Artroplastia articular con titanio elemental…(I)

Sanjiv H. Naidu MD, PhD, Nikhil Kulkarni MS and Marnie Saunders PhD

Department of Orthopaedic Surgery and Rehabilitation, the Pennsylvania State University College of Medicine, Hershey, PA.

Purpose To define the mechanics and determine the clinical outcome of titanium implant arthroplasty in trapeziometacarpal arthritis.

Methods For the finite element analysis (FEA) a 2-dimensional FEA mesh of the titanium arthroplasty was constructed with 8-node quadrilateral elements and analyzed. Flexion–extension displacement of the metacarpal was analyzed. For the clinical study, between 1996 and 2003, 47 patients (50 thumbs) with Eaton stage 3 trapeziometacarpal arthritis were treated with titanium basal joint arthroplasty. The average follow-up period was 2 years. Disabilities of the Arm, Shoulder, and Hand questionnaire answers and grip and pinch measurements were obtained before surgery and at the final follow-up evaluation. Failure was defined strictly as the point when revision to the standard soft-tissue interposition arthroplasty became inevitable.

Results In the FEA the titanium implant showed pistoning behavior with maximum stress concentration in the midmetacarpal shaft of 1.92 MPa. The convex sphere of the implant rotates and lifts out of the trapezial crater with a high stress concentration of 0.51 MPa at the radial and ulnar corner of the trapezium. In the clinical study treatment failed in 10 of the patients before 9 months. All were converted successfully to a standard ligament reconstruction tendon interposition. The remaining 80% of the patients showed significant improvement in Disabilities of the Arm, Shoulder, and Hand questionnaire scores albeit with continued weakness at the 2-year follow-up evaluations. The reconstructed thumbs never attained the strength of the contralateral thumbs; even in the success group residual swelling was not uncommon with any increase in activity level.

Conclusions Anecdotal quotations show success rates for titanium implant arthroplasty for basal joint arthritis to be as high as 97%. Our results are quite to the contrary in that high failure rates were common early in the follow-up period. Our FEA results are confirmed by the clinical study. Titanium implant arthroplasty may have a role in low-demand patients with good bone stock; however, we have stopped offering titanium hemiarthroplasty to patients at our institution.