What do you do about that CMP you have?

Chrondromalacia Patella (CMP) is a description for kneecap pain of the patella/femoral joint (P/F Joint). Pain is aggravated  with squatting activities, prolonged sitting with knee bent, and sometimes with VMO (Vastus Medialis Obliquus) “malfunction”. The knee has to be efficient and reasonably maintenance free. So when the orthopedist sees you, history again will likely reveal the diagnosis. The “Q Angle” is one of the tests that could be physically used to assess a possible cause for anterior knee pain. I post the “Q Angle” link to impress you with why surgeons have to know physics.

The knee would have a hard time generating through-the-range knee power (football linemen, for example) without the patella’s unique function. It helps the quadriceps perform efficiently and at reduced energy cost. It’s a type of green energy system.

This blog isn’t meant as an in-depth arthrokinematics discussion of the P/F joint.  But understanding the joint physics helps the professional treat the painful condition more efficiently and effectively. The joint does create painful symptoms for lots of people (especially young teenage girls).  If orthopedic surgeons, physical therapists, and occupational therapists didn’t take physics, they would “come up short” when helping patients with their knee related problems. In fact, over almost 4 decades, I’ve supervised many clinical aides who were going to night school to complete prerequisite courses in order to be eligible to apply to PT school; but they ended up deciding against the profession because they couldn’t get the “hang of physics”.

So Archimedes in 3^rd century BCE defined 3 lever systems. Good for us because the knee is essentially a class one lever system (like a see-saw). The kneecap in the middle is the fulcrum, the lower leg (with or without resistance weight) is one force arm and the quadriceps muscles above the knee make up the other. One rehabilitation goal is to make the quadriceps muscle group stronger through a progressive resistance exercise (PRE’s) program. The stronger the muscle gets, the “heavier force” it can generate through the fulcrum to more strongly allow the leg to do more: tiptoe reaching a top shelf, jumping as in sports or over a puddle, or just descending stairs.

The doctor also has to understand the sheer force mechanics and the coefficient of friction which essentially means the kneecap contact should be at right angle to the femoral condyles as it goes through its motion. Otherwise it can “skid” on the femoral condyle surface and begin a degenerative process and cause pain. That means in therapy, keeping the kneecap aligned in the femoral trochlear groove; a primary job of the VMO in conjunction with some of the hip muscles. This has to be the goal for a successful recovery.

So dynamic taping (Kinesio) or static taping (McConnell, Mulligan) of the patella can assist the therapist in the acute (early) stages along with close attention to technique in the exercises. Technically, the VMO’s critical role is to provide the joint force necessary to facilitate the tibia’s morphological requirement to externally rotate on the femur as the knee joint goes into full extension (straightening). Most important, the therapist should be sure to teach you the correct hip exercises (especially abduction and adduction) so the VMO ‘s action can be facilitated with proper hip position during rehabilitation.

As an aside, and too complicated to discuss here, some total knee arthroplasties (TKA’s or knee replacements) and post ACL repairs, where these same rehabilitation principles are applicable, develop posterior knee joint pain and can not attain full knee straightening. Ask your therapist about the popliteus muscle and how to address it, if applicable. 

Here are exercises addressing this important concern.

Next blog:  A Closer Look at Rehabilitation Principles for the Knee.