In a kneecap dislocation (patellar luxation) the kneecap moves or slides out of its normal position, namely the patellar groove. This is mostly the result of an acute blow or twisting action of the knee. The dislocation frequently leads to injuries of the ligaments, cartilage, and bone. Most often, the dislocated kneecap jumps back into femoral groove by itself when the knee is extended. After a kneecap luxation, the knee is usually swollen and painful. To accurately assess any possible damage to the joint and to initiate an optimal treatment, a medical examination is highly recommended.
What happens in a kneecap dislocation / patellar luxation?
In a patella kneecap dislocation / luxation, the kneecap jumps forcefully out of its natural position, the patellofemoral groove. In most cases, the kneecap snaps back into its groove when the knee joint is stretched.
The joint capsule burst/tears together with the ligaments and supporting muscles and tendons of the knee cap. The immediate result is a painful swelling of the knee due to a bruise that usually occurs relatively quickly after the event. If the torn ligaments do not heal together, the kneecap remains unstable. As a result, the patella may repeatedly dislocate (slide in and out of its groove) during everyday movements, i.e. without any specific incident, e.g. an accident.
Each time the knee cap is dislocated, further damage to the knee cap itself and the femur occurs. In particular, there is a high risk of cartilage damage that will ultimately lead to osteoarthritis.
If there is a predisposition for instability of the kneecap, it can dislocate even without an accident. This referred by the physicians as "habitual patellar dislocation". Here, there is a particularly high risk that the patella is permanently unstable and will continuously jump in and out of its gliding groove.
Causes for a kneecap dislocation can be an accident. However, the affected individuals are often predisposed to patellar luxation (dislocation of the patella), meaning that they suffer from an unfavorable combination of conditions that promote a dislocation/luxation.
Risk factors for a kneecap luxation / dislocation include:
- Genu valgum, commonly called "knock-knee"
- Abnormal-appearing cartilage (chondromalacia patellea)
- Abnormal formed patella groove at the thigh bone (trochlea dysplasia))
- Loose ligaments (increased band elasticity; hypermobility of the patella)
- High rising kneecap (high-kneecap / patella alta)
- Imbalance of the outer and inner front thigh muscles (muscular imbalance)
The more risk factors there are, the higher the risk of a patella/kneecap luxation/dislocation.
Diagnosis of patellar dislocation / kneecap luxation
In addition to the clinical examination by an orthopedic knee surgeon, who will performs special tests, it is recommended to have an x-ray, and if possible a MRT (magnetic resonance tomography) of the knee joint taken.
Based on an MRT and in addition to a bone assessment, the extent of the damage to the band and holding apparatus as well as the articular cartilage can be assessed accurately. A detailed assessment of a possible joint damage is of major importance for an optimal treatment.
Treatment options for a kneecap luxation / dislocation
Goal of the treatment is to center the patella permanently into the sliding groove since with every recurring luxation the articular cartilage is damaged further. The more often there is a kneecap luxation, the higher the probability of early osteoarthritis patella. There are two types of treatment options, the conservative therapy (without surgery), and operative treatment.
Conservative treatment of a kneecap luxation / kneecap dislocation
A conservative treatment of kneecap luxation / kneecap dislocation is recommended if the (MRT) examination shows no significant damage to the cartilage and ligaments. Here, the knee joint will be immobilized with an appropriate bandage or brace for about 6 weeks.
For a rapid regression of the swelling, cool packs, ointments, and any anti-inflammatory (Diclofenac, Ibuprofen) as well as lymphatic drainage are recommended. To prevent joint stiffness and/or excessive degeneration of the muscles, physiotherapy is also very beneficial. Once the healing process is concluded, a muscle building training and coordination training is strongly recommended.
Surgical treatment of a kneecap luxation / kneecap dislocation
If the MRT examination shows extensive cartilage damage, such as a flaking of the cartilage or a distinct injury to the band supporting structures, a surgical treatment should be considered to repair the damage. Surgery is also recommended when the kneecap habitually dislocates (recurrent patellar dislocation, habitual patella)
What type of surgery is best, depends in each individual case also on
- degree of instability of the knee cap
- frequency of kneecap luxation
- anatomical requirements (malformation of knee cap or slide groove, knock-knee, over the patellar tendon)
- extent of injury (cartilage, ligament, ligaments, MPFL)
- patient's age
The objective of the surgery is to restore the normal anatomy of the kneecap, meaning that the cartilage damage must be treated and the position of the kneecap must be corrected. With an arthroscopy, incurred cartilage damaged can be optimally treated. The repair or correction of the torn ligament system (MPFL reconstruction) gains significance in today’s surgical procedures involving the kneecap. Corrective measures of the bone are only recommended in case of extreme deviation from the normal bone anatomy. Moreover, bone correcting surgeries in young patients should only be performed after the body has reached maturity.
Medial patellofemoral ligament reconstruction (MPFL)
In this surgical procedure, the injured kneecap ligament system is reconstructed by replacing the torn triangular band (medial patello femoral ligament = MPFL) that runs between the inside of the kneecap and the femur, with a tendon. For this, a tendon (gacilis tendon ) is obtained through a small incision on the inside of the shank bone, and then anchored to the inner edge and the patella femoral.
Tibial tubercle transfer (surgery after Elmslie-Trilat) / Bony realignment
A possible bone corrective measure for a severe patella misalignment is the re-alignment of the attachment of the patella tendon on the tibia. This procedure involves transferring the tendon more to the inside (medial) where it is attached at the shin bone (tibial tubercle). As a result of the transfer, the knee cap runs more in the center of the femoral groove. The chance of a recurring kneecap dislocation is thus significantly lower.
Trochleaplasty for the surgical treatment of kneecap luxation / kneecap dislocation
At a distinct abnormality of the kneecap’s gliding groove at the femur (trochlea dysplasia) the depth of the groove can be improved. However, this is a procedure that is only required in exceptional severe cases of patella misalignment.
Post-operative treatment of a kneecap luxation / kneecap dislocation
Post-operative treatment must be adapted to the surgical procedure performed. In addition to an initial relief therapy (to walk on underarm crutches for about 3 weeks), and the protection through a special brace (for 6 weeks), it is important that the thigh muscles are optimally retrained in through physiotherapy.
> Here, special attention must be paid to the training of the inner front thigh muscle (musculus vastus medialis). This also allows the kneecap to run normal in its grooves. <
Prognosis following a kneecap luxation / kneecap dislocation
Each kneecap luxation is a serious injury of the knee joint and is often associated with permanent damage. Even with an ideal treatment of kneecap luxation / kneecap dislocation , a reoccurring dislocation of the kneecap (re-luxation) it cannot be ruled out entirely.
In addition, there is an increased risk that long-term damage is caused to the kneecap’s and thigh’s gliding surface (patella femoral arthritis) . Only through an optimal, individualized treatment by a knee specialist, principal risks can are minimized in order to ensure a long lasting pain free function of the knee joint.
Specialists: Kneecap Luxation / Kneecap Dislocation
For an optimal treatment of a kneecap luxation, the knee experts at the Klinik am Ring are particularly well-qualified. Stefan Preis, M.D. and Jörg Schroeder, M.D., senior physicians at the Practice and Department of Orthopedics and Sports Traumatology at the Klinik am Ring in Cologne, specialize together with their team in the treatment of knee and shoulder disorders. In 2004, they founded the WEST GERMAN SHOULDER KNEE & CENTER, Cologne. The team consisting of eight specialists, treats more than 10,000 patients per year. The team performs more than 2500 surgeries per year of which about 1200 are surgeries of knee joints.