Armando Hasudungan
Biology and Medicine videos

Knee Pain

Knee pain is common. It is important to first identify if it is acute or chronic pain. For acute knee pain it is important to rule out septic arthritis as this can lead to irreversible knee damage. The persons age also help with the possible differential diagnosis of knee pain.

Overview Knee pain accounts for approximately one third of musculoskeletal problems seen in primary care settings. This complaint is most prevalent in physically active patients. Knee pain can be a source of significant disability, restricting the ability to work or perform activities of daily living. Chronic knee pain affects one in four people aged ≥55 years. Usually symptoms are mild to moderate. Osteoarthritis, presenting as activity related pain and limitation of movement, crepitus, and intermittent swelling in the absence of constitutional symptoms, is the commonest working diagnosis.

Aetiology of Joint Pain

  • Acute → Acute-Chronic → Chronic
  • Congenital – Genu recurvatum
  • Acquired – degenerative (osteoarthritis), traumatic (sports)
  • Traumatic
    • High Energy – motorcycle
    • Low Energy – sports injury
  • Atraumatic
    • Acute onset – Gout, Sepsis
    • Gradual onset

Differential Diagnosis

The next section will focus of the differential diagnosis of knee pain and will be divided into the following:

  • Generalised Knee Pain
  • Knee pain based on location
  • Other causes of knee pain
  • Common causes of knee pain by age group

Generalised Knee Pain

Acute knee pain (with swelling)

  • Traumatic synovitis can occur from any severe injury (ie. meniscus tear or torn cruciate ligament) and swelling typically appears only after several hours.
  • Post-traumatic haemarthrosis is blood in the joint from trauma, resulting in intense swelling immediately after injury. The knee is painful and it feels warm, tense and tender. Movement is restricted.
  • Non-traumatic haemarthrosis is blood in the joint from clotting disorders or from tears from vascular lesions in the knee (i.e pigmented villonodular synovitis)
  • Acute septic arthritis is the presence of bacteria in the synovial joint. The joint is swollen, painful and inflamed; this may be accompanied with systemic features such as malaise, pyrexia, a high temperature and elevation of the shite cell cough, erythrocyte sedimentation rate and CRP. Aspiration reveals pus in the joint fluid should be sent for microbiology investigation, including anaerobic culture (this should be done before commencing antimicrobial therapy). Most common cause is S. Aureus, although adult gonococcal infection is almost as common.
  • Crystal arthropathy: Acute swelling without a history of trauma or signs of infection suggests gout or pseudogout. The joint may be inflamed and very tender. Aspiration will provide fluid which may look like pus but is sterile; microscopy (using polarized light) reveals the characteristic crystals. Treatment with anti-inflammatory drugs is usually effective.
  • Reactive arthritis: Another cause of acute inflammatory synovitis, also known as Reiter’s disease (triad: can’t pee; can’t see; can’t climb a tree which means urethritis; conjunctivitis; arthritis)

Chronic knee Pain (with swelling)

  • Osteoarthritis is a inflammatory condition due to degeneration of joint tissue
  • Rheumatoid Arthritis is an systemic inflammatory disease
  • Chronic infective arthritis The most important condition to exclude is tuberculosis, of which there has been a resurgence of cases in the last two decades. Typically, the knee is swollen and the thigh muscles are wasted.

Knee Pain based on Location

Frontal Knee pain

  • Prepatellar bursitis This fluctuant swelling is confined to the front of the patella and the joint itself is normal. It is an uninfected bursitis due to constant friction between skin and bone. As such, it is seen mainly in carpet layers, paving workers, floor cleaners and miners who do not use protective knee pads. Treatment consists of firm bandaging, and kneeling is avoided; occasionally aspiration is needed. In chronic cases the lump is best excised.
  • Infrapatellar bursitis The swelling is below the patella and superficial to the patellar ligament, being more distally placed than prepatellar bursitis. Treatment is similar to that for prepatellar bursitis
Features of bursitis
Exquisite local tenderness at sites where bursae are usually present
Pain on motion and at rest
Occasional loss of active movement
Swelling, erythema, and warmth when bursitis occurs close to the body surface (eg, prepatellar bursitis)
  • Quadriceps tendonitis
  • Patella disorders
    • Patellar tendinopathy (Jumper’s Knee)
    • Recurrent dislocation of the patella
    • Chondromalacia of the patella (Patellofemoral pain syndrome)
  • Osgood-Schlatter’s Disease

Posterior Knee Pain

  • Semimembranosus bursa (Pes anserinus pain syndrome) The bursa between the semimembranosus and the medial head of gastrocnemius may become enlarged in children or adults. It presents usually as a painless lump behind the knee, slightly to the medial side of the midline and is most conspicuous with the knee straight. The lump is fluctuant and transilluminates. The knee joint is normal. A waiting policy, even if the lump causes an ache, is wise as it usually disappears with time.
  • Baker’s Cyst is a bulging of the posterior capsule and synovial herniation may produce a swelling in the popliteal fossa. It is usually caused by rheumatoid or osteoarthritis.Occasionally the ‘cyst’ ruptures and the synovial contents spill into the muscle planes causing pain and swelling in the calf – a combination which can easily be mistaken for deep vein thrombosis. The swelling may diminish following aspiration and injection of hydrocortisone; excision is not advised, because recurrence is common unless the underlying condition is treated.

Lateral Knee pain

  • Lateral Meniscal tears
  • Lateral collateral ligament injury
  • Meniscal cyst This presents as a small, tense swelling, usually on the lateral side at or just below the joint line. Sometimes it is so tense that it can easily be mistaken for a bony lump. It is usually tender on pressure.
  • Bony swellings Bony lumps (exostosis or bone tumours) arising in the metaphyses of the distal femur or proximal tibia may cause visible and palpable swelling on any aspect close to the joint. The diagnosis is revealed by x-ray examination and, if necessary, biopsy
  • Illiotibial band syndrome

Medial Knee Pain

  • Medial Meniscal tears
  • Medial collateral ligament injury
  • Meniscal cyst This presents as a small, tense swelling, usually on the lateral side at or just below the joint line. Sometimes it is so tense that it can easily be mistaken for a bony lump. It is usually tender on pressure.
  • Bony swellings Bony lumps (exostosis or bone tumours) arising in the metaphyses of the distal femur or proximal tibia may cause visible and palpable swelling on any aspect close to the joint. The diagnosis is revealed by x-ray examination and, if necessary, biopsy
  • Semimembranosus bursa (Pes anserinus pain syndrome) 
  • Medial plica syndrome
Remember Osteoarthritis can present with medial, lateral, posterior or anterior knee pain as well

Other causes of knee pain

  • Loose bodies The knee joint offers a relatively capacious haven for loose bodies. These may be produced by
    • Injury (a chip of bone or cartilage)
    • Osteochondritis dissecans (which may produce one or two fragments)
    • Osteoarthritis (pieces of cartilage or osteophyte)
    • Charcot’s disease (large osteocartilaginous bodies, separated by repeated trauma in a joint that has lost protective sensation)
    • Synovial chondromatosis (cartilage metaplasia in the synovium, sometimes producing hundreds of loose bodies).
  • Osteochondritis dissecans
  • Stress fracture
  • Referred pain syndrome (Usually from the hip)
    • Capital femoral epiphysis
    • Legg-Calve-Perthes disease)
Side Note Fractures will not be discussed here

COMMON CAUSES OF KNEE PAIN BY AGE GROUP
Children Adults Elderly
Patellar subluxation Patellofemoral pain syndrome (chondromalacia patellae), Osteoarthritis
Tibial apophysitis (Osgood-Schlatter lesion) Medial plica syndrome Crystal arthropathy: gout, pseudogout
Jumper’s knee (patellar tendonitis) Pes anserine bursitis Popliteal cyst (Baker’s cyst)
Referred pain: slipped capital femoral epiphysis Trauma: ligamentous sprains (anterior cruciate, medial collateral, lateral collateral), meniscal tear
Osteochondritis dissecans Inflammatory arthropathy: rheumatoid arthritis
Reiter’s syndrome
Septic arthritis

Investigations depends on the history and examination and you differential diagnosis

  • X-ray (at least 2 planes)
  • CT scan
  • FBC
  • ESR/CRP
  • Joint Aspiration
  • Rheumatoid factor

View more clinical presentations »