Jennifer S. Wayne

Contribution of the Deltoid Ligament to Ankle Joint Contact Characteristics: A Cadaver Study

Changes in ankle biomechanics lead to altered load transmission through the ankle joint, possibly predisposing it to osteoarthritis. Contributions of the different bands of the deltoid ligament to the contact characteristics in the ankle were examined. Fifteen normal cadaveric lower extremities were axially loaded to 445 N after intra-articular Fuji film placement. Ankles were tested in neutral, 10° dorsiflexion, and 10° plantarflexion. Repeated testing was done following sequential sectioning of the deltoid ligament, and the contact characteristics were analyzed. The greatest significant tibiotalar changes (P < 0.0001) occurred after sectioning of the tibiocalcaneal fibers of the superficial deltoid ligament complex. Contact areas decreased up to 43%, peak pressures increased up to 30%, and centroids moved 4 mm laterally, on average. In contrast, sectioning of the other bands led to insignificant changes in joint contact characteristics. The data indicate that significant changes in contact characteristics occur before radiographic evidence of deltoid ligament damage is evident, and may indicate that greater attention to the medial side of the ankle is indicated to restore normal biomechanics to this joint.

Application of the u-p Finite Element Method to the Study of Articular Cartilage

The finite element method using the principle of virtual work was applied to the biphasic theory to establish a numerical routine for analyses of articular cartilage behavior. The matrix equations that resulted contained displacements of the solid matrix (mu) and true fluid pressure (p) as the unknown variables at the element nodes. Both small and large strain conditions were considered. The algorithms and computer code for the analysis of two-dimensional plane strain, plane stress, and axially symmetric cases were developed. The u-p finite element numerical procedure demonstrated excellent agreement with available closed-form and numerical solutions for the configurations of confined compression and unconfined compression under small strains, and for confined compression under large strains. The model was also used to examine the behavior of a repaired articular surface. The differences in material properties between the repair tissue and normal cartilage resulted in significant deformation gradients across the repair interface as well as increased fluid efflux from the tissue.

A cadaveric study examining acromioclavicular joint congruity after different methods of coracoclavicular loop repair

A basic principle in the treatment of joint injuries is to restore congruity with the hope that restoration may lessen the incidence of late arthritis. The acromioclavicular (AC) joint is frequently injured. Many AC joint injuries are treated nonoperatively; others are treated surgically. Coracoclavicular loop repair of the AC joint is believed to lead to anterior displacement of the clavicle relative to the acromion. This cadaveric study evaluated the effectiveness of three techniques of coracoclavicular loop repair in restoring AC joint congruity through measurement of anterior displacement. Fourteen shoulders were repaired by the three different techniques, all of which consisted of fixation through a drill hole in the clavicle and around the crook of the coracoid with a suture. The techniques only varied by the placement of the drill hole in the clavicle (ie, either posterior, middle, or anterior). The results of this study indicate that as the drill hole moved anteriorly on the clavicle, joint congruity was more closely approached and less anterior displacement of the clavicle occurred. However, none of the methods of coracoclavicular loop fixation restored full AC joint congruity.

Computational modeling to predict mechanical function of joints: application to the lower leg with simulation of two cadaver studies.

Computational models of musculoskeletal joints and limbs can provide useful information about joint mechanics. Validated models can be used as predictive devices for understanding joint function and serve as clinical tools for predicting the outcome of surgical procedures. A new computational modeling approach was developed for simulating joint kinematics that are dictated by bone/joint anatomy, ligamentous constraints, and applied loading. Three-dimensional computational models of the lower leg were created to illustrate the application of this new approach. Model development began with generating three-dimensional surfaces of each bone from CT images and then importing into the three-dimensional solid modeling software SOLIDWORKS and motion simulation package COSMOSMOTION. Through SOLIDWORKS and COSMOSMOTION, each bone surface file was filled to create a solid object and positioned necessary components added, and simulations executed. Three-dimensional contacts were added to inhibit intersection of the bones during motion. Ligaments were represented as linear springs. Model predictions were then validated by comparison to two different cadaver studies, syndesmotic injury and repair and ankle inversion following ligament transection. The syndesmotic injury model was able to predict tibial rotation, fibular rotation, and anterior/posterior displacement. In the inversion simulation, calcaneofibular ligament extension and angles of inversion compared well. Some experimental data proved harder to simulate accurately, due to certain software limitations and lack of complete experimental data. Other parameters that could not be easily obtained experimentally can be predicted and analyzed by the computational simulations. In the syndesmotic injury study, the force generated in the tibionavicular and calcaneofibular ligaments reduced with the insertion of the staple, indicating how this repair technique changes joint function. After transection of the calcaneofibular ligament in the inversion stability study, a major increase in force was seen in several of the ligaments on the lateral aspect of the foot and ankle, indicating the recruitment of other structures to permit function after injury. Overall, the computational models were able to predict joint kinematics of the lower leg with particular focus on the ankle complex. This same approach can be taken to create models of other limb segments such as the elbow and wrist. Additional parameters can be calculated in the models that are not easily obtained experimentally such as ligament forces, force transmission across joints, and three-dimensional movement of all bones. Muscle activation can be incorporated in the model through the action of applied forces within the software for future studies.

Effects of Medializing Calcaneal Osteotomy on Achilles Tendon Lengthening and Plantar Foot Pressures

Posterior tibial tendon insufficiency, or adult acquired flatfoot deformity, involves collapse of the longitudinal arch of the foot with ensuing changes in the bony architecture of the foot as well. While it is generally accepted that a medializing calcaneal osteotomy (MCO) is a very useful treatment for restoring the fallen arch, questions regarding the effects of this procedure upon plantar foot pressures and Achilles tendon length changes need to be answered. This study focuses on changes in plantar foot pressures and Achilles tendon length as the result of performing a MCO. Fourteen fresh-frozen cadaver legs were used to test the effects of MCO on Achilles tendon length changes 2 cm proximal to the Achilles tendon insertion on the calcaneus. Differential variable reluctance transducers were anchored in ventromedial, dorsomedial, dorsolateral, and ventrolateral positions of the Achilles tendon at the aforementioned level. The effects of the MCO on plantar foot pressures were assessed simultaneously using the Tekscan HR Mat. Axial loading (100 lbs) of each specimen was performed in neutral and dorsiflexion (15°). Data were gathered for Achilles tendon length changes and plantar foot pressures for three trials in both the neutral and dorsiflexed positions. A medializing calcaneal osteotomy (1 cm medial translation) was then performed and testing was repeated in the fashion outlined heretofore. Analysis of the data revealed that there was no significant increase in Achilles tendon length as a result of the MCO. The data also showed that average pressure over the first and second metatarsal regions of the forefoot decreased significantly after MCO. At the same time there was a significant increase in average pressure over the medial and lateral aspect of the heel. These findings suggest that the Achilles tendon aids in inversion of the forefoot without undergoing a significant increase in length change of Achilles tendon fibers in any of the regions tested.

Mechanical comparison of fixation techniques for the tibial tubercle osteotomy.

Tibial tubercle osteotomies currently are used as an exposure technique for revision total knee arthroplasty and for distal patellofemoral realignment. A review of the literature reveals no biomechanical studies that evaluate methods of osteotomy fixation in terms of static strength. This study evaluates the fixation strength of common techniques used to repair tibial tubercle osteotomies. Bevel and stepcut tibial tubercle osteotomies were created in 36 anatomic specimen knees and were repaired with either two 4.5-mm cortical screws or 18-gauge stainless steel cerclage wire. The failure load for the bevelcut osteotomies repaired with two-screws was 1654 ± 359 N; for the bevelcut osteotomies repaired with three cerclage wires, 622 ± 283 N; for the stepcut osteotomies repaired with three cerclage wires, was 984 ± 441 N; and for the stepcut osteotomy repaired with four cerclage wires, 1099 ± 632 N. This study shows that two bicortical screws provide the greatest static fixation strength for repairing tibial tubercle osteotomies. When repairing tibial tubercle osteotomies for distal patellofemoral realignment, screw fixation would provide the most reliable fixation. However, the placement of screws around the stem of a revision arthroplasty tibial component is difficult. Cerclage wires are easier to place and provide solid static fixation, especially with the addition of a proximal stepcut osteotomy.

Computational Model of the Lower Leg and Foot/Ankle Complex: Application to Arch Stability

The aim of this work was the design and evaluation of a computational model to predict the functional behavior of the lower leg and foot/ankle complex whereby joint behavior was dictated by three-dimensional articular contact, ligamentous constraints, muscle loading, and external perturbation. Three-dimensional bony anatomy was generated from stacked CT images after which ligament mimicking elements were attached and muscle/body loading added to recreate the experimental conditions of selected cadaveric studies. Comparisons of model predictions to results from two different experimental studies were performed for the function of the medial arch in weight bearing stance and the contributions of soft tissue structures to arch stability. Sensitivity simulations evaluated selected in situ strain and stiffness values for ligament tissue. The greatest contributor to arch stability was the plantar fascia, which provided 79.5% of the resistance to arch collapse, followed by the plantar ligaments (12.5%), and finally the spring ligament (8.0%). Strains measured after plantar fasciotomy increased in the remaining plantar ligament by approximately 300% and spring ligament by approximately 200%. Sensitivity tests varying both in situ strain and stiffness across reported standard deviations showed that functional trends remained the same and true to experimental data, although absolute magnitudes changed. While not measured experimentally, the model also predicted that load can increase dramatically in the remaining plantar tissues when one of such tissues is removed. Overall, computational predictions of stability and soft tissue load sharing compared well with experimental findings. The strength of this simulation approach lies in its capacity to predict biomechanical behavior of modeled structures and to capture physical parameters of interest not measurable in experimental simulations or in vivo.

Biomechanical comparison of ankle arthrodesis techniques: crossed screws vs. blade plate.

Many different techniques for ankle arthrodesis have been described. Experience at our institution with crossed screws internal fixation has not met the 90+% union rate reported in the literature. A compression blade plate is one technique for ankle arthrodesis which has not been evaluated biomechanically. A biomechanical study comparing two groups of sawbone ankle fusion constructs fixed with crossed screws and compression blade plates was performed in order to evaluate the stiffness and rigidity of these two arthrodesis techniques. The crossed screws construct demonstrated superior stiffness during dorsiflexion (p < 0.001) and valgus (p < 0.001) loading. The two constructs were found to have equal strength in resisting plantarflexion, varus and torsional loads although there was a trend for greater resistance by the crossed screws construct. These findings lend biomechanical support to the use of crossed screws for tibiotalar arthrodesis.

The Effects of Low-Intensity Ultrasound on Medial Collateral Ligament Healing in the Rabbit Model

Background Ruptured medial collateral ligaments are capable of healing over time, but biomechanical and biochemical properties remain inferior to normal tissue. Low-intensity ultrasound may improve healing. Hypothesis Medial collateral ligaments treated with ultrasound will demonstrate superior healing. Study Design Controlled laboratory study. Methods Twenty-one late-adolescent male rabbits underwent bilateral ligament transection. One ligament from each rabbit received ultrasound treatment every other day for 6 total treatments. Contralateral ligaments received sham treatments. After 3 or 6 weeks, ligaments were evaluated biomechanically and assayed for collagen concentration and the relative proportions of types I and III collagen. Results Areas of sonicated specimens were significantly larger (10.6% ± 4.90%) at 6 weeks. Ultimate load (39.5% ± 17.0%), ultimate displacement (24.5% ± 8.0%), and energy absorption (69.1% ± 22.0%) were significantly higher for sonicated specimens at 6 weeks. No significant biomechanical differences were observed at 3 weeks. The relative proportion of type I collagen was significantly higher in sonicated ligaments at 3 weeks (8.61% ± 4.0%) and 6 weeks (6.91% ± 3.0%). No significant differences in collagen concentration were observed at either 3 or 6 weeks. Conclusion Subtle improvement with ultrasound treatment may be apparent by 3 weeks after injury, suggested by increased proportion of type I collagen. Ultrasound appears to improve some structural properties and to modestly increase scar cross-sectional area and type I collagen present at 6 weeks after injury in this model. Clinical Relevance Ultrasound treatments after ligament injury may facilitate earlier return to activities and decrease risk of reinjury.

Plantar pressure analysis in cadaver feet after bony procedures commonly used in the treatment of stage II posterior tibial tendon insufficiency.

Background: Bony procedures play an essential role in the operative treatment of stage II posterior tibial tendon insufficiency and often substantially alter the loading characteristics of the foot. Methods: Eight matched pairs of cadaver lower extremities were axially loaded onto a TekScan HR Mat. (TekScan, Inc., South Boston, MA) After intact testing, each specimen had a lateral column lengthening (either a calcaneocuboid distraction arthrodesis [CCDA] or Evans procedure), a medializing calcaneal osteotomy (MCO), and a plantarflexion (Cotton) osteotomy of the medial cuneiform. The measured plantar pressures were divided into three forefoot regions, two midfoot regions, and two hindfoot regions. For each region, average pressure, peak pressure, and contact area data were collected. Results: Despite the fact that both lateral column lengthening procedures resulted in increased lateral forefoot pressures, no significant differences were noted between the CCDA and the Evans procedure. The addition of a MCO did not significantly alter the plantar pressures measured after the lateral column lengthening alone. Although the Cotton osteotomy resulted in increased average pressures within the medial forefoot, a compensatory significant decrease in lateral forefoot pressures was not observed. Conclusions: The present study demonstrated increased lateral forefoot pressures after a combined lateral column lengthening and MCO and does not support the idea that a Cotton osteotomy significantly reduces loading of the lateral forefoot. Clinical Relevance: The incidence of lateral forefoot pain and fifth metatarsal stress fractures subsequent to either lateral column lengthening procedure may not significantly decline after a Cotton osteotomy.