Effect of Quadriceps Tendon Autograft Preparation and Fixation on Graft Laxity During Suspensory Anterior Cruciate Ligament Reconstruction: A Biomechanical Analysis.

Background: Favorable collagen fibril density and thickness combined with advances in graft preparation and fixation have significantly increased interest in the quadriceps tendon (QT) autograft for anterior cruciate ligament (ACL) reconstruction. While various suspensory techniques have been described, the biomechanical profile of these constructs is largely undefined. Purpose: To compare the biomechanics of suspensory techniques for soft tissue QT autograft fixation in an in vitro model of ACL reconstruction. Study Design: Controlled laboratory study. Methods: Full-thickness QT grafts were harvested using a 9-mm graft blade. Adjustable-loop devices (ALDs) were secured to the graft (n = 6 per group) with a combination implant containing the ALD and suture tape-reinforced whipstitching (tape-reinforced [TR] group), tethered superficially to the graft with a whipstitch (onlay [OL] group), luggage-tagged through and around the graft (luggage tag [LT] group), or staggered behind superficial suturing (staggered [SG] group). Grafts were tested on an electromechanical testing machine following a validated in vitro reconstruction model of intraoperative workflow and postoperative ACL kinematics, cyclic loading, and load to failure. Results: The TR group had significantly less postcyclic tension loss (mean, 24%) compared with the OL (56%; P = .002), LT (69%; P < .001), and SG (90%; P < .001) constructs. Cyclic elongation was below the 3.0-mm threshold defined as clinical failure for TR (1.6 mm), but not for OL (3.3 mm), LT (7.9 mm), and SG (11.3 mm). All constructs were within native ACL stiffness limits (220 ± 72 N/mm) without significant differences. Ultimate loads significantly exceeded a normal ACL loading limit of 454 N for TR (739 N; P = .023), OL (547 N; P = .020), and LT (769 N; P = .001), but not for SG (346 N; P = .236). Conclusion: The TR ALD construct demonstrated the most favorable time-zero biomechanical properties of modern soft tissue QT suspensory constructs, with 32% less tension loss and 52% less cyclic elongation versus the closest construct. Failure loading of all constructs was acceptable with respect to the native ACL except for the SG group, which had suboptimal ultimate load. Clinical Relevance: TR ALD implants may protect soft tissue QT autografts before graft-bone healing in ACL reconstruction by minimizing time-zero laxity and fixation failure.

Native anterior talo-fibular ligament tensile characteristics compared to allograft, suture tape, and copolymer augmentation elements: A biomechanical study.

Surgical augmentation methods have been introduced to the Modified Broström (MB) technique to support native anterior talo-fibular ligament (ATFL) healing and function. This study aimed to investigate the isolated biomechanical performance of common MB augmentation elements, including allograft, suture tape, and copolymer, compared to native ATFL. Six cadaveric feet were dissected, isolating the ATFL from all surrounding soft tissue. The fibula and talus were clamped on the testing frame so that the ligament was in line with the load cell. Six samples per augment group were fixed on a test frame with a gauge length of 20 mm to replicate ATFL length. All samples were pulled to failure at 305 mm/min. Biomechanical outcomes included stiffness, elongation, and ultimate load. Mean ± standard deviation was reported. Stiffness was highest for suture tape (246.4 ± 52.1N/mm), followed by allograft (114.2 ± 26.2 N/mm), native ATFL (78.6 ± 31.8 N/mm), and copolymer (9.4 ± 2.9 N/mm). Significant differences in stiffness were observed between all groups except when comparing ATFL stiffness to allograft (P = 0.086). Copolymer resulted in significantly larger elongation at ultimate load compared to native ATFL, suture tape, and allograft (P < 0.001). Elongation at ultimate failure was highest for copolymer (30.0 ± 8.7 mm) and significantly greater than all other groups (P < 0.001). Ultimate load was highest for suture tape (544.1 ± 59.7 N), followed by native ATFL (338.5 ± 63.7 N), allograft (308.3 ± 98.5 N) and copolymer (146.7 ± 8.9 N). Suture tape ultimate load was significantly greater than copolymer (P < 0.001). Isolated biomechanical data of augment materials can be utilized by foot and ankle surgeons when considering appropriate ligament augmentation options. Level of clinical evidence 5, controlled laboratory study.

Double-Row Achilles Insertional Repair With Rip-Stop Increases Construct Strength Compared to Traditional Techniques: A Biomechanical Study.

BACKGROUND: Although double-row suture-anchored (DRSA) techniques for Achilles insertional tendinosis has proven successful, a reoccurring failure mode not yet addressed is suture tearing through the tendon. This study aims to address suture tearing by incorporating a rip-stop element. Authors hypothesized that the Rip-Stop group would demonstrate increased strength compared with more traditional techniques. METHODS: 12 paired cadaveric feet were used in this study (n = 24). One sample from each pair was assigned to receive the standard double-row (SDR) Achilles repair with 4.75-mm knotless anchors (n = 12). The control's matched sides were divided between 2 DRSA bridge groups: modified double-row (MDR) bridge with 3.9-mm anchors or rip-stop double-row (RS-DR) bridge repair with soft proximal anchors and 3.9-mm anchored distal row. In neutral position, specimens underwent 1000 cycles (20-100 N) followed by load to failure. Displacements, stiffness, ultimate load, and failure mode were recorded. RESULTS: RS-DR had the lowest initial displacement values followed by SDR and MDR (1.3 ± 0.4, 2.7 ± 1.4, and 3.2 ± 1.3 mm, respectively). Significance was detected when comparing initial displacement of RS-DR to MDR (P = .038). Cyclic displacement was lowest for RS-DR, followed by MDR and SDR (1.6 ± 0.9, 2.2 ± 1.1, and 4.5 ± 3.2 mm, respectively). Cyclic stiffness was similar for RS-DR and MDR (89.1 ± 24.6 and 81.9 ± 5.6 N/mm, respectively). RS-DR ultimate load (1116.8 ± 405.7 N) was statistically greater than SDR (465.6 ± 352.7, P = .003). CONCLUSION: RS-DR-repaired specimens demonstrated a decrease in displacement values and increased ultimate load and stiffness when compared to other groups. Results of this cadaveric model suggest that the addition of a rip-stop to DRSA Achilles repair is more impactful than anchor size. Limitations include that this was a time-zero biomechanical study, which cannot simulate the performance of the repairs during postoperative healing and recovery. CLINICAL RELEVANCE: A rip-stop technique for Achilles repair effectively improves dynamic mechanical characteristics and may mitigate suture tearing through tendon in a patient cohort.

Acellular Human Dermal Allograft Tuberoplasty Improved the Biomechanics in Mid-Range and Higher Abduction Angles in a Cadaveric Model of Massive Irreparable Rotator Cuff Tears.

Purpose: To evaluate the biomechanical effects of acellular human dermal allograft tuberoplasty (AHDAT) in a cadaveric model of an irreparable supraspinatus + anterior one-half infraspinatus (stage III) rotator cuff tear. Methods: Eight cadaveric shoulders were tested at 20°, 40°, and 60° of glenohumeral abduction (AB) and 0°, 30°, 60°, and 90° of external rotation (ER). Superior humeral translation, acromiohumeral distance, and subacromial contact were quantified for 4 conditions: (1) intact, (2) stage III tear (entire supraspinatus and anterior one-half infraspinatus), (3) single-layer AHDAT, and (4) double-layer AHDAT. Results: Stage III tear significantly increased superior translation at 20° and 40° AB and all ER angles and at 60° AB/60° ER (P ≤ .045 vs intact). Compared to the stage III tear, the single-layer AHDAT significantly decreased superior translation at 60° AB/60° ER (P = .003), whereas the double-layer AHDAT significantly decreased superior translation at 40° and 60° AB at all ER angles except 60° AB/0° ER (P ≤ .028). The stage III tear significantly decreased acromiohumeral distance at 20° AB (P ≤ .003); both grafts increased acromiohumeral distance to intact levels (P ≥ .055 vs intact). Stage III tear increased subacromial contact pressure at 20° and 40° AB/0° and 30° ER and at 60° AB/30° and 60° ER (P ≤ .034). Both AHDAT groups decreased contact pressure at 40° AB/30° and 60° ER back to intact, whereas the double-layer AHDAT also decreased contact pressure at 20° AB/0° and 60° ER and 60° AB/30° ER (P ≥ .051 vs intact). Conclusions: Both single- and double-layer grafts for AHDAT improved superior translation, subacromial contact characteristics, and acromiohumeral distance after a stage III rotator cuff tear, with varying effectiveness due to the position-dependent nature of greater tuberosity to acromial contact with abduction. Clinical Relevance: The best treatment for massive or irreparable rotator cuff tears is a matter of concern. The results of this study will help determine whether an acellular human dermal allograft tuberoplasty is a potential treatment option worthy of further investigation.

Tape-Reinforced Graft Suturing and Retensioning of Adjustable-Loop Cortical Buttons Improve Quadriceps Tendon Autograft Biomechanics in Anterior Cruciate Ligament Reconstruction: A Cadaveric Study.

PURPOSE: To investigate the biomechanical effects of tape-reinforced graft suturing and graft retensioning for all-soft tissue quadriceps tendon (ASTQT) anterior cruciate ligament reconstruction (ACLR) in a full-construct human cadaveric model. METHODS: Harvested cadaveric ASTQT grafts were assigned to either (1) double-suspensory adjustable-loop cortical button device (ALD) fixation in which both graft ends were fixed with a suspensory fixation device with (n = 5) or without (n = 5) tape-reinforced suturing or (2) single-suspensory distal tendon fixation in which only the patellar end was fixed with an ALD (n = 5) or fixed-loop cortical button device (FLD) (n = 5). All specimens were prepared using a No. 2 whipstitch technique, and tape-reinforced specimens had an integrated braided tape implant. Graft preparation time was recorded for double-suspensory constructs. Samples were tested on an electromechanical testing machine using a previously published protocol simulating rehabilitative kinematics and loading. RESULTS: Tape-reinforced graft suturing resulted in greater graft load retention after cycling (11.9% difference, P = .021), less total elongation (mean [95% confidence interval (CI)], 5.57 mm [3.50-7.65 mm] vs 32.14 mm [25.38-38.90 mm]; P < .001), greater ultimate failure stiffness (mean [95% CI], 171.9 N/mm [158.8-185.0 N/mm] vs 119.4 N/mm [108.7-130.0 N/mm]; P < .001), and less graft preparation time (36.4% difference, P < .001) when compared with unreinforced specimens. Retensioned ALD constructs had less cyclic elongation compared with FLD constructs (mean total elongation [95% CI], 7.04 mm [5.47-8.61 mm] vs 12.96 mm [8.67-17.26 mm]; P = .004). CONCLUSIONS: Tape-reinforced graft suturing improves time-zero ASTQT ACLR construct biomechanics in a cadaveric model with 83% less total elongation, 44% greater stiffness, and reduced preparation time compared with a whipstitched graft without tape reinforcement. ALD fixation improves construct mechanics when compared with FLD fixation as evidenced by 46% less total elongation. CLINICAL RELEVANCE: Tape-reinforced implants and graft retensioning using ALDs improve time-zero ACLR graft construct biomechanics in a time-zero biomechanical model. Clinical studies will be necessary to determine whether these implants improve clinical outcomes including knee laxity and the incidence of graft rupture.

Stabilization and Gap Formation of Adjustable Versus Fixed Primary ACL Repair With Internal Brace: An in Vitro Full-Construct Biomechanical Cadaveric Study.

Background: A knotless, tensionable primary anterior cruciate ligament (ACL) repair system preloaded with an internal brace has been released. Currently, there is no biomechanical data on the stabilization and gap formation behavior of the adjustable system when compared with fixed repairs in human ACL tissue. Hypothesis: That knotless adjustable suture repair with an internal brace would provide overall higher construct stability and greater load share on the ACL with less gap formation compared with fixed repair. Study Design: Controlled laboratory study. Methods: Human cadaveric knees were utilized for internal braced ACL repair constructs (each group n = 16). Two fixed groups consisting of a single-cinch loop (SCL), cortical button (SCL group), and knotless suture-anchor (anchor group) were compared with an SCL-adjustable loop device (SCL-ALD) group. Testing was performed at 4 different peak loads (50, 150, 250, 350 N) over 4000 cycles at 0.75 Hz including suture repair preconditioning (10 cycles at 0.5 Hz) for SCL-ALD. Specimens were ultimately pulled to failure with a cut internal brace. The final loading situation of the construct and ACL repair with gap formation and ultimate strength were evaluated. Results: Peak elongation at various peak loads showed a significantly higher (P < .001) stabilization of SCL-ALD when compared with both fixed groups. There was a significantly higher (P < .001) load share of SCL-ALD, especially at lower loads (48% of 50 N), and the gap formation remained restricted up to 250 N. With only a little load share on the fixed constructs (<6%) at lower loads (50, 150 N), gap formation in these groups started at a load of 150 N, leading to significantly higher gaps (P < .001). The ultimate failure load for SCL-ALD and anchor groups was significantly increased (P < .001) as compared with SCL. The stiffness of SCL-ALD (62.9 ± 10.6 N/mm) was significantly increased (P < .001). Conclusion: Internal braced knotless adjustable fixation for ACL repair with preconditioning of the suture repaired ligament increased the overall stabilization with higher load share on the ACL and restricted gap formation (<0.5 mm up to 350 N) compared with fixed suture repair. All internal braced repairs restored stability according to native ACL function. Clinical Relevance: Adjustable ACL repair improved the mechanical characteristics and reduced gap formation, but the overall clinical significance on healing remains unclear.

Biomechanical characteristics of a new looping stitch versus the classic Krackow stitch for distal biceps fixation.

Background: The purpose of this study was to quantify the biomechanical characteristics of a new looping stitch, developed with the concepts of a looping, locking stitch that decreases needle penetrations of the tendon, and compare it to a classic Krackow stitch for distal biceps suture-tendon fixation. Methods: The Krackow stitch with No. 2 braided suture and the looping stitch with a No. 2 braided suture loop attached to a 25-mm-length by 1.3-mm-width polyblend suture tape were compared. The Looping stitch was performed with single strand locking loops and wrapping suture around the tendon, resulting in half the needle penetrations through the graft compared to the Krackow stitch. Ten matched pairs of human distal biceps tendons were used. One side of each pair was randomly assigned to either the Krackow or the looping stitch, and the contralateral side was used for the other stitch. For biomechanical testing, each construct was preloaded to 5 N for 60 seconds, followed by cyclic loading to 20 N, 40 N, and 60 N for 10 cycles each, and then loaded to failure. The deformation of the suture-tendon construct, stiffness, yield load, and ultimate load were quantified. Comparisons between the Krackow and looping stitches were performed with a paired t-test using P < .05 as statistically significant. Results: The Krackow stitch and looping stitch had no significant difference in stiffness, peak deformation, or nonrecoverable deformation after 10 cycles of loading to 20 N, 40 N, and 60 N. There was no difference between the Krackow stitch and looping stitch in load applied to displacement of 1 mm, 2 mm, and 3 mm. The ultimate load showed that the looping stitch was significantly stronger compared to the Krackow stitch (Krackow stitch: 223.7 ± 50.3 N; looping stitch: 312.7 ± 53.8 N) (P = .002). The failure modes were either suture breakage or tendon cut through. For the Krakow stitch, there was 1 suture breakage and 9 tendons cut through. For the looping stitch, there were five suture breakages, and five tendons cut through. Conclusions: With fewer needle penetrations, incorporation of 100% of the tendon diameter, and a higher ultimate load to failure compared to the Krackow stitch, the Looping stitch may be a viable option to reduce deformation, failure, and cut-out of the suture-tendon construct.

Suture Tape Augmentation of Screw Fixation Reduces Fragment Migration in Tibial Tubercle Osteotomy: A Biomechanical Study.

BACKGROUND: Tibial tubercle osteotomy (TTO) is a complex surgical procedure with a significant risk of complications, which include nonunion and tibial fracture. PURPOSE: To determine whether an additional suture tape augmentation can provide better biomechanical stability compared with standard screw fixation. STUDY DESIGN: Controlled laboratory study. METHODS: Five matched pairs of human cadaveric knees were divided into 2 groups: the first group underwent standard TTO fixation with 2 parallel screws (standard group). The second group underwent a novel fixation technique, in which a nonabsorbable suture tape (FiberTape) in a figure-of-8 construct was added to the standard screw fixation for extra stabilization in the inferior-superior direction (augmented group). The specimens were biomechanically tested using a multistep cyclic loading protocol from 400 N up to 800 N to simulate the rehabilitation process. Tubercular fragment migration of >50% of the initial distalization length was defined as clinical failure. A pull-to-failure test was applied to the specimens that survived cyclic loading. Tubercular fragment displacement during cyclic loading and pull-to-failure force were recorded and compared between the 2 groups. RESULTS: Two specimens of the standard group exhibited clinical failure during cyclic loading to 400 N. All other specimens survived cyclic loading to 800 N. The augmented group showed less cyclic tubercular fragment displacement after every load level compared with the standard group, with statistically significant differences starting from 500 N (P < .05; power > 0.8). Mean ± standard deviation tubercular fragment displacement at the end of cyclic loading was 2.56 ± 0.82 mm for the augmented group and 5.21 ± 0.51 mm for the standard group. Mean ultimate failure load after the pull-to-failure test was 2475 ± 554 N for the augmented group and 1475 ± 280 N for the standard group. CONCLUSION: The specimens that underwent suture tape augmentation showed less tubercular fragment displacement during cyclic loading and higher ultimate failure forces compared with those that underwent standard screw fixation. CLINICAL RELEVANCE: The augmentation technique could potentially increase the success of a TTO.

Biomechanical comparison of docking ulnar collateral ligament reconstruction with and without an internal brace.

BACKGROUND: Current ulnar collateral ligament (UCL) reconstruction techniques are substantially less stiff and demonstrate lower load to failure compared with the native UCL. UCL repair with the addition of an internal brace has demonstrated superior biomechanical performance compared with docking UCL reconstruction, but internal bracing has not yet been used in UCL reconstruction. HYPOTHESIS/PURPOSE: To evaluate the time-zero biomechanical performance of a UCL docking technique reconstruction with and without an internal brace compared with native UCL properties. METHODS: Twelve matched pairs of cadaveric elbows were dissected and fixed at 90° for biomechanical testing. A cyclic valgus torque protocol was used to test the anterior band of the UCL in native specimens. After native specimens were failed, palmaris grafts were used for a docking reconstruction with or without internal brace and were subjected to the same valgus torque test protocol. Torsional stiffness, ultimate failure torque, and ulnohumeral gapping were determined. RESULTS: Stiffness in UCL reconstructions using a standard docking technique (3.0 ± 0.4 N m/deg) were significantly less stiff (P < .001) than native UCL (4.0 ± 0.8 N m/deg), whereas reconstructions using an internal brace (3.6 ± 0.6 N m/deg) were not different (P = .120) compared with native. Ultimate failure torque for standard docking (18.3 ± 4.1 N m) was significantly lower (P < .001) than native UCL (36.9 ± 10.1 N m), whereas the internal brace samples (35.3 ± 9.8 N m) were not different (P = .772) than native. CONCLUSION: UCL reconstruction with an internal brace augmentation provides superior stiffness and time-zero failure strength when compared with the standard docking technique.

Identification of Novel Serum Autoantibodies for Differential Diagnosis of Autoimmune Pancreatitis and Pancreatic Ductal Adenocarcinoma.

OBJECTIVES: The lack of specific biochemical markers is a major drawback for the diagnosis of autoimmune pancreatitis (AIP). The aims were to characterize the autoantibody profiles in AIP and pancreatic ductal adenocarcinoma (PDAC) and to identify circulating autoantibodies that could be diagnostic markers differentiating PDAC and the AIP subtypes. METHODS: Tissue lysates obtained from the resected pancreas of patients with AIP and patients with PDAC were separated by 2-dimensional polyacrylamide gel electrophoresis subsequently immunoblotted with autologous sera. The immunoreactive spots were subjected to nanoscale liquid chromatography-electrospray ionization tandem mass spectrometry to identify serum autoantibodies to tissue-derived autoantigens associated with AIP and PDAC. Autoantibody concentrations for selected autoantigens were assessed by enzyme-linked immunosorbent assays. RESULTS: A total of 115 immunoreactive spots were identified by 2-dimensional polyacrylamide gel electrophoresis/immunobloting. Nanoscale liquid chromatography-electrospray ionization tandem mass spectrometry-based analysis revealed 68 autoantigens in AIP, 26 in PDAC, and 21 present in both diseases. Assessment of 13 selected AIP autoantibody serum levels revealed that 7 of them had significantly higher titers in AIP versus PDAC. IgG-directed against transaldolase could significantly differentiate between the 2 AIP subtypes. CONCLUSIONS: The novel panel of AIP autoantibodies is promising to supplement the predictive tests for AIP of the currently known autoantigens and represent a basis for a combined blood test to differentiate AIP from PDAC in the future.

Uric acid accumulation in an Arabidopsis urate oxidase mutant impairs seedling establishment by blocking peroxisome maintenance.

Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants.

Serum protein signatures differentiating autoimmune pancreatitis versus pancreatic cancer.

Autoimmune pancreatitis (AIP) is defined by characteristic lymphoplasmacytic infiltrate, ductal strictures and a pancreatic enlargement or mass that can mimic pancreatic cancer (PaCa). The distinction between this benign disease and pancreatic cancer can be challenging. However, an accurate diagnosis may pre-empt the misdiagnosis of cancer, allowing the appropriate medical treatment of AIP and, consequently, decreasing the number of unnecessary pancreatic resections. Mass spectrometry (MS) and two-dimensional differential gel electrophoresis (2D-DIGE) have been applied to analyse serum protein alterations associated with AIP and PaCa, and to identify protein signatures indicative of the diseases. Patients' sera were immunodepleted from the 20 most prominent serum proteins prior to further 2D-DIGE and image analysis. The identity of the most-discriminatory proteins detected, was performed by MS and ELISAs were applied to confirm their expression. Serum profiling data analysis with 2D-DIGE revealed 39 protein peaks able to discriminate between AIP and PaCa. Proteins were purified and further analysed by MALDI-TOF-MS. Peptide mass fingerprinting led to identification of eleven proteins. Among them apolipoprotein A-I, apolipoprotein A-II, transthyretin, and tetranectin were identified and found as 3.0-, 3.5-, 2-, and 1.6-fold decreased in PaCa sera, respectively, whereas haptoglobin and apolipoprotein E were found to be 3.8- and 1.6-fold elevated in PaCa sera. With the exception of haptoglobin the ELISA results of the identified proteins confirmed the 2D-DIGE image analysis characteristics. Integration of the identified serum proteins as AIP markers may have considerable potential to provide additional information for the diagnosis of AIP to choose the appropriate treatment.