To investigate the possible risk factors for anterior knee pain syndrome (AKP) after the anterior cruciate ligament reconstruction (ACLR) based on multivariate logistic regression analysis and musculoskeletal ultrasound (MSKUS).

A retrospective case-control study was conducted to analysis patients who underwent anterior cruciate ligament reconstruction (ACLR) in the Second Affiliated Hospital of Xi’an Jiaotong University. Patients with a history of surgery or chronic disease around the ipsilateral knee were excluded. A total of 35 patients aged from 18 to 50 years who underwent ACLR with autologous hamstring tendon by the same doctor were enrolled and divided into two groups: the anterior knee pain group (the AKP group) and the non-AKP group, according to the postoperative symptoms and visual analogue scale (VAS) score. The patient baseline characteristics, such as age, gender, were recorded. The patients filled out a questionnaire about the International Knee Documentation Committee (IKDC) scale and sectional Feller scale. Anterior knee laxity and flexion contracture were measured. The morphological features and thickness of the patellar tendon and infrapatellar fat pad (IFP) were measured by two-dimensional ultrasound. The IFP blood flow signal were measured by Doppler ultrasound. The shear wave velocity of the patellar tendon and IFP were measured by ultrasonic elastography. After correlation analysis of some variates with statistical differences, the multivariate logistic regression analysis was conducted to find relevant risk factors.

Univariate analysis showed that the proportion of female patients in the AKP group was higher (P=0.018), the reduction of quadriceps muscle strength in the AKP group was higher than that in the non-AKP group (Z=2.40, P<0.05), ultrasonography showed that the proportion of patients with increased IFP blood flow was higher in the AKP group (P=0.018), and the shear wave velocity of IFP was faster in the AKP group(t=7.64, P<0.05). There was no significant difference in other variates (all P>0.05). Multivariate logistic regression analysis showed that female [odds ratio(OR)=12.13, 95% confidence interval(CI) (1.55, 94.99)], the reduction of quadriceps muscle strength [OR=7.94, 95%CI (1.14, 55.43)] and the increase of IFP blood flow[OR=8.90, 95%CI (1.25, 63.56)] were risk factors for anterior knee pain after ACLR (all P<0.05).

The risk of AKP is higher in female than in men after ACLR. Moreover, the reduction of quadriceps muscle strength, the hyperemia and edema of IFP are risk factors for AKP after ACLR.