Biomechanical comparison of single‐row,double‐row,and transosseous‐equivalent repair techniques after healing in an animal rotator cuff tear model

The transosseous‐equivalent (TOE) rotator cuff repair technique increases failure loads and contact pressure and area between tendon and bone compared to single‐row (SR) and double‐row (DR) repairs, but no study has investigated if this translates into improved healing in vivo. We hypothesized that a TOE repair in a rabbit chronic rotator cuff tear model would demonstrate a better biomechanical profile than SR and DR repairs after 12 weeks of healing. A two‐stage surgical procedure was performed on 21 New Zealand White Rabbits. The right subscapularis tendon was transected and allowed to retract for 6 weeks to simulate a chronic tear. Repair was done with the SR, DR, or TOE technique and allowed to heal for 12 weeks. Cyclic loading and load to failure biomechanical testing was then performed. The TOE repair showed greater biomechanical characteristics than DR, which in turn were greater than SR. These included yield load (p < 0.05), energy absorbed to yield (p < 0.05), and ultimate load (p < 0.05). For repair of a chronic, retracted rotator cuff tear, the TOE technique was the strongest biomechanical construct after healing followed by DR with SR being the weakest. © 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1254–1260, 2013     

Biomechanical comparison of tuberosity-based proximal humeral locking plate compared to standard proximal humeral locking plate in varus cantilever bending

PurposeIn a prior biomechanical study using a tuberosity-based proximal humeral locking plate (TBP) an improvement in greater tuberosity (GT) fixation strength with the TBP compared to a standard proximal humeral locking plate (PHLP) was demonstrated. The purpose of this study is to compare the TBP to the PHLP with a simulated calcar gap fracture under cyclic varus cantilever forces.MethodsSeven matched pairs of cadaveric humeri were studied and 11A2.3 proximal humerus fractures were created by a 1 cm gap osteotomy at the surgical neck. Matched pairs were randomized for fixation using either a PHLP or a TBP. The proximal articular aspect of the humerus was potted and secured to the base of a load frame. The shaft was subjected to cyclic varus cantilever loading with a roller positioned 8 cm from the osteotomy. Change in vertical displacement of the diaphyseal fragment was monitored and digital images were obtained. Failure was defined as vertical displacement greater than 20 mm. Specimens not exhibiting failure over the course of 10,000 cycles were then loaded to 20 mm of vertical displacement. Reactant forces of the specimens at these displacements were recorded.ResultsFour/seven TBP specimens and four/seven PHLP specimens survived 10,000 cycles. The average cycles to failure for TBP specimens was 7325 cycles and 5715 cycles for PHLP specimens (p = 0.525). For the specimens that survived 10,000 cycles, the decrease in calcar gap was superior in the TBP specimens (p = 0.018). A similar trend was seen when these specimens were loaded to failure where the percent calcar gap recovery was higher for the TBP at 74.71 ± 10.07% versus 53.22 ± 30.35% for the PHLP (p = 0.072). In specimens that were loaded to failure after survival of 10,000 cycles the average stiffness of the TBP construct was 20.51 N/mm, and 11.74 N/mm for the PHLP construct (p = 0.024).ConclusionIn addition to superior GT fixation shown in a prior study, the TBP construct demonstrates significantly greater stiffness at the neck fracture compared to the PHLP, when loaded to failure. In addition, there was a trend towards less collapse in this calcar gap model.     

Hybrid screw fixation for femoral neck fractures: Does it prevent mechanical failure?

IntroductionTraditionally, femoral neck fracture fixation has been performed using three partially threaded cancellous screws. However, fracture collapse with femoral neck shortening, and varus deformation frequently occurs due to posterior medial comminution and lack of calcar support. We hypothesize replacing the inferior neck/calcar screw with a fully threaded, length stable, screw will provide improved biomechanical stability, decrease femoral neck shortening and varus collapse.MethodsTen matched cadaveric pairs (20 femurs) were randomly assigned to two screw fixation groups. Group 1 (Hybrid) utilized one fully threaded calcar screw & two partially threaded superior screws. Group 2 (PT) utilized all partially threaded screws. Specimens underwent standardized femoral neck osteotomies, 45° from the horizontal, with 5 mm posteromedial wedge removed to simulate posteromedial comminution. Screws were placed using fluoroscopic guidance. Specimens were biomechanically tested using two loading sequences: 1) Axial load applied up to 700 N, followed by cyclic loading at 2 Hz with loads of 700 to 1,400 N for 10,000 cycles. 2) All surviving constructs were cyclically loaded to failure in stepwise incremental manner with max load of 4,000 N. Paired t-tests used to compare stiffness, cycles to failure, and max load to failure (defined as 15 mm load actuator displacement).ResultsConstruct stiffness was 2848 ± 344 N/mm in PT vs. 2767 ± 665 for Hybrid (P = 0.628). Load to failure demonstrated, hybrid superiority with max cycles to failure (3797 ± 400 cycles) vs. (2981 ± 856 cycles in PT) (p = 0.010), and max load prior to failure (3290 ± 196 N) vs. (2891 ± 421 N in PT) (p = 0.010). No significant difference in bone mineral density was noted in any of the specimens.ConclusionsOur study is the first to assess the biomechanical effects of hybrid fixation for femoral neck fractures. Hybrid screw configuration resulted in significantly stronger constructs, with higher axial load and increased cycles prior to failure. The advantageous mechanical properties demonstrated using a fully threaded inferior calcar screw provides a length stable construct which may prevent the common complication of excessive femoral neck shortening, varus collapse and poor functional outcome.     

A double button adjustable loop device is biomechanically equivalent to tension band wire in the fixation of transverse patellar fractures—A cadaveric study

IntroductionTension-band wire fixation of patellar fractures is associated with significant hardware-related complications and infection. Braided polyester suture fixation is an alternative option. However, these suture fixations have higher failure rates due to the difficulty in achieving rigid suture knot fixation. The Arthrex syndesmotic TightRope, which is a double-button adjustable loop fixation device utilizing a 4-point locking system using FibreWire, may not only offer stiff rigid fixation using a knotless system, but may also obviate the need for implant removal due to hardware related problems. The aim of our study is to compare the fixation rigidity of patella fractures using Tightrope versus conventional tension-band wiring (TBW) in a cadaveric model.Materials and methodsTBW fixation was compared to TightRope fixation of transverse patella fractures in 5 matched pairs of cadaveric knees. The knees were cyclically brought through 0–90° of motion for a total of 500 cycles. Fracture gapping was measured before the start of the cycling, and at 50, 100, 200 and 500 cycles using an extensometer. The mean maximum fracture gapping was derived. Failure of the construct was defined as a displacement of more than 3 mm, patella fracture or implant breakage.ResultsAll but one knee from each group survived 500 cycles. The two failures were due to a fracture gap of more than 3 mm during cycling. There was no significant difference in the mean number of cycles tolerated. There was no implant breakage. There was no statistical significant difference in mean maximum fracture gap between the TBW and TightRope group at all cyclical milestones after 500 cycles (0.3026 ± 0.4091 mm vs 0.3558 ± 0.7173 mm, p = 0.388).ConclusionsWe found no difference between the TBW and Tightrope fixation in terms of fracture gapping and failure. With possible lower risk of complications such as implant migration and soft tissue irritation, we believe tightrope fixation is a feasible alternative in fracture management of transverse patella fractures.     

Collagen Ribbon Augmentation of Achilles Tendon Tears: A Biomechanical Evaluation

Early motion of a repaired Achilles tendon has been accepted to improve both clinical and biomechanical outcomes. It has been postulated that augmenting a primary Achilles tendon repair with a collagen ribbon will improve the repair construct's initial strength, thereby facilitating early motion. The purpose of the present study was to compare the failure load of Achilles tendon defects repaired with suture, with or without augmentation with a collagen ribbon. Ten matched pairs of cadaveric feet and tibiae underwent simulated Achilles tendon tear in the watershed area and were then repaired with 4-strand Krackow sutures only or were sutured and augmented with a box weave collagen ribbon xenograft. The specimens were prepared for testing by keeping the insertion of the Achilles to the calcaneus intact and dissecting the gastrocnemius at its origin, leaving the repair undisturbed. The mean load at failure for the augmented (suture plus collagen ribbon) specimens was 392.4 ± 74.9 N. In contrast, the mean load at failure for the suture-only (control) construct was 98.0 ± 17.6 N (p < .001). The augmented specimens demonstrated a greater mean strength of 4.1 ± 0.9 N (range 3.2 to 5.6). After cyclic loading, the mean gap across the Achilles repair was significantly smaller in the augmented group than in the control group (p = .006). We have concluded that box weave collagen ribbon augmentation of the primary suture Achilles tendon repairs can provide enhanced gap resistance and strength under cyclic loading and ramped tensile testing.     

Cyclic loading of Achilles tendon repairs: a comparison of polyester and polyblend suture

BACKGROUND: Early functional rehabilitation is widely used after open suture repair of the Achilles tendon. To our knowledge, no previous studies have assessed gap formation from cyclic loading and subsequent failure loads of simulated Achilles tendon repairs. A synthetic (polyblend) suture has been introduced for tendon repairs with reportedly greater strength than polyester suture. This stronger, stiffer suture material may provide stronger repairs with less elongation of the tendon repair. METHODS: Simulated Achilles tendon ruptures in bovine Achilles tendon were repaired with a four-strand Krackow suture technique using No. 2 polyester suture. Specimens were loaded for 3,000 cycles at maximal loads of 50, 75, 100, or 125 N, and gap formation at the repair site was continuously measured. After cyclic loading, each specimen was loaded to failure. Identical repairs were performed with number 2 polyblend suture and cyclically loaded to 75 N for 3,000 cycles. All specimens were loaded to failure. RESULTS: Cyclically loading polyester suture repairs to 50, 75, 100, or 125 N for 3,000 cycles resulted in mean gapping at the repair site of 3.0 +/- 0.8, 4.9 +/- 1.0, 7.2 +/- 0.9, and 7.9 +/- 0.8 mm, respectively. Cyclically loading the polyblend suture repairs for 3,000 cycles at 75 N, resulted in 3.3 +/- 0.3 mm of gap formation at the repair site, significantly less than polyester suture repairs (p < 0.001). The mean load to failure for polyester suture repair was 222 +/- 19 N and for polyblend suture repair was 582 +/- 49 N, a statistically significant difference (p < 0.001). Gap formation at 100, 1,000, and 2,000 cycles, as a percentage of total gap formation at 3,000 cycles, was 64.3%, 87.5%, and 95.4% for polyester suture and 45.8%, 78.5%, and 90.1% for polyblend repairs. All specimens in all groups failed at the knots during load-to-failure testing. CONCLUSIONS: Cyclic loading of simulated Achilles tendon repairs using a Krackow, four-core polyester suture technique showed progressive gap formation with increasing load. All repairs failed at the knot, and suture pull-out from tendon was not observed. Polyblend suture repair, when compared to identical repairs with braided polyester suture, resulted in a 260% higher load to failure and 33% less gap formation at the repair site after 3,000 cycles. CLINICAL RELEVANCE: The use of polyblend suture in a four-stranded Krackow configuration provides stronger repairs with less gap formation, which may provide increased security during early functional rehabilitation.     

Interlocking horizontal mattress suture versus Kakiuchi technique in repair of Achilles tendon rupture: a biomechanical study

Background

In recent years, the type of surgical treatment for Achilles tendon rupture has been the subject of controversial debate. This biomechanical study evaluates for the first time in literature the ultimate failure load (UFL) of interlocking horizontal mattress (IHM) suture as compared with Kakiuchi suture in Achilles tendon rupture. The hypothesis is that IHM suture can be performed also for Achilles tendon rupture and ensures higher resistance compared with the traditional Kakiuchi suture.

Materials and methods

Twenty fresh bovine Achilles tendons were obtained. Ten preparations were randomly assigned to each of two different groups: group A (10 specimens) sutured by IHM technique, and group B (10 specimens) sutured by Kakiuchi technique. Each construct was mounted and fixed on a tensile testing machine. Static preconditioning of 50 N was applied for 5 min as initial tensioning to stabilize the mechanical properties of the graft, then a load to failure test was performed at crosshead speed of 500 mm/min.

Results

Ten specimens were tested for each group. The mean UFL was 228.6 ± 98.6 N in the IHM suture group and 96.57 ± 80.1 N in the Kakiuchi suture group. Statistical analysis showed a significant difference (p < 0.05) with better UFL in the IHM group. In both groups, the failure mode registered in each specimen was suture breakage (rupture of suture thread).

Conclusions

IHM suture achieved better UFL compared with Kakiuchi suture in an animal model of Achilles tendon repair. These results seem to support IHM as a valid option in Achilles tendon rupture.

     

Biomechanical Study of a Multifilament Stainless Steel Cable Crimp System Versus a Multistrand Ultra-High Molecular Weight Polyethylene Polyester Suture Krackow Technique for Achilles Tendon Rupture Repair

Currently, Achilles tendon rupture repair is surgically addressed with an open or minimally invasive approach using a heavy, nonabsorbable suture in a locking stitch configuration. However, these sutures have low stiffness and a propensity to stretch, which can result in gapping at the repair site. Our study compares a new multifilament stainless steel cable-crimp repair method to a standard Krackow repair using multistrand, ultra-high molecular weight polyethylene polyester sutures. Eight matched pairs of cadavers were randomly assigned for Achilles tendon repair using either Krackow technique with polyethylene polyester sutures or the multifilament stainless steel cable-crimp technique. Each repair was cyclically loaded from 10 to 50 N for 100 loading cycles, followed by a linear increase in load until complete failure of the repair. During cyclic loading, 4 of the 8 Krackow polyethylene polyester suture repairs failed, whereas none of the multifilament stainless steel cable crimp repairs failed. Load to failure was greater for the multifilament stainless steel cable crimp repairs (321.03 ± 118.71 N) than for the Krackow polyethylene polyester suture repairs (132.47 ± 103.39 N, p = .0078). The ultimate tensile strength of the multifilament stainless steel cable crimp repairs was also greater than that of the Krackow polyethylene polyester suture repairs (485.69 ± 47.93 N vs 378.71 ± 107.23 N, respectively, p = .12). The mode of failure was by suture breakage at the crimp for all cable-crimp repairs and by suture breakage at the knot, within the tendon, or suture pullout for the polyethylene polyester suture repairs. The multifilament stainless steel cable crimp construct may be a better alternative for Achilles tendon rupture repairs.     

Biomechanical comparison of suture anchor versus margin convergence plus suture anchor for rotator cuff repair

Objective: To evaluate results of margin convergence versus suture anchors in rotator cuff repair, and to determine which method is mechanically superior. Methods: Eighteen kangaroo shoulders were randomly divided into three groups (n = 6). A full thickness tendon defect 1.0 cm × 1.5 cm in size was created in the supraspinatus tendon at humeral insertion, simulating a massive rotator cuff tear. Three different techniques were employed for rotator cuff repair: (i) Mitek GII suture anchor alone (Group 1); (ii) margin convergence alone (Group 2); and (iii) margin convergence plus Mitek GII suture anchor (Group 3). Combined loads were applied to each specimen. After completion of cyclic loading, the construct was loaded to failure. ANOVA and LSD (Least Significant Difference) multiple comparisons of the means were applied to results. Results: Cyclic load testing showed progressive gap formation in each repaired specimen with increasing cycles. Group 1 reached 50% failure at an average of 34 cycles, Group 2 at 75 cycles and Group 3 at 73 cycles. There were significant difference between Groups 1 and 2, and Groups 1 and 3 (P ≤ 0.001). After 100 loading cycles, the average gap size was 6.8 mm, 6.1 mm and 4.7 mm in Groups 1, 2 and 3, respectively. There was a significant difference between Groups 1 and 3 (P ≤ 0.015). All specimens eventually reached failure. Conclusion: Rotator cuff repairs with margin convergence +/? suture anchor were far stronger than suture anchor alone, both in gap formation and ultimate failure load. However, progressive gap formation with cyclic loading seems inevitable after cuff repair, which may facilitate clinical understanding of the phenomena of re‐tear or residual defect.     

Overlapping repair and epitenon healing are more stable biomechanically than side to side repair and endotenon healing in achilles tendon lengthening with Z plasty

BackgroundThe current study aimed to compare biomechanical stability and healing process of side-to-side repair with overlapping repair after Achilles tendon lengthening with Z-plasty.MethodsIn our study, 22 Sprague Dawley male rats were used. Side-to-side repairs were classified as group 1 and overlapping repairs as group 2. The left and right legs of seven rats were used to compare early group 1 and early group 2 biomechanical test results at day 0. Seven rats were used to compare late group 1 and late group 2 biomechanical test results at day 28. Both the right and left tendons were tested from the four rats examined in the biomechanically in the untreated control group. The last remaining four rats were used for histopathological evaluation of tendon repair, at 28-days from the index procedure.The ultimate load to failure was compared between groups.ResultsAt time 0, there were no measurable differences between group 1 (3.8 ± 1.4 N) and group 2 (3.7 ± 1.1 N), and both could endure less than one-tenth of the untreated control (49 ± 12). At 28 days, ultimate load to failure improved significantly in both group 1 (16.2 ± 3.5 N) and even more in group 2 (36 ± 8.1 N). While there was a significant difference between group 1 and group 2, neither were able to meet the untreated control (49 ± 12). Histopathological evaluation in the post-healing period showed that fibrosis, neovascularization, and inflammation increased in both groups.ConclusionThe overlapping suture technique and epitenon healing have more stability compared to side-to-side suture technique and endotenon healing. Human population trials may or may not exist, our study suggests it should be considered and further investigation needed before actual clinical application.     

Transosseous tunnels versus suture anchors for the repair of acute quadriceps and patellar tendon ruptures: A systematic review and meta-analysis of biomechanical studies

BackgroundMultiple techniques have been developed for the repair of acute quadriceps and patellar tendon ruptures with the goal of optimizing clinical outcomes while minimizing complications and costs. The purpose of this study was to evaluate the biomechanical properties of transosseous tunnels and suture anchors for the repair of quadriceps and patellar tendon ruptures.MethodsA systematic review of the PubMed and Embase databases was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines using specific search terms and eligibility criteria. Meta-analysis was performed by fixed-effects models for studies of low heterogeneity (I² <25%) and random-effects models for studies of moderate to high heterogeneity (I² ≥25%).ResultsA total of 392 studies were identified from the initial literature search with 7 studies meeting the eligibility criteria for quadriceps tendon repair and 8 studies meeting the eligibility criteria for patellar tendon repair. Based on the random-effects model for total gap formation and load to failure for quadriceps tendon repair, the mean difference was 8.88 mm (95% CI, −8.31 mm to 26.06 mm; p = 0.31) in favor of a larger gap with transosseous tunnels and −117.25N (95%CI, −242.73N to 8.23N; p = 0.07) in favor of a larger load to failure with suture anchors. A similar analysis for patellar tendon repair demonstrated a mean difference of 2.86 mm (95% CI, 1.08 mm to 4.64 mm; p = 0.002) in favor of a larger gap with transosseous tunnels and −56.34N (95% CI, −226.75 to 114.07N; p = 0.52) in favor of a larger load to failure with suture anchor repair.ConclusionsTransosseous tunnels are biomechanically similar to suture anchors for quadriceps tendon repair. Patellar tendon repair may benefit from reduced gap formation after cycling with suture anchor repair, but the load to failure for both techniques is biomechanically similar. Additional studies are necessary to evaluate these and alternative repair techniques.Level of evidenceSystematic review and meta-analysis of biomechanical studies, Level V.     

A comparison of lateral ankle ligament suture anchor strength

BackgroundLateral ankle ligament repairs increasingly use suture anchors instead of bone tunnels. Our purpose was to compare the biomechanical properties of a knotted and knotless suture anchor appropriate for a lateral ankle ligament reconstruction.MethodsIn porcine distal fibulae, 10 samples of 2 different PEEK anchors were inserted. The attached sutures were cyclically loaded between 10 N and 60 N for 200 cycles. A destructive pull was performed and failure loads, cyclic displacement, stiffness, and failure mode recorded.ResultsPushLock 2.5 anchors failed before 200 cycles. PushLock 100 cycle displacement was less than Morphix 2.5 displacement (p < 0.001). Ultimate failure load for anchors completing 200 cycles was 86.5 N (PushLock) and 252.1 N (Morphix) (p < 0.05). The failure mode was suture breaking for all PushLocks while the Morphix failed equally by anchor breaking and suture breakage.ConclusionsThe knotted Morphix demonstrated more displacement and greater failure strength than the knotless PushLock. The PushLock failed consistently with suture breaking. The Morphix anchor failed both by anchor breaking and by suture breaking.     

Cyclic loading of anchor-based rotator cuff repairs: Confirmation of the tension overload phenomenon and comparison of suture anchor fixation with transosseous fixation

Previous experimental studies of failure of rotator cuff repair have involved single pull to ultimate load. Such an experimental design does not represent the cyclic loading conditions experienced in vivo. We created 1 ×2 cm rotator cuff defects in 16 cadaver shoulders, repaired each defect with three MitekRC suture anchors (Mitek Surgical Products, Inc, Westwood, MA) using simple sutures of No. 2 Ethibond, and cyclically loaded the repairs by a servohydraulic materials test system actuator at physiological rates and loads (rate of 33 mm/s, load 180 N). A progressive gap was noted in each specimen, for a 100% rate of failure of the repairs. The central suture always failed first and by the largest magnitude, confirming tension overload centrally. One specimen exhibited combined bone and tendon failure, but the other 15 specimens failed through the tendon. Overall, the repairs failed to 5 mm and 10 mm at an average of 61 cycles and 285 cycles, respectively. Half the specimens were less than 45 years of age and had a 5-mm and 10-mm failure at an average of 107 and 478 cycles, respectively. The other half were over 45 years of age and failed to 5 mm and 10 mm at an average of 17 and 91 cycles, respectively, indicating more rapid failure of the rotator cuff tendons in the older group, and this was statistically significant (P ≤ .02). Comparison of suture anchor fixation in this study with transosseous bone tunnel fixation in a previous cyclic loading study at this institution indicates that bone fixation by suture anchors is significantly less prone to failure than bone fixation through bone tunnels (P = .0008). Changing the bone fixation from bone tunnels to suture anchors effectively transferred the weak link from bone to tendon.     

Biomechanical analysis of bioabsorbable suture anchors for rotator cuff repair using osteoporotic and normal bone models

BackgroundThis study aimed to compare the failure load of suture anchors used in rotator cuff repair between normal and osteoporotic bone models.MethodsA total of 16 anchors made from metal (TwinFix Ti 5.0 or 6.5 mm, Corkscrew FT 4.5, 5.5, or 6.5 mm), polyether ether ketone (HEALICOIL PK [HC-PK] 4.5 or 5.5 mm, SwiveLock PK 4.75 or 5.5 mm), or bioabsorbable material (HEALICOIL RG [HC-RG] 4.75 or 5.5 mm, Corkscrew Bio 4.75, 5.5, or 6.5 mm, SwiveLock BC 4.75 or 5.5 mm) were included. Moreover, 10- and 5-pounds per cubic foot (pcf) Sawbone® models were set as normal and osteoporotic cancellous bone models, respectively. Pullout testing was performed in parallel to the insertion axis at a displacement rate of 12.5 mm/s using a universal testing machine. To evaluate the change in failure load between the two Sawbone® models with different densities, the remaining failure load ratio (RFLR) was defined as the ratio of the failure load in 10 pcf to that in 5 pcf.ResultsIn the 10-pcf Sawbone®, TwinFix Ti 6.5 mm showed the highest mean failure load (304.0 ± 15.2 N). In the 5-pcf Sawbone® model, HC-PK 5.5 mm showed the highest failure load (146.3 ± 5.8 N). Among anchors with the same diameter, HC-PK and HC-RG showed a significantly higher failure load than other anchors in the 10- and 5-pcf Sawbone® models. HC-PK 5.5 mm (62.1%) and HC-PK 4.5 mm (51.1%) have the highest RFLR among anchors with the same diameter.ConclusionsHC-PK and HC-RG showed higher failure load than the other anchors in both normal and osteoporotic bone models, except for TwinFix Ti 6.5 mm in the 10-pcf Sawbone® model. Based on our results, bioabsorbable anchors had sufficient failure load for rotator cuff repair in addition to bioabsorbability.     

Is Dual Semitendinosus Allograft Stronger Than Turndown for Achilles Tendon Reconstruction? An In Vitro Analysis

Background

Large Achilles tendon defects pose a treatment challenge. The standard treatment with a turndown flap requires a large extensile incision, puts the sural nerve at risk, and demands slow, careful rehabilitation. Dual allograft semitendinosus reconstruction is a new clinical alternative that has the theoretical advantages of a smaller incision, less dissection, and a stronger construct that may allow for faster rehabilitation.

Questions/Purposes

In a cadaver biomechanical model, we compared the dual allograft semitendinosus reconstruction with the myofascial turndown in terms of (1) mechanical strength and resistance to deformation and (2) failure mechanisms in reconstruction of large segmental Achilles defects.

Methods

An 8-cm segmental Achilles defect was created in 18 cadaveric lower extremities, nine matched pairs without defect or previous surgery (mean age, 78.4 years; range, 60–97 years; three female and six male pairs). Femoral neck densitometry to determine bone mineral density found that all specimens except two were osteopenic or osteoporotic. Specimens in each pair were assigned to allograft or turndown reconstruction. The constructs were mounted on a load frame and differential variable reluctance transducers were applied to measure deformation. Specimens were preconditioned and then loaded axially. Tensile force and proximal and distal construct deformation were measured at clinical failure, defined as 10 mm of displacement, and at ultimate failure, defined as failure of the reconstruction. Failure mechanism was recorded.

Results

Tensile strength at time zero was higher in the allograft versus the turndown construct at clinical failure (156.9 ± 29.7 N versus 107.2 ± 20.0 N, respectively; mean difference, −49.7 N; 95% CI, −66.3 to −33.0 N; p < 0.001) and at ultimate failure (290.9 ± 83.2 N versus 140.7 ± 43.5 N, respectively; mean difference, −150.2 N; 95% CI, −202.9 to −97.6 N; p < 0.001). Distal construct deformation was lower in the turndown versus the allograft construct at clinical failure (1.6 ± 1.0 mm versus 4.7 ± 0.7 mm medially and 2.2 ± 1.0 mm versus 4.8 ± 1.1 mm laterally; p < 0.001). Semitendinosus allograft failure occurred via calcaneal bone bridge fracture in eight of nine specimens. All myofascial turndowns failed via suture pullout through the fascial tissue at its insertion.

Conclusion

In this comparative biomechanical study, dual semitendinosus allograft reconstruction showed greater tensile strength and construct deformation compared with myofascial turndown in a cadaveric model of large Achilles tendon defects.

Clinical Relevance

Further study of dual semitendinosus allograft for treatment of severe Achilles tendon defects with cyclic loading and investigation of clinical results will better elucidate the clinical utility and indications for this technique.

     

„Ligament bracing“ – die augmentierte Kreuzbandnaht

Background

In the context of acute knee dislocations, suture repair of ruptured cruciate ligaments leads to good clinical results in 80% of cases. Disadvantages are low primary stability and subsequently secondary elongation of the sutured ligaments. In the present study, we compared primary stability of suture repair, reinforced by different suture augments, to cruciate ligament reconstruction.

Objective

The concept of ligament bracing with transosseous suture repair of the cruciate ligaments and additional suture augmentation is biomechanically superior to cruciate ligament reconstruction.

Material and methods

A total of 42 porcine knee joints divided into seven groups were examined. The stability of four different suture/augmentation combinations were compared to cruciate ligament reconstruction with human hamstring tendons. The investigational setup consisted of testing 1000 cycles with 20 N to 154 N load in a.-p. translation and 60° flexion. Elongation and load to failure were measured.

Results

Neither reconstruction (3.13?±?1.65 mm; 362?±?51 N) nor augmented suture repair (1.89–2.5 mm; 464–624 N) achieved the primary stability of the intact cruciate ligament (0.63?±?0.34 mm, 1012?±?91 N). In comparison to ligament reconstruction, all four augmented suture repairs showed minor elongation in the cyclic test and a higher load to failure. The isolated suture repair showed poor results (6.79?±?4.86 mm, 177?±?73 N).

Conclusion

Augmented suture repair provides significantly higher stability compared with isolated suture repair and reconstruction with hamstring tendons. The concept of ligament bracing could be a promising future treatment option in acute knee dislocations. Clinical results remain to be seen.     

Let's think beyond the pedicle: A biomechanical study of a new conceptual extra pedicular screw and hook construct

BackgroundTranspedicular screws have proven the test of time, yet they are not devoid of complications. Many newer techniques such as 2 D and 3D fluoroscopy,O arm Navigation assisted surgery, robotic assisted surgery have come into existence to the increase precision in pedicle screw insertion. But, complications do occur in their presence. We propose an Extra pedicular screw and hook system (EPSH) system with similar biomechanical property, better safety profile and short learning curve compared to traditional pedicle screw.PurposeTo Compare the pull out strength of Traditional Pedicle screw Vs Extra pedicular screw and hook system(EPSH).MethodsBiomechanical testing was conducted according ASTM F543 guidelines to compare the pull-out strength of EPSH based construct and traditional pedicle screw construct. Six saw bone samples in each group considered. Screw of 5.5 mm diameter and length of 35 mm was used in both the groups. Pull out strength assessed by giving 5 mm/min axial load. The axial load Vs displacement of the screw were recorded and plotted. The maximum load required for screw failure is noted in both the group. Statistical analysis was done.ResultsThe mean peak load of pedicle screw group was found to be 1670.9 ± 393.2 N with mean displacement at peak load was found to be 13.44 ± 1.7 mm and in EPSH group it was 1416.4 ± 341.4 N and 15.78 ± 3.9 mm respectively. A paired t-test showed no statistical difference(p < 0.05) between 2 groups.ConclusionEPSH has shown to have almost similar biomechanical property as that pedicle screw construct. With Addition of the hook, it provides an extra rotational stability as well. Being an extra-pedicular screw it has high safety profile and needs less expertise for insertion.     

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.     

In vitro comparison of standard and knotless metal suture anchors

Purpose: Clinical experience after failed Knotless suture anchor (Mitek, Westwood, MA) fixations suggested that the Knotless anchor provides considerably less fixation stability than a standard metal anchor. The purpose of this study was to analyze soft tissue fixation to bone comparing a standard and a Knotless metal suture anchor. Type of Study: In vitro study. Methods: The Mitek GII and Mitek Knotless suture anchors were tested on 7 human cadaveric fresh-frozen glenoids. The anchors were inserted into the glenoid rims, and the sutures of the anchors were fixed to a metal hook attached to the cross-head of a testing machine. Cyclic loading was performed. The gap formation between the metal hook and the glenoid rim, the ultimate failure loads and the modes of failure were determined. Results: The mean gap formation was significantly greater for the Knotless anchor (3.8 ± 1.4 mm) than for the GII anchor (2.4 ± 0.5 mm) after 25 cycles with 50 N repeated load (P = .04). The largest gap of a Knotless fixation was 5.3 mm compared with 3.0 mm for the GII. The ultimate failure load was not significantly different for the Knotless anchor (179 N) and for the GII anchor (129 N). Both anchors failed by either rupture of the suture material or by pullout of the anchors. Conclusions: The GII anchor allows significantly less displacement than the Knotless anchor. Ultimate tensile strength and mode of failure are similar. Greater displacement results in larger gap formation between the soft tissue and the bone. This might weaken and jeopardize the repair. Clincial Relevance: If reattached soft tissues are subjected to postoperative loading, gap formation may result when using the Knotless anchor. For these conditions, suture fixation with knots may be used instead.     

Biomechanical evaluation of retrograde docking nailing to a total hip arthroplasty stem in a periprosthetic femur fracture model

IntroductionSlotted nails allow a connection to a total hip arthroplasty (THA) stem and act as intramedullary load carrier. This study compares construct stiffness, cycles to failure and failure load between a retrograde slotted femur nail construct docked to a THA stem and a lateral locking plate in a human periprosthetic femur fracture model.Materials and methodsIn seven pairs of fresh-frozen human anatomic femora with cemented THA, a transverse osteotomy was set simulating a Vancouver type B1 fracture. The femora were instrumented pairwise with either a retrograde slotted nail coupled to the prosthesis stem, or a locking plate plus a locking attachment plate. Four-point mediolateral bending, torsional and axial bending construct stiffness was investigated via non-destructive tests. Cyclic testing under progressively increasing physiologic loading was performed at 2 Hz until catastrophic construct failure.ResultsMediolateral bending stiffness did not differ significantly between the two groups (P=0.17) but exhibited a biphasic profile with significantly increased stiffness in both groups (P<0.01). Nail constructs provided a significantly lower torsional stiffness (0.49 ± 0.66 Nm/°) than plate constructs (1.70 ± 0.86 Nm/°), P=0.03. Axial bending stiffness did not differ significantly between the groups (Nail: 605 ± 511 N/mm; Plate: 381 ± 428 N/mm), P=0.61. Cycles to failure and failure load were significantly higher for the plate constructs (25’700 ± 8’341; 3’070 ± 1334 N) compared with the nail constructs (20’729 ± 7’949; 2’573 ± 1295 N), P=0.04.ConclusionThe docking nail construct provides an intramedullary fixation with connection to the prosthesis stem; however, it is biomechanically weaker in stable fractures compared to the plate construct.