Assessment of articular cartilage degradation in response to an impact injury using µMRI

PURPOSE

Degradation of articular cartilage (AC) due to injury to the knee joint may initiate post-traumatic osteoarthritis (PTOA). Failure to diagnose the onset of the disease at an early stage makes the cure ineffective for PTOA. This study investigated the consequences of a mechanical injury to the knee in a rabbit model using microscopic magnetic resonance imaging (µMRI) at high resolution.

MATERIALS AND METHODS

A mechanical injury was induced to the knee joints of 12 rabbits. Cartilage blocks were extracted from the non-impacted and impacted knee joints after 2 and 14 weeks post-impact. The specimens were studied using µMRI T2 relaxation and inductively coupled plasma analysis to determine the early degradation of the articular cartilage.

RESULTS

The data established a connection between T2 relaxation time and the early progression of knee PTOA after an impact injury. T2 values were found to be higher in the impacted cartilage at both 2 and 14 weeks, in particular, T2-55° values in the impacted samples displayed a significant rise of 6.93% after 2 weeks and 20.02% after 14 weeks. Lower glycosaminoglycan measurement and higher water content in the impacted cartilage confirmed the µMRI results.

CONCLUSIONS

This µMRI T2 study was able to detect cartilage damage in the impacted knees. In addition, greater degradation in the affected knees at 14 weeks than at 2 weeks indicated the progressive nature of cartilage deterioration over time. The µMRI results were in accord with the biochemical analysis, indicating the detection of early structural damage in the cartilage.

Characteristics of distal femoral articular cartilage in 6 weeks posttraumatic osteoarthritis by a subcritical impact

Traumatized knee greatly contributes to osteoarthritis (OA) of the knee in young adults. To intervene effectively before the onset of severe structural disruption, detection of the disease at the early onset is crucial. In this study, we put together the findings for the detection of OA from the femoral knee joint cartilage of the rabbit at 6 weeks posttrauma. Articular cartilage samples are taken from the impacted and nonimpacted joints at 0 week (serving as the control group) and at 6 weeks posttrauma by minimal force. The samples were imaged using microscopic magnetic resonance imaging (µMRI) at 11.7 µm/pixel and polarized light microscopy (PLM) at 1 µm/pixel. In addition, an inductively coupled plasma - optical emission spectrometry analysis was performed using the adjacent cartilage samples. The outcomes of this study demonstrate an increase in T2 values in 6 weeks samples compared to the 0 week samples by µMRI technique, indicating a general increase of tissue hydration within cartilage. PLM detects a decrease in the average thickness of the superficial zones in the posttraumatic osteoarthritis samples, significant in the impacted femurs. There was an average increasing trend of maximum retardation in the tide mark in comparison to the reported calcium concentration (mg/L) in impacted samples suggesting a possible rise in mineralization in the 6 weeks samples. Qualitatively, physical observation of the joint after 6 weeks showed signs of reddening in the anterior femur suggesting the disease process is a localized phenomenon. Through microscopic imaging, we are able to detect these changes at 6 weeks posttrauma qualitatively and quantitatively.

Location-Specific Study of Young Rabbit Femoral Cartilage by Quantitative µMRI and Polarized Light Microscopy

OBJECTIVE

Microscopic magnetic resonance imaging (µMRI) and polarized light microscopy (PLM) are used to characterize the structural variations at different anatomical locations of femoral cartilage in young rabbits (12-14 weeks old).

DESIGN

Four intact knees were imaged by µMRI at 86 µm resolution. Three small cartilage-bone specimens were harvested from each of 2 femoral medial condyles and imaged by quantitative µMRI (T2 anisotropy) at 9.75 µm resolution (N = 6). These specimens, as well as the other 2 intact femoral condyles, were used for histology and imaged by quantitative PLM (retardation and angle) at 0.25 µm to 4 µm resolutions.

RESULTS

Quantitative MRI relaxation data and PLM fibril data revealed collaboratively distinct topographical variations in both cartilage thickness and its collagen organization in the juvenile joint. Cartilage characteristics from the central location have a 3-zone arcade-like fibril structure and a distinct magic angle effect, commonly seen in mature articular cartilage, while cartilage at the anterior location lacks these characteristics. Overall, the lowest retardation values and isotropic T2 values have been found in the distal femur (trochlear ridge), with predominant parallel fibers with respect to the articular surface. Central cartilage is the thickest (~550 µm), approximately twice as thick as the anterior and posterior locations.

CONCLUSION

Distinctly different characteristics of tissue properties were found in cartilage at different topographical locations on femoral condyle in rabbits. Knowledge of location-specific structural differences in the collagen network over the joint surface can improve the understanding of local mechanobiology and provide insights to tissue engineering and degradation repairs.

Structural differences between immature and mature articular cartilage of rabbits by microscopic MRI and polarized light microscopy

This study aimed to determine the structural features between immature and mature articular cartilage from the humeral and femoral joints of rabbits. Specimens of articular cartilage (n = 6 for immature tissue, n = 6 for mature tissue) that were still attached to the underlying bone from a humerus (shoulder joint) or femur (knee joint) were imaged using microscopic MRI (µMRI) and polarized light microscopy (PLM). Quantitative µMRI data with a pixel resolution of 11.7-13.2 µm revealed a number of differences between the immature and mature cartilage, including total thickness, and T2 and T1ρ relaxation values. Quantitative PLM data with a pixel resolution of 0.25-1 µm confirmed the µMRI results and revealed additional differences in cellular features between the tissues. The mature cartilage had a clearly defined tidemark, which was absent in the immature tissue. The ability to differentiate specific maturation-related cartilage characteristics could be beneficial to translational studies of degenerative diseases such as osteoarthritis.

Structural Morphology of Rabbit Patella and Suprapatella Cartilage by Microscopic MRI and Polarized Light Microscopy

OBJECTIVE

In order to appreciate the roles articular cartilage of sesamoid bones and sesamoid fibrocartilage play in anatomy and pathology, the articular cartilage of the patella (n = 4) and suprapatella (n = 4) (a sesamoid fibrocartilage) of 12 to 14 weeks old New Zealand rabbits were studied qualitatively and quantitatively.

DESIGN/METHOD

The intact knee joints and block specimens from the joints were imaged using microscopic magnetic resonance imaging (µMRI) at a 97.6-µm pixel resolution for the former and 19.5-µm resolution for the latter. Histological sections were made out of the µMRI-imaged specimens, which were imaged using polarized light microscopy (PLM) at 0.25-, 1-, and 4-µm pixel resolutions.

RESULTS

The patella cartilage varied in thickness across the medial to lateral ends of the sesamoid bone with the central medial aspect slightly thicker than the lateral aspect. The suprapatella fibrocartilage decreased proximally away from the knee joint. Quantitative results of patellar cartilage showed strong dependence of fiber orientation with the tissue depth. Three histological zones can be clearly observed, which are similar to articular cartilage from other large animals. The sesamoid fibrocartilage has one thin surface layer (10 µm thick) of parallel-arranged structured fibers followed immediately by the majority of random fibers in bulk tissue. T2 relaxation time anisotropy was observed in the patellar cartilage but not in the bulk fibrocartilage.

CONCLUSION

Given the different functions of these 2 different types of cartilages in joint motion, these quantitative results will be beneficial to future studies of joint diseases using rabbits as the animal model.