Design and Characterization of Poly(Ethylene Glycol) Photopolymerizable Semi-Interpenetrating Networks for Chondrogenesis of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are used extensively in cartilage tissue engineering. We have developed a photopolymerizable poly(ethylene glycol diacrylate) (PEGDA) and poly(ethylene glycol) (PEG) semi-interpenetrating network that facilitates the in vitro chondrogenesis of human MSCs (hMSCs). Network parameters were altered and tested for their effects on subsequent matrix elaboration. The mesh size, calculated for each network based on equilibrium swelling ratios, was larger with lower PEGDA:PEG ratios and with higher PEGDA molecular weight. Changes in xi correlated with changes in extracellular matrix content and deposition in hMSC-seeded networks cultured in vitro for 6 weeks in defined chondrogenic medium. Networks constructed with PEGDA (6 kDa) and PEG (88 kDa) at 1:2 displayed intercellular deposition of proteoglycan. Furthermore, their proteoglycan contents were significantly higher than with PEGDA (6 kDa) hydrogels constructed without the PEG component and those constructed at a PEGDA:PEG ratio of 2:1, which both exhibited pericellular proteoglycan deposition. However, networks constructed with PEGDA (12 and 20 kDa) and PEG (88 kDa) exhibited intercellular deposition of proteoglycan regardless of the ratio employed. Collagen content was lower in networks constructed with PEGDA (12 and 20 kDa) and PEG (88 kDa) at a ratio of 1:2 than in those fabricated at the same PEGDA molecular weights at a ratio of 2:1. This study demonstrated that semi-interpenetrating network parameters influence not only extracellular matrix content, but also the deposition of the matrix molecules by hMSCs undergoing chondrogenesis. It is important that these parameters be considered carefully when creating scaffolds for tissue-engineered cartilage.

Use of pelvic incidence as a guide to reduction of H-type spino-pelvic dissociation injuries

OBJECTIVE

Describe the use of a radiographic parameter (pelvic incidence) to assess the sagittal plane reduction of H-type sacral fractures associated with spinopelvic dissociation, and assess the relationship between standing lumbar lordosis to pelvic incidence after spinopelvic dissociation.

DESIGN

Retrospective radiographic and clinical review of treatment outcomes for patients with spinopelvic dissociation injuries secondary to H-type sacral fractures.

SETTING

Level I Trauma Center.

INTERVENTION

Pelvic incidence (PI), a radiographic parameter that measures the orientation of the lumbar spine relative to the pelvis, has been shown to have a correlation with the adequacy of surgical reduction as well as the risk of progression of high-grade spondylolisthesis. We used this parameter as a measure of sagittal plane reduction of spinopelvic dissociation injuries.

PATIENTS/PARTICIPANTS

The clinical records and radiographs of five patients with spinopelvic dissociation injuries were reviewed.

MAIN OUTCOME MEASUREMENTS

Radiographic measurements included standing PI and lumbar lordosis (LL). The relationship of lumbar lordosis on pelvic incidence was tested by a regression analysis. Clinical outcome was assessed by the self-reported ability of the patient to comfortably maintain an upright stance.

RESULTS

The average follow-up period was 32 (range: 12-53) months. The average final PI was 82 (60-115) degrees. The average final lumbar lordosis was 58.2 (42-77) degrees. LL was found to be significantly related to PI (P<0.05). One patient with an abnormally high PI had lumbar fatigue with persistent stance.

CONCLUSIONS

Pelvic incidence is a potentially useful radiographic parameter that can be used to assess the adequacy of sagittal plane reduction in patients with spinopelvic dissociation injuries.

Mechanical comparison of posterior instrumentation constructs for spinal fixation across the cervicothoracic junction

STUDY DESIGN

A biomechanical study comparing 4 different posterior implant configurations for instrumentation across the cervicothoracic junction.

OBJECTIVE

To compare mechanical parameters during flexion bending and axial rotation testing among 4 different posterior cervicothoracic rod-and-screw constructs.

SUMMARY OF BACKGROUND DATA

Several posterior rod constructs are available for instrumentation across the cervicothoracic junction. No studies have examined the mechanical properties of constructs of varying rod diameters and rod connector types.

METHODS

Four different rod-and-screw-based constructs for posterior cervicothoracic instrumentation underwent flexion bending or axial rotation testing. Stiffness, ultimate and yield forces (torques) were compared using an analysis of variance.

RESULTS

Significantly lower stiffness, ultimate and yield force (torque) was observed with a 3.5-mm rod construct compared with the 3 other constructs. No significant differences were demonstrated between a dual diameter rod (3.5 mm to 5.5 mm) and a solid domino connector extending between 3.5-mm and 5.5-mm rods. A hinged domino connector construct between 3.5-mm and 5.5-mm rods had similar stiffness but lower ultimate and yield force from either the dual diameter rod or the solid domino construct.

CONCLUSIONS

The present results demonstrate that the 3.5-mm rod-and-screw construct is the weakest configuration for posterior fixation across the cervicothoracic junction. The dual diameter rod and fixed domino connector constructs were the strongest and demonstrated similar values for yield and ultimate force.

A bridging demineralized bone implant facilitates posterolateral lumbar fusion in New Zealand white rabbits

STUDY DESIGN

Randomized controlled animal study.

OBJECTIVE

Test the effectiveness of a single-strip demineralized bone matrix with hyaluronan and gelatin.

SUMMARY OF BACKGROUND DATA

Demineralized bone matrix is widely used to augment spinal fusion, however, the effect of changing the physical characteristic and carrier is not known.

METHODS

Demineralized bone matrix was extracted from the bones of New Zealand White rabbits, and combined with hyaluronan and gelatin to form solid strips. Forty-eight rabbits were randomized into a control and 2 experimental groups. In the control group, fusion was attempted with autograft bone. For group 2, demineralized bone matrix strips alone and for group 3, autograft and demineralized bone matrix strips were used. The fusion was assessed with manual manipulation and radiographs. The volume of the fusion mass was determined from computed tomographic images.

RESULTS

By the manual palpation test, the fusion rates were 37.5%, 93.8%, and 100%, for groups 1-3, respectively (P < 0.05). By radiography, the control group fusion rate was 68.7% compared with 100% for the experimental groups (P < 0.05). The mean bone volumes of the fusion mass were 2142.2 +/- 318.5, 3132.9 +/- 632.1, and 4181.6 +/- 609.5 mm3 for groups 1-3, respectively (P < 0.05).

CONCLUSIONS

The demineralized bone matrix-gel strip was able to function as both a bone-graft enhancer and a bone graft substitute in rabbit posterolateral spine fusion.

Ascorbate-enhanced chondrogenesis of ATDC5 cells

The ATDC5 cell line exhibits the multistep chondrogenic differentiation observed during endochondral bone formation. However, it takes up to two months to complete the process of cell expansion, insulin addition to promote differentiation and further changes in culture conditions effectively to induce hypertrophy. We sought to produce consistent chondrogenesis with significant hypertrophic differentiation with simpler conditions in a more practical time period. By adding ascorbate, the prechondrogenic proliferation phase was shortened from 21 to 7 days, with production of cartilaginous nodules during the chondrogenic phase, after insulin addition, that were greater in number and larger in size. Immunohistochemistry indicated much greater matrix elaboration and the mRNA expression of sox9, aggrecan and collagen type II were all significantly increased earlier and to a much higher degree when compared with controls. Moreover, there was a robust induction of hypertrophy: Col10a1, Runx2 and Mmp13 were all induced within 7-10 days. In conclusion, addition of ascorbate to ATDC5 cultures shortened the prechondrogenic proliferation phase, produced earlier chondrogenic differentiation, heightened gene expression and robust hypertrophic differentiation, abrogating the need for extended culture times and the changes in culture conditions. This simple modification considerably enhances the practicality of this cell line for studies of chondrogenesis.

Intraoperative Technique to Define the Safe Lateral Limits of Anterior Cervical Corpectomy

STUDY DESIGN

We describe a surgical radiographic technique during anterior cervical corpectomy to define the safe lateral limit of dissection.

OBJECTIVE

To assess the radiographic technique accuracy using computed tomography (CT) measurements on cadaveric specimens. Two clinical cases are presented.

SUMMARY OF BACKGROUND DATA

During anterior cervical surgery loss of orientation can lead to eccentric decompression and vertebral artery injury.

METHODS

A two-level corpectomy on 4 cadaveric samples was filled with radioopaque dye. An "introperative" antero-posterior x-ray was used to measure the narrowest distance from dye column to uncovertebral joints. A CT scan confirmed the distance from corpectomy to vertebral arteries.

RESULTS

The distance between the x-ray dye column and uncovertebral joints averaged 2.7 mm (range, 0 to 7+/-2.2 mm). A CT scan demonstrated the distance from corpectomy to vertebral artery averaged 4.5 mm (range, 0 to 10+/-4.4 mm). The measured distance underestimated the true distance by an average of 1.8 mm (range, 0 to 8+/-2.2 mm).

CONCLUSION

An intraoperative radiographic technique can estimate the lateral distance between the corpectomy and vertebral arteries by measuring the distance from the dye column to uncovertebral joints. The dye radiographic technique provides the surgeon an additional margin of safety.

Risk Factors for Delayed Extubation After Single-stage, Multi-level Anterior Cervical Decompression and Posterior Fusion

Airway difficulties after single-stage, multilevel anterior and posterior cervical surgery are potentially life-threatening complications. Although extubation delays can occur, overnight intubation can reduce the risk of postoperative airway emergencies. Our protocol was as follows: all patients were kept intubated overnight in an intensive care unit and examined by the intensive care unit staff each morning. Readiness for extubation was based on the cuff-leak test, and extubation done on patients beyond the first postoperative day was considered delayed. Eleven patients were extubated on the first postoperative day (group 1), and 11 extubated beyond day 1 (group 2). No airway emergencies occurred. Patient factors-age, weight, smoking, medical comorbidities, American Society of Anesthesiologist class-were not significantly related to extubation delay. There were no differences between groups in the number of anterior and posterior levels or anterior and posterior operative times. Delayed extubation was significantly related to total operative time (8.2 hours vs. 10.6 hours), volume of crystalloid replacement (3,627 cm3 vs. 6,218 cm3) and intraoperative blood transfused (0.7 units vs. 3.1 units); approaching significance was increased blood loss (1,238 mL vs. 2,820 mL). We have found intraoperative factors-operative time, crystalloid volume, blood loss and replacement-rather than patient characteristics, to be risk factors for delayed extubation. Good communication with anesthesia staff and careful attention to postoperative airway management is essential after single-stage, multilevel anterior cervical decompression and posterior fusion.

The use of simvastatin in rabbit posterolateral lumbar intertransverse process spine fusion

BACKGROUND CONTEXT

There has been recent enthusiasm regarding the potential positive effects of statins on bone. Statins vary in their ability to influence bone activity. Simvastatin has been shown in experimental models to stimulate bone acting growth factors and enhance bone formation.

PURPOSE

The potential efficacy of Simvastatin in enhancing spinal fusion was evaluated in a rabbit posterolateral intertransverse process fusion model.

STUDY DESIGN/SETTING

Posterior lumbar intertransverse process spinal fusion performed on New Zealand White rabbits. PATIENT/STUDY SAMPLE: 44 New Zealand White rabbits.

OUTCOME MEASURES

Spinal fusion as determined by manual palpation testing and fine detail radiography. Bone fusion mass volume and density as determined by CT scan imaging.

METHODS

Forty-four New Zealand White rabbits underwent posterolateral intertransverse process spine fusion using autogenous iliac crest bone graft. Simvastatin was administered orally in 20 animals and the serum lipid profile quantified in test and control animals. The animals were euthanized 9 weeks following index surgery and the lumbar spine was harvested. Spinal fusion was determined by manual palpation testing and fine detail radiography. The volume and density of the bone fusion mass was quantified by computed tomography.

RESULTS

Drug treatment for 9 weeks caused a reduction in serum lipid biochemical markers when compared with controls. The spinal fusion rate, as judged by manual palpation testing (13.0% control group, 16.6% Simvastatin group) and fine detail radiography, was not significantly different comparing treatment with control animals. Accordant with the assessment of spinal fusion, there was no statistically significant effect on the volume of the fusion mass (1,224.7+/-98.7 mm(3) in the control group and 1,075.9+/-66.3 mm(3) in the Simvastatin group), the density of bone in the lumbar spine or that in the formed fusion mass.

CONCLUSIONS

Systemic use of Simvastatin caused a reduction in lipid biochemical parameters in treated animals. Successful spinal fusion as judged by manual palpation testing and fine detail radiography was not significantly different in treated versus untreated animals. The bone volume density of the formed fusion mass was not significantly different in treated versus untreated animals. There did not appear to be a significant advantage or disadvantage to the use of Simvastatin rabbit posterolateral spinal fusion. The potential positive effects of statins on bone require further study.

Lunate arthroplasty with autologous mesenchymal stem cells in a rabbit model

BACKGROUND

There is no ideal treatment for end-stage degenerative wrist disorders and subsequent carpal collapse. The purpose of this study was to investigate whether autologous cartilage constructs tissue-engineered from bone-marrow-derived mesenchymal stem cells can be effective for carpal bone reconstruction.

METHODS

Total lunate excision was performed in twenty-seven adult New Zealand White rabbits. Mesenchymal stem cells were isolated from marrow and then were culture-expanded. Group-1 rabbits underwent excision only. Group-2 animals underwent excision followed by implantation of a scaffold consisting of gelatin and hyaluronan. Group-3 animals underwent excision followed by implantation of a mesenchymal stem cell-seeded scaffold that had been preincubated in chondrogenic medium. The group-1 animals were killed at six weeks, whereas the group-2 and group-3 animals were killed at six or twelve weeks. Tissues were harvested for radiographic and histologic analysis.

RESULTS

Significant carpal collapse (a 5.4% +/- 2.8% reduction in the carpometacarpal index, p < 0.05) was observed in the group-1 animals by six weeks. In contrast, the carpal height was maintained in the group-2 and 3 animals. There was no radiographic evidence of ossification in the group-1 or 2 animals, whereas there was radiographic evidence of ossification in all six group-3 rabbits killed at the twelve-week time-point. Histologic sections from the group-3 animals showed filling of the lunate space with islands of cartilage with interspersed bone ossicles at six weeks. At twelve weeks, there was abundant bone formation as well as evidence of neovascularization. Osseous tissue was present in the central portions of the constructs while the periphery was lined with cartilage. In groups 1 and 2, the lunate space was filled with poorly organized fibrous tissue.

CONCLUSIONS

Cartilaginous implants preformed from autologous mesenchymal stem cells seeded onto biodegradable scaffold can prevent carpal collapse. The newly formed osteochondral tissue appears to function as an adequate biologic lunate spacer for at least twelve weeks in this animal model.

Chondrogenic potential of progenitor cells derived from human bone marrow and adipose tissue: a patient-matched comparison

PURPOSE

Stem cell-based tissue engineering represents a possible alternative for the repair of cartilage defects. Both bone marrow and adipose tissue contain pluripotential cells capable of chondrogenesis. This study was a qualitative and quantitative comparison of the chondrogenic potential of progenitor cells isolated from bone marrow aspirates and adipose tissue.

METHODS

Bone marrow aspirates (BM) and matching adipose tissue (AD) overlying the posterior superior iliac crest were obtained from patients undergoing elective spine surgery. Chondrogenesis was induced using an established aggregate culture technique. Qualitative analysis was performed by histology and immunohistochemistry. DNA and glycosaminoglycan (GAG) quantitative assays were performed. Quantitative RT-PCR analysis was performed to compare expression of type II collagen between BM and AD aggregates. Osteogenic and adipogenic assays were also performed to confirm pluripotentiality of both AD-derived progenitor cells (ADPC) and BM-derived progenitor cells (BMPC).

RESULTS

Toluidine blue metachromasia and type II collagen immunohistochemical staining were more extensive in the aggregates formed by BMPC. Quantitative RT-PCR showed a 500-5000 fold higher expression of type II collagen in the BMPC aggregates. The DNA content was 68% higher in the AD aggregates (p<0.02) but proteoglycan deposition per cell was 120% greater for BM-derived cell aggregates as measured by GAG assays (p<0.05).

CONCLUSIONS

The tissue formed by the aggregate culture of the expanded ADPC population was less cartilaginous. It is unclear whether this is because there are fewer chondroprogenitor cells or if the monolayer expansion culture favors cells with higher proliferative rates but without differentiation potential. Under the conditions described in this study, BMPCs may represent a better choice for progenitor cell-based strategies for cartilage repair.

Degenerative disorders of the lumbar and cervical spine

Degenerative disorders in the spine are normal, age-related phenomena and largely asymptomatic in most cases. Conservative management of lumbar and cervical spondylosis is the mainstay of treatment, and most patients with symptomatic degenerative changes respond appropriately with nonsurgical management. Surgical intervention can be considered an appropriate and viable option when conservative measures have failed. Treatment options should always be directed toward the specific nature and location of the patient's individual pathology. Although current standards in the surgical management of lumbar and cervical degenerative disorders include discectomy, neural decompression, and instrumented spinal arthrodesis, new approaches that address this often-challenging clinical entity are on the horizon.

Accuracy and interobserver agreement for determinations of rabbit posterolateral spinal fusion

STUDY DESIGN

The accuracy and interobserver agreement of fine detail radiography and computed tomography (CT) determination of spinal fusion were evaluated in an established animal spine fusion model.

OBJECTIVE

To determine the accuracy and interobserver agreement of radiographic determinations of spinal fusion in rabbit posterolateral spine fusion.

SUMMARY OF BACKGROUND DATA

The rabbit posterolateral intertransverse process spine fusion model is an established animal model for evaluating bone graft alternatives for spinal fusion. However, little is known regarding the accuracy and interobserver agreement of radiographic determinations of spondylodesis in this model.

METHODS

Forty-two New Zealand White rabbits underwent posterolateral spinal fusion. The animals were killed at 9 weeks and the lumbar spine harvested. Manual manipulation, fine detail radiography, and CT images were used to assess spinal fusion.

RESULTS

Using manual palpation testing as the standard by which to assess fusion, there was high sensitivity and negative predictive value for both radiographic methods. Positive predictive value, however, was poor (26% fine detail radiography, 61% CT scan). CT correlated better with manual palpation testing when compared with fine detail radiographs. There was substantial interobserver agreement of successful fusion using CT scan imaging (kappa = 0.63) and moderate interobserver agreement radiographs (kappa = 0.52).

CONCLUSIONS

Both radiographic techniques used in the study recorded high sensitivity and negative predictive value. However, positive predictive value was poor, especially with fine detail radiographs. Nevertheless, CT with reformatted images did appear to be superior to fine detail radiographs in accurately identifying nonunions in this animal model.

Augmentation of rabbit posterolateral spondylodesis using a novel demineralized bone matrix-hyaluronan putty

STUDY DESIGN

Posterolateral spinal fusion with allogeneic demineralized bone graft-hyaluronan putty in addition to autogenous iliac crest bone graft in a rabbit model.

OBJECTIVES

To determine the potential efficacy of demineralized bone graft-hyaluronan putty as a bone graft enhancer.

SUMMARY OF BACKGROUND DATA

Autograft bone is the material of choice for posterolateral lumbar intertransverse process fusion. Bone graft alternatives such as demineralized bone matrices that can be used as graft extenders, enhancers, or substitutes continue to be developed.

METHODS

One hundred New Zealand white rabbits underwent bilateral posterolateral spinal fusion with autogenous iliac crest bone graft or bone graft with allogeneic rabbit demineralized bone graft-hyaluronan putty. The rabbits were killed 9 weeks later, and the lumbar spines were removed. Manual manipulation and fine detail radiography were used to assess spinal fusion, and computed tomographic images were used to quantify the volume of the fusion mass.

RESULTS

In comparison with autograft bone alone, the fusion rates were greater when demineralized bone graft-hyaluronan putty was used as an adjunct to autogenous bone. Furthermore, the radiographic fusion rate was greater when demineralized bone graft-hyaluronan putty was used in a 2:1 ratio to autograft bone in comparison with a 1:1 ratio (P = 0.001). The addition of demineralized bone graft-hyaluronan putty to autograft bone was found to increase mineralized bone volume in a ratio-dependent manner (P < 0.05).

CONCLUSIONS

Allogeneic demineralized bone matrix-hyaluronan putty enhances rabbit posterolateral spine fusion when used as an adjunct to autogenous bone graft. This new formulation of demineralized bone matrix may facilitate greater bone formation and successful fusion.

Cyclic hydrostatic pressure enhances the chondrogenic phenotype of human mesenchymal progenitor cells differentiated in vitro

Much attention has been given to the influences of bioactive factors on mesenchymal progenitor cell differentiation and proliferation, but few studies have examined the effect of mechanical factors on these cells. This study examined the effects of cyclic hydrostatic pressure on human bone marrow-derived mesenchymal progenitor cells undergoing chondrogenic differentiation. Aggregates of bone marrow-derived mesenchymal progenitor cells were cultured in a defined chondrogenic medium and were subjected to cyclic hydrostatic pressure. Aggregates were loaded at various time points: single (day 1 or 3) or multiple (days 1-7). At 14 and 28 days, aggregates were harvested for histology, immunohistochemistry, and quantitative DNA and matrix macromolecule analysis. The aggregates loaded for a single day did not demonstrate significant changes in proteoglycan and collagen contents compared with the non-loaded controls. In contrast, for the multi-day loaded aggregates, statistically significant increases in proteoglycan and collagen contents were found on both day 14 and day 28. Aggregates loaded for seven days were larger and histological staining indicated a greater matrix/cell ratio. This study indicates that hydrostatic pressure enhances the cartilaginous matrix formation of mesenchymal progenitor cells differentiated in vitro, and suggests that mechanical forces may play an important role in cartilage repair and regeneration in vivo.

Pseudoarthrosis of the cervical spine: a comparison of radiographic diagnostic measures

STUDY DESIGN

A retrospective review was conducted.

OBJECTIVE

To compare the accuracy of two objective radiographic techniques in identifying nonunion after anterior cervical discectomy and fusion.

SUMMARY OF BACKGROUND DATA

The accuracy of diagnostic methods for detecting pseudarthrosis has been poorly documented. Radiographic criteria mentioned in the literature include perceived motion or change in the Cobb angles between the involved segments on flexion-extension views.

METHODS

The participants in this study were 27 patients with 29 cervical fusions ranging from one to three levels. Patients were examined and radiographs obtained. The mean follow-up period was 39 months. Two measurements were obtained from lateral flexion-extension radiographs: Cobb angle and the distance between the tips of the spinous processes of the surgically managed levels. The measurements were obtained independently by three physicians in a blinded fashion.

RESULTS

The reliability among the observers, as measured by Cronbach's alpha, was 0.95 for the spinous process method and 0.74 for the Cobb angle method. A measurement of more than 2 mm between spinous processes was noted in patients with a known pseudarthrosis. The Pearson correlation between pseudarthrosis and use of the spinous process method was 0.77 ( < 0.001). The Pearson correlation between pseudarthrosis and use of the Cobb angle method was 0.28 ( > 0.10). The area under the receiver operating characteristic curve for the spinous process method was found to be 0.980, as compared with 0.662 for the Cobb angle method, for the measurement of pseudarthrosis.

CONCLUSIONS

Measurement of the change in distance between spinous processes is more reproducible and accurate than the Cobb method for making the diagnosis of pseudarthrosis. The authors believe that the measurement of distances between spinous processes on lateral flexion-extension radiographs should be used as a method for evaluating radiographic fusion in patients with pseudarthrosis.

Incidence of dysphagia after anterior cervical spine surgery: a prospective study

STUDY DESIGN

A prospective longitudinal study was conducted to evaluate dysphagia after anterior cervical spine surgery.

OBJECTIVES

To evaluate the incidence and natural history of dysphagia after anterior cervical spine surgery, and to identify risk factors for the development of postoperative dysphagia.

SUMMARY OF BACKGROUND DATA

The literature contains only retrospective evaluations of postoperative dysphagia. A wide range of incidence has been reported in these studies.

METHODS

Altogether, 249 consecutive patients undergoing anterior cervical spine surgery were eligible for the study. These patients were contacted 1, 2, 6, and 12 months after the procedure to evaluate swallowing. Risk factors such as age, gender, procedure type, hardware use, and number and location of surgical levels addressed were assessed.

RESULTS

Dysphagia incidences of 50.2%, 32.2%, 17.8%, and 12.5% were found at 1, 2, 6, and 12 months, respectively. At 6 months after the procedure, only 4.8% of the patients were experiencing moderate or severe dysphagia. Patient age, type of procedure (corpectomy vs. discectomy or primary vs. revision), hardware presence, and location of surgical levels were not statistically significant risk factors for the development of postoperative dysphagia. Female gender was significant for increased risk of dysphagia at 6 months. Surgery at multiple disc levels increased the risk of postoperative dysphagia at 1 and 2 months. The etiology of the dysphagia in most of the patients was unknown. However, vocal cord paresis was identified in 1.3% of the patients at 12 months.

CONCLUSIONS

Dysphagia after anterior cervical spine surgery is a common early finding. However, it decreases significantly by 6 months. The minority of patients experience moderate or severe symptoms by 6 months after the procedure. Female gender and multiple surgical levels could be identified as risk factors for the development of postoperative dysphagia.

BMP-2 induction and TGF-beta 1 modulation of rat periosteal cell chondrogenesis

Periosteum contains osteochondral progenitor cells that can differentiate into osteoblasts and chondrocytes during normal bone growth and fracture healing. TGF-beta 1 and BMP-2 have been implicated in the regulation of the chondrogenic differentiation of these cells, but their roles are not fully defined. This study was undertaken to investigate the chondrogenic effects of TGF-beta 1 and BMP-2 on rat periosteum-derived cells during in vitro chondrogenesis in a three-dimensional aggregate culture. RT-PCR analyses for gene expression of cartilage-specific matrix proteins revealed that treatment with BMP-2 alone and combined treatment with TGF-beta 1 and BMP-2 induced time-dependent mRNA expression of aggrecan core protein and type II collagen. At later times in culture, the aggregates treated with BMP-2 exhibited expression of type X collagen and osteocalcin mRNA, which are markers of chondrocyte hypertrophy. Aggregates incubated with both TGF-beta 1 and BMP-2 showed no such expression. Treatment with TGF-beta 1 alone did not lead to the expression of type II or X collagen mRNA, indicating that this factor itself did not independently induce chondrogenesis in rat periosteal cells. These data were consistent with histological and immunohistochemical results. After 14 days in culture, BMP-2-treated aggregates consisted of many hypertrophic chondrocytes within a metachromatic matrix, which was immunoreactive with anti-type II and type X collagen antibodies. In contrast, at 14 days, TGF-beta 1 + BMP-2-treated aggregates did not contain any morphologically identifiable hypertrophic chondrocytes and their abundant extracellular matrix was not immunoreactive to the anti-type X collagen antibody. Expression of BMPR-IA, TGF-beta RI, and TGF-beta RII receptors was detected at all times in each culture condition, indicating that the distinct responses of aggregates to BMP-2, TGF-beta 1 and TGF-beta 1 + BMP-2 were not due to overt differences in receptor expression. Collectively, our results suggest that BMP-2 induces neochondrogenesis of rat periosteum-derived cells, and that TGF-beta 1 modulates the terminal differentiation in BMP-2 induced chondrogenesis.

Tortuous course of the vertebral artery and anterior cervical decompression: a cadaveric and clinical case study

STUDY DESIGN

Both the cadaveric and clinical examples of anomalous vertebral artery courses are described. The incidence of this anomaly in the general population and recognition, complications, and treatment options for these patients when undergoing anterior cervical decompression are discussed.

OBJECTIVES

Cadaveric study: In this study vertebral artery's course through the cervical spine in the adult population was analyzed. The relation between an abnormal vertebral artery course and surgical landmarks are described. Clinical study: Complications and alternative treatment methods for decompression in patients with the anomaly are described.

SUMMARY OF BACKGROUND DATA

The incidence of anomalous vertebral artery course is low, but failure to recognize a medially located vertebral artery may result in a life-threatening iatrogenic injury during decompression. Neither the relation between the vertebral arteries and the surgical landmarks nor the guidelines for decompression in the face of a tortuous vertebral artery have been well described.

METHODS

Transverse foramens of the cervical spine were measured in 222 cadaveric spines. The measurements were taken describing the relation between transverse foramens and other surgical landmarks. Three patients with anomalies were identified in clinical practice. The complications and treatment options are identified in these patients.

RESULTS

In the cadaveric specimens, a 2.7% incidence of tortuous vertebral artery course was identified. In these abnormal specimens, the transverse foramen was located an average of 0.14 mm medial to the joint of Luschka. In one patient, the abnormal course of the vertebral artery was recognized after laceration of the artery during a routine corpectomy. Anomalies in the other two patients were recognized before surgery, and the patients underwent modified anterior decompression by combining a discectomy at the anomalous level with a corpectomy at other levels. Vertebral artery ectasia is identifiable on axial magnetic resonance or computed tomographic images.

CONCLUSIONS

Aberrant vertebral artery is rare. Preoperative recognition and appropriate modification of anterior decompression can yield excellent clinical results without risking significant complications.

Chondrogenitor cells and gene therapy

The development of isolation and culture techniques for mesenchymal progenitor cells from various tissues has promoted interest in the use of these cells for repair and regeneration of musculoskeletal tissues. The chondrogenic differentiation of these pluripotential cells seems to be mediated by numerous cytokines most of which belong to the transforming growth factor-beta superfamily. Strategies to repair articular cartilage have focused on delivery of these cytokines or progenitor cells to the area of damage. More recently, with the development of gene transfer techniques, these cells have become the target of in vivo gene therapy, which involves direct injection of viral and nonviral vectors carrying transgenes. Furthermore, they are viewed as potential carriers of the transgenes for ex vivo gene therapy, in which the gene transfer is done in vitro with culture-expanded cells that then are implanted or injected. In vitro data suggest that the chondrogenic potential of these cells is maintained with virally mediated ex vivo gene transfer. By transducing these cells with chondroinductive factors, the bioactive factors and the target cells are delivered to the repair site.

Hyaluronan-based polymers in the treatment of osteochondral defects

Articular cartilage in adults has limited ability for self-repair. Some methods devised to augment the natural healing response stimulate some regeneration, but the repair is often incomplete and lacks durability. Hyaluronan-based polymers were tested for their ability to enhance the natural healing response. It is hypothesized that hyaluronan-based polymers recreate an embryonic-like milieu where host progenitor cells can regenerate the damaged articular surface and underlying bone. Osteochondral defects were made on the femoral condyles of 4-month-old rabbits and were left empty or filled with hyaluronan-based polymers. The polymers tested were ACP sponge, made of crosslinked hyaluronan, and HYAFF-11 sponge, made of benzylated hyaluronan. The rabbits were killed 4 and 12 weeks after surgery, and the condyles were processed for histology. All 12-week defects were scored with a 29-point scale, and the scores were compared with a Kruskall-Wallis analysis of variance on ranks. Untreated defects filled with bone tissue up to or beyond the tidemark, and the noncalcified surface layer varied from fibrous to hyaline-like tissue. Four weeks after surgery, defects treated with ACP exhibited bone filling to the level of the tidemark and the surface layer was composed of hyaline-like cartilage well integrated with the adjacent cartilage. At 12 weeks, the specimens had bone beyond the tidemark that was covered with a thin layer of hyaline cartilage. Four weeks after surgery, defects treated with HYAFF-11 contained a rim of chondrogenic cells at the interface of the implant and the host tissue. In general, the 12-week defects exhibited good bone fill and the surface was mainly hyaline cartilage. Treated defects received significantly higher scores than untreated defects (p < 0.05), and ACP-treated defects scored significantly higher than HYAFF-11-treated defects (p < 0.05). The introduction of these hyaluronan-based polymers into defects provides an appropriate scaffolding and favorable microenvironment for the reparative process. Further work is required to fully assess the long-term outcome of defects treated with these polymers.

Morphologic considerations of C2 isthmus dimensions for the placement of transarticular screws

STUDY DESIGN

This study examines the C2 vertebrae using both direct anatomic and computed tomographic measurements.

OBJECTIVE

To define the relation of the C2 vertebrae bony elements to the vertebral artery and the spinal canal, to determine individuals at risk for vertebral artery injury during C1-C2 transarticular screw placement.

SUMMARY OF BACKGROUND DATA

Recent literature assessing the safety of upper cervical spine transarticular screws has concentrated on technique, including the optimal point of entry and path projection of the screw. The actual dimensions of the C2 isthmus of the pars interarticularis has not been examined in a large number of specimens.

METHODS

C2 isthmus width and height measurements were made on 205 human cadaveric C2 vertebrae. Vertebrae predicted to be at risk for vertebral arterial injury were imaged by computed tomography.

RESULTS

There were 102 female and 103 male specimens with mean isthmus widths of 8.2 +/- 1.5 mm and 7.2 +/- 1.3 mm, respectively. Five specimens (2.4%) had an isthmus width less than 5 mm. The mean isthmus heights were 8.6 +/- 2.0 mm and 6.9 +/- 1.5 mm for male and female specimens, respectively. In twenty-four specimens (11.7%), one or both isthmi had a height of less than 5 mm. Six of these specimens were male and 18 were female. The right C2 isthmus was generally smaller than the left. Computed tomographic measurements closely approximated those of the actual dimensions of the isthmi.

CONCLUSIONS

Placing a 3.5 mm screw in a patient with narrow C2 isthmus dimensions (smaller than 5 mm in either the height or width) is technically difficult. Because of narrow C2 isthmus width and/or height, approximately 10% of patients may be at risk for a vertebral artery injury with placement of C1-C2 transarticular screws.

Chondroprogenitor cells of synovial tissue

OBJECTIVE

To assess the chondrogenic potential of cells within the synovium.

METHODS

Explants of synovium taken from various sites in the joint were embedded in agarose and cultured with transforming growth factor beta1 (TGFbeta1) to assess their chondrogenic potential. Isolated synovial cells were also tested for their chondrogenic potential by culturing them as aggregates in a chemically defined medium with TGFbeta1. Cartilage formation was determined with histologic staining and immunohistochemistry. The osteochondral potential of the isolated cells was also assessed after subcutaneous implantation of the cells, loaded into porous calcium phosphate ceramic cubes, in athymic mice.

RESULTS

A total of 48 synovial explants were cultured in agarose with TGFbeta1. The formation of cartilage was observed in the outer region of 21 explants, and type II collagen was localized in that region by immunohistochemistry. A larger percentage of TGFbeta1+ explants from the inner synovium sites formed cartilage compared with those from the outer synovium sites. Chondrogenesis occurred in aggregates incubated with TGFbeta1 as early as day 7, and by day 14, all TGFbeta1+ aggregates demonstrated chondrogenesis. In contrast with the results of the in vitro aggregate assay for chondrogenesis, no formation of cartilage or bone was evident in any section containing synovial cell-loaded ceramic cubes that were harvested at either 3 or 6 weeks after implantation subcutaneously in athymic mice.

CONCLUSION

Synovial explants and isolated synovial cells will undergo chondrogenesis when cultured in the presence of TGFbeta1. The data indicate a possible synovial origin for the chondrocytic cells found in rheumatoid pannus. Furthermore, these data are consistent with the clinical findings of synovial chondrogenesis leading to synovial chondromatosis.

Autologous mesenchymal progenitor cells in articular cartilage repair

The lack of repair of articular cartilage where the damage does not penetrate the subchondral bone indicates the importance of marrow components in the repair of the articular cartilage. In adult animals, there is an inability of articular cartilage chondrocytes to heal chondral defects, but if the damage extends beyond the subchondral bone, a repair process ensues in which mesenchymal progenitor cells migrate into the injured site and undergo chondrogenic differentiation. However, analysis of animal models and human biopsy samples indicates that fibrocartilage, rather than true articular cartilage is the predominant tissue synthesized. To improve this outcome, the use of cell based implants of culture expanded progenitor cells from various sources has been proposed and attempted. This paper describes some of the age related differences in the natural repair of osteochondral defects, the in vitro characterization of the chondrogenic potential of certain mesenchymal cell types, and some of the characteristics required of cell and matrix constructs that may be used for repair or regeneration of articular cartilage.

High variability in rabbit bone marrow-derived mesenchymal cell preparations

The rabbit has been extensively used for preclinical models, especially in orthopedic applications. One of the more troubling features of this model is the high interindividual variability that is encountered and that requires a careful experimental design with sufficient sample size to make judgments valid. We have processed 241 individual preparations of rabbit bone marrow-derived mesenchymal progenitor cells (MPCs) over the last 3 years and have kept detailed records of the performance of these cells in various assays. This communication details the lack of correlation between the analyzed parameters. Bone marrow was harvested from 4-month-old rabbits; the cells were centrifuged, resuspended, and cultured. When cells reached 80% of confluence, they were removed from the plates with trypsin and assayed for their osteo- and chondrogenic potential. The average yield of the 241 individual MPC preparations exhibited a coefficient of variation of 77. An in vivo implantation assay with porous calcium phosphate ceramic cubes exhibited scores with a coefficient of variation of 65. Lastly, an in vitro assay of alkaline phosphatase enzyme activity exhibited the most variability with a coefficient of variation of 132. All of the cell preparations tested in an in vitro aggregate culture assay underwent chondrogenic differentiation. No relationships between any of these parameters were found. The variability of the results within the different assays is interpreted to be the result of the heterogeneity of the preparations. The lack of correlation between the parameters studied shows the importance of the conditions intrinsic to the different assays. These results serve to emphasize that any experimental design involving rabbit progenitor cells must include a sufficiently large sample size to allow statistically significant and rigorous conclusions.

A quadripotential mesenchymal progenitor cell isolated from the marrow of an adult mouse

Adult marrow contains mesenchymal progenitor cells (MPCs) that have multiple differentiation potentials. A conditionally immortalized MPC clone, BMC9, has been identified that exhibits four mesenchymal cell phenotypes: chondrocyte, adipocyte, stromal (support osteoclast formation), and osteoblast. The BMC9 clone, control brain fibroblasts and another marrow-derived clone, BMC10, were isolated from a transgenic mouse (H-2Kb-tsA58) containing a gene for conditional immortality. To test for chondrogenic potential, cells were cultured in defined medium containing 10 ng/ml transforming growth factor beta and 10-7 M dexamethasone in 15-ml polypropylene tubes ("aggregate cultures"). Adipogenic potential was quantitated by flow cytometry of Nile Red-stained cells cultured for 1 and 2 weeks in medium containing isobutyl methylxanthine, indomethacin, insulin, and dexamethasone. Support of osteoclast formation was measured by quantitating multinucleated tartrate-resistant acid phosphatase-positive cells in spleen cell cocultures of test clones (immortomouse clones and positive control ST2 cells) cultured in the presence of 10-7 M vitamin D3 and 150 mM ascorbate-2-phosphate. In vivo osteogenic potential was assayed by histologic examination of bone formation in subcutaneous implants, into athymic mouse hosts, of a composite of cells combined with porous calcium phosphate ceramics. The bone marrow-derived clone BMC9 has the potential to express each of the four mesenchymal characteristics tested, while brain fibroblasts, tested under identical conditions, did not exhibit any of these four mesenchymal characteristics. BMC10 cells exhibited osteogenic and chondrogenic phenotypes, but showed only minimal expression of adipocytic or osteoclast-supportive phenotypes. Clone BMC9 is, minimally, a quadripotential MPC isolated from the marrow of an adult mouse that can differentiate into cartilage and adipose, support osteoclast formation, and form bone. The BMC9 clone is an example of an adult-derived multipotential progenitor cell that is situated early in the mesenchymal lineage.