Nikolaus Wülker

Long-term Results for the Uncemented Zweymuller/Alloclassic Hip Endoprosthesis A 15-Year Minimum Follow-Up of 320 Hip Operations

A follow-up study of 15 (15-17) years of 320 consecutive Zweymuller total hip arthroplasties is presented. Age at surgery was 67 (29-99) years. A total of 164 (51.3%) patients had died. Clinical and radiological examinations were available for 97 (30.3%), phone interviews and radiological examinations for 4 (1.3%) hips, and phone follow-ups for 49 (15.3%). There were 6 (1.9%) patients who were lost to follow-up. The Harris Hip Score results in a median value of 88. According to the Kaplan-Meier method, a survival rate of the cup/inlay of 98% (95% confidence interval, 95%-99%) after 17 years was achieved. For the stem/head, the survival rate was 98% (95% confidence interval, 94%-99%). In 95.2% of patients, no operative revision was required. The rate of aseptic loosening was 2% for the acetabular and 1% for the femoral component.

Severe cartilage damage by broken poly–L–lactic acid (PLLA) interference screw after ACL reconstruction

Poly–L–lactic acid (PLLA) bioabsorbable interference screws are widely used for fixation of tendon to bone and bone to bone in anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) reconstructions. Complications are rare. To our knowledge this is the first report of severe chondral damage caused by late breakage of the screw. Breakage of bioscrews has only been published in cases with tendon to bone fixation.

Forces in anterior cruciate ligament during simulated weight-bearing flexion with anterior and internal rotational tibial load.

This study determined in-vitro anterior cruciate ligament (ACL) force patterns and investigated the effect of external tibial loads on the ACL force patterns during simulated weight-bearing knee flexions. Nine human cadaveric knee specimens were mounted on a dynamic knee simulator, and weight-bearing knee flexions with a 100N of ground reaction force were simulated; while a robotic/universal force sensor (UFS) system was used to provide external tibial loads during the movement. Three external tibial loading conditions were simulated, including no external tibial load (termed BW only), a 50N anterior tibial force (ATF), and a 5Nm internal rotation tibial torque (ITT). The tibial and femoral kinematics was measured with an ultrasonic motion capture system. These movement paths were then accurately reproduced on a robotic testing system, and the in-situ force in the ACL was determined via the principle of superposition. The results showed that the ATF significantly increased the in-situ ACL force by up to 60% during 0-55 degrees of flexion, while the ITT did not. The magnitude of ACL forces decreased with increasing flexion angle for all loading conditions. The tibial anterior translation was not affected by the application of ATF, whereas the tibial internal rotation was significantly increased by the application of ITT. These data indicate that, in a weight-bearing knee flexion, ACL provides substantial resistance to the externally applied ATF but not to the ITT.

In Vitro Simulation of Stance Phase Gait Part I: Model Verification:

An in vitro simulator was developed to reproduce the kinematics and kinetics of stance phase gait on cadaver foot specimens. Ground reaction force was applied by a tilting angle- and force-controlled translation stage upon which a pressure measuring platform was mounted; tibial rotation was reproduced by a servomotor. Force was applied to nine tendons of the foot flexor and extensor muscle groups, and three-dimensional hind- and forefoot motion was measured. The model was verified based on in vivo kinematic and kinetic measurements. It was found to be in good general agreement with some exceptions which include a slightly more lateral gait line.

The Anterior Cruciate Ligament Provides Resistance to Externally Applied Anterior Tibial Force But Not to Internal Rotational Torque During Simulated Weight-Bearing Flexion

PURPOSE We investigated knee kinematics during simulated weight-bearing flexion and determined the effect of 3 different parameters of external tibial loading on the kinematics of the anterior cruciate ligament (ACL)-intact and ACL-deficient knee. METHODS Ten human knee specimens were mounted on a dynamic knee simulator, and weight-bearing muscle-loaded knee flexions were simulated while a robotic/universal force sensor system was used to provide external tibial loads during the motion. Three different loading conditions were simulated: partial body weight only, an additional 50 N of anterior tibial force (ATD), or an additional 5 Nm of internal rotational tibial torque (IRT). After arthroscopic transection of the ACL, these 3 trials were repeated. The kinematics were measured with an ultrasonic measuring system for 3-dimensional motion analysis, and different loading and knee conditions were examined. RESULTS When the ACL was intact, ATD and IRT barely changed the anterior tibial translation. However, in the absence of the ACL, ATD significantly increased the anterior tibial translation by 5 mm whereas IRT did not. The application of IRT increased the internal tibial rotation of ACL-intact knees, but there was no difference in the internal rotation before and after transection of the ACL. Regardless of ACL status, the difference in the anterior tibial translation and the internal tibial rotation across different external tibial loadings was greater at lower flexion angles and gradually diminished with increasing flexion angles. CONCLUSIONS We established an experimental protocol, incorporating a dynamic knee simulator and a robotic/universal force sensor system, to successfully measure the kinematics of the knee joint while applying external forces in weight-bearing flexion. Our findings suggest that, in muscle-loaded knee flexion, the ACL provides substantial resistance to externally applied ATD but not to IRT. CLINICAL RELEVANCE Information from this study allows us to better understand the function of the ACL and, hence, treatment of injuries to this important stabilizing ligament.

Talonavicular arthrodesis or triple arthrodesis: Peak pressure in the adjacent joints measured in 8 cadaver specimens

Background Talonavicular arthrodesis is a differential indication for triple arthrodesis. Differences regarding intraarticular pressure loads on the adjacent joints have not been investigated to date, but they are of clinical relevance when considering long-term joint degeneration. Methods We used a dynamic foot model to measure intraarticular peak pressures with electronic sensors in 8 anatomical specimens in different areas of the ankle joint and in the naviculocuneiform joint. Force was applied to extrinsic tendons via cables attached to computer- regulated hydraulic cylinders. A ground reaction force was simulated in a tilting angle- and force-controlled translation stage. Results We measured significantly higher peak pressures in the ankle joint after triple arthrodesis (5.7 Mpa) than after talonavicular arthrodesis (5.2 Mpa), with differences especially in the anterior section (5.2 Mpa as compared to 4.6 Mpa). Centrally, the peak pressure was similar, at 4.6 MPa and 4.5 Mpa, respectively. In the posterior area, the peak pressure after triple arthrodesis was lower (4.1 MPa as opposed to 4.4 Mpa). After triple arthrodeses, we measured higher values laterally/medially in the ankle joint (5.5 MPa/4.6 Mpa) than after talonavicular arthrodesis (5.1 MPa/4.4 Mpa). In the naviculocuneiform joint, we again saw higher peak pressures after triple arthrodesis than after talonavicular arthrodesis. Interpretation Our findings from this cadaver study indicate a lower and more evenly distributed peak pressure load in the ankle joint after talonavicular arthrodesis than after triple arthrodesis; thus, mechanically, a selective arthrodesis appears to be more favorable. In contrast, triple arthrodesis leads to an increase in peak pressure in the ankle joint, which may in turn lead to joint degeneration.

Changes in Chopart joint load following tibiotalar arthrodesis: in vitro analysis of 8 cadaver specimen in a dynamic model

BackgroundIn the current discussion of surgical treatment of arthroses in the ankle joint, arthrodesis is in competition with artificial joint replacement. Up until now, no valid biomechanical findings have existed on the changes in intraarticular loads following arthrodesis. One argument against tibiotalar arthrodesis is the frequently associated, long-term degeneration of the talonavicular joint, which can be attributed to changes in biomechanical stresses.MethodsWe used a dynamic model to determine the changes in intraarticular forces and peak-pressure in the talonavicular joint and in the calcaneocuboid joint on 8 cadaver feet under stress in a simulated stance phase following tibiotalar arthrodesis.ResultsThe change seen after arthrodesis was a tendency of relocation of average force and maximum pressure from the lateral onto the medial column of the foot. The average force increased from native 92 N to 100 N upon arthrodesis in the talonavicular joint and decreased in the calcaneocuboid joint from 54 N to 48 N. The peak pressure increased from native 3.9 MPa to 4.4 MPa in the talonavicular joint and in the calcaneocuboid joint from 3.3 MPa to 3.4 MPa. The increase of force and peak pressure on the talonavicular joint and decrease of force on the calcaneocuboid joint is statistically significant.ConclusionThe increase in imparted force and peak pressure on the medial column of the foot following tibiotalar arthrodesis, as was demonstrated in a dynamic model, biomechanically explains the clinically observed phenomenon of cartilage degeneration on the medial dorsum of the foot in the long term. As a clinical conclusion from the measurements, it would be desirable to reduce the force imparted on the medial column with displacement onto the lateral forefoot, say by suitable shoe adjustment, in order to achieve a more favourable long-term clinical result.

Translational and rotational knee joint stability in anterior and posterior cruciate-retaining knee arthroplasty.

This study investigated passive translational and rotational stability properties of the intact knee joint, after bicruciate-retaining bi-compartmental knee arthroplasty (BKA) and after posterior cruciate retaining total knee arthroplasty (TKA). Fourteen human cadaveric knee specimens were used in this study, and a robotic manipulator with six-axis force/torque sensor was used to test the joint laxity in anterior-posterior translation, valgus-varus, and internal-external rotation. The results show the knee joint stability after bicruciate-retaining BKA is similar to that of the native knee. On the other hand, the PCL-retaining TKA results in inferior joint stability in valgus, varus, external rotation, anterior and, surprisingly, posterior directions. Our findings suggest that, provided functional ligamentous structures, bicruciate-retaining BKA is a biomechanically attractive treatment for joint degenerative disease.

In Vitro Simulation of Stance Phase Gait Part II: Simulated Anterior Tibial Tendon Dysfunction and Potential Compensation

The diagnosis of anterior tibial tendon tear is often missed. The ability of the remaining ankle extensor muscles to compensate for lost anterior tibial force was thus investigated. The effect of tibialis anterior deficiency on tarsal bone motion and plantar pressure was measured during in vitro simulated stance phase gait on eight cadaver specimens. Increased internal rotation, plantarflexion, and inversion of the talus and calcaneus (p ≤ .001), as well as significant reductions of plantar pressure on the heel (p ≤ .04) were observed during the first half of the stance phase. The observed drop foot was partly compensated by increased extensor muscle force.

Measuring anatomical acetabular cup orientation with a new X-ray technique

Proper alignment of the acetabular cup component is one of the most important requisites for a successful long-term outcome in total hip replacement. However, measurement and indication of cup orientation in an anatomical pelvic reference system is very difficult. We propose a new C-arm-based X-ray technique for determining the values for inclination and anteversion of the acetabular cup component. The proposed method is validated by computer simulation and sources of error are evaluated. The method predicts an accuracy of better then 5° for determination of anteversion of the cup.