Thumb basal joint arthritis is a common, disabling condition of the hand. Ligament reconstruction and tendon interposition (LRTI) is one of the more common surgical solutions. We performed a retrospective study to evaluate long-term radiological and clinical outcomes of modified LRTI procedures in treating thumb basal joint arthritis.A total of 91 hands (84 patients) with full chart records were enrolled in this study. The average age was 65.4 years, and the mean follow-up was 11.7 years (range, 1-21.6 years). We evaluated pain, joint stability, power-grip and key pinch strength, and thumb radial abduction angle as the functional outcomes, and measured the height of the trapezial space as the radiographic result.There were 66 and 23 hands with excellent and good results, respectively. The diminution of the trapezial space was 4.2 mm in the stage III group and 5.2 mm in the stage IV group. Power-grip and key pinch strength, and thumb radial abduction angle were better in those with stage III than in those with stage IV arthritis. Sixty-eight hands were followed up >5 years, and of them, 66 showed excellent or good results.With good and durable surgical outcomes, the modified LRTI procedure could be a good treatment for thumb basal joint arthritis.