Introduction There is a lack of evidence on the best method for rehabilitating extensor tendon injuries in zones V and VI. The purpose of this study was to evaluate the outcomes of modified relative motion splinting compared with immobilization following repair of extensor tendons in zones V and VI. Methods A retrospective analysis compared the outcomes of relative motion splinting with immobilization. Sixteen patients (16 fingers) were treated by conventional immobilization splinting for four weeks (immobilization group) followed by mobilization with avoidance of ‘at-risk/heavy’ activities for a further 4–6 weeks. Twenty-three patients (23 fingers) were treated with the modified relative motion splint (mRMS group) during the day and a resting splint worn overnight for the first four weeks. The relative motion splint was continued for ‘at-risk/heavy’ activities for a further 4–6 weeks. Results The mRMS group demonstrated statistically significant improvement in range of motion compared with the immobilization group. This effect was most marked at six weeks ( P = 0.0194, two-way mixed ANOVA) with the mRMS group achieving a 12% higher mean percentage total active motion ( P = 0.0076, Mann-Whitney U test). Results were similar for both groups 12 weeks postoperatively. Differences in return to work times between groups were statistically significant ( P = 0.0062, Mann-Whitney U test). Average return to work was 9.4 weeks for the immobilization group and 3.3 weeks for the mRMS group, equating to a 42 days earlier return to work for the mRMS group. There was no incidence of tendon rupture in either group. Conclusion This study demonstrates that modified relative motion splintage (finger based without wrist component) can be applied in the postoperative management of single zone V or VI extensor tendon repairs. The main advantages of this protocol, compared with immobilization include the small simple splint design, and straightforward patient instructions that enable earlier mobilization, functional hand use and return to both daily living and work.