The role of the sulcus angle in patellar dislocation: The importance of measuring four magnetic resonance imaging axial levels and utilising corresponding cutoff values.

PURPOSE

The primary purpose was to assess sulcus angle (SA) magnetic resonance imaging (MRI) measurements and determine diagnostic cutoff values along four axial levels on cartilaginous and osseous surfaces comparing those with patellar dislocations (PD) versus controls. A secondary aim was to identify differences in SA between patients with one-time dislocation (OTD) versus recurrent patellar dislocations (RPDs).

METHODS

Paediatric patients with a history of PD were retrospectively grouped into those with an OTD versus RPDs. Age and sex frequency matching controls (ACL injuries without PD history) were identified. The SA was recorded at four levels in the trochlear groove (TG) on cartilaginous and osseous surfaces. Differences between sample means (PDs vs. controls; RPDs vs. OTDs) were assessed; cutoff values for discriminating PDs from controls were identified utilising Youden's index.

RESULTS

There were 173 PDs (106 RPDs, 67 OTDs) and 100 controls. There were differences in mean SA between PD and controls throughout the trochlear groove for both cartilaginous (PD vs. control: SA1 166.1° vs. 152.5°, SA2 161.0° vs. 148.5°, SA3 155.7° vs. 145.9°, SA4 150.7° vs. 142.5°) and osseous surfaces (PD vs. control: SA1 160.2° vs. 146.6, SA2 153.8° vs. 140.2°, SA3 147.2° vs. 134.8°, SA4 142.1° vs. 132.6°) ( < 0.001). Diagnostic cutoffs were higher for cartilaginous versus osseous measurements (SA1 159.6° vs. 153.1°, SA2 153.8° vs. 148.0°, SA3 152.5° vs. 141.6°, SA4 148.1° vs. 137.4°). RPD patients had greater cartilaginous SA than OTDs throughout the TG (SA1 = 0.014, SA2 = 0.004, SA3 = 0.027, SA4 = 0.007), while osseous SA measurements did not differ (SA1 = 0.057, SA2 = 0.070, SA3 = 0.185, SA4 = 0.175).

CONCLUSIONS

SA was greater in PDs than controls at all four levels in the TG for both cartilaginous and osseous measurements. Cartilaginous SA was greater among RPDs than OTDs at all levels; however, osseous SA was not different between cohorts. The diagnostic cutoff of dysplastic SA differed by axial level and surface.

LEVEL OF EVIDENCE

Level III.