Why You Can’t Inject a Torn Knee ACL with Ultrasound

When we first began injecting ACL tears with stem cells many years ago, we tried quite a few techniques. At first, it was a very difficult injection that wasn’t reliable. However, after some anatomy review and testing several methods, we finally settled on a procedure that produced reliable results and then began teaching that through a nonprofit course. This morning I’d like to review a case that shows why injecting an ACL with ultrasound only could cause problems.

Can We Inject the ACL?

Medical illustration showing the anatomy of the knee with a torn anterior cruciate ligament


The anterior cruciate ligament, or ACL, is a ligament that stabilizes the knee in front-back and rotational directions. It can be torn in sports or trauma, and these days it’s often surgically removed when torn and replaced with a tendon graft. However, there are problems with ACL surgery, so the idea of keeping your existing ACL is attractive.

When I first tried to inject the ACL, it was after speaking at a prolotherapy conference. This most basic of regenerative-medicine injections involves using a solution that causes a brief inflammatory healing reaction. However, almost all prolotherapy at the time (and most of it still to this day), is performed blind without guidance. In the case of the ACL, this meant that the physician stuck a needle inside the joint and used outside landmarks to ensure that he or she was injecting into the ligament. After I was back in my practice, I decided to use the blind technique with guidance to determine how often the doctor was really injecting into the ligament. Regrettably, I wasn’t able to accurately inject into the ACL using this technique nor did I believe that many of my prolotherapy colleagues were really injecting it either.

Over the next few months, I set out to document that I was injecting the ACL. However, while I would get lucky in some patients and have solid documentation of an ACL injection, the procedure was hit or miss. One of our doctors suggested trying it with ultrasound as he had seen that procedure at a recent course. The good news was that we could visualize the front part of the ligament (insertion), but it was all but invisible at around one-third to one-half way up or more. About that time, we were experimenting with a mini-arthroscope, and we were able to inject the ligament with that device (which I think is the first ACL injected with stem cells using arthroscopy). The issue here was that it seemed silly to put a patient through an arthroscopy just to inject a ligament (basically using a sledgehammer to put in a finishing nail).

Around that same time, I dug into the literature about ACL anatomy and made a breakthrough using fluoroscopy (real-time X-ray). I figured out how to reliably inject the bottom (insertion) and top (origin). Once this happened, we didn’t need the arthroscope, as an injection is always less invasive than a surgery. In addition, we began to see that one of the problems with the ultrasound method was that the torn ACL often leaked out the back of the synovial covering of the ligament about two-thirds of the way up. So by injecting these torn ligaments with ultrasound, while it looked like the doctor was injecting the whole ligament, the upper part wasn’t getting any cells. Finally, we also began to observe that there was a correlation between how well we were able to cover the ligament with cells and the extent of ligament regeneration we saw on MRI. After that, a smart fellow named Dr. Bashir also helped to make the procedure even better.

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Images That Explain Why Ultrasound ACL Injections Are Suboptimal

Since we invented this ACL stem-cell-injection technique, we get patients from all over the world. In this case, a professional athlete had an ACL tear and went to a respected surgical orthopedic clinic. The tear was read out as “partial,” and surgery wasn’t recommended, so a nonsurgical provider injected bone marrow concentrate into the ACL using ultrasound. The patient was then braced and went back to working out hard. I was told by the athlete’s trainer that all providers thought that the ACL was healing one month later, but when I looked at both films (before and after the injection), the ACL had, in fact, substantially worsened. There was now a new retracted part in the area where an ACL ultrasound image couldn’t reach, the tibial offset measurements that we use to determine candidacy had substantially worsened, and there was new bone swelling. Why had this happened when this technique is usually very reliable in the right patients? Meaning that if performed properly, we usually see the opposite on MRI (i.e., evidence of ACL regeneration, a stable or the same offset measurement, and a reduction in bone swelling). While it’s possible that a poor result would have occurred regardless of injection technique, given the candidacy data we’ve amassed, that seemed unlikely (i.e., he was an excellent candidate coming into the procedure).

I think the image below may help explain what happened. Note that the image on the left below is an ACL ultrasound, and the image on ACL mri vs ultrasound the right is an MRI of the ligament. On the left, note that the yellow-dashed line represents the small part of the ACL that can be easily seen using ultrasound. Note also that the yellow-dashed line represents the part of the ACL that can barely be seen with ultrasound (it’s in shadow). Then look at the MRI on the right , which shows the ACL outlined in white dashes and a yellow box that represents the small part of the total ACL, which can be visualized with ultrasound. Note that the ACL in the white dashes travels up and well beyond the limited filed of view of the ultrasound.

ACL injection fluoro Now consider this image from a fluoroscopy injection (left). The ACL ligament is outlined (dark), but the injection at the bottom, where you would inject using ultrasound, dumps out the back of the torn covering of the ligament and ends up in the back of the knee joint rather than in the top part of the ACL (follows the course of the yellow arrow). This is what I believe happened in this athlete’s knee. The top part of the ACL (origin) was never treated with cells, so it eventually ruptured. Note that there is a needle in position (straight line that comes from the left to right) to inject the top part of the ligament.

Now consider this image of a properly injected ACL tear whereproperly injected fluoro ACL both the top and the bottom of the structure have been injected. Note that the dark ACL (anteromedial bundle) now extends from the bottom to the top. Also note that the other ligament bundle (posterolateral, or PL) also extends all the way up. How? Using this real-time X-ray guidance, the doctor can now see and target the top of the ligament. If the injection from the bottom doesn’t get to the top, he or she can inject the ligament up high to close the gap.

The upshot? While you can likely inject an intact ligament with ultrasound and have it work reasonably well, a torn ACL is another matter. While fluoroscopy is more expensive to own and operate, it’s needed to perform a proper injection of the torn ACL with stem cells. So please, please, please don’t inject a torn ACL with ultrasound, doubly so if the patient depends on that knee to make a living!

Chris Centeno, MD is a specialist in regenerative medicine and the new field of Interventional Orthopedics. Centeno pioneered orthopedic stem cell procedures in 2005 and is responsible for a large amount of the published research on stem cell use for orthopedic applications. View Profile

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NOTE: This blog post provides general information to help the reader better understand regenerative medicine, musculoskeletal health, and related subjects. All content provided in this blog, website, or any linked materials, including text, graphics, images, patient profiles, outcomes, and information, are not intended and should not be considered or used as a substitute for medical advice, diagnosis, or treatment. Please always consult with a professional and certified healthcare provider to discuss if a treatment is right for you.

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