The primary goal of our study was to measure the extent and timing of changes in growth velocity following periosteal resection. Although generally thought to increase growth velocity; in 1991, Garces, et al. 27
wrote, “A review of previous papers shows no agreement concerning the onset and duration of the stimulus to overgrowth following periosteal stripping, nor the extent expected”
What makes our study unique is that, in comparison with previous studies that measured bone lengths, or at best fluorochrome labeling 2, 4, 27, 28, 29, 30, 31, 32
; we are able to measure this effect with near real-time resolution with high precision over a substantial period of time. This technology (because of the physical dimensions/displacement of the microtrasducer) allows 4 weeks of measurements, and fluorochrome labeling at 7 weeks confirm a continued effect of increased growth. Although this study can not document how long, past 7 weeks, and to what degree the effect of increased growth continues (and at which point the growth velocity normalizes) 7 weeks is a substantial fraction of a lamb’s typical 42 week growth period.
Though many authors debate the mechanisms of post-periosteal resection overgrowth at the physeal level, it is generally accepted that the periosteum acts as a mechanical restraint, providing axial compression on the growth plate 3, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 40
. By circumferential division of the periosteal tissue, then, this restraint is released, eventuating in increased longitudinal growth 30, 31, 37, 38, 39, 40
. Although a number of investigators have examined the organ level mechanics of the observed overgrowth, fewer have attempted to do so at the cellular level 41, 42, 43
. Both Hernandez, et al. and Houghton, et al. found no significant differences in histomorphometric parameters between stripped and control growth plates 41
. Taylor, Warrell, and Evans reported an increase in the number of proliferative cells per column and concluded that the observed increase in growth following circumferential periosteal resection in rats was due to a relative increase in the rate of cellular proliferation 42
. We did not find changes in proliferative zone chondrocytes in our study in lambs.
This study, using optimal (RHT) chemical fixation and real time kinetic parameters provides insight into the means by which resection of the periosteum is translated to increased elongation velocity at the level of the hypertrophic chondrocyte. Resection of the periosteum appears to release axial compression, and allow cellular elongation of the hypertrophic chondrocytes in an longitudinal direction, thereby increasing growth velocity. This is reflected in our histomorphometric data in which the eccentricity index is the primary difference between experimental and control physes. Periosteal resection appears to have no effect on chondrocyte or matrix production, and it also does not appear to affect the regulation of cellular swelling by hypertrophic chondrocytes as the mean cellular volumes in the resected tibia and the control tibia were almost identical— the only difference is the alteration of hypertrophic chondrocyte shape change. This mechanism for modulating growth rate has been reported before 10
While the effect of periosteal resection measured in this study clearly is to increase growth velocity, the question remains if periosteal resection, alone, is sufficient to effectively accelerate growth in a clinically relevant manner. In this study, we are concerned that the measured increase in growth velocity of 10% to 20% may be misleading when translated to the clinical patient. In our study after 7 weeks, the overall length of the tibia with the resection was about 2 mm longer than the control. Since the overall length of the lambs’ tibia at this age is 197mm, the effect of periosteal resection, alone, is to increase length by 1–2% over a 4 to 7 week time interval. If the same growth increase could be maintained for several years then this procedure might have clinical utility for smaller discrepancy. While our study provides a longer time window than previous studies, our study can not confirm how long such an effect would exist. We envision that as the growth plate continues to grow the location of periosteal resection migrates away from the growth plate. This could lead to either a re-tethering of the periosteum or a diminished effect as the distance between the previous resection and the physis, with time, continues to increase. Therefore, if sustained growth is needed clinically, release of the periosteum as close to the physis as possible or repeat release of periosteum may be needed, and this may be hard to justify in a patient setting.
If such a growth stimulus is too diminutive to be useful as a primary treatment modality; it may prove useful if employed as an adjunctive procedure. For instance, in the clinical case of hemihypertrophy [with predicted discrepancy from 2 to 5 centimeters]; the standard method of treatment is to perform epiphysiodesis of the long leg. Perhaps a single stage operation where combination of periosteum release on the short leg and growth arrest of the long leg would be beneficial when insufficient growth remains to completely equalize limb length. Similarly, periosteal resection may have some utility in cases of angular deformity where the treatment plan includes guided growth. The ability to correct deformity with a staple or other modular implant implanted on the convexity may be accentuated when a periosteal resection is performed around the circumference of the metaphysis or perhaps when a hemi-resection of the periosteum is concurrently performed on the concavity. This later methodology is not proven as of yet but is the focus of future studies.
Distraction osteogenesis is an effective means to lengthen a limb but concerns exist regarding growth inhibition in the now lengthened limb after the process is over 44, 45, 46, 47
. Distraction osteogenesis exposes the growth plate to high axial compression forces, owing primarily to increased tension in the surrounding soft tissues and periosteum 48, 49, 50, 51
. Such forces alter mechanical loading of the epiphyseal cartilage, and may result in compressive inhibition of longitudinal growth, as described by the Hueter-Volkmann principle 52, 53, 54, 55, 56, 57, 58
. Some have proposed release of tightened soft tissues in order to decrease compressive forces on the growth and some research has been performed to test this hypothesis 46, 59, 60
. In addition to soft tissue release, periosteal resection also may work to decrease axial loading on the physis, thereby counteracting the effects of compression 40, 61
. Our data suggest that periosteal release confers a physeal growth stimulus by way of reducing axial compression, and as such, may be suitable to counteract the compressive forces that sabotage the clinical goals during distraction osteogenesis.
In summary, this study utilizes novel methods to assess growth velocity in real time and high precision. We demonstrate that increased growth from periosteal stripping can be expected immediately and will continue for at least 7 weeks of the 42 week growth period in the lamb model with about a 1% gain in limb length. We further propose that release of the periosteum allows the hypertrophic chondrocytes to “spring” into a more longitudinal configuration with the sum effect of accelerating growth. We can not confirm how long the total effect remains and therefore use of periosteal resection as a primary means to correct large limb length discrepancy remains questionable. This concept of increased growth from resection may however have clinical utility in other conditions.