Tibial tubercle-trochlear groove/trochlear width may identify lateralized tibial tubercle
Published results showed tibial tubercle-trochlear groove/trochlear width may be the best individualized index for diagnosing a lateralized tibial tubercle in patients with recurrent patellar dislocation requiring surgical stabilization.
Researchers calculated six indices that described lateralization of the tibial tubercle using either CT or MRI among 88 patients who underwent surgery for recurrent patellar dislocation (case group) and 53 patients with no history of patellar dislocation (control group) between January 2014 and December 2019. The indices included tibial tubercle lateralization, tibial tubercle-trochlear groove (TT-TG) ratio, tibial tubercle-PCL ratio, TT-TG index, TT-TG/patellar width and TT-TG/trochlear width. Researchers also evaluated diagnostic effectiveness with intra-rater reliability and interrater reliability using the intraclass correlation coefficient, the size of the difference between the case group and the control group, and receiver operating characteristic curve analysis, measuring the area under the receiver operating characteristic curve and the post hoc power.
Results showed all methods had an intraclass correlation coefficient higher than 0.75. Researchers found mean differences of 2% for tibial tubercle lateralization and tibial tubercle-PCL ratio, 8% for TT-TG ratio, 12% for TT-TG index, 24% for TT-TG/patellar width and 56% for TT-TG/trochlear width between the case group and control group. TT-TG/trochlear width had a significantly greater mean difference between the case group and the control group compared with other methods, according to results.
Researchers noted an area under the receiver operating characteristic curve of 0.708 for tibial tubercle lateralization, 0.880 for TT-TG ratio, 0.630 for tibial tubercle-PCL ratio, 0.814 for TT-TG index, 0.822 for TT-TG/patellar width and 0.905 for TT-TG/trochlear width. Results showed TT-TG/trochlear width had a significantly greater area under the receiver operating characteristic curve compared with the tibial tubercle lateralization and tibial tubercle-PCL ratio. Researchers found a post hoc power of 78% for tibial tubercle-PCL ratio, 81% for TT-TG index, 88% for TT-TG/patellar width and TT-TG ratio, 91% for TT-TG/trochlear width and 71% for tibial tubercle lateralization.
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Peng Su, MD, and colleagues compared a group of 100 knees that had undergone surgery for patella dislocation with a control group of 55 knees that had no history of patellar instability. They analyzed six indices used to measure a lateralized tibial tubercle on MRI or CT and concluded that TT-TG/trochlear width was clearly the best and had excellent interrater and intra-rater reliability.
TT-TG distance has traditionally been used to make surgical planning decisions, but there has been variation in defining normal cutoffs. Over the last few years, an individualized approach to measuring TT-TG ratios has been suggested.
This study does a good job of looking at the different indices in a large group of patients, and the authors concluded that TT-TG/trochlear width is the best individualized index for diagnosing a lateralized tibia tubercle. While it can be tedious measuring these ratios in the clinical setting, these are important in surgical decision-making algorithms.
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