Genicular Nerve Block (Diagnostic Knee Block)

Key facts

Who it is for

How a genicular nerve block works

The knee's sensation is carried by a group of small nerves called the genicular nerves that wrap around the ends of the femur and tibia. Three of them run at predictable spots against bone: the superomedial genicular nerve (inner side, above the knee), the superolateral genicular nerve (outer side, above the knee) and the inferomedial genicular nerve (inner side, below the knee). A fourth, the inferolateral nerve, is deliberately left alone because it runs close to the common peroneal nerve, which lifts the foot.

In knee osteoarthritis, pain signals from the worn joint travel through these nerves. Numbing them with about 1–2 mL of local anesthetic at each site does not treat the arthritis; it temporarily switches off the signal. If your usual pain, including pain with standing and walking, drops by at least 50% during the anesthetic window and then returns, the nerves are confirmed as the pathway and genicular radiofrequency ablation of the same three nerves has a good chance of giving 6–12 months of relief. If the block does little, ablation is unlikely to work and we look at other options.

The block is done under fluoroscopy (X-ray), which shows the bony landmarks where each nerve crosses, or under ultrasound, which shows the small artery that runs with each nerve. Both are accurate; ultrasound avoids radiation and is useful in pregnancy or when the knee contains metal from a replacement.

Who this test is for

Knee arthritis, not ready or not eligible for replacement. This is the largest group. Some patients are too young for a replacement that will wear out, some are waiting for a surgery date, and some cannot safely have surgery because of heart, lung, kidney or weight-related risk. Genicular ablation gives these patients months of relief at a time without affecting a future replacement.

Pain after total knee replacement. Around 1 in 5 people still have meaningful knee pain a year after replacement. Once the surgeon has ruled out infection, loosening, instability and malalignment, the remaining pain is often carried by the same genicular nerves, and ablation is one of the few options that does not involve another operation. The block and ablation are done at the skin and bone surfaces away from the implant.

Not a fit. Pain from a torn meniscus or ligament, a hot swollen joint, or a replacement that is loose or infected needs a different answer first.

What happens on procedure day

1. Check-in: we record your baseline knee pain (0–10) at rest and with walking, confirm blood-thinner and allergy details, and hand you a pain diary. Take your usual medications but no extra pain medication that morning.
2. Positioning: you lie on your back with a roll under the knee. The skin around the knee is cleaned and draped. No sedation is used.
3. Numbing: a small amount of lidocaine in the skin at three points, two above the knee and one below on the inner side.
4. Needle placement: under X-ray (or ultrasound), a thin needle is guided to the bone at each of the three genicular nerve targets, where the shaft of the femur or tibia meets the flared end. Position is confirmed in two views.
5. Injection: 1–2 mL of local anesthetic at each site. The whole injection phase takes a few minutes.
6. Testing: after 15–30 minutes we ask you to stand, walk the hallway, and climb a step if that normally hurts, and record your pain. You then go home (driving yourself is usually fine) and keep rating pain hourly for 6 hours.

After the block

First 6 hours. This is the test window. Walk, stand and do the activities that usually hurt, and rate your pain every hour on the diary. Note the time the pain returns. Avoid extra pain medication during this window unless you must (and write it down).

That evening. Expect your usual knee pain to be back. Mild soreness or bruising at the three needle sites for 1–2 days is normal; ice helps.

Next 1–3 weeks. We review the diary. At least 50% relief during the anesthetic window is a positive result and we request authorization for genicular ablation, usually scheduled 2–4 weeks later. If your insurer requires a second confirmatory block, it is done on a separate day. A clearly negative block is not repeated.

Call us for fever, a hot or swollen knee, redness or drainage at the sites, or foot weakness that persists beyond the day.

What the evidence shows

Genicular nerve blocks were introduced alongside genicular radiofrequency ablation, and the ablation evidence is the reason the block matters. In the first randomized sham-controlled trial (Choi and colleagues, 2011), patients selected with a positive genicular block had significantly better pain and function at 12 weeks after ablation than after sham. In a larger multicenter trial of cooled genicular RFA versus steroid injection (Davis and colleagues, 2018), 74% of ablation patients had at least 50% relief at 6 months versus 16% after steroid.

The honest caveat is about the block itself. One randomized trial (McCormick and colleagues, 2018) found that patients selected with a genicular block did not have better ablation outcomes than patients who skipped the block, which raises the question of whether the test adds value. Most insurers still require a positive block, some require two, and we use it because a clearly negative block spares a patient an ablation that is unlikely to help. We tell patients that the block is a reasonable screen rather than a perfect predictor.

The block has no meaningful therapeutic effect on its own and contains no steroid; occasional reports of relief lasting days are placebo or coincidence, and insurers do not cover repeated blocks as treatment.

Alternatives and what comes next

A positive block leads to genicular RFA. A negative block, or a patient who prefers injections, points toward knee joint injections with steroid, or toward a surgical opinion about knee replacement. Exercise, weight management and bracing remain the foundation of osteoarthritis care whichever route is chosen. Genicular nerve blocks are performed at our Houston and Webster offices, and in Pearland when that office opens in November 2026.

Safety and preparation

• Blood thinners: a genicular block is a low bleeding-risk procedure and most patients continue their usual medications. Tell us about warfarin, apixaban, rivaroxaban, dabigatran, clopidogrel, ticagrelor, enoxaparin and aspirin; we decide with your prescriber whether any change is needed. Never stop a blood thinner on your own.
• Diabetes: no steroid is used, so blood sugar is not affected. Eat and take your medication normally.
• Infection or fever: we reschedule if you have a fever, a skin problem over the knee, or a hot, swollen joint; a replaced knee with any sign of infection needs the surgeon, not a block.
• Allergies (contrast, steroid, local anesthetic): tell us about reactions to lidocaine, bupivacaine or dental numbing. Contrast is rarely needed; no steroid is used.
• Pregnancy: tell us if you are or could be pregnant; the block can be done with ultrasound instead of X-ray.
• Sedation and driving: no sedation is used, so that the test is accurate. Most people drive themselves home; if you prefer, bring a driver.
• Pain medication on the day: take your usual scheduled medications but no extra or as-needed pain medication the morning of the block or during the 6-hour diary window unless necessary.
• Knee replacement: bring your surgeon's most recent note or X-ray report so we have confirmation that infection and loosening have been excluded.

Risks and side effects

Frequently asked questions

Related care

Related treatments

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