Faculty Bibliography

BACKGROUND CONTEXT: Prior studies assessed the association between underlying neurological condition and worse outcomes following spinal surgery with recent emphasis of self-reported loss of balance (Imbalance) by Uribe et al. PURPOSE: To investigate if patients with self-reported loss of balance have poorer outcomes following adult spinal deformity (ASD) surgery. STUDY DESIGN/SETTING: Retrospective review of prospectively collected database. PATIENT SAMPLE: ASD patients with baseline and 2-year radiographic and patient-reported outcome measure (PROM) data were included. OUTCOME MEASURES: Demographics, radiographic outcomes, complications, and PROM were compared from baseline to 2-year follow up.
METHOD(S): Patients undergoing a long spinal fusion with no prior history of spine surgery were retained. Patients were grouped according to imbalance and unsteady gait. The groups were propensity matched by age, PI-LL, and surgical invasiveness score. Demographics, radiographic, complications and PROM were compared from baseline to 2-year post-op.
RESULT(S): A total of 212 patients were reported (106 patients in each group). The mean age (64 vs 63 years), BMI (27.2 vs 27.0 kg/m2), and gender (76% vs 87% female) were not significantly different for patients with imbalance and without imbalance respectively (all p >0.05). Patients in the imbalance group had a higher Frailty Index Score compared to patients without imbalance (3.74 vs 2.33, p <0.001). At baseline, the sagittal profile for both groups were comparable with regard to PT, PI-LL, and SVA. Patients with loss of balance had a significantly lower thoracic Cobb angle (25.27degree vs 37.45degree, p <0.001) and lumbar Cobb angle (37.03degree vs 45.53degree, p=0.004), although the global coronal alignment was similar (imbalance:41.51 mm vs 34.25 mm, p=0.155). Patients with imbalance had worse PROM measures, including ODI (45.15 vs 36.62), SF-36 Mental Component Score (44.04 vs 51.76), SF-36 Physical Component Score (30.17 vs 35.10), and SRS-22 Mental domain score (3.28 vs 3.80) (p <0.001 for all). Postoperatively, patients with imbalance had less PT correction (-1.45degree vs -3.60degree, p=0.039) for a comparable correction in their PI-LL (-11.93degree vs-15.08degree, p=0.144) by 2-year follow-up. Both groups demonstrated similar improvements in their coronal plane deformity. Imbalance patients had higher rates of radiographic PJK at 2-year follow-up (26.4% vs 14.2%, p=0.026). Furthermore, patients with reported imbalance have significantly higher rate of implant related complications (47.2% vs 34.0%, p=0.05). After controlling for age, baseline sagittal parameters, PI-LL correction and Charlson Comorbidity Index, patients with imbalance had 2.2 times increased odds of sustaining PJK by 2 years.
CONCLUSION(S): Patients with a self-reported loss of balance and unsteady gait have significantly worse baseline frailty and PROMs, represented by poorer mental health and physical function. Although those patients had higher rates of PJK and implant-related complications, surgical intervention significantly improved their quality of life. Despite the improvement, they remained with lower PROMs by 2-year follow-up. Therefore, in the clinic setting and with limited institutional access to Frailty scores, asking patients if they have loss of balance or unsteady gait is a simple yet powerful question which may trigger their preoperative risk stratification and optimization. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Tranexamic acid (TXA) is commonly used to lower blood loss in ASD surgery. Despite widespread use of TXA in ASD surgery, there is a lack of consensus regarding the optimal dosing intraoperatively. PURPOSE: This study aims to assess differences in blood loss and complications between high-dose, medium-dose, and low-dose TXA regimens. Complex ASD patients who receive high-dose TXA will have decreased blood loss compared to those who receive low-dose TXA. STUDY DESIGN/SETTING: Retrospective Review. PATIENT SAMPLE: A total of 265 ASD patients in a multi-center prospective study were retrospectively analyzed. OUTCOME MEASURES: Blood loss (ml), Major Blood Loss (>90th percentile ml), units transfused intraoperatively, units transfused perioperatively.
METHOD(S): Patients were separated into three cohorts by TXA regimen: 1) low-dose patients had =20mg/kg loading dose with =2mg/kg/hr maintenance dose 2) medium-dose patients had 20-50 mg/kg loading dose with 2-5 mg/kg/hr maintenance dose. 3) high-dose patients had =50mg/kg loading dose with =5mg/kg/hr maintenance dose. Major or minor blood loss was defined as above or below the 90th percentile of our cohort respectively. Multivariable analysis controlled for levels fused, BMI, platelets, Hgb, OR time, 3CO, and radiographic alignment.
RESULT(S): Fifty-four (20%) patients received low-dose regimen, 133 (50%) received medium-dose and 80 (30%) received high dose. Mean blood loss was 1,551+/-1,295 ml, intraoperative units RBCs 1.52+/-2, and perioperative units RBCs 2.3+/-2.3. Mean major blood loss was 4,566+/-1,516ml and minor blood loss 1,236+/-755ml. Compared to the low-dose group, patients in the high-dose group had 77.8% decreased odds of major blood loss (OR 0.222; P=0.007), decreased blood loss (Coef. -540.92ml; P=0.019), units transfused intraoperatively (Coef. -.739 units; P < 0.001), and units transfused perioperatively (Coef. -0.328 units; P=0.025). Compared to medium-dose group, the high-dose group had less units transfused intraoperatively (Coef. -.59 units; P < 0.001) and perioperatively (Coef. -.42 units; P < 0.001) with no difference in blood loss. There was no difference between the medium and low dose groups in blood loss or units transfused. There was no association between high-dose TXA regimen and increased rates of DVT, PE, or any medical complication before six weeks. No patients had a seizure.
CONCLUSION(S): In this multicenter prospectively collected database, ASD patients receiving high-dose intraoperative TXA have decreased odds of major blood loss, less RBC transfusions intraoperatively and 540ml less blood loss compared to low dose TXA, without additional risk of seizure or thromboembolic complications. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Prone LLIF (P-LLIF) is a novel technique allowing for placement of a lateral interbody in the prone position and allowing posterior decompression and revision of posterior instrumentation without repositioning. To date, studies evaluating the P-LLIF have been small single surgeon series. This multicentre retrospective cohort examines perioperative outcomes and complications of single position P-LLIF againsttraditional Lateral LLIF (L-LLIF) technique with patient repositioning in patients undergoing revision lumbar fusion surgery. PURPOSE: To evaluate the feasibility and safety of the single-position P-LLIF technique for revision lumbar fusion surgery. STUDY DESIGN/SETTING: Multicenter retrospective cohort study. PATIENT SAMPLE: A total of 101 patients undergoing revision circumferential fusion with lateral lumbar interbody fusion (LLIF) were included, of which 43 had P-LLIF and 58 had L-LLIF. OUTCOME MEASURES: Outcome measures included levels fused, operative time, estimated blood loss and perioperative complications. Radiographic analysis included lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), PI-LL mismatch and segmental lumbar lordosis.
METHOD(S): A multicenter retrospective cohort study was performed from 4 institutions from the USA and Australia of patients undergoing revision anterior-posterior lumbar fusion via either: 1) single-position prone LLIF (P-LLIF); or 2) lateral decubitus LLIF with repositioning to prone (L-LLIF) between January 2015 and November 2021. Patients with greater than 4 levels fused were excluded. Demographics, perioperative outcomes, complications and radiological outcomes were compared using independent samples t-tests and chi-squared analyses as appropriate with significance set at p<0.05.
RESULT(S): A total of 101 patients undergoing revision lateral lumbar interbody fusion surgery were included, of which 43 had P-LLIF and 58 had L-LLIF. Age, BMI and CCI were similar between groups. The number of posterior levels fused (2.21 P-LLIF vs 2.66 L-LLIF, p=0.469) and interbody levels fused (1.23 P-LLIF vs 1.25 L-LLIF, p=0.838) were similar between groups. Levels decompressed, posterior column osteotomy and anterior column release were similar between groups. Operative time was significantly less in the P-LLIF group compared to the L-LLIF group (151 vs 206 min, p=0.004). EBL was similar between groups (150 mL P-LLIF vs 182 mL L-LLIF, p=0.31) and there was a trend toward reduced length of stay (2.7 vs 3.3 days, p=0.09). No significant difference was demonstrated in perioperative or postoperative complications between P-LLIF and L-LLIF groups. Radiographic analysis demonstrated no significant differences in preoperative or postoperative sagittal alignment as measured by lumbar lordosis, PI-LL mismatch, or segmental lumbar lordosis between groups.
CONCLUSION(S): P-LLIF significantly improves operative efficiency and may reduce length of stay when compared to L-LLIF and repositioning for revision lumbar fusion. No increase in complications was demonstrated by P-LLIF or trade-offs in sagittal alignment restoration. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Sacralization of L5 is a condition that affects 15% of the population. Because of the increased L5 articulations to the sacrum, it is unclear how pelvic incidence and spinopelvic parameters should be measured. PURPOSE: Determine whether patients with L5 sacralization should be radiographically measured with relation to the L5 or S1 vertebrae. STUDY DESIGN/SETTING: Retrospective analysis. PATIENT SAMPLE: Prospective multicenter adult spinal deformity database. OUTCOME MEASURES: ODI, SF36 PCS, radiographic spinopelvic parameters.
METHOD(S): Linear regression modeling was used to determine normative TPA and PI-LL based on PI and age in a database of asymptomatic subjects. In an adult spinal deformity database, patients with radiographic evidence of L5 sacralization, had PI, LL and TPA measured from the superior endplate S1 and then also from L5. Patients with instrumentation below L4 at baseline were excluded. The differences in TPA and PI-LL from normative were calculated in the sacralization cohort relative to L5 and S1 and correlated to ODI. Patients were grouped based on PI-LL Schwab modifier (0, +, ++) utilizing their L5 PI-LL and S1 PI-LL. Baseline ODI and SF36 PCS were compared across and within groups and their respective SRS Schwab class.
RESULT(S): Among 1,179 ASD patients, 276 (23.4%) had transitional anatomy, 176 with sacralized L5 (14.9%) and 100 (8.48%) with lumbarization of S1. The 176 with sacralized L5 were analyzed. PI (24.5 +/- 11.0 vs 55.7 +/- 12.0, p=0.001), TPA (11.2 +/- 12.0 vs 20.3 +/- 12.5, p=0.001) and PI-LL (0.67 +/- 21.1 vs 11.4 +/- 20.8, p=0.001) measured utilizing the L5 superior endplate were significantly smaller than those who were measured relative to S1. When measured from S1, 76 (43. %) of patients were SRS Schwab 0, 45 (25.6%) were Class +, and 55 (31.3%) were class ++ compared to 124 (70.5%), 22 (12.5%), and 30 (17.0%) measured from L5 respectively. There were significant differences in ODI and PCS as the Schwab grade increased regardless of L5 or S1 measurement. The L5 group had higher PCS functional scores for Schwab 0 and ++ relative to same grades in the S1 group. Offset from normative TPA (0.5 +/- 11.1 vs 9.6 +/- 10.8, p=0.001) and PI-LL (0.67 +/- 21.1 vs 11.4 +/- 20.8, p=0.001) were smaller when measuring from L5. Moreover, S1 measurements were more correlated with disability by ODI (TPA offset from normative, S1: R=0.326 vs L5: R=0.285; PI-LL Offset from normative, S1: R=0.318 vs L5: R=0.274).
CONCLUSION(S): Measuring the PI at L5 in sacralized anatomy results in underestimating the PILL Schwab grade in a percentage of patients and less correlation with HRQLs. Patients with sacralized L5s should have spinopelvic parameters measured relative to S1. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Preoperative risk stratification is critical to determining which adult spinal deformity (ASD) patients may develop postop complications and to maximize surgical success. Currently it is unknown if a preoperative inflammatory state results in a higher risk for postop complications. This information can be used in risk stratification models to aid in complication avoidance. PURPOSE: To determine if patients with preoperative elevated serum markers for inflammation have higher rates of postoperative complications STUDY DESIGN/SETTING: Retrospective review of multicenter prospective ASD database. PATIENT SAMPLE: ASD patients. OUTCOME MEASURES: C-reactive protein (CRP), Erythrocyte sedimentation rate (ESR), complications by type and by severity of intervention: none, mild, moderate and severe. Demographic and surgical variables: age, estimated blood loss (EBL), operating room (OR) time, body mass index (BMI), America Society of Anesthesia physical classification scale (ASA), Charlson comorbidity index (CCI), Edmonton frailty scale (EF), 3-column osteotomy (3CO), number of post fusion levels.
METHOD(S): Preoperative labs were drawn on ASD patients and the inflammatory markers were CRP and ESR. CRP thresholds for cardiac risk: normal = 3. The CRP moderate and elevated values were combined into one group named elevated. Normal ESR thresholds: Male age 50, =20, Female >50, =30. Patients were stratified by having normal or elevated markers and rates of complications were compared between the groups. A multivariate model with CRP/ESR and demographic/surgical variables for postoperative complications. Health-related quality of life (HRQOL) metrics were compared RESULTS: The total number of patients with preoperative CRP was 159 and ESR was 158. CRP: normal=114 patients (71.7%), moderate elevation=28 (17.6%), severe elevation=17 (10.7%). Combined elevated=45/159(28.3%). Elevated ESR=25(15.8%), normal=133(84.2%). The elevated CRP group had significantly higher rate of moderate complication 13/45(28.9%) vs 16/114(14.0%), p=0.03 and severe complication 15/45 (33.3%) vs 17/114(14.9%, p=0.009. Elevated ESR patients had significantly higher rate of moderate complication 9/25 (36.0%) vs 20/133 (15.0%), p=0.01. In multivariable logistic regression elevated CRP had odds ratio for moderate complication of 3.3 (95% CI 1.4-7.6, p=0.006), and for severe complication of 2.3 (95% CI 1.05-5.1, p=0.037). Multivariable logistic regression for elevated ESR and moderate complication had odds ratio of 2.9 (95%CI 1.04-7.8, p=0.041). Elevated CRP also had significantly higher rate of wound complications (15.6% vs 3.5%, p=0.007) and MSK complications (11.1% vs 1.8%, p=0.01). Elevated ESR had significantly higher rate of cardiac complications (32.0% vs 13.5%, p=0.02) and neurological complications (24.0% vs 9.0%, p=0.03). Elevated CRP had worse preoperative leg pain, SRS Activity and VR12 PCS(p<0.05). Elevated ESR had worse baseline ODI (p=0.03).
CONCLUSION(S): A preoperative inflammatory state as defined by elevated CRP and ESR is an independent risk factor for the development of moderate and severe postop complications. Having elevated preop CRP is 3.3 and 2.3 times more likely to have a moderate and severe complication, respectively. Elevated ESR is 2.9 times more likely to have a moderate complication. This data can be used in risk stratification models to aid in minimizing postoperative complications. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Evidence on long-term surgical recovery in adult spinal deformity (ASD) patients who are both frail and have an invasive procedure is limited. PURPOSE: This study aims to evaluate frail and invasive patients with 5-year recovery kinetics. We hypothesize that patients who are both frail and have invasive surgeries will have adverse postoperative recovery kinetics STUDY DESIGN/SETTING: Retrospective review. PATIENT SAMPLE: A total of 133 ASD patients with complete HRQOL data at preoperative, 1-year, 2-year, 5-year follow-up were included. OUTCOME MEASURES: Integrated Health State Scores (IHS) in Oswestry Disability Index (ODI), Short-form 36 (SF-36) physical (PCS) and mental (MCS) component score, and Scoliosis Research Society (SRS)-22r measures METHODS: ASD-FI scores were used to stratify non-frail (0.3) patients. ASD-SR scores were used to stratify low invasive (90) surgeries. Using ASD-FI and ASD-SR, patients were separated into four cohorts: non-frail low invasive (NFLI), frail low invasive (FLI), non-frail high invasive (NFHI), and frail high invasive (FHI). HRQOLs at 1 year, 2 years, and 5 years were normalized against preoperative values. AUC was calculated across time points to generate an integrated health state score (IHS). Multivariable linear regression was used to compare IHS scores of FLI, NFHI, and FHI to NFLI while controlling for age, gender, comorbidity, and radiographic alignment.
RESULT(S): Of 633 eligible ASD patients, 339 had 5-year follow-up. Of those, 125 patients with complete HRQOL data at preoperative, 1-year, 2-year, and 5-year visits were included; 27.2% (34) were NFLI, 20.0% (25) were FLI, 26.4% (33) were NFHI, and 26.4% (33) were FHI. Using NFLI as the referent, FLI and NFHI did not have differences in ODI, MCS, PCS or SRS-22r IHS scores (P >0.05). On multivariable analysis of integrated health scores, FHI had higher MCS (7.6 vs 5.47; P=0.0188), SRS activity (6.97 vs 5.67; P=0.0004), SRS pain (8.49 vs 6.4; P=0.001), SRS appearance (8.97 vs 6.81; P=0.0014), SRS satisfaction (11.71 vs 7.97; P=0.0033), and SRS total (7.49 vs. 6.09; P=0.0002), indicating more improved recovery over a 5-year period. Patients who were FHI had higher rates of complications (P <0.05).
CONCLUSION(S): Despite having more complications, patients who were frail and underwent more invasive surgeries were more likely to have greater overall improvement in activity, pain, and satisfaction over a 5-year period relative to preoperative baseline. Our results suggest that frailty in combination with invasiveness do not hinder long-term postoperative recovery kinetics, in comparison to frailty or invasiveness alone. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: As adult spinal deformity (ASD) prevalence increases in our ever-aging population there is a concomitant increase in poor bone quality. ASD surgery is expensive and carries a high complication profile. It is important to optimize modifiable preoperative risk factors, such as osteopenia or osteoporosis. Additional diagnostic modalities such as a DEXA can add cost, delay diagnosis, and can be an additional insurance hurdle. Some studies suggest HU's can be utilized as a proxy for frailty, but it is unclear if this is useful in risk stratification. PURPOSE: Our goal was to evaluate the relationship between bone health as measured by HU's and PJK and identify a HU threshold in which PJK risk is increased. We hypothesize that HU will correlate with occurrence of PJK after ASD surgery. STUDY DESIGN/SETTING: Retrospective review of a prospective, multicenter ASD database. PATIENT SAMPLE: Of 1,330 pts eligible, 997 (74.9%) had complete 2Y follow-up. Of these, 605 meet inclusion criteria with 110 (18.18%) patients having a PJK. OUTCOME MEASURES: Development of PJK within 2 years of surgery.
METHOD(S): Operative ASD patients (scoliosis >20, SVA>5cm, PT>25, or TK>60) with available baseline (BL) and 2-year (2Y) radiographic and HRQL data were included if they had a preop CT. HU were measured from axial views within the cancellous body (x3) at both L1 and UIV with the mean value calculated for each. Threshold linear regression with Bayesian information criteria was utilized to identify optimal cut-offs of risk factors for PJK. Multivariable analysis (MVA) controlled for PJK prophylaxis and surgeon. Additionally, risk factors identified were controlled against each other.
RESULT(S): Threshold regression identified that cut-offs of <125 HU for UIV, >63 years for age, >0.31 for ASD-FI, and >47degree for preoperative T4-12 thoracic kyphosis, and <10 levels fused were predictive of PJK on bivariate analysis (P<0.05 for all). On MVA, age > 63 years old (OR 4.7; P = 0.003), female gender (OR 3.33; P=0.035), HU at UIV vertebrae <125 (2.83; P=0.008), ASD-FI >0.31 (OR 4.02; P=0.011), TK > 46degree (OR 3.75; P=0.003), and < 10 levels fused (OR 3.31; P=0.0310) were associated with increased odds of PJK.
CONCLUSION(S): Bone health as measured by HU appears to be an independent predictor of PJK after ASD surgery, specifically values <125 at the UIV. It also parallels frailty in prediction of PJK and can potentially be used as a proxy for frailty assessment. This can be easily measured and could help with risk stratification in the future. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: While past research has shown racial disparities exist in the outcomes and utilization of spine surgery, those studies were often performed on nondisease-specific national databases, which may capture different patient populations and complication rates compared to prospective multicenter databases. PURPOSE: Purpose: 1) Assess racial disparities for enrollment in two prospective multicenter databases (ASD-

BACKGROUND CONTEXT: Sagittal alignment is integral to a patient's quality of life. Posterior spinal fusion (PSF) is currently the standard for correcting adolescent idiopathic scoliosis (AIS). Vertebral body tethering (VBT) is a fusionless growth modulating surgical technique used to treat AIS. It relies on the Hueter-Volkmann Law. Indications for this procedure include patients who have coronal curves up to 50degree, growth remaining, and no excessive thoracic kyphosis. VBT has been shown to have good coronal plane deformity correction. There have been fewer examinations of the sagittal effects of VBT. PURPOSE: To determine if VBT is a non-inferior treatment for correction of AIS with regard to sagittal alignment compared to PSF. STUDY DESIGN/SETTING: Multicenter retrospective cohort study. PATIENT SAMPLE: Patients with AIS who underwent correction surgeries with LIV in the lumbar spine from 2013 to 2021 with pre- and minimum two-year postoperative standing full spine plain films. OUTCOME MEASURES: Sagittal vertical axis (SVA), cervical SVA (cSVA), pelvic tilt (PT), thoracic kyphosis (TK), cervical lordosis (CL), L4-S1 lordosis (L4L), T1 pelvic angle (TPA) and pelvic incidence lumbar lordosis mismatch (PI-LL).
METHOD(S): Radiographic analyses was completed with independent samples t-test with significance set to p <0.05.
RESULT(S): A total of 99 patients were included, 49 VBT and 50 PSF. There were no differences in age or levels instrumented between groups. The VBT cohort Lenke class breakdown is 23% 1A, 13% 1C, 31% 3C. 18% 5C, and 15% 6C, while the PSF cohort consisted of 42% 1A, 6% 1B, 2% 2C, 2% 3B, 12% 3C, 2% 5B, 24% 5C, and 10% 6C. At Baseline, the VBT cohort had lower SVA (-0.7mm+/-3.7 vs 2.2mm+/-5.0, p=0.001), CL (-0.9degree+/-18.2 vs 11.6degree+/-12.8, p=0.001), L4-S1 Lordosis (20.7degree+/-16.0 vs 41.6degree+/-10.2, p=0.001), and higher cSVA (3.3mm+/-1.6 vs -0.95mm+/-3.1, p=0.001) than those who were fused. Postoperatively, VBT patients have an overall higher L4-S1 Lordosis (36.0degree+/-10.1vs 18.3degree+/-12.5, p=0.001), cSVA (3.4mm+/-1.4 vs -3.7mm+/-2.1, p=0.001), and lower CL (-4.3degree+/-18.4 vs 7.0degree+/-12.2, p=0.001). The PSF cohort had a larger change in cSVA (2.8mm+/-4.0 vs 0mm+/-1.6, p=0.001) from baseline to 2-year follow-up compared to VBT. No differences in the change of L4-S1 Lordosis (VBT 1.5degree+/-12.3 vs 4.1degree+/-10.9, p=0.3), TPA (VBT -1.6degree+/-6.8 vs -1.4degree+/-8.5, p=0.89), PT (VBT -0.5degree+/-7.8 vs -1.9degree+/-8.5, p=0.42), or PI-LL (0.2degree+/-12.0 vs -0.5degree+/-14.0, p=0.81) were observed.
CONCLUSION(S): VBT and PSF for AIS result in statistically similar changes in sagittal alignment parameters. The fact that we showed similar results comparing sagittal alignment in fusion and VBT groups indicates that VBT is non-inferior from a sagittal perspective. It is important to maintain sagittal alignment when correcting AIS. Future work can examine the long-term effect of VBT on sagittal alignment. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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BACKGROUND CONTEXT: Adult spinal deformity (ASD) patients maintain upright posture by compensating through their spine, pelvis and lower extremities. Little data exist quantifying the contribution of lower extremity compensation through the hips, knees, and ankles to maintain upright posture. PURPOSE: Evaluate the effect of the lower limb compensation by numerically unfolding patients. STUDY DESIGN/SETTING: Multicenter, prospective cohort. PATIENT SAMPLE: A total of 288 patients surgically treated for complex ASD with preoperative full body images. OUTCOME MEASURES: Horizontal distance between vertebra centroid and ankle.
METHOD(S): Surgical ASD patients were enrolled into a prospective study based on three criteria deformity severity (PI-LL>25degree, TPA>30degree, SVA>15cm, TCobb>70degree or TLCobb>50degree), procedure complexity (>12 levels fused, 3CO or ACR) and/or age (>65 and >7 levels fused). Preop full-body images were evaluated and age and PI-adjusted normative values were used to model spine alignment based upon three configurations: COMP (all lower extremity compensatory mechanisms maintained), PARTIAL (removal of ankle dorsiflexion and knee flexion, maintained hip extension), UNCOMP (ankle, knee, and hip compensation eliminated by reset PT to the age and PI norms). The three configurations were compared, and COMP alignment was stratified by TPA percentiles to investigate the offsets from each vertebra to the ankle joint acting as a surrogate of the gravity line in free-standing position.
RESULT(S): A total of 288 patients met inclusion criteria (60+/-15yo, 70.5% female, 27.4+/-5.9 BMI). COMP spine deformity magnitude included PI-LL 15+/-24, TPA 24+/-14, and SVA 65+/-69mm. As the model transitioned from COMP to UNCOMP alignment, the initial posterior translation of the pelvis decreased significantly to an anterior translation vs the ankle (P.Shift 30 to -7.6 mm). This was associated with a decrease in pelvic retroversion (PT 24.1 to 16.1), hip extension (SFA 203 to 200), knee flexion (KA 5.5 to -0.4), and ankle dorsiflexion (AA 5.3 to 3.7). As a result, the anterior malalignment of the trunk significantly increased SVA (65 to 120mm) and G-SVA (C7-Ankle from 36 to 127 mm), leading to a three-fold increase in bending moments sustained by the ankle joint. The stratification of the COMP position by TPA percentiles revealed that as the deformity increases, the vertebrae above T8 translate anteriorly, those below T10 move posteriorly, with the T8-T10 segment remaining ~3cm posterior to the ankle joint independently of the deformity severity.
CONCLUSION(S): Removal of lower limbs' compensation revealed an unsustainable truncal malalignment with a three-fold increase of bending moments at the ankle joints. Combined, lower limb compensations permit "reducing" the SVA by two-fold and the C7-ankle SVA by three-fold. From a mechanical point of view, this compensation permits maintaining the trunk center of mass (T9) at a fixed offset of ~3 cm from the ankle joint. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
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