An in vivo comparison of the modified Mason-Allen suture technique versus an inclined horizontal mattress suture technique with regard to tendon-to-bone healing: a biomechanical and histologic study in sheep.

The purpose of this study is to examine long-term tendon-to-bone healing, by use of a sheep animal model, after rotator cuff repairs performed with 2 different suture techniques: an inclined horizontal mattress suture pattern placed with special arthroscopic instrumentation (HMS) and the modified Mason-Allen pattern (MMA). After a pre hoc power analysis, 18 skeletally mature sheep were randomly assigned to either the HMS or MMA repair technique, with contralateral limbs used for the control group. At 26 weeks, the animals were euthanized. Six sheep from each group underwent biomechanical testing. Load-to-failure and stiffness results indicated no statistically significant difference between the 2 groups. Avulsion of the tuberosity was the primary mode of failure for both groups. In the remaining 6 sheep, histologic evaluation demonstrated that, regardless of treatment, the tendon appeared completely healed in the bony trough. Because the long-term biomechanical and histologic properties of healed tendons repaired with an HMA technique are equal to those obtained with an MMA technique, the inclined horizontal mattress suture may be appropriate for arthroscopic rotator cuff repair. Short-term studies are necessary to determine whether these findings are true early after tendon repair, when failure may be most common.

Indentation testing of human articular cartilage: effects of probe tip geometry and indentation depth on intra-tissue strain.

Experimental determination of intra-tissue deformation during clinically applicable rapid indentation testing would be useful for understanding indentation biomechanics and for designing safe indentation probes and protocols. The objectives of this study were to perform two-dimensional (2-D) indentation tests, using indenters and protocols that are analogous to those in clinically oriented probes, of normal adult-human articular cartilage in order to determine: (1) intra-tissue strain maps and regions of high strain magnitude, and (2) the effects on strain of indenter geometry (rectangular prismatic and cylindrical) and indentation depth (40-190 microm). Epifluorescence microscopy of samples undergoing indentation and subsequent video image correlation analysis allowed determination of strain maps. Regions of peak strain were near the "edges" of indenter contact with the cartilage surface, and the strain magnitude in these regions ranged from approximately 0.05 to approximately 0.30 in compression and shear, a range with known biological consequences. With increasing indentation displacement, strain magnitudes generally increased in all regions of the tissue. Compared to indentation using a rectangular prismatic tip, indentation with a cylindrical tip resulted in slightly higher peak strain magnitudes while influencing a smaller region of cartilage. These results may be used to refine clinical indenters and indentation protocols.

The effects of augmentation with Swine small intestine submucosa on tendon healing under tension: histologic and mechanical evaluations in sheep.

BACKGROUND: Rotator cuff failure after surgery may be attributed to inferior tissue healing properties that result from repetitive cyclic loading during early rehabilitation. Enhancing the biological healing process may reduce the incidence of failures after rotator cuff repairs. HYPOTHESIS: Augmentation of rotator cuff tissue using swine small intestine submucosa in a sheep model will improve the rate and quality of tissue repair. STUDY DESIGN: Controlled laboratory study. METHODS: We resected and reattached 26 sheep infraspinatus tendons under tension, with 13 animals receiving a small intestine submucosa patch (augmented group). Animals were sacrificed at 12 weeks, and biomechanical testing and histologic evaluation were performed. Biomechanical testing was completed in 10 tendons from each group. Specimens were loaded to failure at a constant displacement to obtain the load deformation curve used to calculate load to failure and stiffness of the healed bone-tendon interface. Histologic testing addressed tissue healing at the bone-tendon interface. RESULTS: The load-to-failure data did not indicate a significant difference between the augmented and nonaugmented groups (1252 +/- 402 N vs 985 +/- 459 N, respectively; P > .05). However, the augmented group had significantly better stiffness than the nonaugmented group (215 +/- 44 N/mm vs 154 +/- 63 N/mm, respectively; P = .03). Histologic data revealed that the infraspinatus tendon in all specimens inserted into the bone through a zone of fibrocartilage, although none of the patches were intact. CONCLUSION: Although there were no differences in the load-to-failure data between the 2 groups, the statistically significant improvement in stiffness for the augmented group is clinically relevant. Stiffness is the biomechanical parameter representing the tissue response to subdestructive loads seen with early rehabilitation. Augmenting the repair with a collagen matrix improved the early healing characteristics of the repair construct. CLINICAL RELEVANCE: Enhancing the biological process of tendon healing under tension by using a collagen matrix patch may improve the ultimate success of rotator cuff repair.

Evaluation of subchondral bone mineral density associated with articular cartilage structure and integrity in healthy equine joints with different functional demands.

OBJECTIVE: To determine and correlate subchondral bone mineral density and overlying cartilage structure and tensile integrity in mature healthy equine stifle (low magnitude loading) and metacarpophalangeal (high magnitude loading) joints. ANIMALS: 8 healthy horses, 2 to 3 years of age. PROCEDURE: Osteochondral samples were acquired from the medial femoral condyle (FC) and medial trochlear ridge (TR) of the stifle joint and from the dorsal (MC3D) and palmar (MC3P) aspects of the distal medial third metacarpal condyles of the metacarpophalangeal joint. Articular cartilage surface fibrillation (evaluated via India ink staining) and tensile biomechanical properties were determined. The volumetric bone mineral density (vBMD) of the underlying subchondral plate was assessed via dual-energy x-ray absorptiometry. RESULTS: Cartilage staining (fibrillation), tensile moduli, tensile strength, and vBMD were greater in the MC3D and MC3P locations, compared with the FC and TR locations, whereas tensile strain at failure was less in MC3D and MC3P locations than FC and TR locations. Cartilage tensile moduli correlated positively with vBMD, whereas cartilage staining and tensile strain at failure correlated negatively with vBMD. CONCLUSIONS AND CLINICAL RELEVANCE: In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way.

Increased hydraulic conductance of human articular cartilage and subchondral bone plate with progression of osteoarthritis.

OBJECTIVE: Osteoarthritis (OA) is characterized by progressive degeneration of articular cartilage and remodeling of the subchondral bone plate, comprising calcified cartilage and underlying subchondral bone. Calcified cartilage remodeling due to upward invasion by vascular canals or to calcified cartilage erosion may contribute to biomechanical alteration of the osteochondral tissue and its subchondral bone plate component. The study hypothesis was that hydraulic conductance of osteochondral tissue and subchondral bone plate increases with structural changes indicative of increasing stages of OA. METHODS: Osteochondral cores were harvested from the knees of cadaveric tissue donors and from discarded fragments from patients with OA undergoing knee surgery. The osteochondral cores from tissue donors were macroscopically normal, and the cores from patients with OA had partial-thickness or full-thickness erosion to bone. The cores were perfusion-tested to determine the hydraulic conductance, or ease of fluid flow, in their native state and after enzymatic removal of cartilage. Adjacent portions were analyzed by 3-dimensional histology for calcified cartilage, subchondral bone, and subchondral bone plate thickness and vascular canal density. RESULTS: Hydraulic conductance of native osteochondral tissue and subchondral bone plate was higher (2,700-fold and 3-fold, respectively) in fully eroded samples than in normal samples. The calcified cartilage layer was thicker (1.5-fold) in partially eroded samples than in normal samples but thinner and incomplete in fully eroded samples. Subchondral bone plate vascularity was altered with increasing stages of OA. CONCLUSION: During joint loading, increased hydraulic conductance of the osteochondral tissue and subchondral bone plate could have deleterious biomechanical consequences for cartilage. Increased fluid exudation from overlying and opposing cartilage, increased fluid depressurization, and increased cartilage tissue strains could lead to chondrocyte death and cartilage damage.

An assessment of equine cartilage degeneration.

Millions of Americans suffer from osteoarthritis, a joint disease characterized by cartilage degradation and subchondral bone sclerosis. However, little is known about its pathology. It remains to be discovered which comes first in the progression of osteoarthritis: subchondral bone remodeling or cartilage degeneration. This study assessed equine cartilage degeneration, based upon measurements of cartilage thickness and Indian ink stain uptake. By gaining a greater understanding of the determining factors in cartilage degeneration, we may be able to better understand the pathomechanics of osteoarthritis. In seven horses, joint regions of interest were harvested bilaterally and isolated into planar osteochondral samples using a band saw and stored at -20 degrees C. After thawing, the samples' articular surfaces were dyed using an Indian ink stain to highlight articular cartilage degeneration. Digital images of the samples were taken before and after the staining, and mean pixel values for the pre- and post-ink images were measured using image analysis software. Reflectance Score (RS) was calculated using mean pixel values normalized between grayscale calibration standards. Articular cartilage thickness was measured at five random locations on each sample from images taken in the transverse orientation. Statistical analysis found no significant effect of limb side for either RS values or thickness, allowing data from right and left limbs to be grouped for analysis. There is a statistically significant correlation between joint region and thickness, as well as between joint region and RS; however, there was no statistical correlation between thickness and RS.