Radiographic predictors of symptomatic locking screw removal after treatment of tibial fractures with intramedullary nails

IntroductionThe purpose of this study was to determine the radiographic parameters associated with symptomatic locking screw removal after intramedullary tibial nail insertion. Our hypothesis was that locking screws located closer to joints and those extending longer than the width of the bone result in more symptomatic implant removal.MethodsWe conducted a retrospective cohort study at our Level I trauma center. Seventy-five patients underwent surgical removal of symptomatic locking screws from 2007 to 2014 and were compared with a control group of 122 patients from the same time period who did not undergo symptomatic locking screw removal. Our main outcome measures were radiographic and demographic factors associated with implant removal.ResultsMultivariable regression indicated that a proximal locking screw that started anterolateral and was directed posteromedial was the strongest radiographic predictor of symptomatic removal (odds ratio [OR], 2.83; p = 0.03). An Injury Severity Score <11 (OR, 3.10; p < 0.001) and a body mass index <25 kg/m² (OR, 2.15; p = 0.02) were also associated with locking screw removal. The final prediction model discriminated patients requiring symptomatic locking screw removal with moderate accuracy (area under the receiver operating characteristic curve = 0.73).ConclusionsThe strongest radiographic predictor for symptomatic locking screw removal after tibial nail insertion was the direction of the most proximal locking screw. In contrast to previous research on retrograde femoral nails, tibial locking screws that were closer to the joints were not associated with an increased likelihood of symptomatic screw removal. Clinicians can use these data to help counsel patients regarding the likelihood of symptomatic screws and perhaps to help guide screw placement in cases with multiple options.     

A mathematical simulation of the tip-apex distance and the calcar-referenced tip-apex distance for intertrochanteric fractures reduced with lag screws

BackgroundAs a predictor of the risk of lag screw cutout, it was recommended that keeping tip-apex distance (TAD) < 25 mm and placing the screw centrally or inferiorly, but positioning the lag screw too inferiorly in the head would produce TAD > 25 mm. We aim to simulate various positions of the lag screw in the femoral head and identify whether 25 mm is a suitable cut-off value that favours all sizes of femoral heads with intertrochanteric fractures of the hip.MethodsUsing a general mathematical software, the positions of the screw tip points were simulated. The virtual anterior–posterior and lateral views were then visualised, and the locus of the screw tips was projected into a Cartesian coordinate system according to the TAD and calcar-referenced tip-apex distance (CalTAD) formulas. Each original virtual anterior–posterior and lateral image was zoomed and compiled to match a calculated average image. The screw tip points were recorded, traced and compiled into volumes which could be used to visualise the screw's movements and positioning within the femoral head. The extracted volumes were calculated when 10 mm < TAD < 25 mm and 10 mm < CalTAD < 25 mm, and the region where these two volumes overlapped was also calculated. Suitable positions for the screw tip were then assessed.ResultsFor the TAD calculation, the shape of the traced screw tip points had a pancake-like appearance, while the CalTAD plot produced a teardrop-shaped region. The volume ratios of TAD, CalTAD and overlapping region relative to the femoral head volume were respectively 3.51 ± 1.30%, 5.19 ± 1.62% and 2.64 ± 1.32%. The volumes of the traced TAD, CalTAD and overlapping regions increased slower than the volume of an idealised sphere.ConclusionPositioning the lag screw should address geometrical effects of both tip-apex distance and femoral head size, with an emphasis on measuring the position of the screw tip for the suitable zone by volume ratio. The previous 25 mm TAD cut-off value should be adjusted according to the individual femoral head size.     

Trochanteric entry femoral nails yield better femoral version and lower revision rates—A large cohort multivariate regression analysis

IntroductionIntramedullary nailing (IMN) has become the standard of care for the treatment of most femoral shaft fractures. Different IMN options include trochanteric and piriformis entry as well as retrograde nails, which may result in varying degrees of femoral rotation. The objective of this study was to analyze postoperative femoral version between three types of nails and to delineate any significant differences in femoral version (DFV) and revision rates.Materials & methodsOver a 10-year period, 417 patients underwent IMN of a diaphyseal femur fracture (AO/OTA 32A-C). Of these patients, 316 met inclusion criteria and obtained postoperative computed tomography (CT) scanograms to calculate femoral version and were thus included in the study. In this study, our main outcome measure was the difference in femoral version (DFV) between the uninjured limb and the injured limb. The effect of the following variables on DFV and revision rates were determined via univariate, multivariate, and ordinal regression analyses: gender, age, BMI, ethnicity, mechanism of injury, operative side, open fracture, and table type/position. Statistical significance was set at p < 0.05.ResultsA total of 316 patients were included. Piriformis entry nails made up the majority (n = 141), followed by retrograde (n = 108), then trochanteric entry nails (n = 67). Univariate regression analysis revealed that a lower BMI was significantly associated with a lower DFV (p = 0.006). Controlling for possible covariables, multivariate analysis yielded a significantly lower DFV for trochanteric entry nails than piriformis or retrograde nails (7.9 ± 6.10 vs. 9.5 ± 7.4 vs. 9.4 ± 7.8°, p < 0.05). Using revision as an endpoint, trochanteric entry nails also had a significantly lower revision rate, even when controlling for all other variables (p < 0.05).ConclusionComparative, objective comparisons between DFV between different nails based on entry point revealed that trochanteric nails had a significantly lower DFV and a lower revision rate, even after regression analysis. However, this is not to state that the other nail types exhibited abnormal DFV. Translation to the clinical impact of a few degrees of DFV is also unknown. Future studies to more in-depth study the intricacies of femoral version may lead to improved technology in addition to potentially improved clinical outcomes.     

Finite element analysis of the effect of cannulated screw placement and drilling frequency on femoral neck fracture fixation

BackgroundPositioning of the implanted cannulated screw is paramount for stable femoral neck fracture fixation. To avoid overdrilling, the aim of this study is to determine the optimum configuration of three cannulated screws employed in femoral neck fracture fixation.MethodsUsing a CT scan from a 28 year old healthy male, several models of femoral neck fracture fixation were developed using finite element analysis. After drilling small holes (in either fixed or random patterns) for screw insertion, the mechanical stresses on the screws were compared for three fracture types.ResultsThe inverted isosceles triangle was found to be the best screw configuration. Using finite element analysis, the upper limit of drilling frequency and the maximum stress on the screws for 30°, 50°, and 70° drilling were 14, 16, and 19 times and 46.1 MPa, 61.9 MPa, and 51.0 MPa, respectively. The upper limit of drilling frequency and the maximum stress on the screws for subcapital type, transcervical type, and basicervical type were 14, 16, and 40 times and 24.7 MPa, 61.9 MPa, and 113.5 MPa, respectively.ConclusionsResults of this study had supported the use of the inverted isosceles triangle as the best screw configuration for femoral neck fracture fixation. Screw position, Pauwels angle, and drilling frequency can all affect the mechanical strength of femoral neck fracture fixation.     

Changes in the syndesmotic reduction after syndesmotic screw fixation for ankle malleolar fractures: One-year longitudinal evaluations using computer tomography

IntroductionTo evaluate time-dependent changes in the syndesmotic reduction after syndesmotic screw fixation and one year after screw removal for ankle malleolar fractures, and to assess whether the incidence of syndesmotic malreduction changes depending on the measurement method.MethodsWe assessed twenty patients who underwent syndesmotic screw fixation for ankle fractures. The syndesmotic screws were removed after six weeks of the fracture surgery. Syndesmotic reduction was assessed within two weeks of the fracture surgery and one year after the screw removal using the axial computer tomographic images. Side-to-side differences in the anterior and posterior tibiofibular distances, anteroposterior fibular translation, and fibular rotation were measured.ResultsThe mean anterior tibiofibular distance was 0.7 mm after syndesmotic fixation. It increased to 1.9 mm at one year after screw removal (p = 0.002). After syndesmotic fixation, four ankles had malreduction of the anterior tibiofibular distance, including three ankles with widening and one with overtightening. At one year, eight ankles had malreduction, all of whom had widening. The other measurement values did not change over time (0.1 mm vs. 0.6 mm for the posterior tibiofibular distance, 0.2 mm vs. 0.3 mm for the anteroposterior fibular translation, and 0.7 ° vs. 0 ° for the fibular rotation). The incidences of malreduction were significantly different depending on the definition of malreduction, ranging from 10% to 50% after syndesmotic fixation (p = 0.01) and from 20% to 60% at one year after screw removal (p = 0.02).ConclusionsThe anterior tibiofibular distance widened after one year of syndesmotic screw removal. The incidence of malreduction varied depending on the measurement method.     

Working length and proximal screw constructs in plate osteosynthesis of distal femur fractures

BackgroundThe study purpose is to evaluate the working length, proximal screw density, and diaphyseal fixation mode and the correlation to fracture union after locking plate osteosynthesis of distal femoral fractures using bridge-plating technique.MethodsA four-year retrospective review was performed to identify patients undergoing operative fixation of distal femur fractures with a distal femoral locking plate using bridge-plating technique for the metadiaphyseal region. Primary variables included fracture union, secondary surgery for union, plate working length, and diaphyseal screw technique and configuration. Multiple secondary variables including plate metallurgy and coronal plane fracture alignment were also collected.ResultsNinety-six patients with distal femur fractures with a mean age 60 years met inclusion criteria. None of the clinical parameters were statistically significant indicators of union. Likewise, none of the following surgical technique parameters were associated with fracture union: plate metallurgy, the mean working length, screw density and number of proximal screws and screw cortices. However, diaphyseal screw technique did show statistical significance. Hybrid technique had a statistically significant higher chance of union when compared to locking (p = 0.02). All proximal locking screw constructs were 2.9 times more likely to lead to nonunion.ConclusionsPlating constructs with all locking screws used in the diaphysis when bridge-plating distal femur locking plates were 2.9 times more likely to incur a nonunion. However, other factors associated with more flexible fixation constructs such as increased working length, decreased proximal screw number, and decreased proximal screw density were not significantly associated with union in this study.     

Risk factors for cut-out of double lag screw fixation in proximal femoral fractures

ObjectiveWe assessed factors associated with cut-out after internal fixation of proximal femoral fractures using double lag screw nails.DesignRetrospective cohort study.SettingA university hospital.Patients and methodsPatients with non-pathological intertrochanteric femur fractures and a minumum 90 days follow-up who underwent internal fixation with dual lag screw nails were included. Potential risk factors for lag screw cut-out investigated by our study were: age, gender, body mass index, comorbidities (American Society of Anesthesiologists [ASA] classification), type of fracture (AO/OTA classification), fracture stability, side, operation time, implant length, reduction quality, tip-apex distance (TAD), and lag screw configuration. Logistic regression was used to investigate potential predictors of screw cut-out.ResultsEighty-five of the 118 patients with hip fractures treated between February 2010 and November 2013 at our institution met the inclusion criteria for the study. Fifty-eight patients were female (68.2%), mean age was 77.4 (range: 50–95 years), mean follow up was 380 days (range: 150 days-2.5 years), and cut of was observed in 9 patients (10.5%). The following variables identified through univariate analysis with p < 0.2 were included in multivariant logistic regression model: age, side, reduction quality, implant length, TAD and ASA score. Only TAD (p = 0.003) was found to be significant in the multivariant model.ConclusionsOur study confirmed that risk factors for cut-out with single-lag screw devices are also applicable to dual-lag screw implants. We found that TAD was a significant factor for cut-out in dual-lag screw implants. Thus, screw cut-out can be minimized by optimizing screw position.     

“Anterior subcutaneous pelvic internal fixator (INFIX), Is it safe?” A cadaveric study

IntroductionAnterior pelvic internal fixator (INFIX) is used to treat unstable pelvic ring injuries. Nerve injury complications with this procedure have been reported.ObjectivesThis anatomic study attempted to identify structures at risk after application of INFIX.Materials and methodsINFIX was applied in fifteen fresh, frozen, anatomical specimens using polyaxial pedicular screws and subcutaneous rods. Surgical dissection was done to identify the structures at risk including the femoral nerve (FN), femoral artery (FA), femoral vein (FV) and the lateral femoral cutaneous nerve (LFCN) related to which are potentially affected by the implant.ResultsAll structures at risk were closer to the rod than to the pedicular screw. Measurements were made between the rod and the structures at risk. The LFCN was an average of 13.49 ± 1.65 mm (95% CI 12.871–14.103) from the lateral end of the rod. The FN was an average of 12.43 ± 3.42 mm (95% CI 11.151–13.709), the FA was an average of 12.80 ± 3.67 (95% CI 11.430–14.173) and the FV was an average of 13.48 ± 3.73 (95% CI 12.082–14.871) below the rod. No direct compression of the rod to the structure at risk was observed.ConclusionsThe femoral nerve is the structure most at risk of compression by the INFIX rod. Careful surgical technique is required in every step of this surgery. We suggest using polyaxial screws and recommend that during screw insertion the surgeon should leave some space between the screw and rectus fascia. The the rod should be trimmed as short as possible to reduce LFCN irritation.     

Augmentation by cerclage wire improves fixation of vertical shear femoral neck fractures—A biomechanical analysis

BackgroundFemoral neck fractures in young individuals are typically vertical shear fractures. These injuries are difficult to stabilize due to a significant varus displacement force across the hip with weight bearing. The purpose of this study was to evaluate the biomechanical stability offered by the addition of an augmented wire to conventional inverted triangle triple screw fixation for stabilizing vertical shear femoral neck fracture.MethodsSixteen medium 4th-generation synthetic composite femurs (Sawbones Pacific Research Laboratories, Vashon, WA) were divided into two groups. Vertical osteotomy was performed to mimic Pauwels III femoral neck fracture. Group A (n = 8) was fixed with three parallel 6.5-mm cannulated screws (Stryker) with washer in inverted triangle configuration. In group B (n = 8), all the screws were set using methods identical to group A, with the addition of the cerclage wire. Both groups were tested with nondestructive axial compression test at 7 and 25 ° of valgus stress, respectively. Then axial cyclic loading test with 1000 N was applied for 1000 cycles, and interfragmentary displacement was measured with Fastrak magnetic tracking system (Polhemus, Colchester, VT, USA). Finally, destructive axial compression test was conducted at 7°of valgus stress.ResultsAxial stiffness showed that group B had a 66% increase (879 N/mm vs. 1461 N/mm, P < 0.01) at 7° valgus and a 46% increase (1611 N/mm vs. 2349 N/mm, P < 0.01) at 25° valgus in comparison with group A. Interfragmentary fracture displacement after cyclic loading was significantly less for group B compared with group A (0.34 vs 0.13 mm, P = 0.0016). For axial failure load, there was 42% increase in group B compared with group A (2602 N/mm vs. 3686 N/mm, P = 0.0023).ConclusionsOur study demonstrates that the addition of a cerclage wire to inverted triangle triple screws provides substantial improvement in mechanical performance regarding fixation of vertically oriented femoral neck fractures when compared with the conventional construct. Our study provides support from a mechanical analysis perspective for the reported clinical usefulness of the cerclage wire.     

Distal locking in short hip nails: Cause or prevention of peri-implant fractures?

ObjectivesThe most common cause of femoral fractures after osteosynthesis of trochanteric fractures with short nails is weakening of the femoral cortex via distal locking and stress concentrations at the tip of the nail. The aim of the study was to verify whether the incidence of peri-implant fractures is dependent upon the distal locking technique.MethodsWe prospectively analysed a group of 849 pertrochanteric fractures (AO/ASIF 31-A1 + 2) managed with short nails from 2009 to 2013. Unlocked nailing was performed in 70.1% and distal dynamic locking was performed in 29.9%. The mean age was 82.0 years. Peri-implant fractures were divided into 3 groups according to the height of the fracture in relation to the tip of the nail.ResultsIn total 17 fractures (2.0%) were detected. One peri-implant fracture occurred after locked nailing, whereas 16 cases occurred after unlocked nailing (p = 0.037). Patients without distal locking had an 85.7% greater risk of peri-implant fracture. Fractures of the proximal femur (Type I) occurred significantly earlier than fractures at the tip of the nail (Type II) (p = 0.028).ConclusionUnlocked nails do not guarantee sufficient stability. Distal locking serves to prevent postoperative femoral fractures. We recommend the routine use of distal locking when utilizing short nails.     

Fixation of displaced femoral neck fractures in young adults: Fixed-angle devices or Pauwel screws?

BackgroundWe sought to compare the incidence of complications after fixation of displaced femoral neck fractures in young adults treated with fixed-angle devices versus multiple cancellous screws and a trochanteric lag screw (Pauwel screw).MethodsWe conducted a retrospective cohort study at a level I trauma centre. Sixty-two skeletally mature patients (age range, 16–60 years) with displaced femoral neck fractures were included in the study. Forty-seven were treated with a fixed-angle device (sliding hip plate with screw or helical blade) and 15 with multiple cancellous screws placed in a Pauwel configuration. The main outcome measure was postoperative complication of osteonecrosis or nonunion treated with a surgical procedure.ResultsSignificantly fewer failures occurred in the fixed-angle group (21%) than in the screws group (60%) (p = 0.008). Osteonecrosis was rare in the fixed-angle group, occurring in 2% of cases versus 33% of cases in the screws group (p = 0.002). Consistent with previous studies, good to excellent reductions were associated with a failure rate of 25% and fair to poor reductions were associated with a failure rate of 55% (p = 0.07). The best-case scenario of a good to excellent reduction stabilised with a fixed-angle device yielded a success rate of 85%.ConclusionIn young patients with displaced high-energy femoral neck fractures, fixed-angle devices resulted in fewer treatment failures than did Pauwel screws.     

Impact of cement-augmented condylar screws in locking plate osteosynthesis for distal femoral fractures — A biomechanical analysis

IntroductionCompromised bone quality and the need for early mobilization continue to lead to implant failure in elderly patients with distal femoral fractures. The cement augmentation of screws might facilitate improving implant anchorage. The aim of this study was to analyse the impact of cement augmentation of the condylar screws on implant fixation in a human cadaveric bone model.Material and methodsTen pairs of osteoporotic femora (mean age: 90 years, range: 84–99 years) were used. A 2-cm gap osteotomy was created in the metaphyseal region to simulate an unstable AO/OTA 33-A3 fracture. All specimens were treated with a polyaxial locking plate. Specimens randomly assigned to the augmented group received an additional cement augmentation of the condylar screws using bone cement. A servohydraulic testing machine was used to perform incremental cyclic axial loading using a load-to-failure mode.ResultsAll specimens survived at least 800 N of axial compressive force. The mean compressive forces leading to failure were 1620 N (95% CI: 1382–1858 N) in the non-augmented group and 2420 N (95% CI: 2054–2786 N) in the group with cement-augmented condylar screws (p = 0.005).Deformation with cutting out of the condylar screws and condylar fracture were the most common reasons for failure in both groups. Whereas axial stiffness was comparable between both osteosyntheses (p = 0.508), significant differences were observed for the plastic deformation of the constructs (p = 0.014).ConclusionThe results of the present study showed that the cement augmentation of the condylar screws might be a promising technique for the fixation of distal femoral fractures in elderly patients with osteoporotic bones.     

Defining the pubic symphysis angle with respect to the coronal plane — Clinical and biomechanical considerations

BackgroundFixation strength of constructs placed across the pubic symphysis after injury is dependent on screw length, maximisation of which requires knowledge of the bony anatomy. The aim of this study was to describe the ideal angle of drilling to achieve maximal safe screw placement within the pubic body. Furthermore, the influences of age and gender on the skeletal topography were investigated.MethodsThree hundred CT scans of patients without pelvic injury were analysed to record the angle of the pubic body (APB) with respect to the coronal plane, and the depth of the pubic body (DPB) in the sagittal plane.ResultsMean APB and DPB were 54.69° and 55.35 mm, respectively. Females had a significantly higher mean APB than males (57.29° vs. 52.41°; p < 0.001), whereas males had a significant larger mean DPB (59.13 mm vs. 51.03 mm; p < 0.001). Age had no effect on the mean APB. Mean width of the pubic body at the base was 9.38 mm.ConclusionThe anatomy of this region is reliable in terms of angles and sizes; a drill angle of 55° with respect to the operating table will allow maximal screw length, which should be in the region of 55 mm. The mean width of the pubic body should allow for placement of a 3.5 or 4.5 mm diameter screw.     

Computational analysis of the safe zone for the antegrade lag screw in posterior column fixation with the anterior approach in acetabular fracture: A cadaveric study

ObjectiveThe fluoroscopically-guided procedure of antegrade posterior lag screw in posterior column fixation through anterior approach is technique-dependent and requires an experienced surgeon. The purpose of this study was to establish the safe zone for the antegrade posterior lag screw by using computational analysis.MethodThe virtual three-dimensional model of 178 hemi-pelvises was created from the CT data (DICOM format) by using Mimics^® program, and were used to measure the safe zone of antegrade lag screw fixation on the inner table of the iliac wing, and the largest diameter of cylindrical implant inside safe zone. The central point (point A) of the cylinder was assessed and was compared with the intersection point (point B) between the linea terminalis and the anterior border of the sacroiliac articulation.ResultsThe safe zone was triangular with an average area of 670.4 mm² (range, 374.8–1084.5 mm²). The largest diameter of the cylinder was a mean 7.4 mm (range, 5.0–10.0 mm). When height was under 156.3 cm, the diameter of the cylindrical implant was smaller than 7.0 mm (p < 0.001, regression coefficient = 0.09). The linear distance between points A and B was 32.5 mm (range, 19.2–49.3 mm). Point A was far enough away from the well-positioned anterior column plate to prevent collision between the two.ConclusionThe safe zone was shaped like a triangle, and was large enough for multiple screws. Considering the straight-line distance between points A and B, the central screw can be fixed without overlapping with the well-positioned anterior column plate at the point between holes 2 and 3.     

Biomechanical comparison of stability of tibiotalocalcaneal arthrodesis with two different intramedullary retrograde nails

BackgroundThe aim of the study was to compare the initial construct stability of two retrograde intramedullary nail systems for tibiotalocalcaneal arthrodesis (TTCF) (A3, Small Bone Innovations; HAN, Synthes) in a biomechanical cadaver study.MethodsNine pairs of human cadaver bones were instrumented with two different retrograde nail systems. One tibia from each pair was randomized to either rod. The bone mineral density was determined via tomography to ensure the characteristics in each pair of tibiae were similar. All tests were performed in load-control. Displacements and forces were acquired by the sensors of the machine at a rate of 64 Hz. Specimens were tested in a stepwise progression starting with six times ±125N with a frequency of 1 Hz for 250 cycles each step was performed (1500 cycles). The maximum load was then increased to ±250N for another 14 steps or until specimen failure occurred (up to 3500 cycles).ResultsAverage bone mineral density was 67.4 mgHA/ccm and did not differ significantly between groups (t-test, p = .28). Under cyclic loading, the range of motion (dorsiflexion/plantarflexion) at 250N was significantly lower for the HAN-group with 7.2 ± 2.3 mm compared to the A3-group with 11.8 ± 2.9 mm (t-test, p < 0.01). Failure was registered for the HAN after 4571 ± 1134 cycles and after 2344 ± 1195 cycles for the A3 (t-test, p = .031). Bone mineral density significantly correlated with the number of cycles to failure in both groups (Spearman-Rho, r > .69, p < 0.01).ConclusionsThe high specimen age and low bone density simulates an osteoporotic bone situation. The HAN with only lateral distal bend but two calcaneal locking screws showed higher stability (higher number of cycles to failure and lower motion such as dorsiflexion/plantarflexion during cyclic loading) than the A3 with additional distal dorsal bend but only one calcaneal locking screw. Both constructs showed sufficient stability compared with earlier data from a similar test model.Clinical relevanceThe data suggest that both implants allow for sufficient primary stability for TTCF in osteoporotic and consequently also in non-osteoporotic bone.Level of evidenceNot applicable, experimental basic science study.     

The use of interfragmentary positional screw in minimally invasive plate osteosynthesis for simple distal femur fractures in elderly patients: A retrospective,single-centre pilot study

IntroductionMinimally invasive plate osteosynthesis (MIPO) using locking plates has been used in distal femur fractures, but various problems, such as nonunion, malalignment, and implant failure, have been reported. Simple fractures sometimes have poorer outcomes than complex fractures. We studied elderly patients with simple fracture patterns who underwent open reduction followed by placement of a single positional screw to hold the reduced interfragmentary gap, and compared these cases with patients who underwent surgery using conventional MIPO techniques.Patients and methodsA retrospective analysis was conducted on 80 cases of patients with distal femur fractures and simple fracture patterns (33-A1, A2, and C1). The mean age was 74 (60–90) years, and the mean follow-up period was 14 (12–25) months. Group A included 40 patients who underwent conventional MIPO technique while Group B included 40 patients who had surgery using positional screws. Interfragmentary gaps in Group B were reduced using percutaneous reduction clamps, and cortical screws were inserted to sustain the reduction. Then, locking plates were inserted using conventional MIPO techniques.ResultsBony union was achieved in all 80 cases, mean initial callus formation was observed in 11 weeks (8–13 weeks), and radiological union was observed in 27 weeks (15–54 weeks). Time to initial callus formation was not different, but radiologic union was achieved in 30 weeks (18–54 weeks) for Group A and 25 weeks (15–41 weeks) for Group B (p = 0.006). No differences were seen in clinical function at 1 year (p = 0.580). Five cases of malalignment occurred in Group A (p = 0.021). The rate of union during the 1-year period was significantly higher in group B than in group A (p = 0.002).ConclusionsIn a distal femur fracture with a simple fracture pattern, using positional screws to sustain the reduced interfragmentary gap may achieve a more rapid union by reducing fracture gap. Though functional differences were not seen in follow-ups, patients can be expected to return to their normal lives earlier as union is achieved in a shorter time. Performing MIPO using positional screws to sustain the reduced interfragmentary gap after fracture reduction will be helpful in the treatment of simple femoral fracture.     

The biomechanical cost of variable angle locking screws

IntroductionVariable angle (VA) locking plates in fracture fixation surgery allow screws to be fastened to the plate within a conical “locus of vectors” in order to avoid existing prostheses, joint surfaces, or poor quality bone. Clinical failures of VA constructs in which screws have rotated at the plate/screw interface have been reported raising the concern that there may be a biomechanical cost for the increased flexibility that VA provides. The objective of this study was to test the mechanical properties of one commonly used VA locking mechanism with screws placed in both nominal and off–axis trajectories and compare these against the standard locking mechanism.MethodsVA locking screws were inserted into plates for distal femur fractures (VA Curved Condylar) at various angles (0° to 15° away from perpendicular). A control group of standard locking screws/plates was also tested. Maximum moment at the screw/plate interface and moment at two reference displacements were determined.ResultsVA screws locked perpendicular to the plate provided the greatest maximum moment and moment at the reference displacements when using the VA system, and demonstrated lower moments compared to standard locking screws/plates (p < 0.001). Based on linear regression, there was an average decrease of approximately 0.4 Nm screw-plate interface strength for every 1° increase in screw-plate angle (p < 0.001). Decreases (p<0.05) were discovered in both maximum moment and moment at the reference displacements for screws locked at 5° relative to those locked at 0°, 10° relative to 0°, and 15° relative to 10°.DiscussionStandard locking systems provided greater resistance to rotational failure at the screw/plate interface than variable angle locking systems. Variable angle systems provided the greatest resistance to rotation when the screw was inserted perpendicular to the plate. As the off-axis angle increased, the resistance to rotation at the screw/plate interface decreased almost linearly. It is unknown if these differences are clinically significant in an actual fracture construct, but recent reported failures in the distal femur suggest that they might be.ConclusionSurgeons should weigh the risks and benefits of VA systems and attempt to minimize the off-axis angle magnitude when VA systems are selected.     

Biomechanical comparison of suture-button,bioabsorbable screw,and metal screw for ankle syndesmotic repair: A meta-analysis

BackgroundTo compare biomechanically metal screw fixation to suture-button or bioabsorbable screw fixation for ankle syndesmotic injuries.MethodsA literature search of the comparison studies in Pubmed and Google Scholar was conducted. The biomechanical outcomes of interest were syndesmotic stability in the coronal, sagittal, and axial planes as well as torque and rotation at failure.ResultsA total of 11 cadaveric studies were included. In the suture-button group, coronal displacement (MD 1.72 mm, p = 0.02) and sagittal displacement (MD 2.65 mm, p = 0.0003) were increased relative to the metal screw group. In contrast, no difference was found with axial rotation (MD 0.35 degrees, p = 0.57). Bioabsorbable screws exhibited equivalent failure torque (MD ?3.04 Nm, p = 0.53) and rotation at failure (MD 3.77 degrees, p = 0.48) in comparison to metal screws.ConclusionsSuture-button provide less rigidity when compared to metal screw fixation. They afford flexible syndesmotic micromotion which may more closely resemble a physiological state and be helpful for ligament healing. Bioabsorbable screws demonstrate similar mechanical strength properties to metal screws.     

A sliding hip screw augmented with 2 screws is biomechanically similar to an inverted triad of cannulated screws in repair of a Pauwels type-III fracture

ObjectivePauwels III femoral neck fractures are highly unstable. These fractures are commonly treated with three cannulated screws or sliding hip screw (SHS) implants, however high rates of non-union persist. A hybrid SHS construct has recently been proposed. The objective of the study was to compare this construct to the familiar inverted triad of cannulated screws and to a single SHS.MethodsFourth generation biomechanical femur analogs were used to create a highly repeatable injury model. The hybrid SHS construct contained a SHS with two superior cannulated screws in an inverted triangle configuration. Eight samples for each construct were biomechanically evaluated and the results compared using ANOVA (p < 0.05).ResultsThe cannulated triad and hybrid SHS provided similar stiffness and fracture gap motion. The single SHS exhibited significantly lower stiffness and larger fracture plane diastasis than either the inverted triangle of cannulated screws or hybrid SHS (p < 0.05). None of the constructs exhibited catastrophic failure during cyclic loading nor under loading up to 2.5 times body weight.ConclusionsThe single SHS provided the least stable fracture fixation, while the inverted triad and hybrid SHS constructs were mechanically similar. The fracture repair simulated here illustrates how these repairs have the potential to return near pre-fracture strength in ideal conditions with young, healthy bone. However; in clinical situations where comminution impairs load transfer through the cortices the hybrid SHS may be the most favorable option.     

Accurate fixation of plates and screws for the treatment of acetabular fractures using 3D-printed guiding templates: An experimental study

ObjectiveTo investigate the feasibility of the use of 3D-printed guiding templates for accurate placement of plates and screws for internal fixation of acetabular fractures.Methods3D models of the pelvises of 14 adult cadavers were reconstructed using computed tomography (CT). Twenty-eight acetabular fractures were simulated and placement positions for plates and screw trajectories were designed. Bending module was obtained by 3D cutting; guiding template was manufactured using 3D printing, and the plate was pre-bent according to the bending module. Plates and screws were placed in cadaveric pelvises using the guiding template, and 3D model was reconstructed using CT. The designed and real trajectories were matched using 3D registration including the coordinates (entry and exit points) of designed trajectory. The number of qualified points with different accuracy levels was compared using Chi-squared test.ResultsSixty-four plates and 339 screws were placed with no cortical breach. The absolute difference of the X, Y, and Z coordinates between the designed and real entry points were 0.52 ± 0.45, 0.43 ± 0.36, and 0.53 ± 0.44 mm, respectively. The corresponding values for the exit points were 0.83 ± 0.67, 1.22 ± 0.87, and 1.26 ± 0.83 mm, respectively. With an accuracy degree ≥1.9 mm for the entry points and ≥3.8 mm for the exit points, there was no significant difference between the designed and the real trajectories.ConclusionThe 3D-printed guiding template helped achieve accurate placement of plates and screws in the pelvis of adult cadavers.