Introduction

Hip flexion contracture can severely alter the patient’s alignment, and therefore have a negative effect on the patient’s quality of life. Hip contracture is not well studied, partly because of the difficulties of its diagnosis which is often qualitative or based on physical examination. The aim of this study was to propose a quantitative definition of hip flexion contracture in hip osteoarthritis patients, and to analyze sagittal alignment in contracture patients compared to non-contracture ones, before and 12 months after total hip arthroplasty (THA).

Methods

One-hundred twenty-three patients with an indication of THA were included in a prospective and consecutive cohort (101 women and 22 men, median age 70 [63; 76]). Exclusion criteria were: spinal implant more than two vertebral levels or with iliosacral screws, and scoliosis (Cobb angle > 25°). IRB approved the data collection.

Patients underwent lateral full-body radiographs in free standing position and in extension (Figure 1). Acquisitions were obtained preoperatively and, for 70 patients, 12 months postoperatively. Spinopelvic parameters were measured in both radiographs: pelvic tilt, pelvic incidence (PI), T1-pelvic angle and pelvic-femur angle (PFA), i.e. is the angle between the femur and a line drawn from the middle of the sacrum endplate to the centre of the interacetabular hip axis.

Patients with low PI (< 45°) were included in the hip contracture group if their PFA > 5°, or when PFA > -5° for patients with standard or high PI (PI ≥ 45°). Examples are provided in Figure 1.

Results

Thirty-seven patients (30%) were in the hip flexion contracture group (30%). Flexion hip contracture patients showed a specific pattern of sagittal spinopelvic alignment (Table 1), with lower pelvic tilt and T1-pelvis angle, and higher lordosis. A similar pattern was observed postoperatively. In particular, PFA significantly decreased after surgery (p= 0.004, i.e., range of motion improved), but hip contracture was still present in 8% of patients.

Discussion

A method was proposed to identify patients with hip contracture in a cohort of hip osteoarthritis patient, based on PFA in extension. High PFA in extension, corresponding to reduced hip range of motion, was associated with hip flexion contracture; these patients showed a specific pattern of sagittal alignment which involved the whole chain of compensation, from lower limb to the proximal spine. Further studies will show how to improve treatment for these patients.