The primary finding of the present study was that there was a significant correlation between patellar shape and trochlear morphological parameters. The LTA, MTA, MFL, trochlear depth trochlear condyle asymmetry, and trochlear facet asymmetry were increased in subjects with Wiberg type I patellae relative to those with Wiberg type II and III patellae, whereas the opposite finding was observed for the SA in these patients. No significant differences in trochlear morphology were observed when comparing those with type II and III patellae. Correlation analyses revealed that individuals with a more symmetric patellar facet exhibited increased trochlear facet asymmetry and trochlear condyle asymmetry. This suggests an interaction between the patella and trochlear morphology during skeletal development, providing valuable information that can aid in selecting appropriate surgical procedures for treating patellofemoral joint instability.
The Wiberg classification system defines three primary patellar shapes based upon the size relationship between the medial and lateral patellar facets [13]. We observed different trochlear morphological parameters in those with Wiberg type I patellae relative to those with Wiberg type II and III patellae. Those with type I patellae exhibited equal medial and lateral facet lengths and the most symmetric facets. The MFL in group A was increased whereas the LFL was similar relative to other groups such that trochlear facet asymmetry (defined as MFL/LFL) was significantly increased. This suggests that trochlear and patellar morphology changed in a consistent manner across patients. In a study conducted by Fucentese et al. [14], patients with a dysplastic trochlea exhibited a smaller patellar size and an asymmetrical patellar facet. The SA was also evaluated in the present study, revealing that femoral trochlear dysplasia was reproducible and decreased in group A patients, explaining why type I patellae are more stable and associated with a lower incidence of patellar dislocation relative to type II and III patellae.
We detected correlations between patellar shape and femoral trochlear morphology, suggesting that the morphological parameters of these structures interact during development. Several studies have explored patellar and trochlear development, yielding inconsistnet findings. Some reports have suggested that congenital factors regulate femoral trochlear shape [7], whereas other studies have shown the trochlea and patella to develop continuously over time [10, 14, 17, 18]. Fucentese et al. reported morphologic changes in the patellae of trochlear dysplasia patients, detecting molding activity between patellar and trochlear development [14]. In a study of skeletally immature cadavers, concurrent changes in patellar and trochlear shape were detected, consistent with our results and suggesting that these two structures may influence one another during development. We found patellar facet symmetry to be related to trochlear inclination and trochlear facet and condyle asymmetry, indicating that the medial patella is the primary portion that interacts with the trochlear. The mature patellae exhibited lateral facet predominance [19], whereas the medial and lateral patellar facets are equal in size during embryonic development, with medial trochlear morphology variability increasing with age [11]. Biedert et al. also found trochlear dysplasia was mainly located in the center and/or medial trochlea rather than the lateral trochlea [20].
In this study, we found that type I patellae, which exhibited nearly equal medial and lateral facet lengths, had more symmetrical trochlear parameters than type II or III patellae. Patients with increasing medial patellae facets exhibit a concurrent increase in trochlear morphological parameters, suggesting a relationship between patellofemoral structural and functional factors during development [17, 21]. Correct patellar tracking alters patellofemoral joint function and plays a key role in regulating knee joint stability. A deep sulcus and a high lateral trochlea can help to maintain normal patella tracking [6], while abnormal tracking can mold patellar and trochlear morphology and impact patellofemoral joint instability [22]. Causes of trochlear dysplasia may include developmental factors or false patellar tracking during childhood [10, 22]. Stabilization produces changes throughout the knee range of movement, including both bony and soft tissue constraints. Bony constraint is particularly important after the first 20° of knee flexion [2], while the patella begins to engage with the trochlea as the knee flexes to 30°. Poor patellar and trochlear tracking can give rise to trochlear and/or patellar dysplasia [11, 22]. In this report, we observed concurrent patellar and trochlear changes, possibly due to such patellar tracking during skeletal development.
Trochlear and patellar morphology serve to constrain patellofemoral joint instability, and can contribute to patellar dislocation. While trochleoplasty is an effective means of remodeling the trochlea to address patellar instability, it is rarely performed in clinical settings as it is a complex procedure and little information regarding its efficacy as a function of patellar and trochlear morphology is currently available. With sufficient morphological information, trochleoplasty may become a more viable means of addressing joint instability. In the present study, we found that the patellar and trochlear facets were matched in individuals with mature skeletal development such that a more symmetrical patella facet corresponded to a more symmetrical trochlear facet. It is important to take this into account when conducting trochleoplasty, as performing this procedure based on the shape of the patella and the trochlea rather than solely on the shape of the trochlea may reduce the risk of postoperative complications.
There are multiple limitations to this study. For one, we did not evaluate the position of the patella relative to the trochlea, and such positioning may impact the shape of these structures. Second, we did not measure patellar morphological parameters as this study was primarily focused on the relationship between patellar shape and trochlear morphology. Third, all measurements made herein were based on bony structures, and cartilaginous structures of the patellofemoral joint were not included. Finally, we only evaluated patients with mature skeletal development and thus cannot draw conclusions regarding whether the relationships between patellar shape and trochlear morphology arose during embryonic development or after birth. Future research will thus be needed to expand on this study and to address these points.