Anatomical Risk Factors for Anterior Cruciate Ligament Injury Are Not Important As Patellar Instability Risk Factors in Patients with Acute Knee Injury

Characterization of the CT-based risk factors for concomitant patellofemoral instability in patients with anterior cruciate ligament injury

OBJECTIVES

Underestimation of concomitant patellofemoral instability in patients with anterior cruciate ligament (ACL) injury has aroused extensive attention. However, the characteristics of the combined injury is not well recognized. Hence, we aimed to characterize the features of the combined injury, and determine the radiographic risk factors.

METHODS

Fifteen radiological parameters were identified after discussion and pilot-tested. Radiographic measurements were compared using the analysis of variance model with Tukey post hoc analysis. A stepwise binomial logistic regression was performed and a nomogram model combining the significant risk factors was created. The model performance was validated by C-index, calibration plot, and decision curve.

RESULTS

A total of 204 patients (mean [SD] age, 25.1 [6.7] years; 108 [52.9%] male) were included. The final model was updated through regression analysis using 4 parameters as significant risk factors: lateral femoral condyle ratio (OR (95% CI), 1.194 (1.023 to 1.409)), medial anterior tibial subluxation (mATS) (OR (95% CI), 1.234 (1.065 to 1.446)), medial posterior plateau tibial angle (mPPTA) (OR (95% CI), 1.266 (1.088 to 1.500)), and trochlear depth (OR (95% CI), 0.569 (0.397 to 0.784)). C-index for the nomogram was 0.802 (95% CI, 0.731 to 0.873) and was confirmed to be 0.784 through bootstrapping validation. Calibration plot established a good agreement between prediction and observation. Decision curve analysis showed that if threshold probability was over 10%, using the nomogram adds more benefit than either all or none scheme.

CONCLUSIONS

Lateral femoral condyle ratio, mATS, mPPTA, and trochlear depth are strong adverse predictors of patellofemoral instability in patients with ACL injury.

CLINICAL RELEVANCE

This study characterizes the radiological features of the combined injury. Patellofemoral instability should be noted when treating ACL injuries.

KEY POINTS

• The radiological characteristics of the combined ACL injury and patellofemoral instability is not well recognized. • Lateral femoral condyle ratio, mATS, mPPTA, and trochlear depth are predominant risk factors for patellofemoral instability in patients with ACL injury. • Patellofemoral instability should be noted when treating ACL injuries.

Trochlea dysplasia, increased TT-TG distance and patella alta are risk factors for developing first-time and recurrent patella dislocation: a systematic review

PURPOSE

The aim of the study was to perform a systematic review and best knowledge synthesis of the present literature concerning biomechanical risk factors for developing first-time and recurrent patella dislocation.

METHODS

The study was performed as a systematic review following PRISMA guidelines. PubMed and EMBASE were systematically searched. Studies investigating participants with risk factors for first-time as well as recurrent patella dislocation were included. The records were screened, and data extracted independently by two researchers supervised by a third independent assessor. The study was registered in PROSPERO.

RESULTS

A total of 6233 records were screened, and 50 studies met the inclusion criteria. The biomechanical risk factors: trochlear dysplasia, increased tibial tuberosity-trochlear groove distance (TT-TG), and patella alta were found to be statistically significantly associated with patella dislocation in several publications and were thus recognized as risk factors for patella dislocation. The soft-tissue stabilizers: longer and thinner MPFL ligament, increased number of type 2C and decreased number of type 1 muscle fibers, and joint laxity were found to be statistically significantly associated with patella dislocation in a few publications, but due to limited evidence, no conclusion was made on this matter.

CONCLUSION

There is strong evidence in the literature that abnormalities of bony stabilizers, trochlear dysplasia, increased TT-TG distance, and patella alta are risk factors for patella dislocation. There is less evidence that soft-tissue stabilizers are risk factors. The study emphasizes the importance of a thorough investigation of bony stabilizers in clinical decision-making.

LEVEL OF EVIDENCE

Level IV.

Lower anatomical femoral ACL tunnel can be created in the large volume of femoral intercondylar notch

PURPOSE

The purpose of this study was to investigate the correlation between femoral intercondylar notch volume and the characteristics of femoral tunnels in anatomical single bundle anterior cruciate ligament (ACL) reconstruction.

METHODS

Fifty-one subjects (24 male and 27 female: median age 27: range 15-49), were included in this study. Anatomical single bundle ACL reconstruction was performed in all subjects using a trans-portal technique. Femoral tunnel length was measured intra-operatively. Three-dimensional computed tomography (3D-CT) was taken at pre and post-surgery. The intercondylar notch volume was calculated with a truncated-pyramid shape simulation using the pre-operative 3D-CT image. In the post-operative 3D-CT, the modified quadrant method was used to measure femoral ACL tunnel placement.

RESULTS

Femoral tunnel placement was 47.6 ± 10.5% in the high-low (proximal-distal) direction, and 22.6 ± 5.4% in the shallow-deep (anterior-posterior) direction. Femoral tunnel length was 35.3 ± 4.4 cm. Femoral intercondylar notch volume was 8.6 ± 2.1cm³. A significant correlation was found between femoral intercondylar notch volume and high-low (proximal-distal) femoral tunnel placement (Pearson's coefficient correlation: 0.469, p = 0.003).

CONCLUSION

Femoral ACL tunnel placement at a significantly lower level was found in knees with large femoral intercondylar notch volume in the trans-portal technique. For the clinical relevance, although the sample size of this study was limited, surgeons can create femoral ACL tunnel low (distal) in the notch where close to the anatomical ACL footprint in the knees with large femoral intercondylar notch volume.

LEVEL OF EVIDENCE

III.

Knees with straight Blumensaat's line have small volume of femoral intercondylar notch

PURPOSE

Smaller femoral intercondylar notch volume has been identified as a risk factor for anterior cruciate ligament injury. The present study aims to investigate differences in the intercondylar notch volume based on differences in the morphology of Blumensaat's line.

METHODS

Eighty-eight (88) subjects (42 male and 46 female: median age 27: range 15-49), were included in this study. Using 3-dimensional computed tomography (3D-CT), the volume of the intercondylar notch was calculated using a truncated-pyramid shape simulation with the formula: [Formula: see text]. Femoral condyle height (h) was measured in the sagittal plane of the knee in 3D-CT. The area of the intercondylar notch was measured in the axial slice containing the most proximal level (S1) and most distal level (S2) of Blumensaat's line. In the sagittal view of the knee, Blumensaat's line morphology was classified into either straight or hill type. Statistical analysis was performed to compare h, S1, S2, and notch volume between the straight and hill type groups.

RESULTS

Thirty-six subjects were classified as having straight type morphology and 52 subjects were classified as having hill type morphology. The measured h, S1, and S2, of the straight and hill types were 29 ± 4 and 31 ± 4 mm, 213 ± 72 and 205 ± 51 mm², 375 ± 114 and 430 ± 94 mm², respectively. The calculated femoral intercondylar notch volume of the straight and hill types was 8.1 ± 2 and 9.5 ± 2 cm³, respectively. Straight type knees showed significantly smaller S2 (p = 0.04), and notch volume (p = 0.01) when compared with hill type knees.

CONCLUSION

Intercondylar notch volume was significantly smaller in knees with straight type Blumensaat's line morphology. Considering that Blumensaat's line represents the roof of the femoral notch, morphological variations in Blumensaat's line are likely to reflect variation in notch volume. For clinical relevance, as a smaller notch volume is a risk factor for ACL injury, straight type Blumensaat's line may also be considered a potential risk factor for ACL injury.

LEVEL OF EVIDENCE

Level III.