Please welcome Emma Johnson. Please come up. She will be presenting on the differences in the severity and location of patella-femoral cartilage damage between instability patients with and without patella alta. Hello, my name is Emma. I'm a fourth-year medical student and former Rothman Research Fellow. I'd like to thank my co-authors as well as the two societies for having us here today. Our disclosures can be found on the website. Patellar instability affects approximately 150 out of 100,000 adolescents between the age of 14 and 18. This rate is expected to rise over time. Risk factors for patellar dislocation include patella alta, trochlear dysplasia, and elevated TTTG distance. Patella alta increases risk up to four times, which is thought to be due to the patella entering the trochlear groove at a greater degree of knee flexion. Given these changes in biomechanics, patella alta may alter cartilage injury patterns in patella-femoral instability. The purpose of our study was to retrospectively analyze whether preoperative cartilage damage on MRI differs in severity and location between patellar instability patients with and without patella alta. We hypothesize that individuals with patella alta will sustain a greater degree of cartilage damage and that when present, the location of defects would differ compared to individuals with patella norma. We queried patients who underwent patellar realignment surgery, including MPFL reconstruction or TTO, at our institution between 2014 and 2019. Indications for surgery included first-time dislocation with loose body, osteocondal fracture, failure of non-operative treatment, or recurrent dislocation. Patients were included if they had a proton-weighted MRI from within three months of injury on file and, of course, if they had a history of patellar instability. They were excluded if they had prior surgery to the ipsilateral knee or no preoperative MRI on file, or if the preoperative MRI was of too poor quality to properly analyze. The radiographic analysis included Katanda-Chomp's index using a cutoff of 1.3 to establish patella alta versus norma. We also looked at trugular dysplasia using the du jour classification as well as TTTG distance and cartilage damage. In order to assess cartilage damage, we use the area measurement and depth and underlying structures or Amadeus scoring, which you can see here on the right. This characterizes cartilage defect size, defect depth, presence of subchondral bone defects, and bone marrow edema. Independent measurements were performed by two sports medicine fellows on each patient and demonstrated an excellent inter-rater reliability. The two groups are similar in terms of demographics, prior dislocation history, including primary versus recurrent dislocations, with both groups averaging two dislocations, and other MRI measurements such as TTTG distance and trugular dysplasia. There were 40 defects in the patella alta group and 56 defects visualized in the patella norma group. The patella alta group demonstrated overall less severe cartilage damage with a smaller proportion of the full thickness defects, smaller proportion of defect-associated bone marrow edema, and a greater average Amadeus score indicating less severe disease. The defects in the two groups demonstrated similar location with the majority of defects in the medial and lateral patellar facet followed by the lateral femoral condyle. So to summarize our results in the context of no significant differences in prior patellar dislocation history and anatomic radiographic features, we found a similar location of cartilage defects between the two groups and less severe defects in the patella alta group. This study is not without limitations. We do not have patient report outcomes to correlate cartilage damage on MRI with symptoms. MRIs were performed at different facilities, so there was some variability in quality, and direct visualization in the OR was not used to confirm defects. In conclusion, there is a high percentage of cartilage injury in patients with a history of patellar instability with over 60% of patients showing cartilage damage on MRI. Patients with normal patellar height have a higher frequency of full thickness cartilage defects and more severe injury compared to those with patella alta. The location of cartilage injury between the two groups is similar with defects affecting the medial facet, lateral facet, and lateral femoral condyle in descending frequency.

patella-femoral cartilage damage

patella alta

patellar instability

knee biomechanics

MRI