gms | German Medical Science

Objectives/Interrogation: Recent attention has been paid to the carpus-forearm-elbow as a functional unit for longitudinal stability of the forearm. We know the radial head plays an important role, and Essex Lopresti described its fracture associated with DRUJ dislocation. The TFCC and the Interosseous Membrane (IOM) are also key components, and their rupture disrupts the vectors of load and forearm stability. The main focus of IOM reconstructions has centered to restoration of the central band. Recent studies have shown the importance of the Distal Oblique Band (DOB) both for DRUJ and forearm longitudinal stability. We present the strengths and load to failure results when biomechanically comparing a standard central band vs central band plus distal oblique band reconstructions.

Methods: Three pairs of matched fresh frozen cadaver specimens were utilized for our biomechanical testing. We performed a central band (CB) reconstruction with Palmaris Longus graft and FiberTape (Arthrex, Inc. Naples, FL) augmentation on 3 specimens (Group 1), and a central + distal oblique band reconstruction with Palmaris Longus graft and FiberTape augmentation on the other 3 specimens (Group 2). BioComposite 4 x 10 Tenodesis screws (Arthrex, Inc. - Naples, FL) were used for construct fixation. Once the constructs were performed, we proceeded to transect the entirety of the IOM, TFCC, DRUJ, and annular ligaments to isolate the bands we wanted to test. Axial load was applied to the sample at a rate of 20 mm/min using an INSTRON®* ElectroPuls Dynamic Testing System (INSTRON, Canton, MA). A t-test was performed to identify any statistically significant differences in maximum load and load at clinical failure between the groups, (p=0.05). Clinical failure was defined as the load corresponding to 10 mm of longitudinal displacement.

Results and Conclusions: The average maximum load to failure for the Group 1 was 266.81 N (127.7 - 365.07 N) and for Group 2 was 377.8 N (279.37 - 495.82 N). The mechanism of failure was by screw pull out; only one specimen displayed graft stretching. The results of the t-tests indicated that the maximum load and load at clinical failure were both significantly higher for CB + DOB reconstructions (p=0.002, for both comparisons). These results might have clinical relevance when deciding the type of reconstruction when dealing with acute and/or chronic longitudinal forearm instability. We also noticed that as opposed to a pure tendon reconstruction, the Internal Brace augmentation prevented graft stretching.