What Are the Symptoms of Nerve Damage After Knee Replacement?

Nerve damage after knee replacement most commonly shows up as numbness around the knee or, in more serious cases, sudden weakness or inability to lift the front of the foot, a condition called foot drop. These symptoms tend to appear within the first hours to days after surgery, though some sensory changes develop more gradually. The specific pattern of symptoms depends on which nerve is affected, and the common peroneal nerve is by far the most frequently injured.

Which Nerve Gets Hurt Most Often

The knee sits at a crossroads for several nerves, but one is far more vulnerable than the rest. A systematic review and meta-analysis covering nearly 1.6 million knee replacements found that the common peroneal nerve accounted for roughly 85% of all nerve injury events, while tibial, femoral, sciatic, and saphenous nerve injuries together made up the remainder.¹ The reason is anatomy: the common peroneal nerve wraps around the bony head of the fibula just below the outer side of the knee, leaving it exposed to stretching, compression, and swelling in exactly the area where surgeons work. That shallow, superficial path makes it uniquely susceptible to injury during or after the procedure.

The saphenous nerve, specifically its infrapatellar branch, is another frequent casualty, though its injury produces very different symptoms. This tiny sensory nerve runs right through the area of a standard knee incision, and cutting through it is sometimes unavoidable. Because it only carries sensation and not motor signals, its damage shows up as numbness rather than weakness.

Foot Drop and Other Motor Symptoms

The hallmark motor symptom of peroneal nerve injury is foot drop: you cannot lift the front of your foot toward your shin. Walking becomes difficult because the foot slaps down with each step, and you may find yourself catching your toes on the ground or tripping. Patients typically notice this weakness in the early postoperative period, sometimes within hours of waking from surgery.² In some cases the weakness is partial, with the foot feeling floppy rather than completely paralyzed, but even mild foot drop makes normal walking unreliable.

Beyond the ankle, you may also notice difficulty turning the foot outward (eversion). If the injury extends to the tibial nerve as well, which is less common, weakness in pushing the foot downward (plantarflexion) can also develop. In rare instances, a vascular complication like a pseudoaneurysm behind the knee can compress the peroneal nerve over a period of weeks rather than hours, producing a foot drop that worsens gradually rather than appearing overnight.³ That distinction matters because a slowly worsening foot drop after knee replacement warrants urgent investigation for an underlying cause that may be treatable.

Sensory Symptoms and Numbness

Sensory changes are far more common than motor problems. In one study, about 27% of patients reported subjective numbness around the knee after their surgery.⁴ That number is striking when compared to the rate of serious nerve injury, which sits well under 1%. The explanation is that cutting through the infrapatellar branch of the saphenous nerve during the surgical incision is so common it borders on routine, and most surgeons consider it an expected trade-off rather than a complication.

The numbness typically affects the outer side of the knee and the skin below and to the side of the kneecap. You might describe it as a patch of skin that feels “dead,” tingly, or like it belongs to someone else. Some people notice hypersensitivity rather than decreased sensation, with the area around the scar feeling uncomfortably sharp or burning when touched. These sensory symptoms tend to improve over months, though for some people a zone of altered feeling persists indefinitely.

When peroneal nerve damage is involved, the sensory picture is different. Numbness or tingling spreads to the top of the foot and the outer lower leg, following the nerve’s territory rather than just the incision area. If you notice numbness on the top of your foot after knee replacement, especially paired with any weakness in lifting the foot, that combination strongly suggests peroneal nerve involvement rather than simple surgical disruption of the small skin nerves.

How Common Is Nerve Damage

The numbers depend on what you count. Minor sensory nerve disruption from the incision itself affects a substantial minority of patients, as the 27% numbness figure suggests. Clinically significant nerve injury, the kind that produces motor weakness or major sensory loss, is much rarer. A large single-institution series covering nearly 40,000 knee replacements identified confirmed nerve injuries in 0.16% of cases.⁵ A separate study of over 7,700 procedures found common peroneal nerve palsy in 0.32%.⁶ Other published estimates range as high as 4%, depending on how aggressively cases are detected and which nerve injuries are included.²

That wide range reflects genuine disagreement in the literature. Studies that use routine electrodiagnostic testing on every patient after surgery catch subclinical nerve injuries that patients never notice, inflating the rate. Studies that rely on clinical diagnosis catch only the injuries severe enough to cause obvious symptoms. The pooled estimate from the large meta-analysis came in at about 0.29% when using a more conservative analytical approach, but the heterogeneity across studies was extreme.¹ The practical takeaway: serious nerve injury after knee replacement is genuinely rare, but numbness from minor nerve disruption is not.

Who Faces Higher Risk

Certain patients are more likely to experience nerve complications. The knee alignment before surgery appears to be an important factor. Patients with a valgus deformity, where the knee angles outward in a “knock-knee” pattern, are at particular risk for peroneal nerve palsy. A systematic review of valgus knee replacements found peroneal nerve palsy in about 1.9% of cases, roughly five to ten times higher than the overall population rate.⁷ The correction of a severely angled knee requires more soft-tissue work and greater changes in limb alignment, both of which stretch the peroneal nerve.

Surgical factors also play a role. One study found that the use of a tourniquet during surgery and longer operative times were both associated with higher rates of peroneal nerve palsy.⁶ Tourniquets compress the limb to control bleeding, and the peroneal nerve sits right where that compression is applied. Intraoperative monitoring has shown that the peroneal nerve signal can disappear after about 25 minutes of tourniquet use, suggesting that prolonged tourniquet time directly threatens nerve function.⁸ Some surgeons now limit tourniquet use to specific phases of the procedure rather than the entire operation.

Women were also found to be at statistically higher risk in the peroneal nerve palsy study, and patients who developed epidural-related analgesia complications postoperatively were more likely to have nerve injury detected.⁶ One theory is that epidural pain management can mask early nerve symptoms, delaying recognition until the damage is more advanced.

When to Be Concerned Versus When to Wait

Not every unusual sensation after knee replacement means something has gone wrong. Swelling, bruising, and general soreness around the knee can cause temporary tingling or a feeling of tightness that resolves as healing progresses. The numbness from minor saphenous nerve disruption, while common, tends to decrease over time.⁴ An interesting finding from that same study: patients who were told before surgery that numbness might happen were over three times more likely to report it afterward, suggesting that awareness and attention to the area magnify the perception. That does not mean the numbness is imaginary, but it does mean that noticing a numb patch near your scar is expected and usually not a sign of significant nerve damage.

The red flags that warrant prompt medical attention are different in character. Any new weakness, especially an inability to lift the foot or toes, needs to be reported immediately. A foot that suddenly feels floppy or drags during walking is not a normal postoperative finding. Similarly, spreading numbness that extends well beyond the incision site, particularly onto the top of the foot or down the outer calf, suggests more than a minor skin nerve injury. Pain that is burning, electric, or shooting in quality and follows a line down the leg rather than staying around the knee also deserves evaluation. Time matters with motor nerve injuries; the sooner the problem is identified, the more treatment options remain available.

How Nerve Damage Is Diagnosed

In practice, peroneal nerve palsy after knee replacement is usually diagnosed clinically. When you cannot lift your foot and the top of your foot is numb, the pattern is recognizable enough that many surgeons do not immediately order additional tests. A review of 54 cases of neuropathy after knee replacement found that only a minority of patients were referred for electromyography (EMG), with the rest being observed clinically.⁹ Among those who did undergo electrodiagnostic testing, the majority showed peroneal neuropathy that was not sharply localized to one specific point, consistent with a stretch-type injury rather than a clean cut.

When the clinical picture is ambiguous, or when recovery stalls and surgical intervention is being considered, imaging and electrodiagnostic studies become more important. High-resolution ultrasound and MRI neurography are the two main imaging tools used to evaluate peripheral nerves in the lower extremity. Ultrasound offers the advantage of real-time visualization and can quickly identify swelling, compression, or structural disruption of the nerve, while MRI provides excellent contrast between normal and abnormal nerve segments and can also detect early muscle changes from denervation.¹⁰ These studies help distinguish between a nerve that is bruised and swollen versus one that is structurally torn, which directly influences whether surgery is likely to help.

Treatment and Recovery

For sensory-only symptoms like numbness around the incision, the standard approach is watchful waiting. Most patches of numbness shrink over months as small nerves regenerate or the brain adapts to the changed sensation. No specific treatment is needed, and patients can be reassured that this type of sensory change rarely affects function.

Motor nerve injuries are managed differently and on a tighter timeline. The initial treatment is almost always conservative: an ankle-foot orthosis (a lightweight brace that holds the foot up to prevent tripping), physical therapy to maintain range of motion and prevent joint stiffness, and close monitoring to track whether any recovery is occurring. Many peroneal nerve palsies after knee replacement do improve on their own, particularly when the mechanism is stretching or compression rather than a clean transection. Nerves regenerate slowly, roughly a millimeter per day, so patience is required. Improvement can continue for a year or more.

When conservative management fails and the foot drop persists, surgical decompression of the peroneal nerve is an option. In one early series of five patients who had not improved with extended conservative care, all demonstrated improved nerve function after operative decompression, with four of the five achieving full recovery and all able to stop wearing their ankle-foot braces.¹¹ More recent reports have explored acute decompression, performed within days rather than months of the injury, with similarly encouraging results including full neurological recovery.¹² The evidence base for surgical decompression is limited to small case series rather than randomized trials, but the existing data is consistently positive enough that most surgeons consider it reasonable when recovery has plateaued.

Persistent Pain After Knee Replacement and Nerve-Targeted Procedures

Some patients develop chronic knee pain after replacement that does not have a clear mechanical explanation. The implant looks well-positioned on imaging, there is no infection, and the joint is stable, but the knee still hurts. In a subset of these cases, nerve-related pain is the culprit, either from neuroma formation at a severed nerve ending or from ongoing irritation of the small genicular nerves that supply the knee capsule.

One approach that has gained attention is pulsed radiofrequency treatment of the genicular nerves. This technique uses ultrasound or X-ray guidance to deliver short bursts of radiofrequency energy to the nerves supplying the knee joint, aiming to disrupt pain signaling without destroying the nerve. It has been used for osteoarthritis pain and for residual pain after knee replacement when no other cause can be identified.¹³ In a small study that included patients with prior knee replacement, the majority in the post-arthroplasty group experienced at least a 50% reduction in pain scores at three months after the procedure.¹⁴ The results are promising but based on very small numbers, and longer-term data is still limited.

What Patients Often Get Wrong

A common misconception is that any numbness around the knee after replacement indicates something went wrong during surgery. Given that roughly one in four patients reports numbness, and that the surgical incision itself almost inevitably damages tiny sensory branches, numbness near the scar is closer to an expected outcome than a complication. It is worth mentioning to your surgeon, but it is rarely a cause for alarm.

Another misunderstanding involves the timeline of nerve recovery. Patients sometimes assume that if foot drop or significant numbness has not resolved within a few weeks, the damage is permanent. Peripheral nerves are slow healers. The regeneration rate of about a millimeter per day means that a nerve injured near the knee may take many months to send signals all the way down to the muscles and skin of the foot. Recovery that has not begun by six months is more concerning, but continuing improvement at nine or twelve months is well within the range of normal nerve healing.

There is also a tendency to assume that nerve damage during knee replacement is caused by the surgeon cutting a nerve. While that does happen with the small infrapatellar sensory branch, the more significant peroneal nerve injuries are usually caused by stretching, compression from swelling, or tourniquet effects rather than direct surgical trauma. The peroneal nerve is not in the direct surgical field, and surgeons are aware of its location. Understanding the mechanism can help patients make sense of why the injury happened even when the surgery itself went smoothly from a technical standpoint.

Intraoperative Prevention Strategies

Surgeons have explored several strategies to reduce the risk of nerve injury during knee replacement. One approach involves intraoperative monitoring of the peroneal nerve using electromagnetic stimulation. By tracking the nerve’s signal during the procedure, the surgical team can detect when the nerve is being compromised and adjust their technique in real time. Research using this monitoring method demonstrated that peroneal nerve signal is lost after roughly 25 minutes of tourniquet application, which has informed protocols suggesting that tourniquet use be limited to specific portions of the surgery, such as cementing the implant in place, rather than being applied throughout.⁸

For patients with significant valgus deformity, some surgeons perform a prophylactic peroneal nerve release at the time of knee replacement, loosening the tissue around the nerve before correcting the deformity to give it room to accommodate the new alignment. However, a systematic review found no significant difference in palsy rates between procedures that included a peroneal nerve release and those that did not.⁷ The evidence here is mixed enough that the decision about prophylactic release remains a matter of individual surgeon judgment rather than a settled standard of care.

1
PubMed Central. Nerve Injuries After Total Knee Arthroplasty: A Systematic Review and Meta-Analysis
2
PubMed. Acute Common Peroneal Nerve Decompression After Total Knee Arthroplasty
3
PubMed. Popliteal Artery Pseudoaneurysm with Secondary Chronic Common Peroneal Nerve Neuropathy and Foot Drop after Total Knee Replacement
4
PubMed Central. Postoperative numbness of the knee following total knee arthroplasty
5
PubMed Central. Risk Factors for Acute Nerve Injury after Total Knee Arthroplasty
6
Arthroplasty Today. Peroneal Nerve Palsy After Total Knee Arthroplasty
7
PubMed Central. Common peroneal nerve palsy after TKA in valgus deformities; a systematic review
8
PubMed Central. Intra-operative monitoring of the common peroneal nerve during total knee replacement
9
PubMed Central. Clinical spectrum of neuropathy after primary total knee arthroplasty: a series of 54 cases
10
PubMed Central. The role of high-resolution ultrasound and MRI in the evaluation of peripheral nerves in the lower extremity
11
PubMed. Surgical decompression for peroneal nerve palsy after total knee arthroplasty
12
PubMed. Acute Decompression for Peroneal Nerve Palsy Following Primary Total Knee Arthroplasty: A Report of Two Cases
13
Arthroscopy Techniques. Pulsed Radiofrequency Rhizotomy of the Genicular Nerves of the Knee Guided by Radioscopy and Ultrasonography: Step-By-Step Technique
14
PubMed Central. The Efficacy of Ultrasound-Guided Pulsed Radiofrequency of Genicular Nerves in the Treatment of Chronic Knee Pain Due to Severe Degenerative Disease or Previous Total Knee Arthroplasty