Introduction Anatomically, the Transverse Carpal Ligament (TCL) attaches to the carpal bones distally and proximally. Beneath the TCL, during finger and hand movements the median nerve and tendons move in the longitudinal, transverse, volar and dorsal directions [Ugbolue et al, 2005] and become compressed as they move in the dorsal and volar directions [Armstrong, 1979]. Within the carpal tunnel complex, the tendons and median nerve together with the TCL form a pulley system [Brooks et al, 2003; Stecco et al, 2010]. Biomechanically, the TCL has been studied to determine its compressive [Holmes, 2011] and tensile [Li et al, 2009; Sucher et al, 1998] properties. While these methods have involved either excising the TCL or determining the biomechanical properties of the TCL intact / transected, experimentally there is still no widely accepted method designed to specifically evaluate the tensile properties of the TCL and carpal tunnel complex. That is to date, there are no known methods to test the TCL to failure in-situ.
Methods Six embalmed cadaveric specimens amputated at the mid forearm and aged 82 ± 6.29 years were tested. The six hands were from four individuals (two pairs and two individual hands), three males (four hands) and one female (two hands). The tensile properties of the TCL were determined using a commercial Maillon Rapide Delta (S3i Ltd, Bawtry, England, UK) fastened to a steel work piece (Figure 1). The Maillon Rapide Delta (S3i Ltd, Bawtry, England, UK) was fastened on to the TCL and then attached to the upper hydraulic tensile grips connected to the 1000 N load cell. The specimen was adjusted until the TCL was aligned and perpendicular to the Maillon Rapide Delta (S3i Ltd, Bawtry, England, UK). The test protocol started with a preconditioning cycle (10 cycles of 0.5 N loading at a rate of 2Hz) before testing the ligament to failure at a deformation rate of 20 mm/s. Descriptive statistics and tensile properties of the TCL – carpal tunnel complex and Load – Displacement data were also obtained.
Results and discussion The TCL failed either at the mid-substance or at their bony attachments. At maximum deformation the peak load and maximum TCL displacements ranged from 285.74N to 1,369.66N and 7.09 mm to 18.55 mm respectively. The load at tensile strength ranged from 272.09N to 1293.36N and the ultimate tensile strength mean (SD) was 23.99 (10.68) Nmm-2. A unique method of tensile testing the TCL and carpal tunnel complex that is uncomplicated and practical has been developed. The methodology has been validated and is capable of generating highly repeatable data. Useful biomechanical information can be extracted from the results which provide an insight into the tensile properties of the TCL in-situ.
References Armstrong TJ, et al. J Biomech. 1979;12(7):567–570
Brooks JJ, et al. Clin Biomech.2003;18:685–693
Holmes MWR, et al. J Orthop Res. Nov; 2011;29(11):1682–7
Li ZM, et al. J Biomech Eng. 2009;131(8):081011 (6 page) (Abstract)
Stecco C, et al. The Journal of hand surgery 2010;35:746–753
Sucher BM, et al. J Am Osteopath Assoc. 1998;98(12):679–86
Ugbolue UC, et al. Clin Biomech. 2005;20:50–56
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