A knee is considered to be locked when following some incident the patient finds themself unable to take the knee through a full range of movement.
The unusual traumatic locked young knee Miswan MFM, Alsagoff SL, Effendi FM, and MI Ibrahim. Malays Fam Physician. 2019; 14(2): 26–28.
[A Locked Knee Without Previous Trauma] - abstract only - article in Dutch Brouwers HFG, van Raay JJAM and Somford MP. Ned Tijdschr Geneeskd . 2017;161:D964.
Knee locked in flexion: incarcerated semitendinosus tendon around a proximal tibial osteochondroma Andrews K, Rowland A and Tank J. J Surg Case Rep. 2019 Feb; 2019(2): rjy346.