Optimal Position of the Bone Anchor for the Internal Brace Suspensionplasty Technique for Thumb Basal Joint Arthroplasty

Abstract

Purpose: Ligament reconstruction and tendon interposition is a common technique for thumb basal joint arthroplasty. Recently, a variation of this technique, a suture suspensionplasty, has been introduced. The goal of our study was to assess the optimal position of the bone anchor in the thumb metacarpal. We hypothesized that an anchor placed in the radial aspect of the thumb metacarpal base would provide improved stability and resist subsidence more effectively than an ulnar-based thumb anchor. Methods: Eight fresh-frozen cadaver arms were imaged fluoroscopically in anteroposterior and lateral views centered over the thumb carpometacarpal joint before and after trapeziectomy and after the placement of radial-based and ulnar-based bone anchors. The intermetacarpal angle between the thumb and index metacarpals was measured on all images after the application of a standard force. Radial abduction, opposition, subsidence, palmar abduction, and adduction were measured. Subsidence was calculated as the percentage loss of the trapezial space. Results: Both radially and ulnarly placed internal brace constructs allowed more radial abduction, opposition, and palmar abduction than the pretrapeziectomy constructs. They both also reduced subsidence by approximately 20% to 29% compared with the posttrapeziectomy constructs. Comparing radial to ulnar constructs, motion and subsidence were similar. Conclusions: There was immediate stability of the thumb with respect to axial load and subsidence after anchor placement, and this was independent of the anchor position. The position of the bone anchor in the thumb metacarpal base did not affect the range of motion. Although the device can limit subsidence, it does not appear to restrict any range of motion of the thumb, irrespective of anchor position. Clinical relevance: This cadaver study can help hand surgeons understand the effect of positioning of bone anchors when performing a specific suture suspensionplasty technique.