medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...

, joint locking is a

symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

pathology Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...

in a

joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...

. It is a complaint by a person when they are unable to fully flex or fully extend a joint. This term is also used to describe the normal mechanism of lower limb joints held in full extension without much muscular effort when a person is standing. __TOC__

Clinical symptom

Complaints of locking sensation in the

knee joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

can be divided into true locking and pseudo locking. True locking happens when the intra-articular structure (e.g. ligaments) 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". Pseudolocking usually happens when a person feels pain when trying to flex or extend a knee joint while there are no structural causes of the locking. The locking is usually relieved after a massage or taking painkillers. Joint locking is a common symptom of: *

Osteoarthritis Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...

Osteochondritis dissecans Osteochondritis dissecans (OCD or OD) is a joint disorder primarily of the subchondral bone in which cracks form in the articular cartilage and the underlying subchondral bone. OCD usually causes pain during and after sports. In later stages ...

* Synovial osteochondromatosis *

Tear of meniscus A tear of a meniscus is a rupturing of one or more of the fibrocartilage strips in the knee called menisci. When doctors and patients refer to "torn cartilage" in the knee, they actually may be referring to an injury to a meniscus at the top of ...

of the knee *

Anterior cruciate ligament injury An anterior cruciate ligament injury occurs when the anterior cruciate ligament (ACL) is either stretched, partially torn, or completely torn. The most common injury is a complete tear. Symptoms include pain, an audible cracking sound during inju ...

of the knee

Locking mechanism

Normal locking of the knee happens during the last stages of extension when a person is standing up. Medial rotation of

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

occurs as the space available at the lateral condyle of the tibia is being used up by the lateral condyle of the femur during extension. Therefore, lateral femoral condyle acts as an axis for medial femoral condyle to rotate backwards. This movement is aided by the oblique pull of the ligaments of the knee joint and contraction of the

quadriceps The quadriceps femoris muscle (, also called the quadriceps extensor, quadriceps or quads) is a large muscle group that includes the four prevailing muscles on the front of the thigh. It is the sole extensor muscle of the knee, forming a large ...

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 The popliteus muscle in the leg is used for unlocking the knees when walking, by laterally rotating the femur on the tibia during the closed chain portion of the gait cycle (one with the foot in contact with the ground). In open chain movements ...

muscle through the lateral rotation of femur. The locking mechanisms of

hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

and

midtarsal joint The transverse tarsal joint or midtarsal joint or Chopart's joint is formed by the articulation of the calcaneus with the cuboid (the calcaneocuboid joint), and the articulation of the talus with the navicular (the talocalcaneonavicular joint) ...

are also being investigated in

cadaver A cadaver or corpse is a dead human body that is used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue to repair a defect in a living human being. Stud ...

References

Symptoms and signs: musculoskeletal system {{orthopedics-stub