chapter 7: nonarthritic anterior knee pain
Patients with patellofemoral malalignment frequently complain of nondescript aching or pain in the anterior knee. The association of this pain with softened articular carti¬lage has led historically to the assumption that this pain is caused by soft cartilage or chondromalacia. Several authors (6, 11 14) have documented the poor association be¬tween morphologically softened articular cartilage and pain in the anterior knee. Stougard (15), Casscells (16), and Emery and Meachim (17) demonstrated the frequency of softened articular cartilage at the time of autopsy. Pevsner et al (18) pointed out that there is normal age related degeneration of patellar cartilage, further substantiating that intense anterior knee pain cannot be associated routinely with chondromalacia. Furthermore, articular cartilage is devoid of nerve fibers. Fulkerson (1) has shown that tenderness in the lateral retinaculum and vastus lateralis insertion is common in patients with patellofemoral pain. Johnson (14) later substantiated these findings. Recognizing that malalignment is frequently associated with such pain, it is apparent that recurrent stretching or abnormal retinacular stress might be associated with imbalance of the patellofemoral articulation (see Fig. 2.9). Similarly, medial retinaculum might be recur¬rently stretched or abnormally stressed in patients with patellar imbalance.
We showed in 1985 that some patients with chronic anterior knee pain associated with malalignment show evidence of small nerve injury (2) in the lateral retinaculum (Fig. 7.5). In 1991, Mori et al (19) further confirmed the presence of degenerative changes in retinacular nerves of patients with patellofemoral dysfunction. This is not really surprising when one recognizes that a chronic lateral tilt of the patella will even¬tually lead to adaptive shortening of the lateral retinaculum. Upon flexion of the knee, however, a shortened lateral retinaculum will come under excessive stress as the patella is drawn in the trochlea and the iliotibial band pulls posteriorly on the already shortened lateral retinaculum.
Butler Manuel et al (20) noted in 1992 that some patients with anterior knee pain, but without the usual features of reflex sympathetic dystrophy, will respond favorably to sympathetic blockade. One must carefully consider, therefore, the possibility that small nerve injury in these patients could potentially cause concomitant sympathetic stimulation.
Recognizing the pathomechanics of anterior knee pain will help the clinician identify, accurately, a source of pain in most patients, and careful evaluation of the patient with patellar malalignment should include a thorough examination of the peripatellar soft tissues. Commonly, pain has been noted in the inferomedial peripatellar area and in the superolateral aspect of the patella where the lateral retinaculum interdigitates with the vastus lateralis tendon. If a retinacular pain source can be identified, injection of the painful retinacular band may confirm a diagnosis and, on occasion, give lasting relief of pain.
The clinician should pay particular attention to residual bands of lateral retinaculum in patients with continued pain after retinacular release. If a lateral retinacular release is done transecting all of the lateral retinaculum except a specific painful band of the lateral retinaculum, pain may be intensified as stresses are transferred from transected nonpainful portions of the retinaculum to a residual, painful component of the lateral retinaculum. Recognition of this condition may permit a fairly simple solution to persistent pain after lateral retinacular release in some patients.
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