yogabook / pathologie / patellar luxation (atraumatic)

patellar luxation (atraumatic)

Definition of

Patellar dislocation is the displacement of the patella from its femoropatellar bearing. This can occur traumatically, which is described in the article Traumatic patellar dislocation, but also atraumatically, which is described in this article. There are several possible causes. The back of the patella is equipped with a fin for guidance in the trochlea femoris between the two condyles of the femur. On the one hand, this fin may be too small, on the other hand, the trochlea may be too flat. Another favorable factor is a high patella(patella alta), i.e. a patella that is too far cranially as a result of a patellar ligament that is too long, as the trochlea becomes flatter there. There are other possible cofactors. The quadriceps attaches to the entire cranial patellar pole and transmits its contraction force to the tibia via the patella, from lateral to medial: Vastus medialis and rectus femoris, then vastus intermedius and finally medial vastus medialis. In quite a few cases, the traction of the lateral quadriceps parts is too high, which pulls the patella laterally. Another favorable factor is a lower leg exorotated in the knee joint, as the attachment of the patellar ligament is displaced laterally.

Another factor favoring patellar dislocation is a disruption of the medial area of the patellarretinaculum ligament (MPFL). The MPFL consists mainly of fibers of the vastus medialis that run medially past the kneecap in the direction of the tibial tuberosity. The more longitudinally oriented part, the medialretinaculum patellae, is always present, while a transverse medial part, the transverse medialretinaculum patellae, is only present in 30% of cases. As the patellar dislocation tends to damage or tear off the MPFL, this significantly increases the risk of recurrence. A tear usually occurs directly at the medial edge of the patella, only rarely at the medial epicondyle. X-legs also favor patellar luxation, as the patellar tuberosity is displaced laterally. Secondarily, weakness of the exorotatory muscles of the hip joint can also create kinetic situations in which the patella dislocates laterally.

The first occurrence of a patellar dislocation is quite painful and often leads to a blockage of the knee joint. The triggering situation is usually associated with a low tone of the quadriceps and a low flexion angle of the knee joint, as the non-innervated inherent tension of the muscle is lower than with wide flexion. Manual reduction is often necessary. The incidence in Germany is 5.8 / 100,000 / a, making patellar dislocation a common knee injury. Patellar dislocations tend to recur with increasing frequency, so each dislocation that occurs is a favorable factor for the next one. The risk of a first dislocation is 15 – 45%. A longer sequence of dislocations is referred to as chronic patellofemoral instability. In young people, the risk of recurrence is up to 60%, just as patellar dislocations occur much more frequently in younger people. As it is known that every dislocation damages the cartilage, appropriate intervention should be carried out, even non-conservatively if necessary, despite the fact that pain symptoms often decrease slightly with each dislocation. Dislocations are associated with a distinct noise, especially at the beginning, and the sight of the dislocated patella and the feeling of joint blockage often cause anxiety.

Anyone affected by a tendency to dislocate the patella should avoid certain situations, including sports with wide exorotation of the lower leg in the knee joint, such as breaststroke. Likewise, sitting with the feet turned outwards must be avoided, as the 90° rotation of the feet in relation to the pelvis required for this can hardly ever come from the hip joint, but requires a significant exorotation of the lower leg in the knee joint.

Strengthening training with emphasis on the vastus medialis and reduction of hypertonus of the rectus femoris is obligatory if there is a tendency to patellar dislocation. Adequate conservative treatment leads to freedom from recurrence in 50% of cases.

Cause

1. Endorotation of the thigh with foot as punctum fixum
2. especially swinging or careless exorotation of the lower leg as a punctum mobile in the knee joint
3. rarely congenital
4. rarely neurogenic (especially abnormal traction of the vastus lateralis)

Predisposing

1. Patella alta
2. Trochlea femoris too shallow
3. insufficiently pronounced retropatellar fin
4. Coxa antetorta (antetorsion of the femur)
5. X-legs
6. pronounced hyperextension ability (hyperextension ability) of the knee joint
7. Unplanned or awkward movements in team sports, especially but not only in the hall, dancing, gymnastics (also considered an acute dispositional non-traumaticform )
8. Low tone of the quadriceps femoris, especially the vastus medialis
9. Muscular imbalances with hypertonus of the rectus femoris with insufficient tone of the vastus medialis
10. Generally weak connective tissue and loose ligaments, especially in hypermobility syndrome and underlying diseases that promote this, such as Ehlers-Danlos and Marfan syndrome; also in osteogenesis imperfecta
11. female gender, younger age with a slim build and rather atonic musculature
12. anomalously wide lateral attachment of the quadriceps to the tibia

Diagnosis

• X-ray for the diagnosis of bone splinters, if necessary MRI for the assessment of cartilage and ligaments
• Clinical examination to clarify the favoring factors

Symptoms

• Hemarthrosis on rupture of the MPFL
• Blockage of the joint
• Significant capsular tension pain
• Visible and palpable, apositional dislocation position

Complications

• Tear of the medial joint capsule
• (Further) damage to the MPFL
• Recurrence and increased risk of recurrence with each dislocation
• Cartilage damage
• Increased tendency to osteoarthritis after frequent recurrences

Therapy

• Every initial dislocation requires clarification
• In the case of a dislocated patella, absolute cessation of movement for the affected knee joint and rapid professional manual reduction with extension of the knee joint
• PT
• After dislocation: orthosis, reduce strain, take a break from sport, elevate leg, cool
• with intact cartilage and intact capsule: Sports break for up to 3 – 4 months, then slowly build up the load with axis-appropriate movements
• Exercise therapy: strengthening the vastus medialis, stretching the rectus femoris and vastus lateralis
• Surgically, a transverse medialretinaculum patellae can be created from the attachment tendon of the gracilis, more rarely the semitendinosus, in the form of an elongated triangle from the Schoettle point below the tuberculum addductorium to two widely separated points on the medial patella. The operation must be open so that the patella is not under tension.
• If necessary, lateral release, i.e. limited separation of the lateral retinaculum patellae, whereby this intervention has two disadvantages: the stability of the patella decreases further and the arterial supply deteriorates significantly, as it occurs predominantly via the lateral retinaculum.
• Tuberosity osteotomy for patella alta (high patella), i.e. if the patellar ligament is too long ( then offset inferiorly) and if the attachment of the patellar ligament is too far lateral (surgery according to Roux or Elmslie to move it medially).
• If the trochlea is too shallow, a trochleoplasty can be performed by detaching a bone flap with the cartilage and deepening the more profound area medially. This is a less elementary procedure, the success of which is not certain.
• Post-OP early mobilization to avoid adhesions