Hydrodissection is a minimally invasive procedure that uses pressurized fluid, rather than a scalpel, to separate tissues from one another. A doctor injects saline, a sugar-water solution, or a local anesthetic through a needle while watching on ultrasound, and the stream of fluid gently pushes apart layers of tissue that are stuck together, compressed, or too close to a structure that needs protection. It’s used most commonly to free pinched nerves, but surgeons also rely on it during tumor treatments and for chronic tendon problems.
How the Procedure Works
The core principle is simple: the fluid does the work, not the needle. Under real-time ultrasound guidance, a clinician positions a thin needle near the target area and slowly injects fluid. That fluid fans out in front of the needle tip, peeling apart layers of soft tissue and creating a visible pocket of space on the ultrasound screen. The needle then advances into that newly opened space, and more fluid is injected to widen the separation further. This incremental process gives the clinician precise control over exactly which tissues get separated and by how much.
Ultrasound is essential to the technique. It lets the clinician see the needle, the target structure (a nerve, a tendon, or a tumor margin), and the fluid spreading in real time. This continuous visualization is what makes the procedure safe enough to perform near delicate structures like nerves and blood vessels.
Fluids Used in Hydrodissection
Three main fluids are used, and the choice depends on the goal. Normal saline (sterile salt water) is the simplest option and works well when the primary purpose is physical separation, such as creating a buffer zone around a tumor. A local anesthetic like lidocaine provides both separation and immediate pain relief, which is useful when working near irritated nerves. The third option, 5% dextrose in water (essentially a dilute sugar solution), has emerged as a preferred choice for nerve-related hydrodissection because it appears to have a direct pain-relieving effect beyond just physically freeing the nerve.
A randomized controlled trial comparing these fluids for carpal tunnel syndrome found that 10 milliliters of 5% dextrose reduced pain scores and nerve swelling significantly more than saline by the 12th week after the procedure. This suggests the fluid selection isn’t just a technical detail; it can meaningfully affect outcomes.
Nerve Entrapment: The Most Common Use
When a nerve passes through a tight space, surrounding tissue like fascia (the tough connective tissue wrapping around muscles and organs) can compress or stick to it. This creates pain, numbness, tingling, or weakness, depending on which nerve is involved. Hydrodissection addresses this by injecting fluid around the nerve to physically peel it away from whatever is squeezing it.
Carpal tunnel syndrome is one of the most studied applications. The median nerve runs through a narrow channel in the wrist, and when the surrounding tissue swells or tightens, it compresses the nerve. A randomized controlled study comparing hydrodissection to open surgery in patients with severe carpal tunnel syndrome found that both groups showed significant improvements in pain and symptom severity after three months. Pain scores dropped substantially in both groups with no statistically significant difference between them. The surgical group did show better results on nerve conduction tests and one physical exam measure, but from the patient’s perspective, both treatments provided comparable relief.
This matters because traditional carpal tunnel surgery, while effective in 70% to 90% of cases, involves an incision, a longer recovery, and the usual risks of surgery. Hydrodissection offers a needle-based alternative that many patients find less intimidating, with minimal downtime.
Tendon and Musculoskeletal Applications
Beyond nerves, hydrodissection is used for a range of chronic tendon problems. According to clinicians at Mayo Clinic, the technique may be appropriate for tennis elbow, golfer’s elbow, calcific tendinopathy (calcium deposits in tendons), plantar fasciitis, Achilles tendon problems, patellar tendinopathy (jumper’s knee), rotator cuff tendinopathy, and gluteal tendinopathy (a common cause of outer hip pain). In these cases, the pressurized fluid helps break up adhesions and scar tissue around the tendon, restoring smoother movement and reducing pain.
Protecting Organs During Tumor Treatment
Hydrodissection plays a different but equally important role in cancer treatment. When doctors use heat-based techniques like microwave ablation to destroy liver tumors, nearby organs such as the stomach, intestines, or diaphragm can be dangerously close to the treatment zone. By injecting saline between the liver and the adjacent structure, clinicians create a fluid cushion that acts as a thermal barrier, absorbing heat that would otherwise damage healthy tissue.
For this application, the goal is to achieve at least half a centimeter of separation between the tumor and surrounding structures. The saline is infused continuously during the procedure to maintain that protective gap. This technique has made it possible to safely treat tumors in locations that would previously have been considered too risky for ablation.
What the Experience Is Like
For nerve and tendon hydrodissection, the procedure is typically done in an office or outpatient setting. You lie on an exam table while the clinician applies ultrasound gel and scans the area to map out the anatomy. The skin is cleaned and sometimes numbed with a small amount of local anesthetic. A thin needle is then inserted under ultrasound guidance, and you may feel pressure or a brief sting as the fluid is injected. The entire process generally takes 15 to 30 minutes.
Because the procedure involves only a needle puncture rather than an incision, most people can return to normal activities relatively quickly. Some patients notice immediate pain relief from the anesthetic component of the injection, though the full benefits of the tissue separation develop over the following days to weeks. Repeat sessions are sometimes needed, depending on the severity of the entrapment or tendon problem.
Safety and Side Effects
Hydrodissection has a strong safety profile when performed under ultrasound guidance. A systematic review of studies on nerve hydrodissection for entrapment syndromes found no serious adverse events reported across the literature. The most common complaints were minor: temporary pain or swelling at the injection site. In one study, 4% of patients who received a placebo injection reported injection-site pain, and a small number of patients who received steroid-containing injections experienced localized swelling or skin discoloration at the injection site.
Seven of the reviewed studies reported zero complications, nerve injuries, or serious adverse events. The key safety factor is the ultrasound guidance, which allows the clinician to see exactly where the needle is at all times and avoid puncturing nerves, blood vessels, or other structures. Without imaging guidance, the risks would be considerably higher, which is why the ultrasound component is considered non-negotiable for this technique.