Adam J. Bevevino

Update on the evidence for adjacent segment degeneration and disease

BACKGROUND CONTEXT The evidence surrounding the topic of adjacent segment degeneration and disease has increased dramatically with an abundant amount of literature discussing the incidence of and techniques to avoid it. However, this evidence is often confusing to discern because of various definitions of both adjacent segment degeneration and disease. PURPOSE To organize and review the recent evidence for adjacent segment degeneration and disease. RESULTS Although multifactorial, three distinct causes of adjacent segment disease in both the lumbar and cervical spine have been discussed: the natural history of the adjacent disc; biomechanical stress on the adjacent level caused by the fusion; and disruption of the anatomy at the adjacent level with the initial surgery. The incidence of adjacent segment degeneration in the lumbar spine has been widely reported in the literature from 0% to 100%; conversely, the reported incidence in the cervical spine is less variable. Similarly, strategies at avoiding adjacent segment disease in the lumbar spine include arthroplasty, dynamic fixation, and percutaneous fixation, whereas in the cervical spine the focus has remained on arthroplasty. CONCLUSIONS Adjacent segment disease and degeneration remain a multifactorial problem with several techniques being developed recently to minimize them. In the future, it is likely that the popularity of these techniques will be dependent on the long-term results, which are currently unavailable.

Return to sports after surgery to correct adolescent idiopathic scoliosis: a survey of the Spinal Deformity Study Group

BACKGROUND CONTEXT There are no guidelines for when surgeons should allow patients to return to sports and athletic activities after spinal fusion for adolescent idiopathic scoliosis (AIS). Current recommendations are based on anecdotal reports and a survey performed more than a decade ago in the era of first/second-generation posterior implants. PURPOSE To identify current recommendations for return to sports and athletic activities after surgery for AIS. STUDY DESIGN/SETTING Questionnaire-based survey. PATIENT SAMPLE Adolescent idiopathic scoliosis after corrective surgery. OUTCOME MEASURES Type and time to return to sports. METHODS A survey was administered to members of the Spinal Deformity Study Group. The survey consisted of surgeon demographic information, six clinical case scenarios, three different construct types (hooks, pedicle screws, hybrid), and questions regarding the influence of lowest instrumented vertebra (LIV) and postoperative physical therapy. RESULTS Twenty-three surgeons completed the survey, and respondents were all experienced expert deformity surgeons. Pedicle screw instrumentation allows earlier return to noncontact and contact sports, with most patients allowed to return to running by 3 months, both noncontact and contact sports by 6 months, and collision sports by 12 months postoperatively. For all construct types, approximately 20% never allow return to collision sports, whereas all surgeons allow eventual return to contact and noncontact sports regardless of construct type. In addition to construct type, we found progressively distal LIV resulted in more surgeons never allowing return to collision sports, with 12% for selective thoracic fusion to T12/L1 versus 33% for posterior spinal fusion to L4. Most respondents also did not recommend formal postoperative physical therapy (78%). Of all surgeons surveyed, there was only one reported instrumentation failure/pullout without neurologic deficit after a patient went snowboarding 2 weeks postoperatively. CONCLUSIONS Modern posterior instrumentation allows surgeons to recommend earlier return to sports after fusion for AIS, with the majority allowing running by 3 months, noncontact and contact sports by 6 months, and collision sports by 12 months.

What is the best way to optimize thoracic kyphosis correction? A micro-CT and biomechanical analysis of pedicle morphology and screw failure.

Study Design. A human cadaveric biomechanical analysis. Objective. The purpose of this study was to evaluate the bone density/trabecular width of the thoracic pedicle and correlate that with its resistance against compressive loading used during correction maneuvers in the thoracic spine (i.e., cantilever bending). Summary of Background Data. As surgeons perform cantilever correction maneuvers in the spine, it is common to have pedicle screws pullout or displace while placing corrective forces on the construct. Currently, surgeons either compress against the cephalad aspect of the pedicle or vice versa. We set out to establish which aspect of the pedicle was the most dense and to determine the optimal direction for screw compression during kyphosis/deformity correction. Methods. Fifteen fresh-frozen cadaveric vertebrae (n = 15) were examined by micro–computed tomography to determine percent bone volume/total volume (%BV/TV) within the cephalad and caudad aspects of the pedicle. Specimens were sectioned in the sagittal plane. Pedicles were instrumented according to the straightforward trajectory on both sides. Specimens were then mounted and loading to failure was performed perpendicular to the screw axis (either the cephalad or the caudad aspect of the pedicle). Results. Mean failure when loading against the caudad aspect of the pedicle was statistically, significantly greater (454.5 ± 241.3 N vs. 334.79 1 ± 158.435 N) than for the cephalad pedicle (P < 0.001). In concordance with failure data, more trabecular and cortical bones were observed within the caudad half of the pedicle compared with the cephalad half (P < 0.001). Conclusion. Our results suggest that the caudad half of the pedicle is denser and withstands higher forces compared with the cephalad aspect. In turn, the incidence of intraoperative screw loosening and/or pedicle fracture may be reduced if the compressive forces (cantilever bending during deformity correction) placed upon the construct are applied against the caudad portion of the pedicle.

Incidence and Morbidity of Concomitant Spine Fractures in Combat-Related Amputees

BACKGROUND CONTEXT High-energy blasts are the most frequent cause of combat-related amputations in Operations Iraqi and Enduring Freedom (OIF/OEF). The nondiscriminating effects of this mechanism often result in both appendicular and axial skeletal injuries. Despite this recognized coincident injury pattern, the incidence and consequence of spine fractures in trauma-related combat amputees are unknown. PURPOSE This study sought to determine the incidence and morbidity of the associated spine fractures on patients with traumatic lower extremity amputation sustained during OIF/OEF. STUDY DESIGN/SETTING Retrospective case control. PATIENT SAMPLE Two hundred twenty-six combat-related lower extremity amputees presenting to a single institution and injured between 2003 and 2008 were included for analysis. OUTCOME MEASURES Physiologic and functional outcome measures were used to determine the influence of spine fractures on combat amputees. Physiologic measures included intensive care unit (ICU) admission rates, injury severity score (ISS), rate of narcotic/neuropathic pain use, and heterotopic ossification (HO) rates. Functional outcome measures included return-to-duty rates and ambulatory status at final follow-up. METHODS Data from 300 consecutive combat-related lower extremity amputations were retrospectively reviewed and grouped. Group 1 consisted of amputees with associated spine fractures, and Group 2 consisted of amputees without spine fractures. The results of the two groups were compared with regard to initial presentation and final functional outcomes. RESULTS A total of 226 patients sustained 300 lower extremity amputations secondary to combat-related injuries, the most common mechanism being an improvised explosive device. Twenty-nine of these patients had a spine fracture (13%). Group 1 had a higher ISS than Group 2 (30 vs. 19, p<.001). Group 1 patients were also more likely to be admitted to the ICU (86% vs. 46%, p<.001). Furthermore, Group 1 patients had a significantly higher rate of HO in their residual limbs (82% vs. 55%, p<.005). CONCLUSIONS The incidence of spine fractures in combat-related amputees is 13%. The results suggest that combat-related amputees with spine fractures are more likely to sustain severe injuries to other body systems, as indicated by the significantly higher ISS and rates of ICU admission. This group also had a significantly higher rate of HO formation, which may be attributable to the greater local and/or systemic injuries sustained by these patients.

Systematic review and meta-analysis of minimally invasive transforaminal lumbar interbody fusion rates performed without posterolateral fusion

The need for posterolateral fusion (PLF) in addition to interbody fusion during minimally invasive (MIS) transforaminal lumbar interbody fusion (TLIF) has yet to be established. Omitting a PLF significantly reduces overall surface area available for achieving a solid arthrodesis, however it decreases the soft tissue dissection and costs of additional bone graft. The authors sought to perform a meta-analysis to establish the fusion rate of MIS TLIF performed without attempting a PLF. We performed an extensive Medline and Ovid database search through December 2010 revealing 39 articles. Inclusion criteria necessitated that a one or two level TLIF procedure was performed through a paramedian MIS approach with bilateral posterior pedicle screw instrumentation and without posterolateral bone grafting. CT scan verified fusion rates were mandatory for inclusion. Seven studies (case series and case-controls) met inclusion criteria with a total of 408 patients who underwent MIS TLIF as described above. The mean age was 50.7 years and 56.6% of patients were female. A total of 78.9% of patients underwent single level TLIF. Average radiographic follow-up was 15.6 months. All patients had local autologous interbody bone grafting harvested from the pars interarticularis and facet joint of the approach side. Either polyetheretherketone (PEEK) or allograft interbody cages were used in all patients. Overall fusion rate, confirmed by bridging trabecular interbody bone on CT scan, was 94.7%. This meta-analysis suggests that MIS TLIF performed with interbody bone grafting alone has similar fusion rates to MIS or open TLIF performed with interbody supplemented with posterolateral bone grafting and fusion.

Outcomes following cervical disc arthroplasty in an active duty military population.

Symptomatic cervical radiculopathy is a common problem in the active duty military population and can cause significant disability leading to limited duty status and loss of operational readiness and strength. Based on their increasing experience with cervical disc arthroplasty (CDA) in this unique patient population, the authors set out to further evaluate the outcomes and complications of CDA in active duty military patients. A retrospective review of a single military tertiary medical center was performed between August 2008 and August 2012 and the clinical outcomes of patients who underwent cervical disc arthroplasty were evaluated. There were 37 active duty military patients, with a total of 41 CDA. The study found good relief of preoperative symptoms (92%) and the ability to maintain operational readiness with a high rate of return to full unrestricted duty (95%) with an average follow-up of 6 months. There was a low rate of complications related to the anterior cervical approach (5%-8%), with no device- or implant-related complications.

Pedicle screw reinsertion using previous pilot hole and trajectory does not reduce fixation strength.

Study Design. Fresh-frozen human cadaveric biomechanical study. Objective. To evaluate the biomechanical consequence of pedicle screw reinsertion in the thoracic spine. Summary of Background Data. During pedicle screw instrumentation, abnormal appearance on fluoroscopic imaging or low current reading with intraoperatively evoked electromyographic stimulation of a pedicle screw warrants complete removal to reassess for pedicle wall violation or screw malposition. However, screw fixation strength has never been evaluated biomechanically after reinsertion using a previous pilot hole and trajectory. Methods. Thirty-one thoracic individual fresh-frozen human cadaveric vertebral levels were instrumented bilaterally with 5.5-mm titanium polyaxial pedicle screws, and insertional torque (IT) was measured with each revolution. A paired comparison was performed for each level. Screw reinsertion was performed by completely removing the pedicle screw, palpating the tract, and then reinserting along the same trajectory. Screws were tensile loaded to failure “in-line” with the screw axis. Results. There was no significant difference for pedicle screw pullout strength (POS) between reinserted and control screws (732 ± 307 N vs. 742 ± 320 N, respectively; P = 0.78). There was no significant difference in IT between initial insertion for the test group (INI) (0.82 ± 0.40 N·m) and control (0.87 ± 0.50 N·m) (P = 0.33). IT for reinserted screws (0.58 ± 0.47 N·m) had significantly decreased compared with INI and control screws (29% decrease, P = 0.00; 33% decrease, P = 0.00, respectively). The test group screws in the thoracic spine had significant correlations between initial IT and POS (r = 0.79, P = 0.00), and moderate correlations between reinsertion IT and POS in the thoracic spine (r = 0.56, P = 0.00). Conclusion. Despite a significant reduction in pedicle screw IT, there was no significant difference in pedicle screw POS with reinsertion. Therefore, when surgeons must completely remove a pedicle screw for tract inspection, reinsertion along the same trajectory may be performed without significantly compromising fixation strength. Level of Evidence: N/A

Pedicle screw "hubbing" in the immature thoracic spine: a biomechanical and micro-computed tomography evaluation.

Background: A previous biomechanical study using adult thoracic vertebrae (both normal and osteoporotic bone density) demonstrated the deleterious effect of the pedicle screw hubbing technique. Pedicle screw “hubbing” involves seating and engaging the ventral aspect of the screw head onto the dorsal lamina cortex. This technique is postulated to provide a load-sharing effect by improving pullout resistance, as well as decreasing cephalocaudad toggling and implant loosening. We hypothesized the elastic properties of immature bone may mitigate, and perhaps enhance the purported benefits of the hubbing technique. We set out to evaluate pullout strength of fixed-head pedicle screws after hubbing versus standard insertion in the immature thoracic calf spine. Methods: Twenty-two (n=22) single-level disarticulated fresh-frozen immature calf thoracic vertebra specimens (ranging from T2 to T13) were prepared. Twelve specimens were instrumented with pedicle screws in group I (nonhubbed) and group II (hubbed) in the opposite pedicle. Cyclic loading in a cephalocaudad direction was applied for 2000 cycles at a rate of 1 Hz. Pullout testing was performed in-line with the midline of the vertebra and peak pullout strength was measured in Newtons. Ten different specimens underwent micro-computed tomography evaluation to assess for trabecular architecture and incidence of iatrogenic microfractures. Results: Hubbed screws resulted in significantly lower pullout strength (747±197 vs. 922±112 N, P=0.01). With the hubbing technique, the dorsal cortex demonstrated plastic deformation and conformed to the screw head in 83% of cases compared with no visible plastic deformation in the control group. Micro-computed tomography demonstrated microfractures of the dorsal cortex in 10/10 for the hubbed group compared with 1/10 for the control group. Conclusions: This is the largest study ever performed on immature thoracic vertebra to evaluate this topic. Hubbed pedicle screws have significantly decreased pullout strength and frequently cause iatrogenic microfractures of the dorsal cortex. The unique ability of immature bone to exhibit plastic deformation did not provide a protective effect on immediate fixation strength, and the increased insertional torque during the hubbing technique should not give a false sense of added fixation. This study, along with our adult study, provides critical information to the surgeon to avoid this common misunderstanding with screw insertion technique. Clinical Relevance: In vitro fresh-frozen immature calf spine study.

The effect of cervical posterior foraminotomy on segmental range of motion in the setting of total disc arthroplasty.

Study Design. Human cadaveric biomechanical analysis. Objective. To investigate the effect on cervical spine segmental stability that results from a posterior foraminotomy after cervical disc arthroplasty (CDA). Summary of Background Data. Posterior foraminotomy offers the ability to decompress cervical nerves roots while avoiding the need to extend a previous fusion or revise an arthroplasty to a fusion. However, the safety of a foraminotomy in the setting of CDA is unknown. Methods. Segmental nondestructive range of motion (ROM) was analyzed in 9 human cadaveric cervical spine specimens. After intact testing, each specimen was sequentially tested according to the following 4 experimental groups: group 1 = C5–C6 CDA, group 2 = C5–C6 CDA with unilateral C5–C6 foraminotomy, group 3 = C5–C6 CDA with bilateral C5–C6 foraminotomy, and group 4 = C5–C6 CDA with C5–C6 and C4–C5 bilateral foraminotomy. Results. No differences in ROM were found between the intact, CDA, and foraminotomy specimens at C4–C5 or C6–C7. There was a step-wise increase in C5–C6 axial rotation from the intact state (8°) to group 4 (12°), although the difference did not reach statistical significance. At C5–C6, the degree of lateral bending remained relatively constant. Flexion and extension at C5–C6 was significantly higher in the foraminotomy specimens, groups 2 (18.1°), 3 (18.6°), and 4 (18.2°), compared with the intact state, 11.2°. However, no ROM difference was found within foraminotomy groups (2–4) or between the foraminotomy groups and the CDA group (group 1), 15.3°. Conclusion. Our results indicate that cervical stability is not significantly decreased by the presence, number, or level of posterior foraminotomies in the setting of CDA. The addition of foraminotomies to specimens with a pre-existing CDA resulted in small and insignificant increases in segmental ROM. Therefore, biomechanically, posterior foraminotomy/foraminotomies may be considered a safe and viable option in the setting of recurrent or adjacent level radiculopathy after cervical disc replacement. Level of Evidence: N/A

Large caliber ballistic fragment within the spinal canal

Gunshot wounds to the spine continue to be a prodigious clinical problem. We report a case of a 28-year-old male US Marine after a high-energy penetrating spinal cord injury, with associated injuries including a left hemopneumothorax and an open left comminuted scapula body fracture. Computed tomography demonstrated a retained highcaliber (7.62 mm) ballistic fragment within the spinal canal at the level of T6–T7 (Figs. 1 and 2). On physical examination, the patient had an incomplete spinal cord injury (American Spinal Injury Association Grade B) with sacral sparing demonstrating normal rectal tone, voluntary rectal squeeze, and bulbocavernosus reflex. The patient had 0/5 motor strength in bilateral lower extremities, normal sensation T6 right/T5 left, intact proprioception in bilateral ankles and toes, and normal strength/sensation in bilateral upper extremities. On Postinjury Day 5, the patient underwent a T6 laminectomy, removal of the bullet, and subsequent repair of a dural defect. This is the first case of a large caliber bullet being lodged in the spinal canal, with only a few reported case series of combat casualties treated for high-velocity ballistic injuries to the spinal column [1,2]. When treating gunshot wounds to the spine, it is of the utmost importance to differentiate between high- and low-energy ballistic injuries as this dictates the appropriate management [3]. Highenergy ballistic injuries are more common in combat casualties compared with civilian trauma patients and are often associated with significantly greater soft-tissue devitalization and a larger zone of injury. Treatment of high-energy ballistic injuries should consist of early broad-spectrum intravenous antibiotics, aggressive surgical debridement, and, when indicated, decompressive laminectomy with instrumentation at a Level 4 or 5 treatment facility. Fractures of the spine caused by low-velocity bullet wound or ballistic fragmentation are usually stable, and surgical intervention is often unnecessary. Most cases of spine instability and late deformity after penetrating injury have been associated with overly aggressive laminectomy [3,4].