Retaining the Posterior Cruciate Ligament and Restoring the Prearthritic Tibial Joint Line Reduces the Risk of Early-Onset Tibiofemoral Instability After Calipered Kinematically Aligned Total Knee Arthroplasty

Overview

This chapter contains discussion and videos that assist the surgeon in (1) reducing the risk of early-onset tibiofemoral instability) and (2) managing the instability when it occurs after calipered kinematically aligned (KA) total knee arthroplasty (TKA). The chapter draws from the author’s experience treating over 1527 primary TKAs implanted from 2017 through 2019. In each, the target for setting the components was coincident to the patient’s prearthritic joint lines regardless of knee deformity, and the restoration of native tibial compartment forces occurred without ligament release. During this time, 1200 calipered KA TKAs had retention of the posterior cruciate ligament (PCL), and 327 had an excision of the PCL. The first section reports the incidence and discusses the causes of early-onset flexion space anterior-posterior (A-P) instability (i.e., 90 degrees) and extension space varus-valgus (V-V) tibiofemoral instability. The second section recommends the retention of the PCL and the use of verification checks to reduce the risk of tibiofemoral instability. The third introduces three intraoperative methods that compensate for flexion space laxity when the PCL is excised or inadvertently injured from a transection or detachment from the tibia. The final section uses case studies to discuss options for managing symptomatic patients with early-onset flexion and extension space tibiofemoral instability. The educational objective is to encourage surgeons to retain the PCL, not release the collateral ligaments, and restore the native V-V plane and posterior slope of the proximal tibial joint, to reduce the risk of early-onset tibiofemoral instability when performing calipered KA TKA.

Incidence and Causes of Early-Onset Flexion and Extension Space Tibiofemoral Instability After Calipered Kinematically Aligned Total Knee Arthroplasty

Video 20.1 discusses the incidence and causes of early-onset flexion and extension space instability.

A search of a prospectively collected database from 2017 through 2019 identified 1527 primary TKAs, and the treatment for each was calipered kinematic alignment (KA) without ligament release. There were no exclusions because of the severity of the preoperative deformity. Intraoperatively, caliper measurements verified the femoral and tibial components restored the patient’s prearthritic joint lines regardless of limb alignment. There were 1203 KA TKAs with a PCL-retaining (CR) implant design, and 327 with a cruciate-substituting design (CS) after resection of the PCL. A review of the operating room log identified three patients with early revision because of flexion space anterior-posterior (A-P) tibiofemoral instability. One patient had an early revision because of extension space V-V tibiofemoral instability. Therefore, the incidence of revision surgery for early-onset tibiofemoral instability was 0% in those with PCL retention (0 of 1203) and 1.2% (4 of 327) for those with PCL excision.

The cause of the revision in the three patients with early-onset flexion space A-P tibiofemoral instability was inadequate compensation for the increase in flexion space laxity caused by resection of the PCL. Studies have shown that the resection of the PCL increases the mean laxity of the medial gap by 2 ± 1.5 mm and the lateral gap by 3 to 5 mm in 90 degrees of flexion ( Fig. 20.1 ). The standard deviation of ± 1.5 mm indicates that each gap has a different and variable increase in the laxity that ranges from around 0 to 5 mm medially and 0 to 8 mm laterally. ^, The variability of the increases in the medial and lateral flexion gaps makes the intraoperative compensation for the flexion instability caused by PCL resection a challenge.

One technique for reducing flexion space A-P laxity is to set the tibial component in less posterior slope than the patient’s prearthritic slope. The surgical options are to recut the tibia with less posterior slope and a build-up of the posterior third of the proximal tibia with bone graft. Another effective option is to resect more bone from the distal femur and upsize the thickness of the tibial insert to compensate for flexion space laxity. However, the limitation common to all three techniques is the changes of the prearthritic posterior slope and the elevation of the distal femoral joint line, which violates the principles of kinematic alignment.

Retain the Posterior Cruciate Ligament and Use Verification Checks to Reduce the Risk of Early-Onset Tibiofemoral Instability After Calipered Kinematically Aligned Total Knee Arthroplasty

Video 20.2 shows the importance of retaining and protecting the PCL and use of verification checks to reduce the risk of early-onset tibiofemoral instability.