INTRODUCTION: The techniques to stabilize the patella can be divided into two groups: the first group seeks to change the direction of the extensor mechanism in order to medialize the extending force vector of the quadriceps muscle, e.g. by a distal medialization of the tibial tuberosity or a proximal realignment; the second seeks to reconstruct the medial patellofemoral ligament (MPFL). The goal of this study was therefore to measure changes in patellofemoral kinematics in the intact, MPFL deficient knee, after medial transfer of the tibial tuberosity, after proximal realignment as well as after reconstruction of the MPFL. METHODS: Eight fresh frozen right knee specimens were mounted in a knee simulator in which isokinetic flexion-extension motions were simulated. Extension cycles were simulated from 120° flexion to full knee extension with an extension moment of 31 Nm. Movement of the patella relative to the femur was measured using an ultrasound based 3D motion analysis system (Zebris, Isny, Germany). During the first test cycles, patellar movement under intact knee conditions were measured, while a constant 100 N laterally oriented force was applied by means of a steel cable attached to the patella. Subsequently, patellar movement was again measured after: transecting the MPL (deficient knee), performing a medialization of the tibial tuberosity, after reconstruction of the transected MPL using a semitendinosus autograft and after proximal realignment. RESULTS: The patella of the intact knee moved along a medial path with a maximum attained position of 8.8 mm at 25° of knee flexion. The patella of the deficient knee moved up to 4.6 mm (p=0.04) in the medial direction at maximal extension at 30° of knee flexion. After medial transfer of the tibial tuberosity patellar movement reached a maximum medial position of 12.8 mm (p=0.04) at 22° of knee flexion with the laterally oriented force. With a reconstructed MPL, the patella attained a maximum medial position 14.8 mm (p=0.04) at 24.0° of knee flexion. Following proximal realignment, the patella moved on a medial, but significant (p=0.03) different path up to 13.8 mm medially at 30° of knee flexion. In addition, following medialization of the tibial tuberosity and proximal realignment, the center of the patella was significantly (p=0.03) more internally rotated (tilted) than the physiologic patella. DISCUSSION: The shape of the movement curves after the stabilizating procedures resulted in a medialization relative to intact and deficient conditions. With the reconstructed medial patellofemoral ligament, the patella moved along the most medially oriented path with physiologic tilting. The results suggest that a semi-tendinous autograft can provide sufficient stabilization to prevent lateral displacement or subluxation with physiologic patellar tilt.

The purpose of this study was to describe the rationale and to analyse the results of uncemented total hip arthroplasty (THA) in patients with osteoarthritis and congenital dislocation of the hip (CDH) prior to iliofemoral distraction.

Aseptic loosening of the prosthesis is still a problem in artificial joint implants. The loosening can be caused by, among other factors, resorption of the bone surrounding the prosthesis owing to stress shielding. In order to find out the influence of the prosthesis type on post-operative stress shielding, a static finite element analysis of a femur provided with the conventional uncemented stem BICONTACT and of one with the femoral neck prosthesis SPIRON was carried out. Strain energy densities and maximal principal strain distributions were calculated and compared with the physiological situation. Here, stress shielding was demonstrated in both periprosthetic femora. To determine the areas of the stress shielding, the bone in each FE model was subdivided into three regions of interest (ROI): proximal, diaphyseal, and distal. The numerical computations show stress shielding in the proximal ROI of both periprosthetic femora. Diaphyseally, the femoral neck prosthesis SPIRON, in contrast to the conventional uncemented long-stem prosthesis BICONTACT, causes no decrease in the strain distribution and thus no stress shielding. Distally, no change in the load distribution of either periprosthetic femur could be found, compared with the physiological situation.

AIM:This biomechanical study was performed to evaluate the consequences of removing the central part of the patellar tendon on the kinematics and kinetics of the femoro-patellar joint. The tendonectomy was performed in the same manner as is frequently done during anterior cruciate ligament reconstructions. Of particular interest in this study was to identify potential factors of the patellar tendon resection which could result in anterior knee pain.METHOD:A simulated isokinetic knee extension from 120 degrees of flexion to full extension was performed on nine human knee cadaver specimens. Joint kinematics was evaluated with ultrasound sensors, and retropatellar contact pressure was measured using a thin-film resistive ink pressure measuring system. Data were taken before and after resection of the central third of the patellar tendon.RESULTS:Harvesting of the central third of the patellar tendon resulted in an elongation of the remaining patellar tendon by less then 0.5 mm. Furthermore, increases in patellar flexion lower than 1 degree were observed. Small changes in retropatellar pressure were also observed.CONCLUSION:The shortening of the patellar tendon due to tendon removal, as already suggested in several previous studies, is not attributed to the removal of the central portion of the tendon itself, but more likely due to secondary scarring contraction of the tissue. The changes of the patellarkinematics and the retropatellar pressure observed in this study are probably not of any clinical significance.

AIM:This study was performed to evaluate the influence of the postoperative activity level on tibial bone tunnel enlargement following anterior cruciate ligament reconstruction using a mid-third patellar tendon autograft.METHODS:A clinical and radiological assessment was performed on 50 patients (21 male, 29 female, mean age 32 years, range 18 to 57 years) following ACL reconstruction using a patellar tendon autograft. The average follow-up examination was performed 18 (12 to 30) months after the operation.RESULTS:33 patients (66 %) developed a tibial bone tunnel enlargement > 1 mm. We found a positive correlation (+ 0.59) of the grade of activity and the muscle status (+ 0.56) to the tibial bone tunnel enlargement. Patients with a major tibial bone tunnel enlargement performed at a higher (p < 0.05) postoperative activity grade (5.2 versus 4.1 in the Tegner grading), rated higher in the Lysholm (88 versus 77 points) and IKDC scores (p < 0.05) and reported a better subjective functional outcome (p < 0.05). There was no significant correlation of the results of the knee stability tests and the age of the patients to the grade of tibial bone tunnel enlargement.CONCLUSIONS:In ACL reconstruction using a patellar tendon autograft we recommend early rehabilitation as the concomitant tibial bone tunnel enlargement does not significantly influence the clinical outcome or knee stability.

The purpose of the present study was to determine the effect of biological in-growth and pre-tensioning on the load transmission function of meniscal transplants. The ability of meniscal transplants to transfer load to the tibial plateau was measured in an animal model. Thirty-six sheep were divided into six groups: group A was the sham group, in group B a medial meniscectomy was performed, and in groups C–F a medial meniscal transplantation with an autograft was carried out. In groups C–F, different levels of pre-tensioning force were applied via bone tunnel sutures (C=0, D=20, E=40, and F=60 N, respectively). The animals were killed after 6 months. The excised knees were mounted in a materials testing machine at 30, 60, and 90° of flexion, and loaded through the femoral axis to 500 N. A thin film pressure measuring transducer (K-scan, Tekscan®) was positioned underneath the meniscus in the medial compartment in order to determine contact area and pressure. The mean contact pressure (MCP) of the sham group (A) and the groups with the transplanted meniscus (C–F) was significantly lower in relation to the meniscectomized knees (B). Significant increases in contact area and reductions in peak contact pressure were also observed. Only the meniscal transplantation group with 40 N (E) pre-tension consistently showed a significant or strong trend toward increased contact area, compared to the meniscectomized knees (B) at all flexion angles tested. All meniscal transplanted groups with the exception of the 0 N group (C) showed a significant reduction in peak contact pressure in comparison to the meniscectomized group (B). The results indicate that meniscal transplantation reduces the MCP on the tibial plateau independent of the level of intraoperative pre-tensioning. Furthermore, the menisci pre-tensioned to 40 N showed significantly increased contact area and reduced peak contact pressure in comparison to the meniscectomized knees at all flexion angles tested, and revealed results similar to those reported in the literature for meniscal allografts fixated with bone plugs.

Introduction: This biomechanical study evaluates the consequences of a mid-third BPTB-autograft excision on patellofemoral biomechanics and knee kinematics. Of particular interest was the potential role of a BPTB-autograft excision on postoperative anterior knee pain in ACL replacement surgery. Methods: Isokinetic knee extension from 120 of flexion to full extension was simulated on 9 human knee cadaver specimens (5 male, 4 female, average age at death 43 years). Joint kinematics was evaluated by ultrasound sensors (CMS 100TM, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-ScanTM 4000, Tekscan, Boston). All data were taken before and after excision of a mid-third BPTB-autograft. Results: Following excision of a mid-third patella tendon autograft we found a significant (p Conclusions: We conclude that an excision of a mid-third patella tendon autograft results in a lengthening of the tendon with a proximalization of the patella. As the patellofemoral pressure decreases and the patella remains centralized, postoperative anterior knee pain following ACL-replacement using a BPTB autograft can not be explained by the results of our study.

A 3-year-old girl was presented with recurrent pain at the right knee and a "snapping" when walking. A free range of motion of both knee joints, stable cruciate and collateral ligaments and a ventrally subluxating and snapping fibula when flexing the knee were found. Due to a longer course of recurrent subluxation and pain, an operation was performed and the tibiofibular ligaments and joint capsule were tightened by sutures. Other operative techniques proposed in the literature are discussed; most of them could lead to deformities or growth disturbances. The reports of tibiofibular instability in the literature are presented. The girl is the youngest patient with idiopathic proximal tibiofibular instability reported in the literature at least in the last 75 years.

INTRODUCTION:The study analyses the intraoperative findings and the clinical results of hip arthroscopy in sports related groin pain.METHODS:Between june 1998 and october 2002 we performed hip arthroscopy in 30 athletes (12 female, 18 male) with a history of sports related groin pain. Their average age was 36 (20 to 68) years. All patients had a clinical follow-up- examination at an average of 20 (12 to 48) months postoperative. The result was rated using the Larson-Score.RESULTS:We found a lesion of the acetabular labrum and performed a partial resection at 17 patients (57 %) (synovitis: n = 28 [93 %] loose bodies: n = 6 [20 %] torn ligamentum teres: n = 4 [13 %], others: n = 2 [6 %]). 11 patients (37 %) had a cartilage degeneration grade II in the Outerbridge classification (III degrees : n = 9 [30 %], I degrees : n = 4 [13 %], 0 degrees : n = 6 [20 %]). Preoperative 14 patients (47 %) complained severe groin pain (moderate: n = 14 [47 %], slight: n = 2 [6 %]) against only 3 patients (10 %) with severe groin pain at the follow-up examination (moderate: n = 11 [37 %], slight: n = 16 [53 %]). Following hip arthroscopy 28 patients (94 %) returned to full sports activity. The Larson-Score was increased significantly (p < 0.05) rating 43 (10 to 64) points preoperative to 59 (28 to 80) points at the follow-up.DISCUSSION:We found that persistent sports related groin pain was frequently caused by an intraarticular hip disorder. Following hip arthroscopy pain could be reduced in most patients as a return to full sports activity.

Studienziel: Methode: Ergebnisse: Schlussfolgerung: Aim: Method: Results: Conclusion:

The aim of the paper is to prove and to portray the learning curve in total hip arthroplasty. This prospective study included 168 patients who were operated on by three surgeons, all demonstrating different degrees of experience in performing total hip arthroplasty. Perioperative complications and postoperative radiographs were analysed. Patients were re-examined clinically and radiologically five years postoperatively. In addition, a second study with 41 patients was performed, evaluating especially the learning curve of the highly skilled surgeon in using a femoral neck prosthesis. Radiological complications presented by the first 84 operated patients (2nd study: 25 hips) were significantly higher than those in the following 84 patients (2nd study: 26 hips). The learning curve of all surgeons was completed after 20 operations regardless of their experience. Clinical results at follow-up were not influenced by the learning curve. Intensive preoperative planning and exchange of experiences will reduce the length of the learning curve within and outside every clinic.

Objective: To determine the effect of intraoperative pre-tensioning of meniscal transplants on the tibial plateau in an animal experiment: Material and Methods: Thirty-six sheep were used for this animal study. The animals were divided into 6 groups: -group A was the sham group; – in group B medial meniscectomy was performed; in group C-F medial meniscus transplantation with an autograft was carried out. In group C-F different defined pre-tensioning was applied to meniscal transplants via bone tunnel sutures (0N, 20N, 40N and 60N respectively). After 6 months the animals were sacrificed. The lower limb specimen were placed in a material testing machine under standard conditions in 30, 60 and 90 degrees of flexion and loaded through the femoral axis to 500N. For determining contact area a thin film pressure transducer (Tekscan) was positioned underneath the medial meniscus. Statistical analysis was performed using Mann-Whitney test. Results: The mean contact pressure of the sham group and the groups with the transplanted meniscus was significantly lower in relation to meniscectomized knees. Significant increases in contact area and reductions in in peak contact pressure could be identified. At greater flexion angles only the meniscal transplantation group with the 40N pretension showed a significant increase of contact area and/or very strong trend in relation to meniscectomized knees. Concerning peak contact pressure, all meniscal transplantated groups with exception th 0N pre-tension group showed significant reduction in comparison to the meniscectomized group. Conclusion: Regarding the results we can conclude that the biological ingrowth has an influence on the biomechanical effect of meniscal transplantation. For this animal model and with the compressive load of 500N especially 40N pre-tension of meniscal transplants seems to be efficient to provide load transmission function of the meniscus.

Purpose: The study was designed to evaluate the biomechanical and neurohistological properties of the infrapatellar fat especially concerning its potential role in the anterior knee pain syndrome. Methods: Isokinetic knee extension from 120 of flexion to full extension was simulated on 10 human knee cadaver specimens (6 male, 4 female, average age at death 44 years). Joint kinematics was evaluated by ultrasound sensors (CMS 100TM, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-ScanTM 4000, Tekscan, Boston). The infrapatellar tissue pressure was analyzed using a closed sensor cell. The patellar contact pressure was measured before and after resection of the infrapatellar fat pad. The distribution of nerve fibres in the infrapatellar fat pad was assed immunohistologically in a second part of the study. Results: Infrapatellar tissue pressure significantly increased during knee extension 100 ranging from 343 (223) mbar at O- to 60 (64) mbar at 60 of flexion. Total resection of the infrapatellar fat pad resulted in a significant decrease in tibial external rotation of 3° in full knee extension (p=0.011), combined with a significant medial translation of the patella between 29 and 69° knee flexion (p=0.017 to 0.028). Retropatellar contact pressure was significantly (p Conclusions: Based on these results, we conclude that resection of the infrapatellar fat pad could potentially reduce clinical symptoms in the anterior knee pain syndrome, and that, contrary to commonly believed, the infrapatellar fat pad may have a biomechanical function and play a role in the anterior knee pain syndrome.

Total hip arthroplasty (THA) in patients aged 40 years and younger requires decades of increased activity demands. Between 1987 and 2000, 249 primary THAs in patients 40 years of age or younger were performed with the Mallory-Head component. The average age at THA was 34.7 years (range, 20-40 years). Follow-up averaged 91 months with 125 hips having minimum 5-year follow-up and 51 THAs having a minimum of 10 years. Four stems failed the 98.2% overall survivorship. Two stems were revised for loosening for a 99.2% (95% confidence interval, 96.4%-99.8%) survivorship with aseptic loosening as the end-point at 18 years. In young patients, this tapered titanium, proximally porous plasma-sprayed femoral component provides outstanding long-term fixation and function with significant pain relief into the second decade. Overall stem survivorship is 98.2% at up to 18 years.

Introduction: Periprosthetic fractures occurring during implantation of non-cemented Total Hip Arthroplasty (THA) are considered major surgical complications. As a shot-term disadvantage, patients are required to partially weight-bear. Additionally, high risks of stem migration and joint luxation can be assumed. On the other hand, in fear of fracture surgeons may undersize stems and subsequently trigger failure rates in THA.As the long-term consequences of Vancouver A and B1 fractures are not fully known, the goal of this study now was to analyze the postoperative performance of non-cemented THA with respect to perioperative fractures.Materials and Methods: Between 1997 and 2003 41 peri-operative hip fractures were monitored in 1216 primary Total Hip Arthroplasties using the non-cemented Bicon-tact THA stem. Pre-OP and after a follow-up period of 2,2 (+−3,1) years patients were examined clinically and radiographically. Investigation parameters were Harris-Hip-Scores, SF-36 scores, function score, hospital...

Introduction High precision of axis alignement in Total Knee Arthroplasty by usage of navigation tools is a known fact. However, a common disadvantage of navigation tools is the additional time needed for calibration. Especially in time/cost-sensitive hospital environments this can lead to a neglection of navigation tools usage. In this study we address work-economics during navigation assisted total knee arthroplasty. Specifically, we introduce the concept of a well-trained navigator assistant who performs navigation related work steps during surgery while the primary surgeon concentrates on the remaining work-steps. In a prospective study of primary TKA we compared environmental parameters of surgeries performed with and without the Navigator Concept. Materials and Methods 60 Total Knee Arthroplasties were performed using an active navigation system (Stryker Navigation System) (40) or a conventional internal/external alignement jig for implantation of the Interax Knee endoprostheses. Half of the navigated knee arthroplasties were performed using a conventional set-up with a primary surgeon and two assistants serving the navigation system and performing the relevant surgical steps. The other half was done by surgeon teams of a primary surgeon, a navigator assistant and a second assistant. The surgical steps were broken down to a complex work-sharing system. The teams were intensively trained in their work-share by simulating an artificial TKA in a specially designed TKA-Navigation lab. During surgery, the timing of individual steps was recorded. Pre- and postoperative x-rays of the limbs were taken and digitized to an computerized axis-measurement system. Data of both groups were compared using ANOVA and Tuckey post-hoc tests. Results Results showed a significant difference in surgery time between the three groups (p=0,01) with equivalent surgery times of the conventional and navigator concept group, while the remaining navigated group showed longer surgery times. Axis alignments were statistically not influenced, however demonstrated a tendency to higher precision in the navigator concept group. Discussion This study is the first to address work-economics in navigated TKA. With the introduction of a specifically trained navigator assistant, a precise work-sharing plan and an intensive training lab, high precision in TKA can be achieved by navigation usage even in a highly cost-sensitive environment. The basis for success, however, is support and investment in training of team surgeons. This concept may provide the basis for other musculoskeletal surgeries demanding both high-tech for precision and time-effectiveness for cost reduction.

BACKGROUND:This study addresses work sharing during navigation-assisted total knee arthroplasty. Specifically, the concept is introduced of a "navigator" assistant who operates the navigation system during surgery while the surgeon concentrates on the primary steps of surgery.METHODS:In a prospective study of 40 total knee arthroplasties, one group of patients was treated using the navigator concept, a second group was treated using a conventional navigation setup, and a third group was treated with conventional internal and external alignment jigs. Surgery time and outcome parameters were compared.RESULTS:Results show a significant difference in surgery time between the three groups. The conventional and navigator concept groups showed similar surgery times; however, the navigation group without navigation concept exhibited longer surgery time.CONCLUSIONS:The navigator concept represents a highly effective principle to minimize surgery time needed during navigated total knee arthroplasty.

Degrading metal alloys are a new class of implant materials suitable for bone surgery. The aim of this study was to investigate the degradation mechanism at the bone-implant interface of different degrading magnesium alloys in bone and to determine their effect on the surrounding bone. Sample rods of four different magnesium alloys and a degradable polymer as a control were implanted intramedullary into the femora of guinea pigs. After 6 and 18 weeks, uncalcified sections were generated for histomorphologic analysis. The bone-implant interface was characterized in uncalcified sections by scanning electron microscopy (SEM), element mapping and X-ray diffraction. Results showed that metallic implants made of magnesium alloys degrade in vivo depending on the composition of the alloying elements. While the corrosion layer of all magnesium alloys accumulated with biological calcium phosphates, the corrosion layer was in direct contact with the surrounding bone. The results further showed high mineral apposition rates and an increased bone mass around the magnesium rods, while no bone was induced in the surrounding soft tissue. From the results of this study, there is a strong rationale that in this research model, high magnesium ion concentration could lead to bone cell activation.