Collateral ligament length change patterns after joint line elevation may not explain midflexion instability...

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Biomedical Engineering

Background:

• Midflexion instability (MFI), characterized by varus-valgus laxity between 30° and 45° knee flexion, is a recognized complication following total knee arthroplasty (TKA).
• The precise biomechanical factors leading to MFI remain incompletely understood, with joint line elevation (JLE) proposed as a potential contributing mechanism.

Purpose of the Study:

• To investigate the biomechanical effects of joint line elevation (JLE) on collateral ligament length changes during knee flexion in total knee arthroplasty (TKA).
• To assess whether JLE, simulated at 5mm and 10mm, contributes to midflexion instability (MFI) by altering ligamentous tension.

Main Methods:

• Utilized a subject-specific in silico musculoskeletal modeling approach with 4 distinct models.
• Calculated collateral ligament length changes and the distance between attachment sites (DA) during knee flexion for anatomically reconstructed knees and simulated JLE scenarios (5mm and 10mm).

Main Results:

• Simulated JLE resulted in a relative decrease in the distance between collateral ligament attachment sites in midflexion compared to anatomically reconstructed knees.
• However, anterior regions of the medial collateral ligament (MCL) showed increased DA, and the lateral collateral ligament (LCL) showed only a minor DA decrease with JLE.
• These findings suggest anterior ligament portions are unlikely to slacken significantly, questioning JLE's substantial contribution to MFI.

Conclusions:

• The study's results do not support joint line elevation (JLE) as a primary cause of midflexion instability (MFI) for the specific ultra-congruent implant design evaluated.
• Further research may be needed to elucidate the complex etiologies of MFI in TKA, considering other biomechanical factors and implant designs.