To assess the therapeutic effect of hyaluronate acid (HA) injection through the subpatellar route for treatment of chondromalacia patellae (CP).
Eighty-eight patients with the diagnosis of CP were enrolled in this prospective study, including 38 with early CP (CP group) and 50 with advanced CP (patellofemoral arthritis group) diagnosed based on image presentations. All the patients received intra-articular HA injections through a subpatellar route once a week for 5 consecutive weeks. The primary outcome measures included WOMAC index scores and Lequesne scores before and at 4, 12, 26 and 52 weeks after the injections. The secondary outcome measures included the 30-m walking time and stair ascending and descending time (one floor) before and at 1, 2, 3, and 4 weeks after the injections.
In both groups the patients showed significantly decreased WOMAC scores and Lequesne scores at 4, 12, 26 and 52 weeks after HA injections as compared with the baseline scores (all 
HA injection through the subpatellar route is effective for treatment of CP. HA injection produces better long-term efficacy for treatment of early CP than for advanced CP where patellofemoral arthritis occurs.