Roger C. Haut

Tissue-Engineered Rotator Cuff Tendon Using Porcine Small Intestine Submucosa Histologic and Mechanical Evaluation in Dogs

To determine its efficacy in stimulating the regeneration of a rotator cuff tendon, an implant of 10-ply porcine small intestinal submucosa was used to replace a completely resected infraspinatus tendon in 21 adult mongrel dogs. The contralateral infraspinatus tendon was elevated and then reattached to the greater tubercle with sutures to mimic conventional repair (sham operation). Mechanical evaluations were performed at 0, 3, and 6 months (five specimens at each time period). Histologic comparisons were made at 3 and 6 months (three specimens). At both times, the gross appearance, histologic continuity, and failure mode of the constructs mimicked those of sham-operated and native infraspinatus tendons, thus suggesting host tissue ingrowth and implant remodeling with solid integration of the regenerated tissue to muscular and bony interfaces. Tissue ingrowth occurred without histologic evidence of foreign body or immune-mediated reactions or adhesions to peripheral tissues. Sham operations simulated tendon mobilization and reimplantation procedures routinely performed to treat chronic rotator cuff tendon injuries. Although the ultimate strength of small intestinal submucosa-regenerated tendons was significantly less than that of native infraspinatus tendons (P<0.001), it was similar to that of reimplanted tendons at 3 (P<0.05) and 6 months (P<0.05).

A constitutive equation for collagen fibers

Abstract A constitutive equation for collagen fibers is developed in the form of the ‘quasi-linear’ viscoelasticity law suggested by Y. C. Fung. This mathematical model is used to predict the experimental responses of tests of collagen fiber bundles extracted from the tails of mature rats. All experimental tests were conducted with the specimens immersed in a constant temperature saline bath. From relaxation tests, two material constants were obtained and used to predict the results of constant strain rate tests, hysteresis loops, and sinusoidal tests.

The extent of matrix damage and chondrocyte death in mechanically traumatized articular cartilage explants depends on rate of loading

Mechanical loads can lead to matrix damage and chondrocyte death in articular cartilage. This damage has been implicated in the pathogenesis of secondary osteoarthritis. Studies on cartilage explants with the attachment of underlying bone at high rates of loading have documented cell death adjacent to surface lesions. On the other hand, studies involving explants removed from bone at low rates of loading suggest no clear spatial association between cell death and matrix damage. The current study hypothesized that the observed differences in the distribution of cell death in these studies are attributed to the rate of loading. Ninety bovine cartilage explants were cultured for two days. Sixty explants were loaded in unconfined compression to 40 MPa in either a fast rate of loading experiment (∼900 MPa/s) or a low rate of loading experiment (40 MPa/s). The remaining 30 explants served as a control population. All explants were cultured for four days after loading. Matrix damage was assessed by measuring the total length and average depth of surface lesions and the release of glycosaminoglycans to the culture media. Explants were sectioned and stained with calcein and ethidium bromide homodimer to document the number of live and dead cells. Greater matrix damage was documented in explants subjected to a high rate of loading, compared to explants exposed to a low rate of loading. The high rate of loading experiments resulted in cell death adjacent to fissures, whereas more dead cells were observed in the low rate of loading experiments and a more diffuse distribution of dead cells was observed away from the fissures. In conclusion, this study indicated that the rate of loading can significantly affect the degree of matrix damage, the distribution of dead cells, and the amount of cell death in unconfined compression experiments on explants of articular cartilage.

Naturally occurring extracellular matrix as a scaffold for musculoskeletal repair.

The use of naturally occurring extracellular matrix materials as scaffolds for the repair and regeneration of tissues is receiving increased attention. The present study evaluates the use of the extracellular matrix derived from porcine small intestinal submucosa as a scaffold for anterior cruciate ligament replacement in a goat model. Sixty healthy adult female goats were divided into two equal groups of 30 each. The right anterior cruciate ligament of each goat was removed surgically and replaced with either a patellar tendon autograft or a small intestinal submucosa anterior cruciate ligament scaffold. Three animals from each group were sacrificed at 6 weeks, 3 months, 6 months, and 1 year after surgery and grafts were harvested for histopathologic examination. Six animals from each group were sacrificed immediately after surgery, 3 months, and 1 year after surgery and the grafts were harvested for biomechanical testing. There was no evidence for an adverse clinical response to the xenogeneic small intestinal submucosa scaffold. Anterior drawer values were not different between the two groups at any point. The failure force of the patellar tendon autograft increased from 253 N at Time 0 to 879 N at 12 months. The failure force for the small intestinal submucosa repair device was 721 N at Time 0, decreased to 293 N at 3 months, followed by an increase to 706 N at 12 months. Histopathologic analysis showed a mixed inflammatory cell presence within the small intestinal submucosa scaffold including macrophages and lymphocytes in the early months after surgery. The inflammatory cells disappeared in the later stages of remodeling and the histologic appearance of the small intestinal submucosa remodeled grafts and the patellar tendon autografts were indistinguishable at 12 months. Xenogeneic small intestinal submucosa holds promise as a resorbable bioscaffold for anterior cruciate ligament repair in the goat model.

Biomechanical and histological observations of the dog patellar tendon after removal of its central one-third

The use of a central one-third patellar tendon as an autograft for surgical reconstruction of a damaged cru ciate ligament is common. Few complications of its use have been reported. However, recent clinical studies indicate that decreased quadriceps strength, de creased range of motion, decreased thigh circumfer ence, and patellofemoral problems can be associated with this procedure. Some of these complications may result from alterations in the biomechanical properties of the remaining patellar tendon. The objective of this study was to examine biomechanically and histologi cally the fate of the remaining patellar tendon after removal of its central one-third. Three groups of dogs were used for this study. On one knee the central third of the patellar tendon was removed, while the contralateral side was used as a control. One group was immediately euthanized, while the other two groups were euthanized at 3 and 6 months. Control and operated patella-patellar tendon- tibia preparations were harvested and stretched to failure at 100% strain per second. The 3 and 6 month groups had a 10% decrease in length of the operated patellar tendon versus the con tralateral control. There was a very significant increase in cross-sectional area of the patellar tendon at 3 months, and a further increase at 6 months. The failure load was 70% of the controls at 3 months and 60% of the controls at 6 months. The stiffness and modulus of the operated tendon within the physiologic range were dramatically reduced to 70% and 33% of controls at 6 months, respectively. These overall results were observed with the central one-third defect closed or left open in surgery. This study indicated that the canine patellar tendon had not fully recovered 6 months after removal of its central third. The biomechanical changes observed in the remaining tendon may help explain the loss of quadriceps strength that has been documented in re cent clinical studies after using patellar tendon grafts.

Insensitivity of tensile failure properties of human bridging veins to strain rate: Implications in biomechanics of subdural hematoma

The effects of strain rate on tensile failure properties of human parasagittal bridging veins were studied in eight unembalmed cadavers. While bathed in physiological saline at 37 degrees C, the intact vessel was stretched axially by a servo-controlled hydraulic testing machine at either a low strain rate of 0.1-2.5 s-1 or a high rate of 100-250 s-1. The mean ultimate stretch ratios for low and high strain rates, respectively, were 1.51 +/- 0.24 (S.D. n = 29) and 1.55 +/- 0.15 (n = 34), and the ultimate stresses were 3.24 +/- 1.65 (n = 17) and 3.42 +/- 1.38 MPa (n = 20). Neither difference between strain rates was significant (p greater than 0.45). Thus, our results do not support the hypothesis that sensitivity of the ultimate strain of bridging veins to strain rate explains the acceleration tolerance data for subdural hematoma in primates [Gennarelli, R. A. and Thibault, L. E. (1982) Biomechanics of acute subdural hematoma. J. Trauma 22, 680-686].

The state of tissue hydration determines the strain-rate-sensitive stiffness of human patellar tendon

The purpose of this study was to investigate the effect of tissue hydration on the structural properties of human patellar tendon. Specimens were subjected to a load relaxation experiment prior to being stretched to failure. The experiments indicated that tendons relaxed faster in hypotonic solutions when compared to hypertonic solutions. At a strain rate of 50% s-1 the structural stiffness was significantly higher while immersed in a hypotonic versus hypertonic solution. No difference in tensile stiffness was documented between baths for 0.5% s-1. Tendons immersed in the hypotonic solution were significantly stiffer for 50% s-1 against 0.5% s-1. The results indicate that the structural properties of human patellar tendon are more sensitive to time when the tissues are fully hydrated.

Age-dependent influence of strain rate on the tensile failure of rat-tail tendon

Sensitivity of tensile strength, failure strain, and failure energy density to strain rate was studied for rat-tail tendon (RTT), a collagen-rich connective tissue. Tendons from animals aged 1-27 months were stretched at a high (720 percent/s) and low (3.6 percent/s) strain rate. Each failure parameter increased with strain rate. However, the sensitivity of tendon failure to rate of strain decreased rapidly during growth and sexual maturation of the animal. The study provides basic data on the rate-sensitive strength of collagen fibers using RTT.

Anterior cruciate ligament injury induced by internal tibial torsion or tibiofemoral compression.

The knee is one of the most frequently injured joints in the human body. Approximately 91% of ACL injuries occur during sporting activities, usually from a non-contact event. The most common kinetic scenarios related with ACL injuries are internal twisting of the tibia relative to the femur or combined torque and compression during a hard landing. The hypothesis of this study was that the magnitudes and types of motion observed after ACL rupture would significantly change from the relative joint displacements present just before ACL injury. Compression or torsion experiments were conducted on 7 pairs of knee joints with repetitive tests at increasing intensity until catastrophic failure. ACL injury was documented in all cases at 5.4+/-2kN of TF compression or 33+/-13Nm of internal tibial torque. The femur displaced posteriorly relative to the tibia in pre-failure and with a higher magnitude in failure tests under both loading conditions. In compression experiments there was internal rotation of the tibia in pre-failure tests, but external rotation of the tibia after the ACL failed. In torsion experiments, failure occurred at 58+/-19 degrees of internal tibial rotation, and valgus rotation of the femur increased significantly after ACL injury. These new data show that the joint motions can vary in magnitude and direction before and after failure of the ACL. Video-based studies consistently document external rotation of the tibia combined with valgus knee bending as the mechanism of ACL injury although these motions could be occurring after ACL rupture.

Football Playing Surface and Shoe Design Affect Rotational Traction

Background High rotational traction between football shoes and the playing surface may be a potential mechanism of injury for the lower extremity. Hypothesis Rotational traction at the shoe-surface interface depends on shoe design and surface type. Study Design Controlled laboratory study. Methods A mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque at the shoe-surface interface. The mechanical surrogate was used to compare 5 football cleat patterns (total of 10 shoe models) and 4 football surfaces (FieldTurf, AstroPlay, and 2 natural grass systems) on site at actual surface installations. Results Both artificial surfaces yielded significantly higher peak torque and rotational stiffness than the natural grass surfaces. The only cleat pattern that produced a peak torque significantly different than all others was the turf-style cleat, and it yielded the lowest torque. The model of shoe had a significant effect on rotational stiffness. Conclusion The infill artificial surfaces in this study exhibited greater rotational traction characteristics than natural grass. The cleat pattern did not predetermine a shoes peak torque or rotational stiffness. A potential shoe design factor that may influence rotational stiffness is the material(s) used to construct the shoes upper. Clinical Relevance The study provides data on the rotational traction of shoe-surface interfaces currently employed in football. As football shoe and surface designs continue to be updated, new evaluations of their performance must be assessed under simulated loading conditions to ensure that player performance needs are met while minimizing injury risk.