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Kneecap Instability (Specialist Prof. Siebold)

A large number of knee joint deseases affect the joint between the patella and the femur, the so-called patellofemoral joint.

Cause for Kneecap Complaints

Kneecap Complaints are mostly caused by congential bony kneecap or sliding articulation deformities. Overpressure, pain, swelling and increasing cartilage damage are results of the slanted kneecap position. Under strong deformity the kneecap is able to slip out of its bearing which is called a kneecap dislocation or luxation (Figure 2). A (sports) accident may also lead to kneecap luxations.

Figure 2: Centered (a) and externally luxated (b) kneecap (= lateral patella luxation) under x-ray


Kneecap misalingment and instability can lead to unfavorable pressure distribution on the cartilage. Over time cartilage damage behind the kneecap and the femur can occur, which can ultimately result in development of arthrosis. X-ray and MR examinations help to predict the cause and the size of defect.

Non-Surgical Treatment

Commonly physiotherapeutic messures help the patients to improve complaints up to obtaining freedom of pain. Sports such as spinning, crawl swimming, aquajogging, canoe, nordic walking etc. are particulary recommended.

Hyaluronite injections which work as a kind of lube have proven successfully over the last couple of years. As well as repair enzyme injections (ACP) which have a positive effect on cartilage stabilisation. Food supplements such as glucosamine and chondroitin sulfate show improvements too.

Surgical Treatment

In order to treat major cartilage defects we perform arthroscopically cartilage cell transtplantations. For a detailed description on the different cartilage treatments (Figure 3), please consult the topic Cartilage Damage.

Figure 3a: Spheroids ready for their Implantation
Figure 3b: Patella Cartilage Damage with adherent Spheroids
Figure 3c: Early Stage of Cartilage Regeneration: 4 months post-op


Non-Surgical Treatment
The first kneecap luxation can already lead to a ruptured medial patellofemoral ligament (shortform: MPFL) which is significant for the stable kneecap guidance.
With conservative treament the quadriceps muscle gets strengthened as well as coordination training via physiotherapy must be obsolved.

Surgical Treatment

Indications for surgical treatments in case of kneecap instability are: bony kneecap and bearing deformities (Dysplasia), recurring instability, young and active patients or torn down and free joint bodies.

Medial Patellofemoral Ligament (=MPFL)

The so-called MPFL (Figure 1) is a strong internal capsule enhancement extending from the patella edge to the femoral condyle. It prevents the patella from luxating during full knee extension. Anatomical and biological studies show the outstanding MPFL importance as the key stabiliser of the kneecap (patella). Therefore a MPFL reconstruction has proven oneself. A reconstruction of the torn MPFL is necessary for attaching the kneecap inside the joint, remedy cartilage damage and to prevent major further damage.

Surgical Technique

The MPFL replacement is today considered as the most advanced surgical technique. Thereby the torn MPFL is replaced by a endogneous popliteal tendon (gracilis tendon). The tendon is used as a transplant which is pulled into the former MPFL place and fixed with resorbable implants. The operation can be implemented during a minimally invasive open technique (Figure 6).

Figure 6a: Minimally invasive milling of the bone channel, medial edge
Figure 6b: MPFL Transplant fixation with special strings
Figure 6c: Reconstructed MPFL at the kneecap with parallel tendons


Further to the open reconstruction we perform the MPFL reconstrcution arthroscopically. Therefore we developed our own surgical procedure. First of all the MPFL is arthroscopically portraited at the patella and the femoral condyles. The precise understanding of the anatomical course is prerequisite. With acute and recurring patella luxations the MPFL remains can be found as a wide but thin band. The gracilis tendon is then pulled in as the MPFL replacement. Afterwards the transplant is fixated with a bio bolt at the femoral condyle.

The advantage of the arthroscopical procedure is the low invasivity, the individual anatomical reconstruction due to an exact portraited MPFL and the enhanced cosmetic resultst compared to the open surgery. The rehabilitation can be relieved because of limited post-op pain.

The range of motion will be continuously expanded until you can reach the full range of movement within 3-4 weeks. Full weight bearing will be allowed after 2-3 weeks.