Reciprocal Changes Following Cervical Realignment Surgery

Over the last few decades, the importance of the sagittal plane and its contour has gained significant recognition. Through full-body stereoradiography, the understanding of compensatory mechanisms, and the concept of global balance and reciprocal change has expanded. There have been a few reports describing how cervical realignment surgery affects global spinal alignment (GSA) and global balance. Despite the research efforts, the concept of reciprocal change and global balance is still perplexing. Understanding the compensatory status and main drivers of deformity in a patient is vital because the compensatory mechanisms may resolve reciprocally following cervical realignment surgery. A meticulous preoperative evaluation of the whole-body alignment, including the pelvis and lower extremities, is paramount to appreciate optimal GSA in the correction of spinal malalignment. This study aims to summarize relevant literature on the reciprocal changes in the whole body caused by cervical realignment surgery and review recent perspectives regarding cervical compensatory mechanisms.

Systematic Review of Reciprocal Changes after Spinal Reconstruction Surgery : Do Not Miss the Forest for the Trees

The purpose of this review was to synthesize the research on global spinal alignment and reciprocal changes following cervical or thoracolumbar reconstruction surgery. We carried out a search of PubMed, EMBASE, and Cochrane Library for studies through May 2020, and ultimately included 11 articles. The optimal goal of a truly balanced spine is to maintain the head over the femoral heads. When spinal imbalance occurs, the human body reacts through various compensatory mechanisms to maintain the head over the pelvis and to retain a horizontal gaze. Historically, deformity correction has focused on correcting scoliosis and preventing scoliotic curve progression. Following substantial correction of a spinal deformity, reciprocal changes take place in the flexible segments proximal and distal to the area of correction. Restoration of lumbar lordosis following surgery to correct a thoracolumbar deformity induces reciprocal changes in T1 slope, cervical lordosis, pelvic shift, and lower extremity parameters. Patients with cervical kyphosis exhibit different patterns of reciprocal changes depending on whether they have head-balanced or trunk-balanced kyphosis. These reciprocal changes should be considered to in order to prevent secondary spine disorders. We emphasize the importance of evaluating the global spinal alignment to assess postoperative changes.

Thoracolumbar Junction Orientation: A Novel Guide for Sagittal Correction and Proximal Junctional Kyphosis Prediction in Adult Spinal Deformity Patients

BACKGROUND

Novel radiographic sagittal parameters of the thoracolumbar junction orientation (TLJO, thoracolumbar slope [TLS] and thoracolumbar tilt [TLT]) have been introduced and correlated with lumbopelvic parameters and thoracic kyphosis.

OBJECTIVE

To determine a predictive model for reciprocal thoracic kyphosis and proximal junctional kyphosis (PJK) based on the TLJO.

METHODS

A total of 127 patients who had fusion from sacrum to T10-L2 from 2004 to 2014 were reviewed. TK (T5-T12), PI, SS, PT, LL, and proximal junctional angle (PJA) were measured preoperatively, 6 wk postoperatively, and at final follow-up. TLJO was measured by TLS and TLT. Changes between time points were determined (preop-6 wk = ΔParameterPre6wk and preop-final follow/up = ΔParameterPreFinal). Scoliosis Research Society (SRS) and Oswestry Disability Index (ODI) questionnaires were evaluated at final follow-up. Patients were divided into 2 groups based on the presence of PJK (ΔPJAPreFinal >15°). Independent t-tests and receiver operating characteristic (ROC) curves were used to investigate the significance of differences and cut-off values. Pearson correlations and linear regressions were used to analyze the entire cohort to determine the relationship between the changes in parameters.

RESULTS

Compared to patients without PJK (n = 100), those with PJK (n = 27) had significantly lower SRS scores and significantly greater ΔTKPreFinal, ΔLLPre6wk, and ΔTLSPre6wk. To maintain in the nonPJK group, ROC curves demonstrated a cut-off value of -9.4° for ΔTLSPre6wk. PJK was significantly correlated with ΔTKPreFinal and ΔTLSPre6wk. The linear correlation revealed that ΔTLSPre6wk < -25.3° is the risk factor of PJK > 15°.

CONCLUSION

As change of TLS reflects lumbopelvic realignment and influences reciprocal TK, reducing the change of TLS may be a sagittal realignment guideline to reduce the risk of PJK.

Analysis of reciprocal changes in upper cervical profiles after posterior spinal fusion with the simultaneous double rod rotation technique for adolescent idiopathic scoliosis

BACKGROUND

The relationship between postoperative change of cervical lordotic alignment and restoration of thoracic kyphosis with adolescent idiopathic scoliosis (AIS) is still controversial. We investigated reciprocal changes in the sagittal profiles of the upper and middle-lower cervical spinal segments after posterior spinal fusion with the simultaneous double rod rotation technique (SDRRT) for AIS.

HYPOTHESIS

Occiput-C2 and C2-C7 sagittal profiles of patients with AIS could change significantly after surgical adequate increase of thoracic kyphosis with SDRRT.

PATIENTS AND METHODS

Twenty-seven consecutive patients with AIS treated with the SDRRT were retrospectively reviewed. We investigated the following parameters preoperatively, postoperatively, and at the 2-year follow-up: the Cobb angles of main thoracic curves; C7 sagittal vertical axis; thoracic kyphosis (TK) from T5 to T12; lumbar lordosis from L1 to S1; chin-brow vertical angle; McGregor's slope; occiput to C2 Cobb angle (O-C2angle); C2-C7 Cobb angle (C2-C7angle); T1-slope; and C2-C7 sagittal vertical axis. Additionally, the Scoliosis Research Society questionnaire was completed preoperatively and at the 2-year follow-up. Patients were categorized according to preoperative TK (T5-T12) into hypokyphotic (TK<20°) and normo-hyperkyphotic (TK≧20°) groups. To assess the effect of corrective surgery on sagittal profiles, we investigated correlations among the changes in sagittal parameters.

RESULTS

The mean preoperative TK was 6.1±3.7° in the Hypokyphotic group and 23.5±4.7° in the Normo-hyperkyphotic group (p<0.001), which was significantly improved postoperatively (22.3±4.4° and 26.1±2.6°, respectively; p=0.02) and at the 2-year follow-up (23.0±6.3° and 26.8±5.0°, respectively; p=0.04). The mean preoperative C2-C7angle reflected kyphosis (7.4±9.8°) in the Hypokyphotic group, and, in contrast, lordosis (-8.8±6.8°) in the Normo-hyperkyphotic group (p<0.001), which improved toward greater lordosis postoperatively (-3.7±5.8° and -14.8±5.1°, respectively; p<0.001) and at the 2-year follow-up (-5.1±4.4° and -15.3±6.4°, respectively; p<0.001). On the other hand, the mean preoperative O-C2angle was -20.5±6.5° in the Hypokyphotic group and -13.1±2.8° in the Normo-hyperkyphotic group (p=0.002), which was significantly changed postoperatively (-12.6±6.4° and -7.7±4.3°, respectively; p=0.04) and at the 2-year follow-up (-13.1±6.3° and -7.9±4.3°, respectively; p=0.04). ΔC2-C7 was negatively correlated with ΔT5-T12 (r=-0.298) and ΔO-C2angle (r=-0.332).

DISCUSSION

Lordotic reciprocal alignment changes in the C2-C7angle can occur after adequate restoration of TK. The O-C2angle compensates the C2-C7angle for a maintained horizontal gaze. O-C2 and C2-C7 sagittal profiles of patients with AIS changed significantly after corrective surgery with SDRRT.

LEVEL OF EVIDENCE

IV, Case-series.

Surgical Impact on Global Sagittal Alignment and Health-Related Quality of Life Following Cervical Kyphosis Correction Surgery: Systematic Review

When spinal imbalance occurs, the human body reacts through various compensatory mechanisms to maintain the head over the pelvis and to retain a horizontal gaze. These compensations occur through mobile spine segments as well as pelvic tilt and lower extremities. The purpose of this review was to understand the surgical impact on global sagittal alignment and health-related quality of life (HRQoL) following cervical kyphosis correction surgery. The cervical kyphosis correction surgery induces reciprocal changes in craniocervical and thoracolumbar alignment. Successful cervical deformity correction needs to focus not only on restoring proper cervical lordosis, but also on achieving global balance of the cervical spine with other parts of the spine. The goal of the surgery is to achieve occiputtrunk (OT) concordance (the center of gravity-C7 sagittal vertical axis < 30 mm) and cervical sagittal balance. Once OT-concordance is achieved, subsequent thoracolumbar alignment changes occur as needed to harmonize global spinal alignment. Reciprocal changes after surgery exhibit different patterns depending on whether patients have compensation ability in their thoracolumbar spine or not. C2–7 sagittal vertical axis and sagittal morphotype of the cervical kyphosis are correlated with HRQoL. Changes in cervical lordosis minus T1 slope correlate to HRQoL improvements.

Reciprocal change of sagittal profile in unfused spinal segments and lower extremities after complex adult spinal deformity surgery including spinopelvic fixation: a full-body X-ray analysis

BACKGROUND CONTEXT

Few studies have described reciprocal changes of pathologic compensatory mechanisms in the setting of spinopelvic fixation using full-body radiograph.

PURPOSE

To elucidate how sagittal alignment of unfused spinal segments and lower extremities change reciprocally following complex thoracolumbar realignment surgery including fusion to the sacrum in adult spinal deformity.

STUDY DESIGN

Retrospective cohort.

PATIENT SAMPLE

Thirty-four patients who underwent fusion from lower thoracic to the sacrum/pelvis and 49 patients with fusion from upper thoracic to the sacrum/pelvis.

OUTCOME MEASURES

The postoperative sagittal alignment change, and the correlation between the instrumented spinopelvic alignment change and reciprocal changes in unfused spinal segments/lower extremities.

MATERIALS/METHODS

This study included 34 patients who underwent fusion from lower thoracic to the sacrum/pelvis (LT-P group) and 49 patients with fusion from upper thoracic to the sacrum/pelvis (UT-P group). The postoperative sagittal alignment changes were evaluated after subdividing the two groups according to T1 pelvic angle (TPA) (aligned group: TPA<20 and malaligned group: TPA>20). The correlation between the instrumented spinopelvic alignment change (ΔTPA and ΔLL), reciprocal changes in unfused spinal segments and lower extremities, and the cranial sagittal vertical axis-hip/ankle change (ΔCrSVA-Hip/Ankle) were also analyzed.

RESULTS

At the baseline in both LT-P and UT-P groups, the patients in the malaligned subgroups showed greater C2-7 lordosis (C2-7L), sacrofemoral angle (SFA), and knee flexion angle (KA) than those in the aligned subgroups. At average 7.1 months postoperatively, these compensatory mechanisms were restored in accordance with instrumented TPA/LL change, especially in the UT-P group. The mid-thoracic alignment changed significantly kyphotic in the LT-P group. ΔTPA and ΔLL linearly correlated with ΔC2-7L, ΔKA, and ΔAA in the malaligned patients. The multivariate regression analysis revealed that change in lower extremity parameters (ΔSFA, ΔKA, and ΔAA) independently impacted ΔCrSVA-Hip/Ankle.

CONCLUSION

Adequate thoracolumbar realignment surgery results in restoration of the pathologic compensatory mechanisms in the unfused spinal segments and lower extremities, especially in patients fused from upper thoracic spine. A preoperative clinical evaluation of the lower limb joints, as well as a full-body radiographic evaluation, is paramount to achieve optimal global sagittal balance in thoracolumbar realignment surgery.

Reciprocal Changes in Sagittal Alignment With Operative Treatment of Adolescent Scheuermann Kyphosis-Prospective Evaluation of 96 Patients

INTRODUCTION

Sagittal alignment abnormalities in Scheuermann kyphosis (SK) strongly correlate with quality of life measures. The changes in spinopelvic parameters after posterior spinal fusion have not been adequately studied. This study is to evaluate the reciprocal changes in spinopelvic parameters following surgical correction for SK.

METHODS

Ninety-six operative SK patients (65% male; age 16 years) with minimum 2-year follow-up were identified in the prospective multicenter study. Changes in spinopelvic parameters and the incidence of proximal (PJK) and distal (DJK) junctional kyphosis were assessed as were changes in Scoliosis Research Society-22 (SRS-22) questionnaire scores.

RESULTS

Maximum kyphosis improved from 74.4° to 46.1° (p < .0001), and lumbar lordosis was reduced by 10° (-63.3° to -53.3°; p < .0001) at 2-year postoperation. Pelvic tilt, sacral slope, and sagittal vertical axis remained unchanged. PJK and DJK incidence were 24.2% and 0%, respectively. In patients with PI <45°, patients who developed PJK had greater postoperative T2-T12 (54.8° vs. 44.2°, p = .0019), and postoperative maximum kyphosis (56.4° vs. 44.6°, p = .0005) than those without PJK. In patients with PI ≥45°, patients with PJK had less postoperative T5-T12 than those without (23.6° vs. 32.9°, p = .019). Thoracic and lumbar apices migrated closer to the gravity line after surgery (-10.06 to -4.87 mm, p < .0001, and 2.28 to 2.10 mm, p = .001, respectively). Apex location was normalized to between T5-T8 in 68.5% of patients with a preoperative apex caudal to T8, whereas 90% of patients with a preoperative apex between T5 and T8 remained unchanged. Changes in thoracic apex location and lumbar apex translation were associated with improvements in the SRS function domain.

CONCLUSION

PJK occurred in 1 in 4 patients, a lower incidence than previously reported perhaps because of improved techniques and planning. Both thoracic and lumbar apices migrated closer to the gravity line, and preoperative apices caudal to T8 normalized in more than two-thirds of patients, resulting in improved postoperative function. Individualizing kyphosis correction to prevent kyphosis and PI mismatch may be protective against PJK.