chapter 11: Articular Cartilage Lesions in Patellofemoral Pain Patients
LOCATION OF LESIONS
The author has noted that articular cartilage breakdown will occur on different portions of the patellar articular surface, depending on the nature of the malalignment or trauma. Figure 11.5 shows the regions to be considered.
When there is recurrent shear stress and habitual noncontact, the distal central portion of the patella may break down. This area corresponds to Ficat's critical zone (53). Consequently, this area frequently deteriorates in patients with patellar malalignment, but would not be expected to degenerate as a result of direct trauma in the majority of cases if the knee is flexed. Trauma with the knee in extension, however, could result in articular cartilage damage to the distal central portion of the patella. This is less common because the majority of injuries occur with the knee flexed.
The lateral facet, as described by Ficat (53), is a site of articular cartilage breakdown as a result of increased contact stress in the excessive lateral pressure syndrome (ELPS). Concentration of load on this portion of the patella has been well recognized to occur with chronic patellar lateralization and tilt.
The medial facet is more commonly damaged at the time of patellar dislocation and relocation. At this time, a shear fracture of the central medial facet can occur. Sometimes, extensive damage to the entire patellar medial facet can occur as the patella relocates. Unfortunately, this cartilage damage can be severe, leaving little or no articular cartilage on the medial patella, in some cases. This is particularly important to note because the medial facet shear fracture occurs in patients with lateral instability. Consequently, medialization of the patella is necessary to provide stability of the patella, but at the same time this medialization may cause loading onto the damaged medial facet. A skillful surgeon will recognize this and move the patella only enough to provide stability, probably with some anteriorization of the tibial tubercle, and will avoid imbrication of the medial structures that tilts the patella down onto the damaged medial cartilage.
Another cause of medial patella articular breakdown is previous medial tibial tubercle transfer with posterior placement of the tibial tubercle (Hauser procedure). This can result in severe pain related to exposed bone on the distal medial facet (Fig. 11.8). Often there is a reciprocal lesion on the trochlea.
The proximal patella is more commonly damaged as a result of a dashboard or crush type of injury in which the knee is flexed at the time of impact. The patella will be articulating on more proximal cartilage with the knee flexed. This is the lesion that often occurs in litigation‑related and worker's compensation‑related injury. Unfortunately, it is also an injury that frequently defies adequate treatment and responds poorly to tibial tubercle anteriorization procedures, because these procedures will cause load shift onto the more proximal patella that is injured in these patients.
Diffuse articular cartilage damage more frequently occurs as a result of generalized arthritis, or extensive damage following malalignment and recurrent dislocation.
The different patella cartilage breakdown location patterns are shown in Figure 11.9.
Inside Chapter 11: