Biomechanical Comparison of 1- and 2-Tunnel Suture Suspensionplasty Constructs for Basilar Thumb Arthritis

Abstract

Background: Trapeziectomy with suture button suspensionplasty (SBS) is a common treatment for thumb carpometacarpal (CMC) osteoarthritis. This study aimed to evaluate the effect of bone tunnel configuration and suture count on the construct stability.

Methods: Twelve matched specimens underwent trapeziectomy and randomization to either a 2-strand 1-tunnel (single SBS) or divergent 4-strand 2-tunnel suture button (crossed dual SBS) construct. Mechanical stiffness was measured using material testing machine with a semiconstrained axial load over 5-mm displacement. Trapezial space was measured under no load and in a light and heavy physiologic pinch grip models. Subsequently, specimens were randomized to undergo single SBS or divergent 2-strand 2-tunnel suture (crossed suture) constructs, and loaded pinch testing was performed. Primary outcomes were analyzed using matched-pair t-tests.

Results: The crossed dual SBS construct showed significantly higher stiffness compared to the single SBS construct in elastic deformation (19.9 vs 15.5 N/mm, P = .010) and maintained trapezial height better in both light (82% vs 71%, P = .021) and heavy (73% vs 46%, p = .004) pinch grips. The crossed suture technique also preserved trapezial height better than the single SBS construct in light (79% vs 64%, P = 0.021) and heavy (60% vs 44%, P = 0.039) pinch grips.

Conclusions: In the immediate postoperative period, a crossed dual SBS construct was stiffer to axial load and more stable in pinch grip compared to a single SBS construct. The novel crossed suture construct better preserved trapezial height then the singe SBS, suggesting that the crossed configuration may be more relevant than suture count in postoperative stability.

Keywords: CMC; anatomy; arthritis; basic science; biomechanics; diagnosis; specialty; surgery; suspensionplasty; thumb.

Figure 1.

Schematic representations of the suspensionplasty constructs tested. (a) 2-strand, 1-tunnel suture button suspensionplasty (single SBS). (b) Divergent 4-strand, 2-tunnel suture button suspensionplasty (crossed dual SBS). (c) Divergent 2-strand 2-tunnel suture suspensionplasty (crossed suture). Note. SBS = suture button suspensionplasty.

Figure 2.

Experimental setup used to assess mechanical stiffness of crossed dual SBS and single SBS constructs. Note. The specimen was firmly clamped to a custom loading jig using 2.0-mm K wire transfixion pins through the second metacarpal and a screw through the radius. An additional screw was placed longitudinally through the proximal phalanx of the thumb extending into the first metacarpal. This screw was then clamped to actuator of a material testing machine. The construct was preloaded to 15 N, and a semiconstrained axial load was applied over 5 mm of compression. SBS = suture button suspensionplasty.

Figure 3.

Experimental setup for simulated pinch grip model. (a) Illustration adapted from Pellegrini et al with permission. (b) A #2 FiberWire was placed in Krakow fashion in the AP, EPB, EPL and FPL tendons. Note. These were then linked to the appropriate weights using nylon cables. The specimen was secured using a clamp on the radius and transfixed to a board with two 2.0-mm K wires through the 2nd metacarpal and one through the hamate. To ensure appropriate line of pull for the AP, the nylon cable was passed around the K wire placed through the hamate. A bolster was placed between the thumb and index finger to help maintain appropriate position of the thumb during loading. AP = adductor pollicis; APL = abductor pollicis longus; EPB = extensor pollicis brevis; EPL = extensor pollicis longus; FPL = flexor pollicis longus; K wire = Kirschner wire.

Figure 4.

Intraoperative imaging. (a) Fluoroscopic image demonstrating experimental setup with immobilization of the second metacarpal using 2.0-mm Kirschner wires and a third 2.0-mm wire through the hook of the hamate to act as a pully for the adductor pollicis musculotendinous unit. A quarter dollar was used for scale (24.26 mm). (b) Trapezial height was measured using a line at the distal articular surface of the scaphoid and line parallel to this that bisects the midpoint of the proximal first metacarpal articular surface.

Figure 5.

Single SBS versus Crossed Dual SBS Constructs. (a) Stiffness in elastic deformation over 5 mm of semiconstrained axial load for 4-strand 2-tunnel (crossed dual SBS) and 2-strand 1-tunnel (single SBS) constructs (b) Representative plot of elastic deformation under semiconstrained axial loading. Note. SBS = suture button suspensionplasty.

Figure 6.

Divergent 4-strand 2-tunnel (crossed dual SBS) constructs undergo less loss of trapezial height compared to 2-strand 1-tunnel (single SBS) constructs under light (82% vs 71%, P = .021) and heavy (73% versus 46%, P = .004) pinch grips. Note. Vertical bars depict shows pooled mean values ± standard deviation. P value is from matched-pair t-test. SBS = suture button suspensionplasty.

Figure 7.

Divergent 2-strand 2-tunnel (crossed suture) undergoes less loss of trapezial height compared to 2-strand 1-tunnel (single SBS) under light (79% vs 64%, P = .021) and heavy (60% vs 44%, P = 0.039) loaded pinch grip models. Note. Vertical bars depict shows pooled mean values ± standard deviation. P value is from matched-pair t-test. SBS = suture button suspensionplasty.