Trends in Spine Care

Bone Graft Substitutes and Enhancers
The quest for improved fusion rates and sparing the morbidity from bone donor sites has prompted exploration of bone graft alternatives and graft extenders. Non-bone materials such as hydroxyapatite are used as bone graft extenders. They have osteoconductive properties because of their porous features.

Demineralized bone matrix (DBM) is derived from processed allograft bone, and comes in many forms, including gels, putty, pellets, and sheets. DBM has mainly osteoconductive properties, but because it contains some proteins and other factors, it is also weakly osteoinductive.

Platelet-derived growth factors are substances concentrated from peripheral blood that have been found to enhance bone healing at many stages. Platelet-derived growth factors are mainly osteoconductive, and possess weak osteoinductive properties. Blood is drawn from the patient, the plasma component is concentrated, and the concentrate is mixed with autogenous bone graft.

Bone morphogenetic proteins (BMPs) are powerful osteoinductive growth factors that have been isolated from bone tissue. They stimulate new bone growth by recruiting stem cells to the area, promoting angiogenesis, and differentiating stem cells into new bone cells. (163) There are many BMPs and a few show particular promise in spinal fusion applications. Scientists are still determining the type and amount that best stimulates fusion for different uses (e.g., intertransverse fusions, interbody fusions with cages). (164-167)

BMP is now FDA-approved for use in certain lumbar interbody cages. Preliminary research results suggest that the use of BMP could eliminate the need for autologous bone graft completely. (168) Osteoinductive agents also show promise in overcoming the deleterious effects of nicotine use. (169,170) However, the cost of BMP is a barrier.

Gene Therapy
Gene therapy is being explored in the treatment or prevention of many disorders. DNA is altered to 'program' cells to perform or grow in the desired way to change the course of a disease or to prevent its development or progression. Spine research is beginning to focus on actually preventing the degeneration of the intervertebral disc. Local gene therapy is the direct delivery of genes to the site being treated. Discs are the ideal target for gene therapy, because the encapsulated nature of the disc helps maintain high intradiscal concentrations of the genes. The location also protects the locally delivered genes from the body's own immune surveillance system. (171) In one study, nucleus pulposus cells in vitro responded to gene therapy by producing more proteoglycan molecules, which are involved in maintaining structural integrity of the disc. (172)

Intradiscal Electrothermal Annuloplasty (IDET)
Intradiscal Electrothermal Annuloplasty (IDET) has been developed in the last several years as a treatment for discogenic back pain. A thermal catheter is introduced anteriorly into the disc annulus and advanced posteriorly in order to heat the entire posterior annulus. (173) By heating the annulus, the collagen is altered and nociceptive fibers are destroyed, with the goal of reducing pain from the disc. Two-year follow-up data suggest this may be a viable treatment option. At this writing, no randomized prospective double-blind placebo controlled data are available, although a study is underway. (174)

Vertebroplasty and Kyphoplasty
Vertebroplasty is a procedure that has been developed to reduce the pain associated with osteoporotic vertebral compression fractures (and some tumors) and stabilize the affected vertebra. Polymethylmethacrylate (a bone cement) is injected into the affected vertebral body. (175,176) Cement leakage has been problematic, however, leading to rare complications of pulmonary embolism, spinal cord compromise, and radiculopathy. (177)

Kyphoplasty is a newer procedure that uses an inflatable bone tamp to elevate the endplate of the compressed vertebra to restore vertebral height. By compacting the cancellous bone to the periphery, the injected methylmethacrylate is better contained and prevents leakage outside the vertebral body. (178)

Nucleoplasty
Nucleoplasty is a minimally invasive procedure for treating some lumbar disc herniations. Under fluoroscopy, a needle is placed into the disc. Radiofrequencies and thermal energy are used to ablate and coagulate tissue, decompressing the disc. No long-term studies evaluating its effects over time were found in a search of the literature. This procedure may be more effective in younger subjects without significant disc degeneration. In a cadaver study, this technique produced markedly reduced intradiscal pressures in a younger, healthy disc. However, in the older, degenerative disc cadavers, the reduction in intradiscal pressure was very small. (179)

Endoscopic Spine Surgery
Endoscopic techniques for various spine surgical procedures have been developed over the years, in an effort to reduce cost, limit complications and morbidity, and shorten hospital stays.

Percutaneous discectomy procedures allow the surgeon to treat disc herniation through an endoscope, thus sparing the posterior musculature from stripping involved in the traditional open approach. Disadvantages of this technique include limited visibility, a steep learning curve to master the technique and instrument use, and patient exposure to radiation from the intra-operative x-ray used to guide the instruments.

Anterior fusions of the thoracic and lumbar spine are being performed by thoracoscopic and laparoscopic approaches respectively. (180-182)

Video-assisted thoracic surgery (VATS) techniques are also being used for vertebral biopsy, abscess drainage, and discectomy.

Advantages of the VATS approach for thoracic fusions include avoidance of a painful thoracotomy incision, decreased blood loss, ability to address high thoracic targets, improved post-operative pulmonary function, a better cosmetic result (small portal incisions versus a large thoracotomy incision), and shorter hospital stay. (180)

Disadvantages of VATS include a steep learning curve to master the technique and instrument use, potential for not achieving a complete discectomy and endplate decortication necessary to promote fusion, and lack of instrumentation systems specifically developed for use with this approach. (180)

The laparoscopic approach to lumbar fusion allows access to L4-5 and L5-S1, and can be utilized to address painful disc degeneration, or a previously failed attempt at posterior fusion. (181) The laparascopic approach avoids trauma to posterior paraspinal muscles, dural tears, traction on nerve roots, and epidural scarring. Disadvantages of this technique include the inability to fully decompress the spinal canal, as may be required in stenosis or disc herniation. In a study comparing outcomes for laparoscopic interbody fusion with threaded cages to an open approach, the laparoscopic technique was associated with lower blood loss, increased operative time, similar intra-operative complication rates, and higher re-operation rates (for intra-operative disc herniations). (182)

It is clear that these techniques, though promising, require a high level of surgeon and operative team commitment in order to offer real benefit to patients.