564902 research-article2014
JHS0010.1177/1753193414564902The Journal of Hand SurgeryRodger et al.
JHS(E)
Full Length Article
Vein grafts to augment flexor tendon repairs: a biomechanical study on strength and gap resistance
The Journal of Hand Surgery (European Volume) 2015, Vol. 40E(7) 695–699 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1753193414564902 jhs.sagepub.com
M. P. Rodger1, P. Theobald1 and G. Giddins2 Abstract The ultimate tensile repair strength and gap formation of the pig extensor tendons repaired with a standard 4-strand Savage with epitendinous suture repair, was compared with a new technique of adding a vein sleeve. Force and displacement data were recorded, and video images during linear cyclic loading up to failure. At 35 N, video-graphic observation detected significantly smaller gap lengths in the standard and vein repair specimens compared with standard repair specimens (p = 0.047). The incidence of 3 mm gaps between the repaired tendon ends in the standard repair group was 20 %, but no 3 mm gaps were seen in the standard and vein specimens. The addition of a vein sleeve increased the ultimate tensile strength of the standard repair from 50.4 N (4.5) to 55.4 N (4.5); this was statistically significant (p = 0.03). This study demonstrated that the addition of a vein graft prevented gap formation and increased ultimate tensile strength of tendon repair. Keywords Tendon, repair, vein, fibroblast, sleeve, augment, cyclic loading Date received: 15th April 2014; revised: 20th November 2014; accepted: 22nd November 2014
Introduction The literature describes many techniques for tendon repair including legions of variations of suture technique, suture material, suture diameter and augmentation devices, flexor sheath and tissue engineered scaffolds (Galvez et al., 2014; Lowrie and Lees, 2014; Savage, 2014). Vein grafts have been used in cardiac surgery as a replacement for diseased coronary arteries, and the biomechanical properties of a vein have been studied in this context. While vein grafts have been used as a tendon sheath substitute, augmentation of tendon repairs using a vein sleeve has not previously been described in the literature (Moosavi et al., 2005). The ultimate tensile strength of a vein has previously been reported to equal 2.71 MPa (±0.85 MPa), with the associated stress–strain curve demonstrating a ‘J-shape’, which is broadly comparable with other soft tissues. This study evaluates the potential for vein grafts to provide additional mechanical strength during the early stages of tendon repair.
diameters were 3–4 mm, the vein augments were 20 mm long. The specimens were frozen at –25 °C, with intermittent defrosting for harvest, repair and testing. All tendon repairs were performed by the lead author (MR) using 2.5× magnification loupes and standard instruments. The repair performed was a Savage repair modified to four core strands (Savage, 1985). The core suture used was 4-0 Ti-CronTM (Covidien), a coated, braided polyester. The surgical technique aimed to replicate the repair as described by Savage with the grasping bights >1 cm from the cut tendon end to yield maximal strength (Figure 1) (Cao et al., 2006). When used, the repair was completed by one peripheral running suture with 6-0 Ethilon (© Ethicon) with a single run consisting of six bites placed 2 mm from the repair (Merrell et al., 2003; Moriya et al., 2010). The tension of the core
1School
of Engineering, Cardiff University, Cardiff, UK of Mechanical Engineering, University of Bath, Bath,
2Department
Methods Specimen preparation
UK
A total of 30 extensor tendons and veins were harvested from Middle White pig trotters, tendon and vein
Corresponding author: M. P. Rodger, School of Engineering, Cardiff University, The Parade, Cardiff CF24 3AA, UK. Email: [email protected]
Downloaded from jhs.sagepub.com at UNSW Library on August 21, 2015
696
The Journal of Hand Surgery (Eur) 40(7)
Figure 1. The cut end of the tendon was passed through a vein on a tendon-passer device and the core suture repair was completed.
Figure 2. Tendon-passer device front view (1 mm grid).
suture was standardized by placing the core sutures such that the overall length of the tendon encompassed by the core suture reduced by approximately 10% (Wu and Tang, 2012).
Experimental groups This study consisted of three groups, each comprising 10 pig extensor tendons. Group 1: ‘Standard repair’: a A 4-strand modified Savage repair and an epitendinous running suture (Savage, 1985) were used. Group 2: ’Standard and Vein graft repair’: The tendon was repaired with the same core and peripheral sutures in Group 1, augmented with a vein sleeve graft. Group 3: ‘Core and Vein graft repair’: The tendon was repair with a 4-strand modified Savage core suture augmented with a vein sleeve graft, without an epitendinous suture. A tendon-passer device was fabricated from a cold carbon steel strip measuring 0.15 mm by 10 mm, found in the recoil spring of a self-retracting tape measure (Figure 2). It comprises two almost parallel tines. In vivo the vein would be passed over one cut tendon end and drawn back after performing the core suture. The vein-augmented repair tendons were repaired in the same manner and the site of repair was then sleeved with a section of the vein using the tendonpasser device (Figure 2). Each end of the vein was
sutured to the tendon using 6-0 Ethilon in the form of one peripheral running suture (Figure 3).
Mechanical test and recording methods The repaired tendons were mounted in a tensile testing machine (LOS Servocon Systems). The clamps crushed the tendon; this did not lead to any tendon failing at the clamp. The specimen was lit with incandescent lamps against a white background and videographed using a Sony DSC-HX9V camera (16 megapixel, HD video at 25 frames per second) mounted on a Benq tripod. The specimens were wet and defrosted when mounted, though were not wetted during testing as this lasted
JHS0010.1177/1753193414564902The Journal of Hand SurgeryRodger et al.
JHS(E)
Full Length Article
Vein grafts to augment flexor tendon repairs: a biomechanical study on strength and gap resistance
The Journal of Hand Surgery (European Volume) 2015, Vol. 40E(7) 695–699 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1753193414564902 jhs.sagepub.com
M. P. Rodger1, P. Theobald1 and G. Giddins2 Abstract The ultimate tensile repair strength and gap formation of the pig extensor tendons repaired with a standard 4-strand Savage with epitendinous suture repair, was compared with a new technique of adding a vein sleeve. Force and displacement data were recorded, and video images during linear cyclic loading up to failure. At 35 N, video-graphic observation detected significantly smaller gap lengths in the standard and vein repair specimens compared with standard repair specimens (p = 0.047). The incidence of 3 mm gaps between the repaired tendon ends in the standard repair group was 20 %, but no 3 mm gaps were seen in the standard and vein specimens. The addition of a vein sleeve increased the ultimate tensile strength of the standard repair from 50.4 N (4.5) to 55.4 N (4.5); this was statistically significant (p = 0.03). This study demonstrated that the addition of a vein graft prevented gap formation and increased ultimate tensile strength of tendon repair. Keywords Tendon, repair, vein, fibroblast, sleeve, augment, cyclic loading Date received: 15th April 2014; revised: 20th November 2014; accepted: 22nd November 2014
Introduction The literature describes many techniques for tendon repair including legions of variations of suture technique, suture material, suture diameter and augmentation devices, flexor sheath and tissue engineered scaffolds (Galvez et al., 2014; Lowrie and Lees, 2014; Savage, 2014). Vein grafts have been used in cardiac surgery as a replacement for diseased coronary arteries, and the biomechanical properties of a vein have been studied in this context. While vein grafts have been used as a tendon sheath substitute, augmentation of tendon repairs using a vein sleeve has not previously been described in the literature (Moosavi et al., 2005). The ultimate tensile strength of a vein has previously been reported to equal 2.71 MPa (±0.85 MPa), with the associated stress–strain curve demonstrating a ‘J-shape’, which is broadly comparable with other soft tissues. This study evaluates the potential for vein grafts to provide additional mechanical strength during the early stages of tendon repair.
diameters were 3–4 mm, the vein augments were 20 mm long. The specimens were frozen at –25 °C, with intermittent defrosting for harvest, repair and testing. All tendon repairs were performed by the lead author (MR) using 2.5× magnification loupes and standard instruments. The repair performed was a Savage repair modified to four core strands (Savage, 1985). The core suture used was 4-0 Ti-CronTM (Covidien), a coated, braided polyester. The surgical technique aimed to replicate the repair as described by Savage with the grasping bights >1 cm from the cut tendon end to yield maximal strength (Figure 1) (Cao et al., 2006). When used, the repair was completed by one peripheral running suture with 6-0 Ethilon (© Ethicon) with a single run consisting of six bites placed 2 mm from the repair (Merrell et al., 2003; Moriya et al., 2010). The tension of the core
1School
of Engineering, Cardiff University, Cardiff, UK of Mechanical Engineering, University of Bath, Bath,
2Department
Methods Specimen preparation
UK
A total of 30 extensor tendons and veins were harvested from Middle White pig trotters, tendon and vein
Corresponding author: M. P. Rodger, School of Engineering, Cardiff University, The Parade, Cardiff CF24 3AA, UK. Email: [email protected]
Downloaded from jhs.sagepub.com at UNSW Library on August 21, 2015
696
The Journal of Hand Surgery (Eur) 40(7)
Figure 1. The cut end of the tendon was passed through a vein on a tendon-passer device and the core suture repair was completed.
Figure 2. Tendon-passer device front view (1 mm grid).
suture was standardized by placing the core sutures such that the overall length of the tendon encompassed by the core suture reduced by approximately 10% (Wu and Tang, 2012).
Experimental groups This study consisted of three groups, each comprising 10 pig extensor tendons. Group 1: ‘Standard repair’: a A 4-strand modified Savage repair and an epitendinous running suture (Savage, 1985) were used. Group 2: ’Standard and Vein graft repair’: The tendon was repaired with the same core and peripheral sutures in Group 1, augmented with a vein sleeve graft. Group 3: ‘Core and Vein graft repair’: The tendon was repair with a 4-strand modified Savage core suture augmented with a vein sleeve graft, without an epitendinous suture. A tendon-passer device was fabricated from a cold carbon steel strip measuring 0.15 mm by 10 mm, found in the recoil spring of a self-retracting tape measure (Figure 2). It comprises two almost parallel tines. In vivo the vein would be passed over one cut tendon end and drawn back after performing the core suture. The vein-augmented repair tendons were repaired in the same manner and the site of repair was then sleeved with a section of the vein using the tendonpasser device (Figure 2). Each end of the vein was
sutured to the tendon using 6-0 Ethilon in the form of one peripheral running suture (Figure 3).
Mechanical test and recording methods The repaired tendons were mounted in a tensile testing machine (LOS Servocon Systems). The clamps crushed the tendon; this did not lead to any tendon failing at the clamp. The specimen was lit with incandescent lamps against a white background and videographed using a Sony DSC-HX9V camera (16 megapixel, HD video at 25 frames per second) mounted on a Benq tripod. The specimens were wet and defrosted when mounted, though were not wetted during testing as this lasted
