Normal hip joint contact pressure distribution in single-leg standing—effect of gender and anatomic parameters

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Abstract

A practical and easy-to-use analysis technique that can study the patient's hip joint contact force/pressure distribution would be useful to assess the effect of abnormal biomechanical conditions and anatomical deformities on joint contact stress for treatment planning purpose. This technique can also help to establish the normative database on hip joint contact pressure distribution in men and women in different age groups. Twelve anatomic parameters and seven biomechanical parameters of the hip joint in a normal population (41 females, 15 males) were calculated. The inter-parameter correlations were investigated. The pressure distribution in the hip joint was calculated using a three-dimensional discrete element analysis (DEA) technique. The 3D contact geometry of the hip joint was estimated from a 2D radiograph by assuming that the femoral head and the acetabular surface were spherical in shape. The head–trochanter ratio (HT), femoral head radius, pelvic height, the joint contact area, the normalized peak contact pressure, abductor force, and the joint contact force were significantly different between men and women. The normalized peak contact pressure was correlated both with acetabular coverage and head–trochanter ratio. Change of abductor force direction within normal variation did not affect the joint peak contact pressure. However, in simulated dysplastic conditions when the CE angle is small or negative, abductor muscle direction becomes very sensitive in joint contact pressure estimation. The models and the results presented can be used as the reference base in computer simulation for preoperative planning in pelvic or femoral osteotomy.

Introduction

It is well understood in orthopeadics that the long-term results of total hip arthroplasty (THA) in younger patients are not favorable. An alternative procedure for this age group is femoral and/or pelvic osteotomy. Although osteotomy has been reported to be effective in some clinical series (Pauwels, 1976; Bombelli, 1976; Mitchell, 1974) their results are not as predictable as those managed with THA (Calvert et al., 1987; Santore and Bombelli, 1983). One of the key factors responsible for such variability is the lack of objectivity in choosing the optimal operative method and the degree of correction in each patient. In fact, the recommended procedure varies from surgeon to surgeon. An osteotomy will affect leg alignment, muscle orientation and acetabular weight-bearing area. As a result, it changes the joint contact force and pressure distribution. These are the biomechanical factors that should be considered for preoperative planning to improve the long-term results of such operations. However, it is difficult to determine the subtle effects of these factors on the normal biomechanical function of the hip. A practical and easy-to-use analytical technique that can quantitate each patient's preoperative biomechanical condition and compare the changes that can be brought about by different operative procedures would be useful in selecting the most appropriate operation for a given patient.

When an osteotomy is planned, there is no standard to be used as the reference for justifying the optimal correction angle or translation. Certain objective criteria must be established based on reliable normative database. Therefore, in preparing an osteotomy simulation, it would be important to obtain normal values and their variability for the key anatomical and biomechanical parameters. Among these parameters, joint contact pressure distribution and the normalized peak pressure were used to evaluate the biomechanical effects of hip osteotomy on joint function. In addition, for the purpose of repositioning the normal and degenerated cartilage on the femoral head in relationship to hip joint function through osteotomy, it would be important to quantitate joint contact pressure distribution to justify the proposed reconstructive procedure.

The underlying hypothesis of this study was that under normal hip anatomy, joint contact pressure could be estimated using a 2D AP standing radiograph of the lower extremity including the pelvis and these biomechanical parameters would correlate with the basic anatomic parameters of the hip. The objectives of this study were: (1) to determine the normal variation of hip joint anatomical and biomechanical parameters, (2) to calculate the joint contact pressure using the discrete element analysis (DEA) technique and (3) to identify the key anatomical parameters which will affect joint contact pressure magnitude and distribution. These analyses were performed using 2D AP radiographs. We intend to use these results as a guide to plan pelvic and/or femoral osteotomies.

Section snippets

Materials and methods

Forty-one women and fifteen men with normal hips whose ages ranged from 25 to 65 years were selected as the normal adult population for this study. Although we started with equal number of men and women in two age groups in this study, limited X-ray film size and the large width of the pelvis dimension in significant number of men prevented the inclusion of more than half of the X-rays from men in our population. Therefore, the age effect could only be studied in women with sufficient sample

Anatomic parameters in the normal population

In the parameters which represent the shape of the joint, i.e., the CE angle, the AHI and Sharp angle, the AC angle, the Spherical sector angle and ATD, there were no statistical differences between genders or between the two age groups among the women studied (Table 1). When the women were divided into two age groups (25–45 and 46–65), there was no significant difference in any of the anatomical parameters studied. The TIA which related the abductor force angle, also was not significantly

Discussion

There are many anatomic parameters which have been used to describe deformities in the hip joint. Unfortunately, no single parameter can be established as the sole determinant to assess the proper biomechanical function of the hip joint. Consequently, it becomes rather difficult to determine the optimal treatment method and estimate the prognosis of the disease without any knowledge as to which of these parameters are more important in affecting the normal function of the hip. However, most

Summary

The head–trochanter ratio (HT) was significantly larger and femoral head radius was significantly smaller in women when compared to men. Consequently, peak-contact pressure, abductor force and joint contact force were significantly larger in women based on a unified body weight. The peak-contact pressure of the hip joint was correlated both with acetabular coverage and head–trochanter ratio. The change of abductor force direction within its assumed normal range did not affect the joint peak

Acknowledgements

This study was supported in part by ATP Award FONANB 2 H 1259, NIST, the Grant CA23751 awarded by NCI, NIH, DHHS, and the OREF Bristol-Meyers Center of Excellence Grant.

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