pain and stiffness after ACL surgery

3 Common Issues After ACL Surgery

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Undergoing Anterior Cruciate Ligament (ACL) reconstruction surgery is very common, and recovery from this surgery often takes a minimum of 9-12 months. The journey to full recovery is not always smooth sailing. Many individuals face common challenges and complications along the way. Let’s explore three common issues after ACL surgery and how they can impact the rehabilitation process.

1) Arthrofibrosis

A common complication of ACL surgery causing stiffness and pain
Arthrofibrosis of the knee. Source

Arthrofibrosis is an exaggerated immune response to a pro-inflammatory trauma (like surgery) leading to pathological fibrosis around the knee joint and symptomatic joint stiffness. It is similar to another common condition often called Frozen Shoulder. The knee, elbow, and shoulder are particularly susceptible to Arthrofibrosis. It is estimated that up to 8% of patients develop arthrofibrosis following knee surgery (1). With this pathology, the scar tissue inside the joint adheres to surrounding tissues and contracts, and this frequently reduces the range of motion (ROM) of the joint. While not everybody with arthrofibrosis has a significant reduction in ROM, they can be significantly impacted by pain, particularly during and after activity. 

Common symptoms of Arthrofibrosis include persistent swelling, an inability to fully straighten or bend the knee, and pain with movement or weight-bearing. A slow increase in the range of motion after 6 weeks might be a sign of arthrofibrosis. Up to 6 weeks post-surgery, your knee is still recovering from surgical trauma so it is difficult to say how you are recovering and identify issues.

Management of this painful and stiff condition in most cases is physiotherapist lead and involves addressing swelling and modifying activity to control inflammation. You may need to modify your rehab and activity levels to manage your symptoms. Mobilisation of the affected joint can aid swelling control and prevent adhesion formation, and early motion should be promoted whenever possible. Management can be painful as aggressive stretching can help improve the range of motion. Often your physiotherapist will refer you to your GP or surgeon for pain medication to support your physical rehabilitation.

Occasionally, surgical intervention may be necessary to remove scar tissue. Another common procedure is Manipulation Under Anaesthetic (MUA). MUA has been shown to improve ROM in stiff knees after ligament reconstruction and can help with the progression of rehabilitation and exercise tolerance.

Modifiable risk factors include surgical technique, concomitant or multiple procedures, pain management, BMI, rehabilitation, and prolonged immobilisation. Non-modifiable risk factors include the severity of trauma, pre-existing stiffness and/or inflammation, heterotopic ossification, infection, early-onset osteoarthritis, sex, and genetic predisposition (1) .

For more information, here is a great resource from the International Arthrofibrosis Association.

2) Cyclops Lesion

A cyclops lesion in the anterior knee near the ACL attachment site. Image source

A Cyclops Lesion is a complication that can occur after ACL reconstruction surgery. It is characterised by the formation of a nodule of localised scar tissue mass in the front of the knee joint, often near the surgical graft site. This mass acts as a physical barrier, preventing the knee from fully extending or straightening. It is also sometimes known as a localised anterior arthrofibrosis.

Cyclops lesions are often only detected when you are unable to reach full extension in your knee after about 12 weeks. Common symptoms of a Cyclops Lesion are lack of extension range of motion, swelling, and sometimes a painful click or clunk. There is often a plateau in your rehab as these factors make it quite difficult to improve quadriceps strength.

Your physiotherapist or surgeon might refer you back for an MRI to help identify why your knee has not improved along typical timelines. It is estimated that these lesions appear in between 25% to 47% of MRIs following ACL surgery, but only up to 10% of these lesions are symptomatic (2) . Therefore, you will need to consult with your surgeon to determine if a Cyclops lesion is the cause of your symptoms.

Risk Factors for Cyclops Lesions following ACL Surgery (2)

  1. Female sex, because of the bony anatomy (narrow notch)
  2. Increased volume of graft in relation to the notch size
  3. Bony avulsion of anterior cruciate ligament (ACL) from tibia
  4. Bony avulsion of ACL from femur
  5. Anterior placement of tibial tunnel
  6. Double-bundle ACL reconstruction because of a higher volume of graft
  7. Bicruciate-retaining arthroplasty because of ACL injury or sharp tibial bone island
  8. Hamstring contracture

Management of a Cyclops Lesion includes modifying rehabilitation to concentrate on restoring full extension. You can still continue your rehab exercises but some may be modified based on your symptoms. Consult your physiotherapist to get a tailored plan. In some cases, a minimally invasive arthroscopic procedure may be necessary to remove the scar tissue causing the blockage, and your surgeon can discuss this with you. The recovery from this surgery is brief and often leads to dramatic improvement in function and symptoms.

For more information about Cyclops Lesions, please have a read of this article.

3) Patellofemoral Pain

knee pain after ACL surgery
Patellofemoral pain occurs around the front of the knee, around the patella (kneecap) and femur (thigh bone). Source

After ACL reconstruction, some individuals may experience patellofemoral pain, also known as runner’s knee or anterior knee pain. It is a common issue at some point during the rehab journey and is characterised by discomfort around or behind the kneecap (patella). This pain often feels like a dull ache that worsens with activity involving bending of the knee.

Symptoms may include pain with activities such as stairs, squatting, or running, swelling around the kneecap, and audible clicking or popping sensations. It is an umbrella term that covers anterior knee pain generally. You may have underlying cartilage issues that contribute, but this pain can often happen in the absence of any underlying issues and is just due to excessive loads being placed on the knee during movement and exercise.

Following ACL surgery, the knee undergoes significant changes including altered mechanics, swelling, and muscle weakness. These factors can contribute to the development of patellofemoral pain for several reasons including;

  1. Changes in Knee Mechanics: The knee’s stability and movement patterns may be altered after ACL surgery, affecting how the patella tracks along the femur (thigh bone).
  2. Muscle Weakness and Imbalance: Weakness in the quadriceps muscles, particularly the vastus medialis oblique (VMO), can impact patellar alignment and lead to pain.
  3. Overuse or Incorrect Rehabilitation: Engaging in activities too soon or using poor technique during exercise can strain the knee and exacerbate patellofemoral pain.

The management for this is entirely led by your physiotherapist or exercise physiologist. Management generally involves strengthening exercises for the quadriceps and hip muscles, patellar taping or bracing to improve alignment, activity modification to reduce stress on the knee, and exercise supervision to to correct movement patterns and muscle imbalances.

If you’re facing any of these three common issues after ACL surgery, know that you’re not alone. Working closely with your healthcare team, following your rehabilitation plan diligently, and being mindful of your body’s signals can help you navigate these challenges and move closer to a full and active life once again. Remember, recovery from ACL injury is a journey. Our team of experts are here to help, so please reach out with any questions, or book online to get your rehab back on track.


  1. Lee DR, Therrien E, Song BM, Camp CL, Krych AJ, Stuart MJ, Abdel MP, Levy BA. Arthrofibrosis Nightmares: Prevention and Management Strategies. Sports Med Arthrosc Rev. 2022 Mar 1;30(1):29-41. doi: 10.1097/JSA.0000000000000324. PMID: 35113841; PMCID: PMC8830598.
  2. Kambhampati SBS, Gollamudi S, Shanmugasundaram S, Josyula VVS. Cyclops Lesions of the Knee: A Narrative Review of the Literature. Orthop J Sports Med. 2020 Aug 28;8(8):2325967120945671. doi: 10.1177/2325967120945671. PMID: 32923503; PMCID: PMC7457408.
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