First of all, a precise medical history is taken regarding the number of dislocation events and the time course. In addition, the type and nature of the dislocation and the position of the knee joint at the time of injury are also examined in detail. Other aspects such as professional activity and sporting demands are also investigated.
This is followed by a detailed physical examination with clinical testing of patellar instability (in different knee joint positions) and pain provocation tests, among other things. An MRI examination is necessary if a patellar dislocation has occurred and is always carried out before treatment is planned. X-rays and, if necessary, rotational imaging (rotational MRI/CT) are also carried out before any planned surgical treatment.
Alongside bony factors, the medial patellofemoral ligament (MPFL) is one of the most important factors for patellofemoral stability. Studies confirm the enormous importance of the MPFL as a decisive stabilizing factor of the patella, especially in the position close to extension (10°-30° flexion). The MPFL runs from the inner edge of the patella to the inside of the femoral condyle. Dislocation (luxation) of the patella (usually to the outside) results in injury to the MPFL in almost all cases, which is why reconstruction of this structure plays an important role in the successful treatment of patellofemoral instability.
The first step is usually a diagnostic arthroscopy of the knee joint to assess patellar instability and the condition of the cartilage. An autologous tendon (gracilis tendon, alternatively quadriceps strip) is then removed. The tendon is attached in the anatomically correct position to the inside of the kneecap and to the inside of the femur and positioned in the anatomically correct layer on the inside.
Postoperatively, we recommend partial weight-bearing of the operated leg for 4 weeks (in the case of isolated MPFL plastic surgery). The range of motion is increased every 2 weeks after the operation (max. 30° flexion for 2 weeks, then 60°, then 90° up to 6 weeks postoperatively). From week 7, an orthosis is no longer necessary and strength training with full weight-bearing and resistance can be performed.
The tibial tuberosity is a bony process in the area of the upper front edge of the tibia. This is where the patellar tendon attaches. A tuberosity that is located too far outwards or upwards can be a decisive factor in the development of patellofemoral instability, which is why a correction (offset osteotomy) is a sensible therapeutic option in these cases.
The operation is performed in several stages. First, a diagnostic arthroscopy of the knee joint is usually performed to assess patellar instability and the condition of the cartilage. An incision is then made to the side of the tibial tuberosity, the tibial tuberosity is separated from the tibial plateau and the bone flap is moved medially (inwards) or distally (towards the foot) according to the underlying pathology and surgical planning. The bone flap (with insertion of the patellar tendon) is then reattached to the tibia using screws. The procedure can be combined with other procedures to stabilize the patella (e.g. MPFL plastic surgery).
Postoperatively, the operated leg is partially loaded for 6 weeks. The range of motion is increased every 2 weeks after the operation (max. 30° flexion for 2 weeks, then 60°, then 90° until 6 weeks postoperatively). From week 7, an orthosis is no longer necessary and strength training with full weight-bearing and resistance can be performed.
If chronic instability of the patella leads to a shortening of the outer supporting apparatus (lateral retinaculum), it may be necessary to lengthen the retinaculum as part of a stabilization operation. However, this is never performed as the sole surgical procedure, but always in combination with other stabilizing interventions (e.g. MPFL plasty, trochleoplasty, tuberosity offset osteotomy, repositioning osteotomy).
During the operation, a skin incision is made on the outside and the superficial layer of the two-layer lateral retinaculum is then incised. The deep layer of the retinaculum is then dissected and cut approx. 10 to 20 mm further back. In the desired position, the superficial part is then sutured to the deep part without tension. This creates an extension of the retinaculum that is tailored to the individual needs of the patient.
The postoperative follow-up treatment depends on the necessary accompanying interventions and is determined individually for each patient.
If instability of the kneecap is due to an anatomically incorrectly formed trochlear groove (trochlear dysplasia), trochleoplasty is an established surgical procedure. Trochleoplasty improves the bony guidance between the kneecap and the trochlea, which is achieved by deepening the modeling of the trochlear groove. Depending on the findings, the procedure can be combined with other procedures to stabilize the kneecap (e.g. MPFL plastic surgery).
During the operation, the knee joint is opened by means of an arthrotomy, exposing the articular surface of the thigh (trochlea) to the kneecap (patella). The cartilage of the trochlea is then detached from the rest of the femur with a fine layer of bone (bone-cartilage lamella). Bone is then removed from the central part of the trochlea to create a new gliding groove. The bone-cartilage lamella is then reattached over the sculpted bone using suture anchor systems.
Postoperatively, the operated leg is partially weight-beared for 6 weeks. The range of motion is increased every 2 weeks after the operation (max. 30° flexion for 2 weeks, then 60°, then 90° until 6 weeks postoperatively). From week 7, an orthosis is no longer necessary and strength training with full weight-bearing and resistance can be performed.
Probably the most frequently undiagnosed cause of patellofemoral instability is torsional deformity, i.e. a bony rotational defect of the thigh or lower leg. In this case, the increased internal rotation of the femur (femoral internal torsion) or increased external rotation of the tibia (tibial external torsion) leads to a relative outward displacement of the patella and subsequently to instability and pain. In the event of clinical abnormalities, the standard diagnostics performed (X-ray, MRI) are supplemented by a torsion angle CT or MRI. Torsion osteotomy is then used to treat the underlying pathology, which usually affects the femur.
For the femoral torsion osteotomy, the skin is incised on the inside during the operation and the bone is then dissected next to the muscle. The planned location of the saw cut is then located, whereupon a Schanz screw is inserted proximally (above) and distally (below) of the defined osteotomy plane at the desired correction angle. The osteotomy is then performed while protecting the dorsal (posterior) vessels and nerves with hooks. The femur is then rotated so that the two previously inserted Schanz screws are aligned in parallel. Fixation is then carried out using stable-angle plate osteosynthesis and the wound is closed in layers.
Postoperatively, the operated leg is partially weight-bearing without orthoses for 2-4 weeks. In the case of isolated torsion osteotomy, the knee can be moved fully from the start. After the crutches have been removed, muscle building begins from week 3.