The knee joint consists of two main joints, the tibio-femoral and patello-femoral joints. There is a third lesser important joint called the proximal tibiofibular joint which is a fibrous joint between the top of the shin bone and fibula.
The patella (kneecap) is a bone which is contained within the quadriceps tendon. Bones contained within tendons are called sesamoids and the patella is the biggest sesamoid in the body. The function of the patella is to increase the lever-arm of the quadriceps mechanism, by moving it away from the trochlea grove. This increases the strength of the quadriceps. In people who have the patella removed surgically (patellectomy) for various reasons, the power of the quadriceps decreases by 30%, which is why patellectomy should be avoided.
The patella arbitrarily divides the quadriceps tendon into what is known as the patellar tendon below the patella and the quadriceps tendon above the patella. The patella moves against the trochlea groove at the end of the femur. As the patella forms part of the joint it is also covered by articular cartilage.
The patello-femoral joint has to tolerate some of the largest body weight forces in the body and can have to withstand up to 8 to 9 times of body weight with activities such as jumping, running and stair climbing. It is therefore not surprising that the patellar has the thickest articular cartilage of any joint in the body.
An MRI scan showing a cross-section thro the knee at the leve of the Patello-femoral joint.
This is also known as anterior knee pain because the pain is felt at the front of the knee. Anterior knee pain can be a difficult problem to diagnose & treat and can be challenging from both the orthopaedic surgeon’s point of view and the patient’s. It is also known as anterior knee pain syndrome with the term syndrome implying that there are a number of different causes that can lead to anterior knee pain and this is in fact entirely true.
Classically, anterior or patello-femoral knee pain is pain that is felt at the front of the knee. It is commonly worse with prolonged sitting, going up and down stairs or activities that involve bending the knee, such as kneeling and squatting. It is commonly made worse with sports. It can be associated with clicking and grinding of the knee as well as swelling within the knee. The syndrome arises due to damage or irritation to the lining surface cartilage (articular) of the patella causing softening, fibrillation and breakdown of the articular cartilage. Anterior knee pain has in the past also been inappropriately termed chondromalacia patellae (inappropriately because the original definition of chondromalacia patellae was painless softening of the articular cartilage of the patella).
The actual cause of patella pain is not clearly understood. It is indirectly related to irritation and stimulation of nerve fibre endings but it is the cause of the irritation of these nerves that can be difficult to define. Damage to the lining surface of the patella and chronic alteration in the biomechanics of the patella tracking and movement mechanism can lead to irritation, overuse and stimulation of the nerves, causing pain.
There are a number of factors which are known to contribute or potentially predispose to anterior knee pain and these include factors such as:
– Flat feet
– Rotational abnormalities of the femur
– Knocked knees (genu-valgum)
The basic premise of all of these is a biomechanical abnormality in that there is an increased force pulling the kneecap outwards which can lead to increased pressure against the outer part of the kneecap joint causing thinning and damage to the lining surface, leading to pain. This is also known as patella malalignment. Abnormal pressures can be directed through a normal joint but in an excessive amount in activities that lead to repeated overloading of the knee such as jogging, jumping and so forth.
The mainstay of treating anterior knee pain is non surgical. It involves a process of stretching, strengthening and balance work. Occasionally insoles can be used to correct abnormalities such as flat feet.
The stretching refers to stretching of the pelvic muscles, the ilio-tibial band, the quadriceps muscles and the hamstring muscles as well as stretching the structures around the patella and mobilizing the patella. In addition to this, modality treatment can be used incorporating ultrasound, megapulse and occasionally laser. The strengthening refers to strengthening of the lower limb musculature specifically the quadriceps and hamstrings. Historically the emphasis has been on the lowest inner most part of the quadriceps called the vastus medialis obliquis (VMO). The aim of the strengthening is to improve the strength of the muscle fibres themselves but also to improve the firing pattern and co-ordination between the firing of the quadriceps and hamstrings.
A commonly forgotten aspect of treatment is to improve core stability by strengthening lower abdominal and para-spinal muscles. This can be aided by Pilates and Yoga.
Improving balance and co-ordination is also important as this works with the above treatments to improve the firing pattern of the lower limb muscles.
Occasionally, braces and taping can be used in conjunction with the above modalities.
More specific treatment is geared at the underlying abnormality. If there is damage to the lining surface of the knee then the options would be the same as with any chondral damage, including injections of hyaluronic acid, steroids and possibly arthroscopic surgery to entail chondroplasty and microfracture.
The most striking demonstration of patella instability is the acute kneecap dislocation that can occur in some people with sudden twisting movements. The patella can dislocate out of the knee joint and commonly will also relocate back spontaneously. When the patella dislocates the result is tearing of the restraining structures on the medial (inner) side of the patella (medial retinaculum) and specifically the medial patello-femoral ligament. The medial patello-femoral ligament is a primary restraint to lateral patella dislocation.
The patient will present with a history of where they may have heard two clicks in their knee during their activity, one with the patella going out and the second with the patella reducing. They develop immediate swelling of the knee (haemarthrosis – bleeding into a joint) and are usually unable to continue their activity. They have generalized pain around the knee with the tenderness being located to the inner side of the kneecap.
As part of the diagnostic procedure, x-rays would be obtained, as about 15 to 20% of people can develop fractures around the kneecap with resulting bony and cartilaginous loose bodies.
Once a person has experienced a dislocation of any joint they are much more likely to have subsequent dislocations and this is just as true with the patella as with any other joint. The literature on the subject of patella dislocations can be somewhat misleading. The literature would suggest a re-dislocation rate of between 15 to 40%. However, this figure is artificially low because if these studies are scrutinized, it is clear that the people who were being studied had significantly reduced their activity level following the dislocation. In other words, the reason their dislocation rate was this low was because they were not undertaking most of the activities that they were undertaking prior to the dislocation. If the studies are looked at where activity level has not been reduced, then the re-dislocation rate is much higher and can be double these levels.
Once a person has had a patella dislocation they may complain of future true dislocations or lesser symptoms of subluxation when the patient reports that the kneecap slips out but goes back in spontaneously. They may have instability and giving way of the knee or a sensation that the kneecap is going to come out of place. The problems with repetitive episodes of patella subluxation and dislocation is that is causes damage to the lining cartilage surface of the patella which eventually can lead on to the development of arthritis in the knee.
Treatment and Rehabilitation of Patella Dislocation
The traditional treatment of an acute patella dislocation is conservative involving immobilization in a cast or a brace for 4 to 6 weeks. Following this, the patient is put through a physiotherapy programme in an attempt to regain strength and muscle control. Should the patella then continue to re-dislocate further reconstructive surgery may be considered.
The problem with the conservative method of treatment is that, as outlined above, it can lead to a significant risk of re-dislocation and certainly the likelihood that the patient will have to reduce their level of activities from a functional and sporting point of view.
There are now some papers in the literature suggesting that acute repair of a first time traumatic patella dislocation may be warranted and this is the view I take when indicated.
Treatment of Acute First Time Patella Dislocations
The initial treatment once the person has been to the Accident and Emergency Department is to elevate the leg, apply some form of compression such as a TED stocking or a Tubigrip bandage and to apply ice or a Cryocuff. They will be sent for acute physiotherapy to work on their swelling reduction to get their quadriceps control and leg control back as well as trying to maximize the amount of motion they have.
The patient will simultaneously be referred for an urgent MRI scan within the first week. If the MRI scan shows that the medial patello-femoral ligament has been torn from its bony attachment on the femur or the patella (which is the most common scenario) then this can be addressed surgically. If the MRI scan shows an intra-substance tear within the ligament (this is uncommon) then the treatment will continue along the non surgical route although I do not use any casts or braces for immobilization and we continue to work on getting swelling down, motion back and strength back. I will occasionally combine this with taping of the kneecap as a physiotherapy modality for treatment.
The benefit of acute surgery is that it can reduce significantly the risk of re-dislocation of the kneecap. The risk of the surgery is that operating on an inflamed swollen knee can result in stiffness of the knee which is why it is important to commence an aggressive physiotherapy and a swelling control and motion programme prior to any surgery.
The surgery is relatively straightforward compared to chronic patella realignment surgery. The surgery involves an arthroscopy of the knee to assess the articular surface of the patella and to tidy up and debride any chondral damage and possibly also undertake microfracture if there is a piece of cartilage that has been knocked off the kneecap or the trochlea groove. This is followed by an arthroscopic lateral release which divides the outer (lateral) structures of the kneecap which are the tissues that pull the kneecap towards the outside of the knee and are therefore the structures that would tend to re-dislocate the kneecap. Once this has been done then a mini open procedure would be undertaken at the site of the tear of the medial patello-femoral ligament to reattach it back to the thigh bone or the kneecap depending on where it is torn and to repair the medial retinacular structures of the patella.
Following surgery, a TED stocking is applied and a Cryocuff is used and the patient is placed on a CPM machine to both elevate the leg and to passively move the knee. Every two hours an active programme of rehabilitation is undertaken to include active straight leg raises, active and passive assisted knee flexion and hyperextension stretching. Once again, McConnell taping to the kneecap can be used to try and keep the lateral structures stretched out and keep the patella in a more centralized position. The patient will mobilize with crutches, fully weight bearing, using a splint to walk in for 4 weeks. The crutches will continue for as long as there is a tendency for the patient to limp.
The patient is usually in hospital overnight and is then discharged to physiotherapy while being followed up in the outpatient clinic. The long term goals following this procedure are the same as with the patello-femoral rehabilitation programme outlined above, to work on stretching, strengthening, core stability and balance control.
This primary repair procedure can only be performed within 10 to 14 days of the acute injury as beyond that time the injured tissues become too friable and there is nothing to be gained surgically at that stage, which is why there is some urgency to get the investigations instigated and the treatment underway.
For patients who are treated conservatively following their first dislocation then continue to have episodes of instability with either true dislocations or subluxation, the first treatment option would still be physiotherapy and rehabilitation as outlined above. Should this not help, the surgical undertaking is more complex and would be a patella realignment procedure.
The aims of the patella realignment procedure are to reduce the outward going (lateral) forces on the kneecap pulling the kneecap out and to try and increase the inward pull (medial) on the patella, which tends to keep the patella in place.
The realignment can be performed above or below the patella or commonly will involve both above and below the patella.
The procedure involves initially a lateral release. If it has then been decided that only a proximal (above the patella) realignment will be performed then the vastus medialis obliquus muscle and the medial capsule of the patella are advanced onto the patella to increase the medial dynamic pull on the patella.
If a distal (below the patella) realignment is to also be performed then this is done by way of a tibial tubercle osteotomy. The attachment of the patellar tendon to the tibia is on a structure called the tibial tuberosity. This structure is osteotomised (broken) and the whole structure is moved inwards along the tibia and then reattached with a number of screws. This once again has the effect of increasing the medial pull on the patella mechanism. There are variants of this tubercle osteotomy which can be done to move the tibial tubercle both medially and anteriorly so as to reduce the loading forces on the kneecap.
Occasionally the tibial tubercle can also be moved distally (further down the tibia away from the knee). This is done in patients who have long patella tendons, which is one of the predisposing factors for patella dislocation. What is actually being done is that the tendon length is being normalized to approaching a more normal length rather than truly being distalised. If there is any damage to the lining surface of the patella, a distalization/normalization of the patella tendon length is not performed as this may increase the loading forces on the patella.
Overall, this is a much more major surgical undertaking than the patella dislocation repair. Following the surgery the patient is in hospital for one to three days. There are on a CPM machine. It takes much longer to get the ability to straight leg raise back. The patient will usually use a splint to walk in for 4 to 8 weeks and crutches for this period of time. 2-hourly exercises are done in the first week to work on flexion and a TED stocking, Cryocuff or ice packs are used to help control swelling.
The patella realignment procedures do reduce the risks of further patello-femoral dislocation significantly.
As part of the imaging performed for patella dislocation surgery, it is possible to measure the distance between the tibial tuberosity and the deepest point of the trochlea groove on either an MRI or CT scan. The normal distance is up to 8mm. If this distance is significantly increased, as it commonly is in people with patella instability and dislocation, then this would be an indication for undertaking a distal realignment. If the distance is not increased then the first line of surgery would be a proximal realignment.
The patella realignment surgery can be performed in conjunction with cartilage transplantation of the lateral aspect of the patello-femoral joint so as to offload this aspect of the joint and to allow the cartilage transplantation to heal and function normally. Without this realignment, the transplanted cartilage can continue to be overloaded and may eventually breakdown.
Patella Pain and Instability
Patients who have recurrent instability of the patella will sustain increased damage to the lining surface of the patella which will start to cause patello-femoral pain. The treatment of these patients would entail normal treatment for chondral damage including hyaluronic acid and steroid injections, physiotherapy and rehabilitation.
The surgical options would involve realignment procedures to the patello-femoral joint with or without cartilage transplantation procedures, as outlined above.
The mainstay of treatment once again is rehabilitation based.
Patients with patello-femoral pain, whether with maltracking and malalignment or without, can go on to develop isolated patello-femoral arthritis and for these patients an isolated patello-femoral joint replacement may be indicated.
Other Patello-Femoral Conditions
These are folds of synovial membrane within the knee which are normal structures in most people. However, in some people who may have injured their knee the plical band can rub against the thigh bone and get thickened and inflamed and then cause pain. The patient can usually localize the pain to the inner aspect of the knee and when the band is rubbed by the surgeon examining the knee, it reproduces the pain.
The treatment for these in the first instance is physiotherapy modalities including ultrasound and ice. Anti-inflammatory tablets may help. Occasionally a steroid and local anaesthetic injection can be used which may be curative. Very rarely these bands are resistant to treatment and may require arthroscopic excision.
Patellar tendonitis (jumper’s knee)
Tendonitis’ are overuse conditions and are more accurately referred to as tendinopathies because they don’t have an inflammatory basis. The underlying pathology is usually collagen degradation, commonly called tendinosis. The suffix -itis usually refers to an inflammatory pathology which is why the term tendonitis is not correct strictly speaking.
This is an overuse condition that affects the collagen with the patellar tendon at the front of the knee. The symptoms are usually localized to the inferior pole of the patella. Patellar tendinopathy is common in overuse sports that require extensive loading of the extensor mechanism such as jumping sports like basketball and volleyball. It can also occasionally occur in footballers who overload their patellar tendon. Patellar tendinopathy can be a difficult condition to treat and the mainstay of treating this is non surgical. The diagnosis can be made from the history, examination and imaging features.
The history is usually of pain which is localized to the inferior pole of the patella. The patient will initially complain of pain which comes on after a period of aggravating exercise. As the disease severity increases the pain can intrude into the sport and eventually, in the worse categories of patellar tendinopathy, the pain can occur at rest, before sport.
Examination findings will show some thickening at the inferior pole of the patella and point tenderness on palpation of the inferior pole of the patella. Resisted knee extension in an extended position can also be painful as can resisted knee extension from a flexed position. Imaging modalities would include ultrasound scan and MRI scans which would show an area of degenerate tendon at the inferior pole of the patella. Occasionally there is involvement of the patella itself.
The treatment consists initially of trying to offload the tendon and prevent overuse. This is achieved by biomechanical modifications such as use of insoles or patella taping or patellar tendon braces. The offloading can also occur by modifying activities.
It is important to stretch the quadriceps and hamstrings tendon. Physiotherapy modalities can be used such as laser, ultrasound, patella mobilization and deep friction massages. A strengthening programme is commenced which is known as an eccentric strengthening programme as this has been shown to be the most effective way of trying to treat and prevent further tendinopathies occurring.
Should be conservative measures fail, the next line of treatment would be more invasive. The options at this point would include:
– Lithotripsy (shockwave therapy)
– Dry needling
– Aprotinin injections into the tendon sheaths
– Autologous blood / plasma injection into the tendonopathic area
In the past steroid injections have been used but these should not be used as steroid will weaken the collagen and can lead on to tendon ruptures, which can be catastrophic. The tendonopathy in its own right can lead to tendon rupture, usually with sudden explosive actions.
Dry needling is a technique that involves literally passing a sterile needle through the degenerate tendon on numerous occasions with the aim of trying to increase bleeding and blood flow into the area to try and allow the degenerate tendon to heal. Autologous blood / plasma injections are attempting to reproduce the same healing mechanism.
There is some reasonable literature to show the benefit of shockwave treatment, which is used to break up kidney stones. This can also be used in soft tissue tendinopathies and there is literature on this matter to suggest reasonable success rates.
Another option would be a course of Aprotinin injections. Aprotinin is an enzyme blocker, blocking an enzyme that is involved in the tendinopathic pathway to try and allow the tendon degeneration to stop and allow the healing mechanisms to heal the tendon. Once again the literature on Aprotinin injections suggest a reasonable success rate. All these modalities in the literature have been shown to have a reasonable success rate and are certainly worth trying prior to proceeding to surgery, which does not have anything approaching a guaranteed success rate.
The surgery is a last resort treatment and involves excising the degenerate tendon and trying to stimulate blood flow into the tendon. The recovery is slow and return to sports takes 6 to 12 months with a 75 to 80% success rate. Therefore, surgery truly is a last resort in this difficult condition to manage. I have had good success rates with a combination of shockwave therapy, dry needling and Aprotinin injections in resistant patellar tendinopathy combined with physiotherapy modalities.
This condition is also known as housemaid’s knee and can occur in people who spend a lot of time kneeling, such as plumbers, carpet layers, roofers and so forth. Due to the constant irritation of the skin overlying the patellar tendon and tibial tuberosity swelling develops in a bursa, which is a lubricating sac just in front of and behind the patellar tendon. The sac normally allows the skin to glide over the tendon but if it becomes inflamed it becomes a lump. The usual symptoms are of pain and swelling which is localized to the front of the kneecap tendon.
Usually conservative treatment involving rest, ice, elevation, anti-inflammatories and physiotherapy modalities are helpful. Very occasionally they can be aspirated and a steroid injected into it or they can be excised surgically.