Could a Foot Pressure Platform Replace X-ray to Diagnose Hallux Valgus Deformity?
Background: Hallux Valgus (HV) is the most common deformity of the foot. Currently the ‘gold standard’ in diagnosing HV is by X-ray. It has been shown that carcinogenic effects may be associated with the frequent use of diagnostic X-rays. A wide range of foot pressure platforms exist for clinicians to perform biomechanical research of the foot during gait. However, these platforms have not been used as diagnostic tools to evaluate HV. The main aim of this study is to provide a radiation-free diagnostic and screening tool for HV, using a foot pressure platform. Methods and Materials: This study has two parts; a) a cadaveric study and b) a foot clinic study. For the cadaveric study, 20 feet from Thiel embalmed cadavers (five males and five females) were used for the cadaveric pressure study. A portable Novel EMED-M pedography platform collected pressure data from cadavers. A static cadaveric foot pressure was collected by mimicking a weight bearing standing condition for the foot. Plantar pressures, under five anatomical areas (heel, mid-foot, forefoot and toes), were investigated using the following parameters: peak pressure (PP), maximum force (MF) and contact area (CA). For the foot clinic study, 34 participants (17 patients with HV and 17 with healthy feet) were recruited. Plantar pressure during dynamic and static conditions was collected using an EMED Novel X/R high-speed pedography system. Plantar pressure, under ten anatomical areas (heel, mid-foot, 1st metatarsal head (MH), 2nd MH, 3rd MH, 4th MH, 5th MH, great toe, 2nd toe and 3rd to 5th toes), were investigated using six parameters (PP, pressure-time integral (PTI), MF, force-time integral (FTI), contact time (CT) and CA). Additionally, the accuracy of the system, in dividing the foot into multiple anatomical areas (masking), was studied by comparing an automated masking system, and masks created based on X-rays. The Hallux Valgus Angle (HVA) was measured using footprints in both groups. The correlation of X-ray HVA with HVA footprint was measured. A modified clinical scale was produced to classify HV deformities based on the HVA footprint. Finally, questionnaires were distributed to 25 foot and ankle surgeons (nine consultants and six trainees) to evaluate 10 cases of HV deformity, based on X-ray alone, plantar pressure and combined X-ray with plantar pressure. Results: In comparison to live participant feet, cadaveric feet showed significantly lower PP under the mid-foot and toes. Cadaver feet also showed a significant reduction in MF and CA under heel and forefoot. In static conditions, results showed significant increases in PP and PTI in patients with HV deformities under the heel, forefoot and 2nd to 5th toes (P<0.05). However, there were no significant differences under mid-foot and great toe areas. For MF and FTI, the area under the great toe of HV patients showed significant decreases, and under the 2nd to 5th toes, there were significant increases (P<0.05). The study also showed a significant reduction in CA and increased CT under the area of the great toe during static conditions in HV patients, and a significant increase of CA under the 2nd to 5th toes in HV patients. During dynamic conditions, the highest PP in HV patients was found under the 2nd MH, followed by the 3rd MH, great toe, 1st MH and heel. In participants with healthy feet, the highest PP was found under the 2nd MH followed by the great toe, 3rd MH, heel and 1st MH. Only PP under the 1st and 3rd MHs were highly significant (P< 0.05). There were no significant differences between HV patients and healthy feet participants in terms of PTI. The areas under the great toe and mid-foot had a significant reduction of MF and FTI (P<0.05). The CA under the heel, mid-foot and great toe was significantly (P<0.05) reduced in HV patients, when compared with healthy participants. The area under the great toe and the 2nd toe of HV patients showed significant reductions in CT (P<0.05). Comparisons of plantar pressure using Novel masking and X-ray masking, in dividing the foot into 10 anatomical areas, showed a strong correlation r = 0.99, n (24) (P<0.01), between the two methods under all areas except the 2nd toe, which did not correlate. Moreover, a paired T-test of PP comparing both methods showed an underestimation in pressure under the mid-foot and an overestimation under the area of the 3rd to 5th toes. In comparison to X-ray HVAs, footprint HVAs showed a lower angle range, with a minimum mean of 5.3° and a maximum of 6.5°. HVA using footprints had a strong correlation (r=0.98) between the two methods. Based on the correlation of HVA X-ray with HVA print, the HV deformity can be classified on the HVA footprint as follows: for normal, mild, moderate and severe, angles are <10.3°, 10.3°-15.1°, 15.1°-34.1° and >34.1°, respectively. Finally, the study recorded a questionnaire response rate of 60% (15/25). Cronbach’s Alpha for reliability showed that an Alpha coefficient for 40 items was 0.767, implying that items had a good internal consistency. The HV cases questionnaires showed a change in surgeons’ decision-making about diagnoses and treatment options when foot pressure data were combined with X-rays (superimposed). The change was the result of biomechanical information, which supplied pressure data. Eleven (nine consultants and two trainees) of 15 surgeons would appear to recommend plantar pressure assessment in the routine diagnosis of HV deformity in clinical practice. Conclusions: Static cadaveric pressure feet did not have similar representations to live participants. During standing, multiple factors contribute to a normal weight distribution under the foot, comprising weight loading, muscle tone, bone architecture and ligament integrity. The absence of muscle tone and loss of ligament laxity contributed to the current findings. Involvement of the 1st metatarsal phalangeal (MTP) joint alters the biomechanical function of the foot, under static and dynamic conditions. In HV patients, the Novel masking system accurately divides the foot into multiple anatomical areas. HVA can be measured using footprints, which is a reliable method with high correlation to X-ray HVAs. The modified clinical scale of the deformity based on HVA footprints needs to be validated. The combination of X-rays with pressure data, changed surgeons’ evaluation and treatment options for HV deformities. Based on questionnaire feedback, using pressure data as a routine tool in the clinical diagnosis of the HV deformity was recommended. Using pressure data adds value to monitoring progression of the deformity, from a functional point of view. Early diagnosis, using pressure data, may help construct an appropriate conservative treatment for HV deformity, which may further slow progression. Combinations of X-rays with pressure data can provide better evaluations of the HV deformity, and consequently better decision making for its management. From a surgical perspective, the pressure platform cannot substitute for X-rays, as surgeons plan their surgeries based on X-ray images, but the process can be complementary, with a view to replacing it in the future.
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