Can a Fall Damage a Knee Replacement?

A fall can absolutely damage a knee replacement, and the consequences range from minor bruising to fractures of the bone around the implant, torn tendons, dislocation, and even loosening of the prosthetic components. The most common serious injury is a periprosthetic fracture, where the bone next to or around the implant breaks rather than the implant itself. The replaced knee is not more fragile than a natural one in every respect, but the combination of altered bone structure, surgical changes to the surrounding soft tissue, and the physical characteristics of the implant create vulnerabilities that a fall can exploit in ways most people don’t expect.

How Falls Typically Damage a Replaced Knee

The damage a fall inflicts on a knee replacement depends on the direction and force of the impact, the time since surgery, and the condition of the surrounding bone. In roughly nine out of ten cases, the injury that triggers a periprosthetic fracture around a replaced knee is classified as “low energy,” meaning a simple trip, stumble, or fall from standing height rather than a car accident or a fall from a ladder.¹ That fact surprises a lot of people. You might assume a knee made partly of metal and plastic could shrug off a stumble, but the bone surrounding the implant is often thinner or weaker than it was before surgery, and the implant itself acts as a stress concentrator, redirecting forces in ways natural bone does not.

Lab testing on cadaver femurs (the thighbone) has confirmed that the bone around a knee implant experiences significantly higher mechanical strain during a fall-like impact than the same bone would without an implant. Neither stemmed nor stemless implant designs brought those strains back down to normal levels.² In practical terms, this means the bone beside a knee replacement is under more mechanical stress during a fall than the same bone in a knee that was never operated on.

Periprosthetic fractures are not the only risk. A fall can also rupture the quadriceps tendon, the thick tendon above the kneecap that was cut and repaired during surgery. Case reports describe quadriceps rupture occurring after something as ordinary as a stumble while walking or losing balance getting out of a chair.³ In rare cases, a fall can even dislocate the prosthetic joint entirely. One documented case involved a woman who sustained a complete anterior dislocation of her knee prosthesis after a ground-level fall at home.⁴

Why the First Few Weeks Are the Riskiest Window

Falls that happen in the early postoperative period carry especially serious consequences. During the first weeks after surgery, the surgical wound is still healing, the quadriceps repair hasn’t regained its strength, and the bone around the implant hasn’t yet remodeled to accommodate its new hardware. A study of 78 patients who fell after knee replacement found that about one in ten sustained soft-tissue injuries that led to severe complications, including deep infection, unplanned return to the operating room, and in some cases permanent loss of the joint. The factors most strongly linked to a poor outcome were copious wound bleeding immediately after the fall, falling within eight weeks of surgery, and rupturing the surgical wound and the underlying quadriceps repair.⁵

Data from a large cohort of more than 6,400 knee replacement patients showed that in-hospital falls, while uncommon at about 0.6%, tended to cluster on the first and second days after surgery. Most were caused by loss of balance or the knee buckling. The majority of these early falls resulted in no physical injury or only minor ones, but the fall group had a notably higher all-cause revision rate at follow-up compared with those who did not fall.⁶ Even a seemingly harmless stumble in the first days after surgery can set the stage for problems that surface months later, whether from subtle implant loosening or from disruption to the healing tissues.

Who Faces the Greatest Risk

Certain health conditions make the bone around a knee replacement more vulnerable to fracture from a fall. A systematic review and meta-analysis found that osteoporosis raises the odds of a periprosthetic fracture by roughly 70%.⁷ That makes intuitive sense: weaker bone breaks more easily, and the stress-concentrating effect of the implant amplifies the problem. Other recognized risk factors include older age, female sex, inflammatory arthritis, long-term corticosteroid use, and having had a prior revision surgery.⁸

In one case series of periprosthetic fractures, every single fracture followed a low-energy event like a fall, and nine of the twelve patients had at least one predisposing factor: rheumatoid arthritis requiring chronic steroids, diabetes, or obesity.⁹ That cluster of conditions isn’t unusual in people who need knee replacements in the first place, which is part of why periprosthetic fractures are such a persistent problem. People who get knee replacements tend to be older, more likely to have osteoporosis, and more likely to be on medications that thin bone, all of which stack the odds.

Why Knee Replacement Patients Fall More Often

One frustrating piece of the puzzle is that people with knee replacements are more prone to falling than the general population, not less. You might expect that replacing a painful, arthritic knee would improve balance and stability. It does eventually for many people, but the path there is not straightforward. Research has shown that both before and in the months after surgery, knee replacement patients have measurable deficits in two things that matter for staying upright: quadriceps strength and proprioception, which is your body’s sense of where your joints are in space.¹⁰

A systematic review confirmed that these deficits don’t resolve quickly. Knee extension strength, proprioception, and the symmetry of how you distribute your weight between your legs all remain impaired after surgery and continue to affect balance for months.¹¹ This creates a window where you’ve got a knee that’s still recovering, muscles that haven’t rebuilt their full strength, and a joint that doesn’t relay position information to your brain as precisely as it once did. All of that adds up to a higher chance of losing your balance, especially on uneven surfaces, stairs, or when changing direction.

The researchers behind both of these papers make a case that fall-prevention work, including targeted strengthening exercises and balance training, should begin before the surgery itself and continue aggressively afterward. The evidence is clear that waiting until someone has already had a fall to start addressing these deficits is waiting too long.

What Happens If a Fall Does Cause a Fracture

When a periprosthetic fracture does occur, treatment typically depends on two things: where the break is and whether the implant is still solidly fixed in the bone. The most common location is the distal femur, the lower end of the thighbone just above the implant. If the implant remains well fixed and stable, the standard treatment is open reduction and internal fixation, which means surgically repositioning the bone fragments and holding them together with plates and screws. A national-level epidemiologic study confirmed that fixation with plates and screws is the dominant approach for periprosthetic knee fractures, in contrast to hip fractures around implants, which more often require revision of the prosthesis itself.¹²

When the implant has loosened or the fracture pattern won’t support plate fixation, a more extensive procedure called distal femoral replacement may be necessary. This involves removing the damaged bone and the existing implant and replacing them with a larger prosthesis that bridges the gap. A comparative study found that functional scores were higher in the plate-fixation group, though the revision surgery rates were statistically similar between the two approaches. Patients who had plate fixation were more likely to need additional surgeries down the line, often because of infection or the fracture failing to heal.¹³ Neither option is minor surgery, and both carry real risks for an older patient who may already have other health issues.

Recovery from a Periprosthetic Injury Is a Different Experience

People who go through a planned knee replacement have time to prepare. They arrange help at home, set up their recovery space, do prehab exercises, and mentally steel themselves for weeks of hard work. A periprosthetic fracture from a fall allows none of that. Qualitative research with patients who sustained a periprosthetic knee fracture found that the sudden, unplanned nature of the injury leaves people feeling blindsided. The recovery is typically longer and more grueling than the original knee replacement, and patients frequently reported frustration and a sense of isolation as they worked through it.¹⁴

Part of the difficulty is physical: the bone healing has to happen on top of the existing implant, weight-bearing restrictions are strict, and the surrounding muscles that were just starting to recover from the original surgery are now set back dramatically. But a large part is psychological. Patients who had considered their knee replacement a success and were getting back to their lives suddenly find themselves back at square one or worse. The loss of independence and progress can be profoundly demoralizing, and medical teams don’t always anticipate the emotional toll as well as they anticipate the surgical challenges.

Fear of Falling and Its Downstream Effects

Even when a fall doesn’t cause visible structural damage, it can leave a lasting mark on how someone uses their knee. Fear of falling is extremely common among knee replacement patients. A study found that all participants showed elevated fear of falling after their surgery, with scores improving over the first three months but remaining well above normal.¹⁵ People who had both knees replaced showed significantly higher fear scores than those who had a single knee done, which makes sense given the greater sense of vulnerability when both legs have been through surgery.

Fear of falling isn’t just a mental health issue, though it’s that too. When people are afraid of falling, they tend to restrict their activities. They stop going for walks, avoid stairs, and move more cautiously. Over time, that reduced activity leads to further muscle weakening and balance deterioration, which paradoxically increases their actual fall risk. It’s a feedback loop where the fear of the event makes the event more likely. Breaking that cycle usually requires a deliberate, guided return to activity with a physical therapist who can help rebuild both the physical capacity and the confidence to use it.

Practical Steps to Protect a Replaced Knee

Given that most periprosthetic fractures result from low-energy events like household falls, prevention is largely about fall-proofing your environment and your body rather than avoiding extreme activities. Inside the home, the usual fall-prevention advice applies with extra urgency: remove loose rugs, install grab bars in bathrooms, keep walkways clear and well lit, and be especially careful with pets and small children underfoot. Outside, watch for uneven pavement, wet leaves, and ice.

The body side of prevention matters just as much, if not more. Continuing to strengthen your quadriceps, hamstrings, and hip muscles after the immediate postoperative period is over isn’t optional if you want to protect the investment. Balance training, even something as simple as standing on one leg while holding a countertop, directly addresses the proprioceptive deficits that the research has consistently identified as risk factors for falls in this population.¹¹

If you have osteoporosis or are on long-term steroids, it’s worth having a conversation with your doctor about bone-protective medications, because even a perfect fall-prevention program can’t eliminate every stumble. Strengthening the bone around the implant is a second line of defense for people whose bone density puts them at higher risk.⁷

When to Seek Help After a Fall

Not every fall on a replaced knee is an emergency, but some are, and telling the difference isn’t always intuitive. A fall that leaves you unable to bear weight, causes visible deformity around the knee, produces rapid swelling, or results in bleeding from the surgical scar warrants urgent medical evaluation, ideally at a facility with orthopedic capability. Wound bleeding after a fall in the early weeks post-surgery is a particularly red flag, as it suggests disruption of the deep surgical repair.⁵

Falls that seem minor, where you got up fine and can walk, still deserve mention at your next orthopedic appointment. Some periprosthetic fractures, particularly those around the kneecap, can be surprisingly subtle. Up to about nine in ten periprosthetic patella fractures are actually non-traumatic and may even be found incidentally on routine X-rays in patients with few or no symptoms.¹ That said, a fall can accelerate or worsen a stress reaction that was already developing silently. If your knee feels different after a fall, even vaguely, mention it. An X-ray is quick and cheap insurance compared to catching a fracture weeks later after it has displaced.

The long-term outlook after a fall-related injury to a knee replacement varies widely. Minor soft tissue injuries typically resolve with rest and physical therapy. Periprosthetic fractures that are treated promptly and heal well can result in a knee that functions reasonably close to where it was before. But complicated fractures, infection, or implant loosening from a fall can mean revision surgery, prolonged immobility, and in some cases a permanent decline in function. The stakes are high enough that taking fall prevention seriously is one of the best things you can do to protect a knee replacement over its lifetime.