Sagittal Spinopelvic Translation Is Combined With Pelvic Tilt During the Standing to Sitting Position: Pelvic Incidence Is a Key Factor in Patients Who Underwent THA

Abstract

Background: Sagittal spinopelvic translation (SSPT) is the horizontal distance from the hip center to the C7 plumb line (C7PL). SSPT is an important variable showing the overall patient balance in different functional positions which could affect the rate of hip instability. This study investigates the SSPT modification in patients who underwent total hip arthroplasty (THA). Methods: A total of 120 patients were assessed preoperatively and postoperatively on standing and sitting acquisitions (primary unilateral THA without complication). SSPT is zero when the C7PL goes through the center of the femoral heads and positive when the C7PL is posterior to the hips' center (negative if anterior). Three subgroups were defined based on the pelvic incidence (PI): low PI <45 , 45 < normal PI <65 , or high PI >65. Results: The overall mean preoperative SSPT change from standing to sitting was 2.2 cm ([-7.2 to 17.4]) (P < .05). The overall mean postoperative SSPT change from standing to sitting was 1.2 cm ([-14.2 to 22.4]) (P < .05). In low-and normal-PI groups, standing to sitting SSPT and preoperative to postoperative changes in standing SSPT were increased significantly after surgery with the C7PL behind the hips' center (P < .05). In the high-PI group, standing to sitting SSPT was increased postoperatively (P ¼ .034) (no significant changes from preoperative to postoperative status in standing and sitting). Conclusions: Adaptation from standing to sitting positions combines pelvic tilt and anteroposterior pelvic translation. THA implantation induces significant changes in SSPT mainly for low-and standard-PI patients. This is an important variable to consider when investigating the causes of THA subluxation or dislocation.

Association between sagittal spinal alignment and mechanical complications after primary total hip arthroplasty: a systematic review

“…In the discussions, three of the included studies seem to confirm the importance of global spinal alignment when planning THA to better understand the hip–spine relationship and identify those patients at high risk for MCs after THA. 3 , 11 , 12 In the data, however, the articles did not focus on spinal alignment. SVA was the only reported parameter that measures global sagittal alignment of the spine ( Table 4 ).…”

“…found that patients with negative sitting SSPT are at higher risk for THA dislocation than patients with positive sitting SSPT. 3 …”

“… 1 However, several studies have since provided evidence that the Lewinnek safe zone does not always predict stability. 2 – 4 When Lewinnek first described the safe zone, the acetabular anteversion and inclination were measured from a supine radiograph taken perpendicular to the anterior pelvic plane (APP). 1 , 2 During postural changes, however, the acetabular cup does not remain static and instead moves with the spinopelvic motion.…”

“…Furthermore, spinal malalignment may change pelvic mobility and position, which can result in an acetabular cup being out of the expected safe zone. 3 – 5 …”

Imaging in Hip Arthroplasty Management Part 2: Postoperative Diagnostic Imaging Strategy

“…Additionally, the more fused levels, the more acetabular anteversion and inclination decrease (about 1° for each fused group for each value) [ 70 ]. Therefore, it has been proposed by Lazennec et al to evaluate lumbosacral junction using standing and sitting EOS imaging or radiographs in patients with spine fusion in THA planning and follow-up [ 71 , 72 , 73 ], but this attitude is not yet officially recommended.…”