Next Lesson - Conditions of the Thigh
Core
Want more information on anatomy before you begin looking at conditions? Head to our articles on Bones of the Lower Limb, Muscles of the Thigh and Muscles of the Lower Leg.
Infra-patellar bursitis is also known as ‘Clergyman’s knee’. This is inflammation of the infra-patellar bursa. A bursa is a fluid-filled sac that reduces friction at a joint. This one sits just below the patella, between the skin and the patellar tendon (the tendon that runs from the patella to the tibia). Infra-patellar bursitis is caused by repeated microtrauma (small injuries that add up over time), often from upright kneeling (classically in the clergy). Infra-patellar bursitis presents with pain at the front of the knee and swelling just below the patella. The area may also be red (erythematous). It can be hard to tell apart from patellar tendinopathy (pain and irritation of the patellar tendon from overuse).
Infra-patellar bursitis is usually treated with rest, ice, elevation, avoiding kneeling (or using knee pads) and over-the-counter painkillers (painkillers that can be bought without a prescription). The bursa may be infected (septic bursitis). Signs include a hot, increasingly red and tender swelling, a break in the skin or a fever. If infection is suspected, fluid is drawn off the bursa with a needle (aspiration) using a sterile technique, and tested. Antibiotics that cover Staphylococcus and Streptococcus bacteria are started. A steroid injection into the bursa is considered only if there is no response to conservative measures (non-surgical treatment, such as rest and painkillers) and infection has been excluded. Surgery to drain or remove the bursa is rarely needed, for example if the bursitis is severe or keeps returning.
Pre-patellar bursitis is also known as ‘Housemaid’s knee’. This is inflammation of the pre-patellar bursa. A bursa is a fluid-filled sac that reduces friction at a joint. This one sits in front of the patella. Pre-patellar bursitis is caused by repeated microtrauma (small injuries that add up over time) or a fall. This condition presents as a swelling directly over the patella, rather than inside the knee joint. There may be redness (erythema) and warmth, even without infection. The swelling is usually tender, but it may be painless in chronic bursitis. Unlike arthritis, it generally does not limit movement of the knee, except in severe cases. It is called ‘Housemaid’s knee’ because it can occur with repeated kneeling forwards e.g. to scrub a floor by hand.
Pre-patellar bursitis is usually treated with rest, ice, elevation, avoiding kneeling (or using knee pads) and over-the-counter painkillers (painkillers that can be bought without a prescription). The bursa may be infected (septic bursitis). Signs include a hot, increasingly red and tender swelling, a break in the skin or a fever. If infection is suspected, fluid is drawn off the bursa with a needle (aspiration) using a sterile technique, and tested. Antibiotics that cover Staphylococcus and Streptococcus bacteria are started. Aspiration may also be offered to ease a large swelling. A steroid injection into the bursa is considered only if there is no response to conservative measures (non-surgical treatment, such as rest and painkillers) and infection has been excluded. A hot, swollen knee joint that cannot move normally suggests septic arthritis (infection inside the joint) rather than bursitis. This needs immediate specialist assessment in hospital. Surgery to drain or remove the bursa is rarely needed, for example if the bursitis is severe or keeps returning.
Supra-patellar bursitis is inflammation of the supra-patellar bursa. This bursa lies between the quadriceps tendon and the femur, just above the patella. In most adults it communicates with the synovial cavity of the knee joint (the fluid-filled space inside the joint). This makes it a common site of fluid build-up (effusion) in joint disease. Causes include: osteoarthritis (wear-and-tear arthritis), rheumatoid arthritis (arthritis caused by the immune system attacking the joints), infection and gout (crystals of uric acid in the joint). Injury to the ligaments or menisci (the C-shaped pads of cartilage) of the knee can also cause it. This condition presents with swelling and discomfort above the patella, deep to the quadriceps tendon (the tendon that joins the quadriceps muscle to the patella). Redness (erythema) may appear if the bursa is infected or inflamed.
Treatment of supra-patellar bursitis depends on the cause. Rest, ice, elevation and over-the-counter painkillers (painkillers that can be bought without a prescription) are often recommended. The underlying condition is treated as well. A hot, swollen, tender knee that is hard to move may be septic arthritis (infection inside the joint). This needs immediate assessment in hospital.
Diagram - The bursa surrounding the knee joint
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Osgood-Schlatter’s disease is a traction apophysitis (inflammation of a growth area of bone, caused by repeated pulling from a tendon) of the tibial tuberosity. The tibial tuberosity is the bony lump just below the kneecap, where the patellar ligament (often called the patellar tendon) attaches. This condition is common in teenage athletes. It presents with localised pain and swelling. Both knees are affected (bilateral) in up to 30% of cases.
Treatment is generally activity modification (cutting down or changing sport until the pain settles), ice packs, over-the-counter painkillers, and exercises. These stretch the quadriceps and hamstrings (the muscles at the front and back of the thigh) and strengthen the quadriceps. Complete recovery is expected when the growth plate closes (the area of growing bone near the end of the tibia stops growing), usually between 14 and 18 years of age. However, about 1 in 10 people still have symptoms in adulthood. Treatment can interrupt regular training for several months, so it is important to explain this to the young person, especially if they play competitive sport.
Fractures of the patella are often caused by a direct impact (for example, a fall onto the knee) or by indirect force. Indirect force happens when the quadriceps contracts strongly and suddenly while the knee is bending. This puts excessive tension on the patella through the extensor mechanism (the quadriceps muscle, the quadriceps tendon, the patella and the patellar tendon). Patella fractures can occur at any age. In a review of 756 patellar fractures the mean age was 54 years, and the highest incidence was in women aged 60 to 80. Patients with a patella fracture usually present with: swelling (due to bleeding at the site of the fracture) and a palpable defect (a gap that can be felt over the patella). If the fracture is displaced (the broken pieces have moved apart), the person cannot perform a straight leg raise (lifting the straight leg off the bed).
A non-displaced patella fracture with an intact extensor mechanism is usually treated without surgery. A long leg cast or knee immobiliser (a brace that holds the knee straight) keeps the patella in the correct position while it heals. If the patella fracture is displaced, surgery is the most likely option for treatment. In both cases physiotherapy (exercises and rehabilitation led by a physiotherapist) may be needed to return the leg to full function. In stable fractures, weight-bearing with the knee kept straight and supervised physiotherapy can be started early.
A bipartite patella (a patella that has formed in two parts) can be a normal finding, particularly in adolescents. In a young person, a patella in two parts on imaging does not always mean an acute fracture. Management should be guided by the clinical history and examination.
Image - An X-ray of a patella fracture
Creative commons source by Carlo Joseph Moskito [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
Dislocation of the patella most commonly occurs laterally due to internal rotation of the femur on a flexed knee. It most often occurs in athletic teenagers who try to change direction when running on a flexed knee. It usually presents with: severe knee pain, swelling and an inability to straighten the knee. The person sometimes feels a ‘popping’ sensation, and the knee may look out of shape.
A dislocated kneecap often moves back into place by itself. If it does not, treatment is reduction (a doctor moves the kneecap back into place), and pain relief is given first. Either way, the knee still needs to be checked by a doctor. X-rays are usually done to check the patella is in the correct place and that there is no other damage. The leg will usually be immobilised (kept still) with a splint or knee support initially, and crutches are given if walking is painful. Physiotherapy is often recommended to aid recovery. Surgery may be needed if the knee is badly damaged or the kneecap has dislocated more than once.
A knee effusion occurs when excess fluid collects in the knee joint, making it swell. It commonly follows an injury to the knee. Rapid swelling within one to two hours of an injury suggests bleeding into the joint (haemarthrosis), for example from an anterior cruciate ligament (ACL) tear. Swelling that develops more slowly, over several hours, is typical of a meniscal tear. An effusion can also be caused by osteoarthritis (wear-and-tear arthritis) or infection.
Tests may include aspiration of the knee joint (drawing fluid off with a needle) to help determine the cause of the swelling, and imaging to help rule out bony or ligamentous injury. The treatment of a knee effusion depends on the cause, for example giving antibiotics if an infection is present. Rest and simple analgesia (basic painkillers such as paracetamol) may be appropriate in some cases. A hot, swollen, tender knee that is hard to move needs immediate referral to a specialist to exclude septic arthritis (see below).
Septic arthritis is the invasion of joint space by microbes. It can occur elsewhere in the body but is most commonly seen in the knee joint and can present like a knee effusion. Risk factors include: increasing age, rheumatoid arthritis, diabetes and immunosuppression (a weakened immune system, for example from some medicines). Others are IV drug use, recent joint surgery or a recent steroid injection into the joint, and prosthetics in the knee (an artificial joint, from a joint replacement). This condition presents with pain, swelling, warmth and erythema (redness) around the knee, and a decreased range of motion (the knee cannot move as far as normal). A fever is often present, but a normal temperature does not exclude septic arthritis.
Septic arthritis is a medical emergency and needs immediate specialist assessment in hospital. A joint aspirate (fluid drawn from the joint with a needle) is taken and cultured to determine the bacterial cause of the infection. The bacteria involved are most often Staphylococcus aureus, followed by Streptococcus species. Antibiotics are started once the sample has been taken. If the person has signs of sepsis, antibiotics are started straight away, without waiting for the sample. They are given into a vein at first, then as tablets for several weeks. Draining the joint is a standard part of treatment, not only for severe cases. It can be done by repeated aspiration or by arthroscopic washout (keyhole surgery to wash out the joint).
The cruciate ligaments are two crossed ligaments inside the knee. Anterior cruciate ligament (ACL) tears usually occur in one of three ways. The first is sudden deceleration (slowing or stopping quickly). The second is rotation of the knee when changing direction with the foot fixed on the ground. The third is forceful hyperextension (the knee forced to bend backwards past straight). In an ACL injury, the tibia slides anteriorly under the femur.
Posterior cruciate ligament (PCL) tears usually occur due to an external force on a flexed knee (a ‘dashboard injury’, where the front of the shin hits the dashboard in a car crash). They can also occur due to a fall onto a flexed knee with a plantar-flexed ankle (the foot pointing downwards). In a PCL injury, the tibia slides posteriorly under the femur.
ACL tears normally present with: a ‘popping’ sensation, severe pain, rapid swelling and a feeling of instability when weight bearing. The swelling is caused by bleeding into the joint (haemarthrosis) and appears within one to two hours of the injury. The range of motion is also reduced (the knee cannot move as far as normal). PCL tears often cause less swelling, and the person may have few symptoms at first. Cruciate ligament tears can be tested for with the drawer test. With the knee bent to about 90 degrees, the tibia is pulled forwards for the ACL and pushed backwards for the PCL. Lachman’s test is a forward pull on the tibia with the knee bent only slightly, for the ACL only. A tear is suggested if the tibia moves further than normal.
Treatment can range from RICE (rest, ice, compression and elevation) to surgery to reconstruct the ligament with a section of tendon from elsewhere if needed.
Diagram - The anterior drawer test
SimpleMed original by Dr. Bethany Turner
Image - A demonstration of Lachman's test
Creative commons source by Lam et al. Sports Medicine, Arthroscopy, Rehabilitation, Therapy & Technology 2009 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
The collateral ligaments run down each side of the knee: the medial collateral ligament (MCL) on the inner side and the lateral collateral ligament on the outer side. Collateral ligament tears are a common sporting injury. They occur due to a direct blow to the side of the knee or a twisting injury. A varus stress forces the knee outward after a blow to the inner (medial) side. This can damage the lateral collateral ligament. A valgus stress forces the knee inward after a blow to the outer (lateral) side. This can damage the medial collateral ligament.
Medial collateral ligament tears are more common because a blow to the outer (lateral) side of the knee is more likely than a blow to the inner (medial) side. This condition presents with pain, stiffness and instability. In a stress test, the examiner pushes the knee sideways. A valgus stress test (pushing the knee inwards) is positive in a medial collateral ligament tear, and a varus stress test (pushing the knee outwards) is positive in a lateral collateral ligament tear. A positive test is painful, or the joint opens up more than normal. The majority of collateral ligament tears can be treated with ice, painkillers, bracing and strengthening exercises but occasionally surgery may be required.
A torn meniscus is one of the most common knee injuries. The menisci are two C-shaped pads of cartilage in the knee that cushion the joint. A tear is often caused by forceful rotation (twisting or pivoting) of the knee. It often occurs in young athletes. It can also occur in middle-aged or older people with little or no trauma, because of degenerative changes (wear and tear) to the knee. The medial meniscus is more often affected. This condition usually presents with: intermittent pain at the joint line (where the femur and tibia meet), swelling that develops over several hours, and a clicking, catching or locking sensation. The knee may not fully bend or straighten, and it may give way.
Treatment depends on the type of tear. It can range from RICE (rest, ice, compression and elevation) and strengthening exercises to surgery (either to repair the meniscus or to trim it to reduce symptoms). For a degenerative tear in a middle-aged or older person, exercise therapy (supervised physiotherapy) is tried first. Arthroscopic partial meniscectomy (keyhole surgery to trim the torn part of the meniscus) is considered only if symptoms continue despite this.
The unhappy triad is also known as a ‘blown knee’. It describes a combined injury to the ACL, medial collateral ligament (MCL) and medial meniscus, classically due to a blow to the lateral knee. The classic description names the medial meniscus, but later studies found that the lateral meniscus is torn more often in this pattern of injury. It is a very severe injury and can permanently reduce the function of the knee.
Most cases need surgery, and recovery takes about 6 to 9 months. The surgery is often arthroscopic (keyhole surgery). The ACL is reconstructed, which means it is rebuilt using a graft (a piece of tendon taken from elsewhere). The torn meniscus is repaired or trimmed. The MCL can sometimes heal without surgery, and the choice of treatment for it is made case by case. Physiotherapy is an important part of recovery whether surgery is required or not.
Reviewed by: Dr. Thomas Burnell and Dr. Marcus Judge
Edited by: Dr. Maddie Swannack
- 8551
