Ideally, standardized wear testing protocols replicate the in vivo motions and forces of TKR patients. In a previous study with 30 TKR patients, two distinct in vivo gait patterns emerged, one characterized as having low anteroposterior (AP-L) motion and the other high anteroposterior (AP-H) motion. The aim of this study was to determine the effect of the two in vivo-determined gait patterns on total and backside insert wear in comparison with the ISO standard 14243-3. In order to differentiate and accurately quantify topside and backside wear, a novel technique was employed where different lanthanide tracers are incorporated into the polyethylene during manufacture. Components from the Zimmer NexGen CR Knee Replacement System were used. Europium (Eu) and Gadolinium (Gd)-stearates were mechanically mixed with GUR1050 UHMWPE resin to obtain two tracer-UHMWPE resins containing 49.1±1.5 ppm Eu and 68.8±1.6 ppm Gd, respectively. 12 grams of the Eu-doped resin was placed on the bottom, 10 grams of virgin GUR1050 resin was placed in the middle, and 10 grams of Gd-doped resin was placed on the top to mold NexGen CR tibial inserts. The backside was then machined to interlock with the tibial baseplate. The minimum insert thickness was 10 mm. All inserts were packaged in nitrogen and gamma sterilized. The wear test was conducted on a 4-station knee simulator in displacement-control mode. Simulator input was obtained from ISO 14243-3 and from gait of 30 NexGen TKR subjects, previously categorized into low (AP-L) and high (AP-H) anteroposterior motion groups. Per station, each insert was sequentially subjected to ISO, AP-L, AP-H motion for 2 Mc at 1 Hz. Subsequently, the ISO profile was repeated. Tibial inserts were weighed and lubricant samples were taken after every 0.5 Mc interval. Knowing the Eu and Gd concentrations from ICP-MS analysis, and normalizing those to the concentrations in the polyethylene inserts, the localized (Eu – backside; Gd – topside) wear was calculated. Wear particle analysis was conducted following established protocols.Introduction
Materials and Methods
Wear debris from polyethylene tibial inserts has been associated with limited longevity of total knee replacements (TKRs). While material factors were studied extensively and considerable progress has been made, there is little knowledge about surgical factors, particularly on how the wear rate is related to implant positioning. It was the purpose of this study to determine the combined effect of patient and implant positioning factors on the volumetric wear rate of TKRs. Our hypothesis was that implant alignment has a significant impact on the wear rate when controlled for other patient factors. This study included 59 tibial inserts of a cruciate retaining TKR design (Nexgen, Zimmer Inc.). The patients' age, sex, weight, height, and implant size were obtained. All implants were scanned with a coordinate measuring machine. Volumetric wear was determined using an autonomous mathematical reconstruction method (Figure 1). Radiographs were used to determine the anatomic lateral distal femoral angle (aLDFA), anatomic medial proximal tibial angle (aMPTA), femoral tilt angle (FTA) and posterior tibial slope (PTS). Also, the patella position was assessed using the Blackburne-Peel Index (BPI) and the Insall-Salvati Ratio (Figure 2). General linear modeling (SPSS) was conducted in order to determine the most significant patient and implant positioning factors on wear rate.Introduction
Methods
Computer-assisted navigation systems for total knee arthroplasty (TKA) were introduced to improve implantation accuracy and to optimize ligament balancing. Several comparative studies in the literature confirmed an effect on the component position and other studies could not confirm these results. For ligament balancing most studies found no significant influence on the clinical outcome using a navigation system for TKA. In the literature there were no reports of mid-term results after navigated TKA. With our study we wanted to show if the use of a navigation system for TKA will have an influence on the component's position and on the clinical results at 5-year follow up. We enrolled 200 patients in a prospective randomized study with a minimum follow up of 5 years. 100 TKA were operated on without using a navigation system (Group A) and 100 surgeries (Group B) were done with computer assistance. Radiological investigation by standard radiographs including a long-leg X-ray was performed with a follow up rate in Group A of 86.2% versus 80.2% in Group B. We measured the mechanical axis of the leg, lateral distal femoral angel (LDFA), medial proximal tibial angle (MPTA), tibial slope and the alpha-angle of the patella. Clinical investigation was performed with a follow up rate in Group A of 85.7% versus 79.8% in Group B including the parameters for the range of motion (ROM), ligament balancing, anterior drawer test, feeling of instability, anterior knee pain, effusion, WOMAC Score, Insall Score and HSS Knee Score.Background
Methods
