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Autologous Chondrocyte Transplantation (ACT) (Specialist Prof. Siebold)

Conservative treatment

In case of small cartilage lesions or superficial cartilage damage a conservative treatment without surgery is recommanded. Physiotherapy, injections of hyaline acid or stem cells, antiinflammatory therapy might help to reduce symptoms. Very important is also adaptation of activity to a lower level.

Operative cartilage repair (Specialist Prof. Siebold)

In constrast,with traumatic and7or deep cartilage defects in younger patients surgical treatment is reasonable in order to prevent premature arthrosis.
Causes for traumatic cartilage holes are injuries or accidents, e.g. during body-intensive sports as soccer, handball or hockey, but also leasure sports ( skiing or snowboarding).
At the same time there is an intense force on the joint leading to cartilage damage. Serious traumatic cartilage defects unfortunatley frequently occur after ACL ruptures por kneecap luxation. Thereby healthy cartilage breaks out of the articular surface and chondral or osteochondral flakes ( free joint bodies) result.

[F]How do cartilage damages affect?

Articular cartilage damages represent a major problem, as the cartilage regenerative capacity is rather limited. Nowadays it is known that damaged cartilage would not grow back into its “normal” structure. Untreatened cartilage forms inferior scar tissue instead which has neither the functional biomechanical nor the microscopic properties of healthy articular cartilage. This so-called fibrous cartilage is relatively soft and is therefore soon worn out again. As a resulst premature joint wear and tear occurs (Figure 1) which leads to pain, load inability and arthrosis (Figure 2 and 3).

Figure 1: Arthroscopical Picture: degenerative cartilage defect with bare bone
Figure 2: X-Ray: repealed interior joint line with arthrosis (left)
Figure 3: MRI: serious interior cartilage damage and bone bruise (left)


Reattachment of freshly sheared off cartilage-bone-fragments
After serious knee injuries cartilage -bone fragments often are teared off the articular cartilage. Due to x-ray, Ct and MRI this can be determined. If the patient undergoes surgery in time cartilage-bone fragments can be reattached (Figure 6-8). In the event of a successful restoration of the articular surface this treatment is preferred.

Figure 6: Recent cartilage-bone defect
Figure 7: Preparation of the fragment
Figure 8: Reattachment and fixation with two resorbable pins

The arthroscopic microfracturing is a bone marrow stimulating procedure .
Small holes are yielded into the bone with the help of pointed prickers beneith the absentee cartilage layer.

The results is the stem cell exemption which are located inside the bone marrow (Figure 9 and 10). Due to bleeding stem cells adhere in the microfracturing zone (superclot) (Figure 11). Through load-relief on the knee joint the stem cells then differentiate into fibrocartilage and refill the cartilage damage within several months. Under normal loading the patient can get pain free again.

Figure 9: Arthroscopic Microfracturing
Figure 10: Subchondral bone opening with cartilage damage (4°)
Figure 11: Leakage of stem cells

The disadvantage is that the fibrious cartilage which gets produced is of very inferior quality.

Abrasion Plastic
Alternatively, the so-called abrasion plastic is an option. Thereby the underlying bone is brushed up with a small milling machine. Here too, the stem cells are flushed out and recreate a fibriouscartilage in the damaged area.

Osteochondral Transplanatation ("transplantation of an autologous bone cylinder")
Withhin the so-called osteochondral transplantation the cartilage defect is blanked out roundly and replaced with a second autolougous cylinder with healthy cartilage. This treatment is very demanding and therefore requires a precise operation including an exact restoration of the articular cartilage plane


We perform approx. 90-100 ACT in the knee per year. Already in the year 2006 we began to work with the autologous chondrocyte transplantation as one of the first centers in Germany. The procedure which was developed by co.don® AG (Berlin) enables to implanate the cartilage cells minimally invasive (arthroscopically). Therfore a cartilage piece only a few millimeters in size is removed from a less loaded knee joint area (Figure 20).

Figure 20: Cartilage removal for culturing

This cartilage cells are then cultured and collected into 3D- balls (shperoids). These spheroids contain approximatly 200 000 cartilage cells and have a diameter of 0,5-0,7 mm (Figure 22). Another special feature of this treatment is that the cutlture of the cells and the production of the spheroids is implemented with autologous blood serum. As a result side effects and reactions because of alien tissue can be avoided.

Figure 21: Spheroids for implantation

As soon as the spheroids approach to the cartilage defect they stick mechanically stabil to the subchondral bone due to adhesion proteins (Figure 22a,22b). We commonly treat several defects all at once.

Figure 22a,b: Spheroid application in cartilage defect, location: kneecap bearing ( Trochlea)

In spite of the arthroscopic rinsing fluid the spheroids stick to the bone after their implantation (Figure 23).

Figure 23: In spite of the arthroscopic rinsing fluid the spheroids stick

In the meantime Prof. Siebold refined the operation technique insofar as the procedure is now arthroscopically. The cells can be transplantated in every area in the knee, e.g. in the femoral condryle (Figure 24a-c, 25a+b, 26a-c), in the tibial plateau (Figure 27a+b) and in the kneecap area (Figure 22a+b, 28a-d).

Figure 24a: forth degree defect at the medial femoral condyle
Figure 24b: ACT with spheroids
Figure 24c: cartilage regenerate 4,5 months post-op

Figure 25a: defect at the medial femoral condyle
Figure 25b: result 9 months post-op after ACT and corrective osteotomy

Figure 26a: defect at the lateral femoral condyle
Figure 26b: applicated spheroids
Figure 26c: result 12 months post-op after ACT

Figure 26b: MRI 18 months post-op; complete regenerated cartilage surface

Figure 27a: deep cartilage damage after tibial plateau fracture
Figure 27b: ACT at the tibial plateau


Over the last 12 years we were able to treat approx. 700 patients with spheroids successfully. Every patients has a follow-up treatment, in most of the cases the clinical outcome is very promising. With several patients there were post-op examinations after 6 weeks, 4 months, 6 and 18 months. in 91% of the cases a complete defect closure, due to the ACT was found ( see also published study) (Figure 24c, 25b, 26c, 28d). MRI pictures show the good results (Figure 26d).


Due to a movement treatment the new cartilage cells can recreate quality cartilage. It connects with the healthy cartilage with similar biomechanical characteristics. Passive movement using a movement-sleeve (CPM) should be performed 2 hours a day over a 4-6 week period. There will be a partial load relief (10-20kg)for approx. 6-8 weeks post-op. Subdued footwear is neccessary. Cartilage massage in the form of ergometer training (cycling without great resistance) should be done regulary. Heavy sports activities (e.g.: Jogging and Impact-Sport) can be earliest introduced after 12 months.


We are convinced of the raliable results of autolougous chondrocyte transplanations. We were able to treat approx. 300 patients successfully from 2014 to 2016. Several medical studies showed that in 85% of the cases a complete defect closure was achieved.