Changes in Foot Loading Following Plantar Fasciotomy: A Computer Modeling Study

Mechanical drivers of intrinsic foot muscle for maximum toe flexor strength in upright standing across different body size

This study aimed to evaluate maximum toe flexor strength, foot arch height, intrinsic toe flexor muscle size and foot arch stiffness among individuals with different body sizes, and to compare these variables between sitting and standing positions. Maximum toe flexor strength in sitting and standing, and intrinsic foot muscle thicknesses (flexor hallucis brevis: FHB, flexor digitorum brevis: FDB, abductor hallucis: AH and quadratus plantae: QP), were measured using a toe grip dynamometer and a B-mode ultrasound in healthy young men. FHB was thicker than AH, FDB and QP, AH was thicker than FDB and QP, and no significant difference was found between FDB and QP. Toe flexor strength was correlated with FHB and AH, and foot arch height was correlated with FHB. Toe flexor strength was greater in standing than in sitting. Stepwise multiple regression analysis identified FHB and AH as determinants of toe flexor strength in standing, and the relative muscle strength values per body weight in standing were determined by QP, foot arch index and foot arch stiffness. Overweight individuals had a decreased rate of increase in relative toe flexor strength compared to normal individuals. These results suggest that a large muscle thickness of intrinsic foot muscle a key contributor to toe flexor strength. Moreover, toe flexor muscle in upright standing could have the potential to generate force independently of intrinsic foot muscle size, but obese individuals who chronically put weight on their feet might impair the force amplification mechanism in upright standing.

Regional differences in the mechanical properties of the plantar aponeurosis

The plantar aponeurosis functions to support the foot arch during weight bearing. Accurate anatomy and material properties are critical in developing analytical and computational models of this tissue. We determined the cross-sectional areas and material properties of four regions of the plantar aponeurosis: the proximal middle and distal middle portions of the tissue and the medial (to the first ray) and lateral (to the fifth ray) regions. Bone-plantar aponeurosis-bone specimens were harvested from fifteen cadaveric feet. Cross-sectional areas were measured using molding, casting, and sectioning methods. Mechanical testing was performed using displacement control triangle waves (0.5, 1, 2, 5, and 10 Hz) loaded to physiologic tension by estimating from body weight and area ratio of the region. Five specimens were tested for each region. Regional deformations were recorded by a high-speed video camera. There were overall differences in cross-sectional areas and biomechanical behavior across regions. The stress-strain responses are non-linear and mainly elastic (energy loss 3.6% to 7.2%). Moduli at the proximal middle and distal middle regions (400 and 522 MPa) were significantly higher than the medial and lateral regions (225 and 242 MPa). The effect of frequency on biomechanical outcomes was small (e.g., 3.5% change in modulus), except for energy loss (107% increase as frequency increased from 0.5 to 10 Hz). These results indicate that the plantar aponeurosis tensile response is non-linear, nearly elastic, and frequency independent. The cross-sectional area and material properties differ by region, and we suggest that such differences be included to accurately model this structure.

The mechanical role of the metatarsophalangeal joint in human jumping

This study investigated the mechanical role of metatarsophalangeal (MTP) joints in human jumping. Eighteen healthy young men performed three types of single-leg jumps (SJ: squat jump; CMJ: countermovement jump; HJ: standing horizontal jump) on a force plate under barefoot (BARE) and forefoot immobilisation (FFIM) conditions. For FFIM, the forefoot was immobilised around the MTP joints of the dominant leg by a custom-made splint. Force-time components and the centre of pressure (COP) trajectory were measured from the ground reaction force (GRF) in the take-off phase of jumping. The vertical jump heights calculated from the net vertical impulse were lower under FFIM than under BARE during the CMJ (p < 0.05). The HJ distance under FFIM was significantly shorter than that under BARE (p < 0.01). The relative net vertical impulse was lower under FFIM than under BARE during the CMJ (p < 0.05). During the HJ, all the horizontal GRF variables were significantly lower under FFIM than under BARE (p < 0.01), but none of the vertical GRF variables differed between the two conditions. The horizontal relative GRF in the 90–95% of the final take-off phase during the HJ was significantly lower under FFIM than under BARE (p < 0.01). Under FFIM, the COP range in the antero-posterior direction in the take-off phase of the HJ decreased (p < 0.05), whereas its range in the anterior direction for the SJ and CMJ increased (p < 0.05). The results of this study indicate that MTP joint motion can play an important role in regulating force-generating capacities of toe flexor muscles in the take-off phase of human jumping, especially in the horizontal direction of horizontal jumping.

Percutaneous plantar fasciotomy: An anatomical study about its safety and efficacy

BACKGROUND

Percutaneous plantar fasciotomy is one of the available options for recalcitrant cases of plantar fasciopathy, but there is a mismatch in the clinical results between different author's experience, possibly due to variability when choosing the exact cutaneous entry point. The purpose of this study is to validate the plantar approach in the surgical treatment of plantar fasciopathy, describing a safe path and cutaneous entry point to perform a percutaneous plantar fasciotomy with a 2 mm incision testing the procedure on cadavers.

METHODS

a unicentric cross-sectional analytical study was conducted in 12 cadaveric feet to verify the accuracy of the percutaneous fasciotomy entry point. Independent variables analysed were: extent of fasciotomy, entry point location, spur resection, and soft tissues injuries. A double evaluation was performed: an indirect evaluation under fluoroscopic vision, and a direct evaluation after anatomical dissection.

RESULTS

No cases of plantar cortical lesion on the calcaneus was observed. Satisfactory fasciotomy was performed in 91.7% of the cases. An optimal entry point was noticed in all cases with a mean distance to the tip of tibial malleolus of 22.5 mm (±6.9; 35.1-12.1) and a mean distance to foot midline of 7.8 mm (±1.7; 11.8-5.1). No neurological nor vascular lesions were found. In all the feet, a laceration of the plantar part of flexor digitorum brevis muscle was noted.

CONCLUSION

the plantar approach for percutaneous total plantar fasciotomy is a safe procedure. The current study provides an intraoperative guideline for minimising the possible risks.

Percutaneous plantar fasciotomy: radiological evolution of medial longitudinal arch and clinical results after one year

PURPOSE

Plantar fasciitis (PF) is the most common cause of plantar heel pain. Conservative treatment and corrections of risks factors are the first line of care. For the 10% of patients who do not respond to conservative treatment, surgical release can offer relief of symptoms. Due to the critical role of the PF in the function of the foot and its architectural maintenance, its surgical release could cause a collapse of the internal arch of the foot and an alteration of its function. With the hypothesis that an isolated percutaneous PF release may not lead to these alterations of the foot while providing relief to the patients, we evaluated the radiological evolution and clinical results of this surgery after one year.

MATERIAL AND METHOD

Between January 2013 and Augustus 2017, we conducted a single arm monocentric prospective study on 22 patients (25 feet) aged from 33 to 84 years, with plantar fasciitis and failure of conservative management who benefited a percutaneous total plantar fasciotomy through a plantar approach. The American Orthopedic Foot and Ankle Score (AOFAS) and the Djian-Annonier's angle were evaluated preoperatively and postoperatively.

RESULTS

Among the 22 patients, sixteen patients were female and six patients were male. Three patients (2 females and 1 male) for six feet were operated for bilateral plantar fasciitis. The mean pre-operative Djian-Annonier's angle was 117.6° (range 101-132.9°), and the mean post-operative angle was 119.3° (range 102-137°). There was no statistically significant difference in Djian-Annonier's angle before and after surgery. The mean pre-operative AOFAS was 42.8 (range 32-51). The scores at 15 days, six weeks, and three months show a gradual increase up to 89.9 in the results with significant differences between the groups (p < 0.05). There was no difference between the scores after three months.

CONCLUSION

Complete percutaneous plantar fasciotomy is simple and safe and allows a quick recovery to activity without impacting the MLA.

Subject-specific muscle properties from diffusion tensor imaging significantly improve the accuracy of musculoskeletal models

Musculoskeletal modelling is an important platform on which to study the biomechanics of morphological structures in vertebrates and is widely used in clinical, zoological and palaeontological fields. The popularity of this approach stems from the potential to non-invasively quantify biologically important but difficult-to-measure functional parameters. However, while it is known that model predictions are highly sensitive to input values, it is standard practice to build models by combining musculoskeletal data from different sources resulting in 'generic' models for a given species. At present, there are little quantitative data on how merging disparate anatomical data in models impacts the accuracy of these functional predictions. This issue is addressed herein by quantifying the accuracy of both subject-specific human limb models containing individualised muscle force-generating properties and models built using generic properties from both elderly and young individuals, relative to experimental muscle torques obtained from an isokinetic dynamometer. The results show that subject-specific models predict isokinetic muscle torques to a greater degree of accuracy than generic models at the ankle (root-mean-squared error - 7.9% vs. 49.3% in elderly anatomy-based models), knee (13.2% vs. 57.3%) and hip (21.9% vs. 32.8%). These results have important implications for the choice of musculoskeletal properties in future modelling studies, and the relatively high level of accuracy achieved in the subject-specific models suggests that such models can potentially address questions about inter-subject variations of muscle functions. However, despite relatively high levels of overall accuracy, models built using averaged generic muscle architecture data from young, healthy individuals may lack the resolution and accuracy required to study such differences between individuals, at least in certain circumstances. The results do not wholly discourage the continued use of averaged generic data in musculoskeletal modelling studies but do emphasise the need for to maximise the accuracy of input values if studying intra-species form-function relationships in the musculoskeletal system.

Does the minimally invasive complete plantar fasciotomy result in deformity of the Plantar arch? A prospective study

BACKGROUND

Complete plantar fasciotomy has been associated with changes in foot loading, leading to medial longitudinal arch collapse. The purpose of this study is to analyse our clinical experience with percutaneous complete plantar fasciotomy and quantify the possible changes in foot loading measured by the calcaneal pitch angle.

METHODS

A prospective case series study with patients operated between 2005-2012 was conducted, where AOFAS, Maryland Foot Score (MFS), VAS and radiological calcaneal pitch (CP) were recorded. Postoperative data were collected, where the surgeon evaluated the presence of complications, and an independent investigator performed radiological and scale evaluations follow-up: AOFAS, MFS, VAS and Benton-Weil questionnaire.

RESULTS

A total of 60 patients, 62 feet, with a mean follow-up of 57 months (range 13-107) were studied. The MFS increased a mean of 21 points (p=.001), the AOFAS score a mean of 25 points (p=.001), and the VAS decreased a mean of 8.89 points (p=.001). A total of fifty-seven feet (91.9%) were pain-free at the end of follow-up. The mean CP dropped from 20.2° (range 11-34) preoperatively to 19.3° (range 11-34) at the end of follow-up (p=.05). In 25 feet (40.3%) there were no changes in the calcaneus pitch angle, in 21 feet dropped 1° (33.9%), in 11 dropped 2° (17.8%), 3 feet 3° (4.8%) and 2 feet (3.2%) 4°. Postoperative complications were noted in 4 feet (6.4%), with lateral column pain. The surgery meets the expectations of all patients.

CONCLUSIONS

Percutaneous total fascia release is safe and does not produce a significant drop in arch height based on the radiological finding. Lack of success after surgery may be explained by other pathologies that might appear like plantar fasciitis. Further studies with gait analysis after total plantar fascia release in patients are needed.

Anatomy and biomechanical properties of the plantar aponeurosis: a cadaveric study

Objectives

To explore the anatomy of the plantar aponeurosis (PA) and its biomechanical effects on the first metatarsophalangeal (MTP) joint and foot arch.

Methods

Anatomic parameters (length, width and thickness of each central PA bundle and the main body of the central part) were measured in 8 cadaveric specimens. The ratios of the length and width of each bundle to the length and width of the central part were used to describe these bundles. Six cadaveric specimens were used to measure the range of motion of the first MTP joint before and after releasing the first bundle of the PA. Another 6 specimens were used to evaluate simulated static weight-bearing. Changes in foot arch height and plantar pressure were measured before and after dividing the first bundle.

Results

The average width and thickness of the origin of the central part at the calcaneal tubercle were 15.45 mm and 2.79 mm respectively. The ratio of the length of each bundle to the length of the central part was (from medial to lateral) 0.29, 0.30, 0.28, 0.25, and 0.27, respectively. Similarly, the ratio of the widths was 0.26, 0.25, 0.23, 0.19 and 0.17. The thickness of each bundle at the bifurcation of the PA into bundles was (from medial to lateral) 1.26 mm, 1.04 mm, 0.91 mm, 0.84 mm and 0.72 mm. The average dorsiflexion of the first MTP joint increased 10.16° after the first bundle was divided. Marked acute changes in the foot arch height and the plantar pressure were not observed after division.

Conclusions

The first PA bundle was not the longest, widest, or the thickest bundle. Releasing the first bundle increased the range of motion of the first MTP joint, but did not acutely change foot arch height or plantar pressure during static load testing.

Comparative Trial of the Foot Pressure Patterns between Corrective Orthotics, Formthotics, Bone Spur Pads and Flat Insoles in Patients with Chronic Plantar Fasciitis

Introduction: The objective of the study is to compare the efficacy of flat insoles, bone spur pads, pre-fabricated orthotics and customised orthotics in reducing plantar contact pressure of subjects with plantar fasciitis. Materials and Methods: This is a controlled non-blinded com- parative study conducted in a tertiary medical institute. Thirty subjects with unilateral plantar fasciitis between the ages of 20 and 65 years were recruited at the sports medicine clinic. The contact pressures and pressure distribution patterns in both feet for each subject were measured with sensor pressure mats while standing. Repeat measurements were made with the subjects wearing shoes, flat insoles, bone spur heel pads, pre-fabricated insoles and customised orthotics on both feet. The asymptomatic side was used as the control. Contact pressure measurements of the symptomatic and asymptomatic feet and power ratio of the pressure distribution pattern of the rearfoot were then compared. Results: Contact pressure was higher on the asymptomatic side due to unequal distribution of weight. Bone spur heel pads were ineffective in reducing rearfoot pressure while formthotics and customised orthotics reduced peak rearfoot pressures significantly. The power ratio of the rearfoot region decreased with the use of formthotics and customised orthotics. Conclusion: Pre-fabricated orthotics and customised orthotics reduced rearfoot peak forces on both sides while bone spurs heel pad increase rearfoot peak pressures. Pre-fabricated and customised orthotics are useful in distributing pressure uniformly over the rearfoot region. Key words: Biomechanics, Heel pain

An elaborate data set characterizing the mechanical response of the foot

Mechanical properties of the foot are responsible for its normal function and play a role in various clinical problems. Specifically, we are interested in quantification of foot mechanical properties to assist the development of computational models for movement analysis and detailed simulations of tissue deformation. Current available data are specific to a foot region and the loading scenarios are limited to a single direction. A data set that incorporates regional response, to quantify individual function of foot components, as well as the overall response, to illustrate their combined operation, does not exist. Furthermore, the combined three-dimensional loading scenarios while measuring the complete three-dimensional deformation response are lacking. When combined with an anatomical image data set, development of anatomically realistic and mechanically validated models becomes possible. Therefore, the goal of this study was to record and disseminate the mechanical response of a foot specimen, supported by imaging data. Robotic testing was conducted at the rear foot, forefoot, metatarsal heads, and the foot as a whole. Complex foot deformations were induced by single mode loading, e.g., compression, and combined loading, e.g., compression and shear. Small and large indenters were used for heel and metatarsal head loading, an elevated platform was utilized to isolate the rear foot and forefoot, and a full platform compressed the whole foot. Three-dimensional tool movements and reaction loads were recorded simultaneously. Computed tomography scans of the same specimen were collected for anatomical reconstruction a priori. The three-dimensional mechanical response of the specimen was nonlinear and viscoelastic. A low stiffness region was observed starting with contact between the tool and foot regions, increasing with loading. Loading and unloading responses portrayed hysteresis. Loading range ensured capturing the toe and linear regions of the load deformation curves for the dominant loading direction, with the rates approximating those of walking. A large data set was successfully obtained to characterize the overall and the regional mechanical responses of an intact foot specimen under single and combined loads. Medical imaging complemented the mechanical testing data to establish the potential relationship between the anatomical architecture and mechanical responses and to further develop foot models that are mechanically realistic and anatomically consistent. This combined data set has been documented and disseminated in the public domain to promote future development in foot biomechanics.

Normal and abnormal function of the first ray

The first ray is the most important structure of the forefoot in its contribution to normal locomotion. Because first ray dysfunction is encountered in clinical practice with the development of hallux valgus, metatarsus primus varus, and hallux rigidus, there has been a belief that there is a mechanical basis for these conditions. Since publications in the 1930s, there has been significant research focused on the first ray. This article discusses the subtleties of normal and abnormal mechanics of the first ray to promote a better understanding for foot and ankle practitioners when treating these various disorders.

Extracorporeal shock wave for chronic proximal plantar fasciitis: 225 patients with results and outcome predictors

Plantar fasciitis can be a chronic and disabling cause of foot pain in the adult population. For refractory cases, extracorporeal shock wave therapy (ESWT) has been proposed as therapeutic option to avoid the morbidity of surgery. We hypothesized that the success of extracorporeal shock wave therapy in patients with chronic plantar fasciitis is affected by patient-related factors. A retrospective review of 225 patients (246 feet) who underwent consecutive ESWT treatment by a single physician at our institution between July 2002 and July 2004 was performed. Subjects were included only if they had plantar fasciitis for more than 6 months and failure to response to at least 5 conservative modalities. Patients were evaluated prospectively with health questionnaires, Roles and Maudsley scores, and American Orthopaedic Foot and Ankle Society (AOFAS) ankle and hindfoot scores at regular intervals. Follow-up was 30.2 +/- 8.7 months post procedure. Multivariable analysis was performed to assess factors leading to successful outcomes. Success rates of 70.7% at 3 months and 77.2% at 12 months were noted in this population. Previous cortisone injections, body mass index, duration of symptoms, presence of bilateral symptoms, and plantar fascia thickness did not influence the outcome of ESWT. The presence of diabetes mellitus, psychological issues, and older age were found to negatively influence ESWT outcome. Whereas many factors have been implicated in the development of plantar fasciitis, only diabetes mellitus, psychological issues, and age were found to negatively influence ESWT outcome.

LEVEL OF CLINICAL EVIDENCE

2.

OpenSim: open-source software to create and analyze dynamic simulations of movement

Dynamic simulations of movement allow one to study neuromuscular coordination, analyze athletic performance, and estimate internal loading of the musculoskeletal system. Simulations can also be used to identify the sources of pathological movement and establish a scientific basis for treatment planning. We have developed a freely available, open-source software system (OpenSim) that lets users develop models of musculoskeletal structures and create dynamic simulations of a wide variety of movements. We are using this system to simulate the dynamics of individuals with pathological gait and to explore the biomechanical effects of treatments. OpenSim provides a platform on which the biomechanics community can build a library of simulations that can be exchanged, tested, analyzed, and improved through a multi-institutional collaboration. Developing software that enables a concerted effort from many investigators poses technical and sociological challenges. Meeting those challenges will accelerate the discovery of principles that govern movement control and improve treatments for individuals with movement pathologies.

Model-based estimation of muscle forces exerted during movements

Estimation of individual muscle forces during human movement can provide insight into neural control and tissue loading and can thus contribute to improved diagnosis and management of both neurological and orthopaedic conditions. Direct measurement of muscle forces is generally not feasible in a clinical setting, and non-invasive methods based on musculoskeletal modeling should therefore be considered. The current state of the art in clinical movement analysis is that resultant joint torques can be reliably estimated from motion data and external forces (inverse dynamic analysis). Static optimization methods to transform joint torques into estimates of individual muscle forces using musculoskeletal models, have been known for several decades. To date however, none of these methods have been successfully translated into clinical practice. The main obstacles are the lack of studies reporting successful validation of muscle force estimates, and the lack of user-friendly and efficient computer software. Recent advances in forward dynamics methods have opened up new opportunities. Forward dynamic optimization can be performed such that solutions are less dependent on measured kinematics and ground reaction forces, and are consistent with additional knowledge, such as the force-length-velocity-activation relationships of the muscles, and with observed electromyography signals during movement. We conclude that clinical applications of current research should be encouraged, supported by further development of computational tools and research into new algorithms for muscle force estimation and their validation.

Real-time subject-specific monitoring of internal deformations and stresses in the soft tissues of the foot: A new approach in gait analysis

No technology is presently available to provide real-time information on internal deformations and stresses in plantar soft tissues of individuals during evaluation of the gait pattern. Because internal deformations and stresses in the plantar pad are critical factors in foot injuries such as diabetic foot ulceration, this severely limits evaluation of patients. To allow such real-time subject-specific analysis, we developed a hierarchal modeling system which integrates a two-dimensional gross structural model of the foot (high-order model) with local finite element (FE) models of the plantar tissue padding the calcaneus and medial metatarsal heads (low-order models). The high-order whole-foot model provides real-time analytical evaluations of the time-dependent plantar fascia tensile forces during the stance phase. These force evaluations are transferred, together with foot-shoe local reaction forces, also measured in real time (under the calcaneus, medial metatarsals and hallux), to the low-order FE models of the plantar pad, where they serve as boundary conditions for analyses of local deformations and stresses in the plantar pad. After careful verification of our custom-made FE solver and of our foot model system with respect to previous literature and against experimental results from a synthetic foot phantom, we conducted human studies in which plantar tissue loading was evaluated in real time during treadmill gait in healthy individuals (N = 4). We concluded that internal deformations and stresses in the plantar pad during gait cannot be predicted from merely measuring the foot-shoe force reactions. Internal loading of the plantar pad is constituted by a complex interaction between the anatomical structure and mechanical behavior of the foot skeleton and soft tissues, the body characteristics, the gait pattern and footwear. Real-time FE monitoring of internal deformations and stresses in the plantar pad is therefore required to identify elevated deformation/stress exposures toward utilizing it in gait laboratories to protect feet that are susceptible to injury.