Mean Maximum Load Research Articles

Biomechanical Comparison of Different Suturing Techniques in Rabbit Medial Gastrocnemius Muscle Laceration Repair

Skeletal muscle laceration is a common injury. Repair of disrupted delicate tissue is still a clinical challenge for surgeons. A few different muscle repair techniques have been reported. However, the best muscle repair technique has not been identified. The aim of the present study is to compare the biomechanical features of different repair techniques in muscles to identify the most effective one. New Zealand white rabbits (2.5-3 kg) were euthanized and medial gastrocnemius muscles were isolated. The muscles were completely transected with scalpels and then repaired by 3 different techniques, namely, (1) 2-strand mattress, (2) 4-strand Kessler (with epitendinous suture), and (3) Mason-Allen. To measure suture performance, the repaired specimens were mounted onto a mechanical testing machine Instron 5543. The muscles were loaded to failure at a constant speed of 60 mm/min. Data collected from Merlin v5.31 software were used to compute the biomechanical properties of each specimen. There was no significant difference in the mean maximum load of Kessler group (15.5 N) and Mason-Allen group (13.2 N), whereas the mean maximum load of the control (Mattress) group (4.4 N) was significantly smaller than the other 2 groups. Moreover, Kessler stitches were the stiffest among the 3. It is noteworthy that the mechanisms of failure were different: Kessler stitches were all pulled out longitudinally, whereas Mason-Allen stitches transmitted load across the laceration and ruptures occur at areas adjacent to the stitches, indicating that muscle is the weakest element in the biomechanical testing. Both Kessler and Mason-Allen stitches have shown better biomechanical features compared with the control group. Further study has to be done to compare the effect of these 2 techniques on muscle regeneration and scar formation in an in vivo model.

Defining the biomechanical properties of the rabbit trachea.

Surgical advancements rely heavily on validated animal models. The New Zealand White (NZW) rabbit is a widely used model for airway research, including regenerative medicine applications. Currently, the biomechanical properties of the normal rabbit trachea are not known. Our objective was to define these properties to assist in the standardization and understanding of future airway research using this model. Laboratory-based study. Fresh tracheas from four adult NZW rabbits were dissected into 20 segments. To examine the biomechanical properties, segments were subjected to uniaxial tension (n = 9) and compression (n = 11) testing. Yield and maximum load (tension) and force at 50% displacement (compression) were recorded, and differences between segments were examined using analysis of covariance. Normative data for native rabbit trachea show mean maximum load = 6.44 newtons (N), yield load = 5.93 N, and compressive strength = 2.10 N. In addition to establishing the baseline measurements, statistically significant differences in tensile measures based on location along the trachea and diameter were identified. Proximal segments had significantly higher maximum load (P = .0029) and yield load (P = .0062) than distal segments. Association between diameter and both maximum load (P = .0139) and yield load (P = .0082) was observed. The adult NZW rabbit trachea is intrinsically less able to withstand tensile and compressive forces, compared to other airway models such as sheep or cadaveric human. Establishment of normative values will enable future research into changes in tracheal biomechanical properties during regenerative medicine manipulation and processing.

Strength of Arthroscopic Meniscal Root Repair Constructs

Clinical study has illustrated the prevalence of meniscal root injury and potential for degenerative sequel without repair. Repair constructs have been presented by authors, and repair strengths determined. However, prior studies have evaluated constructs placed ex vivo without method to place the strongest construct in an arthroscopic fashion nor strength evaluation of constructs placed arthroscopically. We present two new meniscal root repair constructs with arthroscopic technique and strength evaluation of arthroscopically placed repair constructs. Pullout strength, stiffness, and time of suture construct for the different meniscal repair patterns was evaluated. This will aid the clinician in determining the best method for arthroscopic meniscal root repair and aid in the development of appropriate postoperative rehabilitation plans. The hypothesis of this study is that maximum failure load, stiffness, and repair execution time will vary based upon suture construct, with higher strengths and execution times with increased repair technique complexity. Twenty cadaveric knees were mounted in a simulated surgical position, and sutures were placed arthroscopically at the root of the medial and lateral menisci. Four repair constructs were tested including 2 novel repair constructs: 2 simple stitches, 1 inverted mattress stitch, 1 double locking loop stitch, and 2 double locking loop stitches. Arthroscopic placement of suture repair construct was timed. In total 40 posterior meniscal roots, both lateral and medial from 21 cadaveric specimens were tested, with 10 trials for each construct. Specimens were dissected, and the medial and lateral menisci harvested. Individual meniscus specimens were cycled and then tested to failure on an Instron machine with a custom baseplate mimicking the transosseous suture tunnel utilized in meniscal root repair. The Kruskal-Wallis Test was used to evaluate for statistical significance between groups. The mean maximum failure loads were: 2 simple stitches (2SS) 137±49 N, 1 inverted mattress stitch (1MS) 126±44 N, 1 double loop locking stitch (1DLS) 201±44 N, 2 double loop locking stitches (2DLS) 396±69 N. Inter-construct comparison revealed statistical difference between 2DLS (p < 0.01) and all three remaining constructs (< 0.01), and 1DLS when compared to 2SS and 1MS (p <0.01, <0.01). Statistical significance was not found between 2SS and 1MS (p=0.8). The average time for repair of the 4 fixation techniques were: 2SS 1.78 ± 0.87 minutes, 1MS 2.40 ± 1.90 minutes, 1DLS 4.67 ± 2.01minutes, 2DLS 5.38 ± 0.62 minutes. Constructs with four suture limbs within the simulated repair tunnel illustrated stiffer constructs. Arthroscopically placed locking loop repair constructs are stronger than current arthroscopic techniques with increase in time of repair. As complexity of the repair construct increases so does time for fixation and pullout strength. With this study, an arthroscopic technique is presented to produce stronger meniscal root repair constructs with little increase in surgical time.

Mechanical Properties of Bioresorbable Self-reinforced Posterior Cervical Rods

A biomechanical study. To test the mechanical and physical properties of self-reinforced copolymer bioresorbable posterior cervical rods and compare their mechanical properties to commonly used Irene titanium alloy rods. Bioresorbable instrumentation is becoming increasingly common in surgical spine procedures. Compared with metallic implants, bioresorbable implants are gradually reabsorbed as the bone heals, transferring the load from the instrumentation to bone, eliminating the need for hardware removal. In addition, bioresorbable implants produce less stress shielding due to a more physiological modulus of elasticity. Three types of rods were used: (1) 5.5 mm copolymer rods and (2) 3.5 mm and (3) 5.5 mm titanium alloy rods. Four tests were used on each rod: (1) 3-point bending test, (2) 4-point bending test, (3) shear test, and (4) differential scanning calorimeter test. The outcomes were recorded: Young modulus (E), stiffness, maximum load, deflection at maximum load, load at 1.0% strain of the rod's outer surface, and maximum bending stress. The Young modulus (E) for the copolymer rods (mean range, 6.4-6.8 GPa) was significantly lower than the 3.5 mm titanium rods (106 GPa) and the 5.5 mm titanium rods (95 GPa). The stiffness of the copolymer rods (mean range, 16.6-21.4 N/mm) was also significantly lower than the 3.5 mm titanium alloy rods (43.6 N/mm) and the 5.5 mm titanium alloy rods (239.6 N/mm). The mean maximum shear load of the copolymer rods was 2735 N and they had significantly lower mean maximum loads than the titanium rods. Copolymer rods have adequate shear resistance, but less load resistance and stiffness compared with titanium rods. Their stiffness is closer to that of bone, causing less stress shielding and better gradual dynamic loading. Their use in semirigid posterior stabilization of the cervical spine may be considered.

Comparative biomechanical study on three miniplates osteosynthesis systems for stabilisation of low condylar fractures of the mandible

Open reduction and fixation of low condylar fractures of the mandible can be achieved by many osteosynthesis systems that differ in size, shape, and site of placement according to the surgical approach. We investigated the maximum load and rigidity of 4 osteosynthesis systems: the standard double 4-hole straight miniplates, the inverted y-miniplate (with and without self-drilling screws), and the TriLock Delta condyle trauma plate. The standard double 4-hole straight miniplate osteosynthesis achieved the best fixation and resistance in view of a mean (SD) maximum load of 539.8 (100.2)N, followed by the inverted y-miniplate with the self-drilling screws (246.5 (23.8)N), the inverted y-miniplate with standard screws (242.4 (27.2)N), and finally the TriLock Delta plate (167.4 (39.2)N). Analysis of the slope of the force–displacement diagram from 80N to 100N in each group showed that the TriLock Delta miniplate had the highest values for rigidity (17.3 (5.1)N/μm), followed by the inverted y-miniplate groups with self-drilling screws (14.1 (6.4)N/μm), and with standard screws (12.6 (2.5)N/μm). The double 4-hole straight miniplate osteosynthesis had the lowest rigidity (8.7 1.4)N/μm). Despite the significant difference in the maximum load between the double 4-hole miniplates and other investigated osteosynthesis patterns, all groups had sufficient load for the fixation of low condylar fractures of the mandible when postoperative bite forces and the slowly increasing voluntary clenching during healing were considered.

Strength Determination of Brittle Materials as Curved Monolithic Structures

The dental literature is replete with “crunch the crown” monotonic load-to-failure studies of all-ceramic materials despite fracture behavior being dominated by the indenter contact surface. Load-to-failure data provide no information on stress patterns, and comparisons among studies are impossible owing to variable testing protocols. We investigated the influence of nonplanar geometries on the maximum principal stress of curved discs tested in biaxial flexure in the absence of analytical solutions. Radii of curvature analogous to elements of complex dental geometries and a finite element analysis method were integrated with experimental testing as a surrogate solution to calculate the maximum principal stress at failure. We employed soda-lime glass discs, a planar control (group P, n = 20), with curvature applied to the remaining discs by slump forming to different radii of curvature (30, 20, 15, and 10 mm; groups R30-R10). The mean deflection (group P) and radii of curvature obtained on slumping (groups R30-R10) were determined by profilometry before and after annealing and surface treatment protocols. Finite element analysis used the biaxial flexure load-to-failure data to determine the maximum principal stress at failure. Mean maximum principal stresses and load to failure were analyzed with one-way analyses of variance and post hoc Tukey tests (α = 0.05). The measured radii of curvature differed significantly among groups, and the radii of curvature were not influenced by annealing. Significant increases in the mean load to failure were observed as the radius of curvature was reduced. The maximum principal stress did not demonstrate sensitivity to radius of curvature. The findings highlight the sensitivity of failure load to specimen shape. The data also support the synergistic use of bespoke computational analysis with conventional mechanical testing and highlight a solution to complications with complex specimen geometries.

Timing matters: NSAIDs interfere with the late proliferation stage of a repaired rotator cuff tendon healing in rats

Rotator cuff (RC) tear is a common problem that causes pain and can limit shoulder function. Non-steroidal anti-inflammatory drugs (NSAIDs) are often prescribed for musculoskeletal pain, including the pain subsequent to RC repair. NSAIDs have been reported to affect bone metabolism and fracture healing(,) but there is little evidence about their effect on tendon healing. We investigated the effect of meloxicam (non-steroidal anti-inflammatory drug) on the healing of RC tendons when given immediately after surgical repair. Thirty-nine rats underwent acute RC tear and repair. Group A (n = 13) received daily intraperitoneal (IP) injections of meloxicam for the first 10 postoperative days. Group B (n = 13) received IP injections of meloxicam starting from postoperative day 11. Group C (n = 13, controls) received daily IP injections of saline for 3 weeks. The animals were killed 3 weeks after surgery and the RC was evaluated by gross inspection, biomechanical testing and histological examination. Group B displayed a significantly lower mean maximal load at 3 weeks than group C (P = 0.02) and group A (P = 0.05). Stiffness was significantly lower in B group as compared to A group (P = 0.05). Qualitative examination of histology specimens did not disclose any apparent differences with respect to cellularity, vascularity, healing, and collagen orientation. We conclude that meloxicam decreases the biomechanical strength of repaired rat RCs when administered between 11 and 20 days after the repair.

Minimally invasive reconstruction of lateral tibial plateau fractures using the jail technique: a biomechanical study

BackgroundThis study described a novel, minimally invasive reconstruction technique of lateral tibial plateau fractures using a three-screw jail technique and compared it to a conventional two-screw osteosynthesis technique. The benefit of an additional screw implanted in the proximal tibia from the anterior at an angle of 90° below the conventional two-screw reconstruction after lateral tibial plateau fracture was evaluated. This new method was called the jail technique.MethodsThe two reconstruction techniques were tested using a porcine model (n = 40). Fracture was simulated using a defined osteotomy of the lateral tibial plateau. Load-to-failure and multiple cyclic loading tests were conducted using a material testing machine. Twenty tibias were used for each reconstruction technique, ten of which were loaded in a load-to-failure protocol and ten cyclically loaded (5000 times) between 200 and 1000 N using a ramp protocol. Displacement, stiffness and yield load were determined from the resulting load displacement curve. Failure was macroscopically documented.ResultsIn the load-to-failure testing, the jail technique showed a significantly higher mean maximum load (2275.9 N) in comparison to the conventional reconstruction (1796.5 N, p < 0.001). The trend for better outcomes for the novel technique in terms of stiffness and yield load did not reach statistical significance (p > 0.05). In cyclic testing, the jail technique also showed better trends in displacement that were not statistically significant. Failure modes showed a tendency of screws cutting through the bone (cut-out) in the conventional reconstruction. No cut-out but a bending of the lag screws at the site of the additional third screw was observed in the jail technique.ConclusionsThe results of this study indicate that the jail and the conventional technique have seemingly similar biomechanical properties. This suggests that the jail technique may be a feasible alternative to conventional screw osteosynthesis in the minimally invasive reconstruction of lateral tibial plateau fractures. A potential advantage of the jail technique is the prevention of screw cut-outs through the cancellous bone.

In vitro assessment of three types of zirconia implant abutments under static load

Although various zirconia abutments have been introduced, insufficient data exist regarding the maximum load capacity of internal tri-channel connection zirconia implant abutments with various implant-abutment interfaces. The purpose of this in vitro study was to compare the maximum load capacity of 3 different types of internal tri-channel connection zirconia abutments and to assess their mode of failure. The study investigated 3 groups (n=20) of zirconia implant abutments with different implant-abutment interfaces. Group AllZr consisted entirely of zirconia (Aadva CAD/CAM Zirconia Abutment), group FrZr of a titanium insert friction-fitted to the zirconia abutment component (NobelProcera Abutment Zirconia), and group BondZr of a titanium insert bonded to the zirconia abutment component (Lava Zirconia abutment). All the abutments were thermal cycled for 20 000 cycles between 5°C and 55°C. Sixty test implants made of titanium (Dummy NobelReplace) were embedded in autopolymerizing acrylic resin, and 60 zirconia copings (Lava Zirconia) with a uniform thickness of 2.0 mm were fabricated and bonded to the abutments. A universal testing machine was used to statically load all the specimens at a crosshead speed of 1 mm/min. The maximum load was recorded and used as the failure load. The fractured specimens were collected and representative specimens were studied with a stereomicroscope and scanning electron microscope (SEM). One-way ANOVA and post hoc comparisons with the Tukey HSD tests were used for statistical analysis (α=.05). The mean (SD) maximum load capacity was 484.6 (56.6) N for NobelProcera, 503.9 (46.3) N for Aadva, and 729.2 (35.9) N for Lava abutments. The maximum load capacity of Lava abutments was significantly higher than that of Aadva or NobelProcera (P< 05). No significant difference between Aadva and NobelProcera abutments was noted. The mode of failure among the Aadva, NobelProcera, and Lava abutments was different. With standard diameter internal tri-channel connection implants, the maximum load capacity of the Lava abutment was significantly higher than that of the Aadva or NobelProcera abutment. No significant difference in maximum load capacity was noted between Aadva and NobelProcera abutments. However, the fracture behavior of all 3 abutments was different.

Mechanical testing of thin-walled zirconia abutments

Although the use of zirconia abutments for implant-supported restorations has gained momentum with the increasing demand for esthetics, little informed design rationale has been developed to characterize their fatigue behavior under different clinical scenarios. However, to prevent the zirconia from fracturing, the use of a titanium connection in bicomponent aesthetic abutments has been suggested.Objective:Mechanical testing of customized thin-walled titanium-zirconia abutments at the connection with the implant was performed in order to characterize the fatigue behavior and the failure modes for straight and angled abutments.Material and Methods:Twenty custom-made bi-component abutments were tested according to ISO 14801:2007 either at a straight or a 25º angle inclination (n=10 each group). Fatigue was conducted at 15 Hz for 5 million cycles in dry conditions at 20ºC±5ºC. Mean values and standard deviations were calculated for each group. All comparisons were performed by t-tests assuming unequal variances. The level of statistical significance was set at p≤0.05. Failed samples were inspected in a polarized-light and then in a scanning electron microscope.Results:Straight and angled abutments mean maximum load was 296.7 N and 1,145 N, the dynamic loading mean Fmax was 237.4 N and 240.7 N, respectively. No significant differences resulted between the straight and angled bi-component abutments in both static (p=0.253) and dynamic testing (p=0.135). A significant difference in the bending moment required for fracture was detected between the groups (p=0.01). Fractures in the angled group occurred mainly at the point of load application, whereas in the straight abutments, fractures were located coronally and close to the thinly designed areas at the cervical region.Conclusion:Angled or straight thin-walled zirconia abutments presented similar Fmax under fatigue testing despite the different bending moments required for fracture. The main implication is that although zirconia angled or straight abutments presented similar mechanical behavior, the failure mode tended to be more catastrophic in straight (fracture at the cervical region) compared to angled abutments.

Biomechanical Analysis of Knotless Flexor Tendon Repair Using Large-Diameter Unidirection Barbed Suture

In traditional flexor tendon repairs, suture knots can be sites of weakness, impair tendon healing, stimulate an inflammatory response, and increase the bulk of the tendon repair. Because of this, there has been an increased interest in knotless flexor tendon repair using barbed suture. Since knots are not required, it may be possible to increase the strength of the tendon repair by using a large-diameter barbed suture. The purpose of this study was to biomechanically compare a traditional four-strand tendon repair using 3-0 braided polyester with a similar knotless four-strand tendon repair using 0 unidirectional barbed suture. Twenty-two matched cadaveric flexor digitorum profundus tendons were lacerated and assigned to repair by a four-strand modified Kirchmayr-Kessler technique using 3-0 braided polyester (n = 11) or knotless four-strand modified Kirchmayr-Kessler repair using 0 unidirectional barbed suture (n = 11). Repaired tendons were linearly distracted to failure at 20mm/min after 1N preload. Maximum load and load at 2-mm gap formation were recorded. Maximum load and load at 2-mm gap formation were compared with the Student's t test, and p values ≤ 0.05 were considered significant. The mean maximum load of the barbed, knotless suture repair was higher than that of the traditional repair (52 vs. 42N). There was no difference between the two groups in the mean load required to produce a 2-mm gap. The four-strand knotless tendon repairs using a large-diameter unidirectional barbed suture were stronger than the traditional four-strand repairs using 3-0 braided polyester, and had similar 2-mm gap resistance.

In vitrocomparison of two different materials for the repair of urethan dimethacrylate denture bases

PURPOSEThe purpose of this in vitro study was to investigate the flexural properties of a recently introduced urethane dimethacrylate denture base material (Eclipse) after being repaired with two different materials.MATERIALS AND METHODSTwo repair groups and a control group consisting of 10 specimens each were generated. The ES group was repaired with auto-polymerizing polymer. The EE group was repaired with the Eclipse. The E group was left intact as a control group. A 3-point bending test device which was set to travel at a crosshead speed of 5 mm/min was used. Specimens were loaded until fracture occurred and the mean displacement, maximum load, flexural modulus and flexural strength values and standard deviations were calculated for each group and the data were statistically analyzed. The results were assessed at a significance level of P<.05.RESULTSThe mean "displacement", "maximum load before fracture", "flexural strength" and "flexural modulus" rates of Group E were statistically significant higher than those of Groups ES and EE, but no significant difference (P>.05) was found between the mean values of Group ES and EE. There was a statistically significant positive relation (P<.01) between the displacement and maximum load of Group ES (99.5%), Group EE (94.3%) and Group E (84.4%).CONCLUSIONThe more economic and commonly used self-curing acrylic resin can be recommended as an alternative repair material for Eclipse denture bases.

Fixation of the Achilles Tendon Insertion Using Suture Button Technology

Background: In the operative treatment of Achilles insertional tendinopathy, no guidelines exist concerning which form of fixation of the Achilles tendon insertion is superior. Hypothesis: Transcalcaneal drill pin passage does not place any major plantar structures at risk, and the addition of a Krackow stitch and suture button to the fixation technique provides a significant increase in ultimate load to failure in Achilles tendon insertional repairs. Study Design: Controlled laboratory study. Methods: The Achilles tendon insertions in 6 fresh-frozen cadaveric ankles were detached, and transcalcaneal drill pins were passed. Plantar dissection took place to evaluate the drill pin relationship to the plantar fascia, lateral plantar nerve and artery, flexor digitorum longus tendon, and master knot of Henry. The Achilles tendons were then repaired with a double-row suture anchor construct alone or with a suture button and Krackow stitch added to the double-row suture anchor construct. The repairs were then tested to maximum load to failure at 20 mm/min. The mode of failure was recorded, and the mean maximum load to failure was assessed using the Student t test for distributions with equal variance. Results: Transcalcaneal drill pin passage did not place any selected anatomic structures at risk. The mean maximum load to failure for the suture bridge group was 239.2 N; it was 391.4 N for the group with the suture button (P = .014). The lateral plantar artery was the structure placed at greatest risk from drill pin placement, with a mean distance of 22.7 mm (range, 16.5-29.2 mm) between the pin and artery. Conclusion: In this laboratory study, transcalcaneal drill pin passage appeared to be anatomically safe, and the use of suture button technology with a Krackow stitch for Achilles tendon insertional repair significantly increased repair strength. Clinical Relevance: Achilles tendon insertional repair with suture button fixation and a Krackow stitch may facilitate the earlier institution of postoperative rehabilitation and improve clinical outcomes.

Acromioclavicular and coracoclavicular PDS augmentation for complete AC joint dislocation showed insufficient properties in a cadaver model

Optimal surgical treatment of high-grade acromioclavicular joint dislocations is still controversially discussed. The purpose of the present controlled laboratory study was to evaluate whether a polydioxansulfate (PDS(®)) cord augmentation with separate reconstruction of the coracoclavicular (CC) ligaments and the acromioclavicular (AC) complex provides sufficient vertical stability in a biomechanical cadaver model. Twenty-four shoulders of fresh-frozen cadaveric specimen were tested. Cyclic loading and load to failure protocol was performed in vertical direction on 12 native AC joints and repeated after reconstruction. The reconstruction of the coracoclavicular ligament was performed using two CC PDS cerclages and an additional AC PDS cerclage. In static load testing for vertical force, the native AC joint complex measured 590.1N (±95.8N), elongation 13.4mm (±2.1mm) and stiffness 48.7N/mm (±12.0N/mm). The mean maximum load to failure in the reconstructed joints was 569.9N (±97.9N), elongation 18.8mm (±4.7mm) and stiffness 37.9N/mm (±8.0N/mm). During dynamic testing of the reconstructed AC joints, all specimens reached the critical elongation of 12.0mm, defined as clinical failure between 200 and 300N. The mean amount of repetitions at clinical failure was 305. A plastic deformation of the reconstructed specimens throughout cyclic loading could not be detected. The AC joint reconstruction with acromioclavicular and coracoclavicular PDS cord cerclages did not provide the aspired vertical stability in a cadaver model. Basic Science Study.

A biomechanical comparison of the primary stability of two minimally invasive techniques for repair of ruptured Achilles tendon

To compare the primary stability of two minimally invasive procedures of Achilles tendon (AT) repair, namely a modified percutaneous repair of ruptured AT and the Achillon suture configuration. Eighteen (nine matched pairs) frozen ovine ATs were tenotomized 5cm from the calcaneal insertion. In each pair, one tendon was randomly allocated to one of the two techniques: a modified percutaneous repair group and the Achillon device suture configuration. Specimens were tested performing an unidirectional tensile load to failure using a servo-hydraulic testing device (MTS Systems, Eden Prairie, MN, USA), controlled by an electropulse e3000 INSTRON machine (Instron Ltd, Buckinghamshire, UK). The tendons were then loaded to failure at a rate of 10mm/s. Two of the nine pairs of specimens were discarded because one specimen for each of the pair pulled out of the pneumatic clamp during mechanical testing. The remaining seven matched pairs were successfully tested. There were no differences in mean strength, mean maximum load, mean failure elongation, tension, stiffness and mode of failure between the two groups. The Achillon-like configuration and the modified percutaneous repair of ruptured AT provided similar biomechanical performance.

Paper # 189: Pitfall in ACL Reconstruction Using a Medial Portal Approach: Penetration of the Second Femoral Cortex

Paper # 189: Pitfall in ACL Reconstruction Using a Medial Portal Approach: Penetration of the Second Femoral Cortex

Biomechanical Comparison of Arthroscopic Repairs for Acromioclavicular Joint Instability

Background: Arthroscopic procedures for reconstruction of acromioclavicular (AC) joint separations are increasingly used in clinical practice. Multiple surgical techniques exist, but there are still few data on biomechanical performances of commonly used arthroscopic techniques and fixation methods. Hypothesis: Single and double clavicular tunnel reconstructions show comparable primary stability with a modified Weaver-Dunn procedure, and double tunnel constructs show superior horizontal stability. Study Design: Controlled laboratory study. Methods: The AC joints of 40 cadaveric shoulders were tested for anterior, posterior, and superior translation (70-N load) and maximal load to failure (superior) with the MTS 858 Bionix II Servohydraulic testing system. Shoulders were assigned to 4 groups: (1) native (n = 18), (2) coracoclavicular (CC) reconstruction with 1 clavicular and 1 coracoid tunnel (SCT) fixed with a suture pulley and 2 buttons (n = 8), (3) CC reconstruction with 2 clavicular and 1 coracoid tunnel (DCT) fixed with a suture pulley and 3 buttons (n = 8), and (4) modified Weaver-Dunn reconstruction (n = 6). Results: Native specimens showed a mean anterior translation of 7.92 mm (±1.69 mm), a mean posterior translation of 7.84 mm (±2.09 mm), and a superior translation of 4.28 mm (±1.81 mm). Maximal load to failure was 579.44 N (±148.01 N). The SCT technique showed a mean anterior translation of 5.81 mm (±1.16 mm), posterior translation of 8.30 mm (±1.94 mm), and a superior translation of 2.28 mm (±0.52 mm). The maximal load to failure was 591.35 N (±231.17 N). Anterior and superior translations were significantly less compared with the native specimen (P = .005 and P = .003). The DCT technique had an anterior translation of 4.68 mm (±0.6 mm), posterior translation of 6.85 mm (±0.83 mm), and superior translation of 2.09 mm (±0.86 mm). The mean maximal load to failure was 651.16 N (±226.93 N). Anterior and superior translations were significantly less compared with the native specimens (P = .000 and P = .001). No statistically significant differences were shown between SCT and DCT reconstruction for all measurements (P > .05). One reconstruction of the modified Weaver-Dunn procedure failed directly after mounting it into the testing device. The remaining 5 showed a mean anterior translation of 11.36 mm (±3.17 mm), a mean posterior translation of 13.51 mm (±2.21 mm), and a mean superior translation of 3.31 mm (±0.47 mm). Anterior and posterior translations were significantly increased compared with the native specimen (P = .019 and P = .000). The mean maximal load to failure measured 311.13 N (±52.2 N) and was significantly less compared with the native specimen (P = .000). The Weaver-Dunn technique showed significantly less maximal load to failure and more anterior and posterior translation compared with SCT and DCT (P ≤ .05). Conclusion: Isolated reconstruction of the CC ligaments using single and double clavicular tunnel techniques results in a high load to failure for superior translation, which is equal to the native stability, and less translation in all 3 directions as well as higher superior stability when compared with the modified Weaver-Dunn procedure. A potential drawback is the risk of coracoid fracture, as the high load to failure of the device may exceed load to failure of cortical bone prior to device breakage. Clinical Relevance: Single clavicular tunnel arthroscopic reconstructions of the coracoacromial ligaments show good biomechanical results.

Evaluation of a one-stage ACL revision Technique using bone void filler after cyclic loading

BackgroundRevision anterior cruciate ligament (ACL) reconstruction often requires a two-stage approach. This study analyzes the biomechanical properties after cyclic loading of a one-stage ACL revision technique using a calcium phosphate bone cement. MethodsArthroscopic reconstruction of the ACL was performed in 5 matched pairs of fresh–frozen cadaveric knees separated into two groups. The control group underwent a standard reconstruction with a bone-patellar tendon–bone autograft with bioabsorbable interference screw fixation. The experimental group simulated a failed reconstruction by drilling a 12mm hole and underwent a revision after filling it with a bioabsorbable calcium phosphate bone cement. The specimens were dissected, scanned for bone mineral density, and cyclically loaded on a mechanical testing system (preload of 250cycles of 5–75N at 0.5Hz followed by 10,000cycles of 20–150N at 1Hz). Intact specifmens underwent a load-to-failure protocol of 50mm/min. Ultimate load, stiffness, and modes of failure were recorded. Data was analyzed using paired t-tests. FindingsAll specimens completed the mechanical testing protocol. The control group had a mean maximum load of 471.33N (SD 220.73N) and the experimental group had 453.54N (SD 152.36; p=0.84). There were no statistically significant differences in maximum load or stiffness. No correlation between bone mineral density (BMD) and maximum load was found. InterpretationUsing calcium phosphate filler in a single-stage ACL revision is biomechanically viable. Further testing of long-term incorporation of the ACL graft in an animal model, along with human clinical trials, should be performed before there is clinical acceptance of this technique.

Biomechanical properties of the scapholunate ligament and the importance of its portions in the capitate intrusion injury

BackgroundRepair of the dorsal component of the scapholunate ligament alone is the usual surgical treatment for scapholunate injuries. Recent literature has suggested that additionally repairing the palmar component of the scapholunate ligament leads to improved and lasting clinical outcomes. The aim of this study was to determine the biomechanical properties of both portions of scapholunate ligaments derived from the same wrist and compare them with the whole scapholunate ligament. The goal was to further elucidate the importance of the palmar portion of the scapholunate ligament from a biomechanical perspective. MethodsScapholunate ligaments and their components were harvested from the same fresh frozen cadaveric wrists. Force at failure and stiffness were measured. FindingsThe mean maximum loads to failure for the entire scapholunate ligament, dοrsal and palmar portions were found to be 147 (SD 54)N, 83 (SD 18)N and 86 (SD 16)N respectively. No statistical difference was found between the mean maximum load and stiffness for palmar and dorsal components (P=0.05). Mean maximum load and stiffness, of the intermediate portion, were 36 (SD 15)N and 25 (SD 23)N/mm. InterpretationOur biomechanical findings on the dorsal and palmar portions of the scapholunate ligament suggest that each portion contributes approximately 50% to the whole ligament tensile force. These results appear to agree with other reports about the stabilizing role of the palmar portion of the scapholunate ligament and suggest that the palmar portion of the ligament should be considered for surgical repair.

The mechanics of the in vivo infant and toddler trunk during respiratory physiotherapy

Background The purpose of this study is to quantify the in vivo mechanical response of the child trunk under loading during physiotherapy treatments. Methods Twenty-six children aged 45 days to 7 years (14 girls and 12 boys) took part in this study. The forces applied by the physiotherapist were recorded using a force-plate embedded in the manipulation table supporting the child. Two synchronized cameras filmed the scene in a calibrated environment. The displacement of reflective targets glued on the physiotherapist's hands was calculated using an automatic tracking procedure and the 3D reconstruction “Direct Linear Transformation” algorithm. The progression of physical parameters was evaluated according to the age of the child. They included force, displacement, normalized displacement, loading speed, displacement and normalized displacement at the maximum force, force at the maximum displacement, viscous criterion and effective stiffness. Findings For all patients, the mean maximum displacement and load were 22 mm (SD 9 mm) and 240 N (SD 46 N) respectively. The force–displacement curves had shown the complexity of the in vivo behavior: four phases have been distinguished with cycles in respect with the respiratory phases. The increase in force always occurred before the increase in displacement. Interpretation This study helps to understand the in vivo behavior of the child trunk subjected to repetitive non-injurious mechanical loading. Further analysis in other populations and with different therapeutic maneuvers would refine the results.