Meniscal tears are common knee injuries that subsequently lead to degenerative arthritis, attributed to changes in stress distribution in the knee. In such cases there is need to protect the articular cartilage by repairing or replacing the menisci. While traditionally, meniscal replacement involves implantation of allografts, problems related to availability, size matching, cost and risk of disease transmission limit their use. Another optional treatment is that of biodegradable scaffolds which are based principally on tissue engineering concepts. The variability in body response to biodegradable implants and the quality of the tissue formed still pose a problem in this respect, under intense knee loading conditions. Moreover, biological solutions are mostly limited to younger patients <40 years old. Therefore, the goal of this study was, to develop a synthetic meniscal implant which can replace the injured meniscus, restore its function, and relieve pain. A composite, non-fixed self-centering discoid-shaped meniscus implant (NUsurafce®, AIC, Memphis, TN), composed of polycarbonate-urethane (PCU) and reinforced circumferentially with UHMWPE fibers is proposed (Fig. 1). The implant geometry was based on an extensive MRI study of over 100 knee scans [1]. The proposed structure aims to mimic the circumferential collagen reinforcement of the natural meniscus. Biomechanical evaluation of the implant was focused on in-vitro measurements of contact pressure under the implant in cadaver knees and computational finite element (FE) analyses [2,3]. Pressure distribution on the tibial plateau (under the meniscus implant) was measured by pressure sensitive films (Tekscan, MA) and quantified with respect to the natural meniscus. FE analyses were used to evaluate internal stress and strains, and to support the selection of optimal implant configuration. The last pre-clinical step was a large-animal (sheep) study in which the cartilage condition was evaluated microscopically over six months [4].Statement of Purpose
Methods
The aim of tissue sparing surgery in total knee arthroplasty is to reduce surgical invasivity to the entire knee joint. Surgical invasion should not be limited only toward soft tissues but also toward bone. The classic technique for total knee arthroplasty implies intramedullary canal invasion for proper femoral component positioning. This phase is associated to fat embolism, activation of coagulation, and occult bleeding from the reamed canal. The purpose of our study was to validate a new extramedullary device which relies on templated data. Two-hundred patients in four different orthopaedics centres were randomized to undergo primary total knee arthroplasty either using standard intramedullary femoral instruments (IM group) or using a new extramedullary device (EM group). A new set of instruments was developed to control the sagittal and coranl plane of the distal femoral resection. The extramedullary instrument was calibrated referencing to templated data obtained from the preoperative long-limb radiograph (Fig 1, 2). Varus-valgus orientation of the resection were established by moving the two paddles according to templated data. An L-shaped sliding tool (5 centimetres long) over the anterior cortex controls the flexion-extension parameter of the resection and is intended to allow a cut flush with the anterior cortex at 0° of angulation with the distal aspect of the femoral diaphysis on the sagittal plane Femoral component coronal alignment was within 0±3° of the mechanical axis in 86% of the IM group and 88% of the EM group. Sagittal alignment of the femoral component was 0±3° in 80% of the IM group and 94% of the EM group. There was no difference in the average operative time between the two groups. The EM group showed a trend toward less postoperative blood loss Extramedullary reference with careful preoperative templating can be safely utilized during total knee arthroplasty.
