Pain on the outside of the knee
The lateral or outer side of the knee has many structures that can cause pain.
A lateral meniscal tear is the most common cause inside the joint but there are many other structures that can be a source of lateral sided knee pain.
About 20% of the time patellofemoral or kneecap pain is felt at the joint margin. This can be on the medial or inside of the knee or on the lateral or outside of the knee. This might be from a chondral injury to the trochlear (also known as a lunge lesion) or from patellofemoral arthritis. Kneecap instability does not usually present with lateral knee pain. The mainstay of treatment for this is physiotherapy but arthroscopy of the knee can sometimes help.
The proximal tibiofibular joint is a rare source of knee pain on the lateral or outide part of the knee. Once diagnosed this is usually treated with a cortisone injection or occasionally surgery to the joint.
Pain around the ITB or IlioTibial Band almost always responds to physiotherapy.
Radicular pain or pain from the nerves of the lower back can be misinterpreted as pain in the back or outside of the knee or down the calf. The knee is usually normal in this situation.
Lateral compartment arthritis of the knee is much less common than medial knee arthritis. It responds less well to arthroscopy or unicompartmental knee replacement and often requires a total knee replacement. Rheumatoid arthritis is more likely to cause a valgus (knock knee appearance) knee and osteoarthritis is more likely to cause a varus knee (bow legged appearance).
Lateral meniscal tears are much less common than medial meniscal tears. The symptoms are often less specific with a complaint of a general ache in the area rather than a sharp pain localized specifically to the joint line. The clinical examination often is less convincing than a medial meniscal tear and the diagnosis is confirmed on MRI scanning. It is rare for this to settle without a knee arthroscopy and even then can take twice as long as a medial meniscal tear to allow return to sporting activities.
Acute injuries to the knee can damage the lateral collateral ligament which may lead to pain or instability at the lateral side of the knee. Unlike medial collateral ligament injuries, lateral ligament injuries often require surgical repair or reconstruction.
A careful history and detailed clinical examination combined with appropriate investigations will lead to optimal treatment of lateral sided knee pain.