Epidural fibrosis is scar tissue that forms inside the spinal canal after back surgery. It develops in the epidural space, the area between the spinal cord’s protective covering (the dura) and the surrounding bone. While some scarring is a normal part of healing, excessive scar tissue can bind to nerve roots and the dura itself, restricting their natural movement and causing persistent pain. It is estimated to be the causative or contributing factor in 20 to 36% of cases where pain continues or returns after spinal surgery, a condition broadly known as failed back surgery syndrome.
How Scar Tissue Forms After Surgery
Any spinal operation creates tissue damage that triggers the body’s repair process. That process follows three overlapping stages. First, within 3 to 5 days, the body launches an early inflammatory response: bleeding is controlled, clotting factors activate, and immune cells flood the surgical site. Over the next 2 to 3 weeks, specialized repair cells called fibroblasts begin producing dense connective tissue in response to inflammatory signals. Finally, a remodeling phase unfolds over months to years, during which the scar tissue matures and contracts.
In most people, this scarring stays minimal and causes no problems. In others, the body deposits an unusually large amount of fibrous tissue in and around the epidural space. Some researchers have compared this to the way certain people form raised, thickened scars on their skin (keloids), suggesting a possible genetic predisposition. When the scar tissue is extensive enough to tether nerve roots or the dura to surrounding structures, it becomes clinically significant.
Why It Causes Pain
Nerves in the spinal canal normally slide and shift with every movement you make, bending, walking, even just changing position in a chair. When dense scar tissue anchors those nerves in place, they can no longer move freely. Straightening your back, extending your spine, or simply going through daily position changes pulls on the immobilized nerve, generating pain signals. Over time, this repeated mechanical irritation can heighten pain sensitivity, meaning movements that wouldn’t normally hurt start producing significant discomfort.
The result is typically some combination of leg pain (from nerve root tethering) and back pain (from adhesions to the dura and surrounding tissues). Symptoms often emerge gradually during the months after surgery, as the scar tissue matures and tightens, though they can also appear after an initial period of post-surgical relief.
Diagnosing Epidural Fibrosis on MRI
The standard way to identify epidural fibrosis is an MRI scan with a contrast dye injected into a vein. The critical distinction is between scar tissue and a recurrent disc herniation, because the two can look similar on a plain MRI and the treatment approaches differ significantly.
Scar tissue lights up quickly. On images taken within 10 minutes of contrast injection, epidural fibrosis shows irregular, patchy enhancement. A herniated disc, by contrast, does not enhance on those early images, though it may show some enhancement on delayed scans. This timing difference makes pre-contrast and early post-contrast scans highly accurate at separating the two conditions.
Doctors can also grade the severity of scarring. One commonly used system divides the epidural space at each spinal level into four quadrants (right and left, front and back) and scores each on a 0 to 4 scale based on what percentage is filled with scar tissue. A score of 0 means no scarring, while 4 means 76 to 100% of that quadrant is affected. This gives a standardized way to track how extensive the fibrosis is and compare outcomes after treatment.
Prevention During Surgery
Because treating established scar tissue is difficult, surgeons have focused on preventing it from forming in the first place. The main strategy involves placing a physical barrier between the exposed dura and the surrounding muscles and bone at the end of surgery. These barriers are typically gels made from large, complex biological molecules designed to keep tissues separated during the critical early healing window.
A meta-analysis of randomized clinical trials found that barrier gels placed during lumbar disc surgery significantly reduced leg pain after the operation. The effect on back pain, however, was not statistically significant, and neither was the effect on overall disability scores. So these gels offer a real but partial benefit: they seem to reduce nerve root adhesions enough to ease radiating leg symptoms, but they don’t solve the broader problem of spinal pain and functional limitation.
Treatment Options for Existing Fibrosis
Percutaneous Adhesiolysis
The most targeted non-surgical treatment is a procedure called percutaneous adhesiolysis, sometimes known as the Racz procedure. A specialized catheter is threaded through a small opening in the tailbone into the epidural space, guided by real-time X-ray. The catheter is used to mechanically break up scar tissue and decompress nerve roots, while also delivering concentrated medication directly to the affected area.
Beyond physically disrupting adhesions, the procedure works by flushing out inflammatory chemicals at the damaged site, improving blood flow to nerve roots that may be starved of oxygen by the surrounding scar, and ensuring pain-relieving medications can actually reach nerves that were previously walled off by fibrosis. Published success rates, defined as at least a 50% reduction in pain, range from about 49% to 83%, depending on the study and protocol used. The original technique involves keeping the catheter in place for three days with different medications injected each day, though shorter one-day protocols have shown comparable results.
Epidural Injections
Standard epidural steroid injections can help manage pain, but their effectiveness in the presence of significant fibrosis is limited precisely because the scar tissue can block medication from reaching the affected nerves. One approach to overcome this is adding an enzyme called hyaluronidase, which breaks down connective tissue components and increases the permeability of the scar. In a clinical study, patients who received both a steroid and hyaluronidase had the best long-term outcomes: at 12 weeks, over 52% reported at least a 50% pain reduction. Patients who received the steroid alone or the enzyme alone fared much worse, with neither group achieving meaningful pain relief at that same time point. The enzyme appears to work by helping the steroid penetrate through scar tissue to reach inflamed nerve roots.
Revision Surgery
Reoperation to remove scar tissue is generally considered a last resort, and for good reason. Success rates drop dramatically with each additional surgery: roughly 30% after a second operation, 15% after a third, and as low as 5% after a fourth. Each reoperation creates new tissue trauma that triggers the same inflammatory cascade, often producing new scar tissue that can be as bad as or worse than the original. Repeated surgeries also carry increasing risks of tearing the dura, injuring nerve roots, and significant bleeding. This pattern is one of the central frustrations of managing epidural fibrosis: the very act of surgically removing scar tissue tends to generate more of it.
Epidural Fibrosis vs. Arachnoiditis
These two conditions frequently coexist and can be difficult to separate clinically. Epidural fibrosis involves scarring outside the dura, in the epidural space. Arachnoiditis involves inflammation and scarring inside the dura, affecting the delicate membrane (arachnoid) that directly surrounds the spinal nerves. Both can follow spinal surgery and both cause persistent pain, but arachnoiditis tends to produce more diffuse, burning pain and is generally harder to treat because the scarring directly involves the nerve tissue itself. When the two occur together, as they often do, the combination makes reoperation particularly challenging and reduces the likelihood of a good surgical outcome.