Risk of PCL avulsion during the tibial cut in cruciate retaining total knee arthroplasty and sagittal slope of tibial plateau

Fluoroscopic investigations have shown that femoral rollback is more often preserved in posterior stabilized (PS) than posterior cruciate-retaining (CR) implants. Possible explanations include degenerative changes of PCL and iatrogenic division of PCL fibres insertion during the tibial cut. In this study we evaluated the effects of a tibial cut with different degrees of posterior slope on the PCL insertion and whether a correlation does exist between the entity of PCL avulsion during the tibial cut and patients sagittal slope of tibial plateaus. MATHERIALS AND METHODS: We analyzed 83 MRI of the knee of patients with mild or moderate knee pain with no history of previous knee surgery or trauma. There were 42 males and 41 females, with a mean age of 49 years (range 45-52 years). The sagittal anatomical axis of the tibia was first identified on MR images and translated in the sagittal scan in which PCL fibers insertion in the tibia was best visualized. In the latter, tibial cuts with angles of different posterior slope ( 0,3°, 5° and parallel to the tibial plateaus) were simulated. The effects of each tibial cut on PCL fiber insertion was assessed. We also evaluated whether any correlation was present between the entity of PCL avulsion due to the tibial cut and the degree of posterior slope of tibial plateaus. RESULTS: A tibial cut of 0° caused a detachment of 63% of PCL fibers insertion; this figure raised to 70% and 75% when a 3° and 5° tibial cut was performed, respectively. The greatest percentage of PCL fibers avulsion (85%) was found with a tibial cut parallel to the sagittal slope of patient’s tibial plateaus. The percentage of PCL avulsion for each tibial cut was found to be significantly higher in patients showing a mild sagittal slope (<5°) than in those with a marked sagittal slope (>8°) of tibial plateaus. DISCUSSION: In this study we analyzed the effects of different tibial cuts on PCL preservation. Our results demonstrated that any tibial resection angle we used for tibial cut caused a PCL avulsion greater than 50%. Patients with a marked sagittal slope of the tibial plateaus showed reduced PCL avulsion compared with those with mild sagittal slope. However, even in the former group, a PCL avulsion greater than 50% was observed. CONCLUSION: When performing a CR TKA, most of PCL fibers may be lost during the tibial cut. As a result, techniques to preserve PCL insertion should be planned to avoid that a CR TKA is implanted without a functioning PCL.