ABSTRACT: Orthoses can be used to accommodate residual clubfoot after Ponseti casting. Traditionally, orthoses are constructed using nonweightbearing casts or foam imprints. Technological advances in pressure analysis and in three-dimensional (3D) geometry assessment by computed tomographic (CT) scans can assist in designing and fabricating orthoses. The purpose of this study was to validate the new Milwaukee Foot Orthosis (MFO) using pressure metrics. Five typically developing children (mean age of 7.2 years) and five children with residual clubfoot deformities (eight residual clubfeet and mean age of 6 years) were recruited. All children with residual clubfoot had undergone Ponseti casting as an initial treatment. Each child underwent plantar pressure measurements and acquisition of 3D foot dimensions by a CT scanner. A computer-aided design (CAD) was used to develop a customized MFO for each of the five children. The MFO was manufactured for each foot with residual deformities using a rapid prototyping system. After the use of the MFO, pressure data showed significant reduction of maximal force, peak pressure, and other measurements at the heel and the lateral forefoot. There was significant reduction of the center of pressure (CoP) deviation in the forefoot (7.9%) and the midfoot (4.0%) compared with barefoot. The new MFO is effective in reducing residual clubfoot deformities, such as supination and adduction.
XUE-CHENG LIU, MD, PhD; CHANNING TASSONE, MD; ERIC LINFORD, MD; JOHN G. THOMETZ, MD; and ROGER LYON, MD, are affiliated with Department of Orthopaedic Surgery, Children’s Hospital of Wisconsin, Medical College of Wisconsin, Milwaukee, Wisconsin.
XUE-CHENG LIU, MD, PhD, is affiliated with Musculoskeletal Functional Assessment Center, Children’s Hospital of Wisconsin, Medical College of Wisconsin, Milwaukee, Wisconsin.
ROBERT RIZZA, PhD, is affiliated with Department of Mechanical Engineering, Milwaukee School of Engineering, Milwaukee, Wisconsin.
SERGEY TARIMA, PhD, is affiliated with Division of Biostatistics, Medical College of Wisconsin, Milwaukee, Wisconsin.
Disclosure: The authors declare no conflict of interest.
This study was supported by a grant from the National Institute on Disability and Rehabilitation Research (NIDRR H133G060142).
Correspondence to: Xue-Cheng Liu, MD, PhD, Musculoskeletal Functional Assessment Center and Department of Orthopaedic Surgery, Children’s Hospital of Wisconsin, Medical College of Wisconsin, 9000 W Wisconsin Ave, PO Box 1997, Suite C360, Milwaukee, WI 53201; email: email@example.com
Congenital talipes equinovarus (clubfoot) is one of the most common congenital musculoskeletal birth defects requiring treatment.1 Excellent clinical outcomes have been found using conservative treatment modalities including the Ponseti and French physiotherapy methods.1 Despite high overall success rates, studies report that in 32% to 41% of patients, initial treatment will fail and further manipulation, casting, and/or soft tissue releases will be required.2–4 A much smaller subset of patients will have residual static or dynamic deformities. Common late deformities include residual heel varus, equinovarus or cavus, as well as midfoot and forefoot adduction.5 These residual deformities can cause significant functional problems for patients’ mobility, ambulation, and ability to wear normal footwear. These problems are further compounded by the negative social impact of corrective footwear as the developing child reaches school age. Orthoses can be used to accommodate foot deformities, prevent worsening of the deformities, and improve gait.6 Orthoses have also been shown to have significant effects on foot motion.7 Optimal clinical improvements occur with a complete understanding of foot and ankle biomechanics using pressure analysis. The technique to make a traditional orthosis is dependent on skilled professional judgment using nonweightbearing casting or partial weightbearing foam imprints. Technological advances in analysis can provide valuable clinical data to assist the clinician in formulating corrective footwear.
We have designed a new method using plantar pressure data and computed tomographic (CT) scans for fabricating a new orthosis, the Milwaukee Foot Orthosis (MFO), that provides mechanical forces that may aid in the correction of residual clubfoot deformities.8,9 The center of pressure (CoP) trajectory in children with no foot dysfunction has been shown to fall within a defined range, and deviations from the normal CoP trajectory range denote foot loading abnormalities.10 Usually, the CoP starts at the back of the hindfoot, progresses down the middle of the hindfoot, stays on the medial side of the midfoot and the forefoot, and ends near the lateral side of the hallux.10 The CoP trajectory and pressure measurements of patients whose clubfeet have been treated have been shown to be different from those found in control subjects.11,12 In nonsurgically treated patients with clubfoot, the CoP trajectory shifts laterally and starts closer to the midfoot, whereas there is increased pressure at the midfoot and decreased pressure at the heel.11 Although the MFO is built taking into account the CoP trajectory and plantar pressure, its effect on those parameters remains unclear. The goals of this research were to determine how 1) pressure metrics differed between the residual clubfeet and the control subjects’ feet, 2) the use of the MFO changes pressure metrics in different foot segments, and 3) the use of the MFO shifts the CoP trajectory.
MATERIALS AND METHODS
Five control children with a mean age of 7.2 years (two girls and three boys) and five children with residual clubfoot deformities with a mean age of 6 years (one girl and four boys) were recruited for this study. Of the five patients with residual clubfoot, three had been treated for bilateral clubfeet and two had been treated for unilateral clubfeet, for a total of eight residual clubfeet. All children with residual clubfoot received Ponseti casting as the initial treatment modality. After the failure of serial castings, two clubfeet received complete subtalar releases, two clubfeet had Achilles tendon lengthening, one clubfoot underwent posterior medial release with anterior tibial tendon transfer to the lateral cuneiform, one clubfoot had wedge osteotomy of the cuboid, and one received osteotomies of multiple metatarsals. Before participating in our study, two children used a solid ankle-foot orthosis (AFO) at night.
An inclusion criterion for use of the MFO was residual clubfoot deformity. This was defined as flexible mild to moderate metatarsal adductus, forefoot supination, and hindfoot varus. This study was approved by the Children’s Hospital of Wisconsin institutional review board, and consent was acquired before data were collected.
All study participants had several pressure measurements taken. The foot pressure distribution of the participants’ feet was recorded while walking using an EMED-NT platform system (Novel Inc, Munich, Germany). Each subject stepped on the EMED pressure platform three times with each foot while walking at self-selected pace along a 15-m walkway. The pressure data were processed using NOVEL Scientific Software (Novel Inc, Munich, Germany). Three pressure measurements were averaged for each foot studied. Our model mapped eight anatomical regions: lateral hindfoot, medial hindfoot, midfoot, fifth metatarsal head, second to fourth metatarsal head, first metatarsal head, fifth to second toes, and hallux.9,13,14 At each of these foot segments, five pressure parameters were calculated: plantar contact area (cm2), maximal ground reaction force (N), peak pressure (N/cm2), CoP, medial-lateral linear displacement (mm), and pressure-time integral (loading) (N · s/cm2).
Additional data were gathered from the participants with residual clubfeet before custom MFOs were made for them. Their degree of passive ankle joint motion and foot muscle strength were measured as well as the length and the width of their hindfeet, midfeet, and forefeet. Three-dimensional (3D) geometry for each of the patient’s feet with residual clubfoot deformities was obtained by taking CT scans of the feet (GE, Milwaukee, WI, USA).
Using the processed pressure data in combination with the 3D bone geometry data gathered from the CT scans, a computer-aided design (CAD) program, Pro/Engineer (PTC, Needham, MA, USA), was used to develop a customized MFO for each of the five children with residual clubfoot. No orthoses were built for the control subjects. The CAD model of the MFO created was imported into a finite element (FE) analysis software package (Patran/Natran; MSC, Santa Ana, CA, USA). Each MFO was designed with a custom wedge in the medial layer. The plantar pressure measured was used in the FE analysis to evaluate the effect of varying this wedge’s slope on the CoP trajectory. The optimal slope of the wedge was found when the CoP trajectory in the MFO was improved toward the control CoP in the FE analysis. The custom software called OrthoticPro was developed jointly by the Department of Mechanical Engineering at the Milwaukee School of Engineering and the Department of Orthopaedic Surgery at the Medical College of Wisconsin.8 Finally, the CAD model was imported into a selective laser sintering™ system (SLS®, 3D Systems, Rock Hill, SC, USA) that produced the finished MFO.8 The MFO was designed with an external hard layer, which included a medial component and a lateral component. The interior and plantar surfaces of the hard layer were covered with foam (Figure 1). The hard layer of the MFO was constructed using a process that adds one layer of a material on top of another until the entire part is completed.15
After the MFOs were built, these were trimmed by an experienced orthotist to fit the feet of the patients with clubfoot. The effect the MFOs had on the foot pressure distribution of the patients with residual clubfoot while walking was measured, using the PEDAR insole pressure system (Novel Inc, Munich, Germany). While the subjects were walking with and without orthoses in their shoes, the PEDAR system recorded insole pressure. Data from 10 steps were averaged for each foot with residual clubfoot deformity.
A one-way analysis of variance (ANOVA) was performed to compare barefoot pressure differences between the 8 residual clubfeet and the 10 control feet. A Wilcoxon matched pairs test was used to compare pressure differences in the feet of the patients with residual clubfoot when they used the MFO in their shoes and when they did not. A probability of less than 0.05 is considered statistically significant.
Physical examination demonstrated persistent deformity, including mild to moderate forefoot supination and adduction, and midfoot supination for eight residual clubfeet and hindfoot varus for two residual clubfeet. All feet with residual clubfoot deformities had significant pressure differences when compared with the control group. The feet with residual clubfoot deformities had increased contact area in the midfoot and the midforefoot and decreased contact area in the hallux as compared with the controls (p < 0.05; Table 1). There were also decreased peak pressure in the lateral heel and increased peak pressures in the lateral forefoot and the midforefoot of the patients with residual clubfoot deformity as compared with the controls (p < 0.05; Table 1).
After the use of the MFO by the subjects with residual clubfoot deformities, pressure data showed significant reductions of maximal force, peak pressure, and pressure-time integral at the heel and the lateral forefoot (p < 0.05; Table 2). There was significant reduction of the CoP trajectory deviation from the control CoP trajectory after the use of the MFO (Figures 2, 3). The maximum reduction of the CoP deviation from the control CoP with the use of the MFO occurred in the forefoot (7.9%) and the midfoot (4.0%), whereas little change was observed (0.6%) in the hindfoot.
The forces placed on the foot during ambulation can be analyzed using several pressure parameters. These include peak pressure, contact area, contact time, CoP, maximum force, and force time integrals.14 Foot pathology has been shown to have a significant impact on these parameters, with abnormal CoP trajectories indicating abnormal foot loading.10 Patients with residual clubfoot deformities have significant pressure differences compared with control subjects’ feet including less pressure in the hindfoot and more pressure in the forefoot and the midfoot, resulting in excessive supination and lateral shifting of the CoP trajectory.11,13,15,16 The increase in contact area at the midfoot, the decrease in pressure at the lateral heel, and the increase in pressure at the midforefoot found in the patients with residual clubfoot deformities as compared with the controls are consistent with results from another study comparing pressure difference between children who have received treatment of clubfeet and controls.11 These abnormal pressure readings in the treated clubfeet may be the result of residual varus and equines deformities.
Patients with clubfoot have been found to have persistent abnormal motion at the feet after both surgical and nonsurgical treatment, including intoeing, supination, and adduction.17–20 Night splinting and AFOs have been shown to be effective in correcting static deformities; however, there are few data to show a positive effect on dynamic deformities in the clubfoot population. Some controversy exists regarding the predictive value of abnormal pressure readings for the population with residual clubfoot deformities. Sinclair et al.21 studied 28 patients treated for clubfeet and found that pressure analysis did not predict successful clinical outcomes. They found that many patients with excellent clinical outcomes still had significant pressure differences when compared with established normal data. More data need to be provided regarding the correlation of abnormal dynamic parameters with static deformities and overall clinical outcomes.
Orthoses have been shown to correct gait in children with cerebral palsy and congenital flatfeet; however, there are few data addressing orthosis use in patients with residual clubfoot deformities.6,22 Ki et al.23 showed a redistribution of peak pressure and maximum force using orthoses formed by two separate methods. They were able to show that an orthosis made from a computer-aided design (CAD) and computer-aided manufacturing (CAM) method obtained similar corrective results to an orthosis formed by foam impression. Similarly, our data show that the MFO shifts the CoP medially at the forefoot, which suggests a less supinated foot loading position according to Jameson et al.10 (Table 2; Figures 2, 3).
This study shows that the new MFO may be effective in reducing residual clubfoot deformities such as supination and adduction during ambulation. In addition, this may promote foot bone remodeling over time. The MFO can help bridge a clinical gap that exists for patients with residual clubfoot deformities for which night splinting is no longer a viable option. Because this pilot study has been considered as the first step of developing the new modality, the limitations of this study include small sample size, lack of functional outcome data, and short-term results. More data are being gathered regarding compliance rates, parent and patient satisfaction, and functional outcomes at 1 year. More data need to be gathered to assess the effectiveness of the MFO in preventing the recurrence and the progression of residual clubfoot deformities.
The authors thank the National Institute on Disability and Rehabilitation Research for the grant (NIDRR H133G060142) and Carlos Marquez-Barrientos, MS, Musculoskeletal Functional Assessment Center, Pediatric Orthopaedic Division, Medical College of Wisconsin, for his contributions to this study.
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KEY INDEXING TERMS: clubfoot; pressure analysis; orthosis CAD