Warren D. Yu

Perioperative complications of threaded cylindrical lumbar interbody fusion devices: anterior versus posterior approach.

Few data are available to evaluate approach-related differences in perioperative complications with lumbar interbody fusion devices. Complications occurring in the intraoperative and immediate postoperative period were identified and categorized for 31 consecutive posterior lumbar interbody fusions (PLIFs) and 88 consecutive anterior lumbar interbody fusions (ALIFs). In this study, all lumbar interbody fusions were conducted with threaded cylindrical devices as stand-alone internal fixation devices. Multivariate analysis was used to account for potential covariates and identify factors associated with an increased complication risk. Twenty-two percent of the patients had a perioperative complication. The relative risk of having a perioperative complication was 4.75 times higher for the PLIF group. All intraoperative complications occurred in the PLIF group. The relative risk of having a major postoperative complication was 6.8 times higher in the PLIF group than the ALIF group. Anterior approached patients tended to have visceral (ileus, 6%) and vascular (deep venous thrombosis, 2%) complications. In the posterior group, complications were neurologic and dura related (pseudomeningocele, 16%; epidural hematoma, 3%) and occurred most frequently in patients that had had previous posterior lumbar surgery (31% with major complication).

An anatomic study of the S2 iliac technique for lumbopelvic screw placement.

Study Design. An anatomic study conducted on cadaveric specimens. Objectives. The objectives of the study were (1) to determine course of S2 lumbopelvic screws with reference to the articular cartilage of the sacroiliac joint, (2) to determine the length and trajectory of screws placed using anatomic placement techniques, and (3) to determine vital structures at risk using this technique. Summary of Background Data. Multiple techniques exist for fixation distal to S1 including alar screws, iliac post bolts, and transiliac rods. Distal fixation is crucial in adult deformity surgery when fusion to the sacrum is indicated. Methods. Five female and 5 male cadaveric specimens were instrumented with S1 promontory screws and S2 iliac lumbopelvic screws. The specimens then underwent computed tomography scanning to determine structures at risk, cortical violations, and characteristics of screws placed. The sacroiliac joints were opened to examine articular cartilage penetration. Results. Articular violation occurred in 60% of screws placed. Average length was 84 mm. No vital structures were at risk from screw placement. No intrapelvic cortical violations occurred. Conclusion. S2 iliac technique is a potential option for distal fixation in spine surgery. Biomechanical and clinical data are required to fully evaluate the potential of this technique.

A Comparison of Magnetic Resonance and Computed Tomographic Image Quality After the Implantation of Tantalum and Titanium Spinal Instrumentation

Study Design. Tantalum‐ and titanium‐based lumbar interbody fusion devices were implanted into two fresh human cadavers, and magnetic resonance and computed tomographic imaging were performed to evaluate adjacent spinal structures and the amount of metallic artifact. Objective. The objective of this study was to prospectively compare the preliminary results of magnetic resonance imaging and computed tomography scanning image quality after the implantation of both titanium and tantalum spinal implants. Summary of Background Data. The availability of tantalum and titanium spinal implants brings theoretical magnetic resonance imaging compatibility along with several other desirable characteristics. The magnetic resonance imaging and computed tomographic imaging of tantalum spinal instrumentation has never been studied previously or compared with titanium instrumentation. Methods. Titanium and tantalum spinal implants produced for anterior spinal fusion were each placed at two levels in the lumbar spine of two fresh cadaver specimens. Sequential spin echo T1‐weighted and T2‐weighted magnetic resonance imaging studies and computed tomographic scans were obtained. The resulting images were then graded to describe and compare the behavior of tantalum metal in magnetic resonance imaging and computed tomographic studies. Results. Good T1 and T2 images were obtained that allowed visualization of the neural structures with minimal artifact. The optimal T1 images for tantalum metal were similar in quality to the optimal T1 parameters for titanium metal. T2 images for both tantalum and titanium metal were obtained with similar results for both metals. Gradient echo magnetic resonance imaging scans of both were poorly imaged with a large amount of artifact. Computed tomographic studies of tantalum implants produced a large amount of metal artifact when compared with computed tomographic studies of titanium implants. Conclusions. High‐quality magnetic resonance imaging studies can be obtained after the implantation of both titanium and tantalum spinal instrumentation. Both of the metals produce similar images on magnetic resonance imaging studies with comparable amounts of metallic artifact. High‐quality computed tomographic scans of titanium implants can be obtained with minimal distortion secondary to artifact. However, computed tomographic scanning is not the imaging modality of choice for the tantalum spinal implants because of the large amounts of artifact.

Metal debris from titanium spinal implants.

STUDY DESIGN A prospective study of tissue surrounding spinal instrumentation was performed using histologic and chemical analysis. OBJECTIVES To identify and quantify the amount of metal debris generated by titanium pedicle screw instrumentation and to evaluate the histologic response in the spinal tissues. SUMMARY OF BACKGROUND DATA Microscopic metal particles from the soft tissue surrounding joint arthroplasties have been shown to activate a macrophage response that leads to bone resorption and increased inflammation. The use of titanium spinal implants for spine surgery projects the possibility of generating wear debris in the spine. METHODS Nine patients with titanium instrumentation from a prior lumbar decompression and fusion procedure who were undergoing reoperation were entered into this study. Tissue samples were collected from areas near the pedicle screw-rod junction, the scar tissue overlying the dura, and the pedicle screw holes. Metal levels for titanium were determined by electrothermal atomic absorption spectroscopy, and histologic analysis was performed by light and electron microscopy. RESULTS Tissue concentrations of titanium were highest in patients with a pseudarthrosis (30.36 micrograms/g of dry tissue). Patients with a solid fusion had low concentrations of titanium (0.586 microgram/g of dry tissue). Standard light microscopy identified metal particles in the soft tissues. Transmission electron microscopy demonstrated macrophages with numerous secondary lysosomes containing electron-dense bodies and collagenous stroma with electron-dense rod-like profiles consistent with metal debris. CONCLUSIONS Wear debris is generated by the use of titanium spinal instrumentation in patients with a pseudarthrosis. These particles activate a macrophage cellular response in the spinal tissues similar to that seen in surrounding joint prostheses. Patients with a solid spinal fusion have negligible levels of particulate matter.

Fractures of the fifth metatarsal : Careful identification for optimal treatment

Fractures of the fifth metatarsal are common in active people. Proximal metaphyseal and distal fractures are usually amenable to conservative treatment, but some proximal fractures, such as Jones, stress, and acute-on-chronic fractures, are often associated with nonunion or delayed union. Such fractures are often best treated by early operative intervention. Correct identification of fifth metatarsal fractures is important because prompt surgical treatment when indicated can shorten recovery and allow a quick return to sports activity. Other causes of lateral foot pain, including accessory ossicles, neuromas, osteoporosis, herniated disks, and osteoid osteoma, should be considered when suspected fractures fail to show up on radiographs.

Feasibility of minimally invasive sacropelvic fixation: percutaneous S2 alar iliac fixation.

Study Design. A cadaveric study with postoperative computed tomography scan to evaluate instrumentation placement. Objective. To successfully place percutaneous sacropelvic instrumentation. Summary of Background Data. S2 iliac fixation has been in use clinically at some centers. Recently, anatomic data have been presented on the technique. The purpose of this study is to determine the feasibility of percutaneous placement of S2 iliac sacropelvic fixation (1) without damage to vital structures and (2) with in-line placement with S1 pedicle screws. Methods. Eight cadaveric spines were used in this study. Percutaneous pedicle screws were placed from L3–S1 in 4 and from L2–S1 in the remainder. Percutaneous S2 iliac screws were placed using a modification of the open technique. Rods were placed using minimally invasive techniques. All specimens were CT scanned. Trajectory of the screws was measured from CT scans. Maximal length was judged by a k-wire left in the S2 iliac screw. CT scans were critically evaluated for risks to visceral and neurovascular structures as well as cortical breaches. Results. Average length of the screws was 92.5 mm (range, 69–120 mm). No screw was intrapelvic or risked any visceral or neurovascular structure. No screws violated the cortex of the ilium. All S2 iliac screws were in-line with the S1 pedicle screws. The average cephalocaudad trajectory was 29° caudal from direct lateral. The average anterior-posterior angulation was 42° from a horizontal line connecting the PSIS. Conclusion. Use of the S2 iliac technique may be a viable option in minimally invasive thoracolumbar deformity surgery. The screws were all in-line and connected easily to the cephalad instrumentation. On average, a length of approximately 90 mm was attained. No visceral or neurovascular structure was injured. Visualization of the first dorsal foramen and a standard anteroposterior and inlet radiograph were used for placement.

MR Parameters for Imaging Titanium Spinal Instrumentation

The presence of stainless steel implants along a spinal column causes extreme distortion of data collected by magnetic resonance (MR) imaging. The recent availability of titanium alloy spinal instrumentation systems suggests that MR imaging evaluation of the instrumented spine may now be feasible. The objective of this study was to perform MR imaging examinations on spines implanted with titanium alloy instrumentation and to determine the parameters that yield the highest quality images with the least amount of artifact. A titanium pedicle screw construct was implanted into the lumbar spine of two fresh human cadaveric specimens. Sequential spin echo MR scans were performed using various TE and TR ratios on each intact specimen. The resultant images were quantitatively graded for clarity of adjacent soft tissue and osseous structures. Excellent T1- and T2-weighted images with well-defined neural structures were obtained with minimal artifact. The optimal T1-weighted image was obtained with TE = 16 and TR = 500-600, whereas the optimal T2-weighted image was obtained with TE = 60 and TR = 1,300-1,600. By using appropriate settings, high-quality MR scans in both the T1- and T2-weighted modes can be obtained with minimal metal artifact.

An S-2 alar iliac pelvic fixation. Technical note.

Multiple techniques of pelvic fixation exist. Distal fixation to the pelvis is crucial for spinal deformity surgery. Fixation techniques such as transiliac bars, iliac bolts, and iliosacral screws are commonly used, but these techniques may require separate incisions for placement, leading to potential wound complications and increased dissection. Additionally, the use of transverse connector bars is almost always necessary with these techniques, as their placement is not in line with the S-1 pedicle screw and cephalad instrumentation. The S-2 alar iliac pelvic fixation is a newer technique that has been developed to address some of these issues. It is an in-line technique that can be placed during an open procedure or percutaneously.

Biomechanical comparison of transpedicular versus intralaminar C2 fixation in C2-C6 subaxial constructs.

Study Design. Biomechanical study. Objective. To compare the relative rigidity of C2 transpedicular versus intralaminar fixation with and without offset connectors in C2–C6 subaxial constructs. Summary of Background Data. Insufficient biomechanical data exists on C2 laminar fixation in subaxial constructs, and no study has considered C2–C6 subaxial constructs or the use of offset connectors. Methods. Six fresh-frozen cadaveric cervical spines underwent rigidity testing in the intact condition and after a destabilizing C3–C6 laminectomy. Specimens were instrumented with 20 mm pedicle and 20 mm intralaminar screws at C2, and with 14 mm lateral mass screws from C3–C6. In random order, three conditions (C2 pedicle screws, C2 laminar screws, and C2 laminar screws with offset connectors) were tested in flexion-extension, axial rotation, and lateral bending. Results. Laminar screws in C2–C6 constructs were equivalent to transpedicular fixation in flexion-extension (P = 0.985), were significantly more rigid than pedicle screws in axial rotation (P = 0.002), and were significantly less rigid than pedicle screws in lateral bending (P = 0.002). Laminar screw constructs were more rigid than the intact condition in all planes.

The anatomic suitability of the C2 vertebra for intralaminar and pedicular fixation: a computed tomography study

BACKGROUND CONTEXT Several methods have been used to stabilize the atlantoaxial joint, including the use of C2 pedicle and laminar screws. No report has used computed tomography (CT) angiograms to compare the risk to the vertebral artery or assess the suitability for each fixation technique. PURPOSE To compare the suitability of C2 pedicle versus laminar screws using CT angiograms. STUDY DESIGN We retrospectively evaluated the anatomic dimensions of the C2 lamina and pedicle in 50 patients using CT angiograms. METHODS We retrospectively reviewed the last 50 patients admitted who underwent CT angiograms of the head and neck. Data recorded included the pedicle length and width and the laminar length and width. Vertebral artery anatomy was also assessed to determine if an aberrant location would preclude pedicle fixation. RESULTS Mean pedicle length and width were 15.5±3.5 and 4.7±1.7 mm, respectively, with 24% of patients having anatomy that would preclude 3.5-mm pedicle screw fixation. The mean lamina length and width were 25.2±3.6 and 5.5±1.4 mm, and more than 90% of patients could tolerate a 3.5-mm C2 laminar screw. CONCLUSION Preoperative CT angiography or noncontrast CT is an excellent method to delineate the anatomy at C2 to determine the suitability for pedicle or intralaminar fixation. In cases where vertebral artery anatomy precludes C2 pedicle fixation, more than 90% of patients may be a candidate for C2 intralaminar fixation.