Effect of Flat Foot Deformity on Strength of Selected Lower Limb Muscles: Cross Sectional Observational Study

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1 Med. J. Cairo Univ., Vol. 85, No. 7, December: , Effect of Flat Foot Deformity on Strength of Selected Lower Limb Muscles: Cross Sectional Observational Study MAYADA A. MAHMOUD, M.Sc.* and OMAIMA M.A. KATTABEI, Ph.D.** The Departments of Basic Sciences* and Basic Science for Physical Therapy**, Faculty of Physical Therapy, Cairo University Abstract Objective: The purpose of this study was to investigate the effect of flat foot deformity on strength of invertor and evertor muscles. Design : Observational study. Setting: The Faculty of Physical Therapy, Cairo University. Material and Methods: Sixty subjects were classified in to two groups each group contains thirty subjects, age range from years. All subjects were assessed for flat foot by foot print and measure inversion, eversion peak and average torque at 60º/sec by Bidoex system three dynamometer. Results: There was no significant difference between two groups in their ages, weight, height and BMI where their F and p-values were (2.359, 0.104), (0.845, 0.435), (0.340, 0.714) and (2.359, 0.104) respectively. Measuring evertors peak torque revealed that there was no significant difference among the 2 groups at angular velocity 60 /sec as F-value was (0.432) and p-value was (0.651). Measuring invertors peak torque revealed that there was no significant difference among the 2 groups at angular velocity 60 /sec as F-value was (0.149) and p-value was (0.862). Conclusions : The results of this study suggest that there is no statistical difference between flat foot deformity and strength of invertor and evertor muscles. Key Words: Flat foot Strength Invertor muscles Evertor muscles. Introduction FLAT feet (also called pes planus or fallen arches) is a postural deformity in which the arches of the foot collapse, with the entire sole of the foot coming into complete or near-complete contact with the ground. Some individuals (an estimated 20-30% of the general population) have an arch that simply never develops in one foot (unilaterally) or both feet (bilaterally) [1]. Correspondence to: Dr. Mayada A. Mahmoud, The Department of Basic Sciences, Faculty of Physical Therapy, Cairo University, Egypt Pes planus may occur in up to 20% of adults, many of whom are flexible and have no resulting difficulties [2]. Pes planus is common in young children, who typically have a minimal longitudinal arch with forefoot pronation and heel valgus on weight-bearing. This is present to a greater degree in children of African ethnicity [3]. Studies suggest around 45% of children aged 3-6 years, with around 5.5º of valgus, although the prevalence decreases with age. The prevalence of pathological pes planus in this group was less than 1%. Higher prevalence was associated with obesity and with male gender. Most children develop a normal longitudinal arch by the age of 10 years. There is a functional relationship between the structure of the arch of the foot and the biomechanics of the lower leg. The arch provides an elastic, springy connection between the forefoot and the hind foot. This association safeguards so that a majority of the forces incurred during weight bearing of the foot can be dissipated before the force reaches the long bones of the leg and thigh [4]. Flat footedness tends to run in families, which suggests it is an inherited condition, particularly in cases of flexible flatfoot and rigid flatfoot. Flatfoot also has been associated with the metabolic disease rickets. Adult-acquired flatfoot affects women four times as often as men. It also tends to occur in older adults, with the average age being about 60 [5]. Pes planus, collapse of the medial longitudinal arch everts the calcaneus in relation to the talus, so lead to foot pronation so the transmission of force medially occur as the weight is transferred forward on the working foot [5]. In the majority of cases of flexible flatfoot, no complications emerge. When complications occur, 2433

2 2434 Effect of Flat Foot Deformity on Strength of Selected Lower Limb Muscles they usually involve foot pain and fatigue. Untreated rigid and adult-acquired flatfoot can lead to severe pain and permanent foot deformity [1]. The link between variations in foot posture and increased risk of lower limb injury may arise from abnormal muscle activity. For example, it has been suggested that the flat-arched foot relies on additional muscular support during gait, and that fatigue of these controlling strengthening programs muscles with exercise can result in the development of various injuries such as tibial stress fractures [6]. The association between strength and flatfoot kinematics may guide treatment such as the use of targeting the tibialis posterior muscle [7]. Assessment of muscle strength is a vital component of diagnosing and treating patients in which muscle weakness is present [8]. Since there is lack in research concerning the relation between flat foot and muscle strength of invertors and evertor muscles, so the current study was conducted to investigate the effect of flat foot deformity on the strength of selected lower limb muscles( invertors and evertor muscles). Material and Methods Sixty subjects selected from both gender were participated in the study after signing institutionally approved consent form prior to data collection, they were recruited from the students, employees and the out clinic of Faculty of Physical Therapy with their age from years old [9]. The study was done from May 2016 to December Exclusive criteria, the subjects were excluded if they had: Musculoskeletal disorders that influence standing and walking, history of neurologic disorders, lower limb surgery. The subjects divided in to two groups, thirty patients with a diagnosis of flat foot involving the ankle(s) and thirty healthy subjects (control group) matched for age, gender, body mass index were studied. Inversion and eversion were evaluated in all subjects on system 3 pro isokinetic dynamometer. The variables were compared between the flat foot and control groups and the invertor/evertor muscle strength ratio, peak torque and total work were determined. Instrumentation 1- Methods used to differentiate between flat foot and normal foot: Demographic information was obtained, and the presence of flatfoot determined by footprint analysis and grading according to Denis flatfoot staging. The plantar footprint was classified according to Denis [10] into three grades of flatfoot: Grade 1, in which the support of the lateral edge of the foot is half of that of the metatarsal support; grade 2, in which the support of the central zone and forefoot are equal; and grade 3, in which the support in the central zone of the foot is greater than the width of the metatarsal support Fig. (1). We defined children who displayed a second or third grade plantar footprint as flatfooted [8]. N N = Normal 1 = Grade 1 2 = Grade 2 3 = Grade 3 Fig. (1): The plantar footprint was classified into three grades of flatfoot: Grade 1, the support of the lateral edge of the foot is half of that of the metatarsal support; grade 2, the support of the central zone and forefoot are equal; and grade 3, the support in the central zone of the foot is greater than the width of the metatarsal support. Though there are various methods to evaluate the arch of the foot (direct, arthropometric and radiographic; indirect, footprint and photographic analysis) there have been many reports published concerning the use of footprint analysis for population screening and to classify flatfeet. Footprint analysis is easy to perform, readily available, economical, and reliably indicates the shape of the MLA [11] 2- Isokinetic dynamometer to measure peak torque: Biodex system 3 pro Isoklinetic dynamometer (Biodex Medical INC., Sherley, New York, USA), was used to measure strength of invertor and evertor muscles. Maximal isokinetic strength is usually determined by peak torque. In the Biodex manual (Biodex Medical Systems, Inc., Shirley, New York, USA) it is suggested that work is a better indicator of the functional ability of a joint than peak torque, since the muscle must maintain force throughout the range of motion as opposed to force in one instant. The measurement of both peak torque and work in the same individual could therefore address different aspects of neuromuscular performance [13].

3 Mayada A. Mahmoud & Omaima M.A. Kattabei 2435 Procedure: Subjects performed a five minute warm up of general range of motion and stretching exercises for the joint movements of inversion/eversion. After the warm up, they were appropriately positioned on the isokinetic dynamometer which was calibrated before testing each subject. All subjects were tested without shoes. Each subject was seated in the adjustable chair of the Dynamometer and the leg being tested was elevated by a support arm under the knee. Two diagonal standard straps stabilized the trunk and one strap secured the hip. The arms were crossed over the chest, and the contralateral foot was placed on a support arm attached to the chair. The subject's ankle was placed on the foot plate, and the foot was secured with two straps. For each subject, the attachments of the dynamometer were readjusted so that center of motion of the lever arm was aligned as accurately as possible with the slightly changing axis of the joint. The stability of the foot on the foot plate was enhanced with a rubber heel cup, and adjustable thermoplastic stays were positioned on the medial and lateral borders of the foot. Statistical analysis: Data analysis was performed using the SPSS 20.0 for Windows statistical software. The normality of data distribution was tested through the Shapiro-Wilk test. Descriptive data for participants, characteristics and dependent variables was calculated as mean ± SD. 2 X 3 mixed model ANOVA was carried out to compare the two groups (between-subject effect) at each of the velocity conditions (within-subject effect) for each group for the tested variable (peak torque of invertor and evertor muscles). Furthermore, testing for the interaction effects between both independent variables was conducted. The alpha level of significance was adopted at Results Evertors peak torque: I- Between group: To determine the difference in the mean value of the peak torque of evertor muscles between the 2 groups analysis of variance (ANOVA) test was performed. It revealed that there was no significant difference among the 2 groups at angular velocity 60 /sec as F-value was (0.432) and p-value was (0.651). Table (1): Results of ANOVA among the three groups for evertors peak torque. Evertors peak torque 60 /sec: Between groups Within groups Total SS MS F p-value S NS *SS: Sum of Square. P: Probability. S: Significant. MS : Mean Square. S: Significance. Fig. (2): Patient position and stabilization on isokinetic device for inversion/eversion test protocol. The dynamometer orientation, tilt, and seat orientations were kept at 0º, 50º, and 90º during eversion/inversion. The end range setting was standardized for all subjects from 40º eversion to 45º inversion. Each subject performed three to five sub maximal warm up repetitions before each test. Then bilateral isokinetic (concentric/concentric) eversion/inversion measurements were performed within the protocol of 60º/s (five repetitions). Between the two sessions, the subjects had a one minute period of rest. Vocal encouragement during the tests was consistent and standardized. Peak torque/body weight was obtained [12,13]. Invertors peak torque: II- Between group: To determine the difference in the mean value of the peak torque of invertor muscles between the 2 groups analysis of variance (ANOVA) test was performed. It revealed that there was no significant difference among the 2 groups at angular velocity 60 /sec as F-value was (0.149) and p-value was (0.862). Table (2): Results of ANOVA among the two groups for invertors peak torque. Invertors peak torque 60 /sec: Between groups Within groups Total SS MS F p-value S NS

4 2436 Effect of Flat Foot Deformity on Strength of Selected Lower Limb Muscles Discussion The current study was conducted to investigate the effect of flat foot deformity on strength of invertor and evertor muscles of subtalar joint was studied. Sixty subjects participated in the study with age ranged from 18 to 47 years old. Subjects were assigned into two equal groups, each group consists of 30 subjects. Group (A) (the study group) with flat foot and group (B) (the control group) normal subjects. Foot pronation is the most common foot disorders that can be used as an example to illustrate how alterations in its function can be followed by a series of biomechanical changes that produce a wide variety of signs and symptoms through the interrelated structures and systems of the body. As the pronated foot presents with multiple site fixations that could include the posterior subtalar joint, the calcaneotalonavicular complex, the cuboid, ankle joint and the first ray. Weight will be borne on the medial structures and there will be an internal rotation of the entire lower extremity [14]. When the plantar vault is functioning well, both rotational and shock forces are maintained within tolerable limits. With arch collapse and/or asymmetry of biomechanical function, increased forces are transmitted and eventually cause joint dysfunction and breakdown in the knees, hips, sacroiliac joints and spine [15]. In this study, Denis footprint method was used for evaluation of the flatfoot, this is a valid method to differentiate between flat foot and normal foot. In this study Biodex system 3 pro Isokinetic dynamometer was used to asses peak torque of invertors and evertor muscles at 60º/sec. The rationale for the use of this evaluation procedure was based on the following considerations. It was cocluded from the results of this study that there was no significant difference between persons with flat feet deformity and normal persons concerning strength of invertor and evertor muscles of subtalar joint revealed by measuring peak torque at angular velocity 60º/sec using isokinetic dynamometer system 3 sherly NY. The findings of this study might be attributed to: This study was performed in open kinetic chain, in other words in Non-Weight Bearing position (NWB) where there was no stress or tension on any structure, so the effect of prolonged excessive pronation in individuals with flat foot didn't have an apparent effect on peak torque of tested muscles. Structural malalignment that resulted from flat foot deformity was a source of biomechanical stress to the bones, muscles, ligaments and nerves which occur in a Weight Bearing (WB) position that result in abnormal tension, torque and compressive forces. The previous changes might occur in closed kinetic chain, where the feet play a critical role by providing support, mobility and shock absorption during standing, walking or running. A possible explanation for this may be the degree of the severity of the flat foot deformity as when the severity of the flat foot increases the biomechanical changes that can result from this foot deformity will increase [16]. Another explanation for the lack of changes in the strength of muscles of invertors and evertors may be the age of the study group as the age range included was from years old and it was reported that most subjects with flat feet are generally asymptomatic until the third or forth decade of life and as the person matures, the foot cannot support the increased body weight and the deformity progress leading to more biomechanical changes [17]. In a study done to see the effect of strength and proprioception training on eversion to inversion strength ratios in subjects with unilateral functional ankle instability: There were no significant differences in average torque and peak torque E/I ratios of the functionally unstable ankle for any of the groups after training compared with before [18]. The information gained in this study may be useful for diagnosis, planning, prognosis, surgical procedure and rehabilitation program of treatment flat foot. Conclusion: The results of this study suggest that there is no relationship between flat foot deformity and strength of invertor and evertor muscles. References 1- ASHWINI C., VIDIT P., EROHIT K. and SUDIPTA P.: Screening of Body Mass Index and Functional Flat Foot in Adult an Observational Study, Int. J. Physiother. Res., 3 (3): , CHARSCHAN D.: Understanding Lower Body Mechanics andits Relationship to Chiropractic principles. Dynamic Chiropractic, 16 (5): , 1998.

5 Mayada A. Mahmoud & Omaima M.A. Kattabei DENIS A.: Pied plat valgus statique. Encyclopedie Medico- Chirurgicale Appareil Locomoteur. Editions Techniques, Paris, foot.com ; The Foot and Ankle Clinic.com. 5- GEORGE S., HYLTON B., MENZ and KARL B.: Foot posture influences the electromyographic activity of selected lower limb muscles during gait Journal of Foot and Ankle Research Journal of Foot and Ankle Research, doi: / , HALL J.: Basic Biomechanics, 4 th edition, the biomechanics of the human lower extremity, Mc Graw Hill, 254, JANKOWICZ-SZYMANSKA A. and MIKOLAJCZYK E.: Effect of excessive body weight on foot arch changes in preschoolers a 2-year follow-up study. J. Am. Podiatr. Med. Assoc., 105 (4): doi: / , JEN-HUEI C., SHENG-HAO W., CHUN-LIN K., HSIAN CHUNG S., YA-WEN H. and LEOU-CHYR L.: Prevalence of flexible flatfoot in Taiwanese school-aged children in relation to obesity, gender, and age 169, European Journal of Pediatrics, , KEITH A. INNES.: Gait Analysis-Implications for Diagnosis, Treatment, and Rehabilitation, Pressure distribution in Mortons foot structure. Med. Sci., 83: 251-4, MICKLE K.J., STEELE J.R. and MUNRO B.J.: The feet of overweight and obese young children: Are they flat or fat? Obesity (Silver Spring), 14 (11): , PFEIFFER M. and KOTZ R., LEDL T., et al.: Prevalence of flat foot in preschool-aged children. Pediatrics, 118 (2): 634-9, Pes planus/flat foot; WWW. Wheeless' Textbook of Orthopaedics.com. 13- ROTHBART B. and ESTABROOK L.: Excessive pronation: A major biomechanical determinant in the development of chondromalacia pelvic lists. J. Manipul. Physiol. Ther., 11 (5): 373-9, STEVEN D., STOVITZ M. and COETZEE C.: Hyperpronation and Foot Pain. The Physician and Sport Medicine, 32: 8, SCAND J.: Reliability of Isokinetic Ankle Dorsiflexors Strength Measurements in Healthy Young Men and Women. Rehab. Med., 31: , T.W. KAMINSKI, B.D. BUCKLEY, M.E. POWERS, T. J. HUBBARD and C. ORTIZ B.R.: Effect of strength and proprioception training on eversion to inversion strength ratios in subjects with unilateral functional ankle instability. J. Sports. Med., 37: , THOMAS W. KAMINSKI and GEOFF C. DOVER: Reliability of Inversion and Eversion Peak- and Average- Torque Measurements From the Biodex System 3 Dynamometer. 18- CHRISTOPHER NEVILLE, ADOLPH S. FLEMISTER and JEFF R. HOUCK: Deep Posterior Compartment Strength and Foot Kinematics in Subjects With Stage II Posterior Tibial Tendon Dysfunction. Foot Ankle Int., 31 (4): doi: /FAI , 2010.