Objective patellar instability: MR-based quantitative assessment of potentially associated anatomical features

Abstract

To evaluate and compare the diagnostic utility of multiple quantitative parameters as measured on knee magnetic resonance (MR) examinations of patients suffering objective patellar instability (OPI). We performed a retrospective evaluation of knee MR examinations in a group of 46 patients (59 knees) with clinically proven OPI, and in a control group of 69 patients (71 knees). Multiple quantitative parameters in both groups were statistically evaluated and compared for their association with OPI. OPI patients tend to present shallower trochlear groove (<5 mm), larger Insall-Salvati index (>1.2), shorter patellar nose (<9 mm), smaller morphology ratio (<1.2), and larger patellar tilt (>11 degrees ) than control patients. The best sensitivities were those of the lateral patellar tilt (92.7%), the trochlear groove depth at the roman arch level (85.7%) and the Insall-Salvati index (78%). The best specificities were those of the morphology ratio (86.9%), the patellar nose (84.5%) and the patellar tendon length (84.5%). Shallow trochlear groove may be confidently identified at the roman arch view in OPI patients. Patella alta may be more reliably detected by the Insall-Salvati index in OPI patients. Patellar nose and morphology ratio are very specific indicators of OPI. A short patellar nose (that is to say, a patellar nose ratio of <0.25) has a high association with OPI. Lateral patellar tilt remains the single feature with the highest sensitivity and specificity for identifying OPI patients.

Patient-specific modeling of the trochlear morphologic anomalies by means of hyperbolic paraboloids

“…The main advantage is that the model provides a continuous representation of morphologic variations in HP parameter space taking into account the full geometrical complexity of trochlea unlike the traditional morphometric parameters, as the trochlear depth or the sulcus angle, which basically encode the shape variation into a single axial plane. [2,16,17] This approach is novel in the literature with respect to alternative 3D techniques based on statistical shape models that in contrast cannot easily correlated parameter variations with specific morphologic features. [29,30] Second, we found that similar morphologic anomalies of the trochlear aspect, as encoded by similar HP parameters, are actually attributed to different severity grades in the Dejour classification.…”

“…From a diagnostic point of view, understanding how morphologic variations correlate with disease can help clinicians to identify risk factors for the setting of cartilage lesions at patella-femur interface. [1][2][3] This information has been acknowledged to be beneficial in preventing and treating patellofemoral disorders. [4,5] From a surgical point of view, the extent of the morphologic variations is determinant for the selection of the optimal implant in trochleoplasty interventions.…”

“…However, this grading has been extensively questioned in the literature due to difficulty in clustering the large variability of the morphologic anomalies into such specific classes, suggesting that morphometric measures can yield more reliable criteria to score the anomaly degree. [2,16,17] Morphometric parameters, such as the trochlear depth, the sulcus angle, the lateral trochlear facet inclination and the trochlear facet asymmetry ratio, to cite the most relevant, are based on anatomical landmarks manually digitized in computed tomography (CT) and magnetic resonance (MR) images. [12,[18][19][20][21] The use of such parameters have been criticized as well because of difficulties in the precise localization of landmarks, especially in case of large morphologic deviations, [20] dependency on the adopted measurement protocol [2,5,17] and interobserver variability.…”

Modern management of patellar instability

“…In addition, Dejour et al [4] correlated VMO insufficiency to patellar tilt. Lateral patellar tilt (as defined by the angle intersection made from a line along the lateral slope of the trochlea groove and with a line through the widest diameter of the patellar on axial views) greater than 11°proved to be the most sensitive measure and occurred in 93 % of patients with objective patellar instability [21]. As well as influencing the patella in a lateral-medial direction, the vastii muscles also exert a posterior force vector.…”

“…Lateral radiographs yield information relating to patella height which can be quantified, using the Insall-Salvati [28,29], Blackburne Peel [30] and Caton Deschamps [31] indices or with using Blumensaats line [32]. Trochlear depth can be quantitatively elucidated from true lateral views, with reports of 85 % sensitivity for this measurement in cases of objective patellar instability [21]. Dejour et al [4] reported that trochlear dysplasia can be defined by the crossing sign (present in 96 % of cases) which is quantitatively expressed by the presence of a trochlear bump greater than 3 mm (present in 66 % of cases) (Fig.…”