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

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  • Department of Orthopedics, Hospital for Special Surgery, New York, New York
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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.

ABBREVIATIONS

ASD = adult spinal deformity; BMI = body mass index; LL = lumbar lordosis; PI = pelvic incidence; PJA = proximal junctional angle; PJK = proximal junctional kyphosis; PT = pelvic tilt; SVA = sagittal vertical axis; TK = thoracic kyphosis; TPA = T1 pelvic angle; UIV = uppermost instrumented vertebra; 3CO = 3-column osteotomy.

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Contributor Notes

Correspondence Francis Lovecchio: Hospital for Special Surgery, New York, NY. francis.lovecchio@gmail.com.

INCLUDE WHEN CITING Published online May 7, 2021; DOI: 10.3171/2020.11.SPINE201565.

Disclosures Dr. Kim reports personal fees from K2 Medical LLC, personal fees from Zimmer Biomet, fees from International Spine Study Group (ISSG), and fees from AO Spine. Dr. Schwab reports being a consultant for and receiving royalties from Zimmer Biomet and MSD; he has also received funding for non–study-related clinical or research efforts that he oversees from DePuy Synthes, K2M, NuVasive, Medtronic, AlloSource, Orthofix, and SI-Bone through ISSG. Dr. V. LaFage is a consultant for Globus Medical; receives royalties from NuVasive and honoraria from The Permanente Group, DePuy Synthes, and Implanet; and has ownership in Nemaris, Inc. Mr. R. LaFage reports owning stock in Nemaris.

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