INTRODUCTION: In practice, the use of a whip stitch versus a locking stitch in anterior cruciate ligament (ACL) graft preparation is based on surgeon preference. Those who prefer efficiency and shorter stitch time typically choose a whip stitch, while those who require improved biomechanical properties select a locking stitch, the gold standard of which is the Krackow method. The purpose of this study was to evaluate a novel suture needle design that can be used to perform two commonly used stitch methods, a whip stitch, and a locking stitch, by comparing the speed of graft preparation and biomechanical properties. It was hypothesized that adding a locking mechanism to the whip stitch would improve biomechanical performance but would also require more time to complete due to additional steps required for the locking technique.
METHODS: Graft preparation was performed by four orthopaedic surgeons of different training levels where User 1 and User 2 were both attendings and User’s 3 and 4 were both fellows. A total of 24 matched pair cadaveric knees were dissected and a total of 48 semitendinosus tendons were harvested. All grafts were standardized to the same size. Tendons were randomly divided into 4 groups (12 tendons per group) such that each User performed analogous stitch on matched pair: Group 1, User 1 and User 3 performed whip stitches; Group 2, User 1 and User 3 performed locking stitches; Group 3, User 2 and User 4 performed whip stitches; Group 4, User 2 and User 4 performed locking stitches. For instrumentation, the two ends of tendon grafts were clamped to a preparation stand. A skin marker was used to mark five evenly spaced points, 0.5 cm apart, as a guide to create a 5-stitch series. The stitches were performed with EasyWhip, a novel two-part suture needle which allows one to do both a traditional whip stitch and a locking whip stitch, referred to as WhipLock (Figure 1). The speed for graft preparation was timed for each User. Biomechanical testing was performed using a servohydraulic testing machine (MTS Bionix) equipped with a 5kN load cell (Figure 2). A standardized length of tendon, 10 cm, was coupled to the MTS actuator by passing it through a cryoclamp cooled by dry ice to a temperature of -5°C. All testing samples were pre-conditioned to normalize viscoelastic effects and testing variability through application of cyclical loading to 25-100 N for three cycles. The samples were then held at 89 N for 15 minutes. Thereafter, the samples were loaded to 50-200 N for 500 cycles at 1 Hz. If samples survived, they were ramped to failure at 20 mm/min. Displacement and force data was collected throughout testing. Metrics of interest were peak-to-peak displacement (mm), stiffness (N/mm), ultimate failure load (N) and failure mode. Data are presented as averages and standard deviations. A Wilcoxon signed-rank test was used to evaluate the groups for time to complete stitch and biomechanical performance. Statistical significance was set at P = .05.
RESULTS SECTION: In Group 1, the time to complete the whip stitch was not significantly different between User 1 and User 3, where the average completion time was 1 min 13 sec. Similarly, there were no differences between Users when performing the WhipLock (Group 2) with an average time of 1 min 49 sec. In Group 3 (whip stitch), User 2 took 1 min 48 sec to complete the whip stitch, whereas User 4 took 1 min 25 sec (p=.033). The time to complete the WhipLock stitch (Group 4) was significantly different, where User 2 took 3 min and 44 sec, while User 4 only took 2 min 3 sec (p=.002). Overall, the whip stitch took on average 1 min 25 sec whereas the WhipLock took 2 min 20 sec (p=.001).
For whip stitch constructs, no differences were found between Users and all stitches were biomechanically equivalent. Correspondingly, for WhipLock stitches, no differences were found between Users and all suture constructs were likewise biomechanically equivalent. Averages for peak-to-peak displacement (mm), stiffness (N/mm), and ultimate failure load (N) are presented in Table 1. Moreover, when the two stitch methods were compared, the WhipLock constructs significantly increased stiffness by 25% (p <.001), increased ultimate failure load by 35% (p<.001) and reduced peak-to-peak displacement by 55% (p=.001). The common mode of failure for grafts with whip stitch failed by suture pullout from tendon (18/24), where a few instances occurred by suture breakage (6/24). Tendon grafts with WhipLock stitch commonly failed by suture breakage (22/24), where two instances of combined tendon tear and suture breakage were noted.
DISCUSSION: The WhipLock stitch significantly increased average construct stiffness and ultimate failure load, while significantly reducing the peak-to- peak displacement compared to the whip stitch. These added strength benefits of the WhipLock stitch took 55 seconds more to complete than the whip stitch. No statistically significant difference in biomechanical performance was found between the Users. Data suggests equivalent stitch performance regardless of the time to complete stitch and surgeon training level.
SIGNIFICANCE/CLINICAL RELEVANCE: Clinically, having a suture needle device available which can be used to easily perform different constructs including one with significant strength advantages regardless of level of experience is of benefit.