This is probably the most chapter of my ebook, for Anterior Knee Pain Syndrome (AKPS) is the commonest knee problem encountered in clinical practice. Probably 80% of the knees that present to my practice will have this complaint. No age group is exempt.

Surgical treatment is rarely indicated and with few exceptions, rarely effective [1] .

Classifying anterior knee pain

Group one- pathological conditions that cause anterior knee pain

There are two broad categories of diagnosis.

Firstly, patients with anterior knee pain may have a known pathology. The possible diagnoses are listed. In this case, one can make a definite diagnosis.

Group two- anterior knee pain syndrome

In most cases the cause for pain is to be found in the tissues that support the patella (patellar retinaculae). No specific diagnosis can be made, but certain common symptoms are shared and quite often there are patient factors that are common to the group such as rotational malalignment and patellar dysplasia. There is enough commonality to group these patients.

It must be the major aim of our assessment to make a pathological diagnosis if possible, or, if not, then to document factors that predispose the patient to suffer the condition. Thus, the diagnosis of anterior knee pain syndrome should have as a qualifier, "tight hamstrings," or, "overweight, with unrealistic training methods", etc.

Anterior Knee Pain Syndrome

The Syndrome

Pain is felt in the front of the knee, and, usually, it is felt adjacent to the medial side of the patella. point test

As an aside: the location of the pain may give some idea of a pathological diagnosis- for example, the pain of patellar tendonitis is usually felt at the inferior pole of the patella.

Pain is worse for bent knee activities. Often going down steps is worse than moving up steps. Pain is worst after stressful activities but the severity is variable. The patient may be very disabled. Running activities may not be possible or cause post exertional pain. Sports minded persons will note a deterioration of their performance. Swelling may or may not be present (when it is present it supports a pathological diagnosis). The knee may give out because of weak quadriceps or patellar instability (the former is more common)

Most of the patients fall into two groups: adolescents / young adults and the middle aged to elderly age groups. The younger age groups are often physically very active. Older patients are likely to have degenerative disease as a causative factor, though, nowadays, many are quite physically active also. Many patients in both groups are overweight or have a degree of lower limb malalignment or patellar dysplasia [2] .

Investigations are usually not that helpful in diagnosis & less so in treatment.

“Chondromalacia patellae” is not an accurate descriptor of the condition: it should not be used as a generic name for anterior knee pain syndrome.

Synonyms

Synonyms exist for this condition because of its varied presentations and because of presumed pathologies (which are often incorrect).

Synonym	Presumed Pathology or group
adolescent anterior knee pain,	Especially applied to adolescents with anterior knee pain. Common in females
patella stress syndrome	Non specific term
peripatellar stress syndrome	Tight retinacular tissues, quadriceps or hamstrings
chondromalacia patellae	Softening of the under-surface of the patellar cartilage- *this is a pathological diagnosis and should not be used unless it is known to be the truly present and causative of the pain.*
Table of Synonyms for anterior knee pain syndrome

Differential Diagnosis and traps

Extrinsic Pain, ie. referred pain:

Pain can be referred to the front of the knee from the hip especially in paediatric age groups though adults frequently also complain of knee pain with hip pathology . The lumbosacral spine can also be a source of referred pain.

Spinal causes

The pain is usually more generalised. It would be helpful if the pain was in a dermatomal distribution, but this is not often the case. The pain usually has a more dysaesthetic character than anterior knee pain, i.e., it has a burning or paraesthetic feel. It is not necessarily exertional but may be claudicant. It is not always easy to tell on symptoms alone [3] ! Local signs should indicate that the knee is the site of the pathology in most cases.

Hip Pain

In the paediatric age group, knee pain means hip pathology until proven otherwise.

Other "Internal Derangements [4] " and Synovitis

Other intrinsic knee pathology is often expressed as pain in the front of the knee & so it is important to examine the knee carefully. Synovitis pain, from whatever cause, will also be most felt in the front of the knee as this is where most of the synovial tissue is.

The front of the knee acts as a indicator of the general well-being of the knee. Minor derangements that cause synovial irritation will cause anterior knee discomfort as well.

Synovitis-True articular causes for the pain such as osteoarthritis, inflammatory arthritis, cartilage softening (chondromalacia [5] ) or a degenerate meniscus can all cause synovitis. After trauma, the knee often swells -post traumatic synovitis.

Conditions in the front of the knee of Known Pathology

I have already referred to these as belonging to the first group of patients with anterior knee pain. It will always be the aim to make a pathological diagnosis where possible.

Condition	Distinguishing features
Patellar tendonitis- AKA Jumper’s knee, Runner’s knee	Infrapatellar pain and tenderness of the inferior pole of the patella?
Lateral Patellar compression syndrome AKA- Excess lateral pressure syndrome (ELPS), patellar tilt syndrome	Pain is lateral patellar tenderness is under lateral patellar facet Patellar is tight to medial displacement Laurin skyline view (fig) may show tilt, prolonged lateral facet, osteophyte, fracture osteophyte or evidence of osteoarthritis of the lateral part of the patellofemoral joint (Fig). Bone scan may show this part of joint hot
Osteoarthritis of the patellofemoral joint	Commoner in older age, the sequel to “patellar tilt syndrome” shares the clinical symptoms and features
Painful bipartite patella	This presents similarly to ELPS or tilt syndrome: there may be a link between bipartite patellae and ELPS (see below)-
Inflamed plicae [6]	Tender fold adjacent to medial side of patella. Knee may clunk
Osteochondritis dissecans of the patella	Quite rare (Fig) 1 and 2
Chondromalacia Patella	Commoner than it is pathological. May cause intractable anterior knee pain- “patellar migraine”
Osgood-Schlatters Syndrome	This occurs in a pubescent boy (fewer in females). The pain is exertional and is felt over the tibial tuberosity where there will be swelling and tenderness. Xrays may show fragmentation of the apophysis
Old Osgood-Schlatters disease	Tenderness and swelling over the tibial tuberosity in skeletally mature person. Little ossicles in the distal most patellar tendon on xray
Pre Patellar Bursitis	There should not be too much trouble in diagnosing this condition (fig)

Examining a knee with anterior knee pain

Look for referred pain- hip especially.

Point to where there is pain- the point test

At the knee, is there an effusion- is there a synovitis due to disease elswhere in the knee joint

Stand- look at varus- valgus, extension of joint. Walk [7] , sit patient, squat patient.

With the patient seated, observe the quadriceps for wasting and look at the insertion of the patella tendon at the tuberosity. The tuberosity should lie immediately below the inferior pole of the patella- see video. The patella should track in a relatively smooth movement when the patient extends and flexes the knee - sudden flicks are abnormal- see second part of the video.

Is the quads wasted and in particular, the VMO [8] . Test strength over the side of bed. Look at tracking with foot over side of bed (Fig)

Palpate quads for bulk, measure in exceptional circumstances

Palpate patellar facets for tenderness, look for plicae

Patellar size and mobility, stability (apprehension test if knee gives out). Test for medial mobility of patella with knee in 30 deg flexion- pain and crepitus with tilt or OA

Look for tight muscle groups- hams, quads, calf group, iliotibial band

Investigating anterior knee pain:

Xrays

If there are no suspicious circumstances, an Xray is unnecessary at the first visit. If patients are not responding to physical treatment in 6 weeks then an Xray is required. We need plain AP and a lateral with the knee in 30o flexion and some sort of patellofemoral skyline view with the knee as straight as possible: The technique of Laurin is preferred. In adolescent patients a tunnel or intercondylar view completes the series.

The Skyline viewThis is a key view because it shows us the shape of the patella, the congruity of the patellofemoral joint and whether there is tilting or tipping of the patella in its joint- “patellar tilt syndrome”. There may be signs of osteoarthritis (narrowing of the lateral joint space and sclerosis of the lateral facet and trochlear ridge, and prolongation of the lateral patellar facet by an osteophyte. (fig)

This view needs to be taken as near full extension of the knee as possible (fig)

AP and lateral views

The lateral view is taken in 30 deg flexion because the crimp is taken out of the patellar tendon in this position and a reliable assessment of patellar height is possible.

We will be able to diagnose bipartite patella on the plain AP and any associated arthritis of the femorotibial joint if it is present.

On the lateral xray we will be able to judge patellar height [9] using the Blackburn Peel index. We will be able to see fragmentation of the tibial apophysis in Osgood- Schlatter's disease

Summary of possible findings on Xray in anterior knee pain

Patella dysplasia
Bipartite Patellae
Patellar tilt
Patella alta
Osteochondritis dissecans
Patello-femoral arthritis
Osteochondroses- Osgood- Schlatter’s disease
Co morbidity- e.g. osteoarthritis

Certain patellae are misshapen or small and are therefore more likely to present problems. We talk of patellar dysplasia when describing small patellae with usually small and relatively short, vertical medial facets. The shapes of patellae have been classified. A good patella should have a generous medial facet which is either gently convex or straight.

Many patients with resistant anterior knee pain syndrome have dysplastic patellae. Dysplastic patellae are associated with poor VMO development and shallow trochlear grooves.

Patients with dysplastic patellae and anterior knee pain which persists despite adequate treatment may need counselling to restrict their activity. This may be difficult if the patient is athletic.

Another patellar anomaly is a bipartite patella. This usually occurs in the lateral facet. It is usually asymptomatic and can occur in 2% of knees and is bilateral in 40%. In many people it probably represents an accessory centre of ossification that never united but it may also represent a chronic chondro-osseous tensile disruption (with tight lateral retinaculae). It is therefore often associated with patellar tilt syndrome- see below. The patella may feel large and in the region of the defect there is tenderness in symptomatic patients.

Tightly tethered patellae tend to tilt laterally in the skyline view but just as often there are no findings on xray. The lateral facet may appear to be too lateral and the median ridge of the patella may, likewise, be laterally placed in relation to the groove of the femoral trochlea. We can talk of patellar tilt with the inference that the lateral retinaculum is too tight and too much pressure is being taken under the lateral patellar facet- this is also called “excess lateral pressure syndrome.” This excess lateral pressure syndrome can cause lateral patellar facet osteoarthritis, and, before this anterolateral pain and tenderness.

Patella alta : a patella that is higher than it should be is prone to be associated with pain and frequently instability of the patella. The patellar height is measured on the 30o flexed lateral [10] . The easiest measure is the Blackburn-Peel ratio which should be less than 1(see figure).

Osteochondritis dissecans

This is rare in the patellofemoral joint. However it is well described and cases are seen occasionally. CT scanning would show the lesion more reliably. [11]

Osgood- Schlatter's Disease

This is predominately a disorder of teenage boys. The male:female ratio is 9:1. The boys are typically 12 to 14 years old and are quite sporty. They have often been growing quickly- no doubt a factor in the aetiology, i.e., tensile failure of the tendon-apophyseal junction [12] . The physical signs are very typical: swelling of the tibial tuberosity and tenderness. Xrays may show intratendonous calcification or fragmentation of the apophysis. Treatment is non-operative with some reassurance that most patients are asymptomatic in twelve months -occasionally it takes two years to recover.

Patello-femoral arthritis

It manifest as sharpening of the patellofemoral outline especially in the lateral view with osteophytes and tilt of the patella and lateral patellofemoral joint space narrowing and extension of the lateral facet by osteophyte or spur on the skyline view. Clinically the patella is tethered laterally (and generally hypomobile) and tenderness is in the lateral patellofemoral interval or under the lateral patellar facet where the pain is generally felt. The lateral facet bears the brunt of the load of the patellofemoral joint and is most involved.

Patellofemoral arthritis is usually the end result of excessive lateral patellar tilt and retinacular tightness and as such it shares common radiological features with that condition.

CT, MRI and bone scans

A CT scan taken through the middle of the patellofemoral joint to pick up tilt or subluxation can be quite useful prior to considering a lateral retinacular release. A bone scan can detect abnormal uptake in the patella when it is arthritic, overloaded, the site of osteochondritis dissecans or if it has been fractured. Sometimes the attachment of the patellar tendon at the inferior pole of the patella is hot on bone scan in patellar tendonitis. An ultrasound of the patellar tendon or an MRI (which seems to be better) (Fig) may detect a disruption of the patellar tendon substance in patellar tendonitis (jumper's knee).

Treatment:

Treatment should be conservative and specific to the diagnosis or aetiology. Contributing factors that can be discovered from the history and physical examination should also be treated.

Nonoperative treatment

"Victory belongs to the most persevering" -Napoleon

The physical examination will identify certain pathology or contributory factors that can be addressed. Some standard advise follows:

Weight: Obesity is very bad. Joint pressure in the patellofemoral joint is measured in multiples of body weight. Getting the patient to lose weight is the single best thing that can be done.

Wasted quadriceps: The quadriceps control patellar tracking to some degree. Unfortunately the quadriceps also load up the patellofemoral joint and so steps taken to exercise this muscle must be very controlled. The biomechanics of the patellofemoral joint are such that the joint surface is not loaded maximally until the knee is acutely flexed. Exercises should be therefore carried out in the terminal arc of extension, i.e., with the knee near fully straight. Start with straight leg raising exercises and semi squatting exercises, the so-called "closed kinetic chain", and combine these with stretches. Some form of general body conditioning is also necessary and cycling for 20 minutes on a static exercise bike or swimming (kicking) in a pool for 20 minutes 3X per week is suggested. This is physiotherapy that can be administered by anybody who has the time and patience to supervise it. A physiotherapist can be of great benefit as long as the patient is made to understand that the treatment programme is their responsibility and that they are in charge of making themselves better.

Whatever exercise routine is suggested, it must be demonstrated and written down. Numbers of each particular exercise per day are specified. The patient should be able to recite fluently their routine and demonstrate it to me when I review them or I suspect that they are not conforming.

In cases where the patient has had physiotherapy, enquire as to what was done. If it is ultrasound or just massage that your patient is getting, then swap physiotherapists.

Tight muscle groups: I show my patients how to stretch out their quads, hamstrings and their iliotibial tracts. They do these stretches for 2mins for each stretch and they do it twice per day. The calves may also need to be stretched out.

Pronated feet and “orthotics”: there are some patients with pronated (flat) feet who derive a great amount of symptomatic improvement from the fitting of an orthotic insole. Thes are the patients whose patellae squint when the medial sides of the feet are brought together. It is never my first line of treatment. I reserve it for patients with flat feet who wear sensible shoes for a considerable part of their day and who are not responding to other measures. The orthotics need to be fairly firm to work. When the patient stands in their orthotic it will be observed that the whole lower limb will externally rotate. This subtle change of alignment may be how orthotics work [13] .

Ice massage, rest, reduced and graduated retraining. Anti-inflammatory are used sparingly and only if there is evidence of inflammation. In Osgood-Schlatters Disease rest from the aggravating activity is really the only treatment necessary. Occasionally this may need to be enforced with plaster!

Splints and wraps: Most patients will feel more secure with a splint or a wrap on. However, this is just a symptomatic measure. I don’t prescribe them except in the patient who has symptoms of patellar instability. In this case a simple "knee guard" or neoprene corset with a patellar hole is all that is required. Many patients can avoid patellar subluxation during sport by donning such a simple appliance (and also by strengthening their quadriceps). Patellar taping can assist patients acutely by altering patellar contact & soft tissue tension. It is part of the Mc Connell programme that all physiotherapists (especially in Australia) know.

Rarely is operative treatment recommended and rarely is it useful.

Operative treatment

Operative treatment is not generally required.

Indications

There is some pathology that can be reasonably and successfully addressed
The patient has a significant disability
Non operative treatment has failed

Options for operative treatment

Arthroscopy may be of some diagnostic and therapeutic benefit if a treatable lesion such a meniscus tear is found. Debridement of cartilaginous flaps and chondromalacic areas seems to be of some benefit. There are many reports on this subject but such reports are invariably uncontrolled and usually retrospective studies of a mixed sample of patients. It is certain that many asymptomatic knees have areas of cartilage ulceration and softening under the patella. In an synovitic knee with such surface lesions arthroscopy can be of some benefit because it rids the joint of inflammatory debris and cartilage that is about to fall into the joint.

The indications for arthroscopy will vary depending on the treating physician.

Plicae: these are a normal finding in knees. Up to 30% or more knees have a prominent medial fold of synovial tissue that extends from the medial edge of the fat pad around the patellar tendon to the medial part of the suprapatellar pouch. After a direct trauma (a blow to the front of the knee), this plica can become inflamed or fibrotic in time. Occasionally the plica can get caught or impact on the medial femoral condyle and cause chondromalacia and localised synovitis. The knee may click with flexion and extension. Pain should be localised to the fold which flicks over the medial femoral condyl as the knee is flexed. The fold is usually palpable. In such rare cases removing the fold arthroscopically can be a very useful procedure.

Tight lateral retinaculae and patellar tilt-

In cases of patellar tilt with tight lateral retinacular structures , the lateral tethers of the patella can be released, a lateral release. The ideal patient will have mainly lateral peri-and retro-patellar pain and tenderness. Naturally, physical measures are tried first, i.e., stretches taping of the patella. Physiotherapists are useful in this condition. The ideal candidate is uncommon. Sometimes an early good result does not last. Lateral release can be performed arthroscopically or through a minimal incision equally well and both give similar results.

Tibial tubercle elevation: Osteoarthritic patellofemoral joints can be difficult to manage successfully. Once again, physical therapy is the mainstay of treatment. In younger patients one can elevate the tibial tubercle to reduce pressure under the patella. 1.5cm of elevation seems necessary. This will cause some unsightliness and a disability for kneeling on the front of the knee. There is a very high failure rate if patients are not chosen appropriately.

Recurrent patellar instability:

Recurrent patellar subluxation or dislocation can be quite debilitating. Surgical realignment is possible both proximal and distal to the patella .

Distal realignment means detaching the patellar tendon insertion, i.e., the tibial tuberosity and moving it medially and securing it with a screw. In practice both a proximal soft tissue plication and a distal realignment of the tibial tubercle are usually performed together.

Joint replacement

Yes, the patellofemoral joint can be replaced and the results in the literature are not that bad! Mechanical failure of the implant is rare.

Patellectomy:

Sometimes nothing seems to help when the patellar has a large area of chondromalacia. Some of my most grateful patients are those who after several years of battling with this condition have gone on to a patellectomy. I have not performed, as yet, patellectomy for isolated patellofemoral osteoarthritis.

Summary:

Anterior knee pain can be due to a number of causes.

You should aim should be to identify the exact pathology, to understand all the contributing factors and to direct treatment to the pathology and causative factors when possible.

Many patients just have anterior knee pain without any likely pathological diagnosis. These patients are described as having “anterior knee pain syndrome.”

You should master Special techniques in the physical examination of anterior knee pain.

Xrays are important in resistant cases and should confirm your suspicions.

The vast majority of patients should be treated with physical therapy which is carefully crafted and monitored with enthusiasm. Reassurance in generous doses is also necessary.