Summary

This novel arthroscopic measurement technique uses the size of the lateral femoral condyle medial wall cartilage margin to accurately identify the femoral ACL center for ACL reconstruction, and has resulted in positive post-operative clinical outcome scores.

Abstract

Introduction

The purpose of this study is to introduce a new measurement technique for femoral tunnel placement in anterior cruciate ligament reconstruction (ACLR). The goal is to use the lateral femoral condyle medial wall cartilage margin diameter to determine the optimal placement of the ACL femoral tunnel.

Methods

Knee anatomic landmarks were visualized through a 30-degree arthroscope from a standard anterolateral portal. All measurements were obtained with a graduated intra-articular ruler. First, the anterior to posterior distance of the lateral femoral condyle medial wall cartilage margin was measured, and knees were categorized into three groups based on this measurement: less than 21 mm, 21 to 25 mm, and greater than 25 mm. The center of the AM and PL bundles were identified through previously published methods, using measurements based on the anterior to posterior cartilage margin size calibrated for the three cartilage margin diameter groups. The anatomic center for ACL femoral tunnel placement was measured midway between the AM and PL centers . The accuracy of ACL center localization was validated through use of the Bernard-Hertel grid method in 10 knees. After validation, our measurement technique was applied to 65 consecutive knees. Once the AM, PL, and ACL centers were located and marked, the distance from each center to the anterior, posterior, and inferior cartilage margins of the lateral femoral condyle medial wall were measured. Correlation and linear regression analyses were performed to determine the correlation between the results and previously published anatomic values. The recorded diameter values of the patients were converted to a standard normal distribution, and the expected values for AM, PL, and ACL center measurements were estimated using the available anatomic measurements (mean, SD) reported in the literature. Clinical outcomes of a small cohort of patients were evaluated. Pre-operative and post-operative IKDC and Lysholm scores were obtained. A two-tailed distribution paired t-test was used to determine statistical significance (p < 0.05) between pre-operative and post-operative scores.

Results

65 consecutive ACL deficient knees were included to evaluate the novel measurement technique. The number of patients in each lateral femoral condyle medial wall cartilage margin diameter group (<21 mm, 21-25 mm, >25 mm) were 28, 28, and 9, respectively. Overall, the mean distance from the ACL center to the anterior, posterior, and inferior cartilage borders was 11.97 ± 2.15, 9.29 ± 1.84, and 9.55 ± 1.97mm, respectively. There was a significant correlation between our findings and anatomic measurements of the ACL center to the anterior, posterior, and inferior cartilage borders reported in the literature (anterior: 12.50 ± 2.10; Pearson correlation coefficients (PCC)= 0.860, p=0.001); (posterior: 11.50 ± 1.30; PCC= 0.812; p=0.001); (inferior: 8.70 ± 0.6; PCC= 0.462; p= 0.001). The linear regression analysis revealed the ACL center is located at 38.5% of the anterior to posterior diameter of the medial wall of the lateral femoral condyle cartilage border. Clinical outcome scores of 21 patients were obtained, with an average follow up period of 2.84 years. The mean IKDC score significantly increased from 48.43 (SD = 19.15) pre-operatively to 91.54 (SD = 7.38) post-operatively (p < 0.0001). The mean Lysholm score significantly increased from 57.86 (SD = 23.87) pre-operatively to 89.57 (SD = 10.17) post-operatively (p < 0.0001).

Conclusion

We present a new method to find optimal femoral tunnel placement for ACLR based on arthroscopic landmarks. We determined the AM and PL center of the lateral condyle medial wall based on anatomic measurements established in the literature. The technique was categorized based on three different sizes of the medial wall cartilage margin. Our results show that the femoral ACL footprint center can be accurately identified using arthroscopic measurements based on the size of the lateral femoral condyle medial wall cartilage margins. This new measurement technique could be used to precisely locate femoral tunnel placement in ACLR. A small cohort of patients demonstrated strong post-operative clinical outcome scores.