Vol 1 | Issue 1 | July – Dec 2016 | Page 52-55 | Avi Shah, Mandar Agashe
Authors: Avi Shah , Mandar Agashe .
 Department of Orthopaedics, BJ Wadia hospital for children, Mumbai, India.
Address of Correspondence
Dr Mandar Agashe,
Department of Orthopaedics,
BJ Wadia hospital for children,
Growth modulation for angular deformities in the limbs in paediatric age group has been known for many decades . Phemister had described his method of epiphyseodesis in the early 20th century  and Blount popularized his method of epiphyseal stapling which became the treatment of choice for hemi-epiphyseal growth modulation for many years . However, both these methods caused permanent epiphyseodesis and were also associated with significant complications related to the implants and instrumentation [4-7]. This scenario changed drastically with the introduction of the revolutionary “8-plate” or “tension-band plate” by Dr. Peter Stevens in 2007 [8.] This “8-plate” was a low- profile, easy to use and relatively inexpensive implant and had the biggest advantage of causing minimal disturbance of physeal and periosteal blood supply- thus making it an ideal choice for temporary hemi-epiphyseodesis for correction of angular deformities at any age before skeletal maturity. The early results of this method were uniformly encouraging and it gained widespread acceptance over the next few years. However, as with any new method, more and more usage meant more and more nuances were understood of the method and clinicians all over the world started sharing their experiences, difficulties, modifications and technical tips about these tension band plates [9-12]. This has led to a preponderance of literature about this topic over the last few years. It is our endeavor in this article to put forth a brief summary of the recent literature related to 8 plates as regards Biomechanics, results, Failure, comparison of various implants and use in pathological physes.
A number of articles have been written about the various biomechanical aspects of hemiepiphyseodesis. Since the basic scientific explanation by Hueter in 1862 about the phenomenon of mechanical manipulation of bone growth  as well as Volkmanns description of assymetrical growth of the physis , these two articles have formed the basis of the concept of epiphyseal stapling and hemi-epiphyseodesis for deformity correction.
Over the last decade and a half, various authors have described many animal models about stimulation and manipulation of physeal growth. One of the best studies which described the pros and cons of hemiepiphyseal stapling versus other methods of growth modulation was described by Aykut in 2005 . In his study, he compared sub-periosteal placement of staples to extra-periosteal placement in an animal model and found extra-periosteal placement to be better in terms of reliable correction as well as physeal growth after removal. This led to the start of the research for a more reliable and reversible method of epiphyseodesis which can be applied extra-periosteally (as against staples which require sub-periosteal placement).
Peter Stevens first put forth his series of patients with angular deformities of the knee treated with 8-plate epiphyseodesis in 2007 . As a follow-up to that article, he also published a very important basic science/animal model article in 2008 . He had then stated that at least as per animal studies, 8 plates and staple systems have equivalent rate of correction but with the 8 plates being the method with theoretically lesser complications. This was a time when the 8 plates were just being introduced and there was still a question whether the correction was as good as the epiphyseal staples. Another article by Sanpera et al  also put forth an interesting proposition. In this article published in 2012, the authors put forth the importance of the single tether which was more effective in the angular correction of deformities rather than the implant itself. This article showed that the 8 plate applied singly is equally effective with a single staple, but is more effective than the double staples which are more commonly applied. Hence the authors have commented that 8 plate works as a single tether on which the correction takes place. Thus they have said that it is better to put a single staple rather than put a double one.
One of the latest article about basic biomechanics about growth modulation was the one written by Schoenleber et al in 2014 . This article studied the very important topic of screw size, number and configuration in a bone model. They concluded that screw size and number had no effect on the rate of angular correction but described the configuration of screws to be the most important. The authors have stated that parallel screws are the best as regards the rate of angular correction as compared to divergent screws. This is very important clinically and has advised the clinician about perfectly parallel placement of the screws for better correction.
The minimally invasive techniques of epiphyseodesis viz Blounts stapling, screw epiphyseodesis and 8 plate epiphyseodesis have made this procedure much more simple, predictable and technically less challenging than the epiphsyeo-metaphyseal fusion as proposed by Phemister . Haas described reversible retardation of the physeal growth with his wire loop technique, mostly in animal experiments but also in a small number of patients . Based on his work, Blount and Clarke described their early results of physeal stapling in 1949  and this method revolutionized the treatment of angular deformities especially around the knees in paediatric patients. The technique evolved over the years and two extra-periosteal Vitallium staples became the standard of care for a number of years. During the course of many years, many authors then started showing their own results of Blounts stapling which were not as good as those shown by Blounts own unit [6-7]. Though experimentally, Blounts staples were shown to retard but not stop physeal growth, a number of patients developed permanent epiphyseodesis. Also, since the plates needed to be hammered in, the extra-periosteal placement of the plates used to become sub-periosteal and hence physeal bars were commonly seen. The other important complications of the Blounts staples were the three “B’s” i.e Backing out, Breakage and Bending. This led to a number of difficulties in the long term outcome of staples leading people to look for better alternatives. The other main problem with Staple epiphyseodesis used to be its timing1. A number of complicated methods of predicting the time for epiphyseodesis have been developed namely the Green-Andersens charts, Multiplier methods etc . There used to be significant problems with using these methods. The accuracy of most of these methods is similar, with significant inter-and intra observer variability. Hence clinicians started looking for a more reversible method of epiphyseodesis which does not cause any permanent damage to the physis. Peter Stevens published his series of patients with angular deformities in the knee treated with his new “8-plate” system . The 8-plates were small, low-profile, two-hole plates with a small central hole for the guiding hole for the physis. Two screws are placed- one on each side of the physis and the plate is necessarily placed in the extra-periosteal fashion. The screws have got good anchorage in the cancellous meta- and epi-physeal bone and the screws can diverge at the screw-plate interface as the physeal growth occurs at the other end of the physis. Due to this, the incidence of back-out, bending and breaking of the screws is much less as compared to the staples. Due to the extra-periosteal nature of the implant, there is very little chance of a physeal bar formation and hence very little chance of permanent epiphyseodesis. Also, as a single extra-periosteal plate is sufficient for all but one indication (correction of flexion deformity of the knee), the application of the 8-plate is simple and can be done without much difficulty even in the most distorted anatomy. This multi-faceted feature of the 8-plate was a great improvement over the staples and this has led to a rapid expansion of indications for epiphyseodesis and a renewed interest in this field. A number of authors then described the good early results of this simple to use technique. Ballal et al described their results of hemiepiphyseodesis for genu valgum and showed good to excellent correction in most of the patients . Many researchers have also endeavoured to find out the average rate of correction with femoral and tibial 8-plates. On an average, the rate of correction for a femoral 8plate is about 0.7-0.9 degrees per month, 0.5-0.6 degrees per month for the tibia and about 1.4-1.6 degrees per month for both femur and tibia [3,21,22]. However this rate depends on the age of the child, menarchal status in the female as well as rate of overall growth of the child. There has been a growing consensus that the 8-plate has superseded the staple. However there have been only a few prospective studies which have directly compared 8-plates with the staples. Two of the earliest articles comparing to methods of epiphyseodesis were by Weimann et al  (which was a comparative analysis in patients) and Goyeneche et al  (which was an animal experiment). Both studies concluded that 8-plates were almost equivalent in the magnitude and degree of correction though 8-plates had better adherence to the bone as compared to staples and this was very useful in preventing back-outs which were very common with staples. Another very high quality article by Gotleibsen et al has described the results of a randomized control trial comparing the 8 plates with staples . This article showed equivalent results of 10 patients treated with staples as compared to 10 patients treated with 8 plates in terms of rate of correction, complications as well as pain scores with the difference being statistically insignificant. This was a very important article which proved that even though the primary results of 8 plates are good and the 8-plate as a system is very easy to use, modular and low-profile, actual improvement over the old system has not been documented and hence stapling still remains the gold standard as far as growth modulation is concerned. The search is still on for a study which emphatically proves the superiority of the 8-plates over the staples.
Failures and special situations:
After the great initial enthusiasm about the 8 plates, there was a rampant use of this method in a large number of indications which included not just idiopathic (or nutritional) angular deformities but also conditions with pathological and sick physis. The results of these series were not that encouraging and the initial euphoria was slightly dampened by these results.
Blounts disease is one condition in which 8-plates were used quite frequently. However Schroerlucke et al were one of the first to describe their series of patients of Blounts disease treated with 8 plates . In this series, there was a failure/complication rate of as much as 44% which was unacceptably high. Another article from the Baltimore group also put forth similar results especially in obese patients with Blounts disease . They also said that it is the metaphyseal screw which almost always breaks and the breakage is at the level of the screw bone junction and not the screw plate junction. Thus they have suggested that especially in obese kids, it is best to use solid noncannulated screws to prevent such complications and failures. Another article by Masquijo et al in 2016 , discussed the causes of failure in a heterogenous group of patients of which the commonest was hypophosphatemic rickets. A few others have described their results in pathological physes with mixed results. Dr. Peter Stevens from Utah has one of the highest number of patients with pathological physes treated with 8 plates and he has shown good results in a select group of patients . Some other authors like Mckenzie et al from DuPont institute  and Grill et al  have also shown their results in skeletal dysplasia, Hypophosphatemic rickets, etc. The most prominent advantage which has been cited by these authors is the fact that 8-plates can be safely used in very young children without any risk of permanent physeal damage which is a very important factor in skeletal dysplasia where the rate of growth is very poor.
Growth modulation for angular deformities around the knee is a very important tool in the armamentarium of the orthopaedic surgeon. With the advent of the 8-plates, this procedure has become safe, easy to reproduce and with very few complications.
Extra-periosteal placement of a single tether (8-plate) is the most important factor in producing the best results. The screws have to be placed parallel for the best correction rather than convergent or divergent. The average rate of correction is about 0.7-0.8 degree per month for femur, 0.5-0.6 degrees per month for the tibia and 1.4-1.6 degrees per month for both simultaneously. 8-plates can definitely be attempted in pathological physes like Blount disease, hypophosphatemic rickets, Skeletal dysplasia etc, though the rate of correction is much less predictable and failure rate is relatively high.
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|How to Cite this article: Shah A, Agashe M. Growth Modulation for Angular Deformities around the Knee: Literature Review. Journal of Clinical Orthopaedics July – Dec 2016; 1(1):52-55.