Do Stem Cell Injections Improve Outcomes Following ACL Surgery?
My last blog was a little disappointing because I wasn’t able to find much research comparing stem cell injections to surgery for recovery from an ACL tear. However, I was able to find some research on the 2nd most important question: what happens when you combine the two approaches. Today we will go through the research that examines the benefits of surgery plus stem cell injections for the treatment of a completely torn ACL.
Human Studies
A majority of the information for this blog comes from this paper published in 2021, which reported that at the time of publication, there have been a total of 9 studies examining the effect of stem cells on ACL reconstruction outcomes in humans, with 4 being completed at the time of publication. Unfortunately, this one was behind a paywall, so I only have 3 to review. Let’s go through them.
Study 1
The first study to be published on this topic came out in 2014 and was a RCT with 20 patients in the experimental arm and 23 patients in the control arm. All subjects underwent an ACL reconstruction (ACLR) plus standard rehab, with the experimental group receiving injections of mesenchymal stem cells (MSCs) from bone marrow into the femoral end of the graft and the area surrounding the femoral end of the graft. All patients underwent a follow-up MRI approximately 3 months after surgery (94 +/- 5 days). This study found no differences in graft-to-bone healing at the 3-month follow up based on MRI results.
This result is in contrast with a study from 2004 in rabbits that found that a MSC injection at the time of surgery resulted in a change in composition of the graft to more closely resemble the native ACL; these grafts also had enhanced biomechanical properties compared to the control group; it is possible that these enhanced properties were also present in the human study but were unable to be determined because humans don’t like having their new ACL cut out of their knee for further testing.
Study 2
The second study was published in 2017 and examined 17 patients following ACL surgery. All subjects received an injection of hyaluronic acid (HA) and 11 subjects also received an injection of stem cells. At the 24-month follow-up, all patients completed a series of knee function questionnaires and underwent an x-ray and MRI. This study found significant improvements in self-reported knee function in the experimental group compared to the control group. The study also found no statistically significant differences in medial and lateral tibial cartilage volume (a marker for the presence and progression of osteoarthritis). However, a significant improvement was seen in lateral joint space width (another arthritis marker) at 24 months in the experimental group compared to the control group.
Study 3
The third study was published in 2019 and examined 39 subjects following ACL surgery with a patellar graft, 20 of which received stem cell injections into the graft at the time of surgery. Subjects received MRIs and performed knee pain and function questionnaires at 2-, 4-, 6-, and 12-month follow-ups. This study found that overall, there was no statistically significant improvement in pain scores, knee function, activity levels, or MRI-based graft maturation between the groups 12 months after surgery.
Summary
Unfortunately, the use of stem cell injections in conjunction with ACL reconstruction does not appear to currently provide significant benefit . The one area that appeared to show some benefit from the injections was in the development of osteoarthritis, but the limited follow-up period (2 years) was not long enough to fully assess this difference. If we are lucky, those researchers will continue to follow up with the subjects at longer time intervals to determine if the stem cells continued to provide a protective effect against the development of knee osteoarthritis following surgery.
I am still hopeful that stem cells can play a beneficial role in recovery from ACL surgery – and orthopedic surgeries in general – but the current evidence does not seem to support that conclusion. If you have the extra money, it may still be worth considering the use of stem cells in conjunction to ACL surgery, since the risk of complications is low and there may be some benefit for preventing the development of arthritis.
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