Biomechanical testing of hamstring graft tibial tunnel fixation with bioabsorbable interference screws

Purpose:This study evaluated the failure mode, maximum load at failure, displacement at failure, and stiffness differences of quadrupled hamstring graft-tibial tunnel fixation using 28-mm, tapered 35-mm, or bicortical 17- and 20-mm bioabsorbable interference screws (Arthrex, Naples, FL).Type of Study:Biomechanical study.Methods:Nine matched pairs (18 specimens) of young cadaver tibias (mean bone mineral density [BMD] = 0.847 g/cm², range, 0.689 to 1.11 g/cm²) were divided into 3 groups of 6 specimens. Kruskal Wallis analysis of variance and Mann-Whitney U tests post hoc comparisons were used to assess group differences (P < .05).Results:Maximum load at failure for the 28-mm screw was 488.2 ± 197 N, with a displacement of 18.4 ± 7.5 mm and a stiffness modulus of 38.9 ± 7.0 N/mm. Maximum load at failure for the tapered 35-mm screw was 844.8 ± 121.4 N, with a displacement of 15.3 ± 1.6 mm and a stiffness modulus of 70.5 ± 21.1 N/mm. Maximum load at failure for bicortical screw fixation was 543.7 ± 266.5 N, with a displacement of 17.7 ± 6.6 mm and a stiffness modulus of 57.7 ± 14.9 N/mm. Fixation using the tapered 35-mm screw displayed greater maximum load at failure than either 28-mm screw fixation (P = .015) or bicortical screw fixation (P = .037). Significant differences were not evident for displacement. Both tapered 35-mm (P = .016) and bicortical screw (P = .026) fixation displayed greater stiffness than 28-mm screw fixation. All constructs failed by pullout.Conclusions:Fixation using a single tapered 35-mm screw displayed increased maximum load at failure compared with the 28-mm screw or bicortical fixation. Both the tapered 35-mm screw and bicortical fixation showed greater stiffness than fixation using a 28-mm screw. Use of a single 35-mm screw for quadrupled hamstring graft-tibial tunnel fixation may be preferred for patients with poor tibial BMD.     

Analysis of Three Types of Fixation of the Weil Osteotomy

This study assessed 3 methods of fixation for the Weil osteotomy. A total of 40 bone models were divided equally into 4 groups: a control group consisting of intact lesser rays; and Weil osteotomies that were fixated with 2 crossed Kirschner wires (0.045-in K-wires), 2.0-mm cortical screws, or cannulated 2.4-mm cortical screws. Each specimen was stressed in a computer-controlled hydraulic tensile testing machine, and maximum load, energy to failure, and stiffness were recorded. The following mean load to failure measurements were found: control, 62.9 Newtons (N); K-wire, 22.9 N; cannulated screw, 31.3 N; and noncannulated screw, 19.9 N. There was no statistical difference among the 3 groups of fixation methods in terms of the maximum load. The mean energy to failure of the control group was 326 joule (J); K-wire, 79 J; cannulated screw, 163 J; and noncannulated screw, 66 J. The cannulated screw generated a statistically greater amount of energy at failure than the noncannulated screw (P < .05). The mean structural stiffness of the control group was 7.3 N/mm; K-wire, 2.8 N/mm; cannulated screw 3.3 N/mm; and noncannulated screw, 3.2 N/mm. There was no statistical difference in structural stiffness among the 3 groups of fixation methods. The results indicated a trend toward better biomechanical stability with the 2.4-mm cannulated screw than the 2.0-mm noncannulated screw for fixation of the Weil osteotomy.     

The evolgate: a method to improve the pullout strength of interference screws in tibial fixation of anterior cruciate ligament reconstruction with doubled gracilis and semitendinosus tendons

Purpose:The goal of the study was to investigate the biomechanical properties of a new device for tibial fixation in arthroscopic anterior cruciate ligament reconstruction using doubled semitendinosus and gracilis tendons.Type of Study:Biomechanical study.Methods:This study compares the initial pullout strength, stiffness, and failure modes of 7 pairs of 4-strand human semitendinosus and gracilis grafts fixed to porcine tibias using either the Evolgate (Citieffe, Bologna, Italy) or 1 round threaded titanium interference screw. Structural tests of the graft fixation method tibia complexes were performed using a materials testing machine (MTS Bionix 855, Minneapolis, MN) at a strain rate of 50 mm/second.Results:The mean failure load was 1,237 ± 191 N for the Evolgate and 537 ± 65 N for the interference screw (P < .05) and the mean stiffness was 168 ± 37 N/m for the Evolgate and 105 ± 17 N/m for the interference screws (P ≤ .05). Although in all the cases fixed with the Evolgate failure occurred because of tendon rupture inside the tibial tunnel close to the fixation device, in 4 of the 7 cases fixed with interference screws, failure occurred because of tendon slippage at the fixation site.Conclusions:These results indicate that initial pullout strength of hamstring tendon graft interference screw fixation can be significantly increased using the Evolgate. In fact, because the screws purchase only in the cancellous bone, the Evolgate reinforces the walls of the tibial tunnel with a titanium involute, avoiding the loss of fixation strength related to the low density of the cancellous bone of the proximal metaphysis of the tibia.     

Quadrupled semitendinosus-gracilis autograft fixation in the femoral tunnel: a comparison between a metal and a bioabsorbable interference screw

Although semitendinosus-gracilis (SG) grafts for anterior cruciate ligament reconstruction have many potential benefits, effective fixation remains a challenge. This study assessed differences between the maximum pullout forces needed to detach a quadrupled SG graft from a femoral tunnel when secured by either a metal or a bioabsorbable interference screw. Sixteen paired fresh frozen quadrupled SG autografts (x, 8.4 mm; range, 7-10 mm) from 8 donors were anchored into cadaveric femoral tunnels by either a 7-mm metal or a 7-mm bioabsorbable screw after bone mineral density (BMD) assessment and before undergoing a longitudinal 20 mm/min traction force. Statistical analysis compared BMD (gm/cm2), insertional torque (N-m), and maximum load at pullout (N) between screw types. Insertional torques (.28-1.21, N-m range) did not correlate (P>.05) to BMD or maximum load at pullout (x ± S.D.) 242 ± 90.7 N (metal screw) and 341.1 ± 162.9 N (bioabsorbable screw). Differences did not exist between the maximum load at pullout for bioabsorbable or metal screw fixation (P = .16). Careful graft preparation, sizing, and matched tunnel placement enables interference fit and fixation capable of reliably withstanding the low- level rehabilitation loads to which the graft is exposed until bony ingrowth occurs.Arthroscopy 1998 Apr;14(3):241-5     

Biomechanical evaluation of a bioabsorbable expansion bolt for hamstring graft fixation in ACL reconstruction: an experimental study in calf tibial bone

Introduction: The purpose of our study was to evaluate and compare the primary fixation strength of a novel bioabsorbable two shell expansion bolt (EB) with that of a well-established interference screw-fixation technique in hamstring reconstruction of the anterior cruciate ligament. Materials and methods: Thirty calf tibia plateaus (age 5–6 months) were assigned to three groups: In group I (n=10) triple-stranded hamstring grafts were fixed with titanium interference screws (7 mm thread / 8 mm head × 25 mm). Specimens of group II (n=10) received bioabsorbable poly-L-lactide interference screws (8×23 mm). In group III (n=10), the grafts were fixed using bioabsorbable poly-D,L-lactide expansion bolts (5.8/8.5/10 mm × 35 mm). The tensile axis was placed parallel to the bone tunnel. The construction was then loaded until failure under a displacement rate of 1 mm per second. Results: There were no significant differences concerning the maximum pullout force (group I: 357 N ± 61; group II: 326 N ± 92; group III: 343 N ± 55). In case of the expansion bolt, we found the stiffness to be higher (61 N/mm) when compared to group I (48 N/mm), and group II (52 N/mm) (P<0.01 I vs. III). Using interference screws, we were able to demonstrate a strong correlation between torque and pullout forces (group I: r ²=0.7; group II: r ²=0.92). Ruptures of the suturing material occurred only in groups I and II. Conclusion: We conclude that hamstring graft fixation, using the presented expansion bolt, demonstrates fixation strength similar to the established screw fixation and can therefore be regarded as a reasonable alternative fixation method. Especially, since some specific disadvantages of screw fixation can be prevented by application of the bolt fixation.     

Hamstring tendon fixation using interference screws: a biomechanical study in calf tibial bone

It has recently been shown that graft fixation close to the ACL insertion site is optimal in order to increase anterior knee stability. Hamstring tendon fixation using interference screws offers this possibility and a round threaded titanium interference screw has been previously developed. The use of a round threaded biodegradable interference screw may be equivalent. In addition, to increase initial fixation strength, graft harvest with a distally attached bone plug may be advantageous, but biomechanical data do not exist. This study compares the initial pullout force, stiffness of fixation, and failure modes of three strand semitendinosus grafts in 36 proximal calf tibiae using either biodegradable poly-(D,L-lactide) (Sysorb; Sulzer Orthopaedics Ltd, Munsingen, Switzerland) or round threaded titanium (RCI; Smith & Nephew DonJoy, Carlsbad, CA) interference screws, harvested either without (biodegradable: group I, titanium III) or with (biodegradable: group II, titanium: group IV) attached tibial bone plugs. Maximum pullout force in group I (507 ± 93 N) was significantly higher than in group III (419 ± 77 N). Pullout force of bone plug fixation was significantly higher than that of direct tendon fixation (717 ± 90 N in group II and 602 ± 117 N in group IV). Pullout force of biodegradable fixation was significantly higher in both settings. These results indicate that initial pullout force of hamstring-tendon graft interference screw fixation can be increased by using a biodegradable interference screw. In addition, initial pullout force of hamstring-tendon graft fixation with an interference screw can be greatly increased by harvesting the graft with its distally attached tibial bone plug.Arthroscopy 1998 Jan-Feb;14(1):29-37     

Intramedullary screw fixation of proximal fifth metatarsal fractures: a biomechanical study

Intramedullary screw fixation is a popular technique for treatment of proximal fifth metatarsal fractures. The purpose of this study was to compare the fixation rigidity of a 5.5 mm partially threaded cannulated titanium screw, with presumed superior endosteal purchase, to a similar 4.5 mm screw. Acute fifth metatarsal fractures were simulated in cadavers, stabilized with intramedullary screws, and loaded to failure in three-point bending. The initial failure loads for the metatarsals fixed with 4.5 mm and 5.5 mm screws were not significantly different (332.4 N vs. 335.2 N, respectively), nor were the ultimate failure loads (849.8 N vs. 702.2 N, respectively). Based upon our results, maximizing screw diameter does not appear to be critical for fixation rigidity and may increase the risk of intraoperative or postoperative fracture.     

Bioabsorbable expansion bolt fixation in anterior cruciate ligament reconstruction

The current study evaluated initial fixation strength of a bioabsorbable expansion bolt compared with interference screw fixation in anterior cruciate ligament reconstruction using a bone-patellar tendon-bone graft. Thirty calf tibial plateaus with adjacent patella and extensor ligaments were used. Bioabsorbable poly-L-lactide interference screws were used for graft fixation in Group I, titanium screws in Group II, and bioabsorbable poly-DL-lactide expansion bolts were used in Group III. The mean force-to-failure (+/- standard deviation) in the three groups was 487 +/- 205 N, 713 +/- 218 N, and 594 +/- 224 N, respectively. The differences between Groups I and II were significant. No statistical differences were found regarding stiffness. Graft damage was significantly less in Group III compared with screw fixation. The fixation concept of an expansion bolt shows similar fixation strength and less graft damage compared with the established interference screw fixation. Because of the total absence of torque forces in contrast to bioabsorbable screws, the risk of implant breakage is minimized.     

锁定重建接骨板治疗髋臼横行骨折的生物力学研究

背景：髋臼横形骨折治疗较为困难,常采用内固定的治疗方法。近年来有学者尝试采用锁定重建接骨板,但对其的研究报道较少。 目的：比较4种不同锁定重建接骨板后方入路内固定方式治疗髋臼横行骨折的生物力学稳定性。 方法：采用成人防腐标本10具,制成髋臼横行骨折模型20个,随机分为4组,每组5个标本。A组：重建接骨板两端各固定3枚螺钉。B组：重建接骨板两端各固定3枚螺钉及距骨折线最近的两侧螺孔各1枚螺钉。C组：锁定重建接骨板两端各3枚单皮质螺钉。D组：锁定重建接骨板两端各3枚单皮质螺钉及距骨折线最近的两侧螺孔各1枚单皮质螺钉。行轴向的加载实验,记录内固定失效时最大负载和轴向刚度。 结果：A、B、C、D组所能承受的最大负载分别为（180.60±11.781）N、（240.80±7.981）N、（243.80±11.755）N和（438.00±23.227）N;轴向刚度分别为（95.21±6.32）N/mm、（123.47±23.95）N/mm、（126.39±18.52）N/mm和（227.35±13.74）N/mm。除B、C两组数据比较无统计学差异（P〉0.05）,其余各组的最大负载和轴向刚度差异均有统计学意义（〈0.05）。 结论：髋臼横形骨折采用接骨板后方入路内固定时,锁定重建接骨板固定的稳定性优于重建接骨板,而且距骨折线最近的两侧螺孔给予螺钉固定能增强内固定的稳定性。     

Biomechanical stability of bioabsorbable screws for fixation of acetabular osteotomies

The purpose of this study was to compare the biomechanical stability of triple innominate osteotomies fixed with either bioabsorbable or stainless steel screws. Triple innominate osteotomies were performed on composite hemipelves and fixed with either three 4.5-mm bioabsorbable screws or three stainless steel 4.5-mm screws. Two screws were placed from the iliac wing into the acetabular fragment, and 1 screw was placed from below the acetabular fragment into the iliac wing. Eight specimens for each screw type were biomechanically tested in an anatomical position (replicating weight bearing) and in a flexed and abducted position (replicating spica cast positioning). Specimens were cyclically loaded between 10 and 450 N to simulate the hip contact force in this population. Lower screws were then removed, and specimens were tested under identical conditions. Fragment displacement (mm) and construct stiffness (N/mm) were compared with a 2-way analysis of variance (P < 0.05). There were no significant differences between materials for fragment displacement or construct stiffness. Anatomical position showed significantly less displacement than spica position for both materials. Initial displacement in the spica position was significantly less during lower loads for stainless steel fixation. Bioabsorbable screws demonstrate comparable biomechanical stability to stainless steel screws in anatomical and spica positions at physiological loads. Flexion and abduction of the femur adversely affect the stability of the construct for both materials. Bioabsorbable screws behave similarly to steel screws when stabilizing triple innominate osteotomies and would have the advantage of not requiring a second surgery for screw removal. Confirmation of biocompatibility should be completed before widespread clinical application.     

Tendon transfer fixation: comparing a tendon to tendon technique vs. bioabsorbable interference-fit screw fixation

Tendon transfer techniques in the foot and ankle are used for tendon ruptures, deformities, and instabilities. This fresh cadaver study compares the tendon fixation strength in 10 paired specimens by performing a tendon to tendon fixation technique or using 7 x 20-25 mm bioabsorbable interference-fit screw tendon fixation technique. Load at failure of the tendon to tendon fixation method averaged 279N (Standard Deviation 81N) and the bioabsorbable screw 148N (Standard Deviation 72N) [p = 0.0008]. Bioabsorbable interference-fit screws in these specimens show decreased fixation strength relative to the traditional fixation technique. However, the mean bioabsorbable screw fixation strength of 148N provides physiologic strength at the tendon-bone interface.     

Magnesium-based bioabsorbable screw fixation for hallux valgus surgery – A suitable alternative to metallic implants

BackgroundThe primary aim of this pilot study was to prospectively evaluate outcomes of the MgYREZr bioabsorbable screw in the setting of hallux valgus corrective surgery. The secondary aim was to compare the outcomes against a control group treated with conventional titanium screws.MethodsA consecutive series of patients with hallux valgus deformity (n = 24) underwent forefoot reconstruction surgery with a scarf osteotomy to the first metatarsal using MgYREZr screws. Functional scores, radiological outcomes, and complication profile were recorded over 12 months. Results were compared against a control group of patients (n = 69) using titanium alloy screws.ResultsAt 1-year post-operative, both functional and radiological outcomes showed significant improvements. Compared to the control group, there was no significant difference in functional outcomes, yet radiological improvements were significantly better in the control group.ConclusionsThe MgYREZr bioabsorbable screw is a suitable alternative to titanium alloy screws for hallux valgus corrective surgery.     

Biomechanical properties of bioabsorbable cannulated screws for surgical fixation of dislocated epiphysiolysis capitis femoris

Bioabsorbable materials are well suited for fixation of slipped capital femoral epiphysis (SCFE) as they are resorbable, compatible with magnetic resonance imaging, and well tolerated by the pediatric population. We compared cannulated 4.5-mm bioabsorbable screws made of self-reinforced polylevolactic acid (SR-PLLA) to cannulated 4.5-mm steel and titanium screws for their resistance to shear stress and ability to generate compression in a polyurethane foam model of SCFE fixation. The maximum shear stress resisted by the three screw types was similar (SR-PLLA 371 +/- 146, steel 442 +/- 43, titanium 470 +/- 91 MPa, NS). The maximum compression generated by both the SR-PLLA screw (68.5 +/- 3.3 N) and the steel screw (63.3 +/- 5.9 N) was greater than that for the titanium screw (3.0 +/- 1.4 N, p < 0.05). These data suggest that cannulated SR-PLLA screws have sufficient biomechanical strength to be used in the treatment of SCFE.     

Locking plate fixation of humeral head fractures with a telescoping screw. A comparative biomechanical study versus a standard plate

ObjectivesLocking plate fixation of humeral head fractures bares the risk of glenohumeral screw penetration. In order to circumvent this problem it is recommended to insert shorter locking screws having at least a 6 mm distance to the humeral head cortex. This in turn may reduce fixation stability and may lead to early varus displacement. One second frequent failure mechanism is cranial displacement of the greater tubercle. The study evaluates the biomechanical properties of a locking plate employing an additional telescoping screw that may enhance resistance to varus displacement. Screw in screw fixation of the greater tubercle may reduce the rate of cranial displacement.MethodsIn four paired fresh-frozen human cadaver humeri (age > 70 years) a Neer IV/3 fracture was created with a 5 mm osteotomy gap simulating metaphyseal comminution. Limbs were randomly assigned to receive plate fixation with an additional telescoping screw (Humerus Tele Screw: HTS) and on the contralateral limb Philos plate fixation before biomechanical evaluation (MTS-Bionix 858.2). Standard locking screws were placed in both groups 6 mm below the radiological head circumference; the telescoping screw was placed in the subchondral layer. The greater tubercle was fixed with an additional screw in both techniques, in the HTS group the screw was anchored in the sleeve of the telescrew (screw in screw fixation).FindingsFixation stability with a mean stiffness of 300.9 ± 28.8 N/mm in the HTS plate group proved to be significantly higher than in the Philos plate group (184.2 ± 23.4 N/mm; p = 0.006). The HTS plate also resisted higher loads in terms of fixation failure with loss of reduction at 290 ± 58.6 N in comparison to 205 ± 8.6 N for the Philos plate (p = 0.2). Displacement of the greater tubercle occurred in no case of the HTS plate group and in two out of four cases in the Philos plate group.InterpretationThe HTS plate provides high fixation stability in an in vitro humeral head fracture model and securely prevents displacement of the greater tubercle.     

Biomechanical testing of bioabsorbable cannulated screws for slipped capital femoral epiphysis fixation

This study compared cannulated 4.5-mm bioabsorbable screws made of self-reinforced poly-levolactic acid to cannulated 4.5-mm steel and titanium screws for resistance to shear stress and ability to generate compression in a polyurethane foam model of slipped capital femoral epiphysis fixation. The maximum shear stress resisted by the three screw types was similar (self-reinforced poly-levolactic acid 371 +/- 146 MPa, steel 442 +/- 43 MPa, and titanium 470 +/- 91 MPa). The maximum compression generated by both the self-reinforced poly-levolactic acid screw (68.5 +/- 3.3 N) and the steel screw (63.3 +/- 5.9 N) was greater than that for the titanium screw (3 +/- 1.4 N, P <.05). These data suggest cannulated self-reinforced poly-levolactic acid screws can be used in the treatment of slipped capital femoral epiphysis because of their sufficient biomechanical strength.     

胫骨平台塌陷性骨折克氏针网状固定的生物力学评价

目的：评价采用克氏针束网状支撑固定治疗胫骨平台塌陷性骨折的生物力学性能。方法：在自行设计的骨折模型上,分别用8枚1．5mm克氏针网状固定和2枚3．5mm皮质骨螺钉固定,分别进行面压缩试验和点压缩试验,对这两种固定方式在最大抗压缩力、固定强度等方面进行生物力学评价。结果：面压缩试验中,平均最大抗压缩力,螺钉固定为（1925．31±444．26）N,克氏针束网状固定为（1609．62±277．72）N;平均最大固定强度,螺钉固定为（2．28±0．53）N／mm2,克氏针束网状固定为（1．90±0．33）N／mm2,两种固定方式生物力学性能接近（P〉0．05）;在点压缩试验组中平均最大抗压缩力,螺钉固定为（411．13±233．88）N,克氏针束网状固定为（1105．58±290．66）N;平均最大固定强度,螺钉固定为（2．66±1．52）N／mm2,克氏针束网状固定为（7．18±1．89）N／mm2,网状固定明显具有生物力学优势（P〈0．01）。结论：克氏针网状支撑固定胫骨平台骨折,对骨折施行生物学固定,固定牢靠。     

Treatment of patellar fractures using bioresorbable forged composites of raw particulate unsintered hydroxyapatite/poly-L-lactide cannulated screws and nonabsorbable sutures

BackgroundForged composites of raw particulate unsintered hydroxyapatite/poly-L-lactide (F-u-HA/PLLA) implants are widely used in surgeries because they possess high mechanical strength, bioactivity, and radio-opacity. We previously reported that F-u-HA/PLLA implants were useful for treating lateral tibial condylar, lateral humeral condylar, and ankle fractures. The study aim was to investigate the efficacy of F-u-HA/PLLA cannulated screws and FiberLoop® for treating transverse patellar fractures.MethodsFrom April 2013 to February 2019, 15 patients with transverse patellar fractures were treated with F-u-HA/PLLA cannulated screws and FiberLoop® as follows: Open reduction and internal fixation (ORIF) were performed with two F-u-HA/PLLA cannulated screws and a temporary fixation Kirshner wire (K-wire). Three No. 2 FiberLoops® were inserted into these two screw holes and the K-wire hole for temporary fixation. All patients were allowed to full weight-bearing gaits using a knee brace. Knee range of motion exercise was initiated on postoperative day 1. Knee flexion was restricted to ≤90° for 1 month postoperatively. Radiograph was performed to evaluate fracture healing, screw breakage, reduction loss, and screw radio-opacity. Clinical outcomes and postoperative complications were assessed.ResultsThe average follow-up was 16.0 months. All fractures were successfully united. Screw breakage, reduction loss, osteolysis, and radiolucent zones around the screws were not observed at the final radiographic follow-up. All F-u-HA/PLLA screw shadows were observed during the follow-up. The average range of flexion and extension were 132.0° and −2.7°, respectively. No patients experienced deep infection episodes, late aseptic tissue reactions, or foreign body reactions postoperatively. No patients complained of pain at the final follow-up. All patients returned to their pre-injury work level and activities of daily living.ConclusionOur results strongly suggest that ORIF with F-u-HA/PLLA screws and FiberLoop® could be an alternative treatment option for transverse patellar fractures.     

Dual pitch screw design provides equivalent fixation to upsized screw diameter in revision pedicle screw instrumentation: a cadaveric biomechanical study

Background ContextThere are situations that require the replacement of pedicle screws. They are often exchanged when loose or broken or to accommodate a different sized rod or pedicle screw system. Traditionally, pedicle screws are replaced by up-sizing the core diameter until an interference fit is obtained. However, this method carries a risk of pedicle screw breach.PurposeTo determine if dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch throughout the pedicle, allows for in-line screw revision without upsizing screw diameter.Study DesignCadaveric biomechanical StudyPatient SampleNot applicableOutcome MeasuresNot applicableMethodsPedicle screws were tested in the lumbar vertebrae from eleven cadavers. Standard pitch 5.5 mm screws were inserted and loaded using a "break-in" protocol. Screws were removed and replaced with one of four screw types: 5.5 mm Standard Pitch, 5.5 mm Dual Pitch, 6.0 mm Standard Pitch, or 6.0 mm Dual Pitch. Failure testing was done using a stepwise increasing cyclic loading protocol for 100 cycles at each increasing load level. The loading consisted of a combined axial and bending load simulating the load seen by the most inferior screw.ResultsFailure was consistent, with the tip of the screw displacing inferiorly into the vertebral body while simultaneously pulling out. Failure strength was lowest in the 5.5mm Standard (135.8±29.4N) followed by 6.0mm Standard (141.8±38.6N), 5.5mm Dual (158.1±53.8N), and 6.0mm Dual (173.6±52.1N, p=.023). There was no difference in the failure strength between the 5.5mm Dual and 6.0mm Standard. Lumbar level (p=.701) and donor spine (p=.062) were not associated with failure strength.ConclusionsAfter pedicle screw removal, screws with a larger core diameter or with a dual pitch have similar failure strengths. Dual pitch screws may allow for in-line revision of screws without upsizing screw diameter, minimizing the risk of pedicle breach or fracture.Clinical SignificanceDual pitch screws, with cancellous pitch in the vertebral body and cortical pitch through the pedicle, allows for in-line revision of pedicle screws without upsizing screw diameter; reducing the risk of pedicle breach or fracture when exchanging screws.     

Biomechanical evaluation of calcaneocuboid distraction arthrodesis: a cadaver study of two different fixation methods

Calcaneocuboid distraction arthrodesis can be used to treat stage 2 posterior tibial tendon dysfunction. Nonunion, graft resorption, and implant failure have been reported after this procedure. This study compared two of the most commonly used methods for fixation of calcaneocuboid distraction arthrodesis. Twelve pairs of cadaver feet underwent simulated calcaneocuboid distraction arthrodesis. One specimen in each pair was fixed with two crossed 3.5 mm cortical lag screws. The contralateral specimen was fixed with a cervical H-plate. The calcaneus was fixed and a load was applied to the plantar aspect of the cuboid at a rate of 5 mm/minute until joint separation of 3 mm or fracture occurred. The average applied load to failure at 1.0 mm of joint separation was 30.5 +/- 11.6 N for the crossed screws and 77.7 +/- 36.4 N for the cervical H-plate (p = 0.001). The average stiffness at 1.0 mm of joint separation was 27.5 +/- 10.9 N/mm for the crossed screws and 43 +/- 21.2 N/mm for the cervical H-plate (p = 0.036). The higher stiffness and load to failure may account for the decreased nonunion rate noted anecdotally by some surgeons with H-plate fixation over crossed screw fixation for calcaneocuboid distraction arthrodesis.     

Angle bisector method to determine the accurate angle for tibiofibular syndesmotic fixation: A validation study with 3D-printed anatomical models

PurposeThis study aimed to validate the angle bisector method on 3D-printed ankle models to reveal whether it aids in placing syndesmotic screws at an accurate trajectory that is patient- and level-specific and also not surgeon-dependent.MethodsDICOM data of 16 ankles were used to create 3D anatomical models. Then the models were printed in their original size and two trauma surgeons performed the syndesmotic fixations with the angle bisector method at 2 cm and 3.5 cm proximal to joint space. Afterward, the models were sectioned to reveal the trajectory of the screws. The photos of the axial sections were processed in a software to determine the centroidal axis which is defined as true syndesmotic axis and analyze its relationship with the screws inserted. The angle between the centroidal axis and syndesmotic screw was measured by two-blinded observers 2 times with 2 weeks interval.ResultsThe average angle between the centroidal axis and screw trajectory was 2.4° ± 2° at 2 cm-level and 1.3° ± 1.5° at 3.5 cm-level, indicating a reliable direction with minimal differences at both levels. The average distance between fibular entry points of the centroidal axis and screw trajectory was less than 1 mm at both levels indicating that the angle bisector method can provide an excellent entry point from fibula for syndesmotic fixation. The inter- & intra-observer consistencies were excellent with all ICC values above 0.90.ConclusionThe angle bisector method provided an accurate syndesmotic axis for implant placement which is patient- & level-specific and not surgeon-dependent, in 3D-printed anatomical ankle models.