Reducing the Risk and Methods of Managing Stiffness After Calipered Kinematically Aligned Total Knee Arthroplasty

Overview

This chapter contains a discussion and videos to assist the surgeon in reducing the risk and managing stiffness management after calipered kinematically aligned (KA) total knee arthroplasty (TKA). The treatment of over 5300 primary TKAs from 2006 to 2020 with the anatomic target of restoring the patient’s prearthritic femoral and tibial joint lines regardless of knee deformity, without ligament release with posterior cruciate ligament (PCL)–retaining implants (CR), provides the background. The first section reports the 10-year incidence of treatment of stiffness with manipulation under anesthesia (MUA), which declined in 2018 with the initiation of intraoperative verification checks and self-administered flexion/extension stretching exercises after hospital discharge. The second and third sections review that results of in vitro and in vivo studies that show the biomechanical targets for balancing a calipered KA TKA are the restoration of the native medial and lateral tibial compartment forces and prearthritic ligament lengths that determine knee laxities. The fourth section describes seven intraoperative verification checks that restore the native medial and lateral tibial compartment forces and most laxities. The final section uses instructional case studies to discuss the options for managing motion loss from stiffness with self-administered flexion/extension stretching exercises and manipulation under anesthesia. The educational objective is to encourage surgeons to use a caliper and verification checks when performing KA with manual, patient-specific, navigational, and robotic instrumentation, to reduce the risks of stiffness and motion loss.

Incidence of Stiffness After Calipered Kinematically Aligned Total Knee Replacement Declines With Use of Intraoperative Verification Checks

Video 17.1 discusses the decline in the incidence of manipulation under anesthesia beginning in 2018.

From 2010 to 2019, over 4500 consecutive, primary TKAs were performed with calipered KA and CR implant designs ( Fig. 17.1 ). The anatomic target for setting the femoral and tibial components was to restore the patient’s prearthritic joint lines regardless of the degree of knee deformity and without ligament release. During this time, 114 MUAs were performed. Between 2010 and 2017, the rate of MUA fluctuated between 2% and 4% per year, which is lower than the 5% to 7% rate reported for MA TKA. ^,

In 2018, two practice changes were made. One change was the intraoperative use of a verification worksheet to record caliper measurements and corrections based on a decision tree. All corrections to balance the TKA were on the tibial side and included fine-tuning the varus-valgus (V-V) and posterior slope of the tibial resection and adjusting the thickness of the insert. The second change was instructing the patient to self-administer flexion/extension stretching exercises instead of prescribing outpatient or at-home physical therapy. From 2018 to 2019, the incidence of MUA dropped to 1% per year. Hence, intraoperative checks consisting of caliper measurements of bone resections, use of a verification worksheet, and home-based, self-administered exercises were associated with a lower risk of stiffness.

Calipered Kinematically Aligned Total Knee Replacement Restores Native Tibial Compartment Forces, Which Reduces the Risks of Stiffness and Loss of Motion

Video 17.2 discusses studies showing calipered kinematically aligned total knee replacement restoring native tibial compartment forces.

The first biomechanical target for balancing a TKA is the restoration of the medial and lateral tibial compartment forces to those of the native knee. To balance the TKA, the surgeon must have an understanding of the mean and variability of the medial and lateral compartment forces of the native knee. A cadaveric study of normal knees measured the medial and lateral tibial compartment forces at 0, 45, and 90 degrees of flexion. The mean medial force was 14 ± 5 lbs and the mean lateral force was 6 ± 2 lbs. The mean forces are ideal physiologic targets for TKA, as forces as little as two times higher cause stiffness as measured by intraoperative loss of flexion and extension and anterior tibial subluxation.

In vivo and in vitro studies showed that calipered KA TKA with a CR implant design performed without ligament release restored medial and lateral tibial compartment forces comparable to those of the native knee. ^, An in vivo study of 67 osteoarthritic knees treated with KA TKA reported a medial force of 21 ± 17 lbs and lateral force of 7 ± 8 lbs in the tibial compartment, which were comparable to the medial force of 14 lbs and lateral force of 6 lbs reported for the native knee, respectively.

In contrast to calipered KA TKA, there are no reports of MA TKA being able to restore the native tibial compartment forces, even after ligament release ( Fig. 17.2 ). ^, One cause for uncorrectable tibial compartment forces higher than the native knee is that MA changes the patient’s prearthritic distal femoral and proximal tibial joint lines more than ±1.5 degrees in 85% and 70% of patients, respectively. Placing a component either outside or inside the boundary of the patient’s prearthritic joint line by removing less or more bone and cartilage than the thicknesses of the femoral and tibial components causes higher or lower compartment forces, overtensioning or slackening of ligaments, and knee stiffness or instability, respectively. Because MA causes obligatory deviations from the patient’s prearthritic femoral and tibial joint lines, most knees have distal and posterior femoral resections within a compartment whose thicknesses deviate differently from the target thickness of the distal and posterior condyles of the femoral component, which cause a wide range of complex collateral ligament imbalances that are uncorrectable with ligament releases. ^, The inability of MA TKA to restore the native tibial compartment forces release was reported by three surgeons that used either measured resection or gap-balancing techniques checked with navigation and performed with release of healthy ligaments. The tibial force after MA TKA after ligament release were three to four times higher in the medial compartment and five to six times higher in the lateral tibial compartment than those reported for the native knee and calipered KA TKA. ^{, ,}

Although the intraoperative use of tibiofemoral force sensors allows surgeons to measure forces very precisely, the level of precision is not called for to achieve a good/excellent result after calipered KA TKA. This is mostly because the soft tissue balance and contact forces appropriate for any knee are not known and vary widely. Thus, when the goal is to restore normal function, the use of this generation of force sensors may simply add expense and time without improving the surgeon’s ability to achieve an individual patient’s normal soft tissue tension and loads.