74: Patellofemoral Syndrome

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Patellofemoral Syndrome

Rathi L. Joseph, DO; Joseph T. Alleva, MD, MBA; Thomas H. Hudgins, MD


Anterior knee pain

Chondromalacia patellae

Patellofemoral arthralgia

Patellar pain


Patellalgia [1,2]

ICD-9 Codes

715.36  Patellofemoral degenerative joint disease

716.96  Arthritis, patellofemoral

718.86  Patellofemoral instability

719.46  Patellofemoral pain syndrome

ICD-10 Codes

M17.9 Osteoarthritis of knee, unspecified

M13.861  Other specified arthritis, right knee

M13.862  Other specified arthritis, left knee

M13.869  Other specified arthritis, unspecified knee

M23.50 Chronic instability of knee, unspecified knee

M23.51 Chronic instability of knee, right knee

M23.52 Chronic instability of knee, left knee

M25.561   Pain in right knee

M25.562   Pain in left knee

M25.569  Pain in unspecified knee

M22.2X1  Patellofemoral disorders, right knee

M22.2X2  Patellofemoral disorders, left knee

M22.2X9  Patellofemoral disorders, unspecified knee

M22.3X1  Other derangement of patella, right knee

M22.3X2  Other derangement of patella, left knee

M22.3X9  Other derangement of patella, unspecified knee

M22.40 Chondromalacia patellae, unspecified knee

M22.41 Chondromalacia patellae, right knee

M22.42 Chondromalacia patellae, left knee


Patellofemoral syndrome is the most common ailment involving the knee in both the athletic and the nonathletic population [35]. In sports medicine clinics, 25% of patients complaining of knee pain are diagnosed with this syndrome, and it affects women twice as often as men [3]. Yet despite the common occurrence of this disorder, there is no clear consensus on the definition, etiology, and pathophysiology [6]. The most common theory is that the syndrome is an overuse injury from repetitive overload at the patellofemoral joint. This increased stress results in physical and biomechanical changes of the patellofemoral joint [6]. The literature has focused on identification of risk factors leading to altered biomechanics that produce poor patellar tracking in the femoral trochlear groove and thus stress at the patellofemoral joint. Possible pain generators include the subchondral bone, retinacula, capsule, and synovial membrane [7]. Historically, the histologic diagnosis of chondromalacia, or deterioration of the cartilage, had been associated with patellofemoral syndrome. However, chondromalacia is poorly associated with the incidence of patellofemoral syndrome [5]. Electromyographic comparison of vastus medialis oblique (VMO) to vastus lateralis activation has shown delayed VMO activation in those patients with patellofemoral syndrome [8]. A pilot investigation has been done with 64-channel surface electromyography and motion capture to evaluate activation of the four heads of the quadriceps muscle in three dimensions. That study showed increased variability in the pattern of activation in the patellofemoral group compared with controls, resulting in altered patellar kinematics and loading of the patellar facets [9].


The patient with patellofemoral syndrome will complain of diffuse, vague ache of insidious onset [3]. The anterior knee is the most common location for pain, but some patients describe posterior knee discomfort in the popliteal fossa [4]. The discomfort is aggravated by prolonged sitting with knees flexed (“theater” sign) as well as on ascending or descending of stairs and squatting because these positions place the greatest force on the patellofemoral joint [10]. The patient may also experience pseudolocking when the knee momentarily locks in an extended position [11,12].

Physical Examination

The examination focuses on identification of risk factors that contribute to malalignment and rules out other pathologic processes associated with anterior knee pain. Tenderness to palpation at the medial and lateral borders of the patella may be appreciated [3]. A minimal effusion may also be present. The results of manual testing for intra-articular disease, such as the Lachman (anterior cruciate ligament) and McMurray (meniscal) maneuvers, will be negative.

The presence of femoral anteversion, tibia internal rotation, excessive pronation at the foot, increased Q angle, and inflexibility of the hip flexors, quadriceps, iliotibial band, and gastrocnemius-soleus should be determined [13]. The patella position (baja or alta, internal or external rotation) should also be assessed with the patient sitting and standing. Each of these factors has either a direct or an indirect influence on the tracking of the patella with the femur (Fig. 74.1).

FIGURE 74.1 Forces on the patella in patellofemoral syndrome.

The Q angle is the intersection of a line from the anterior superior iliac spine to the patella with a line from the tibial tubercle to the patella (Fig. 74.2). This angle is typically less than 15 degrees in men and less than 20 degrees in women. An increased angle is associated with increased femoral anteversion and thus patellofemoral joint torsion [11]. However, a consensus on the importance of an increased Q angle is lacking [6

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