Abnormal Axial Rotations in TKA Contribute to Reduced Weightbearing Flexion

Abstract

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°v ersus 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. Level of Evidence Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

In vivo kinematics of knee replacement during daily living activities: Condylar and post-cam contact assessment by three-dimensional fluoroscopy and finite element analyses

“…A large internal rotation was observed throughout the knee range from hyperextension to the maximum flexion, apart from the range between 10° and 35°. This is very important, particularly considering that the restoration of the normal axial rotation is essential also to gain physiological flexion in weight bearing . As for the post‐cam mechanism and its engagements, the observed high variability over patients and over motor tasks may be accounted for to the subject‐specific action of the agonist and antagonist muscles, necessary for knee balancing during highly demanding weight bearing activities.…”

Differences in Anatomy and Kinematics in Asian and Caucasian TKA Patients: Influence on Implant Positioning and Subsequent Loading Conditions in Mobile Bearing Knees

“…The recently published study of Meccia et al [45] included a group of 58 TKA patients, forty with fixed (34PS, 5PCR, and 1ACL-R) and 18 with mobile (5PS, 5PCR, and 8PCS) bearing designs. This cohort showed an average relative tibial rotation of 18.1° (min.…”

Characterization and Correction of Errors in Computing Contact Location Between Curved Articular Surfaces: Application to Total Knee Arthroplasty

“…The orientation of the surface normal relative to the normal of the tibial baseplate in both the coronal (u) and sagittal (h) planes was determined by taking the inverse tangent of the partial derivatives of the surface fit functions with respect to the ML and AP directions, respectively (Eqs. (7) and (8)). Virtually generated errors in the ML and AP coordinates of the contact locations were determined using the error prediction functions (Eqs.…”

“…These inflated amounts of external rotation and anterior translation might lead to false identification of clinically undesirable contact kinematics. External rotation of the tibia on the femur between 3 deg and 6 deg [6,7,9] and changes in the anteriorposterior position of the femur on the tibia between 1 mm and 2 mm [6,8] are associated with accelerated wear [6], limited flexion [7,8], and decreased function [9]. Hence, as demonstrated by the two previous hypothetical cases, the errors in computed contact location caused by the curved articular surface of the tibial component should be corrected to prevent false identification of clinically undesirable contact kinematics.…”

“…Tibiofemoral contact kinematics are determined based on the movement of the contact locations in the medial and lateral compartments of the tibia [5]. Abnormal contact kinematics, which include external rotation of the tibia on the femur and anterior translation of the femur on the tibia during knee flexion, are associated with accelerated wear [6], limited flexion [7,8], and decreased function [9].…”