Woojin Cho

Major complications in revision adult deformity surgery: Risk factors and clinical outcomes with 2- to 7-year follow-up

Study Design. Retrospective cohort comparative study. Objective. To determine the prevalence of major complications, identify risk factors, and assess long-term clinical benefit after revision adult spinal deformity surgery. Summary of Background Data. No study has analyzed risk factors for major complications in long revision fusion surgery and whether or not occurrence of a major complication affects ultimate clinical outcome. Methods. Analysis of consecutive adult patients who underwent multilevel revision surgery for spinal deformity with a minimum 2-year follow-up was performed. All complications were classified as either major or minor. Outcome analysis was conducted with the Scoliosis Research Society and Oswestry Disability Index scores. Results. A total of 166 patients (mean age = 53.8 years) were identified with a mean follow-up of 3.5 years (range: 2–7). Primary diagnoses included idiopathic/de novo scoliosis (107), degenerative (35), trauma (7), neuromuscular scoliosis (6), congenital deformity (5), ankylosing spondylitis (2), tumor (2), Scheuermann kyphosis (1), and rheumatoid arthritis (1). Most common secondary diagnoses that necessitated revision surgery were adjacent segment disease, fixed sagittal imbalance, and pseudarthrosis. Overall, 34.3% of patients developed major complications (19.3% perioperative; 18.7% follow-up). Associated risk factors for perioperative complications were patient- (age > 60 years, medical comorbidities, obesity) and surgery-related (pedicle subtraction osteotomy). Performance of a 3-column osteotomy and postoperative radiographic changes that suggested progressive loss of sagittal correction were recognized as risk factors for follow-up complications. Equivalent outcome scores were reported by patients preoperatively, but those experiencing follow-up complications reported lower scores at the final follow-up. Conclusion. Overall, 34.4% of patients experienced major complications after long revision fusion surgery. Different risk factors were identified for perioperative versus follow-up complications. The occurrence of a follow-up, not but perioperative, major complication seemed to have a negative impact on ultimate clinical outcome.

The biomechanics of pedicle screw-based instrumentation

There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.

Prospective study of postoperative lumbar epidural hematoma: incidence and risk factors.

Study Design. Prospective clinical series. Objective. To determine the incidence, volume, and extent of postoperative epidural hematoma resulting in thecal sac compression, and to identify risk factors correlated with measured hematoma volumes. Summary of Background Data. Risk factors for postoperative hematoma development have been retrospectively determined in small populations of symptomatic patients. A prospective study of hematoma characteristics and associated risk factors in a consecutive series of patients could significantly enhance our understanding of postoperative hematoma. Methods. Preoperative magnetic resonance imaging and clinical data on 13 pre- and intraoperative risk factors were prospectively collected on 50 consecutive patients undergoing lumbar decompression surgery with or without fusion. Postoperative magnetic resonance imagings were performed within 2 to 5 days of surgery. Thecal sac cross-sectional area was calculated at each disc space. Relative thecal sac compression due to hematoma was calculated at all levels where postoperative cross-sectional area was smaller than preoperative. Hematoma volumes were calculated. Multivariate analysis identified risk factors associated with postoperative hematoma volume. Results. After decompression, 58% of patients developed epidural hematoma of sufficient magnitude to compress the thecal sac beyond its preoperative state at one or more levels. None developed new postoperative neurologic deficits. A mean of 1.4 levels were decompressed. Hematoma extended over a mean of 1.9 levels. Maximal thecal sac compression due to hematoma occurred at an adjacent, nondecompressed level in 28% of patients. Multivariate analysis found age greater than 60, multilevel procedures, and preoperative international normalized ratio to be associated with larger hematoma volumes. Conclusion. Lumbar decompression surgery results in a 58% incidence of asymptomatic compressive postoperative epidural hematoma. Adjacent level compression by hematoma occurs in 28% of patients. Advanced age, multilevel procedures, and international normalized ratio are independently associated with postoperative hematoma volume.

Does a long-fusion "t3-Sacrum" portend a worse outcome than a short-fusion "t10-Sacrum" in primary surgery for adult scoliosis?

Study Design. Retrospective clinicoradiographic analysis. Objective. To compare the upper thoracic (UT) and lower thoracic (LT) spines as the upper instrumented vertebra in primary fusions to the sacrum for adult scoliosis. Summary of Background Data. The optimal level at which a fusion to the sacrum is terminated proximally for adult scoliosis remains controversial. We hypothesized that (1) UT spine would have an increased pseudarthrosis, more perioperative complications, and worse outcomes and (2) LT spine would have more proximal junctional kyphosis. Methods. Patients who underwent primary surgery for adult scoliosis between 2002 and 2006 were studied. UT and LT groups were matched cohorts. Minimum follow-up for all patients was 2 years. Scoliosis Research Society scores and Oswestry Disability Index were the clinical outcome measures. Results. Fifty-eight patients (UT = 20, LT = 38) with a mean age of 55.7 years were followed for an average of 3.0 ± 1.1 years. The UT group had greater preoperative thoracic kyphosis and coronal Cobb values (P < 0.05). Diagnoses were idiopathic scoliosis (75.9%) and degenerative scoliosis (24.1%). The UT cohort had a greater number of levels fused (15.8 vs. 8.6) and higher blood loss (1350 mL vs. 811 mL). Operative time, recombinant human bone morphogenetic protein-2 per level, and caudal interbody grafting (80.0% UT vs. 89.5% LT) were similar. The UT group experienced an increased number of perioperative complications (30.0% vs. 15.8%), more pseudarthrosis (20.0% vs. 5.3%), and a higher prevalence of revision surgery (20.0% vs. 10.5%). The LT group had more proximal junctional kyphosis (18.4% vs. 10.0%). Scoliosis Research Society scores and Oswestry Disability Index were improved in both cohorts in all domains (P < 0.001), except function (P = 0.07) and mental health (P = 0.27), which were not significantly improved in the UT group. Conclusion. With long fusions to the sacrum, one should anticipate more perioperative complications, a higher pseudarthrosis rate, and perhaps more revision surgery than short fusions. Short fusions may result in a more proximal junctional kyphosis, only rarely requiring revision surgery.

Proximal Junctional Kyphosis in Primary Adult Deformity Surgery: Evaluation of 20 Degrees as a Critical Angle

BACKGROUND : Multiple studies have reported on the prevalence of proximal junctional kyphosis (PJK) following spinal deformity surgery; however, none have demonstrated its significance with respect to functional outcome scores or revision surgery. OBJECTIVE : To evaluate if 20° is a possible critical PJK angle in primary adult scoliosis surgery patients as a threshold for worse patient-reported outcomes. METHODS : Clinical and radiographic data of 90 consecutive primary surgical patients at a single institution (2002-2007) with adult idiopathic/degenerative scoliosis and 2-year minimum follow-up were analyzed. Assessment included radiographic measurements, but most notably sagittal Cobb angle of the proximal junctional angle at preoperation, between 1 and 2 months, 2 years, and ultimate follow-up. RESULTS : Prevalence of PJK ≥20° at 3.5 years was 27.8% (n = 25). Those with PJK ≥20° at ultimate follow-up were older (mean 56 vs 46 years), had lower number of levels fused (median 8 vs 11), and were proximally fused to the lower thoracic spine more often than upper thoracic spine (all P < .001). PJK ≥20° was associated with significantly higher body mass index and fusion to the sacrum with iliac screws (P < .016, P < .029, respectively). Scoliosis Research Society outcome score changes were lower for PJK patients, but not significantly different from those in the non-PJK group. CONCLUSION : PJK ≥20° in primary adult idiopathic/degenerative scoliosis does not lead to revision surgery for PJK, but is univariately associated with older age, shorter constructs starting in the lower thoracic spine, obesity, and fusion to the sacrum. The negative results, supported by Scoliosis Research Society outcome data, provide important guidance on the postoperative management of such PJK patients. ABBREVIATIONS : BMI, body mass indexLIV, lowest instrumented vertebraeODI, Oswestry Disability IndexPJ, proximal junctionalPJK, proximal junctional kyphosisSRS, Scoliosis Research SocietyUIV, upper instrumented vertebra.

Comparison of anterior cervical fusion after two-level discectomy or single-level corpectomy: sagittal alignment, cervical lordosis, graft collapse, and adjacent-level ossification

BACKGROUND CONTEXT Single-level corpectomy and two-level discectomy with anterior cervical plating have been reported to have comparable fusion and complication rates. However, there are few large series that have compared the two for sagittal alignment, cervical lordosis, graft subsidence, and adjacent-level ossification. PURPOSE To determine the differences between these two procedures for patients with two-level spondylosis by comparing the pre- and postoperative radiographic data. STUDY DESIGN Retrospective review of prospectively collected data in an academic institution. PATIENT SAMPLE Fifty-two with a single-level corpectomy and 45 with a two-level anterior cervical discectomy and fusion (ACDF). OUTCOME MEASURES Pre- and postoperative radiographic data for sagittal alignment, cervical lordosis, subsidence, and adjacent-level ossification. METHODS We retrospectively reviewed the lateral cervical radiographs of patients who had a solid fusion after a single-level cervical corpectomy or a two-level ACDF for the treatment of a degenerative cervical spondylosis by a surgeon at an academic institution. The choice of the operation was dependent on the presence or absence of retrovertebral compression. All patients underwent anterior cervical fusion using fibula strut allograft and variable-angle screw-plate fixation. None had had prior cervical spine surgery. Twenty-five were excluded because of inadequate radiographs and follow-up. There were 52 with a single-level corpectomy and 45 with a two-level ACDF. The following were analyzed: 1) sagittal alignment (modified method of Toyama); 2) cervical lordosis measured by Cobb angles of fusion constructs (fusion Cobb) and C2-C7 (C2-C7 Cobb); 3) graft collapse determined by the subsidence of anterior/posterior body height of fused segments (anterior/posterior subsidence) and the cranial/caudal plate-to-disc distances (cranial/caudal subsidence), and the difference between anterior and posterior body height for the fused levels (anteroposterior [AP] difference); and 4) the severity of ossification at two adjacent levels. RESULTS The mean durations of follow-up were 23.3+/-6.6 (corpectomy) and 25.7+/-6.2 (ACDF) months, range 12 to 45 months. There were no significant differences between the two groups in sagittal alignment, cervical lordosis, graft collapse, and adjacent-level ossification. Graft subsidence and loss of cervical lordosis occurred significantly more during the first 6 weeks after surgery (all measurements, p<.0001) than after 6 weeks, with no significant difference between the two groups. Posterior and caudal end plate subsidence significantly progressed after 6 weeks in Group 1 (p=.04, p=.02). The final follow-up Cobb angle positively correlated with preoperative and immediate postoperative Cobb angles (r=0.437, p<.0001; r=0.727, p<.0001), caudal subsidence (r=0.270, p=.008), and the final AP difference (r=0.915, p<.0001) but did not correlate with surgery level, preoperative and final sagittal alignments, anterior/posterior subsidence, and cranial subsidence. Anterior/posterior subsidence was significantly more strongly related with caudal subsidence (r=0.607, p<.0001; r=0.424, p<.0001) than cranial (r=0.277, p=.007; r=0.211, p=.040) but did not correlate with pre- and postoperative fusion Cobb, and preoperative and the last sagittal alignments. CONCLUSIONS Our data suggest that the two procedures yield comparable results in terms of sagittal alignment, cervical lordosis, graft subsidence, and adjacent-level ossification. Graft subsidence and loss of cervical lordosis appeared to occur mainly during the first 6 weeks after surgery. Single-level corpectomy and fusion continued to subside at the posterior portion of caudal end plate even after 6 weeks. On the other hand, graft subsidence did not correlate with preoperative and final postoperative sagittal alignments.

Comparative analysis of clinical outcome and complications in primary versus revision adult scoliosis surgery

Study Design. A retrospective case comparison study. Objective. We compared clinical outcome and complications in adult patients who underwent primary (P) versus revision (R) scoliosis surgery. Summary of Background Data. There is a paucity of data comparing P versus R adult scoliosis patients with respect to their complication rates and clinical outcome. Methods. Assessment of 250 consecutive adult patients who underwent P versus R surgery for idiopathic or de novo scoliosis between 2002 and 2007, with a minimum 2-year follow-up, was performed. Results. There were 126 patients in the P group and 124 in the R group. Mean age at surgery (P = 51.2 vs. R = 51.6 years, P = 0.79), length of follow-up (P = 3.6 vs. R = 3.6 years, P = 0.94), comorbidities (P = 0.43), and smoking status (P = 0.98) were similar between the 2 groups. Body mass index (P = 25.5 vs. R = 27.4 kg/m2, P = 0.01), number of final instrumented levels (P = 10.5 vs. R 12.1 levels, P = 0.00), fusion to the sacrum (P = 61.0% vs. R = 87.1%, P = 0.00), osteotomy (P = 14.3% vs. R = 54.9%, P = 0.00), length of surgery (P = 6.5 vs. R = 8.2 hours, P = 0.00), and estimated blood loss (P = 1072.1 vs. R = 1401.3 mL, P = 0.05) were different. Primary patients had significantly lower overall complications than revision patients (P = 45.2% vs. R = 58.2%, P = 0.042). Primary patients reported significantly higher preoperative and final clinical outcome measures in function, pain, and subscore SRS domains and ODI compared with revision patients (all P < 0.05). Patients older than 60 years of age, however, reported similar SRS and ODI scores between the 2 groups. The extent of surgical benefit patients received, that is, final minus preoperative score, was similar in all categories between the 2 groups. Conclusion. Adult patients undergoing primary scoliosis surgery had significantly lower overall complications compared with revision patients. Primary patients reported higher preoperative and final clinical outcome measures than revision patients, although this difference disappeared in older patients. The benefit of surgery was similar between the 2 groups.

Predicting the outcome of selective thoracic fusion in false double major lumbar "C" cases with five- to twenty-four-year follow-up.

Study Design. Retrospective radiographic and clinical study. Objective. To examine the long-term outcome of selective thoracic fusion (STF) performed for lumbar “C” modifier curves in adolescent idiopathic scoliosis. Summary of Background Data. The efficacy of STF in lumbar “C” false double major curves is controversial. We examined the 5- to 24-year outcomes of patients with “C” lumbar curves who underwent STF at a single institution to determine which factors help predict successful outcome. Methods. Thirty-two patients (age, 14.8 ± 2.0 years) with a lumbar “C” modifier underwent primary STF and had minimum 5-year follow-up (mean, 6.8 years). All patients were fused distally to either T12 or L1. At latest follow-up, 18 were considered successful (group S), 2 required reoperation to accommodate worsening deformity (group R), and 12 were considered marginal outcomes (group M), as defined by >3 cm coronal imbalance (n = 5), >5 mm worsening of lumbar apical vertebra translation compared with preoperative (n = 4), >1 Nash-Moe grade worsening of lumbar apical vertebra rotation (n = 1), >10° thoracolumbar junction kyphosis which was at least 5° worse than preoperative (n = 5), and lumbar Cobb angle >5° worse than preoperative (n = 2). Clinical outcomes were determined by Scoliosis Research Society (SRS)-30 at final follow-up. Results. Of the multiple factors considered, 2-month postoperative standing lumbar sagittal alignment was most predictive for long-term outcome (P < 0.019 by Kruskal-Wallis ANOVA). Satisfactory outcomes had statistically significantly greater T12-S1 lordosis than those that were marginal (64.8° (group S) vs. 52.0° ° (group M); P = 0.014) or required reoperation (64.8° [group S] vs. 38.0° [group R]; P < 0.001). Traditionally considered variables such as apical vertebra rotation, apical vertebra translation, Cobb angle magnitudes, coronal and sagittal balance, and their respective thoracic-to-lumbar ratios were not independently significant. Conclusion. Selective thoracic fusions performed for lumbar “C” modifier scoliotic deformities generally have excellent long-term radiographic and SRS-30 outcomes at 5- to 24-year follow-up. Care should be taken to ensure that overcorrection of the thoracic curve is not performed beyond the ability of the lumbar curve to compensate. Furthermore, consideration of selective thoracic fusion should not be ruled out simply because the patient may have a somewhat stiff lumbar curve based on side-bending radiographs.

The Effect on the Pullout Strength by the Timing of Pedicle Screw Insertion After Calcium Phosphate Cement Injection

Study Design Biomechanical Cadaveric Study. Objective To characterize the pullout strength of calcium phosphate cement augmented screws between 0 and 6 minutes after cement injection. Summary of Background Data Earlier studies with calcium phosphate cement on pedicle screws inserted into a metal mold or sawbone have shown that the augmentation strength can be affected by the time between cement injection and screw insertion. However, these studies only compared soft cement to completely hardened cement with extended waiting times. These extended waiting times are impractical in live spinal surgeries. Methods Twenty-four pedicle screws were inserted and pulled out axially from cadaveric bone to make revision models. The 24 screw holes were randomly divided into 4 groups, with each group having 6 holes. For each group, identical pedicle screws were inserted at 0, 2, 4, and 6 minutes after injection with bioresorbable calcium phosphate cement (CPC). After 24 hours, the augmented screws were pulled out axially and their pullout strengths were compared. Results The difference between secondary pullout strength and primary pullout strength increased up to 4 minutes after cement injection but decreased after 6 minutes but without statistical difference among the 4 time settings (P>0.3). Conclusions The augmented screws had similar fixation strength regardless of the time between cement mixture and screw insertion as long as they are inserted within 6 minutes. Augmentation power tends to increase up to 4 minutes after cement injection but decreases after 6 minutes.

Comparison of cage designs for transforaminal lumbar interbody fusion: A biomechanical study

BACKGROUND Prior biomechanical studies of transforaminal lumbar interbody fusion were primarily focused on various posterior instrumentation options, comparison with other fusion techniques, and cage positioning inside disc space. Few studies investigated the biomechanics of various cage designs in terms of construct stability. METHODS Twelve lumbar motion segments were used in this study. The experimental procedure has two steps: multidirectional flexibility test and cyclic test. In the multidirectional flexibility test, all twelve specimens were tested following intact and five different cages (straight or banana shaped). The straight cages had biconvex or flat profile. In the cyclic test, the twelve specimens were randomly divided into two groups for biconvex and flat cages. Three thousand cycles in axial torsion, lateral bending and flexion extension were applied sequentially and cage migration was measured. FINDINGS On average, the cage and posterior fixation reduced the range of motion of the intact condition by 40%, 69% and 75% in axial torsion, lateral bending and flexion extension, respectively. There was no statistical difference in construct stability among all five cages. The cage migration (biconvex vs flat) under cyclic loading was less than 0.2mm and no statistical difference was found. INTERPRETATION The experimental results suggest that the geometry of cages, including shape (banana or straight), length, and surface profile (biconvex or flat), does not affect construct stability when the cages are used in conjunction with posterior fixation. With posterior fixation and surface serration, cage migration was minimal under cyclic loading for both biconvex and flat cages.