Clinical and radiological outcome of the treatment of osteonecrosis of the femoral head using the osteonecrosis intervention implant.

The aim of this study was to evaluate the clinical and radiological outcome of the treatment of osteonecrosis of the femoral head by implantation of an osteonecrosis intervention rod. In this retrospective study the follow-up of 19 patients with 23 osteonecrotic femoral heads treated with implantation of an osteonecrosis intervention implant was assessed. From 19 patients with 23 necrotic femoral heads, there were 13 cases in which a total hip replacement was necessary. This implies a survival rate of 44% after implantation of an osteonecrosis intervention rod after a mean follow-up of 1.45 years. The outcome after core decompression combined with the insertion of a tantalum osteonecrosis intervention implant did not show superior results compared to core decompression alone. This is in contrast to existing studies. In addition, this study showed that in cases of total hip replacement, no problems appeared during explantation of the tantalum rod.

Cup positioning in primary total hip arthroplasty using an imageless navigation device: is there a learning curve?

In this study, the success of cup positioning in total hip arthroplasty (THA) using an imageless navigation system was analyzed (1) during the learning period and (2) after the learning period for using the navigation system. Sixty THAs were performed in which threaded cups were placed with use of a computer-assisted navigation device (B. Braun Aesculap, Tuttlingen, Germany). Half of the procedures (30), group A, were done by the same surgeons under the learning curve for using the navigation system; the other half (30), group B, were done by surgeons who were no longer considered under the learning curve. Intraoperative acetabular component parameters (inclination, anteversion) for both groups were compared with postoperative radiographic alignment values. In group A, significant differences were seen between intraoperative and postoperative cup orientation. In group B, no significant differences were seen between intraoperative and postoperative cup orientation. Additionally, the percentage of outliers decreased in group B. Operating and anesthesia times significantly decreased with the surgeon's experience in imageless cup navigation. There was an individual increase of precision during the learning curve for all surgeons. Imageless navigation is a dependable and accurate method of cup positioning during THA. However, accuracy of cup placement and length of operating room time were affected by surgeons' experience using the system. Imageless navigation may lead to a reduction in the length of the learning curve for surgeons beginning to perform THAs, improvement in the surgeon's ability to perform this procedure safely, and minimization of outliers.

Influence of an infrapatellar fat pad edema on patellofemoral biomechanics and knee kinematics: a possible relation to the anterior knee pain syndrome.

INTRODUCTION: An edema of the infrapatellar fat pad following knee arthroscopy or in case of chronic anterior knee pain syndrome is suspected to increase the patellofemoral pressure by a modification of the patellofemoral glide mechanism. The study was performed to evaluate this hypothesis. MATERIALS AND METHODS: Isokinetic knee extension from 120 degrees of flexion to full extension was simulated on 10 human knee cadaver specimens (six males, four females, average age at death 42 years) using a knee kinemator. Joint kinematics was evaluated by ultrasound sensors (CMS 100, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-Scan 4000, Tekscan, Boston). Infrapatellar tissue pressure was analyzed using a closed sensor cell which was implanted inside the fat pad (GISMA, Buggingen, Germany). An inflatable fluid cell was implanted by ultrasound control in the center of the infrapatellar fat pad and filled subsequently with water to simulate a fat pad edema. All parameters were recorded and analyzed from 0 to 5 ml volume of the fluid cell. RESULTS: Simulating a fat pad edema resulted in a significant (P < 0.01) increase of the infrapatellar fat pad pressure (247 mbar at 0 ml to 615 mbar at 5 ml volume). In knee extension and flexion the patella flexion (sagittal plane) was decreased while we did not find any other significant influence of the edema on knee kinematics. During the analysis of the patellofemoral biomechanics, a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degree-30 degrees) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%. CONCLUSION: An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism. Anterior knee pain in case of a fat pad edema may be related to a significant increase of the tissue pressure and possible histochemical reactions.

The influence of patellar bracing on patellar and knee load-distribution and kinematics: an experimental cadaver study.

The aim of this study was to analyze the biomechanical consequences of patella bracing in order to evaluate possible mechanisms supporting its clinical application. The hypothesis is that the patellar bracing reduces patellofemoral pressure by influencing patellar and knee kinematics, and load distribution. Physiologic isokinetic knee extension motions were simulated on ten human knee cadaver specimens using a knee kinematic simulator. Joint kinematics were evaluated using an ultrasound-based motion analysis system and patellofemoral contact pressure was measured using a thin-film piezoresistive pressure measuring system. Infrapatellar tissue pressure was analyzed using a closed sensor-cell. Three different patella braces were fitted to the knee cadavers and their influence on the kinematic and kinetic biomechanical parameters were evaluated and compared to the physiologic situation. Patellar bracing resulted in a significant (p = 0.05) proximalization of the patella up to 3 mm. Depending on the type of brace used, a decrease in the infrapatellar fat pad pressure was found and the patellofemoral contact area was decreased significantly (p = 0.05) between 60 degrees of knee flexion and full extension (maximum 22%). Patella bracing significantly (p = 0.05) reduced the patellofemoral contact pressure an average of 10%, as well as the peak contact pressure which occurred. Patellar bracing significantly influences patella biomechanics in a reduction of the patellofemoral contact area and contact pressure as well as a decrease in the infrapatellar tissue pressure. The application of infrapatellar straps is suggested for the treatment and prevention of anterior knee pain, especially in high level sports.