Constipation after ACL surgery is extremely common, and it’s not your fault. The combination of opioid pain medication, anesthesia, reduced movement, and changes in your diet creates a perfect storm for your digestive system to slow down or stall entirely. Most people have their first bowel movement within one to three days after surgery, but some go longer. If you haven’t gone within two days, it’s time to take active steps.
Why ACL Surgery Makes It So Hard to Go
The biggest culprit is opioid pain medication. Opioids don’t just block pain signals in your brain. They bind to receptors throughout your entire digestive tract, slowing everything down in multiple ways at once. They reduce the normal wave-like contractions that push food through your intestines, while simultaneously decreasing the amount of water your gut secretes into stool. The result is stool that moves slower and gets drier and harder the longer it sits. On top of that, opioids increase the tightness of the internal anal sphincter, making it physically harder to pass anything even when stool does reach the end of the line. This is why straining and a feeling of incomplete evacuation are so common.
General anesthesia adds to the problem by temporarily suppressing your gut’s normal activity. And after ACL surgery, you’re largely immobile for the first few days, sitting or lying with your leg elevated. Physical movement is one of the main signals your colon uses to stay active, so being stuck on the couch removes that stimulus too.
Start a Stool Softener Before You Need It
The single most important thing you can do is start a stool softener the same day you begin taking opioids, not after you’re already constipated. A stool softener like docusate sodium works by pulling water into your stool so it stays soft and passable. The standard adult dose is one to four teaspoonfuls once a day, depending on the product concentration. It won’t cause cramping or urgency. It just keeps things from turning to concrete while your gut is slowed down.
If a stool softener alone isn’t enough after a day or two, add an osmotic laxative. Polyethylene glycol 3350 (sold as MiraLAX) is the go-to option. The standard dose is 17 grams, about one capful, mixed into any beverage once daily. It draws water into your colon and is gentle enough for daily use. Many orthopedic surgeons send patients home with instructions to take both a stool softener and MiraLAX together from day one.
If you still haven’t had a bowel movement after two full days, a stimulant laxative like bisacodyl (Dulcolax) can help. Stimulant laxatives actively trigger contractions in your colon to move things along. They’re stronger than stool softeners and can cause some cramping, but waiting three or four days with a bloated, uncomfortable abdomen is far worse. University of Utah Health recommends reaching for a stimulant if you haven’t gone within two days post-surgery.
What to Eat and Drink
Aim for 25 to 30 grams of fiber per day from actual food. Good sources include oatmeal, berries, pears, beans, lentils, and whole grain bread. If you’ve barely been eating since surgery, even getting to 15 or 20 grams is a meaningful improvement over crackers and white toast.
Prune juice is worth singling out. A randomized, placebo-controlled trial published in the American Journal of Gastroenterology found that prune juice significantly decreased hard stools and increased normal, well-formed stools compared to placebo. The effect comes from a combination of sorbitol (a natural sugar alcohol that draws water into the colon), pectin, and polyphenols working together. A glass or two per day is a simple addition that genuinely helps.
Hydration matters more than usual right now. UW Medicine recommends drinking six to eight 8-ounce glasses of water per day on top of whatever you drink with meals. That’s roughly 1.5 to 2 liters of extra water. When your gut is absorbing more water from stool than normal (because opioids tell it to), you need to compensate by putting more fluid in.
Get Moving as Soon as You Can
You don’t need to go for a walk around the block. Even small amounts of movement help wake up your digestive tract. Getting up to use the bathroom, standing for a few minutes, or doing gentle upper-body movements from a chair all send signals to your gut that it’s time to get back to work. Enhanced recovery guidelines recommend early ambulation starting the day after surgery for exactly this reason: it shortens the time to your first bowel movement.
If your surgeon has cleared you for crutch-walking, even a slow trip to the kitchen and back a few times a day makes a difference. The goal isn’t exercise. It’s just not being completely still.
How to Use the Toilet With a Knee Brace
This is the part nobody warns you about. Sitting down on a standard toilet with a locked knee brace or limited knee flexion can feel awkward and painful. A raised toilet seat is the simplest fix. It reduces how deeply you need to bend your knee and makes both sitting down and standing up significantly easier. You can find them at any pharmacy or order one before surgery.
When lowering yourself, keep your surgical leg extended slightly forward and use your arms on handrails, the counter, or a stable grab bar to control your descent. Don’t drop your weight down quickly. When standing up, push through your arms and your good leg, keeping the surgical knee aligned and avoiding any twisting. A small step stool under your operated foot can also help keep the leg in a more comfortable position while you’re sitting.
Positioning matters for the actual bowel movement too. Leaning forward slightly and placing your feet on a low stool (even just under your good foot) mimics a squatting posture that relaxes the pelvic floor and straightens the path for stool to exit. This can make a real difference when you’re dealing with hardened stool and a tightened anal sphincter from opioids.
Reduce Your Opioid Use When Possible
Every day you take opioids, the constipation continues. The effects on your gut don’t build tolerance the way pain relief does, meaning the constipation stays just as bad or gets worse over time even as your pain improves. Switching to acetaminophen or an anti-inflammatory (if your surgeon approves) as soon as your pain allows is one of the most effective ways to get your bowels moving again.
Some people find they can drop opioids entirely by day three or four and manage with over-the-counter pain relievers. Others need them longer. But even cutting from four doses a day to two can meaningfully improve gut motility.
Warning Signs That Need Medical Attention
Normal post-surgical constipation is uncomfortable but not dangerous. It becomes a medical concern if you develop severe crampy abdominal pain that comes and goes, vomiting, visible abdominal swelling, a complete inability to pass gas, or total loss of appetite. These can indicate a bowel obstruction, which is rare after orthopedic surgery but requires prompt evaluation. If you’re passing gas but just haven’t had a full bowel movement yet, that’s a reassuring sign that things are moving, just slowly.