Knee jerk Health Dictionary

The joint formed by the FEMUR, TIBIA and patella (knee-cap). It belongs to the class of hinge-joints, although movements are much more complex than the simple motion of a hinge, the condyles of the femur partly rolling, partly sliding over the ?at surfaces on the upper end of the tibia, and the acts of straightening and of bending the limb being ?nished and begun, respectively, by a certain amount of rotation. The cavity of the joint is very intricate: it consists really of three joints fused into one, but separated in part by ligaments and folds of the synovial membrane. The ligaments which bind the bones together are extremely strong, and include the popliteal and the collateral ligaments, a very strong patellar ligament uniting the patella to the front of the tibia, two CRUCIATE LIGAMENTS in the interior of the joint, and two ?brocartilages which are interposed between the surfaces of tibia and femur at their edge. All these structures give to the knee-joint great strength, so that it is seldom dislocated. The cruciate ligaments, although strong, sometimes rupture or stretch under severe physical stress such as contact sports or athletics. Surgical repair may be required, followed by prolonged physiotherapy.

A troublesome condition often found in the knee – and common among athletes, footballers and other energetic sportspeople – consists of the loosening of one of the ?bro-cartilages lying at the head of the tibia, especially of that on the inner side of the joint. The cartilage may either be loosened from its attachment and tend to slip beyond the edges of the bones, or it may become folded on itself. In either case, it tends to cause locking of the joint when sudden movements are made. This causes temporary inability to use the joint until the cartilage is replaced by forcible straightening, and the accident is apt to be followed by an attack of synovitis, which may last some weeks, causing lameness with pain and tenderness especially felt at a point on the inner side of the knee. This condition can be relieved by an operation

– sometimes by keyhole surgery (see MINIMALLY INVASIVE SURGERY (MIS)) – to remove the loose portion of the cartilage. Patients whose knees are severely affected by osteoarthritis or rheumatoid arthritis which cause pain and sti?ness can now have the joint replaced with an arti?cial one. (See also ARTHROPLASTY; JOINTS, DISEASES OF.)... knee

Knock-knee, or genu valgum, is a deformity of the lower limbs in such a direction that when the limbs are straightened the legs diverge from one another. As a result, in walking the knees knock against each other. The amount of knock-knee is measured by the distance between the medial malleoli of the ankles, with the inner surfaces of the knee touching and the knee-caps facing forwards. The condition is so common in children between the ages of 2–6 years that it may almost be regarded as a normal phase in childhood. When marked, or persisting into later childhood, it can be corrected by surgery (osteotomy).... knock-knee

A sudden involuntary movement. The term is often used to describe the tendon re?exes.... jerk

A surgical operation to replace a diseased – usually osteoarthritic – KNEE with an arti?cial (metal or plastic) implant which covers the worn cartilage. As much of the original joint as possible is retained. The operations, like hip replacements, are usually done on older people (there is some restriction of movement) and about 90 per cent are successful.... knee-joint replacement

An in?ammation of the bursa in front of the knee-cap, often mistaken for some disease in the joint itself (see BURSITIS).... housemaid’s knee

See PATELLAR TENDINITIS.... jumper’s knee

Inflammation of the bursa that cushions the pressure point over the tibial tubercle (the bony prominence just below the knee) caused by prolonged kneeling (see bursitis).... clergyman’s knee

A temporary inability to move the knee joint. A locked knee may be caused by a torn cartilage or by loose bodies in the joint.... locked knee

A popular term for accumulation of fluid within or around the knee joint. The most common cause is bursitis. (See also effusion, joint).... water on the knee

a deep tendon reflex elicited when the Achilles tendon is stretched and then struck with a tendon hammer. The normal response is reflex contraction of the calf muscles and plantar flexion of the ankle. The ankle jerk may be increased if the spinal cord is compressed above the level of the first sacral spinal nerve (which arises at the level of the second lumbar vertebra). If the nerve itself is cut or compressed the reflex is reduced or absent.... ankle jerk

a deep tendon reflex mediated by the fifth cervical *spinal nerve (C5). The examiner’s thumb or index finger is placed over the patient’s biceps tendon in the elbow crease and struck sharply with a tendon hammer; the normal response is a reflex contraction of the biceps and flexion of the elbow. The jerk is exaggerated in upper *motor neuron lesions, such as a stroke, and reduced or absent in lower motor neuron lesions, such as a disc herniation, peripheral nerve injury, or peripheral neuropathy (e.g. diabetes, alcoholism).... biceps jerk

(prepatellar bursitis) inflammation and resultant swelling of the bursa in front of the kneecap, usually due to repetitive friction and pressure over the kneecap, as from frequent episodes of prolonged kneeling. Treatment includes pressure bandaging, *NSAIDs, and avoidance of kneeling. See bursitis.... housemaid’s knee

an abnormal reflex elicited by lightly placing the index finger across the chin of the patient and tapping it with a tendon hammer while the jaw hangs loosely open. A brisk upward movement of the jaw indicates an upper *motor neuron disorder above the brainstem.... jaw-jerk reflex

(patellar tendinitis) a form of *tendinitis that is common in athletes and dancers. Repeated sudden contracture of the quadriceps muscle at take-off causes inflammation of the attachment of the patellar tendon to the lower end of the patella. Treatment includes rest, physiotherapy, and anti-inflammatory medication.... jumper’s knee

the buttocks-up position assumed by patients undergoing anorectal examinations, now commonly performed in the left lateral position. It is useful for helping patients dispel excess flatus following colonoscopy.... knee-elbow position

a tendon reflex that acts at the level of the seventh cervical spinal nerve. With the elbow flexed and relaxed, the triceps tendon is struck just above the elbow, causing contraction of the triceps and extension of the elbow. This reflex is increased in upper *motor neuron lesions and absent in lower motor neuron lesions.... triceps jerk