Spine-Pelvis-Hip Relationship in the Functioning of a Total Hip Replacement

Abstract

* Spine-pelvis-hip motion is normally coordinated to allow balance of the mass of the trunk and hip motion with standing and sitting.* Normal motion from standing to sitting involves hip flexion of 55° to 70° and pelvic posterior tilt of 20°. Because the acetabulum is part of the pelvis, as the pelvis tilts posteriorly during sitting, the inclination and anteversion increase (the acetabulum opens) to allow clearance of the femoral head and neck during hip flexion. This can be considered the biological opening of the acetabulum.* Decreased tilt of the pelvis during movement occurs with stiffness of the spine. Loss of pelvic mobility forces hip motion to increase to accommodate postural change. Increased hip motion combined with change in the opening of the acetabulum increases the risk of impingement.* Hip stiffness can also reduce pelvic mobility because pelvic mobility is affected by both the spine and the hip. Relief of hip stiffness with total hip replacement can improve pelvic mobility postoperatively.* For hip surgeons, the clinical consequences of changes in the mobility of the spine and pelvis (spinopelvic mobility) can be impingement after total hip replacement, with the most obvious complication being dislocation. The reported increased dislocations in patients with surgical spine fusions is a clinical example of this consequence.

Posterior Pelvic Tilt From Supine to Standing in Patients With Symptomatic Developmental Dysplasia of the Hip

“…As the dynamics of the spine-pelvis-hip construct, the pelvis is controlled by two hinges, posteriorly the lumbosacral joint and anteriorly the hip joint. 12,13 Theoretically, the acetabular morphology has less impact on the sagittal tilt of the pelvis, while some studies reported that DDH patients tilt the pelvis anteriorly in standing to compensate for insufficient femoral head coverage by the dysplastic acetabulum. [14][15][16] On the other hand, others found a posterior rotation of the pelvis occurring from the supine to the standing position.…”

Pelvic Tilt Cannot Be Accurately Predicted Using Anteroposterior Radiographs

“…While lateral pelvic radiographs in the standing and seated positions should be used to calculate the change in pelvic tilt and assess for the presence of spinal stiffness or deformity that may predispose a patient to dislocation, they are not yet routinely used in clinical practice [1,7,13,[20][21][22]. Rather, orthopaedic surgeons typically refer to AP radiographs for surgical planning; which alone are not routinely used for evaluating spinopelvic mobility [1,[10][11][12]. Prior literature suggests that AP radiographs can be used to estimate spinopelvic parameters with some degree of reliability [15,18,22].…”

“…Although lateral radiographs are considered to be the gold standard modality for assessing APPt in patients undergoing THA, hip surgeons have been accustomed to assessing the acetabulum in a coronal plane using AP radiographs [1]. Traditional component positioning and postoperative assessment of THA has been based on coronal safe zones determined in the supine position [23].…”

“…Spinopelvic mobility refers to the motion that occurs between the spine, pelvis, and hips between changes in body positioning to maintain sagittal alignment and upright balance [1]. The rotation that occurs at the pelvis in the sagittal plane between these positions as the pelvis rotates around the femoral heads is referred to as pelvic tilt [2].…”

“…Two-dimensional, antero-posterior (AP) pelvic radiographs are considered by many hip surgeons to be the standard imaging modality for assessment of the hip in THA [1,[10][11][12]. The use of lateral radiographs of the lumbar spine and pelvis to study postural change and spinopelvic mobility is a relatively new concept [2,7,13].…”