No major muscles are fully cut through during a total knee replacement. The surgery primarily involves cutting into tendons, ligaments, and the joint capsule to access the knee, while the muscles themselves are split along their fibers, partially detached from their insertion points, or retracted out of the way. The quadriceps muscle group on the front of your thigh is the most affected, but the degree of disruption depends on which surgical approach your surgeon uses.
What Actually Gets Cut Open
The most common technique, called the medial parapatellar approach, begins with a longitudinal cut through the quadriceps tendon, which is the thick band of tissue connecting the quadriceps muscles to the kneecap. The surgeon cuts along the tendon to a point about 1 cm from the vastus medialis (the teardrop-shaped muscle on the inner side of your thigh just above the knee). From there, the incision continues down along the inner edge of the kneecap, cutting through the medial patellofemoral ligament and the joint capsule. The cut extends to the inner border of the patellar tendon, which connects the kneecap to the shinbone.
The vastus medialis tendon is incised, and the muscle itself is detached from the kneecap. A deeper ligament on the inner side of the knee is also released to expose the top of the shinbone. Once these structures are opened, the kneecap can be flipped to the side, giving the surgeon a clear view of the worn joint surfaces that need to be replaced.
So while your quadriceps muscle fibers aren’t sliced across their width, the tendon that transmits their force is cut lengthwise, and the vastus medialis is separated from its attachment to the kneecap. This is the main reason your leg feels weak after surgery and why rebuilding quadriceps strength is such a central part of rehabilitation.
How Different Approaches Affect Muscle Damage
Surgeons have developed several variations of the standard approach specifically to reduce disruption to the quadriceps mechanism. The differences matter for your early recovery, particularly how quickly you regain the ability to lift your leg and bend your knee.
Subvastus Approach
Instead of cutting through the quadriceps tendon and detaching the vastus medialis, the surgeon works underneath the muscle, lifting it up to access the joint. Only about 1 to 2 cm of the vastus medialis tendon is incised. Because the muscle itself isn’t split or separated from surrounding tissue, blood supply to the area is better preserved. This approach leaves the extensor mechanism (the system of muscles and tendons that straightens your knee) more intact, which allows better kneecap tracking right after surgery.
Midvastus Approach
This technique splits through the lower portion of the vastus medialis muscle along the direction of its fibers rather than cutting through the quadriceps tendon above the kneecap. A substantial portion of the muscle is still detached from the kneecap, and the blood vessel network on the inner side of the knee is disrupted. It offers somewhat less muscle preservation than the subvastus approach but provides the surgeon with better visibility of the joint.
Quadriceps-Sparing Approach
The most conservative option limits the incision into the quadriceps tendon to just 2 cm from the top of the kneecap. The vastus medialis is not split at all if its attachment doesn’t extend below the upper edge of the kneecap. Instead of flipping the kneecap completely over, the surgeon displaces it to the side while it remains upright. This smaller window makes the surgery more technically demanding, but it preserves the most muscle and tendon tissue.
The Lateral Retinaculum Release
In some cases, an additional cut is made on the outer side of the kneecap. The lateral retinaculum is a band of fibrous tissue that connects to the vastus lateralis (the muscle on the outer part of your thigh). If the kneecap doesn’t track properly in its groove after the implant is placed, the surgeon releases this tissue to allow the kneecap to sit centered. In conventional surgery, about 66% of knees require one or more soft tissue releases of this kind. This isn’t a muscle cut per se, but it changes the balance of forces that the outer thigh muscle exerts on the kneecap.
Ligaments and Other Soft Tissue
Beyond the muscle and tendon work, several ligaments are cut or removed entirely. The anterior cruciate ligament (ACL) is removed in every total knee replacement because the implant’s design replaces its function. The posterior cruciate ligament (PCL) is either preserved or removed depending on the type of implant used. The medial patellofemoral ligament is cut as part of the standard opening. Portions of the joint capsule, the fibrous envelope surrounding the knee, are incised along the inner side to allow access.
The meniscus cartilage on both sides of the knee is also removed, since the plastic spacer in the implant takes over its cushioning role.
Robotic-Assisted Surgery and Soft Tissue Preservation
Robotic-assisted knee replacement uses the same incisions to open the joint, so the same tendons and muscle attachments are disrupted during the approach. Where robotic systems show a difference is in the precision of bone cuts and implant positioning, which reduces the need for additional soft tissue releases to balance the knee. In one multicenter study, only 31% of knees needed one or more soft tissue releases with robotic gap-balancing, compared to 66% with conventional techniques. A cadaveric study found that conventional surgery produced more overall soft tissue trauma around the joint, while robotic-assisted cases showed better preservation of surrounding structures, including zero posterior cruciate ligament injuries compared to 28% in the conventional group.
What Recovery Feels Like
Because tendons and muscle attachments are disrupted rather than muscles being sliced through, the healing process involves tendon reattachment to bone and scar tissue formation along the surgical incision line. Strength in all major muscle groups around the knee typically returns to pre-operative levels by three to six months after surgery. That timeline reflects the healing of the tendon incisions and the neuromuscular reactivation of the quadriceps, which often “shut down” temporarily after joint surgery due to pain and swelling.
Many people describe the post-surgical sensation not as a sharp muscle pain but as heaviness, tightness, pressure, or numbness around the knee. Some experience a feeling of external compression, as though something is pressing on or holding the knee, rather than a pulling sensation from within the muscles. Pain and functional improvements can continue for up to 12 months, though some people report residual tightness or discomfort well beyond that window.
The early weeks of rehabilitation focus heavily on reactivating the quadriceps. Straight leg raises, quad sets (tightening the thigh muscle while your leg is extended), and progressive bending exercises all work to restore the connection between your brain and the muscles that were disrupted during surgery. The vastus medialis, because it’s the muscle most directly affected by the incision, is often the slowest to regain full activation.