Most athletes, recreational or professional, have knee pain sooner or later. Dramatic injuries such as anterior cruciate ligament tears may be fairly simple to diagnose. On the other hand, the more common sources of knee pain in runners can be a challenge to decipher.

Extensor chain pain is by far the most common source of knee pain. Leg extension is the movement of the bent leg toward a straight position. The extensor chain is the series of muscles, tendons, cartilage, and bone, which connect the thigh to the lower leg and hinge at the knee. The four-part quadriceps muscle forming the bulk of the front of the thigh is attached to the patella at the front of the knee. From the patella at the top of the lower leg, the patella tendon connects the patella to the tibia at the tibial tubercle (the bump you feel at the front of the tibia just below the patella.) Feel the large quadriceps muscle as it attaches to the patella and the smaller thumb sized patellar tendon going from the lower end of the patella to the tibial tubercle. This patellar tendon is what is tapped when your doctor checks your reflex, called the patellar tendon reflex. When the extensor chain is functioning normally it is the powerful extender of the knee that gives us running and leaping ability and prevents giving way and falls. When a defect in this chain causes knee pain, often it must be distinguished between meniscal pain and patellar pain.

Meniscal Pain
The meniscus is a fibrocartilagenous crescent shaped pad at the inner and outer side of the knee joint similar to the fibrous tissue that holds the shape of your external ear. A meniscal tear usually occurs with a twisting weight-bearing movement. A right-handed pitcher throwing his weight forward onto the left leg and twisting is an example. A misstep can lead to an acute tear of the meniscus. Chronic and repetitive stress can cause slow degeneration and tearing, often seen in the older patient.

With meniscal pain the tenderness is localized to the side of the knee with the tear. Meniscal pain is usually sharp and occurs during athletic cutting maneuvers. A meniscal tear causes pain with a full squat because the tear is compressed between the femur (the large thighbone) and the tibia (the shinbone). A meniscal tear or flap may get caught between the femur and the tibia at the joint resulting in a painful locking sensation.

You can kneel, jump somewhat, and go down stairs pretty well with a meniscal tear, but climbing stairs, which loads the meniscus can hurt. Sitting is not a problem for the patient with meniscal injury.

When a meniscal tear is present there may be swelling due to an accumulation of fluid within the joint and tenderness at the joint line right over the tear. Twisting tests for a meniscal tear will produce a painful palpable clunk felt by the examiner. There may be quadriceps atrophy accompanying a meniscal injury, which can create an additional malfunction in the extensor chain causing secondary problems. This can complicate treatment and recovery. An x-ray may show narrowing of the joint space at the side of the tear. An MRI or an arthrogram can confirm the diagnosis of meniscal tear. However, clear symptoms along with a careful history and examination are often sufficient to confirm meniscal injury and there may be no need for these expensive tests.

Quadriceps exercises to build strength in the extensor chair may help somewhat, but can't eliminate the pain of the meniscal tear. The definitive treatment for meniscal injury and pain is surgery to remove the torn portion of the meniscus. In some cases the torn piece can be stitched back in place.

Patellar Pain
The patella (kneecap) is a wedge-shaped structure, which normally slides up and down in the femoral groove (trochlea) during extensor chain movements. When the patella tracks poorly in the femoral groove, it can lead to painful overuse problems. The patella has the thickest articular cartilage in the body because the stress on the patella as it glides in the femoral groove is so great. Patello-femoral stress with walking is three times the body weight on each step and a weight lifter in a clean and jerk lift may load the patella and patellar tendon to 13 times the body weight.

Normal motion of the patella in the femoral groove does not cause degeneration or pain. The smooth articular cartilage of the femur and the tibia gliding on each other lubricated by joint (synovial) fluid has the least amount of friction of any two surfaces on earth. The joint fluid is pumped in and out of the articular cartilage by the squish and release caused by each step during the normal gait. Joint fluid released during movement nourishes the articular cartilage, which has no blood supply of its own. Pain with immobility is often characteristic of patellar inflammation since this pumping effect is missing at rest.

Patellar inflammation is usually related to chronic stress of the extensor chain as in downhill skiing or downhill running where the extra stress overloads the patella on a repetitive basis. Sometimes the patella has a tendency to move outward on the knee due to a bowstring effect with the knee inside of the line connecting the hip to the ankle. This natural slightly knock-kneed arrangement is more common in women than men. Compared to an equal leg length in men, a woman's hips are wider creating an even greater bowstring force.

Symptoms and tenderness at the front of the knee characterize patellar pain. Problems originating at the patella do not cause true locking but may give a ratcheting sensation with stress, especially going downhill or down stairs. Patella pain often occurs after a period of immobility ("movie goer's knee"). Patella pain is most often felt after cumulative stress on the extensor chain, for example in the evening after a long run. Patellar aching may disrupt sleep.

If you have patellar pain you can drop down into a full squat but you will have trouble using the extensor chain to rise up from the squat, often needing the hands to climb up the body or reach for a table to help the extensors straighten the legs. Direct pressure on a sore or inflamed patella with kneeling will produce pain. The athlete with patellar pain will have pain during jumping and landing. Downhill stepping, downhill running or rapidly going down stairs will cause pain.

Unlike meniscal injuries, there is only occasional swelling with patellar pain. An examiner's manipulation of the knee may produce grinding, but no clunk. Tenderness is usually on the underside of the patella with pressure of the patella against the femur. Sometimes the patellar tendon is the site of the pain response in extensor overuse syndrome and then the tenderness will be directly at the tendon at its attachment to the patella. There is sometimes quadriceps atrophy in patients with patellar pain, but not as commonly as in meniscal injuries. MRI and arthrogram are often not as helpful for patellar pain diagnosis as in the diagnosis of meniscal tears.

Non-surgical treatment is usually the key to patellar problems. Patellar pain may be fully treated with early selective quadriceps muscle strengthening over the last 30 degrees of extension. This type of strengthening combats the tendency of the patella to slip outward or dislocate. Increasing quadriceps tone and strength may help the patella to track more smoothly and efficiently in the femoral groove and is the best bet to relieve patellar pain. Use of a patellar tendon strap or a patellar stabilizing brace can help to insure smooth tracking of the patella in the trochlea until the supporting muscles are stronger and balanced. Ice and anti-inflammatory drugs provide temporary relief at the patella and an arch support is often helpful for patellar tracking.

Rest and training improvements can be very helpful with patellar pain. Training errors that can cause injury to the patella include:

* Excessive downhill running,

* Running in worn shoes that allow excessive pronation

* Running on a canted surface-(running near the curb, always on the same side of the road can be a problem),

* Running in excess of the 10% per week rule-(never increase mileage or intensity by more than 10% per week and never increase both at the same time),

* Training with no rest days.

The causes of knee pain due to meniscal injury or patellar and extensor malfunction may be complex and your physician should be consulted for any ongoing knee pain. However, awareness of some of these concepts may help you and your knees avoid problems.

(Marvin H. Bloom, M.D., is an Associate Clinical Professor of orthopaedic surgery at the University of California at San Francisco, Department of Orthopaedic Surgery. He is the sports medicine consultant to the San Francisco General Hospital Sports Medical Clinic. Dr. Bloom ran in the San Francisco Marathon in 1983 and 1986.)

Volume 17, Number 2, Running & FitNews
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