Vascularization of cancellous chip bone grafts.

Fresh autogenous, frozen allogeneic, and commercially prepared xenogeneic cancellous chip bone grafts were placed into plug holes in the tibia and into surgically simulated nonunion defects in the ulna of dogs. The microvascular and correlated histologic reactions were studied at given times up to 12 weeks after the graft implantation. Marked and characteristic differences were noted among the 3 graft materials. Fresh autogenous chips were extensively vascularized by 1 week, and subsequent microscopic healing was rapid. Allogeneic chips were incorporated into all defects, but vascularization and histologic healing rates were slower than those with the fresh autogenous graft material. The xenogeneic graft was poorly incorporated. A foreign body reaction was seen histologically, and corresponding vascularization of the graft was slow and incomplete.

Microvascular and histologic effect of circumferential wire on appositional bone growth in immature dogs.

Circumferential wires were placed around both midshaft femora of six immature dogs. On one side the wires were placed under the periosteum and on the other side the wires were placed over the periosteum. All wires were tightened to an equivalent tension. A diffuse growth of periosteal new bone occurred in those femora in which wires were placed under the periosteum but not in those over the periosteum. Corresponding microangiographs at 3 weeks in those femora in which wires were placed under the periosteum revealed dramatically increased medullary and periosteal vascularity coupled with histologic active trabecular bone formation. In those femora in which the wires were placed over the periosteum, even though the placement of the wires should supposedly have been the most detrimental, vascularity was not restricted. There were perfused vessels within the cortex directly under the wires. At 8 weeks the wires in both preparations were becoming encased in the growing cortical bone. Cerclage did not devitalize immature bone nor did it restrict adjacent appositional bone growth.

Experimental fixation of femoral osteotomies by cerclage with nylon straps.

Following the successful experience of Partridge in the fixation of human femoral fractures by nylon-strap cerclage, this research in 23 mature dogs was performed to compare nylon-strap with wire-loop cerclage for healing periods of up to 12 weeks. Supplemented by intramedullary fixation with Steinmann pins, long oblique femoral osteotomies were fixed in one femur of each dog by nylon straps and in the other femur by wire loops, at separate operations. The nylon straps were all secured at the same tension by a special "gun." The wire loops were all secured at the same tension by the Rhinelander tightener-twister. Half of the nylon straps had "bumps" along the inner surface, which were added by Partridge in an effort to circumvent the microvascular disturbance reported with Parham bands. On examination by microangiography and correlated histology, all of the osteotomies, regardless of the type of fixation, showed good progress toward osseous union. After fixation by wire cerclage no loss of position or disturbance of blood supply was noted. After fixation by nylon straps slight (clinically insignificant) longitudinal displacement, attributed to slight lengthening of the straps, with consequent loosening was noted in all cases. This loosening was considered advantageous because it appeared to be responsible for the unexpected lack of impairment of the vascularization of the underlying cortical bone by any of the straps. The bumps on the undersurface of some of the straps were, thus, of no vascular advantage, and their presence made accurate fixation of the ostectomy fragments more difficult on the small bones. These studies support the value of fixation by plain nylon straps and show their advantage over straps with bumps for fixation of long oblique single osteotomies of bones the size of the canine femur.

Growth of tissue into a porous, low modulus coating on intramedullary nails: an experimental study.

The ingrowth of tissue into a coating of inert, highly porous, low-modulus composite of polytetrafluorethylene polymer and pyrolytic graphite on four-fluted intramedullary nails was used for stabilization of middiaphyseal femoral osteotomies and examined by microangiography. The observations were correlated with information obtained by histologic, microradiographic and tetracycline fluorescence technology. There was rapid healing of the osteotomy. The coating was invaded throughout by blood vessels and fibrous tissue. Invasion by bone was negligible. The composite thus appeared to retain its initial flexibility when implanted into the femoral intramedullary cavity. The force to distract both coated and uncoated nails was measured on intact femora. The unit retention strength increased to an average of 6.3 kg/cm2 up to 24 weeks, which is consistent with reported values. The composite would thus appear to have potential use as a coating for endoprostheses to produce enduring physiologic fixation.

Experimental reaming of the proximal femur and acrylic cement implantation: vascular and histologic effects.

The technique of microangiography and correlated histology was used, in experiments on the proximal femora of mature mongrel dogs, to study the effects of simple medullary reaming and of reaming followed by insertion of acrylic cement. The hip joints were not disturbed. A segment of Steinmann pin, representing the stem of a hip prosthesis, was inserted into the cement as it was polymerizing. The most significant results, after reaming alone, were devascularization and apparent necrosis of large areas of the cortex of the subtrochanteric femoral diaphysis. Full recovery was observed in 6 months. However, when acrylic cement was introduced following the reaming, extensive necrosis of the inner layers of the diaphyseal cortex was still present after a year, when the observations were terminated. The presence of necrosis of bone was judged by the lack of visible osteocytes in the lacunae. After the devascularization caused by filling the diaphyseal medulla with acrylic cement, the apparently necrotic cortex was revitalized without osteoclasia. That is in contrast to the results in another study in which osteoclasia and osteoneogenesis were required to restore cortex with empty cell lacunae. This raises the question of dormant osteonecrosis in contrast to total osteonecrosis. These studies show, in thin histologic preparations, acrylic bone cement in situ in the tissues. A fibrous membrane was found at the cement-bone interface in most areas. It was thicker in the diaphysis than in the metaphysis. The physiologic effects of acrylic cement implantation are considered to be likely factors in the loosening which is observed clinically when the femoral components of hip prostheses are under protracted stress.

Minimal internal fixation of tibial fractures.

Flexible wire and small pins cause minimal disturbance of osseous blood supply, and introduce minimal foreign material into the wound. Supplemental support by a plaster cast or by traction is required, but the external support can generally be discontinued early for joint mobilization. Several simple auxillary fixation devices extend the usefulness of wire fixation. Removal of metal is not required. Many common fractures of the tibia are amenable to this method of minimal internal fixation. In the diaphysis, long oblique fractures are the most suitable for this application; the firmness of their fixation by cerclage is augmented by muscle pull. Rotation is effectively controlled by a plate which is L-shaped in cross section, and is held in position by cerclage. In the metaphysis, articular fractures of the knee and ankle are securely fixed by a flattened loop of wire and two washers (wire-washer set), supplemented sometimes by pins or hand-made staples. Two pins alone provide excellent fixation of the medial malleolus. A single pin, or a single wire loop through drill holes, may be sufficient to impart stability to an unstable tibial fracture. A key-type graft of iliac bone, maintained by crossed wire loops through cortical drill holes, is effective in the tibial diaphysis. Autogenous iliac cancellous chips provide minimal and effective internal fixation for an infected ununited fracture of the tibia. The surgical instrument most important for making wire fixation highly successful is a tightener-twister which protects wire loops from excessive strain during application, and permits twisting at a predetermined and therefore reproducible tension. Other special and ordinary instruments are valuable assets.