R. Todd Allen

Prolonged Storage Effects on the Articular Cartilage of Fresh Human Osteochondral Allografts

BACKGROUND Fresh osteochondral allograft transplantation is a well-established technique for the treatment of cartilage defects of the knee. It is believed that the basic paradigm of the technique is that the transplantation of viable chondrocytes maintains the articular cartilage matrix over time. Allograft tissue is typically transplanted up to forty-two days after the death of the donor, but it is unknown how the conditions and duration of storage affect the properties of fresh human osteochondral allografts. This study examined the quality of human allograft cartilage as a function of storage for a duration of one, seven, fourteen, and twenty-eight days. We hypothesized that chondrocyte viability, chondrocyte metabolic activity, and the biochemical and biomechanical properties of articular cartilage would remain unchanged after storage for twenty-eight days. METHODS Sixty osteochondral plugs were harvested from ten fresh human femoral condyles within forty-eight hours after the death of the donor and were stored in culture medium at 4 degrees C. At one, seven, fourteen, and twenty-eight days after harvest, the osteochondral plugs were analyzed for (1) viability and viable cell density by confocal microscopy, (2) proteoglycan synthesis by quantification of (35)SO(4) incorporation, (3) glycosaminoglycan content, (4) indentation stiffness, (5) compressive modulus and hydraulic permeability by static and dynamic compression testing, and (6) tensile modulus by equilibrium tensile testing. RESULTS Chondrocyte viability and viable cell density remained unchanged after storage for seven and fourteen days (p > 0.7) and then declined at twenty-eight days (p < 0.001). Proteoglycan synthesis remained unchanged at seven days (p > 0.1) and then declined at fourteen days (p < 0.01) and twenty-eight days (p < 0.001). No significant differences were detected in glycosaminoglycan content (p > 0.8), indentation stiffness (p > 0.4), compressive modulus (p > 0.05), permeability (p > 0.3), or equilibrium tensile modulus after storage for twenty-eight days (p > 0.9). CONCLUSIONS These data demonstrate that fresh human osteochondral allograft tissue stored for more than fourteen days undergoes significant decreases in chondrocyte viability, viable cell density, and metabolic activity, with preservation of glycosaminoglycan content and biomechanical properties. The cartilage matrix is preserved during storage for twenty-eight days, but the chondrocytes necessary to maintain the matrix after transplantation decreased over that time-period.

Minimally Invasive Spine Surgery

Paul C. McAfee, MD, MBA, Frank M. Phillips, MD, Gunnar Andersson, MD, PhD, Asokumar Buvenenadran, MD, Choll W. Kim, MD, Carl Lauryssen, MD, Robert E. Isaacs, MD, Jim A. Youssef, MD, Darrel S. Brodke, MD, Andrew Cappuccino, MD, Behrooz A. Akbarnia, MD, Gregory M. Mundis, MD, William D. Smith, MD, Juan S. Uribe, MD, Steve Garfin, MD, R. Todd Allen, MD, William Blake Rodgers, MD, Luiz Pimenta, MD, PhD, and William Taylor, MD

Analysis of Stored Osteochondral Allografts at the Time of Surgical Implantation

Background To date, the morphological, biochemical, and biomechanical characteristics of articular cartilage in osteochondral allografts that have been stored have not been fully described. Hypothesis Osteochondral allografts procured and stored commercially for a standard period as determined by tissue banking protocol will have compromised chondrocyte viability but preserved extracellular matrix quality. Study Design Controlled laboratory study. Methods Unused cartilage from 16 consecutive osteochondral allografts was sampled during surgery after tissue bank processing and storage. Ten grafts were examined for cell viability and viable cell density using confocal microscopy, proteoglycan synthesis via 35SO4 uptake, and glycosaminoglycan content and compared with fresh cadaveric articular cartilage. Biomechanical assessment was performed on the 6 remaining grafts by measuring the indentation stiffness of the cartilage. Results The mean storage time for the transplanted specimens was 20.3 ± 2.9 days. Chondrocyte viability, viable cell density, and 35SO4 uptake were significantly lower in allografts at implantation when compared to fresh, unstored controls, whereas matrix characteristics, specifically glycosaminoglycan content and biomechanical measures, were unchanged. In addition, chondrocyte viability in the stored allografts was preferentially decreased in the superficial zone of cartilage. Conclusion Human osteochondral allografts stored for a standard period (approximately 3 weeks) before implantation undergo decreases in cell viability, especially in the critically important superficial zone, as well as in cell density and metabolic activity, whereas matrix and biomechanical characteristics appear conserved. The exact clinical significance of these findings, however, is unknown, as there are no prospective studies examining clinical outcomes using grafts stored for extended periods. Clinical Relevance Surgeons who perform this procedure should understand the cartilage characteristics of the graft after 21 days of commercial storage in serum-free media.

Analysis of Cartilage Tissue on a Cellular Level in Fresh Osteochondral Allograft Retrievals

Background Fresh human osteochondral allografting is a biological cartilage replacement technique used to treat articular and osteoarticular defects in the knee. A small number of grafts fail, and we analyzed every retrieved graft during a 4-year period in order to learn more about the potential causes of failure. Hypothesis A large percentage of chondrocytes still remain viable many years after fresh osteochondral allografting. Study Design Descriptive laboratory study. Methods Retrieval specimens were obtained at the time of revision surgery and immediately analyzed. Chondrocyte viability and viable cell density were determined using a live/dead staining technique followed by confocal microscopy. Glycosaminoglycan content was a measure of the cartilage matrix. Radiolabeled sulfate uptake served as a biochemical marker of chondrocyte metabolic activity. Cartilage and subchondral bone were examined histologically. Results Fourteen patients yielded a total of 26 retrieval specimens that had been originally implanted as individual fresh osteochondral allografts. Average graft survival was 42 months. Chondrocyte viability was 82% ± 17%, and chondrocyte viable cell density was 15 590 ± 5900 viable cells/mm3. Retrieved tissue demonstrated radiolabeled sulfate uptake of 437 ± 270 counts per minute and 3.5% ± 0.8% hexosamine per dry weight. Histologically, all specimens showed some degree of cartilage fibrillation. There was evidence of bone allograft incorporation in most specimens, as well as pannus formation in 4 specimens, but no evidence of immune rejection. Conclusion A small percentage of fresh osteochondral allografts fail, but the precise cause is unknown. The main theories for failure investigated here include immunologic rejection, failure of bony incorporation, and chondrocyte death causing breakdown of the cartilage matrix. We show that chondrocytes remain viable many years after transplantation, allograft bone incorporates, and immune rejection does not seem to play a primary role in failure. Clinical Relevance Fresh osteochondral allografting is becoming more common in the treatment of articular cartilage defects in the knee. Our findings support the paradigm of fresh osteochondral allografting, the transplantation of hyaline cartilage with biological incorporation of the underlying bone scaffold. The reasons for failure of a small percentage of grafts remain unclear.

Bone Morphogenetic Protein-2 (BMP-2) in the Treatment of Pyogenic Vertebral Osteomyelitis

Study Design. Retrospective case series. Objective. To present results of recombinant human bone morphogenetic protein-2 (rhBMP-2) use in medically nonresponsive pyogenic vertebral osteomyelitis (PVO), treated by anterior/posterior debridement and instrumented fusion in the cervical, thoracic, and lumbosacral spine. Summary of Background Data. Surgical options for PVO vary, as do their outcomes, and can be complicated by recurrence, pseudarthrosis, and death. Although rhBMP-2 use in spinal fusion is increasing, its utility in PVO is unknown. Additionally, use in areas of infection is listed as a contraindication, although this is not supported by laboratory (animal) studies or clinical studies in long bones. Methods. Between 2003 and 2005, 14 patients who underwent circumferential fusion for PVO were included in this study. Average patient age was 54 years (range, 27–77 years). Eight (57%) patients had 3 or more vertebral bodies involved. Diagnostic studies included radiographs, CT, MRI, and markers of infection [(C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), white blood count (WBC)]. All patients underwent anterior fusion with rhBMP-2 inserted in structural allograft (11 patients) or titanium cylindrical cages (3 patients), followed by posterior instrumented fusion with autogenous iliac crest graft (8 occurring on the same day). Follow-up averaged 22 months (range, 11–30 months). All were studied with plain radiographs, including flexion-extension lateral films and fine cut CT scans with reconstruction. Pain ratings were recorded by visual analog scores (VAS). Results. Clinical resolution of infections, normalization of lab values, and bony fusion, based on dynamic radiographs and CT scans, were seen in all patients at latest follow-up. Staphylococcus aureus was the most frequently identified organism (8 patients). Four (29%) patients had positive blood cultures (all MRSA). Predisposing comorbidities were present in 12 patients. Six patients had epidural abscesses. Eight (57%) patients presented with neurologic deficits, ranging from paraparesis to quadriplegia. Complete recovery was seen in 7 (quadriplegia unchanged). At 1 year, mean VAS pain scores improved significantly (P < 0.05) from 7.9 (range, 3–10) to 2.8 (range, 0–6). Perioperative complications (non-BMP related) occurred in 2 patients. There were no surgically-related deaths. Conclusion. rhBMP-2 use, in combination with antibiotics and circumferential instrumented fusion, provides a safe and successful surgical treatment of medically nonresponsive PVO, with solid fusions obtained, good clinical results, and no adverse side effects from the BMP.

The Economics of Minimally Invasive Spine Surgery: The Value Perspective

Study Design. Review of the literature. Objective. To summarize current cost and clinical efficacy data in minimally invasive spine (MIS) surgery. Summary of Background Data. Cost effectiveness (CE), using cost per quality-adjusted life-years gained, has been shown for lumbar discectomy, decompressive laminectomy, and for instrumented and noninstrumented lumbar fusions in several high-quality studies using conventional, open surgical procedures. Currently, comparisons of costs and clinical outcomes of MIS surgery to open (or nonoperative) approaches are rare and of lesser quality, but suggest that a potential for cost benefits exist using less-invasive surgical approaches. Methods. A literature review was performed using the database of the National Center for Biotechnology Information (NCBI), PUBMED/Medline. Results. Reports of clinical results of MIS approaches are far more common than economic evaluations. MIS techniques can be classified as endoscopic or nonendoscopic. Although endoscopic approaches decrease some approach morbidities, the high cost of instrumentation, steep learning curves, and new complication profiles introduced have prevented widespread adoption. Additionally, the high costs have not been shown to be justified by superior clinical benefits. Nonendoscopic MIS approaches, such as percutaneous posterior or lateral, and mini-open lateral and anterior approaches, use direct visualization, standard operative techniques, and report lower complication rates, reduced length of stay, and faster recovery time. For newer MIS and mini-open techniques, significantly lower acute and subacute costs were observed compared with open techniques, mainly due to lower rates of complications, shorter length of stay, and less blood loss, as well as fewer discharges to rehab. Although this suggests that certain MIS procedures produce early cost benefits, the quality of the existing data are low. Conclusion. Although the CE of MIS surgery is yet to be carefully studied, the few economic studies that do exist suggest that MIS has the potential to be a cost-effective intervention, but only if improved clinical outcomes are maintained (durable). Longer follow-up and better outcome and cost data are needed to determine if incremental CE exists with MIS techniques, versus open or nonsurgical interventions.

Chondrocyte viability after intra-articular calcaneal fractures in humans

Background: Chondral damage from the impact of injury may contribute to the high incidence of post-traumatic arthritis after calcaneal fractures, but this has yet to be proven. We sought to study the effect of intra-articular calcaneal fractures on chondrocyte viability and to correlate these effects with injury severity, time from injury to surgery, and patient age and co-morbidities. Methods: Irreducible osteochondral fragments from 12 patients undergoing operative treatment for intra-articular calcaneal fractures were analyzed. Control cartilage was obtained from four tissue donors who died of unrelated causes. The cartilage was assessed for chondrocyte viability through the full thickness of tissue using a Live/Dead assay followed by laser scanning confocal microscopy. Patient demographics including injury classification and severity, time from injury to surgery, and patient age were recorded. Results: Chondrocyte viability from fracture patients averaged 72.8% ± 12.9% (range 53% to 95%), which was significantly lower than the 94.8% ± 1.5% viability observed in the control specimens (p = 0.005). Chondrocyte viability declined with higher energy injuries (p = 0.13), time from injury to surgery (p = 0.07), and increasing patient age (p = 0.07). However, none of these factors reached a level of statistical significance. Conclusions: A significant decline in chondrocyte viability occurs after intra-articular fractures of the calcaneus. This may contribute to the development of post-traumatic arthritis.

An Evidence-Based Approach to Spine Surgery:

Health care reform will emphasize evidence-based medicine to provide the highest quality care. Recent literature has emerged in spinal surgery that has profoundly increased the evidence base for several spinal procedures. There is now good evidence from randomized controlled trials that surgical treatment of symptomatic lumbar disc herniation, decompression for spinal stenosis, and decompression and fusion for degenerative spondylolisthesis all offer significant clinical benefit in the face of serious back and radicular pain when compared with nonsurgical care. Studies of nonsurgical and surgical treatments for chronic low back pain are inconclusive, limited by study design/methodology. Continuing to increase study quality in the field of spine surgery is more important now than ever before. Optimizing diagnostic specificity, surgical indications, and measuring outcomes with validated instruments should help the spine care community acquire essential data to provide the highest quality evidence-based care, while simultaneously eliminating procedures that lack evidence of efficacy or value.

Upregulation of apoptotic and matrix-related gene expression during fresh osteochondral allograft storage.

We identified changes in proapoptotic and extracellular matrix-related gene expression with prolonged storage of fresh osteochondral allografts using gene array analysis to better understand the process of graft degradation during storage. Six human distal femurs were obtained according to standard organ harvesting protocol and stored in serum-free allograft media. Each was examined at baseline (within 72 hours postmortem), 21 days (average time of implantation), and 35 days (maximum time to implantation) for proapoptotic and extracellular matrix-related gene expression using two 100-gene microarrays, cell viability using confocal microscopy, and proteoglycan synthesis via 35SO4 incorporation. We found numerous genes showing upregulation associated with increased storage time, including CD30, CD30 ligand, Fas, Fas ligand, tumor necrosis factor-α, and several caspases. Cell viability and proteoglycan synthesis also were significantly decreased with increased storage. Loss of chondrocytes via apoptosis is likely a key determinant of osteochondral allograft viability during storage, whereas extracellular matrix degeneration may occur at a later stage. These findings provide targets for future media modulation. Improved graft viability and the potential for lengthened storage periods through improved storage conditions may improve clinical outcomes and availability of fresh osteochondral allografts.

Contribution of Lumbar Spine Pathology and Age to Paraspinal Muscle Size and Fatty Infiltration

Study Design. Retrospective chart analysis of 199 individuals aged 18 to 80 years scheduled for lumbar spine surgery. Objective. The purpose of this study was to quantify changes in muscle cross-sectional area (CSA) and fat signal fraction (FSF) with age in men and women with lumbar spine pathology and compare them to published normative data. Summary of Background Data. Pathological changes in lumbar paraspinal muscle are often confounded by age-related decline in muscle size (CSA) and quality (fatty infiltration). Individuals with pathology have been shown to have decreased CSA and fatty infiltration of both the multifidus and erector spinae muscles, but the magnitude of these changes in the context of normal aging is unknown. Methods. Individuals aged 18 to 80 years who were scheduled for lumbar surgery for diagnoses associated with lumbar spine pain or pathology were included. Muscle CSA and FSF of the multifidus and erector spinae were measured from preoperative T2-weighted magnetic resonance images at the L4 level. Univariate and multiple linear regression analyses were performed for each outcome using age and sex as predictor variables. Statistical comparisons of univariate regression parameters (slope and intercept) to published normative data were also performed. Results. There was no change in CSA with age in either sex (P > 0.05), but women had lower CSAs than men in both muscles (P < 0.0001). There was an increase in FSF with age in erector spinae and multifidus muscles in both sexes (P < 0.0001). Multifidus FSF values were higher in women with lumbar spine pathology than published values for healthy controls (P = 0.03), and slopes tended to be steeper with pathology for both muscles in women (P < 0.08) but not in men (P > 0.31). Conclusion. Lumbar muscle fat content, but not CSA, changes with age in individuals with pathology. In women, this increase is more profound than age-related increases in healthy individuals. Level of Evidence: 3