The muscles and joints of our legs work together in complex ways that aren't completely understood. Knee problems in particular can lead to problems in other joints or muscles. If the underlying knee problem is not treated, reinjury or further problems are likely.
These doctors report two cases of injuries to the vastus lateralis muscle located in the outer thigh. The vastus lateralis muscle is one of four muscles making up the quadriceps muscle of the thigh.
Both patients were injured while playing softball. Both patients went to a doctor for severe thigh pain, and both reported having generalized pain in the front of the knee for at least a year before their thigh injuries.
The type of pain they described in the front of the knee is called patellofemoral pain syndrome, or PFPS. This condition is common, especially among runners. It usually comes on slowly and causes low levels of knee pain, especially during activities such as going up and down stairs. PFPS may happen because of injury to the cartilage behind the kneecap or because the kneecap isn't tracking correctly as the knee bends.
These doctors think changes caused by PFPS led to the muscle injury in these two patients. The quadriceps muscle attaches to the kneecap. The kneecap gives the quadriceps muscle a lever for added force. It is possible that the presence of PFPS lead to an imbalance in the quadriceps muscle, setting the stage for muscle injury.
Both patients responded well to treatment for the muscle strain. The authors conclude that it is important for doctors to look for possible underlying causes of knee strains.
Adam J. LaBore, MD, and David J. Weiss, MD. Vastus Lateralis Strain Associated With Patellofemoral Pain Syndrome: A Report of 2 Cases. In Archives of Physical Medicine and Rehabilitation. April 2003. Vol. 84. No. 4. Pp. 613-615.'