The impact of surgeon experience on perioperative complications and operative measures following thoracolumbar 3-column osteotomy for adult spinal deformity: overcoming the learning curve

Darryl Lau Departments of Neurological Surgery and

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Vedat Deviren Orthopedic Surgery, University of California, San Francisco, California

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Christopher P. Ames Departments of Neurological Surgery and

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OBJECTIVE

Posterior-based thoracolumbar 3-column osteotomy (3CO) is a formidable surgical procedure. Surgeon experience and case volume are known factors that influence surgical complication rates, but these factors have not been studied well in cases of adult spinal deformity (ASD). This study examines how surgeon experience affects perioperative complications and operative measures following thoracolumbar 3CO in ASD.

METHODS

A retrospective study was performed of a consecutive cohort of thoracolumbar ASD patients who underwent 3CO performed by the senior authors from 2006 to 2018. Multivariate analysis was used to assess whether experience (years of experience and/or number of procedures) is associated with perioperative complications, operative duration, and blood loss.

RESULTS

A total of 362 patients underwent 66 vertebral column resections (VCRs) and 296 pedicle subtraction osteotomies (PSOs). The overall complication rate was 29.4%, and the surgical complication rate was 8.0%. The rate of postoperative neurological deficits was 6.2%. There was a trend toward lower overall complication rates with greater operative years of experience (from 44.4% to 28.0%) (p = 0.115). Years of operative experience was associated with a significantly lower rate of neurological deficits (p = 0.027); the incidence dropped from 22.2% to 4.0%. The mean operative time was 310.7 minutes overall. Both increased years of experience and higher case numbers were significantly associated with shorter operative times (p < 0.001 and p = 0.001, respectively). Only operative years of experience was independently associated with operative times (p < 0.001): 358.3 minutes from 2006 to 2008 to 275.5 minutes in 2018 (82.8 minutes shorter). Over time, there was less deviation and more consistency in operative times, despite the implementation of various interventions to promote fusion and prevent construct failure: utilization of multiple-rod constructs (standard, satellite, and nested rods), bone morphogenetic protein, vertebroplasty, and ligament augmentation. Of note, the use of tranexamic acid did not significantly lower blood loss.

CONCLUSIONS

Surgeon years of experience, rather than number of 3COs performed, was a significant factor in mitigating neurological complications and improving quality measures following thoracolumbar 3CO for ASD. The 3- to 5-year experience mark was when the senior surgeon overcame a learning curve and was able to minimize neurological complication rates. There was a continuous decrease in operative time as the surgeon’s experience increased; this was in concurrence with the implementation of additional preventative surgical interventions. Ongoing practice changes should be implemented and can be done safely, but it is imperative to self-assess the risks and benefits of those practice changes.

ABBREVIATIONS

ASD = adult spinal deformity; BMP = bone morphogenetic protein; EBL = estimated blood loss; PSO = pedicle subtraction osteotomy; SRS = Scoliosis Research Society; TXA = tranexamic acid; UIV = upper instrumented vertebra; VCR = vertebral column resection; 3CO = 3-column osteotomy.

OBJECTIVE

Posterior-based thoracolumbar 3-column osteotomy (3CO) is a formidable surgical procedure. Surgeon experience and case volume are known factors that influence surgical complication rates, but these factors have not been studied well in cases of adult spinal deformity (ASD). This study examines how surgeon experience affects perioperative complications and operative measures following thoracolumbar 3CO in ASD.

METHODS

A retrospective study was performed of a consecutive cohort of thoracolumbar ASD patients who underwent 3CO performed by the senior authors from 2006 to 2018. Multivariate analysis was used to assess whether experience (years of experience and/or number of procedures) is associated with perioperative complications, operative duration, and blood loss.

RESULTS

A total of 362 patients underwent 66 vertebral column resections (VCRs) and 296 pedicle subtraction osteotomies (PSOs). The overall complication rate was 29.4%, and the surgical complication rate was 8.0%. The rate of postoperative neurological deficits was 6.2%. There was a trend toward lower overall complication rates with greater operative years of experience (from 44.4% to 28.0%) (p = 0.115). Years of operative experience was associated with a significantly lower rate of neurological deficits (p = 0.027); the incidence dropped from 22.2% to 4.0%. The mean operative time was 310.7 minutes overall. Both increased years of experience and higher case numbers were significantly associated with shorter operative times (p < 0.001 and p = 0.001, respectively). Only operative years of experience was independently associated with operative times (p < 0.001): 358.3 minutes from 2006 to 2008 to 275.5 minutes in 2018 (82.8 minutes shorter). Over time, there was less deviation and more consistency in operative times, despite the implementation of various interventions to promote fusion and prevent construct failure: utilization of multiple-rod constructs (standard, satellite, and nested rods), bone morphogenetic protein, vertebroplasty, and ligament augmentation. Of note, the use of tranexamic acid did not significantly lower blood loss.

CONCLUSIONS

Surgeon years of experience, rather than number of 3COs performed, was a significant factor in mitigating neurological complications and improving quality measures following thoracolumbar 3CO for ASD. The 3- to 5-year experience mark was when the senior surgeon overcame a learning curve and was able to minimize neurological complication rates. There was a continuous decrease in operative time as the surgeon’s experience increased; this was in concurrence with the implementation of additional preventative surgical interventions. Ongoing practice changes should be implemented and can be done safely, but it is imperative to self-assess the risks and benefits of those practice changes.

In Brief

This study examines how surgeon experience affects perioperative complications and quality measures following thoracolumbar 3-column osteotomy (3CO) in adult spinal deformity. This study is important because it helps identify complications associated with 3CO early in a surgeon's career and helps understand when surgeons overcome the learning curve.

Adult spinal deformity (ASD) arises from multiple etiologies, but most commonly it arises from arthritic spondylosis and iatrogenic causes that lead to asymmetrical degeneration of discs, facet joints, and other spinal elements. Imbalance and spinal misalignment are strongly correlated with disability and pain outcomes—greater imbalance results in greater functional disability.14,22,39 Fortunately, the surgical correction and reestablishment of age-appropriate global spinal alignment and spinopelvic parameters have been demonstrated to significantly improve patient function, pain level, and appearance on multiple validated outcome scales.21,37

The surgical correction of fixed spinal deformities often requires extensive osteotomies, aggressive spinal manipulation, and long-construct instrumented reconstruction. Surgical correction of fixed, nonmobile deformities can be technically challenging and require high-grade osteotomies such as grade 3–5 osteotomies (pedicle subtraction osteotomy [PSO] to vertebral column resection [VCR]).38 In such cases, surgery can be associated with a high risk for major complications, neurological morbidity, and a large volume of blood loss.3,5,17,41–43 According to the literature, complication rates range widely from 8% to 59% depending on various factors.1,11,12,19,27,28,40 The previously reported rate of intraoperative complications is approximately 7%, and new neurological deficits are observed immediately after surgery in 7%–35% of the cases.5,13,17,26 Fortunately, catastrophic permanent neurological injury occurs in fewer than 3% of the cases.7

Surgeon experience has been shown to significantly correlate with perioperative complications,10,24 operative time,2,6,9,10,24,30,32,36 length of stay,2 blood loss,10,24,30,35 rate of reoperations,6 and superior postoperative radiological parameters35 in a variety of spinal procedures, including anterior cervical discectomy and fusion,30 lumbar decompression,2,32 minimally invasive transforaminal lumbar interbody fusion,25,31 and spinal deformity surgery.6,10,24 The cutoff as to what constitutes an “experienced” surgeon varies by series: experience thresholds utilized in the spine surgery outcomes literature include 10 years,9 15 years, and the designation of junior versus senior attending.35 An additional body of literature has focused on characterizing the early learning curve for surgical approaches, with analyses indicating that adequate competency can be achieved following 58 endoscopic lumbar decompressive laminectomies,32 52 procedures (or 312 pedicle screws) for free-hand pedicle screw placement,33 23–25 procedures for ASD surgery,36 and 29 procedures for VCR.24 However, studies have indicated that the learning curve for 3-column osteotomy (3CO) for ASD can be prolonged,6 and published data regarding the learning curve for 3CO specifically are presently limited to consecutive series of 34–102 patients.6,10,24 Therefore, the learning curve for thoracolumbar 3CO in patients with ASD is not well defined, and it is unclear how perioperative results are affected by the surgeon’s experience. In this study, we examine a single surgeon’s consecutive 13-year experience in thoracolumbar 3CO for ASD and evaluate how experience affects perioperative results.

Methods

This study was formally approved by the Committee of Human Research at the University of California, San Francisco.

Patients

All adult patients (18 years or older) with ASD who underwent a 3CO for spinal deformity correction performed by the senior author (C.P.A.) were retrospectively identified from the years of 2006–2018. All procedures involved the same two attending surgeons (C.P.A. and V.D.). Patients who had a diagnosis of infection, acute trauma, and/or tumor were excluded. Indications for surgery were as follows: fixed, nonmobile spinal deformity causing abnormal spinal imbalance; significant dysfunction; debilitating axial back pain; and/or neurological deficits (radiculopathy and/or myelopathy). All patients underwent open deformity correction with placement of long-segment instrumentation.

Data Points

Demographics, baseline clinical variables, and surgical details were retrospectively reviewed and recorded: age (grouped into < 50, 50–75, 76–80, and > 80 years), sex, weight (< 80 or ≥ 80 kg), preoperative neurological deficit (normal strength vs weakness), osteotomy type (PSO vs VCR), osteotomy level (L1, L2, L3, L4, L5, or S1), number of instrumented levels (≤ 10 or > 10), upper instrumented vertebra (UIV) (upper vs lower thoracic), prior instrumentation, staged anterior/lateral posterior, and comorbidities (cardiac disease, hypertension, vascular disease, diabetes, pulmonary disease, renal disease, stroke, psychiatric disease, hyperlipidemia, and thyroid disease). Upper thoracic levels were defined as T1, T2, T3, T4, T5, T6, and T7. Thoracolumbar junction levels were defined as T8, T9, T10, T11, T12, L1, and L2. Several intervention and practice changes over the time period of interest were also recorded: transition to multiple-rod constructs, use of bone morphogenetic protein (BMP), tranexamic acid (TXA), vertebroplasty of the UIV, and intraoperative 3D imaging system to check free-hand screw placement. Consideration of vertebroplasty at the UIV and 1 level above the UIV was made in cases in which the UIV was in the lower thoracic spine.

The primary outcomes of interest were overall complications, surgical complications, and postoperative neurological complications/deficits (new or worsened weakness or sensation changes after surgery) during the perioperative period. The perioperative period was defined as 30 days following surgery or longer if the patient remained in the hospital after the 30-day period. Both clinical and radiological data were screened for complications. A complication was defined as any unforeseen event requiring additional observation and medical and/or surgical intervention. While uncommon, all patients with symptomatic instrumentation failures and/or screw breaches that were identified in the perioperative period underwent reoperation and revision. The secondary outcomes of interest were operative time and estimated blood loss (EBL). Operative time was defined as the total minutes from skin incision to skin closure. For patients who underwent a staged anterior-posterior approach, operative time was only inclusive of the posterior fusion portion in which the 3CO was performed. The operative time for the anterior stage was not included. Typically, staged procedures were performed on different days.

Statistical Analysis

Surgeon experience was categorized by consecutive case number and years of experience in order to examine its associations with the outcomes of interest. First, descriptive statistics were used to summarize the cohort, and univariate statistics were used to assess for associations between covariates and outcomes of interest. The chi-square test was used for categorical outcomes, and ANOVA was used for continuous outcomes. Multivariate analysis models were then employed to assess whether surgeon experience and other covariates were independently associated with the outcomes of interests. Logistic regression models were used for categorical outcomes, and analysis of covariance models were used for continuous outcomes. From the univariate analysis, all covariates with p values < 0.200 were included in the multivariate model. A p value < 0.050 was used as the threshold of statistical significance. All statistics were performed with the use of SAS 9.4 (SAS Institute, Inc.).

Results

A total of 362 patients were included in the study (Table 1). Their mean age was 64.4 years, and 37.8% were male patients. Preoperatively, 73.2% had normal strength in their lower extremities. Of the 362 patients, 81.8% underwent PSO. The distribution of 3CO levels was as follows: thoracic (14.9%), L1 (6.6%), L2 (7.2%), L3 (37.3%), L4 (28.2%), L5 (4.4%), and S1 (1.4%). The number of 3COs by level can be seen in Fig. 1. The UIV was upper thoracic level in 46.4%, and 50.8% underwent more than a 10-level instrumented fusion. With regard to rod constructs, standard single-rod constructs were used in 34.3% of the cases, satellite rods in 13.5%, and nested rods in 52.2%. BMP was used in 44.8% of the cases, and TXA was used in 51.7% of the cases. Vertebroplasty was performed in 37.4% of the cases with the UIV in the lower thoracic spine. Staged anterior-posterior approaches were performed in 21.8% of the patients.

TABLE 1.

Association of perioperative complications following 3CO for ASD with various variables

Overall ComplicationsSurgical ComplicationsNeurological Deficits
VariableNo. of Cases%No.%p ValueNo.%p ValueNo.%p Value
Total no. of patients3629929.4278.0216.2
Years of practice0.1150.6440.027
 2006–2008185.0844.4211.1422.2
 2009–20119927.32525.377.155.1
 2012–201412334.02621.175.743.3
 2015–20179726.82929.91010.377.2
 2018256.9728.014.014.0
No. of 3COs performed0.4030.6900.166
 505013.81530.0612.0714.0
 1005013.81530.036.024.0
 1505013.81326.024.036.0
 2005013.81020.024.012.0
 2505013.8918.048.012.0
 3005013.81836.0510.036.0
 3626217.1812.958.146.5
Intervention change
 Rod type0.7220.7280.284
  Standard12434.33125.097.3108.1
  Satellite4913.51326.5510.212.0
  Nested18952.25529.1136.9105.3
 BMP0.5530.5970.335
  Yes16244.85030.9138.095.6
  No17147.24928.7148.2127.0
 TXA0.8390.2220.406
  Yes18751.75227.8179.194.8
  No17548.34726.9105.7126.9
 Vertebroplasty0.6080.8260.765
  Yes7137.41521.168.545.6
  No11962.62924.497.686.7
 O-arm0.7720.5770.065
  Yes29681.88027.0217.1144.7
  No6618.21928.869.1710.6
Age<0.0010.3920.976
 <55 yrs349.4411.812.925.9
 50–75 yrs12835.42318.075.575.5
 76–80 yrs17648.65833.0179.7116.3
 >80 yrs246.61458.328.314.2
Sex0.8970.6150.367
 Male13737.83827.796.664.4
 Female22562.26127.1188.0156.7
Weight0.6150.3950.320
 <80 kg17147.25331.0169.4137.6
 ≥80 kg15342.34630.1117.285.2
Strength0.2340.5770.486
 Normal26573.26825.7217.9145.3
 Weak9726.83132.066.277.2
3CO type0.1310.5770.206
 VCR6618.22334.869.169.1
 PSO29681.87625.7217.1155.1
Osteotomy level0.1290.6580.297
 Thoracic5414.91731.547.459.3
 L1246.6729.214.214.2
 L2267.2934.613.827.7
 L313537.32820.785.932.2
 L410228.23332.41110.887.8
 L5164.4212.516.316.3
 S151.4360.0120.0120.0
Instrumented levels0.0120.6100.883
 ≤1017849.23821.3126.7105.6
 >1018450.86133.2158.2116.0
UIV0.0610.8620.918
 Upper thoracic16846.45432.1137.7106.0
 Lower thoracic19353.34523.3147.3115.7
Prior instrumentation/fusion0.3320.5190.248
 Yes24868.56425.8176.9124.8
 No11431.53530.7108.897.9
Two-stage anterior-posterior op0.3030.3070.820
 Yes7921.81822.8810.156.3
 No28378.28128.6196.7165.7
Comorbidities
 Cardiac disease0.0380.8460.293
  Yes8623.83136.067.033.5
  No27676.26824.6217.6186.5
 Hypertension0.0900.3140.976
  Yes20857.56430.8188.7125.8
  No15442.53522.795.895.8
 Vascular disease0.6710.1560.918
  Yes195.2631.6315.815.3
  No34394.89327.1247.0205.8
 Diabetes0.3980.1730.139
  Yes6116.91423.023.369.8
  No30183.18528.2258.3155.0
 Pulmonary disease0.4920.3610.403
  Yes5816.01831.0610.323.4
  No30484.08126.6216.9196.3
 Renal disease<0.0010.0230.711
  Yes277.51763.0518.527.4
  No33592.58224.5226.6195.7
 Stroke/TIA0.0080.4320.023
  Yes164.4956.3212.5318.8
  No34695.69026.0257.2185.2
 Psychiatric disease0.6950.7300.182
  Yes9726.82828.988.233.1
  No26573.27126.8197.2186.8
 Hyperlipidemia0.2460.4790.038
  Yes8724.02832.289.2910.3
  No27576.07125.8196.9124.4
 Thyroid disease0.1530.8900.420
  Yes5715.72035.147.023.5
  No30584.37925.9237.5196.2

TIA = transient ischemic attack.

FIG. 1.
FIG. 1.

Summary of total number of 3COs performed for ASD and trends of associated perioperative results. The total number of osteotomies performed was 362. The distribution of osteotomy level was as follows: thoracic (14.9%), L1 (6.6%), L2 (7.2%), L3 (37.3%), L4 (28.2%), L5 (4.4%), and S1 (1.4%). Over time, there were lower complications rates and shorter operative times. Figure is available in color online only.

Table 1 shows the univariate analysis results of how surgeon experience was associated with overall complications, surgical complications, and new neurological deficit. The overall complication rate was 29.4%, and the surgical complication rate was 8.0%. The overall neurological deficit rate was 6.2%. Based on both years of experience and case number, there was a clear trend for decreased overall complication rates. The trend toward a decrease in the complication rate based on years of experience is as follows: 2006–2008 (44.4%), 2009–2011 (25.3%), 2012–2014 (21.1%), 2015–2017 (29.9%), and 2018 (28.0%) (p = 0.115) (Fig. 2). The trend toward a decreased complication rate based on case number is as follows: first 50 cases (30.0%), 100 cases (30.0%), 150 cases (26.0%), 200 cases (20.0%), 250 cases (18.0%), 300 cases (36.0%), and 362 cases (12.9%) (p = 0.403). However, these findings were not statistically significant. On multivariate analysis, neither surgeon experience by years of experience nor surgeon experience by case number was an independent factor for overall complications. Rather, older age, an S1 3CO, and the presence of preoperative renal disease were independent factors for higher odds of complications (Table 2).

FIG. 2.
FIG. 2.

Trend of perioperative complication rates over surgeon years of experience. There was a trend for decreased overall and surgery-specific complications over the 13-year period. The rate of neurological complications decreased significantly, especially following 2010 (p = 0.027). Figure is available in color online only.

TABLE 2.

Independent risk factors for complications following 3CO for ASD

95% CI
Risk Factor for ComplicationsORLowerUpperp Value
Age
 <50 yrsRefRefRefRef
 55–75 yrs3.891.1313.390.031
 76–80 yrs9.271.9244.650.006
 >80 yrs10.231.0620.830.026
Osteotomy level
 ThoracicRefRefRefRef
 L11.690.476.060.424
 L22.220.4810.260.307
 L32.140.528.840.292
 L43.100.7512.850.119
 L52.690.3222.640.362
 S139.603.12503.410.005
Renal disease
 Yes5.0921.99512.9950.001
 NoRefRefRefRef
Surgical complication
 Renal disease
  Yes3.981.2912.330.017
  NoRefRefRefRef
Neurological deficit
 Prior stroke
  Yes4.441.0019.670.049
  NoRefRefRefRef

Ref = reference.

Surgeon experience (by both years of experience and case number) was not associated with surgical complications (Table 1 and Fig. 1). On multivariate analysis, renal disease was an independent risk factor for surgical complications (Table 2). With regard to neurological deficits and complications, greater years of experience was significantly associated with a decrease in the rate of neurological deficits: 2006–2008 (22.2%), 2009–2011 (5.1%), 2012–2014 (3.3%), 2015–2017 (7.2%), and 2018 (4.0%) (p = 0.027) (Fig. 1). While not statistically significant, a similar trend was also seen when analyzing rate of neurological deficits by case number as well: first 50 cases (14.0%), 100 cases (4.0%), 150 cases (6.0%), 200 cases (2.0%), 250 cases (2.0%), 300 cases (6.0%), and 362 cases (6.5%) (p = 0.166). Multivariate analysis identified prior stroke as an independent risk factor for new neurological deficits (Table 2).

Table 3 shows the results of univariate and multivariate analyses of surgeon experience in relationship to operative time and EBL. The overall mean operative time was 310.7 minutes, and the overall mean EBL was 1984.2 ml. There was a significant decrease in operative length based on years of experience (2006–2008 [358.3 minutes], 2009–2011 [316.5 minutes], 2012–2014 [319.7 minutes], 2015–2017 [293.7 minutes], and 2018 [275.5 minutes]; p < 0.001) and case number (first 50 cases [326.1 minutes], 100 cases [316.9 minutes], 150 cases [327.5 minutes], 200 cases [324.8 minutes], 250 cases [306.7 minutes], 300 cases [296.1 minutes], and 362 cases [283.4 minutes]; p = 0.001). On multivariate analysis, only operative years of experience was an independent factor associated with operative time relative to 2006–2008: 2009–2011 (p = 0.015), 2012–2014 (p = 0.027), 2015–2017 (p = 0.013), and 2018 (p < 0.001). Figure 3 is a density plot of operative time data points over years of surgeon experience. The trend line demonstrates a progressive decrease in procedure duration over time. In addition, there is less variance and more consistency in procedure duration toward the end of the series. Surgeon experience, when stratified by years of experience and case number, was not significantly associated with EBL. Table 4 shows the specific complications encountered. Neurological complications are highlighted and organized by year. The most common neurological complication was quadriceps weakness secondary to L3 and L4 nerve root compression.

TABLE 3.

Association of surgeon experience by year of practice and case number with quality measures following 3CO for ASD

Operative TimeEBL
MeanSDUni p ValueMulti p ValueMeanSDUni p ValueMulti p Value
Total310.766.51984.21256.4
Years of practice<0.0010.280
 2006–2008358.381.6Ref2616.72727.8Ref
 2009–2011316.563.70.0151917.11461.30.595
 2012–2014319.768.50.0271928.71057.90.348
 2015–2017293.760.20.0132171.61308.70.121
 2018275.547.1<0.0011656.01029.20.201
No. of 3COs performed0.0010.356
 50326.172.7Ref1930.81727.5Ref
 100316.967.00.6402093.21516.40.224
 150327.567.20.8951759.41151.00.456
 200324.865.80.6301966.01016.60.970
 250306.767.80.2691975.0975.40.684
 300296.153.10.6742342.01209.70.166
 362283.461.00.7131849.21338.00.814
Intervention change
 Rod type0.3570.621
  Standard314.168.61917.21440.2
  Satellite319.665.51879.81115.5
  Nested306.265.42041.01201.1
 BMP0.0250.172
  Yes303.365.60.2202066.81269.60.290
  No319.066.8Ref1873.61234.5Ref
 TXA0.0050.255
  Yes301.161.50.7991892.01351.3
  No321.070.2Ref2053.01179.8
 Vertebroplasty0.0010.460
  Yes278.941.90.4341886.61000.7
  No308.569.8Ref1741.51383.4
 O-arm0.1050.589
  Yes308.064.70.3641997.41218.4
  No322.773.4Ref1875.71551.2
Age0.0040.387
 <55 yrs290.161.2Ref1672.41102.8
 50–75 yrs325.271.70.1902109.71278.4
 76–80 yrs307.762.80.2111961.91284.8
 >80 yrs284.656.20.8261909.51095.1
Sex0.4060.039
 Male307.062.12172.71437.70.021
 Female313.069.11874.31126.7Ref
Weight0.9480.272
 <80 kg310.961.82061.91330.4
 ≥80 kg310.570.91908.01178.5
Strength0.3840.118
 Normal312.670.12049.01317.2Ref
 Weak305.755.71800.01050.30.203
3CO type0.0340.535
 VCR326.475.3Ref1888.21278.7
 PSO307.264.00.1892003.91253.3
Osteotomy level0.8390.673
 Thoracic319.372.31727.81114.1
 L1311.272.01916.71425.0
 L2318.672.91864.3832.0
 L3311.461.82075.41295.6
 L4302.959.82009.01343.2
 L5310.1107.11913.3960.6
 S1319.655.62600.01503.3
Instrumented levels<0.0010.002
 ≤10287.662.0Ref1752.61231.5Ref
 >10333.063.20.1022192.61245.60.002
UIV<0.0010.002
 Upper thoracic333.062.80.1572199.41279.60.322
 Lower thoracic291.463.9Ref1773.81204.3Ref
Prior instrumentation/fusion0.0940.365
 Yes306.763.10.8661941.41151.8
 No319.473.0Ref2078.21462.4
Two-stage anterior-posterior op0.8070.442
 Yes309.165.81876.91396.6
 No311.266.82011.21220.1
Comorbidities
 Cardiac disease0.7220.224
  Yes308.564.12136.41260.2
  No311.467.41936.61254.0
 Hypertension0.8140.364
  Yes311.466.61930.31128.4
  No309.866.62059.31416.6
 Vascular disease0.2740.048
  Yes327.053.42570.61591.00.169
  No309.867.11951.61230.3Ref
 Diabetes0.0220.079
  Yes293.067.90.1031712.7942.50.087
  No314.365.8Ref2039.91306.1Ref
 Pulmonary disease0.6940.984
  Yes307.664.01987.51257.3
  No311.367.11983.61258.6
 Renal disease0.5340.483
  Yes303.062.12154.01498.4
  No311.366.91970.01235.9
 Stroke/TIA0.1930.458
  Yes289.547.40.7062228.61413.0
  No311.767.2Ref1973.11250.3
 Psychiatric disease0.7420.965
  Yes312.665.51979.51348.4
  No310.067.01986.21219.2
 Hyperlipidemia0.9860.790
  Yes310.862.22017.51142.6
  No310.768.01973.81292.0
 Thyroid disease0.4140.526
  Yes317.367.12085.61437.4
  No309.566.51964.81220.7

Multi = multivariate; Uni = univariate.

FIG. 3.
FIG. 3.

Scatterplot of operative duration over a surgeon’s years of experience. Years of experience was an independent factor associated with operative time (p < 0.001). There is a clear trend for shorter operative time as greater experience is gained. In addition, there is increased consistency and less deviation of the linear trend line with greater years of experience. Figure is available in color online only.

TABLE 4.

Specific complications encountered following 3CO for ASD

Medical ComplicationsSurgical ComplicationsNeurological Complications (year)
PneumoniaPosterior surgical wound infectionQuadriparesis secondary to meningitis (2006)
Deep vein thrombosisAnterior abdominal wound infectionParaparesis (2008)
Cecal volvulus requiring hemicolectomyConsumptive coagulopathy leading to abortion of the procedureParaparesis secondary to anterior spinal artery infarct (2008)
PancreatitisIntraoperative cardiac arrestParaplegia, gradual improvement with blood pressure augmentation (2008)
Stroke/intracranial infarctIliac vein injury requiring vascular repair following anterior lumbar interbody fusionRadiculopathy and allodynia; removal of medially breached L4 screw and release of osteotomy (2009)
Urinary tract infectionIntraoperative hypotension requiring abortion of the procedureParaparesis requiring reduction of correction (2009)
MeningitisFecal incontinence requiring hematoma evacuation (2010)
Shock liverRight quadriceps weakness requiring release of correction (2011)
Myocardial infarctRight leg numbness requiring release of correction (2011)
Acute kidney injuryLeft anterior tibialis and extensor hallucis longus weakness (2012)
SepsisRight quadriceps weakness (2012)
Respiratory failure requiring intubationBilateral quadriceps and foot weakness requiring hematoma evacuation (2012)
Hip infectionRight quadriceps weakness requiring L3–4 foraminotomy and decompression (2013)
SeizuresRight anterior tibialis and extensor hallucis weakness requiring evacuation of hematoma and reduction of correction (2015)
Cardiac arrhythmiasGeneralized left lower-extremity weakness (2015)
Prolonged ileus requiring nasogastric tubePainful left lower-extremity radiculopathy requiring reduction of correction (2016)
Clostridium difficileRight anterior tibialis and extensor hallucis weakness (2016)
Pulmonary embolusParaplegia due to anterior spinal artery infarct (2016)
Pleural effusionLeft radiculopathy and quadriceps weakness (2017)
RhabdomyolysisLeft quadriceps weakness requiring foraminotomy, decompression, reduction of correction (2017)
Pneumothorax requiring chest tubeRight quadriceps weakness (2018)
Horner’s syndrome
Gastrointestinal tract bleed

Discussion

Spinal imbalance secondary to fixed, nonmobile thoracolumbar spinal deformities is a formidable procedure because many patients require 3COs and long-construct fusions for adequate correction and stabilization. The technical difficulties with such surgeries are several-fold, as there are many critical components to achieving the most optimal outcomes: operative planning (construct length), adequate spinal exposure, accurate and sufficient pedicle screw placement, performing the PSO or VCR (with adequate decompression of surrounding neural structures), closure of the osteotomy, rod contouring, insertion of the rod without screw pullout, and adequate arthrodesis.45 Inherently, ASD surgery can be associated with a relatively high morbidity rate in the form of high EBL, long operative duration, and complications; minimizing these risks should be the goal.3–5,17,41–43 The findings from the present study support the notion that operative experience is correlated with significantly lower neurological complications and shorter operative duration.

Based on our multivariate analysis, years of practice was more correlative to outcomes than the absolute number of 3CO procedures performed. This may indirectly represent the additional surgical skills gained in other types of surgical procedures performed by the senior author during his time of practice. At the start of the surgical series, the senior author’s practice was composed of the treatment of a variety of spinal diseases and pathologies, such as degenerative disease, deformity, tumor (primary and metastatic), infection, and a small portion of trauma. As his practice matured, he has since transitioned to one that involves treatment of approximately 90% ASDs and primary spinal tumors requiring en bloc resections, with the last 10% comprising instrumented degenerative spinal disease. The knowledge and technical skills from other complex procedures are likely applicable to performing a 3CO for ASD. Over time, we observed a decrease in the overall complication rate—from 44.4% in the years of 2006–2008 to 28.0% in 2018. This was not statistically significant but the absolute difference of 16.4% is clinically significant. Over the 13-year period, there was a significant decrease in the neurological complication rate, from 22.2% to 4.0%, and shorter operative duration, from 358.1 minutes to 283.4 minutes. There is a paucity of studies looking at surgeon experience in ASD surgery. Our findings, however, generally corroborate those of prior spinal deformity studies assessing the relationship between surgeon experience and outcomes. Cahill et al. performed a comparative study of the surgical outcomes for adolescent idiopathic scoliosis between young surgeons (< 5 years’ experience) and experienced surgeons (> 5 years’ experience).8 They observed similar complication rates, but experienced surgeons had significantly less blood loss (1029 ml), a shorter duration of surgery (193 minutes), and better Scoliosis Research Society (SRS)–22 scores at follow-up (0.4 points). The study by Cahill et al. did not evaluate an individual surgeon’s learning curve or experience. Bourghli et al. performed a retrospective review of 102 patients who underwent lumbar PSOs performed by a single surgeon and found that shorter operative times (29 minutes), lower blood loss (281 ml), and shorter hospital stays were correlated with increased surgeon experience.6

A key mutual finding identified in our study and prior studies is the fact that greater surgical experience results in a significantly shorter operative time.6,8 The significantly shorter operative duration is likely the result of mainly a surgeon’s experience and, to a smaller extent, external factors. From this series and clinical experience, it is clear that the surgeons became much more adept at and confident in certain procedures, which results in a shorter operative time for almost every step of the procedure: faster exposures, free-hand pedicle screw placement, 3CO, decompression, rod contouring, and rod placement. More accurate screw placement also results in shorter operative duration because less time is spent revising screws. External factors that likely helped shorten operative time included improvement of the workflow of the anesthesiologist, operating room staff, radiology technologist, and neurophysiologist. A prolonged surgical duration is not benign, as there are many potential side effects and complications that can result in worse outcomes. Modern-day general anesthesia is considered to be associated with a low risk profile and with safety in carefully selected patients. However, there is an accumulation of scientific and mechanistic evidence that prolonged anesthesia can trigger long-term morphological and functional alterations in the brain, especially in elderly patients.44 Neural morphological changes include cell death, inhibition of neurogenesis, and synapse loss.15,16,29 In addition, a long operative and anesthesia duration has been identified as an independent risk factor for complications following spinal surgery. In a retrospective study of 3801 patients who underwent elective anterior cervical discectomy and fusion, prolonged anesthesia duration was found to be independently associated with increased odds of complications, venous thromboembolism, increased length of stay, and return to the operating room.34 Similarly, Kim et al. performed an analytical study of 4588 patients who underwent single-level lumbar fusion and found that an increase in operative duration was associated with a stepwise increase in complications: medical complications, surgical complications, wound infection, reoperation, sepsis, and deep vein thrombosis.18

Unlike prior studies in which surgeon experience was correlated to less blood loss, we did not see similar results, and there was no obvious trend in our data for this finding as well.6,8 It is unclear why these findings differ, but it may be related to the variability of how blood loss is estimated and recorded by the operative staff over time.

Defining a learning curve for a specific procedure is difficult and is dependent on the outcome being measured. Choi et al. performed a retrospective study of 40 consecutive patients who underwent lumbar PSO and reported that 20 cases was the threshold of being able to perform lumbar PSO safely and effectively.10 They determined this by evaluating multiple perioperative outcomes, radiographic measures, and follow-up SRS-22 scores. However, in order to specifically define the technical learning curve for 3CO, radiographic measures and surgery-specific complications need to be reviewed. One of the most important factors is neurological outcome and related complications. Choi et al. performed a comparative subgroup analysis of neurological complications between the first 20 and last 20 procedures, but their finding was inconclusive because there were only 3 (2 vs 1) neurological complications. Therefore, their defined learning curve of 20 cases is likely not applicable to assessing neurological safety and risk profile. Based on our study, the rate of new neurological deficits drops dramatically after the 3- to 5-year time point. When performing 3CO, the neurological compilations encountered are secondary to direct injury, inadequate decompression, or overcorrection with closure of the osteotomy site. The prevention of neurological deficits in thoracolumbar 3CO procedures involves technical aspects such as ensuring that there is adequate release/decompression of superior and inferior nerve roots and preventing subluxation, dorsal impingement, and significant dural buckling.8 Avoiding such complications requires surgical experience and clinical expertise. Therefore, the neurological deficit rate following 3CO seems to be correlated with a surgeon’s experience and less influenced by external factors. Neuromonitoring should be used with all major deformity corrections; however, transcranial motor evoked potential monitoring may have low accuracy, sensitivity, and specificity for lumbar PSO procedures.23

One of the main limitations to this study relates to the difficulty in defining a generalizable learning curve for thoracolumbar 3CO for ASD because really there are few tangible and many unmeasurable components to a surgeon’s learning experience. Surgical case volume and years of experience are concrete measurements of surgical and clinical experience. Components such as innate natural talent, case difficulty, specific lessons learned in each case, applicability of other nondeformity surgeries, and goals of each surgery are somewhat abstract details that influence a surgeon’s learning curve for a particular procedure. Another drawback to this study is the difficulty in determining if surgeon skill/experience is the sole driver of better outcomes and lower complications. Studies of learning curves that span a relatively long period of time are subject to influences in new techniques, the introduction of surgical adjuncts, and advancements in the field. While these advancements may be considered to be confounders, such items are integrated into surgeons’ experience as they strive to improve outcomes by implementing and adopting better methodologies into their practice. For example, the senior author transitioned from using the drill to almost strictly using osteotomes to perform decompressions (laminectomies/facetectomies) and 3COs. In addition, the senior author transitioned to using spinal racks rather than temporary rods to stabilize the spine during 3CO; this also allows rapid and controlled compression and distraction of the 3CO site. Despite these limitations, it is still important to define the potential risk profile of complications at the start of the learning curve for thoracolumbar 3CO and demonstrate that experience is correlated with improved outcomes.

It is clear that the technical skill to performing a 3CO improves with experience and training, but a surgeon’s learning curve also involves practice changes over time. This is especially the case for ASD surgery and the implementation of methods to improve fusion and prevent construct failure and proximal disease. Additionally, it is important to evaluate whether such interventions are safe in the perioperative period and if they provide long-term benefit. In efforts to prevent pseudarthrosis and proximal failure, the senior author transitioned to using various multiple-rod constructs, BMP, hooks at the UIV, and vertebroplasty at the UIV. He also implemented the routine use of TXA and an intraoperative 3D imaging system to check free-hand screw placement. All of the aforementioned interventions were not associated with perioperative complications or any of the outcomes of interest. In fact, despite implementing all of those changes, there were still lower perioperative complications and a shorter operative time. With regard to blood loss, it should be noted that the use of TXA did not seem to provide the benefit it is thought to offer—that is, less blood loss. This needs to be further evaluated because there are known risks of using TXA, such as deep vein thrombosis, pulmonary embolism, heart attacks, and, at high doses, seizures.20 It remains unclear why TXA did not lower blood loss. However, there are many factors that go into properly utilizing TXA for spine surgery: timing (preoperative, intraoperative, and postoperative), dosage, and the unpredictable physiological idiosyncratic response to TXA.

Conclusions

Surgical learning curves are individualized and are based on various factors, such as training, background experience, natural talent, case volume, and case complexity. Nonetheless, defining the morbidities and understanding the rationale for those complications, while overcoming the learning curve, are necessary and critical for less experienced surgeons. This study demonstrates that overcoming a major part of the learning curve for thoracolumbar 3CO in ASD seems to occur around the 3- to 5-year experience mark and is not necessarily based on the 3CO case number. This is particularly true for lowering the incidence of neurological complications; operative years of experience was significantly associated with lower neurological deficits, with the incidence dropping from 22.2% to 4.0% over a 13-year period. Understanding the surgical and technical strategies implemented during this time to prevent such neurological complications is essential. These findings may suggest that close mentorship under a more experienced surgeon could be beneficial and help mitigate complications during the initial phase of a surgeon’s learning curve for thoracolumbar 3CO. Operative experience also results in a linear decrease in procedure length; this is in concurrence with the implementation of additional preventative interventions. Ongoing advancements and practice changes should be implemented and can be done so safely, but it is imperative to self-assess the risks and benefits of those practice changes as well.

Disclosures

Dr. Deviren reports being a consultant for the following companies: NuVasive, Biomet, SeaSpine, Medicrea, and Alphatec Spine; he receives institutional fellowship work in spine surgery from AOSpine, Omega, and NuVasive. Dr. Ames reports being an employee of UCSF. He reports being a consultant for DePuy Synthes, Medtronic, Stryker, Medicrea, Biomet Zimmer Spine, and KM2. He receives royalties from Stryker, Biomet Zimmer Spine, DePuy Synthes, NuVasive, Next Orthosurgical, K2M, and Medicrea. He does research for Titan Spine, DePuy Synthes, and ISSG. He is on the editorial board of Operative Neurosurgery. He receives grant funding from the SRS. He is on the executive committee of ISSG. He is the director for Global Spine Analytics.

Author Contributions

Conception and design: Lau. Acquisition of data: Lau. Analysis and interpretation of data: all authors. Drafting the article: Lau. Critically revising the article: Lau, Ames. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Lau. Statistical analysis: Lau. Study supervision: Ames.

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  • Collapse
  • Expand

Image from Tiwari et al. (pp 258–268).

  • FIG. 1.

    Summary of total number of 3COs performed for ASD and trends of associated perioperative results. The total number of osteotomies performed was 362. The distribution of osteotomy level was as follows: thoracic (14.9%), L1 (6.6%), L2 (7.2%), L3 (37.3%), L4 (28.2%), L5 (4.4%), and S1 (1.4%). Over time, there were lower complications rates and shorter operative times. Figure is available in color online only.

  • FIG. 2.

    Trend of perioperative complication rates over surgeon years of experience. There was a trend for decreased overall and surgery-specific complications over the 13-year period. The rate of neurological complications decreased significantly, especially following 2010 (p = 0.027). Figure is available in color online only.

  • FIG. 3.

    Scatterplot of operative duration over a surgeon’s years of experience. Years of experience was an independent factor associated with operative time (p < 0.001). There is a clear trend for shorter operative time as greater experience is gained. In addition, there is increased consistency and less deviation of the linear trend line with greater years of experience. Figure is available in color online only.

  • 1

    Acosta FL Jr, McClendon J Jr, O’Shaughnessy BA, Koller H, Neal CJ, Meier O, et al.: Morbidity and mortality after spinal deformity surgery in patients 75 years and older: complications and predictive factors. J Neurosurg Spine 15:667674, 2011

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Ahn J, Iqbal A, Manning BT, Leblang S, Bohl DD, Mayo BC, et al.: Minimally invasive lumbar decompression—the surgical learning curve. Spine J 16:909916, 2016

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Auerbach JD, Lenke LG, Bridwell KH, Sehn JK, Milby AH, Bumpass D, et al.: Major complications and comparison between 3-column osteotomy techniques in 105 consecutive spinal deformity procedures. Spine (Phila Pa 1976) 37:11981210, 2012