Truly Tension Free Nerve Repairs Using a Nerve Connector:

A Biomechanical Study in an Animal Model

Kumaran Rasappan(1), Vaikunthan Rajaratnam(1), Yoke Rung Wong(2), Shian Chao Tay(3)

1 - Department of Orthopaedic Surgery, Khoo Teck Puat Hospital2 - Biomechanics Laboratory, Singapore General Hospital3 - Department of Hand Surgery, Singapore General Hospital

Introduction• Primary nerve repair / Autologous nerve repair

• Shortcomings (1)

• General• Failure• Neuroma• Axonal mismatch

• Primary repair• Immobilisation of joint• Tension

• Nerve graft• Donor tissue morbidity

• Avoidance of tension – Ultimate Goal (2,3)

1) Gerth DJ, Tashiro J, Thaller SR. Clinical outcomes for Conduits and Scaffolds in peripheral nerve repair. World Journal of Clinical Cases: WJCC. 2015 Feb 16;3(2):1412) Terzis J, Faibisoff B, Williams B. The nerve gap: suture under tension vs. graft. Plast Reconstr Surg 1975; 56: 166-170 [PMID: 1096197] 3) Wang WZ, Crain GM, Baylis W, Tsai TM. Outcome of digital nerve injuries in adults. J Hand Surg Am 1996; 21: 138-143 [PMID: 8775209]

Nerve Conduits

• Axonal regeneration in conduits (1)

• Neuro trophism (2,3)

1) Williams LR, Longo FM, Powell HC, Lundborg G, Varon S. Spatial-temporal progress of peripheral nerve regeneration within a silicone chamber: parameters for a bioassay. J Comp Neurol 1983; 218: 460-470 [PMID: 6619324 DOI: 10.1002/cne.902180409] 2) Politis MJ, Ederle K, Spencer PS. Tropism in nerve regeneration in vivo. Attraction of regenerating axons by diffusible factors derived from cells in distal nerve stumps of transected peripheral nerves. Brain research. 1982 Dec 16;253(1):1-2.3) Lundborg G, Dahlin L, Danielsen N, Zhao Q. Trophism, tropism and specificity in nerve regeneration. Journal of reconstructive microsurgery. 1994 Sep;10(05):345-54.

Source: http://www.whichmedicaldevice.com/by-manufacturer/245/583/neurolac-nerve-guides

Source: http://www.aleobme.com/peripheral-nerve-repair.html

Aims of Study

• Tension free repair• Repair failure

• Biomechanical breaking strength of nerves

Repair with primary repair VS

Repair with nerve connector

Methodology

Methodology

Methodology

Methodology

Methodology

Nerve Connector• Neurolac ® Thin Wall (TW) nerve connector

• Fully synthetic, Non-Immunogenic

• Retain mechanical properties up to 10 weeks

• Hydrolysis and natural degradation within 2 years

Source: http://www.whichmedicaldevice.com/by-manufacturer/245/583/neurolac-nerve-guides

Source: http://www.aleobme.com/peripheral-nerve-repair.html

10 mm

5 mm 2.5 mm2.5 mm

2.5 mmNerve Nerve

Nerve Connector

Ethilon 8-0 round body suture

Methodology

Instron E – 1000 Dynamic Tester

Methodology

Methodology

Nerve Failure

Results

 Diameter 

(mm)

Cross-sectional Area 

(mm^2)Max Load 

(N)Max Disp(mm)

Max Stress 

(N/mm^2)

Max Strain (%)

Elasticity (Young's Modulus) (MPa)

Intact Nerve (x2)

1.43 -

2.02

1.60-

3.23

3.95 -

 5.15

7.45 -

10.2

1.22 -

 3.21

74.5 -

102

2.08 -

4.84

Control(x6)

1.64-

 2.48

2.12 -

4.84

0.35 -

0.58

4.82 -

 7.46

0.07 -

 0.25

19.28 -

 49.73

0.4 -

 2.11

Connector(x6)

1.28 -

 3.19

1.28 -

 7.98

0.63 -

 1.34

6.68 -

 11.78

0.08 -

 0.47

38.25 -

 58.9

0.25 -

 2.07

Maximal load/displacement

Results

 Diameter 

(mm)

Cross-sectional Area 

(mm^2)Max Load 

(N)Max Disp(mm)

Max Stress 

(N/mm^2)

Max Strain (%)

Elasticity (Young's Modulus) (MPa)

Intact Nerve 1.73 2.415 4.55 8.83 2.22 88.25% 3.46

Control 1.96 3.095 0.46 5.87 0.17 31.52% 0.93

Connector 2.07 3.635 0.92 9.8 0.35 49.02% 0.95

P-value 0.716 0.716 0.001 0.003 0.078 0.011 0.974

Limitations

• Animal cadaveric model• Small sample size• Nerves not uniform (diameter, quality, shape)• Ex-Vivo repair• Uniform stress applied

Conclusion

• Nerve connectors increase distance of nerve repairs• Thus minimizing tension

• Nerve connectors increase breaking strength of nerve repairs

• Possible clinical implications• Reducing need for nerve grafts• Immediate mobilization of joints post repair• Decreased worry of repair failure

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