Post-ACL Surgery: the Popping Sound in Your Knee

A popping sound may occur when straightening the knee after anterior cruciate ligament (ACL) surgery?

On March 11 of this year, I underwent surgery for a torn anterior cruciate ligament (ACL) in my left knee, using an autograft.
In July, I discovered that the surgery had failed, and on August 11, I had a second surgery using the previous autograft.
Four weeks post-surgery, I had my brace removed, and six weeks later, I was able to walk without crutches.
About a month after the surgery, I began to notice a popping sound when fully extending my knee, and also when I first moved after standing for a long time.
However, there is no pain associated with it.
Sometimes, when I get out of bed at night, my walking feels a bit awkward until I take a few steps to the bathroom, at which point I hear the popping sound and then it feels normal.
My knee is not very swollen, but I do experience slight stiffness, and I can bend it to over 120 degrees.
Could this popping sound be due to insufficient rehabilitation or other possible factors?

Xiao Wen, 40~49 year old female. Ask Date: 2020/10/27

Dr. You Dianqi reply Orthopedics

Hello, I would like to fully understand your questions before responding, as I find the two sections of your article a bit unclear: 1) Did you use the same autologous ligament again after the first surgery failed? 2) The knee is not very swollen, but there is a slight stiffness—I'm not quite sure what you mean by that.
Therefore, I want to clarify your questions before answering.
Regarding your current discomfort, I believe that undergoing two surgeries in a short period of time may lead to a slower recovery overall.

Reply Date: 2020/10/27

More Info

Post-ACL surgery, experiencing a popping sound in the knee can be a common concern for many patients. This phenomenon, often described as a "clicking" or "popping" noise, can arise from various factors related to the surgical procedure, rehabilitation process, and the overall condition of the knee joint.

Firstly, it is essential to understand that the knee joint is a complex structure composed of bones, cartilage, ligaments, tendons, and synovial fluid. After an ACL reconstruction, the knee undergoes a healing process that can lead to changes in the way these components interact. The popping sound you are experiencing may be attributed to several reasons:
1. Tendon and Ligament Movement: After surgery, the tendons and ligaments around the knee may not have fully adapted to their new positions. As you move your knee, these structures can shift slightly, causing a popping or clicking sound. This is often benign and may decrease as you continue to rehabilitate and strengthen the knee.

2. Scar Tissue Formation: Post-surgical healing often involves the formation of scar tissue. This tissue can sometimes cause friction between the moving parts of the knee, leading to audible sounds. Over time, as you engage in physical therapy and exercises, this scar tissue may become more pliable, potentially reducing the popping.

3. Cartilage and Meniscus: If there are any underlying issues with the cartilage or meniscus (such as tears or degeneration), these can also contribute to popping sounds. Since you mentioned that your knee does not feel painful and has only slight stiffness, it is less likely that significant cartilage damage is the cause, but it is still worth monitoring.

4. Knee Mechanics: The mechanics of your knee joint may have changed due to the surgery. As you recover, your body may be compensating for the altered biomechanics, which can lead to unusual sounds during movement. This is particularly true if you have been favoring one leg over the other during your recovery.

5. Rehabilitation Progress: It is crucial to ensure that your rehabilitation program is appropriately tailored to your needs. Engaging in a structured physical therapy regimen can help improve strength, flexibility, and overall function of the knee. If you feel that your rehabilitation is insufficient, it may be beneficial to consult with your physical therapist or orthopedic surgeon to adjust your program.

In terms of management, if the popping sound is not accompanied by pain, swelling, or instability, it may not be a cause for concern. However, it is essential to keep an eye on any changes in your symptoms. If the popping becomes painful or if you experience increased swelling or instability, it would be prudent to seek further evaluation from your healthcare provider.

In conclusion, while the popping sound in your knee post-ACL surgery can be concerning, it is often a normal part of the healing process. Continuing with your rehabilitation, focusing on strengthening exercises, and maintaining open communication with your healthcare team will be key to your recovery. If you have any doubts or if your symptoms change, do not hesitate to reach out to your orthopedic specialist for further guidance.

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