Your knee is a complex joint at the intersection between the thigh and the lower leg. The anterior cruciate ligament, or ACL, is one of two major knee ligaments that stabilize your knee joint. The other is the meniscus, which acts as a shock absorber. When you have both a torn meniscus and torn ACL your knee joint moves from side to side when you walk or run. This lateral movement puts extra stress on the muscles, tendons and ligaments that connect the knee to the hip and can cause pain in the hip as well as in the knee.
The thighbone, or femur, is the upper structure of the leg. The two bones of the lower leg, the tibia and fibula, are the lower structure. The patella, or kneecap, is in the middle of these three bones and slides up and down in a groove in the bottom of the femur as the knee bends. Tendons, ligaments and muscles hold all of these bones in position and give the knee stability. A weakness or injury to the supporting structures of the knee can cause pain above or below the knee joint because of the interconnections between hip, knee, calf and ankle.
The ACL is the ligament that connects your tibia, or shinbone, to the femur. The ACL runs from side to side just behind the patella in the front of the knee, while the posterior collateral ligament, or PCL, runs across the back. The two ligaments form an X-shape and provide much of your knee’s stability. A tear in either ligament is similar to a loose guy wire holding up a tent, which can begin to sag from lack of support.
A study in the October 2011 “Journal of Electromyography and Kinesiology” found that people with anterior knee pain, similar to that which can occur with a torn ACL, were more likely to have instability when performing step exercises. The instability caused pain in the hip as well as knee pain on the affected side. A report in the October 2001 “Journal of Orthopaedic Research” on patients who had ACL injuries found patients had changes in both calf and thigh muscles to compensate for the knee injury, which increased the load on the hip to compensate for the injured and unstable knee.
Considerations and Warnings
Running puts the equivalent of eight times your body weight on your knee joint, according to eOrthopod. If the joint is unstable because of an injury, you may need to stop running until it heals. Sometimes a torn meniscus will heal with rest. Physical therapy can increase muscle strength and improve the structural support of the knee joint. An ACL injury may require surgery, especially if the tear is large and if you frequently participate in active sports such as running, basketball, skiing or other activities that put high demand on the knee.