Knee replacement surgery is a common and effective procedure performed to alleviate chronic knee pain, often stemming from severe arthritis. While some pain is expected during initial recovery, many individuals experience distinct pain on the outer side of the knee after the procedure. This lateral knee pain can be perplexing and may impact rehabilitation progress.
Anatomy of the Outer Knee
The outer, or lateral, aspect of the knee joint is a complex region comprising several structures that contribute to its stability and movement.
The iliotibial (IT) band is a thick band of connective tissue that extends along the outside of the thigh from the hip to the knee. The IT band plays a role in stabilizing both the hip and knee joints during walking and running.
The lateral collateral ligament (LCL) is a cord-like band positioned on the outer side of the knee. The LCL connects the thigh bone (femur) to the smaller lower leg bone (fibula), acting as a primary stabilizer against sideways forces.
Additionally, the common peroneal nerve, a branch of the sciatic nerve, travels down the back of the thigh and wraps around the fibula head near the knee. This nerve is responsible for sensation in the outer lower leg and the top of the foot, and it controls muscles that lift the toes and ankle.
Common Causes of Outer Knee Pain
Pain on the outer side of the knee after knee replacement can stem from various sources, often related to the body’s adaptation to the new joint.
One frequent cause is Iliotibial (IT) Band Friction Syndrome, which occurs when the IT band becomes irritated or inflamed. This can happen if the IT band rubs against bony prominences on the outside of the knee due to changes in gait, muscle imbalances, or slight component fit variations after surgery. The new alignment of the knee can alter the forces acting on the IT band, leading to this irritation.
Another potential cause involves the common peroneal nerve, which can experience irritation or damage during the surgical procedure. While the incidence of this nerve injury is relatively low, it can lead to pain, numbness, tingling, or weakness in the foot and ankle, sometimes resulting in a “foot drop.” The nerve can be stretched, compressed by swelling or a hematoma, or affected by prolonged tourniquet use.
The lateral collateral ligament (LCL) can also be a source of pain. It can be stressed or irritated by the surgical components or by post-operative swelling and scar tissue. The new mechanics of the knee joint might place unaccustomed stress on the LCL, leading to discomfort.
Issues related to the prosthetic components may also contribute to outer knee pain. A slight overhang of the tibial tray (the lower component of the knee replacement) or extruded cement can irritate the surrounding soft tissues. Less commonly, outer knee pain might be referred pain, meaning it originates from another area, such as the hip or lower back.
When to Consult a Healthcare Professional
While some discomfort is expected during recovery from knee replacement surgery, certain signs warrant prompt medical attention. Consult a healthcare professional if you experience:
- Sudden, severe, or worsening pain that does not improve with rest or over-the-counter pain relievers.
- New or increasing swelling, redness, or warmth around the knee.
- Systemic symptoms such as fever or chills, which could signal an infection.
- An inability to bear weight on the leg or a feeling that the knee is giving way.
- Numbness, tingling, or weakness in the foot or ankle, particularly if it includes difficulty lifting the foot (foot drop).
- Calf pain or swelling, which may indicate a deep vein thrombosis (DVT).
Treatment and Management Strategies
Treatment approaches for outer knee pain vary based on the specific cause.
Initial management often includes conservative measures aimed at reducing inflammation and discomfort. This typically involves rest, applying ice to the affected area, using compression, and elevating the leg. Over-the-counter pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen, are commonly recommended to help manage pain and reduce inflammation. Activity modification, which involves adjusting movements that aggravate the pain, is also an important part of conservative care.
Physical therapy plays a central role in addressing outer knee pain. Therapists can guide patients through targeted exercises to strengthen surrounding muscles, improve flexibility, and correct gait abnormalities that may contribute to irritation of structures like the IT band. Stretching exercises specifically for the IT band are often incorporated to improve its mobility.
For localized inflammation or nerve pain, injections may be considered. Corticosteroid injections can reduce inflammation in specific areas, while local anesthetic injections can help pinpoint the source of pain and provide temporary relief. If nerve pain persists, prescription medications specifically designed to manage neuropathic pain, such as gabapentin, pregabalin, or certain antidepressants and anticonvulsants, might be prescribed. In rare cases, when conservative treatments fail to resolve symptoms and a clear structural issue is identified, further surgical intervention, such as nerve decompression, might be considered. The treatment plan is always individualized to the patient’s specific condition and guided by a healthcare professional.