This was a retrospective review of the nine open wedge high tibial osteotomy (HTO) done in a regional hospital in Hong Kong from 2006 to 2008. The mechanical hip-knee-ankle angle improved from average 169.5°(164°-175°) to average 183.9° (179°-187°). Patellar descent was noted in all patients postoperatively, with Blackburne-Peel (BP) index significantly changing from 0.78 (0.64-0.93) to 0.59 (0.38-0.78) (p < 0.05). This change was strongly correlated with the size of anterior bone graft (r = -0.766; p = 0.016). The patellar tendon length as measured by Insall-Salvati index was not changed (pre-operative: 1.02 (0.88-1.25), final: 1.09 (0.8-1.22) (p = 0.683)), inferring that scarring contracture of patellar tendon was not related to patellar descent.