Total Knee Replacement: Muscle Involvement, Surgical Approaches, and Recovery

What Muscle Is Cut During TKR?

During Total Knee Replacement (TKR) surgery, major muscles are generally not "cut" or transected in the traditional sense. Instead, surgeons typically incise the joint capsule and may partially incise or detach the quadriceps tendon for access, while the bulk of the quadriceps muscles are carefully retracted or split along their fibers.

Understanding Total Knee Replacement (TKR)

Total Knee Replacement (TKR), also known as total knee arthroplasty, is a surgical procedure designed to resurface a knee damaged by arthritis or injury. The primary goal is to alleviate pain and restore function by replacing the damaged bone and cartilage with prosthetic components. To achieve this, surgeons must gain access to the knee joint, which involves navigating through various anatomical layers including skin, subcutaneous tissue, fascia, muscle, and the joint capsule.

Surgical Access: More Than Just "Cutting Muscle"

The term "cutting" can be misleading when discussing muscle involvement in TKR. Unlike some other orthopedic procedures where muscles might be purposefully detached and reattached (e.g., rotator cuff repair), TKR primarily focuses on gaining access to the joint itself. This often involves:

• Incision of the skin and subcutaneous tissue: The initial cut is made through the outermost layers.
• Fascial incision: The tough connective tissue (fascia) overlying the muscles is incised.
• Muscle retraction or splitting: Rather than transecting entire muscle bellies, surgeons typically retract (pull aside) muscles or make an incision between muscle fibers (a "split") to create a pathway to the joint. This approach minimizes muscle damage and aids in quicker recovery.
• Joint capsule incision: The fibrous capsule enclosing the knee joint is incised to expose the articular surfaces of the femur, tibia, and patella.

Specific Anatomical Structures Involved

While major muscle bellies are largely spared from being "cut," several structures closely associated with muscles are directly manipulated during TKR:

• Quadriceps Tendon: This strong tendon connects the quadriceps femoris muscle group (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) to the patella. In the most common surgical approach, the medial parapatellar approach, a portion of the quadriceps tendon, along with the retinaculum (fibrous tissue supporting the patella), is incised along its medial border to allow the patella to be everted (flipped over) and expose the joint. While not a complete transection of the entire tendon, this incision is necessary for adequate visualization and component placement.
• Patellar Tendon (Ligament): This structure connects the patella to the tibia. It is generally preserved during TKR, as it is crucial for knee extension and stability.
• Joint Capsule and Ligaments: The fibrous joint capsule and often the anterior and posterior cruciate ligaments are incised or removed to prepare the bone surfaces for the prosthetic implants. The collateral ligaments (medial and lateral) are typically preserved to maintain knee stability.
• Muscles (Indirect Involvement): The vastus medialis obliquus (VMO), the innermost head of the quadriceps group, is often encountered. In the medial parapatellar approach, its fibers may be partially incised or split. In "muscle-sparing" approaches, special care is taken to avoid or minimize disruption to the VMO and other quadriceps muscles.

Surgical Approaches in TKR

The specific way anatomical structures are handled depends on the surgical approach utilized:

• Medial Parapatellar Approach: This is the most traditional and widely used approach. It involves a longitudinal incision along the medial side of the patella, incising the medial retinaculum and often a portion of the quadriceps tendon and vastus medialis obliquus (VMO) fibers. This allows the patella to be dislocated laterally, providing excellent exposure of the joint. While effective, it does involve some disruption to the extensor mechanism.
• Subvastus Approach: Considered a "muscle-sparing" approach, this technique aims to avoid incising the quadriceps tendon or the VMO muscle. Instead, the surgical plane is developed under the vastus medialis muscle, retracting it laterally to gain access to the joint. This approach theoretically leads to less post-operative pain and potentially faster quadriceps recovery.
• Midvastus Approach: Another muscle-sparing technique, this approach involves splitting the fibers of the vastus medialis muscle longitudinally rather than incising the quadriceps tendon or detaching the VMO. This also aims to preserve the integrity of the extensor mechanism.

Implications for Post-Surgical Recovery

The extent of muscle and tendon manipulation during TKR directly impacts the initial recovery phase. Approaches that minimize disruption to the quadriceps extensor mechanism (like subvastus or midvastus) may lead to:

• Less immediate post-operative pain.
• Potentially faster quadriceps strength recovery in the very early stages.
• Quicker return to functional activities.

However, the long-term outcomes in terms of pain relief and overall function are generally comparable across different approaches. The skill of the surgeon and the effectiveness of the rehabilitation program are paramount.

Role of Rehabilitation

Regardless of the surgical approach, the quadriceps muscle group plays a critical role in post-TKR recovery. Its strength is essential for knee extension, walking, climbing stairs, and overall mobility. Therefore, a comprehensive rehabilitation program focusing on:

• Early range of motion: Restoring flexibility to the new joint.
• Quadriceps strengthening: Crucial for regaining functional independence.
• Gait training: Re-educating walking patterns.
• Balance and proprioception: Improving stability and awareness of joint position.

Physical therapy is vital to restore strength, function, and stability to the knee, helping patients maximize the benefits of their new joint.

Conclusion

While the question "What muscle is cut during TKR?" is common, the reality is more nuanced. Major muscles are typically not transected. Instead, surgeons carefully navigate the anatomy by incising the joint capsule and often making a partial incision or detachment of the quadriceps tendon (in the medial parapatellar approach) or splitting/retracting muscle fibers (in muscle-sparing approaches) to access the knee joint. The primary goal is to replace the damaged joint surfaces while preserving as much of the surrounding soft tissue integrity as possible to facilitate a robust and effective rehabilitation process.