Foot Deformations In Coconut Tree Climbers Of South India

Introduction

Evolution of a functional bipedal gait has been the hallmark in the transition dynamics that project man from the pithecoides era ⁽¹⁾. The change in the usage or function of foot from arboreal existence to terrestrial living has been responsible for the anatomical changes seen in more distal segments of the upper and lower limbs ^{(2, 3)}

The human foot is designed to bear weight and aid bipedal locomotion ⁽⁴⁾. The ligaments, joints, bones, muscles and soft tissue components of the foot contribute in its own unique manner in making man alone among his mammalian cousins, to have mastered the art of walking on hind limbs⁽⁵⁾ . Combined effect of hereditary and acquired life style, such as occupation play a significant role in shaping foot morphometrics^(6,7). It is interesting to note that the foot morphology does undergo tremendous morphological changes in its transition from arboreal to terrestrial form ⁽⁸⁾.

In coastal south India, traditionally trained people, mostly belonging to the special communities, climb trees, particularly coconut trees. The tree climbers use their hands and legs to climb the tree. When they climb, the legs are flexed on each side of the tree with the soles of the feet applied around the tree trunk. (Usually they use a loop of coir at the ankle for support, Fig.1). Hands encircle the tree trunk. A few of them use coir loop between the hands to grab the tree trunk. By gripping the tree with extended upper limbs, they lift the body upwards. During this process of tree climbing hip joint makes flexion, extension, abduction and lateral rotation, knee joint undergoes flexion and extension and inversion at the subtalar joints, along with the flexion of toes. The climbers carry a sickle or special type of knife with hood at their holster or collar. When they reach the top the tree, they hold one of the coconut tree leaves, with one hand and pull out the coconuts with the knife in other hand. The whole process of climbing and plucking coconut take 8-10 minutes, wherein they use 1 to 2minutes to climb and 30 seconds to 1 minute to climb down. A healthy coconut tree climber starts his work very early in the morning (5.30 - 6.00 hrs.)and end the work by 11.00hrs., as the sun rays does not suit for vertical ascend after that time. During this period they can harvest 20-30 trees, depending on the proximity of the trees. They usually work seven days a week. Gripping the tree trunk with fully inverted feet, which bears the climbers body weight, demands tremendous stress and strain at the osteoarchitecture of the foot. Climbing large diameter trees like coconut tree require higher costs of locomotion ⁽⁶⁾.

Osteoarchitectural adaptations of foot in professional dancers, and athletes have been studied ⁽⁹⁾. Foot ankle injuries in occupational medicine are also studied ⁽¹⁰⁾. But we hardly find any reference to occupation induced adaptation or change of foot in tree climbing professionals. The study is of importance in this circumstance as we may uncover the causative factors of the main occupational deformations in this particular agricultural industry and recommend measures to avoid them. It has been observed that a number of grievous injuries and fatalities occurred due to accidental fall from trees according to local daily news reports. It is intriguing that most of these casualties occur in the more experienced and older tree climbers in the community

Occupation based permanent change and adaptations to the foot due to pressure, and fall from tree have attracted far less attention. The present study was aimed to study the morphological and functional changes and adaptation of foot to the stress and strain demanded by tree climbing occupation.

Objective

To record the observable changes in the foot anatomy of professional coconut tree climbers in south India.

Subjects and methods

The data presented in this paper were obtained from an observational study conducted on professional coconut tree climbers between January 2006 and December 2008. A total of 220 volunteers aged less than 55 years from the few villages of Kerala (Kozhikode, Ernakulam, Kollam, Idukki districts) and Tamilnadu (Body, Bodynayakannur districts) states. All the subjects were regular professional tree climbers who climb large diameter (450-600mm) coconut trees without using any external climbing aids.

Study Design

Results

a. Observations on foot deformities

Complex movements of foot which were used by climbers while ascending and descending are plantarflexion and dorsiflexion at ankle joint, inversion at subtalar joint, flexion of metatarsophalangeal and interphalangeal joints. The climbing induces tremendous strain on the ankle, subtalar and intertarsal joint. The large areas of the tree trunk, along with the loop worn at the ankles, give a lateral thrust at the metatarsophalangeal joints. In the coconut tree climbers we observed the following deformities in the foot. (i) Plantar flexed first ray(Fig.2A),(ii) Abducted hallux, (iii) Hammer toe(Fig.2B), (iv) Hallux valgus and laterally deviated toe (Fig.2C), (v) Varus foot with medially deviated toe(Fig.2D),(vi)Cavus foot(Fig.3A),(vii) Varus hind foot(Fig.3C,D). We have also found callous formation in the plantar aspect of foot in coconut tree climbers having more than ten years of experience

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Figure 1

A. a rope belt or ankle belt (arrow) used by the coconut tree climbers (A),B. Climber climbing the coconut tree by gripping the tree trunk with the ankle belt ( arrow).

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Figure 2

Foot modifications in different individuals having the coconut tree climbing as their occupation. A-Medial aspect of the foot with plantar flexed first ray, B-Medial aspect foot with hallux hammer toe, C-Plantar aspect of the foot with hallux valgus, D -Dorsal aspect of the feet with varus forefoot,abducted hallux and medially deviated toes.

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Discussion

The kinematics of the first ray plays a key role in medial longitudal arch during gait ⁽¹⁴⁾). The first ray is a critical element in controlling the structural integrity of the foot. Faulty mechanics of the first ray can contribute to foot pathology ⁽¹⁵⁾. First ray can be classified as rigid plantar flexed when the first metatarsal is plantar flexed in a fixed position relative to the other metatarsals. In normal gait, the plantarflexed first ray restricts the internal rotation of the tibia in stance phase which in turn results in inability of calcaneous to evert and therefore the shock absorbtion of the foot ⁽¹⁶⁾. It is observed that people with plantarflexed first rays have callus formation beneath the head of first metatarsal bone as well as the great toe ⁽¹⁷⁾. We have found the similar type of callous formation in coconut tree climbers having more than ten years of experience. This suggests that sheer and compressive forces acting on the first metatarsal may be abnormally high during stance phase of the tree ascend. Thus the callus formation provides evidence that rigid plantarflexed first ray compromises the ability of the medial arch to attenuate the shock of impact during weight acceptance ^{(18, 19)} .

In the present study we found that 26.4% (right foot) and 18.2% (left foot)of rigid plantarflexed first ray. This suggests the strong adaptation of medial longitudinal arch with their occupation. The callus formation found on the plantar aspect of first metatarsal head and hallux gives strong evidence that the ability of the medial longitudinal arch to absorb shock is questionable.

Disturbances of fingers and toes are reported in isolated cases; where they were found to be deviated from the normal pattern ⁽²⁰⁾. Laterally deviated great toe or hallux valgus is one of the common disorders of the foot. Laterally deviated toe is commonly associated with a deformity of the first metacarpophalangeal joint ^(21,22). The complex relationship of the first ray biomechanics and hind foot mechanics influence bunion development. Bunion can be secondary to any structural adaptation and over the time may lead to callus formation ^(22-25). Biomechanics of laterally deviated toe exerts pressure on first metatarsal to deviate medially. Thus hallux valgus is usually associated with medial deviation of first metatarsal resulting in a forefoot disorder rather than deformation restricted to great toe ⁽⁷⁾.The evidence shows that the most common cause of hallux valgus in adults starts with lateral deviation of the hallux from external forces such as shoe wear ^(7,26). Incidence of hallux valgus varies in literature .On an average 16-33% of the male population of shoe wearing races is said to be affected by hallux valgus ^(25,27).

As the present set up is the non-shoe wearing, socio economically backward community of a developing country, it may not be feasible to compare the data with the reported ones. We noticed less than 6% of the people in the coconut tree climbing communities and 1% of nonclimbers had observationally prominent hallux valgus. Varus force applied to the first metatarsal while climbing trees might be acting as a compensatory biomechanics of the first metatarsophalangeal joint to subluxate and produce valgus of the great toe (Hypothesis supported by the literature ^(28-31. It is interesting to note that 23.18% of the coconut climbers presented with laterally deviated (2nd to 5^th) toes, while none of the non climbers showed such pattern in their toes. The external force induced by the tree ascend towards lateral direction of toe together with spreading pressure on lateral toes to grip the tree may be the reason for it.

Underlying toes and overlapping toes are reported as congenital foot anomalies⁽³²⁾. Congenital over riding of the little toe alone is also reported ^(32,33). But there is no report of overlapping of adult toes due to external pressure. The increase in percentage of overlapping of toes in coconut climbers (5 to 5.45%) compared to non climbers (0.45%) suggests the probable incidence of a new variety of occupation induced overlapping of toes.

Data regarding complications or impairment due to hindfoot varus is lacking in literature. This may be because goniometric and visual clinical assessment of rear foot is considered as unreliable⁽³²⁾. Many suggest the radiographic analysis of the rear foot is the best way of analyzing its deformities or deviation^{( 34-38)}. In the present study we have not done procedure such as radiography. But the observational hind foot varus seen in 6.39% (Table-1) people draws attention for future studies using radiography. Small percentage (1.8%, Table-1) of people with medially deviated toes (Fig.2D.), and hammer toes (Fig.2B) raises the question, whether they need to be considered as adaptations due to subjective change of usage of foot in climbing.

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Figure 3

Foot of coconut tree climber's and non climbers. A-Cavus foot in a coconut tree climber, B- a non climber's foot. C and D -Climber's feet showing bilateral hind foot varus.

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Conclusion

Hallux valgus, laterally deviated toes, callosities over the first metatarsal joint area, varus hind foot and overlapping of the toes were the major observational changes found in foot of coconut climbers apart from the prominent cavus foot in most of them. None of the deformations were associated with pain at the time of survey. We hope this study add more information to the field of occupational medicine, to highlight the occupationally induced foot adaptations/deformation. This information bought by this study may help for further study on the impact of deformation in coconut tree climber's occupational habitat, their gait analysis and thus improve their health status by re-educating or rehabilitating them.