Knee swelling after ACL surgery: what it means, what usually helps, and when to get checked - Camberwell
- Emma Glynn
- 5 days ago
- 5 min read
By Emma Glynn - Hip & Knee Physiotherapist
This information is general in nature and not a substitute for personalised medical advice.
Persistent knee swelling after ACL surgery is common but it’s not something to ignore. While some joint effusion is expected early on, ongoing or recurrent swelling can interfere with strength recovery, movement quality, and confidence if it’s not addressed properly.
This article explains what post‑operative knee swelling is, why it often lingers beyond the first few weeks, what helps, and when an individual review is warranted.
What swelling (effusion) is
After ACL surgery, most swelling is joint effusion - fluid that accumulates inside the knee joint capsule. This fluid is produced by the synovial lining in response to surgical trauma, inflammation, or joint irritation. It is different from surface bruising or general soft‑tissue puffiness.
Small to moderate effusions are expected in the early post‑operative period and typically fluctuate with activity levels. However, research shows that persistent effusion can inhibit quadriceps activation, delay strength recovery, and negatively affect knee mechanics if not managed appropriately [1,2].
What’s common vs what’s a red flag
Common and expected
Mild to moderate swelling in the first 4–8 weeks
Swelling that increases slightly after busy or high‑load days
A feeling of tightness or “fullness” without heat or sharp pain
Red flags that should be assessed promptly
Fever, chills, or feeling systemically unwell
Increasing redness, warmth, or severe tightness around the knee
Rapid escalation in swelling or pain
Calf swelling or pain (possible DVT)
Sudden loss of knee extension or flexion
True instability or giving way
If any of these are present, early clinical review is recommended.
Why swelling sticks around after ACL surgery
Persistent swelling rarely means something has “gone wrong,” but it often indicates that the knee is being asked to tolerate more load than it is currently ready for.
Load spikes
Returning to work, increasing step count, standing for longer periods, or progressing gym‑based rehab too quickly can all provoke effusion. Sudden changes in training volume are a well‑recognised driver of post‑operative swelling [3].
Extension not fully restored
Loss of terminal knee extension keeps the joint in a slightly irritated position, increasing synovial fluid production. Early and sustained restoration of full extension is strongly associated with better outcomes after ACL reconstruction [1].
Quadriceps weakness and gait compensation
Quadriceps inhibition is closely linked to joint effusion. When quad strength is reduced, people often compensate with altered gait or movement patterns, increasing joint load and perpetuating swelling [2,4].
Meniscus or cartilage involvement
Concomitant meniscal or chondral injuries may contribute to longer‑lasting inflammatory responses. While common, these factors can increase the likelihood of effusion fluctuations during rehab [5].
Recovery debt
Poor sleep, elevated stress, and inadequate recovery can amplify inflammatory responses. These factors are increasingly recognised as contributors to delayed post‑surgical recovery, including swelling persistence [6].
How to track swelling at home
You don’t need imaging to monitor swelling trends. Useful strategies include:
Checking your knee at the same time each day, ideally in the morning
Comparing size, shape, and contours with the non‑injured knee
Noting “bogginess” around the kneecap or joint line
Tracking how swelling responds 6–24 hours after activity
Patterns over time are more informative than single measurements.
What usually helps
Smart load management
Complete rest is rarely helpful long‑term. Instead, aim for gradual, predictable increases in activity. Breaking activity into shorter bouts often reduces effusion compared to single long sessions [3].
Compression, elevation, and cooling
These strategies can reduce symptom severity and swelling accumulation when used strategically, particularly after higher‑load days. They do not replace progressive rehabilitation but can support it [7].
Circulation and activation
Simple strategies such as ankle pumps, calf contractions, and quadriceps isometrics can assist venous return and neuromuscular activation, especially after prolonged sitting or standing [2].
The 24‑hour response rule
If swelling or stiffness is worse the following day, the knee was likely overloaded. This feedback helps guide appropriate progression and reduce repeated flare‑ups.
When swelling blocks progress (and what clinicians assess)
When effusion persists or limits progression, clinicians typically assess:
Effusion grading
Knee range of motion (especially extension)
Quadriceps and hamstring strength
Movement quality (walking, stairs, squats)
Confidence, fear, and symptom behaviour
Addressing swelling early can prevent delays in later rehab milestones such as running, jumping, and return to sport [4,8].
Next steps in Camberwell
If your knee is still swollen beyond the expected timeframe, or if swelling keeps returning with normal activity, an individual assessment can clarify what’s driving it and how to adjust your rehab plan.
You can:
Download our guide: “Why is my knee still swollen after ACL surgery?”
Call the clinic to discuss your symptoms
Can't Find What You're Looking For?
Explore more of our most popular services and guides:
Still stuck? Contact us and we’ll point you in the right direction
Disclaimer
The content provided on this website is for general information and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
While The Hip and Knee Physio strives to present accurate and up-to-date information, we do not guarantee results or outcomes based on the information provided. Any exercises, strategies, or recommendations featured on this site should not be considered a personalised treatment plan.
Always seek the advice of a qualified healthcare provider before starting any exercise program, particularly if you are experiencing pain, injury, or a pre-existing medical condition.
Use of this website does not create a physiotherapist–patient relationship. The Hip and Knee Physio accepts no responsibility for any injury or loss arising from reliance on or use of this information.
By using this website, you agree to these terms.
References
Adams D, Logerstedt D, Hunter-Giordano A, Axe MJ, Snyder-Mackler L. Current concepts for anterior cruciate ligament reconstruction: A criterion‑based rehabilitation progression. J Orthop Sports Phys Ther. 2012;42(7):601–614.
Palmieri-Smith RM, Thomas AC, Wojtys EM. Maximizing quadriceps strength after ACL reconstruction. Clin Sports Med. 2008;27(3):405–424.
Grindem H, Risberg MA, Eitzen I. Two factors that may underpin slower recovery after ACL reconstruction: load management and neuromuscular deficits. Br J Sports Med. 2015;49(21):1420–1425.
Dingenen B, Gokeler A. Optimization of the return‑to‑sport paradigm after ACL reconstruction: A critical step back to move forward. Sports Med. 2017;47(8):1487–1500.
Filbay SR, Ackerman IN, Russell TG, Macri EM, Crossley KM. Health‑related quality of life after ACL reconstruction: A systematic review. Am J Sports Med. 2014;42(5):1247–1255.
Ardern CL, Taylor NF, Feller JA, Webster KE. Psychological responses matter in returning to sport after ACL reconstruction. Sports Med. 2013;43(11):1103–1123.
Bleakley CM, Glasgow P, Webb MJ. Cooling an acute muscle injury: can basic scientific theory translate into the clinical setting? Br J Sports Med. 2012;46(4):296–298.
Paterno MV, Rauh MJ, Schmitt LC, Ford KR, Hewett TE. Incidence of second ACL injuries 2 years after primary ACL reconstruction and return to sport. Am J Sports Med. 2014;42(7):1567–1573.
Comments