The Forgotten Joint, Part 2

Last month, we talked about what the patellofemoral joint (PFJ) is and where it is located (The Forgotten Joint, Part 1). This month, we will continue with how to differentiate pain from the knee area and pain from the PFJ. But first we need to understand the biomechanics of the PFJ.

Biomechanics of the PFJ
The knee cap works as a single pulley with the quadriceps and the patellar tendon being the ropes attached to the top and bottom ends, respectively. Its function is to increase the efficiency of the quadriceps muscle in stabilizing the knee, especially in weight bearing position. The resultant force from the pull of these two ropes is the compression force to the PFJ. Just like in other joint pain, the more compression is at the joint, the more pain a patient will experience. At the PFJ, the compression increases as the knee goes into more bent positions.

Pain Behavior
Pain behavior is the term that we use to describe how the pain changes (either better or worse) with various activities, positions, or as the day goes on. It is one of the key pieces of information in finding the source of the pain, and more important—whether it can be helped by physical therapy.

  • a) Sitting
    Pain from the true knee joint usually increases in all weight-bearing activities. Therefore, knee pain will decrease in sitting. However, PFJ pain may increase or decrease in sitting, depending on the knee position. As we recall the biomechanics of PFJ, the more the knee bends, the more compression in the PFJ and thus, more pain in the PFJ. Therefore. PFJ pain will increase while sitting with the knee bend at or beyond 90 degrees, but true knee pain does not.
  • b) Standing
    PFJ pain does not change in standing with the knee straight, but it does if the knee is bending—such as in half or full squat. However, true knee pain increases regardless the knee positions.
  • c) Walking
    True knee joint pain increases in walking, but PFJ pain does not have much change.
  • d) Stairs
    Both types of pain increase with stairs. PFJ pain increases especially traversing down stairs. The same applies with downward slope.

Treatment Approach
With all this information in mind, it is not difficult to figure out the difference in the treatment for knee pain and PFJ pain. If the goal of therapy is to strengthen the quadriceps muscles, it is okay to go through the full range for true knee pain. However, for PFJ pain, it needs to be done in a slight knee bend position, and to avoid any strengthening at or beyond 90 degrees knee bent position. The favorable range is about 0–60 degrees. For more irritable PFJ pain, one may need to limit the range to 0–30 degrees.

That is all for the PFJ pain. I hope it helps. Next month, we will learn about “the forgotten muscle,” the psoas muscle, and its relation to back pain.

Read The Forgotten Joint, Part 1

Peggy Hau, PT, MscPT is a licensed physical therapist at Mettler Center. Experiencing knee pain? Ask an Expert. Knee pain is best evaluated by a physical therapist who can detect functional problems and make the best possible recommendation for treatment. Call 217-398-9800 to schedule a free 30-minute consultation with a physical therapist or request an appointment online.