Summary

To evaluate the correlation between the anterior knee pain (AKP) at 6 months after anterior cruciate ligament reconstruction with a hamstring autograft and the dynamic change in the infrapatellar fat pad (IPFP), the IPFP in 43 patients was assessed by ultrasonography. This study showed that AKP assessed using the Kujala score had a strong association with the thickness change rate of the IPFP.

Abstract

Anterior knee pain (AKP) is a common postoperative complication of anterior cruciate ligament (ACL) reconstruction. Age, body mass index, increased blood flow of the infrapatellar fat pad (IPFP) have been reported as the factors that affect AKP. However, no report has evaluated the correlation between the movement of the IPFP and AKP. The purpose of this study was to evaluate whether the dynamic change in IPFP affects AKP at 6 months after ACL reconstruction with a hamstring (HT) autograft.

Materials And Methods

Forty-three patients (mean age, 22.9 ± 10.0 years; 20 males and 23 females) who underwent a primary anatomical single-bundle ACL reconstruction with a HT autograft were examined to evaluate the correlation between AKP and the dynamic change of the IPFP at 6 months after surgery. AKP was assessed using the Kujala score. We evaluated the thickness of the IPFP at 10° and 90° knee flexion, the thickness change ratio of the IPFP, and the degree of increased blood flow in the IPFP by ultrasonography. Longitudinal ultrasonographic images were recorded at the center of the patellar tendon, along the tendon fiber, to analyze the IPFP and patellar apex. The IPFP in the images was divided into the superficial and deep parts. The superficial part of IPFP was defined as the low-echo intensity area of the upper layer of the IPFP, and the thickness was measured at a distance of 10 mm from the patellar apex. The thickness of the superficial part of IPFP at 10° and 90° knee flexion was measured with Image J. The thickness change ratio of the superficial area of the IPFP was calculated as the thickness at 90° knee flexion divided by that at 10° knee flexion. The degree of increased blood flow in the IPFP was evaluated using power Doppler. For the statistical analysis, the correlation between the Kujala score and the IPFP was examined using the Spearman’ correlation coefficient. The p value of <0.05 was considered statistically significant.

Results

The mean Kujala score was 88.8 ± 9.5. The mean thickness of the IPFP at 10° and 90° knee flexion were respectively 5.5 ± 3.2 and 10.4 ± 5.0 mm. The mean thickness change rate of the IPFP was 211% ± 84%. In short, the thickness of the IPFP at a knee flexion of 90° was approximately about twice as thick as 10°. Statistically, significant correlations were found between the Kujala score and the thicknesses of the IPFP at 10° and 90° knee flexion (r = -0.38 and, -0.45, respectively), the thickness change ratio of the IPFP (r = 0.73), and the degree of increased blood flow in the IPFP (r = - 0.42) ; (p < 0.05, respectively).

Conclusion

The Kujala score and thickness change ratio of the superficial area of the IPFP significantly correlated at 6 months after primary anatomical single-bundle ACL reconstruction with the hamstring autograft. The restriction of the thickness change ratio of the IPFP can cause AKP.