrogenic risk to PCR and PS patients, suggesting a need for TKA-specific distraction protocols to prevent soft tissue failure.