Correction to: Indian Journal of Orthopaedics https://doi.org/10.1007/s43465-020-00293-2

The original version of this article unfortunately contained some mistakes. Some figures were incorrect and interchanged respectively. The correct assignment of figures is as follows: Figs. 2, 4 and 6 were replaced by new figures. The previous Fig. 2 in the article is actually Fig. 3, the previous Fig. 3 in the article is actually Fig. 5, and the previous Fig. 5 was deleted. In addition, reference [3] was presented incorrectly. The correct figures and reference are given below.

Fig. 2
figure 2

Pathological grade of knee joint cartilage he (× 100). Grade I–IV degeneration of the cartilage of the knee joint: the chondrocyte matrix is unevenly stained and the chondrocytes are disordered; the cartilage surface is rough, the normal structure of the cartilage surface is destroyed, and the matrix is unevenly stained; the chondrocytes are suddenly reduced and the structure is disordered; obviously the cartilage structure was damaged and the chondrocytes were necrotic

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Fig. 3
figure 3

MMP-1 immunohistochemical staining of knee cartilage (× 100). With the increase of knee cartilage degeneration, brown cells increased and the expression of MMP-1 increased significantly

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Fig. 4
figure 4

Scatter plot of T2 value and MMP1 expression in OA knee articular cartilage

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Fig. 5
figure 5

MMP-3 immunohistochemical staining of knee cartilage (× 100). The expression of MMP-3 increased with the degree of degeneration of cartilage in the knee joint, and it was found that the expression of MMP-3 was higher in the lower and deep layers of cartilage

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Fig. 6
figure 6

The expression of MMP1, MMP3 in various grades. The comparison between b and grade I, P < 0.05, The comparison between c and grade II, P < 0.05, The com-parison between d and grade III, P < 0.05

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The original article has been corrected.