Humeral Head Articular Cartilage Research Articles

Biomechanical, Morphological, and Biochemical Characteristics of Articular Cartilage of the Ovine Humeral Head.

Objective.Shoulder pain is commonly attributed to rotator cuff injury or osteoarthritis. Ovine translational models are used to investigate novel treatments aimed at remedying these conditions to prevent articular cartilage degeneration and subsequent joint degradation. However, topographical properties of articular cartilage in the ovine shoulder are undefined. This study investigates the biomechanical, morphological, and biochemical attributes of healthy ovine humeral head articular cartilage and characterizes topographical variations between surface locations.Design.Ten humeral heads were collected from healthy skeletally mature sheep and each was segregated into 4 quadrants using 16 regions of interest (ROIs) across the articular surface. Articular cartilage of each ROI was analyzed for creep indentation, thickness, and sulfated glycosaminoglycan (sGAG) and collagen quantity. Comparisons of each variable were made between quadrants and between ROIs within each quadrant.Results.Percent creep, thickness, and sGAG content, but not collagen content, were significantly different between humeral head quadrants. Subregion analysis of the ROIs within each surface quadrant revealed differences in all measured variables within at least one quadrant. Percent creep was correlated with sGAG (r = −0.32, P = 0.0001). Collagen content was correlated with percent creep (r = 0.32, P = 0.0009), sGAG (r = −0.19, P = 0.049), and thickness (r = −0.19, P = 0.04).Conclusions.Topographical variations exist in mechanical, morphologic, and biochemical properties across the articular surface of the ovine humeral head. Recognizing this variability in ovine humeral head cartilage will provide researchers and clinicians with accurate information that could impact study outcomes.

Chondral Damage After Arthroscopic Repair Techniques for Acute Bony Bankart Lesions: A Biomechanical Study

Background: Bony Bankart lesions can be encountered during treatment of shoulder instability. Current arthroscopic bony Bankart repair techniques involve intra-articular suture placement, but the effect of these repair techniques on the integrity of the humeral head articular surface warrants further investigation. Purpose: To quantify the degree of humeral head articular cartilage damage secondary to current arthroscopic bony Bankart repair techniques in a cadaveric model. Study Design: Controlled laboratory study. Methods: Testing was performed in 13 matched pairs of cadaveric glenoids with simulated bony Bankart fractures, with a defect width of 25% of the glenoid diameter. Half of the fractures were repaired with a double-row technique, while the contralateral glenoids were repaired with a single-row technique. Samples were subjected to 20,000 cycles of internal-external rotation across a 90° arc at 2 Hz after a compressive load of 750 N, or 90% body weight (whichever was less) was applied to simulate wear. Cartilage defects on the humeral head were quantified through a custom MATLAB script. Mean cartilage cutout differences were analyzed by the Wilcoxon rank-sum test. Results: Both single- and double-row repairs showed macroscopic damage. The histomorphometric analysis demonstrated that the double-row technique resulted in a significantly (P = .036) more chondral damage (mean, 57,489.1 µm2; SD, 61,262.2 µm2) than the single-row repair (mean, 28,763.5 µm2; SD, 24,4990.2 µm2). Conclusion: Both single-row and double-row arthroscopic bony Bankart fixation techniques resulted in damage to the humeral head articular cartilage in the concavity-compression model utilized in this study. The double-row fixation technique resulted in a significantly increased cutout to the humeral head cartilage after simulated wear in this cadaveric model. Clinical Relevance: This study provides data demonstrating that placement of intra-articular suture during arthroscopic bony Bankart repair techniques may harm the humeral head cartilage. While the double-row repair of bony Bankart lesions is more stable, it results in increased cartilage damage. These findings suggest that alternative, cartilage-sparing arthroscopic techniques for bony Bankart repair should be investigated.

Evaluation of humeral head cartilage using magnetic resonance imaging T1 rho mapping for patients with small-to-medium rotator cuff tears: A pilot study

BackgroundIt is unclear whether smaller rotator cuff tears cause cartilage degeneration. This study was designed to detect early humeral head cartilage degeneration in patients with small-to-medium cuff tears using magnetic-resonance-imaging T1 rho mapping. MethodsFive male and 5 female volunteers without shoulder symptoms (control group) and 5 male and 5 female patients with small-to-medium (<3 cm) rotator cuff tears underwent 3.0-T magnetic resonance imaging of a single shoulder. T1 rho values of the humeral head cartilage were measured and analyzed. ResultsThe total mean T1 rho value was 40.4 ± 3.4 ms for the control group and 45.0 ± 5.3 ms for the patient group. In the control group, the T1 rho values in the inferior articular cartilage were significantly higher than those in the superior and middle articular cartilage. In the patient group, there was no significant difference between all regions. A comparison between the patient and control groups showed that the mean T1 rho values in the superior-to-middle articular cartilage were significantly higher for the patient group than for the control group. However, in the inferior articular cartilage, there was no significant difference between both groups. ConclusionsThis study showed the possibility of early cartilage degenerative changes in the superior-to-middle humeral head articular cartilage of patients with small-to-medium rotator cuff tears.

Viscoelasticity of articular cartilage: Analysing the effect of induced stress and the restraint of bone in a dynamic environment.

The aim of this study was to determine the effect of the induced stress and restraint provided by the underlying bone on the frequency-dependent storage and loss stiffness (for bone restraint) or modulus (for induced stress) of articular cartilage, which characterise its viscoelasticity. Dynamic mechanical analysis has been used to determine the frequency-dependent viscoelastic properties of bovine femoral and humeral head articular cartilage. A sinusoidal load was applied to the specimens and out-of-phase displacement response was measured to determine the phase angle, the storage and loss stiffness or modulus. As induced stress increased, the storage modulus significantly increased (p < 0.05). The phase angle decreased significantly (p < 0.05) as the induced stress increased; reducing from 13.1° to 3.5°. The median storage stiffness ranged from 548 N/mm to 707 N/mm for cartilage tested on-bone and 544 N/mm to 732 N/mm for cartilage tested off-bone. On-bone articular cartilage loss stiffness was frequency independent (p > 0.05); however, off-bone, articular cartilage loss stiffness demonstrated a logarithmic frequency-dependency (p < 0.05). In conclusion, the frequency-dependent trends of storage and loss moduli of articular cartilage are dependent on the induced stress, while the restraint provided by the underlying bone removes the frequency-dependency of the loss stiffness.

Supraspinatus tendon overuse results in degenerative changes to tendon insertion region and adjacent humeral cartilage in a rat model.

The etiology of rotator cuff tendon overuse injuries is still not well understood. Furthermore, how this overuse injury impacts other components of the glenohumeral joint, including nearby articular cartilage, is also unclear. Therefore, this study sought to better understand the time course of tendon protease activity in a rat model of supraspinatus overuse, as well as determine effects of 10 weeks of overuse on humeral head articular cartilage. For these studies, multiplex gelatin zymography was used to characterize protease activity profiles in tendon and cartilage, while histological scoring/mechanical testing and micro-computed tomography (μCT) imaging were used to quantify structural damage in the supraspinatus tendon insertion and humeral articular cartilage, respectively. Histological scoring of supraspinatus tendon insertions revealed tendinopathic cellular and collagen fiber changes after 10 weeks of overuse when compared to controls, while mechanical testing revealed no significant differences between tensile moduli (overuse: 24.5 ± 11.5 MPa; control: 16.3 ± 8.7 MPa). EPIC-μCT imaging on humeral articular cartilage demonstrated significant cartilage thinning (overuse: 119.6 ± 6.34 μm; control: 195.4 ± 13.4μm), decreased proteoglycan content (overuse: 2.1 ± 0.18 cm-1 ; control: 1.65 ± 0.14 cm-1 ), and increased subchondral bone thickness (overuse: 216.2 ± 10.9 μm; control: 192 ± 17.8μm) in the overuse animals. Zymography results showed no significant upregulation of cathepsins or matrix metalloproteinases in tendon or cartilage at 2 or 10 weeks of overuse compared to controls. These results have further elucidated timing of protease activity over 10 weeks and suggest that damage occurs to other tissues in addition to the supraspinatus tendon in this overuse injury model. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1910-1918, 2017.

“V”ictory Transosseous Equivalent Suture Configuration for Arthroscopic Rotator Cuff Tear Repairs of Iatrogenically Completed PASTA Lesions and Full-Thickness “U”-shaped Tears

The cost of numerous anchors in rotator cuff surgery is high from both an economic standpoint as well as a physiologic one. More anchors means increased cost and increased surgical time; additionally, the greater number of anchors placed, the greater the expense on the native bone that they inevitably replace. It is therefore in the surgeon's and patient's best interest to use the appropriate number of anchors, no more and no less, with the appropriate number being that which allows for strong, stable fixation with minimal gap formation and maximal healing potential and recovery. The transosseous equivalent repair technique described herein uses a single double-loaded bioabsorbable suture anchor placed along the medial border of the rotator cuff foot print and the humeral head articular cartilage margin followed by 1 pushlock (Arthrex, Naples, Florida) anchor placed laterally on the vertical aspect of the greater tuberosity. It is designed for small to medium "U"-shaped tears and for iatrogenically completed partial articular supraspinatus tendon avulsions of moderate to large size, the so-called PASTA lesion. The use of selective knot placement allows for the conversion of a linear construct into a "V" configuration, optimizing repair strength and allowing for earlier rehabilitation while maximizing the healing biology seen with increased footprint contact dimensions and less repair gap formation.

Articular Cartilage Thickness of the Humeral Head: An Anatomic Study

This study determined the thickness of normal humeral head articular cartilage by anatomic cross section using computer-aided image analysis software. Sixteen adult cadaveric humeral heads were analyzed. Our findings reveal that the thickness of humeral articular cartilage is substantially thinner than articular cartilage found in the knee. The cartilage is thickest in the central portion of the head and becomes progressively thinner towards the periphery. Surgical techniques used to treat pathology in the glenohumeral joint, specifically thermal energy or mechanical debridement, may have deleterious effects on the relatively thin humeral articular cartilage.

Internal impingement: findings on magnetic resonance imaging and arthroscopic evaluation.

The purpose of this study was to examine preoperative shoulder magnetic resonance imaging (MRI) and intraoperative arthroscopic findings in throwing athletes with a clinical diagnosis of internal impingement. Retrospective review. A retrospective review of the surgical indications for 769 shoulder arthroscopic procedures performed from 1997 to 2000 revealed 9 throwing athletes with a diagnosis of severe internal impingement. Each had failed treatment that included a minimum of 3 months of rehabilitation. Preoperative MRIs in all 9 were read by a fellowship-trained musculoskeletal radiologist blinded to the operative findings. Findings at arthroscopy were culled from the operative reports. On both MRI and at arthroscopy, all 9 athletes had posterosuperior labral lesions, 1 had a humeral head articular cartilage lesion, and 1 had a SLAP lesion. Additional findings on MRI included humeral head edema, subchondral cystic changes, posterosuperior glenoid sclerosis, and rotator cuff tendonopathy predominantly in the infraspinatus. At arthroscopy, there were additional findings of articular-sided partial rotator cuff tears not shown on MRI. Both MRI and arthroscopic findings described labral and humeral head articular cartilage lesions. These findings may be indicative of internal impingement in throwing athletes. Level III, diagnostic.

A Conewise Linear Elasticity mixture model for the analysis of tension-compression nonlinearity in articular cartilage.

A biphasic mixture model is developed that can account for the observed tension-compression nonlinearity of cartilage by employing the continuum-based Conewise Linear Elasticity (CLE) model of Curnier et al. (J. Elasticity, 37, 1-38, 1995) to describe the solid phase of the mixture. In this first investigation, the orthotropic octantwise linear elasticity model was reduced to the more specialized case of cubic symmetry, to reduce the number of elastic constants from twelve to four. Confined and unconfined compression stress-relaxation, and torsional shear testing were performed on each of nine bovine humeral head articular cartilage cylindrical plugs from 6 month old calves. Using the CLE model with cubic symmetry, the aggregate modulus in compression and axial permeability were obtained from confined compression (H-A = 0.64 +/- 0.22 MPa, k2 = 3.62 +/- 0.97 x 10(-16) m4/N.s, r2 = 0.95 +/- 0.03), the tensile modulus, compressive Poisson ratio, and radial permeability were obtained from unconfined compression (E+Y = 12.75 +/- 1.56 MPa, v- = 0.03 +/- 0.01, kr = 6.06 +/- 2.10 x 10(-16) m4/N.s, r2 = 0.99 +/- 0.00), and the shear modulus was obtained from torsional shear (mu = 0.17 +/- 0.06 MPa). The model was also employed to predict the interstitial fluid pressure successfully at the center of the cartilage plug in unconfined compression (r2 = 0.98 +/- 0.01). The results of this study demonstrate that the integration of the CLE model with the biphasic mixture theory can provide a model of cartilage that can successfully curve-fit three distinct testing configurations while producing material parameters consistent with previous reports in the literature.

Volumetric changes of articular cartilage during stress relaxation in unconfined compression

The time-dependent lateral expansion and load relaxation of cartilage cylinders subjected to unconfined compression were simultaneously recorded. These measurements were used to (1) test the assumption of incompressibility for articular cartilage, (2) measure the Poisson's ratio of articular cartilage in compression and (3) investigate the relationship between stress relaxation and volumetric change. Mechanical tests were performed on fetal, calf, and adult humeral head articular cartilage. The instantaneous Poisson's ratio of adult cartilage was 0.49±0.08 (mean+S.D.), thus confirming the assumption of incompressibility for this tissue. The instantaneous Poisson's ratio was significantly lower for calf (0.38±0.04) and fetal cartilage (0.36±0.04). The equilibrium Poisson's ratio, i.e. true Poisson's ratio of the solid matrix, was significantly higher for the adult tissue (0.26±0.11) compared to both the fetal (0.09±0.02) and calf (0.11±0.03) cartilage. A linear relationship between time-matched load and lateral expansion after the first minute of stress relaxation was observed.

Optical and mechanical determination of poisson's ratio of adult bovine humeral articular cartilage

The equilibrium stiffness of articular cartilage is controlled by flow-independent elastie properties (Young's modulus, E s, and Poisson's ratio, v s) of the hydrated tissue matrix. In the current study, an optical (microscopic) method has been developed for the visualization of the boundaries of cylindrical bovine humeral head articular cartilage disks ( n = 9), immersed in physiological solution, and compressed in unconfined geometry. This method allowed a direct, model-independent estimation of Poisson's ratio of the tissue at equilibrium, as well as characterization of the shape changes of the sample during the nonequilibrium dynamic phase. In addition to optical analyses, the equilibrium behavior of cartilage disks in unconfined and confined ramp-stress relaxation tests provided a direct estimation of the aggregate modulus, H a, and Young's modulus and, indirectly. Poisson's ratio for the articular cartilage. The mean value for Poisson's ratio obtained from the optical analysis was 0.185 ± 0.065 (mean ± S.D., n = 9). Values of elastic parameters obtained from the mechanical tests were 0.754 ± 0.198 MPa, 0.677 ± 0.223 MPa, and 0.174 ± 0.106 for H a, E s, and v s, respectively (mean ± S.D., n = 7). The similar v s-values obtained with optical and mechanical techniques imply that, at equilibrium, for these two tests, the isotropic model is acceptable for mechanical analysis. However, the microscopic techniques revealed that the lateral expansion, especially during the initial phase of relaxation, was inhomogeneous through the tissue depth. The superficial cartilage zone expanded less than the radial zone. The zonal differences in expansion were attributed to the known zonal differences in the fibrillar collagen architecture and proteoglycan concentration.

Surface and Subsurface Morphology of Bovine Humeral Articular Cartilage as Assessed by Atomic Force and Transmission Electron Microscopy

Maintenance of superficial structural integrity is essential for the load-bearing function of articular cartilage. In this study, we used atomic force microscopy (AFM) to image the 3-D surface and subsurface morphology of fresh bovine humeral head articular cartilage maintained in physiological solution. Complementary ultrastructural data were obtained by transmission electron microscopy (TEM) of cryoprocessed samples. The surface irregularities observed in previous scanning electron microscopic studies were not apparent with AFM. The most superficial layer, typically 200–500 nm thick, consisted of acellular and nonfibrous tissue. Occasionally, it exhibited local discontinuities through which the underlying network of collagen fibrils, oriented parallel to the surface and displaying the characteristic periodic banding, could been seen. Local variations in force-curve measurements indicate the existence of differences in micromechanical properties along the articular surface. AFM thus furnishes a new method for characterizing the surface structure and properties of freshly excised articular cartilage in physiologically relevant conditions. It confirms the existence of an amorphous, nonfibrous articular surface which may be vital for its normal lubrication and wearing propertiesin vivo.

A method of quantitative autoradiography for the spatial localization of proteoglycan synthesis rates in cartilage.

Incorporation of [35S]-sulfate into cartilage tissue indicates the synthesis of aggrecan, the large aggregating proteoglycan (PG) that endows cartilage with resistance to compression. Scintillation counting of tissue digests provides a quantitative measure of incorporated sulfate but does not provide information on the spatial location of synthesis within the tissue. Such spatially specific information is necessary to determine which cell populations respond to diffusible factors and to correlate local mechanical events (e.g., deformation, interstitial fluid stress) to cellular biosynthetic responses. The aim of this study was to develop and characterize a liquid emulsion autoradiography technique, including an automated grain counting procedure, to derive spatial profiles of aggrecan synthesis rates in cartilage. We chose mature 10-14-month-old bovine humeral head articular cartilage as a model system and applied a liquid emulsion autoradiography technique to [35S]-sulfate-labeled, resin-embedded, and semithin-sectioned tissue explants. High-magnification light microscopy color images were captured on a computer. Automated image analysis for grain number determination included a color thresholding procedure to discriminate grains from the lightly stained structural image and computation of the average area of a single grain from each image. Determination of grain number, whether originating from single grains or grain clusters, was performed by dividing the total grain area in the image by the average area of a single grain in the same image. This procedure largely eliminated the effects of variations of microscope light intensity, camera performance, image focus, section stain intensity, and thresholding on the resulting grain numbers. By altering the specific activity of the medium radiolabel and the emulsion exposure times, we demonstrated a linear dose dependence, without saturation, of grain number on radioactive content in the underlying section. By cutting specimens in half and performing liquid scintillation counting on one half and autoradiography on the other half, we found that each disintegration occurring in the section during exposure resulted in 0.67 +/- 0.21 grains (mean +/- SD; n = 58). Therefore, counted grain numbers can be directly converted to incorporated sulfate, largely reflecting the synthesis of the PG aggrecan. As an example of calculated intratissue profiles of aggrecan synthesis rates, we found for the mature bovine tissue in serum-free medium that aggrecan synthesis increases monotonically from the articular surface to the radial zone by as much as tenfold.