Chondromalacia Patellae

Hema N. Choudur, Anthony G. Ryan, Peter L. Munk, and Laurel O. Marchinkow

An elderly woman presented complaining of long-standing anterior knee pain, especially when descending stairs and rising from a chair.

Figure 12A

Figure 12B

Chondromalacia patella.

• Osteoarthritis
  
• Peripatellar tendinitis/bursitis
  
• Patellar fracture
  
• Subluxation/dislocation of the patella

Softening or wearing away of the patellar articular cartilage (chondromalacia patella) causes varying degrees of inflammation and pain. The underlying bone becomes involved when the entire thickness of articular cartilage is destroyed. Severity is graded on a scale from 1 to 4.

The patella serves primarily to increase the leverage and therefore the efficiency of the quadriceps muscle. Considerable retropatellar forces are present throughout the entire range of motion of the knee. The articular cartilage is thus compressed against the femoral condyles, exacerbated by acute trauma or chronic overuse.

Other anatomical factors causing excessive compression forces are

1. Patellar malalignment This can result from an increased Q angle (line of action of the quadriceps force to the line of patellar motion). This angle lies between a line drawn from the anterior superior iliac spine to the center of the patella and a line from the tibial tuberosity to the center of the patella. With anteversion of the femur and tibial torsion, the angle increases. With the quadriceps relaxed, the normal angle is ~13 to 18 degrees.
   
2. Sulcus angle An increase in this angle (formed by lines drawn from the apices of the femoral condyles to the nadir of the condylar sulcus) causes excessive patellar motion, secondary to the resulting shallow trough.
   
3. Position of the patella relative to the femoral condyle If the patella is high-placed (patella alta) or low-placed (patella baja), there is an alteration of the normal biomechanical forces.
   
4. Strength of the quadriceps An imbalance of patellar tracking can occur secondary to eccentric contraction of the separate components of the quadriceps. The patellar retinaculae and iliotibial tracts may also contribute to patellar maltracking. Atrophy of the vastus medialis (congenital or secondary), reflex inhibition due to pain, and a dystrophic medial mass are potential causes.
   
5. Patellar facets An alteration of the facet surfaces, as compared with the normal, also leads to chondromalacia patella. As per Wilberg’s classification, a small convex (type 3) medial facet tends to cause chondromalacia.
   
6. Trauma Ten percent of chondromalacic knees are due to sports injuries, especially football and soccer, where the quadriceps is overused. Abnormal patellar tracking also occurs in running around a bend, especially on a chamfered surface.

The articular cartilage of the patella consists of collagen fibers oriented tangentially from the articular surface to the subchondral bone; these fibers are disrupted to varying degrees secondary to applied compressive forces. Most of the resulting changes occur at the median ridge of the patella, where the cartilage is thickest. Associated microfractures and sclerosis of the subchondral bone occur in association.

Pain along the anterior aspect of the knee while walking, running, or jumping is the usual complaint. It is often aggravated while descending or ascending stairs. Swelling of the knee with crepitus occurs with chronicity.