Synonyms
Patella luxation, patella dislocation, dislocation of the patella, patella dysplasia, cartilage damage behind the patella, cartilage flake, articular mouse, rupture medial retinaculum
Definition
In the typical patella dislocation, the patella jumps out of the intended slideway. This leads too often to injuries of ligaments, cartilage and bone.
Epidemiology
Women are more frequently affected by patellar luxation than menThe first luxation event usually occurs before the age of 20.
Causes of patellar dislocation
In most cases, this is an unfavorable combination of luxation-promoting components. From an anatomical point of view, a knock-knees, an incorrectly positioned patella (patellar dysplasia, so-called hunter’s hat patella) and a too far outwardly positioned attachment of the patellar tendon (patellar tendon) are risk factors. From the ligamentous apparatus side, a loose ligamentous apparatus (ligament laxity = hypermobility of the patella) and a protruding patella (patella alta) are considered unfavorable. From a muscular point of view, an imbalance of the outer and inner front thigh muscles promotes luxation. The more risk fractures come together, the higher the probability of patellar dislocation.
Classification of the patellar luxation
Patellar stability is divided into three degrees of patellar instability: 1. patellar lateralisation (where the patella slides too far out (laterally) in the patellar sliding bearing2. Subluxation of the patella (in this case the patella almost dislocates)3. Luxation of the patella (complete dislocation of the patella) The first patella luxation with an accident event is medically called traumatic patella luxation.
Renewed dislocation events are referred to as chronic recurrent (posttraumatic) patella dislocation. A patellar dislocation that occurs without a real accident event is called a habitual patella luxation. In this case the patella jumps out and back in without major discomfort.
This instability is particularly evident in the first 45° of flexion.
- Patella with lateralization
- Knee-cap sliding bearing (femoro-patellar joint)
- Thigh (femoral condyle)
A patella luxation can be diagnosed by observation alone. In almost all cases, the patella jumps outwards beyond the intended glide path.
There it is visible, the patella slide bearing is empty. In most cases a so-called self-reposition occurs. This means that the kneecap springs back into its slideway with slight movements.
In these cases, a detailed medical history is necessary. If the kneecap luxates, the inner ligamentous and retaining apparatus of the kneecap (medial retinaculum) ruptures. As the patella moves out of the sliding path, further damage to the patella and the femur often occurs. The traumatic dislocation of the patella results in a knee joint effusion (articular effusion) and distinct pressure pain under the inner patella facet (tearing (rupture) of the medial retinaculum). Traumatic patella dislocation is indicated by the sudden subsidence of the knee joint during the dislocation process (Giving way).
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