ABSTRACT:

OBJECTIVE The present study aims to evaluate the prevalence of foot and ankle pain complaints, radiographic parameters, and functional performance in subjects with severe obesity (body mass index [BMI] > 40) who are candidates to bariatric surgery.
METHODS Forty severely obese patients were evaluated at a bariatric surgery outpatient facility. These severely obese subjects (BMI > 40) were divided into two subgroups: those with BMI < 50 (n = 24) and BMI > 50 (n = 16). These patients were compared with a control group of 42 volunteers with a mean BMI value of 24. The following parameters were assessed: foot pain (according to the visual analog scale [VAS]), functional performance (according to the American Orthopeadic Foot and Ankle Society [AOFAS] scale, including forefoot, midfoot and hindfoot domains), age, gender, hallux metatarsal-phalangeal angle, hallux intermetatarsal angle, talocalcaneal angle, calcanean pitch angle and Meary angle.
RESULTS Incidence of foot pain was higher in the severely obese group compared with the control group (p < 0.0001; odds ratio [OR]: 4.2). Functional performance according to the AOFAS scale was lower in obese subjects compared with the control group (p < 0.0001; OR for hindfoot, 4.81; OR for midfoot, 3.33).
CONCLUSION The incidence of foot pain was higher in the group of severely obese patients compared with the control group. According to the AOFAS scale, functional forefoot, midfoot and hindfoot performance was worse in severely obese individuals.

Keywords: foot; obesity; pain; AOFAS scale.

RESUMO:

OBJETIVO Avaliar a prevalência de queixas álgicas no pé e tornozelo, parâmetros radiográficos e o desempenho funcional de indivíduos com obesidade grave, Índice de Massa Corpórea (IMC) com valor > 40 e indicação de cirurgia bariátrica.
MÉTODOS Foram avaliados 40 pacientes com obesidade grave acompanhados em ambulatório de cirurgia bariátrica. Este grupo de obesos graves (IMC > 40) foi subdividido em dois subgrupos: obesos com IMC < 50 (n = 24); e outro de obesos com IMC > 50 (n = 16). Foi realizada comparação com grupo controle de 42 indivíduo voluntários com IMC médio de 24. Foram avaliados a presença de dor no pé pela escala visual (EVA), o desempenho funcional pela escala da Associação Americana de Cirurgia do Pé e Tornozelo (AOFAS, na sigla em inglês) (domínios antepé, mediopé e retropé), idade, gênero, ângulo (âng) metatarso-falangeano do hálux, âng intermetatarsal do hálux , âng talocalcaneano, "pitch" calcaneano e âng de Meary.
RESULTADOS Foi observada maior incidência de dor no pé no grupo de obesos graves em relação ao controle (p < 0,0001, razão de chances [odds ratio, OR]: 4,2). O desempenho funcional pela escala AOFAS foi inferior no grupo de obesos em relação ao controle (p < 0,0001, retropé com OR = 4,81; mediopé com OR = 3,33).
CONCLUSÃO Houve maior incidência de dor no pé no grupo de obesos graves em relação ao controle. Houve pior desempenho funcional pela escala AOFAS nas regiões do antepé, mediopé e retropé no grupo de obesos graves.

Palavras-chave: pé; obesidade; dor; escala AOFAS.

FIGURES

Citation: Martins GC, Fraga PHG, Teixeira LB, Valle BRG, Martins Filho LF, Gama MP. Functional Evaluation and Pain Symptomatology of the Foot and Ankle in Individuals with Severe Obesity - Controlled Transversal Study*. 56(2):235. doi:10.1055/s-0040-1713757
Note: * Study developed at the Hospital Federal de Ipanema, Rio de Janeiro, RJ, Brazil.
Conflict of Interests The authors have no conflict of interests to declare.
Received: August 08 2019; Accepted: April 15 2020
 

INTRODUCTION

Today, obesity is one of the most challenging public health problems in modern society. It is estimated that there are currently over one billion overweight people in the world, with 300 million obese people.1 This condition affects not only developed countries, but also developing countries, where carbohydrates ingestion is widespread due to their low cost.2

Population studies have shown that obesity is an independent risk factor for knee pain and arthrosis.3-5

In obese patients, feet pain incidence has been less studied in the literature than obesity-related knee pain.3-5

Obesity results in feet pain and biomechanical changes secondary to flat foot deformity, plantar fat alterations, decreased muscle strength and gait pattern abnormalities.6 This process leads to loss of balance and risk of falling, interfering with the mobility of these individuals.6,7

Currently, there is a new strand of studies due to the discovery of visceral fat-generate proteins, the so-called adipokines. The best known adipokine is leptin, which plays a role in insulin action and inflammatory cytokines production by chondrocytes.8 Recent studies have shown a higher incidence of knee pain and osteoarthritis related to high levels of serum adipokines and metabolic syndrome.9

The literature on pain incidence, functional performance level and foot and ankle radiographic alignment parameters in severely obese individuals, with a body mass index (BMI) > 40, is scarce. A compilation of these data is required to properly ascertain the importance of this problem. Clinical and imaging parameters that may indicate the need for early intervention are essential to formulate therapeutic and preventive strategies for this growing group of economically active people.

The main objective of the present study is to evaluate the prevalence of pain, determined by a visual analog scale (VAS), in a sample of severely obese individuals (BMI > 40) and compare it to a control group consisting of people with a mean BMI of 24. The secondary objectives are the determination of functional differences according to the American Orthopaedic Foot and Ankle Society (AOFAS) scale10 and radiographic parameters for morphological evaluation of the foot in both groups. Our initial hypothesis is that a higher prevalence of pain and a lower functional performance are expected in people with severe obesity compared with the control group.

 

METHODOLOGY

The present study complies with the Declaration of Helsinki rules and it was approved by the hospital's Research Ethics Committee (CAAE 69073215.2.0000.5646, opinion 2.127.775). All participants (both from the obese and control groups) signed an informed consent form.

This was an observational, cross-sectional study. Data for the present research were collected by orthopedics residents from our service from June 2017 to April 2018.

Forty patients (►Table 1) from the bariatric surgery outpatient facility at our hospital were included. The sample consisted of 10 men and 30 women, with an average age of 45.45 years old (range, 25 to 63 years old).

Table 1. Study group (obese patients)
  GENDER AGE (years) WEIGHT (kg) CLASSIFICATION HEIGHT (m) BMI VAS SIDE H M F AMF AIMº APCº ATC
1 Female 61 92 PATIENT 1.5 40.9 9 LEFT 47 79 93 normal normal NORMAL FLAT
2 Female 42 110 PATIENT 1.64 40.9 9 RIGHT 49 60 95 mild normal NORMAL NORMAL
3 Female 64 105 PATIENT 1.6 41 8 RIGHT 28 52 100 normal normal NORMAL FLAT
4 Female 45 108 PATIENT 1.62 41.2 10 LEFT 65 53 74 normal mild NORMAL NORMAL
5 Female 32 99 PATIENT 1.55 41.6 8 RIGHT 50 65 93 normal moderate FLAT NORMAL
6 Male 27 158 PATIENT 1.95 41.6 8 LEFT 85 82 85 normal normal NORMAL NORMAL
7 Female 47 97.5 PATIENT 1.52 42.2 7 RIGHT 67 64 95 normal normal NORMAL NORMAL
8 Male 47 123 PATIENT 1.7 42.6 0 LEFT 80 85 85 normal normal NORMAL NORMAL
9 Male 62 108 PATIENT 1.59 42.7 8 RIGHT 72 76 93 normal moderate NORMAL NORMAL
10 Male 25 143 PATIENT 1.83 42.7 10 RIGHT 67 100 100 moderate moderate NORMAL NORMAL
11 Male 30 128 PATIENT 1.73 42.77 7 RIGHT 82 100 73 normal mild NORMAL NORMAL
12 Male 40 150 PATIENT 1.87 42.9 6 RIGHT 79 85 82 normal normal NORMAL FLAT
13 Female 58 136 PATIENT 1.77 43.4 9 RIGHT 30 32 83 moderate severe NORMAL NORMAL
14 Female 53 102 PATIENT 1.52 44.15 5 RIGHT 67 100 100 moderate moderate NORMAL NORMAL
15 Female 19 109 PATIENT 1.57 44.2 8 RIGHT 67 49 100 moderate mild NORMAL NORMAL
16 Female 38 122 PATIENT 1.66 44.3 9 LEFT 80 82 93 normal mild FLAT NORMAL
17 Female 49 103 PATIENT 1.52 44.58 8 RIGHT 71 56 100 normal normal NORMAL NORMAL
18 Female 47 124 PATIENT 1.65 45.5 7 RIGHT 72 60 77 normal moderate NORMAL CAVUS
19 Female 53 97 PATIENT 152 45.8 0 RIGHT 88 89 90 normal mild NORMAL NORMAL
20 Female 43 126 PATIENT 1.65 46.3 8 RIGHT 68 45 90 normal normal NORMAL CAVUS
21 Female 63 116 PATIENT 1.58 46.5 7 RIGHT 52 87 100 normal mild CAVUS NORMAL
22 Male 50 142 PATIENT 1.72 48 6 RIGHT 60 100 78 moderate moderate NORMAL NORMAL
23 Female 63 115 PATIENT 1.55 48.87 8 LEFT 82 100 73 moderate mild FLAT NORMAL
24 Female 33 140 PATIENT 1.68 49.6 5 RIGHT 67 89 70 mild moderate NORMAL NORMAL
25 Female 52 130 PATIENT 1.61 50.2 3 LEFT 78 75 100 moderate mild NORMAL NORMAL
26 Male 61 146 PATIENT 1.69 51.12 10 LEFT 57 100 57 mild mild NORMAL FLAT
27 Female 45 120 PATIENT 1.53 51.26 3 RIGHT 73 62 100 moderate moderate NORMAL NORMAL
28 Female 41 140 PATIENT 1.65 51.42 8 RIGHT 93 53 100 moderate mild NORMAL NORMAL
29 Female 44 120 PATIENT 1.52 51.94 5 LEFT 84 82 100 mild mild FLAT NORMAL
30 Female 55 116 PATIENT 1.48 52.16 8 LEFT 51 100 100 mild moderate NORMAL NORMAL
31 Female 42 113 PATIENT 1.47 52.29 6 RIGHT 50 45 72 normal normal NORMAL CAVUS
32 Female 36 123 PATIENT 1.53 52.59 5 LEFT 58 100 100 moderate moderate NORMAL NORMAL
33 Female 27 135 PATIENT 1.58 54.08 7 RIGHT 41 61 100 normal normal NORMAL NORMAL
34 Female 37 145 PATIENT 1.62 55.25 7 LEFT 64 100 100 mild mild NORMAL NORMAL
35 Female 51 133 PATIENT 1.55 55.4 10 LEFT 29 39 90 normal normal NORMAL NORMAL
36 Female 40 132 PATIENT 1.54 55.66 8 RIGHT 81 100 83 moderate moderate NORMAL NORMAL
37 Male 40 165 PATIENT 1.72 55.77 5 LEFT 69 100 70 moderate mild NORMAL NORMAL
38 Female 36 162 PATIENT 1.65 59.5 7 LEFT 88 73 95 normal mild NORMAL NORMAL
39 Female 37 153 PATIENT 1.58 61.29 5 RIGHT 55 64 100 normal normal NORMAL NORMAL
40 Male 59 181 PATIENT 1.79 71.6 7 RIGHT 89 100 100 normal severe NORMAL NORMAL

Abbreviations: AIM, hallux intermetatarsal angle; AMF, hallux metatarsal-phalangeal angle; APC, calcanean pitch angle; ATC, talocalcaneal angle; BMI, Body mass index; H, M, F, hindfoot, midfoot, forefoot (respectively) functional performance according to the American Orthopeadic Foot and Ankle Society scale; VAS, visual analogue scale.

Table 1. Study group (obese patients)

The control group (►Table 2) consisted of volunteers (employees, resident physicians, and patients from the general, non-bariatric surgery outpatient facility) from matched gender and age for comparison with the obese group. The control group consisted of 42 people, including 12 men and 30 women, with an average age of 43.9 years old (range, 24 to 61 years old).

Table 2. Control group
  GENDER AGE WEIGHT (kg) CLASSIFICATION HEIGHT (m) BMI VAS SIDE H M F AMF AIM APC ATC AM
1 Female 61 80 CONTROL 1.62 30.48 3 LEFT 49 66 100 normal normal CAVUS NORMAL CAVUS
2 Female 58 61 CONTROL 1.54 25.72 3 LEFT 41 58 100 moderate mild NORMAL NORMAL NORMAL
3 Female 45 62 CONTROL 1.54 26.14 0 RIGHT 100 100 100 normal mild NORMAL NORMAL NORMAL
4 Female 44 65 CONTROL 1.68 23.03 0 RIGHT 58 58 100 normal moderate FLAT NORMAL FLAT
5 Female 38 74 CONTROL 1.74 22.4 0 LEFT 60 90 90 normal normal NORMAL NORMAL NORMAL
6 Female 54 89 CONTROL 1.7 30.45 3 RIGHT 41 56 100 normal moderate FLAT NORMAL FLAT
7 Female 27 57 CONTROL 1.71 19.15 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
8 Female 38 59 CONTROL 1.63 22.21 5 LEFT 100 100 100 moderate mild NORMAL NORMAL NORMAL
9 Female 60 62 CONTROL 1.59 24.52 0 RIGHT 57 53 100 mild mild NORMAL NORMAL NORMAL
10 Female 35 69 CONTROL 1.71 23.6 0 RIGHT 100 100 100 mild mild NORMAL NORMAL NORMAL
11 Female 37 72 CONTROL 1.73 24.06 6 LEFT 100 100 100 mild mild FLAT NORMAL FLAT
12 Female 53 69 CONTROL 1.62 26.29 7 RIGHT 58 66 100 moderate moderate FLAT NORMAL FLAT
13 Female 41 72 CONTROL 1.7 24.91 4 LEFT 100 100 100 mild mild NORMAL NORMAL NORMAL
14 Female 20 54 CONTROL 1.59 21.36 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
15 Male 42 87 CONTROL 1.81 26.56 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
16 Male 30 70 CONTROL 1.71 23.66 0 RIGHT 100 100 100 moderate moderate NORMAL NORMAL NORMAL
17 Male 47 74 CONTROL 1.73 25.01 4 LEFT 100 100 100 normal mild NORMAL NORMAL NORMAL
18 Male 24 76 CONTROL 1.74 25.1 0 RIGHT 100 100 100 moderate normal NORMAL NORMAL NORMAL
19 Male 27 78 CONTROL 1.7 26.99 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
20 Male 35 76 CONTROL 1.69 26.61 6 LEFT 100 100 100 moderate mild NORMAL NORMAL NORMAL
21 Male 61 76 CONTROL 1.72 25.69 0 RIGHT 53 49 100 normal normal NORMAL NORMAL NORMAL
22 Male 56 92 CONTROL 1.79 28.71 3 RIGHT 100 100 100 mild mild NORMAL NORMAL NORMAL
23 Female 25 50 CONTROL 1.65 18.4 0 LEFT 100 100 100 normal mild NORMAL NORMAL NORMAL
24 Female 56 52 CONTROL 1.6 20.3 0 RIGHT 100 100 100 normal normal NORMAL NORMAL CAVUS
25 Female 35 55 CONTROL 1.53 23.5 0 RIGHT 100 100 75 moderate normal NORMAL NORMAL NORMAL
26 Female 50 57 CONTROL 1.6 22.3 3 RIGHT 100 90 100 normal normal NORMAL NORMAL CAVUS
27 Female 33 65 CONTROL 1.68 23 1 RIGHT 100 100 92 normal mild NORMAL NORMAL NORMAL
28 Male 34 79 CONTROL 1.81 24 0 RIGHT 100 100 100 normal mild NORMAL NORMAL CAVUS
29 Female 60 60 CONTROL 1.54 25.3 2 LEFT 88 100 100 normal mild NORMAL NORMAL NORMAL
30 Female 47 575 CONTROL 1.67 20.4 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
31 Female 61 57 CONTROL 1.53 24.3 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
32 Female 51 54 CONTROL 1.55 22.5 0 LEFT 100 100 100 normal normal CAVUS NORMAL CAVUS
33 Male 58 73 CONTROL 1.7 25.3 0 RIGHT 100 100 100 normal normal NORMAL NORMAL NORMAL
34 Male 52 83 CONTROL 1.8 25 0 LEFT 100 100 100 normal normal NORMAL NORMAL CAVUS
35 Female 40 62 CONTROL 1.71 21.2 0 LEFT 100 100 100 normal mild NORMAL NORMAL NORMAL
36 Female 42 58 CONTROL 1.55 24.1 5 LEFT 90 100 100 normal normal NORMAL NORMAL NORMAL
37 Female 53 60 CONTROL 1.57 24.3 2 RIGHT 87 92 92 moderate moderate NORMAL FLAT NORMAL
38 Female 60 49 CONTROL 1.55 20.4 6 LEFT 64 95 100 normal normal NORMAL NORMAL NORMAL
39 Male 27 82 CONTROL 1.79 25.2 0 RIGHT 100 100 100 normal moderate NORMAL NORMAL NORMAL
40 Female 43 54 CONTROL 1.53 23.1 0 LEFT 85 85 75 normal moderate NORMAL NORMAL NORMAL
41 Female 48 63 CONTROL 1.59 24.9 0 LEFT 75 72 75 moderate severe NORMAL NORMAL NORMAL
42 Female 35 75 CONTROL 1.75 24.5 0 LEFT 100 100 100 normal mild NORMAL NORMAL NORMAL

Abbreviations: AIM, hallux intermetatarsal angle; AM, Meary Angle; AMF, hallux metatarsal-phalangeal angle; APC, calcanean pitch angle; ATC, talocalcaneal angle; BMI, Body mass index; H, M, F, hindfoot, midfoot, forefoot (respectively) functional performance according to the American Orthopeadic Foot and Ankle Society scale; VAS, visual analogue scale.

Table 2. Control group

The inclusion criteria for the obese group were adult patients with BMI > 40 who were candidates for bariatric surgery and consented to participate in the study. The exclusion criteria were previous performance of surgical procedures (orthopedic, vascular, dermatological, or plastic surgery) in any segment of the lower limbs (hip, knee, ankle, and foot). Individuals with sequelae from lower limb fractures or conditions with surgical indication, whether orthopedic (hip or knee arthrosis, ankle or foot arthrosis) or vascular (arterial or venous insufficiency, ulcers, digital or skin necrosis) were excluded from the research.

Weight and height were measured at the Bariatric Surgery Outpatient Facility. The BMI was calculated by dividing the weight in kilograms (kg) by the square of the height in meters. For classification purposes, a BMI < 20 is considered underweight, whereas values from 20 to 24.9 are normal, and between 25 and 29.9 indicate overweight; BMIs > 30, 40 and 50, respectively, represent obesity, morbid obesity, and superobesity.7

Anteroposterior (AP) and lateral radiographs from both feet from obese and control subjects were taken under load.

The following radiological parameters were measured:

1) hallux metatarsal-phalangeal angle (AMF) measured in AP radiographs: normal, < 15º; mild, 15 to 19º; moderate, 20 to 39º; severe, > 40º;

2) intermetatarsal angle (AIM) measured in AP radiographs: normal, < 9; mild, 9-11; moderate, 12-15; severe, > 16;

3) talocalcaneal angle (ATC) measured in AP radiographs: cavus foot, < 20º; normal, 20 to 30º; flat foot, > 40º;

4) Calcaneal pitch angle (APC) measured in lateral radiographs: flat foot, < 10; normal, 10-30; cavus foot, > 30;

5) Meary angle (AM) or talus-first metatarsal bone angle measured in lateral radiographs. A normal value would be zero. A plantar deviation > 10º indicates a cavus foot, whereas a dorsal deviation > 10º indicates a flat foot.

The AMF and the AIM assess and grade hallux valgus deformity. The ATC, APC and AM assess whether feet are normal or present deformities such as flat or cavus feet.

Pain in daily living activities (walking, going up and down stairs, rest) was assessed in a simple way by the VAS, with values ranging from 0 (no pain) to 10 (most severe pain possible). For a more objective assessment, a score from 1 to 3 was classified as mild pain, from 4 to 6, moderate pain, and from 7 to 10, severe pain. Values > 3 were noted as significant for odds ratio (OR).

The AOFAS scale10 was used for functional evaluation of the feet. This classification addresses pain, function, use of shoes, distance covered, poor foot alignment and gait pattern. It analyzes the forefoot (hallux and small toes), midfoot and hindfoot/ankle as separate domains. The scale has decreasing values from 100 to zero for each domain (values < 70 are deemed unsatisfactory).

The following parameters from the study and control groups were statistically correlated: VAS, AOFAS scale (forefoot [F], midfoot [M] and hindfoot [H]), AMF, AM, ATC, APC and AIM. The relationship between the VAS and age and the VAS and gender was also assessed.

Visual analogue scale and BMI values were correlated.

Obese subjects were divided in two subgroups: patients with morbid obesity, with a BMI between 40 and 50, and those with superobesity, with a BMI > 50. These subgroups consisted of 24 and 16 subjects, respectively. Visual analogue scale and AOFAS scale parameters were evaluated comparatively between these two subgroups.

Data analysis was performed focusing on the most symptomatic limb (most responsible for VAS score). This methodology aims to avoid compromising the statistical analysis if both limbs (feet) are evaluated as separate statistical units, as previously described by Menz.11

 

STATISTICAL ANALYSIS

The G2 Wilks test was used to assess pain (VAS) in control and obese groups and between obese subgroups; in addition, it was used to determine the relationship between VAS score and gender and VAS score and age. This test was also used to analyze radiographic angles (AMF, AIM, APC, AM and ATC). The Mann-Whitney test was used to analyze AOFAS scale scores. A Pearson correlation matrix was used to ascertain the correlation between VAS and BMI scores. Significance was determined at p < 0.05.

 

RESULTS

Foot pain was reported by 38 out of 40 (95%) obese patients and by 16 out of 42 (38%) control subjects (►Figure 1). Among obese patients, there were 19 (47.5%) cases of severe pain, 17 (42.5%) cases of moderate pain, 2 (5%) cases of mild pain, and 2 (5%) subjects referred no pain. In the control group, there were 8 (19.05%) cases of moderate pain, 8 (19.05%) cases of mild pain and 26 (61.90%) subjects referred no pain.

Fig. 1. Two-dimensional representation of visual analog scale (VAS) for pain in obese (blue) and control (red) subjects.

There was no difference between the obese and control groups regarding age and gender, as shown by t-student tests (p = 0.3554) and difference in proportion test (p = 0.539), respectively (►Table 3).

Table 3. Correlations in obese and control groups
PARAMETER OBESE GROUP CONTROL GROUP STATISTICAL ANALYSIS
Gender Male. 25%; Female. 75% Male. 28.5%; Female. 71.5% p= 0.539
Age 44.85 43.8 (Mean value) p= 0.3554
VAS 95% with pain 40% with pain p= 0.0001
AOFAS H (mean value) 65.87 88.23 p < 0.0001
AOFAS M (mean value) 76.1 91.19 p< 0.0001
AOFAS F (mean value) 89.59 97.59 p< 0.0001
APC N = 87.5% N = 85.71% p= 0.8585
C = 2.5% C = 4.70%
F = 10% F = 9.52%
ATC N = 82.5% N = 97.6% p= 0.031
C = 7.5% C = 0%
F = 10% F = 2.6%
AM N = 67.5% N = 76.2% p= 0.743
C = 12.5% C = 14.3%
F = 17.5% F = 9.5%
AMF N = 45% N = 66.6% p= 0.743
AIM N = 30% N = 42.85% p= 0.54
Gender x VAS ---------------------------- -------------------------- p= 0.33 for obese subjects
p= 0.6417 for control subjects
BMI X VAS ---------------------------- -------------------------- p= 0.1407 for obese subjects
p= 0.2343 for control subjects

Abbreviations: AIM, hallux intermetatarsal angle; AMF, hallux metatarsal-phalangeal angle; APC, calcanean pitch angle; ATC, talocalcaneal angle; BMI, Body mass index; C, cavus; F, flat; H, M, F, hindfoot, midfoot, forefoot (respectively) functional performance according to the American Orthopeadic Foot and Ankle Society scale; N, normal; p, p-value, VAS, visual analogue scale.

Table 3. Correlations in obese and control groups

The referred pain scale (VAS) showed a higher prevalence of feet pain in the obese group compared with the control group according to the G2-Wilks test (p = 0.0001), with an OR value of 4.2.

The AOFAS scale in its three domains, that is, forefoot, midfoot and hindfoot, showed a lower functional performance in the obese group compared with control subjects according to the Mann-Whitney test (p < 0.0001) (►Figure 2). Odds ratios for hindfoot and midfoot were 4.810 and 3.33, respectively. The OR value for the forefoot could not be determined because no control subject presented a value < 70.

Fig. 2. Box plot graphs showing the American Orthopeadic Foot and Ankle Society (AOFAS) score for forefoot, midfoot and hindfoot domains in obese (left) and control (right) subjects.

Pain, as assessed by the VAS, was not related to BMI in the obese or control groups, as shown by Pearson tests (p = - 0.1407 and p = 0.2343, respectively.)

The ATC values were higher in the obese group, configuring a higher prevalence of flat feet, as shown by the G2 Wilks test (p = 0.0317).

There were no statistical differences between the obese and control groups regarding the remaining evaluated parameters (►Table 3).

Comparison between morbidly obese and supermorbidly obese subjects did not show statistical differences regarding the evaluated parameters (►Table 4).

Table 4. Correlations in subgroups with body mass index below or above 50
PARAMETER OBESE BMI < 50 OBESE BMI > 50 STATISTICAL ANALYSIS
VAS 91.6 100% p= 0.075
Severe pain = 58% Severe pain = 31.2%
AOFAS Hindfoot domain 65.62 66.25 p= 0.428
AOFAS Midfoot domain 74.58 78.37 p= 0.264

Abbreviations: AOFAS, American Orthopeadic Foot and Ankle Society; BMI, body mass index; p , p-value; VAS, visual analogue scale.

Table 4. Correlations in subgroups with body mass index below or above 50
 

DISCUSSION

The present case series agrees with other studies from the literature2,11 that show an increased prevalence of foot pain in obese individuals in relation to the general population. In this study, there was 95% pain in the obese group and 40% in the control group. Melo et al.12 described similar data, with 85% pain in lower limbs from morbidly obese patients undergoing reduction gastroplasty. In the general population, these rates range from 14% in adolescents to 42% in people > 65 years old.11 Our study revealed that a severely obese patient (BMI > 40) presents an OR of 4.2 for significant foot pain compared to a control group of people with a mean BMI of 24. In a meta-analysis, Butterworh et al.2 described an OR of 3.1 for feet pain in obese patients compared with people with a BMI < 25.

All three domains from the AOFAS functional scale10 were more altered in obese patients than in control subjects. This finding agrees with the higher report of calcaneal posterior pain by obese people,2 as well as with the greater mechanical overload in the midfoot that result in local pain.6,13 Compared to the control group, OR values corresponding to the hindfoot and midfoot from severely obese individuals (BMI > 40) of 4.81 and 3.33, respectively, ratify the higher incidence of poor functional performance for daily activities, quality of life and movement.

Even though the interplay between increased body weight and BMI and lower limb pain initially seems to result from biomechanical factors determined by increased load alone, new evidence relates joint pain to systemic metabolic syndrome.2,14-16

Visceral adipose tissue, as well as the truncal light fatty tissue, constitute true endocrine organs that secrete cytokines, interleukins, adipokines and leptins.17 Leptin is reportedly related to pro-inflammatory effects and the destruction of chondrocytes.14

Our study showed no statistical relationship between referred pain (VAS) and BMI when comparing obese subjects. Other authors2,11 reported that BMI would not be independently associated with foot pain. Butterworth et al.2 emphasized that a high fat mass would be especially related to foot pain. Body mass alone would not be an independent factor for pain.2,12 These observations suggest the presence of systemic, not just biomechanical, factors determining the onset of foot pain in obese individuals.

Case series18,19 from the literature described a higher prevalence of flat feet in obese subjects. Our study showed a higher prevalence of increased ATC, consistent with flat feet, in obese individuals. There were no statistical differences between obese and control subjects regarding other studied angles. Some authors20 reported that there is little relationship between joint pain and radiographic changes. Another factor to consider is that morbidly obese subjects are usually younger.21 As a result, there was no time to develop radiological arthrosis or secondary deformities, and radiological changes would not be identified despite the pain.21

Our research showed no statistical difference regarding angular measurements in radiographs to assess the prevalence of conditions such as hallux valgus. A hallux valgus deformity would not be necessarily associated with pain. However, data on its prevalence in obese people are conflicting. For Frey et al.,22 hallux valgus would be related to normal BMI, and not to obesity. However, Cho et al.23 correlated hallux valgus to increased BMI values. Nguyen et al.24 reported that obesity and female gender would be protective factors for hallux valgus. This would be due to the fact that women with BMI < 25 tend to wear high heels, pointed toes shoes, whereas obese females, for having wider feet, wear flat shoes that do not compress the forefoot area.24

Menz et al.25 described a higher prevalence of foot pain in women compared to men (25% versus 19%) in a general population from Framinghan, MA, USA. However, our study revealed no differences between severely obese men and women regarding both the prevalence and severity of feet pain.

Our case series showed no differences in feet functional parameters using the AOFAS scale and in the level of pain (VAS) when comparing morbidly and supermorbidly obese subjects. Our data disagrees from other authors who showed greater functional impairment in superobese individuals.7 Further studies, including a larger number of individuals, may evidence such differences.

Our study is limited by its cross-sectional design; although the studied parameters may present correlations, it is not possible to determine a cause-effect relationship. Therefore, our statistical analysis cannot affirm that excessive obesity results in pain and low functional level or if these factors would have a reverse causal effect, that is, determining the occurrence of obesity due to the sedentary lifestyle. Another factor worth mentioning is the nondiscrimination of clinical comorbidities such as hypertension, diabetes, and other systemic diseases in obese and control subjects, which may have generated bias in data analysis. In addition, the sample studied was relatively small, which limits the scope of conclusions. However, it should be noted that the study group constitutes a very specific universe of people with extremely severe (morbid) obesity (BMI > 40) and indication for bariatric surgery, while most data from the researched literature2,12 refer to overweight or mildly obese individuals.

A higher prevalence of foot pain and functional impairment was demonstrated in the studied obese population. The indirect relationship between increased BMI in severely obese patients and pain according to the VAS corroborates the suspicions that systemic mechanisms, not only biomechanical factors, determine pain and functional impairment. These findings reinforce the importance of further studying the involvement of the musculoskeletal system in people with severe obesity.

Our data will help to understand musculoskeletal conditions resulting from obese-related metabolic syndrome and to formulate preventive and therapeutic strategies in this special subgroup of individuals.

 

CONCLUSIONS

Severe obesity (BMI > 40) is related to a higher prevalence of foot pain. Severely obese people have a worse AOFAS functional score in the forefoot, midfoot and hindfoot regions.

 

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