What Anesthesia Is Used for Knee Replacement?

Spinal anesthesia is the most widely used primary technique for total knee replacement today, often combined with one or more peripheral nerve blocks and a local anesthetic injection around the joint itself. General anesthesia remains a safe and effective alternative, and in some patients it is the better choice. The real story is that modern knee replacement anesthesia is rarely a single drug or single technique; it is a layered strategy designed to control pain from multiple angles while getting you moving as quickly as possible after surgery.

Spinal Anesthesia and Why It Became the Default

If you are scheduled for a knee replacement, there is a strong chance your anesthesiologist will recommend a spinal. Data from a large historical comparison at one center showed that spinal anesthesia use for knee replacement jumped from about 24% of cases in the early 2000s to over 96% by the late 2010s and early 2020s.¹ That shift happened because accumulating evidence showed spinal anesthesia offered a modestly shorter hospital stay and lower odds of certain complications compared with general anesthesia, without introducing new major risks.

A systematic review comparing neuraxial techniques (spinal or epidural) with general anesthesia across multiple studies found that neuraxial anesthesia reduced length of stay by roughly half a day on average, while showing no significant differences in mortality, surgical site infections, blood clots (when standard prevention was used), or nerve injuries.² A large database study reinforced this, finding that spinal anesthesia was linked to lower odds of staying in the hospital more than three days, lower 90-day readmission rates, and lower rates of revision surgery within 90 days.³ A retrospective study from Singapore similarly found that patients receiving regional anesthesia went home about a day sooner than those under general anesthesia after adjusting for other factors.⁴

During a spinal, the anesthesiologist injects a small dose of local anesthetic into the fluid around the spinal cord in the lower back. You lose sensation and the ability to move your legs for a few hours. You stay awake or lightly sedated, depending on your preference, and the surgical team can get to work without you feeling a thing below the waist.

When General Anesthesia Is Used Instead

General anesthesia has not disappeared from knee replacement. It is used when a patient has a condition that makes spinal anesthesia unsafe or impractical, such as bleeding disorders, certain spinal abnormalities, infections near the injection site, or very low blood pressure.⁵ Some patients are also anxious about being awake during surgery and strongly prefer to be fully asleep, which is a valid reason that anesthesiologists take seriously.

Under general anesthesia for knee replacement, you are given intravenous drugs to put you to sleep and keep you pain-free, your airway is typically secured with a laryngeal mask, and you breathe with the help of a ventilator. Anesthesia is maintained with a continuous infusion of medications, adjusted throughout the procedure to keep you at the right depth of unconsciousness.⁶

One randomized trial actually found that modern general anesthesia using target-controlled drug infusions led to a shorter time to meeting discharge criteria, less nausea and dizziness, and earlier walking compared with spinal anesthesia alone. Patients in the spinal group also had higher pain scores after the initial numbness wore off and were more likely to say they would choose a different method next time.⁷ This highlights an important nuance: a spinal on its own, without the additional nerve blocks and multimodal pain strategies that are now routine, can leave you in considerable pain once it wears off. The advantage of spinal anesthesia in modern practice comes from combining it with those additional layers of pain control.

Spinal Versus Epidural Versus Combined

The term “neuraxial anesthesia” covers three related options. A spinal is a single injection that provides dense, fast-onset numbness lasting a few hours. An epidural involves threading a thin catheter into the space just outside the spinal membrane, which allows continuous or repeated doses for longer-lasting pain control that extends into the postoperative period. A combined spinal-epidural does both: a spinal injection for immediate surgical anesthesia, plus an epidural catheter that can be used afterward for pain management.

Among these, the single-shot spinal has emerged as the preferred technique for knee replacement. A study of joint arthroplasty patients found that compared with a combined spinal-epidural, a plain spinal was associated with lower odds of cardiac, lung, gut, and blood-clot complications, along with shorter hospital stays.⁸ Epidurals do have an advantage in managing postoperative inflammation, which some research suggests could matter for recovery. One study found that epidural anesthesia followed by epidural pain relief produced a smaller inflammatory response than spinal anesthesia followed by intravenous morphine.⁹ But this benefit comes with a practical cost: epidural catheters are associated with significantly higher rates of urinary retention. One study found urinary retention in nearly half of patients with continuous epidural analgesia compared with under 7% of those who received a single-shot femoral nerve block.¹⁰ Since getting a urinary catheter is unpleasant and slows you down, most centers have moved away from epidurals for knee replacement in favor of the spinal-plus-nerve-block approach.

The Adductor Canal Block

If you talk to someone who had a knee replacement in the 2000s, they might mention a “femoral nerve block” that made their whole thigh numb and weak. That technique worked well for pain but had an obvious drawback: it knocked out the quadriceps muscle, making it hard or even dangerous to stand and walk in the first day or two after surgery. The adductor canal block has largely replaced it because it targets the sensory nerves heading to the knee while mostly sparing the motor nerves to the quadriceps.

A meta-analysis pooling data from multiple randomized trials found that patients receiving an adductor canal block had significantly better preserved quadriceps strength and better early mobility compared with those who received a femoral nerve block. The adductor canal block group also had a shorter average hospital stay.¹¹ Another meta-analysis found a roughly 70% reduction in fall risk with the adductor canal block compared to the femoral nerve block.¹² That is a meaningful safety difference, especially for older patients who are already at higher risk of falling in the hospital. The adductor canal block has become the workhorse peripheral nerve block for knee replacement, used in over 70% of cases in modern practice at centers that track their trends.¹

The IPACK Block for Posterior Knee Pain

One gap in the adductor canal block is that it primarily covers the front and inner side of the knee. The back of the knee, innervated by different nerves, can remain a source of pain. This led to the development of the IPACK block, which stands for “infiltration between the popliteal artery and capsule of the knee.” The anesthesiologist uses ultrasound to deposit local anesthetic behind the knee, targeting the nerves that supply the posterior joint capsule without affecting the muscles of the lower leg.

The evidence for IPACK is still evolving, and the results are mixed. One study incorporating IPACK into a multimodal pain protocol found that patients who received it after surgery had lower pain scores on the day of surgery compared with those who received it beforehand.¹³ However, a separate study found that while the IPACK group had statistically lower resting pain scores in the recovery room, the difference was small enough to be questionable clinically, and there was no benefit in pain during physical therapy, opioid consumption, walking distance, or length of stay. That study concluded that routine use of the IPACK was not supported.¹⁴ Some centers still offer it as part of their standard protocol, while others reserve it for patients who have significant posterior knee pain. The research has not reached the clear consensus that exists for the adductor canal block.

Periarticular Injection During Surgery

Alongside whatever nerve block you receive, your surgeon will likely inject a cocktail of medications directly into and around the knee tissues during the operation itself. This is called periarticular injection or local infiltration analgesia. The cocktail typically contains a long-acting local anesthetic like ropivacaine or bupivacaine, and research has shown that adding an anti-inflammatory drug (ketorolac) or a corticosteroid to the mix provides additional pain relief.¹⁵ Including morphine in the cocktail, on the other hand, does not add meaningful benefit and may increase nausea.

A study that compared the injected knee with the non-injected knee in patients undergoing bilateral knee replacement (a built-in control group) found significantly lower pain scores in the treated knee for the first 48 hours. Patients also reached 90 degrees of knee bending about a day sooner in the injected knee.¹⁶ A review of the technique found periarticular injection to be equivalent to peripheral nerve blocks for postoperative pain management.¹⁷ In many centers, both a nerve block and a periarticular injection are used together as overlapping layers of the same pain strategy.

Multimodal Pain Management and Reducing Opioids

The broader trend in knee replacement anesthesia is “multimodal analgesia,” which is the medical way of saying “attack pain from every available direction so no single drug has to do all the work.” Instead of relying heavily on opioids after surgery, the modern approach stacks non-opioid oral medications (anti-inflammatories, acetaminophen, sometimes a nerve-pain medication like gabapentin), a nerve block, a periarticular injection, and careful use of ice and early physical therapy. Opioids become the backup, not the foundation.

This approach works. One study found that implementing a multimodal opioid-sparing protocol that included periarticular bupivacaine injection and non-opioid oral medications produced better pain relief and faster functional gains with fewer rescue opioid doses compared with traditional opioid-based protocols.¹⁸ In a case series of 40 patients managed with a multimodal opioid-sparing strategy, about two-thirds recovered without taking any oral opioids at all. Among patients who had never used opioids before surgery, only about 16% needed them afterward.¹⁹ An earlier study implementing a comprehensive multimodal protocol showed shorter hospital stays, better pain control at rest, greater walking distance on the first two days, and less total narcotic use.²⁰

Sedation During Spinal Anesthesia

If you are getting a spinal, you will not feel the surgery, but you might not want to hear the conversation in the operating room or the sounds of the procedure. Most patients receive some level of sedation through an intravenous line to keep them relaxed, drowsy, or lightly sleeping. The two main sedation options are propofol, which acts quickly and wears off fast, and dexmedetomidine, which provides a more natural-feeling sedation and has analgesic properties of its own.

A randomized trial comparing the two found that dexmedetomidine led to substantially less fentanyl consumption in the first 48 hours after surgery and lower pain scores at every measured time point, from 6 through 48 hours post-surgery.²¹ That is a meaningful practical advantage. The choice of sedation drug might sound like a minor detail compared with the main anesthetic technique, but it contributes to how comfortable you are in the hours after surgery.

Cognitive Effects in Older Patients

One concern that comes up frequently for older patients and their families is postoperative confusion or cognitive fog. This short-lived cognitive dip, sometimes called postoperative cognitive dysfunction, is more common after major surgery in people over 65. There is evidence suggesting that spinal anesthesia carries a lower risk of this problem compared with general anesthesia.

A study comparing the cognitive effects of general anesthesia using sevoflurane with spinal anesthesia plus intravenous sedation in elderly patients undergoing joint replacement found that cognitive impairment occurred in half of the general anesthesia group but in only about 17-27% of the spinal anesthesia groups, depending on which sedation drug was used. Postoperative delirium was also roughly twice as common with general anesthesia.²² Another study looking specifically at hip and knee surgery patients found some differences in cognitive outcomes favoring epidural over general anesthesia, though the differences narrowed after statistical correction for multiple comparisons.²³ The effect is typically temporary, but for a patient in their seventies or eighties, even a day or two of confusion can increase fall risk and slow the start of rehabilitation.

Nerve Injury Risk

Any surgery around the knee carries a small risk of nerve injury, and a natural question is whether the anesthetic itself makes that risk higher. A 20-year study tracking nerve injuries after knee replacement found an overall incidence of about 0.8%. The reassuring finding was that nerve injury was not associated with the use of peripheral nerve blocks or the type of anesthesia (spinal versus general). The factors that did increase risk were longer tourniquet time and having both knees done in the same session.²⁴ One caveat from the same study: patients who did develop nerve injury after receiving a peripheral nerve block were less likely to recover fully from the nerve problem. This does not mean the block caused the injury; it may simply mean the block masked early symptoms or that there was an overlap of surgical and block-related nerve stress.

Femoral nerve blocks specifically carry a complication rate of about 2%, mostly sensory changes like numbness or tingling in the thigh area. This rate was higher in women and in patients who received a single large injection rather than a continuous catheter technique.²⁵ This is another reason the field has shifted toward adductor canal blocks, which involve a smaller, more targeted injection.

Getting Moving After Surgery

The ultimate goal of the anesthetic plan is not just to get you through surgery comfortably but to have you walking and bending your knee within hours of leaving the operating room. The reason modern protocols layer so many pain-control techniques together is that early mobilization is one of the strongest predictors of a good long-term outcome from knee replacement.

Peripheral nerve blocks using low doses of local anesthetic have been shown to improve participation in physical therapy on the first postoperative day. One study found that over 96% of patients who received nerve blocks were able to participate in physical therapy on postoperative day one, compared with 57% of those who did not.²⁶ Enhanced recovery protocols that bundle spinal anesthesia, nerve blocks, periarticular injection, and structured physical therapy have become standard at high-volume joint replacement centers. In one hospital, introducing such a protocol significantly reduced length of stay even after controlling for other variables.²⁷

Does Tourniquet Use Affect Pain Outcomes?

Many surgeons use a tourniquet on the thigh during knee replacement to reduce bleeding and improve visibility. Patients sometimes worry that the tourniquet squeezing their leg will cause extra pain afterward, especially under regional anesthesia where they might become aware of it. A randomized controlled trial that compared four groups — spinal with and without tourniquet, and general with and without tourniquet — found no significant differences in postoperative opioid consumption between any of the groups. Whether you had a tourniquet or not, and whether you were under spinal or general anesthesia, did not meaningfully change how much pain medication you needed. The one notable finding was a somewhat higher rate of vomiting in the spinal anesthesia groups compared with general anesthesia.²⁸

What About Costs?

You might assume that avoiding general anesthesia and its associated equipment would save money. The reality is less clear-cut. A Canadian cost comparison found no significant difference in perioperative costs or total hospital costs between spinal and general anesthesia for joint replacement, and no significant difference in length of stay either.²⁹ A Korean study using national insurance data did find higher overall costs in the general anesthesia group, which the authors attributed partly to higher complication rates and more frequent ICU admissions.³⁰ The cost picture depends heavily on the healthcare system, the specific complications that arise, and how quickly a patient gets discharged. For most patients, cost should not drive the anesthesia decision; the clinical factors and your own preferences matter more.

How the Decision Gets Made

In practice, the anesthesiologist evaluates your medical history, current medications, body habitus, and any previous experiences with anesthesia. Conditions like significant spinal stenosis, prior lower-back surgery with hardware, active blood-thinning therapy that cannot be paused, or a local infection near the injection site can all rule out a spinal. Severe anxiety about being awake is also taken seriously, because a patient who is distressed during surgery does not have a good experience regardless of what the textbooks say about outcomes.

Obesity can make spinal anesthesia technically more difficult, and it may affect how the drug spreads once injected, potentially making the block less predictable. Your anesthesiologist will weigh this when making a recommendation. Similarly, patients with certain neurological conditions may be better served by general anesthesia to avoid any theoretical risk of worsening a pre-existing nerve problem.

The conversation should be a genuine two-way discussion. If you have had a bad experience with one technique in the past, say so. If you strongly prefer to be asleep, that is a legitimate preference — the outcome differences between modern spinal and modern general anesthesia, while real, are modest enough that patient comfort and safety in the specific clinical situation should be the deciding factors.