Thumb Base Osteoarthritis: Prevalence, Occupational Risk, and Surgical Outcomes

Abstract: Osteoarthritis of the carpometacarpal joint at the base of the thumb (CMC1 OA) is common and causes difficulty in grasp, grip, and fine manipulation of the hand. Surgery is recommended after failure of non-operative treatment, andevidence from short and medium-term follow-up studies shows successful relief of pain and return of function. Previous investigations of epidemiology and risk factors were drawn from small case series or radiographic reviews; similarly,surgical outcomes studies have been limited by lack of robust follow-up.The objectives of this thesis were to: 1) evaluate the clinically important prevalence of CMC1 OA by age and sex using physician-assigned diagnoses; 2) study the impact of occupational load on the occurrence of CMC1 OA; and 3) evaluate surgical outcomes including register-based sick leave length as well as long-term follow-up in a tightlycaptured population.Epidemiologic analysis using the Skåne Healthcare Register showed a sex difference in prevalence of CMC1 OA with 2.2% of women compared to 0.6% of men assigned this diagnosis over a 15-year period, with peak prevalence inwomen at age 70-74 years. Occupational load analysis showed that jobs with the heaviest manual work stress conferred the greatest risk of a diagnosis of CMC1 OA, with a monotonic relationship between work load and thumbbase OA in men. Lengthy sick leave periods were noted after both soft tissue and prosthetic implant arthroplasty, but prosthetic implant surgery patients returned to work a mean of 30 days earlier than those treated with soft tissue reconstruction. Finally, in a single-site cohort with 17 years mean follow-up of 96 of 100 (96%) patients after abductor pollicis longus (APL) tendon suspension interposition arthroplasty, we noted good to excellent patient-rated pain and functional outcomes as well as grip and pinch comparable to the non-operated side. These findings confirm long-held beliefs that there is greater female prevalence of CMC1 OA and that heavy labor is associated with increased risk of CMC1 OA. Surgical treatment can relieve pain and improve function, with prosthetic implant arthroplasty associated with earlier return to work.