High incidence of patellofemoral pain and patellofemoral joint osteoarthritis was found following anterior cruciate ligament (ACL) reconstruction. The unstability of patellofemoral joint might be an important contribution factor. This study was designed to define the relationship between the unstability of patellofemoral joint and quadriceps femoris atrophy. Twenty patients underwent MRI scan before ACL reconstruction and every two weeks after surgery, until 12 weeks. The merchant's patellar congruence angle, lateral inclination angle, and quadriceps femoris muscle cross-sectional area were measured and the relationship between the changes of angles and the ratio of quadriceps femoris atrophy was studied by multiple regression analysis. Significant quadriceps femoris atrophy was observed after ACL reconstruction during the follow-up period of 12 weeks. The merchant's patellar congruence angle and lateral inclination angle significantly changed after surgery. The alterations of the merchant's patellar congruence angle were significantly correlated with the atrophy ratio of vastus medialis (coefficient=-15.76) and vastus lateralis (coefficient=8.35) during the follow-up period of 12 weeks. The alterations of lateral inclination angle were significantly correlated with the atrophy ratio of vastus medialis (coefficient=20.62), vastus lateralis (coefficient=-11.38) and rectus femoris (coefficient=-0.469) during the follow-up period 12 weeks. To sum up, ACL reconstruction can alleviate the dysfunction of patellofemoral joint to a certain extent. But, the unbalanced atrophy of quadriceps femoris once again destroyed the stability of patellofemoral joint following the operation, which might be one cause of patellofemoral joint pain and early onset of osteoarthritis after ACL reconstruction. So, rehabilitation training that focuses on quadriceps femoris especially the vastus medialis shortly following operation is suggested.
Keywords: anterior cruciate ligament reconstruction; joint instability; patellofemoral joint osteoarthritis; quadriceps femoris atrophy.