Animal tissue will build ligaments and tendons of the future

Imagine that in the future, you badly tore a ligament or a tendon and it was beyond repair. Imagine again that instead of replacing the tissue by taking tissue from your body, the surgeon could replace it with something stronger, yet still biologic, something that your body would remodel into being all you. For some, that future is now.

Z-lig animal tissue scaffold device ACL

This week, a patient in Poland had his anterior cruciate ligament (ACL) replaced with a Z-lig, an off-the-shelf scaffold device made from a pig ligament. It’s the first commercial use of this device and the culmination of many years of work, which my team and I began over 19 years ago with early-stage development and pilot trials. The Z-lig was subsequently developed by Aperion Biologics, and was cleared last year for marketing and distribution in the European Union and other markets which recognize the CE Mark.

Having an off-the-shelf replacement device solves a number of problems. Today when tissues are torn and not repairable, surgeons use either tissues from another part of the patient (robbing Peter to pay Paul; weakening another area to substitute in the primary injury) or use human donor tissue. The first approach, taking tissue from the injured patient creates a second injury. Since there are no truly expendable tissues, all have important functions; this solution cannot be thought of as the future. Human donor tissues work quite well but the number of young healthy people dying and donating their tissues just doesn’t meet the need.

There is no reason that in the 21st century we shouldn’t be able to find, not just suitable substitutes, but better ones. And if we are truly going to advance the science of human reconstruction, couldn’t we do better than just replacing what broke?

In marches the lowly pig. Pigs grow to over 400 pounds in just six months. Some of the tissues are stronger than human tissues due to their thickness, yet they have the same collagen organization as humans do. In evolutionary terms, we say the collagen is quite “conserved” meaning it matches ours. There is a long history of using pig tissues for heart valves, insulin, and skin. Pigs are plentiful and the unused medical parts can be eaten. Even many Muslim and Jewish orthodox authorities allow the use of pig tissues for medical necessity.

The problem with using any animal tissue is immunologic rejection. There are specific carbohydrates on animal tissues that are recognized when transplanted into humans. In the past, these immunologic red flags were blocked by aldehyde fixation, turning the tissues into shoe leather. This worked for some applications but not where the tissues had to be both flexible and able to be remodeled, as in the case for ligaments and tendons.

The new solution is to strip away the carbohydrates with a specific enzyme, thereby humanizing them. This solution, called the Z-Process, was successfully tested in a randomized prospective double-blind trial in Europe and approved for use. The patient in Poland this week became the first patient outside of the trial to receive their grafts. Patients in Italy and South Africa will be next. A pivotal trial in the US has been approved as well.

WATCH Dr. Stone explain the process of humanizing animal tissue so it can be used to rebuild human joints

Ligaments and tendons of the future will be stronger than those that they replace. Torn ACLs and PCLs, rotator cuffs of the shoulder, collateral ligaments of the elbow, tendons in the hands and feet, when ruptured, will all be replaced by stronger, younger, and healthier tissues from pigs. And these pig tissues may be preloaded with growth factors from the injured patient.

Fixing broken people with the goal of making them better than they have been in years is a dream come true for surgeons around the world. IF the patients do their part, our goal of helping people become fitter, faster and stronger will be realized more often than not.


Medically authored by
Kevin R. Stone, MD
Orthopaedic surgeon, clinician, scientist, inventor, and founder of multiple companies. Dr. Stone was trained at Harvard University in internal medicine and orthopaedic surgery and at Stanford University in general surgery.