Table 1.

Criteria for the diagnosis, classification and severity grading of soft-tissue fibrosis after TKA established by Kalson et al.

	Category	Criteria	Exclude
Main diagnostic criteria	Restricted ROM	①Soft-tissue fibrosis that was not present preoperation. ②Loss of movement on extension>5°. ③Flexion range ≤ 100°	Problems with implant (malpositioning, cement, ectopic bone formation, loosening, malalignment); ligament reconstruction, infection, pain, CRPS or other specific causes; wound issues, incorrect surgical indication
Secondary diagnostic criteria	Stiffness
	Pain
	Inflammatory markers	CRP, WBCs
	Aspiration of the joint	Microbiological culture and cell count
Auxiliary diagnosis	X-ray, CT		Component malalignment; heterotopic ossification; patella infera
	MRI	Measurement of perisynovial thickness or quantification of fibrotic tissue in the parapatellar gutters	Focal fibroses; scar tissue
	Open or arthroscopic surgery	Direct visualization of fibrosis
	Pathological anatomy and histopathology	Supply evidence of fibrosis, not essential; characterized by a varying degree of cellularity of fibroblasts.