Background In clinical trial of medical treatment, bone erosion and joint space narrowing in serial x-rays of the hand are important to assess structural damage of the joint affected by rheumatoid arthritis (RA). For the assessment of hand function, three-dimensional (3D) malalignment including flexed or rotational deformities and dislocation at the finger joint is one of the important findings.

Objectives In a two-dimensional (2D) x-ray, it is difficult to measure complex deformity at the metacarpophalangeal (MP) joint. The objective of this study is to prove usefulness of three-dimensional computed tomogram (3D-CT) ¹⁾for the accurate measurement of palmo-ulnar flexion deformity at the MP joint of the rheumatoid hand.

Methods Between April 2006 and April 2011, Swanson implant arthroplasty at the 2nd through the 5th MP joints was performed at 179 joints in 46 hands of 40 patients with RA. Before and after the operation, a postero-anterior view of the hand X-ray and a 3D-CT were taken. Using a hand X-ray, Larsen grade at the MP joint was determined, and ulnar flexion angle at the MP joint was measured. Using a 3D-CT, ulnar flexion angle, palmar flexion angle, and resected bone length were measured using Aquarius iN tuition (Tera Recon co.V4.4.5.49). Grade of the MP joint dislocation was determined according to this criterion; “subluxation”: partial contact of two bones, “dislocation”: no contact of two bones, and “severe dislocation”: no contact and overlapping of two bones more than 1cm.

Results Preoperative ulnar flexion angle in a X-ray was approximately 9 degrees smaller than that in a 3D-CT. Larsen grade III was 47 joints (26.3%), IV was 93 joints (52.0%), and V was 39 joints (21.2%). The MP joint “subluxation” was 72 joints (42.2%), “dislocation” was 53 joints (29.6%), and “severe dislocation” was 21 joints (11.7%). With progression of Larsen grade, ulnar flexion angle at the MP joint increased. Average ulnar flexion angle was 18.7±16.0 (mean±SD) degrees in grade III, 38.4±21.2 degrees in IV, and 40.1±21.1degrees in V. With progression of the MP joint dislocation, ulnar flexion angle increased. Average ulnar angle was 29.6±16.0 degrees in “subluxation”, 24.8±21.2 degrees in “dislocation”, and 41.1±22.2degrees in “severe dislocation”. There was no significant difference between grade of the MP joint dislocation and palmar flexion angle. Average palmar flexion angle was 41.5±22.6 degrees in “subluxation” group, 36.6±29.9 degrees in “dislocation” group and 38.4±32.2 degrees in “severe dislocation”group. After the operation, flexion angle at the proximal interphalangeal (PIP) joint increased along with correction of palmar flexion deformity at the MP joint. Average length of bone resection at the metacarpal head was 9.6mm and that at the base of proximal phalanx was 4.5mm. Along with progression of the MP joint dislocation, resected bone length increased.

Conclusions A 3D-CT is useful to assess malalignment at the MP joint in the rheumatoid hand. It gives accurate information about deformity of the hand. Also, an appropriate length of bone resection can be determined in the preoperative planning.

References

1. Ishikawa H, Abe A, Murasawa A, et al. Rheumatoid wrist deformity and risk of extensor tendon rupture evaluated by 3DCT imaging. Skeletal Radiol2010;39:467-72.

Disclosure of Interest None Declared