Transphyseal Implanting Absorbable Rods In The Treatment Of Epiphyseal Injury: An Experimental And Clinnical Study

Part one:The effect of a transphyseal drilling injury on the deve Io pment of epiphyseal plate:An experimental study on growing rabbitsObjectiveTo investigate the effect of perpendicular/oblique transphyseal drilling injuries of various sizes on the development of rabbit epiphyseal plate with the purpose of providing experimental data to internal fixation for pediatric epiphyseal fractures.MethodSeventy two 5-week-old Japanese white rabbits were evenly randomized into 6 experimental groups according to the diameter of drilling and the direction of drilling. Kirschner wires with diameters of 1.0 mm,2.0mm and 3.2mm were used to perpendic ularly/diagonally penetrate central regions of right distal femoral epiphyseal plate of rabbits. As acomparison, a similar arthrotomy was conducted in the left knee, but without being penetrated. The area of injured epiphyseal plates was calculated by computer.The animals were respectively killed at 6,12 and 24 weeks.Measurements of both femora bones length, tansverse diameter of femoralcondyles, radiographic measurement of both femora condyle valgus angles, histology sections, tetracycline fluorescence labeling and ground section were carried out to observe the development of epiphyseal plate.ResultThe percentage of injured growth plates in three perpendicularly penetrated groups were (1.39±0.09)%、(3.33＋0.92)% and (7.44±1.26)% respectively. The percentage of injured growth plates in three diagonally penetrated groups were (1.42±0.10)% (3. 62±0.18)% and (10.15±0.49)% respectively. At 6,12,24 weeks after operation,There was no significant difference in femora condyle valgus angles and tansverse diameter of femaral condyles between the experimental side and the comparing side in each group(P> 0. 05).But the shortening of experimental femur in the 3.2 mm perpendicularly/diagonally penetrated group has happened, whereas no permanent growth disturbance has occurred in the other groups. Histological studies showed that the bone bridges began to form at 6 weeks postoperatively. At 24 weeks after the operation, the bone bridges matured in each group until controlled growth plates were closed.ConclusionThe bone bridges were seen to form in all the perpendicular/oblique transphyseal drilling injuries.The growth retardation of epiphyseal plate depends on the area of injured epiphyseal plate; A injured area which is not over 3.5% of the cross-section area in epiphyseal plate may not cause the growth retardation of it.Part two:The effect of a transphyseal implanting absorbable rod on the development of epiphyseal plate:An exper imental study on growing rabbitsObjectiveTo investigate the influence of absorbable poly-D, L-lactide acid rods on the development of epiphyseal plate after perpendicularly/ diagonally implanted into the distal femoral epiphysis in skeletally immature Japanese white rabbits, with the purpose of providing theoretical data to clinical application of PDLLA rod in the treatment of pediatric epiphyseal fractures.MethodsSeventy two 5-week-old Japanese white rabbits were evenly randomized into 6 experimental groups according to the diameter of rods and the direction of implanting:1.0 mm perpendicularly/ diagonally implanted PDLLA rod group,2.0 mm perpendicularly/ diagonally implanted PDLLA rod group,3.2mm perpendicularly/ diagonally implanted PDLLA rod group. The absorbable PDLLA rods were perpendicularly/diagonally placed into a drill hole of equal size in the intercondylar portion of the right femur, crossing the central portion of epiphyseal plate; A similar arthrotomy was performed in the left knee, served as a control, where no drilling and no implanting were carried out. The area of injured epiphyseal plates was calculated by computer. The animals were respectively sacrificed at 6,12 and 24 weeks. Gross observation, measurements of both femora bones length, tansverse diameter of femoral condyles, radiographic measurement of both femora condyle valgus angles, histology sections and ground section were performed to evaluate the development of epiphyseal plate.ResultsThe proportions of injured area caused by the perpendicularly implanted rod in 1.0 mm group,2.0 mm group,3.2mm group were (1.39±0.09)%, (3.33±0.92)% and (7.44±1.26)% respectively. The proportions of injured area caused by the diagonally implanted PDLLA rod in 1.0 mm group,2.0 mm group,3.2mm group were (1.42±0.10) %、(3.62±0.18)% and (10.15±0.49)% respectively. At 6,12,24 weeks after operation, There was no significant difference in femora condyle valgus angles and tansverse diameter of femaral condyles between the experimental side and the comparing side in each group(P > 0.05).But, at 6,12,24 weeks after operation, a perpendicularly/ diagonally transphyseal implanted PDLLA 3.2 mm in diameter caused a growth disturbance similar to a drill hole of equal bore, whereas no permanent growth disturbance was observed on the other groups in a growing rabbit. Histological studies showed that there were not bone bridges to form in each group until growth plates were closed.ConclusionsPDLLA rod itself does not cause any disturbance to the development of the epiphyseal plate. The growth disturbance of epiphyseal plate depends on the area of injured epiphyseal plate by implants; an injured area over 7.5% of the cross-section area in epiphyseal plate may cause the growth disturbance of epiphyseal plate.Part three:Transphyseal implanting absorbable rods in the treatment of pediatric epiphyseal fracturesObjectiveTo explore the clinical curative results and the effects on the development of epiphy seal plate in treating epiphyseal fractures with absorbable rodsMethodsTo collect 19 patients with epiphyseal fracture that were fixed with absorbable rods from Oct, in 2003 to Oct, in 2008, among which 13 males and 6 femaleswere selected,whose age ranges from 6 to 16 year-old. Postop erative recovery was undergone by observing fracture healing and the growth of injured epiphyseal plate and functional recovery.ResultsThe observation on patients has been done for 6 to 60 months (on average,24 months). Primary healing was achieved for all patients’incision; all fractures were unioni zed well too. No nonunion and no delayed union occurred. According to the criteria, the results of treatment were evaluated as "Excellent" in16 patients and "Good" in 3 patients. The rate of "Excellent" and "Good" was 90%. There were two patients who had growth disfunction of epiphyseal plate, resulting in limitation of limbs function.ConclusionsAbsorbable rod is a safe and reliable fixing material for the treatment of epiphyseal fractures.