The utility of supine radiographs in the assessment of thoracic flexibility and risk of proximal junctional kyphosis

Abstract

OBJECTIVE Supine radiographs have successfully been used for preoperative planning of lumbar deformity corrections. However, they have not been used to assess thoracic flexibility, which has recently garnered attention as a potential contributor to proximal junctional kyphosis (PJK). The purpose of this study was to compare supine to standing radiographs to assess thoracic flexibility and to determine whether thoracic flexibility is associated with PJK. METHODS A retrospective study was conducted of a single-institution database of patients with adult spinal deformity (ASD). Sagittal alignment parameters were compared between standing and supine and between pre- and postoperative radiographs. Thoracic flexibility was determined as the change between preoperative standing thoracic kyphosis (TK) and preoperative supine TK, and these changes were measured over the overall thoracic spine and the fused portion of the thoracic spine (i.e., TK fused). A case-control analysis was performed to compare thoracic flexibility between patients with PJK and those without (no PJK). The cohort was also stratified into three groups based on thoracic flexibility: kyphotic change (increased TK), lordotic change (decreased TK), and no change. The PJK rate was compared between the cohorts. RESULTS A total of 101 patients (mean 63 years old, 82.2% female, mean BMI 27.4 kg/m2) were included. Preoperative Scoliosis Research Society–Schwab ASD classification showed moderate preoperative deformity (pelvic tilt 27.7% [score ++]; pelvic incidence–lumbar lordosis mismatch 44.6% [score ++]; sagittal vertical axis 42.6% [score ++]). Postoperatively, the average offset from age-adjusted alignment goals demonstrated slight overcorrection in the study sample (−8.5° ± 15.6° pelvic incidence–lumbar lordosis mismatch, −29.2 ± 53.1 mm sagittal vertical axis, −5.4 ± 10.8 pelvic tilt, and −7.6 ± 11.7 T1 pelvic angle). TK decreased between standing and supine radiographs and increased postoperatively (TK fused: −25.3° vs −19.6° vs −29.9°; all p < 0.001). The overall rate of radiographic PJK was 23.8%. Comparisons between PJK and no PJK demonstrated that offsets from age-adjusted alignment goals were similar (p > 0.05 for all). There was a significant difference in the PJK rate when stratified by thoracic flexibility cohorts (kyphotic: 0.0% vs no change: 18.4% vs lordotic: 35.0%; p = 0.049). Logistic regression revealed thoracic flexibility (p = 0.045) as the only independent correlate of PJK. CONCLUSIONS Half of patients with ASD experienced significant changes in TK during supine positioning, a quality that may influence surgical strategy. Increased thoracic flexibility is associated with PJK, possibly secondary to fusing the patient’s spine in a flattened position intraoperatively.

The Role of Thoracic Tilt in Identifying Thoracic Compensation and Predicting Proximal Junctional Kyphosis in Degenerative Lumbar Scoliosis

“…Similarly, there was no significant difference of preoperative TK and GTK between the PJK group and the non-PJK group in our study. Therefore, evaluation of thoracic spine has been extended to not only the magnitude of kyphotic angle but also thoracic flexibility, [26][27][28] thoracic distribution, 22,29,30 and thoracic inclination. 31,32 Reciprocal changes of thoracic shape in degenerative lumbar deformity remain understudied.…”

Revision Free Loss of Sagittal Correction > 3 Years After Adult Spinal Deformity Surgery

“…We hypothesize that some of those who underwent revision may have been aligned outside this range, possibly leading to mechanical complications or poor clinical outcomes. 16,17 Understanding the initial alignment of patients who go on to revision may require a more nuanced assessment, including intraoperative and predischarge radiographs, especially considering that the majority of junctional kyphosis occurs before the first postoperative follow-up. [18][19][20][21] This is currently the subject of further investigation by our group.…”

How Does Gravity Influence the Distribution of Lordosis in Patients With Sagittal Malalignment?

“…While supine imaging may produce more optimal lumbar spine parameters, the reverse may be the case in the thoracic spine. Lovecchio et al, 10 using supine imaging, caution that proximal fusion constructs incorporating a flexible thoracic spine risk the creation of a "flattened" thoracic spine and truncated thoracic kyphosis, which has been shown to contribute to PJK. 21,30,31 Our stepwise linear regression of the normative alignment measurements of healthy volunteers found that while distal lumbar alignment was negatively impacted by advancing age, proximal lumbar lordosis was related to pelvic incidence.…”

“…6 Considerations to this end include age-dependent correction of PI-LL mismatch, 7,8 judicious use of osteotomies in "stiff spines," 9 and accounting for the patient's intrinsic ability to use thoracic kyphosis to compensate for residual malalignment above the upper instrumented vertebra (UIV). 10,11 Standing radiographs are representative of the multifactorial character of sagittal malalignment, which includes impaired muscle strength, 12,13 axial loading, and compensatory mechanisms within the axial and appendicular anatomy. 14,15 Barrey et al 16 proposed a multistep process for identifying and accounting for compensatory mechanisms in patients with ASD, which include changes in lumbar lordosis/ thoracic kyphosis, the presence of translational pathology such as retrolisthesis, and compensation through the appendicular anatomy such as knee flexion and ankle extension.…”