SYMMETRICAL ANALYSIS : AN X-RAY STUDY OF TALUS WITH ITS PHYSIOLOGICAL CORRELATION

Kavya 1 , Sowmya Panju 2 and Ashwin Kumar 3 . 1. Assistant professor, Department of Anatomy, Bowring and Lady Curzon medical college and research institute, Bangalore. 2. Assistant professor, Department of Physiology, Bowring and Lady Curzon medical college and research institute, Bangalore. 3. Professor & HOD, Department of Radiology, Kasturba Medical college, Mangalore. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History Received: 15 April 2019 Final Accepted: 17 May 2019 Published: June 2019

Talus helps in receiving the body weight and transmitting it to the plantar below. The dome of the talus articulates with the tibia and fibula, and has a key role in ankle motion and also supports the axial load during weight bearing. The subtalar joint is a simple single axis joint which behaves like a oblique hinge. The average inclination of the subtalar joint axis is 42 degree from the horizontal in a sagittal plane and 16 degree from the longitudinal axis of the foot in the transverse plane thus; the axis is aligned in an oblique direction. The oblique orientation of the axis allows it to traverse all three cardinal planes and movement about the axis is termed "triplane motion." It is important to note that these motions occur about the subtalar joint axis only and do not include talocural or midtarsal joint motions. When the foot is weight bearing in stance phase, pronation and supination of the subtalar joint continue to occur. In an open kinetic chain, minimal movement occurs between the talus and the calcaneus as motion occurs distal to the subtalar joint axis. In a closed kinetic chain, movement occurs both proximal and distal to the axis of the subtalar joint, i.e., leg rotation and foot movement, respectively. The direct effect of subtalar joint is to create an immediate shortening of the lower extremity at heel strike, thus providing a small degree of shock absorption 3 .

Aim:
To study the talar symmetry and to identify the incidence, possible etiological factors and its clinical significance.

Materials and methods:-
This study included 96 healthy normal subjects whose age and sex are known who were referred as patients to the radiology department, for an ankle x-ray (anterior posterior and laterl) with hind foot disorder. Ankle joint radiograph having talar and subtalar pathology were excluded and normal ankle radiograph were included from the study The data was collected for a period of 2 years in the Department of Radiology, K.M.C. Mangalore.
Study sample size calculation: With 95% Confidence level and 80% Power, a sample size of 96 was calculated by using the formula, Sample size (n) = 2 × (Zα + Zβ) 2 × σ 2 δ 2 The data collected was tabulated in Microsoft excel worksheet and computer-based analysis was done using the statistical package for social sciences software IBM SPSS 20.0 (Chicago, IL, USA) for windows. The general descriptive statistics was done for all the parameters providing means and standard deviations (S.D) separately. Student's t test was used to check whether significant differences exist (p≤ 0.05) between right and left mean measurements.

Measurements of dimensions on radiograph:
On anterior posterior radiograph 1. Breadth of the body of talus-the distance between the medial and the lateral surface.On lateral radiograph 2. Length of talus-the distance between the foremost part of the rounded articular surface of the head to the apex of the lateral tubercle. 3. Height of talus-the distance between the superior and inferior surface. 4. Volume is calculated by multiplying the value of length, breath and height.

Discussion:-
The human foot is called upon to support the weight of the body when standing and to provide a smooth functioning interface between the body and the ground during gait. Its function depends on relatively complex mechanical interactions of numerous small bones; pain free motion of small joints, an intact soft tissue envelop, including the plantar pad; and an appropriate secondary feedback 4 . It is important to analyze the anatomical features of talus that predispose it to complex injury. Restoration of the normal anatomy is very important to prevent development of secondary pathology and morbidity.
In the present study average length of the right talus on radiograph are 5.7359 cms and the left talus is 5.6306 cms respectively. It has been observed that right talus were longer than the left. According to Ari  In the present study the average volume of right talus on radiographs is 57.8570 cu cms and left talus is 57.2086 cu cms respectively.
Studies of lateral asymmetry of the legs have confirmed that the left leg is heavier than the right but the results of differences in length are not uniform (Latimer & Lowrance 1965; Singh 1970).The dominance of the lower extremity is less marked than that of the upper. The dominant leg is expressed by the stronger tibia usually on the opposite side of the dominant arm 11 . In the present study right tali exhibited greater dimensions than left except breadth of talus. In a study by Harris SM, Case DT 10 they observed that talus on the right side was generally exhibited greater dimensions than those from the left side. The asymmetry was less pronounced in case of tarsals and metatarsals. Structural asymmetry in fetal metatarsal bones on the right and left side was reported by

Conclusion:-
Body asymmetries indicate the developmental instability of an individual (Watson & Thornhill 1994) and may indicate association with various disorders in the body. Knowledge and understanding of these asymmetries is important to achieve a good diagnosis and focus on an appropriate treatment and management plan. Evidence from behavioural, electrophysiological, and functional neuroimaging studies should be used to understand how these developmental disorders differ so that accurate differential diagnoses and appropriate targeted techniques can be effectively applied for remediation. Likewise, there are various etiological factors: genetic, environmental and functional to be well understood for a proper diagnosis and thus appropriate to focus on a plan treatment. Morphological parameters were different for right and left tali, where right tali exhibited greater dimensions compared to the left indicating the right tali is under more stress compared to left. Although this study shows the different in measurements for right and left tali but it is statistically insignificant.