Nerve pain after knee replacement

Why pain can persist after knee replacement

Total knee replacement relieves pain for most people, but about 20% report ongoing pain after surgery.^[1] Ongoing pain has many possible sources. Your surgeon will first look for problems with the implant such as loosening, misalignment, instability and infection. If these are excluded, a nerve problem becomes more likely.^[4]

Neuroma formation in the infrapatellar branch of the saphenous nerve is an underrecognized cause of persistent front-of-knee pain after knee replacement.^[2] This small nerve crosses the front of the knee, and damage to it is often the result of surgery. It has also been linked to anterior cruciate ligament reconstruction and other knee operations, and other causes include entrapment of the nerve, neuromas and benign nerve-sheath tumours.^[3]

Symptoms that suggest a nerve

• burning, electric or shooting pain at the front or inner side of the knee
• numbness or a hypersensitive patch of skin near the scar
• a small tender spot along the path of the nerve, where tapping sends a tingling or shock-like feeling
• pain that persists beyond the usual recovery period

These are clues, not proof. Knee stiffness, swelling or instability can have other causes and need their own evaluation.

How it is evaluated

Your knee surgeon usually leads the first part of the evaluation to exclude problems with the implant. Features that point to the nerve include a positive Tinel sign, which is tingling when the nerve is tapped, and relief of pain after a selective nerve block with local anaesthetic.^[4] In a study of 55 people with suspected infrapatellar saphenous neuralgia after knee surgery, 37 responded to a diagnostic block. A positive Tinel sign and the absence of knee instability predicted a good response, and every person with full relief after nerve treatment had a neuroma or an entrapped nerve on imaging.^[5] Ultrasound can show a neuroma or scarring around the nerve. Diagnostic blocks and imaging are arranged with another specialist.

Your own pain history also matters. A review of 15 studies found a higher risk of long-term pain after knee replacement in people who had nerve-type pain (neuropathic-like pain) or heightened pain sensitivity (central sensitisation) before their operation.^[6]

Treatment options

• Non-surgical: desensitization, padding or a knee sleeve, medicines for nerve pain (see non-surgical treatment), and injections around the nerve
• Procedures that interrupt the nerve’s signal, such as radiofrequency ablation of the genicular nerves, or cryoablation. A review of studies of genicular radiofrequency ablation for pain after knee surgery found only low-quality evidence of benefit.^[7] Another review reported that pain improved for up to three months with few complications.^[8]
• Surgery on the nerve: removing the neuroma (neurectomy, also called selective denervation) or releasing a trapped nerve^[3,2]

In a study of 15 people with pain lasting more than six months after knee replacement who had the neuroma removed, pain scores fell from 8.6 to 0.8 out of 10 at an average of eight months.^[4] In another series of 13 people, pain improved by an average of 4.2 points on a 10-point scale.^[2] These are small, uncontrolled studies with short follow-up, so the results may not apply to everyone.

Which treatment fits

The plan depends on how strongly the nerve block relieved your pain, whether the joint is stable, the implant’s condition, and your other health conditions. Feelings of anxiety, worry about pain, and depression before surgery were linked to a harder early recovery in one study, and are addressed as part of care.^[1] For neuromas elsewhere in the leg, see painful neuroma of the foot, ankle and leg and neuroma surgery options.

When to seek care

Consider an evaluation if knee pain after a replacement is burning, electric or numb, or lasts beyond the expected recovery period.