Regional variations in MR relaxation of hip joint cartilage in subjects with and without femoralacetabular impingement

The objective of this study was to analyze regional variations of magnetic resonance (MR) relaxation times (T_1ρ and T₂) in hip joint cartilage of healthy volunteers and subjects with femoral acetabular impingement (FAI). Morphological and quantitative images of the hip joints of 12 healthy volunteers and 9 FAI patients were obtained using a 3 T MR scanner. Both femoral and acetabular cartilage layers in each joint were semi-automatically segmented on sagittal 3D high-resolution spoiled gradient echo (SPGR) images. These segmented regions of interest (ROIs) were automatically divided radially into twelve equal sub-regions (30⁰ intervals) based on the fitted center of the femur head. The mean value of T_1ρ/T₂ was calculated in each sub-region after superimposing the divided cartilage contours on the MR relaxation (T_1ρ/T₂) maps to quantify the relaxation times. T_1ρ and T₂ relaxation times of the femoral cartilage were significantly higher in FAI subjects compared to healthy controls (39.9 ± 3.3 msec in FAI vs. 35.4 ± 2.3 msec in controls for T_1ρ (P = 0.0020); 33.9 ± 3.1 msec in FAI vs. 31.1 ± 1.7 msec in controls for T₂ (P = 0.0160)). Sub-regional analysis showed significantly different T_1ρ and T₂ relaxation times in the anterior-superior region (R9) of the hip joint cartilage between subjects with FAI and healthy subjects, suggesting possible regional differences in cartilage matrix composition between these two groups. Receiver operating characteristic (ROC) analysis showed that sub-regional analysis in femoral cartilage was more sensitive in discriminating FAI joint cartilage from that of healthy joints than global analysis of the whole region (T_1ρ: area under the curve (AUC) = 0.981, P = 0.0001 for R9 sub-region; AUC = 0.901, P = 0.002 for whole region; T₂: AUC = 0.976, P = 0.0005 for R9 sub-region; AUC = 0.808, P = 0.0124 for whole region). The results of this study demonstrated regional variations in hip cartilage composition using MR relaxation times (T_1ρ and T₂) and suggested that analysis based on local regions was more sensitive than global measures in subjects with and without FAI.     

Application of non-linear strain waves to the study of the growth of long bones

A non-linear dynamic model is developed to account for material inhomogeneities in a growth plate in long bones. The governing equations are obtained to account for non-linear dispersive, viscoelastic and inhomogeneous features of the growth plate. The evolution of non-linear strain waves over the material inhomogeneities is obtained via the asymptotic solutions. It is shown that variations in the amplitude and the width of both the bell-shaped and kink-shaped waves reflect the position and the size of the inhomogeneity. This may be used for a detection of the growing plate features and in the development of the reaction-diffusion equation for the stimulus of the growth of long bones.     

MR T1ρ quantification of cartilage focal lesions in acutely injured knees: correlation with arthroscopic evaluation

Objective

Quantitative T₁ρ MRI has been suggested as a promising tool to detect changes in cartilage composition that are characteristic of cartilage damage and degeneration. The objective of this study was to evaluate the capability of MR T₁ρ to detect cartilage lesions as evaluated by arthroscopy in acutely ACL-injured knees and to compare with the Whole-Organ Magnetic Resonance Imaging Score (WORMS) using clinical standard MRI.

Method

Ten healthy controls (mean age 35) with no ACL injury or history of osteoarthritis (OA) and 10 patients with acute ACL injuries (mean age 39) were scanned at 3 Tesla (3 T). ACL patients underwent ACL reconstruction, where focal lesions were graded according to an Outerbridge grading system during arthroscopic evaluation. Normalized MR T₁ρ values (T₁ρ z-scores normalized to control values in matched regions) in full thickness, and superficial and deep layers of cartilage were compared between defined sub-compartments with and without focal lesions. Intraclass (ICC) correlation and the root mean square coefficient of variation (RMS-CV) were performed to evaluate the inter-observer reproducibility of T₁ρ quantification. Sub-compartments of cartilage were also evaluated using WORMS scoring and compared to their Outerbridge score respectively.

Results

The inter-observer ICC and the RMS-CV of the sub-compartment T₁ρ quantification were 0.961 and 3.9%, respectively. The average T₁ρ z-scores were significantly increased in sub-compartments with focal lesions compared to those without focal lesions and to the control cohort (p < 0.05).

Conclusion

Our results indicate that T₁ρ provided a better diagnostic capability than clinical standard MRI grading in detecting focal cartilage abnormalities after acute injuries. Quantitative MRI may have great potential in detecting cartilage abnormalities and degeneration non-invasively, which are occult with standard morphological MRI.     

A hybrid scaffold of poly(lactide-<Emphasis Type="Italic">co</Emphasis>-glycolide) sponge filled with fibrin gel for cartilage tissue engineering

The poly(lactide-co-glycolide)(PLGA) sponge fabricated by a gelatin porogen leaching method was filled with fibrin gel to obtain a hybrid scaffold for chondrocytes culture in vitro.The fibrin gel evenly distributed in the hybrid scaffold with visible fibrinogen fibers after drying.In vitro culture it was found that in the hybrid scaffold the chondrocytes distributed more evenly and kept a round morphology as that in the normal cartilage.Although the chondrocytes seeded in the control PLGA sponges showed similar proliferation behavior with that in the hybrid scaffolds,they were remarkably elongated,forming a fibroblast-like morphology.Moreover,a larger amount of glycosaminoglycans was secreted in the hybrid scaffolds than that in the PLGA sponges after in vitro culture of chondrocytes for 4 weeks.The results suggest that the fibrin/PLGA hybrid scaffold may be favorably applied for cartilage tissue engineering.     

Strategies to optimize two-dimensional gel electrophoresis analysis of the human joint proteome

Due to the complex structure of the articular joint, it requires great effort to fully understand joint disease pathogenesis. The proteomic analysis of articular joint tissues could contribute greatly to our insight into the endogenous control mechanisms of matrix turnover and the unravelling of the molecular and cellular mechanisms involved in the progression of the arthritides. To date, most proteome analysis strategies use the two-dimensional gel electrophoresis (2-DE) technique to separate proteins according to their isoelectric point, molecular mass, solubility and relative abundance. In this work, we describe optimization of human joint sample preparation techniques to obtain high quality 2-DE maps of human joint tissues (cartilage and synovium), cells (chondrocytes and synoviocytes) and synovial fluid. These techniques improve the performance of gel-based differential proteomic analysis, and facilitate the application of proteomics to rheumatology studies.     

T1ρ-weighted MRI using a surface coil to transmit spin-lock pulses

T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.     

Bioinspired dual dynamic network hydrogels promote cartilage regeneration through regulating BMSC chondrogenic differentiation

How to improve the therapeutic efficacy of cell delivery during mechanical injection has been a great challenge for tissue engineering. Here, we present a facile strategy based on dynamic chemistry to prepare injectable hydrogels for efficient stem cell delivery using hyaluronic acid (HA) and poly(γ-glutamic acid) (γ-PGA). The combination of the guest–host (GH) complexation and dynamic hydrazone bonds enable the HA/γ-PGA hydrogels with physical and chemical dual dynamic network and endow hydrogels a stable structure, rapid self-healing ability, and injectability. The mechanical properties, self-healing ability, and adaptability can be programmed by changing the ratio of GH network to hydrazine bond cross-linked network. Benefitting from the dynamic cross-linking networks, mild preparation process, and cytocompatibility of HA/γ-PGA hydrogels, bone marrow mesenchymal stem cells (BMSCs) show high cell viability in this system following mechanical injection. Moreover, HA/γ-PGA hydrogels can promote BMSC proliferation and upregulate the expression of cartilage-critical genes. Notably, in a rabbit auricular cartilage defect model, BMSC-laden HA/γ-PGA hydrogels can effectively promote cartilage regeneration. Together, we propose a general strategy to develop injectable self-healing HA/γ-PGA hydrogels for effective stem cell delivery in cartilage tissue engineering.     

The Role of Osmotic Pressure and Tension-Compression Nonlinearity in the Frictional Response of Articular Cartilage

Articular cartilage is the bearing material of diarthrodial joints such as the knee, hip, or shoulder. Some studies of cartilage lubrication have hypothesized that pressurization of its interstitial fluid may contribute predominantly to reducing the friction coefficient at the contact interface of articular layers. This study introduces a formulation for the dependence of the frictional response of articular cartilage on interstitial fluid pressurization, which accounts for the osmotic pressure in cartilage as well as the tissue's tension-compression nonlinearity, and is based on the theory of mixtures for soft hydrated charged tissues. Theoretical predictions of this model are obtained for the configuration of unconfined compression creep. It is observed from theory that increasing the salt concentration of the tissue's bathing solution reduces the minimum friction coefficient that can be achieved, relative to its equilibrium value; the model also predicts that increasing the applied load can similarly reduce the minimum friction coefficient. Physical interpretations of these phenomena are provided by the model. Experimental results are presented which support these theoretical findings and produce time-dependent responses in good agreement with model predictions. Furthermore, it is observed that the equilibrium friction coefficient does not remain constant under various loads or salt concentrations, and correlation analyses suggest that the equilibrium value depends in part on the compressive strain in the tissue.     

Diffusion tensor imaging of native and degenerated human articular cartilage

Diffusion tensor imaging (DTI) is potentially sensitive to collagen degeneration in cartilage. In this study, DTI was measured on human cartilage samples with interventions of trypsin and collagenase. The measured preferred diffusion direction was consistent with the zonal structure of collagen network. The glycosaminoglycan concentration decreased and apparent diffusion coefficient increased with both interventions. The fractional anisotropy (FA) was not affected by trypsin and showed a slight increase with combined trypsin and collagenase intervention. DTI in cartilage is technically challenging due to the low FA and the almost undetectable change with collagen disruption seen here.     

Vocal Process Avulsion

Vocal process avulsion is a rare complication of intubation or external laryngeal trauma that can cause significant dysphonia. The vocal process develops independently from the body of the arytenoid cartilage, which results in a fusion plane that is vulnerable to trauma. The findings of vocal process avulsion may be subtle, and the relationship of the vocal process to the body of the arytenoid cartilage must be examined closely. Stroboscopy is critical in the evaluation. We describe three cases of vocal process avulsion encountered by the senior author (R.T.S.) over the last 5 years and discuss our approaches to evaluation and treatment. All cases were repaired endoscopically. However, we used three different techniques. These include chemical tenotomy with botulinum toxin, closed reduction with fat injection, and open reduction via cordotomy.