Key points for patellofemoral osteoarthritis (OA) and chondromalacia

Introduction

Isolated patellofemoral OA is not an uncommon disease process; it can be an etiology of anterior knee pain or simply an incidental finding on radiographs without clinical significance. In a study conducted by Davies and colleagues,1 of 206 knees of patients older than 60 presenting with symptomatic knee pain, 15.4% of men and 13.6% of women had isolated patellofemoral osteoarthritis. In another study, of 240 asymptomatic knees of patients 55 years and older, 19% of men and 34% of women had radiologic evidence of isolated patellofemoral osteoarthritis.2 Patellofemoral osteoarthritis, defined as a loss of the cartilage in the trochlear groove and retro-patella surface, is found in approximately half of patients who are diagnosed with degenerative arthritis of the knee.3 Chondromalacia is a softening of the patellofemoral cartilage, and may be a precursor to degenerative joint disease in this compartment of the knee. For the purposes of this article, both chondromalacia and OA can be the cause of anterior knee pain related to the cartilage in this knee compartment.

Diagnosis

Patients with patellofemoral OA or chondromalacia will typically present with anterior knee pain. There is no one single defining symptom that is characteristic of patellofemoral OA. The presenting anterior knee discomfort may be exacerbated by kneeling or squatting, walking up or down hills or inclines, climbing or descending stairs, rising from a seated position, or being in one position for too long (typically sitting).3 There may be crepitus or a cracking sensation. Often, patients will complain of stiffness in the knee, especially in the morning on first waking; occasionally there may be a sensation of locking (which is really a pseudo locking) or catching, secondary to irritation between the patella and trochlea groove when friction occurs between the bones.3 Iwano and colleagues4 tried to assess a patient’s activities of daily living (ADLs) to further support a diagnosis of patellofemoral OA. In this scale, the highest attainable score was 14 points. Iwano and colleagues4 had found that a score of 4.1 was more predictive of patellofemoral OA combined with femorotibial OA; however, a score of 9.4 was more predictive of isolated patellofemoral OA. Iwano and colleagues4 used the following 7 items to help predict the presence and type of OA: (1) Clarke test (positive when patients complained of pain during knee extension with patella compression), (2) limitation of patellar mobility, (3) pain on compression of the patella, (4) peripatellar tenderness, (5) crepitation during knee movement, (6) crepitation on grinding of the patella, and (7) pain on grinding the patella. Each item was given a score of 0 to 2 points. Two points equaled maneuvers completed without any problem, 1 point equaled maneuvers completed with some difficultly, and 0 equaled maneuvers completed with great difficulty.

Evaluating a patient with suspected patellofemoral OA or chondromalacia may be challenging for the busy primary care provider. The physical examination may often have nonspecific findings. Leslie and Bentley5 found retro patellar crepitus, effusion, and quadriceps wasting greater than 2 cm as the most important findings for detection of chondromalacia of the patella. According to Grelsamer,6 the most important sign for patellofemoral OA is tenderness over the medial or lateral patellar facet. Often radiographic evidence can largely aid in diagnosis. One of the most important views that should be obtained is the Merchant or skyline view (45° angle). Radiographically, patellofemoral joint arthritis can be classified into 4 stages of severity. The stages are as follows: stage 1, mild with more than 3 mm of joint space preserved; stage 2, moderate with less than 3 mm of joint space preserved but no bony contacts; stage 3, severe with the bony surfaces in contact with less than one-quarter of the joint surface; and stage 4, very severe with bony contact throughout the entirety of the joint.7

Treatment

In patients who have symptomatic...