WASHINGTON — Atraumatic knee pain, especially on the outside of the knee, is a common complaint in primary care offices, and although its mechanisms are poorly understood, the pain is real, even in those lacking clinical symptoms such as redness or swelling.
Often, atraumatic knee pain is related to the cartilage behind the kneecap, Dr. Scott Flinn said at the annual meeting of the American Academy of Family Physicians.
“The retropatellar cartilage behind the knee is the thickest in the body—5 mm—and when the patella is extended, the cartilage causes pressure across the knee,” said Dr. Flinn, a family physician, Specialty Leader for Sports Medicine to the Surgeon General, and Force Surgeon for Commander Naval Surface Forces in San Diego, Calif.
Dr. Flinn presented diagnostic pearls, treatment strategies, and rehabilitation tips for getting patients with the following common causes of anterior atraumatic knee pain back to strength without surgery:
Patellofemoral Pain Syndrome
Patellofemoral pain syndrome (PFPS) is also known as runner's knee, chondromalacia patella, and patellofemoral arthralgia. Evidence suggests that there is a 20% prevalence of PFPS among individuals aged 12–20 years, and that this type of knee pain accounts for up to 30% of visits in some sports injury clinics.
With any type of atraumatic knee pain, Dr. Flinn said to be sure to ask patients about a history of trauma; feelings that the knee is catching, popping, locking, or giving way; and a history of swelling in or around the knee joint.
Other symptoms include patient reports of anterior knee pain while sitting for a long time (known as the “theater sign”); pain when walking down stairs, which is more common than pain walking up stairs; and pain when squatting, running, or jumping.
On physical examination, check for the quadriceps angle, or Q-angle, which is the angle created between a line drawn from the center of the anterior superior iliac spine on the pelvis to the center of the patella and a second line from the center of the patella to the middle of the tibial tubercle.
The greater the Q-angle the more likely a patient is to have PFPS, according to some studies. Patients who overpronate are more likely to have PFPS than are those whose stride is even. On palpation, clinicians may feel a tight lateral retinaculum. There may be a trace effusion, and patients with PFPS do not usually complain of instability or joint tenderness.
Rehab for PFPS includes improving flexibility in the hamstrings, iliotibial band, and lateral retinaculum. In particular, tightness in the lateral retinaculum (one of the fibrous bands that hold the patella in alignment) could contribute to the pain by causing the patella to ride laterally, which may contribute to the retropatellar pain of PFPS.
Many atraumatic injuries of the knee are caused by incorrect training or poor biomechanics, or a combination of the two. Consequently, the best treatment for PFPS includes physical therapy, with a focus on strengthening exercises for the outside of the quadriceps muscle (with an attempted focus on the vastus medialis oblique). Also, consider foot orthotics for patients who need to correct excessive pronation and imbalance.
Patellar Tendinitis
Patellar tendinitis is a misnomer because the condition is actually more of a tendinosis than tendinitis, Dr. Flinn said. Despite an initial inflammation, histology tends to show few inflammatory cells. Patients with “jumper's knee” usually hurt themselves by overusing the knee in an activity such as basketball or volleyball.
Patients present with almost no swelling, but they report anterior knee pain that worsens with activities such as running, jumping, using stairs, and squatting. Patellar tendinitis can occur in conjunction with PFPS, but the patient with patellar tendinitis alone usually does not experience the fullness in the knee that can accompany PFPS, nor do these patients tend to report feelings of locking, catching, or giving way in the knee. Foot orthotics or new shoes may correct overpronation.
Some patients with jumper's knee will find pain relief by using a patellar tendon strap, such as the Chopat strap—a rubber strap designed to change the forces across the patellar tendon and relieve the pain—which is available from most sporting goods stores, catalogs, and Web sites. “The patellar tendon strap tricks the body into thinking that forces are distributed differently around the knee,” Dr. Flinn explained.
Treatment and rehab strategies include anti-inflammatories; stretches for the quadriceps, hamstrings, and calf muscles (gastrocnemius and soleus); and exercises for the adductor muscles of the hip. Patients can usually ride a bike to help maintain fitness during recovery.