Anterior knee pain
Original Editors - Maxime Tuerlinckx as part of the Vrije Universiteit Brussel Evidence-based Practice Project
Anterior knee pain is pain that occurs in the anterior and central aspect of the knee. Its cause can be due to a number of conditions: 
- Patellofemoral pain syndrome
- Chondromalacia Patellae
- Osgood-Schlatter’s disease
- Sinding Larsen Johansson syndrome
- Plica synovialis syndrome
- Knee bursitis/Hoffa’s disease
- Articular cartilage injury
- Bone tumours: Most patients will experience pain in the area of the tumour. Pain can become worse during physical activity and often awakens patients during the night. Bone mass around the tumour becomes weaker and the bone may fracture as a result. 
- Osteochondritis dissecans
- Patellafemoral instability/subluxation
- Patellar stress fracture: A stress fracture in the patella is caused either by fatigue as a result of submaximal stress loads or insufficiency where the bone has been previously weakened due to physiological stress. It reduces shock absorption such that high repetitions of load may lead to a stress fracture. 
- Patellar tendinitis
- Patellofemoral osteoarthritis
- Pes anserine bursitis: The anserine bursa is one of 13 bursae found around the knee, located just below the pes anserinus. Patients with pes anserine bursitis often complain of spontaneous knee pain with tenderness in the inferomedial aspect of the knee joint. 
- Quadriceps tendinopathy
- Prepatellar bursitis
- Iliotibial band syndrome 
The aetiology of anterior knee pain is multifactorial and not well defined due to the variety of symptoms, pain location and pain level experienced by the patient. Underlying factors could be patella abnormalities, muscular imbalances or weakness leading to patella malalignment on flexion and extension. The can cause include overuse injuries such as; tendinopathy, insertional tendinopathy, patellar instability, chondral and osteochondral damage .
There is no clear definition of anterior knee pain as patients can present with various symptoms. There may be functional deficit, crepitus and/or instability. With activities of daily living pain often occurs or gets worse when walking down stairs, squatting, depressing the clutch pedal in a car, wearing high-heeled shoes or sitting for long periods with the knees in a flexed position, known as 'movie sign'. Patients can also experience a degree of instability, especially on walking up and down stairs or over ramps . Individuals with overuse injuries may report a feeling of instability or giving way, although this may not be a true giving way (which is associated with internal injury to the knee), but a neuromuscular inhibition as a result of pain, muscle weakness, patellar or joint instability 
- Referred pain from hip joint pathology such as capital femoral epiphysis
- Referred pain from the Saphenous nerve 
Evaluation of anterior pain is challenging as it can be non-specific and differential diagnosis is extensive. It requires a thorough examination, symptom history, an in-depth knowledge of the associated structures and typical injury patterns. In younger individuals, an assessment of their general growth and development is also essential to determine a diagnosis.
Hip and lumbar spine disorders can refer to the knee and need to be excluded.
Some key factors in obtaining an accurate diagnosis are; the pain characteristics, i.e. its location, character, onset, duration, change with activity or rest, aggravating and alleviating factors and any night pain; trauma (acute macrotrauma, repetitive microtrauma, recent/remote); mechanical symptoms (locking or extension block, instability, worse during or after activity); inflammatory symptoms such as morning stiffness, swelling; effects of previous treatments and the current level of function of the patient: if there is any history of gout, pseudogout, rheumatoid arthritis, or other degenerative joint diseases. Selective use of appropriate imaging, such as Ultrasound and MRI are excellent tools for differential diagnosis and for ruling out sources of intra-articular derangements 
Diagnosing and thus selecting an individual specific, non-operative treatment protocol can be vexing. The European Rehabilitation Panel have devised a guideline which should lead to improved treatment choice and outcomes. They suggest the following assessment parameters:
- Symptoms: Pain (location and type) or instability problems?
- Alignment of the entire lower extremity: Squinting patella? High Q-angle? Genu valgus? Genu recurvatum? Pronation of the subtalar joint?P
- Patellar position: Patella alta? Patella baja? Patellar glide? Patellar tilt? Patellar rotation?
- Muscles and soft tissues: Hypotrophy of VMO? An imbalance between VM and VL? Weakness of knee extensors, hip flexors and/or hip abductors? Tightness of the medial retinaculum? Tightness of lateral muscle structures, hamstrings and/or rectus femoris?
- Knee function (pain and/or maltracking of the patella): During different dynamic activities, e.g. stair walking, step-up/step-down exercises and one-leg squat?
The 13 item screening Kujala Anterior Knee Pain Scale (AKPS) can also be used to identify patellofemoral pain in adolescents and young adults. Ittenbach et all suggest that is highly reliable, but not without its limitations and further research is needed for its use outside of a clinical environment and application to the general population. The AKPS has shown to have good test-retest reliability.
The Lower Extremity Functional Scale (LEFS) is a further self-report test, to assess difficulties that the patient has with activities. This questionnaire is less specific for anterior knee pain patient than the anterior knee pain scale. The LEFS also demonstrates a high test-retest reliability and its reliability and responsiveness is slightly higher than that of the AKPS 
The Kujala anterior knee pain scale and the Lower extremity functional scale can be used for both an initial screening tool as well as to detect changes with treatment and as outcome measures.
Where there is bony abnormality or retinaculum dysfunction, non-operative treatment may be less successful, but operative treatment should be reserved for those with correctable anatomical abnormalities that have failed conservative therapy
Physical Therapy Management
For long term non-operative results, any postural mal-alignment or altered movement patterns should be addressed initially before introducing a strengthening programme. When assessing functional abnormality and compensatory patterns the whole lower limb should be observed, not restricting assessment to the knee area. Any significant leg length discrepancy should be addressed as well any intrinsic imbalances in the foot where these are contributing factors. Eng et all suggest that orthotics alongside exercise can result in more effective outcomes for sufferers of anterior knee pain compared to exercise alone , but any exercise and/or stretching programme needs to be individualised relative to the presenting symptoms and the movement dysfunction.
Where the retinaculum is tight, affecting the patellofemoral joint, manual stretching or McConnell taping may improve symptoms. But taping alone does not significantly reduce pain. However, there is evidence that knee taping, including placebo-taping, combined with exercise provides a superior reduction in pain compared with exercise alone. Therapies such as proprioceptive training, shoe inserts and taping may be best utilized as a complement to traditional exercise therapy; however, they have not been effective when implemented alone.
With an exercise programme, improving the eccentric muscular control is more effective than concentric exercises, with closed chain exercises being more functional and minimising stress on the patellofemoral joint. Reduced knee extensor strength is commonly seen in anterior knee pain patients, as well as weakness in the vastus medialis obliquus (VMO), although Witvrouw et al concluded that the VMO can not be worked in isolation, VMO designed exercises activating both VM and VL. A neuromuscular dysfunction is thought to be the cause of a VMO deficit.
Muscle length in the hamstrings, gastrocnemius and Rectus femoris all effect patellofemoral mechanics. Tight hamstrings can generate an increased reaction force over the patellofemoral joint as a greater force is required by the quadriceps for movement, so regular stretching is advised. But according to Mason et al, who compared the effectiveness of quadriceps stretching, quadriceps strengthening and taping in isolation and in combination, quadriceps stretching and quadriceps strengthening resulted in isolation in more improvements than taping. They also concluded that combining these treatments is recommended as the initial approach to treating patellofemoral pain but further individualized more functional, global treatment is essential. 
|| Case Study: Adolescent Anterior Knee Pain
This presentation was created by Omolara Ajayi in collaboration with: EIM Clinical Excellence Network and Physical Therapy Central.
Clinical Bottom Line
Anterior knee pain is a symptom, not a diagnosis. Any diagnosis for the pain is, essentially, via exclusion due to the numerous possible conditions, where patella abnormality or muscular imbalances are important factors, determined by a thorough history and patient examination. There is also a high correlation between AKP and faulty hip mechanics, so any assessment needs to involve the entire kinetic chain. Treatment is highly individualised and the European Rehabilitation Panel's guideline is a useful tool for choosing a non-operative treatment protocol.
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