Background: Various techniques of opponensplasty have been developed with the aim of restoring the thumb function. The modified Camitz opponensplasty is a simple technique done together with an open carpal tunnel release. It restores thumb palmar abduction soon after the procedure, during such time that the abductor pollicis brevis (APB) is still recovering. The aim of this study was to assess the recovery and level of activity of the abductor pollicis brevis and palmaris longus (PL) muscles during thumb opposition and abduction after performing the modified Camitz opponensplasty. Methods: The records of 21 patients who underwent modified Camitz opponensplasty for severe carpal tunnel syndrome were reviewed. Thumb function was evaluated using the Van Wetter Apogee test, Kapandji index, tripod pinch strength, and power grip. Electromyography was utilized to evaluate APB recovery; ultrasonography was employed to evaluate PL activity. Results: Twenty patients reached 80% of the abduction height of the contralateral hand; the Kapandji index was good in thirteen. Palmaris longus activity was evaluated together with the APB muscle recovery. There was significant improvement in the average grip strength and average tripod pinch strength. However, this did not correlate with the degree of neurologic and muscular recovery of the APB. We surmise that the palmaris longus augmented the abductor pollicis brevis muscle even in those with full muscle recovery. Conclusions: The modified Camitz opponensplasty is a practical option for patients suffering from severe carpal tunnel syndrome with diminished thumb function.