This cross-sectional study was conducted on 104 dry human adult hip bones of unknown sex belonging to both sides (54 right and 50 left) in the Department of Anatomy of Dhanalakshmi Srinivasan Medical College and Hospital, Perambalur, Tamil Nadu and Government Dharmapuri Medical College, Dharmapuri, Tamil Nadu, India from February 2017 to September 2019 after obtaining ethical clearance from Institutional Ethics Committee of human studies (Project no. IECHS/DSMCH/026). Bones with evidence of wear and tear, congenital defects and fracture were excluded from the study.

The morphometric parameters taken in the present study were depth and diameter of the acetabulum. The procedures for measuring the depth and diameter were taken from previous studies [11,12]. The parameters were measured as follows:

Diameter of the acetabulum- The distance between the acetabular ridge nearest to the body of ischium and anterior iliac margin intersecting the acetabular ridge was measured as acetabular diameter using digital vernier caliper [Table/Fig-1]. [Table/Fig-1]:

Measurement of diameter of acetabulum.

Depth of the acetabulum- Maximum vertical distance from the deepest point in the acetabular cavity to the brim of the acetabulum was taken as depth. A metallic strip was placed across the acetabular margin and depth of the acetabulum was measured in millimeters using digital vernier caliper from the deepest point in the acetabulum to metallic scale [Table/Fig-2]. [Table/Fig-2]:

Measurement of depth of acetabulum.

The morphology of anterior acetabular ridge in the study was evaluated. The shape of the anterior acetabular ridge was categorised into curved, angular, straight and irregular types [Table/Fig-3a-d] [11-14].

[Table/Fig-3]:

a) Angular shaped anterior acetabular ridge; b) Curved shaped anterior acetabular ridge; c) Straight shaped anterior acetabular ridge; d) Irregular shaped anterior acetabular ridge.

The data collected for all parameters were entered in Microsoft Excel (version 2019) and analysed statistically to find range, mean, standard deviation and Student’s t-test was applied. Pearson’s test was used to evaluate the correlation between the diameter and depth of the acetabulum. The p-value <0.05 were considered as statistically significant. All data were analysed using statistical software SPSS version 16.0.

The morphometric parameters (diameter and depth) of acetabulum presented in [Table/Fig-4] show the average values, standard deviation and maximum and minimum values of the parameters on right and left side. The average values of acetabular diameter and depth obtained in present study were 48.98±2.91 mm and 24.12±2.54 mm, respectively. The maximum and minimum diameter of acetabulum measured were 56 mm and 41 mm, respectively. The range of maximum and minimum acetabular depth in present study was from 30 mm to 20 mm. Range of maximum and minimum values of these parameters shows the variations in the normal population. Although the measurements of parameters on left side were slightly higher than the right side, there was no statistically significant difference between right and left side (p>0.05). There was a positive correlation between average dimensions of diameter and depth of the acetabulum (r-value -0.388; strength of correlation was weakly positive, p-value <0.001). Thus, it can be inferred that there is a possibility of increase in the depth of acetabulum, when diameter increases.

[Table/Fig-5] shows the frequency of different shapes of acetabular ridge. The most common shape of anterior acetabular ridge in present study was curved (63.46%) followed by angular shape (23.08%). The least common shape of acetabular margin observed in present study was straight type (2.88%).

The primary objective of the study was to emphasise the significance of anthropometry of acetabulum. One of the essential preconditions for the normal biomechanics of hip joint is its normal shape. The abnormalities in the dimensions of acetabulum are important in understanding the pathology of hip joint diseases like primary osteoarthrosis [13]. The incongruous hip joint is more prone for degeneration than a joint having normal anatomy [5].

An effort has been made in the present study to examine the dry hip bones with the available data in relation to various parameters. The parameters were selected from the literature available in the previously published articles [11-14]. In order to get better insight on the results obtained, the present study was compared to some of the earlier investigations [Table/Fig-6] [12-19].

Aksu F et al., reported the average diameter of acetabulum in Turkish population as 54.29±3.8 mm [14]. In a study done by Ukoha UU et al., in the African population, the mean diameter was 54.8±3.5 mm and 53.9±3.0 mm on right and left side, respectively [15], closer to the results of Indurjeeth K et al., who also did study on African population [18]. But the studies done on Indian population by previous authors {Devi TB and Philip CX, Sreedevi G and Sangam MR, and Bahl I et al., [13,17,19]} revealed the average diameter around 49 mm which is similar to present study results. These differences in the results can be attributed to racial variations and Chauhan R et al., opined that smaller values of the acetabulum parameters are due to short stature of Indians when compared to Africans [11]. But Paramara G et al., reported average diameter as 42.54±3.6 mm in Indians which was lower when compared to present study [12]. Chauhan R et al., who measured the parameters on cadavers found the mean diameter as 47.10±2.90 mm (right side), 47.48±3.05 mm (left side) in males and 44.38±3.01 mm (right side), 46.0±2.28 mm (left side) in females which is more or less similar to present study findings on dry bones [11].

Acetabular depth is essential in maintaining normal hip mechanics and establishing a good range of movement. It acts as one of the contributing factors in component dislocation [16]. The acetabular depth has been considered by many investigators as an important measurement in defining acetabular dysplasia. The acetabulum with depth of less than 9 mm is regarded as acetabular dysplasia [20]. The average depth of acetabulum in present study was 24.12±2.54 mm which is similar to the findings of Sreedevi G and Sangam MR [17] but greater than the measurements done by Parmara G et al., as represented in [Table/Fig-6] [12]. Devi TB and Philip CX, Khobragade L and Vatsalaswamy P, and Bahl I et al., reported slightly higher values in Indian population when compared to the present study [13,16,19]. Aksu F et al., Ukoha UU et al., and Indurjeeth K et al., found higher values of mean depth of acetabulum but their studies were conducted on people from different races [14,15,18].

Chauhan R et al., after studying the diameter of both acetabulum and femoral head described that the average diameter of femoral head is smaller than the average diameter of acetabulum in North Indian cadavers so that the femoral head is snugly fitted into the acetabular depression which is one of the major reasons why primary osteoarthritis of hip joint is not so common in Indians [11].

The morphometric parameters measured in present study had a higher value on left side when compared to right side but were not statistically significant. According to Chhibber SR and Singh I, left limb was dominant [21]. More people use left lower limb for weight bearing, whether they are right-handed or left-handed. Hence, in order to bear greater loading force on femur on left side, the dimensions of the bones forming the hip joint of left side should be more than the right [21].

Thus, from the findings of the present study it can be inferred that, acetabular dimensions in Indian population were smaller when compared to other populations and measurements on left side were greater than right side since most people use left lower limb for weight bearing. The frequency of different shapes of anterior acetabular ridge in present study was in near coincidence with Devi TB and Philip CX, and Maruyama M et al., [13,22]. Present study observed curved type as the most common shape of anterior acetabular ridge similar to previous studies done on Indian population [12,13,17,19]. But Indurjeeth K et al., found angular shape to be the most common in African population [18]. This disparity in the findings could be attributed to racial variations [15]. Present study observed straight type as the least common shape of anterior acetabular ridge which is similar to Devi TB and Philip CX, and Bahl I et al., [13,19], whereas Sreedevi G and Sangam MR, and Pratibha K et al., noted irregular type in Indian population as the least common [Table/Fig-7] [12-15,17-19,22,23].

The aetiopathogenesis of hip joint diseases like acetabular dysplasia and pincer femoro-acetabular impingement are often associated with variations in the morphology of acetabulum including the acetabular diameter, depth and orientation [24]. The total hip arthroplasty is one of the most common surgeries done now-a-days in the field of orthopaedics. The knowledge of anatomical parameters of hip joint reduces the complications arising from the mismatch of prosthesis in hip arthroplasty [13]. The significant information about the average dimensions of acetabulum and morphology of anterior acetabular ridge will help the surgeon to determine the ideal size of acetabular cup during total hip arthroplasty. Using acetabular cups that replicate the curvaceous acetabular profile could reduce the incidence of iliopsoas impingement and prevent prosthetic overlap and mechanical loosening [23].

Failure to discriminate between the genders of the bones was the major limitation of this study.

The dimensions of acetabulum in Indians are smaller when compared to other populations and a weakly positive correlation between the mean values of acetabular diameter and depth was observed as per present study. Based on the findings of the current study, some amendments in the current knowledge of morphological and morphometric parameters of acetabulum were presented. Present study have provided a set of reference ranges for normal acetabular dimensions, which we believe, will be helpful for determining the safe position of acetabular implant during hip replacement surgery. Authors are hopeful that this study will also be valuable for the anthropologists in their racial and population studies.