Something that we as researchers have to admit at this point if we are up to date with the amount of research we have already done is that people with growth plates can achieve increased height and being taller much easier than people without their growth plates. Another word to describe the growth plates is the medical term “Physis” and when we are describing anything that is related to the term “physis” we say it is “physeal” or “epiphyseal”.
The 2nd thing the research has almost shown with definite conclusiveness is that distraction will help make the epiphyseal plates increase in thickness faster which translates to the overall human body to make them taller. Distraction, or even wounds in terms of fractures themselves give the bones a chance to either heal or develop pieces of mesenchyme progenitor cells which can lead to the chondrogenic lineage and develop into longitudinal growth.
This post is to see what we have available at this time from studies done to see how effective or feasible is the idea of doing distraction or by applying a tensile load on growth plate cartilage or just the epiphyseal ends of long bones to make them longer, thus make the person taller.
Study #1: Experimental limb lengthening by epiphyseal distraction.
- Clin Orthop Relat Res. 1978 Oct;(136):111-9.
- Sledge CB, Noble J.
- PMID: 729274
Kirshner wires were placed either side of the right distal femoral epiphysis and a constant tension device applied a distracting force across the plate in rabbits. Growth increase was measured between the wires and found to be about 150% greater than the concurrent normal growth between 2 control (undistracted) wires on the left; such growth increase can occur in the absence of fracturing. The forces required to do this were between 1/5 and 1/10 of those shown to cause fracturing in vitro. The growth increase was shown to be associated with hyperplasia and hypertrophy of the plate, as well as an increased rate of cell division and sulfated polysaccharide synthesis. This was in turn shown to be associated with an increase in new bone formation.
Study #2: Response of the growth plate to distraction close to skeletal maturity. Is fracture necessary?
- Clin Orthop Relat Res. 1990 Jan;(250):61-72.
- Kenwright J, Spriggins AJ, Cunningham JL.
- Source: Nuffield Orthopaedic Centre, Oxford, England.
- PMID: 2293946
Abstract
Axial force applied during epiphyseal distraction has been measured close to skeletal maturity in patients having leg lengthening, in a rabbit model, and in vitro from an amputation specimen. In the patient study, both slow distraction rates and low constant distraction loads were applied. For all the distraction regimens, it was not possible to lengthen the limb significantly without evidence of fracture as demonstrated by a sudden decrease in distraction force. Growth plate failure was observed from 600 to 800 N, these levels being lower than those recorded from the in vitro tests. In the animal study, three distraction regimens (0.13, 0.26, and 0.53 mm/day) were applied across the upper tibial growth plate of New Zealand white rabbits close to skeletal maturity. Distraction was applied and force measured using a strain-gauge dual-frame external fixator. The force-time results revealed two distinct patterns. One pattern, in which the forces rapidly increased to maximum values of approximately 25 N and then suddenly decreased, indicated fracture of the growth plate, which was confirmed histologically. In the other pattern, forces increased steadily throughout distraction, reaching maximum values at the end of distraction of approximately 16 N. Histologic observations indicated hyperplasia of the growth plate without fracture, however, only a small increase in limb length was detectable. Hence, if a significant increase in leg length is required close to skeletal maturity, then fracture of the growth plate must occur.
Study #3: Limb lengthening by epiphyseal distraction. An experimental study in the caprine femur.
- J Orthop Res. 1987;5(4):592-9.
- Steen H, Fjeld TO, Rønningen H, Langeland N, Gjerdet NR, Bjerkreim I.
- Source: Sophies Minde Orthopaedic Hospital, University of Oslo, Norway.
- PMID: 3681532
Abstract
Epiphyseal distraction of the left distal femur was accomplished in 10 goats (aged 3-4.5 months). A modified Hoffmann external fixation device was used as a unilateral distraction frame. A distraction rate of 1.5 mm/day was applied for 5.5 weeks. Epiphysiolysis occurred after 3-7 days of distraction. After the lengthening procedure, the growth plate had reduced in height in eight animals on radiographic examination. In two animals the growth plate was fused. Three animals were killed at 4 (Group 1) and 8 (Group 2) weeks and four animals at 16 (Group 3) weeks after the end of the distraction period. The gain in leg length obtained by distraction was reduced owing to growth retardation in the distal femur of the operated limb. The average final lengthening was 24.9, 19.4, and 13.4% in Groups 1, 2, and 3, respectively. Femur and tibia from both sides were tested mechanically in torsion. Only one femur fractured in the elongation area. All but one elongated femur fractured in the area of the diaphysis subjected to distractional force. The torsional strength of the elongated femur compared with control was reduced to approximately 50% in all groups. The corresponding torsional strength of the tibia on the elongated extremity compared with control was reduced to approximately 75% in all groups. The difference in relative strength of femur compared with that of tibia was statistically significant. This finding can be explained by a stress-protective effect on the femur in the distraction area caused by the external device.
Study #4: Epiphysiolysis as a method of limb lengthening.
- Clin Orthop Relat Res. 1978 Jun;(133):230-7.
- Letts RM, Meadows L.
- PMID: 688713
Abstract
Epiphysiolysis followed by distraction was performed at the proximal tibial growth plates in 18 young rabbits. Union across the distracted plate occurred in all animals. In 12 rabbits skeletally immature at operation, premature fusion of the separated plate resulted in growth arrest of the operated limb. The contralateral control limb was longer at maturity by an average 1.10 cm. In 6 rabbits near skeletal maturity at epiphysiolysis, the operated limb was the longer at maturity by the amount distracted, an average of 0.62 cm. In all animals a permanent loss of joint motion resulted. Epiphyseal distraction in the very young rabbit does not appear to be practical due to consistent premature fusion of the distracted growth plate. It is possible to lengthen the limbs of rabbits near skeletal maturity with this procedure. An added advantage is that union between the epiphysis and the metaphysis always occurred, eliminated the problem of delayed ana non union found in diaphyseal lengthening. However, at this time, until the effects of distraction and compression on the adjacent joint can be minimized, epiphysiolysis as a method of limb lengthening is not recommended in children.
Analysis & Interpretation:
Study #1 seems to show that at least in lab rabbits, when you use steel wires wrapped around the distal epiphysis end of the femur and pull with the force/area or load that is just 1/5th of the amount needed to cause the bone to fracture, you can get the cartilage of the growth plate to increase its growth rate by 150%. The cause of the increased growth is from chondrocyte hypertrophy, hyperplasia, increased cell proliferation, and sulfated polysaccharide synthesis. What is important to note for this study is that the load was increased gradually in tension fashion.
Study #2 is one of the most significant studies yet to show what will probably happen with bone tissue if we tried to stretch out the bones for bone lengthening. However the study was done where the cartilage in growth plates were stretched out, not bones. The researchers were testing the behavior of growth plates for people or lab animals who were close to bone maturity. What is noticed for both situations where either the slow distraction rates and low constant distraction loads were applied, the researchers noticed that if one tried to lengthen the bone significantly the distraction force will reach a certain point before decreasing dramatically. The sudden decrease in the needed distraction force indicates that the pulling motion had caused a fracture in the growth plate. The failure of the growth plate in being able to continue doing plastic or elastic deformation is seen around the 600 Newtons to 800 Newtons level, which I don’t think is all that high in value for a load. It seems that the in vivo results are lower than the in vitro results.
In lab animals, specifically New Zealand rabbits of the 2nd study, the equipment used is a strain-gauge dual-frame external fixator. The rabbits were also close to bone maturity. When the results are graphed in terms of force vs. time, there seems to be two possible patterns seen in the results. Either the process of slowly increasing the tension load up to 16 Newtons while the distraction is done slowly or the process is increased to 25 Newtons rapidly and there is a sudden drop in the load force indicating fracture. The researchers note for a conclusion…
Hence, if a significant increase in leg length is required close to skeletal maturity, then fracture of the growth plate must occur.
If these results can be translated to human subjects, then we can say that the idea of using tension forces to slowly stretch out the growth plate cartilage in teenagers with plates that are almost closed may not be the best idea since it could result in the fracture of the cartilage. It seems that plastic or elastic deformation is a very low possibility, unless there is special equipment that can make the distraction very slow, in terms of maybe only 0.1 mm/day in bone lengthening.
In the 3rd study, the experiment was done on very young goats. There was only 10 goats used in the experiment. I am not sure at this time whether the goats of only 3-4 months years old would have open or closed growth plates but I would assume now that the growth plates were open since the goats were less than 1 years old. There was an unilateral distraction frame used. The rate of lengthening was 1.5 mm/day for 5.5 weeks (or around 40 days). What seems to happen is that the growth plates seem to decrease in length from the distraction. two of the goats actually had the growth plates completely fuse from the distraction.
After the experiment the goats were killed either 4, 8, or 16 weeks after in groups of 1,2, and 3 respectively. It seems that if one waited later to kill the goats, the measured increase in bone length actually decreased from some type of growth stunting. The goats that were killed later showed less bone lengthening. The long bones that were lengthening were also put in a device that would twist the bone to see how much weaker the torsional load strength had become. For most of the goats, the torsion strength after distraction of the femur had decreased to just 50% of what it was before. For the tibia who was put to the torsion load, the torsion strength dropped to just 75% of what it was before. This study is useful to see what would happen to the growth plates and overall bone strength if we tried to lengthen the femur or tibia in people with open growth plates.
In study #4, the long bones in rabbits are first cut at the section between the epiphysis and the growth plates. Then the entire long bone is stretched apart. What is evident from most of the rabbits is that from the epiphysiolysis, if it is done to young subjects, it will lead to premature fusion of the growth plate leading to growth stunting. If the epiphysiolysis is done on subjects which are close to skeletal maturity, the distraction would lead to longer bones compared to control subjects which didn’t have the epiphysis cut apart from the metaphysis. It seems that overall, there is a reducing in the bone joint mobility in all subjects if the cut is done. The researchers note…
“Epiphyseal distraction in the very young rabbit does not appear to be practical due to consistent premature fusion of the distracted growth plate.”
However they do say that the idea of bone lengthening right before the cartilage is completely ossified might be possible but anything before the time of skeletal maturity will only stunt the longitudinal growth of the full long bone.
It is important to note what the researchers say at the very end of the abstract for any orthopedic surgeons who wants to do limb lengthening on children…
“However, at this time, until the effects of distraction and compression on the adjacent joint can be minimized, epiphysiolysis as a method of limb lengthening is not recommended in children.”