In most knees, there is a groove on the end of the femur, called the trochlea, in which the kneecap sits. This provides a certain amount of bony stability to the kneecap joint to prevent it from sliding, mainly to the outside. When this groove is flatter or completely flat or concave in shape, the bony stability that is normally present is absent and is a much higher risk of having the patella dislocate or partially dislocate (sublux5-) to the outside.
In patients who underwent isolated medial patellofemoral ligament reconstruction, trochlear dysplasia correlated with patellofemoral cartilage lesions, according to study results.
“In a population of patients with chronic lateral patellar instability undergoing [medial patellofemoral ligament] MPFL reconstruction, the prevalence of both trochlear dysplasia and cartilage damage was each about 85%,” John A. Grant, MD, PhD, FRCSC, Dip. Sport Med, told Healio Orthopedics. “About half of the patients with trochlear dysplasia had evidence of high-grade dysplasia. The majority of cartilage lesions (67%), which were primarily in the central and distal medial patella, were partial thickness (ICRS grade 2-3). The presence of trochlear dysplasia was the strongest predictor of cartilage lesions in these patients. Interestingly, short term (2 year) follow-up, did not identify a relationship between cartilage lesion presence, size, or location and disease-specific quality of life.”
Researchers collected preoperative, intraoperative and postoperative demographic, anthropometric, radiographic, cartilage lesion morphology and outcome data of patients who underwent isolated medial patellofemoral ligament reconstruction. Investigators used single-variable and multivariable logistic regression analyses to determine whether patellar instability risk factors impacted the chance of cartilage lesions in 264 knees. Investigators used single-variable linear regression analysis to determine whether the presence, size or ICRS grade of cartilage lesions could predict 12-month or more than 24-month postoperative Banff Patellar Instability Instrument 2.0 scores in 121 patients with unilateral symptoms.
Results showed 84.5% of knees had patellofemoral cartilage lesions, of which 88.3% were involved in the distal medial patella. There was a correlation between trochlear dysplasia and the presence of a cartilage lesion. Investigators noted no correlation between the presence, size and grade of cartilage of lesions and the 12-month or more than 24-month postoperative Banff Patellar Instability Instrument 2.0 scores.
“Future research is needed to determine how these cartilage lesions will affect disease-specific quality of life over the long-term and whether earlier intervention with surgical stabilization can decrease the burden of cartilage injury and perhaps improve long-term quality of life for these patients,” he said. “Given the most common location for patellar cartilage damage in this population, the use of medializing tibial tubercle osteotomies as part of the treatment algorithm for patellar instability should be considered with caution.”– by Monica Jaramillo
This is a valuable study reiterating the high incidence of distal medial patella articular lesions related to patella dislocation. What is somewhat surprising is the lack of correlation between more severe articular damage and postoperative pain. Many who do patella instability surgery, myself included, find that extent of articular damage does correlate with pain and is in fact a leading cause of difficulty following well done medial PF stabilization. The discrepancy in this study is easily explained by their exclusions, as patients with high TT-TG ratios and those who had tibial tubercle transfer surgery were excluded from the Holliday study.
Patellofemoral surgeons recognize that some patella instability patients benefit from tibial tubercle osteotomy (TTO), particularly anteromedialization TTO (AMZ) which specifically tips up and thereby unloads distal medial and lateral patella articular lesions. Asymptomatic articular lesions in the Holliday study likely reflect a population of patients (MPFL reconstruction alone) separated from those who had required a TTO. The Holliday study establishes nicely that articular lesions in trochlea dysplasia patients without lateral tracking should fare well with medial reconstruction alone. I believe the study is testimony to the surgeon’s skill at selecting outpatients who benefit from TTO. Thus, this selected study notably precludes those patients who had already had TTO of any sort for lateral tracking and/or a symptomatic patellofemoral articular lesion. The results reflect excellent patient selection for isolated medial patellofemoral complex reconstruction.