Structure and mechanical properties of supercritical carbon dioxide processed porous resorbable polymer constructs

Current bone graft substitute materials do not address the complex architectural and biomechanical requirements to achieve a successful spinal fusion. The development of porous, structural constructs for use in spinal fusion surgeries is thus an area of intense interest. Numerous techniques have been introduced to fabricate porous resorbable polymer constructs. However, these techniques have been associated with the use of potentially harmful organic solvents, and resulted in materials with less than optimal properties. Supercritical carbon dioxide (scCO(2)) processing appears to be a promising technique for producing reinforced biodegradable foams. The structure, mechanical properties and water uptake capacity of PDLGA constructs processed with scCO(2) were examined. Porous morphology of the constructs was found to depend strongly on processing temperature and the confinement of the structures after processing. The resulting constructs had a dense "cortical" shell about 15-20 microm thick and an interconnected porous core with pore diameters in the range of 236-239 microm, similar to iliac crest bone grafts currently used in spinal fusion procedures. Mechanical properties and the water uptake capacity of the constructs were found to depend on the glycolic acid content (copolymer composition). Supercritical CO(2) processing is a promising technology to develop porous, resorbable polymer constructs with structural and mechanical properties similar to human bone.

Effect of polyethylene pretreatments on the biomimetic deposition and adhesion of calcium phosphate films

The effect of ultraviolet irradiation and glow discharge (GD) processing of the polyethylene (PE) substrates on deposition of calcium phosphate (CaP) films from supersaturated aqueous calcium phosphate solutions was investigated in this study. CaP coatings deposited on the PE substrates were comprised of elongated clusters of spherical particles and 100% of the free surface area of nearly all of the substrates was covered with a porous CaP film after a 3 day immersion. Nano-scratch tests determined that PE-CaP adhesion was most improved when PE substrates were subjected to 50W GD treatments. As determined by contact angle measurements, the GD-treated PE samples had the highest electron donor parameter of surface energy, suggesting that enhancing the electron donor parameter of PE leads to improved adhesion with the biomimetic CaP coating.

Development and calibration of a load sensing cervical distractor capable of withstanding autoclave sterilization

In surgery of the cervical spine, a Caspar pin distractor is often used to apply a tensile load to the spine in order to open up the disc space. This is often done in order to place a graft or other interbody fusion device in the spine. Ideally a tight interference fit is achieved. If the spine is over distracted, allowing for a large graft, there is an increased risk of subsidence into the endplate. If there is too little distraction, there is an increased risk of graft dislodgement or pseudoarthrosis. Generally, graft height is selected from preoperative measurements and observed distraction without knowing the intraoperative compressive load. This device was designed to give the surgeon an assessment of this applied load. Instrumentation of the device involved the application of strain gauges and the selection of materials that would survive standard autoclave sterilization. The device was calibrated, sterilized and once again calibrated to demonstrate its suitability for surgical use. Results demonstrate excellent linearity in the calibration, and no difference was detected in the pre- and post-sterilization calibrations.

Anterior cervical interbody fusion with rhBMP-2 and tantalum in a goat model

BACKGROUND CONTEXT

Tricortical autogenous iliac crest has long served as the gold standard for arthrodesis after cervical discectomy. The added morbidity resulting from bone graft harvest may be eliminated by the use of a biocompatible synthetic bone graft substitute with osteoconductive abilities, and when used with an osteoinductive agent, such as recombinant bone morphogenic protein (rhBMP)-2, it may facilitate arthrodesis similar to autograft.

PURPOSE

To determine by radiographic and histologic analysis whether tantalum with and without rhBMP-2 can facilitate bony ingrowth and arthrodesis in an animal model.

STUDY DESIGN/SETTING

Single-level anterior cervical discectomy and fusion was performed using a tantalum bone graft substitute with and without rhBMP-2 in a previously established goat model for anterior cervical fusion.

METHODS

Eight goats underwent single-level anterior cervical discectomy and stabilization with a porous tantalum implant. There were four goats in each experimental group. Group A underwent anterior cervical stabilization with tantalum alone, whereas in Group B rhBMP-2 was added to the tantalum implant. The goats were sacrificed at 12 weeks, and their cervical spines were removed for histologic and radiological analysis.

RESULTS

Only one of four goats in Group A had any bony ingrowth into the tantalum. Three of four goats in Group B demonstrated bony ingrowth. The average extent of bony ingrowth at the perimeter of the tantalum in Group A was 2.5% compared with 12.5% in Group B. Similarly, the volume of bony ingrowth within the tantalum was 2.5% in Group A and 10% in Group B. The difference was not statistically significant.

CONCLUSIONS

The data in this pilot study suggest that tantalum may function as a synthetic osteoconductive bone graft substitute. The addition of rhBMP-2 may facilitate osteoinduction within a synthetic osteoconductive implant. The sample size in this study was too small for statistical significance. The present animal model as used in this study was inadequate for cervical arthrodesis where rigid implant fixation is desired.

Cervical spondylotic myelopathy and radiculopathy

Appropriate management of degenerative cervical spine conditions requires careful elucidation of the presenting clinical syndrome. Because of the pervasiveness of degenerative changes in asymptomatic patients, a clear correlation of symptoms, physical signs, and imaging findings is required before any specific diagnosis can be made. At this time, surgery is not recommended for prophylactic decompression in asymptomatic patients or in those patients with neck pain in the absence of extremity symptoms. In most patients with radiculopathy or mild myelopathy, a trial of nonsurgical management is recommended. Ultimately, patients with neurologic complaints and in whom nonsurgical measures have failed, as well as those with more pronounced myelopathy, should be offered surgical intervention. Selection of the safest, yet sufficient, approach requires a clear understanding of the benefits and expected outcomes. The outlook for patients with both cervical radiculopathy and early myelopathy is good. Radicular symptoms usually improve, but gait and hand changes may not. LF is preferred in younger patients with posterolateral or lateral soft disk herniations, or focal foraminal osteophyte impingement and predominance of upper extremity symptoms. More central 1- or 2-level pathology should be treated with ACDF. Anterior cervical corpectomy should be entertained in patients with nondisk level encroachment and in those with 3 contiguous levels of pathology. This approach is also required in cases of kyphosis and instability. Laminoplasty is indicated in patients with 4 or more levels of stenosis, particularly in those with global conditions such as continuous OPLL or congenital stenosis. In these patients, kyphosis or severe deformity may be addressed with a circumferential approach.

Effect of anular repair on the healing strength of the intervertebral disc: a sheep model

STUDY DESIGN

The intervertebral disc, in a sheep model, was used to assess the effect of directly repairing three different anular incisions on the subsequent healing strength of the intervertebral disc.

OBJECTIVES

To assess whether directly repairing an anular defect, made at the time of lumbar discectomy, could influence the healing rate and strength of the anulus fibrosus.

METHODS

Twenty-four sheep underwent a retroperitoneal approach to five lumbar disc levels. An anular incision, followed by partial discectomy was done at each exposed level. Anular incisions used in this study consisted of 1) a straight transverse slit, 2) a cruciate incision, and 3) a window or box excision. Healing strength was measured at three time intervals: 2 weeks, 4 weeks, and 6 weeks. Each anular incision type was performed on 30 lumbar discs, 10 discs in each time interval. Five discs in each time interval underwent direct repair, and five discs were left unrepaired to heal as controls. The sheep were killed at 2, 4, and 6 weeks after surgery. The lumbar spines were removed en bloc, and the intervertebral discs were subjected to pressure-volume testing to assess the anular strength of repaired versus unrepaired disc injuries at each time interval.

RESULTS

Statistical analysis was performed to evaluate the effects of healing time, incision technique, and repair on the pressure-volume characteristics of the involved discs. Pressure-volume testing showed trends of stronger healing for repaired discs, but at no time interval was any significant difference found between repaired and nonrepaired anular strength. Of the nonrepaired discs, the box incision was only 40 to 50% as strong as the slit or cruciate incised discs during early healing.

CONCLUSION

Direct repair of anular incisions in the lumbar spine does not significantly alter the healing strength of the intervertebral disc after lumbar discectomy.

Complication, survival rates, and risk factors of surgery for metastatic disease of the spine

STUDY DESIGN

The risk factors for complications and complication and survival rates in patients with metastatic disease of the spine were reviewed. A retrospective study was performed.

OBJECTIVES

To determine the surgical complication and survival rates of patients with metastatic disease of the spine and risk factors for complication occurrence.

SUMMARY OF BACKGROUND DATA

The role of surgical intervention for patients with metastatic disease of the spine has been controversial. Several risk factors for surgical complications have been identified. Short survival times and high complication rates have failed to justify surgical intervention in many cases.

METHODS

Patients (n = 80) undergoing surgical treatment for metastatic disease of the spine were reviewed. Surgical indications included progressive neurologic deficit, neurologic deficit failing to respond to, or progressing after, radiation treatment; intractable pain; radioresistant tumors; or the need for histologic diagnosis. Patients underwent anterior, posterior, or combined decompression and stabilization procedures. Neurologic examination was recorded before surgery, postoperative period, and at least follow-up. Complication and survival rates were calculated. Several variables were examined for risk of complication.

RESULTS

The mean age at time of surgery was 55.6 years (range, 20-84 years). Mean survival time after the diagnosis of spinal metastasis was 26.0 months (range, 1-107.25 months). Mean survival time after surgery was 15.9 months (range, 0.25-55.5 months). Sixty-five patients showed no change in Frankel grade, 19 improved one Frankel grade, and 1 deteriorated one Frankel grade; 1 patient had paraplegia. Thirty-five complications occurred in 20 patients (25.0%). Ten patients (12.5%) had multiple complications accounting for 23 of the 35 postoperative problems (65.7%). Sixty patients had no surgical complications (75%). There were no intraoperative deaths.

CONCLUSIONS

The likelihood that a complication occurred was significantly related to Harrington classifications demonstrating significant neurologic deficits and the use of preoperative radiation therapy. In general, Harrington classifications with neurologic deficits and lower Frankel grades before and after surgery were associated with an increased risk of complication. Overall, the major complication rate was relatively low, and minor complications were successfully treated with minimal morbidity. The relatively long survival time after spinal surgery in this group of patients justifies surgical treatment for metastatic disease. Most complications occurred in a small percentage of patients. To minimize complications, patients must be carefully selected based on expected length of survival, the use of radiation therapy, presence of neurologic deficit, and impending spinal instability or collapse caused by bone destruction.

Management of degenerative disc disease above an L5-S1 segment requiring arthrodesis

Clear guidelines exist for treating spondylolisthetic deformity and instability. How the surgeon handles adjacent-level degenerative disease is not as well established. Because magnetic resonance imaging now provides us with far more information on the "health" of radiographically normal intervertebral discs, the treatment of dehydrated or degenerated discs adjacent to a fusion is becoming more problematic. In this discussion, two experts discuss their approach to symptomatic lumbosacral spondolisthesis accompanied by adjacent-level disc degeneration. Drs. Herkowitz and Abraham believe strongly that the adjacent segment should be left alone, whereas Dr. Albert recommends extending the fusion in many instances.

The use of recombinant human bone morphogenetic protein 2 (rhBMP-2) to promote spinal fusion in a nonhuman primate anterior interbody fusion model

STUDY DESIGN

A study on the efficacy of recombinant human bone morphogenetic protein 2 (rhBMP-2) in a nonhuman primate anterior interbody fusion model.

OBJECTIVES

To investigate the efficacy of rhBMP-2 with an absorbable collagen sponge carrier to promote spinal fusion in a nonhuman primate anterior interbody fusion model.

SUMMARY OF BACKGROUND DATA

RhBMP-2 is an osteoinductive growth factor capable of inducing new bone formation in vivo. Although dosage studies using rhBMP-2 have been performed on species of lower phylogenetic level, they cannot be extrapolated to the primate. Dosage studies on nonhuman primates are essential before proceeding with human primate application.

METHODS

Six female adult Macaca mulatta (rhesus macaque) monkeys underwent an anterior L7-S1 interbody lumbar fusion. All six sites were assigned randomly to one of two fusion methods: 1) autogenous bone graft within a single freeze-dried smooth cortical dowel allograft cylinder (control) or 2) rhBMP-2-soaked absorbable collagen sponges within a single freeze-dried smooth cortical dowel allograft cylinder also soaked in rhBMP-2. The animals underwent a baseline computed tomography scan followed by 3- and 6-month postoperation scans. Anteroposterior and lateral radiographs of the lumbosacral spine were performed monthly. After the monkeys were killed, the lumbar spine fusion sites were evaluated. Histologic evaluation of all fusion sites was performed.

RESULTS

The three monkeys receiving rhBMP-2-soaked collagen sponges with a freeze-dried allograft demonstrated radiographic signs of fusion as early as 8 weeks. The control animals were slower to reveal new bone formation. The computed tomography scans revealed extensive fusion of the L7-S1 lumbar vertebrae in the group with rhBMP-2. A pseudarthrosis was present in two of the control animals.

CONCLUSIONS

This study was able to document the efficacy of rhBMP-2 with an absorbable collagen sponge carrier and a cortical dowel allograft to promote anterior interbody fusion in a nonhuman primate model at a dose of 0.4 mg per implant site (1.5 mg/mL concentration). The late of new bone formation and fusion with the use of rhBMP-2 and cortical dowel allograft appears to be far superior to that of autogenous cancellous iliac crest graft with cortical dowel allograft.

Indications and trends in use in cervical spinal fusions

Anterior cervical decompression and arthrodesis has evolved over the last 40 years and has become the preferred procedure for managing many cervical spine disorders. The first half of this article discusses the indications for cervical fusion in the management of traumatic, degenerative, neoplastic, infectious, and congenital conditions of the cervical spine. The second half of this article discusses the recent trends in use of cervical spine fusions that demonstrate the increasing frequency of this procedure in the United States over the last 10 years.

Indications for thoracic and lumbar spine fusion and trends in use

Over the last 10 years, the annual number of spinal procedures performed in the United States has more than doubled. In 1996, there were roughly 29,000 thoracic or dorsal fusion procedures, which made up almost 13% of all spine fusions performed. Scoliosis was the most common condition necessitating posterior thoracic fusion. The first half of this article focuses on the indications for thoracic and lumbar fusions; whereas, the second half of this article discusses the trends in use of thoracic and lumbar spine fusions.

The role of prophylactic antibiotics in spinal instrumentation. A rabbit model

STUDY DESIGN

A rabbit model was used to test the efficacy of cefazolin administered in various therapeutic regimens in preventing iatrogenic Staphylococcus aureus infections during spinal instrumentation.

OBJECTIVE

To assess the efficacy of various prophylactic therapeutic regimens of cefazolin in preventing iatrogenic S. aureus infections during spinal instrumentation.

SUMMARY OF BACKGROUND DATA

Previous studies have not dealt specifically with the occurrence of iatrogenic S. aureus infections during spinal instrumentation in a prospective fashion.

METHODS

Twenty New Zealand White rabbits underwent a posterior approach to the lumbar spine. Fifteen of the animals then had double-braided 26-gauge surgical wire placed around bilateral L3-L4 and L4-L5 facet joints. A standardized volume of a 103 S. aureus/mL of solution was then inoculated onto the fusion-hardware site in all rabbits. The rabbits were divided into four groups receiving various antibiotic dose regimens. Five days after surgery, the animals were killed, and cultures were obtained.

RESULTS

All of the rabbits receiving no antibiotic had fusion sites infected with S. aureus. None of the animals who received prophylactic cefazolin produced cultures that grew S. aureus. A specimen from one fusion site cultured Staphylococcus epidermidis, which is not sensitive to cefazolin. Analysis of these data using Fisher's exact test resulted in a P value of 0.008 when results in antibiotic groups were compared with those in a group receiving no antibiotics and a P value of 0.0003 when all groups were compared.

CONCLUSIONS

This model was valid and reproducible for the study of spinal instrumentation and infection. In addition, the data support the efficacy and use of prophylactic intravenous antibiotics in preventing infection in spinal instrumentation and fusion surgery.

Computed tomography-guided biopsy of the spine. A review of 103 patients

STUDY DESIGN

A retrospective study of 103 computed tomography-guided biopsies of the spine. These represent a consecutive series of patients with spinal lesions or disorders observed over a 32-month period.

OBJECTIVES

To determine the diagnostic accuracy and clinical usefulness of computed tomography-guided biopsies with respect to major influencing variables.

SUMMARY OF BACKGROUND DATA

Computer tomographic-guided biopsy of the spine is considered a safe, accurate, and relatively inexpensive examination technique. A study comparing its diagnostic accuracy with respect to all the variables of age, gender, radiographic appearance, spinal level, tissue type, or pathologic diagnosis has not been done.

METHODS

Biopsy specimens were sent for cytologic and histologic analysis. Bacteriologic studies were performed when clinically indicated. The biopsy results were analyzed for adequacy and diagnostic accuracy, i.e., the ability to generate a tissue sample adequate for pathologic examination and one that yields diagnostic information.

RESULTS

The mean age of patients was 60 years, with a range of 4-91 years. The spines of 52 males and 51 females were studied. There were eight cervical, 28 thoracic, 53 lumbar, and 14 sacral lesions used as biopsy sites. The radiographic appearance of spinal lesions were lytic in 74 cases, blastic in four cases, and mixed in two cases. Tissues undergoing biopsy included bone (63 cases), soft tissue (35 cases), and mixed specimens (five cases). The pathologic examinations revealed 18 infections, 23 primary neoplasms, 34 metastases, and 19 normal tissues. An adequate specimen for pathologic examination was obtained in 90 biopsies (87%). A diagnosis was achieved in 67 of 94 patients (71%). Diagnostic rates obtained in thoracic level biopsies were lower than those from biopsies of other spinal levels (P = .007).

CONCLUSION

Computed tomography-guided biopsy is an important tool in the evaluation of spinal lesions. A positive biopsy result may preclude the need for open surgical intervention. This study included one of the largest series of patients in the medical literature. In addition, it determined the diagnostic rates of this procedure with respect to the major influencing variables. Thoracic-level biopsies have a diagnostic rate that is significantly lower than that of other spinal levels. No significant correlation was found between diagnostic accuracy and age, gender, radiographic appearance, tissue type, or eventual diagnosis.

1997 Volvo Award winner in clinical studies. Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation

STUDY DESIGN

This prospective study analyzed the influence of transpedicular instrumented on the operative treatment of patients with degenerative spondylolisthesis and spinal stenosis.

OBJECTIVES

To determine whether the addition of transpedicular instrumented improves the clinical outcome and fusion rate of patients undergoing posterolateral fusion after decompression for spinal stenosis with concomitant degenerative spondylolisthesis.

SUMMARY OF BACKGROUND DATA

Decompression is often necessary in the treatment of symptomatic patients who have degenerative spondylolisthesis and spinal stenosis. Results of recent studies demonstrated that outcomes are significantly improved if posterolateral arthrodesis is performed at the listhesed level. A meta-analysis of the literature concluded that adjunctive spinal instrumentation for this procedure can enhance the fusion rate, although the effect on clinical outcome remains uncertain.

METHODS

Seventy-six patients who had symptomatic spinal stenosis associated with degenerative lumbar spondylolisthesis were prospectively studied. All patients underwent posterior decompression with concomitant posterolateral intertransverse process arthrodesis. The patients were randomized to a segmental transpedicular instrumented or noninstrumented group.

RESULTS

Sixty-seven patients were available for a 2-year follow-up. Clinical outcome was excellent or good in 76% of the patients in whom instrumentation was placed and in 85% of those in whom no instrumentation was placed (P = 0.45). Successful arthrodesis occurred in 82% of the instrumented cases versus 45% of the noninstrumented cases (P = 0.0015). Overall, successful fusion did not influence patient outcome (P = 0.435).

CONCLUSIONS

In patients undergoing single-level posterolateral fusion for degenerative spondylolisthesis with spinal stenosis, the use of pedicle screws may lead to a higher fusion rate, but clinical outcome shows no improvement in pain in the back and lower limbs.

Augmentation of autograft using rhBMP-2 and different carrier media in the canine spinal fusion model

This study evaluated the use of recombinant human bone morphogenetic protein (rhBMP-2) with various types of carrier media, and the effect of rhBMP-2 as an adjunct to autogenous iliac crest bone graft in the canine spinal fusion model. BMP induces mesenchymal cells to differentiate into cartilage and bone. The recent availability of rhBMP-2 has created the opportunity to evaluate this material's properties in augmenting autogenous bone graft in spinal fusion. Currently, the most appropriate type of carrier media for rhBMP-2 is undetermined. Bilateral intertransverse spinal fusions were performed on six canine lumbar spines at L1-L2, L3-L4, and L5-L6, using autogenous posterior iliac crest bone graft at each level, creating a total of 18 segmental fusion sites. All 18 sites were then randomly assigned to one of six fusion methods: autogenous bone graft (ABG) alone, ABG + rhBMP-2, ABG + collagen (Helistat) "sandwich" + rhBMP-2, ABG + collagen (Helistat) morsels + rhBMP-2, ABG + polylactic/glycolic acid sponge (PLGA) sandwich + rhBMP-2, and ABG + open-pore polylactic acid morsels + rhBMP-2. Each material was evaluated for ease of handling and application at the index surgery. The animals underwent computed tomography (CT) scanning of the lumbar fusion sites after 8 weeks. Volumetric measurements of total fusion mass at each level were performed using two-dimensional CT scan slices and a volumetric program supplied by the Siemens Medical System. The animals were killed after imaging studies. The lumbar spine fusion sites were evaluated for integrity of the fusion mass, both visually and with manual mechanical stressing. Crossover of the fusion mass to adjoining levels was also evaluated. Histologic evaluation of all fusion sites was performed. The addition of rhBMP-2 significantly increased bone graft volume as noted on CT scan. Carrier that could be mixed with morselized bone graft offered easier handling and application and all spine segments fused. Polylactic/glycolic acid (PLGA) sites were associated with a greater incidence of voids within the fusion mass. No significant difference in carrier media for rhBMP-2 could be determined. However, PLGA was associated with a higher rate of fusion mass void formation. rhBMP-2, when added to autograft, significantly increased the volume and the maturity of the resulting fusion mass.

Spinal instrumentation in the management of degenerative disorders of the lumbar spine

The use of spinal instrumentation as an adjunct to fusion for the treatment of degenerative disorders of the lumbar spine is controversial. Instrumented lumbar fusions, in specific instances, may improve patient outcomes. For patients undergoing single level primary lumbar arthrodesis, the available data do not conclusively support the efficacy of spinal instrumentation. However, in the setting of previous failed lumbar surgery, iatrogenic or degenerative lumbar spondylolisthesis, spinal instrumentation may be useful as an adjunct to fusion. Possible advantages associated with the use of instrumentation include: correction of deformity in frontal and sagittal planes; decreased pseudarthrosis rates; prevention of progression of spondylolisthesis, and provision of spinal stability in the absence of intact posterior elements. Complications associated with the use of instrumentation include: increased cost; increased operative times; increased infection rate; increased reoperation rate; and a steep learning curve. Therefore, when instrumentation is to be used, the benefits must outweigh the risks. These risks can be minimized by the judicious use of instrumentation by experienced surgeons, for specific indications as supported by the literature.

Efficacy of closed wound suction drainage after single-level lumbar laminectomy

The use of closed suction drainage after spinal surgery remains controversial. The purpose of this study was to determine the indications for closed suction drainage after single-level lumbar surgery. Two hundred patients who were scheduled to undergo single-level lumbar surgery without fusion were prospectively randomized into two groups. One group had a closed wound suction drain placed deep to the lumbodorsal fascia before routine closure, whereas the second group had no drain placed. Hemostasis was achieved in all patients before the surgeon had knowledge of the randomization outcome. All drains were removed on the 2nd postoperative day, and the amount of drainage was recorded. After surgery, the patients were evaluated for signs and symptoms of continued wound drainage, hematoma/seroma formation, and/or infection as well as evidence of an acquired neurologic deficit. One hundred three patients had a drain placed before closure and two patients developed postoperative wound infection, both of which were successfully treated with orally administered antibiotics. Of the 97 patients who had no drain placed after the surgical procedure, one patient developed a postoperative wound infection that was treated with surgical incision and drainage, as well as intravenously administered antibiotics. Statistical analysis revealed that the presence or absence of a drain did not affect the postoperative infection rate. No new neurologic deficits occurred in any postoperative patient. The use of drains in single-level lumbar laminectomy without fusion did not affect patient outcome. There was no significant difference in the rate of infection or wound healing and no patient developed a postoperative neurologic deficit.

Is pathology examination of disc specimens necessary after routine anterior cervical discectomy and fusion?

STUDY DESIGN

A retrospective chart review was performed from 1990-1994.

OBJECTIVES

To evaluate the outcome of pathologic examination of cervical disc specimens submitted after anterior cervical discectomy.

SUMMARY OF BACKGROUND DATA

This study is the first to review the outcome of pathologic examination of disc specimens after anterior cervical discectomy and fusion.

METHODS

Charts were reviewed based on the procedure code of anterior cervical fusion and the main diagnoses of cervical disc and spondylosis. The following data were recorded for each patient: symptoms, examination, diagnostic studies, operative procedure, operative findings, and pathology report. Statistical analysis was performed.

RESULTS

Five hundred six disc levels in 394 patients were reviewed. All patients had symptoms and examination results consistent with cervical radiculopathy. All patients had cervical radiographs and some combination of myelography, computed tomography, or magnetic resonance imaging. Findings at the time of surgery included the presence of either a herniated disc or degenerative spondylitic changes. The pathologic examination results of all specimens reported fibrocartilaginous tissue consistent with disc material with the presence of degenerative changes. No infectious, benign, or malignant process was identified at the time of surgery or on gross and histologic examination of any of the disc specimens. Using confidence intervals (95%) for exact proportions and given 500 negatives, the chance the next occurrence would be positive would be 0.0060 or 0.60% or six of 1000.

CONCLUSIONS

This study shows that if the symptoms, physical examination, radiographic diagnostic studies, and surgical findings are consistent with those of cervical disc herniation of spondylosis, the chance of an unexpected, clinically important pathologic finding within the disc specimen is extremely small. The time and expense involved in routine pathologic examination of cervical disc specimens can be avoided.

The effect of interposition membrane on the outcome of lumbar laminectomy and discectomy

STUDY DESIGN

This study evaluated clinical and magnetic resonance imaging differences of patients treated surgically for lumbar disc herniation. Clinical follow-up and magnetic resonance imaging evaluation of epidural fibrosis were used to assess patient outcome.

OBJECTIVES

The purpose of this study was to evaluate the difference in clinical outcome with either free-fat graft, Gelfoam, or no interposition membrane placed in the laminectomy defect after nerve root decompression.

SUMMARY OF BACKGROUND DATA

Epidural fibrosis has been considered a cause of recurrent symptoms after lumbar laminectomy, and numerous materials have been evaluated for prophylaxis of the "laminectomy membrane." These have been mainly histologic and animal studies with no data correlating clinical symptoms and postoperative epidural scar formation.

METHODS

One hundred fifty-six patients who were treated surgically for lumbar disc herniation were randomly assigned to one of three groups and followed prospectively for at least 1 year. Thirty-three of these patients were received magnetic resonance imaging evaluations after 6 months by an independent radiologist who graded the amount of epidural scar formation. The patients were assessed at 1 year and given a rating of excellent, good, fair, or poor, and the scar was graded as none, minimal, or moderate.

RESULTS

Although 97% of all patients improved, 83% were rated excellent or good. There were no statistical differences between the three groups clinically and radiographically. Patients with workers compensation had a statistically significant lower success rate (P < 0.001).

CONCLUSIONS

Clinical outcome after lumbar disc surgery does not correlate with the use or type of interposition membrane used to prevent epidural fibrosis.

Spine update. Degenerative lumbar spondylolisthesis

Degenerative lumbar spondylolisthesis associated with spinal stenosis is a common condition of the aging spine. This article presents a detailed description of the pathophysiology, clinical presentation, and nonoperative and operative intervention of this condition.

Conus medullaris injury due to herniated disk and intraoperative positioning for arthroscopy

This report discusses the occurrence of a cauda equina syndrome from a herniated L1-L2 disc following knee arthroscopy.

The effect of prophylactic antibiotics on iatrogenic intervertebral disc infections. a rabbit model

STUDY DESIGN

A rabbit model was used to test the efficacy of two commonly used prophylactic antibiotics, cefazolin and vancomycin, in preventing iatrogenically introduced Staphylococcus aureus intervertebral disc infections.

OBJECTIVE

This study was performed to assess the efficacy of two prophylactic antibiotics in preventing iatrogenically introduced Staphylococcus aureus intervertebral disc infections.

SUMMARY OF BACKGROUND DATA

Previous studies have had conflicting results regarding the penetration of antibiotics into the nucleus pulposus and their ability to eradicate infection.

METHODS

In this study, 40 adult New Zealand White rabbits underwent inoculation of 10(1) or 10(3) Staphylococcus aureus/ml into 3-6 lumbar intervertebral discs under direct visualization. Either no antibiotics (control groups) or various preoperative and postoperative dosing schedules of cefazolin or vancomycin were given intravenously. Five days after surgery, the discs were harvested and cultured.

RESULTS

All 40 discs inoculated in the control groups became infected. None of the 35 discs inoculated in the cefazolin groups became infected. Infection developed in 23 of 107 discs inoculated in the vancomycin groups. Most notable of these were 17 of 17 positive cultures in animals given vancomycin 8 hours preoperatively only.

CONCLUSIONS

Based on these results, it was concluded that intravenous cefazolin or vancomycin given within 1 hour before surgery can effectively prevent postoperative discitis. No advantage was found with additional postoperative antibiotics.

A modified posterolateral approach to the thoracic spine

We describe a modified technique for posterolateral approach to the thoracic spine and report the use of this procedure in 21 patients. The technique is safe and effective for selected indications. The evolution of the posterolateral or costotransversectomy approach to the thoracic spine has in large part focused on enlarging the exposure to the vertebral bodies and epidural space by resecting an increasing number of ribs and removing a wider portion of those ribs resected. In this modified approach to the thoracic spine, the costovertebral articulation is preserved, and no rib resection is necessary to gain adequate exposure to the thoracic vertebral body and epidural space. We did a retrospective review of 21 patients undergoing 22 modified posterolateral approaches to the thoracic spine. Sixteen patients had biopsies of thoracic vertebral lesions through this approach; 3 underwent decompression of the thoracic spinal cord; 2 approaches were done for the removal of a herniated thoracic disc; and in one, the pedicle was removed. This modified posterolateral approach allowed adequate exposure for selected indications. One complication, a wound infection, developed after biopsy for suspected osteomyelitis. This modified posterolateral approach is well suited to provide access for biopsy of thoracic spinal lesions; for decompression of a paraspinal abscess; and for decompression of the thoracic spinal cord by anterolateral compressive lesions such as herniated thoracic disc or epidural tumor when resection of the vertebral body is not necessary; or the approach may be used for patients who are debilitated or at poor risk to undergo thoracotomy.

Anular incision technique on the strength and multidirectional flexibility of the healing intervertebral disc

STUDY DESIGN

This study used a sheep model to biomechanically analyze the healing strength of the anulus fibrosus after two types of anular incisions.

OBJECTIVE

This study evaluated whether the type of anular incision made at the time of lumbar discectomy plays a role in the subsequent healing strength of the anulus and the biomechanical flexibility of the corresponding motion segment.

METHODS

Two types of anular incision, a full thickness removal of a box or window of anulus and a full thickness straight transverse slit through the anulus, were made in the intervertebral discs of 18 adult sheep. After healing times of 2, 4, and 6 weeks, the intervertebral discs were tested versus control levels for strength of anular healing and biomechanical flexibility of the corresponding motion segment.

RESULTS

The box incised discs showed a significantly greater loss in strength during the early healing phase (2 to 4 weeks) and a longer response before recovering anular strength when compared with the slit-incised discs. The type of incision also affected the multidirectional flexibility of the motion segments in a differentiated manner. Larger amounts of motion were seen with the box incision when compared with the slit incision at all time periods and in all pure moments.

CONCLUSION

The technique of anular incision plays a definite role in the timing and strength of subsequent anular healing. The box incision through the anulus led to significantly weaker healing than did the slit incision in the early healing phase (2-4 weeks). Also, larger amounts of motion were seen in the vertebral motion segments of those discs undergoing box incision when compared with slit or control levels.

A biomechanical comparison of cervical laminaplasty and cervical laminectomy with progressive facetectomy

The effects of multilevel cervical laminaplasty and laminectomy with increasing amounts of facetectomy on stability of the cervical spine were tested with physiologic loading in nine cadaveric specimens. Cervical spines, levels C2-C7, were tested with physiologic loading in a constraint-free test system, the motion of each body being tracked in a three-dimensional coordinate system. Cervical laminectomy with 25% or more facetectomy resulted in a highly significant increase in cervical motion compared to the intact specimens for the dominant motions of flexion/extension (P < 0.003), axial torsion (P < 0.001), and lateral bending (P < 0.001). Cervical laminaplasty was not significantly different from the intact control, except for a marginal increase in axial torsion. Coupled motion did not change with laminaplasty or laminectomy with progressive facetectomy. As little as 25% facetectomy adversely affects stability after multilevel cervical laminectomy. Cervical laminaplasty avoids this problem, while still affording multilevel decompression. Therefore in patients undergoing cervical laminectomy accompanied by more than 25% bilateral facetectomy, concurrent arthrodesis should be performed.

Spinal pedicle fixation. Confirmation of an image-based technique for screw placement

Although many advances in the technique of pedicle screw insertion have been made, there still exist unacceptable rates of perforations through the pedicle cortex. Successful placement of a pedicle screw requires accurate identification of the entry point, correct transverse and sagittal plane angulation, safe preparation of a pilot hole, and appropriate depth of insertion. The authors propose that a technique of pedicle screw insertion using posteroanterior image intensification angled in the axis of the pedicle to define the entry point and guide insertion would improve the accuracy of this procedure. This study tests the accuracy of pedicle screw placement using this technique. Ninety pedicle screws were placed in human cadaveric lumbar spines. All specimens were then dissected and split longitudinally to assess accuracy of pedicle insertion by both visual and palpatory means. Five of 90 (5.5%) pedicle screws were found to have perforated the pedicle. Three of these were at L1, two of which were due to the transverse pedicle diameter being smaller than the screw diameter. Therefore, a 3.4% incidence of pedicle perforation due to malpositioning and a 2.1% incidence of pedicle perforation secondary to pedicle/screw size discrepancy was determined. This technique may lead to significant improvements over recently reported rates of pedicle screw perforations; however, this in vitro condition eliminated many potentially complicating factors that might be encountered in the clinical setting.

Upper lumbar disc herniations

This study reviews the presentation, diagnosis, and outcomes of upper lumbar disc herniations (L1-2, L2-3, L3-4). One hundred forty-one patients operated upon at three centers between 1980 and 1990 were analyzed (102 men, 39 women; 3 L1-2, 21 L2-3, 117 L3-4; average age 51.6 years; 10.4% of all lumbar discectomies performed). Preoperative signs and symptoms were highly variable. Sensory, motor, and reflex testing was variable and potentially misleading in suggesting a level of herniation. In analyzing radiographic studies (noncontrast CT, myelography, MRI) individually and using other radiographic studies and operative findings as a standard for comparison, a high false-negative rate was found for all studies when considered individually, especially at the higher L2-3 level. Intraoperative radiographs were employed with increasing frequency as the level of herniation ascended. Six operative complications (4.3%) were identified, all of which were treated and were resolving at the time of discharge. Follow-up obtained at an average of 2.2 years in 87% of patients by chart review showed no reoperations or late complications. Noncompensation patients had a significantly higher percentage of good/excellent results (86%) than those with compensation or legal claims pending (45% good/excellent results). Based upon these data, we recommend myelogram with postmyelogram CT and/or MRI in the workup of these patients and intraoperative radiographs in all cases when decompressing an upper lumbar disc herniation. Patients with compensation/legal claims should be approached cautiously, because their subjective results are significantly worse than those of noncompensation patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudarthrosis of the spine

Pseudarthrosis remains the leading cause of failed spinal fusions. The common causes of this complication are inadequate surgical technique, excessive stresses across the fusion site, insufficient internal or external stabilization, and unrecognized metabolic abnormalities. Many radiologic techniques have been used to diagnose pseudarthrosis in the spine. Nonetheless, the diagnosis of a nonunion as well as the ability to correlate the nonunion with the patient's clinical symptoms remains a challenge. In treating a symptomatic pseudarthrosis, the surgeon should first attempt to identify those factors that contributed to the development of a nonunion. The approach can then either be exploration of the fusion mass with regrafting of the pseudarthrosis or extending a fusion to locations within the abnormal segment of spinal motion.

Surgical management of myelopathy

We have presented a comparative analysis of the ability of four surgical procedures to address adequately the problems sustained by a patient with symptomatic cervical myelopathy. AIA is a safe procedure whose effectiveness may be limited when the extent of disease is more than three intervertebral disk levels. ACA permits more direct and extensive access to the spinal cord and is the procedure of choice for cervical spondylotic myelopathy associated with spinal deformity. However, rigid external immobilization is necessary, and operative morbidity may be greater. Cervical laminectomy may be effective for decompressing the spinal cord when no associated spinal deformity or instability is present, provided that extensive resection of facet joints is avoided. Cervical laminaplasty is ideally suited for the patient with three or more levels contributing to a cervical myeloradiculopathy. Mild instability may be addressed by performing arthrodesis on the hinge side.

Modified anterior approach to the cervicothoracic junction

The surgical management of tumors at the cervicothoracic junction is hindered by various anatomic structures. Standard approaches to the cervical or thoracic spine provide inadequate exposure. An approach to the cervicothoracic junction that provides exposure from C3 to T4 is described. The approach allows extensive bony resection, spinal cord decompression, correction of deformity, spinal reconstruction, and stabilization. Four patients with tumors metastatic to the cervicothoracic junction underwent this surgical approach. All had significant kyphosis and neck pain unresponsive to nonsurgical treatment. After surgery, neurologic function improved in three patients and remained normal in one. All patients had relief of neck pain and reduction of kyphosis.

Degenerative lumbar spondylolisthesis with spinal stenosis. A prospective study comparing decompression with decompression and intertransverse process arthrodesis

Fifty patients who had spinal stenosis associated with degenerative lumbar spondylolisthesis were prospectively studied clinically and radiographically to determine if concomitant intertransverse-process arthrodesis provided better results than decompressive laminectomy alone. There were thirty-six women and fourteen men. The mean age of the twenty-five patients who had had an arthrodesis was 63.5 years and that of the twenty-five patients who had not had an arthrodesis, sixty-five years. The level of the operation was between the fourth and fifth lumbar vertebrae in forty-one patients and between the third and fourth lumbar vertebrae in nine patients. The patients were followed for a mean of three years (range, 2.4 to four years). In the patients who had had a concomitant arthrodesis, the results were significantly better with respect to relief of pain in the back and lower limbs.

Current status of percutaneous discectomy and chemonucleolysis

This article provides an updated review of chemonucleolysis and percutaneous discectomy. Dr. Herkowitz recommends discontinuing the use of chymopapain. Percutaneous discectomy may play a small role in the invasive management of a lumbar disc herniation.

Natural history of os odontoideum

Os odontoideum has recently been considered an acquired lesion of the second cervical vertebrae. This case documents the natural progression of the formation of os odontoideum and correlates it with a traumatic event. This is the first case reported in the literature.

Osteolytic monostotic Paget's disease of the fifth lumbar vertebra. A case report

Osteolytic monostotic Paget's disease or osteitis deformans of the fifth lumbar vertebra occurred in a 55-year-old woman. An isolated lytic process involving the entire vertebral body and posterior elements and an open biopsy showed extensive remodeling with cement lines, myelofibrosis, and osteoclastic resorption typical of Paget's disease.

Surgical management of cervical soft disc herniation. A comparison between the anterior and posterior approach

Anterior cervical fusion was initially described in the 1950s for cervical spondylotic radiculopathy. The indications for this procedure in the management of soft disc herniation have not been clearly defined. In addition, controversy exists as to whether a cervical soft herniation should be managed by an anterior approach or a posterior cervical laminotomy-foraminotomy. The authors report the results of a prospective study comparing anterior discectomy and fusion to posterior laminotomy-foraminotomy for the management of soft cervical disc herniation. Twenty-eight patients underwent anterior discectomy and fusion (Robinson horseshoe graft) while 16 patients underwent posterior laminotomy-foraminotomy. The disc herniations were classified into two types. Type I were single level anterolateral herniations (33 patients) while type II were central soft disc herniations (11 patients). Clinically, patients with type I herniations manifested signs and symptoms of radiculopathy while patients with type II herniations manifested signs of myelopathy or neck pain and bilateral upper extremity paresthesias in 4 patients. Confirmatory studies were myelography in 12 patients, myelography combined with computed tomography (CT) in 26 patients, and magnetic resonance imaging (MRI) in 6 patients. For type I herniations, 17 patients underwent anterior fusion while 16 patients had a posterior laminotomy-foraminotomy. The 11 patients classified as type II herniation all underwent anterior discectomy and fusion. There were 27 men and 17 women. The age range was 21 to 52 years (mean, 41 years). The follow-up was 1.6 to 8.2 years (mean, 4.2 years).(ABSTRACT TRUNCATED AT 250 WORDS)

The surgical management of cervical spondylotic radiculopathy and myelopathy

Anterior fusion, laminectomy, and laminaplasty are recommended for the following conditions. For the treatment of one- or two-level spondylotic radiculopathy, anterior discectomy and fusion are preferred. For the treatment of spondylotic radiculopathy involving three or more levels, the open-door laminaplasty may be considered an alternative to anterior fusion. In this situation, laminaplasty is preferred for patients with developmental cervical canal stenosis, failed anterior fusion, or various prior anterior neck operations. Cervical laminectomy is indicated for patients with anterior bony ankylosis secondary to degenerative or inflammatory disorders and for patients in whom anterior fusion may be technically difficult, i.e., at C1-C3 or C7-T1. Anterior fusion is advisable for patients who have a structural reversal of the normal lordotic curve.

A comparison of anterior cervical fusion, cervical laminectomy, and cervical laminoplasty for the surgical management of multiple level spondylotic radiculopathy

The risks and success of surgery for multiple level cervical spondylotic radiculopathy differs from that of single level disease. The problems associated with multiple level anterior fusion over single level fusion include higher pseudoarthrosis rates than that associated with single level disease. Bilateral and multiple level laminectomy carries the risk of potential instability. Cervical laminoplasty, until recently, has only been performed for myelopathy secondary to ossification of the posterior longitudinal ligament (OPLL) or cervical stenosis. The purpose of this report is to compare the results and complications of 45 patients with a least a 2-year follow-up who had undergone anterior fusion, cervical laminectomy, or cervical laminoplasty for the surgical management of multiple level cervical radiculopathy due to cervical spondylosis. 18 patients (58 levels) underwent anterior fusion, 12 patients (38 levels) had a cervical laminectomy, and 15 patients (57 levels) underwent a cervical laminoplasty. Roentgenograms indicated spinal stenosis (sagittal diameter less than 12 mm) at 28 levels (15 patients) for the anterior fusion group, 14 levels (9 patients) in the laminectomy group, and 24 levels (13 patients) in the laminoplasty group. Subluxation (2 mm or less) was present at 14 levels (13 patients) in the anterior fusion group, nine levels (9 patients) in the laminectomy group, and 15 levels (8 patients) in the laminoplasty group. Loss of lordosis was present in eight patients undergoing anterior fusion, six patients undergoing laminectomy, and six patients who had a laminoplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of computerized tomography in evaluating non-visualized vertebral levels caudad to a complete block on a lumbar myelogram. A review of thirty-two cases

In thirty-two patients who demonstrated a complete or almost complete block on a lumbar myelogram, computerized tomography of the non-visualized vertebral levels caudad to the block was performed prior to surgical intervention. The purpose of this study was to evaluate the clinical value of computerized tomography in detecting a lesion that is caudad to the level of a myelographic block. For twenty-three patients the cause of the myelographic block was stenosis of the spine; for five patients, a combination of stenosis of the spine and herniation of a disc; for one patient, herniation of a disc between the fourth and fifth lumbar vertebrae alone; for two patients, arachnoiditis; and for one patient, kyphosis secondary to fracture. A total of fifty vertebral levels that could not be visualized because of the block were evaluated. Thirty (60 per cent) of the non-visualized vertebral levels, in nineteen (59 per cent) of the thirty-two patients, demonstrated stenosis of the spine or a herniated disc that was confirmed at the time of surgical treatment. The value of computerized tomography for the evaluation of the vertebral levels caudad to the level of a complete or almost complete block on a lumbar myelogram was threefold. First, it provided visualization of the vertebral levels that could not be evaluated by the myelography. Second, the findings on computerized tomography provided information that was essential for preoperative planning and it removed the so-called exploratory element from the operative procedure.(ABSTRACT TRUNCATED AT 250 WORDS)

The cervical spine in hemophilia

Fifty-three patients with known hemophilia A or B were retrospectively reviewed to determine the incidence of cervical spine involvement. Twenty-five were examined prospectively, including a detailed history and physical examination and cervical spine roentgenograms consisting of an AP and lateral flexion-extension series. All roentgenograms were reviewed by a board-certified radiologist. The mean age of patients in both groups was 25.4 years (range, eight to 54 years). In the retrospective review, no patients were noted to have complaints referable to the cervical spine, although five patients had prior trauma to the cervical spine. In the prospective study, 8 of 25 patients complained of intermittent neck discomfort and 9 of 25 had restricted lateral rotation and/or lateral flexion. No patient had radicular symptoms or objective neurologic deficits. Roentgenograms showed abnormalities in 13 of 25 patients. Ten patients (aged 19 to 54 years; mean, 32 years) showed cystic changes or endplate irregularity within one or more vertebral bodies. Two patients, aged 15 to 19 years, had an increased atlanto-dens interval of 5 mm (normal, 3 mm). No odontoid erosion was noted. No correlation was found between the severity of peripheral involvement and the cervical spine roentgenograms. Occult instability of the cervical spine is discussed, along with ramifications for patients with hemophilia.

Chemonucleolysis. The relationship of the physical findings, discography, and myelography to the clinical result

Fifty consecutive patients undergoing chemonucleolysis with chymopapain at William Beaumont Hospital were analyzed with special reference to the following factors: the physical examination, the dye pattern noted on discogram, and the size of the preoperative myelographic defect. Discogram pattern was divided in four types: normal disc, degenerative pattern, degenerative pattern with extravasation, and annular injection. The myelograms were graded into a mild defect, a moderate defect, or a severe defect. Follow-up averaged 20 months. Conclusions of this study were Chymopapain can be considered as an alternative to lumbar laminectomy for relief of sciatica secondary to herniated disc. Statistically significant improved postinjection results were noted when patients presented with three out of four objective physical findings consisting of positive straight leg raising, reflex change, dermatomal paresthesia pattern, and/or mild motor weakness. Placement of the needle within the nucleus leads to a statistically significant improved result over placement of the needle into the annulus. A severe myelographic defect greater than 50% dura sac compression is a relative contraindication to the injection of chymopapain.

Subacute instability of the cervical spine

The purpose of this article is to describe a new entity, subacute instability of the cervical spine. It is defined as the development of radiographic evidence of cervical instability within 3 weeks of a cervical spine injury when initial adequate roentgenograms show no bony or soft tissue abnormality. Six patients who conform to this definition are reported. Each was found to have developed neurologic deficit and radiographic evidence of instability of the cervical spine on repeat examination when none was present initially. There were four unilateral facet dislocations (two C5-C6, one C6-C7, one C4-C5), one perched facet (C5-C6), and one extension subluxation (C4-C5). The mechanism of subacute instability is thought to be due to the elastic and plastic deformation of the ligamentous structures and discs of the cervical spine. An algorithm has been developed and is described for evaluation of patients with cervical trauma and initial normal radiographs. By alerting physicians to the entity of subacute instability of the cervical spine, it is hoped that injuries of this nature will be discovered so that appropriate treatment can be rendered before a fixed deformity develops.