Your Knee Was Replaced. The Muscles, Tendons, and Ligaments Around It Were Not.

Your Knee Was Replaced. The Muscles, Tendons, and Ligaments Around It Were Not.

Key Takeaways

• A knee replacement swaps the worn joint surfaces for metal and plastic. Your muscles, tendons, most ligaments, the joint capsule, and the nerves around the knee are the same tissues you had before surgery.
• Those soft tissues often go into surgery already weak from years of arthritis, and surgery adds swelling, scar tissue, and a thigh muscle that struggles to switch on.
• Research shows the quadriceps can lose more than half its strength in the first month after knee replacement, mostly because the nervous system stops fully activating it. [1]
• Progressive strength training after knee replacement has been shown to lead to better strength and function a year later than standard care. [3]
• At Unpain Clinic in Edmonton, we work through the soft tissue in order: calm the inflammation, loosen scar tissue, switch the muscles back on, then build strength you can keep.

In this article

• What does a knee replacement actually replace?
• Why does my knee still feel weak after knee replacement?
• Why is my knee stiff months after knee replacement?
• Why didn't my rehab after knee replacement hold?
• What helps the soft tissue recover after knee replacement?
• How does Unpain Clinic work through the soft tissue after a knee replacement?
• How long does soft tissue recovery take after knee replacement?
• What does the research say?
• Frequently asked questions

Your surgeon did the job. The X-ray looks great. So why do stairs still feel like a negotiation, and why does the knee feel stiff and unsure every time you stand up?

A knee replacement replaces the joint surfaces, not the soft tissue around them. The muscles, tendons, ligaments, and scar tissue around your new knee decide how well it moves. That is where recovery after knee replacement is won or lost.

What does a knee replacement actually replace?

A total knee replacement removes the worn cartilage and a thin layer of bone from the end of the thigh bone and the top of the shin bone, then caps them with metal and a plastic spacer. The back of the kneecap may also be resurfaced. The menisci and the ACL are removed, and in some implant designs the PCL too. Almost everything else around the knee stays. [6]

What stays is the soft tissue. Your quadriceps and hamstrings, the quadriceps tendon and patellar tendon, the collateral ligaments on each side of the knee, the joint capsule, the skin, and the nerves are the same tissues you walked in with.

That is the part of recovery no implant can do for you. The implant gives you a smooth new surface. The soft tissue decides how strong, stable, and comfortable that surface feels when you use it.

What was replaced and what stayed

Replaced or removed: The cartilage surfaces of the thigh bone and shin bone (now metal and a plastic spacer), often the back of the kneecap, both menisci, the ACL, and in some designs the PCL.

Stayed, but went through surgery: The quadriceps and hamstring muscles, the quadriceps tendon and patellar tendon, the medial and lateral collateral ligaments, the joint capsule, and the skin and fascia around the incision.

Stayed, and often overlooked: The hip, calf, and ankle muscles that help control the knee every time you take a step.

Why does my knee still feel weak after knee replacement?

Most people feel weak after knee replacement because the quadriceps, the big muscle on the front of the thigh, partly shuts down after surgery. Swelling and surgical trauma make it harder for your nervous system to fully switch the muscle on. Research shows this loss of activation drives more of the early weakness than the muscle actually shrinking. [1]

In one study, quadriceps strength one month after surgery was about 60 percent lower than before surgery. The muscle not switching on fully contributed nearly twice as much to that loss as muscle shrinkage did. [1]

This changes what the muscle needs. A muscle that is not firing properly does not just need more repetitions. It needs help reconnecting with the nervous system first, then steadily heavier load.

Many people also walked into surgery with a weak thigh after years of protecting a painful arthritic knee. If knee osteoarthritis is what led you to surgery, your soft tissue likely started recovery behind before day one. Our guide to knee osteoarthritis relief explains how that weakness builds up over time.

Why is my knee stiff months after knee replacement?

Stiffness months after knee replacement usually comes from the soft tissue, not the implant. Every surgery heals with scar tissue. In some people, the joint capsule and the tissue around the incision lay down more scar than they need, which can tighten the knee and limit how far it bends and straightens. When this becomes excessive, it is called arthrofibrosis. [5]

Researchers describe arthrofibrosis as too much scar tissue forming during a healing response that has gone off track, and they point to supervised physiotherapy as the main way to prevent it. [5]

Stiffness and weakness also feed each other. A knee that cannot fully straighten makes the quadriceps work at a disadvantage. A quadriceps that will not switch on makes it harder to push the knee straight. Breaking that loop is a big part of recovery.

Scars do not only affect the spot where they sit. We have written more about how surgery scars can change the way your body moves, sometimes for years after the incision has healed.

Why didn't my rehab after knee replacement hold?

Rehab after knee replacement often winds down once the knee bends well and the incision has healed, but strength is usually still well behind at that point. Studies have found quadriceps weakness can persist for years after knee replacement compared with healthy adults of the same age. [4] If the muscles never fully caught up, the knee can feel unsure, tired, or sore with activity long after surgery.

That is not a failure on your part. Range of motion and pain are the easiest things to measure in the early weeks. Strength and control take longer, and they often get less attention once you are walking without a cane.

It may also help explain why about one in five people in a large Ontario study were not satisfied with the result of their knee replacement. [2] Many things affect satisfaction, including expectations and pain before surgery, so soft tissue is not the whole story. It is the part we can train.

What helps the soft tissue recover after knee replacement?

What helps most is working through the soft tissue in the right order: calm the swelling, keep scar tissue from locking the knee down, get the quadriceps firing again, then build strength progressively. Research strongly supports that last step. People who did progressive quadriceps strengthening after knee replacement were stronger and moved better a year later than people who had standard care. [3]

Progressive means the load goes up as you get stronger. Light leg lifts in week three are fine. Doing the same light leg lifts in month six is usually not enough to bring a weak thigh back.

The work also goes beyond the knee. Your hip muscles help control where your knee points on every step, and your calf and ankle absorb load before it reaches the knee. A strong knee sits inside a strong leg.

How does Unpain Clinic work through the soft tissue after a knee replacement?

At Unpain Clinic in Edmonton, we treat the tissue around the implant, not the implant itself. We start by finding which soft tissue problems are holding you back, whether that is swelling, scar tissue, muscles that will not switch on, or other joints compensating. Then we work through them in order, adjusting the plan as you progress and always within your surgeon's guidance.

Here is how that usually unfolds:

1. Whole-chain assessment. Your first visit is a one-on-one assessment of how your hip, knee, and ankle move and how strong each leg is, so we know which tissue is limiting you.
2. Calm the inflammation. Lingering swelling keeps the quadriceps switched off. EMTT, a magnetic therapy that reaches deep tissue, is often used to help settle it, typically starting around two weeks after surgery.
3. Loosen scar tissue and restore motion. Focused shockwave therapy, usually from about four to six weeks after surgery, combined with hands-on work and range of motion exercises, may help soften adhesions around the incision and joint capsule. Massage therapy can help keep the tissue moving later on.
4. Switch the quadriceps back on. We use activation work so the muscle fires fully before we load it heavily. Where it fits, our AI Robot Trainers measure force and coordination in each leg, so we can see exactly where the operated side is lagging.
5. Build strength progressively. Physiotherapy-guided strengthening for the quadriceps, hamstrings, hips, and calves, with the load going up as you get stronger.
6. Return to what you want to do. Stairs, longer walks, getting up off the floor, golf, or travel. We build toward your goals and keep checking in so the gains last.

Every plan is individual. Some people need more scar tissue work, others need more strength work, and results vary between individuals.

How long does soft tissue recovery take after knee replacement?

Most of the early recovery after knee replacement happens over the first three months, but soft tissue strength often keeps improving for a year or more with the right training. In the progressive strengthening study, people kept improving between three and twelve months after surgery. [3] Timelines vary, and they depend on how strong you were going in and how consistently you train.

If you are months or even years out from surgery and still feel weak, it is usually not too late. Muscle tends to respond to progressive training at any age. If you are unsure whether your knee needs another look, our article on when to see a physiotherapist for pain can help you decide.

What does the research say about soft tissue recovery after knee replacement?

The research points one way: surgery fixes the joint surface, but strength and mobility depend on what happens to the muscles and scar tissue afterward.

• Strength drops fast, and the nervous system is a big part of why. One month after knee replacement, quadriceps strength in one study was about 60 percent below where it was before surgery, mostly because the muscle was not being fully activated. [1] Weakness compared with healthy adults has been found many years later. [4]
• Progressive training changes the outcome. In a trial of 200 people, six weeks of progressive strengthening that started a few weeks after surgery led to better strength and function at one year than standard care. [3]
• Scar tissue needs early attention. A review of arthrofibrosis after knee replacement concluded that "Postoperative, supervised physiotherapy remains the first line of defense against the development of arthrofibrosis." [5]

For a longer conversation about why knee pain hangs on, listen to our podcast episode on chronic knee pain causes and treatment.

Frequently asked questions

Why does my knee still feel weak after knee replacement?

The quadriceps muscle usually loses a large amount of strength after knee replacement, mainly because swelling and surgery make it harder for your nervous system to fully switch the muscle on. Many people also had a weak thigh before surgery from years of arthritis. Progressive strength training that first reconnects and then loads the muscle may help bring that strength back.

Is it normal to have stiffness months after knee replacement?

Some stiffness is common for the first few months after knee replacement while swelling settles and scar tissue matures. Stiffness that is not improving, or a knee that will not fully bend or straighten, is often a soft tissue problem such as excess scar tissue around the joint. It is worth having it assessed, and you should always tell your surgeon about any sudden change.

What parts of the knee are not replaced in a knee replacement?

A knee replacement does not replace your muscles, tendons, collateral ligaments, joint capsule, skin, or nerves. The surgeon replaces the worn joint surfaces and removes the menisci, the ACL, and sometimes the PCL. The soft tissue that stays is what controls how strong and stable the new knee feels.

When can I start strengthening after knee replacement?

Gentle muscle activation usually starts within days of knee replacement, guided by your surgical team. Progressive strengthening, where the load steadily increases, often begins a few weeks after surgery once the incision has healed and swelling is under control. Your surgeon and physiotherapist will set the timing for your situation.

Is shockwave therapy safe if I have a knee implant?

At Unpain Clinic, focused shockwave therapy and EMTT are aimed at the soft tissue around the knee, not at the implant itself. Timing is planned around your surgery, with EMTT often starting around two weeks after surgery and shockwave around four to six weeks, once the incision has healed and your surgeon has no concerns. We will tell you honestly if we do not think you are a good candidate.

Is it too late to strengthen my knee years after knee replacement?

It is usually not too late. Quadriceps weakness can last for years after knee replacement, which means many people still have room to improve. Muscle tends to respond to progressive training at any age, and results vary between individuals.

Do I need a referral to book at Unpain Clinic?

No referral is needed to book an assessment at Unpain Clinic. In Alberta you can see a physiotherapist directly. Some insurance plans ask for a doctor's note for reimbursement, so check your plan if you are using coverage.

About the author

Written and medically reviewed by Uran Berisha, Founder of Unpain Clinic and Medical Shockwave Institute. Uran has spent more than 20 years in rehabilitation and over 13 years focused on shockwave therapy. He founded Unpain Clinic in Edmonton to treat persistent pain by looking at the whole body, not just the sore spot. Last reviewed: November 10, 2026. unpainclinic.com

Ready to strengthen what surgery did not replace?

Your new knee is only as good as the muscles, tendons, and tissue around it. If you are months or years out from surgery and your knee still feels weak, stiff, or unsure, the next step is a one-on-one assessment. We will find which soft tissue is holding you back and build you a clear plan.

No referral needed. No pressure, no contracts. And if we do not think we are the right fit for you, we will tell you honestly.

Book your assessment!

References

1. Mizner RL, Petterson SC, Stevens JE, Vandenborne K, Snyder-Mackler L. Early quadriceps strength loss after total knee arthroplasty: the contributions of muscle atrophy and failure of voluntary muscle activation. Journal of Bone and Joint Surgery (American). 2005, 87(5), 1047-1053.
2. Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KD. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clinical Orthopaedics and Related Research. 2010, 468(1), 57-63.
3. Petterson SC, Mizner RL, Stevens JE, et al. Improved function from progressive strengthening interventions after total knee arthroplasty: a randomized clinical trial with an imbedded prospective cohort. Arthritis and Rheumatism. 2009, 61(2), 174-183.
4. Stevens-Lapsley JE, Balter JE, Wolfe P, Eckhoff DG, Kohrt WM. Early neuromuscular electrical stimulation to improve quadriceps muscle strength after total knee arthroplasty: a randomized controlled trial. Physical Therapy. 2012, 92(2), 210-226.
5. Cheuy VA, Foran JRH, Paxton RJ, Bade MJ, Zeni JA, Stevens-Lapsley JE. Arthrofibrosis associated with total knee arthroplasty. Journal of Arthroplasty. 2017, 32(8), 2604-2611.
6. American Academy of Orthopaedic Surgeons. Knee replacement implants. OrthoInfo. Accessed November 2026.