Background: We compared the clinical results of a newly modified abductor pollicis longus (APL) suspension arthroplasty with trapeziectomy procedure (modified Thompson procedure) with those of the original APL suspension arthroplasty with trapeziectomy procedure (original Thompson procedure) for treatment of advanced osteoarthritis of the thumb carpometacarpal (CMC) joint and assessed the effectiveness of the modified Thompson procedure for thumb CMC osteoarthritis. Methods: Ten hands of 10 patients (Group 1) were treated with the original Thompson procedure. Twenty hands of 16 patients (Group 2) were treated with the modified Thompson procedure, in which the bone tunnel positions were rearranged for a more dorsoradial passage of the transferred APL. Results: Significant differences between values before and after surgery were noted in thumb palmar and radial abduction angles, pinch power, grip strength, Quick Disability of Arm, Shoulder, and Hand questionnaire (Quick DASH) score, and visual analog scale (VAS) score. There was no statistically significant difference in thumb palmar abduction angle, pinch power, grip strength, Quick DASH score, or VAS score between Groups 1 and 2. However, range of motion of radial abduction in the thumb was significantly better for patients in Group 2 than for those in Group 1. Conclusions: The modified Thompson procedure is a simple, effective technique that results in greater improvement in thumb radial abduction angle, as compared with the original technique, in patients with advanced thumb CMC osteoarthritis. Additionally, the modified technique is as useful as the original procedure for early restoration of thumb function and pain relief.