In valgus knees, ligament balance remain difficult when implanting a total knee arthroplasty (TKA), this leads some authors to systematically propose the use of constrained devices. Others prefer reserving higher constraints to cases where it is not possible to obtain final satisfactory balance: less than 5 of residual frontal laxity in extension in each compartment, and a tibiofemoral gap difference not in excess to 3mm between flexion and extension. The goal of the study was to assess if is possible to establish preoperative criteria that can predict a constrained design prosthetic implantation at surgery. A consecutive series of 93 total knee prostheses, implanted to treat a valgus deformity of more than 5 was retrospectively analysed. Preoperatively, full weight bearing long axis AP views A-P were performed: hip knee angle (HKA) averaged 195 (186 to 226), 36 knees had more than 15 of valgus, and 19 others more than 20 of valgus. Laxity was measured by stress radiographies with a TelosTM system at 100 N. Fifty-two knees had preoperative laxity in the coronal plane of more than 10. Fourteen knees had more than 5 laxity on the convex (medial) side, 21 knees had more than 10 laxity on the concave (lateral) side. Statistical assessment, using univariate analysis, identified the factors that led, at surgery, to an elevated constraint selection level; these factors of independence were tested by multivariate analysis. Logistical regression permitted the classification of the said factors by their odds ratios (OR).Introduction
Materials and Methods
The same cup orientation is classically applied to all cases of hip replacement (45° abduction, 20° anteversion). We hypothesize that this orientation must be adapted to the patient's hip range of motion. We tested this hypothesis by means of an experimental study with respect to hip range of motion, comparing the classical orientation (45° and 20°), and the orientation obtained with computer-assisted navigation. The experimental model included a hemipelvis equipped with a femur whose mobility was controlled for three configurations: stiff (60°/0°, 15°/10°, 10°/10°), average (80°/10°, 35°/30°,35°/25°), mobile (130°/30°, 50°/50°, 45°/35°). The hemipelvis and the cup holder were equipped with an electromagnetic system (Fastrack ™) to measure cup orientation. The Pleos™ navigation system (equipping the hemipelvis, the femur, and the cup holder) guided the cup orientation by detecting the positions risking impingement through a kinematic study of the hip. Nine operators each performed 18 navigation-guided implantations (162 hip abduction, anteversion, and range of movement measurements) in two series scheduled 2 months apart.Introduction
Material and Methods
The prosthetic impingement occurs if the range of motion of the hip exceeds implant mobility or in case of component malorientation. This retrieval study was designed to assess the frequency and the risk factors of this phenomenon. The frequency and the severity of the impingement were calculated from a continuous series of 311 cups retrievals collected between 1989 and 2004 by a single surgeon. The reason for retrieval was loosening (131 cases), infection (43 cases), instability (56 cases), osteolysis (28 cases), unexplained pain (48 cases) and prosthetic impingent (5 cases all with hard bearings). The notching at the cup rim was assessed twice by two examiners with optic magnification. The risk factors were analyzed from clinical charts by univariate and cox multihazard.Introduction
Material and Methods
