• Exclude a serious cause for knee pain.
• Suspect another cause if knee pain:
• Starts suddenly after trauma to the knee.
• Is associated with systemic symptoms, including fever, weight loss, or general malaise.
• Is associated with pain in bones or joints at other sites.
• Persists at night or after rest.
• Is associated with an abnormal examination of the hip or knee joint.
• For information on other causes of knee pain, see Differential diagnosis.
• If a serious cause is suspected, urgently investigate or refer for specialist assessment to confirm or exclude the diagnosis.
• Diagnose Osgood–Schlatter's disease on the basis of clinical features alone when:
• There are no features of another cause for knee pain.
• Knee pain starts in adolescence and is localized to the tibial tuberosity. Typically, pain is:
• Unilateral, but may occur bilaterally in up to 30% of people.
• Gradual in onset.
• Relieved by rest and made worse by activity, particularly activities that involve running or jumping.
• Tenderness is present over the tibial tuberosity that is provoked by knee extension against resistance or by hyperflexing the knee with the person lying prone.
• Firm enlargement of the tibial tuberosity may be present.
• Routine X-ray examination of the knee is not recommended because it lacks sensitivity to diagnose the condition. If undertaken, the X-ray may be normal or difficult to interpret, or it may demonstrate fragmentation of the tubercle.

Differentiating knee pain with systemic symptoms, knee pain without systemic symptoms, and traumatic knee pain

• The usefulness of differentiating knee pain into these categories to aid diagnosis is based on expert opinion published in guidelines on the assessment and management of knee pain and swelling [University of Michigan Health System, 2005].

Clinical features of Osgood–Schlatter's disease

• These are based on commonly observed symptoms and signs of the condition published in authoritative texts [Davidson et al, 2008].

Investigation of someone with knee pain

• It is expert opinion that Osgood–Schlatter's disease can be diagnosed on the basis of clinical features alone if there are no features of a serious cause for knee pain because [Gholve et al, 2007; Houghton, 2007]:
• Clinical features are sufficiently sensitive and specific to make the diagnosis with a reasonable degree of certainty.
• Routine X-ray examination of the knee lacks sensitivity to diagnose Osgood–Schlatter's disease [Royal College of Radiologists, 2007].
• Investigations to exclude serious causes of knee pain are widely recommended by experts when alerting features for a serious cause are present [Gholve et al, 2007; Houghton, 2007; Royal College of Radiologists, 2007].
• The alerting features of serious causes of knee pain are based on expert opinion published in guidelines on the assessment and management of anterior knee pain [Australian Acute Musculoskeletal Pain Guidelines Group, 2003a].

Knee pain that is severe, persists at night or at rest, or is associated with bone pain at other sites

• Urgently investigate or refer children with knee pain that is severe, persists at night or at rest, or is associated with bone pain at other sites — a bone tumour should be suspected.

Knee pain associated with systemic symptoms

• Urgently investigate or refer children with knee pain associated with systemic symptoms [University of Michigan Health System, 2005]. Causes include [Davidson et al, 2008]:
• Septic arthritis — presents with severe pain, swelling, warmth, and marked reluctance to move the affected joint. It is usually associated with systemic symptoms.
• Bone tumours — are a rare cause of knee pain. They may be associated with weight loss or general malaise [Australian Acute Musculoskeletal Pain Guidelines Group, 2003b].
• Juvenile idiopathic arthritis — may affect the knee joint alone or with other joints presenting with acute pain, swelling, and erythema. Arthritis may occasionally occur with, or be preceded by, fever, rash, lymphadenopathy, or hepatosplenomegaly.

Knee pain associated with an abnormal examination of the hip

• Urgently investigate or refer children with knee pain referred from the hip. Conditions that may cause referred pain include [Davidson et al, 2008]:
• Slipped proximal femoral epiphysis. This condition typically presents during the adolescent growth spurt, most frequently in obese children. When there is sudden displacement of the epiphysis, the child presents with sudden onset of severe hip pain with the leg held in external rotation. Gradual displacement of the epiphysis may cause only mild discomfort of the hip or only referred knee pain.
• Transient synovitis. Characteristically, this presents as transient hip pain in a systemically well child younger than of 10 years of age. In up to 70% of children, it occurs with, or follows, upper respiratory tract infection.
• Perthes disease. This is caused by avascular necrosis of the femoral head epiphysis due to a disturbance of its blood supply. It is much more common in boys and most often presents between 4 and 9 years of age with a persistent irritable hip.

Knee pain associated with injury

• A serious traumatic knee injury is likely when knee pain starts suddenly and is associated with abnormal physical signs [University of Michigan Health System, 2005]. Consider referral for specialist assessment of the cause. Causes include [Gholve et al, 2007; Davidson et al, 2008]:
• Meniscal injuries.
• Collateral and cruciate ligament injuries.
• Stress fractures of the patella.
• Tibial tuberosity fracture.
• Prepatellar and infrapatellar bursitis.

Knee pain not associated with trauma or systemic symptoms

• Osteochondritis dissecans is caused by avascular necrosis of subchondral bone of an articular surface and commonly affects the knee joint [Houghton, 2007]. If suspected, refer for specialist assessment.
• It presents in adolescents, with an insidious onset of activity-related pain and swelling. Locking of the knee may occur owing to a loose body within the knee.
• Examination may reveal focal bony tenderness, an effusion, or evidence of a loose body.
• Sinding–Larsen–Johansson syndrome has the same cause as Osgood–Schlatter's disease, except that the lower pole of the patella is affected instead of the tibial tuberosity [Houghton, 2007].
• It presents with knee pain that is typically exacerbated by activity and relieved by rest.
• Pain over the lower pole of the patella is provoked by knee extension against resistance.
• Patellofemoral pain syndrome is thought to be caused by abnormal tracking of the patella within the trochlear groove [Houghton, 2007]. Abnormal tracking of the patella may be associated with abnormal alignment of the bony structures or by quadriceps muscle weakness or imbalance.
• It most commonly presents during the adolescent growth spurt with diffuse pain around the patellofemoral joint. Usually both knees are affected, with one side worse than the other.
• It is confirmed by pain or crepitus with the patella grind test. This involves the person lying supine while the examiner pushes the patella distally in the trochlear groove. The person then tightens their quadriceps against patella resistance.

Differentiating knee pain with systemic symptoms, knee pain without systemic symptoms, and traumatic knee pain

• The usefulness of differentiating knee pain into these categories to aid diagnosis is based on expert opinion published in guidelines on the assessment and management of knee pain and swelling [University of Michigan Health System, 2005].

Clinical features of the common differential diagnoses of knee pain

• These are based on commonly observed symptoms and signs of these conditions published in authoritative texts and expert review articles [Houghton, 2007; Davidson et al, 2008].

When to investigate children with knee pain

• These recommendations are based on expert opinion [Houghton, 2007; Royal College of Radiologists, 2007; Davidson et al, 2008].