Rhizoarthrosis is a chronic health condition characterized by progressive degeneration of the trapeziometacarpal joint. This implies a decreased range of motion, muscle weakness, and pain in the thumb base. Thus, the loss of structure and function of the hand can interfere with the characteristics of activities and participation of these subjects. These, however, can be minimized by the 1st dorsal interosseous muscle strengthening, an important trapeziometacarpal joint dynamic stabilizer. This strengthening is not usually included in physical rehabilitation, which also does not detail the exercises' load, progression, and number of repetitions.

To reduce the impact of rhizoarthrosis on activities and the social participation of affected subjects, this study aimed to investigate the effect of an intervention with a shaping method focused on the 1st dorsal interosseous' strengthening.

Subjects with rizoarthrosis, diagnosed according to the Eaton- Littler -Burton criteria, were included. These were evaluated before, after 4 weeks, and at the end of treatment. For the evaluation of aspects of body structure and function, the pain was assessed using the Numerical Pain Scale, handgrip and pinch strength, and the Nine-Hole Peg Test (NHPT). Activity and participation were assessed using the Australian/Canadian Hand Osteoarthritis Index (AUSCAN) and Canadian Occupational Performance Measure (COPM) questionnaires, in addition to some of the tasks of the Bilateral Upper Limb Function Test (TEBIM). Data was presented in mean and standard deviation. To verify the effects of the treatment, the delta of change for each variable was calculated and the percentage change was presented before and after evaluations.

An increase of 4.35% in handgrip strength, 2.88% in pulp-pulp pinch strength and 14.93% in lateral pinch strength were observed. There was a reduction only in tripod pinch strength (10.35%). An improvement of 14.95% was also observed in the execution time of the NHPT and of up to 64.08% in the selected TEBIM activities. The AUSCAN and COPM questionnaires showed a 16.67% reduction in the difficulty of performing ADLs, a 37.5% reduction in stiffness and a 60.98% in pain, in addition to a 7.94% improvement in performance perception and 43.36% in satisfaction performing activities.

The data obtained so far suggest that the use of the shaping method in a treatment protocol focused on strengthening the 1st ID has effects on pain, function, dexterity, and grip and pinch strength in individuals with rizoarthrosis.

The results of the study may contribute to future physiotherapy studies regarding the intervention protocols for the population with thumb osteoarthritis. The existing clinical trials that focus on exercise-based rehabilitation for hand function in patients with OA at the base of the thumb describe this protocol with poor-quality information. In addition, this study provides preliminary results on the importance of including strengthening of the 1st dorsal interosseous bone in the rehabilitation of patients with rizoarthrosis.