The knee-cap (patella) is a sesamoid bone (a bone embedded within a tendon) to support the extensor tendon of the thigh. It does not have any firm osseous joint guidance, but is only attached to muscles, tendons and ligaments; it glides in a V-shaped groove of the femur (femoral trochlea or sliding bearing).
For this reason, the knee-cap is susceptible to problems in reaction to changes in muscle balance or as the result of congenital malformation of the trochlea.
The term "anterior knee pain" comprises a range of different causes.
The most common causes are:
- Functional disorders
Disorders without pathological changes to the knee cartilage or in the joint space. These are frequently caused by hip disorders or problems with the lumbar or cervical spine, a good indication for physiotherapy. - Plica syndrome
Enlarged synovial folds and thickened synovial membranes may be painful after repeated entrapments and may even cause changes to the free movement of the knee-cap, resulting in inappropriate or excessive stress loading with subsequent damage to the cartilage of the patella. . If conservative treatment involving physiotherapy, medication and temporary rest is not sufficient, the troublesome folds are removed in an arthroscopic procedure. In some cases, this is combined with partial removal of the synovial membrane (synovectomy) to reduce the number of pain receptors there.
It is our view that the tilting of the patella caused by excessively enlarged plica membranes in the long term favours the development of an arthrosis of the patella cartilage. - Muscular dysbalances
Uneven muscle strain caused by weakening of the inside thigh extensor (M. vastus medialis) results in the predominance of the thigh extensor pulling towards the outside of the leg and thus in increased pressure of the patella on the outside trochlea. As a consequence, the knee-cap no longer runs exactly within its cartilage bearings (tracking), resulting in fraying and abrasion of the articular cartilage, particularly at the centre and outer side of the patella.
Typical symptoms include piercing pain behind the patella when climbing stairs or descending a mountain as well as after long periods of sitting down.
Treatment options for anterior knee pain
If conservative treatment with a particular focus on strengthening weak muscle groups and extending shortened muscles does not remedy the situation, an arthroscopically performed lateral release may be an option. This procedure involves cutting the exterior capsule and ligaments holding the patella and may in some cases be combined with a tightening of the patella ligaments on the inside of the joint (medial tightening), also a microsurgical procedure.
If cartilage damage has already occurred, various measures can be taken in the same operation to improve the situation, as described under "Cartilage damage" elsewhere. A bone-cartilage transplant at the knee-cap generally involves a minor opening of the joint. All other procedures can be carried out microsurgically at the closed joint.
Knee-cap dislocation
Instability of the knee-cap may be caused by an accident (luxation towards the outside) or may have congenital causes such as shallowness of the tracks or weakness of ligaments or muscles.
In these cases, conservative treatment alone is often insufficient; corrective surgery should not be unduly delayed in order to prevent progressive cartilage damage. Lateral release and medial tightening are often not enough. The attachment of the patellar ligament at the tibia is detached from the bone and reattached (using screws) about 1-2 cm further inside. During aftercare, the straightened leg can be exposed to full weight-bearing after 2-3 weeks, but knee bends and stair climbing are only possible after about 5-6 weeks. A programme of intensive muscle stamina training should ensure the strengthening of the interior thigh flexor (M. vastus medialis), which tends to weaken particularly fast.
In some instances it makes sense to perform this surgery in children in order to avoid long-term damage.
Cartilage-bone damage after impact injuries
Gradual softening of cartilage, which can worsen over many months and ultimately result in the destruction of the cartilage (chrondolysis), as described earlier. Alleviation can be provided by arthrosis treatment.
Spontaneous dissolution of cartilage-bone areas (osteochondrosis dissecans)
Through mechanisms still largely unknown, areas of bone at the round articular areas of the femur (condyles) can be insufficiently supplied with blood and begin to die off. At advanced stages, the covering cartilage is also destroyed.
Initial treatment is conservative observation, i.e. rest, no sporting activities and so on; if X-ray or MRI examinations show the process to be progressive, small holes should be surgically drilled into the seat of the problem in order to stimulate improved vascularization and healing. In some cases, the necrotized tissue has to be removed before it becomes detached and turns into a loose body in the joint, thus causing further damage to cartilage at sections of the joint that are still unaffected. In recent years, we have increasingly been able to perform bone-cartilage transplants in the treatment of such disorders.
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| Osteochondrosis dissecans of the patella in an MRI image |
Complete restoration of the posterior surface of the patella after bone-cartilage transplantation |
Fractures of the patella
Simple longitudinal fractures generally heal well with a plaster splint and careful movement. Horizontal fractures have to be surgically fixed (with screws or wire). Fragmented fractures after falls are particularly unpleasant. Despite extensive surgical measures, development of an arthrosis is generally impossible to avoid in these cases.
Summary
It is our task initially to use careful examinations and diagnosis to attempt conservative treatment of the not always straightforward problems of the knee-cap; if surgery is indicated, we try to employ all measures at the right level. Arthrosis problems require close cooperation with the patient and patient endurance over often extended periods of time, frequently involving a number of smaller surgical procedures, to achieve careful restoration of the damaged cartilage. If this is not achievable in the long run, there are early encouraging reports about prosthetic replacement of just the knee-cap, but medium and long-term results are not yet available.