MRI measurement of neuroforaminal dimension at the index and supradjacent levels after anterior lumbar interbody fusion: a prospective study.

BACKGROUND: Anterior interbody fusion has previously been demonstrated to increase neuroforaminal height in a cadaveric model using cages. No prior study has prospectively assessed the relative change in magnetic resonance imaging (MRI) demonstrated neuroforaminal dimensions at the index and supradjacent levels, after anterior interbody fusion with a corticocancellous allograft in a series of patients without posterior decompression. The objective of this study was to determine how much foraminal dimension can be increased with indirect foraminal decompression alone via anterior interbody fusion, and to determine the effect of anterior lumbar interbody fusion on the dimensions of the supradjacent neuroforamina. METHODS: A prospective study comparing pre- and postoperative neuroforaminal dimensions on MRI scan among 26 consecutive patients undergoing anterior lumbar interbody fusion without posterior decompression was performed. We studies 26 consecutive patients (50 index levels) that had undergone anterior interbody fusion followed by posterior pedicle screw fixation without distraction or foraminotomy. We used preoperative and postoperative MRI imaging to assess the foraminal dimensions at each operated level on which the lumbar spine had been operated. The relative indirect foraminal decompression achieved was calculated. The foraminal dimension of the 26 supradjacent untreated levels was measured pre- and postoperatively to serve as a control and to determine any effects after anterior interbody fusion. RESULTS: In this study, 8 patients underwent 1 level fusion (L5-S1), 12 patients had 2 levels (L4-S1) and 6 patients had 3 levels (L3-S1). The average increase in foraminal dimension was 43.3% (p < 0.05)-19.2% for L3-4, 57.1% for L4-5, and 40.1% for L5-S1. Mean pre- and postoperative supradjacent neuroforaminal dimension measurements were 125.84 mm(2) and 124.89 mm(2), respectively. No significant difference was noted (p > 0.05). CONCLUSIONS: Anterior interbody fusion with a coriticocancellous allograft can significantly increase neuroforaminal dimension even in the absence of formal posterior distraction or foraminotomy; anterior interbody fusion with a coriticocancellous allograft has little effect on supradjacent neuroforaminal dimensions.

Load sharing properties of cervical pedicle screw-rod constructs versus lateral mass screw-rod constructs.

Lateral mass screws have a history of successful clinical use, but cannot always be used in the subaxial cervical spine. Despite safety concerns, cervical pedicle screws have been proposed as an alternative. Pedicle screws have been shown to be biomechanically stronger than lateral mass screws. No study, however, has investigated the load sharing properties comparing constructs using these screws. To investigate this, 12 fresh-frozen single cervical spine motion segments (C4-5 and C6-7) from six cadavers were isolated. They were randomized to receive either lateral mass or pedicle screw-rod constructs. After preloading, the segments were cyclically loaded with a uniplanar axial load from 0 to 90 N both with and without the construct in place. Pressure data at the disc space were continuously collected using a dynamic pressure sensor. The reduction in disc space pressure between the two constructs was calculated to see if pedicle screw and lateral mass screw-rod constructs differed in their load sharing properties. In both the pedicle screw and lateral mass screw-rod constructs, there was a significant reduction in the disc space pressures from the no-construct to construct conditions. The percentage decrease for the pedicle screw constructs was significantly greater than the percentage decrease for the lateral mass screw constructs for average pressure (p < or = 0.002), peak pressure (p < or = 0.03) and force (p < or = 0.04). We conclude that cervical pedicle screw-rod constructs demonstrated a greater reduction in axial load transfer through the intervertebral disc than lateral mass screw-rod constructs. Though there are dangers associated with the insertion of cervical pedicle screws, their use might be advantageous in some clinical conditions when increased load sharing is necessary.

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.

Postoperative lumbar epidural hematoma: does size really matter?

STUDY DESIGN: Prospective clinical series with comparison to retrospectively collected data. OBJECTIVE: To compare direct measures of postoperative hematoma volume against a new measure of hematoma effect on the thecal sac: the critical ratio. SUMMARY OF BACKGROUND DATA: Asymptomatic epidural hematoma is common after lumbar surgery. Symptomatic patients demonstrate a typical progression from sharp peri-incisional pain to bilateral neurologic deficits. Little is known about what differentiates symptomatic and asymptomatic patients. Magnetic resonance imaging (MRI) measures of hematoma size or mass effect may correlate with postoperative symptoms. METHODS: The study population consisted of 3 patient groups evaluated by MRI 2 to 5 days after lumbar decompression with or without fusion. Fifty-seven consecutive prospectively enrolled patients comprised the asymptomatic group. No patient developed severe postoperative pain or neurologic deficit. Search of our institutional database identified 4978 surgical patients within the last 24 months. Seventeen developed new postoperative symptoms. The painful group included 12 patients with severe peri-incisional pain without neurologic deficit. The cauda equina (CE) group included 5 patients with postoperative CE syndrome. Digital imaging software was used to calculate thecal sac cross sectional area on pre- and postoperative MRI at each level, hematoma volume, volume per level decompressed, and critical ratio for each patient. Critical ratio was defined as the smallest ratio of postoperative to preoperative cross sectional area within the lumbar spine. RESULTS.: The critical ratio was the only measure found to differ significantly (P < 0.05) among all 3 groups. Mean critical ratios were asymptomatic (0.8), painful (0.5), and CE (0.2). CONCLUSION: The critical ratio correlates more closely with the presence or absence of postoperative symptoms than measures of hematoma volume, and is consistent with the clinical expectation that greater thecal sac compression may result in more severe symptoms. Few guidelines exist for postoperative lumbar MRI interpretation. The critical ratio is an important contribution.

Acute outcomes of cervical spine injuries in the elderly: atlantaxial vs subaxial injuries.

BACKGROUND/OBJECTIVE: Recent studies have reported on the outcomes of spinal cord injuries in the elderly. Our aim was to identify acute survival differences between elderly patients with atlantoaxial injuries relative to subaxial injuries at our institution and to determine whether operative treatment is associated with improved survival rates in either population. STUDY DESIGN: Retrospective database review of all traumatic cervical spine injuries in patients at least 65 years of age at a single tertiary care center. METHODS: A total of 193 consecutive patients at least 65 years of age treated at a single tertiary care center over a 12-year period were identified. Initial hospitalization records were reviewed. Patients were divided by anatomic level of injury: atlantoaxial (C1 or C2) and subaxial (C3 or below). Demographics, mechanism, and mortality rates were compared. Each group was further divided by treatment (operative or nonoperative), and inpatient survival rates were compared. RESULTS: Statistically similar survival rates were observed among patients with atlantoaxial and subaxial injuries (P = 0.10). Patients with nonoperatively treated subaxial injuries died at significantly higher rates than did their operatively treated peers (P < 0.05). CONCLUSIONS: In this large comprehensive series of elderly patients with cervical spine injuries, survival rates were comparable regardless of anatomic level of injury. The operative treatment of subaxial injuries was associated with an improved acute survival rate vs nonoperative management. Further prospective study is needed to better assess this relationship.

Acute mortality and complications of cervical spine injuries in the elderly at a single tertiary care center.

STUDY DESIGN: Retrospective database review of all traumatic cervical spine injuries at a single tertiary care center. OBJECTIVE: To determine the acute survival of patients aged 65 and over with a variety of cervical spine injuries, regardless of operative or conservative treatment. SUMMARY OF BACKGROUND DATA: Elderly patients with cervical spine injuries have historically suffered from high mortality rates. More recent literature has demonstrated improved outcomes among operatively treated elderly, but has suggested that the nonoperative treatment of cervical injuries in this population may itself contribute to increased mortality rates. METHODS: One thousand seventy-three consecutive patients were identified and initial hospitalization records reviewed. Ninety-four patients were excluded for incomplete data. The remaining 979 patients were divided by age into young and elderly groups. Sex distribution, mechanism, injury type, comorbidities, and mortality and complication rates were compared. Elderly patients were further divided into operative and nonoperative groups and acute outcomes were compared. RESULTS: The overall acute mortality rate for all patients with cervical spine injuries was 5.92%. Eighty-six percent of all patients 65 and over survived, as did 96.1% of younger patients. Seventy-three percent of elderly patients with complete injuries survived, as did 80% of those with incomplete injuries, and 95.6% of intact elderly. Acute mortality rates were statistically comparable in both the operatively and nonoperatively treated groups of elderly. CONCLUSIONS: In this large comprehensive series of elderly patients with cervical spine injuries, statistically comparable survival rates were achieved in both operatively treated and nonoperatively treated patient populations. This finding challenges the conclusion that the nonoperative treatment of the elderly necessarily results in increased acute mortality.

Delayed epidural hematoma after spinal surgery: a report of 4 cases.

Symptomatic postoperative epidural hematoma is a rare and potentially devastating complication of spinal surgery. The overwhelming majority of reported cases have occurred in the immediate postoperative period. A recent publication defined the clinical entity of delayed postoperative epidural spinal hematoma as neurologic deterioration due to an epidural hematoma occurring at least 3 days after the index procedure. Only 2 such cases have been reported in the lumbar spine to date. Four cases of delayed postoperative spinal epidural hematoma were identified over a 6-year period among the spine surgeons at a single large academic institution. Each case involved the lumbar spine. The details of each patient's initial surgery, presentation, and hospital course were then gathered from a retrospective chart review. The 4 patients presented are unusual in their delayed symptomatic presentations of postoperative spinal epidural hematoma. Despite the longer time to onset, however, our patients exhibited many of the characteristics common to cases that presented in the acute postoperative period. The spine surgeon must remain vigilant for the possibility of postoperative spinal epidural hematoma in at-risk patients, even weeks after the original surgical procedure.