Old ACL Reconstruction Pain Returning

Scar development at the site of the patella tendon could be causing your pain.  Other factors that may contribute to your symptoms may be your biomechanics, structural alignment of the tibia and femur, inflexibility, muscle weakness and running technique.  The discomfort below your patella can occur when someone overpronates at the foot and/or has poor control of the pelvis while running due to muscle weakness of the hips and core.  Other factors that can affect your lower extremity mechanics may be related to your back and/or sacroiliac area.  If you have any back pain, this may be a place to consider to indirectly affect your knee.  If the tibia and femur are aligned in such a way that you present more "knocked-kneed," the groove below your patella has been altered and can cause pain below the patella that refers distally into the region of the patella tendon.  Finally, overstriding (your foot initially contacts the ground and the knee remains straight) when running can cause anterior knee pain.

As a physical therapist in the clinical setting, I must first determine the cause of the problem before creating a plan of treatment.  It would be best to consult a medical professional that is also an experienced endurance athlete to determine the cause.  It is very difficult to determine if only scar tissue is the cause of the problem.  All factors must be considered.  I hope this information provides some clarity and thought.