Bi-unicondylar knee prosthesis functional assessment utilizing force-control wear testing

Abstract

Recent in vivo studies have identified variations in knee prosthesis function depending on prosthesis geometry, kinematic conditions, and the absence/presence of soft-tissue constraints after knee replacement surgery. In particular, unicondylar knee replacements (UKR) are highly sensitive to such variations. However, rigorous descriptions of UKR function through experimental simulation studies, performed under physiological force-controlled conditions, are lacking. The current study evaluated the long-term functional performance of a widely used fixed-bearing unicompartmental knee replacement, mounted in a bi-unicondylar configuration (Bi-UKR), utilizing a force-controlled knee simulator during a simulated (ISO 14243) walking cycle. The wear behaviour, the femoral-tibial kinematics, and the incurred damage scars were analysed. The wear rates for the medial and the lateral compartments were 10.27 +/- 1.83 mg/million cycles and 4.49 +/- 0.53 mg/million cycles, respectively. Although constant-input force-controlled loading conditions were maintained throughout the simulation, femoral-tibial contact point kinematics decreased by 65 to 68 per cent for average anterior/posterior travel and by 58 to 74 per cent for average medial/lateral travel with increasing cycling time up to 2 million cycles. There were no significant differences in damage area or damage extent between the medial and the lateral compartments. Focal damage scars representing the working region of the femoral component on the articular surface extended over a range of 16-21 mm in the anterior-posterior direction. Kinematics on the shear plane showed slight variations with increasing cycling time, and the platform exhibited medial pivoting over the entire test. These measures provide valuable experimental insight into the effect of the prosthesis design on wear, kinematics, and working area. These functional assessments of Bi-UKR under force-controlled knee joint wear simulation show that accumulated changes in the UKR articular conformity manifested as altered kinematics both for anterior/posterior translations and internal/external rotations.

Classification of combined partial knee arthroplasty

“…4-18 There was little consensus on the terminology for ipsilateral medial and lateral unicompartmental arthroplasty, with some preferring bi-unicompartmental 4,5 while others used bi-uni 6 or bi-unicondylar. 7 This procedure was most commonly abbreviated to Bi-UKA or Bi-Uni. Others preferred to refer to all configurations as “bicompartmental”, explaining the exact configurations in parenthesis.…”

Displacement or Force Control Knee Simulators? Variations in Kinematics and in Wear

“…In the FC simulation group , a larger variety of kinematic motion schemes was observed. There was evidence of combined sliding and rolling at the initiation of the terminal stance phase and the initiation of the toe‐off phase.…”

“…The second study was conducted by Affatato and coworkers in two different steps: in particular, two identical sets of flat unicompartmental knee prostheses were considered. Six Efdios symmetric unicompartmental knee system (Citieffe, Bologna, Italy) femoral and tibial components, size “Maximum,” were tested on three stations of a DC wear‐testing knee simulator as per ISO 14243‐3.…”

“…The degree of reliability of these tests depends on the accuracy in recreating in vitro the conditions of a prosthetic implant in the human body. In recent years, several types of knee wear simulators have been developed and a variety of protocols have been used in simulating wear in total knee replacement (TKR) designs . A variety of total knee prostheses (TKP) are in use today , and the knee wear simulators should have the capability to compare the performance of each type of TKP.…”

“…This paper goes beyond the current status of available knee simulations comparing literature results. In particular, to the best of the author's knowledge, there are only two studies that evaluate both simulation concepts under otherwise identical conditions. In particular, in these studies the authors (Spinelli and Affatato) used two different simulators in order to assess the wear from the same bi‐unicondylar knee prostheses.…”