Are metric parameters sufficient alone in evaluation of the patellar instability? New angular measuring parameters

Purposes: When the evaluation of patellar instability is examined from the aspect of the conical-cylindrical anatomy of the tibia, metric measurement parameters such as the tuberositas tibia (TT)–trochlear groove (TG) and patellar tendon (PT) insertion–trochlear groove (TG) distances are not sufficient. We asked whether defined angular parameters reveal the rotational movement of the tuberositas tibia on the tibia shaft, additional to the metric parameters and there is a correlation between the metric and angular parameters. Methods: 19 patients with patellar instability and 22 patients without patellar instability were evaluated. For all patients, two angle and three length parameters were evaluated on the slices taken. Evaluations were made of the TT-TG, the midpoint of the PT insertion-TG distances, the anatomic midpoint of the dome of the TT-TG, the TG-PT angle, and the TG-dome angle (DA). The Pearson correlation test was used for the statistical analysis of correlations between groups. Results: A statistically significant increase was determined in the patellar instability group in the TG-DA and TG-PT angle values compared to the group without patellar instability (p < 0.05). In both groups, a positive and strong correlation was determined between the TT-TG and the TG-PT and dome of the TT-TG distances, but no statistically significant correlation was determined between the tuberositas TT-TG and TG-PT angle and TG-DA. Conclusion: Metric parameters may not be sufficient alone in the evaluation of patellar instability. Metric parameters should be supported by additional angular parameters which reveal the rotational movement of the TT on the tibia shaft.