Biomechanical Effects of an Oblique Lumbar PEEK Cage and Posterior Augmentation.

OBJECTIVE: Lumbar interbody spacers are widely used in lumbar spinal fusion. The goal of this study is to analyze the biomechanics of a lumbar interbody spacer (Clydesdale Spinal System, Medtronic Sofamor Danek, Memphis, Tennessee, USA) inserted via oblique lumbar interbody fusion (OLIF) or direct lateral interbody fusion (DLIF) approaches, with and without posterior cortical screw and rod (CSR) or pedicle screw and rod (PSR) instrumentation. METHODS: Lumbar human cadaveric specimens (L2-L5) underwent nondestructive flexibility testing in intact and instrumented conditions at L3-L4, including OLIF or DLIF, with and without CSR or PSR. RESULTS: OLIF alone significantly reduced range of motion (ROM) in flexion-extension (P = 0.005) but not during lateral bending or axial rotation (P ≥ 0.63). OLIF alone reduced laxity in the lax zone (LZ) during flexion-extension (P < 0.001) but did not affect the LZ during lateral bending or axial rotation (P ≥ 0.14). The stiff zone (SZ) was unaffected in all directions (P ≥ 0.88). OLIF plus posterior instrumentation (cortical, pedicle, or hybrid) reduced the mean ROM in all directions of loading but only significantly so with PSR during lateral bending (P = 0.004), without affecting the compressive stiffness (P > 0.20). The compressive stiffness with the OLIF device without any posterior instrumentation did not differ from that of the intact condition (P = 0.97). In terms of ROM, LZ, or SZ, there were no differences between OLIF and DLIF as standalone devices or OLIF and DLIF with posterior instrumentation (CSR or PSR) (P > 0.5). CONCLUSIONS: OLIF alone significantly reduced mobility during flexion-extension while maintaining axial compressive stiffness compared with the intact condition. Adding posterior instrumentation to the interbody spacer increased the construct stability significantly, regardless of cage insertion trajectory or screw type.

Biomechanical Analysis of an Expandable Lumbar Interbody Spacer.

OBJECTIVE: Recently developed expandable interbody spacers are widely accepted in spinal surgery; however, the resulting biomechanical effects of their use have not yet been fully studied. We analyzed the biomechanical effects of an expandable polyetheretherketone interbody spacer inserted through a bilateral posterior approach with and without different modalities of posterior augmentation. METHODS: Biomechanical nondestructive flexibility testing was performed in 7 human cadaveric lumbar (L2-L5) specimens followed by axial compressive loading. Each specimen was tested under 6 conditions: 1) intact, 2) bilateral L3-L4 cortical screw/rod (CSR) alone, 3) WaveD alone, 4) WaveD + CSR, 5) WaveD + bilateral L3-L4 pedicle screw/rod (PSR), and 6) WaveD + CSR/PSR, where CSR/PSR was a hybrid construct comprising bilateral cortical-level L3 and pedicle-level L4 screws interconnected by rods. RESULTS: The range of motion (ROM) with the interbody spacer alone decreased significantly compared with the intact condition during flexion-extension (P = 0.02) but not during lateral bending or axial rotation (P ≥ 0.19). The addition of CSR or PSR to the interbody spacer alone condition significantly decreased the ROM compared with the interbody spacer alone (P ≤ 0.002); and WaveD + CSR, WaveD + PSR, and WaveD + CSR/PSR (hybrid) (P ≥ 0.29) did not differ. The axial compressive stiffness (resistance to change in foraminal height during compressive loading) with the interbody spacer alone did not differ from the intact condition (P = 0.96), whereas WaveD + posterior instrumentation significantly increased compressive stiffness compared with the intact condition and the interbody spacer alone (P ≤ 0.001). CONCLUSIONS: The WaveD alone significantly reduced ROM during flexion-extension while maintaining the axial compressive stiffness. CSR, PSR, and CSR/PSR hybrid constructs were all effective in augmenting the expandable interbody spacer system and improving its stability.

Cardiac screening to prevent sudden death in young athletes.

Sudden cardiac death (SCD) is a sudden and unexpected death caused by loss of heart of function. SCD may occur in any population, but when it occurs on the playing field in a young individual, communities worldwide are affected. Although these events are rare, media coverage of sudden cardiac arrests in young athletes have created the impression that these events are far more common than they appear. With a heightened awareness of SCD in young athletes, screening methods have been developed to try and prevent these events from occurring. The American Heart Associations (AHA) currently employs history and physical examination alone during the preparticipation physical exam (PPE), which clears a young athlete for participation in sports. There has been recent discussion on whether to include screening electrocardiogram (ECG) in the PPE especially after one study in Italy by Corrado et al. found that using routine ECG reduced the annual incidence of SCD by 90%. In this article we will discuss how effective the current screening recommendations are, whether routine ECG use should be included in the PPE and if it is cost effective, and review other screening modalities that may be useful in the detection of young athletes at risk for SCD.

Comparison of CT versus MRI measurements of transverse atlantal ligament integrity in craniovertebral junction injuries. Part 2: A new CT-based alternative for assessing transverse ligament integrity.

OBJECTIVE The rule of Spence is inaccurate for assessing integrity of the transverse atlantal ligament (TAL). Because CT is quick and easy to perform at most trauma centers, the authors propose a novel sequence of obtaining 2 CT scans to improve the diagnosis of TAL impairment. The sensitivity of a new CT-based method for diagnosing a TAL injury in a cadaveric model was assessed. METHODS Ten human cadaveric occipitocervical specimens were mounted horizontally in a supine posture with wooden inserts attached to the back of the skull to maintain a neutral or flexed (10°) posture. Specimens were scanned in neutral and flexed postures in a total of 4 conditions (3 conditions in each specimen): 1) intact (n = 10); either 2A) after a simulated Jefferson fracture with an intact TAL (n = 5) or 2B) after a TAL disruption with no Jefferson fracture (n = 5); and 3) after TAL disruption and a simulated Jefferson fracture (n = 10). The atlantodental interval (ADI) and cross-sectional canal area were measured. RESULTS From the neutral to the flexed posture, ADI increased an average of 2.5% in intact spines, 6.25% after a Jefferson fracture without TAL disruption, 34% after a TAL disruption without fracture, and 25% after TAL disruption with fracture. The increase in ADI was significant with both TAL disruption and TAL disruption and fracture (p < 0.005) but not in the other 2 conditions (p > 0.6). Changes in spinal canal area were not significant (p > 0.70). CONCLUSIONS This novel method was more sensitive than the rule of Spence for evaluating the integrity of the TAL on CT and does not increase the risk of further neurological damage.

Comparison of CT versus MRI measurements of transverse atlantal ligament integrity in craniovertebral junction injuries. Part 1: A clinical study.

OBJECTIVE Craniovertebral junction (CVJ) injuries complicated by transverse atlantal ligament (TAL) disruption often require surgical stabilization. Measurements based on the atlantodental interval (ADI), atlas lateral diameter (ALD1), and axis lateral diameter (ALD2) may help clinicians identify TAL disruption. This study used CT scanning to evaluate the reliability of these measurements and other variants in the clinical setting. METHODS Patients with CVJ injuries treated at the authors' institution between 2004 and 2011 were evaluated retrospectively for demographics, mechanism and location of CVJ injury, classification of injury, treatment, and modified Japanese Orthopaedic Association score at the time of injury and follow-up. The integrity of the TAL was evaluated using MRI. The ADI, ALD1, and ALD2 were measured on CT to identify TAL disruption indirectly. RESULTS Among the 125 patients identified, 40 (32%) had atlas fractures, 59 (47.2%) odontoid fractures, 31 (24.8%) axis fractures, and 4 (3.2%) occipital condyle fractures. TAL disruption was documented on MRI in 11 cases (8.8%). The average ADI for TAL injury was 1.8 mm (range 0.9-3.9 mm). Nine (81.8%) of the 11 patients with TAL injury had an ADI of less than 3 mm. In 10 patients (90.9%) with TAL injury, overhang of the C-1 lateral masses on C-2 was less than 7 mm. ADI, ALD1, ALD2, ALD1 - ALD2, and ALD1/ALD2 did not correlate with the integrity of the TAL. CONCLUSIONS No current measurement method using CT, including the ADI, ALD1, and ALD2 or their differences or ratios, consistently indicates the integrity of the TAL. A more reliable CT-based criterion is needed to diagnose TAL disruption when MRI is unavailable.

Biomechanics of Nested Transforaminal Lumbar Interbody Cages.

BACKGROUND: Arthrodesis is optimized when the structural graft occupies most of the surface area within a disc space. The transforaminal corridor inherently limits interbody size. OBJECTIVE: To evaluate the biomechanical implications of nested interbody spacers (ie, a second curved cage placed behind a first) to increase disc space coverage in transforaminal approaches. METHODS: Seven lumbar human cadaveric specimens (L3-S1) underwent nondestructive flexibility and axial compression testing intact and after transforaminal instrumentation at L4-L5. Specimens were tested in 5 conditions: (1) intact, (2) interbody, (3) interbody plus bilateral pedicle screws and rods (PSR), (4) 2 nested interbodies, and (5) 2 nested interbodies plus PSR. RESULTS: Mean range of motion (ROM) with 1 interbody vs 2 nested interbodies, respectively, was: flexion, 101% vs 85%; extension, 97% vs 92%; lateral bending, 127% vs 132%; and axial rotation, 145% vs 154%. One interbody and 2 nested interbodies did not differ significantly by loading mode (P > .10). With PSR, ROM decreased significantly compared with intact, but not between interbody and interbody plus PSR or 2 interbodies plus PSR (P > .80). Mean vertical height during compressive loading (ie, axial compressive stiffness) was significantly different with 2 nested interbodies vs 1 interbody alone (P < .001) (compressive stiffness, 89% of intact vs 67% of intact, respectively). CONCLUSION: Inserting a second interbody using a transforaminal approach is anatomically feasible and nearly doubles the disc space covered without affecting ROM. Compressive stiffness significantly increased with 2 nested interbodies, and foraminal height increased. Evaluation of the clinical safety and efficacy of nested interbodies is underway.

Instrumentation of the posterior thoracolumbar spine: from wires to pedicle screws.

Over the past 120 years, spinal stabilization has advanced immensely. An updated review highlighting these advancements has not been performed in the past 20 years. The objective of this report is to provide a historical assessment of the decades outlining various key innovators, their techniques, and instrumentation. It is important to provide new generations of surgeons and students with historical evidence of the value of developing new techniques and instrumentation to improve patient care and outcomes.