Filling bone defects – replacement tissue with its own blood supply

Interview with Prof. Raymund Horch, Head of the Department of Plastic and Hand Surgery University Hospital Erlangen

First grow tissue in the lab, then insert it into patients when they need it and you’re done! Unfortunately, things are not as easy as people hoped at the onset of “tissue engineering”. Although robust tissues for bone defects can be grown in a petri dish, for example, they unfortunately quickly die off again inside the body if there is no corresponding nutrient supply.


Foto: Prof. Raymund Horch

Prof. Raymund Horch; © privat

Prof. Raymund Horch of the University Medical Center Erlangen developed a method to supply tissue with its own blood supply. spoke with him about this technique.

Prof. Horch, you specifically developed a method to fill tissue and bone defects with vascularized tissue. How does your treatment work?

Raymund Horch: Our approach initially targets the restoration of vascularization and in a subsequent step the insertion of new cells into the defect site. We conducted our first experiments with this process using bone defects since these defects cause particular problems for patients. The established treatment removes bones from another part of the body, the pelvic bone or shoulder blade for example. Of course, this means that these sites are damaged which could have an adverse effect on the patient. You ultimately don’t want to cause bigger damage than the one you are trying to treat. This is why we first treat the affected area with new blood vessels and subsequently add the patient’s stem cells mixed with bone replacement materials. That’s why our approach is not to make something in the lab but rather to assist the body in restoring functions on its own. This is especially helpful for patients suffering from larger defects because these cannot just simply be filled with a tissue replacement – it would quickly die off due to the lack of blood supply because it might take weeks for new blood vessels to form on their own. Until that happens, the replacement tissue remains unsupported.

Graphic of the operation

A patient’s bone marrow stem cells and bone replacement material are inserted into the defect with fibrin glue. Tiny blood vessels are able to sprout and repair the defect using the matrix; © private

How is the new blood vessel structure integrated into the defect?

Horch: We create a bypass. To do this, we use a superficial vein, a varicose vein for instance, whose removal doesn’t cause any noteworthy damage. It is connected to an artery and transforms. This creates a brand-new blood vessel structure that previously did not exist. This new system sprouts, creates tiny branches and subsequently partially supplies the transported stem cells. With the help of this building material, the body is then able to repair the hole at this site. This is actually quite a simple process.

How do you ensure that enough blood vessel sprouting takes place?

Horch: There are multiple research studies on this subject that were conducted over many years. This is how we know that sprouting takes place at the tip of a blood vessel with this so-called low-pressure system. This does not happen with a coronary bypass of course – the blood pressure is too high. The difference might be that we create an arteriovenous (AV) loop where blood flows in under high pressure and flows back into the vein with normal pressure. We know from research that angiogenesis always takes place at the tip, in the transition area between the high-pressure and low-pressure systems. Apparently, the body is stimulated here.

Your approach seems so simple. Why didn’t anyone already think of this years ago?

Horch: I have pursued this approach for many years. We already tested this procedure on small animals several years ago and then switched to large animals testing. I have worked on tissue engineering since the early nineties. I always knew that we ultimately need to use it in everyday clinical practice. When it became clear that taking a scaffold and cells to firmly fill in a defect does not work, we tried to create a different approach. We include microsurgery in our treatment. As plastic surgeons, we transplant tiny blood vessels and tissue from Point A to Point B every day. This is generally not the case in basic research. It typically takes several months before we have trained an associate to where he/she is able to conduct micro-surgical procedures. This is not something you would do in a "normal" lab. We have developed this over many years which is why it took a little while perhaps. But now we can offer this process to patients with a clear conscience.

Are there patients who are not suited for this type of treatment?

Horch: You would not want to use this treatment in acute infection settings. We treat wounds where an infection is under control or where it cannot be treated with other methods. Of course, this type of surgery is slightly more involved than a regular surgical procedure. Honestly, I am also not able to promise that the treatment is reflected in the current reimbursement structure. But I am certain there will more applications in the future for this type of defect treatment.
Photo: Simone Ernst; Copyright: B. Frommann

© B. Frommann

The interview was conducted by Simone Ernst and translated by Elena O'Meara.