Anterior Knee Pain
Anterior knee pain is pain on the front side of the knee, behind the kneecap.
Anterior and posterior are anatomic terms for front and back. Anterior knee pain almost always results from irritation of the undersurface of the kneecap (patella) and the underlying trochlear groove of the femur (thigh bone). (Figure 1a & b).
An abnormally shallow trochlear groove or high or low-riding kneecap may also predispose to anterior knee pain. In some people, the pain is a result of arthritis, in others, it is due to poor joint mechanics related to inadequate muscle or the unusual shape of the kneecap. In advanced cases of arthritis behind the kneecap, grinding or popping open are complained of due to irregular or roughened cartilage surface. This usually has been termed patellofemoral chondromalacia which literally means "sick cartilage." (Figure 2)
Symptoms usually include some or all of the following: increased discomfort climbing stairs, difficulty kneeling and squatting, a grating sensation with knee motion, a feeling that the knee is going to give out, and swelling. In fact, this is the most common reason for the complaint of knee instability.*
Women teenage or older experience this problem much more frequently than men. This is probably related to the greater angulation (valgus) in a woman's knee after the age of puberty, when the pelvis becomes wider and the knees remain centered toward the midline, giving many women the appearance of ''knocked knees." Additionally, most women have greater ligamentous laxity and less muscle tone than men. Often a combination of outward migration and abnormal tilting of the kneecap are treatable causes of the symptoms (Figure 3a, 3b, & 3c). This is called patellar subluxation.
Occasionally, anterior knee pain is a result of inflammation in the bursa directly in front of the kneecap. When this occurs there is usually an infection associated with swelling and redness. It can also appear this way with gout.
A very rare cause of anterior knee pain is plica syndrome (3d & 3e). This is a scenario wherein a thickened, abnormally large fold of the inner lining of the knee (synovium) begins rubbing on the front of the femoral condyle (one of the cartilage-covered ends of the thigh bone).
The anatomy of the knee is very simple. The front of the knee is comprised of the kneecap or patella, which is suspended with the patellar ligament below, extending to the upper surface of the Leg bone (tibia), and the quadriceps tendon above coming from the quadriceps muscle. The kneecap rides in a cartilage-lined trough on the end of the thigh bone (femur) called the trochlear groove. Because the knee does not move simply as a hinge, the kneecap tends to slide outwardly at some point in the arc of knee flexion. This results in subtle, visible, and in some people, audible clunking. Normally, this is not painful. The kneecap is stabilized by patella femoral ligaments (bands of soft tissue on either side of the end of the thigh bone) in addition to the quadriceps and patellar tendons and the medial or lateral retinacula. (Figure 3a & 3c above)
Diagnosis requires a careful physical exam, sunrise x-rays (Figure 5), and a review of complaints.
Treatment varies depending upon diagnosis as well as the patient's age, duration, and magnitude of the problem. For the purposes of this brochure, the discussion will be limited to the treatment of pain behind the A-kneecap, i.e., patellofemoral irritation. Specific exercise, oral nonsteroidal anti-inflammatory medication (NSAID), and a neoprene stabilizing sleeve are usually the first options. Avoidance of kneeling and repetitive squatting is often beneficial for symptom relief For more stubborn cases, a "cortisone" injection may be given into the joint. If a person is overweight, dieting is important to decrease the forces upon the kneecap. This is much akin to pressing firmly or lightly on a piece of sandpaper: the harder the force, the more surface is abraded.
For anterior knee pain in adults, 80% without specific treatment got pain relief (Finestone et al). Anti-inflammatory medication resulted in relief of pain in 60% of the patients after 5 days (Fulkerson and Folcik).
A lot of research has been done in rehabilitation centers to determine the best exercise, if any, to subject a person to when they are complaining of anterior knee pain. The argument over the past few years has centered around closed vs. open chain exercises.** It appears that a combination of these will yield the best result. It's easier to discuss this exercise directly with a physical therapist than to read about it here. The duration of nonoperative treatment depends on the severity of one's symptoms and whether or not they are making progress. Generally, about six months of conservative management would be considered a minimum.
In severe cases, those where nonoperative means, i.e., medications, exercises, and braces have failed to relieve symptoms, arthroscopic surgery may be of benefit. Arthroscopic surgery is performed through small puncture wounds on the knee as an outpatient. The inside of the knee is viewed and instrumented using fiberoptic visualization. (Figure 6a - 6d) Release of the lateral retinaculum may allow enough shifting of the kneecap and local denervation of inflamed or damaged nerve fibers without affecting skin sensibility to provide relief of pain. For more severe cases, changing the direction of pull of the ligaments on the kneecap by relocating the patellar tendon and shifting its attachment inward (towards the other knee) may be necessary.***
In the case of severe arthritis behind the kneecap which is normally the result of trauma, i.e., post-traumatic arthritis, complete removal of the kneecap is sometimes warranted (patellectomy). Patellofemoral joint replacement, i.e., insertion of a metal and plastic gliding surface in just this localized part of the knee, has been available for well over a decade. There is limited experience with this and it would generally only be considered for older, more sedentary people because implants have a tendency to loosen over time in very active individuals. Traditionally, most people who are old enough to require any kind of joint replacement are best treated with total joint replacement, not just the surface between the patella and the trochlear groove.
Complications of Surgery
The reported rate for infection of arthroscopic surgery varies from a high of 1 in 500 to a low of 1 in 2000 people. Of people who undergo lateral retinacular release, the most chronic knee pain is being trimmed away as common surgery for anterior knee pain, 7% develop painful swelling of the knee due to immediate postoperative bleeding. This can usually be prevented by wearing a compressive wrap for a few days after the operation. The person may have a visible tender scar that persists after surgery and it is possible, though unlikely, that the surgery will have no effect on the preoperative pain and surgery could even worsen a person s complaints. Clotting of veins in a patient's case (phlebitis) rarely occurs.
Recovery from Surgery
Recovery depends upon the type of operation performed. Generally, a couple of days after surgery the person spends their time lying around with an ice pack on the knee doing every exercise. Over the next few weeks, they progress to relatively normal mobility. Usually, we will let patients walk on the leg immediately. Return to participation in sports depends on the operation performed, generally about six weeks. It generally takes six months or more, however, to reach maximum medical improvement after reconstructive knee surgery. The main benefit is usually achieved within 3 to 4 months
Surgical Treatment: (Performed only on patients who failed nonoperative treatment.)
Lateral release: 77-88% good to excellent results (JBJS 1997).
*Other causes of knee instability symptoms are torn cruciate ligament, unstable torn meniscus, or a loose body within the knee.
**Open chain exercises are those that are performed without machinery or any direct resistance such as straight leg raising. Closed chain exercises are those that are done with contact with the floor such as squatting, leg presses. etc.
***e.g. Fulkerson osteotomy