Clinical Failure Loads Research Articles

Biomechanical comparison of two InternalBrace™ reinforced thumb ulnar collateral ligament reconstruction techniques.

Chronic ulnar collateral ligament ruptures of the thumb metacarpophalangeal joint are often not eligible for direct surgical repair and ligament reconstruction could be considered. Several reconstruction techniques are published, with different types of configurations and fixation methods of the tendon grafts. However, failure of the reconstruction with recurrent instability is still a problem, despite stable graft to bone fixation. Augmentation of the free tendon graft with non-resorbable suture material is gaining popularity, aiming to withstand elongation or rupture of the graft. The purpose of this study was to compare two different augmented ulnar collateral ligament reconstruction methods in a cadaver model. Ten matched pairs of cadaveric upper extremities were used. The thumbs were disarticulated at the trapezometacarpal joint and the ulnar collateral ligament was excised then reconstructed with InternalBrace™ reinforced tendon graft, which was fixed to the bones using either a Tenodesis screw or DX Swivelock® anchor. The thumbs were biomechanically tested with valgus stress, while the force and displacement were simultaneously measured and plotted. The mean (SD) load at clinical failure and maximum load were 19.4 (5.3) and 31.4 (9.5) N in the Tenodesis group, and 21.0 (10.0) and 31.4 (13.9) N in the DX SwiveLock® group, respectively. None of these differences were significant. These results are comparable with previous publications. The Tenodesis screw and the DX SwiveLock® thumb ulnar collateral ligament reconstruction with InternalBrace™ reinforced free tendon graft showed equal strength, both methods are feasible alternatives in the clinical setting.

Comparison of Biomechanical Failure Loads Between Tape-Type and Conventional Sutures in Internal Knotless Anchor-Based Constructs.

Background:Despite the increasing prevalence of tape-type sutures, whether internal knotless anchors can consistently affix tape-type sutures has not been thoroughly investigated.Purpose:To evaluate whether substituting tape-type sutures for conventional sutures influences the suture-holding strength of internal knotless anchors.Study Design:Controlled laboratory study. Level of evidence, 5.Methods:A total of 3 internal knotless anchors were tested: a spiral core clamping anchor (Footprint Ultra PK), a winged clamping anchor (PopLok), and a spooling anchor (ReelX STT). Four constructs were compared for each type of anchor, with the anchor double or quadruple loaded with tape-type sutures or conventional sutures. The testing protocol comprised preloading suture tension to 10 N; cyclic loading, in which tension increased in increments of 10 N from 10 to 90 N; and a load-to-failure stage set at a speed of 0.5 mm/s. The clinical failure load (CFL) was defined as suture slippage of ≥3 mm. Also, 1-way analysis of variance and power analysis were used to compare the CFLs of the constructs.Results:For the quadruple-loaded spiral core clamping anchors, a significant reduction in CFLs was seen with conventional sutures over tape-type sutures (138.10 ± 4.73 vs 80.00 ± 12.25 N, respectively; P < .001). This reduction was not observed under the double-loaded condition (conventional vs tape type: 76.00 ± 5.48 vs 80.00 ± 10.00 N, respectively). Substitution of the suture materials did not significantly reduce the CFLs for the winged clamping anchors (conventional vs tape type: 40.00 ± 10.00 vs 30.00 ± 7.07 N for double loaded, respectively, and 64.00 ± 13.41 vs 50.00 ± 10.00 N for quadruple loaded, respectively) or the spooling anchors (conventional vs tape type: 62.00 ± 19.23 vs 56.32 ± 20.20N for double loaded, respectively, and 72.00 ± 21.68 vs 84.00 ± 13.42 N for quadruple loaded, respectively).Conclusion:Substituting tape-type sutures for conventional sutures increased the CFLs of some internal knotless anchors. With specific suture-anchor combinations, quadruple-loaded conventional suture anchors had CFLs higher than those of double-loaded conventional suture anchors.Clinical Relevance:When multiple tape-type sutures are used in conjunction with a clamping anchor, clinicians should note a possible reduction in CFLs and resultant early suture slippage.

The number of loaded sutures alters the suture-holding strength in different knotless suture anchors, a biomechanical study

Abstract Background Due to advances in arthroscopic rotator cuff repair, a knotless suture anchor is expected to hold more than two suture limbs. The objective of this study is to investigate whether when employing different fixation mechanisms, the suture-holding strength of knotless anchors are altered by the number of loaded sutures. Methods Three types of knotless anchors (spiral core clamping, winged clamping, and spooling) were tested, with each anchor double-loaded or quadruple-loaded. Cyclic loading was applied, followed by a tensile load until failure. Clinical failure load (CFL) was defined by 3mm slippage, and ultimate failure load (UFL) was defined as a sharp deviation in the linear load-versus-displacement curve. A two-way ANOVA was performed to examine the effects of suture anchors and suture number. Results The two-way ANOVA showed significant interaction between the type of suture anchor and the number of sutures (p Conclusions The number of loaded sutures does affect the suture-holding strength of knotless suture anchors, and anchors with different fixation mechanisms are affected differently.

Knots Tied With High-Tensile Strength Tape Biomechanically Outperform Knots Tied With Round Suture.

Background:Tape-type suture material is well-accepted in arthroscopy surgery.Purpose:To compare the knot security of a high–tensile strength round suture and high–tensile strength tape with commonly used arthroscopic knots.Study Design:Controlled laboratory study.Methods:We compared the performance of No. 2 braided nonabsorbable high-strength suture with that of 1.3-mm braided nonabsorbable high-strength tape. Five commonly used arthroscopic knots were investigated: the Roeder knot; the Western knot; the Samsung Medical Center (SMC) knot; the Tennessee knot; and a static surgeon’s knot. Seven knots were tied for each combination of knots and suture types. Knots were tied on a 30-mm circumferential metal post, and the suture loops were transferred to a materials testing machine. After preloading to 5 N, all specimens were loaded to failure. The clinical failure load, defined as the maximal force to failure at 3 mm of crosshead displacement, yield load, and stiffness, were recorded. A 2-way analysis of variance was used to determine differences between the groups.Results:Both suture type and knot type significantly affected the clinical failure load, yield load, and stiffness (P = .002). The high-strength tape resulted in a significantly greater clinical failure load than the high-strength suture in the case of the Roeder knot, Western knot, and SMC knot (P = .027, .005, and .016, respectively). When the high-strength round suture was used, the Roeder knot, Western knot, and SMC knot resulted in significantly smaller clinical failure loads compared with the Tennessee knot (P = .011, .003, and .035, respectively) and the static surgeon’s knot (P < .001 for all). When the high-strength tape was used, the Roeder knot, Western knot, and SMC knot resulted in significantly smaller clinical failure loads compared with the static surgeon’s knot (P = .001, .001, and .003, respectively).Conclusion:The results of this study indicated that arthroscopic knots tied using 1.3-mm high-strength tape biomechanically outperformed knots tied using a No. 2 high-strength suture. While the static surgeon’s knot exhibited the best biomechanical properties, the Tennessee knot resulted in generally better biomechanical properties among the arthroscopic sliding knots.Clinical Relevance:Elongation and loosening of tied knots possibly affects the clinical results of repaired constructs.

Are Suture Tape Knots as Secure as Standard Suture? A Biomechanical Study.

Background:Few studies have investigated the biomechanical performance of flat-braided suture tapes versus round-braided sutures after being knotted.Purpose:To compare the loop security and knot strength of a standard round-braided suture with 3 commercially available flat-braided suture tapes using 2 types of arthroscopic knots.Study Design:Controlled laboratory study.Methods:One standard suture (SS) and 3 suture tapes (T1, T2, and T3) were tied with the surgeon’s knot (SK) and the Tennessee slider (TS), 25 times each, by a single surgeon. Each combination of knots and sutures underwent a preload, cyclic loading, and load to failure. Outcomes were loop security (defined by loop stretch after a 5-N preload), load at clinical failure (3 mm of displacement), and load at ultimate failure (suture rupture or knot slippage). Two-way analysis of variance was used for analysis.Results:Overall, the SK group had greater overall loop security than that of the TS group (0.4 ± 0.3 vs 0.5 ± 0.3 mm of stretch, respectively; P = .020). The clinical failure load varied by suture type (P < .001) but not knot type (P = .106). For both knot types, the SS had the lowest mean ± SD clinical failure load (SK, 171 ± 49 N; TS, 176 ± 37 N), which was significantly less than that of T2 (247 ± 85 N; P < .001) and T3 (251 ± 96 N; P < .001) for the SK type and T2 (231 ± 67 N; P = .023) for the TS type. T2 sutures had the greatest ultimate failure load for both knot types (SK, 418 ± 45 N; TS, 461 ± 57 N), which was significantly greater than SS, T1, and T3 (P < .001 for all). The TS knot had greater overall ultimate failure load than the SK (375 ± 64 vs 350 ± 66 N; P < .001).Conclusion:Not all suture tape knots had the same biomechanical properties, although knot security and strength appeared to be adequate for all suture tapes as well as for SS. There was no evidence that suture tape knots are lower profile than SS knots.Clinical Relevance:Surgeons should not use suture tape based only on the assumption that it has superior biomechanical properties to a standard round-braided suture.

Biomechanical Comparison of All-Soft Suture Anchor Single-Row vs Double-Row Bridging Construct for Insertional Achilles Tendinopathy.

Two common operative fixation techniques for insertional Achilles tendinopathy are the use of all-soft suture anchors vs synthetic anchors with a suture bridge. Despite increasing emphasis on early postoperative mobilization, the biomechanical profile of these repairs is not currently known. We hypothesized that the biomechanical profiles of single-row all-soft suture anchor repairs would differ when compared to double-row suture bridge repairs. Achilles tendons were detached from their calcaneal insertions on 6 matched-pair, fresh-frozen cadaver through-knee amputation specimens. Group 1 underwent a single-row repair with all-soft suture anchors. Group 2 was repaired with a double-row bridging suture bridge construct. Achilles-calcaneal displacement was tracked while specimens were cyclically loaded from 10 to 100 N for 2000 cycles and then loaded to failure. Linear mixed models were used to analyze the independent effects of age, body mass index, tendon morphology, repair construct, and footprint size on clinical and ultimate failure loads, Achilles-calcaneal displacement, and mode of failure. The suture bridge group was independently associated with an approximately 50-N increase in the load to clinical failure (defined as more than 5 mm tendon displacement). There was no difference in ultimate load to failure or tendon/anchor displacement between the 2 groups. This cadaveric study found that a double-row synthetic bridge construct had less displacement during cyclic loading but was not able to carry more load before clinical failure when compared to a single-row suture anchor construct for the operative repair of insertional Achilles tendinopathy. Our data suggest that double-row suture bridge constructs increase the load to clinical failure for operative repairs of insertional Achilles tendinopathy. It must be noted that these loads are well below what occurs during gait and the repair must be protected postoperatively without early mobilization. This study also identified several clinical factors that may help predict repair strength and inform further research.

Biomechanical analysis of transverse acetabular fracture fixation in the elderly via the posterior versus the anterior approach with and without a total hip arthroplasty.

This study provides the first biomechanical comparison of the fixation constructs that can be created to treat transverse acetabular fractures when using the "gold-standard" posterior versus the anterior approach with and without a total hip arthroplasty in the elderly. Synthetic hemipelvises partially simulating osteoporosis (n = 24) were osteotomized to create a transverse acetabular fracture and then repaired using plates/screws, lag screws, and total hip arthroplasty acetabular components in one of four ways: posterior approach (n = 6), posterior approach plus a total hip arthroplasty acetabular component (n = 6), anterior approach (n = 6), and anterior approach plus a total hip arthroplasty acetabular component (n = 6). All specimens were biomechanically tested. No differences existed between groups for stiffness (range, 324.6-387.3 N/mm, p = 0.629), clinical failure load at 5 mm of femoral head displacement (range, 1630.1-2203.9 N, p = 0.072), or interfragmentary gapping (range, 0.67-1.33 mm, p = 0.359). Adding a total hip arthroplasty acetabular component increased ultimate mechanical failure load for posterior (2904.4 vs. 3652.3 N, p = 0.005) and anterior (3204.9 vs. 4396.0 N, p = 0.000) approaches. Adding a total hip arthroplasty acetabular component also substantially reduced interfragmentary sliding for posterior (3.08 vs. 0.50 mm, p = 0.002) and anterior (2.17 vs. 0.29 mm, p = 0.024) approaches. Consequently, the anterior approach with a total hip arthroplasty may provide the best biomechanical stability for elderly patients, since this fixation group had the highest mechanical failure load and least interfragmentary sliding, while providing equivalent stiffness, clinical failure load, and gapping compared to other surgical options.

Comparing the Influence of Different Overhand/Underhand Stacking Combinations of Reversing Half-Hitches on Alternating Posts on Arthroscopic Knot Security

Previous literature demonstrated the importance of stacking at least three reversing half-hitches on alternating posts (RHAPs) following arthroscopic knot placement. However, RHAPs construction involves looping the suture in either an "overhand" or an "underhand" manner as it relates to the post, which may affect knot security. This study investigated the presently unidentified influence of different stacking combinations of three RHAPs and suture material on arthroscopic knot security. Four different RHAPs stacking combinations were tied with three different suture materials. Ten knots of each configuration were tied using each suture material, resulting in 120 evaluated knots. A single load-to-failure test was performed. The mode of failure and mean ultimate clinical failure load were recorded. Different overhand/underhand stacking combinations of three RHAPs had a statistically significant effect on arthroscopic knot strength and security; however, all combinations surpassed the minimum ultimate clinical failure threshold. Knots constructed with either Force Fiber® or braided fishing line had mean ultimate clinical failure loads of greater than 200 N and most commonly failed due to suture material breakage (100%, 60 - 80% respectively). Conversely, FiberWire® demonstrated lower mean ultimate clinical failure loads and had a higher incidence of elongated but intact failure (60 - 90%). Different overhand/underhand stacking combinations of three RHAPs yielded an arthroscopic knot capable of secure tissue fixation. A significant effect was observed for suture materials on the knot strength. This study increases our understanding of suitable RHAPs construction following arthroscopic knot placement that can lead to improving the ultimate clinical failure loads of constructed arthroscopic knots observed between orthopedic surgeons.

Validation of Different Combination of Three Reversing Half-Hitches Alternating Posts (RHAPs) Effects on Arthroscopic Knot Integrity

With arthroscopic techniques being used, the importance of knot tying has been examined. Previous literature has examined the use of reversing half-hitches on alternating posts (RHAPs) on knot security. Separately, there has been research regarding different suture materials commonly used in the operating room. The specific aim of this study was to validate the effect of different stacked half-hitch configuration and different braided suture materials on arthroscopic knot integrity. Three different suture materials tied with five different RHAPs in arthroscopic knots were compared. A single load-to-failure test was performed and the mean ultimate clinical failure load was obtained. Significant knot holding strength improvement was found when one half-hitch was reversed as compared to baseline knot. When two of the half-hitches were reversed, there was a greater improvement with all knots having a mean ultimate clinical failure load greater than 150 newtons (N). Comparison of the suture materials demonstrated a higher mean ultimate clinical failure load when Force Fiber® was used and at least one half-hitch was reversed. Knots tied with either Force Fiber® or Orthocord® showed 0% chance of knot slippage while knots tied with FiberWire® or braided fishing line had about 10 and 30% knot slippage chances, respectively. A significant effect was observed in regards to both stacked half-hitch configuration and suture materials used on knot loop and knot security. Caution should be used with tying three RHAPs in arthroscopic surgery, particularly with a standard knot pusher and arthroscopic cannulas. The findings of this study indicated the importance of three RHAPs in performing arthroscopic knot tying and provided evidence regarding discrepancies of maximum clinical failure loads observed between orthopaedic surgeons, thereby leading to better surgical outcomes in the future.

All Soft-suture Anchor versus Suture Bridge Construct for Insertional Achilles

Category: Ankle Introduction/Purpose: New techniques and anchors have been developed for the surgical treatment of insertional Achilles tendinopathy and rupture to allow for earlier return to postoperative weight bearing and accelerated rehabilitation. Two recently introduced soft tissue-to-bone anchor technology have purported advantages for insertional Achilles repairs. Knotless suture anchors allow suture tension to be precisely controlled with a ratcheting mechanism. The other is a suture bridge construct fastened with biotenodesis screws, increasing the soft tissue footprint and reducing the risk of suture pullout through the tendon. However, neither technology has been studied in a biomechanical model of Achilles tendon repair. We hypothesized that there would be no difference in the biomechanical characteristics of a single-row all-suture anchor repair to a double-row repair with knotless anchors and suture tape. Methods: Six matched-pairs of fresh-frozen lower leg cadaveric specimens (12 total) were obtained. All tendons were completely detached from their calcaneal insertions and tendon thickness was measured. Calcaneal exostectomies were performed (e.g., Haglunds removal) above the Achilles insertion. Group 1 was repaired with a single-row construct with two all-soft anchors. Group 2 was repaired with a double-row suture bridge construct with two knotless anchors distally and two suture tape anchors proximally. The repaired specimens were cyclically loaded from 10N to 100N at 1 Hz for 2,000 cycles then to failure at 1mm/sec. A motion capture system measured Achilles-calcaneal displacement at the medial and lateral anchors. Paired t-tests and linear mixed models (LMMs) were used to analyze the following outcomes: clinical failure load, ultimate failure load, Achilles-calcaneal medial and lateral displacement, distance at ultimate failure load, tendon thickness, footprint, and mode of failure. A p-value of &lt;0.05 was considered statistically significant. Results: Group 2 showed significantly less Achilles-calcaneal overall medial and lateral displacement, 19.5% and 36.9% respectively (Table 1). Group 2 showed a statistical trend toward greater clinical and ultimate failure load, 23.8% and 34.2%, respectively (Table1). LMM analyses showed that a suture bridge repair over all-soft anchor repair was independently associated with a 50.24N increase in the load to clinical failure (p=0.0011). Higher clinical failure loads were associated with higher BMI (p&lt;0.0001), thinner tendons (p&lt;0.0001), and smaller tendon footprints on the calcaneus (p=0.0013). Higher absolute failure loads were associated with older age (p&lt;0.0001), higher BMI (p&lt;0.0001), thinner tendons (p=0.0028), and larger footprints (p&lt;0.0001). Conclusion: These data suggest a trend toward higher clinical and ultimate failure loads in a suture bridge construct compared to all-soft suture anchors for insertional Achilles repair. Loads to failure in both groups were higher than previously reported pull-out strengths for most suture anchors (150-300 N), but are lower than typical loads at the Achilles insertion during walking activities. The use of the suture bridge repair method may result in superior loads to failure compared to all-soft anchors. Patient age, BMI and tendon thickness impact failure loads. Adequate healing should be allowed followed repair of complete Achilles detachment.

Validation of Improvement of Basic Competency in Arthroscopic Knot Tying Using a Bench Top Simulator in Orthopaedic Residency Education

To validate basic competency in arthroscopic knot tying using a unique simulator device to compare the level of training needed for learning and tying the arthroscopic knot by evaluating the tensile properties of the arthroscopic knots. Three groups of surgeons of various experience levels (postgraduate year [PGY] 1, PGY 3, and experienced surgeons) tied 2 different arthroscopic knots (Tennessee Slider, considered easier, and Weston, considered more difficult) over a 10-week period. Each group went through 3 separate stages of knot tying: stage 1, tying 8 knots without cannula or knot pusher; stage 2, tying 12 knots with knot pusher; and stage 3, tying 20 knots with knot pusher through a cannula that simulates knot tying during surgery. A single load-to-failure test was performed and ultimate clinical failure loads were recorded. Time needed to tie each knot was also recorded. At stages 1 and 2, the PGY 1 group had a significantly weak knot tensile strength (Tennessee Slider stage 1: 60 v 129N, P= .001; Tennessee Slider stage 2: 69 v 132N, P= .0029; Weston stage 1: 73 v 184N, P= .0000; Weston stage 2: 125 v 173N, P= .0045) and were slower (Weston: 56 v 30seconds, P= .0010) than the experienced surgeon group for both knots. At stage 3, only the initial 2weeks of Tennessee Slider showed a significant difference between groups 1 and 3 (week 6: 87 v 118N, P= .0492; week 7: 89 v 126, P= .01485). Even though the Tennessee Slider knot is one of the easier arthroscopic knots to learn to tie, the results showed a slow trend of improvement in this knot-tying skill for group 1 after each stage. The data validated an important learning effect in all trainees in arthroscopic knot tying over a 10-week period and showed that inexperienced trainees will be able to improve their knot-tying skill with training in 3 stages with a simulator environment. The findings of this study indicated the importance of hands-on experience in performing arthroscopic knot tying, as determined by both knot performance and ultimate suture loop strength. In addition, each orthopaedic resident learned and developed his or her arthroscopic knot-tying skills and provided a foundation for his or her future practice in orthopaedic medicine.

Knot Strength Varies Widely Among Expert Arthroscopists

Background: While most surgeons can tie visually appealing knots under an arthroscope, few surgeons have undergone an objective evaluation of their ability to consistently tie knots with maximum loop and knot security. Purpose/Hypotheses: The purpose of this study was to evaluate and compare variations in ultimate load to failure, 3-mm displacement (clinical failure), and knot stack height of arthroscopic suture knots tied by 73 independent expert orthopaedic arthroscopists. The hypotheses were (1) that skilled arthroscopic surgeons would be able to routinely tie arthroscopic knots of similar strength, (2) that surgeons with <10 years of clinical practice would tie stronger and more consistent knots, and (3) that surgeons who performed >200 arthroscopic shoulder cases per year would produce stronger and more consistent knots than would surgeons who performed fewer cases. Study Design: Controlled laboratory study. Methods: Each surgeon tied 5 of the same type of their preferred arthroscopic knot and half-hitch locking mechanism. Each knot was mechanically tested for ultimate load to failure and clinical failure. Results: For the 365 individual knots tested, the mean ultimate load across each knot was 231 N (range, 29-360 N). The mean clinical failure load was 139 N (range, 16-328 N). The average knot stack height among the 365 knots was 5.61 mm (range, 2.89-10.32 mm). For an individual surgeon, the standard deviations of the 5 consecutive knots tied ranged from 6 to 133 N. The ultimate load and clinical failure load for surgeons with <10 years of practice (n = 39) were 248 ± 93 N and 142 ± 56 N, respectively. The mean ± SD ultimate and clinical failure loads for surgeons with >10 years of practice (n = 34) were 211 ± 111 N and 136 ± 69 N, respectively. When knot strength was used to measure performance, significant differences existed in ultimate load (P = .001); however, there were no differences in clinical failure load (P = .329). Surgeons with <10 years of practice were able to tie knots more consistently than were surgeons in practice for >10 years, for both ultimate load (P = .018) and clinical failure load (P = .005). There was no significant difference based on number of cases performed with respect to ultimate load or clinical failure load (P = .292 and .479, respectively). There was no difference in consistency, as both groups had similar standard deviations (P = .814 for ultimate load, P = .545 for clinical failure). Conclusion: Considerable variations in knot strength exist between arthroscopic knots tied by surgeons. Study findings revealed that surgeons were unable to tie 5 consecutive knots of the same type consistently; that for both ultimate load and clinical failure load, surgeons with <10 years in practice were able to tie knots more consistently than surgeons with >10 years; and that surgeons performing >200 arthroscopic shoulder cases annually failed to tie stronger or more consistent knots than their counterparts performing fewer cases. Clinical Relevance: This variation in knot tying has the potential to affect the integrity of arthroscopic repairs. Independent objective testing of the ability to tie secure knots as part of a surgeons’ training may be necessary.

Shortcuts in Arthroscopic Knot Tying

Background: Shortcuts for throwing 3 alternating reversed half-hitches on alternating posts (RHAPs), in which the post is switched by alternating strand tension to “flip” the knot, have been advocated but never validated in a biomechanical study. Hypothesis: Shortcut tying techniques will affect knot security or loop security. Study Design: Controlled laboratory study. Methods: A single surgeon tied 90 knots using No. 2 FiberWire through an arthroscopic cannula. Half had a static “surgeon’s base,” and half had a Tennessee slider base. Three techniques were used to create 3 RHAPs: (1) rethreading, (2) knot “flipping” where half-hitches were tensioned by past-pointing, and (3) knot “flipping” where half-hitches were tensioned by alternating past-pointing and over-pointing. Each knot was subjected to a preload of 5 N, followed by 1000 cycles of 5 N to 45 N at 1 Hz, and a single load to failure. Results: When compared with Tennessee knots, surgeon’s knots had a lower incidence of knot slippage and catastrophic failure as well as higher loads to clinical and ultimate failure. Shortcut techniques did not affect the properties of surgeon’s knots. However, when used to secure Tennessee knots, past-pointing decreased load to clinical failure and ultimate load to failure. Over-pointing increased the incidence of knot slippage and catastrophic failure and decreased load to clinical failure and ultimate load to failure. Loop security was marginally increased by both past-pointing and over-pointing. Conclusion: When all tying techniques are considered, surgeon’s knots outperform Tennessee sliding knots. Shortcut techniques do not alter the properties of surgeon’s knots. However, when used to secure Tennessee sliding knots, shortcuts lead to unacceptably high rates of knot slippage and catastrophic failure as well as decreased knot security. Clinical Relevance: The outcomes of arthroscopic rotator cuff or labral repairs can be compromised when using shortcut tying methods to secure sliding Tennessee knots.

Influence of Testing Conditions on Primary Stability of Arthroscopic Knot Tying for Rotator Cuff Repair: Slippery When Wet?

The purpose was to evaluate whether the knot security of sliding and nonsliding knots with different sutures is influenced by dry or wet conditions. We tested 5 suture materials, all of them US Pharmacopeia No. 2: PDS (polydioxanone) II (Ethicon, Somerville, NJ), Ethibond (Ethicon), and 3 ultrahigh-molecular weight polyethylene (UHMWPE) sutures-FiberWire (Arthrex, Naples, FL), Orthocord (DePuy Mitek, Raynham, MA), and Herculine (Linvatec, Largo, FL). Testing was performed under dry and wet conditions with sutures soaked in a saline solution. Cyclic loading was performed to simulate physiologic conditions. We started with a tensile load of 25 N. After 100 cycles, the load was increased to 50 N for another 100 cycles. The tensile load was gradually increased by 25 N per 100 cycles until suture rupture or knot slippage, defined as lengthening over 3 mm. Under dry conditions, 170 suture ruptures and 30 knot slippages were reported; and under wet testing conditions, 186 suture ruptures and 14 knot slippages were reported, with P < .044 and P < .027, respectively. Failure by knot slippage (n = 44) was seen under dry and saline solution conditions mainly with UHMWPE sutures, in particular with the Herculine suture using a Roeder knot showing comparable maximum failure loads in dry (274.5 ± 58.2 N) and saline solution (312.5 ± 14.2 N) conditions (P > .056). Knot slippage occurred only with sliding knots. With the Ethibond suture, no knot slippage was found regardless of the testing conditions and knot type. Across all knot types, the UHMWPE sutures were significantly stronger with respect to clinical and maximum failure loads in ultimate load to failure than Ethibond and PDS II under dry and wet testing conditions (P < .001 for both). We conclude that testing of different suture materials and knot types is different in wet versus dry conditions and believe that biomechanical testing might be more realistic in a wet environment. Suture knots behave differently in a wet versus dry environment, and testing of knot mechanics might better be carried out in wet environments.

Significance of the internal locking mechanism for loop security enhancement in the arthroscopic knot

Purpose: Secure tissue fixation of an arthroscopic knot depends on the security of the initial loop and additional locking half-hitches. The purpose of this report is to evaluate the loop and knot security relative to the internal locking mechanism of arthroscopic slip knot. Type of Study: This is an experimental study designed for knot and loop security on a material testing system. The measurements were carried out in a blinded fashion in which the tester was not aware of the type of knot being tested. Methods: Five configurations of arthroscopic knots (overhand throw, Duncan loop, Revo knot, Tennessee slider, and SMC knot) were created around a 5-mm diameter metal bar using a No. 2 braided suture. For each knot configuration, 10 knots were tested for displacement at cyclic loading, load to clinical failure (3-mm displacement), ultimate failure load, and mode of failure on the servo-hydraulic material testing system (MTS 858 MiniBionix test system; NITS, Minneapolis, MN). A 1-way analysis of variance was used to determine the statistical difference in displacement at cyclic loading, load to clinical failure, and ultimate failure load between each knot configuration. Results: In the cyclic loading test, the average displacement of all knots was clinically insignificant, with the average being less than 0.24 mm. The overhand throw had the worst characteristic in the load to failure test. The other 4 knots had an optimal load to failure. The SMC knot, which has an internal locking mechanism, had good loop and knot security in the load to clinical failure and ultimate failure load (P < .05). The SMC and the Revo knots failed by knot breakage (material failure) whereas the other knots failed by knot slippage (loop failure). Conclusions: The internal locking mechanism flips the post strand to convert the loop strand into a new post strand while rerouting the original post strand around a new post. An arthroscopic knot with an internal locking mechanism can enhance loop security.

Libricated three-body abrasive wear-contaminant condition versus bounding surface material hardness

The response of wear rate and clinical failure load to contamination and material hardness has been determined for AISI 52100 steel. A ball-on-roller contact geometry was used, in which the stationary rollers had three grades of hardness: 42, 56, and 63 HRC. The test contaminant, aluminium oxide (Al 2O 3) powder in <10, 10–20, and 20–30 μm sizes, was injected into an SAE 10 base oil at 10, 100, and 200 mg/litre concentration levels. Machine load and sliding speed were varied in the range 15 to 210 kg and 0.26 to 1.05 m/s, respectively. A qualitative assessment of worn surfaces was also undertaken. For the largest contaminant size and concentration, the load-carrying capacity to failure was about half that for the uncontaminated condition of operation.