Repair of chronic Achilles tendon rupture is technically complex. Flexor jallucis longus (FHL) and peroneus brevis (PB) tendon transfers have been described, but the mechanical properties of these tissues have not been well reported. The FHL, PB and tendo achilles (TA) tendons were harvested from 17 fresh frozen human cadavers free of gross pathology (mean age 69 years). Samples were tested in uniaxial tension at 100% per minute. Samples were secured using special jigs for the bony aspect or by freezing the tendons in cryogrips using liquid carbon dioxide. The peak load (N), linear stiffness (N/mm) and energy to peak load (N*mm) were determined. Mechanical data was analysed using one way analysis of variance (ANOVA) followed by a Games Howell multiple comparison post-hoc test. Fifty one tendons were harvested and mechanical testing was successfully completed in all samples apart from one PB that slipped from the grips during testing (sample was omitted from the analysis). The mean ultimate loads differed for each group, with the TA tendons being the strongest (1724.5 N ± 514.3) followed by FHL (511.0 N ± 164.3) and PB (333.1 N ± 137.2) (P<
0.05). Similar results were found with respect to energy, with TA tendons absorbing the most energy followed by FHL and PB (P<
0.05). Stiffness for the TA tendons (175.5 N/mm ± 94.8) was greater than FHL (43.3 N/mm ± 14.1) and PB (43.6 N/mm ± 18.9), which did not differ from each other. FHL is stronger than PB, but have similar stiffness. The mechanical properties of PB and FHL were both inferior to TA. Graft stiffness appears to be an important variable rather than ultimate load based on the clinical success of both techniques.
Treatment of chronic Achilles tendon ruptures can be technically demanding due to tendon retraction, atrophy and short distal stumps. Although rare, re-rupture following surgical treatment is a major late complication. Biomechanical studies on the strength of reconstructed Achilles tendon using autologous tendon grafts have not been well documented. This study examined the time zero in vitro mechanical properties of a reconstructed Achilles tendon (TA) using the peroneus brevis (PB) or the flexor hallucis longus (FHL) tendons in a human cadaver model (n=17). The TA was reconstructed using the same technique for all specimens. Biomechanical testing was performed using an MTS 858 Bionix testing machine and structural properties (failure load, stiffness and mode of failure) were determined. Average failure load was significantly higher in the PB-group (p=0.0116) (PB: 343.82 N (+/− 124.90 N, FHL: 241.54 N (+/− 82.17 N)). There was no significant difference in stiffness (p=0.212), (PB: 16.53 N/mm (+/− 6.25 N/mm), FHL: 14.00 N/mm (+/− 3.84 N/mm)) or energy (p=0.075). Mode of failure was the same for all specimens, with the tendon graft cutting through either the distal or proximal TA-stump. Reinforcement of these stumps could lead to increased failure loads. Based on the biomechanical data, the present study supports the use of either FHL or PB to reconstruction chronic TA tendon ruptures. The greater failures loads for PB may not be clinically relevant considering the peak loads. The addition of the suturing pattern, whilst is does reconstruct the tendon, does not provide a similar ability to resist the load.
