Joint Pain       Knee      
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Functional Anatomy

The knee joint is the largest synovial joint in the body. The important parts of the knee are:-

  • Inner (medial) compartment - the inner part of the femur (medial condyle) articulates with the inner part of the tibia (medial tibial plateau) via the inner cartilage (medial meniscus).
  • Outer (lateral) compartment - the outer part of the femur (lateral condyle) articulates with the outer part of the tibia (lateral tibial plateau) via the outer cartilage (lateral meniscus).
  • Knee cap (patello-femoral joint) - the knee cap (patella) articulates with the medial and lateral femoral condyles. The underside of the patella is V-shaped and fits in to the groove between the two condyles of the femur. The quadriceps tendon attaches to its upper surface, and it connects with the tibia (tibial tuberosity) via the patella tendon.
  • Knee capsule - flexible sac around the joint allowing a wide range of movements. The capsule keeps in place the lubricating synovial fluid.
  • Ligaments
    • Medial Collateral Ligament - supports the inner compartment of the knee, helping to prevent excessive valgus strains . At one end it attaches to the inner side of the medial femoral condyle, and at the other to the inner surface of the tibia. It is supported by the anterior and posterior capsular ligaments.
    • Lateral Collateral Ligament - supports the outer compartment of the knee, helping to prevent excessive varus strains . At one end it attaches to the outer surface of the lateral femoral condyle, and at the other to the head of the fibula. It is supported by the anterior and posterior capsular ligaments.
    • Cruciate Ligaments - the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are found in the central intercondylar part of the knee, and are so-called because they cross over each other. The name of each is based on their tibial attachment:-
      • ACL - comprises of 3 bands of differing lengths. Participates in the "screw home" mechanism during knee extension, where the ACL becomes taut as the femur internally rotates on the tibia during the last few degrees of knee extension. Contributes to knee lateral and rotatory stability, and helps to prevent hyper-extension.
      • PCL - is a stronger ligament as it receives more support from the posterior capsular ligaments. It is taut at all times during knee flexion / extension. Main function is to prevent backwards displacement of the tibia. It forms the main axis of movement during flexion / extension / rotation.
    • Coronary Ligaments - these small ligaments bind the edges of the cartilages (medial and lateral menisci) down to the top of the tibia (tibial plateau).
  • Cartilage (Meniscus)
    • Each knee joint has two cartilages (plural = menisci). The outside one is called the lateral meniscus, the inner one the medial meniscus.
    • Each is a half moon shaped piece of fibro-cartilage that lies between the weight bearing joint surfaces of the femur and the tibia. They are triangular in cross section and are attached to the lining of the knee joint along its periphery.
    • Each meniscus can be divided into thirds
      • Front third = anterior horn
      • Middle third = body
      • Back third = posterior horn
    • The menisci function as shock absorbers (absorbing 33% of forces during activity), and also help to guide and stabilise the femoral condyles during knee movements.
  • Muscles
    • Extension (straightening) is controlled by the Quadriceps Muscles (Rectus Femoris, Vastus Medialis, Vastus Lateralis, Vastus Intermedialis).
    • Flexion (bending) is controlled by the Hamstring Muscles ( Biceps Femoris, Semimembranosus, Semitendinosus), Sartorius, Gracilis and Popliteus.
    • Unlocking of the knee is controlled by Popliteus.
    • Outward Rotation of the tibia on the femur is controlled by Biceps Femoris.
    • Inward Rotation of the tibia on the femur is controlled by Semitendinosus and the Pes Anserinus Muscles (Gracilis and Sartorius).
    • NB - Inward and outward rotation of the tibia can only occur with the knee in the flexed position.
Ligament Injuries

Soft tissue ligament sprains / tears are the most common form of knee injury seen in the clinic. The knee is at it's most stable and resistant to injury in full extension (straight), and whilst in the locked home position (the femur turns inwards on the tibia during the last few degrees of extension). It is most vulnerable in the flexed position, particularly to rotation injuries.

Ligament injuries can be classified as 1st, 2nd or 3rd degree sprains:-

  • 1st degree sprain
    • Clinical Features - Only a few fibres of the ligament are torn. Pain is reproduced by stressing the suspected ligament. Tenderness and swelling is localised to the site of the injury, usually over the bony attachment points of the ligament concerned. Applying a valgus strain causes pain on the inside of the knee when the medial collateral is sprained. Applying a varus strain causes pain on the outside of the knee when the lateral collateral is sprained.
    • Management - Protect the knee from further injury for 24 hours. Apply ice to the sprain to reduce pain and swelling. Complete rest is inadvisable - isometric quadriceps exercises are useful in maintaining good muscle bulk and tone. Normal activities can normally be resumed when the pain and swelling has resolved. Prolotherapy may be useful for persistent pain.
  • 2nd degree sprain
    • Clinical Features - A greater degree of ligament fibre tearing occurs, short of being a full rupture. It may be associated with damage to other articular structures. May be associated with a haemarthrosis (bleeding into the joint) or a joint effusion (clear fluid swelling). Clinical assessment may be more difficult due to the greater degree of pain, swelling and disability.
    • Management - initially as for 1st degree sprains. Large effusions / haemarthroses should be drained. If pain and instability persist, further investigation with an MRI scan is advised to check on the other intra-articular structures. Prolotherapy to the affected ligament may be helpful.
  • 3rd degree sprains
    • Clinical Features - There is complete rupture of the ligament concerned. The medial collateral ligament tears at its upper femoral condyle attachment, whilst the lateral collateral ligament tears at its lower fibular attachment. A small fragment of bone (seen on X-ray) may be avulsed with the ligament at the time of injury. A greater degree of pain, swelling and disability is seen. Stress X-rays in varus and valgus can reveal opening up of the joint space on the side with the complete rupture. Damage to other intra-articular structures is common.
    • Management
      • Initially Rest, Ice, Compression, Elevation (RICE).
      • Investigation with an MRI scan and surgical repair reconstruction is the treatment of choice for complete ruptures.
  • Anterior Cruciate Tears
    • Clinical Features - although isolated ACL tears may occur, they are much more likely to be associated with injuries to other structures such as other knee ligament and the posterior horn of the meniscus. Once the ACL has torn, this may then lead to rotational instability in the knee due to progressive damage to the capsular ligaments.
    • ACL tears occur most frequently during hyper-extension injuries (knee pushed backwards when it's straight), or during a rotational injury with the knee flexed (changing direction when running). The knee swells badly over 24 hours due to bleeding within the joint.
    • Management
      • Initially Rest, Ice, Compression, Elevation (RICE).
      • MRI scanning and/or arthroscopy should be performed to confirm the diagnosis. If the tear involves the middle portion of the ligament, a surgical repair is not possible, and therefore requires a reconstuction. If the ligament has not torn in the middle portion, but has avulsed a small piece of bone from the tibial plateau, then it may be possible to repair it without reconstruction.
  • Ligament Instability
    • Ligamentous instability is a common and under diagnosed condition of the knee joint. There is always a history of previous trauma to the knee, but some patients may forget about the original injury as it happened so long ago. Instability may be classified as Straight or Rotational.
    • Straight Instability may be subdivided into 4 groups:-
      1. Medial Instability - A valgus strain is applied with the knee bent at 30 degrees and with it straight. If the medial joint space opens up only with the knee bent at 30 degrees but not with it straight, then a complete medial collateral ligament tear is suspected. If the medial joint space opens up both with the knee straight and bent at 30 degrees, then complete tears of the medial collateral and cruciates is suspected.
      2. Lateral Instability - This is less common than medial instability. A varus strain is applied with the knee bent at 30 degrees and with it straight. If the lateral joint space opens up only with is bent at 30 degrees but not with it straight, then a complete lateral collateral ligament tear is suspected. If the lateral joint space opens up both with the knee straight and bent at 30 degrees, then complete tears of the lateral collateral and cruciates is suspected.
      3. Anterior Instability - Excessive forwards movement of the tibia during the anterior drawer test suggests a complete tear of the anterior cruciate ligament. However false positives and false negatives are common with this test, and therefore require further investigation with an MRI scan and / or arthroscopy.
      4. Posterior Instability - Excessive backwards movement of the tibia during the posterior drawer test suggests a complete tear of the posterior cruciate ligament (usually associated with a posterior capsular ligament tear).
    • Rotatory Instability can occur due to various combinations of rupture of the anterior or posterior cruciate ligaments combined with rupture of the medial or lateral collateral ligaments and the medial or lateral capsular ligaments. The examination tests for discovering these complex ligamentous lesions involve combining the anterior or posterior drawer tests with either internal or external rotation of the tibia on the femur. Confirmation with an MRI scan and arthroscopy is advised. An orthopaedic opinion should be sought about possible surgical repair.
Muscles and tendons

Quadriceps Injury

  • Loss of quadriceps bulk and strength rapidly commonly occurs after the muscle has been injured. Vastus medialis obliquus (VMO) is particularly affected causing muscle imbalance around the knee cap (patella). This may lead to self-perpetuating knee pain and chrondromalacia patellae (changes to the cartilage behind the knee cap).
  • Treatment with quadriceps exercises is essential to recover quadriceps strength and normal patellar tracking on the femur.

Quadriceps Tendon

  • A partial or complete tear of the quadriceps tendon may occur where it attaches to the upper surface of the patella.
  • Such an injury is more likely to occur during eccentric exercise (flexing the knee whilst actively contracting the quadriceps muscle), and also in older men where a degree of degenerative change may have already taken place in the tendon.
  • With a full tear there is painless total weakness of resisted knee extension.
  • With a partial tear resisted knee extension is weak and painful. The tear may be palpated as a small defect at the upper edge of the patella.
  • Surgical repair is necessary for full tendon tears. Prolotherapy and quadriceps exercises are useful for partial tears.

Patellar Tendinitis

  • The patellar tendon is formed from the lower part of the quadriceps and runs from the lower pole of the patella to the tibial tuberosity on the tibia .
  • Overuse during sports can injure the tendon attachment on the tibial tuberosity. In adolescents this produces Osgood-Schlatters Disease.
  • Central core degeneration may occur in the patellar tendon in middle age as it does in the achilles tendon. This may leave it vulnerable to complete rupture.
  • Jumper's Knee
    • Jumper's may develop degeneration of the patellar tendon at the lower pole of the patella. This causes localised severe pain and tenderness worse after activity. May be associated with the knee giving way (pain induced).
    • Examination - pain on resisted knee extension with crepitus over the lower part of the patella.
    • Investigations - X-rays are required to exclude a stress fracture of the patella.
    • Complications - the tendon may partially or completely rupture.
    • Treatment - Initial rest, oral analgesics, LA / steroid injections , Prolotherapy, Surgical repair. Excessive steroid injections should be avoided as they cause ligament softening and may increase the risk of a complete rupture.

Gastrocnemius Tendinitis

  • Overuse especially by runners, leads to a sprain of the tendon of the medial head of the muscle where it attaches to the back of the medial femoral condyle. Muscular sprains may also occur in the body of the medial and lateral heads.
  • Pain on palpation is localised to the attachment point on the back of the medial femoral condyle. Referred pain down the leg may occur. Examination reveals pain on resisted knee flexion in the prone position.
  • Treatment consists of initial rest, oral analgesics, progressive calf stretches with the knee straight, and trigger point injections.

Bicipital Tendinitis

  • Biceps femoris muscle inserts into the lateral fibular head. Tendinitis occurs usually after running, and may be associated with bursitis.
  • Examination reveals tenderness and / or swelling around the tendon insertion point, and painful resisted knee flexion in the prone position.
  • Treatment consists of initial rest, oral analgesics, hamstring stretches, and trigger point injections.

Popliteal Tendinitis

  • The popliteus muscle runs from the back of the tibia to be inserted by a tendon onto the lateral surface of the lateral femoral condyle.
  • Pain is usually felt behind the outer aspect of the knee, usually coming on after running. The tendon may slide past the lateral femoral condyle producing a painful click.
  • Examination reveals painful resisted knee flexion , with pain reproduction behind the knee.
  • Treatment consists of initial rest, oral analgesics, hamstring stretches with the knee fully extended, and trigger point injections.

Iliotibial Tract

  • The iliotibial tract may become inflamed in runners where it crosses the lateral aspect of the lateral femoral condyle . May be associated with clicking.
  • Examination reveals pain in the lateral knee when the knee is flexed / extended with pressure over the tract with a finger 3 cm above the joint line.
  • Treatment consists of initial rest, oral analgesics, iliotibial tract stretches, trigger point injections , and surgery.

Prepatellar Bursitis

  • Otherwise known as "Housemaid's Knee". Brought on by unaccustomed kneeling on hard surfaces. The bursa lies between the front of the patella and the overlying skin .
  • Examination reveals a tender inflamed lump.
  • Treatment - LA / Steroid injection and avoiding kneeling.
  • Needs to differentiated from infection and Gout.

Infrapatellar Bursitis

  • The bursa lies under the patellar tendon and the infrapatellar fat pad. When inflamed, it is best seen with the knee fully extended, where there is bulging on either side of the patella ligament.
  • Treatment - LA / steroid injection .

Anserine Bursitis

  • The bursa lies between the lower end of the medial collateral ligament and the tibia.
  • May present after overuse and direct trauma.
  • Examination reveals well localised tenderness and pain on resisted knee flexion.
  • Treatment - LA / steroid injection .

Semimembranosus Bursitis

  • The bursa lies between the medial head of gastrocnemius and the semimembranosus tendon at the back of the knee on the medial side. The bursa may connect directly with the knee joint.
  • In adults it is associated with synovitis of the knee joint. In children it presents as a large cyst behind the knee.

Biceps Femoris Bursitis

  • The bursa lies between the biceps femoris tendon and the head of the fibula bone at the back of the knee on the lateral side.
  • It presents as a small cyst which becomes more obvious on resisted flexion of the knee. Needs to be differentiated from a cyst of the lateral meniscus (cartilage).
Cartilage Injuries

The medial and lateral cartilages (menisci) act as washers between the ends of the femur and tibia, where they have role in maintaining stability in the knee. They also have elastic properties acting as shock absorbers.

Aetiology / Mechanism

  • Meniscal tears are more common between the ages of 20 - 30 years, with the medial meniscus being affected 3 times more commonly than the lateral one. More common in sportsmen and in those where the knee is bent a lot of the time. Usually associated with a sprained / torn ligament history.
  • The medial meniscus is commonly torn when the knee is flexed, with the tibia fixed and held in external rotation (foot turned out).

Associated Injuries

  • Often associated with tears of the medial collateral, cruciate, and capsular ligaments. Ligamentous instability increases the risk of developing a meniscal tear.
  • Damage to the load bearing surface of the femur (femoral condyles) may occur (osteochondritis dessicans).
  • Wear of the load bearing surface of the patella may occur following a meniscal tear, probably due to disturbance in the patello-femoral rhythm.
  • Secondary osteoarthritis may occur at a later date.

Types of Meniscal Tear

  • Tears may be of two types - longitudinal (along the length of the meniscus) or horizontal (across the transverse width of the meniscus).
  • Longitudinal tears are more common and may affect the anterior horn, body or posterior horn.
  • A Bucket Handle Tear is one which extends from the anterior horn all the way round to the posterior horn. The inner free section of the meniscus may then break free into the centre of the joint, causing locking symptoms. Sometimes a meniscal tear can be so extensive that the meniscus breaks away from all of its attachments.
  • Transverse or horizontal tears more commonly affect the lateral meniscus at the junction between the front and middle thirds. It is often called a Parrot-Beak Tear. It may be associated with a lateral cyst of the meniscus.


  • Pain - there is often a history of sudden onset of pain and disability, felt deep in the knee or over one of the compartments.
  • Activity - with a torn meniscus it is usually impossible to carry on with normal activities, whereas this is not the case with a ligament tear.
  • Swelling - a torn ligament will produce tense swelling in the knee (haemarthrosis) within an hour of the injury, whereas a torn meniscus will produce an effusion over several hours.
  • Locking - a detached fragment of meniscus can become trapped between the femur and tibia causing the knee to lock preventing full extension. This can usually be unlocked by flexing the knee, then slowly trying to straighten it.
  • Clicking - recurrent painful clicking may occur associated with a snapping sensation.
  • Instability - there may be a history of sudden giving way or something slipping in the knee. This needs to be differentiated from instability due to a ligamentous tear.
  • Examination - often reveals an effusion, loss of vastus medialis muscle bulk, loss of full extension, and loss of the normal range of rotation movements of the tibia on the femur. A tear of the anterior horn causes a loss of external rotation (foot turned out), whereas a tear of the posterior horn causes loss of internal rotation (foot turned in). Various examination routines have been described to test for a possible meniscal tear, although none is fool proof:-
    • McMurrays Test - the knee is bent to 90 degrees and the foot externally rotated with a slight valgus strain applied. Whilst the knee is slowly straightened a audible or painful click is produced.
    • Apley's Test - the knee is bent to 90 degrees with the patient lying face down. Rotation combined with downward force by the examiner usually means a meniscal tear, whereas rotation combined with traction upwards usually means a ligament sprain.

Investigations - MRI scans and knee arthroscopy .


  • Meniscectomy (removal of the meniscus) should be avoided at all costs to reduce the risk of developing secondary osteoarthritis. In partial tears, a partial meniscectomy may suffice. meniscectomy also increases the risk of rotational instability afterwards.
  • An active quadriceps retraining program is essential in all cases of torn meniscus. Failure to recover normal VMO function leads to instability in the knee as well as increasing the risk of chondromalacia patellae (worn cartilage behind the knee cap).
  • Episodes of locking of the knee can treated by skilful manipulation of the knee to encourage the torn fragment to move from under the femoral condyle. Frequent locking requires meniscectomy.
Traumatic Synovitis


  • Trauma to the knee may cause internal bleeding (haemarthrosis), with rapid onset swelling, and an extremely painful, warm and tender joint. The joint is usually held in a degree of flexion (partially bent). Bleeding can occur after an injury to the joint capsule, ligament sprains, and meniscal tears.
  • Non-traumatic bleeding into the joint can occur with haemophilia and other blood disorders, anticoagulant treatment with warfarin and heparin, and secondary cancer spread.
  • Other conditions which can cause sudden swelling (effusion) of the joint without a haemarthrosis include crystal deposition disease (gout), inflammatory arthritis (rheumatoid arthritis), and septic arthritis (infected joint).

Chronic Traumatic Synovitis

  • Developing an effusion in the knee without there being a history of trauma is common in sportsmen (water on the knee). It is important to realise that this is a symptom of internal derangements rather than being a defined condition, and requires further investigation to find the cause.
  • It is important to make a thorough history and examination, with X-rays, arthroscopy and MRI scan if necessary.

The knee is prone to osteoarthritis because it is often subjected to trauma. Osteoarthritis may develop secondarily to previous meniscal tears, fractures of the joint surfaces, or instability due to ligamentous injuries.

Degenerative changes may occur in any or all of the 3 compartments of the knee (medial, lateral and patello-femoral). Single compartment degeneration can lead to knee deformity - medial compartment causing a varus deformity (bandy legged), lateral compartment causing a valgus deformity (knock kneed). As the disease process progresses, so does the degree of deformity. Leg length inequality usually causes degenerative changes on the side with the longer leg.

The meniscus also becomes involved in the arthritic process. Narrowing of the joint space exerts more pressure on the meniscus, making it more prone to cleavage tears. Most wear occurs in the anterior horn part of the meniscus.


  • Multimodal Oral analgesics.
  • Stretches and Exercises help to maintain quadriceps flexibility and strength and are essential to maintain knee stability.
  • Think about trying the Pain Gone Pen - a simple low-cost non-drug self-help pain device for home use.
  • Glucosamine supplements have been shown to reduce pain in mild to moderate osteoarthritis.
  • Viscosupplementation with hyaluronic acid injections (Ostenil) can help to reduce pain, swelling, as well as improve joint function. Injections are most effective in mild to moderate osteoarthritis, where they have been shown to increase the depth of the cartilage within the joint.
  • Prolotherapy is a useful treatment in knee pain. It can be used to help heal partial sprains of the collateral, coronary, and patellar ligaments. It can also be used inside the joint in severe osteoarthritis where knee replacement has been ruled out if the patient's general medical condition precludes surgery / anaesthesia.
  • Knee Bracing is indicated in those with severe osteoarthritis where replacement surgery is not possible, and also in those with ligamentous instability . For further advice ask your GP or Consultant to refer you to your local hospital Orthotics Department.
  • Total Knee Replacement Surgery can drastically reduce knee pain. It requires that the patient is fit for either a general or spinal anaesthetic, and that they can participate adequately in the post-operative rehabilitation program. Failure to get the knee moving afterwards results in a joint that is unable to bend past 90 degrees.
Bony Injuries

Bony injuries can be classified as chondral (damage to the articular cartilage) or osteochondral (damage to the cartilage and underlying bone). Osteochondral injuries can be picked up on X-ray, but chondral injuries are not visible.

Osteochondritis Dissecans

  • This is one type of bony injury in the knee where a piece of cartilage and underlying bone break away completely to form a loose body . In some cases the fragment remains attached. It tends to occur on the convex surfaces of all joints including the knee.
  • In the knee 85% of cases involve the medial femoral condyle, with 15% affecting the lateral femoral condyle. The commonest cause is trauma usually in high performance athletes.
  • A juvenile form exists between the ages of 4 - 15 years with the cause being hereditary and trauma.
  • Symptoms
    • An attached fragment causes a dull, poorly localised pain where activity aggravates the pain and causes an effusion.
    • A free fragment can cause locking of the knee with an effusion, and can be difficult to distinguish from a torn cartilage.
  • Treatment
    • If the fragment is still attached then avoidance of weight bearing and a plaster cast for 6 weeks can help healing.
    • Large loose fragments can be pinned back in place. Smaller ones can be removed through the arthroscope or via an arthrotomy.


  • Death of a small piece of bone and overlying cartilage occurs when there is occlusion of the arterial blood supply to that area. Also known as avascular necrosis. It occurs more commonly on the weight bearing surface of the medial femoral condyle in females over 65 years.
  • Symptoms - sudden, severe, persistent pain in the knee with swelling and stiffness.
  • Examination - marked tenderness over the part of the femoral condyle affected.
  • Investigations - MRI scans show up the bony defect much earlier than X-rays . Over several months the affected part of the femoral condyle becomes flattened showing up on X-ray. Bone scans may be useful.
  • Management - initially rest and avoiding weight bearing. May lead to secondary osteoarthritis of the knee requiring knee replacement.
Patellar Pain

Pain behind the knee cap (retropatellar pain) is the commonest cause of knee pain. In older people the diagnosis is usually osteoarthritis. In younger people chondromalacia patellae is often diagnosed. However, the presence or not of structural changes in the retropatellar cartilage does not correlate well with pain. Abnormal loading of the patella can occur in various structural abnormalities of the foot and leg - varus deformity of the rear foot, tibial torsion, being knock kneed, and abnormalities of the femoral neck (hip region). Therefore whenever retropatellar pain presents, a proper assessment of the whole lower limb should be undertaken.

Plica Syndrome

  • Although not directly related to the patella, this syndrome causes pain in the front of the knee. It is the result of a remnant of fetal tissue in the knee. The synovial plica are membranes that separate the knee into the compartments during fetal development. These plica normally diminish in size during the second trimester of fetal development. In adults, they exist as sleeves of tissue called "synovial folds," or plica. In some individuals, the synovial plica is more prominent and prone to irritation (SPP = suprapatellar plica, MPP = medio-patellar plica, IPP = infrapatellar plica, ACL = anterior cruciate ligament).
  • The plica on the inside of the knee, called the medial patellar plica, is the synovial tissue most prone to irritation and injury. When the knee is flexed, the plica is exposed to direct trauma, and it may also be injured in overuse syndromes.
  • Diagnosis is best made by physical examination or at the time of arthroscopic surgery. Plica syndrome has similar characteristics to meniscal tears and patellar tendonitis, and these may be confused. An MRI may be done, but it is often not terribly helpful in the diagnostic work-up.

Chondromalacia Patellae

A disorder of the retropatellar articular cartilage which causes severe pain and disability in the knee. The cartilage shows signs of premature degeneration with softening, fibrillation and roughening similar to those changes found in osteoarthritis.

  • Causes
    • Acute trauma may cause damage to the articular cartilage.
    • Previous trauma causing meniscal tears, synovitis, or ligamentous instability.
    • Bony anatomical abnormalities e.g. abnormally shaped patella, or femoral groove in which the patella glides.
    • Recurrent dislocation of the patella.
    • Tight hamstrings often cause a disturbance in patello-femoral rhythm.
    • Foot deformities which cause forefoot pronation (foot turned outwards with fallen inside arch).
    • Sporting activities with abnormal loading of the patella . The greater the degree of knee flexion, the greater the degree of pressure of the patella on the femoral condyle . This is aggravated by tight quadriceps.
  • History
    • More common in females in the late teens. Pain is described as deep seated under the knee cap. Usually worse going up and down stairs as well as after prolonged sitting.
    • May be associated with stiffness, swelling, catching, locking, insecurity, and a feeling of giving way, but needs to be differentiated from other intra-articular abnormalities.
  • Examination
    • The knee pain is reproduced by the patellar grating test. This involves getting the patient to tense their quadriceps muscles whilst the examiner holds the patella down onto the femoral condyles.
    • Crepitus can be felt or heard when the patella is passively moved around on the femoral condyles.
    • Tenderness around the medial edge of the patella.
    • A synovial effusion may be found.
    • Wasting of the vastus medialis muscle is common.
    • X-rays (skyline view) may show cartilage wear .
  • Treatment
    • Lower limb abnormalities should be ruled out and treated first.
    • Initial rest, avoiding the activity that provokes the pain.
    • Oral analgesics with applied heat.
    • Isometric quadriceps exercises. Tensing the quadriceps muscles with the knee in full extension and with the ankle held in dorsiflexion (foot flexed towards you) recruits the vastus medialis muscle . Firming up vastus medialis helps to maintain proper tracking of the patella on the femur. Performing this exercise with the knee in full extension should minimise the movement of the patella and therefore not be too painful. Stretching the hamstrings is essential.
    • Passive patellar mobilisation techniques may be helpful.
    • Electroacupuncture around the 4 poles of the patella can help.
    • Trigger point injections around the patella and lower quadriceps.
    • Glucosamine can help cartilage recovery.
    • Viscosupplementation with Ostenil can be very useful.
    • Surgery - Patellar resurfacing.

Recurrent Subluxation

The patella can slip off the femoral condyles towards the lateral side (outside) of the knee - this is called subluxation. It is more common in athletes and in knock-kneed teenage girls. In some young girls the patella can be shown to be riding on the femoral condyles in an abnormally high position, making it more likely to slip out of position.

  • Apprehension Test - The patella is gently pushed laterally whilst the knee is gently flexed. As the patella begins to move outwards, the patient feels pain, causing the quadriceps muscles to tense, and preventing any further movement of the patella.
  • Investigations - Skyline X-ray views of the knee may reveal an abnormally seated patella, chondromalacia patellae, or an avulsion injury.
  • Treatment
  • Isometric quadriceps exercises as above
  • Bracing the knee during sporting activities with a felt pad which helps prevent lateral movement of the patella
  • Surgery
    • Releasing a tight lateral capsules, whilst tightening the medial capsule may allow the patella to track normally.
    • Realignment of the patellar tendon insertion.
Infrapatellar Fat Pad

Functional Anatomy

  • The Infrapatellar Fat Pad (IPFP) , also know as Hoffa's fat pad, lies behind the patellar tendon in the front of the knee.
  • It is positioned within the joint capsule, but outside the synovial lining of the joint. It has fibrous attachments to the cartilages and to the area between the femoral condyles (intercondylar notch).
  • Its main functions are to act as a cushion for the front part of the knee, to provide blood supply to the knee joint, and to improve the lubrication efficiency of the knee by reducing the volume of the infrapatellar space.
  • There may be a connection to the main knee joint via a posterior cleft which is lined with synovium.


  • The IFFP may become trapped (impinged) between the femur and the tibia during the last few degrees of knee extension, causing inflammation and enlargement of the fat pad, and perpetuation of the problem (Hoffa's Disease).
  • Repeated inflammation and trauma to the fat pad may cause it to become calcified (ossification).
  • The IFFP may also become injured and subsequently fibrosed during surgical procedures like arthroscopy and total knee replacement.
  • It has been suggested that IPFP fibrosis may contribute to patellar mistracking, eventually leading to problems there.
  • Rarely there may be benign growths affecting the IPFP (chondroma's, fibroma's, pigmented villonodular synovitis).
  • Loose bodies in the main knee joint may become lodged in the IPFP via the posterior cleft.


  • Those with Hoffa's disease present with well localised pain over the front of the knee, mild loss of knee extension, and mild anterior swelling.
  • Those with fibrosis of the IPFP may complain of anterior knee pain on squatting.
  • Those with a fibrotic posterior band may complain of crepitus or clicking in the anterior part of the knee.


  • The pain can be reproduced when the knee is placed into the last few degrees of passive extension, then gently bounced into passive hyperextension.
  • Hoffa's sign consists of placing a thumb over the medial IPFP with the knee in flexion, and then extending the joint passively, producing pain anteriorly when the IFPF becomes impinged.


  • X-rays may show calcification in the IPFP.
  • MRI scanning shows most pathologies.


  • Injection of the IPFP can be used both diagnostically and for treatment.
  • Surgical removal of a fibrosed or contracted IPFP is recommended if conservative treatment fails, especially if full knee extension is restricted.
  • Arthroscopic tumour removal if picked up on MRI scanning.
  • It has been suggested that the IPFP may spontaneously regenerate within 2 years of removal.
Superior Tibiofibular Joint

Functional Anatomy

  • The two long bones of the lower leg, the tibia and the fibula, are connected to each other at their ends by the superior (upper) and inferior (lower) tibiofibular joints. These two joints form a functional unit which are involved in movements of the ankle. The upper joint however, can cause outer knee pain radiating down the shin.
  • On dorsiflexing the foot at the ankle (bringing your foot up), the superior tibiofibular joint slides upwards and inwards on the tibia.
  • On plantar flexing the foot at the ankle (pushing your foot down), the superior tibiofibular joint moves downwards and outwards.
  • The superior tibiofibular joint also moves when the foot is inverted (turned in) or everted (turned out) at the ankle.

Causes of Pain

  • Direct Trauma
    • Blunt injury to the lower leg can injure the superior tibiofibular joint causing a haemarthrosis (joint bleeding), leading to calcification / fibrosis of the joint capsule. Calcification shows up on X-rays.
    • This leads to stiff movements of the joint, with pain being reproduced by ankle movements.
    • Hyaluronic acid viscosupplementation can improve cartilage function within the joint.
    • Joint mobilisation can improve the range of movements.
  • Subluxation
    • Inversion sprains of the ankle joint can cause subluxation / dislocation of the superior tibiofibular joint by damaging the posterior tibiofibular ligament.
    • This occurs more commonly when the ankle is sprained with the knee flexed e.g. footballers and parachute jumpers.
    • X-rays show prominence of the head of the fibula.
  • Instability
    • Joint instability may the result of an injury or rheumatoid arthritis.
    • Pain is localised over the lower lateral knee and radiates down the leg. The joint clicks on walking and can be mistaken for a torn lateral knee meniscus.
    • Ankle movements reproduce the pain.
    • Prolotherapy intra-articularly and to the local supporting ligaments can help reduce pain and improve stability.
Referred Pain

All of the above conditions are examples of local pain problems around the knee joint. Below are some conditions which can mimic knee pain by causing referred pain there because of a shared nerve supply:-

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