Joint locking (medicine)

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In medicine, joint locking is a symptom of pathology in a joint. It is a complaint by a person when he is unable to fully flex or fully extend a joint. This term is also used to describe the mechanism of lower limb joints held in full extension without much muscular effort when a person is standing.

Clinical symptom[edit]

Complaints of locking sensation in the knee joint can be divided into true locking and pseudolocking. True locking happens when the intra-articular structure (e.g. ligaments)[1] is damaged, or a loose body is present inside the joint, or there is a meniscal tear. The knee can be unlocked by rotating the leg and full movement can be restored. A person may feel the presence of a loose body in the suprapatellar region, or lateral and medial gutter. Once the loose body is felt, it may slide and move to another area, thus it is also called a "joint mouse".[2]

Pseudolocking usually happens when a person feels pain when trying to flex or extend a knee joint while there is no structural causes of the locking. The locking is usually relieved after massage or taking painkillers.[2]

Joint locking is a common symptom of:

Locking mechanism[edit]

Locking of the knee happens during the last stages of extension when a person is standing up. Medial rotation of femur occurs as the space available at the lateral condyle of tibia is being used up by the lateral condyle of femur during extension. Therefore, lateral femoral condyle acts as an axis for medial femoral condyle to rotate backwards. This movement is aided by oblique pull of the ligaments of the knee joint and contraction of the quadriceps muscles. The ligaments are pulled taut when the knee joint is locked in place during standing. When the knee is flexed, it is unlocked by the popliteus muscle through the lateral rotation of femur.[4]

The locking mechanisms of hip joint[5] and midtarsal joint[6][7] are also being investigated in cadavers.


  1. ^ a b Roald, Bahr; Sverre, Mæhlum (2004). Clinical Guide to Sports Injuries. Human Kinetics. p. 325. ISBN 9780736041171. Retrieved 19 January 2018.
  2. ^ a b c Nick, Harris (2003). Advanced Examination Techniques in Orthopaedics. Cambridge University Press. p. 150. ISBN 9781841100739. Retrieved 19 January 2018.
  3. ^ Hixon AL, Gibbs LM (January 2000). "What Should I Know About Osteochondritis Dissecans?". American Family Physician. 61 (1): 158.
  4. ^ Krishna, Garg (2010). "12 - Joints of lower limb". BD Chaurasia's Human Anatomy (Regional and Applied Dissection and Clinical) Volume 2 - Lower limb, abdomen, and pelvis (Fifth ed.). India: CBS Publishers and Distributors Pvt Ltd. p. 156. ISBN 978-81-239-1864-8. Locking is a mechanism that allows the knee to remain the position of full extension as in standing without much muscular effort
  5. ^ W.H, Roberts (November 1963). "The locking mechanism of the hip joint". The Anatomical Record. 147 (3): 321–324. doi:10.1002/ar.1091470303.
  6. ^ Blackwood, CB; Yuen, TJ; Sangeorzan, BJ; Leodux, WR (December 2005). "The midtarsal joint locking mechanism". Foot & Ankle International. 26 (12): 1074–1080. doi:10.1177/107110070502601213. PMID 16390642.
  7. ^ Okita, N; Meyers, SA; Challis, JH; Sharkey, NA (January 2014). "Midtarsal joint locking: new perspectives on an old paradigm". Journal of Orthopaedic Research. 32 (1). doi:10.1002/jor.22477. PMID 24038197.