MP joint arthroplasty is one of the treatment options for the rheumatoid thumb with boutonniere deformity. The use of flexible hinge toe implant for MP joint reconstruction was introduced; however, the outcome of flexible toe implantation for the reconstruction of the MP joint has not as yet been reported in detail. Therefore, in this study, we retrospectively investigated the clinical outcome and radiological findings.
We assessed 56 Swanson implant arthroplasties that used flexible hinge toe implants with grommets to address boutonnière deformity of the thumb MP joint. The minimum follow-up period was 6 months. Pain, the range of motion, grip strength, pinch strength, General health Visual analogue scale and DASH (Disabilities of Hand, Shoulder and Hand) were assessed.
For most of the patients, the procedure provided painless motion and stability to the thumb. In the radiological assessments, the preoperative flexion angles at the MP joint were 45° improved to 17°. The origin of arc was shifted toward the extended position and the average arc of motion was 21°, with a flexion arc from 23° to 44°. The severity of boutonniere deformity was improved in most cases. The average grip strength changed from 110 to 121 mmHg and the average side pinch power changed from 1.5 to 2.2 kgf. General health VAS improved from 40 to 29 (p = 0.019), and the DAS28-CRP decreased from 3.3 to 2.4 (p < 0.001). Infection occurred in one case, and there were no implant fractures.
Swanson flexible hinge toe implant arthroplasty with grommets applied to the MP joint of the thumb was one of the recommended procedures for the reconstruction of boutonnière deformity of the thumb.