febrero 08, 2018
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Autologous or autogenous bone harvesting has long been the procedure of choice by specialists looking to perform spinal fusion therapy. Because it has all the properties and characteristics needed to foster new bone growth in a patient, such as the right bone growing cells (osteophytes), the right morphogenic proteins, and the right calcium scaffolding, bone harvesting has been recognised as the gold standard treatment. Yet despite this, it isn't without problems.
Surgical wound issues including infection, the limited supply of the right type of autologous bone, and the fact that autograft procedures bring with them the risk of ongoing chronic pain at the harvesting site, means that the search for the best alternative bone graft substitutes has stepped up over the last few years.
There are an overwhelming amount of alternatives that can be utilised either as enhancement or substitute for autologous bone including allografts, platelet gels, and ceramics. In order to try to shed some clarity on what is otherwise a vague area of spinal surgery, a detailed review of over one hundred separate studies was undertaken to determine the best recommendations for these synthetic types. Each type was given a grade, based on the Guyatt criteria grading scale where each autologous replacement is given a number (either 1 or 2) based on the benefits vs the trade off between risks and costs, and a letter designation (either A, B, or C) based on the quality of underlying evidence available.
As an example, the use of short-term aspirin after heart attack has been shown through many randomised trials to reduce further risk of death with minimal side effects and low cost. As a result it would be graded 1A – strong recommendations due to minimal risk with many randomised trials detailing the same positive outcome.
With this in mind, let's take a look at the findings…
There are two key studies that relate to all types of fresh-frozen and freeze-dried allografts in spinal surgery. The first evaluates the rate of post-operative bacterial infections and was a review carried out on 1435 patients who underwent spine fusion procedures using allograft replacement. Each patient had a minimum of a 1 year follow up and it was found that there was no increased risk or significant difference of post-operative infections.
The second clinical study was carried out by Buck et al and evaluated the risk of viral transmission particularly the HIV virus with allograft bone use. In this study it was found that the chances of receiving an HIV infected bone from a cryopreserved specimen is less than 1:1.67 million. 1A recommendations were given to allografts used in anterior cervical discectomy/fusion and adolescent idiopathic scoliosis; whereas, 1B recommendations were given to allografts used in posterolateral lumbar and anterior inter-body lumbar procedure.
According to the review, DBM didn't fair quite so well in certain areas, yet in others it did better than expected. In one study, higher levels of graft collapse and pseudarthrosis were found in those who underwent multilevel anterior cervical decompression and fusion (ACDF). However the authors later said that this could have been down to the higher levels of smokers within the trial group.
Conversely, other studies which support the efficacy of DBM during lumbar posterolateral fusions stated that the use of DBM as a bone grafter or extender in conjunction with bone marrow has shown 'good to excellent' outcomes. The systematic review recommends that usage should depend on whether DBM is being used as a bone graft extender or a bone graft substitute and more importantly, where it's being used.
It would be logical to think that by adding platelet gel to the autologous Iliac crest, it would enhance fusion rates due to platelet derived growth factor (PDGF) and the presence of transforming growth factor beta (TGFβ). However you may be surprised to learn that clinical findings don't agree. Various studies found that rapid dissolving of the platelet gels and insufficient concentration of growth factors were the main reasons for poor fusion status. Ultimately the clinical review found that the required concentrations of growth factors within platelet gels are still a 'work in progress'. As such they shouldn't be used as either a bone graft substitute or an extender for spinal fusion.
The review found that ceramic bone grafts work best as osteoconductors but not without the use of additional osteoinductive materials. This is because any confirmation of fusion is noted purely by x-ray or CT scanning, making it virtually impossible to ascertain for sure whether any growth is down to successful bone formation, or an un-fused ceramic mass. That said, there are multiple studies showing good patient outcomes when ceramic bone grafts are used as extenders, especially in posterolateral lumbar fusions. Others show that the use of ceramics in adolescent idiopathic sclerosis can yield successful results. Overall however, the review is more cautious, opting to take an hypothesised view that any radiographic findings represent true bone growth, rather than a proven or definitive one..
There are over 1400 bone graft alternatives for spinal fusion, so any used should be clinically evaluated to confirm safety, efficacy, and to highlight any associated risk factors.
However, for those types listed and evaluated in the review, autografts come out on top and are still considered the gold standard. Allografts also work well particularly as osteoconductive scaffolds, while the use of demineralised bone matrix (DBM) can lead to variable outcomes, depending upon the batch. However there is little true evidence to suggest that platelet gels work. Finally, ceramics are promising as osteoconductors and therefore bone extenders. Perhaps though, the key message that surgeons should take away is that treatments should always be carefully selected based on patient needs, requirements, and circumstances.
marzo 07, 2018
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