Assessment of the hip-spine relationship in total hip arthroplasty for childhood hip disorders sequelae

Abstract

In this article, we comment on the article by Oommen et al. Oommen et al provided a comprehensive overview of the management of hip centre restoration in total hip arthroplasty (THA) for childhood hip disorder sequelae. Given the developmental disparity in this population, specific preoperative planning is an essential prerequisite for the success of THA procedures. In the review by Oommen et al, assessments of acetabular and femoral anatomic variations were fully described. However, spinal malalignment and stiffness are common in physical and radiological examinations and should be taken into careful consideration when planning surgical procedures. Poor outcomes of THA for patients with comorbid hip and spinopelvic pathologies have been widely reported, especially for hips with childhood disorder sequelae. Therefore, in this editorial, we would like to emphasize the need for a thorough hip-spine evaluation of patients with childhood hip disorder sequelae before THA.

Key Words: Relationship between the hip and spine; Total hip arthroplasty; Childhood disorder sequelae; Preoperative assessment; Hip-spine classification

Core Tip: In patients with childhood hip disorder sequelae, spinal malalignment and stiffness are common in physical and radiological examinations and should be carefully considered during planning of total hip arthroplasty. A comprehensive assessment of acetabular, femoral, and spinopelvic pathologies is crucial. The anterior pelvic plane and sacral slope on standing and sitting lateral radiographs could provide useful information for assessing the hip-spine relationship. Preoperative assessment and hip-spine classification will help plan component positions.

TO THE EDITOR

Concomitant spinopelvic pathologies, such as lumbar spine stiffness and sagittal spinal deformity, are commonly found in patients with paediatric hip problems[1,2]. Total hip arthroplasty (THA) is associated with considerable risk of postsurgical problems, such as instability, dislocation, and revision surgery[3]. The hip-spine relationship should be thoroughly evaluated as a separate risk factor to identify the appropriate component positioning[4].

In normal patients, when changing position from standing to sitting, accommodation of the hip joint can lead to approximately 15.6 degrees of an increase in acetabular anteversion and reduce anterior impingement as the hip flexes[5]. With hip flexion, the increase in acetabular inclination with increasing pelvic tilt may protect against anterior impingement. Supplementary radiographs should be routinely obtained to evaluate spinopelvic kinematics for patients with sequelae of childhood hip disorders. These should include a lateral view of the lumbar spine and pelvis in both standing and sitting postures and a standing anteroposterior view of the pelvis. Furthermore, the anterior pelvic plane (APP), characterised by the points of the two anterior superior iliac spines and the pubic symphysis on a lateral pelvic radiograph, is advised[4]. Anterior and posterior pelvic tilt refer to the movement direction of the upper portion of the ilium. The angle formed by the superior endplate of the S1 vertebra and a horizontal reference, usually the inferior border of the radiograph, is known as the sacral slope (SS). APP and SS are effective measurements for evaluating spinopelvic motion in relation to postural changes[6].

During the transition from standing to sitting, the pelvis undergoes posterior tilting, accompanied by a concomitant decrease in lumbar lordosis and a flattening of the SS. The typical SS alteration varies from 11 to 30 degrees between the two functional postures[7]. Spinopelvic stiffness is characterised by an SS alteration of less than 10 degrees. For patients with spinopelvic stiffness, reduced pelvic rollback increases hip joint flexion while seated, increasing the possibility of anterior-inferior iliac spine bone impingement and decreasing posterior-inferior acetabular covering of the femoral head[8]. Accordingly, greater compensation for the anteversion of the acetabular cup will be needed to accommodate altered spinopelvic motion in these patients.

The angle formed between a line that runs from the centre of the femoral head to the centre of the superior endplate of S1 and another line that is orthogonal to the S1 endplate is known as the pelvic incidence. This value represents the anterior-to-posterior relationship of the femoral head to the lower lumbar spine and is usually constant during posture alterations[9]. It can be utilised to identify flatback spinal deformities with excessive posterior pelvic tilt in an upright position. This increases the functional anteversion of the acetabulum while standing, thereby resulting in anterior instability. Consequently, it might be necessary to reduce acetabular cup anteversion in these patients[2,10].

Conventional Lewinnek's safe zone is not a suitable guideline for component placement and orientation for patients with the aftereffects of childhood hip problems. Increased anteversion and inclination can lower the possibility of posterior-inferior acetabular under coverage of the femoral head and anterior impingement[6,11]. The implementation of a preoperative assessment and hip-spine classification will facilitate the planning of component placements.

CONCLUSION

For patients with childhood hip disorder sequelae prior to THA, it is crucial to perform a comprehensive assessment of acetabular, femoral, and spinopelvic pathologies. The APP and SS on standing and sitting lateral radiographs could provide useful information for assessing the hip-spine relationship. Preoperative examination and hip-spine classification are helpful for planning component positions.

ACKNOWLEDGEMENTS

We would like to express our sincere gratitude to Dr. Wang Yan from Chongqing Medical University for her valuable contributions to correcting the grammar and polishing the manuscript’s language.