Spatial organization of types I and II collagen in the canine meniscus.

The meniscus of the knee joint is a fibrocartilage mainly composed of type I collagen and smaller amounts of type II collagen. The distribution of type II collagen in the canine meniscus and its spatial relationship to type I collagen was examined by immunohistochemistry and confocal microscopy. Dorsal and coronal slices of the mid-section of medial and lateral menisci from the knee joints of skeletally mature dogs were predigested with Streptomyces hyaluronate lyase and bacterial Protease enzyme XXIV. Monoclonal antibodies against type I collagen (CP17L) and type II collagen (II-II6B3) and an anti-type II collagen polyclonal antibody (AB759) were employed. The staining for type II collagen in the extracellular matrix of hyaline articular cartilage was diffuse without any identifiable spatial organization. In striking contrast, type II collagen in the fibrocartilage of the meniscus stained as an organized network. Type II collagen was distributed throughout the meniscus with the exception of the outer zone containing the blood vessels. Coronal and dorsal staining of the meniscus showed bundles of circumferential fibrils of type I that colocalized with type II collagen in specific sites. These bundles were enwrapped in a second organizational fibrillar system of types I and II collagen that also colocalized. Bundles of circumferential fibrils appeared in cross-section in coronal sections as dots within the interstitial spaces framed by the network of types I and II collagen of the second system. Confocal overlays showed that types I and II collagens were superimposed, suggesting a close spatial proximity between the two collagens. The cells were confined to the types I and II collagen fibrils that enwrapped the bundles. A striking feature of the radial tie fibers was patches of type II collagen without colocalized type I collagen. Our study reveals a unique network of type II collagen in fibrocartilage of the meniscus that serves as a morphological distinction between fibro- and hyaline cartilage.

A biomechanical comparison of posterior cruciate ligament reconstructions using single- and double-bundle tibial inlay techniques.

BACKGROUND: The efficacy of using a double-bundle versus single-bundle graft for posterior cruciate ligament reconstruction has not been demonstrated. HYPOTHESIS: A double-bundle graft restores knee kinematics better than a single-bundle graft does in tibial inlay PCL reconstructions. STUDY DESIGN: Controlled laboratory study. METHODS: Eight cadaveric knees were subjected to 6 cycles from a 40-N anterior reference point to a 100-N posterior translational force at 10 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. Testing was performed for the intact and posterior cruciate deficient knee as well as for both reconstructed conditions. Achilles tendons, divided into 2 equal sections, were prepared as both single-bundle and double-bundle grafts. Both grafts were employed in the same knee, and the order of graft reconstruction was randomized. RESULTS: There were no statistical differences in translation between the intact state and either of the reconstructions (P > .05) or between either of the reconstructions at any flexion angle (P > .05). CONCLUSION: No differences in translation between the 2 graft options were identified. CLINICAL RELEVANCE: The use of a double-bundle graft may not offer any advantages over a single-bundle graft for tibial inlay posterior cruciate reconstructions.

Torsional stability of cross-link configurations: a biomechanical analysis.

BACKGROUND CONTEXT: Cross-link systems have been used to augment segmental spinal instrumentation since the earliest introduction of these fixation systems. Although transverse cross-links have little impact on sagittal motion of spinal constructs, cross-linkage does affect torsional rigidity. Despite the wide variety of cross-link designs, almost all have been configured as transverse devices. The relative mechanical benefit of different cross-link configurations is not known. PURPOSE: The purpose of this study was to compare the torsional stability of three different cross-link configurations. STUDY DESIGN: Biomechanical analysis of segmental instrumentation constructs using porcine spines. METHODS: Thoracic porcine spines (T4 to T10) were instrumented with 6.5-mm conical pedicle screws and 7.0-mm connecting rods from T5 to T9. Terminal vertebrae were embedded in polymethylmethacrylate (PMMA) after a T7 corpectomy. Four cross-link configurations were tested in a randomized manner: Un-cross-linked Control (CONT); Transverse Rod-Rod (RR); Transverse Screw-Screw (SS); and Diagonal Screw-Screw (DX) Cross-links. The specimens were rotated to 3 Nm at a rate of 0.2 degrees/s and cycled six times with data acquisition over the final two cycles. Stiffness, rotation, and energy data were normalized to each control. A Newman-Keuls repeated measures analysis of variance was used to infer significant differences. RESULTS: Diagonal cross-link configurations provided the most rigid construct. Transverse cross-links did not significantly change torsional behavior compared with the unlinked control. Rotation and energy expended were not significantly greater torsional stiffness compared with other constructs tested (p<.01). CONCLUSIONS: The diagonal cross-link configuration provided increased torsional stiffness as compared with unlinked or transverse configurations. This observation should be considered in future cross-link designs.

Selective retention of bone marrow-derived cells to enhance spinal fusion.

Connective tissue progenitors can be concentrated rapidly from fresh bone marrow aspirates using some porous matrices as a surface for cell attachment and selective retention, and for creating a cellular graft that is enriched with respect to the number of progenitor cells. We evaluated the potential value of this method using demineralized cortical bone powder as the matrix. Matrix alone, matrix plus marrow, and matrix enriched with marrow cells were compared in an established canine spinal fusion model. Fusions were compared based on union score, fusion mass, fusion volume, and by mechanical testing. Enriched matrix grafts delivered a mean of 2.3 times more cells and approximately 5.6 times more progenitors than matrix mixed with bone marrow. The union score with enriched matrix was superior to matrix alone and matrix plus marrow. Fusion volume and fusion area also were greater with the enriched matrix. These data suggest that the strategy of selective retention provides a rapid, simple, and effective method for concentration and delivery of marrow-derived cells and connective tissue progenitors that may improve the outcome of bone grafting procedures in various clinical settings.