What Causes Chills After Knee Replacement Surgery?

Chills after knee replacement surgery are overwhelmingly caused by a drop in core body temperature during the operation itself, driven by anesthesia’s disruption of your body’s normal heat regulation. Roughly one in five patients who undergo total knee arthroplasty develops postoperative shivering, and the triggers range from straightforward cold exposure in the operating room to subtler factors like pain medications and the body’s inflammatory reaction to surgical trauma. While these chills are uncomfortable and sometimes alarming, they are usually a predictable physiological response rather than a sign of serious complication, though there are specific warning signs worth knowing.

How Anesthesia Disrupts Your Internal Thermostat

Your body normally maintains its core temperature within a narrow range by constantly balancing heat production and heat loss. Anesthesia throws this balance off in a fundamental way. Both general anesthesia and regional techniques like spinal or epidural blocks suppress the brain’s thermoregulatory center, lowering the threshold at which your body recognizes it is getting cold and triggers warming responses like shivering or redirecting blood to your core. The result is that your temperature can drift downward for a significant period before your body even registers the problem.

In one study of patients undergoing hip and knee arthroplasty under combined epidural-general anesthesia, core temperature dropped significantly within 30 minutes of anesthesia induction in all patients. By the end of surgery, those who received no active warming had lost about 2.0°C from their baseline temperature, a substantial drop that the body would ordinarily fight hard to prevent.¹ That kind of heat deficit means your body has significant catching up to do once the anesthesia wears off, and shivering is its primary tool for generating heat quickly.

What makes this more confusing for patients is that shivering can occur even when core temperature is technically normal. The phenomenon is not fully understood, but pain and the rapid clearance of short-acting opioids from the system are thought to play a role. Your body’s thermoregulatory wiring can misfire during recovery even without actual hypothermia, producing involuntary muscle contractions that feel identical to being cold.²

The Operating Room Is Deliberately Cold

Operating rooms are kept cool for good reason: surgeons wearing layers of sterile gowns and working under bright lights need a comfortable working temperature, and cooler air reduces bacterial growth. But for a patient lying still on a table with large areas of skin exposed, the OR environment works against maintaining body heat. Knee replacement surgery specifically involves exposing the joint and surrounding tissue, creating a direct avenue for heat loss.

A study of 685 knee replacement patients found that when the operating room temperature was 21°C (about 70°F) or lower, the odds of postoperative shivering roughly tripled compared to warmer rooms.³ The same study identified intravenous fluid volume as another independent risk factor: receiving more than 1,500 mL of IV fluids during surgery nearly doubled the odds of shivering. Room-temperature IV fluids flowing directly into your bloodstream act as a sustained internal cooling system during a procedure that can last two hours or more.

This is why warming intravenous fluids has become a focus in orthopedic surgery. Research on knee arthroplasty patients found that those who received warmed IV fluids were more likely to maintain a perioperative temperature above 36.5°C and experienced shorter hospital stays compared to those who received standard-temperature fluids.⁴ The temperature of the fluids matters because even small persistent drains on core body heat add up over a long procedure.

Who Is Most Likely to Get the Chills

Not everyone shivers after knee replacement, and certain patient and surgical characteristics make it more or less likely. The same large study that identified room temperature and fluid volume as risk factors also found that age over 65 and anesthesia duration exceeding 150 minutes were independent predictors. Longer time under anesthesia means more time for heat to escape, and older patients tend to have less efficient thermoregulatory responses.³

Interestingly, separate research looking at shivering even in patients whose core temperature was maintained after surgery found that younger patients were actually at higher risk when other factors were accounted for. In that analysis, each additional year of age slightly reduced shivering odds, and longer operation time increased them. The study also found that higher concentrations of the opioid fentanyl at the time the breathing tube was removed reduced shivering, as did receiving acetaminophen during surgery.⁵ The age finding seems contradictory at first, but the distinction matters: older patients are more vulnerable to hypothermia-driven shivering, while younger patients may be more prone to the non-hypothermic kind, where the body shivers despite a normal temperature. The two pathways can produce different risk profiles depending on the circumstances.

Pain Pumps and Opioid Withdrawal

One cause of post-surgical chills that surprises many patients involves the very medications designed to keep them comfortable. Pain pumps, which deliver a continuous or intermittent mix of opioids and local anesthetics directly to the surgical site or into the bloodstream, were identified as an independent risk factor for shivering after knee replacement.³

The mechanism involves how opioids interact with the brain’s temperature control center. Opioid drugs suppress the hypothalamus’s sensitivity to cold, essentially raising the bar for when the body decides to generate heat. While the drugs are flowing, you might not feel cold even though your temperature is dropping. But as opioid levels fluctuate or decline, the thermoregulatory center “wakes up” and reacts to the deficit all at once, triggering intense shivering. This is sometimes described as acute opioid withdrawal in the context of anesthesia, even though the patient has not been on opioids long-term. Short-acting narcotics like fentanyl and remifentanil are particularly associated with this rebound effect because they clear the system quickly.²

The practical takeaway is that chills after knee surgery are not always a sign that something went wrong with temperature management. They can be a side effect of the pain management strategy itself, and your surgical team expects this possibility.

Inflammatory Reactions and Bone Cement

Knee replacement surgery is significant trauma to the body, and the immune system responds accordingly. The installation of a prosthetic joint involves cutting bone, inserting metal and plastic components, and in many cases securing them with polymethylmethacrylate (PMMA) bone cement. Each of these steps provokes an inflammatory response that can produce fever and chills independent of infection.

Research comparing cemented and uncemented hip replacements found that patients who received PMMA bone cement had significantly higher levels of inflammatory markers, including histamine, TNF-α, IL-6, and C-reactive protein, compared to those with uncemented implants. The polymerization of the cement releases heat and residual chemical monomers that trigger both local and systemic inflammatory cascades.⁶ The same cement is widely used in knee replacements. Histamine release in particular can produce chills, flushing, and a general feeling of unwellness that mimics an allergic or infectious reaction.

Autotransfusion, the practice of collecting blood lost during surgery and returning it to the patient, can produce a similar inflammatory response. A study of 40 autotransfusion events in knee replacement patients found that the most common adverse reaction was a rise in temperature, attributed to cytokines and other inflammatory mediators that accumulate in the collected blood.⁷ These fevers tend to be self-limiting but can be accompanied by chills that feel concerning in the moment.

Blood Transfusion Reactions

If you needed a blood transfusion after knee replacement due to surgical blood loss, chills could signal a transfusion reaction. These reactions range from mild febrile responses to life-threatening immune-mediated events. A case report documented a knee replacement patient who developed fever, chills, palpitations, and rapid breathing after receiving a one-pint packed red blood cell transfusion for significant postoperative blood loss.⁸

The onset of chills during or shortly after a blood transfusion is treated as a red flag by nursing staff. The transfusion is typically stopped immediately while the team evaluates whether the reaction is a simple febrile response (common and usually harmless) or something more dangerous like a hemolytic reaction, where the immune system attacks the transfused blood cells. Most transfusion-related chills in the orthopedic setting fall into the mild category, but the timing and context matter. If your chills begin during or within an hour of receiving blood products, tell your nurse immediately rather than waiting to see if they pass.

When Chills and Fever Point to Infection

The concern that keeps both patients and surgeons alert is infection, and chills accompanied by fever can sometimes be an early signal. Distinguishing normal postoperative temperature fluctuations from infection-related fever is one of the trickier aspects of recovery.

A study tracking 400 knee replacements found that roughly 37% of patients developed postoperative fever, with most reaching their peak temperature on the day of surgery itself. That early fever is almost always a normal inflammatory response. The picture changes in the weeks that follow. Among patients who developed fever with a peak of 38°C or higher during weeks two through four after surgery, the causes included respiratory infections, urinary tract infections, superficial wound infections, and in one case, a deep periprosthetic infection.⁹ The timing matters: fever on day one is expected, but new or worsening fever that appears a week or more after surgery warrants investigation.

Periprosthetic joint infection, an infection around the implant itself, is the most feared complication. A meta-analysis of chronic periprosthetic joint infections found that about 38% of patients with a confirmed infection had fever, while pain was present in roughly 86% and local signs of inflammation in about 62%.¹⁰ Chills paired with a warm, swollen, increasingly painful knee and persistent fever are the combination that should prompt urgent evaluation. Chills alone on day one or two after surgery, without those additional red flags, are far more likely to reflect anesthesia recovery, medication effects, or normal inflammation.

Pneumonia and Other Non-Joint Infections

It is worth noting that infections causing postoperative chills do not always involve the knee itself. Respiratory and urinary tract infections were the most common identifiable causes of delayed fever in the study cited above, outnumbering wound and joint infections combined. A prospective study using CT scans found that about 14% of knee replacement patients had radiographic evidence of pneumonia after surgery under general anesthesia, though only one patient in that group developed obvious symptoms like fever and productive cough.¹¹

This disconnect between imaging findings and symptoms suggests that mild pulmonary complications after knee surgery are more common than typically recognized. If you develop chills along with a cough or shortness of breath in the days following surgery, it is worth mentioning to your care team even if the knee itself looks fine. Urinary tract infections are similarly common in the postoperative period, especially in patients who had an indwelling catheter during surgery, and they can produce fever and chills that have nothing to do with the joint.

How Hospitals Prevent Hypothermia During Surgery

Knowing that perioperative hypothermia drives most postoperative shivering, surgical teams have developed specific strategies to keep patients warm. The most effective is forced-air warming, essentially a blanket connected to a warm-air blower that covers the parts of the body not involved in the surgical field. In the study of arthroplasty patients described earlier, those who received forced-air warming maintained a core temperature close to their preoperative baseline throughout surgery, while patients covered with ordinary blankets still lost about 1.6°C.¹ Passive insulation alone was not enough to offset the heat loss caused by anesthesia and the cold OR environment.

Warmed intravenous fluids are another standard measure. Research on knee arthroplasty patients showed that those who received both warmed IV fluids and forced-air warming devices had higher perioperative temperatures and shorter hospital stays than those who received only the warming device.⁴ These warming strategies are now part of enhanced recovery protocols at many hospitals, though implementation varies. If you are preparing for knee replacement surgery, asking your surgical team about their warming protocol is reasonable. Preventing hypothermia during surgery is the single most effective way to reduce the chances of uncomfortable shivering afterward.

What to Do When You Are Shivering After Surgery

If you are in the recovery room shaking uncontrollably, the nursing staff will usually check your temperature first. If you are hypothermic, active warming measures like heated blankets or a forced-air warming device will be applied. Warm IV fluids may be continued or started. In some cases, medications can help: the research on maintained-temperature patients found that acetaminophen given during surgery reduced shivering odds by about two-thirds.⁵ Other medications sometimes used to treat established shivering include meperidine (a specific opioid with anti-shivering properties) and clonidine.

For patients who are already home and experiencing chills, the important distinction is between residual recovery effects in the first day or two and new symptoms appearing later. Early chills without high fever that resolve with warm blankets and time are generally benign. New-onset chills with fever above 38°C appearing several days to weeks after surgery, especially combined with increasing knee pain, redness, or swelling, deserve a call to your surgeon. The study of 400 knee replacements found that patients who ultimately needed additional surgery for infection all had elevated inflammatory blood markers and local symptoms before the second operation, reinforcing that joint infections rarely announce themselves with fever alone.⁹

Chills Without Fever

Some patients experience a sensation of chills, goosebumps, or coldness in the operated leg specifically, without any systemic fever. This is a different phenomenon from the thermoregulatory shivering discussed above. Regional nerve blocks and epidural anesthesia can temporarily alter sensation in the affected limb, producing feelings of coldness or abnormal temperature perception that do not reflect an actual change in tissue temperature. Tourniquet use during surgery, which temporarily cuts off blood flow to the leg, can also contribute to the limb feeling cold during the immediate recovery period as blood flow returns and the tissue warms back up.

Persistent feelings of coldness in the knee area weeks or months after surgery are occasionally reported and may relate to altered nerve function around the surgical site. Knee replacement surgery inevitably disrupts small cutaneous nerves, and changes in local sensation, including temperature perception, can take months to stabilize. These localized sensations are different from the systemic shivering and chills that come from hypothermia or infection, and they do not carry the same clinical significance. If the sensation is isolated to the knee area without fever, drainage, or worsening pain, it is typically a normal part of nerve recovery rather than a reason for alarm.