Nearly half of patients undergoing patellar stabilization surgery for recurrent patellar dislocation experienced articular cartilage injury, according to results from an MRI study of 35 patients. Researchers also found that articular cartilage injury incidence and severity increased with subsequent dislocations. The findings were presented yesterday.

“Articular cartilage injury following patellar dislocation is common, and delayed surgical treatment may lead to an increase in articular cartilage damage,” study author Christopher Hadley, clinical research coordinator at Rothman Orthopaedic Institute in Philadelphia, told AAOS Now Daily Edition. “This study points to the importance of obtaining an MRI after each dislocation. These data will provide a better understanding about how quickly articular cartilage injury progresses in patients with patellar dislocations.”

With this study, the researchers sought a better understanding of why this process occurs so quickly. “Our concern in these patients is whether subsequent dislocations, particularly between a first and second dislocation, creates an increase in the size of articular cartilage injury,” Mr. Hadley said. “In these cases where articular cartilage injury worsens, a more involved surgery may then be necessary.”

Researchers identified 35 patients undergoing patellar stabilization who had an MRI after initial dislocation and after subsequent dislocations prior to surgery. MRIs were blindly examined to assess the Outerbridge classification grade of articular cartilage injury following each dislocation. Each MRI was then compared for frequency, severity, and location of articular damage.

The incidence of articular cartilage injury following initial dislocation was 45.7 percent (n = 16). Following a second dislocation, that incidence increased to 62.9 percent (n = 22). Of note, 17.1 percent of patients (n = 6) had no initial injury but did experience articular cartilage injury following the second dislocation.

Among the 16 patients with articular injury following initial dislocation, nine (56.2 percent) had an increase in grade of articular cartilage injury following the second dislocation. The remaining patients had no progression in articular cartilage injury.

The high incidence of articular cartilage injury worsening between initial and recurrent dislocation was “surprising,” Mr. Hadley commented, as was the low number of patients who had an MRI between each dislocation episode. “Following patients by MRI, while costly, may be important even in the absence of dislocation, to further quantify the natural history of articular cartilage injury after a primary patellar dislocation.”

The study raises the question of whether surgical treatment should be more strongly considered in patients with articular cartilage injury following initial dislocation, or whether the progressive cartilage degeneration seen by MRI is more indicative of a natural history process in these patients. “To more fully explore this clinical question, future studies with larger patient numbers are necessary,” Mr. Hadley noted.

Studies with greater patient numbers could also identify factors that increase the likelihood of articular cartilage injury, which was not possible to determine in this small population.

Other limitations of the study include its retrospective design and reliance on patient recall, which makes it difficult “to draw definitive conclusions about the number of dislocations a patient experienced,” Mr. Hadley said. Sole use of MRI—which has demonstrated more accurate assessment for grade III and grade IV articular cartilage injuries but poor sensitivity for grade I and grade II injuries—also is a potential limitation.

In addition, this study did not include a control group to account for the contribution of recurrent dislocation events to progressive articular cartilage degeneration. “It may be that the progressive damage seen to the articular cartilage is from the natural history of the initial injury, and not from the trauma of a repeat dislocation episode,” Mr. Hadley added.

Mr. Hadley’s coauthors of “Does Articular Cartilage Damage Worsen from First Time to Recurrent Patellar Dislocation? A Longitudinal MRI Study” are Somnath Rao, MD; Gavin M. Ajami, MPH; Leanne Ludwick, BS; James Liu, MD; Fotios Paul Tjoumakaris, MD; and Kevin Blake Freedman, MD.

Ariel DeMaio is the managing editor of AAOS Now. She can be reached at ademaio@aaos.org.