In 1911 the first “feathered fusion” was performed by Russell Hibbs. He used local autologous bone (not from the ileum) for the purpose of spine stabilization. This concept of utilizing autologous local tissue for reconstructive purposes has been widely utilized in specialties such as plastic surgery but, to-date, have been underutilized in spine surgery. Reconstructive spine surgery represents a more modern and refined application of the Hibbs “feathered fusion” technique. Inherent in advanced non-rigid applications are the use of modern bone mills, inert and biocompatible bone extenders, autologous tissue grafts and the use of stem cells as well as external bone growth stimulators designed to enhance the osteogenic process particularly in the promotion of motion preserving spine stabilization surgery. The concepts are the basis of modern Restorative Spine Surgery.
Should one care to examine the state of present rigid spine fixation from the biomechanical perspective it is clear that it is associated with a host of important liabilities. These problems are only magnified when rigid fixation (of any type) is applied in the treatment of patients with multi-level degenerative changes. This becomes particularly true when rigid fixation is used in the surgical management of genomic disorders which can be diagnosed from a MRI examination alone. In fact, the application of rigid fixation, in such cases, can be a ill-advised treatment as it often creates more problems for the patient than it solves by placing inordinate stress on adjacent (abnormal) spine segments as well as structures such as the pelvis.
As we enter the 21st century it is evident that a careful re-examination of the entire subject of spine stabilization is required as well as a need to focus attention on more physiologic and rational paradigms of thought in spine surgery.
Unfortunately when a surgeon mentions the word “fusion” they are typically referring to rigid instrumented (often multi-level pedicle screw and rod instrumentation) as being representative of all means of achieving acute mechanical spine stabilization. This often means that the patient is not made aware of other treatment options. Under such circumstances it is clear that true informed consent has not been provided and does not exist.
In the 1970s the Editor of Burton Report began the laboratory testing of alternative rigid fusion devices. This entailed the design of metallic and non-metallic flexible stabilization systems as well as studying alternatives to the harvest of bone from a patient’s pelvis. Because the ilial graft site has long been the notorious cause of continued donor site pain and disability and, in some cases, intractable pain secondary to local neuroma formation, autologous bone graft obtained from the primary operative field (in most cases usually discarded) was selected as the best possible source of autologous bone tissue.
Laminectomized bone is normally removed for the process of obtaining decompression and operative exposure and is then typically, discarded. The bone removed (i.e. dorsal processes, lamina and articular facets) represents a significant volume of valuable autologous cortico-cancellous tissue. Autologous tissue represents the very best in transplant material for any patient. Local autogenous bone has consistently been a underutilized surgical resource in spine surgery.
Advances in the utilization of autologous tissues have been common in restorative plastic surgery but not in spine surgery. Shown above is the bone processor invented by Paul Tessier, the pioneering French plastic surgeon, who initiated the modern era of cranio-facial reconstructive surgery. This has been key in the milling of autologous bone for use in spinal surgery.
Carefully harvested autogenous cortico-cancellous bone from the primary operative site is shown here after bone mill processing. The advantages of autologous bone are many and include safety, ready availability, and low cost. Some of the many advantages of autogenous milled bone include it’s ability to be utilized with other autologous tissues such as bone marrow and fat grafts which allow separation of the milled bone from contact with meninges and nerve elements. The use of such an important natural resource as autologous local bone almost seems out of place in a world where exorbitant pricing for surgical implants and biomaterials appears to be the norm.
Once autogenous bone has been fully processed its osteogenic properties can be enhanced. Some enhancers to osteogenesis, are bone morphogenic protein (BMP), which has been extensively marketed A but has been shown to have many potential liabilities. At it’s initial commercial introduction a single vial of BMP typically costed about $5,000. Less expensive, and more effective means of enhancing osteogenesis, is autologous bone marrow (another natural resource) which continues to show promise in serving as a source of stem cells for a variety of clinical applications including transformation into muscle and blood vessels. Shown to the left is a disposable aspiration needle used to draw marrow from the ileum. Continuing research in bone physiology makes clear that the patient’s own bone marrow not only represents an excellent source of stem cells to “jump start” local bone growth but actually contains BMP as well. Bone growth depends directly on a neo-vascular network of nutrient blood vessels being established. It is now well known that this process is seriously impaired by carbon monoxide and nicotine being present in the blood stream from cigarette smoking.
The Burton Experience of over a quarter century utilizing autologous fat grafts on a regular basis to avoid excessive post-surgical epidural fibrosis has led to the appreciation that milled bone could be readily placed around these grafts (thus separating the milled bone from the neural structures) to form non-rigid posterior arthrodesis.
Fat grafts, in addition to serving as another protective barrier for spinal contents have a number of additional post-surgical benefits. Note that lateral fat grafts are placed before dorsal grafts to provide some “buttressing” to avoid dural compression. Once again, for those possessing some degree of cost consciousness, “the price is right” for autogenous fat (similar to the price of autologous milled bone) and thus consistent with William of Occam’s Razor.
Shown to the left is an illustration of a surgical decompression which has been carried out from the L3 level to the sacrum. Autogenous fat (yellow) has been harvested and placed, for protective purposes, over the exposed nerve roots and dura . The stippled area shows the punctuate decortication created from the lamina and facets of L3 to the sacral ala. The sacrum also serves as the base of the autogenous bone which will “mold” around the fat grafts to produce a posterior arthrodesis.
In this photograph the milled bone has been place around the fat graft. A dorso-lateral (or dorsal) non-instrumented non-rigid arthrodesis for the purpose of stabilization has thusly been created. This approach serves as a more physiologic means of restoration normal spine function. In cases where the harvested bone is insufficient additional volume extenders can be utilized.
The Burton Experience has demonstrated that there is a great variability among extenders with some, possessing non-physiologic pHs causing hemolysis, and, as such, likely adding to fusion failure rather than enhancement. It is now clear that potentiating extender substances can be of significant value to autogenous milled cortico-cancellous bone.
The Functional Restoration Of Spine Stability
Non-rigid posterior arthrodeses have the capability of absorbing energy and thus producing less direct stress and loading on adjacent vertebral segments. The concept is demonstrated on the left. A posterior arthrodesis techniqe imployed
in this manner has been effectively employed in stabilizing spines with multi-level degeneration or simply used as “shock absorbers” above or below rigid fusions. These techniques are representative of the advanced paradigms inherent in restorative spine surgery.
As the geriatric population rapidly increases, and as we become wiser in recognizing and understanding genomic entities such as juvenile discogenic disease, non-rigid stabilizations are needed need to replace the ill-advised rigid instrumented stabilizations now being applied in the treatment of multi-level degenerative disease and avoid the serious problems resulting from stress-related complications. Inherently, patients need to recognize that spine stabilization rather than rigid fusion is more in keeping with William of Occam’s Razor and also more logical in not creating more problems for the patient than those for which the surgery was done in the first place.
Non-rigid posterior arthrodeses can be readily monitored by two or three dimensional computed tomographic scans. These 3D views allow accurate visualization of the arthrodesis.
Shown here are are bilateral posterior arthrodeses with good tissue maintenance sjown three months after surgery. Because of the liabilities associated with cigarette smoking potential arthrodesis patients need to be medically documented non-smokers by blood carboxyhemoglobin levels .
It takes approximately three months to clear body tissues of residual nicotine. Because both nicotine and carbon monoxide block bone growth by impairing the development of neo-vascular networks essential to bone growth these become critical considerations for chronic cigarette smokers.
In the image to the left the mature dorso-lateral arthrodesis bone which formed 2 years after surgery is demonstrated. The bone column runs from a lamina to the sacrum and serves to further enhance spine stability.
Advantages of Non-Rigid Autogenous Bone Arthrodesis
Increase in flexible spinal support in a more physiologic procedure and represents the principal of restorative surgery. The procedure does not exclude performing future MRI imaging studies.
Disadvantages of Non-Rigid Autogenous Bone Arthrodesis: Three to six months months is required for bone implant maturation to occur. During the maturation process additional collapse of intervertebral segments can occur. During the maturation process lateral spinal stenosis can reoccur.
Example of Liability
The image to the left shows an example of post-operative spondylolisthesis caused by the progression of spinal degeneration following surgery. The problem was addressed by performing restorative spine surgery where a single posterior titanium cage was placed for the purpose of acute mechanical spine stabilization and a posterior arthrodesis was performed.
Typical Clinical Case
M.K. was a 71 year old physician when he presented with a sciatic radiculopathy and inability to stand or walk. Imaging studies documented long-standing multi-level degenerative changes in the spine producing a degenerative spondylolisthesis at the L4-5 and multi-level central, spinal recess and lateral spinal stenosis. Following multi-level decompression, with relief of stenosis, a posterior placement of a Ray self-tapping titanium threaded fusion cage posteriorly associated with a non-rigid arthrodesis which was then created from L3 to the sacrum. M.K. was relieved of all back and leg pain. In the third image the autogenous posterior bone strut is shown with 3D CT strut reconstruction imaging.
At the 3½ year follow-up this M.K. continued to be free of back and leg pain, and was functioning normally. The follow-up films documented good bony incorporation of the titanium cages (see left), and there was no evidence of “adjacent level disease” having
occurred. A good example of “restorative spine surgery” being achieved.
Frequently Asked Questions;
Is a non-rigid posterior arthrodesis utilizing autologous bone a experimental or investigational procedure?
No, it is neither experimental nor investigational. The strut stabilization procedure is actually something which represents a return to the roots of spine surgery in the United States. Russell Hibbs was the first to use what was basically the same procedure in 1911.
For the purposes of clarification the term “experimental” refers to something which has not yet been proven on a basic level (animal experimentation, cell culture, etc.). When something advances from “experimental” it comes into clinical testing and then can be considered “investigational.” At this point basic efficacy has been determined but preferred means of application need to be determined.
Arthrodesis, posterior technique is a basic spine procedure. More is known about the use of autogenous bone for reconstructive spinal surgery than any other form of spinal surgery.
What are the advantages of non-rigid spine stabilizations?
Non-rigid spine stabilizations are more physiologic for the body. Their role is to stabilize and also to decrease stress on adjacent vertebral segments, particularly when these are not normal as in a case of a genomic condition such as juvenile discogenic disease or any case of multi-level degeneration. The use of metallic multi-level instrumentation increases operating time, cost, and is not infrequently creates a need for additional surgery. In contrast, non-rigid stabilization, utilizing autogenous tissue in conjunction with a titanium threaded fusion cage, can produce a result which can last for the life of a patient. When applied in an appropriate patient with degenerative problems efficacy has been higher than other means of stabilizing the spine.
Through the development of newer, and better, means of processing laminectomized cortico-cancellous bone (something which was, in the past, discarded) it is now possible to avoid harvesting bone from the patient’s ileum, thus decreasing common post-operative patient problems.
Non-rigid spine stabilizations, whether they be referred to as flexible, dynamic, or other terms are inherently more rational from the biomechanical standpoint. But, stabilizations of any sort need to be tailored to the needs of the patient and often also need to be accompanied by effective prior adequate nerve decompression. For the right patient a non-instrumented flexible stabilization is more functional, less invasive, less costly, requires less future maintenance and has demonstrated great efficacy in protecting the patient against future disability, incapacitation, as well as the need for unnecessary additional surgeries.