Patellofemoral Disorders

CHAPTER 34

Patellofemoral Disorders

Patellofemoral Pain Syndrome

INTRODUCTION/ETIOLOGY/EPIDEMIOLOGY

• Patellofemoral pain syndrome (PFPS), also called “runner’s knee,” is one of the most common knee disorders.

— Affects up to 29% of adolescents per year, including 5% to 15% of adolescent athletes during a single sports season

— Also common in those who do not participate in sports

— Twice as common in females as in males

• Pain comes from mechanical strain or stress on the medial or lateral retinaculum or subchondral bone (Figure 34-1).

• The etiology is often multifactorial and involves some combination of abnormal patellar tracking, direct trauma, and overuse.

— The most frequent causes of abnormal patellar tracking are quadriceps weakness and tightness along with hip muscle weakness. These muscle imbalances are more common during periods of rapid growth.

— Less frequently, anatomic variants such as femoral anteversion or external tibial torsion cause abnormal patellar tracking (see Chapter 25, Out-toeing).

Figure 34-1. Anterior knee anatomy.

From Dixit S, DiFiori JP, Burton M, Mines B. Management of patellofemoral pain syndrome. Am Fam Physician. 2007;75(2):195. © Todd Buck.

• Other risk factors include rapid increase in activity, direct trauma (eg, a fall onto the patella), and patellar hypermobility

— PFPS occurs in 20% to 27% of patients with chronic anterior cruciate ligament (ACL) deficiency, and in 48% of patients with chronic posterior cruciate ligament deficiency.

— PFPS is reported by 32% of patients after ACL reconstruction.

• PFPS should be distinguished from chondromalacia, which is not a diagnosis, but rather a surgical finding of softening or fibrillation of the patellar articular cartilage.

— Many people with PFPS do not have chondromalacia, and many with chondromalacia do not have PFPS.

— In those with chondromalacia and PFPS symptoms, no correlation exists between severity of chondromalacia and severity of symptoms.

SIGNS AND SYMPTOMS

History

• Anterior knee pain that is worse with activity, especially running and knee flexion movements such as jumping, using stairs (especially descending), squatting, and prolonged sitting (theatre sign).

• Pain is often peripatellar, but many patients are unable to localize pain to one specific location and use the “grab sign” (patient grabs the entire front of the knee) to show where the pain is felt.

• Pain is frequently bilateral.

• There may be mild swelling or grinding, popping, or cracking around the patella with knee extension or flexion.

• Some patients report a “giving way” sensation. This is caused by pain inhibiting the quadriceps muscle, resulting in knee collapse without joint instability.

Physical Examination

• In many cases the physical examination is normal.

• In some cases, one or more of the following findings may be noted:

— Patella

■Infrapatellar swelling or mild effusion

❖ Tenderness along the patellar facets or retinaculum (Figure 34-2)

Figure 34-2. Palpation of medial and lateral patellar facets.

From Dixit S, DiFiori JP, Burton M, Mines B. Management of patellofemoral pain syndrome. Am Fam Physician. 2007;75(2):194–202.

Figure 34-3. Patellar maltracking: “J” sign. As the patient actively extends the knee, the patella follows an inverse “J” path from point A to point B, rather than gliding normally along a straight line.

From Dixit S, DiFiori JP, Burton M, Mines B. Management of patellofemoral pain syndrome. Am Fam Physician. 2007;75(2):195. © Todd Buck.

❖ Pain with compression of patella

❖ Lateral patellar tracking with knee extension, known as the inverted “J” sign (Figure 34-3)

❖ Hypermobile patella (can be displaced either medially or laterally more than 25%–50% of its width)

— Other contributing factors that may be present include

■Weak hip external rotators or hip abductors

■Tight lateral structures, including lateral retinaculum (lateral patellar tilt), iliotibial band, and vastus lateralis

■Weak medial quadriceps, especially vastus medialis, leading to insufficient medial pull on the patella

■Tight quadriceps (see Chapter 4, Physical Examination, Figure 4-6)

■Tight gastrocnemius (see Chapter 4, Physical Examination, Figure 4-4)

■Miserable malalignment—internal femoral rotation (femoral anteversion), external tibial rotation, and pes planus

■Excessive lateralization of the tibial tubercle, such as from external tibial rotation

DIFFERENTIAL DIAGNOSIS

• Patella dislocation or subluxation

• Patellar tendinopathy

• Osgood-Schlatter disease

• Sinding-Larsen–Johansson syndrome

• Iliotibial band friction syndrome

• Focal chondral or osteochondral lesion of the trochlea or patella

• Focal chondral or osteochondral fracture of the trochlea or patella

• Inflamed infrapatellar fat pat

• Osteochondritis dissecans

• Meniscus tear

• Plica syndrome

• Inflammatory arthropathy

• Infection

• Hip conditions such as Perthes disease or slipped capital femoral epiphysis can produce vague knee pain in the setting of a normal physical examination.

DIAGNOSTIC CONSIDERATIONS

• The diagnosis can be made clinically.

• Imaging studies and laboratory tests are normal in patients with PFPS, but they may be necessary to rule out other causes of anterior knee pain (see “Differential Diagnosis” above).

— Radiographs of the knee (anteroposterior [AP], lateral, notch, and sunrise or Merchant views) should be the first step in the evaluation for alternate causes of knee pain suggested by history or examination, including

■History of direct trauma

■Significant bruising, swelling, or effusion

■Restricted motion

■Pain at rest

■Mechanical symptoms (catching, locking, or giving way)

■Focal tenderness not around the patella (eg, femoral condyle or joint line)

■Patients younger than 10 years

■Bipartite patella occurs in less than 2% of the population and is rarely a cause of patellofemoral pain.

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