Prevalence of lower limb deformities among primary school students

Lower limb deformities could affect child's quality of life and may worsen with time. This work aims to study the prevalence of lower limb deformities among primary school students in our governorate. This cross-sectional descriptive study was carried out on 4689 students attending 12 public primary schools during the academic year 2019–2020.Complete clinical examination was done for picking of cases of genu varum, genu valgum, genu recurvatum, flat foot, pes cavus, hallux valgus, in-toeing, and lower limb discrepancy, and x-ray on both feet, pelvis, and full-length lower limb was requested. This cross-sectional descriptive study included 4689 students. The prevalence of lower limb (LL) deformities was 16.61%. One hundred twenty-three (2.62%) children had a positive history of musculoskeletal pain, 0.09% had genu varum, 0.11% had genu valgum, 0.75% had Genu recurvatum, 0.03% had LL discrepancy, 13.86% had flexible flat foot, 1.22% had rigid flat foot, 0.23% had pes cavus, 1.04 % had in-toeing, 0.06% had hallux varus, and 0.11% had hallux valgus. Lower limb deformities are a considerable problem in primary school students that need early diagnosis because it could affect child’s future, health, and career. Further studies are needed to investigate spinal deformity, vit D level, calcium level, foot wear, and school bag weight as hidden factors.


Background
Lower limb (LL) deformities are common among pediatric population. Though some of them are typical for some periods of growth and development, others could result in serious health problems and reduced quality of life [1]. Deformities could start in childhood and their harmful effects may continue till adulthood [2]. LL deformity causes mechanical load maldistribution and mass center functional alterations and requires adaptation to the new body scheme creating many vectors across multiple joints [3]. Prevalence of postural deformities has increased significantly over the past decades due to life pattern modification ranging from 10 to 70%. Physical inactivity, playing electronic games, heavy backpacks, and prolonged unhealthy diet have been demonstrated in this regard [4].Genu varum predisposes an individual to various injuries and weakening of the articular cartilage as force line shifts farther medially away from joint center generating a medial joint reaction force that is nearly three and a half times that of the lateral compartment being a risk factor for the development of the patellofemoral pain syndrome in athletes and osteoarthritis later in life [5].New-born is usually described as having physiological genu valgum, around 18 to 24 months; the tibiofemoral angle (TFA) variation aligns to 0°then reaches the maximum deviation value of 12°at 3 years and decreases until it stabilizes at 5 to 6°by 6 or 7 years of age [6], so in children aging 2 to 6 years, valgus knee is normal within certain limits of knee angle, therefore being characterized as physiological, and most of children presenting this condition at these ages have spontaneous correction [7]. Foot posture acts a pivotal role in lower limb performance. Flexible flat foot (FFF) fade with non-weight-bearing and infrequently requires treatment, even though overuse may cause pain meanwhile rigid FF occurs due to acquired or congenital factors as collagen disorders, trauma, spastic conditions, or neuromuscular conditions [8]. Hallux valgus may be induced by genetics, pes planus, metatarsus primus varus, first metatarsal length, and hypermobility of the metatarsocuneiform joint. Also, unfit shoes seem to be a major extrinsic factor [9]. Lower limb (LL) discrepancy is one of the common musculoskeletal deformities which may be complicated by scoliosis [10]. In-toeing is caused by a rotational variation anywhere in the lower extremity that causes the foot to point inward like metatarsus adductus, internal tibial torsion, and femoral anteversion [11]. This work aims to study the prevalence of lower limb deformities among primary school students in our governorate.

Study design
This cross-sectional descriptive study was carried out on 4689 students attending 12 public primary schools during the academic year 2019-2020. Students with a known history of rheumatic fever, juvenile idiopathic arthritis, juvenile dermatomyositis, juvenile systemic lupus erythematosus, lower limb weakness, or paralysis were excluded. A written consent was obtained from the parents of each student. Permission was gotten from the Ministry of Education. Ethical committee of Faculty of Medicine of our university approved this study.

Sample size determination
In total, 707,503 primary school children were registered as students in private and government schools by the local government school authority bureau. The required sample size was calculated using Epi Info software version 7.0 (Centers for Disease Control and Prevention, USA) and was based on this registered population. The following assumptions were used to determine the sample size based on single population proportion: prevalence of 50% since there is a widely variable prevalence rate in epidemiological studies, confidence level of 95%, and design effect of 1 required sample size was n = 384.
Sample size was calculated using Epi Info software version 7.0 (Centers for Disease Control and Prevention, USA).

Clinical assessment
Our students' demographic data were documented; they were subjected to full history taking and thorough clinical examination. Musculoskeletal symptoms in different body regions were assessed using an Arabic translation of 1st part of the standardized Nordic questionnaires for musculoskeletal symptoms [12]. Their heights and weights were assessed in a standing position with light cloths. According to the Centers for Disease Control and Prevention (CDC) body mass index (BMI) calculator for children and teens, BMI was calculated as follows: weight (kg) / height squared (m 2 ). It was then used to find the corresponding BMI-for-age percentile on a growth chart for the child's age and sex, and the children were categorized as underweight and normal weight [13]. Our students were evaluated from anterior, posterior, medial, and lateral aspects. Using a goniometer, lateral tibiofemoral angle (lateral TFA) was measured. With both knees or ankles touching using a tape, intercondylar (ICD) and intermalleolar (IMD) distances were measured. Intermalleolar distance in our students age group up to 8 cm, intercondylar distance up to 5 cm, and tibiofemoral angle up to 12°are documented as normal [14]. From the inferior aspect of the anterior superior iliac spine (ASIS) to the inferior aspect of the medial malleolus, the actual limb length was measured [15]. To measure hindfoot valgus, the angle between longitudinal axes of the Achilles tendon and calcaneus was used [16]. Longitudinal arch angle (LAA) defined as the superior angle formed by two vectors: one passing through the midpoint of the medial malleolus to the navicular tuberosity and the other passing through the midpoint of the medial aspect of the first metatarsal head to the navicular tuberosity [17]. If the child's plantar arch appeared flat and his or her heel was valgus, the child was asked to stand on tiptoes. In the tiptoes test, the absence of heel inversion indicates a rigid FF, while the disappearance of the collapse of the arch of the foot and the valgus of the rear foot indicates FFF [18]. Detection of increase in the medial angle between the long axes of the first metatarsal and the proximal phalanx of the great toe implied a hallux valgus deformity [19].

Radiological investigations
Lateral weight-bearing x-ray of the feet was done for cases with flat foot, anteroposterior (AP) view of the pelvis for cases of in-toeing and limb discrepancy, and fulllength lower limb anteroposterior x-ray films were taken for cases of limb discrepancy or knee deformity.

Statistical analysis
All data were tabulated, coded, and analyzed using STATA/SE version 11.2 (College Station, TX). The collected data were tabulated as mean ± standard deviation (SD), range (for numerical data) and frequency and percentage (for categorical data). Comparisons between the different study groups were performed using the Student t-test (t) to compare the groups regarding the numerical data. The chi-square test (χ 2 ) or the Fisher exact test (FET) was used to compare the categorical data as appropriate. A statistical significance is considered when a P-value was ≤ 0.05.

Discussion
This study explored FF in 15.08% of school children in close to the result of Sadeghi et al. [20] being 17% of 667 Iranian children. Our study demonstrated that there was a higher prevalence in males with a statistically significant difference in similarity to Kharbuja and Dhungel [21] in their study of 5-10 years Nepalese children despite Bogut et al. [22] denied any relation between gender and flat foot in their study of 426 Slavonian children of the same age group. This contradiction may be due to their small sample size. Moreover, we identified a highly significant relation between FF and age in similarity to Alsuhaymi et al. [7], but Hazzaa et al. [23] concluded insignificant relation in their study on 150 children only. This work emphasized a highly significant relation between flat foot and BMI in similarity with Suciati et al. [24] and Chen et al. [25]. We evinced a highly significant  relation between FF and lower extremity pain in line with Abich et al. [26] in their study on Ethiopian children. Pain could be argued to altered stress distribution on the lower extremity parts. Noteworthy, FFF and rigid FF were 13.86% and 1.22%, respectively, and accounted for 91.94% and 8.06% of the positive cases, respectively, so we were close to Ali et al. [27], who found the prevalence of FFF in Pakistani children was 89.6%, and prevalence of rigid FF was 10.4% of flat foot cases. Sonia et al. [28] in their study of Tunisian children and Ezema et al. [29] in their study of Nigerian primary school students found bilateral FF prevalence in flat foot cases was 75% and 91.5%, whereas bilateral FF was present in 90.8% of our flat foot cases. We demonstrated that the prevalence of pes cavus was 0.23%; this was in the vicinity with Bafor and Chibuzom [30], Chou et al. [31], Yoosefinejad and Ghalamghash [32], and Bogut et al. [21], who found that the prevalence of pes cavus in children was 0.7%, 1.32%, 2.5%, and 3.68% respectively. Another point of similarity with them when our study demonstrated that there were statistically insignificant relations between pes cavus, age, sex, residence, weight, and height. On the other hand, we disagreed with Kharbuja and Dhungel [20] who found pes cavus in 25.5% of 157 children. This contradiction with higher percent may be due to their small sample compared with our study and terrain difference between the two countries. On the other hand, we are agreed with them when we found significant relation between pes cavus and LL pain. We found that the prevalence of hallux valgus was 0.11%, in proximity to the results of Bafor and Chibuzom [30], who found the prevalence was 0.6% among Nigerian school children between 5 and 13 years, and Chou et al. [31] who found the prevalence was 1.40% among Chinese students. We detected the prevalence of genu varum (GVR) deformity was 0.09% in discrepancy with Udoaka et al. [33] who found GVR in 4.6% of their eight hundred Nigerian children of the same age group. This discrepancy could be attributed to different ethnicity. Although we disagreed with Karimi et al. [34] who documented the prevalence of GVR was 7.9% in three thousand Iranian children, we agreed with them regarding the insignificant relation between GVR and age. We revealed an insignificant relation between GVR and BMI, supporting the result of Bafor et al. [35] who denied any effect of BMI on the tibiofemoral angle. We emphasized insignificant relation between GVR and gender in line with Zakeri et al. [36] in their study of 383 Iranian children between 6 and 13 years. We found that the prevalence of GVL was 0.11%, but we disagreed with Ciaccia et al. [37], who found it in 7.1% of 1050 Brazilian students between 5 and 13 years.
Our study demonstrated a significant relation between GVL and BMI despite insignificant relation between GVL, age, and gender in agreement with Shapouri et al. [38] in their study of 1450 Iranian children although we disagreed with Zakeri et al. [36] who found significant relations between GVL, age, and gender. Genu recurvatum was noticed in 0.75% (35 children) of our students with significant relations with height and BMI in contrast to Souza et al. [39] in their study of 6-18-year old school students in Brazil [36]. Furthermore, we found a significant LLD of more than 2cm in 0.06% of our children, but we disagreed with Drnach et al. [40], who found it in 6.67% of 42 girls and 63 boys between 8 and 12 years. There was a significant relation between LLD and the presence and the presence of musculoskeletal pain in agreement with Rannisto et al. [41]. Our work explored that in-toeing deformity was noticed in 1.04% of our students in proximity to the result of Altinel et al. [42] being 5.9%. However, we disagreed with them as this deformity was bilateral in 76.1% of their children while it was unilateral in 71.4% of ours. This discrepancy could be attributed to different age groups. Conversely, Verch et al. [43] found the prevalence of in-toeing gait was calculated to be 16.3% among their children between 1 and 14 years and unilateral in-toeing being much more frequent, but their higher rate might be due to different method of detection of in-toeing by pressure measurement platform and different age group, but they supported our finding of a highly significant relation between age and in-toeing. Noteworthy, we found significant relations between in-toeing, percentile, and musculoskeletal pain in consistence with Perotti et al. [44].
Some limitations were present in our study as it was conducted in only one governorate and the study results may not be generalizable in addition to absence of diagnostic modalities used for diagnosis of malalignment like foot print and pressure measurement platform. Also absence of complete study of spinal deformity and its hidden role.

Conclusions
Lower limb deformities are a considerable problem in primary school students that need early diagnosis because it could affect child ' s future, health and career. Further studies are needed to investigate spinal deformity, vit D level, calcium level, foot wear, and school bag weight as hidden factors.