Pin-site myiasis: a rare complication of halo orthosis.

STUDY DESIGN: Case report. OBJECTIVE: To report a rare complication following halo placement for cervical fracture. SETTING: United States University Teaching Hospital. CASE REPORT: A 39-year-old woman who sustained a spinal cord injury from a C6-7 fracture underwent halo placement. She subsequently developed an infection adjacent to the right posterior pin, which then became infected with Diptera larvae (maggots), necessitating removal of the pin and debridement of the wound site. CONCLUSION: Halo orthosis continues to be an effective means of immobilizing the cervical spine. Incidence of complications ranges from 6.4 to 36.0% of cases. Commonly reported complications include pin-site infection, pin penetration, pin loosening, pressure sores, nerve injury, bleeding, and head ring migration. Pin-site myiasis is rare, with no known reports found in the literature. Poor pin-site care by the patient and her failure to keep follow-up appointments after development of the initial infection likely contributed to the development of this complication.

Incorporation of perforated and demineralized cortical bone allografts. Part I: radiographic and histologic evaluation.

Massive cortical bone allografts have been found to incorporate slowly into host bone. They are subject to complications such as nonunion, fatigue fracture and infection. In an attempt to improve osteoinduction in cortical bone allografts, laser perforated and partially demineralized cortical bone allografts were orthotopically transplanted into the sheep tibia. In this model, mid-shaft tibial bone allografts from out-bred sheep donor animals were prepared by partial demineralization and drilling of 0.33-mm diameter holes with a pulsed, 2.94-microm wavelength Erbium:Yttrium-Aluminum-Garnet laser. Recipient animals of the same out-bred strain were divided into three groups of eight according to the type of cortical allograft used: group 1, fresh-frozen, no treatment; group 2, laser hole grid; and group 3, laser hole grid and partial demineralization. Plain films were taken in two standard views at monthly intervals. Incorporation was evaluated at nine months postoperatively. Longitudinal radiographic data was correlated to a histologic and morphometric evaluation of each bone graft. Computer tomography was used for the latter analysis. Results showed that untreated allografts, although surrounded by a periosteal bone cuff, were poorly incorporated. Partial demineralization lead to excessive resorption of allografts, but little new bone formation. Laser perforation and partial demineralization induced complete incorporation of allografts into the host bone. Based on the results of the radiographic, histologic and morphometric evaluation, the development of laser-perforated and partially demineralized bone allografts was proposed for clinical use.

Incorporation of perforated and demineralized cortical bone allografts. Part II: A mechanical and histologic evaluation.

Laser perforated and partially demineralized cortical bone allografts were orthotopically transplanted into sheep tibiae. This paper reports results of the mechanical testing of the transplanted bones, which was done at nine months postoperatively. Animals were divided into three groups of eight according to the type of cortical allograft used: group 1, no treatment; group 2, laser hole grid; and group 3, laser hole grid and partial demineralization. Thus, changes in flexural rigidity of 24 transplanted whole tibiae were investigated. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive 4-point bending test. The elliptical distribution of the flexural rigidity was compared to the untreated contralateral control bone of each animal. Mechanical parameters were defined as percentage rates for comparative analysis between groups. Flexural rigidity measurement showed that bones transplanted with untreated allografts were stiffer than contralateral control bones. Partial demineralization of allografts reduced the flexural rigidity of transplanted bones below the level of contralateral control bones. Flexural rigidities of test bones transplanted with laser perforated and partially demineralized allografts were higher than those seen in bones transplanted with partially demineralized allografts. These results were corroborated by the histologic analysis which showed that untreated allografts, although surrounded by a periosteal bone cuff that effectively increased their outer diameter. In contrast, excessive bone resorption was observed in partially demineralized allografts. Laser-perforated and partially demineralized allografts showed histologic evidence of complete incorporation into the host bone. Based on this mechanical evaluation, it was concluded that processing of cortical bone allografts by the combination of perforation and partial demineralization resulted in improved mechanical strength of the transplanted bones as compared to processing by partial demineralization alone.

[Mechanical comparison of biodegradable intervertebral lumbar cages]. / Mechanischer Vergleich biodegradierbarer intervertebraler lumbaler Cages.

INTRODUCTION: A biodegradable interbody cage for lumbar spine fusion would be able to solve several problems associated with the use of metallic cages. In a biomechanical in vitro study using human lumbar spines three different biodegradable poly(L-lactide-co-D,L-lacitide)(PLDLLA) cages were compared to metallic cages of the same design. MATERIAL AND METHOD: 40 human cadaver lumbar specimens (L3-S1) were tested in flexion, extension, rotation, and bending with a non-destructive flexibility method using a nonconstrained testing apparatus. Seven different groups were examined: (1) control group (intact) (n = 40); (2) unstable group (after discectomy L4/5) (n = 40), (3) autologous iliac crest bone graft (n = 8), (4) BAK-Cage (n = 8), (5) BIO-Cage 1 (PLDLLA) (n = 8), (6) BIO-Cage 2 (PLD-LLA/hydroxylapatite-buffer) (n = 8) and (7) BIO-Cage 3 (PLDLLA/hydroxylapatite particles of different size) (n = 8). Additionally, destructive compression tests of all implants were performed. RESULTS: In comparison to the intact motion segment all cages showed significantly lower range of motion (ROM) in all test modes (P < 0.01). There was no significant difference in stiffness values and ROM between BIO-Cages and metallic cages. Axial compression stiffness and failure load were significantly highest for metallic BAK-cages (P < 0.05). No significant difference for failure load was observed between BIO-cage 1 and the intact motion segment. However, in comparison to the intact motion segment failure load was significantly lower for BIO-cage 2 and 3 (P < 0.05). CONCLUSION: The results of this study are encouraging, because the biodegradable cages were able to limit lumbar spine motion similar to the metallic cages. Especially, the biodegradable PLDLLA cage consisting of pure polymer (BIO-Cage 1) showed adequate initial compression strength. However, further in vivo animal experiments are essential prior to the clinical application of biodegradable lumbar interbody fusion cages.

Immune response to perforated and partially demineralized bone allografts.

Immune responses have been shown to be involved in the pathogenesis of clinical complications of cortical bone allografts. In an attempt to reduce the immunogenicity of these allografts, we evaluated cortical bone allografts modified by laser perforation and partial demineralization transplanted orthotopically into sheep tibiae. The recipient animals were divided into three groups, of eight animals each, according to the type of cortical allograft that was transplanted: group 1, no treatment (control); group 2, demineralization only; and group 3, laser perforation and partial demineralization. All animals were tissue-typed by biochemical definition of MHC class I molecules, using unidimensional isoelectric focusing and Western blotting. Mismatches of donors and recipients were assessed by testing samples of each donor and recipient pair in parallel and by comparing their individual bands. Donor-specific alloantibodies were detected by a similar technique, using an enzyme-linked immunosorbent assay (ELISA) format. Negative controls were included in all tests. All grafts were poorly immunogenic, whether they were untreated, processed by partial demineralization, or processed by both laser perforation and partial demineralization. Only two recipient animals showed a transient, antibody-mediated donor-specific immune response. One of these animals had received a control allograft, whereas the other animal had received a laser-perforated and partially demineralized bone allograft. All of the grafts in this study, including control grafts, were stripped of soft tissues and their bone marrow was removed; cellular sources of alloantibody stimulation may have been eliminated by these processes. The results of this study suggest that immune responses to bone allografts may be reduced by removing the bone marrow and adjacent soft tissues. The processing of cortical bone allografts by laser perforation and partial demineralization appeared to have little effect on immune responses.

Observations on fiber-forming collagens in the anulus fibrosus.

STUDY DESIGN: The spatial distribution of fiber-forming collagens in the anulus fibrosus was investigated in the complete longitudinal and horizontal sections of human lumbar intervertebral discs of seven individuals. OBJECTIVES: To obtain a more detailed structural definition of the anulus fibrosus because structural alterations of its collagen fiber network have been implicated in discal degeneration and other spinal pathologies. SUMMARY OF BACKGROUND DATA: Prior biochemical or immunofluorescence studies permitted only limited conclusions concerning the spatial distribution of the fiber-forming collagens in relation to anatomic structures because they were based on intraoperative tissue specimens or performed on incomplete sections of human intervertebral discs. METHODS: Complete human intervertebral discs with their adjacent vertebral bodies were fixed, decalcified, and embedded in paraffin. The intervertebral disc and its adjacent structures were reviewed in their entirety on one histologic slide. Monoclonal antibodies against human Types I, II, and III collagen were used for immunohistochemistry. A comparative analysis based on both immunohistochemical and histologic evaluation was performed. RESULTS: Type I collagen was seen abundantly in the outer zone and outer lamellas of the inner zone of the anulus fibrosus. On longitudinal sections, the Type I collagen distribution took the shape of a wedge. On horizontal sections, the Type I collagen positive area took the shape of a ring that was wider anteriorly than posteriorly. This suggests that the three-dimensional shape of the Type I collagen-positive tissue in the anulus fibrosus can be described by a donut that is wider anteriorly than posteriorly. Type II collagen was present in the entire inner of the anulus fibrosus, but not in the outer zone. In addition, it was found in the cartilaginous endplates. Type III collagen showed some codistribution with Type II collagen, particularly in pericellular locations in areas of spondylosis, which was noted at the endplates, vertebral rim, and insertion sites of the anulus fibrosus. CONCLUSIONS: These observations on the location of Types I and II collagen provide a more detailed structural definition of the anulus fibrosus, which may assist in further investigation of discal herniation.

Experimental anterior spine fusion using bovine bone morphogenetic protein: a study in rabbits.

We developed an experimental model to study the merit of bovine bone morphogenic protein (bBMP) injection into the intervertebral disc to induce anterior interbody fusion. A total of 24 rabbits, divided into three groups of 8 animals each, were used. One hundred and fifty microg of partially purified bBMP was employed in the first group and 10 microg bBMP in the second group. In the control group, a sham operation was performed. The animals were followed radiographically at weekly intervals and animals were killed 3, 6, and 12 weeks postoperatively. After sacrifice, a mechanical and histologic evaluation of fusion was performed. Results of radiographic and histologic evaluation showed bone formation, which had resulted in the bridging of adjacent endplates, in the 150-microg group. In the 10-microg group, new bone formation was less extensive. In the control group, intradiscal bone formation was seen in only 1 animal. Range of motion measurements on flexion/extension films showed significantly decreased motion in segments that were fused with 150-microg of BMP. This study demonstrated the utility of an experimental model which allowed investigation of how anterior spine fusion may be further studied. Intradiscal injection of BMP could ultimately play a role in the development of minimally invasive techniques for anterior spinal fusion.

Biodegradable foam coating of cortical allografts.

Clinical outcomes of bone allograft procedures may be improved by modifying the surface of the graft with an osteoconductive biopolymeric coating. In this comparative in vitro study, we evaluated the dimensional stability, mechanical strength, hydrophilicity, and water uptake of biodegradable foams of poly(propylene fumarate) (PPF) and poly(d,l-lactic-co glycolic acid) (PLGA) when applied as surface coatings to cortical bone. Cortical bone samples were divided into four groups: Type I, untreated bone; Type II, laser-perforated bone; Type III, partially demineralized bone; and Type IV, laser-perforated and partially demineralized bone. Results show that PPF wets easily, achieving 12.5% wt/wt in 30 min. Compressive tests on the PPF foam material showed that the compressive strength was 6.8 MPa prior to in vitro incubation but then gradually reduced to 1.9 MPa at 8 weeks. Push-out and pulloff strength tests showed that initially both PPF and PLGA foam coatings had comparable adherence strengths to the cortical bone samples (100-150 N). When additional geometrical surface alteration by perforation and demineralization of the bony substrate was employed, in vitro adherence of the PPF foam coating was further increased to 120 N, demonstrating a statistically significant improvement of push-out strength throughout the entire 8-week observation period (p<0.0002 for all four data points). The pore geometry of PPF-foam coatings changed little over the 2-month evaluation period. In comparison, PLGA foam coating around the cortical bone samples rapidly lost structure with a decrease of 67% in strength seen after 1-week in vitro incubation. These new types of bone allografts may be particularly useful where the use of other replacement materials is not feasible or practical.

High strength bioresorbable bone plates: preparation, mechanical properties and in vitro analysis.

Biodegradable bone plates were prepared as semi-interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide-co-glycolide)-85:15 (PLGA) or poly(1-lactide-co-d,l-lactide)-70:30 (PLA) using N-vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100-140 degrees C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50-67 MPa, (3) flexural modulus of 7-13 GPa, and (4) manufacturability stiffness of 300-600 N/m. HAP-loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF-SIPN did not show any additional improvement of mechanical properties.

Tissue responses to molecularly reinforced polylactide-co-glycolide implants.

Plates for internal fixation fabricated from biodegradable polymers degrade via an autocatalytic route. When they are used in bone implants of significant size and thickness, hollowing of the implant may occur while the overall dimensions appear unchanged. We hypothesized that incorporation of a cross-linked polypropylene fumarate matrix into polylactide-co-glycolide bone plates may provide an internal molecular network which prevents implant collapse. Cross-linking reagents of varying hydrophilicity including N-vinylpyrrolidone (VP), hydroxyethylmethacrylate (HEMA), and ethyleneglycol dimethacrylate (EGDMA) were employed. With the objective of determining the most biocompatible and structurally sound composition for molecular reinforcement, we investigated tissue responses in both subcutaneous and orthotopic rodent implantation models in relation to maintenance of implant integrity by histologic, histomorphometric, and stereomicroscopic analysis. Results showed that tissue responses were correlated with dimensional stability of the implants. The most favorable results were seen with the hydrophobic cross-linker EGDMA; this may have been related to the initial reduction of the water uptake by the implant. Cross-linking of polypropylene fumarate with EGDMA within a polylactide-co-glycolide bone plate may offer a means to maintain excellent biocompatibility while improving dimensional stability of biodegradable bone plates.

Bioresorbable bone graft substitutes of different osteoconductivities: a histologic evaluation of osteointegration of poly(propylene glycol-co-fumaric acid)-based cement implants in rats.

Bioresorbable bone graft substitutes may significantly reduce the disadvantages associated with autografts, allografts and other synthetic materials currently used in bone graft procedures. We investigated the biocompatibility and osteointegration of a bioresorbable bone graft substitute made from the unsaturated polyester poly(propylene-glycol-co-fumaric acid), or simply poly(propylene fumarate), PPF, which is crosslinked in the presence of soluble and insoluble calcium filler salts. Four sets of animals each having three groups of 8 were evaluated by grouting bone graft substitutes of varying compositions into 3-mm holes that were made into the anteromedial tibial metaphysis of rats. Four different formulations varying as to the type of soluble salt filler employed were used: set 1--calcium acetate, set 2--calcium gluconate, set 3--calcium propionate, and set 4--control with hydroxapatite, HA, only. Animals of each of the three sets were sacrificed in groups of 8 at postoperative week 1, 3, and 7. Histologic analysis revealed that in vivo biocompatibility and osteointegration of bone graft substitutes was optimal when calcium acetate was employed as a soluble salt filler. Other formulations demonstrated implant surface erosion and disintegration which was ultimately accompanied by an inflammatory response. This study suggested that PPF-based bone graft substitutes can be designed to provide an osteoconductive pathway by which bone will grow in faster because of its capacity to develop controlled porosities in vivo. Immediate applicability of this bone graft substitute, the porosity of which can be tailored for the reconstruction of defects of varying size and quality of the recipient bed, is to defects caused by surgical debridement of infections, previous surgery, tumor removal, trauma, implant revisions and joint fusion. Clinical implications of the relation between developing porosity, resulting osteoconduction, and bone repair in vivo are discussed.

Osteoconductivity of an injectable and bioresorbable poly(propylene glycol-co-fumaric acid) bone cement.

We have investigated an injectable form of a resorbable bone cement based on in situ crosslinking of the unsaturated polyester, poly(propylene glycol-co-fumaric acid) (PPF). This material, filled with calcium gluconate/hydroxyapatite (CG/HA), cures to a hard cement degradable by hydrolysis. The purpose of this study was to evaluate the osteoconductive properties of this injectable cement. The cement was used as an adjunct to fixation with an intramedullary rod in the rat femoral osteotomy model. Ingrowth of new bone into the cement was examined in vivo. Negative and positive controls with rigid and loose internal fixation were included for comparison. Animals were evaluated histologically and histomorphometrically at 4 weeks postoperatively. Results of this study showed osteoblastic activity and new bone formation at the interface between the femoral bone and the cement in the experimental group. However, there was little bone remodeling at the endosteal surface in positive and negative controls. Histologic evaluation of the cement revealed the formation of cavitations, which likely resulted from leaching of the highly soluble calcium gluconate portion of the filler from the cement. These cavitations were sites of ingrowth of vascular and bony tissues. Intimate contact between the bone cement and the endosteal surface of the cortex was found. Quantitative histomorphometric analysis corroborated these observations. Findings of this study demonstrated the osteoconductivity of this type of injectable PPF-based bone cement.

Developing porosity of poly(propylene glycol-co-fumaric acid) bone graft substitutes and the effect on osteointegration: a preliminary histology study in rats.

Bioresorbable bone graft substitutes could eliminate disadvantages associated with the use of autografts, allografts and other synthetic materials. We investigated a bioresorbable bone graft substitute made from the unsaturated polyester poly(propylene fumarate) which is crosslinked in the presence of soluble and insoluble calcium filler salts. This compact bone graft substitute material develops porosity in vivo by leaching of the soluble filler salts. In attempt to develop materials whose in vivo porosity can be designed such that implant degradation would occur at a rate that remains supportive of the overall structural integrity of the repairing defect site, we studied the early tissue response upon implantation in a bony defect. Three grout formulations of varying solubilities using slightly soluble hydroxyapatite (HA) and soluble calcium acetate (CA) were evaluated in 3 mm holes made in the anteromedial tibial metaphysis of 200 g Sprague Dawley rats (n = 16 per formulation for a total of 48 animals). Grout formulations cured in situ. Animals from each formulation were sacrificed in groups of 8 at 4 days and 3 weeks postoperatively. Histologic analysis of the healing process revealed improved in vivo osteointegration of bone graft substitutes when a higher loading of calcium acetate was employed. All formulations maintained implant integrity and did not provoke sustained inflammatory responses. This study suggested that the presence of a soluble salt permits in vivo development of porosity of a poly(propylene fumarate) based bone graft substitute material.

Role of bone bark during growth in width of tubular bones. A study in human fetuses.

The morphologic features of bone bark, a structure surrounding the distal and proximal ends of long bones, were studied in the distal femur, proximal tibia, and proximal fibula of 77 spontaneously aborted human fetuses varying in gestational age from 10 to 20 weeks. Standard histologic techniques used in addition to in situ immunohistochemical staining allowed the examination of the structure of the bone bark and localization of Types 1, 2, and 3 collagens at different gestational ages. The bone bark was shaped like a cylindrical sheath of bone lamellae of varying thickness. The epiphyseal end of the bone bark, known as the groove of Ranvier, was covered outwardly by a fibrous layer and inwardly by the epiphyseal cartilage and contained mesenchymal cells, chondroblastic precursor cells, and densely packed cells differentiating into osteoblasts. Neither the cell density in the groove nor the thickness of the bone bark were identical circumferentially, indicating an unequal growth in width. In addition, the presence of periosteal apposition and endosteal resorption of the bone bark on one side and of endosteal bone deposition accompanied by periosteal resorption of the bone bark on the opposite side support the concept of a spatial drift of bones. These observations furnish histologic proof that groove and bone bark, although assuring an equal growth in length, contribute to an unequal and eccentric growth in width.

Effect of a poly(propylene fumarate) foaming cement on the healing of bone defects.

Regeneration of skeletal tissues has been recognized as a new means for reconstruction of skeletal defects. We investigated the feasibility of an injectable and expandable porous implant system for in situ regeneration of bone. Therefore, a composite biodegradable foaming cement based on poly(propylene fumarate) was injected into a critical size defect made in the rat tibia. Animals were divided into two groups comparing the foam in the experimental group against sham-operated animals having a drill hole but no implant in the control group. Eight animals were included in each group. Animals were sacrificed at 1, 3, and 7 weeks postoperatively. Implantation sites were then evaluated with histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham-operated animals. In the experimental group, metaphyseal and cortical defects healed within the first postoperative week by formation of immature woven bone. At the site of the cortical drill hole defect, healing was noted to progress to complete closure by formation of mature bone. Histomorphometry corroborated these findings and showed that metaphyseal bone remodeling peaked at 1 week postoperatively and then decreased as healing of the cortical defect progressed. This suggests that near-complete restoration of the original state of the tibial bone occurred in this animal model supporting the concept of in situ bone regeneration by application of engineered biodegradable porous scaffolds. () ()

Improved osteoconduction of cortical bone grafts by biodegradable foam coating.

Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I--cortical bone without coating (control), Type II--cortical bone coated with PLGA-foam, Type III--cortical bone coated with PPF-foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post-operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam-coated grafts was significantly higher than in the control group (uncoated; p < 0.02). Although both foam formulations were initially equally osteoconductive, PLGA-based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF-based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA-coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF-based foams suggesting that PPF-coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.

Augmentation of osteoinduction with a biodegradable poly(propylene glycol-co-fumaric acid) bone graft extender. A histologic and histomorphometric study in rats.

We investigated the feasibility of enhancing the regeneration of skeletal tissues by augmenting bone grafts with a composite biodegradable bone graft extender material based on the polymer poly(propylene fumarate), PPF. The material was mixed with autograft and allograft and placed directly into a cylindrical metaphyseal defect made in the rat tibia. These formulations were compared to defects without any graft material, autografts, allografts and PPF alone. Nine animals were included in each group. Animals were sacrificed at 1 and 4 weeks postoperatively. Implantation sites were then evaluated using histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham operated animals. In the experimental groups, there was early new woven bone formation in the autograft group with near complete healing of the defect at four weeks. When PPF was used alone, gradual ingrowth of new bone was seen. Mixing of the PPF bone graft extender with either allograft or autograft material resulted in enhancement of new bone formation with both allo- and autograft. However, significantly more new bone formation than in the autograft group was only seen when the PPF bone graft extender was mixed with fresh autograft. Histomorphometry corroborated these findings. Results of this study suggest that a PPF-based material may be used to increase the volume of smaller amounts of bone grafts supporting the concept of "bone graft extenders" by application of engineered biodegradable porous scaffolds.

Mechanical properties of perforated and partially demineralized bone grafts.

Changes in flexural rigidity and compression strength of 18 sheep tibias were investigated after laser perforation and partial demineralization. Test bones were divided into three groups: Group 1, no treatment; Group 2, laser hole grid; and Group 3, laser hole grid and partial demineralization. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive four-point bending test. The elliptical distribution of the flexural rigidity before and after a specific treatment was compared. After the bending test, a cylindrical center section of each test bone was loaded axially to failure to determine subsequent changes in compression strength. Results showed that perforation alone produced minimal reduction of rigidity and insignificant changes in compression strength. However, additional partial demineralization resulted in larger reductions. In compression testing, perforated and partially demineralized bone specimen showed marked decrease of the ultimate failure stress. The observed increase in failure strain appeared to be related to compression of the laser holes. The findings of this study suggest that partial demineralization and perforation can be applied to diaphyseal bone grafts and that their decreased mechanical properties are a function of the bone volume reductions produced by both processes.

Concomitant meniscal and articular cartilage lesions in the femorotibial joint.

The frequency of concomitant meniscal and articular cartilage lesions in the femorotibial joint was analyzed in a retrospective study of 1740 knee joints examined arthroscopically with the objective of determining possible correlations between the two knee joint abnormalities. Articular cartilage lesions were found in 81.4% (N = 1416) of femorotibial joints examined and meniscal derangements were noted in 72.8% (N = 1268). In the medial compartment, concomitance was noted in 76.3% (821 of 1076) on the femoral condyles and in 48.6% (523 of 1076) on the tibial plateau. In the lateral compartment, 43.1% (212 of 492) of the knees with deranged menisci had femoral and 55.1% (271 of 492) had tibial articular lesions. Medial meniscal lesions were more frequently associated with femoral and tibial chondral degeneration than lateral meniscal derangements (P < 0.001). Longitudinal, bucket-handle, and complex tears of the medial meniscus were significantly more often associated with articular cartilage damage than horizontal cleavage, flap, or radial tears. Degeneration of the meniscus was highly correlated with chondral destruction in both compartments. No cause-and-effect relationship could be established, but practical implications of these findings are discussed.

Improved osteoinduction of cortical bone allografts: a study of the effects of laser perforation and partial demineralization.

Massive cortical bone allografts have been found to incorporate slowly into host bone and thus are subject to complications such as nonunion, fatigue fracture, and infection. To better understand and improve the process of osteoinduction in these types of bone grafts, a new experimental model was developed with use of diaphyseal cortical bone grafts from rat tibiae that were prepared by partial demineralization and drilling of 0.33 mm diameter holes with a pulsed, 2.94 microns wavelength, erbium:yttrium-aluminum-garnet laser. Six types of grafts were analyzed: untreated (Type I), demineralized 25 microns deep (Type II), demineralized 150 microns deep (Type III), laser perforated (Type V), laser perforated and then demineralized 25 microns deep (Type V), and laser perforated and then demineralized 150 microns deep (Type VI). The graft was orthotopically transplanted in the tibia of an adult Sprague-Dawley rat and followed for as long as 4 months. Histologic evaluation at 1 and 4 months postoperatively with use of hematoxylin and eosin staining confirmed that there was new bone growth in Types II, III, V, and VI grafts. The amount of growth was estimated by comparing bone mineral density before implantation with values obtained after retrieval of the graft. These measurements were correlated to histomorphometric analysis of graft incorporation. The results show that the processes of partial demineralization (p < 0.000001) and laser perforation with partial demineralization (p < 0.000001) were both significant in enhancing bone growth in this model. New bone growth was significantly increased when the grafts were prepared with extensive demineralization (p < 0.015). This study demonstrates that osteogenesis in cortical bone grafts can be fostered through the process of partial demineralization and laser perforation. To the extent that minimal partial demineralization and laser perforation allow maintenance of structural integrity while altering the osteoinductive properties in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts may be improved.