Tibial rotation influences anterior knee stability--a robot-aided in-vitro study.

BACKGROUND: Anterior cruciate ligament rupture can lead to symptomatic instability, especially during pivoting activities, which are often associated with increased anterior and rotational tibial loading. Therefore, the purpose of our robot-aided in-vitro study was to analyze the influence of tibial rotation on anterior knee stability under three anterior cruciate ligament conditions. METHODS: Ten human knee specimens were examined using a robotic system. Anterior tibial translations were measured during anterior force application at internally and externally rotated positions of the tibia (5° steps until 4 Nm was reached) at 20°, 60°, and 90° of flexion. The native knee was compared with the knee with deficient and replaced anterior cruciate ligament. FINDINGS: Tibial rotation significantly influenced anterior tibial translation (P<0.001), with differences of up to 12 mm between the largest and smallest anterior translation in the deficient knee. The largest influence of the anterior cruciate ligament on anterior translation was found in slightly externally rotated positions of the tibia (5°-10° at 20° of flexion; 0°-5° at 90° of flexion). Significantly increased anterior tibial translation (up to 7 mm) was measured after anterior cruciate ligament resection, which could be almost completely restored by the replacement (remaining difference<1mm) over a wide range of tibial rotations. INTERPRETATION: Tibial rotation clearly influences anterior tibial translation. Because the greatest effect of the anterior cruciate ligament was found in slightly externally rotated positions of the tibia, increased attention to tibial rotation should be paid when performing the Lachman and anterior drawer tests.

Biomechanical comparison of two surgical techniques for press-fit reconstruction of the posterolateral complex of the knee.

BACKGROUND: To date, various surgical techniques to treat posterolateral knee instability have been described. Recent studies recommended an anatomical and isometric reconstruction of the posterolateral corner addressing the key structures, such as lateral collateral ligament (LCL), popliteus tendon (POP) and popliteofibular ligament (PFL). Two clinical established autologous respective local reconstruction methods of the posterolateral complex were tested for knot-bone cylinder press-fit fixation to assess efficacy of each reconstruction technique in comparison to the intact knee. NULL HYPOTHESIS: The knot-bone cylinder press-fit fixation for both anatomic and isometric reconstruction techniques of the posterolateral complex shows equal biomechanical stability as the intact posterolateral knee structures. STUDY DESIGN: This was a controlled laboratory study. METHODS: Two surgical techniques (Larson: fibula-based semitendinosus autograft for LCL and PFL reconstruction/Kawano: biceps femoris and iliotibial tract autograft for LCL, PFL and POP reconstruction) with press-fit fixation were used for restoration of posterolateral knee stability. Seven cadaveric knees (66 ± 3.4 years) were tested under three conditions: intact knee, sectioned state and reconstructed knee for each surgical technique. Biomechanical stress tests were performed for every state at 30° and 90° knee flexion for anterior-posterior translation (60 N), internal-external and varus-valgus rotation (5 Nm) at 0°, 30° and 90° using a kinemator (Kuka robot). RESULTS: At 30° and 90° knee flexion, no significant differences between the four knee states were registered for anterior-posterior translation loading. Internal-external and varus-valgus rotational loading showed significantly higher instability for the sectioned state than for the intact or reconstructed posterolateral structures (p < 0.05). There were no significant differences between the intact and reconstructed knee states for internal-external rotation, varus-valgus rotation and anterior-posterior translation at any flexion angles (p > 0.05). Comparing both reconstruction techniques, significant higher varus-/valgus stability was registered for the fibula-based Larson technique at 90° knee flexion (p < 0.05). CONCLUSIONS: Both PLC reconstructions showed equal biomechanical stability as the intact posterolateral knee structures when using knot-bone cylinder press-fit fixation. We registered restoration of the rotational and varus-valgus stability with both surgical techniques. The anterior-posterior translational stability was not influenced significantly. The Larson technique showed significant higher varus/valgus stability in 90° flexion. The latter is easier to perform and takes half the preparation time, but needs grafting of the semitendinosus tendon. The Kawano reconstruction technique is an interesting alternative in cases of missing autografts.

Robot-aided in vitro measurement of patellar stability with consideration to the influence of muscle loading.

BACKGROUND: Anterior knee pain is often associated with patellar maltracking and instability. However, objective measurement of patellar stability under clinical and experimental conditions is difficult, and muscular activity influences the results. In the present study, a new experimental setting for in vitro measurement of patellar stability was developed and the mediolateral force-displacement behavior of the native knee analyzed with special emphasis on patellar tilt and muscle loading. METHODS: In the new experimental setup, two established testing methods were combined: an upright knee simulator for positioning and loading of the knee specimens, and an industry robot for mediolateral patellar displacement. A minimally invasive coupling and force control mechanism enabled unconstrained motion of the patella as well as measurement of patellar motion in all six degrees of freedom via an external ultrasonic motion-tracking system. Lateral and medial patellar displacement were measured on seven fresh-frozen human knee specimens in six flexion angles with varying muscle force levels, muscle force distributions, and displacement forces. RESULTS: Substantial repeatability was achieved for patellar shift (ICC(3,1) = 0.67) and tilt (ICC(3,1) = 0.75). Patellar lateral and medial shift decreased slightly with increasing flexion angle. Additional measurement of patellar tilt provided interesting insights into the different displacement mechanisms in lateral and medial directions. For lateral displacement, the patella tilted in the same (lateral) direction, and tilted in the opposite direction (again laterally) for medial displacement. With regard to asymmetric muscle loading, a significant influence (p < 0.03, up to 5 mm shift and 8° tilt) was found for lateral displacement and a reasonable relationship between muscle and patellar force, whereas no effect was visible in the medial direction. CONCLUSION: The developed experimental setup delivered reproducible results and was found to be an excellent testing method for the in vitro analysis of patellar stability and future investigation of surgical techniques for patellar stabilization and total knee arthroplasty. We demonstrated a significant influence of asymmetric quadriceps loading on patellar stability. In particular, increased force application on the vastus lateralis muscle led to a clear increase of lateral patellar displacement.

Simulation of in vivo dynamics during robot assisted joint movement.

BACKGROUND: Robots are very useful tools in orthopedic research. They can provide force/torque controlled specimen motion with high repeatability and precision. A method to analyze dissipative energy outcome in an entire joint was developed in our group. In a previous study, a sheep knee was flexed while axial load remained constant during the measurement of dissipated energy. We intend to apply this method for the investigation of osteoarthritis. Additionally, the method should be improved by simulation of in vivo knee dynamics. Thus, a new biomechanical testing tool will be developed for analyzing in vitro joint properties after different treatments. METHODS: Discretization of passive knee flexion was used to construct a complex flexion movement by a robot and simulate altering axial load similar to in vivo sheep knee dynamics described in a previous experimental study. RESULTS: The robot applied an in vivo like axial force profile with high reproducibility during the corresponding knee flexion (total standard deviation of 0.025 body weight (BW)). A total residual error between the in vivo and simulated axial force was 0.16 BW. Posterior-anterior and medio-lateral forces were detected by the robot as a backlash of joint structures. Their curve forms were similar to curve forms of corresponding in vivo measured forces, but in contrast to the axial force, they showed higher total standard deviation of 0.118 and 0.203 BW and higher total residual error of 0.79 and 0.21 BW for posterior-anterior and medio-lateral forces respectively. CONCLUSIONS: We developed and evaluated an algorithm for the robotic simulation of complex in vivo joint dynamics using a joint specimen. This should be a new biomechanical testing tool for analyzing joint properties after different treatments.

Changes in dissipated energy and contact pressure after osteochondral graft transplantation.

Osteochondral autologous transplantation is frequently used to repair small cartilage defects. Incongruence between the osteochondral graft surface and the adjacent cartilage leads to changed friction and contact pressure. The present study wanted to analyze the differences between intact and surgically treated cartilage surface in respect to contact pressure and frictional characteristic (dissipated energy). Six ovine carpometacarpal joints were used in the present study. Dissipated energy during instrumentally controlled joint movement as well as static contact pressure were measured in different cartilage states (intact, defect, deep-, flush-, high-implanted osteochondral graft and cartilage failure simulation on a high-implanted graft). The best contact area restoration was observed after the flush implantation. However, the dissipated energy measurements did not reveal an advantage of the flush implantation compared to the defect and deep-implanted graft states. The high-implanted graft was associated with a significant increase of the mean contact pressure and decrease of the contact area but the dissipated energy was on the level of intact cartilage in contrast to other treatments where the dissipated energy was significantly higher as in the intact state. However the cartilage failure simulation on the high-implanted graft showed the highest increase of the dissipated energy.

Cartilage surface characterization by frictional dissipated energy during axially loaded knee flexion--an in vitro sheep model.

Cartilage defects and osteoarthritis (OA) have an increasing incidence in the aging population. A wide range of treatment options are available. The introduction of each new treatment requires controlled, evidence based, histological and biomechanical studies to identify potential benefits. Especially for the biomechanical testing there is a lack of established methods which combine a physiologic testing environment of complete joints with the possibility of body-weight simulation. The current in-vitro study presents a new method for the measurement of friction properties of cartilage on cartilage in its individual joint environment including the synovial fluid. Seven sheep knee joints were cyclically flexed and extended under constant axial load with intact joint capsule using a 6° of freedom robotic system. During the cyclic motion, the flexion angle and the respective torque were recorded and the dissipated energy was calculated. Different mechanically induced cartilage defect sizes (16 mm², 50 mm², 200 mm²) were examined and compared to the intact situation at varying levels of the axial load. The introduced setup could significantly distinguish between most of the defect sizes for all load levels above 200 N. For these higher load levels, a high reproducibility was achieved (coefficient of variation between 4% and 17%). The proposed method simulates a natural environment for the analysis of cartilage on cartilage friction properties and is able to differentiate between different cartilage defect sizes. Therefore, it is considered as an innovative method for the testing of new treatment options for cartilage defects.

Dissipated energy as a method to characterize the cartilage damage in large animal joints: an in vitro testing model.

Several quantitative methods for the in vitro characterization of cartilage quality are available. However, only a few of these methods allow surgical cartilage manipulations and the subsequent analysis of the friction properties of complete joints. This study introduces an alternative approach to the characterization of the friction properties of entire joint surfaces using the dissipated energy during motion of the joint surfaces. Seven sheep wrist joints obtained post mortem were proximally and distally fixed to a material testing machine. With the exception of the carpometacarpal articulation surface, all joint articulations were fixed with 'Kirschner' wires. Three cartilage defects were simulated with a surgically introduced groove (16 mm(2), 32 mm(2), 300 mm(2)) and compared to intact cartilage without an artificial defect. The mean dissipated energy per cycle was calculated from the hysteresis curve during ten torsional motion cycles (±10°) under constant axial preload (100-900 N). A significant increase in dissipated energy was observed with increasing cartilage defect size and axial load (p<0.001). At lower load levels, the intact and 16 mm(2) defect showed a similar dissipated energy (p>0.073), while all other defect conditions were significantly different (p=0.015). All defect sizes were significantly different (p=0.049) at 900 N axial load. We conclude that the method introduced here could be an alternative for the study of cartilage damage, and further applications based on the principles of this method could be developed for the evaluation of different cartilage treatments.

Biomechanical comparison of open and arthroscopic Latarjet procedures.

PURPOSE: To biomechanically compare the effectiveness of the standard open and arthroscopic techniques of the Latarjet procedure to address a critical anterior glenoid defect in combination with a capsular insufficiency. METHODS: Translation testing of 12 human cadaveric shoulder specimens was performed in a robot-assisted setup under 3 different conditions: (1) intact/vented shoulder joint, (2) combined anterior glenoid bone and capsular defect, and (3) open and arthroscopic Latarjet procedures. Testing was performed for each condition in 2 test positions: 60° of glenohumeral abduction with neutral rotation (ABD position) and 60° of abduction and external rotation (ABER position). Each position was tested with a passive humerus load of 30 N in the anterior, inferior, and anteroinferior directions. Translational movement of the humeral head was evaluated with and without the application of a 10-N load to the conjoint tendon (CJT). RESULTS: In the ABD position, translations after the open Latarjet procedure significantly differed from the arthroscopic technique in the anterior and anteroinferior directions when testing was performed with loading of the CJTs (CJT loading). Without CJT loading, the open Latarjet technique showed significantly lower translations in the anterior, inferior (P = .004), and anteroinferior (P = .001) testing directions in the ABD position. In the ABER position, the arthroscopic procedure showed no significant difference compared with the standard open procedure. CONCLUSIONS: We found a superior stabilization effect of the open Latarjet technique in the ABD position. The difference is ascribed to the anterior capsular repair, which was performed within the open technique and omitted during the arthroscopic procedure. CLINICAL RELEVANCE: The reduction of translation in a pure abduction position of the arm is more effectively performed with a conventional open Latarjet technique that includes a capsular repair. In combined ABER position, there was no difference found between the open and arthroscopic Latarjet techniques.

Biomechanical in vitro - stability testing on human specimens of a locking plate system against conventional screw fixation of a proximal first metatarsal lateral displacement osteotomy.

INTRODUCTION: The aim of this study was to examine resistance to angulation and displacement of the internal fixation of a proximal first metatarsal lateral displacement osteotomy, using a locking plate system compared with a conventional crossed screw fixation. MATERIALS AND METHODOLOGY: Seven anatomical human specimens were tested. Each specimen was tested with a locking screw plate as well as a crossed cancellous srew fixation. The statistical analysis was performed by the Friedman test. The level of significance was p = 0.05. RESULTS: We found larger stability about all three axes of movement analyzed for the PLATE than the crossed screws osteosynthesis (CSO). The Friedman test showed statistical significance at a level of p = 0.05 for all groups and both translational and rotational movements. CONCLUSION: The results of our study confirm that the fixation of the lateral proximal first metatarsal displacement osteotomy with a locking plate fixation is a technically simple procedure of superior stability.

The influence of superior labrum anterior to posterior (SLAP) repair on restoring baseline glenohumeral translation and increased biceps loading after simulated SLAP tear and the effectiveness of SLAP repair after long head of biceps tenotomy.

HYPOTHESIS: Biomechanical studies have shown increased glenohumeral translation and loading of the long head biceps (LHB) tendon after superior labrum anterior to posterior (SLAP) tears. This may explain some of the typical clinical findings, including the prevalence of humeral chondral lesions, after SLAP lesions. The first hypothesis was that SLAP repair could restore the original glenohumeral translation and reduce the increased LHB load after SLAP lesions. The second hypothesis was that SLAP repair after LHB tenotomy could significantly reduce the increased glenohumeral translation. MATERIALS AND METHODS: Biomechanical testing was performed on 21 fresh frozen human cadaveric shoulders with an intact shoulder girdle using a sensor-guided industrial robot to apply 20 N of compression in the joint and 50 N translational force at 0°, 30°, and 60° of abduction. LHB loading was measured by a load-cell with 5 N and 25 N preload. Type IIC SLAP lesions were created arthroscopically, and a standardized SLAP repair was done combined with or without LHB tenotomy. RESULTS: No significant difference of glenohumeral translation and increased LHB load in SLAP repair compared with the intact shoulder was observed under 5 N and 25 LHB preload, except for anterior translation under 25 N LHB preload. After LHB tenotomy after SLAP lesions, no significant difference of translation was observed with or without SLAP repair. CONCLUSIONS: SLAP repair without associated LHB tenotomy helps normalize glenohumeral translation and LHB loading. The stabilizing effect of the SLAP complex is dependent on the LHB. After biceps tenotomy, SLAP repair does not affect glenohumeral translation.

Biomechanical comparison of arthroscopically performable techniques for suprapectoral biceps tenodesis.

PURPOSE: The aim of this study was to biomechanically compare the cyclic and ultimate failure load (UFL) of 4 widely used techniques for arthroscopically performable suprapectoral tenodesis of the long head of the biceps tendon (LHB). METHODS: We used 28 fresh-frozen human cadaveric specimens (mean age, 65 years [range, 43 to 78 years; SD, 6.7 years]; 43% male specimens) to investigate 4 different techniques for LHB tenodesis. All techniques were performed in an open manner, with localization at the entrance of the bicipital groove. Two suture anchor techniques (Healix [DePuy Mitek, Raynham, MA], 5.5 mm, with modified lasso-loop stitch; BioSwiveLock [Arthrex, Naples, FL], 5.5 mm, with interlocking Krackow stitch) and two techniques using tenodesis screws (Bio-Tenodesis screw [Arthrex], 8 × 23 mm; Biceptor [Smith & Nephew, Andover, MA], 8 × 25 mm) were investigated. Under a 10-N preload, an axial cyclic load with 100 cycles, 1-Hz frequency, and 50-N maximum load was applied. UFL was evaluated with an axial traction of 0.2 mm/s. LHB displacement during testing was measured by 3-dimensional photogrammetry. RESULTS: All techniques had a mean displacement of less than 3 mm after cyclic loading. The highest UFL was measured with the Bio-Tenodesis screw (mean, 218.3 N; range, 134.0 to 313.0 N; SD, 59.7 N) and the lowest with the BioSwiveLock (mean, 111.2 N; range, 60.0 to 156.8 N; SD, 32.3 N). The Healix had the second highest UFL (mean, 187.1 N; range, 144.7 to 245.0 N; SD, 35.5 N), followed by the Biceptor (mean, 173.9 N; range, 147.0 to 209.3 N; SD, 27.2 N). There was no significant difference between the Healix, Bio-Tenodesis screw, and Biceptor (P > .05), but the Healix and Bio-Tenodesis screw had a significantly higher UFL than the BioSwiveLock (P < .01). The failure mode was either suture cutout or failure at the anchor-suture-bone interface or of the tendon itself and was generally dependent on technique. CONCLUSIONS: All techniques resisted cyclic testing without a higher grade of displacement, and all devices except the BioSwiveLock had a satisfactory UFL whereas different failure mechanisms were present. The modified lasso-loop stitch provides sufficient tendon fixation and is equivalent to interference screws. CLINICAL RELEVANCE: The lasso-loop suture anchor technique is an appropriate alternative for suprapectoral LHB tenodesis compared with tenodesis screw techniques.

Digital stereophotogrammetry based on circular markers and zooming cameras: evaluation of a method for 3D analysis of small motions in orthopaedic research.

BACKGROUND: Orthopaedic research projects focusing on small displacements in a small measurement volume require a radiation free, three dimensional motion analysis system. A stereophotogrammetrical motion analysis system can track wireless, small, light-weight markers attached to the objects. Thereby the disturbance of the measured objects through the marker tracking can be kept at minimum. The purpose of this study was to develop and evaluate a non-position fixed compact motion analysis system configured for a small measurement volume and able to zoom while tracking small round flat markers in respect to a fiducial marker which was used for the camera pose estimation. METHODS: The system consisted of two web cameras and the fiducial marker placed in front of them. The markers to track were black circles on a white background. The algorithm to detect a centre of the projected circle on the image plane was described and applied. In order to evaluate the accuracy (mean measurement error) and precision (standard deviation of the measurement error) of the optical measurement system, two experiments were performed: 1) inter-marker distance measurement and 2) marker displacement measurement. RESULTS: The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm. In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm. The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°. CONCLUSIONS: The description of the non-proprietary measurement device with very good levels of accuracy and precision may provide opportunities for new, cost effective applications of stereophotogrammetrical analysis in musculoskeletal research projects, focusing on kinematics of small displacements in a small measurement volume.

Biomechanical effectiveness of an arthroscopic posterior bankart repair versus an open bone block procedure for posterior shoulder instability.

BACKGROUND: The most effective surgical treatment for traumatic posterior shoulder instability remains unclear. HYPOTHESIS: An arthroscopic posterior Bankart repair is as effective as an open posterior bone block-capsulorrhaphy procedure regarding the restoration of humeral displacement with posterior and inferior forces. STUDY DESIGN: Controlled laboratory study. METHODS: Biomechanical testing of 16 human shoulders was performed in 3 testing conditions: after ventilation (intact joint), after creation of a posteroinferior Bankart lesion with an additional cut of the posterior band of the inferior glenohumeral ligament, and after surgical shoulder stabilization. The shoulder stabilization was performed either by an open posterior bone block procedure and glenoid-based T-capsulorrhaphy or by an arthroscopic Bankart repair. Testing was performed in 2 positions-the sulcus test position and the jerk test position-with a passive humerus load of 50 N applied in the posterior, posteroinferior, and inferior directions. RESULTS: After the arthroscopic repair, there was no significant difference between the translation and the intact state for all tested directions. The bone block repair-capsulorrhaphy caused a significant decrease of posterior translation (sulcus test and jerk test positions) and posteroinferior translation (jerk test position). But the resulting posterior and posteroinferior translation was even significantly lower than the translation measured for the intact joints. However, the reduction of inferior translation, compared with that of the defect condition, was not significant after the bone block repair (sulcus test and jerk test positions). Compared with that of the intact joint, inferior translation after the bone block repair was significantly higher. CONCLUSION: The posterior bone block repair-capsulorrhaphy overcorrects posterior translation and does not effectively restore inferior stability, whereas the arthroscopic posterior Bankart repair restores posterior and inferior laxity of the intact joint. CLINICAL RELEVANCE: An arthroscopic posterior capsulolabral repair more precisely restores posterior and inferior glenohumeral joint laxity and is therefore recommended as the first choice of treatment.

Evaluation of a 3D object registration method for analysis of humeral kinematics.

In 3D image-based studies of joint kinematics, 3D registration methods should be automatic, insensitive to segmentation inconsistencies and use coordinate systems that have clinically relevant orientations and locations because this is important for analyzing rotation angles and translation directions. We developed and evaluated a registration method, which is based on the cylindrical geometry of the humerus shaft and an analysis of the inertia moments of the humerus head, in order to consistently and automatically orient the humerus coordinate system according to its anatomy. Registration techniques must be thoroughly evaluated. In this study we used a well-detectable marker as reference, from which coordinate system determination errors of a 3D object could be measured. This allowed us to quantify by means of unique error analysis the translational and rotational errors in terms of how much and about/along which humeral axis errors occurred. The evaluation experiments were performed using virtual rotations of 3D humeral binary image, a humerus model and a 3D image of a volunteer's shoulder. They indicated that the humeral coordinate system determination errors primarily originated from segmentation inconsistencies, which influenced mostly the humeral transverse axes orientation. The error analysis revealed that the developed registration method reduced the effect of manual segmentation inconsistencies on the orientation of the humeral transverse axes up to 37%, in comparison to the commonly used inertia registration.