Abrasiveness of high-strength sutures used in rotator cuff surgery: are they all the same?

BACKGROUND: The suture-tendon interface remains the most common point of failure in rotator cuff repairs via suture pullout. Several high-strength braided sutures are available for rotator cuff surgery and are more abrasive than monofilaments. However, a comparison of these sutures has not been performed in a tissue model. METHODS: Ninety infraspinatus sheep tendons were randomized among 9 groups of sutures (n = 10), including FiberWire (Arthrex, Naples, FL, USA), Collagen Coated FiberWire (Arthrex), Orthocord (DePuy Mitek, Raynham, MA, USA), MaxBraid (Biomet, Warsaw, IN, USA), Force Fiber (Teleflex, Research Triangle Park, NC, USA), ULTRABRAID (Smith & Nephew, Memphis, TN, USA), Phantom Fiber BioFiber (Tornier, Bloomington, MN, USA), and Ti-Cron (Syneture, Mansfield, MA), with Surgipro (Syneture) monofilament as a control. Each suture was cycled 50 times through the tendon, which was fixed to a mechanical testing system under a constant load in saline solution. The distance cut through the tendon was measured and divided by the distance of suture sliding to determine displacement (mm/cm). Twist angle and picks per inch of each suture were measured using digital photography. One-way analysis of variance was used to compare the displacement and twist angle between sutures. RESULTS: Collagen Coated FiberWire was the most abrasive of the high-strength sutures. Four of the sutures (Collagen Coated FiberWire, Phantom Fiber BioFiber, FiberWire, Ti-Cron) had a mean displacement rate greater than 0.150 mm/cm. The remainder of the sutures had a mean displacement rate less than 0.050 mm/cm (Orthocord, Force Fiber, MaxBraid, ULTRABRAID). The difference in the displacement rates between these 2 groups was significant (P < .0001) and was related to both the twist angle and the picks per inch. CONCLUSION: Significant differences in suture abrasiveness were identified among high-strength braided sutures and correlated with lower twist angle and lower picks per inch.

Biomechanical Analysis of Screws Versus K-Wires for Lateral Humeral Condyle Fractures.

BACKGROUND: Good outcomes have been described for pediatric lateral condyle fractures treated by open reduction and fixation using either screws or Kirschner wires (K-wires). No studies have compared the biomechanical properties of the 2 fixation methods. We hypothesized that screw fixation would be more biomechanically stable than K-wire fixation. METHODS: Synthetic humerus models were used for biomechanical testing, following a previously published protocol. A miter saw was used to make an oblique cut to simulate a Milch type II fracture. Fractures were anatomically reduced and fixed with either 2 divergent 0.062-inch K-wires placed bicortically or a 4.0-mm lag screw placed obliquely (perpendicular to the fracture line). Specimens were then embedded in polymethyl methacrylate bone cement for testing. Mechanical testing using displacement control was performed applying compression or distraction from 0 to 1.5 mm at a rate of 0.5 mm/s for 10 cycles. The maximum force was calculated based on the maximum force averaged over the 10 cycles. Stiffness was calculated based on the slope of the force-displacement curve of the 10th cycle. A 2-sample t test was used to determine significant differences between the stiffness and maximum force comparing the K-wire and screw groups. A P-value of <0.05 was considered statistically significant. RESULTS: Stiffness and maximum force in tension testing were significantly greater with screw fixation compared with K-wire fixation. Testing in compression revealed statistically significant increased maximum force and a trend towards increased stiffness. CONCLUSION: Screw fixation in a synthetic bone model of pediatric lateral condyle fractures (Milch type II) provides increased biomechanical stability of the construct as compared with K-wires. CLINICAL RELEVANCE: If similar effects were seen in vivo, increased biomechanical stability with screw fixation could decrease the occurrence of complications such as loss of reduction and nonunion.

The effect of sliding knots on the suture-tendon interface strength: a biomechanical analysis comparing sliding and static arthroscopic knots.

BACKGROUND: The tissue-suture interface remains the most common site of failure in rotator cuff repairs. It is currently unknown if arthroscopic sliding knots injure the tissue and weaken the suture-tendon interface. PURPOSE: To evaluate the effect sliding knots have on the strength of the suture-tendon interface. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 32 sheep infraspinatus tendons were randomized among 4 groups of stitches (n = 8): simple-static, simple-sliding, mattress-static, and mattress-sliding. All high-strength, No. 2 suture stitch-knot combinations were created in an arthroscopic simulated environment, and sliding knots were tied with shortening of the suture and sliding of the knot down to the tissue interface to simulate surgical technique. Each graft was cyclically loaded on a mechanical testing system from 5 to 20 N for 20 cycles and then loaded to failure. A least squares analysis of variance model was used to test significance of sliding stitches upon cyclic elongation, peak-to-peak displacement, and ultimate load. Estimated means and standard deviations are reported from the regression model. RESULTS: A mattress-static stitch (116 N) was significantly stronger than a mattress-sliding stitch (70 N; P < .001). The ultimate loads for the simple-static (46 N) and sliding (50 N) stitches were not statistically different. For cyclic elongation, the only difference was the mattress-sliding stitch (0.95 mm) having a greater elongation than the simple-static (0.61 mm; P = .01) and simple-sliding (0.68 mm; P = .04) stitches. Both mattress stitches had significantly less peak-to-peak displacement (0.39 and 0.41 mm) than the simple stitches (0.47 and 0.46 mm; P < .001). CONCLUSION: Sliding suture through tissue weakens the suture-tendon interface in mattress stitch constructs but not in simple stitch constructs. Mattress stitches have superior holding strength compared with simple stitches. CLINICAL RELEVANCE: Clinical relevance is uncertain. In situations with poor tissue quality or concern regarding tension across the repair, consideration should be given to using static knots as opposed to sliding knots when placing mattress stitches.