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

Abstract

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.

Keywords: articular cartilage; inductively coupled plasma‐optical emission spectrometry; microscopic magnetic resonance imaging; polarized light microscopy; posttraumatic osteoarthritis.

FIGURE 1

Photo of A) the cut slice of the femur with the dotted box showing where cartilage block was taken from the medial side, B) the anterior surface of the femur of a 0week post-impact joint, and C) is a photo of a similar location of a 6week post-impact from impact and non-impacted joint. The white arrows in C) show color changes on the joint surface.

FIGURE 2

2D intensity images from μMRI T2 experiments. A) shows the intensity images of 0week cartilage blocks from impact and non-impact joint and B) shows the intensity images from 6weeks of cartilage blocks from impact and non-impact joint. The quantitative T2 maps are shown on the rightest panel. Similar cartilage characteristics are observed in both sample groups

FIGURE 3

Averaged bulk T2 values of cartilage between impact and non-impact joints for 0week and 6weeks samples with their surface oriented at a magic angle (55°) to the external magnetic field (B_o). Note a general increase in 6weeks samples (fitted with a black solid line) in bulk than in 0week samples (fitted with a grey solid line). Corresponding dashed lines represent the 95% confidence intervals for the average T2 mean values of the individual samples (markers).

FIGURE 4

Averaged zonal T2 values of cartilage between impact and non-impact joints for 0week and 6week samples with their surface oriented at A) at magic angle (55°) to the external magnetic field (B_o), B) at 0° to B_o. The 6weeks samples are fitted with the black solid lines and 0week with grey solid lines. Corresponding dashed line fits represent the 95% confidence intervals for the average T2 mean values of the individual samples (markers).

FIGURE 5

2D images of angle (A) and retardation (B) PLM technique at higher resolution 1μm/pixel for 0week and 6weeks samples of impact and non-impact joints. SZ, TZ, and RZ represent superficial, transitional, and Radial zones.

FIGURE 6

Averaged depth-dependent profiles of the angle in the impacted A) and non-impacted C) joints for 0week and 6weeks cartilage blocks. Arrow in A) shows a reduction in SZ thickness of the impact SZ thickness. Averaged depth-dependent profiles of the retardation in the impact B) and non-impacted D) for 0week and 6weeks of cartilage blocks. In B), the surface arrow points to the reduction of the retardation in the 6week group; while the deep arrow points to the estimated tide mark of the cartilage.