Mini Tightrope Fixation Versus Ligament Reconstruction – Tendon Interposition for Maintenance of Post-trapeziectomy Space Height: A Biomechanical Study

Abstract

To test the biomechanical stability of ligament reconstruction and tendon interposition (LRTI) compared with Mini TightRope fixation for thumb metacarpal subsidence after trapeziectomy. Fifteen fresh human cadaveric hands underwent trapeziectomy and were divided into 3 treatment groups: LRTI using a biotenodesis screw and single versus dual Mini TightRope fixation. The thumb and index fingers were removed distal to the metacarpal; the distal ends of the metacarpals and proximal radius were potted in urethane resin and mounted onto a servohydraulic testing machine. A cyclic axial load was applied to stress the trapezial cavity. We recorded displacement of the first metacarpal via the position of the actuator head and computed the size of the trapezial space as the difference of the initial size and first metacarpal displacement. Each specimen underwent cyclical loading until the first metacarpal had collapsed completely onto the scaphoid (failure of the repair) or until 6 hours of testing had been completed. The number of cycles to failure, change in the size of the trapezium cavity, and relative change in size of the trapezium cavity were determined. The trapezial space had completely closed before 6 hours of testing were completed in all biotenodesis screw-augmented LRTI specimens and remained present in all single and dual Mini TightRope specimens. Absolute (and normalized) changes in the size of the trapezial cavity in the single and dual Mini TightRope specimens were 11 ± 2 and 10 ± 2 mm, respectively. Dual Mini TightRope fixation provided superior load bearing and maintenance of trapezial space height compared with single Mini TightRope or LRTI biotenodesis screw procedures. This study demonstrates that patients who undergo suture suspension arthroplasty may be able to move earlier because of the immediate stability the construct affords.