Biomechanical Comparison of Tape Versus Suture in Simulated Achilles Tendon Midsubstance Rupture.

As sutures have progressed in strength, increasing evidence supports the suture tendon interface as the site where most tendon repairs fail. We hypothesized that suture tape would have a higher load to failure versus polyblend suture due to its larger surface area. Eleven matched pairs of cadaveric Achilles tendons were sutured with 2 mm wide braided ultrahigh molecular weight polyethylene tape (Tape) or 2 mm wide braided ultrahigh molecular weight polyethylene suture (Suture) using a Krackow repair method. All Achilles repair constructs were cyclically loaded, after which they were loaded to failure. Change in suture footprint height, clinical and ultimate load to failure, and location of failure was recorded. Clinical loads to failure for Tape and Suture were 290.4 ± 74.8 and 231.7 ± 70.4 Newtons, respectively (p= .01). Ultimate loads to failure for Tape and Suture were 352.9 ± 108.1 and 289.8 ± 53.7 Newtons, respectively (p = .11). Cyclic testing resulted in significant changes in footprint height for both Tape and Suture, but the 2 sutures did not differ in terms of the magnitude of change in footprint height (p = .52). The suture tendon interface was the most common site of failure for both Tape and Suture. Our results suggest that Tape may provide added repair strength in vivo for Achilles midsubstance rupture.

A biomechanical cadaver comparison of suture button fixation to plate fixation for pubic symphysis diastasis.

OBJECTIVES: To determine whether suture button fixation of the pubic symphysis is biomechanically similar to plate fixation in the treatment of partially stable pelvic ring injuries. METHODS: Twelve pelvis specimens were harvested from fresh frozen cadavers. Dual-x-ray-absorptiometry (DXA) scans were obtained for all specimens. The pubic symphysis of each specimen was sectioned to simulate a partially stable pelvic ring injury. Six of the pelvises were instrumented using a 6 hole, 3.5 mm low profile pelvis plate and six of the pelvises were instrumented with two suture button devices. Biomechanical testing was performed on a pneumatic testing apparatus in a manner that simulates vertical stance. Displacement measurements of the superior, middle, and inferior pubic symphysis were obtained prior to loading, after an initial 440 N load, and after 30,000 and 60,000 rounds of cyclic loading. Statistical analysis was performed using Wilcoxon-Mann-Whitney tests, Fisher's exact test, and Cohen's d to calculate effect size. Significance was set at p < 0.05. RESULTS: There was no difference between groups for DXA T scores (p = 0.749). Between group differences in clinical load to failure (p = 0.65) and ultimate load to failure (p = 0.52) were not statistically significant. For symphysis displacement, the change in fixation strength and displacement with progressive cyclic loading was not significant when comparing fixation types (superior: p = 0.174; middle: p = 0.382; inferior: p = 0.120). CONCLUSION: Suture button fixation of the pubic symphysis is biomechanically similar to plate fixation in the management of partially stable pelvic ring injuries.

Flexor Hallucis Longus Tendon Transfer Fixation.

INTRODUCTION: Flexor hallucis longus (FHL) tendon transfer to the calcaneus is commonly used in the surgical treatment of chronic Achilles tendinopathy. This study assesses the integrity of FHL tendon biotenodesis screw fixation with respect to 2 variables: incorporation of a terminal whipstitch and tunnel depth. MATERIALS AND METHODS: A total of 60 fresh-frozen cadaver FHL tendons and 28 calcanei were harvested for analysis in 4 sets of fixation constructs; 14 whipstitched tendons were compared against their nonwhipstitched paired tendon via pull-out strength load testing, and 16 tendon pairs were randomized for fixation in either a full-depth tunnel (bicortical) or a 25-mm partial tunnel (unicortical). All comparisons were carried out in native bone and synthetic models. RESULTS: Whipstitched tendons demonstrated significantly stronger mean clinical load (253.68 vs 177.24 N, P = .008) and maximum load to failure (294.31N vs 194.57 N, P = .001) compared with the nonwhipstitched tendons in synthetic bone. There were no statistical differences in mean clinical load (200.96 vs 228.31 N, P = .63) and maximum load to failure (192.69 vs 217.74 N, P = .73) between full and partial tunnel groups. There were no significant differences found in trials carried out in cadaveric bone. CONCLUSION: Use of a terminal whipstitch achieves greater fixation strength in FHL tendon biotenodesis transfers. Complete and partial tunnel constructs are equivocal in their pull-out strength. Data produced in a homogeneous bone substitute model demonstrate the biomechanical superiority of the whipstitch as well as the noninferiority of the partial tunnel technique. LEVELS OF EVIDENCE: Level IIb.

Proximal phalanx and flexor digitorum longus tendon biomechanics in flexor to extensor tendon transfer.

BACKGROUND: The flexor to extensor transfer of the flexor digitorum longus (FDL) tendon has been a relatively common operative procedure for the treatment of a flexible hammer toe deformity and chronic metatarsophalangeal (MTP) joint dislocation. A possible complication of using the tunnel technique rather than the tendon splitting technique is iatrogenic fracture through the drilled tunnel site. The purpose of this investigation was to study the FDL tendon and proximal phalanx dimensions in the area of the transfer procedure in order to improve preoperative planning and minimize postoperative complications. Additionally, this study investigated the force necessary to create a fracture in a predrilled proximal phalanx and attempted to elucidate a relationship between that force and the percentage of bone remaining after the drilling process. METHODS: The proximal phalanx and FDL tendon of the second, third, and fourth toes from both the right and the left foot of 14 fresh frozen cadavers were dissected, and the digit was amputated at the MTP joint. A total of 84 toes (42 right, 42 left) were obtained from 14 cadavers. The diameter of the FDL tendon was measured, and the circumference and volume were calculated. Fourteen proximal phalanges of either the right or the left foot were then drilled with a 3.5-mm drill, as is often done in a tendon transfer procedure. The 14 nondrilled bones from the contralateral foot were used as matched controls. Radiographs were then taken of the proximal phalanges, and the dimensions of the drill tunnel and remaining bone were calculated. These measurements were used to calculate the volume of the bone, the volume of the drill tunnel, and the percentage of bone remaining after the drilling process. The bones were then tested for load-to-failure using a biomechanical loading apparatus. RESULTS: The average bone and tendon diameter measurements showed a gradual decrease in size from the second to the fourth digits. The bone removed by drilling the tunnel accounted for approximately 20% to 30% of the total volume of bone. Half of the bones fractured with forces between 100 and 200 N, and the majority of bones with a diameter of less than 6 mm fractured with a force of less than 100 N. CONCLUSIONS: The average proximal phalanx and FDL tendon size both showed an overall decrease from the second to the fourth digit, albeit not symmetrically. The proximal phalanx diameter appeared to be the most important factor in determining the strength of the structure. CLINICAL RELEVANCE: Iatrogenic fracture may occur in proximal phalanges with a diameter of bone less than 6 mm, as there may not be adequate bone strength remaining to withstand postoperative forces.