Patellar crepitation in the P.F.C. sigma total knee system.

Painless and painful patellar crepitation and patellar clunk syndrome represent a spectrum of peripatellar scar formation particular to posterior-stabilized knee components, although it may occur with cruciate-retaining designs as well. The formation of peripatellar inflammatory scar tissue is related to implant design and surgical technique, with microscopic and gross findings indicating varying degrees of inflammatory fibrous hyperplasia. These well recognized clinical entities have an incidence ranging between 1% and 5% in different series. The majority of patients with mildly painful or painless patellar crepitation will improve within 6 months to 1 year. In patients with more disabling symptoms such as catching, early intervention with open scar excision should be considered.

Evolution of customization design for total knee arthroplasty.

Total Knee Arthroplasty (TKA) is a highly successful surgical procedure with more than 600,000 TKA's performed annually in the US. Interest in improving surgical outcomes has led to improvements in surgical technique, instrumentation, and implant design. Computer navigation and robotic systems were introduced to further refine the mechanical alignment of joint replacement procedures. The cost to implement some of these technologies and the additional time required in the operating room to utilize these developments has limited the acceptance of them broadly. The introduction of custom instrumentation and cutting blocks based on computed tomography (CT) or magnetic resonance imaging (MRI) has allowed for better restoration of mechanical alignment. Unfortunately, little has changed in patient satisfaction in the past ten years. The recent introduction of patient specific instrumentation and patient specific implants is another step forward to restore the pre-deformity anatomy and joint geometry. This new technology can benefit the hospital by improving operating room time efficiencies through having shorter set-up times, and the elimination of cleaning, sterilization and inventory costs. The patient can potentially benefit by a shorter operative time, improved postoperative alignment and better fitting implants.

Unicompartmental knee resurfacing: enlarged tibio-femoral contact area and reduced contact stress using novel patient-derived geometries.

Advances in imaging technology and computer-assisted design (CAD) have recently enabled the introduction of patient-specific knee implant designs that hold the potential to improve functional performance on the basis of patient-specific geometries, namely a patient-specific sagittal and coronal curvature, as well as enhanced bone preservation. The objective of this study was to investigate the use of a novel implant design utilizing a patient specific sagittal J-curve on the femoral component combined with a novel constant, patient-derived femoral coronal curvature and to assess tibio-femoral contact area and contact stress on a femur matched curved tibial polyethylene insert. Mean contact area and standard deviations were 81+/-5, 96+/-5 and 74+/-4 mm(2) for the heel strike, toe off and mid-stance positions, respectively. Mean contact stress and standard deviations were 23.83+/-1.39, 23.27+/-1.14 and 20.78+/-0.54 MPa for the heel strike, toe off and mid-stance positions, respectively. Standard deviations of the measurements were small, not exceeding 6-7% confirming the consistency of loading conditions across different flexion angles. The results were comparable to those reported for standard, off-the-shelf fixed-bearing implants with paired femoral and tibial geometries. These data show that a constant coronal curvature can be applied to a patient-specific implant by measuring coronal curvatures across the femoral condyle in each patient and by deriving an average curvature. This novel approach combines unique benefits of patient-specific geometry with proven design concepts for minimizing polyethylene wear.

Osteolysis after total knee arthroplasty.

Osteolysis ranks as the most significant cause of revision surgery in both total hip arthroplasty and total knee arthroplasty (TKA). The factors leading to osteolysis in TKA are unique and sometimes preventable. Changes in polyethylene manufacturing and implant design are striving to improve overall wear. In this review, we discuss osteolysis as it relates to TKAs. The etiology, diagnosis, contributing factors, and management are presented. The final section focuses on future improvements in TKA design, which may ultimately decrease the rate of osteolysis.

Tibial forces measured in vivo after total knee arthroplasty.

An instrumented tibial prosthesis was developed to measure forces in vivo after total tibial arthroplasty. This prosthesis was implanted in a 67-kg, 80-year-old man. The prosthesis measured forces at the 4 quadrants of the tibial tray. Tibial forces were measured postoperatively during rehabilitation, rising from a chair, standing, walking, and climbing stairs. By the sixth postoperative week, the peak tibial forces during walking averaged 2.2 times body weight (BW). Stair climbing increased from 1.9 times BW on day 6 to 2.5 times BW at 6 weeks. This represents the first direct in vivo measurement of tibial forces, which should lead to refined surgical techniques and enhanced prosthetic designs. Technical design improvements will enhance function, quality of life, and longevity of total knee arthroplasty.

The Chitranjan Ranawat Award: in vivo knee forces after total knee arthroplasty.

Tibial forces were measured in vivo during the first year after total knee arthroplasty in a 66 kg, 80-year-old man. Forces were measured during activities of daily living, rehabilitation, and exercise. Peak tibial forces recorded during walking increased up to 12 months postoperatively (2.8 times body weight). Tibial forces correlated with increasing speed during treadmill walking. Rising from a chair generated peak forces of 2.6 times body weight. Stair descent generated higher peak forces than stair ascent (3.3 versus 2.9 times body weight, respectively). Exercising on a stair-climbing machine generated forces close to two times body weight whereas stationary bicycling generated even lower forces, near one times body weight. In general, the tibial forces recorded during walking and stair climbing were lower than most predicted values. These measurements can be used to validate in vitro and mathematical models of the knee. This should lead to refined surgical techniques and to enhanced prosthetic designs that will improve patient function, patient quality of life, and longevity of total knee arthroplasty implants.