Deciphering knee pain.

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.

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 as a result of 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 also lead to an acute tear of the meniscus. Chronic and repetitive stress can cause slow degeneration and tearing, often seen in older runners.

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 cuffing 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 exercises alone can't eliminate the pain of the meniscal teat The definitive treatment for meniscal injury 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. For example, patello-femoral stress from walking is three times the body weight on each step, while weightlifters in a clean and jerk lift may load the patella and patellar tendon up to 13 times their 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 men, women'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. Kneeling puts direct pressure on a sore or inflamed patella and 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 also 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 the extensor overuse syndrome. In these cases 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. Mifi and arthrograin are often not as helpful for patellar pain diagnosis as they are in the diagnosis of meniscal tears.

Non-surgical treatment is usually the key to patellar problems. Pateliar 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 patelia 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),

* 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), and

* 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.

How to Distinguish Meniscal vs. Patellar Syndromes

What You Notice        Meniscus                   Patella

Onset of symptoms      Usually an acute twisting  Usually insidious
                       injury with recurrences    onset related
                                                  to overuse

Symptom site           Localized jointline pain   More diffuse pain
                                                  in the front of
                                                  the knee

History of locking     Sometimes present          Grating, ratcheting,
                                                  but not locking

With weight bearing    Pain during activity       Pain after activity

With cutting sports    Pain with rotation         Less pain

When you squat         Pain at full knee          Pain coming up
                       fiexion with               out of a squat
                       inability to duck walk

When you kneel         Rarely painful             Painful with direct
                                                  patellar compression

When you jump          May be painful             Painful and difficult

Doing stairs or hills  Painful going up           Painful going down

When you sit           No Pain                    Pain in front of knee

Strengthening the      Helpful, but won't         Often the solution,
quadriceps             solve the problem          especially quad
                                                  Isometrics

RELATED ARTICLE: Knee Anatomy 101

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 die knee. The four-part quadriceps muscle, which forms the bulk of the front of the thigh is attached to the patella at the front of the knee. The patella tendon connects the patella to the tibia (shin bone) at the tibial tubercle (the bump you feel at the front of the tibia just below the patella). The large quadriceps muscle attaches to the patella and the smaller thumb sized patellar tendon goes 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 falls. When a defect in this chain caus es knee pain, often it must be distinguished between meniscal pain and patellar pain.

Marvin H. Bloom, MD., is an Associate Clinical Professor of Orthopaedic surgery at the University of California at San Francisco, Department of Ortbopaedic Surgery. He is a consultant at the San Francisco General Hospital Sports Medical Clinic. Dr. Bloom ran in the San Francisco Marathon in 1983 and 1986.