Loss of extension after ACL surgery: How to assess for a cyclops lesion


Lenny Macrina

Physical Therapist United States

Loss of extension after an ACL reconstruction can be debilitating for the patient. It’s not as common as you would think but I see it enough in the clinic from people that are months out from surgery. Usually, this loss of knee extension after an ACL reconstruction is caused by a cyclops lesion. Let’s dive deeper into this!

Often times, they’ll present with anterior knee pain, posterior knee soreness and a relatively weakened quadriceps muscle that just won’t return. No matter what they do to get the motion back, the knee just never feels normal.

I’ve written about the loss of extension after an ACL reconstruction in the past. In this post, I discussed how I like to work on knee extension immediately after an ACL surgery. There are a few ways that I think are most effective and with minimal patient efforts.

What is a Cyclops Lesion?

For those not familiar, a cyclops lesion is a wad of scar tissue in the anterior aspect of the knee joint. It is believed to be a remnant of the previous ACL stump that had remained during the reconstruction surgery. At least that’s one theory. Another theory states that it may be fibrocartilage as a result of drilling the tibial tunnels.

Whatever the case, this arthrofibrosis (scar tissue) physically blocks the knee joint from locking out into full extension. Check out this MRI that shows the scar tissue in the anterior knee.


Cyclops lesion in the anterior knee blocking full (hyper) extension

How do I assess for a cyclops lesion after ACL surgery?

In this video, I describe why and how I assess for a cyclops lesion. Check it out.

Is it a Cyclops lesion or just a tight knee?

From the video, you can clearly note that anterior pain, in my experiences, is most often related to a cyclops lesion. Other factors to consider include:

  1. temporary/transient gains in extension
  2. anterior knee pain after increasing activity
  3. poor patella mobility
  4. quads just won’t come back
  5. continued hamstring/calf soreness

These are tell-tale signs that there’s more going on and you should refer back to the doctor so they can order an MRI to rule in/out the anterior scarring. If diagnosed, the best (and only) option is to have a knee scope and remove that scar tissue.

There’s nothing else that can be done. No PT, injections or manual therapy can restore full symmetrical knee extension.

The scar tissue needs to be removed by surgical excision. Aggressive PT should commence immediately after surgery to restore the extension range of motion.

The Best and Easiest Way to Restore Knee Extension after an ACL

Rehab after an ACL is never easy. There are many things that could affect a patient’s outcome. I’ve treated hundreds of patients after an ACL reconstruction and each one is a unique challenge. I wrote about this in a previous post here..check it out and let me know what you think.

I put this video together for Mike Reinold’s website so you could see what I exactly do to gain knee extension back….and why I’m not a fan of prone hangs. Hope it helps with some of your knee patients.

Final Cyclops Thoughts

As a PT or athletic trainer, don’t blame yourself if the patient needs another surgery to remove the scarring. It seems as if it was inevitable and was going to occur no matter the efforts to work on knee extension. I think the lesson here is:

  • work on extension early and often
  • maintain good compliance at home
  • assess/measure each visit to determine gains or losses
  • early patella mobility and knee PROM
  • get the pain and swelling out as quickly as possible
  • refer back to the doctor if the ROM not improving despite your best efforts

Hope this post helps you get better outcomes for your ACL patients!


If you want to learn more about how I treat ACL’s, then you can check out our all online knee seminar. If interested, check it out at www.onlinekneeseminar.com and let me know what you think. We cover the anatomy, rehab prescription, ACL, knee replacements and patellofemoral issues both non-operative treatment and post-operative treatment. This is an awesome course if you’re interested in learning more about rehabilitating the knee joint. And if you’re a PT, there’s a good chance you can get CEU’s as well.

This was originally posted on Lenny Macrina’s website. You can click here to read more blogs from them.


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About the Author


Lenny Macrina

Physical Therapist United States

Lenny Macrina has been a practicing physical therapist since 2003 and currently serves as the Director of Physical Therapy at Champion Physical Therapy and Performance in Waltham, MA. His interests include research and rehabilitation of the shoulder, elbow and knee joints. He has successfully treated many orthopaedic and sports medicine related injuries that are both post-operative and non-operative in nature, in recreational athletes to the high-level professional athletes. Lenny is a board certified sports physical therapist by the APTA and a certified strength and conditioning specialist by the National Strength and Conditioning Association. In 2010, he was nominated by his peers to be included in the prestigious American Sports Medicine Fellowship Society which includes top fellowship-trained orthopaedic surgeons and physical therapists. Along with maintaining a full clinic schedule, he has co-authored various current concept papers, book chapters, research papers and a home study course for the APTA’s Orthopaedic section. He is a peer reviewer for the esteemed JOSPT and has reviewed rehabilitation textbooks and research papers for that journal. Through this research, he has been involved in numerous published articles in journals including: AJSM, JOSPT, Journal of Sports Health, Journal of Athletic Training, CORR, Operative Techniques in Sports Medicine, and many others. He has presented at various national conferences including APTA’s Combines Sections Meeting, ASMI’s “Injuries in Baseball Course”. Lenny received his Bachelor’s degree in Biotechnology from Worcester Polytechnic Institute and his Master’s degree in physical therapy from Boston University.

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