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Forefoot plantar shear stress distribution in hallux valgus patients
Gait & Posture 30 (2009) 257–259
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Short communication
Forefoot plantar shear stress distribution in hallux valgus patients Metin Yavuz a,b,c, Vincent J. Hetherington c, Georgeanne Botek d, Gordon B. Hirschman e, Lynn Bardsley e, Brian L. Davis a,* a
Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195, USA Department of Chemical & Biomedical Engineering, Cleveland State University, Cleveland, OH 44115, USA c Ohio College of Podiatric Medicine, Independence, OH 44131, USA d Department of Orthopedic Surgery, Cleveland Clinic, Cleveland, OH 44195, USA e Infoscitex Corporation, Albany, NY 12205, USA b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 October 2007 Received in revised form 29 April 2009 Accepted 4 May 2009
Background: Hallux valgus is a common foot disorder often experienced with secondary callosities and metatarsalgia. Many factors including improper shoes might be responsible in the pathophysiology of the problem. Hallux valgus deformity has been shown to alter the biomechanics of the whole foot rather than affecting only the great toe. Due to changes in the biomechanical functioning of the first ray, other regions of the forefoot area have been shown to bear abnormal loads with increased vertical loading on medial, central and lateral forefoot regions. The purpose of this study was to investigate the pattern of forefoot plantar shear loading in hallux valgus patients and compare these results with those of control subjects. Methods: A total of 28 subjects were recruited for the study of which 14 were clinically diagnosed with hallux valgus. A custom built platform was used to collect peak pressure and shear data. A repeated measures analysis of variance was used to analyze the recorded data. Findings: Antero-posterior shear was significantly lower in the deformity group (p < 0.05). The lateral forefeet of the patients, however, experienced slightly higher shear loads (p > 0.05). Interpretation: Propulsive shear force generation mechanism under the medial forefoot was impaired in the disorder group. In general, shear loading of the plantar feet shifted laterally. Previously hypothesized higher medio-lateral shear magnitudes under the hallux were not confirmed. ß 2009 Published by Elsevier B.V.
Keywords: Biomechanics Foot Hallux valgus Plantar stresses Plantar shear Instrumentation
1. Introduction Hallux abductovalgus, or shortly hallux valgus, is a degenerative joint disease that results in the lateral deviation of the big toe and medial deviation of the first metatarsal bone. Hallux valgus (HV) often leads to pain and limited mobility in patients [1]. Many factors might contribute to the etiology of HV including a potential genetic predisposition, altered biomechanics of the first ray and shoes [2–4]. Patients with HV may experience complications such as metatarsalgia, plantar callosities, hammer toe deformities and impaired quality of life [5,6]. Load bearing capability of the hallux is perturbed in HV, in addition to the unfavorable loading conditions at other regions of
* Corresponding author at: Department Biomedical Engineering (ND20), Orthopedic Research Center, Cleveland Clinic, 9500 Euclid Ave, Cleveland, OH 44195, USA. Tel.: +1 216 444 1055; fax: +1 216 444 9198. E-mail address: [email protected] (B.L. Davis). 0966-6362/$ – see front matter ß 2009 Published by Elsevier B.V. doi:10.1016/j.gaitpost.2009.05.002
the forefoot [7,9–11]. A number of reports explored plantar pressure distribution in order to reveal the foot function in HV patients. However being restricted to only uni-axial stress distribution, one cannot derive a comprehensive biomechanical evaluation of the foot in disorders like HV. A number of investigators, directly or indirectly, hypothesized an increase in local shear stress under the hallux, but this was never verified [8,12]. A particular theory states that due to force changes in flexor tendons traversing the first phalangeal– metatarsal joint in HV patients, medio-lateral shear forces under the great toe should increase [8]. The purpose of this study was to examine plantar shear stress distribution in patients with HV and compare findings with that of healthy control subjects. It was hypothesized that the propulsive shear loading under the hallux and first metatarsal head (MTH) would be reduced due to the impaired dorsiflexion capability of the first metatarsophalangeal joint. Also expected, was that hallux would experience higher medio-lateral shear forces.
M. Yavuz et al. / Gait & Posture 30 (2009) 257–259
258 Table 1 Characteristics of the subjects.
No. of subjects Gender Age (years) Body mass index
HV
Control
14 13 females, 1 male 55.2 14.7 (25–77) 26.8 4.8 (19.1–35.8)
14 9 females, 5 males 53.6 18.7 (24–82) 24.6 3.8 (19.1–33.7)
Values are presented as the mean standard deviation, with the range in parentheses.
instance of push-off phase and the initial phase of the forefoot contact phase. Due to a small sample size, Anderson–Darling normality tests were performed. As the results indicated normal distribution, data were analyzed by implementing a repeated measures ANOVA. Pairwise comparisons of group-site means were run for each variable. Tukey–Kramer test was used for this purpose. Age, BMI and stance duration of the subjects were analyzed by two-sample t-tests. p values smaller than 0.05 were considered significant. Minitab (Minitab Inc., PA) software was used to perform the statistical analyses.
2. Methods
3. Results
Twenty-eight volunteers (Table 1) were recruited. Of the recruited subjects, fourteen were clinically diagnosed with HV deformity (HV group), whereas the other 14 were deformity free volunteers (control group). Foot pain was not an inclusion criterion for HV patients, although almost half of the patients had antalgic gait. Each participant signed an informed consent form approved by the Institutional Review Board of the Cleveland Clinic. Radiography results were available for nine of the HV patients. Hallux valgus angle (HVA) was determined by calculating the intersection angle between the first metatarsal and proximal phalanx. The angle between the longitudinal axes of the first and second metatarsal was noted as the intermetatarsal angle (IMA). A custom-built pressure–shear distribution device consisting of 80 transducers arranged in a 10 8 array was set flush with the ground. Each sensor measured 1.25 cm 1.25 cm, generating a surface area of 1.56 cm2. Further specifications of the platform have been explained elsewhere [13]. Only forefeet of the subjects were assessed since HV is forefoot specific. The two-step method was preferred in data acquisition [14]. Subjects were allowed to walk at self-selected speeds. The tests were carried out for only one (surgery free) foot, and five trials were obtained for each subject. Only three trials in which the forefoot was properly placed on the device were selected. A Matlab (Mathworks Inc., MA) code was written to mask five anatomical regions of the foot; hallux, lesser toes, 1st metatarsal head (MTH1), central metatarsal heads (MTHC) and lateral metatarsal heads (MTHL). For each foot site, five parameters were determined; peak pressure (PP), peak resultant shear stress (RES), peak-to-peak antero-posterior shear (ppAP), peak-to-peak mediolateral shear (ppML) and peak propulsive shear (pPS). Stance duration was calculated as the time difference between the last
Mean age and BMI of the subject groups were not significantly different (p > 0.05). HV patients had a mean HVA of 25.68 (9.08) and IMA of 14.18 (3.28). Statistical analysis yielded a significant difference (p = 0.013) in only peak-to-peak antero-posterior shear (ppAP) variable between the groups. No significant group–site interaction was recorded. Table 2 displays the mean values of pressure and shear variables for both groups. ppAP showed a 25% and 17% decrease under the hallux and MTH1, respectively, and a 4% increase under MTHL in the HV group. Peak propulsive shear stress (pPS) was decreased by 22% and 32%, respectively, under the MTH1 and hallux of the disorder group. HV group experienced 15% more pPS than the control group at MTHL region. However, all of these differences were not significant (p > 0.05). Surprisingly, peak-to-peak mediolateral shear (ppML) was similar under the hallux in both groups (p > 0.05). Stance duration for control group was recorded as 0.69 s which was a little faster than HV group with 0.72 s. The difference was not statistically different (p = 0.66). 4. Discussion Previous pressure assessment studies in HV patients suggest a vertical loading shift towards the lateral forefoot [7,9–11]. The results of this study supported this finding. Shear stresses were also slightly higher in the MTHL area of the feet with HV. Moreover, while no control subject had their peak shear values occur at the lateral aspect of the forefoot; this was the case in 4 of the 14 HV patients (Fig. 1). Peak propulsive shear stress (pPS) occurred at MTHC in 86% of the control subjects. MTHC experienced the maximal pPS (48.8 kPa) in 57% of the HV patients. In 29% of the
Table 2 Mean (standard deviation) pressure and shear values for control and HV groups. Hallux
Lesser toes
MTH1
MTHC
MTHL
PP (kPa) Control feet HV feet
291.4(110.6) 276.0(141.1)
116.0 (50.3) 111.6 (48.1)
276.1 (86.8) 314.1 (171.8)
428.8 (100.6) 446.7 (224.8)
217.6 (72.2) 262.0 (123.5)
RES (kPa) Control feet HV feet
48.0(15.9) 44.7 (24.8)
36.8 (14.2) 35.6 (13.1)
43.3 (14.3) 38.5 (20.0)
60.3 (15.9) 57.3 (19.0)
46.1 (12.9) 49.2 (20.1)
ppAP* (kPa) Control feet HV feet
49.9 (15.4) 37.2 (23.4)
33.0 (13.6) 32.8 (13.6)
48.8 (13.8) 40.4 (19.5)
64.9 (14.8) 59.5 (19.9)
48.7 (14.2) 50.5 (18.9)
ppML (kPa) Control feet HV feet
29.7(13.4) 29.6 (15.6)
22.5 (8.4) 22.9 (8.9)
29.6 (11.9) 28.6 (14.6)
40.0 (7.6) 45.7 (14.0)
28.4 (8.5) 35.8 (13.9)
pPS (kPa) Control feet HV feet
17.4(9.5) 11.8 (13.0)
23.5 (14.1) 24.9 (14.2)
35.9 (12.6) 27.9 (17.8)
55.6 (16.5) 48.8 (20.2)
40.5 (16.1) 46.4 (20.4)
*
A significant group difference (p < 0.05).
M. Yavuz et al. / Gait & Posture 30 (2009) 257–259
259
observable alterations on the plantar surface and (ii) patients with metatarsalgia altered their gait to minimize pain. In fact, among all HV patients, individuals with foot pain tended to have shorter forefoot stance durations which may be attributed to selective alterations in gait. Limitations of the current study include the spatial resolution and overall size of the pressure–shear platform. Some clinical parameters such as the passive range of motion in the subtalar and talocrural joints were not included. This study has shown the potential of plantar shear distribution in feet with bunions. Assessment of plantar shear stress distribution might aid clinicians and researchers in better understanding the biomechanical functioning of the HV disorder and help test hypotheses that have previously eluded scientific validation.
Conflict of interest statement The authors hereby disclose no conflict of interest that would inappropriately influence this study. References
Fig. 1. Peak pressure and resultant shear stress profiles of: (a) a representative control subject (peak RES under the hallux) and (b) a representative hallux valgus subject (peak RES under MTHL). Data were visualized by the FootVis software (Infoscitex Inc., Waltham, MA).
patients pPS was under MTHL. Only in one control subject (7%), pPS occurred under MTHL. These observations indicate that there is also a shift in shear loading of the HV foot towards the lateral aspect of the plantar surface. In 43% of the HV patients (6 out of 14), peak pressure (PP) and peak resultant shear (RES) occurred at different plantar regions. This was similar to the findings in diabetic patients [15]. This finding along with previous results implicates that in individuals, whether a foot disorder is present or not, pattern of plantar shear distribution may deviate significantly from normal plantar loading pattern. Increased medio-lateral shearing of the hallux, which was hypothesized by Talbot et al. [8], was not observed in this study. There are two explanations for this outcome: (i) biomechanical changes in flexor tendons were not significant enough to create
[1] Phillips D. Biomechanics: hallux valgus and forefoot surgery. Churchill Livingstone; 1994. pp. 39–66. [2] Thomas S, Barrington R. Hallux valgus. Curr Orthop 2003;17:299–307. [3] Mays SA. Paleopathological study of hallux valgus. Am J Phys Anthropol 2005;126(2):139–49. [4] Schweitzer ME, Maheshwari S, Shabshin N. Hallux valgus and hallux rigidus: MRI findings. Clin Imaging 1999;23(6):397–402. [5] Saro C, Andren B, Fellander-Tsai L, Lindgren U, Arndt A. Plantar pressure distribution and pain after distal osteotomy for hallux valgus: a prospective study of 22 patients with 12-month follow-up. Foot 2007;17:84–93. [6] Lorei TJ, Kinast C, Klarner H, Rosenbaum D. Pedographic, clinical and functional outcome after Scarf osteotomy. Clin Orthop Relat Res 2006;451:161–6. [7] Hutton WC, Dhanendran M. The mechanics of normal and hallux valgus feet—a quantitative study. Clin Orthop Relat Res 1981;157:7–13. [8] Talbot KD, Brown TD, Saltzman CL. Hallucal flexor force direction change in hallux valgus. Foot Ankle Surg 1999;5:73–8. [9] Waldecker U. Metatarsalgia in hallux valgus deformity: a pedographic analysis. J Foot Ankle Surg 2002;41(5):300–8. [10] Stokes IA, Hutton WC, Stott JR, Lowe LW. Forces under the hallux valgus foot before and after surgery. Clin Orthop Relat Res 1979;142:64–72. [11] Kernozek TW, Elfessi A, Sterriker S. Clinical and biomechanical risk factors of patients diagnosed with hallux valgus. J Am Podiatr Med Assoc 2003; 93(2):97–103. [12] Sanders AP, Snijders CJ, van Linge B. Medial deviation of the first metatarsal head as a result of flexion forces in hallux valgus. Foot Ankle 1992;13(9): 515–22. [13] Yavuz M, Botek G, Davis BL. Plantar shear stress distributions: comparing actual and predicted frictional forces at the foot–ground interface. J Biomech 2007;40(13):3045–9. [14] McPoil TG, Cornwall MW, Dupuis L, Cornwell M. Variability of plantar pressure data. A comparison of the two-step and midgait methods. J Am Podiatr Med Assoc 1999;89(10):495–501. [15] Yavuz M, Erdemir A, Botek G, Hirschman GB, Bardsley L, Davis BL. Peak plantar pressure and shear locations: relevance to diabetic patients. Diabetes Care 2007;30(10):2643–5.
Contents lists available at ScienceDirect
Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost
Short communication
Forefoot plantar shear stress distribution in hallux valgus patients Metin Yavuz a,b,c, Vincent J. Hetherington c, Georgeanne Botek d, Gordon B. Hirschman e, Lynn Bardsley e, Brian L. Davis a,* a
Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH 44195, USA Department of Chemical & Biomedical Engineering, Cleveland State University, Cleveland, OH 44115, USA c Ohio College of Podiatric Medicine, Independence, OH 44131, USA d Department of Orthopedic Surgery, Cleveland Clinic, Cleveland, OH 44195, USA e Infoscitex Corporation, Albany, NY 12205, USA b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 2 October 2007 Received in revised form 29 April 2009 Accepted 4 May 2009
Background: Hallux valgus is a common foot disorder often experienced with secondary callosities and metatarsalgia. Many factors including improper shoes might be responsible in the pathophysiology of the problem. Hallux valgus deformity has been shown to alter the biomechanics of the whole foot rather than affecting only the great toe. Due to changes in the biomechanical functioning of the first ray, other regions of the forefoot area have been shown to bear abnormal loads with increased vertical loading on medial, central and lateral forefoot regions. The purpose of this study was to investigate the pattern of forefoot plantar shear loading in hallux valgus patients and compare these results with those of control subjects. Methods: A total of 28 subjects were recruited for the study of which 14 were clinically diagnosed with hallux valgus. A custom built platform was used to collect peak pressure and shear data. A repeated measures analysis of variance was used to analyze the recorded data. Findings: Antero-posterior shear was significantly lower in the deformity group (p < 0.05). The lateral forefeet of the patients, however, experienced slightly higher shear loads (p > 0.05). Interpretation: Propulsive shear force generation mechanism under the medial forefoot was impaired in the disorder group. In general, shear loading of the plantar feet shifted laterally. Previously hypothesized higher medio-lateral shear magnitudes under the hallux were not confirmed. ß 2009 Published by Elsevier B.V.
Keywords: Biomechanics Foot Hallux valgus Plantar stresses Plantar shear Instrumentation
1. Introduction Hallux abductovalgus, or shortly hallux valgus, is a degenerative joint disease that results in the lateral deviation of the big toe and medial deviation of the first metatarsal bone. Hallux valgus (HV) often leads to pain and limited mobility in patients [1]. Many factors might contribute to the etiology of HV including a potential genetic predisposition, altered biomechanics of the first ray and shoes [2–4]. Patients with HV may experience complications such as metatarsalgia, plantar callosities, hammer toe deformities and impaired quality of life [5,6]. Load bearing capability of the hallux is perturbed in HV, in addition to the unfavorable loading conditions at other regions of
* Corresponding author at: Department Biomedical Engineering (ND20), Orthopedic Research Center, Cleveland Clinic, 9500 Euclid Ave, Cleveland, OH 44195, USA. Tel.: +1 216 444 1055; fax: +1 216 444 9198. E-mail address: [email protected] (B.L. Davis). 0966-6362/$ – see front matter ß 2009 Published by Elsevier B.V. doi:10.1016/j.gaitpost.2009.05.002
the forefoot [7,9–11]. A number of reports explored plantar pressure distribution in order to reveal the foot function in HV patients. However being restricted to only uni-axial stress distribution, one cannot derive a comprehensive biomechanical evaluation of the foot in disorders like HV. A number of investigators, directly or indirectly, hypothesized an increase in local shear stress under the hallux, but this was never verified [8,12]. A particular theory states that due to force changes in flexor tendons traversing the first phalangeal– metatarsal joint in HV patients, medio-lateral shear forces under the great toe should increase [8]. The purpose of this study was to examine plantar shear stress distribution in patients with HV and compare findings with that of healthy control subjects. It was hypothesized that the propulsive shear loading under the hallux and first metatarsal head (MTH) would be reduced due to the impaired dorsiflexion capability of the first metatarsophalangeal joint. Also expected, was that hallux would experience higher medio-lateral shear forces.
M. Yavuz et al. / Gait & Posture 30 (2009) 257–259
258 Table 1 Characteristics of the subjects.
No. of subjects Gender Age (years) Body mass index
HV
Control
14 13 females, 1 male 55.2 14.7 (25–77) 26.8 4.8 (19.1–35.8)
14 9 females, 5 males 53.6 18.7 (24–82) 24.6 3.8 (19.1–33.7)
Values are presented as the mean standard deviation, with the range in parentheses.
instance of push-off phase and the initial phase of the forefoot contact phase. Due to a small sample size, Anderson–Darling normality tests were performed. As the results indicated normal distribution, data were analyzed by implementing a repeated measures ANOVA. Pairwise comparisons of group-site means were run for each variable. Tukey–Kramer test was used for this purpose. Age, BMI and stance duration of the subjects were analyzed by two-sample t-tests. p values smaller than 0.05 were considered significant. Minitab (Minitab Inc., PA) software was used to perform the statistical analyses.
2. Methods
3. Results
Twenty-eight volunteers (Table 1) were recruited. Of the recruited subjects, fourteen were clinically diagnosed with HV deformity (HV group), whereas the other 14 were deformity free volunteers (control group). Foot pain was not an inclusion criterion for HV patients, although almost half of the patients had antalgic gait. Each participant signed an informed consent form approved by the Institutional Review Board of the Cleveland Clinic. Radiography results were available for nine of the HV patients. Hallux valgus angle (HVA) was determined by calculating the intersection angle between the first metatarsal and proximal phalanx. The angle between the longitudinal axes of the first and second metatarsal was noted as the intermetatarsal angle (IMA). A custom-built pressure–shear distribution device consisting of 80 transducers arranged in a 10 8 array was set flush with the ground. Each sensor measured 1.25 cm 1.25 cm, generating a surface area of 1.56 cm2. Further specifications of the platform have been explained elsewhere [13]. Only forefeet of the subjects were assessed since HV is forefoot specific. The two-step method was preferred in data acquisition [14]. Subjects were allowed to walk at self-selected speeds. The tests were carried out for only one (surgery free) foot, and five trials were obtained for each subject. Only three trials in which the forefoot was properly placed on the device were selected. A Matlab (Mathworks Inc., MA) code was written to mask five anatomical regions of the foot; hallux, lesser toes, 1st metatarsal head (MTH1), central metatarsal heads (MTHC) and lateral metatarsal heads (MTHL). For each foot site, five parameters were determined; peak pressure (PP), peak resultant shear stress (RES), peak-to-peak antero-posterior shear (ppAP), peak-to-peak mediolateral shear (ppML) and peak propulsive shear (pPS). Stance duration was calculated as the time difference between the last
Mean age and BMI of the subject groups were not significantly different (p > 0.05). HV patients had a mean HVA of 25.68 (9.08) and IMA of 14.18 (3.28). Statistical analysis yielded a significant difference (p = 0.013) in only peak-to-peak antero-posterior shear (ppAP) variable between the groups. No significant group–site interaction was recorded. Table 2 displays the mean values of pressure and shear variables for both groups. ppAP showed a 25% and 17% decrease under the hallux and MTH1, respectively, and a 4% increase under MTHL in the HV group. Peak propulsive shear stress (pPS) was decreased by 22% and 32%, respectively, under the MTH1 and hallux of the disorder group. HV group experienced 15% more pPS than the control group at MTHL region. However, all of these differences were not significant (p > 0.05). Surprisingly, peak-to-peak mediolateral shear (ppML) was similar under the hallux in both groups (p > 0.05). Stance duration for control group was recorded as 0.69 s which was a little faster than HV group with 0.72 s. The difference was not statistically different (p = 0.66). 4. Discussion Previous pressure assessment studies in HV patients suggest a vertical loading shift towards the lateral forefoot [7,9–11]. The results of this study supported this finding. Shear stresses were also slightly higher in the MTHL area of the feet with HV. Moreover, while no control subject had their peak shear values occur at the lateral aspect of the forefoot; this was the case in 4 of the 14 HV patients (Fig. 1). Peak propulsive shear stress (pPS) occurred at MTHC in 86% of the control subjects. MTHC experienced the maximal pPS (48.8 kPa) in 57% of the HV patients. In 29% of the
Table 2 Mean (standard deviation) pressure and shear values for control and HV groups. Hallux
Lesser toes
MTH1
MTHC
MTHL
PP (kPa) Control feet HV feet
291.4(110.6) 276.0(141.1)
116.0 (50.3) 111.6 (48.1)
276.1 (86.8) 314.1 (171.8)
428.8 (100.6) 446.7 (224.8)
217.6 (72.2) 262.0 (123.5)
RES (kPa) Control feet HV feet
48.0(15.9) 44.7 (24.8)
36.8 (14.2) 35.6 (13.1)
43.3 (14.3) 38.5 (20.0)
60.3 (15.9) 57.3 (19.0)
46.1 (12.9) 49.2 (20.1)
ppAP* (kPa) Control feet HV feet
49.9 (15.4) 37.2 (23.4)
33.0 (13.6) 32.8 (13.6)
48.8 (13.8) 40.4 (19.5)
64.9 (14.8) 59.5 (19.9)
48.7 (14.2) 50.5 (18.9)
ppML (kPa) Control feet HV feet
29.7(13.4) 29.6 (15.6)
22.5 (8.4) 22.9 (8.9)
29.6 (11.9) 28.6 (14.6)
40.0 (7.6) 45.7 (14.0)
28.4 (8.5) 35.8 (13.9)
pPS (kPa) Control feet HV feet
17.4(9.5) 11.8 (13.0)
23.5 (14.1) 24.9 (14.2)
35.9 (12.6) 27.9 (17.8)
55.6 (16.5) 48.8 (20.2)
40.5 (16.1) 46.4 (20.4)
*
A significant group difference (p < 0.05).
M. Yavuz et al. / Gait & Posture 30 (2009) 257–259
259
observable alterations on the plantar surface and (ii) patients with metatarsalgia altered their gait to minimize pain. In fact, among all HV patients, individuals with foot pain tended to have shorter forefoot stance durations which may be attributed to selective alterations in gait. Limitations of the current study include the spatial resolution and overall size of the pressure–shear platform. Some clinical parameters such as the passive range of motion in the subtalar and talocrural joints were not included. This study has shown the potential of plantar shear distribution in feet with bunions. Assessment of plantar shear stress distribution might aid clinicians and researchers in better understanding the biomechanical functioning of the HV disorder and help test hypotheses that have previously eluded scientific validation.
Conflict of interest statement The authors hereby disclose no conflict of interest that would inappropriately influence this study. References
Fig. 1. Peak pressure and resultant shear stress profiles of: (a) a representative control subject (peak RES under the hallux) and (b) a representative hallux valgus subject (peak RES under MTHL). Data were visualized by the FootVis software (Infoscitex Inc., Waltham, MA).
patients pPS was under MTHL. Only in one control subject (7%), pPS occurred under MTHL. These observations indicate that there is also a shift in shear loading of the HV foot towards the lateral aspect of the plantar surface. In 43% of the HV patients (6 out of 14), peak pressure (PP) and peak resultant shear (RES) occurred at different plantar regions. This was similar to the findings in diabetic patients [15]. This finding along with previous results implicates that in individuals, whether a foot disorder is present or not, pattern of plantar shear distribution may deviate significantly from normal plantar loading pattern. Increased medio-lateral shearing of the hallux, which was hypothesized by Talbot et al. [8], was not observed in this study. There are two explanations for this outcome: (i) biomechanical changes in flexor tendons were not significant enough to create
[1] Phillips D. Biomechanics: hallux valgus and forefoot surgery. Churchill Livingstone; 1994. pp. 39–66. [2] Thomas S, Barrington R. Hallux valgus. Curr Orthop 2003;17:299–307. [3] Mays SA. Paleopathological study of hallux valgus. Am J Phys Anthropol 2005;126(2):139–49. [4] Schweitzer ME, Maheshwari S, Shabshin N. Hallux valgus and hallux rigidus: MRI findings. Clin Imaging 1999;23(6):397–402. [5] Saro C, Andren B, Fellander-Tsai L, Lindgren U, Arndt A. Plantar pressure distribution and pain after distal osteotomy for hallux valgus: a prospective study of 22 patients with 12-month follow-up. Foot 2007;17:84–93. [6] Lorei TJ, Kinast C, Klarner H, Rosenbaum D. Pedographic, clinical and functional outcome after Scarf osteotomy. Clin Orthop Relat Res 2006;451:161–6. [7] Hutton WC, Dhanendran M. The mechanics of normal and hallux valgus feet—a quantitative study. Clin Orthop Relat Res 1981;157:7–13. [8] Talbot KD, Brown TD, Saltzman CL. Hallucal flexor force direction change in hallux valgus. Foot Ankle Surg 1999;5:73–8. [9] Waldecker U. Metatarsalgia in hallux valgus deformity: a pedographic analysis. J Foot Ankle Surg 2002;41(5):300–8. [10] Stokes IA, Hutton WC, Stott JR, Lowe LW. Forces under the hallux valgus foot before and after surgery. Clin Orthop Relat Res 1979;142:64–72. [11] Kernozek TW, Elfessi A, Sterriker S. Clinical and biomechanical risk factors of patients diagnosed with hallux valgus. J Am Podiatr Med Assoc 2003; 93(2):97–103. [12] Sanders AP, Snijders CJ, van Linge B. Medial deviation of the first metatarsal head as a result of flexion forces in hallux valgus. Foot Ankle 1992;13(9): 515–22. [13] Yavuz M, Botek G, Davis BL. Plantar shear stress distributions: comparing actual and predicted frictional forces at the foot–ground interface. J Biomech 2007;40(13):3045–9. [14] McPoil TG, Cornwall MW, Dupuis L, Cornwell M. Variability of plantar pressure data. A comparison of the two-step and midgait methods. J Am Podiatr Med Assoc 1999;89(10):495–501. [15] Yavuz M, Erdemir A, Botek G, Hirschman GB, Bardsley L, Davis BL. Peak plantar pressure and shear locations: relevance to diabetic patients. Diabetes Care 2007;30(10):2643–5.