Anterior knee pain in adolescents

Anterior knee pain in adolescents is a common presentation in general practice. At any one time 5-35 per cent of adolescents and school children complain of knee pain. There are a number causes.

Patellofemoral overload
Intrinsic patellofemoral overload is due to changes in the articular cartilage or subchondral bone. It occurs commonly in young girls; the patient gives a history of pain after sitting with the knee flexed for long periods, for example in air travel.

The first line of treatment is activity modification and physiotherapy. Arthroscopic cartilage debridement is required in rare cases.

Patellar maltracking occurs because of increased quadriceps angle, high-lying patella, femoral neck anteversion, genu valgum, tibial torsion or joint laxity.

Treatment is conservative and includes activity modification and quadriceps strengthening exercises.

Hyperpronation syndrome
Valgus flat feet results in hyperpronation of the feet and this results in overloading of the patella producing anterior knee pain. This can be treated effectively with orthotics and physiotherapy.

Patellar instability
Patellar instability presents as recurrent dislocation or subluxation of the patella. The patient presents with recurrent disabling patella dislocations that require repeated manipulations, or with minimally abnormal patellar tracking in the form of a tilt due to weakness of the vastus medialis.

Initial treatment includes activity modification, insoles, braces and quadriceps-strengthening exercises. With the advent of minimally invasive orthopaedic surgery there is an increasing trend of arthroscopic lateral release of patellar retinaculum.

Significant physiological changes in three-dimensional alignment occur during adolescent growth. Pain is often transient, and supportive, rather than interventional treatment, is appropriate.

Intra-articular pathology
A plica is the remnant of synovial partition that persists into adult life. The most common pathological plica is medial. The plica in itself is not pathological but if it becomes inflamed it can become oedematous or fibrosed; it then acts as a tight bowstring impinging on other structures in the joint and causes further synovial irritation.

Adolescents usually present with anterior knee pain aggravated by exercise and climbing. On examination there is muscle wasting or joint effusion with tenderness over the upper pole of patella and the femoral condyle. Occasionally the band is palpable and movements of the knee may cause catching and snapping. The diagnosis can also be made on arthroscopy or MRI of the knee.

Treatment is conservative, with analgesics and exercises. If symptoms persist arthroscopy and excision of the plica may be necessary.

Meniscal disorders
In discoid meniscus, the patient can present with knee pain or a clicking knee. The characteristic click is felt at 110 degs as the knee is flexed and at 10 degs as it is straightened. The diagnosis is confirmed on MRI.

No treatment is indicated unless pain is disturbing, then arthroscopic partial excision may be carried out.

Hypermobile meniscus presents as knee pain with an intact meniscus. The best treatment is conservative, as joints are relatively hypermobile in adolescents. The hypermobility decreases with age and the condition improves.

It is less common to see meniscal injuries in adolescents unless they have a discoid meniscus. Tears of the anterior horn may give rise to anterior knee pain.

Bipartite or accessory ossicles of the patella can become inflamed after acute or repetitive strain. Stress fractures of tibia and patella can present as anterior knee pain.

Osteochondritis dessecans
Osteochondritis dessecans is a small well-demarcated avascular fragment of bone and overlying cartilage, which can sometimes separate from one of the femoral condyles and appear loose within the joint.

It presents in males aged 15-20 years with intermittent knee pain and swelling. There can be quadriceps wasting and knee effusion. Diagnostic signs are tenderness localised to one femoral condyle, and Wilson's sign. Investigations include X-ray and MRI.

Stable lesions can be treated with curtailment of activities for 6-12 months. If the fragment is large and 'unstable' the treatment involves internal fixation or arthroscopic excision with or without articular cartilage transplantation.

Patellofemoral arthritis
Patellofemoral arthritis may be primary or secondary to previous trauma to the patella. There can be inflammation involvement of the joint due to rheumatoid arthritis or sero-negative arthritis. It is important to look for other signs of these diseases.

Peripatellar disorders
There are approximately 13 bursae around the knee joint; four are on the anterior aspect of the knee. Adolescents are predisposed to bursitis, apophysitis and tendinitis. Impact sports can produce stress on the growth plates or related tendons and attachments. Treatment is conservative, involving activity modification and physiotherapy.

Osgood-Schlatter disease is a type of juvenile traction osteochondritis. It is an inflammation caused by recurrent irritation of the growth plate by the musculotendinous unit. Isometric strengthening, quadriceps and hamstring stretching exercises can be initiated once the inflammation has subsided. In severe cases it may need a splint to rest the knee.

Sinding-Larsen-Johansson disease is a type of osteochondritis occurring mostly in adolescence. The cause appears to be a traction phenomenon attributable to contusion or tendinitis of the proximal attachment of the patella tendon with subsequent calcification and ossification. It is self-limiting and benign.

Bipartite patella
Bipartite patella is a congenital condition in which the superolateral corner of the patella is joined to the rest of the patella by fibrocartilagenous tissue. It is seen in 1 per cent of the population and is usually painless but is picked up on X-ray. Children can have pain because of repetitive strain or separation of the bipartite segment.

The usual treatment is activity modification with muscle strengthening exercises or a cylinder cast.

Tumours of the patella
The most common benign tumour of the patella is the giant cell tumour. There are published case reports of various malignant bone tumours such as osteosarcoma and chondrosarcoma affecting the patella.

Referred pain
In any patient with knee pain, the hip should be examined as there may be underlying hip pathology, such as slipped capital femoral epiphysis or developmental dysplasia of the hip leading to referred pain in the knee. The cause of referred pain is that the obturator nerve supplying the hip joint gives a branch to the knee joint.

Mr Mohan is orthopaedic registrar and Mr Coates is consultant orthopaedic surgeon at the Royal Surrey County Hospital, Guildford.