Recommends discussion of contrasting pelvic osteotomy studies.
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Animals↗
Biomedical subjects
Karl H Kraus
Publications and source records attributed to Karl H Kraus.
Bone grafts prepared with selective cell retention technology heal canine segmental defects as effectively as autograft.
Using a canine critical-size segmental defect model, a two-phased study was undertaken to evaluate the healing efficacy of demineralized bone and cancellous chips (DBM-CC) enriched with osteoprogenitor cells using a Selective Cell Retention (SCR) technology. The goals of this study were: 1) to determine the bone-healing efficacy of SCR-enriched grafts versus autograft, and 2) to assess the value of clotting SCR-enriched grafts with platelet-rich plasma (PRP). Thirty dogs were included in Phase I: 18 dogs were treated with an SCR-enriched DBM-CC graft clotted with autologous bone marrow, and were compared to 12 autograft controls. In Phase II, 24 animals were divided into 4 groups of 6 animals, each treated with a different bone graft material: 1) iliac crest autograft, 2) DBM-CC alone, 3) DBM-CC saturated with marrow, and 4) SCR-enriched DBM-CC clotted with PRP. All grafts were placed unilaterally in a 21-mm long osteoperiosteal femoral, instrumented, critical-size defect. Radiographs were obtained for all animals postoperatively and every 4-16 weeks; animals were then sacrificed. All femurs were prepared for histology. Femurs in the Phase II study were also analyzed by micro-CT. At 16 weeks, healing--defined by bridging bone across the defects--was observed in 50% of the DBM-CC alone group and 67% of the DBM-CC saturated with marrow group; 100% of the autograft and SCR-enriched DBM-CC groups were healed. Histologically, grafts clotted with PRP showed more mature bone than those implanted with autologous bone, which in turn were similar to those implanted with bone marrow clotted SCR-enriched grafts. These results demonstrated that: 1) SCR-enriched DBM-CC was equivalent to autograft to repair critical-size defects, and 2) while not statistically significant, PRP may have accelerated bone maturation when used to clot osteoprogenitor-enriched DBM-CC grafts--as compared to cell-enriched, DBM-CC grafts without PRP--in large animal models.
Animals↗
Mesenchymal stem cells and bone regeneration.
OBJECTIVE: To review the role of mesenchymal stem cells (MSC) in bone formation and regeneration, and outline the development of strategies that use MSC in bone healing and regeneration. STUDY DESIGN: Literature review. METHODS: Medline review, synopses of authors' published research. RESULTS: The MSC is the basic cellular unit of embryologic bone formation. Secondary bone healing mimics bone formation with proliferation of MSC then their differentiation into components of fracture callus. Bone regeneration, where large amounts of bone must form, mimics bone healing and can be achieved with MSC combined with strategies of osteogenesis, osteoinduction, osteoconduction, and osteopromotion. MSC based strategies first employed isolated and culture expanded stem cells in an osteoconductive carrier to successfully regenerate a critical segmental defect in the femur of dogs, which was as effective as autogenous cancellous bone. Because MSC appeared to be immunologically privileged, a study using mismatched allogeneic stem cells demonstrated that these cells would regenerate bone without inciting an immunologic response, documenting the possibility of banked allogeneic MSC for bone regeneration. A technique was developed for selectively retaining MSC from large bone marrow aspirates at surgery for bone regeneration. These techniques utilized osteoconductive and osteoinductive carriers and resulted in bone regeneration that was similar to autogenous cancellous bone. CONCLUSION: MSC can be manipulated and combined with carriers that will result in bone regeneration of critically sized bone defects. CLINICAL RELEVANCE: These techniques can be employed clinically to regenerate bone and serve as an alternative to autogenous cancellous bone.
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Nonlinear stiffness profiles of external fixators constructed with composite rods.
OBJECTIVE: To determine if composite connecting rods confer nonlinear stiffness characteristics on unilateral and bilateral external skeletal fixators (ESF) in cranial-caudal bending and axial loading. STUDY DESIGN: Mechanical testing performed on models. SAMPLE POPULATION: Six models of 6-pin ESF constructs composed of birch dowels, a commercial ESF system, and composite connecting rods. METHODS: Unilateral and bilateral ESF configurations were assembled using either specially designed composite titanium and silicone (composite group) or solid titanium (solid group) connecting rods. Mechanical testing was performed in axial loading and 4-point cranial-caudal bending. Stiffness was determined at a low and high-load range, and was considered increasing and nonlinear if the stiffness at high loads was greater than at low loads. RESULTS: The stiffness of the solid group was linear in all testing modes and configurations. Bilateral composite fixators had a nonlinear increasing stiffness in axial loading and cranial-caudal bending. Unilateral composite fixators had a nonlinear increasing stiffness in axial loading, but not cranial-caudal bending. Solid connecting rods conferred a higher stiffness in all testing modes and configurations. CONCLUSIONS: Composite connecting rods resulted in nonlinear increasing axial and bending stiffness in bilateral fixators, and in axial load in unilateral fixators. CLINICAL RELEVANCE: Conventional ESF can be constructed so that the stiffness increases as load increases. This provides the surgeon with additional options to control the local mechanical environment of a healing fracture, which may be used to enhance fracture healing.
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Fluorescently labeled mesenchymal stem cells (MSCs) maintain multilineage potential and can be detected following implantation into articular cartilage defects.
Several studies have reported enhanced repair of damaged cartilage following implantation of mesenchymal stem cells (MSCs) into full-thickness cartilage defects suggesting that the cells in the repair tissue were derived from the implant. However, it cannot be excluded that the enhanced tissue repair is derived from host cells recruited to the defect in response to the implant, rather than the re-population of the tissue by the implanted MSCs. Our objective was to study the short-term fate of fluorescently labeled MSCs after implantation into full-thickness cartilage defects in vivo. The fluorescent dye used in our studies did not affect MSC viability or their ability to undergo osteogenic and chondrogenic differentiation in vitro. MSC gelatin constructs were implanted into full-thickness cartilage defects in goats. These cells retained the dye and were detectable by histology and flow cytometry. At intervals spanning 2 weeks post-implantation we observed gradual loss of implanted cells in the defect as well as fragments of gelatin sponge containing labeled MSCs in deep marrow spaces indicating fragmentation, dislodgement and passive migration. Fluorescent labeling enabled us to determine whether the implanted cells were lost during early time points after implantation as well as their spatial orientation throughout the defect. By determining the fate of implanted cells, new biomaterials could be engineered to correct undesirable characteristics. Testing of new biomaterials in short-term in vivo models would provide faster optimization for cell retention needed for successful, long-term cartilage regeneration.
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Efficacious use of a cap shaped coil for transcranial magnetic stimulation of descending motor paths.
We report another technique of transcranial magnetic stimulation (TMS) for exciting the originating cells of the descending corticospinal tract. A cap shaped TMS coil has been described for simultaneously exciting muscles in all four extremities. This TMS coil is useful for monitoring the functional integrity of the descending motor paths during spinal cord surgery, because information regarding the integrity of both the left and right sides of the spinal cord motor paths can be obtained concurrently. Despite the improved design of the cap coil, careful placement is required for achieving bilateral spinal cord motor responses. Cortical mapping was used to identify the optimum scalp foci for the muscles studied. The cap coil must overlap these foci to simultaneously elicit compound muscle action potentials (CMAPs) in all four extremities. Increasing TMS stimulation intensity will increase the magnitude of the acquired CMAPs responses without significantly changing latency.
Action Potentials↗
Effect of a supplemental plate on the stiffness of a type I external fixator.
OBJECTIVE: To assess the effect of a supplemental plate on the stiffness of a six-pin unilateral external skeletal fixator. STUDY DESIGN: Mechanical testing performed on models. METHODS: Wooden (birch) dowels were used to create five models of a fracture. A commercially available external fixation system was applied to the model with a uniform unilateral six-pin fixator design. The models were mechanically tested with and without a supplemental plate attached to the 2 clamps adjacent to the fracture gap. Testing was conducted in axial loading, medial to lateral bending, and cranial to caudal bending. RESULTS: Results showed a 4.42-fold increase in stiffness in axial load, a 4.23-fold increase in stiffness in medial to lateral bending, and a 1.94-fold increase in stiffness in cranial to caudal bending with the addition of the plate. CONCLUSIONS: The addition of a supplemental plate increases the mechanical stiffness of unilateral fixators. This was especially true in axial load and medial to lateral bending. CLINICAL RELEVANCE: A supplemental plate can be used with unilateral fixators to increase stiffness of the fixator. Conversely, the plate can be removed to decrease stiffness without the removal of fixation pins.
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Nonlinear increasing axial gap stiffness in type II external skeletal fixation: a mechanical study.
OBJECTIVE: To quantify the effect on gap stiffness and cranial to caudal bending stiffness of conversion of the 6 distal clamps of planar bilateral fixator models to sliding clamps and the effect of attachment of composite beams to the sliding clamp models. STUDY DESIGN: Mdash;Mechanical testing performed on models. SAMPLE POPULATION: Five models using birch dowels and a commercially available external skeletal fixator system. METHODS: A segmentally comminuted, middiaphyseal fracture was simulated with the use of wooden dowels, and a bilateral 6-pin fixator was applied to create each of 5 models. The models were mechanically tested with all fixed clamps, with the 6 distal clamps converted to sliding clamps and with composite beams attached to the sliding clamp models. Testing was carried out in axial loading with physiologically relevant loads for a canine model, and in bending in the cranial to caudal plane. RESULTS: Sliding clamp fixators with composite beams attached exhibited a nonlinear increase in axial loading gap stiffness as load increased. The composite beam group also exhibited an increase in cranial to caudal bending stiffness as compared with fixed clamp and sliding clamp models. CONCLUSIONS: Using composite beam elements, planar bilateral external fixators can be constructed such that the fracture site would undergo controlled amounts of displacement at low loads and lessening displacement at higher loads. CLINICAL RELEVANCE: The nonlinear stiffness profile attained by the addition of composite beam elements to a planar external fixator allows controlled axial micromotion at the fracture site. Because controlled axial micromotion appears to stimulate fracture healing, a nonlinear stiffness profile of this type should enhance fracture healing.
Animals↗
Mechanical performance of a screw-type veterinary suture anchor subjected to single load to failure and cyclic loads.
OBJECTIVE: To characterize the mechanical performance of a veterinary bone anchor under static and cyclic loads. STUDY DESIGN: Mechanical testing study. ANIMALS: Cadaveric canine humeri. METHODS: Humeri (6 pairs) were collected from skeletally mature dogs (mean [+/-SD] age, 17.2+/-2.1 months; weight, 20.8+/-1.5 kg). Bone anchors were inserted in the proximal metaphysis using nylon, and were longitudinally extracted. For the opposite humerus, anchors were subjected to longitudinal cyclic load (50% of the load at failure of their pair) for 1200 cycles then longitudinally loaded to failure. Anchors were then installed in a similar and adjacent area of these 2(nd) humeri with nylon and cyclically tested perpendicular to the axis of anchor insertion (100% of the longitudinal holding power of their pair) for 1200 cycles, then perpendicularly loaded to failure. Paired t-tests were used to compare holding power before and after longitudinal cyclic testing. RESULTS: Longitudinal holding power of the screw-type anchor in the proximal humerus was 385+/-30 N. Anchor pullout was the only mode of failure. Anchors in the paired humeri did not fail after 1200 cycles of 50% longitudinal loading, and post-cycle holding strength was not different (335+/-87 N; P=.32). Perpendicularly loaded anchors did not fail after 1200 cycles of 100% of opposite longitudinal holding strength, and had post-cycle perpendicular holding strengths of 514+/-72 N. Suture breakage was the mode of failure. CLINICAL RELEVANCE: Bone anchor holding strength is dependent on orientation of suture load. Screw-type bone anchor holding strength was not affected by longitudinal cyclic loading, and holding strengths of approximately 385 N can be expected in metaphyseal bone of large-breed mature dogs. Perpendicularly loaded anchors have higher failure loads, and holding strength of approximately 514 N can be expected in metaphyseal bone of the proximal humerus.
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Increased sacral screw purchase minimizes screw loosening in canine triple pelvic osteotomy.
OBJECTIVE: To determine if screw loosening in triple pelvic osteotomies (TPO) is minimized when screws cranial to the ilial osteotomy had maximal sacral purchase. STUDY DESIGN: Prospective study. ANIMALS: Forty-six dogs with decreased acetabular coverage of the femoral head and minimal degenerative joint changes. METHODS: TPOs were performed where screws cranial to the ilial osteotomy were inserted to maximally engage sacral bone. Data collected were: use of ilial and ischial cerclage wire, screw length, ventrodorsal radiographic sacral width (most caudal aspect), pelvic canal diameter, and sacral penetration of the 3 cranial screws. On all subsequent radiographs, changes in screw position, pelvic canal diameter, and sacral purchase were noted. RESULTS: For 69 TPOs, 414 screws were used. Mean radiographic cranial screw length was 34.54 mm. Combined sacral depth of all 3 screws was 93.3% of sacral width. All osteotomies healed uneventfully. Twenty-four screws (6%) loosened with 12 being in the most cranial positions. Use of ischial or ilial cerclage wires did not statistically influence screw loosening. Pelvic diameter decreased by a mean of 7.79% from postoperative radiographs to the last radiographic recheck. CONCLUSIONS: By sufficiently engaging the sacrum with screws cranial to the ilial osteotomy, implant failures can be avoided and screw loosening minimized when a 6-hole TPO plate is used. CLINICAL RELEVANCE: To minimize screw-loosening in TPO, screws inserted cranial to the ilial osteotomy should be inserted to maximum sacral depth without penetrating the vertebral canal.
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