Craig A. Kuhns

Neurologic complications of lumbar pedicle subtraction osteotomy: a 10-year assessment.

Study Design. Clinical, radiographic, and outcomes assessment focusing on neurologic complications in patients undergoing pedicle subtraction osteotomy (PSO). Clinical data were collected prospectively. Radiographic analysis was performed retrospectively. Objective. To evaluate intraoperative and postoperative neurologic deficits following lumbar PSOs in order to determine risk factors, treatment strategies, and patient outcome. Summary of Background Data. Although technically demanding, PSOs have been increasingly used to restore lumbar lordosis and correct sagittal deformity. Although some reports have commented on various complications of the procedure, to our knowledge, there have been no studies focusing on neurologic complications of the osteotomy. Methods. An analysis of 108 consecutive patients with an average age of 54.8 ± 14.0 years and treated with a lumbar PSO at 1 institution over a 10-year period (1995–2005) was performed. Medical records, radiographs, and neuromonitoring data were analyzed. Clinical outcome was assessed using the Oswestry Disability Index and the Scoliosis Research Society (SRS)-24 instruments. Results. A total of 108 PSOs were performed. Following surgery, lumbar lordosis increased from −17.1° ± 19.3° to −49.3° ± 14.7° (P < 0.000), and sagittal balance improved from 131 ± 73 mm to 23 ± 48 mm (P < 0.000). Intraoperative and postoperative deficits (defined as motor loss of 2 grades or more or loss of bowel/bladder control) were seen in 12 patients (11.1%) and were permanent in 3 patients (2.8%). With time motor function improved by 1 grade in 2 patients and all 3 were able to ambulate. Intraoperative neuromonitoring did not detect the deficits. In 9 patients, additional surgical intervention consisted of central enlargement and further decompression. Deficits were thought to be due to a combination of subluxation, residual dorsal impingement, and dural buckling. Conclusion. Intraoperative or postoperative neurologic deficits are relatively common following a PSO; however, in a majority of cases, deficits are not likely to be permanent.

Operative treatment of adolescent idiopathic scoliosis with posterior pedicle screw-only constructs: minimum three-year follow-up of one hundred fourteen cases.

Study Design. Preoperative review of a prospective study, single institution, consecutive series. Objective. To analyze the intermediate-term follow-up of consecutive adolescent idiopathic scoliosis (AIS) patients treated with pedicle screw constructs. Summary of Background Data. There have been no reports of the intermediate-term findings in North America following posterior spinal fusion with the use of pedicle screw-only constructs. Methods. One hundred and fourteen consecutive patients having a minimum 3-year follow-up (mean 4.8 ± 1.1; range, 3.0–7.3 years) with AIS were evaluated. The average age at surgery was 14.9 ± 2.2 years. Radiographic measurements included preoperative (Preop), postoperative (PO), 2-year (2 years), and final follow-up (FFU). A chart review evaluated PFTs, Scoliosis Research Society scores, presence of thoracoplasty, Risser sign, Lenke classification, and complications. Results. The most frequent curve pattern was Lenke type 1 (45.6%), followed by type 3 (21.9%). The average main thoracic curve measured 59.2° ± 12.2 SD Preop, and corrected to 16.8° ± 9.9 PO (P < 0.0001). Sagittal thoracic alignment (T5–T12) decreased from 25.8° to 15.5° at FFU (P = 0.05). Nash-Moe grading for apical vertebral rotation (AVR) in the proximal thoracic curve decreased from 2.0 Preop to 1.1 at FFU (P < 0.0001), and AVR in the thoracolumbar/lumbar spine decreased from 1.6 Preop to 1.1 at FFU (P < 0.0001). Importantly, the horizontalization of the subjacent disc measured −8.3° Preop which decreased to −0.9° PO (P < 0.001). PFT follow-up averaged 2.4 years with a 7.1% improvement in FVC (P = 0.004) and 8.8% in FEV1 (P < 0.0001). SRS scores averaged 83.0% at latest follow-up. Age, gender, Risser sign, or complications did not have a significant effect on outcomes. There were 2 cases of adding-on, 3 late onset infections, 1 with a single pseudarthrosis, but no neurologic complications. Conclusion. This is the largest (N = 114), consecutive series of North American patients with AIS treated with pedicle screws having a minimum of 3-year follow-up. The average curve correction was 68% for the main thoracic, 50% for the proximal thoracic, and 66% for the thoracolumbar/lumbar curve at final follow-up.

Thoracolumbar deformity arthrodesis stopping at L5: Fate of the L5-S1 disc, minimum 5-year follow-up

Study Design. A retrospective long-term follow-up study. Objective. Evaluate the fate of L5-S1 disc analyzing subsequent disc degeneration and associated risk factors for degeneration at minimum 5-year follow-up (average 9-year follow-up). Summary of Background Data. Two previous studies reported the results of long deformity fusions terminating at L5 with minimum 2-year follow-up only. Methods. Thirty-one consecutive patients with an average age of 45 years (range, 20–62 years) were fused from the thoracic spine to L5 and were evaluated at a mean follow-up of 9.4 years (range, 5–20.1 year). Patients were evaluated before surgery, after surgery, and latest follow-up with radiographs and Scoliosis Research Society Patient Questionnaire-24 scores. Disc degeneration using validated radiographic Weiner grades. Grade 0 to 1 discs were “healthy” and Grade 2 to 3 were degenerated. Patients with “healthy” discs preoperative that subsequently degenerated were designated subsequent advanced degeneration (SAD). Results. Two out of 31 patients had preoperative advanced degeneration of the L5-S1 disc (Weiner grade 2–3). Three additional patients had an early revision to the sacrum secondary to sagittal imbalance not thought to be related to SAD. Twenty-six out of 31 patients were assessed as “healthy discs” preoperative (Weiner grade 0–1) and were evaluated for SAD. By latest follow-up, L5-S1 SAD developed in 18 of these 26 patients (69%). Risk factors for the development of SAD included long fusions extending into the upper thoracic spine down to L5 (P = 0.02) and having a circumferential lumbar fusion (P = 0.02). Although preoperative sagittal balance was not significantly different between the “healthy” and SAD group, sagittal balance at follow-up was: C7 plumb >5 cm in 67% of SAD patients and only 13% of “healthy” disc patients (P = 0.009). There was a trend toward inferior Scoliosis Research Society Patient Questionnaire-24 pain scores at follow-up in SAD patients (average score 4.1 vs. 3.4, P = 0.13). Eleven out of 30 patients (35%) had subsequent spinal surgery with 7 of 31 (23%) having extension of their fusion to the sacrum. An additional 6 of 31 (19%) were considered for extension to the sacrum but comorbidities precluded surgery (3 patients) or the patients declined further surgery (3 patients). Conclusion. Advanced L5-S1 DDD developed in 69% of deformity patients after long fusions to L5 with 5 to 15 year follow-up. SAD frequently results in significant positive sagittal balance at a minimum 5-year follow-up. Long fusions to the upper thoracic spine down to L5 and circumferential fusion may further promote subsequent L5-S1 disc degeneration.

Loss of spinal cord monitoring signals in children during thoracic kyphosis correction with spinal osteotomy: why does it occur and what should you do?

Study Design. A retrospective review of pediatric kyphosis patients undergoing a spinal cord-level osteotomy for correction. Objective. To evaluate the prevalence, etiology, timing, and intervention related to loss of spinal cord monitoring data during surgical correction of pediatric kyphosis in the spinal cord region. Summary of Background Data. Although much has been written regarding the risks inherent to scoliosis surgery, there is less literature available regarding the neurologic outcomes of pediatric kyphosis surgery. As more surgeons contemplate posterior-only kyphosis correction with spinal cord-level osteotomies, the importance of maintaining spinal cord neurologic function is paramount. Methods. Forty-two patients with pediatric kyphosis undergoing a posterior-only spinal reconstruction with a spinal cord level osteotomy or posterior-based vertebral column resection performed were reviewed. Patients were categorized by diagnosis, type and incidence of osteotomies, and loss of neurogenic mixed-evoked potential (NMEP) data. Interventions required to regain data and postoperative neurologic outcomes were also reviewed. Results. Of the 42 patients, 9 (21.4%) demonstrated a complete loss of NMEP data sometime during surgery while concomitant somatosensory sensory-evoked potentials (SSEP) remained within acceptable limits of baseline values. All 9 patients had intraoperative intervention including: blood pressure elevation (n = 1), release of corrective forces (n = 2), blood pressure elevation and correction release (n = 3), malalignment/subluxation adjustment (n = 1), further bony decompression (n = 1), or restoration of anterior column height via a titanium cage along with further posterior decompression (n = 1). In all cases, SSEPs were unchanged and NMEPs returned varying from 8 to 20 minutes after loss, with all patients having a normal wake-up test intraoperatively and a normal neurologic examination after surgery. Conclusion. Intraoperative multimodality monitoring with some form of motor tract assessment is a fundamental component of kyphosis correction surgery in the spinal cord region in order to create a safer, optimal environment and to minimize neurologic deficit. The surgeon must be able to trust the information monitoring provides and act on it accordingly.

An outcomes analysis of the treatment of cervical pseudarthrosis with posterior fusion.

Study Design. A retrospective review of 33 consecutive patients treated with posterior fusion and selective nerve root decompression for the treatment of pseudarthrosis following anterior cervical discectomy and fusion. Objectives. Use standardized outcome measures to evaluate the results of posterior fusion with selective nerve root decompression as a treatment option for symptomatic pseudarthrosis of the cervical spine. Summary of Background Data. Pseudarthrosis after anterior cervical discectomy and fusion has been recognized as a cause of continued cervical pain and unsatisfactory outcomes. Debate continues as to whether a revision anterior approach or a posterior fusion procedure is the best treatment for symptomatic cervical pseudarthrosis. To our knowledge, standardized outcome measures have not been used to evaluate the results of either surgical treatment option; therefore, it is difficult to evaluate outcomes in these patients, let alone compare surgical treatment options. Data on fusion rates in these two surgical treatment groups suggest a trend of a higher fusion rate with utilization of a posterior revision procedure, but the largest study to date includes the study of only 19 patients treated with a posterior fusion. Methods. Thirty-three consecutive patients with symptomatic pseudarthrosis following anterior cervical discectomy and fusion were treated with selective nerve root decompression and posterior fusion using iliac crest or local bone graft as well as posterior wiring and/or lateral mass plating. The average follow-up period was 46 months (range, 20–86 months). Patients were assessed using physical examination, flexion-extension lateral radiographs, and standardized outcome measures including the SF-36, Arthritis Impact Measurement Scales 2, and Cervical Spine Outcomes Questionnaire. Results. All 33 patients (100%) demonstrated a solid fusion at their most recent follow-up, and all 33 patients noted significant improvement in their preoperative symptoms. No difference in fusion status was noted between those treated with iliac crest versus patients treated with local bone graft—all had a solid fusion; 72% of the patients were satisfied with the result of their surgery. Cervical Spine Outcomes Questionnaire pain scales demonstrated 52% of patients reported mild or nopain at follow-up, whereas 20% described their pain as “discomforting” and 28% of the patients continued to report moderate to severe pain. Conclusions. This is the first study to our knowledge to use standardized outcome measures to assess clinical outcome in patients treated with posterior fusion for pseudarthrosis after anterior cervical discectomy and fusion. Patients and surgeons need to understand the potential for success with this revision procedure but also be aware of the relatively high rate of continued moderate to severe pain observed in this patient population even after a solid fusion is achieved. All of the patients in this study fused with a single posterior fusion procedure, further supporting the relatively higher fusion rates observed in the literature using posterior fusion as a treatment for cervical pseudarthrosis. Our results also support the ability of surgeons to use local bone graft without iliac crest in a posterior fusion for cervical pseudarthrosis and therefore avoid the morbidity associated with iliac crest bone graft harvest.

Acute and Long-term Stability of Atlantoaxial Fixation Methods: A Biomechanical Comparison of Pars, Pedicle, and Intralaminar Fixation in an Intact and Odontoid Fracture Model

Study Design. In vitro human cadaveric biomechanical study. Objective. The aims of this project were to evaluate the acute segmental fixation and long-term screw stability afforded by 3 C2 fixation techniques: intralaminar, pars, and pedicle. Summary of Background Data. C2 intralaminar screws offer the advantages of avoiding the vertebral artery; however, direct biomechanical comparison of this technique to the other methods of instrumenting C2 has not been performed. Methods. Fourteen cadaveric specimens were dual energy radiograph absorptiometry scanned and segregated into 2 groups (n = 7/group) matching the C2 bone mineral density. All specimens were instrumented with C1 lateral mass and C2 intralaminar screws while measuring the insertional torque (IT). In group 1 C2 pars screws were inserted while in group 2 pedicle screws were placed. Nondestructive testing was performed in axial rotation, flexion/extension (FE), and lateral bending. The odontoid was then resected and loading repeated. Subsequently, specimens were disarticulated about C2 and individually loaded for 2000 cycles in the cephalocaudad plane. The screws were then failed by a tensile load directed in the parasagittal plane. Full range of motion over C1–C2 and peak screw pull-out force was quantified. Results. Transpedicular technique generated significantly higher IT than the pars screws and marginally greater IT than intralaminar screws. With the intact atlantoaxial ligamentous complex, intralaminar fixation was superior to pars and similar to pedicle instrumentation at limiting axial torsion. After odontoid destabilization, however, this technique was less effective at reducing the lateral bending range of motion. Destructive loading revealed the highest pull-out forces with the pedicle screws, followed by intralaminar and pars screws. Conclusion. Our results suggest that C2 intralaminar fixation provides a viable alternative to pedicle screws and is superior to pars instrumentation in cases with preserved atlantoaxial ligamentous attachments. In the presence of a traumatic dens fracture, however, intralaminar fixation may not be the optimal choice.

Ketorolac and spinal fusion: does the perioperative use of ketorolac really inhibit spinal fusion?

Study Design. Retrospective review. Objective. To evaluate the effect of postoperative use of ketorolac (Toradol) on spinal fusion in humans. Summary of Background Data. The value of parenteral ketorolac in postoperative analgesia has been well documented across surgical specialties. However, some studies have shown that ketorolac may adversely affect osteogenic activity and fracture healing. Methods. A total of 405 consecutive patients who underwent primary lumbar posterolateral intertransverse process fusion with pedicle screw instrumentation were included in this retrospective study. A subtotal of 228 patients received Toradol after surgery for adjunctive analgesia. Each patient received a mandatory dose of 30 mg intravenously every 6 hours for 48 hours. The same surgeon performed the fusion procedure on all of these patients. Historical controls included 177 patients who did not receive Toradol after surgery. The minimum follow-up period was 24 months. Nonunions were diagnosed by analyzing sequential radiographs, flexion-extension radiographs, and computed tomography with multiplanar reconstructions. The gold standard of surgical exploration was performed in symptomatic patients with diagnostic ambiguity or nonunions diagnosed by imaging. Results. There were no smokers in the study population. Pseudarthrosis was identified in 12 of 228 patients (5.3%) who received Toradol after surgery, and in 11 of 177 patients (6.2%) who did not. There was no significant difference detected in the nonunion rates between the two groups (P > 0.05, &khgr;2 method). Conclusion. Use of ketorolac after spinal fusion surgery in humans, limited to 48 hours after surgery for adjunctive analgesia, has no significant effect on ultimate fusion rates.

Surgical strategies to improve fixation in the osteoporotic spine: the effects of tapping, cement augmentation, and screw trajectory.

Study Design Biomechanical study of pedicle screw fixation in osteoporotic bone. Objective To investigate whether it is better to tap or not tap osteoporotic bone prior to placing a cement-augmented pedicle screw. Methods Initially, we evaluated load to failure of screws placed in cancellous bone blocks with or without prior tapping as well as after varying the depths of tapping prior to screw insertion. Then we evaluated load to failure of screws placed in bone block models with a straight-ahead screw trajectory as well as with screws having a 23-degree cephalad trajectory (toward the end plate). These techniques were tested with nonaugmented (NA) screws as well as with bioactive cement (BioC) augmentation prior to screw insertion. Results In the NA group, pretapping decreased fixation strength in a dose-dependent fashion. In the BioC group, the tapped screws had significantly greater loads to failure (p < 0.01). Comparing only the screw orientation, the screws oriented at 23 degrees cephalad had a significantly higher failure force than their respective counterparts at 0 degrees (p < 0.01). Conclusions Standard pedicle screw fixation is often inadequate in the osteoporotic spine, but this study suggests tapping prior to cement augmentation will substantially improve fixation when compared with not tapping. Angulating screws more cephalad also seems to enhance aging spine fixation.

Injectable gelatin used as hemostatic agent to stop pedicle bleeding in long deformity surgical procedures: does it embolize?

Study Design. Prospective porcine animal model. Objective. Determine if injecting FloSeal into pedicles for hemostasis causes emboli. Summary of Background Data. Bleeding from spinal deformity cases can be substantial, especially when surgical procedures involve bilateral fixation at multiple segments. It is not unusual to observe hemorrhage from vascular pedicles during each step of pedicle screw tract preparation. When multiple fixation points are required, blood loss can be excessive. To minimize estimated blood loss and associated morbidity, surgeons have injected liquefied gelatin into pedicles after drilling, palpating, and/or tapping. FloSeal is one of the most popular commercially available injectable agents and we sought to investigate the potential for embolization when used as an intrapedicular hemostatic agent. Methods. Two adult minipigs were anesthetized and underwent sequential bilateral pedicle cannulation from T-spine to sacrum. At every level, tracts were cannulated, palpated, and tapped. In every tract, FloSeal was injected into each pedicle until back pressure was detected on the syringe or to a maximum volume of 2 mL, then pedicle screws were inserted. The right ventricular outflow tract was visualized real time using transesophageal echocardiography. Postmortem evaluation of heart and lungs was performed. Results. FloSeal injected into pedicles caused a consistent large showering of the right ventricular outflow tract in both pigs as visualized on intraoperative transesophageal echocardiography. A second large showering occurred during screw insertion after FloSeal was injected. Microscopic examination of lungs clearly identified amphophilic amorphous material in many small vessels consistent with FloSeal. Conclusion. This study suggests caution when injecting gelatin hemostatic agents into pedicles to stop bleeding during spinal surgery as we saw clear evidence of fat and gelatin emboli when used in this animal model. Further investigation into how to minimize this embolic showering may help the cardiopulmonary at risk patient who requires spinal surgery, especially when multiple points of pedicle screw fixation are used. Level of Evidence: N/A

Is Polymethyl Methacrylate a Viable Option for Salvaging Lateral Mass Screw Failure in the Subaxial Cervical Spine

Study Design Biomechanical analysis of lateral mass screw pullout strength. Objective We compare the pullout strength of our bone cement–revised lateral mass screw with the standard lateral mass screw. Methods In cadaveric cervical spines, we simulated lateral mass screw “cutouts” unilaterally from C3 to C7. We salvaged fixation in the cutout side with polymethyl methacrylate (PMMA) or Cortoss cement (Orthovita, Malvern, Pennsylvania, United States), allowed the cement to harden, and then drilled and placed lateral mass screws back into the cement-augmented lateral masses. On the contralateral side, we placed standard lateral mass screws into the native, or normal lateral, masses and then compared pullout strength of the cement-augmented side to the standard lateral mass screw. For pullout testing, each augmentation group was fixed to a servohydraulic load frame and a specially designed pullout fixture was attached to each lateral mass screw head. Results Quick-mix PMMA-salvaged lateral mass screws required greater force to fail when compared with native lateral mass screws. Cortoss cement and PMMA standard-mix cement-augmented screws demonstrated less strength of fixation when compared with control-side lateral mass screws. Attempts at a second round of cement salvage of the same lateral masses led to more variations in load to failure, but quick-mix PMMA again demonstrated greater load to failure when compared with the nonaugmented control lateral mass screws. Conclusion Quick-mix PMMA cement revision equips the spinal surgeon with a much needed salvage option for a failed lateral mass screw in the subaxial cervical spine.