There are many causes of posterior knee pain or pain in the back of the knee. According to the U.S. National Library of Medicine and the National Institutes of Health, or NIH, knee pain--including posterior knee pain--may be caused by repetitive overuse injuries, poor body mechanics during physical activity and traumatic injuries. The NIH states that some knee problems self-resolve, while other knee problems require intervention by a health care professional.
Baker's Cyst
A Baker's cyst can cause posterior knee pain. According to the Mayo Clinic website, a Baker's cyst, also known as a popliteal cyst, is a fluid-filled cyst that creates a bulge and a sensation of tightness behind the knee. The pain associated with a Baker's cyst can be exacerbated or made worse by flexing and extending the knee or with activity. The appearance of a Baker's cyst is often secondary to another knee problem, such as osteoarthritis or a cartilage tear. These conditions cause the knee to generate excessive amounts of fluid, which can result in the formation of a Baker's cyst. Common signs and symptoms associated with a Baker's cyst include the following: posterior knee swelling, knee pain and stiffness and a posterior knee mass that has a texture similar to that of a water balloon. The Mayo Clinic website states that, although it rarely occurs, a Baker's cyst can rupture and leak fluid into the involved knee joint, causing sharp knee pain, knee swelling and calf redness.
Biceps Femoris Tendon Avulsion
A biceps femoris avulsion can cause posterior knee pain. The Sports Injury Clinic website states that the biceps femoris is one of three hamstring muscles. The biceps femoris muscle is comprised of two distinct muscle bellies--a short head and a long head--that originate from different locations. A tear or strain of the biceps femoris muscle and tendon is a relatively common injury among athletes participating in sports that require explosive movements of the knee, such as sprinting or football. Biceps femoris tendon avulsions--a complete tearing away of the tendon from it's insertion point on the bone--can be a serious injury and require surgical intervention to reattach the avulsed tendon and bone fragment. Common signs and symptoms associated with a biceps femoris avulsion include the following: extreme pain in the affected area, swelling, reduced hamstring strength and, in some cases, a bone fragment that can be palpated or felt through the overlying tissues.
Popliteus Strain
A popliteus muscle strain can cause posterior knee pain. According to the Sports Injury Clinic website, the popliteus is a tiny muscle situated at the back of the knee joint. The popliteus assists with internal or medial rotation of the tibia or shin bone and helps unlock the knee joint when a person initiates knee flexion or bends his knee from a fully extended or straightened position. The Sports Injury Clinic website states that the popliteus can be injured in several different ways, including repetitive overuse injuries, injuries caused by muscle imbalances around the knee and traumatic knee hyperextension injuries. Popliteus injuries are often accompanied by posterior cruciate ligament or PCL tears. Common symptoms associated with popliteus strains include the following: pain in the posterior knee compartment, a popliteus muscle that's tender to the touch, pain with certain types of resisted knee flexion, tight hamstring muscles and uncomfortable knee extension.
