Kneecap pain

The components of the kneecap

The kneecap (patella) is a flat, disc-shaped bone. Viewed from the front, the kneecap is triangular and approx. 2 cm thick. It lies in front of the knee joint and protects it. The lower surface of the kneecap is covered with cartilage and slides in the groove (trochlea) of the femoral cartilage, thus forming the second joint in the knee joint. The kneecap is connected to the knee capsule with tendons and ligaments and is thus guided in the groove on the thigh bone (femur). The tendon of the four-headed thigh muscle (quadriceps tendon) attaches to the upper pole of the kneecap and leads via the lower pole of the kneecap to the patellar ligament (patella ligament), which is connected to the lower leg.

What functions does the kneecap fulfil?

The kneecap serves as a pulley so that the powerful thigh muscles can transfer their force optimally to the lower leg. In this sense, the kneecap reinforces the leverage effect of the thigh muscle. The kneecap and the thigh bone are covered with cartilage and thus form a separate joint in the knee joint. This reduces the frictional forces during movement of the knee joint. As the kneecap is a small bone, enormous forces (contact pressure) act on the cartilage of the kneecap during knee movement.

Due to the position and the high forces acting on the kneecaps, as well as their special guidance by the ligaments and sliding groove on the thigh, pain and restricted movement can quickly occur. Pain, insecurity or restricted movement around the kneecap can be caused by an accident, sport, overloading, a congenital malposition or abnormal development.

Outward displacement (lateralisation of the patella)

In the case of patellar lateralisation, the kneecap does not run in the intended sliding groove on the thigh, but outside of it. Patients report pain in the area of the kneecap, insecurity and rubbing noises. The fact that the kneecap runs off track causes significantly higher pressure on the cartilage of the kneecap, but also on the thigh cartilage. This results in rapid cartilage wear(osteoarthritis). Patellar lateralisation can lead to permanent instability and wear of the joint cartilage under the kneecap (patellar arthrosis, chondropathia patellae) or in the femoral gliding bearing, causing severe pain and audible rubbing noises (crepitations). Lateralisation of the kneecap can be caused by

• a muscle imbalance (imbalance), as the outer thigh muscle is stronger than the inner thigh muscle;
• Adhesions;
• Malalignment (knock-knee, twisted thigh);
• Malformation (sliding groove not properly formed or too tight an attachment to the outside of the patellar tendon);
• Tearing or overstretching of the inner patellofemoral ligament (MPFL: medial patellofemoral ligament).

A thorough examination of the knee joint and appropriate imaging examinations are required to find out the cause of a painful patella moving outwards (lateralisation).

Treatment

If the main cause is a muscular imbalance in the thigh muscles, this can be treated very effectively with the help of physiotherapy. The inner thigh muscle in particular is specifically built up in order to combat the tendency of the kneecap to move sideways and thus prevent permanent damage and signs of wear to the cartilage.

Surgery is performed if conservative treatment has been unsuccessful or if further cartilage damage to the kneecap or femur is to be prevented. The aim of this operation is to restore the natural movement of the kneecap and thus reduce the pressure on the cartilage. This can significantly reduce pain and long-term cartilage damage. The following surgical options are available to normalise the movement of the kneecap. Depending on the cause of the malalignment of the kneecap, the operations can also be combined.

• Initially, the problem is treated arthroscopically (by means of lateral retinaculum splitting, lateral lengthening plasty), then openly by medialising the tuberosity (bony displacement of the patellar tendon attachment inwards)
• If the stable medial patellofemoral ligament, which is important for patellar guidance, is torn or overstretched, or if the above-mentioned operations have not led to any significant improvement in patellar guidance, then this ligament should be reconstructed as part of an MPFL reconstruction (MPFL: medial patellofemoral ligament). To do this, the patient's own tendon is removed from the inner thigh. The patient's own replacement ligament is fixed to the inside of the kneecap and the inside of the thigh with appropriate screws to optimise the position of the kneecap again
• If the sliding groove for the kneecap on the thigh is not formed or only partially formed, it can be recreated if the cartilage is good enough. The cartilage is detached from the thigh with a little bone. The new sliding groove for the kneecap is reshaped and formed on the underlying femur using a saw/drill. Once the new groove has reached a sufficient depth, the mobilised cartilage-bone flap is reattached using screws and sutures
• If the femur has a good gliding groove, but the entire femur is turned too far outwards, the lower femur can be cut with a saw (targeted bone fracture: osteotomy) and turned into the appropriate position so that the kneecap runs in the groove again. Once this is achieved, this position is secured with an appropriately long plate so that the femoral fracture can heal in this position. This procedure is called a rotational osteotomy of the femur
• If a pronounced knock-knee position leads to incorrect movement of the kneecap and also to overloading of the outer articular cartilage of the knee joint, this can be corrected by selectively cutting through the femur above the joint pulley and removing a corresponding bone wedge on the inside of the femur (medial closing osteotomy). By removing the bone wedge on the inside, the leg is straight again and the kneecap runs in the natural sliding groove of the thigh again. An appropriate plate and screws are needed to fix this position
• If the cartilage wear is so advanced that bone rubs against bone (final stage of osteoarthritis), an artificial partial prosthesis can help. This involves replacing the damaged cartilage on the back of the kneecap with a plastic disc. On the other hand, the cartilage loss on the femoral gliding bearing is replaced by a partial prosthesis (metal). This patella back surface and gliding bearing replacement is cemented to the bone. This allows the knee to be loaded and moved immediately

Depending on which procedures are carried out to optimise the movement of the kneecap, the amount of surgery and subsequent therapy and the corresponding loss of sport and work will vary.

Jumping out of the kneecap (patellar luxation)

In a patellar dislocation, the kneecap (patella) usually jumps outwards (laterally) from its thigh groove (trochlea). A distinction is made between traumatic and chronic patellar luxation. A traumatic patellar dislocation is a dislocation of the kneecap caused by an accident (e.g. a fall). In the case of repeated (chronic) dislocation of the kneecap, the kneecap jumps out of its guiding groove without much force being exerted. This is caused by a malformation of the patella groove or a weakness of the ligaments and muscles.

If the kneecap jumps out of its guide rail, this can lead to cartilage shearing and corresponding cartilage damage. In addition, the joint capsule can tear when the kneecap pops out and the sturdy inner patellar ligament can stretch or tear. Patients complain of severe pain, swelling, bruising in the joint and unsteadiness when walking after patellar dislocation. Repositioning of the kneecap usually occurs spontaneously.

Treatment

Conservative treatment is possible for a traumatic initial dislocation of the kneecap if other concomitant injuries have been ruled out. The first step, if it has not already happened spontaneously as in most cases, is to reposition (reduce) the kneecap to its original position. If the joint effusion is severe, the knee joint may have to be relieved by means of a puncture. The knee joint must then be immobilised for a few days. This is followed by wearing a special splint for six weeks, which holds the kneecap in the femoral gliding groove. Accompanying physiotherapy is used to reduce swelling, strengthen the inner anterior thigh muscle in particular and stretch the posterior thigh muscles. There is a high recurrence rate (renewed protrusion of the kneecap) of approx. 50 per cent if adequate treatment is not provided.

If the conservative attempt was unsuccessful, the instability persists or the kneecap pops out again, surgical methods are used to prevent permanent cartilage damage and tearing of the inner joint capsule or the stable inner patellar ligament.

The stability of the patella can be restored using various surgical methods. After evaluation of the clinical and, above all, imaging results, these surgical therapies can be combined with each other and must be individually tailored to the patient. A basic distinction is made between soft tissue repair and corrective measures on the bone with the aim of keeping the kneecap in its sliding groove on the femur in the long term.

Jumper's knee / patellar tendinopathy

This is also known as "jumper's knee". It refers to an overload of the patellar tendon at the origin of the tendon at the lower pole of the kneecap (patellar tip). Overloading this patellar tendon leads to small tears, haemorrhaging, inflammation, hardening and ultimately calcification at the tendon insertion of the kneecap. This can lead to chronic inflammation of the tendon. Those affected complain of needle-like pain in the area of the tip of the kneecap.

Patella tip syndrome is favoured by unusual, violent and repetitive overloading and tensile stress on the patellar tendon, as is the case with sports involving jumping and movement such as basketball, volleyball, tennis, football and running. A high position of the kneecap (patella alta) and shortening of the thigh muscles can favour patellar tendinopathy.

Treatment

Conservative therapy is always the mainstay of treatment for patellar tendinopathy. The first step is to reduce the intensity of sporting activity on the patellar tendon or even to take a break. Physiotherapy and additional treatments with ultrasound, electrotherapy (TENS), laser or shock wave therapy are also essential. These aim to reduce the inflammation of the patellar tendon.

Other complementary options alongside anti-inflammatory medication are hyaluronic acid injections. Special knee supports can also help. If conservative therapies are unsuccessful, patellar tendinopathy can be treated as follows:

• Arthroscopy (arthroscopy): With the help of arthroscopy, the painful scarring in the area of the tendon insertion at the tip of the kneecap is removed and sclerosed. At the same time, the movement of the kneecap is checked and optimised
• Distalisation of the tuberosity (bony downward displacement of the patellar tendon insertion): If the kneecap is too high (patella alta) in relation to the thigh and there is correspondingly increased tension from the patellar tendon on the tip of the kneecap, the bony attachment point of the kneecap can be moved downwards (distally) and the height of the kneecap corrected in this way

Plica syndrome (thickened fold of joint mucosa)

Plica syndrome is an enlargement and thickening of the synovial membrane (synovium), which forms a fold (plica). This fold can get in the way during knee flexion. Overloading this fold leads to swelling and corresponding inflammation of the fold, resulting in painful pinching and cracking of the fold in the knee joint. These thickened folds are found around the kneecap (above, below and to the side). The consequences are a swollen knee and pain behind the kneecap: the fold also leads to overloading of the cartilage when jumping, which can cause permanent cartilage damage (osteoarthritis). Patients report the feeling that the knee is not stable, gives way or locks.

The painful folds can be congenital, result from previous injuries or operations, but can also be caused by overuse. Instability of the knee can also be a trigger for plica syndrome.

Treatment

Conservative treatment consists primarily of rest, avoiding overloading, physiotherapy and pain-relieving medication. In the following cases, the plica should be removed arthroscopically (arthroscopy): if conservative therapies do not work and the plica still interferes with everyday life or sport; to prevent possible long-term consequences; if the painful fold in the joint lining has already caused cartilage damage.

Chondromalacia patellae (soft cartilage on the back surface of the kneecap)

Chondromalacia patellae is a softening and degeneration of the cartilage on the underside of the kneecap. This corresponds to the onset of osteoarthritis. If the load-bearing capacity of the cartilage is exceeded, superficial tears occur in the cartilage, which, in addition to pain, can also cause a noise (crepitation) behind the kneecap under load. The cartilage abrasion behind the kneecap also causes an effusion in the knee joint. Young people and athletes are particularly affected. The pain often occurs on the front of the knee or kneecap. The pain worsens after prolonged sitting or when going up and down stairs, and the joint effusion can increase.

The causes of chondromalacia patellae always involve an imbalance between the load-bearing capacity of the patellar cartilage and the actual load on the patella cartilage. This can be caused by the following: overuse, trauma, particularly high forces acting on the knee cartilage, functional disorders of the thigh muscles, chronic wear and tear and inflammation of the knee joint, knock knees, incorrect guidance of the kneecap, high kneecap and ligament weakness.

Treatment

The treatment of chondromalacia patellae is centred on conservative therapy. On the one hand, this consists of physical therapy and physiotherapy exercises. Painkillers and cartilage-supporting agents are also administered, and hyaluronic acid injections can also help. Above all, those affected should take it easy on their knee and only bend it a little; active knee supports can also help.

If conservative therapies are unsuccessful, chondromalacia patellae can be treated surgically as follows with the aim of reducing the pressure on the kneecap cartilage:

• With the help of arthroscopy, the superficial cartilage tears behind the kneecap are smoothed and sealed and painful scarring in the area of the tendon insertion at the tip of the kneecap is removed and cauterised. At the same time, the movement of the kneecap is checked and optimised
• If the cartilage damage is more advanced, specific surgical techniques such as microfracturing or the AMIC technique can be used
• If the kneecap is too high (patella alta) in relation to the thigh and there is therefore increased tension from the patellar tendon on the kneecap, the bony attachment point of the kneecap can also be moved downwards (distally) and the height of the kneecap corrected (so-called distalisation of the tuberosity). distalisation of the tuberosity/bony downward displacement of the patellar tendon insertion). The bony displacement of the attachment point of the patellar tendon inwards occurs when it is clearly attached to the outside (lateral) of the lower leg bone and the back surface of the patella is therefore exposed to increased pressure. A saw is used to detach the attachment point with the corresponding bone flap (osteotomy) and move it inwards. At the same time, arthroscopy is used to check how far the inward displacement must be so that the kneecap can once again run in the original gliding groove. Once this has been determined, the bone block with the attachment point of the patellar tendon is fixed accordingly and attached to the lower leg bone with two screws (so-called medialisation of the tuberosity/bony displacement of the patellar tendon attachment inwards)
• If a pronounced knock-knee position leads to excessive pressure behind the kneecap, this can be corrected by selectively cutting through the femur above the joint pulley and removing a corresponding bone wedge on the inside of the femur (medial closing osteotomy). By removing the bone wedge on the inside, the leg is straight again and the kneecap runs in the natural sliding groove of the thigh again. An appropriate plate and screws are required to fix the new position of the femur

The follow-up treatment must be customised to the previous operation. Depending on which procedures are carried out, the surgical effort and subsequent therapy and the corresponding loss of sport and work will vary. This must be customised.

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