Postoperative Sagittal Vertical Axis Research Articles

Preoperative low Hounsfield units in the lumbar spine are associated with postoperative mechanical complications in adult spinal deformity.

To determine the most valid bone health parameter to predict mechanical complications (MCs) following surgery for adult spinal deformity (ASD). This multicenter study retrospectively examined the records of patients who had undergone fusion of three or more motion segments, including the pelvis, with a minimum two-year follow-up period. Patients with moderate and severe global alignment and proportion scores were included in the study and divided into two groups: those who developed MCs and those who did not. Bone mineral density (BMD) of the lumbar spine and femoral neck was measured using dual-energy X-ray absorptiometry, and Hounsfield units (HUs) were measured in the lumbar spine on computed tomography. Radiographic parameters were evaluated preoperatively, immediately after surgery, and at final follow-up. Of 108 patients, 30 (27.8%) developed MCs, including 26 cases of proximal junctional kyphosis/failure, 2 of distal junctional failure, 6 of rod fracture, and 11 reoperations. HUs were significantly lower in patients who experienced MCs (113.7 ± 41.1) than in those who did not (137.0 ± 46.8; P = 0.02). BMD did not differ significantly between the two groups. The preoperative and two-year postoperative global tilt, as well as the immediately postoperative sagittal vertical axis, were significantly greater in patients who developed MCs than in those who did not (P = 0.02, P < 0.01, and P = 0.01, respectively). Patients who experienced MCs following surgery for ASD had lower HUs than those who did not. HUs may therefore be more useful than BMD for predicting MCs following surgery for ASD.

Impact of the sagittal spinopelvic and coronal lower extremity alignments on clinical outcomes after medial unicompartmental knee arthroplasty

IntroductionWe evaluated whether the clinical outcomes, including postoperative knee range of motion (ROM), after unicompartmental knee arthroplasty (UKA) were associated with the sagittal spinopelvic parameters and coronal alignment of the full lower extremity. MethodsForty-two patients (50 knees: six men, seven knees; 36 women, 43 knees) who underwent medial UKA between April 2015 and December 2022 were included. Preoperative radiographic examinations of the index for sagittal spinopelvic alignment included the sagittal vertical axis (SVA), lumbar lordosis, sacral slope (SS), pelvic tilt (PT), and pelvic incidence. The anteroposterior hip-knee-ankle angle (HKAA) was calculated. The relationship of clinical outcomes and the risk of knee flexion angle ≤125° and knee flexion contracture ≥10° 1-year post-UKA with radiographic parameters were evaluated. ResultsPreoperative HKA angle affected postoperative knee flexion angle ≤125° (p = 0.017, 95% confidence interval [CI]: 0.473–0.930) in logistic regression analysis. Patients with a knee flexion angle ≤125° had a higher preoperative HKAA (9.8 ± 3.0°), higher SVA (83.8 ± 37.0 mm), and lower SS (23.7 ± 9.0°) than those with a flexion angle >125° (preoperative HKAA: 6.6 ± 4.0°, SVA: 40.3 ± 46.5 mm, SS: 32.0 ± 6.3°) (p = 0.029, 0.012, and 0.004, respectively). PT related to postoperative knee flexion contracture ≥10° (p = 0.010, 95% CI: 0.770–0.965) in the logistic regression analysis. Patients with flexion contracture ≥10° had higher PT (35.0 ± 6.6°) and SVA (82.2 ± 40.5 mm) than those with flexion contracture <10° (PT, 19.3 ± 9.0°; SVA, 42.4 ± 46.5 mm) (p = 0.001 and 0.028, respectively). The postoperative clinical outcome was correlated with the postoperative knee flexion angle and SVA (p = 0.036 and 0.020, respectively). ConclusionsThe preoperative HKAA affected postoperative knee flexion angle, and the knee flexion contracture and clinical outcomes post-UKA were associated with PT and SVA, respectively. To predict outcomes for knee ROM and clinical scores after UKA, radiographic examination, including the sagittal spinopelvic parameters and the coronal view of the full lower extremity, is essential.

Correlation analysis of surgical outcomes and spino-pelvic parameters in patients with degenerative lumbar scoliosis.

The study aims to analyze factors that affect the postoperative health-related quality of life (HRQOL) of degenerative lumbar scoliosis (DLS) patients and explore the appropriate pelvic incidence minus lumbar lordosis (PI-LL) value for Chinese DLS patients. DLS patients who met the inclusion and exclusion criteria were included in this study. General information, spino-pelvic parameters, and HRQOL were collected. Correlation analysis was used to explore the spino-pelvic parameters that affect the postoperative HRQOL. Thresholds of each parameter were obtained using the receiver operating characteristic (ROC) curve. Regardless of the effect of age, DLS patients were classified into three groups according to the SRS-Schwab classification: group 0 means PI-LL < 10°, group+means PI-LL = 10-20°, and group ++ means PI-LL > 20°. Postoperative HRQOL was analyzed using variance methods. The ROC curve was used to measure the appropriate PI-LL threshold. When considering the effect of age, the patients with Oswestry Disability Index (ODI) < 75% percentile were considered to have a satisfactory clinical outcome, which was drawn to an equation between PI-LL, age, and PI by multiple linear regression equation. A total of 71 patients were included. Compared with the control group, there were significant differences in both postoperative ODI and Scoliosis Research Society 22 (SRS-22) scores when the postoperative Cobb angle ≤11°, postoperative lumbar lordosis index (LLI) > 0.8, postoperative sagittal vertical axis (SVA) ≤ 5 cm, postoperative T1 pelvic angle (TPA) ≤ 16° and postoperative global tilt (GT) ≤ 22°, respectively. Regardless of the effect of age, there was a statistical difference in postoperative HRQOL between group 0 and group ++. The PI-LL threshold derived from the ROC curve was 14.4°. Compared with the PI-LL > 14° group, the PI-LL ≤ 14° group achieved a lower postoperative ODI score and a higher postoperative SRS-22 score. Considering the influence of age, the equation for ideal PI-LL was PI-LL = 0.52age + 0.38PI-39.4 (R = 0.509, p = 0.001). PI-LL was an important parameter that affects the postoperative HRQOL of DLS patients. Sufficient LL should be restored during the operation (LL ≥ PI-14°). The appropriate PI-LL value was affected by age. Smaller LL needed to be restored as the age increased.

Sarcopenia in paraspinal muscle as a risk factor of proximal junctional kyphosis and proximal junctional failure after adult spinal deformity surgery.

The aim of this study was to identify the risk factors for proximal junctional kyphosis (PJK) and proximal junctional failure (PJF), including paraspinal muscle atrophy. Fifty-seven consecutive patients who underwent a long-instrumented fusion for adult spinal deformity (ASD) with a minimum follow-up of 2 years were included in the study. Patient, surgical, and radiological factors were evaluated. Muscle volume was measured using the muscle/vertebra ratio of the multifidus, erector spinae (ES), and psoas muscles, and muscle function was evaluated using the degree of fat infiltration at the L4-5 level. The study included 57 consecutive patients: 25 patients in the combined PJK/PJF group (13 with PJK and 12 with PJF) and 32 in the control group (without PJK or PJF). The mean time to onset of PJK and PJF was 15.7 and 1.7 months, respectively. Multivariate analysis showed that greater pre- and postoperative sagittal vertical axis was associated with the occurrence of PJK/PJF. ES muscle atrophy was more significant in the PJK/PJF group than in the control group, and more severe in the PJF than in the PJK group. This study showed that PJF occurred much earlier than PJK after ASD surgery. Paraspinal muscle atrophy was identified as a significant risk factor for PJK and PJF, especially PJF. The possibility of PJK and PJF development should be considered when long-segment fusion is planned for patients with paraspinal muscle atrophy.

Patient-specific spinal rods in adult spinal deformity surgery reduce proximal junctional failure: a review of patient outcomes and surgical technique in a prospective observational cohort.

Spinal rods used for adult spinal deformity (ASD) correction are usually manufactured straight and bent manually during surgery. Pre-bent patient-specific spinal rods (PSSR) developed with software provide the surgeon with an intraoperative deformity correction consistent with the surgical plan. Our aim was to report clinical and radiological outcomes using PSSR. We investigated rates of junctional complications both proximally [kyphosis (PJK) and failure (PJF)] and distally [failure (DJF)]. Prospective case series of 20 consecutive patients who underwent ≥4 level ASD surgery with PSSR at a single institution between January 2019 and December 2022. Preoperative, 6-week, 6-month, 12-month, 24-month, and final follow-ups assessed patient satisfaction (Ottawa decision regret questionnaire) and patient reported outcome measures (PROMs) [visual analogue scale (VAS; Back/Leg), Oswestry disability index (ODI), and 12-Item Short Form Survey (SF-12)]. Sagittal spinopelvic parameters [sagittal vertical axis (SVA), pelvic tilt (PT), and pelvic incidence and lumbar lordosis mismatch (PI-LL)] measured by serial EOS scans were performed preoperatively then compared to planned correction and postoperative measures. Interoperative cages (narrow/wide) were placed for interbody support. PJK risk score assessed likelihood of developing kyphosis. Serial computed tomography (CT) imaging assessed complication (fusion/subsidence). The mean age of the patients (75% female) was 71.9±6.9 years, and the mean follow-up was 25.2±8.6 [7-40] months. Preoperative mean PROMs showed statistically significant overall improvement (P<0.001) postoperatively to final follow-up. Four patients without wide footprint cages at L4/5 or L5/S1, suffered DJF and reported regret undergoing surgery. Statistically significant difference (P<0.001) between preoperative and surgical plan in SVA and PI-LL but not in PT (P=0.058). No statistically significant difference in surgical plan versus the postoperative SVA, PI-LL, and PT (due to difficulty achieving the surgical plan, and also to maintaining the correction). One patient suffered PJF. There was a mean proximal kyphotic angle (PKA) of 17.8±13.0 degrees and PJK risk score of 3.7±1.0 with 40% who experienced PJK. No rod breakages were observed. In this series, PSSR improved PROMs and treated ASD. Sagittal parameters planned preoperatively correlated with postoperative correction. PJF was reduced, compared to the literature (35%), but PJK was observed over time. DJF occurred and was related to the absence of interbody cages at the lumbosacral junction and decisional regret.

Junctional Failures at Both Ends After Long Fusion Arthrodesis Stopping at L5: Incidences and Risk Factors

Junctional failures after long fusion stopping at L5 can present at both proximal and distal ends. The purpose of this study was to investigate incidences and risk factors of proximal junctional failure (PJF) and distal junctional failure (DJF) after long lumbar instrumented fusion stopping at L5 for adult spinal deformity. Sixty-three patients who underwent long fusion surgery stopping at L5 with a minimum follow-up of 3 years were reviewed retrospectively. PJF and DJF were defined as newly developed back pain and/or radiculopathy with corresponding radiographic failures. The incidence and risk factors of each junctional failure were analyzed using a log-rank test and Cox proportional hazards model. Twelve men and 51 women were included in our study. Their mean age was 68.5 ± 7.0 years and the mean follow-up period was 84.5 ± 45.3 months. PJF and DJF occurred in 17 (27%) and 16 patients (25.4%), respectively. PJF and DJF developed at median durations of 32.1 months and 13.3 months, respectively, showing no significant difference between the two. Three patients presented with both PJF and DJF. Risk factors for PJF included lower body mass index, higher preoperative lumbar lordosis, and higher postoperative sagittal vertical axis (SVA) (hazard ratio, 0.570, 1.055, and 1.040, respectively). For DJF, higher preoperative SVA was an independent risk factor (hazard ratio, 1.010). After long fusion surgery stopping at L5, PJF and DJF occurred at similar rates. Lower body mass index, higher preoperative lumbar lordosis, and higher postoperative SVA were risk factors for PJF. Higher preoperative SVA was an independent risk factor for DJF.

L1-pelvic angle: a convenient measurement to attain optimal deformity correction.

(1) Evaluate the associations between L1-pelvic angle (L1PA) and both sagittal vertical axis (SVA) and T1-pelvic angle (T1PA), and (2) assess the clinical impact of L1PA. A single-institution retrospective cohort study was undertaken for patients undergoing adult spinal deformity (ASD) surgery from 2013 to 2017. Ideal L1PA was defined as (0.5xPelvic Incidence)-21. Pearson correlation was performed to compare L1PA, SVA, and T1PA. Univariate/multivariate regression was performed to assess the effect of L1PA on mechanical complications, controlling for age, BMI, and postoperative pelvic incidence-lumbar lordosis mismatch (PI/LL). Due to the overlapping nature of patients with pseudarthrosis and rod fracture, these patients were analyzed together. A total of 145 patients were included. Mean preoperative L1PA, SVA, and T1PA were 15.5 ± 8.9°, 90.7 ± 66.8mm, and 27.1 ± 13.0°, respectively. Mean postoperative L1PA, SVA, and T1PA were 15.0 ± 8.9°, 66.7 ± 52.8mm, and 22.3 ± 11.1°, respectively. Thirty-six (24.8%) patients achieved ideal L1PA. Though the correlation was modest, preoperative L1PA was linearly correlated with preoperative SVA (r2 = 0.16, r = 0.40, 95%CI = 0.22-0.60, p < 0.001) and T1PA (r2 = 0.41, r = 0.62, 95%CI = 0.46-0.76, p < 0.001). Postoperative L1PA was linearly correlated with postoperative SVA (r2 = 0.12, r = 0.37, 95%CI = 0.18-0.56, p < 0.001) and T1PA (r2 = 0.40, r = 0.62, 95%CI = 0.45-0.74, p < 0.001). Achieving ideal L1PA ± 5° was associated with a decreased risk of rod fracture/pseudarthrosis on univariate and multivariate regression (OR = 0.33, 95%CI = 0.12-0.86, p = 0.024). No association between achieving ideal L1PA and patient-reported outcomes was observed. L1PA was modestly correlated with SVA and T1PA, and achieving ideal L1PA was associated with lower rates of rod fracture/pseudarthrosis. Future studies are warranted to better define the clinical implications of achieving a normal L1PA. III.

Perioperative Complications and Radiographic Outcomes Following Cervical Laminoplasty: A Review of 105 Cases from a Single Academic Center

To assess complications and to compare preoperative and postoperative radiographic measures in patients who underwent cervical laminoplasty. We evaluated patients undergoing cervical laminoplasty between 2011 and 2022 at an academic medical center. Patient demographics, intraoperative and postoperative complications, and preoperative and postoperative radiographic parameters were recorded. Of 150 patients undergoing cervical laminoplasty during 2011-2022, 105 met the inclusion criteria. We identified 22 (21.0%) adverse events in 20 patients: 4 intraoperative (3.8%), 10 perioperative (9.5%), and 8 delayed postoperative (7.6%). Among adverse events, 13 (12.4%) were judged to be minor and 9 (8.6%) were judged to be major complications. Revision surgery was required in 6 (5.7%) patients. Both preoperative and postoperative cervical spine radiographic imaging was available in 47 (44.8%) of the 105 patients. Mean preoperative and postoperative C2-7 Cobb angles were 14.7° and 12.3°, respectively (P= 0.04). Mean preoperative and postoperative sagittal vertical axis measurements were 29.2 mm and 33.3 mm, respectively (P= 0.07). Mean preoperative and postoperative T1 slopes were 32.3° and 30.2°, respectively (P= 0.07). Cervical laminoplasty carries a significant risk of adverse events, the majority of which are minor, and has a low rate of reoperation (5.7%). The procedure does not result in significant changes in sagittal vertical axis or T1 slope. Cervical laminoplasty remains a valuable surgical option for selected patients with cervical myelopathy.

Which Bone Mineral Density Measure Offers a More Reliable Prediction of Mechanical Complications in Adult Spinal Deformity Surgery: Hounsfield Units or DEXA Scan?

In patients undergoing adult spinal deformity (ASD) surgery, we sought to: (1) determine the relationship between dual-energy x-ray absorptiometry (DEXA)-measured bone mineral density (BMD), T-scores, and Hounsfield units (HU), and (2) compare the ability of DEXA-measured BMD, T-scores, and HU to predict mechanical complications and reoperations. A single-institution retrospective cohort study was undertaken for cases from 2013 to 2017. ≥5-level-fusion, sagittal/coronal deformity, and 2-year follow-up. Multivariable regression controlled for age, body mass index, receiving anabolic medications, and postoperative sagittal vertical axis and pelvic-incidence lumbar-lordosis mismatch. A subanalysis was performed for osteopenic patients (-1 < T-score < -2). Of 145 patients undergoing ASD surgery, 72 (49.6%) had both preoperative DEXA and computed tomography scans. Mean DEXA-measured BMD was 0.91 ± 0.52 g/cm2, mean T-score was -1.61 ± 1.03, and mean HU was 153.5 ± 52.8. While no correlation was found between DEXA-measured BMD and HU (r= 0.17, P= 0.144), T-score and HU had a weakly positive correlation (r= 0.31, P= 0.007). Mechanical complications occurred in 48 (66.7%) patients, including 27 (37.5%) proximal junctional kyphosis (PJK), 1 (1.4%) distal junctional kyphosis, 5 (6.9%) implant failure, 30 (41.7%) rod fracture/pseudarthrosis, 42 (58.3%) reoperations, and 16 (22.2%) reoperations due to PJK. No association was found between DEXA-measured BMD or T-scores with mechanical complications or reoperations. While univariate regression showed a significant association between lower HU and PJK (OR 0.98, 95%CI 0.97-0.99, P= 0.011), the significance was lost after multivariable analysis. When considering osteopenic patients (n= 37), only DEXA-measured BMD was an independent risk factor for PJK (OR 0.01, 95%CI 0.00-0.09, P= 0.017), with a threshold of 0.82 g/cm2 (AUC 0.70, 95%CI 0.53-0.84, P= 0.019). Poor correlation was found between the 3 BMD modalities. DEXA-measured BMD may be superior to T-scores and HU in predicting PJK among patients with osteopenia with a threshold of BMD <0.82 g/cm2.

The role of lumbosacral paraspinal muscle degeneration and low vertebral bone mineral density on distal instrumentation-related problems following long-instrumented spinal fusion for degenerative lumbar scoliosis: a retrospective cohort study.

This study aimed to confirm the role of paraspinal muscle degeneration and low vertebral bone mineral density (vBMD) of the lumbosacral region in the development of distal instrumentation-related problems (DIPs) in degenerative lumbar scoliosis (DLS) patients undergoing long-instrumented spinal fusion. From 2013 to 2019, 125 DLS patients with 24-month follow-up after long-instrumented spinal fusion in Beijing Chao-Yang Hospital were retrospectively recruited and divided into DIP and non-DIP groups. Demographic characteristics, surgical data, and radiographic parameters were statistically compared between the groups. Degeneration of the paraspinal muscle was evaluated using the relative gross cross-sectional area (rGCSA), relative functional cross-sectional area (rFCSA), ratio of the rFCSA to rGCSA, gross muscle-fat index, and functional muscle-fat index of the multifidus (MF), erector spinae (ES), paraspinal extensor muscle (PSE), and psoas major determined by preoperative magnetic resonance imaging (MRI). The vBMD of the lumbosacral region and lower instrumented vertebra (LIV) was assessed using Hounsfield unit (HU) values determined by computed tomography (CT) scans. The DeLong test was performed to select MRI and CT scan variables. Multivariable logistic regression analysis was applied to determine the independent predictive factors of DIPs. The incidence of DIPs was 16.0% (20/105). There were no significant differences in demographic characteristics or surgical data between the groups. The rFCSAs of the MF (65.74±21.51 vs. 92.37±21.68; P<0.001), ES (82.67±21.44 vs. 111.48±24.21; P<0.001) and PSE (144.31±36.12 vs. 208.48±41.57; P<0.001) and the HU values of the lumbosacral region (103.80±22.64 vs.. 132.19±19.17; P<0.001) and LIV (111.70±23.23 vs. 128.69±20.70; P=0.005) were significantly lower in the DIP group. Significantly less preoperative pelvic tilt and greater postoperative lumbosacral lordosis and sagittal vertical axis (SVA) values were observed in the DIP group. The rFCSA of the PSE, the HU value of the lumbosacral region, and the postoperative SVA value were detected as independent predictive factors of DIPs. Lower muscularity of the PSE, a lower vBMD of the lumbosacral region, and postoperative sagittal malalignment were independent predictive factors of DIPs. Surgeons should emphasize the preoperative evaluation of paraspinal muscle and bone mass in DLS patients.

The importance of Hounsfield units in adult spinal deformity surgery: finding an optimal threshold to minimize the risk of mechanical complications.

Low bone mineral density (BMD) is a well-established risk factor for mechanical complications following adult spinal deformity (ASD) surgery. Hounsfield units (HU) measured on computed tomography (CT) scans are a proxy of BMD. In ASD surgery, we sought to: (I) evaluate the association of HU with mechanical complications and reoperation, and (II) identify optimal HU threshold to predict the occurrence of mechanical complications. A single-institution retrospective cohort study was undertaken for patients undergoing ASD surgery from 2013-2017. Inclusion criteria were: ≥5-level fusion, sagittal/coronal deformity, and 2-year follow-up. HU were measured on 3 axial slices of one vertebra, either at the upper instrumented vertebra (UIV) itself or UIV ±4 from CT scans. Multivariable regression controlled for age, body mass index (BMI), postoperative sagittal vertical axis (SVA), and postoperative pelvic-incidence lumbar-lordosis mismatch. Of 145 patients undergoing ASD surgery, 121 (83.4%) had a preoperative CT from which HU were measured. Mean age was 64.4±10.7 years, mean total instrumented levels was 9.8±2.6, and mean HU was 153.5±52.8. Mean preoperative SVA and T1PA were 95.5±71.1 mm and 28.8°±12.8°, respectively. Postoperative SVA and T1PA significantly improved to 61.2±61.6 mm (P<0.001) and 23.0°±11.0° (P<0.001). Mechanical complications occurred in 74 (61.2%) patients, including 42 (34.7%) proximal junctional kyphosis (PJK), 3 (2.5%) distal junctional kyphosis (DJK), 9 (7.4%) implant failure, 48 (39.7%) rod fracture/pseudarthrosis, and 61 (52.2%) reoperations within 2 years. Univariate logistic regression showed a significant association between low HU and PJK [odds ratio (OR) =0.99; 95% confidence interval (CI): 0.98-0.99; P=0.023], but not on multivariable analysis. No association was found regarding other mechanical complications, overall reoperations, and reoperations due to PJK. HU below 163 were associated with increased PJK on receiver operating characteristic (ROC) curve analysis [area under the curve (AUC) =0.63; 95% CI: 0.53-0.73; P<0.001]. Though several factors contribute to PJK, it appears that 163 HU may serve as a preliminary threshold when planning ASD surgery to mitigate the risk of PJK.

Long-Term Changes in Sagittal Balance After Microsurgical Decompression of Lumbar Spinal Canal Stenosis in Elderly Patients: A Follow-Up Study for 5-Years After Surgery

The purpose of this study is to investigate long-term changes in spinal sagittal balance after microsurgical decompression in lumbar canal stenosis (LCS). Fifty-two patients who underwent microsurgical decompression for symptomatic single level L4/5 spinal canal stenosis at our hospital were included in the study. All patients had standing full spine radiographs taken preoperatively, 1year postoperatively, and 5years postoperatively. Spinal parameters including sagittal balance were measured from the obtained images. First, preoperative parameters were compared with 50 age-matched asymptomatic volunteers. Next, the parameters before and after surgery were compared to examine long-term changes. Sagittal vertical axis (SVA) was significantly increased in the LCS cases compared to the volunteers (P= 0.03). Postoperative lumbar lordosis (LL) was significantly increased (P= 0.03). Postoperative mean SVA decreased but the difference was not significant (P= 0.12). Although there was no correlation between preoperative parameters and the Japanese Orthopedic Association score, postoperative pelvic incidence (PI)-LL and pelvic tilt changes correlated with changes in Japanese Orthopedic Association score (PI-LL; P= 0.0001, pelvic tilt; P= 0.04). However, after 5years of surgery, LL decreased and PI-LL increased (LL; P= 0.08, PI-LL; P= 0.03). Sagittal balance began to deteriorate but was not significant (P= 0.31). At 5years postoperatively, 18 of 52 patients (34.6%) were found to have L3/4 adjacent segment disease. Cases with adjacent segment disease showed significantly worse SVA and PI-LL (SVA; P= 0.01, PI-LL; P < 0.01). In LCS, lumbar kyphosis improves and sagittal balance tends to improve after microsurgical decompression. However, after 5years, adjacent intervertebral degeneration occurs more frequently and sagittal balance begins to deteriorate in about one third of cases.

Prediction formulae of sagittal alignment in thoracolumbar kyphosis secondary to ankylosing spondylitis after osteotomy

To construct and validate prediction formulae of sagittal alignment in thoracolumbar kyphosis secondary to ankylosing spondylitis (AS) after osteotomy. A total of 115 AS patients who suffered from thoracolumbar kyphosis and underwent osteotomy were enrolled, with 85 patients in derivation group and 30 patients in validation group. Radiographic parameters were measured on lateral radiographs, including thoracic kyphosis, lumbar lordosis (LL), T1 pelvic angel (TPA), sagittal vertical axis (SVA), osteotomized vertebral angle, pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI and LL mismatch (PI-LL). Prediction formulae of SS, PT, TPA and SVA were established; and their effectiveness was evaluated. There was no significant difference in baseline characteristics between the two groups (p > 0.05). In derivation group, LL and PI-LL were correlated with SS, and were then used to establish the prediction formula of SS[SS = − 12.791–0.765 × (LL) + 0.357 × (PI-LL), R2 = 68.3%]; PI and PI-LL were correlated with PT, and the prediction formula of PT were thus established[PT = 12.108 + 0.402 × (PI-LL) + 0.252 × (PI), R2 = 56.8%]; PT, PI-LL and LL were correlated with TPA, and were used to establish the prediction formula of TPA[TPA = 0.225 + 0.597 × (PT) + 0.464 × (PI-LL)-0.161 × (LL), R2 = 87.4%]; PT, PI-LL and age were correlated with SVA, and were used to establish the prediction formula of SVA[SVA = 36.157 + 2.790 × (PI-LL) + 1.657 × (Age)-1.813 × (PT), R2 = 41.5%]. In validation group, the predictive SS, PT, TPA and SVA were basically consistent with corresponding real values; and the mean error between predictive values and real values was of 1.3° in SS, 1.2° in PT, 1.1° in TPA and 8.6 mm in SVA. Postoperative SS, PT, TPA and SVA could be predicted with PI and the planned LL and PI-LL using prediction formulae, providing a method for AS kyphosis to plan postoperative sagittal alignment. Change of pelvic posture after osteotomy was quantitatively evaluated using the formulae.

430 Cranially Directed Upper Instrumented Vertebrae Screw Angles are Associated with Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery

INTRODUCTION: The effect of the upper instrumented vertebral (UIV) screw angle in adult spinal deformity (ASD) surgery on surgical complications and patient outcomes remains understudied. METHODS: A single-institution, retrospective cohort study was undertaken from 2011-17. UIV screw angle was trichotomized into: 1) Positive: cranially-directed screws relative to the UIV superior endplate (2° ≤ Θ); 2) Neutral: screws parallel to the UIV superior endplate (-2° &lt;Θ &lt;2°); and 3) Negative: caudally-directed screws relative to the UIV superior endplate (-2° ≥ Θ). The primary outcome was PJK/F. Secondary outcomes included remaining mechanical complications, reoperation, and PROMs: Oswestry Disability Index (ODI), Numeric Rating Scale (NRS) back/leg, and EuroQol (EQ-5D). Regression controlled for age, BMI, postoperative sagittal vertical axis, and pelvic-incidence to lumbar-lordosis mismatch. RESULTS: Among 145 patients undergoing ASD surgery, UIV screw angles were: 35(24.1%) cranially directed, 24(16.6%) neutral, and 86(59.3%) caudally directed. PJK occurred in 47(32.4%) patients. The incidence of PJK was highest for patients with cranially-directed screws (51.43%, p = 0.022). Cranially-directed screws were independently associated with PJK (OR = 4.88, 95%CI = 1.85-13.5, p = 0.002) and PJF (OR = 3.06, 95%CI = 1.32-12.30, p = 0.015), with a threshold value of -8.9° on ROC analysis (AUC = 0.64, 95%CI = 0.55-0.74, p&lt;0.001). There was no association between UIV screw angle and remaining mechanical complications, reoperations, or PROMs. In addition, cranially directed screw angle was associated with increased risk of PJK (OR = 5.56, 95%CI = 1.86-17.90, p = 0.003) in lower thoracic cohort (T8 or below, N = 37), but not in the upper thoracic group (T7 or above, N = 37). CONCLUSIONS: Positive, cranially-directed UIV screw angles significantly increased the odds of PJK/F but not other mechanical complications, reoperation, or PROMs. Meticulous attention should be paid to UIV screw angle to reduce PJK/F.

Cranially Directed Upper Instrumented Vertebrae Screw Angles Are Associated With Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery.

A retrospective cohort study. To evaluate the impact of the upper instrumented vertebral (UIV) screw angle in adult spinal deformity (ASD) surgery on: (1) proximal junctional kyphosis/failure (PJK/F), (2) mechanical complications and radiographic measurements, and (3) patient-reported outcome measures (PROMs). The effect of UIV screw angle in ASD surgery on patient outcomes remains understudied. A single-institution, retrospective study was undertaken from 2011 to 2017. UIV screw angle was trichotomized into positive: cranially directed screws relative to the superior endplate (2°≤θ), neutral: parallel to the superior endplate (-2°<θ<2°), and negative: caudally directed screws relative to the superior endplate (-2°≥θ). The primary outcome was PJK/F. Secondary outcomes included remaining mechanical complications, reoperation, and PROMs: Oswestry Disability Index, Numeric Rating Scale (NRS) back/leg, and EuroQol. Regression controlled for age, body mass index, postoperative sagittal vertical axis (SVA), and pelvic incidence lumbar-lordosis mismatch. Among 145 patients undergoing ASD surgery, UIV screw angles were 35 (24.1%) cranially directed, 24 (16.6%) neutral, and 86 (59.3%) caudally directed. PJK occurred in 47(32.4%) patients. Positive screws were independently associated with increased PJK [odds ratio (OR)=4.88; 95% CI, 1.85-13.5, P =0.002] and PJF (OR=3.06; 95% CI, 1.32-12.30, P =0.015). Among 108 (74.5%) patients with lower thoracic UIV, PJK occurred in 38 (35.1%). Cranially directed screws were independently associated with an increased odds of PJK (OR=5.56; 95% CI, 1.86-17.90, P =0.003) with a threshold of 0.2° (area under the curve =0.65; 95% CI, 0.54-0.76, P <0.001), above which the risk of PJK significantly increased. No association was found between positive screw angle and PJF (OR=3.13; 95% CI, 0.91-11.40, P =0.073). Because of the low number of patients with an upper thoracic UIV (N=37, 25.5%), no meaningful conclusions could be drawn from this subgroup. There was no association between UIV screw angle and remaining mechanical complications, reoperations, postoperative SVA and T1-pelvic angle, or PROMs. Cranially directed UIV screw angles increased the odds of PJK in patients with lower thoracic UIV. Meticulous attention should be paid to the lower thoracic UIV screw angle to mitigate the risk of PJK in ASD.

Effects of preoperative spinopelvic compensation states on the patient-reported outcomes of adult spinal deformity surgery: three-dimensional motion analysis results.

This study aimed to investigate how preoperative motion analysis results affect the postoperative clinical outcomes of patients undergoing surgery for adult spinal deformity (ASD). Patients who underwent surgery for ASD and whose motion analysis results were available were included. All patients underwent preoperative three-dimensional gait analysis using a motion analysis system. Univariate and multivariate regression analyses were performed to determine the predictive parameters of the 12-month postoperative Oswestry Disability Index (ODI). According to the mean anterior pelvic tilt (Ant-PT) angle in the motion analysis, the patients were divided into two groups: small and high Ant-PT angle groups. The 12-month postoperative ODI between the two groups was compared. A total of 111 patients who met the inclusion criteria were enrolled in the study. In the multivariate regression analysis, the preoperative sacral slope and mean Ant-PT angle were significant predictors of the 12-month postoperative ODI (p = 0.013 and p = 0.009, respectively). The high Ant-PT angle group showed a poorer 12-month postoperative ODI than did the small Ant-PT angle group, with a mean ODI of 21.9 ± 8.4 and 16.7 ± 8.5, respectively (p = 0.002). Simple linear regression analysis revealed that the Ant-PT angle was positively correlated with the postoperative sagittal vertical axis in all follow-up periods. The study highlights that a high preoperative Ant-PT angle in motion analyses is associated with poor clinical outcomes after surgery for ASD. Therefore, it is necessary to observe and consider the dynamic gait pattern related to the compensatory mechanism for sagittal imbalance in the decision-making process for ASD surgery.

Optimal immediate sagittal alignment for kyphosis in ankylosing spondylitis following corrective osteotomy.

PurposeTo investigate the optimal immediate sagittal alignment of kyphosis in ankylosing spondylitis (AS) following corrective osteotomy.MethodsSeventy-seven AS patients who underwent osteotomy were enrolled. Radiographic parameters, including global kyphosis (GK), lumbar lordosis (LL), T1 spinopelvic inclination (T1SPI), sagittal vertical axis (SVA), T1 pelvic angle (TPA), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI and LL mismatch (PI–LL), were collected. The clinical outcome was evaluated using the Scoliosis Research Society-22 (SRS-22) questionnaire and Oswestry Disability Index (ODI). At the final follow-up, SVA > 5 cm was regarded as sagittal imbalance, and a total ODI ≤ 20 or total SRS-22 score ≥4 was considered to indicate a good clinical outcome.ResultsSeventy-seven patients with an average age of 37.4 ± 8.6 years were followed up for 29.4 ± 4.2 months. At the final follow-up, GK, LL, PT, SS, TPA, and T1SPI showed some degree of correction loss (P < 0.05). The follow-up parameters could be predicted with the immediate postoperative parameters through their linear regression equation (P < 0.05). The postoperative immediate T1SPI, TPA, SVA, and PI were also highly correlated with the clinical outcome (ODI and/or SRS-22) at the final follow-up (P < 0.05). Based on the relationship, the optimal immediate sagittal alignment for obtaining good clinical outcome was determined: T1SPI ≤ 0.9°, TPA ≤ 31.5°, and SVA ≤ 9.3cm. AS patients with PI ≤ 49.2° were more likely to achieve the optimal alignment and obtained lower ODI and a lower incidence of sagittal imbalance than those with PI > 49.2° at the final follow-up (P < 0.05).ConclusionPostoperative immediate parameters could be used to predict the final follow-up parameters and clinical outcome. The optimal postoperative immediate sagittal alignment of AS patients was T1SPI ≤ 0.9°, TPA ≤ 31.5°, and SVA ≤ 9.3 cm, providing a reference for kyphosis correction and a means for clinical outcome evaluation. Patients with a lower PI (≤49.2°) were more likely to achieve optimal alignment and obtain satisfactory clinical outcomes.

Risk Factors for Progressive Spinal Sagittal Imbalance in the Short-Term Course after Total Hip Arthroplasty: A 3 Year Follow-Up Study of Female Patients.

Total hip arthroplasty (THA) for patients with hip osteoarthritis improves hip flexion contracture, subsequently improving spinal sagittal balance. However, in some cases, spinal sagittal imbalance develops in the course after THA, and its risk factors remain unknown. We aimed to investigate the risk factors of progressive spinal sagittal imbalance after THA. This retrospective cohort study of a prospectively maintained database included female patients aged ≥50 years who underwent THA. Before performing THA, we obtained each patient’s anthropometric and muscle strength measurements and whole-spine radiographs. Three years postoperatively, patients underwent whole-spine radiography to examine changes in the spinal sagittal balance. Patients were assigned into groups on the basis of their preoperative and 3 year postoperative sagittal vertical axis (SVA) values. Patients with 3 year postoperative SVA values ≥40 mm with an increase ≥30 mm were categorized into the imbalance group; the other patients were categorized into the non-imbalance group. Of 103 patients, 11 (10.7%) were in the imbalance group. In multiple logistic regression analysis, preoperative weak abdominal trunk muscle strength (ATMS) (p = 0.007) and small sacral slope (SS) (p = 0.005) were significant risk factors for progressive spinal sagittal imbalance. In conclusion, risk factors for progressive spinal sagittal imbalance after THA were weak preoperative ATMS and small SS.

Clinical and radiographic benefits of skipping C7 instrumentation in posterior cervicothoracic fusion: a retrospective analysis.

BackgroundC7 instrumentation during posterior cervicothoracic fusion can be challenging because it requires additional work of either placing side connectors to a single rod or placing two rods. Our clinical observations suggested that skipping instrumentation at C7 in a multi-level posterior cervicothoracic fusion will result in minimal intraoperative complications and decreased blood-loss while still maintaining sagittal balance parameters of cervical fusion. The objective of this study is to determine the clinical and radiographic outcomes of skipping C7 instrumentation compared to instrumenting the C7 vertebra in posterior cervicothoracic fusion.MethodsThis is a retrospective chart review of 314 consecutive patients who underwent multilevel posterior cervical fusion (PCF) at our institution. Out of 314 patients, 19 were instrumented at C7 serving as the control group, while the remaining 295 patients were not. Evaluation of efficacy was based on intraoperative complications, operative time, estimated blood loss (EBL), significant long-term complications, and radiographic evidence of fusion.ResultsSkipping the C7 level resulted in a significant reduction in EBL (488±576 vs. 822±1,137; P=0.007); however, operative time was similar between groups (174±95 vs. 184±86 minutes; P=0.844). Complications were minimal in both groups and not statistically significant. Radiographic analysis revealed C7 bridge patients had a significantly increased postoperative sagittal vertical axis (SVA) (29.3±13.1 vs. 20.2±3.1 mm; P=0.008); however, there was no significant difference between groups in SVA correction (−0.3±16.2 vs. −16.1±16.0 mm; P=0.867), T1 slope correction (3.4°±9.9° vs. 3.2°±5.5°; P=0.127), or cervical cobb angle correction (−5.7°±14.2° vs. −7.0°±12.2°; P=0.519). There were no significant long-term complications in either group.ConclusionsSkipping instrumentation at C7 in a multilevel posterior cervicothoracic fusion is associated with significantly reduced operative blood loss without loss of radiographic correction. This study demonstrates the clinical benefits of skipping C7 instrumentation in posterior cervicothoracic fusion with maintenance of radiographic correction parameters.

Association of Craniocervical Sagittal Alignment With the Outcomes of Cervical Disc Replacement.

Retrospective cohort study. To explore the association between craniocervical sagittal balance and clinical and radiological outcomes of cervical disc replacement (CDR). Patients who underwent 1-level and 2-level CDR were retrospectively analyzed. Clinical outcomes were evaluated using scores on the Japanese Orthopaedic Association (JOA), Visual Analogue Scale (VAS), and Neck Disability Index (NDI). The craniocervical sagittal alignment parameters, including the C0-C2 Cobb angle, C2-C7 Cobb angle, C2 slope, T1 slope, C2-C7 sagittal vertical axis (SVA), C1-C7 SVA, the center of gravity of the head (CGH)-C7 SVA, and range of motion (ROM) at the surgical segments were measured. A total of 169 patients were involved. Significantly lower pre- and postoperative C2 slope and CGH-C7 SVA were found in arthroplasty levels with better ROMs. Patients with a higher preoperative C2 slope and CGH-C7 SVA had lower cervical lordosis and ROM after surgery. There were no significant differences in the clinical outcomes between patients with different sagittal balance statuses. C2-C7 SVA and CGH-C7 SVA were significantly associated with radiographic adjacent segment pathology (rASP). Craniocervical sagittal balance is associated with cervical lordosis and ROM at the index level after CDR. A higher preoperative SVA is related to the presence and progression of rASP. A relationship between sagittal alignment and clinical outcomes was not observed.