Extended foot-ankle musculoskeletal models for application in movement analysis.

Multibody simulations of human motion require representative models of the anatomical structures. A model that captures the complexity of the foot is still lacking. In the present work, two detailed 3D multibody foot-ankle models generated based on CT scans using a semi-automatic tool are described. The proposed models consists of five rigid segments (talus, calcaneus, midfoot, forefoot and toes), connected by five joints (ankle, subtalar, midtarsal, tarsometatarsal and metatarsophalangeal), one with 15DOF and the other with 8DOF. The calculated kinematics of both models were evaluated using gait trials and compared against literature, both presenting realistic results. An inverse dynamic analysis was performed for the 8DOF model, again presenting feasible dynamic results.

Foot-ankle simulators: A tool to advance biomechanical understanding of a complex anatomical structure.

In vitro gait simulations have been available to researchers for more than two decades and have become an invaluable tool for understanding fundamental foot-ankle biomechanics. This has been realised through several incremental technological and methodological developments, such as the actuation of muscle tendons, the increase in controlled degrees of freedom and the use of advanced control schemes. Furthermore, in vitro experimentation enabled performing highly repeatable and controllable simulations of gait during simultaneous measurement of several biomechanical signals (e.g. bone kinematics, intra-articular pressure distribution, bone strain). Such signals cannot always be captured in detail using in vivo techniques, and the importance of in vitro experimentation is therefore highlighted. The information provided by in vitro gait simulations enabled researchers to answer numerous clinical questions related to pathology, injury and surgery. In this article, first an overview of the developments in design and methodology of the various foot-ankle simulators is presented. Furthermore, an overview of the conducted studies is outlined and an example of a study aiming at understanding the differences in kinematics of the hindfoot, ankle and subtalar joints after total ankle arthroplasty is presented. Finally, the limitations and future perspectives of in vitro experimentation and in particular of foot-ankle gait simulators are discussed. It is expected that the biofidelic nature of the controllers will be improved in order to make them more subject-specific and to link foot motion to the simulated behaviour of the entire missing body, providing additional information for understanding the complex anatomical structure of the foot.

Insertion of a pressure sensing arrayminimally affects hindfoot bone kinematics.

BACKGROUND: Understanding the development of ankle osteoarthritis (OA) is of high importance and interest; however its causality is poorly understood and several links to joint loading conditions have been made. One way of quantifying joint loading conditions is by measuring the intra-articular pressure distribution during gait simulations performed by in-vitro experimental set-ups. However the effect of inserting a pressure sensing array in the ankle joint could potentially disturb the proper kinematics and therefore the loading conditions. METHODS: In this study, we performed in-vitro gait simulations in 7 cadaveric feet, before and after inserting a pressure sensing array and quantified the effect on the joints range of motion (ROM). The gait was simulated with a stance phase duration of one second using a custom build cadaveric gait simulator (CGS). RESULTS: The results show a limited effect in the ROM for all the joints of the hind foot, not exceeding the variability observed in specimens without a sensor. However, no consistent direction (increase/decrease) can be observed. CONCLUSION: The results suggest that even though the effect of inserting a pressure sensing array is minimal, it needs to be evaluated against the demands/requirements of the application.

Extrinsic Muscle Forces Affect Ankle Loading Before and After Total Ankle Arthroplasty.

BACKGROUND: Joint loading conditions have an effect on the development and management of ankle osteoarthritis and on aseptic loosening after total ankle arthroplasty (TAA). Apart from body weight, compressive forces induced by muscle action may affect joint loading. However, few studies have evaluated the influence of individual muscles on the intraarticular pressure distribution in the ankle. QUESTION/PURPOSES: The purpose of this study was to measure intraarticular pressure distribution and, in particular, (1) to quantify the effect of individual muscle action on peak-pressure magnitude; and (2) to identify the location of the center of pressure in the weightbearing native ankles and ankles that had TAA. METHODS: Peak pressure and intraarticular center of pressure were quantified during force alterations of four muscle groups (peronei, tibialis anterior, tibialis posterior, and triceps surae) in 10 cadaveric feet. The pressure was measured with a pressure sensitive array before and after implantation of a three-component mobile-bearing TAA prosthesis. Linear mixed-effects models were calculated and the y-intercept (b0) and the slope (b1) of the regression were used to quantify the size of the effect. RESULTS: Mean maximum peak pressures of 2 MPa (± 2.6 MPa) and 6.2 MPa (± 3.6 MPa) were measured for the native and TAA joint respectively. The triceps surae greatly affect the magnitude of peak pressure in the native ankle (slope b1 = 0.174; p = 0.001) and TAA joint (slope b1 = 0.416; p = 0.001). Furthermore, the force of most muscles caused a posterior and lateral shift of the center of pressure in both conditions. CONCLUSIONS: Our results suggest that muscle force production has the potential to alter the pressure distribution in the native ankles and those with and TAA. CLINICAL RELEVANCE: Our study results help us to understand the effect of muscle forces on joint loading conditions which could be used in muscle training strategies and the design of better prosthetic components. Physical therapy or guided exercises may provide the potential to relieve areas in the joint that show signs of early osteoarthritis or reduce the contact stress on prosthetic components, potentially reducing the risk of TAA failure attributable to wear.

An in vitro approach to the evaluation of foot-ankle kinematics: performance evaluation of a custom-built gait simulator.

Despite their well-known limitations, in vitro experiments have several benefits over in vivo techniques when exploring foot biomechanics under conditions characteristic of gait. In this study, we present a new setup for dynamic in vitro gait simulation that integrates a numerical model for generating the tibial kinematics control input, and we present an innovative methodology to measure full three-dimensional joint kinematics during gait simulations. The gait simulator applies forces to the tendons. Tibial kinematics in the sagittal plane is controlled using a numerical model that takes into account foot morphology. The methodology is validated by comparing joint rotations measured during gait simulation with those measured in vivo. In addition, reliability and accuracy of the control system as well as simulation input and output repeatability are quantified. The results reflect good control performance and repeatability of the control inputs, vertical ground reaction force, center of pressure displacement, and joint rotations and translations. In addition, there is a good correspondence to in vivo kinematics for most patterns of motion at the ankle, subtalar, and Chopart's joints. Therefore, these results show the relevance and validity of including specimen-specific information for defining the control inputs.

Specimen-specific tibial kinematics model for in vitro gait simulations.

Until now, the methods used to set up in vitro gait simulations were not specimen specific, inflicting several problems when dealing with specimens of considerably different dimensions and requiring arbitrary parameter tuning of the control variables. We constructed a model that accounts for the geometric dimensions of the specimen and is able to predict the tibial kinematics during the stance phase. The model predicts tibial kinematics of in vivo subjects with very good accuracy. Furthermore, if used in in vitro gait simulation studies, it is able to recreate physiological vertical ground reaction forces. By using this methodology, in vitro studies can be performed by taking the specimen variability into account, avoiding pitfalls with specimens of different dimensions.

Alterated talar and navicular bone morphology is associated with pes planus deformity: a CT-scan study.

We compared bone and articular morphology of the talus and navicular in clinically diagnosed flatfeet and evaluated their potential contribution to talo-navicular joint instability. We used CT images to develop 3D models of talus and navicular bones of 10 clinically diagnosed flatfeet and 15 non-flatfeet. We quantified their global bone dimensions, inclination and dimensions of the articular surfaces and their curvatures. Additionally, ratios of six talar and navicular dimensions were calculated. The values for these parameters were then compared between both groups. In flatfeet, the talar head faced more proximal and its width was larger compared to non-flatfeet. Also the navicular cup faced more proximal and its depth was significantly increased. Furthermore, we observed a more protruding talar head compared to the navicular cup in the control group with the articular surface depth being relatively larger for the navicular cups when compared to the talus in flatfeet. The ratio of the talar and navicular articular surface height was decreased in flatfeet, suggesting increased height of navicular cups relative to the articulating talar heads. Our results show that flatfoot deformity is associated with morphological changes of talar and navicular articular surfaces that can favor medial arch collapse and forefoot abduction.

In vitro analysis of muscle activity illustrates mediolateral decoupling of hind and mid foot bone motion.

Activity of the extrinsic ankle-foot muscles is typically described for the whole foot. This study determines if this muscle activity is also confirmed for individual foot segments defined in multi-segment foot models used for clinical gait analysis. Analysis of the individual bone motion can identify functional complexes within the foot and evaluates the influence of an altered foot position on muscle activity. A custom designed and built gait simulator incorporating pneumatic actuators is used to control the muscle force of six muscle groups in cadaveric feet. Measurements were performed in three static postures in which individual muscle force was incrementally changed. The motion of four bone embedded LED-clusters was measured using a Krypton motion capture system and resulting motion of calcaneus, talus, navicular and cuboid was calculated. Results indicate that primary muscle activity at bone level corresponds with that described for the whole foot. Secondary activity is not always coherent for bones within one segment: decoupling of the movement of medial and lateral foot bones is documented. Furthermore, secondary muscle activity can alter according to foot position. The observed medio-lateral decoupling of the foot bones dictates the need to extend some of the multi-segment foot models currently used in clinical gait analysis.

The first metatarsophalangeal joint meniscus and its relation to hallux valgus deformity--an anatomical and clinical study.

BACKGROUND: This study describes the anatomy and incidence of the metatarsophalangeal (MTP) joint meniscus, a structure not mentioned before in literature. METHODS: An anatomical cadaver study on 102 feet was performed with special attention to the first MTP joint anatomy. These results were compared with the per-operative findings in a clinical prospective study on 100 consecutive hallux valgus surgeries. RESULTS: On cadavers this meniscus is more common in patients with hallux valgus. Clinically, in patients with a mild hallux valgus the meniscus is found in more than half of cases during surgery, while it is seldom found in patients with moderate or severe deformities. CONCLUSIONS: The presence of this structure seems to stabilize the MTP joint preventing progression of the hallux valgus deformity and may explain the pain, which is often seen in mild bunions in younger, patients. Once the rotational deformity increases the meniscus tears and slips into the joint. In the more advanced hallux valgus deformity this meniscus plays little function and seems to disappear, leading to arthrosis.

Donor site morbidity after articular cartilage repair procedures: a review.

In order to perform an Osteochondral Autologous Transplantation (OAT) or an Autologous Chondrocyte Implantation (ACI), the integrity of healthy intact articular cartilage at a second location needs to be violated. This creates the possibility for donor site morbidity. Only recently have any publications addressed this issue. The aim of this manuscript is to review the current knowledge on donor site morbidity after an OAT or an ACI. Reports were identified by searching Medline and Pubmed up to March 2010. Donor site morbidity was described mostly considering a clinical outcome, both in a qualitative (parameters in history or physical examination) and/or quantitative way (knee status reported by means of a numerical score). An increasing rate of problems is noted when using quantitative instead of qualitative parameters, and when donor site morbidity is the focus of attention, affecting up to more than half of the patients, in particular for an OAT procedure. The decision to harvest an osteochondral or cartilage biopsy to perform a repair procedure should therefore be taken with caution. This also underscores the need for further research to identify safe donor sites or to develop techniques that eliminate the need for a formal biopsy ccompletely.

Total ankle replacement. Design evolution and results.

The ankle joint has unique anatomical, biomechanical and cartilaginous structural characteristics that allow the joint to withstand the very high mechanical stresses and strains over years. Any minor changes to any of these features predispose the joint to osteoarthritis. Total ankle replacement (TAR) is evolving as an alternative to ankle arthrodesis for the treatment of end-stage ankle osteoarthritis. Initial implant designs from the early 1970s had unacceptably high failure and complication rates. As a result many orthopaedic surgeons have restricted the use of TAR in favour of ankle arthrodesis. Long term follow-up studies following ankle arthrodesis show risks of developing adjacent joint osteoarthritis. Therefore research towards a successful ankle replacement continues. Newer designs and longer-term outcome studies have renewed the interest in ankle joint replacement. We present an overview of the evolution, results and current concepts of total ankle replacement.

High inter-specimen variability of baseline data for the tibio-talar contact area.

BACKGROUND: The tibio-talar contact area has been widely investigated to monitor biomechanical changes due to articular incongruities or an altered loading. This study aims to investigate for the first time in a systematic way the extent of the inter-specimen variability of the tibio-talar contact area, and its repercussions when analyzing data concerning this parameter. METHODS: Ten specimens were loaded to record the tibio-talar contact characteristics by use of pressure sensitive film. The size of the talar dome area, the size of the (normalized) tibio-talar contact area, the position of the tibio-talar contact area, and the shape of the latter were determined and analyzed. Inter-specimen variability was expressed as the coefficient of variation and was calculated for the datasets of previous studies as well. FINDINGS: The size of the tibio-talar contact area showed a very high inter-specimen variability, as is the case in previous studies. This high variability persisted when a normalized tibio-talar contact area was calculated. The shape of the tibio-talar contact area showed some basic characteristics, but a high variation in details could be observed. INTERPRETATION: Every specimen can be considered to have its own "ankle print". By this variability, articular incongruities are expected to have a different effect on local biomechanical characteristics in every single individual. Therefore, every single case has to be evaluated and reported for significant changes. In case of modeling, this also underscores the need to use subject specific models fed by sets of parameters derived from a series of single specimens.

Risk of neurovascular injuries in flexor hallucis longus tendon transfers: an anatomic cadaver study.

BACKGROUND: Flexor hallucis longus (FHL) tendon transfer is a frequently used treatment for both posterior tibial tendon insufficiency and chronic Achilles tendinopathy. We observed difficulties in harvesting the FHL tendon that may arise from cross-attachments with the flexor digitorum longus (FDL) tendon near the knot of Henry. The posterior tibial nerve is located nearby the decussation of these tendons. This study examined whether the difficult harvesting may be the cause of nerve injury. METHODS: A cadaver study was performed on 24 foot specimens. In all feet, we used a double-incision technique. The FHL tendon was transected in the distal medial midfoot incision and retracted through the posteromedial hindfoot incision. After harvesting the FHL tendon, we exposed the posterior tibial nerve and its lateral and medial plantar branches to identify if any lesion had occurred. RESULTS: The retraction failed at the first attempt in all specimens because of the presence of cross-attachments between the FHL and FDL tendons. A more extensive dissection of the FHL and FDL tendons was therefore required. We found lesions in 33% of all foot specimens, including two complete ruptures of the medial plantar nerve. CONCLUSIONS: Harvesting of the FHL tendon when transection is made distal to the knot of Henry may cause injuries to the medial and lateral plantar nerves. Experience in this procedure may reduce the risk of nerve injuries but even then nerve lesions remain possible. The clinical significance of these nerve lesions is not described in literature and remains to be determined.

Economic aspects of diabetic foot care in a multidisciplinary setting: a review.

BACKGROUND: To evaluate the economic aspects of diabetic foot care in a multidisciplinary setting. METHOD: A review of the English language literature, published from 1966 to November 2005. RESULTS: The results of available studies on the cost-of-illness of diabetic foot problems are difficult to compare. Nevertheless trends concerning excess of costs, protraction in time of costs, positive correlation to severity of ulcer and/or peripheral vascular disease, contribution of in-hospital stay and length of stay, and the patient's own contribution to total costs, are obvious. Only a few cost-effectiveness and cost-utility studies are available. Most use a Markov based model to predict outcome and show an acceptable result on long-term. CONCLUSIONS: Diabetic foot problems are frequent and are associated with high costs. A multidisciplinary approach to diabetic foot problems has proved to be cost saving with regard to cost of treatment itself. Nevertheless, it remained unclear if these savings could offset the overall costs involved in implementing this kind of approach. The few studies that address this issue specifically all show an acceptable cost-effectiveness, but often the profit will be evident after some years only, because long-term costs are involved. Based on these data, policymakers should foresee sufficient reimbursement for preventive and early curative measures, and not only for 'salvage manoeuvres'.

Biphalangeal fifth toe.

BACKGROUND: A biphalangeal fifth toe is a common variant in the European population. The frequency is higher in the Japanese population. It is considered an anatomical variant of the normal triphalangeal fifth toe. METHODS: Patients divided into three study groups were retrospectively reviewed to determine the effect of a biphalangeal fifth toe on the occurrence of clinically symptomatic pathology of the fifth ray. RESULTS: The prevalence of a biphalangeal fifth toe in patients with hammer or claw toes was 65%, bunionettes 47%, and overriding fifth toe 37%. Only for the group with hammer or claw toes was prevalence significantly higher than that in the control group (39%). CONCLUSION: The stiffness and rigidity of the biphalangeal fifth toe may predispose it for symptomatic hammer or claw toe.

The posteromedial rim of the talar dome as the site for harvesting cartilage in the ankle: an anatomic study.

PURPOSE: The goal of this study was to determine whether a biopsy specimen of a fixed size can be harvested reliably and consistently by arthroscopy at the posteromedial rim of the talar dome. METHODS: A cartilage biopsy specimen was taken post mortem arthroscopically from the posteromedial rim of the talar dome in 20 ankles. We aimed to take a full-thickness biopsy specimen of 10 x 5 mm in size. The shape, length, width, position, and depth of the created defect were determined. Subsequently, 2 observers analyzed the biopsy sites twice. The same set of parameters and the surface area of the lesion were determined. Differences between aimed and observed sizes were studied. RESULTS: In all ankles the aimed biopsy site could be seen and reached. The observed mean size of the biopsy specimens, when compared with the aimed size, was only significantly different for the mediolateral size. A wide variation of surface area was found. Nearly all biopsy specimens started exactly at the posterior border of the dome, but they were somewhat more lateral than intended. In only half of the biopsy specimens was the shape linear or oval, the others being rounded or irregular. In case a pre-existing posteromedial cartilage lesion was present, its position did not coincide with that of the biopsy specimen. CONCLUSIONS: A limited cartilage biopsy specimen could be harvested reliably and consistently by arthroscopy at the posteromedial rim of the talar dome, although the size tended to be somewhat larger than we intended. Containment of a pre-existing posteromedial lesion was never jeopardized. CLINICAL RELEVANCE: A safe biopsy site for cartilage in the ankle eliminates donor-site morbidity in the knee and may improve the suitability and biology of the obtained chondrocytes for successful repair of symptomatic joint surface defects of the ankle.

The HINTEGRA ankle: rationale and short-term results of 122 consecutive ankles.

The HINTEGRA ankle was developed as an attempt to specifically address the needs of minimal bone resection, extended bone support, proper ligament balancing, and minimal contact stresses within and around the prosthesis. The purpose of this study was to determine the short-term results in a consecutive series of 116 patients (122 ankles). Preoperative diagnoses were posttraumatic osteoarthrosis in 91 ankles (75%), primary osteoarthrosis in 16 ankles (13%), and systemic arthritis in 15 ankles (12%). Eight ankles had to be revised. Four were revised because of loosening of at least one component; one because of dislocation of the meniscus; and three for other reasons. All revisions were successful. After an average of 18.9 months (range, 1-3 years), 84% of patients were satisfied, and the clinical result was rated as good or excellent in 82% of the cases. The American Orthopaedic Foot and Ankle Society hindfoot score improved from 40 points preoperatively to 85 points at followup. Eighty-three ankles (68%) were completely pain-free. The average range of motion clinically was 39 degrees (range, 15 degrees-55 degrees) and under fluoroscopy (true ankle motion) it was 37 degrees (range, 7 degrees-62 degrees). Radiographically, the tibial component was stable in all ankles, and no tilting of the component occurred since surgery. However, migration of the talar component was observed in two ankles. The concept of minimal bone resection and wide bony support was shown to be successful on the tibial and talar sides. Obtained function, pain relief, and patient satisfaction were promising and, compared with other devices, the results mostly were superior. This may support the idea that anatomic-shaped surfaces, as is the case in the HINTEGRA ankle, may be successful in total ankle replacement.

Outcome and recurrence rate of diabetic foot ulcers treated by a total contact cast: short-term follow-up.

Foot ulcers in patients with diabetes present an increasing burden to healthcare. Total contact cast (TCC) is a well established treatment option for many of these ulcers, but little seems to be known about the final outcome once healing has been reached. The study examined healing and final outcome after TCC treatment among patients with diabetes. During a 22-month period, 15 consecutive patients with a total of 17 ulcers started treatment with a TCC. Three patients (three ulcers) were lost to follow-up (FU). Average FU was 91 weeks. The patients were followed with emphasis on healing, complications during FU, footwear, compliance, and frequency of visits. All ulcers healed, some after additional surgery. During FU, control visits were performed at an average of one visit every 4.7 weeks. Notwithstanding this, a high frequency of ulcer recurrence and/or other complications was noticed. Only four patients out of 12 remained without any new (ulcer) problem during FU. TCC proved to be a very efficient tool to heal neuropathic foot ulcers, but the recurrence rate and frequency of other complications remained very high. These data show how difficult it is to achieve reliable (secondary) preventive general foot care, and to prescribe and manufacture reliable footwear.

Severe Lisfrancs injuries: primary arthrodesis or ORIF?

Twenty-eight patients, with severe, acute Lisfranc dislocations, requiring operative intervention, were treated between 1989 and 1992 in a level one Trauma Center. Different treatment protocols were used by the two senior staff surgeons. This allowed ORIF to be compared to complete arthrodesis and partial arthrodesis. Twelve patients were treated with primary arthrodesis after open reduction of the dislocation. Partial (5) or complete arthrodesis (6) (depending on the type of fracture) was performed in these 12 patients. Sixteen patients were treated with open reduction and temporary fixation with stabilization and compression screw fixation (ORIF group). The subgroups were identical in age (mean 30.5 years), follow-up (30.1 months), type of fracture, type of injury and time to intervention. Anatomical reduction was achieved in eight of the 12 patients in the arthrodesis groups and in 12 of the 16 patients in the ORIF group. The Baltimore Painful foot Score (PFS) was higher in the ORIF group then in the complete arthrodesis group meaning the ORIF group had less pain. No difference in the PFS was found between the ORIF group and the partial arthrodesis group. Subsequent revision surgery was necessary in two cases in the arthrodesis groups and two cases in the ORIF group. Stiffness of the forefoot, loss of metatarsal arch, and sympathetic dystrophy occurred more frequently in the complete arthrodesis group. Open reduction and internal fixation with screws or partial arthrodesis is the treatment of choice in severe tarsometatarsal fracture dislocations. Primary complete arthrodesis should be reserved as a salvage procedure.