Spinopelvic Motion: A Simplified Approach to a Complex Subject

Abstract

Knowledge of the relationship between the hip and spine is essential in the effort to minimize instability and improve outcomes following total hip arthroplasty (THA). A detailed yet straightforward preoperative imaging workup can provide valuable information on pelvic positioning, which may be helpful for optimum placement of the acetabular cup. For a streamlined preoperative assessment of THA candidates, classification systems with a capacity for providing a more personalized approach to performance of THA have been introduced. Familiarity with these systems and their clinical application is important in the effort to optimize component placement and reduce the risk of instability. Looking ahead, the principles of the hip-spine relationship are being integrated using emerging innovative technologies, promising further streamlining of the evaluation process.

Keywords: Arthroplasty; Hip; Spinal curvatures; Spine; Spinopelvic mobility.

Fig. 1

Standing anteroposterior pelvis and standing lateral radiographs for the evaluation of pelvic tilt, rotation, and obliquity.

Fig. 2

Standing (A) and sitting (B) lateral measurements for evaluation of the hip-spine relationship. APPt: anterior pelvic plane tilt, SS: sacral slope, PI: pelvic incidence, LL: lumbar lordosis.

Fig. 3

Sitting and standing radiographs in a patient with flatback deformity. This figure illustrates the key spinal parameters: anterior pelvic plane tilt (APPt), sacral slope (SS), lumbar lordosis (LL), and pelvic incidence (PI). A discrepancy greater than 10° between PI and LL is indicative of flatback deformity. The radiographs displayed show a PI-LL mismatch of 14°, confirming the presence of the deformity in the patient under study.

Fig. 4

Standing (A) and sitting (B) lateral EOS stereoradiographs imaging of a patient in the 1A group. Spinal deformity is not present with a PI-LL <10° (PI-LL=5°) and a relatively neutral pelvic tilt of –3°. Spinal mobility between standing and seated positions is appropriate with a ΔSS >10° (ΔSS=21°). APPt: anterior pelvic plane tilt, SS: sacral slope, LL: lumbar lordosis, PI: pelvic incidence.

Fig. 5

Standing (A) and sitting (B) lateral EOS stereoradiographs imaging of a patient in the 2B group. Spinal deformity is present with a PI-LL >10° (PI-LL=14°) and a posterior pelvic tilt of –11°. Spinopelvic mobility is decreased with a ΔSS <10° (ΔSS=5°) from standing to seated. APPt: anterior pelvic plane tilt, SS: sacral slope, LL: lumbar lordosis, PI: pelvic incidence.

Fig. 6

Lateral seated (A) and standing (B) X-rays.

Fig. 7

Cuptimize Hip-Spine Analysis preoperative planning screen. In this example, with a target cup position of 40° of inclination and 23° of anteversion, the predicted values in standing and seated positions is 41° of inclination and 25° of anteversion.

Fig. 8

Intraoperative fluoroscopic image demonstrating acetabular cup positioning with seated and standing prediction of anteversion and inclination.