chapter 7: nonarthritic anterior knee pain
Anterior knee pain is often described as dull and aching or throbbing, but occasionally there may be episodes of acute, sharp pain. Pain is characteristically provoked by prolonged sitting with the knee flexed to 90 degrees, particularly in a theater or automobile where change of position is constrained by the physical setting. Going up and down stairs often precipitates a period of pain. Squatting may be impossible. The surgeon should learn to characterize the pain and determine if the specific pain described by a patient suggests neuroma (sharp, dysesthetic) or articular damage (position related, aching, related to crepitation).
Some patients report uncomfortable grating while flexing or extending the knee. This complaint may be constantly present with knee movement. Occasionally, crepitus will be audible, as well as sensed internally by the patient, although audible crepitus is a more common feature of patellofemoral arthrosis. Crepitus is not always present in patients with clinically significant anterior knee pain. Also, when it is present, it does not necessarily cause anterior knee pain.
This is another common symptom that may point to the patellofemoral joint; it consists of a sudden reflex relaxation of the quadriceps while performing some movement with the knee flexing or extending under load. Giving way is also a frequent complaint in association with ligamentous instability or meniscal lesions but, under those circumstances, the giving way is generally associated with a turning movement. Giving way of patellofemoral origin is most frequent while ascending stairs or walking down an incline. This may even occasionally lead to a fall. Quadriceps weakness alone is another common cause of giving way.
Patients may report locking of the knee related to a lesion on the patella or trochlea but, on closer questioning, they seldom mean anything more than a catching sensation on attempting to straighten the knee under load. These episodes of "locking" are usually transient, and one must not incorrectly diagnose a meniscal lesion. Asking the patient to define his/her meaning of locking will almost always bring out the difference, which is then confirmed on physical examination.
Patients sometimes complain of knee swelling, although this is not a frequent physical finding. The complaints are often intermittent, and it is possible that a mild effusion may also be transiently present when there is significant patellar malalignment. In general, the presence of effusion will indicate synovial irritation from significant chondral disruption with free proteoglycan and cartilage fragments in the joint, a primary synovial disease, or trauma with bleeding.
Careful history and precise examination are extremely important in determining a nonarthritic source of anterior knee pain (7). With the patient supine and the knee supported on the examining table in full extension with the quadriceps relaxed, the patella may be grasped with the examining thumb and finger and forced distally into the superior entrance of the trochlear sulcus. The examiner must be careful not to catch some of the suprapatellar synovial membrane, thus causing discomfort from pinching of the synovium between the articular surfaces. This can be avoided by drawing the patella into the sulcus before applying any pressure. Moving the patella distally and proximally in the sulcus (passively) with some, pressure applied may bring out symptoms. This must be done carefully, with the knee slightly flexed to assure articular contact. Any pain elicited must be differentiated from soft tissue or retinacular pain. With the quadriceps relaxed, the patella can be tilted medially and then laterally in an attempt to differentiate the side or area of the patella that is causing the discomfort. The patella can also be tilted medially and laterally to palpate peripatellar retinaculum with the examining finger. Palpating specific facets is impossible without stressing the intervening retinaculum.
The retinaculum itself must be examined completely (1). First, the examiner should palpate the entire lateral retinaculum to see if there is any specifically tender area (Fig. 7.1). Displacement of the patella in a lateral direction may be very helpful to place the lateral retinaculum on slight tension as the patella rides up the lateral trochlear facet (Fig. 7.2). This also permits the examiner to evaluate better the tension in the lateral retinaculum (tight lateral retinaculum is commonly associated with excessive patellar tilt). Tenderness has been noted particularly at the junction of the vastus lateralis and the lateral retinaculum in some patients with patellar malalignment.
Similarly, the examiner should proceed with gentle palpation of the medial retinaculum, distal quadriceps, and patellar tendon. Sometimes pain may be localized to the infrapatellar tendon region, completely separate from the patella itself.
Soft tissue retinacular pain is common in many patients with anterior knee pain problems, and the source of this pain can be localized accurately if some time is de¬voted to careful clinical evaluation of the peripatellar soft tissues, including the quadri¬ceps tendon, patellar tendon, and all retinacular structures (Fig. 7.3). Even patients who have had lateral retinacular release may have pain in a residual band of lateral retinaculum.
The patella should be compressed against the trochlea with the examining hand to test for articular pain. This should be done in varying degrees of flexion.
It is important to observe the course of the patella throughout the entire range of movement of the knee. With the patient supine and the quadriceps relaxed, the patella is drawn to the opening of the trochlear sulcus by the peripatellar retinaculum. Tightening the quadriceps produces a proximal and generally slightly lateral movement of the patella. It should be noted if this proximal and lateral movement is excessive. Next, with the patient sitting on the edge of the examining table with the thigh well sup¬ported, beginning with the knee at 90 degrees of flexion, the course of the patella is carefully observed during active extension and then flexion. Of particular importance is the exit from, and re entry into, the trochlear sulcus. This should be smooth, with no abrupt or sudden movement. Lateral movement is normal in the last few degrees of ex¬tension, emphasizing the importance of obtaining tomographic studies of the patello¬femoral joint with the knee slightly flexed in order to understand aberrations in contact pressure.
The Q angle may be measured, although the Q angle itself is not a reliable indica¬tor of patellar malalignment. It should be regarded as one bit of information that may be correlated with other clinical findings in order to understand a malalignment prob¬lem as fully as possible. It is an error to treat a Q angle, or to assume that a patient with a high Q angle will require tibial tubercle transfer in every case that resists con¬servative treatment. The Q angle is measured with the quadriceps relaxed and also with the patella localized in the trochlea. It is of interest to note the orientation of the patel¬lar tendon with the knee flexed to 90 degrees. Under normal circumstances, the tibia has derotated, markedly reducing the Q angle in flexion (8, 9) (Fig. 7.4). The presence or absence of effusion should be noted. It is our impression that effusion is more com¬mon when cartilage changes are more advanced.
Next, the patient should roll into the prone position, and the examiner should evaluate knee flexion passively to see if the quadriceps is excessively tight (Figure A). This is also an ideal time to palpate the patellar tendon, particularly at its origin and in¬sertion.
In any evaluation of a knee complaint, complete examination is necessary, includ¬ing testing of the medial and lateral collateral ligaments, the anterior and posterior drawer signs, tests for rotatory stability, and evaluation for evidence of meniscus de¬rangement or osteoarthritis. Insall (10) emphasized the importance of differentiating pain of patellar origin from other disorders of the knee.
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