Proximal femur has a significant functional modification on erect bipedal posture. The morphology of the proximal femur, especially the relationship between proximal femur and the shaft of femur is an interesting subject in orthopedic literature. The geometry of the proximal femur is determined by genetic and environmental factors such as age, race, sex, and lifestyle.[1] Anthropometric dimensions described for proximal femur in Westerners might be quite different from those encountered among Indians. Hence, the knowledge regarding proximal femur is important for understanding the biomechanics of the hip as well as surgical planning.[2] Anthropometric analysis of the proximal femur will be useful in the management of the pathological conditions such as osteoarthritis of the hip, fracture neck of femur, and pertrochanteric fractures.[3]

During surgery of the acetabular fractures or during the placement of acetabular cups in arthroplasty, placement of the screws in the acetabulum is very critical because of the neurovascular structures that surround it. Therefore, it is very important to know the anatomical landmarks as well as the average length of the screws that can be placed safely at various quadrants of the acetabulum.[4]

In medico legal cases determination of stature, sex and age from skeletal remains of the deceased person is often referred to the anatomist and other professionals in the field of anthropology. Knowledge of various dimensions of the femoral head in both the sexes is of great help in manufacture of the prosthesis of femoral head which may be used by the orthopaedic surgeons in femoral head replacement surgery, [5,6] Present study was aimed to study, gender and age based morphometric study of hip joint in plain radiographs of adult Indian population.

This prospective observational study was undertaken at a tertiary healthcare facility situated in Western Rajasthan. All pelvic radiographs obtained in the radiology department between 2023 and 2024 were sourced from the hospital’s Picture Archiving and Communication System (PACS). The X-rays reviewed included images from inpatient admissions, outpatient consultations, and emergency room evaluations.

A total of 206 anteroposterior pelvic radiographs, representing 412 hip joints, from healthy adult participants were included in the analysis. The study population comprised 138 male and 68 female subjects, aged between 20 and 80 years.

Inclusion Criteria:

Only radiographs demonstrating normal hip morphology on both sides were considered suitable for inclusion.

Exclusion Criteria:

Images showing abnormalities such as fractures, arthritic changes, sequelae of prior infections, skeletal dysplasias, or those with improper positioning or poor image quality were excluded. The majority of radiographs were originally acquired for complaints such as low back pain, hip discomfort, or as part of a trauma evaluation series.

Radiographic Technique

Each subject was positioned in a supine posture on a radiolucent examination table, with the knees fully extended and the feet held in neutral rotation using a stabilizing foot holder. The source-to-image distance was maintained at 1.2 meters, and the central X-ray beam was focused on the lesser trochanter. A roentgenographic ruler was used to compensate for magnification, which was estimated to be approximately 15%. Proper positioning was ensured by aligning the coccyx centrally over the pubic symphysis and maintaining a distance of 2–4 cm above it.

Radiographic Measurements

Determination of Femoral Head Center: Three reference points were marked along the curved contour of the femoral head on the radiograph. Lines connecting these points were drawn, followed by construction of perpendicular bisectors. The intersection of these bisectors was identified as the center of the femoral head.

Femoral Shaft Axis:

This was determined by drawing a straight line through the midpoint of the femoral shaft at the isthmus, ensuring it passed centrally through the medullary canal.

Neck Shaft Axis (NSA):

The NSA was constructed by connecting the center of the femoral head to the midpoint of the femoral neck isthmus, extending the line until it intersected with the femoral shaft axis.

Neck Shaft Angle:

This angle represents the intersection between the femoral shaft axis and the neck axis [Figure 1a]. The femoral shaft axis was drawn through two equidistant points located at the center of the femoral shaft. The neck axis was formed by linking two points equidistant from the superior and inferior margins of the femoral neck.

Femoral Neck Width:

This was assessed by drawing a perpendicular line across the narrowest section of the femoral neck, aligned to the neck axis [Figure 1c].

Lesser Trochanter (LT):

The lesser trochanter is described as a cone-shaped bony projection located on the posteromedial aspect where the femoral neck joins the shaft.

Radiographic Parameters Measured (See Figures 1 and 2):

Vertical Offset(VO):

Defined as the perpendicular distance from the center of the femoral head to a horizontal line drawn at the upper margin of the lesser trochanter. In some studies, this is also referred to as the vertical drop.

Horizontal Offset(HO): The perpendicular measurement from the center of the femoral head to the femoral shaft axis. Clinically, this is often referred to as the lateral offset.

All radiographic measurements were carried out using RadiAnt DICOM viewer (version 4.6.5.18450, 64-bit). Statistical analyses, including calculation of mean values and standard deviations, were performed using SPSS software. The obtained values were compared with those reported in Western populations.

A total of 206 standard pelvic radiographs, comprising 412 hip joints from healthy subjects, were analyzed. The sample included 138 males and 68 females aged between 20 and 80 years. Various anatomical parameters were assessed. Among the male participants, the average neck-shaft angle was recorded as 127.74° (±3.93), with a horizontal offset of 34.48 mm (±6.52) and a vertical offset of 39.22 mm (±5.91) (refer to Table 1). In female subjects, the mean neck-shaft angle was found to be

125.88° (±4.72), while the horizontal and vertical offsets measured 32.91 mm (±7.02) and 36.42 mm (±6.25), respectively (refer to Table 2). All three parameters demonstrated a normal (Gaussian) distribution pattern (Figures 3–5).

Fig. 1. A sample radiograph of the hip joint on which the calculations were made

Fig. 2. Illustration to demonstrate how various parameters were calculated. As a first step all the important land marks – centre of the femoral head, lesser trochanter (LT), femoral shaft axis (FSA) and neck shaft axis (NSA) were templated. The neck shaft angle, vertical and horizontal offsets were then calculated using method described in the text.

Table 1 For male hip joint radiographs (n = 138, no. of hip joints = 276).

Table 2 For female hip joint radiographs (n = 68, no. of hip joints = 136).

Fig. 3. Graph showing variation in neck shaft angle

Fig. 4. Graph showing variation in vertical offset

Fig. 5. Graph showing variation in horizontal offset.

Inter-observer reliability

Inter-observer reliability (three rater un-weighted Kappa (χ) statistic) was determined for each parameter on the structured assessment. All the parameters observed by three observers returned a substantial inter- observer reliability (χ > 0.60).

Comparison with existing data

A comparison with existing data on western population is provided in Table 3. The results showed that there exist significant differences in parameters measured specifically the lateral or horizontal offset. There was a statistically significant difference (p < 0.05) among the results observed in three most recent studies by Pouget et al., Lequesen et al. and Girard et al. (Table 3).

Table 3 Existing study data on western population

Skeletal geometry is inherently unique to each individual. Prior anthropometric research has consistently demonstrated that anatomical differences in skeletal structures are influenced by ethnicity and geographic location. This is supported by Bergmann’s rule, which relates body mass to latitude, and Allen’s rule, which links appendage length to climate conditions [7]. Historically, studies have reported that Indian and other Asian populations typically have smaller body frames and statures when compared to Western populations [8,9].

Several earlier investigations have emphasized the importance of using anatomical data to guide femoral component design. Even slight discrepancies between prosthetic components and patient anatomy can significantly impact biomechanics [13–16]. Restoring the native anatomy of the hip joint is crucial for minimizing joint reaction forces. Any deviation in the position of the femoral head center can alter lever mechanics. For example, an increased offset enhances the abductor muscle moment arm, reducing the muscle force needed and, in turn, lowering joint reaction forces. However, excessive offset may raise the bending moment on the prosthesis, potentially increasing mechanical stress at the prosthesis-bone interface and leading to complications such as loosening or breakage [17]. Thus, achieving anatomical accuracy in hip reconstruction is essential. Inadequate restoration of hip geometry during total hip arthroplasty (THA) has been linked to higher rates of dislocation [18], muscle weakness [16], limping [15], limb length discrepancies [19], impingement, and early implant loosening [24–27]. Incorrect offset can also affect polyethylene wear rates [28,29]. Research in other joints has similarly shown that anatomical reconstruction leads to better clinical outcomes [30].

Numerous anthropometric studies of the hip have demonstrated substantial individual variability and wide standard deviations in neck- shaft angles (NSA) across populations. For instance, Lequesne et al. reported a mean NSA of 132.8° in Western populations, with a standard deviation of 4.37. More recent works by Pouget [11] and Girard et al. [12] found similar values, close to 135°, which likely influenced the design of many femoral stems with a standard NSA of 135°. In contrast, comparative studies involving Chinese [10], Nigerian [30,31], and other ethnic groups have documented notable differences in these anatomical parameters. Hoaglund and Low highlighted considerable discrepancies in femoral head, neck, and shaft dimensions between Caucasians and Hong Kong Chinese individuals [10].

In India, only a few studies have recently addressed the normal anthropometry of the hip [32–36]. Jain et al. [32] observed significant.

variations in femoral neck anteversion among Indians and proposed that such differences might reflect evolutionary adaptations related to frequent floor-level postures, which involve greater abduction and external rotation. This adaptation could also contribute to the relatively low prevalence of primary hip osteoarthritis in the Indian population. A cadaveric study by Siwach and Dahiya [37] reported a mean NSA of 123.5°, along with differences in anteversion and neck length. Despite the relevance of these findings, they have yet to influence implant design, possibly because the study lacked radiographic validation and did not focus on crucial parameters like lateral offset and vertical drop— important considerations in hip arthroplasty. The present study, which features a broader sample base, aligns closely with Siwach et al.’s findings and further substantiates their conclusions.

In our research, the average NSA was 127.74° in males and 125.88° in females (Males: range = 20°, Max = 139°, Min = 119°, SD = ±3.93; Females: range = 23°, Max = 137°, Min = 114°, SD = ±4.72). Similarly, the mean horizontal (or lateral) offset was 36.8 mm, which is significantly lower than the values reported in Western studies. Although vertical offset is not a standard radiographic parameter, it is frequently used by surgeons in preoperative planning. Even without existing comparative data, our findings offer useful baseline values. Tables 1 and 2 reveal two key insights: first, there is no statistically significant difference between male and female hip anthropometry; second, there is a notable divergence between Indian and Western populations. The absence of gender-specific differences may indicate that separate implants for males and females are unnecessary. However, the clear ethnic variation highlights the need for race-specific prosthetic designs. Similar anthropometric data in the past have led to adjustments in trauma implants, such as the Gamma nail [38– 40]. Therefore, considering racial variation is crucial when developing arthroplasty implants, and this study may serve as a foundational reference for future designs. Moreover, this data could assist in exploring the underlying factors contributing to the lower incidence of primary hip osteoarthritis among Indians.

One strategy to accommodate anatomical diversity and enhance surgical flexibility is through modular implant designs [41]. However, most modular prostheses primarily offer variation in offset, with fewer allowing changes to the neck-shaft angle or lateral offset. Additionally, modular systems are often costlier and may generate more particulate debris. Consequently, having accurate normative anatomical data is critical for designing widely used, fixed-angle implants. Surface replacement arthroplasty (SRA) offers another method for achieving anatomical alignment, though it too depends on precise measurements of the femoral neck and head [42].

A potential limitation of this study could be the reliability of radiographic methods and inter-observer consistency. To address this, we utilized standard anatomical landmarks and mathematical models to determine the center of the femoral head, femoral shaft axis, and neck axis. Involving three observers from different specialties and achieving strong statistical agreement reinforces the reproducibility of our technique [43]. Although radiographic NSA measurements may be slightly affected by patient positioning, such methods remain well-established in lower limb arthroplasty [44]. Most studies have shown a minor error (1–2°) in NSA measurement from plain X-rays in normal anteverted necks, and even in cases with 30° anteversion, the margin of error is under 5° [45,46]. CT imaging, however, remains the preferred method for assessing femoral canal shape and neck anteversion.

To conclude, this study underscores significant differences between Indian and Western hip anthropometry. These insights are expected to inform the development of more anatomically suitable hip implants for individuals from the Indian subcontinent, a population where the demand for hip replacement procedures is projected to rise substantially.

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