Can high-flexion tibial inserts improve range of motion after posterior cruciate-retaining total knee arthroplasty?

Relationship between the form and function of implant design in total knee replacement

The implant design in total knee replacement affects postoperative functionality greatly, therefore, its optimization is of major concern. However, little is known about how implant design parameters affect active knee kinematics. Comprehensive in silico and in vitro sensitivity analyses were performed, based on one patient-specific, physical knee implant set and corresponding bone and knee implant surface geometry data. The implant surfaces were parametrized and varied systematically, resulting in 85 different knee implant surface models. In addition, four variations of extensor mechanism parameters, being the muscular attachment points defining the Q-Angle, were investigated. The variations were evaluated in a patient-specific multibody simulation model and an experimental testing rig and contributions of different implant designs and extensor mechanism parameters on kinematics were analysed. The results of the in silico and in vitro analyses showed good qualitative agreement. The highest deviations from the implant's reference kinematics were found for parameter variations of the femoral sagittal radii, the lateral trochlear elevation, the tibial sagittal slopes, the mediolateral position of the patellar ridge and the mediolateral position of the tuberositas tibiae. The implant design parameters identified with the highest functional relevance should be focused on in implant design. As the tuberositas tibiae's position constituted a main impact factor, it should also be considered during implant design and preoperative planning. Due to the competing influence of implant design parameters on active kinematics, respective parameters should be designed which are compatible to each other to avoid adverse constraints and associated functional limitations.

Comparison of High-Flexion and Conventional Implants in Total Knee Arthroplasty: A Meta-Analysis

Background

The purpose of this study was to evaluate whether high-flexion prostheses are superior to conventional prostheses after total knee arthroplasty (TKA).

Material/Methods

We searched the PubMed and Embase databases for randomized trials and cohort studies comparing high-flexion with conventional knee implants. The heterogeneity across studies was examined by I² and Cochran’s Q-tests. Then the overall weighted mean differences of range of motion (ROM) and knee functional scores were evaluated.

Results

A total of 16 trials involving 2643 knees met our inclusion criteria. The results revealed that high-flexion implants were superior to conventional implants in the improvement of range of motion (weighted mean difference, 2.92; 95% CI, 1.63–4.22; p<0.0001). The clear advantage of high-flex PS (posterior stabilized) as well as high-flex CR (cruciate retaining) implants was found in ROM when compared to PS implants (2.73; 95% CI, 1.27–4.20; p=0.0003) and CR implants (3.24; 95% CI, 0.28–6.20; p=0.003), respectively. However, there was no difference in Knee Society Scores (0.42; 95% CI, −0.60–1.43; p=0.42), Knee Society function (0.37; 95% CI, −1.48–2.22; p=0.70) and Hospital for Special Surgery scores (0.26; 95% CI, −0.47–1.00; p=0.48) between high-flexion and conventional groups.

Conclusions

The current meta-analysis revealed that high-flexion implants were superior to conventional implants in the improvement of ROM but not in functional outcome scores.

Elongation of the collateral ligaments after cruciate retaining total knee arthroplasty and the maximum flexion of the knee

The mechanisms that affect knee flexion after total knee arthroplasty (TKA) are still debatable. This study investigated the elongation of the superficial medial (sMCL) and lateral collateral ligaments (LCL) before and after a posterior cruciate retaining (CR) TKA. We hypothesized that overstretching of the collateral ligaments in high flexion after TKA could reduce maximal flexion of the knee. Three-dimensional models of 11 osteoarthritic knees of 11 patients including the insertions of the collateral ligaments were created using MR images. Each ligament was divided into three equal portions: anterior, middle and posterior portions. The shortest 3D wrapping length of each ligament portion was determined before and after the TKA surgery along a weight-bearing, single leg flexion path. The relationship between the changes of ligament elongation and the changes of the maximal knee flexion after TKAs was quantitatively analyzed. The sMCL showed significant increases in length only at low flexion after TKA; the LCL showed decreases in length at full extension, but increases with further flexion after TKA. The amount of increases of the maximum flexion angle after TKA was negatively correlated with the increases of the elongations of the anterior portion (p=0.010, r=0.733) and middle portion (p=0.049, r=0.604) of the sMCL as well as the anterior portion (p=0.010, r=0.733) of the LCL at maximal flexion of the knee. The results indicated that the increases of the length of the collateral ligaments at maximal flexion after TKA were associated with the decreases of the maximal flexion of the knee. Our data suggest that collateral ligament management should also be evaluated at higher knee flexion angles in order to optimize maximal flexion of the knee after TKAs.

Abnormal axial rotations in TKA contribute to reduced weightbearing flexion

BACKGROUND

Previous in vivo fluoroscopy studies have documented that axial rotation for patients having a TKA was significantly less than those having a normal knee. In fact, many subjects having a TKA experience a reverse axial rotation pattern where the femur internally rotates with increasing flexion. However, no previous studies have been conducted to determine if this reverse axial rotation pattern affects TKA performance.

QUESTIONS/PURPOSES

The purposes of this study were: (1) Do normal and reverse axial rotation patterns of a TKA affect the maximum flexion angle postoperatively? (2) Does the axial rotation angle of the knee at maximum flexion during weightbearing impact the magnitude of the maximum flexion achieved in weightbearing?

METHODS

One hundred twenty patients having TKA, previously analyzed under in vivo conditions using fluoroscopy and a three-dimensional model-fitting software package, were further evaluated to determine if reverse axial rotation patterns limit weightbearing TKA flexion. In this retrospective cohort, we identified 58 patients who had a normal axial rotation pattern (greater than 15° normal rotation). Sixty-two patients experienced greater than 3° of reverse axial rotation, defined as internal rotation of the femur relative to the tibia.

RESULTS

Patients having a normal axial rotation achieved greater weightbearing knee flexion than those with reverse axial rotation (115° versus 109°, p = 0.02). Additionally, patients with greater than 3° of normal axial rotation at maximum flexion had more flexion than those with less than 3° of normal axial rotation at ending flexion (115° versus 107°, p < 0.001).

CONCLUSIONS

These findings show reverse axial rotation and a smaller magnitude of normal axial rotation reduce weightbearing knee flexion. This is likely the result of increased posterior movement of the lateral condyle and is an important consideration in future implant designs.