Hidden blood loss during posterior spine fusion surgery.

BACKGROUND CONTEXT: Posterior spine fusion is associated with significant intra- and postoperative blood losses. When referring to the total blood loss during spine surgery, the standard is to measure the intraoperative bleeding plus the postoperative drainage. This ignores the "hidden" blood loss that was found to be significant in other fields of surgery. PURPOSE: The purpose of this study was to examine whether posterior spine fusion carries a substantial hidden blood loss. STUDY DESIGN/SETTING: A prospective study. PATIENT SAMPLE: We prospectively studied 114 patients undergoing instrumented posterior spinal fusion at one center between January 2011 and April 2011. OUTCOME MEASURES: Total blood loss, visible blood loss, and hidden blood loss. METHODS: For each patient, the hidden blood loss was calculated by deducting the observed perioperative blood loss from the calculated total blood loss based on the hematocrit changes. We compared the percentage of the hidden blood loss out of the total blood loss for primary versus revision posterior spine fusion. RESULTS: Primary decompression and posterior fusion patients had a mean total true loss of 1,439 mL. Their calculated hidden loss was 600 mL, 42% of the total loss. After revision posterior spinal fusion surgery, the mean total blood loss was 1,606 mL. The mean visible loss was 975 mL, and the mean hidden loss was 631 mL, 39% of the total loss. Thus, there was no statistical difference in the hidden blood loss between primary and revision posterior spinal fusion surgeries (p>.05). We did not find a significant difference in the percentage of the hidden blood loss between patients who underwent one, two, or three or more levels of surgery. CONCLUSIONS: After posterior spinal fusion, there may be a large amount of the hidden blood loss.

Cervical intervertebral disc replacement.

Symptomatic adjacent-level disease after cervical fusion has led to the development and testing of several disc-replacement prostheses. Randomized controlled trials of cervical disc replacement (CDR) compared with anterior cervical discectomy and fusion (ACDF) have demonstrated at least equivalent clinical results for CDR with similar or lower complication rates. Biomechanical, kinematic, and radiographic studies of CDR reveal that the surgical level and adjacent vertebral level motion and center of rotation more closely mimic the native state. Lower intradiscal pressures adjacent to CDR may help decrease the incidence of adjacent spinal-level disease, but long-term follow-up is necessary to evaluate this theory.

Single- versus multilevel fusion for single-level degenerative spondylolisthesis and multilevel lumbar stenosis: four-year results of the spine patient outcomes research trial.

STUDY DESIGN: A subanalysis study. OBJECTIVE: To compare surgical outcomes and complications of multilevel decompression and single-level fusion with multilevel decompression and multilevel fusion for patients with multilevel lumbar stenosis and single-level degenerative spondylolisthesis (DS). SUMMARY OF BACKGROUND DATA: In patients with DS who are treated surgically, decompression and fusion provide a better clinical outcome than decompression alone. Surgical treatment for multilevel lumbar stenosis and DS typically includes decompression and fusion of the spondylolisthesis segment and decompression with or without fusion for the other stenotic segments. To date, no study has compared the results of these 2 surgical options for single-level DS with multilevel stenosis. METHODS: The results from a multicenter randomized and observational study, the Spine Patient Outcomes Research Trial comparing multilevel decompression and single-level fusion and multilevel decompression and multilevel fusion for spinal stenosis with spondylolisthesis, were analyzed. The primary outcome measures were the bodily pain and physical function scales of the Medical Outcomes Study 36-item Short-Form General Health Survey (SF-36) and the modified Oswestry Disability Index at 1, 2, 3, and 4 years postoperatively. Secondary analysis consisted of stenosis bothersomeness index, low back pain bothersomeness, leg pain, patient satisfaction, and self-rated progress. RESULTS: Overall, 207 patients were enrolled for the study, 130 had multlilevel decompression with 1 level fusion and 77 patients had multilevel decompression and multilevel fusion. For all primary and secondary outcome measures, there were no statistically significant differences in surgical outcomes between the 2 surgical techniques. However, operative time and intraoperative blood loss were significantly higher in the multilevel fusion group. CONCLUSION: Decompression and single-level fusion and decompression and multilevel fusion provide similar outcomes in patients with multilevel lumbar stenosis and single-level DS.

Pedicle screw-based posterior dynamic stabilization: literature review.

Posterior dynamic stabilization (PDS) indicates motion preservation devices that are aimed for surgical treatment of activity related mechanical low back pain. A large number of such devices have been introduced during the last 2 decades, without biomechanical design rationale, or clinical evidence of efficacy to address back pain. Implant failure is the commonest complication, which has resulted in withdrawal of some of the PDS devices from the market. In this paper the authors presented the current understanding of clinical instability of lumbar motions segment, proposed a classification, and described the clinical experience of the pedicle screw-based posterior dynamic stabilization devices.

Lateral transpsoas fusion: indications and outcomes.

Spinal fusion historically has been used extensively, and, recently, the lateral transpsoas approach to the thoracic and lumbar spine has become an increasingly common method to achieve fusion. Recent literature on this approach has elucidated its advantage over more traditional anterior and posterior approaches, which include a smaller tissue dissection, potentially lower blood loss, no need for an access surgeon, and a shorter hospital stay. Indications for the procedure have now expanded to include degenerative disc disease, spinal stenosis, degenerative scoliosis, nonunion, trauma, infection, and low-grade spondylolisthesis. Lateral interbody fusion has a similar if not lower rate of complications compared to traditional anterior and posterior approaches to interbody fusion. However, lateral interbody fusion has unique complications that include transient neurologic symptoms, motor deficits, and neural injuries that range from 1 to 60% in the literature. Additional studies are required to further evaluate and monitor the short- and long-term safety, efficacy, outcomes, and complications of lateral transpsoas procedures.

In vitro response of human chondrocytes to a combination of growth factors and a proteinase inhibitor.

Degenerative disk disease is an accelerating cascade of tissue degeneration in the intervertebral disk. A harsh catabolic environment perpetuates the degeneration of the intervertebral disk. Tissue engineering-based techniques offer effective treatment to slow the progression of degenerative disk disease and regenerate intervertebral disk tissue. The purpose of this study was to assess the efficacy of a regenerative therapy for degenerative disk disease by treating human chondrocytes with anabolic growth factors and a proteinase inhibitor. The use of both proved effective in upregulating important extracellular matrix markers of human chondrocytes. These successful in vitro results have implications for the regeneration of the intervertebral disk.

Supercritical carbon dioxide processed resorbable polymer nanocomposite bone graft substitutes.

The development of synthetic bone graft substitutes is an intense area of research due to the complications associated with the harvest of autogenous bone and concerns about the supply of allogenic bone. Porous resorbable polymers have been used extensively in hard tissue engineering applications, but currently lack load-bearing capacity. Supercritical carbon dioxide (scCO(2)) processing is used as a novel method to simultaneously impart a porous structure and disperse a nano-clay in a resorbable polymer matrix suitable for load-bearing applications. Porous resorbable polylactic acid (PLA)/cloisite clay nanocomposite constructs prepared using scCO(2) processing exhibit a 2.5-fold increase in compressive strength compared with pure polymer constructs. The resulting mechanical properties are comparable with human cancellous and cortico-cancellous bone. In addition to the significant improvements in mechanical properties, the nanocomposite constructs display a biocompatibility greater than that of polystyrene culture plate controls. Furthermore, calcium phosphate-rich deposits could clearly be seen on the surface of the constructs, as well as at the center of the cultured constructs, indicating that osteoblasts are able to penetrate the porous network of the nanocomposite constructs. Cellular infiltration of these constructs is important for their in vivo use as bone graft substitutes. The diameter of the pores suggests that these constructs would also support neovascularization, which is integral for nutrient transport.

Analysis of in vivo corrosion of 316L stainless steel posterior thoracolumbar plate systems: a retrieval study.

STUDY DESIGN: One hundred eighteen patients retrieved 316L stainless steel thoracolumbar plates, of 3 different designs, used for fusion in 60 patients were examined for evidence of corrosion. A medical record review and statistical analysis were also carried out. OBJECTIVE: This study aims to identify types of corrosion and examine preferential metal ion release and the possibility of statistical correlation to clinical effects. SUMMARY OF BACKGROUND DATA: Earlier studies have found that stainless steel spine devices showed evidence of mild-to-severe corrosion; fretting and crevice corrosion were the most commonly reported types. Studies have also shown the toxicity of metal ions released from stainless steel corrosion and how the ions may adversely affect bone formation and/or induce granulomatous foreign body responses. METHODS: The retrieved plates were visually inspected and graded based on the degree of corrosion. The plates were then analyzed with optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. A retrospective medical record review was performed and statistical analysis was carried out to determine any correlations between experimental findings and patient data. RESULTS: More than 70% of the plates exhibited some degree of corrosion. Both fretting and crevice corrosion mechanisms were observed, primarily at the screw plate interface. Energy dispersive x-ray spectroscopy analysis indicated reductions in nickel content in corroded areas, suggestive of nickel ion release to the surrounding biological environment. The incidence and severity of corrosion was significantly correlated with the design of the implant. CONCLUSIONS: Stainless steel thoracolumbar plates show a high incidence of corrosion, with statistical dependence on device design.

Biomimetic calcium phosphate coatings as bone morphogenetic protein delivery systems in spinal fusion.

BACKGROUND CONTEXT: Use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to enhance spinal fusion rates. Case reports of soft-tissue swelling, ectopic bone formation, and osteolysis have recently surfaced. It is hypothesized that incorporation of rhBMP-2 within a calcium phosphate (CaP) coating may help to localize delivery and mitigate these complications. PURPOSE: To compare the characteristics of posterolateral fusion between rabbits receiving rhBMP-2 delivered via physical adsorption to a collagen sponge or rhBMP-2 incorporated within the physical structure of a CaP coating on a collagen sponge. STUDY DESIGN/SETTING: New Zealand white rabbit model of posterolateral lumbar fusion at L5-L6. METHODS: Eighteen (18) New Zealand white rabbits underwent posterolateral spinal fusion at L5-L6. Rabbits received bilateral collagen sponges that were either coated with CaP (n=3), coated with CaP and dipped in rhBMP-2 (n=3), coated with a hybrid CaP-rhBMP-2 film (n=6), or coated with a hybrid CaP-rhBMP-2 film and dipped in rhBMP-2 (n=6). Animals were followed weekly with radiographs and were sacrificed at 6 weeks. Fusion masses were further characterized by manual palpation, computed tomography, and histology. RESULTS: Radiographic evaluation showed that animals in Group 3 (incorporated BMP) fused at 4 weeks, whereas animals in Group 2 (adsorbed BMP) and Group 4 (incorporated and adsorbed BMP) fused by 6 weeks. Animals that received rhBMP-2 physically adsorbed to the collagen sponge showed extension of the fusion mass beyond the L5-L6 level in 56% of cases and bone resorption in 78%. Histology of fusion masses showed mature bone formation in animals belonging to Groups 2, 3, and 4 and extensive osteoclast recruitment in animals belonging to Groups 2 and 4. CONCLUSIONS: Delivery of rhBMP-2 via incorporation within CaP coatings results in increased rates of radiographic fusion. The burst release profile of rhBMP-2 adsorbed to surfaces, although effective in achieving fusion, may result in increased osteoclast recruitment.

Instant axis of rotation of L4-5 motion segment--a biomechanical study on cadaver lumbar spine.

The instant axis of rotation (IAR) is an important kinematic property to characterise of lumbar spine motion. The goal of this biomechanical study on cadaver lumbar spine was to determine the excursion of the IAR for flexion (FE), lateral bending (LB) and axial rotation (AR) motion at L4-5 segment. Ten cadaver lumbar spine specimens were tested in a 6 degrees-of-freedom spine tester with continuous clyclical loading using pure moment and follower pre-load, to produce physiological motion. The specimens were x-rayed and CT scanned prior to testing to identify marker position. Continuous motion tracking was done by Optotrak motion capture device. A continuous tracking of the IAR excursion was calculated from the continuous motions capturedata using a computer programme. IAR translates forward in flexion and backwards in extension with mean excursion of 26.5 mm (+/- 5.6 SD). During LB motion, IAR translates laterally in the same direction, and the mean excursion was 15.35 mm (+/- 8.75 SD). During axial rotation the IAR translates in the horizontal plane in a semicircular arc, around the centre of the vertebral body, but the IAR translates in the opposite direction of rotation. The IAR excursion was faster and larger during neutral zone motion in FE and LB, but uniform for AR motion. This is the first published data on the continuous excursion of IAR of a lumbar motion segment. The methodology is accurate and precise, but not practicable for in vivo testing.

Spinal orthoses.

External orthoses are used in the management of a variety of spinal disorders. Many types of brace are available to support the cervical, thoracic, and lumbar spine as well as junctional regions, which have special mechanical considerations. Many prefabricated and custom-made devices are available, made by a variety of manufacturers in this unregulated area of medical practice. Despite the widespread use of spinal orthoses, evidence of their efficacy in managing many spinal conditions is lacking. The most compelling indication for their use is in the management of traumatic spine injury. However, studies evaluating the efficacy of spinal orthoses have several shortcomings; many have evaluated orthoses that are no longer used. Recent data provide general guidelines to help the clinician choose the appropriate device.

Debating the value of spine surgery.

Lumbar arthrodesis is a commonly performed operative procedure for the treatment of low back pain. Recently, total disc arthroplasty has gained some acceptance among surgeons and patients. However, the indications for and results of back pain surgery remain controversial and confusing. Available information suggests that meaningful functional improvement from these procedures is debatable and that the cost of such elective operations is high. Currently, lumbar disc replacement has gained minimal support from governmental and private payers. Among those attending this symposium at the 2009 Annual Meeting of the AOA, the vast majority concurred that Medicare and private insurance should not necessarily pay for disc replacement surgery. Interestingly, among this skeptical group of orthopaedic surgeons, only 23% believed that degeneration of the intervertebral disc is the major cause of low back pain. When asked the hypothetical question, "If you experienced chronic low back pain with degenerative changes at one level, what course of treatment would you opt for?" 61% responded that they would choose nonoperative treatment and 38%, that they would choose no treatment. Of more than 100 respondents, only one responded that he or she would undergo fusion and one admitted a willingness to undergo disc replacement in this hypothetical scenario.

Distractive force relative to initial graft compression in an in vivo anterior cervical discectomy and fusion model.

STUDY DESIGN: An in vivo biomechanical anterior cervical discectomy and instrumented fusion (ACDFI) model employing a calibrated distractor and a subminiature load cell used to intraoperatively measure distractive force across the discectomy site and subsequent compressive force across the interbody load cell following distractor removal. OBJECTIVE: To determine the relationship between the distractive force and resultant initial graft compression in an in vivo ACDFI model. SUMMARY OF BACKGROUND DATA: The relationship between the distractive force and subsequent graft compression following distractor removal has not been studied in an in vivo ACDFI model. The consequences of over or under distraction and its subsequent effect on graft compression with regards to axial neck pain, endplate failure with graft subsidence, and fusion rates is an area of clinical significance for ACDFI. METHODS: Intraoperative measurements were obtained from 17 discectomy sites in 12 patients undergoing one and two level ACDFI. Informed consent was obtained from all subjects before surgery. A calibrated Caspar distractor was used to measure the distraction across the discectomy site and a subminiature interbody load cell was placed into the discectomy site and used to measure the resultant initial compressive force following distractor removal. The statistical significance and correlation between the distractive force across the discectomy site and the subsequent compressive force across the load cell were investigated with the Pearson correlation coefficient. RESULTS: The average distractive force across the discectomy site was 33.5 +/- 11.6 lbs and the subsequent compressive force across the interbody load cell was 16.9 +/- 5.9 lbs following distractor removal. The Pearson correlation coefficient was r = 0.912 (P < 0.0005). The data showed a statistically significant linear correlation between the distractive force and the subsequent compressive force across the range of distraction investigated. CONCLUSION: This study demonstrated a statistically significant linear correlation between the distractive force applied across the discectomy site and the subsequent compressive force across a load cell placed in the interbody space following distractor removal in an in vivo ACDFI model.

Biomechanical evaluation of the kinematics of the cadaver lumbar spine following disc replacement with the ProDisc-L prosthesis.

STUDY DESIGN: Biomechanical study of the ProDisc-L in a cadaveric model under pure moment loading. OBJECTIVE.: To determine the kinematic properties of a lumbar spine motion segment and the adjacent level following ProDisc-L disc replacement in the cadaveric spine. SUMMARY OF BACKGROUND DATA: Total disc replacement is intended to preserve native motion, in an attempt to prevent accelerated adjacent segment degeneration. The quality and quantity of the motion following TDR may have important consequences on the facet joints of the same motion segment, as well as the motion at the prosthetic component interface. METHODS: Ten cadaveric lumbar spines were radiographed (L3-L5) and tested under pure moments (+10 Nm to -10 Nm) with an applied follower load (200 N). Load-deformation was tested in flexion/extension, lateral bending (LB), and axial rotation (AR). Range of Motion (ROM) data were recorded. Superior adjacent disc pressure (L3-L4) was measured using subminiature pressure transducers. The L4-L5 disc was subsequently instrumented with a ProDisc-L. Radiographs and biomechanical tests were repeated. RESULTS: Disc replacement significantly reduced extension (ROM 2.2 degrees +/- 0.5 degrees before and 1.2 degrees +/- 0.7 degrees after instrumentation) (P = 0.001), but not flexion (ROM 5.6 degrees +/- 3.1 degrees before and 6.2 degrees +/- 1.2 degrees after) (P = 0.34). Combined flexion/extension motion was marginally reduced (P = 0.517). LB ROM (7.4 degrees +/- 2.0 degrees ) was marginally reduced (P = 0.072) following instrumentation (6.2 degrees +/- 2.5 degrees ), while ROM in AR (3.4 degrees +/- 1.1 degrees ) was significantly increased (4.4 degrees +/- 1.2 degrees ) (P = 0.001). Superior adjacent segment ROM was preserved.No significant differences in disc pressure were observed at the adjacent motion segment before (199 kPa at maximum flexion and 171 kPa at maximum extension) or after disc replacement (252 kPa and 208 kPa, respectively). CONCLUSION: In cadaveric spines, ROM of operated and adjacent motion segments was preserved following ProDisc-L insertion. Excision of the anterior anulus may increase laxity, which is taken up by the restoration of disc height and lordosis, at the cost of a moderate loss of flexion/extension motion. Adjacent segment kinematics were unaffected following TDR.

Degenerative lumbar spondylolisthesis: evolution of surgical management.

COMMENTARY ON: Watters III WC, Bono CM, Gilbert TJ, et al. An evidence-based clinical guideline for the diagnosis and treatment of degenerative lumbar spondylolisthesis. Spine J 2009;9:609-14 (this issue).