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
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
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.
Calipered Kinematically Aligned Total Knee Replacement Restores the Native Ligament Lengths That Determine Knee Laxities, Which Reduces the Risks of Stiffness and Loss of Motion
discusses studies that show calipered kinematically aligned total knee replacement restores native ligament lengths and laxities.
The second biomechanical target for balancing a TKA is the restoration of the lengths of the patient’s PCL, and collateral and retinacular ligaments, which are the primary restraints of the knee laxities. To balance the TKA, the surgeon must have an understanding of the mean and variability of the V-V and internal and external (I-E) rotation of the native knee in full extension and at 90-degrees of flexion where intraoperative verification checks are made. ,
The V-V laxity of the native knee is negligible in full extension and greater at 90 degrees of flexion. In full extension, the space is rectangular and tight with a 0.4 ± 0.3 mm opening in the medial compartment and a 0.7 ± 0.3 mm opening in the lateral compartment under a ± 5 Nm V-V load. When the native knee is flexed to 90 degrees, the space becomes trapezoidal and looser lateral than medial, and the lateral compartment opens 3.2 ± 1 mm and the medial compartment opens 1.4 ± 0.6 mm. In full extension, where the V-V verification checks are made with spacer block and trial components, the medial and lateral openings are generally 1 mm (or less) in most native knees. In 90 degrees of flexion the lateral opening can range from 1 to 5 mm and the medial opening can range from 0.2 to 2.6 mm in most native knees. Those surgeons that perform arthroscopy are aware of this variability, as it explains the variation in the ease and difficulty of performing medial and lateral meniscectomies between compartments and between patients.
The I-E rotational laxity of the tibia in the native knee is minimal in full extension and greater at 90 degrees of flexion. In full extension, the space is rectangular and has 4.6 ± 1.4 degrees of internal rotation and –4.4 ± 1.7 degrees of external rotation under a ± 3 Nm I-E load. When the native knee is flexed to 90 degrees, the space becomes trapezoidal and has 14.6 ± 5.5 degrees of internal rotation and –14.5 ± 3.8 degrees of external rotation. In 90 degrees of flexion where the verification check is made with a spacer block, the surgeon should notice that I-E rotating the handle of the block causes a pivot to occur about the center of the medial compartment, indicating restoration of a trapezoidal flexion space. In 90 degrees of flexion where the verification check is made with trial components, the surgeon should verify that the I-E rotation with trial components matches those of the knee during an examination at the time of exposure. Because each knee has a specific I-E laxity, the internal rotation should range from 5 degrees to 25 degrees and the external rotation should range from –8 degrees to –23 degrees.
These patient-specific differences in V-V and I-E laxity and shape between the extension and flexion space do not support the concept of the gap-balancing, which is a common and ill-conceived MA technique. , Because native ligaments are not tight in flexion, there is no role for the use of tensiometers, as they adversely overtighten the flexion space. When gap balancing “equalizes” the medial and lateral gaps in the flexion space to those of the extension space, the laxity of the lateral flexion gap is tightened more than the medial flexion gap, which distorts the trapezoidal shape to rectangular and over-constrains I-E rotation of the tibia on the femur. The clinical effects of gap balancing are tibial compartment forces higher than the native knee, which cause stiffness, loss of motion, and pain. , ,
In vitro studies of calipered KA TKA performed in normal knees with a CR implant and without the use of ligament releases restored V-V and I-E laxities to those of the native knee. The CR implant did not, however, restore anterior laxity at 30 degrees of flexion because the low-conforming insert functioned like an ACL and partial meniscal deficient knee, allowing more anterior laxity than the native knee. , One implant design that provides anterior stability is the medial ball-in-socket implant. The medial ball-in-socket restores more normal kinematics and medial anterior-posterior stability during walking than a CR, posterior stabilized (PS), or ultra-congruent (UC) implant design. , It follows that when a patient wants the TKA to function and feel like the prearthritic knee, the ligament lengths and laxities of the extension and flexion space should match those of the native knee and ligament releases should not be performed.
Seven Intraoperative Verification Checks That Restore Native Tibial Compartment Forces and Laxities to the Kinematically Aligned Total Knee Replacement
discusses studies that show the intraoperative use of verification checks.
We recommend performing a series of seven verification checks to achieve the anatomic and biomechanical targets of restoring the prearthritic joint lines, tibial compartment forces, ligament lengths, and laxities to those specific for the patient’s pre-arthritic knee.
The first two verification checks rely on assessments made with a spacer block to determine whether the tibial resection restored the ligament lengths and the V-V laxity of the extension space and the I-E laxity of the flexion space ( Fig. 17.3 ).
Place the knee in 90 degrees of flexion, insert and I-E rotate the tightest-fitting spacer block. The surgeon should notice that the I-E rotation of the handle of the spacer block causes a pivot to occur about the center of the medial compartment, indicating restoration of a trapezoidal flexion space.
Place the knee in extension and insert a spacer block. The surgeon should notice negligible V-V laxity indicating the restoration of the native tight rectangular extension space. When a compartment is tighter than the other, refer to the decision tree for balancing the KA TKA. When the medial side opens 1 to 2 mm, perform a varus recut of 1 degree. When the lateral side opens 1 to 2 mm, perform a valgus recut of 1 degree.
The next five verification checks use trial components to provide a final assessment of whether the KA TKA restores the native tibial compartment forces, ligament lengths, and laxities.
Place the knee in maximum extension and verify that there are 3 to 5 degrees of hyperextension like the native knee. Adjust the insert thickness to set the degree of hyperextension. When the extension is limited, insert a thinner insert.
Apply a V-V load to the tibia and verify the V-V laxity is negligible. When one tibial compartment opens 1 to 2 mm, fine-tune the V-V plane 1 or 2 degrees until the V-V laxity is negligible like the native knee. ,
Place the knee in 15 to 30 degrees of flexion and apply a V-V load to the tibia. Verify that the medial side does not open more than 1 mm and the lateral side opens 2 to 3 mm.
Place the knee in 90 degrees of flexion and verify there is ±15 degrees of I-E rotation, which restores the native laxity of the flexion space. ,
With the knee in 90 degrees of flexion, use an offset caliper and measure the distance between the anterior tibia and the distal medial femoral condyle. Compare this offset to the one taken at the time of exposure. When the offset is greater and the I-E rotation is more than ±15 degrees, add more posterior slope. When the offset is less, add a thicker insert or set the tibial component in less posterior slope.