Introduction

Anterior knee pain is a very common complaint. The most common diagnosis is that of patellofemoral joint pain syndrome (PFJPS), which may affect up to 25% of the population at some stage. The differential diagnoses of anterior knee pain may include patella tendinopathy, osteochondritis dissecans (OCD), osteoarthritis, plica syndrome, fat fad impingement and Osgood-Schlatter’s syndrome in children.

Aetiology

Patellofemoral pain is felt to be due to a lateral mal-tracking of the patella in the femoral trochlea. It is initiated either by a single bout of excessive exercise (eg. a whole day bushwalking with hills), or a more low grade but repetitive overload (eg. a new running program).The key factor causing mal-tracking is weakness of the vastus medialis obliqus (VMO), which is the main dynamic stabilizer of the patella. As pain is a significant inhibitor of the quadriceps, then there is a continued negative effect on VMO function. Tightness in the lateral soft tissues such as the ITB and lateral patella retinaculum also cause lateral mal-tracking. Anatomical predisposing factors to PFJPS include increased knee valgus, increased Q angle, patella alta and foot hyperpronation.

Fig 1. VMO Wasting

Diagnosis

Historically the patient will complain of a deep, poorly localized pain in the front of the knee. It is worse with loaded knee flexion, such as walking up stairs, and with prolonged knee flexion when sitting (the ‘Moviegoers sign’). There may be complaints of grinding or crepitus in the knee and catching or giving way.

Clinical examination may demonstrate the anatomical factors described above, such as increased knee valgus or foot hyperpronation. Crepitus may be elicited with knee flexion and there may be tenderness on palpation of the undersurface of the patella. An effusion is generally not present. VMO wasting is usually apparent, and there will be stiffness of the patellofemoral joint and illiotibial band tightness. Calf and hamstring tightness should also be elicited. Lastly there may be functional weakness of the gluteal muscles on dynamic trendellenberg testing.

Investigation

Whilst the diagnosis is clinical, a plain x-ray is important to exclude other pathology such as osteochondritis dissecans, osteoarthritis in the older patient, and other bony pathology. An MRI may be indicated if there is a failure to improve with an appropriate rehabilitation program or if there is associated swelling or mechanical symptoms. Pathology seen on an MRI scan may include a meniscal tear or OCD.

Treatment

The treatment of PFJPS involves a combination of ‘hands on’ physiotherapy and an exercise based rehabilitation program. Anti-inflammatories may help to reduce pain. The physiotherapist needs to address lateral soft tissue tightness and patella stiffness. This is done through deep tissue massage to the ITB and patella mobilizations. The exercise program aims to strengthen primarily the VMO and also the buttock. Initial exercises include terminal knee extensions (such as straightening the knee over a rolled up towel) and inner range squats.  Rehabilitation proceeds to more functional exercises such as lunges and step downs. A trial of patellofemoral (McConnell) taping may improve the patella position and reduce pain. The kneecap is taped from the lateral to medial side to align it in the femoral trochlea. If taping reduces pain it will enhance the quality of the rehabilitation exercises and lead to improvement in VMO function. Good level 1 & 2 evidence exists for physical therapies, including taping and strength training.

If  rehabilitation exercises are performed diligently on a daily basis for 6 weeks then it is uncommon for there not to be improvement in knee pain. Surgery is generally not indicated in the treatment of anterior knee pain, except in recalcitrant cases.

Fig 2. Single leg inner range squat with fitball (advanced rehabilitation exercise)

Key Points

• Anterior knee pain is a very common condition, usually mediated by patellofemoral joint pain syndrome.
• It is caused by patella maltracking secondary to anatomical and soft tissue issues
• Pain is worsened on stairs and with prolonged sitting.
• VMO wasting and patella stiffness are key examination findings
• Exercise rehabilitation leads to improvement in the majority of patients