Mechanical properties of microcallus in human cancellous bone.

Until now, the mechanical properties of the microcalluses that form in human cancellous bone have been unexplained. We measured the microhardnesses of microcalluses in cancellous bone, of the trabeculae within the microcalluses, of the trabeculae adjacent to microcalluses, and of trabeculae lacking microcalluses in a human tibia and femur. We observed no important differences between materials at the four different sites. Because the microhardness of bone is very closely related to its stiffness, this finding indicates that microcalluses are likely to stiffen the trabeculae in which they are formed, even though they may surround unhealed fractures of the cancellous trabeculae.     

Mechanical properties of bone in a paraplegic rat model

Pathologic fractures may occur with minimal trauma after spinal cord injury (SCI) because of osteoporosis. Rats were evaluated to determine whether they could be used as an SCI animal model. Male Sprague-Dawley rats underwent spinal cord transection at the ninth thoracic vertebrae. Control rats underwent a sham procedure. Mechanical testing of the humeral shaft, femoral shaft, tibial shaft, femoral neck, distal femur, and proximal tibia was performed separately at 0, 8, and 24 weeks after surgery. At 24 weeks, significant differences between SCI and control rats were found in maximum torque needed to produce failure in the femoral shaft (63 percent of control, p < 0.05) and tibial shaft (63 percent, p < 0.01), and in compressive load to produce failure in cross-sectional specimens of the distal femur (51 percent, p < 0.05) and proximal tibia (50 percent, p < 0.01). No differences were found in the maximum torque needed to produce failure of the humeral shaft (106 percent, p = 0.77) between SCI and control rats. Reductions in relative bone strength in SCI rats at 24 weeks were similar in magnitude to bone mineral density changes reported in humans with chronic paraplegia. Thus, Sprague-Dawley rats appear to be good animal models in which to evaluate changes in bone strength following SCI.     

Purification and properties of a growth factor from human bone matrix

A growth factor was isolated from demineralized human bone-matrix and purified approximately 2,300-fold with 5.6% yield by the procedures of acetone treatment, Blue-A matrix gel chromatography, Sephadex G-75 gel filtration and Mono-Q fast protein liquid chromatography. The final preparation was homogeneous and a single polypeptide of 18,000 daltons as judged by SDS-polyacrylamide gel electrophoresis. The purified growth factor stimulated DNA synthesis in embryonic chick osteoblast in a dose-dependent manner and was saturated at the concentration of 4 ng/ml. By comparing various properties of the final preparation with those of other growth factors derived from bone, it appears to be a novel growth factor, and may be one of the important local regulators of bone remodeling.     

Biomechanical evaluation of spinal fixation devices. Part III. Stability provided by six spinal fixation devices and interbody bone graft

The three-dimentional stability provided by six spinal fixation devices with or without interbody bone graft has been studied in an in vitro biomechanical model using five-vertebral (T11-L3) fresh cadaveric thoracolumbar specimens. An injury was created at T12-L1 by complete transection of the posterior elements and posterior half of the intervertebral disc, leaving the anterior half of the intervertebral disc and anterior longitudinal ligament intact. The three-dimensional rotations and translations, measures of biomechanical instabilities, were determined under physiologic loads for the intact spine and the spinal constructs, ie, injured spine plus instrumentation. The tested devices were: Harrington reverse ratchet rods (HR); Luque rectangle rod (LR); Kaneda device without transverse fixator (KD); Kaneda device with transverse fixators (KT); transpedicular external fixator (EF). In addition, stability tests were performed for KT, EF, and Harrington compression rods with interbody bone graft following a corpectomy (KTB, EFB, and HCB). The constructs were more stable than the intact spine under the four loads in the following order: flexion: EFB, HCB, EF, HR, LR, KTB, and KT; extension: EFB, LR, EF, KTB, HR, and KT; lateral bending: KTB, KT, EFB, KD, EF, HCB, and HR; and axial rotation: EFB.     

Strength comparison of allogenic bone screws, bioabsorbable screws, and stainless steel screw fixation.

Allogenic bone screws are new to the fixation market and have yet to be tested against current fixation materials. An in vitro comparison of the same sizes of stainless steel, bioabsorbable, and allogenic bone screws was undertaken to assess screw resistance to the forces of bending, pullout, and shear. Using aluminum plates to support the screws, forces up to 1000 Newtons were applied to six to eight samples of each type of screw. During each test, stainless steel screws withstood the maximum force that could be exerted by the testing apparatus without failing (bending, 113.9 +/- 11.8 N mean +/- SE; pullout 999.1 +/- 33.7 N; and shear, 997.5 +/- 108.8 N). In each test, compared to bioabsorbable screws, allogenic bone screws failed faster (pullout, allogenic: 12.4 +/- 1.1 seconds vs. bioabsorbable, 120.6 +/- 13.8 seconds; p = .001; bending, allogenic: 53.4 +/- 4.8 seconds vs. bioabsorbable, 201.9 +/- 11.1 seconds; p = .001; shear, allogenic 13.5 +/- 1.4 seconds vs. bioabsorbable, 43.8 +/- 0.9 seconds; p = .001) under equivalent (pullout: bioabsorbable, 385.0 +/- 18.4 N vs. allogenic, 401.0 +/- 35.9 N; p = .001) or lower (bending, allogenic: 4.7 +/- 0.2 N vs. bioabsorbable, 11.0 +/- 0.9 N; p = .675; shear, allogenic: 312.1 +/- 15.5 N vs. bioabsorbable 680.9 +/- 8.5 N; p = .001) loads, and in a highly variable fashion. Overall, the bioabsorbable screws withstood the forces of bending, pullout, and shear better than the allogenic screws, and stainless steel screws outperformed both bioabsorbable and allogenic screws. Despite these results, allogenic screws could still be useful in compliant patients who would benefit from their osteoconductive properties.     

Comparison of biomechanical properties of periosteal suture fixation and bone anchor fixation to the pubic bone

Objectives. To compare the relative strength of fixation using bone anchors (BAs) compared with direct suture placement into the periosteum.Methods. The anterior bony pelvis was harvested from 21 female cadavers. In each pelvis, BA suture fixation was performed using Cinch anchors on one side of the pubic bone and direct periosteal suture fixation (PSF) on the contralateral side of the same pelvis. We used No. 1 polyproprolene suture for all cases. Using a hydraulic mechanical testing machine, all specimens were loaded in uniaxial tension until failure.Results. Failure modes for BA-fixed pelves were as follows: 11 BA pull-out, 1 midsuture failure, and 9 suture cut by BA. Failure modes for the PSF pelves were as follows: 6 suture pull-outs through the bone, 14 midsuture failures, and 1 suture cut at the bone. PSF pelves required significantly higher loads to induce failure compared with BA pelves (PSF 92.63 ± 22.62 N, BA 71.32 ± 19.76 N, P <0.0002). In many cases, both PSF and BA were adequate points of fixation, and the major mechanism of failure was suture rupture. In pelves with suture failure, the load to induce failure was significantly higher in the PSF group (PSF 105.06 ± 12.55 N, BA 86.06 ± 7.78 N, P <0.0025). When the suture failed, PSF was better because BA fixation actually broke some sutures. The load required to induce failure was higher in the PSF groups in 19 (90.5%) of 21 pelves.Conclusions. Biomechanical testing using permanent monofilament suture did not demonstrate a superiority of BA suture fixation to PSF fixation. PSF appears superior, since BAs induced suture failure in many cases.     

Mechanical properties of human pulleys

In order to determine the mechanical properties of the fibro-osseous pulleys in the hand, the diaphyseal annular pulleys, the volar plate annular pulleys and the cruciate or condensable portions were tested. A custom-made loading device provided proper fit of the soft tissues for a uniform distribution of the pulley load during testing. The A2 pulley was found to be the strongest of the pulleys; the A1 and A4 were the next strongest. The A3 pulley was nearly equal in mean breaking strength to the other annular pulleys, but in absolute breaking load was considerably weaker because of its shortness. The A4 was the least compliant of the pulleys. We concluded that the fibro-osseous A2 and A4 were mechanically stronger and stiffer pulleys than the A1, A3, A5 (volar plate) pulleys. In testing one type of pulley reconstruction, we found that the "belt loop" technique of Karev nearly matched the annular pulleys in strength and energy absorption.     

Mechanical evaluation of fracture fixation augmented with tricalcium phosphate bone cement in a porous osteoporotic cancellous bone model

OBJECTIVE: The purpose of this study was to examine the effects of resorbable bone cement on screw and plate-screw fracture fixation in a porous osteoporotic bone model. METHODS: Experiment 1: Screw pullout strength was assessed for 4 sets of 4.5-mm cortical screws inserted into a synthetic osteoporotic cancellous bone model, including screws inserted without cement augmentation (control), screws augmented with tricalcium phosphate (TCP) bone cement (Norian SRS; Synthes USA, Paoli, PA), and screws augmented with polymethylmethacrylate. Experiment 2: The effects of cement augmentation on plate-screw fixation strength were examined by performing cantilever bending tests on 4 sets of 8 plate-screw constructions, including nonaugmented and TCP-augmented standard and locked screw-plate constructions in a similar bone model. RESULTS: Experiment 1: Cement augmentation with both TCP and polymethylmethacrylate increased screw pullout strength from a porous osteoporotic cancellous bone model by about 4-fold (P < 0.05), and there was no significant difference between the 2 cements (P > 0.1). Experiment 2: Fixation strength was 1.5 times higher for locked plates compared with standard plates when neither was augmented with cement (P = 0.07). Cement augmentation with TCP improved fixation strength by 3.6 times for a standard plate-screw construction (P < 0.05) and 3.3 times for a locked plate-screw construction (P < 0.05). The most stable construction was the TCP-augmented locked plate, in which a 5-fold increase was observed compared with that of standard plates without TCP (P < 0.05). CONCLUSIONS: This study indicates augmenting screws with TCP cement during osteosynthesis improves fixation strength in an osteoporotic cancellous bone model. CLINICAL RELEVANCE:: In fracture situations in which osteoporotic bone makes screw and screw-plate fixation tenuous, screw augmentation with TCP cement should be considered as adjunct treatment.     

Mechanical efficacy of different internal fixation devices in the treatment of thoracolumbar fractures]

To know the efficacy of different internal fixation devices used in the treatment of thoracolumbar fractures, specimens of 15 adult cadaveric (T-8 to L-4) were prepared and were divided into 5 groups for comparative study. Except the control group, the vertebra of T-12 of every specimen in other 4 groups was artificially fractured, imitating flexion fracture dislocation, with standard technic. Then, they were fixed in each group, with Luque's rod, Dick's screw, pedicle screw plate or Dunn's device respectively. The stress distribution and yielding stress under load and dimensional motions in each group were recorded and compared among the groups and with the control. In the experimental groups, Dunn's device gave the strongest support, against load on the anterior and middle columns. Dick's screw and pedicle screw plate could theoretically fix the anterior, middle and posterior columns rigidly; however, because of the weakness persisted in the connection of their components, their fixation effectiveness was reduced. Luque's rod acted though effectively against bending on every direction, it could not stand much axial load. It is obvious that each of these 4 devices has its own advantages and could be used to prevent horizontal displacement of the fixed fracture, but fail to control torsional stress.     

Development of synthetic bone models for the evaluation of fracture fixation devices]

Mechanical tests are indispensable for the research and development of internal devices used for fracture fixation. It is ideal to use fresh human bones even for in vitro experiments. However, fresh human bones are difficult to access, so that alternative materials have been developed. In this study, the applicability of synthetic tibia or femur models made from polyurethane resin (Hiprox) was studied, comparing the mechanical properties of both the synthetic models and the fresh human bones under fracture-fixation conditions using various fixation devices. When the models were designed to simulate the cortical bone with solid resin and the cancellous bone with porous resin, the mechanical properties can be fairly approximated to those of the fresh human bones. It was concluded that the Hiprox models are useful in for preliminary testing of fracture fixation devices.     

Mechanical comparison of fixation techniques for the offset V osteotomy: a saw bone study

Four different techniques for the fixation of an offset V bunionectomy were tested on solid-foam saw-bone models for the purpose of determining the strongest form of fixation for the osteotomy. Twenty identical models were placed into 4 different groups. Groups varied as to the placement and caliber of fixation. Models were loaded with a servo-hydraulic testing machine until failure of fixation occurred. Video analysis was used to record the pattern of failure of the fixation. Failure occurred either distal to the first screw, through the first screw hole, between the 2 screws, through the second screw hole, or proximal to the second screw. The mean force to failure of the groups was group 1, 58.1 N; group 2, 59.3 N; group 3, 64.0 N; and group 4, 105.66 N. There was a statistical significant difference between group 4 and the other 3 groups (F₁ = 55.45, P < 0.05). There was no statistical difference between groups 1 to 3. In groups 1 to 3, 87% of the failures were through the distal screw hole, whereas the remaining 13% were through the proximal screw hole. In group 4, 60% of the failures were through the proximal screw hole and 40% were through the distal screw hole. It was concluded that, in this model, the strongest form of fixation for an offset V osteotomy was the 2.7-mm cortical screw placed distally with the proximal point of fixation being a threaded 0.062-inch Kirschner wire.     

Mechanical properties of dried defatted spongy bone.

A study has been made of the compressive strength, compression at rupture, limit of proportionality, compression at the limit of proportionality and the modulus of elasticity of spongy bone from vertebrae and tibias. The specimens were obtained from autopsy subjects of both sexes aged 14 to 89 years. There was a qualitative deterioration of most of the strength parameters with age, and also differences between the sexes and between vertebrae and tibia. Spongy bone was found to have the unusual mechanical property that, despite rupture, its compressive strength often steadily increased; this was especially the case for vertebrae from young males.     

Method of fracture fixation using external fixation devices

An improvement of the results of treatment can be reached, beside respecting the indication of external fixateurs, with correct tactics of the treatment. Because of the disadvantages of the fixateur externe, we strive to restrict their use, to the time by all means necessary, and if possible to use other methods of fixation. This is motivated especially by the effect on fracture healing and the hindering of the movements and activity of the patient.     

有限切开锁定加压钢板内固定加异体骨植入治疗复杂性肱骨干骨折

目的 介绍有限切开锁定加压钢板内固定加异体骨植入治疗复杂性肱骨干骨折的临床疗效.方法 2005年1月至2008年2月,应用有限切开AO锁定加压钢板(locking compression plate,LCP)加异体骨植入治疗复杂性肱骨干骨折15例,均为粉碎性骨折;按AO分类:属C型骨折,其中2例为肱骨干骨折伴有同侧肱骨近端骨折,5例骨折线延伸至肱骨近端.结果 所有患者伤口均Ⅰ期愈合.术后随访6～40个月,平均21.6个月,骨折愈合时间为12～36周,平均22.5周.2例发生医源性桡神经损伤(占13.3％),与原有的3例桡神经损伤均于术后3个月内完全恢复.肩、肘关节功能恢复良好.结论 有限切开锁定加压钢板内固定加异体骨植入是治疗复杂性肱骨干骨折的一种安全、有效的方法.     

Comparison of lumbosacral fixation devices

Fusion of L4 and L5 to the sacrum has a high incidence of success. Using conventional methods, nonunion is common when long scoliosis fusions are extended to the sacrum. Three methods of instrumentation for fusing the lumbar spine to the sacrum were compared on a spine simulator test stand. Harrington distraction rods from the sacral ala to L1, Luque rods from L1 to the sacrum, and Harrington compression rods from L1 to the sacrum were tested. The use of a spine instrumentation test stand discounted biologic variation in spinal structure. Sequential loading of each test stand-instrumentation construct in torsion, flexion, extension, and lateral bending gave stiffness constants (Ks) for each test mode. Test values had reproducibility of greater than 94%. Ks illustrates the inability of Harrington distraction rods to the sacrum to resist flexion and torsion, but the ability to resist lateral bend and extension. Harrington compression rod and Luque rod constructs have equivalent stiffness in flexion and torsion. Harrington compression rods efficiently resist extension, and Luque rods resist lateral bending. Harrington distraction rods have limited use in lumbosacral junction fixation other than to correct and resist lateral bending.     

Biomechanical evaluation of occipitocervical fixation devices

Human cadaveric occipitocervical specimens were implanted with three types of instrumentation. The devices were tested biomechanically under three modes of loading to determine the stiffness of spinal constructs and the failure mechanisms of the constructs under extreme flexion. The devices tested were the AXIS Fixation System (with custom plate), the Y-Plate, and the Luque rectangle. No significant differences in stiffness among the devices were found under compression and flexion. The stiffnesses of the plate systems were statistically higher than the Luque rectangle in extension and torsion. In extreme flexion, the plate systems failed by fracture of the C2 pedicles. Modern plate systems, for occipitocervical fixation, provide more stiffness and stability than traditional wiring techniques. This study provides surgeons with information on the relative merits of modern plate and screw systems compared with traditional rod and wire constructs.     

Biomechanical evaluation of spinal fixation devices: II. Stability provided by eight internal fixation devices

The three-dimensional stability provided by eight spinal fixation devices has been studied in an in vitro biomechanical model using seven-vertebrae (T9-L3) fresh cadaveric thoracolumbar specimens. An injury was created at T12-L1 by complete transection of the posterior elements and posterior half of the intervertebral disc, leaving the anterior half of the intervertebral disc and anterior longitudinal ligament intact. The three-dimensional rotational and translational motions, measures of biomechanical instabilities, were determined under physiologic loads for the intact specimen after injury and instrumentation with each of the eight fixation devices. The tested devices were: Dunn's anterior device (DD); Harrington distraction (HD); Harrington compression (HC); Harrington distraction-compression combination (HDC); Harrington distraction with sleeves (HDS); Luque rods (LQ); Luque rectangle (LR); and Luque short rectangle (LSR). The following devices were stable under the four loads: Flexion: HC, HD, HDC, HDS, LQ, and LR; Extension: HD, HDC, HDS, LQ, and LR; Lateral Bending: LQ and LR; and Axial Rotation: none.