chapter 11: Articular Cartilage Lesions in Patellofemoral Pain Patients

Radiologic Features

Patients with simple, medial facet "chondromalacia," in addition to being asymptomatic in most cases, will generally have normal radiographs. If there is associated malalignment, differentiation between tilt and subluxation is most important, and the clinician, using criteria described in Chapter 4 should determine the specific malalignment patterns. In short, radiographic studies should enable the clinician to determine whether or not the patient has chondromalacia or arthrosis related to abnormal patellar alignment. Radiographic findings of osteophytes and patellofemoral arthritis with subchondral sclerosis may be found independent of malalignment, but will most often be related to earlier trauma and articular cartilage injury or generalized knee arthritis. A superolateral osteolytic lesion in the patella, particularly if there is peripatellar calcified soft tissue, may indicate gout (80). Metastasis of adenocarcinoma to the patella is another rare cause of anterior knee pain (81).

The simple tangential/axial radiograph will give some idea about articular cartilage integrity and patellar alignment. The lateral knee radiograph will also give an indication if there is significant subchondral sclerosis or other evidence of arthrosis. In the patient who is a candidate for reconstructive surgery because of patellar arthritis, however, it is most important to recognize if there is significant malalignment, because treatment will thereby be determined more accurately. Advanced chondromalacia or arthritis (Outerbridge Grades 3 to 4) without evidence of malalignment on standard radiographs and CT may be handled differently than arthritis in the patient with clear lateral tilt/compression. Traditional axial radiographs may not always demonstrate the extent of abnormal alignment. Bentley and Dowd (82) have commented specifically on the limited usefulness of traditional radiologic measurements in evaluating patients with chondromalacia.

If subluxation and tilt were present when the joint still had cartilage, when the cartilage is gone, both tilt and subluxation may be greater, with osteophyte production even more prominent.

A tilt/compression syndrome is the most common cause of lateral patellofemoral arthrosis. CT may show mild lateral tilt (Fig. 11.50) due to articular cartilage softening and loss of normal articular cartilage mechanical properties (83) (Fig. 11.51). If the patella starts out subluxated and tilted, and then loses articular cartilage, subluxation and tilt will often progress (Fig. 11.51). The extent of this progression can be best determined using either CT or MRI.

In evaluating tomographic images, the clinician may note changes on the trochlear side that correlate with pain and require surgical correction (Fig. 11.52 A, B, C).



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