More intrinsic parameters should be used in assessing degeneration of articular cartilage with quantitative ultrasound

Ultrasound can detect macroscopically undetectable changes in osteoarthritis reflecting the superficial histological and biochemical degeneration: ex vivo study of rabbit and human cartilage

Recognizing subtle cartilage changes in the preclinical stage of osteoarthritis (OA) is essential for early diagnosis. To this end, the ability of the ultrasound signal intensity to detect macroscopically undetectable cartilage change was investigated. In this study, cartilage of rabbit OA model and human OA samples was examined by macroscopic evaluation, ultrasound signal intensity, histology with Mankin scores, and Fourier transform infrared imaging (FTIRI) analysis. Rabbit OA was induced by anterior cruciate ligament transection and evaluated at 1, 2, 4 and 12 weeks. Twenty human samples were harvested during total knee arthroplasty from OA patients who had macroscopically normal human cartilage (ICRS grade 0) on the lateral femoral condyle. In the animal study, there was no macroscopic OA change at 2 weeks, but histology detected degenerative changes at this time point. Ultrasound signal intensity also detected degeneration at 2 weeks. In human samples, all samples were obtained from macroscopically intact site, however nearly normal (0≤ Mankin score <2), early OA (2≤ Mankin score <6), and moderate OA (6≤ Mankin score <10) samples were actually intermixed. Ultrasound signal intensity was significantly different among these 3 stages and was well correlated with Mankin scores (R = −0.80) and FTIR parameters related to collagen and proteoglycan content in superficial zone. In conclusion, ultrasound can detect microscopic cartilage deterioration when such changes do not exist macroscopically, reflecting superficial histological and biochemical changes.

Site dependence of thickness and speed of sound in articular cartilage of bovine patella

Researchers have made efforts to quantify thickness of articular cartilage as well as its acoustic and mechanical properties using various ultrasound (US) techniques during the last decades, because they are important indicators of articular cartilage degeneration. However, the variation of the thickness and speed of sound of articular cartilage at different anatomical sites would result in the uncertainty of US assessment of degeneration. In this paper, the site dependences of speed of sound and thickness of bovine patellar articular cartilage (n = 10) were investigated using a custom-made US measurement system. The thickness and speed of sound of articular cartilage at different locations of the bovine patella were measured on excised specimens ex situ using a noncontact US approach. A total of 10 patellae were tested. The results showed the overall mean value of the speed of sound in the articular cartilage at the 25 measured sites was 1626 +/- 86 m/s (range, 1507 to 1834 m/s). No statistically significant difference in the speed of sound was observed among the 25 locations or among the four quadrants of the patella. The highest speed of sound (1834 +/- 74 m/s) was obtained at the medial-upper quadrant and the lowest value (1507 +/- 74 m/s) at the medial-lower quadrant. Further grouping of the data revealed that the speed of sound in the central region (1633 +/- 21 m/s) was significantly (p < 0.01) larger than that for the surrounding region (1621 +/- 22 m/s). The overall mean thickness of the patellar articular cartilage was 1.34 +/- 0.34 mm. No significant difference was obtained in the thickness among the 25 locations and also among the four quadrants. However, when the thickness values were divided diagonally, a significant difference (p < 0.01) was observed between the upper region (1.27 +/- 0.11 mm) and the lower region (1.31 +/- 0.41 mm) of the patellae. Although no significant differences in the thickness and speed of sound among the tested sites were observed, it was demonstrated in this study that they did show some degree of site dependence.

Mechanical effects of surgical procedures on osteochondral grafts elucidated by osmotic loading and real-time ultrasound

Introduction

Osteochondral grafts have become popular for treating small, isolated and full-thickness cartilage lesions. It is recommended that a slightly oversized, rather than an exact-sized, osteochondral plug is transplanted to achieve a tight fit. Consequently, impacting forces are required to insert the osteochondral plug into the recipient site. However, it remains controversial whether these impacting forces affect the biomechanical condition of the grafted articular cartilage. The present study aimed to investigate the mechanical effects of osteochondral plug implantation using osmotic loading and real-time ultrasound.

Methods

A full-thickness cylindrical osteochondral defect (diameter, 3.5 mm; depth, 5 mm) was created in the lateral lower quarter of the patella. Using graft-harvesting instruments, an osteochondral plug (diameter, 3.5 mm as exact-size or 4.5 mm as oversize; depth, 5 mm) was harvested from the lateral upper quarter of the patella and transplanted into the defect. Intact patella was used as a control. The samples were monitored by real-time ultrasound during sequential changes of the bathing solution from 0.15 M to 2 M saline (shrinkage phase) and back to 0.15 M saline (swelling phase). For cartilage sample assessment, three indices were selected, namely the change in amplitude from the cartilage surface (amplitude recovery rate: ARR) and the maximum echo shifts from the cartilage surface and the cartilage-bone interface.

Results

The ARR is closely related to the cartilage surface integrity, while the echo shifts from the cartilage surface and the cartilage-bone interface are closely related to tissue deformation and NaCl diffusion, respectively. The ARR values of the oversized plugs were significantly lower than those of the control and exact-sized plugs. Regarding the maximum echo shifts from the cartilage surface and the cartilage-bone interface, no significant differences were observed among the three groups.

Conclusions

These findings demonstrated that osmotic loading and real-time ultrasound were able to assess the mechanical condition of cartilage plugs after osteochondral grafting. In particular, the ARR was able to detect damage to the superficial collagen network in a non-destructive manner. Therefore, osmotic loading and real-time ultrasound are promising as minimally invasive methods for evaluating cartilage damage in the superficial zone after trauma or impact loading for osteochondral grafting.

Intravascular Ultrasound (IVUS): A Potential Arthroscopic Tool for Quantitative Assessment of Articular Cartilage

Conventional ultrasound examination of the articular cartilage performed externally on the body surface around the joint has limited accuracy due to the inadequacy in frequency used. In contrast to this, minimally invasive arthroscopy-based ultrasound with adequately high frequency may be a better alternative to assess the cartilage. Up to date, no special ultrasound transducer for imaging the cartilage in arthroscopic use has been designed. In this study, we introduced the intravascular ultrasound (IVUS) for this purpose. An IVUS system with a catheter-based probe (Ø approximately 1mm) was used to measure the thickness and surface acoustical reflection of the bovine patellar articular cartilage in vitro before and after degeneration induced by enzyme treatments. Similar measurement was performed using another high frequency ultrasound system (Vevo) with a probe of much larger size and the results were compared between the two systems. The thickness measured using IVUS was highly correlated (r = 0.985, p < 0.001) with that obtained by Vevo. Thickness and surface reflection amplitude measured using IVUS on the enzymatically digested articular cartilage showed changes similar to those obtained by Vevo, which were expectedly consistent with previous investigations. IVUS can be potentially used for the quantitative assessment of articular cartilage, with its ready-to-use arthroscopic feature.