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ANTHROPOMETRIC ANALYSIS OF THE HIP JOINT IN CENTRAL INDIA POPULATION USING COMPUTED TOMOGRAPHY

The prosthesis used in hip arthroplasty are on the anthropometry of patients. These prosthesis do not replicate the exact anatomy of patients, leading to postoperative complications and requiring surgery for If the in considering the anthropometric parameters of Indians while designing the prosthesis, this may to better clinical and functional outcome and higher patient satisfaction.


ISSN: 2320-5407
Int. J. Adv. Res. 9(09), 108-116 109 Introduction:-An excellent functional outcome in hip arthroplasty depends on how well the prosthesis is able to replicate the biomechanics of the original hip joint. Longevity has led to increase in the number of hip arthroplasties across the globe. Annually over 8 lac hip arthroplasties are performed. [1] Prosthetics are designed according to the anatomy of Western patients. The built of Indian patients is different from that of Western counterparts leading to mismatch between prosthesis and the original anatomy of the hip joint. This leads to complications such as aseptic loosening, uneven load distribution and discomfort after undergoing arthroplasty. A dimensional difference between femur bone and prosthetic components may lead to micromotion of the prosthetic stem during postoperative rehabilitation and hampers the trabecular bone in growth. A large implant size leads to femur fracture, and to prevent this the inclination is kept undersized. A small implant size leads to failure to hold the bone. [2] An appropriate size implant help overcome these problems. Prosthetics available in the market do not provide perfect fit to Indian patients, who are smaller in built in comparison to the western counterparts. [3] Hence, the present study was undertaken to evaluate and compare the proximal femur dimensions of the central India population with population from other regions of India and western population. This will help the prosthetic manufacturers in designing region specific prosthesis.

Materials & Methods:-
The present prospective, comparative study was conducted on 200 individuals, aged between 20 to 70 years of either sex and having no hip abnormalities. Individuals having pre-existing hip pathologies like osteoarthritis, rheumatoid arthritis, tuberculosis of hip, old hip fractures, tumors of hip, lower limb deformity were excluded from the study.
All the individuals undergoing computed tomography of abdomen for reasons other than for hip pathologies. Were included in the study. These computed tomography images were used for evaluating the anthropometric parameters. In all the patients bilateral hip joints were evaluated. The Neck-Shaft Angle (NSA), Head Diameter (HD), Neck Width (NW), Acetabular Angle of sharp(AA), Horizontal Offset (HO), Vertical Offset (VO), Medullary Canal Diameter at the level of Lesser Trochanter (MD LT ), and Acetabular Version (AV) were measured in all these individuals. To use the computed tomography images for evaluating the anthropometric parameters, a voluntary written consent was obtained from these individuals. Individuals who were not willing, their computed tomography images were not included for analysis. Permission to conduct the study was obtained from the Ethics Committee of our institution. The statistical analysis was carried out using online statistical packages GraphPad and Epi Info. Comparison of left and right side of various anthropometric variables was done using Paired 't' test and comparison of anthropometric variables in relation to sex was done using Unpaired 't' test. The male and female comparison of anthropometric variables was done after calculating the average of right and left side. A p value of < 0.05 was taken as statistically significant.

Methodology:-
We had used the computed tomography images of all the individuals enrolled in the study and following parameters were analyzed

Neck Shaft Angle (NSA)
It is the angle that lies between the long-axis of shaft femur and long-axis of femur neck. Long-axis of shaft femur lies in the center of medullary canal and long-axis of femur neck is equidistant from the superior and inferior surface of femoral neck. (Fig. 1). All the data was captured in a customized proforma and then transferred to Microsoft Excel for analysis. Paired 't' test was applied to compare the means between right and left side. A p value of < 0.05 was taken as statistically significant.

Results:-
In the present study we had included 200 individuals with no hip abnormalities. Anthropometric measurements were done using the computed tomographic images. There were 94 (47%) females and 106 (53%) males. The mean age was 44.58 ± 19.68 years with a range from 20 to 70 years. All the anthropometric variables for left and right side were calculated separately.

Neck-shaft angle
The mean neck-shaft angle (NSA) was similar on the right side in comparison to left side (132.73 ± 6.12 vs. 132.33 ± 5.91, P=0.037) and was comparable between the males and females (133.41 ± 4.3 vs. 131.65 ± 4.46, P=0.227). The mean neck-shaft angle was 132.53 ± 4.37 degree with a range from 117 to 148 degrees.

Femoral head diameter
The mean femoral head diameter (HD) was similar on the right side in comparison to left side (43.39 ± 3.51 vs. 44.49 ± 3.46, P=0.001) and was comparable between the males and females (44.54 ± 2.53 vs. 43.34±2.37, P=0.641). The mean femoral head diameter was 43.94 ± 2.46 mm with a range from 38.0 to 51.2 mm.

Neck width
The mean neck width (NW) was similar between right side in comparison to left side (24.99 ± 3.28 vs. 25.23 ± 3.36, P=0.105) and was comparable between the males and females (25.16 ± 2.99 vs. 25.06 ± 3.00, P=0.579). The mean neck width was 25.11 ± 2.99 mm with a range from 15.50 to 33.50 mm.

Horizontal offset
The mean horizontal offset (HO) was similar on the both side in (43.97 ± 7.32 vs. 43.55 ± 7.82, P=0.018) and was comparable between the males and females (44.55 ± 5.29 vs. 42.97 ± 5.31, P=0.150). The mean horizontal offset was 43.76 ± 5.31 mm with a range from 25.31 to 57.0 mm.

Acetabular version
The mean acetabular version (AV) was similar on the right side in comparison to left side (19.54 ± 5.25 vs. 19.40 ± 5.68, P=0.001) and was comparable between the males and females (20.43 ± 3.85 vs. 18.54 ± 4.13, P=0.759). The mean acetabular version was 19.47 ± 3.96 degree with a range from 11.0 to 30.0 degree.

Discussion:-
We had included 200 participants whose anthropometric analysis was carried out from the available CT scans done for other purposes. There is a male predominance in the study (53%) with a mean age was 44.58 ± 19.68 years with a range from 20 to 70 years.  [6] reported similar neck-shaft angle in Southern Assamese population. While the studies done by Rubin et al [7] in Swiss population, Mahaisavariya et al [8] in Thai population and Noble et al [9] in Caucasian population found a lower neck-shaft angle in comparison to our study. A study done by Husmann et al [10] in French population found similar neck-shaft angle in their population. There is a large variation in the neck-shaft angle within India also, with higher angles seen in South Indians, North-East Indians and Southern Assamese. The available prosthesis in arthroplasty comes with a 131 degree neck-shaft angle, which is comparable to the Central Indian population, while it is smaller for other Indian Ethnic groups.
The mean femoral head diameter (HD) was 43.94 ± 2.46 mm (range: 38.0-51.2 mm). This diameter is comparable between the males and females. The femoral head diameter reported by Sengodan et al [4] (South India) and Agarwala et al [6] (Southern Assam) were slightly smaller; and that reported by Rawal et al [11] (North India) was larger than the present study. Noble et al [9] (Caucasian) also reported a higher femoral head diameter. Here also, the mean femoral head diameter varies from other Indian ethnic groups.
The mean neck width (NW) was 25.11 ± 2.99 mm (range: 15.50 to 33.50 mm), being comparable on the both the sides. The neck width is comparable between males and females. Sengodan et al [4] (South India), Ravichandran et al [12] (India) and Agarwala et al [6] (South Assam) reported a larger mean neck width in comparison to our study. For fixing fracture neck femur, usually 3 cancellous screws of size 6.5 mm are required, which becomes difficult. The thread diameter of DHS is 12.5 mm and that of barrel is 12.6 cm, for inserting the Richards screw rimming upto 11.5 mm and tapping upto 13.5 mm is required. This removes bone stock from neck and the implant occupies the available space in the neck, resulting in non-union and avascular necrosis, making it difficult to place the DHS. [12] The mean horizontal offset (HO) was 43.76 ± 5.31 mm. The mean horizontal offset are comparable between the males and females. The mean horizontal offset reported by Sengodan et al [4] and Agarwala et al [6] was much smaller in comparison to our study results. Rawal et al [11] and Husmann et al [10] also reported smaller horizontal offset but were quite comparable to our study results. Rubin et al [7] (Swiss study) reported a larger horizontal offset in comparison to our study.

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The mean vertical offset (VO) was 56.37 ± 3.89 mm. The mean vertical offset are comparable between the males and females. Sengodan et al [4], Rawal et al [11] and Agarwala et al [6] reported smaller vertical offset in their study. While the studies done by, Rubin et al [7], Husmann et al [10] reported a similar mean vertical offset in comparison to our study. The difference in size of femoral head offset leads to tension in the joint soft tissue and can cause postsurgery dislocation. [10,12] Maintaining the leg length (VO) and HO helps to preserve proper hip biomechanics and improves overall postsurgical patient satisfaction in total hip replacement. [13,14] The mean acetabular angle of sharp (AA) was 43.11 ± 1.35 degree (range: 36.07 to 47.00 degrees). It is comparable between the males and females. Sengodan et al [4], Saikia et al [5] and Agarwala et al [6] found mean acetabular angle of sharp to be smaller in comparison to our study. There is a large variation among the Indian ethnic groups. The mean acetabular version (AV) was 19.47 ± 3.96 degree (range: 11 to 30 degrees). This was comparable between the males and females. It was slightly lower in Sengodan et al [4] study and comparable with Agarwala et al [6] study. If the cup has been excessively anteverted, anterior dislocation can occur during hip extension, adduction, and external rotation. If the cup is retroverted, dislocation occurs posteriorly with flexion, adduction, and internal rotation. Excessive inclination of the cup can lead to superior dislocation with adduction, especially if there is a residual adduction contracture, or if the femur impinges on osteophytes left along the inferior margin of the acetabulum. Conversely, if the cup is inclined almost horizontally, impingement occurs in early flexion, and the hip dislocates posteriorly, this is accentuated if the cup also is in less anteversion.

Limitation Of the Study
The limitation of the study is that we have considered the data of other Indian Ethnic groups from the available literature, but no primary data collection was performed. A study with similar parameters on a larger population across India, would provide much more accurate data and will help in designing the prosthesis replicating the actual biomechanics of the hip bone. But definitely our study will provide baseline information for the manufacturers of prosthesis for designing the prosthesis and the surgeons for selecting appropriate prosthesis for their patients.

Conclusion:-
A prosthesis which replicates the actual hip joint biomechanics will give a better patient satisfaction and longevity to the prosthesis. In order to achieve that, while designing the prosthesis the ethnic differences should be kept in mind by the manufacturers. An incompatible prosthesis leads to many postoperative complications. Apart from geographical differences in the anthropometric parameters of Indians as compared to other countries, our study found that within India also, there are differences in these anthropometric parameters. Hence, we recommend that biomechanical engineers should develop implant designs to suit specific Indian population, which will improve the clinical and functional outcome, reduce the chances of revision surgery and ultimately saving the patients money.