Increased mechanical strength of healing rat tibial fractures treated with biosynthetic human growth hormone

The effects of biosynthetic human growth hormone on the biomechanical properties of healing tibial fractures and intact bones in the rat were studied after 20 and 40 days of healing. Growth hormone, 2.0 mg per kg per day, was given subcutaneously in two daily doses. Control animals were injected with a corresponding volume of saline. After 20 days of fracture healing, there were no differences in mechanical properties between the healing fractures and intact bones. After 40 days, the ultimate load and maximum stiffness of the fractures of the b-hGH injected animals had increased to more than 400% of the corresponding values of the saline injected animals, and ultimate stress and energy absorption at ultimate load had increased to 270% compared with the saline injected animals. Ultimate load, stiffness, and energy absorption of the intact bones increased in the b-hGH injected animals, but no differences were found in ultimate stress values or normalized energy, indicating that the changes in the intact bones were quantitative phenomena.     

Congenital Coxa Vara and Perthes' Disease

Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure.

The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals.

The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.     

Influence of Age on Mechanical Properties of Healing Fractures and Intact Bones in Rats

Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure.

The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals.

The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.     

Standardization of tibial fractures in the rat.

The influence of the fracture level on the biomechanical properties of healing rat tibial fractures has not been investigated so far, despite the widespread use of rats in fracture healing studies. Fractures were produced in four different zones in the right rat tibia and immobilized with a K-wire. A fifth group of rats was not fractured. After 40 days of healing the fractures and the non-fractured bones were tested in three-point bending. A distinct correlation was found between fracture level and mechanical parameters: maximum load, maximum stiffness, and maximum stress decreased the more distal the fracture was located. In the non-fractured bones, maximum load and maximum stress were constant in all four zones tested, whereas energy absorption increased in the distal part of the tibia. No influence of the healing fracture was found on the contralateral, non-fractured tibia, compared with the animals left undisturbed, and the mechanical properties of the right and the left tibia were found to be symmetrical in terms of mean values. Four different methods of determining the area moment of inertia were investigated, and the simple method of approximating the cross section to an elliptical annulus was found to correlate well with the area moment of inertia, determined from computer tracings of bone slices prepared from the test specimens after the bending test. The computer tracings were corrected for the compression of the specimens caused by the mechanical test.     

Hypoandrogenism related to early skin wound healing resistance in rats

The purpose of this study was to verify the effect of testosterone depletion on healing of surgical skin wounds at different ages and post‐operative periods. Forty‐four Wistar male rats were divided into four groups: Group 1Y (n = 11) – young control, sham‐operated rats (30‐day old); Group 1A (n = 10) – adult control, sham‐operated rats (3 to 4‐month old); Group 2Y (n = 10) – young rats after bilateral orchiectomy; and Group 2A (n = 11) – adult rats after bilateral orchiectomy. After 6 months, a linear incision was performed on the dorsal region of the animals. The resistance of the wound healing was measured in a skin fragment using a tensiometer, on the 7th and 21st post‐operative days. The wound healing resistance was higher in Group 1Y than in Group 2Y after 7 days (P < 0.05). Wound healing resistance at 21 days was higher than at 7 days in all groups (P < 0.05). Late wound healing resistance was not different between young and adult rats. It is concluded that bilateral orchiectomy diminished the wound healing resistance only in young animals at the 7th post‐operative day.     

Reduced energy absorption of healed fracture in the rat

Mechanical testing of closed tibial fractures in rat fixed with a medullary nail was performed after 10-80 days of healing. In the three-point bending test, the maximum load at fracture and maximum stiffness of the fracture gradually increased, reaching 81 and 118 percent, respectively, of intact bone values after 80 days. The fracture failed immediately after the maximum load had been reached in contrast to intact bone, where further bending resulted in gradually decreasing load values until failure occurred at 73-85 percent of the maximum load values. Therefore, the resulting energy absorption until load at fracture and until failure of the healing bone was only 33 and 13 percent, respectively, of intact values after 80 days of healing, and thus markedly reduced even though the maximum stiffness and the load at fracture (maximum load) approximated the values of intact bone.     

Dose response of growth hormone on fracture healing in the rat

The effect of different doses of biosynthetic human growth hormone on the mechanical properties of tibial fractures and intact bones was studied in a rat model; a three-point bending test was applied 40 days after fracturing. Ninety-day-old female rats received a daily dose of 0, 0.08, 0.4, 2.0, or 10 mg of growth hormone/kg body weight starting 1 week before fracture and continuing until mechanical testing. In the animals given 2.0 and 10 mg of hormone, the ultimate load sustained by the fractures, stiffness, and energy absorption at ultimate load increased, while the ultimate stress increased only in the latter group. In the intact bones, ultimate load of the bones increased in the same groups, while stiffness and energy absorption at ultimate load increased only in the group given the highest dose of hormone.     

Reduced energy absorption of healed fracture in the rat

Mechanical testing of closed tibial fractures in rat fixed with a medullary nail was performed after 10-80 days of healing. In the three-point bending test, the maximum load at fracture and maximum stiffness of the fracture gradually increased, reaching 81 and 118 percent, respectively, of intact bone values after 80 days. The fracture failed immediately after the maximum load had been reached in contrast to intact bone, where further bending resulted in gradually decreasing load values until failure occurred at 73-85 percent of the maximum load values. Therefore, the resulting energy absorption until load at fracture and until failure of the healing bone was only 33 and 13 percent, respectively, of intact values after 80 days of healing, and thus markedly reduced even though the maximum stiffness and the load at fracture (maximum load) approximated the values of intact bone.     

Growth hormone promotes healing of tibial fractures in the rat

The effect of administering growth hormone for different periods of time on the mechanical properties of healing rat tibial fractures was investigated after 40 days of healing. Biosynthetic human growth hormone, 2.7 mg/kg body weight/day, was administered to three groups of rats for 1, 2, or 3 weeks following fracture, whereas isotonic saline was administered to a control group for 3 weeks. The ultimate load values and maximum stiffness of the fractures increased in the groups injected with growth hormone for 2 or 3 weeks; linear regression analysis revealed a high probability of a positive linear relationship. In the intact bones an increase in ultimate load, maximum stiffness, and energy absorption at ultimate load was found in the group injected with growth hormone for 3 weeks, with linear regression analysis again showing a high probability of a positive linear relationship.     

Dose response of growth hormone on fracture healing in the rat

The effect of different doses of biosynthetic human growth hormone on the mechanical properties of tibial fractures and intact bones was studied in a rat model; a three-point bending test was applied 40 days after fracturing. Ninety-day-old female rats received a daily dose of 0, 0.08, 0.4, 2.0, or 10 mg of growth hormone/kg body weight starting 1 week before fracture and continuing until mechanical testing. In the animals given 2.0 and 10 mg of hormone, the ultimate load sustained by the fractures, stiffness, and energy absorption at ultimate load increased, while the ultimate stress increased only in the latter groups. In the intact bones, ultimate load of the bones increased in the same groups, while stiffness and energy absorption at ultimate load increased only in the group given the highest dose of hormone.     

The effect of growth hormone on fracture healing in old rats

The healing of fractures is known to decrease with age. Several mechanisms have been identified that might explain this age-related decrease in capacity for fracture repair, one of them being a decrease in growth hormone secretion. In the present experiment, two-year-old male rats with a standardized tibial fracture were given biosynthetic human growth hormone (b-hGH, 2.7 mg/kg/day in two daily injections) during the first 40 days of fracture healing and the controls were injected with saline. After 40 or 80 days of healing, the mechanical properties of the healing fractures were evaluated by three-point bending. At day 40, no differences were found in mechanical properties of fractured and intact tibiae between b-hGH injected rats and saline injected controls. At day 80, ultimate load, stiffness, and ultimate stress of the fractures had increased by 78%, 63%, and 58%, respectively, compared with the controls. In the contralateral, intact tibiae, ultimate load and energy absorption had increased by 12% and 17%, respectively, compared with the controls.     

Growth hormone promotes healing of tibial fractures in the rat

The effect of administering growth hormone for different periods of time on the mechanical properties of healing rat tibial fractures was investigated after 40 days of healing. Biosynthetic human growth hormone, 2.7 mg/kg body weight/ day, was administered to three groups of rats for 1, 2, or 3 weeks following fracture, whereas isotonic saline was administered to a control group for 3 weeks. The ultimate load values and maximum stiffness of the fractures increased in the groups injected with growth hormone for 2 or 3 weeks; linear regression analysis revealed a high probability of a positive linear relationship. In the intact bones an increase in ultimate load, maximum stiffness, and energy absorption at ultimate load was found in the group injected with growth hormone for 3 weeks, with linear regression analysis again showing a high probability of a positive linear relationship.     

The stimulating effect of growth hormone on fracture healing is dependent on onset and duration of administration

The effect of onset and duration of growth hormone administration on the biomechanical properties of healing rat tibial fractures was investigated after 40 days of healing. Biosynthetic human growth hormone, 2.7 mg/kg body weight/day, was given in two daily injections to three groups of rats: (1) for the entire healing period; (2) for the first 20 days; and (3) for the last 20 days of healing. Three corresponding groups of control rats were injected with saline. In Group 1, maximum load and stiffness of the healing fractures increased to 165% and 175%, respectively, compared to the control group. In Group 2, maximum load, stiffness, maximum stress, and energy absorption at maximum load increased to 222%, 175%, 171%, and 247%, respectively, compared to the control group. In Group 3, no statistically detectable effects were found. The results show that growth hormone stimulates fracture healing both when given during the first part of the healing period and when given during the entire healing period.     

有机镓促进卵巢切除大鼠骨折愈合及生长的实验研究

目的 本研究的目的 是证实有机镓对卵巢切除大鼠骨折愈合的作用.方法 40只雌性Wistar大鼠被分为2组:(1)假手术组(对照n=10只),(2)卵巢切除组(n=30只),无菌条件下腹侧入路行完整双侧卵巢摘除;假手术组摘除与卵巢重量相同的卵巢周围脂肪组织各1块.12w后对40只大鼠制造开放性骨折并予克氏针内固定.术后分为假手术组(n=10)和一个卵巢切除组(n=15)用PBS治疗,另外一个卵巢切除组(n=15)用有机镓治疗.治疗共持续4w,取骨折愈合的大鼠股骨分别进行micro-CT测定骨小梁组织结构;组织形态学测定骨组织愈合面积;生物力学测定愈合股骨的最大负荷载力;骨矿含量检测评价钙盐含量.结果 经过4w治疗,micro-CT显示有机镓治疗组平均骨小梁厚度(Tb.Th)、平均骨小梁数目(Tb.N)均明显高于对照组(P<0.05).卵巢切除组的愈合组织骨面积较假手术组降低9.2%,有机镓治疗组比卵巢切除组高34.9%(P<0.05).有机镓治疗组股骨骨折愈合强度显著高于卵巢切除组,最大负荷载力增加50.6%,结构强度增加36.5%,能量吸收增加90.9%,但是均低于假手术组.与卵巢切除组相比,有机镓治疗组显著提高愈合组织的骨矿含量.结论 有机镓能够抑制骨折后的骨量丢失,促进骨折愈合组织的生长,改善骨小梁三维结构及骨组织的力学性能,可用来促进骨质疏松性骨折的愈合并改善骨质量,预防再骨折.     

Influence of flexible nailing in the later phase of fracture healing: strength and mineralization in rat femora

In this experimental study, the influence of flex-ible nailing in the later phase of femoral fracture healing was investigated. Sixty rats were randomly assigned to three groups. In 20 rats no intervention was performed, and they served as a control group. Fracture and reamed nailing with a rigid steel nail was performed in the left femur in the other 40 rats. These rats were reoperated after 30 days, and the medullary nail was removed. In one group (20 rats) a flexible polyethylene nail was installed (flexibly nailed group), while the rats in the other group received a steel nail identical to the one that was removed (rigidly nailed group). At 60 and 90 days, the left femurs of 10 animals in each group were studied clinically, radiologically, and biomechanically, and bone mineralization was measured by dual-energy X-ray absorptiometry. Radiographs in two planes revealed a clearly visible fracture line in both intervention groups at 60 days. At 90 days, the fracture line was clearly visible in the flexibly nailed group, while bridging callus was apparent after the rigid nailing. At 60 and 90 days, the callus area in the flexibly nailed group was significantly larger than that in the rigidly nailed bones. Biomechanically, flexible nailing reduced maximum bending load and fracture energy at 60 and 90 days compared with findings in rigidly nailed bones, while bending rigidity was similar in the two groups. All values for biomechanical characteristics were reduced at 60 and 90 days in flexibly nailed bones compared with intact femurs, while in the rigid nailing group, bending load and fracture energy were similar to those in intact bones at 90 days. Bone mineral content in the callus segment and diaphysis was greater in the rigidly nailed bones than in the flexible nailing group at 60 days, while at 90 days, no differences were detected. In conclusion, this animal study indicates that: (1) flexible nailing in the later phase of fracture healing increases callus formation, while (2) the quality of bone healing is reduced. Received: March 1, 2001 / Accepted: July 26, 2001     

Local injection of TGF-β increases the strength of tibial fractures in the rat

The effect of Transforming Growth Factor B (TGF-β) administered locally around the fracture line of healing rat tibial fractures was investigated after 40 days of healing. TGF-β in a dose of 4 ng or 40 ng was injected every second day during the healing period. The strength, stiffness, energy absorption and deflection of the fractures were measured in a materials-testing machine. Compared with placebo-treated animals, the ultimate load of the fractures increased in the group injected with 40 ng of TGF-B, but not in those injected with 4 ng. TGF-β induced a dose-dependent increase in the cross-sectional area of the callus and bone at the fracture line. Consequently, local treatment of fractures with TGF-β increases the callus formation and strength. The energy absorption and deflection capacities of the healing fractures are preserved.     

骨折愈合的应力适应性研究

目的 探讨骨折端受力、肌肉动力、骨痂密度与骨折愈合的关系。方法 通过传感器电测技术与X线灰度分析的方法，从三个方面对骨折愈合的应力适应性进行了研究：①分别对14只1岁龄山羊进行了断端受力与骨折愈合的关系的研究；②对10只健康成年家兔进行了肌肉动力与骨折愈合的关系的研究；③对56只健康成年家兔进行了骨痂密度与骨折愈合的关系的研究。结果与结论 ①理想的骨折愈合与最佳的应力状态相适应；②肌肉动力是应力适应的反馈调节因素；③骨痂密度是应力适应的反馈结果。     

Traumatic late dissociation of the polyethylene articulating surface in a total knee arthroplasty--a case report

Clodronate was administered daily 28 days before and after an experimental tibial fracture in 35 male rats, and the effect on fracture healing and posttraumatic bone loss was studied. 5 groups were tested. The clodronate/clodronate group received clodronate in daily doses of 10 mg/ kg body weight for 28 days before being subjected to a standardized fracture of the right tibia, and during the fracture healing period of 28 days. The clodronate/ saline group received clodronate before fracture and saline during the healing period. The saline/ clodronate group received saline before and clodronate after fracture. The saline/saline group received saline only, while the control group served as unfractured, untreated controls. After 28 days of fracture healing, the tibias were evaluated with dual energy x-ray absorptiometry, and tested mechanically in a 3-point ventral bending test. Bone mineral content and bone mineral density were approximately 30% higher in the groups receiving clodronate during the experiment, compared to the untreated groups. The weight and cross-sectional area of the fracture callus were equal in all groups. Whether clodronate was administered before the fracture, after the fracture or both, did not affect the bone mineral. Ultimate bending moment, energy absorption, stiffness and deflection were not significantly different between the groups. Our findings suggest that clodronate increases bone mineral both when given before and after a tibial shaft fracture, without affecting fracture healing at 28 days.