Far cortical locking can reduce stiffness of locked plating constructs while retaining construct strength

Computational comparison of different plating strategies in medial open-wedge high tibial osteotomy with lateral hinge fractures

Background

Lateral hinge fracture (LHF) is associated with nonunion and plate breakage in high tibial osteotomy (HTO). Mechanical studies investigating fixation strategies for LHFs to restore stability and avoid plate breakage are absent. This study used computer simulation to compare mechanical stabilities in HTO for different LHFs fixed with medial and bilateral locking plates.

Methods

A finite element knee model was created with HTO and three types of LHF, namely T1, T2, and T3 fractures, based on the Takeuchi classification. Either medial plating or bilateral plating was used to fix the HTO with LHFs. Furthermore, the significance of the locking screw at the combi hole (D-hole) of the medial TomoFix plate was evaluated.

Results

The osteotomy gap shortening distance increased from 0.53 to 0.76, 0.79, and 0.72 mm after T1, T2, and T3 LHFs, respectively, with medial plating only. Bilateral plating could efficiently restore stability and maintain the osteotomy gap. Furthermore, using the D-hole screw reduced the peak stress on the medial plate by 28.7% (from 495 to 353 MPa), 26.6% (from 470 to 345 MPa), and 32.6% (from 454 to 306 MPa) in T1, T2, and T3 LHFs, respectively.

Conclusion

Bilateral plating is a recommended strategy to restore HTO stability in LHFs. Furthermore, using a D-hole locking screw is strongly recommended to reduce the stress on the medial plate for lowering plate breakage risk.

Dynamic limited axial compression yields favorable functional outcomes in the fixation of Pauwels type-3 femoral neck fractures: A retrospective cohort study

PURPOSE

Pauwels type-3 femoral neck fractures are challenging injuries to manage with high rates of complications after internal fixation and no consensus has been reached regarding the optimal fixation construct. The current study aims to evaluate the effect of dynamic limited axial compression in parallel screws combined with medial buttress plate (SMBP) or lateral compression plate (LCP) fixation of Pauwels type-3 femoral neck fractures.

METHODS

We performed a retrospective analysis of 51 cases of Pauwels type-3 femoral neck fractures who were fixed by SMBP or LCP. Specifically, the screw fixing the femoral head in the buttress plate was omitted. Postoperative complications and functional outcomes were mainly studied.

RESULTS

With a mean follow-up of 19.9 months, the rate of neck shortening was higher in the LCP group than that in SMBP group (32.1% vs. 8.7%, p = 0.04). Neither nonunion nor avascular necrosis was observed in both groups. Good-to-excellent Harris hip score accounts for 95.2% in SMBP group and 89.3% in LCP group (p = 0.40). Moreover, older age, fracture comminution and compression plate fixation predispose to neck shortening.

CONCLUSION

Dynamic limited axial compression by SMBP or LCP fixation was effective to improve the functional outcome of patients with Pauwels type-3 femoral neck fractures.

Locking Screws With a Threaded Degradable Polymer Collar Reduce Construct Stiffness Over Time

OBJECTIVES

The stiffness of locking plates provide increased stability for early fracture healing but may limit late interfragmentary motion (IFM) necessary for secondary bone healing. An ideal plating construct would provide early rigidity and late flexibility to optimize bone healing. A novel screw plate construct utilizing locking screws with a degradable polymer locking mechanism is a dynamic option.

METHODS

Conventional locked plating constructs (group A) were compared with locking screws with a threaded degradable polymer collar before (group B) and after polymer dissolution (group C). Monotonic axial compression, monotonic torsion, cyclic axial load to failure, and IFM at the near and far cortices were tested on synthetic bone models.

RESULTS

One-way analysis of variance and post hoc Tukey-Kramer testing demonstrated similar axial stiffness in group A (873 ± 146 N/mm) and B (694 ± 314 N/mm) but significantly less stiffness in group C (379 ± 59 N/mm; F(2,15) = 9.12, P = 0.003). Groups A and B also had similar IFM, but group C had significantly increased IFM at both the near (F(2, 15) = 48.66, P = 2.76E-07) and far (F(2, 15) = 11.78, P = 0.0008) cortices. In cyclic axial load to failure, group A (1593 ± 233 N) and B (1277 ± 141 N) were again similar, but group C was significantly less (912 ± 256 N; F(2, 15) = 15.00, P = 0.0003). All failures were above the 500-N threshold seen in typical weight-bearing restrictions for fracture care. Torsional stiffness demonstrated significant differences between all groups (F(2, 15) = 106.64, P = 1.4E-09).

CONCLUSIONS

Use of locking plates with a degradable polymer collar show potential for in vitro construct dynamization. Future in vivo studies are warranted to assess performance under combined loading and the effects of decreasing construct stiffness during the course of bony healing.

Investigating the biomechanical function of the plate-type external fixator in the treatment of tibial fractures: a biomechanical study

Background

The design of an external fixator with the optimal biomechanical function and the lowest profile has been highly pursued, as fracture healing is dependent on the stability and durability of fixation, and a low profile is more desired by patients. The plate-type external fixator, a novel prototype of an external tibial fixation device, is a low profile construct. However, its biomechanical properties remain unclear. The objective of this study was to investigate the stiffness and strength of the plate-type external fixator and the unilateral external fixator. We hypothesized that the plate-type external fixator could provide higher stiffness while retaining sufficient strength.

Methods

Fifty-four cadaver tibias underwent a standardized midshaft osteotomy to create a fracture gap model to simulate a comminuted diaphyseal fracture. All specimens were randomly divided into three groups of eighteen specimens each and stabilized with either a unilateral external fixator or two configurations of the plate-type external fixator. Six specimens of each configuration were tested to determine fixation stiffness in axial compression, four-point bending, and torsion, respectively. Afterwards, dynamic loading until failure was performed in each loading mode to determine the construct strength and failure mode.

Results

The plate-type external fixator provided higher stiffness and strength than the traditional unilateral external fixator. The highest biomechanics were observed for the classical plate-type external fixator, closely followed by the extended plate-type external fixator.

Conclusions

The plate-type external fixator is stiffer and stronger than the traditional unilateral external fixator under axial compression, four-point bending and torsion loading conditions.

Clinical outcomes in periarticular knee fractures with flexible fixation using far cortical locking screws in locking plate: a prospective study

PURPOSE

Periarticular fractures around the knee joint are treated traditionally by locking plates which provide excellent stability but suppress callus formation. Far cortical locking (FCL) screws allow axial motion and enhance uniform callus formation. Our study aims to evaluate the outcomes of FCL screws in traditional locking plate in periarticular fractures of the knee.

METHODS

Thirty patients with periarticular fractures of the knee joint were operated with locking plate using FCL screws. All patients were evaluated clinically and radiographically using X-rays at 6, 12, 24 weeks, 1 year and with CT scan at 12-weeks follow-up.

RESULTS

The average time for complete union was 20 weeks in tibial fractures and 24 weeks in femur fractures. Average time to full weight bearing ambulation was 4.8 ± 0.93 weeks. One patient had delayed union in which union was complete after 9 months.

CONCLUSION

This study shows that FCL screws in locking plates allow uniform callus formation and fracture union with minimal complication rates.

A biomechanical comparison of two plating techniques in lateral clavicle fractures

BACKGROUND

Neer Type IIb lateral clavicle fractures typically lead to dislocation of the medial fragment. Therefore, most surgeons recommend surgical treatment for such a fracture pattern. The use of a locking compression plate with a lateral extension has produced satisfactory results in various studies over recent years. Double-plate fixation is a common technique in the treatment of complex distal radius fractures. The authors use this technique as a routine procedure in the treatment of Neer type IIb fractures. In this biomechanical testing study, the mechanical properties of the two techniques were compared.

METHODS

On 20 clavicles from fresh frozen cadavers a Neer Type IIb fracture-like osteotomy was performed. A cyclic loading test followed by a load-to-failure test was carried out. Parameters for statistical evaluation were the stiffness at cycles 1, 100 and 17,500 as well as the ultimate tensile load and the deformation at the point of failure.

FINDINGS

All specimens withstood the cyclic loading test without any noticeable damage. At cycles 100 and 17,500, the double-plate technique was less stiff. Failure loads were not significantly different from each other, but deformation at the point of failure was significantly greater for the double-plate technique.

INTERPRETATION

Both techniques provided sufficient fixation to the fracture site to endure the cyclic loading test, which is supposed to simulate an incident-free week postoperatively. In summary, the double-plate technique offers biomechanically a feasible alternative to the single-plate technique in lateral clavicle fractures of Neer Type IIb.

Radiographic Healing of Far Cortical Locking Constructs in Distal Femur Fractures: A Comparative Study With Standard Locking Plates

OBJECTIVES

To investigate the radiographic healing of far cortical locking (FCL) construct fixation in distal femur fractures compared with traditional locking plate (LP) constructs.

DESIGN

A retrospective cohort of 143 consecutive patients with 146 distal femur fractures.

SETTING

Level I trauma center.

PATIENTS/PARTICIPANTS

After excluding patients with OTA/AO type B fractures, referred nonunion cases, patients younger than 16 years, and patients with less than 24 weeks of follow-up, 69 patients with 70 total fractures were included for analysis.

INTERVENTION

AP and lateral knee radiographs were blinded to type of screws and individually reviewed by 3 orthopaedic trauma surgeons.

OUTCOME MEASUREMENTS

The modified RUST (mRUST) score was our primary outcome measure. mRUST scores were assigned at 6, 12, and 24 weeks and final follow-up based on AP and lateral radiographs and compared between FCL and LP groups as a tool for evaluating fracture healing. Secondary outcomes compared between FCL and LP included union rate and postoperative complications.

RESULTS

Statistically significant differences in mRUST scores were noted between FCL and LP groups at 6 weeks (P = 0.040), 12 weeks (P = 0.034), 24 weeks (0.044), and final follow-up (P = 0.048). There was no significant difference in union or specific complication rates between the 2 groups. The union rate was 90.5% and 82.1% for the FCL and LP groups, respectively, at final follow-up.

CONCLUSIONS

To our knowledge, this is the first comparative study between FCL and LP constructs. The FCL group was noted to have significantly higher mRUST scores at all periods indicating increased callus formation, but the differences seen were small and there were no differences in healing rates or complications between the 2 groups, thus bringing the clinical benefit of FCL into question. Further prospective study designs are needed to compare FCL with LP constructs and to investigate the role of interfragmentary motion on callus formation in distal femur fractures.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Plating System Design Determines Mechanical Environment in Long Bone Mid-shaft Fractures: A Finite Element Analysis

Purpose: Internal fixation device failure is rare but unavoidable. Fatigue-related mechanisms are responsible for most mechanical failures of orthopedic plates. Plate design needs to be optimized for both long fatigue life and bone healing. Only in this way can we reduce the occurrence of internal fixation failure. To address this issue, we aimed to provide a theoretical basis for improving the design of orthopedic plates. Material and Methods: The finite element method was used to conduct a computational investigation. Three groups of plate models were designed with varied working lengths and other elements. By fixing these plates to tibial mid-shaft fracture models, parameters of the mechanical environment around the fracture site were recorded and analyzed. Results: Plate working length, existence of holes within the working length, and plate length are important factors that influence the mechanical environment of the fracture site. The screw-bone interface is the weakest part in internal fixation failure. Fractures fixed by traditional plates that had holes in the working length have larger interfragmentary movement, and these plates have more severe stress concentration than plates without holes in the working length. Conclusions: We presented some suggestions for the plating system. First, partial weight bearing is recommended in the early postoperative period. Second, the working length of the plate does have an optimal range, depending on the fracture types. Finally, the hole within the working length should be removed to avoid stress concentration and facilitate fracture healing. Based on the findings from this study, recommendations can be developed to improve clinical practices and plating system design.

Importance of a moderate plate-to-bone distance for the functioning of the far cortical locking system

The far cortical locking (FCL) system, a novel bridge-plating technique, aims to deliver controlled and symmetric interfragmentary motion for a potential uniform callus distribution. However, clinical data for the practical use of this system are limited. The current study investigated the biomechanical effect of a locking plate/far cortical locking construct on a simulated comminuted diaphyseal fracture of the synthetic bones at different distance between the plate and the bone. Biomechanical in vitro experiments were performed using composite sawbones as bone models. A 10-mm osteotomy gap was created and bridged with FCL constructs to determine the construct stiffness, strength, and interfragmentary movement under axial compression, which comprised one of three methods: locking plates applied flush to bone, at 2 mm, or at 4 mm from the bone. The plate applied flush to the bone exhibited higher stiffness than those at 2 mm and 4 mm plate elevation. A homogeneous interfragmentary motion at the near and far cortices was observed for the plate at 2 mm, whereas a relatively large movement was observed at the far cortex for the plate applied at 4 mm. A plate-to-bone distance of 2 mm had the advantages of reducing axial stiffness and providing nearly parallel interfragmentary motion. The plate flush to the bone prohibits the dynamic function of the far cortical locking mechanism, and the 4-mm offset was too unstable for fracture healing.

Clinical effects and risk factors of far cortical locking system in the treatment of lower limb fractures

INTRODUCTION

This study aims to analyze clinical effects between far cortical locking (FCL) system and standard plating techniques in the treatment of lower limb fractures and identify potential preoperative risk factors for complications in patients treated with FCL system.

METHOD

We retrospectively analyzed 76 patients treated with FCL system (the study group) and 68 patients treated with standard plating techniques (the control group) between January 2014 and January 2017. Patients were followed up for a minimum of one year. Surgery-related complications, fixation features, fracture healing rates, the radiographic union scores, and knee functions (Kolment scores) were analyzed between the two groups in the study. Besides, we analyzed eight preoperative characteristics for surgery-related complications, including age, gender, presence of risk factors affecting bone healing, cause of injury, AO/OTA fracture classifications, facture sites, presence of open fractures, and presence of bone losses.

RESULTS

The distributions of baseline date were similar between the two groups (P＞0.05). The average number of FCL screws was 4.5 (range: 3-9) in the study group. The average time to union was 2.8 ± 0.9 months in the study group and 3.6 ± 1.0 months in the control group (P＜0.001), and average time to whole weight bearing was 2.3 ± 0.8 months and 2.8 ± 1.2 months, respectively (P = 0.004). Regarding radiographic union score, the study group scores were significantly higher than the control group scores at 1 and 3 months after surgery (P＜0.001), while it becomes insignificant between the two groups at 6 and 12 months after surgery (P = 0.19 and P = 0.15).The working lengths, fracture healing rates, complication rates, and Kolment scores were similar between the two groups (P＞0.05). In the multivariate analysis, fracture sites (OR = 5.34; 95% CI, 1.11-25.75; P = 0.03) and presence of open fractures (OR = 6.19; 95% CI, 1.05-36.38; P = 0.04) were significant associated with complications, whereas other variables were not included.

DISCUSSION

FCL system can truly accelerating bone healing and allow earlier whole weight bearing. Fracture healing rates and complication rates were similar between patients treated with FCL implants or conventional plating techniques. Patients with shaft fractures and open fractures trended to have higher complication rates.

CONCLUSIONS

FCL system is superior to standard plating technique in terms of early callus formation, but standard plating technique is not inferior to FCL system in terms of final fracture healing, surgery-related complication, and function outcome. Fracture site and presence of open fracture are the independent factors for complications in patients treated with FCL system.

Biomechanical investigation of the type and configuration of screws used in high tibial osteotomy with titanium locking plate and screw fixation

Background

To maintain the corrected alignment after high tibial osteotomy (HTO), fixation with titanium locking plate and screws is widely used in current practice; however, screw breakage is a common complication. Thus, this study was to investigate the mechanical stability of HTO with locking plate and various screw fixations, including the length as well as the type.

Methods

A finite element (FE) model involving a distal femur, meniscus, and a proximal tibia with HTO fixed with a titanium locking plate and screws was created. The angle of the medial open wedge was 12°, and bone graft was not used. Two types of screws, namely conventional locking and far-cortical locking screws, with various lengths and configurations were used. At the proximal tibia, conventional locking screws with different lengths, 30 and 55 mm, were used; at the tibia shaft, different screw fixations including one-cortical, two-cortical, and far-cortical locking screws were used.

Results

The use of far-cortical locking screw generated the highest equivalent stress on the screws, which was four times (from 137.3 to 541 MPa) higher than that of the one-cortical screw. Also, it led to the maximum deformation of the tibia and a greater gap deformation at the osteotomy site, which was twice (from 0.222 to 0.442 mm) larger than that of the one-cortical screw. The effect of different locking screw length on tibia deformation and implant stress was minor.

Conclusion

Thus, far-cortical locking screws and plates increase interfragmentary movement but the screw stress is relatively high. Increasing the protection time (partial weight duration) is suggested to decrease the risk of screw breakage in HTO through fixation with titanium far-cortical locking screws and plates.

Novel Treatment Options for the Surgical Management of Young Femoral Neck Fractures

In physiologically young patients with displaced femoral neck fractures, surgical treatment is aimed at achieving fracture union while preserving native hip anatomy and biomechanics. The intracapsular environment, tenuous vascular supply, and unfavorable hip biomechanics contribute to the high complication rates seen after osteosynthesis of these fractures. Conventional fixation methods for osteosynthesis of femoral neck fractures include multiple cancellous screws, fixed-angle dynamic implants, and fixed-angle length-stable constructs. Despite several biomechanical and clinical studies evaluating various surgical options, the optimal fixation construct to allow healing and prevent nonunion of displaced femoral neck fractures is not known. This article will review the clinical data regarding conventional fixation constructs and describe the technique and rationale behind 2 novel alternative treatment options for these challenging fractures. The surgical technique and clinical examples for constructs involving multiple cannulated screws/Pauwels screw augmented with a fibular strut graft, as well as a novel fixed-angle locking plate with controlled dynamic compression, are presented.

Periprosthetic fracture fixation of the femur following total hip arthroplasty: A review of biomechanical testing - Part II

BACKGROUND

Periprosthetic femoral fracture is a severe complication of total hip arthroplasty. A previous review published in 2011 summarised the biomechanical studies regarding periprosthetic femoral fracture and its fixation techniques. Since then, there have been several commercially available fracture plates designed specifically for the treatment of these fractures. However, several clinical studies still report failure of fixation treatments used for these fractures.

METHODS

The current literature on biomechanical models of periprosthetic femoral fracture fixation since 2010 to present is reviewed. The methodologies involved in the experimental and computational studies of periprosthetic femoral fracture fixation are described and compared with particular focus on the recent developments.

FINDINGS

Several issues raised in the previous review paper have been addressed by current studies; such as validating computational results with experimental data. Current experimental studies are more sophisticated in design. Computational studies have been useful in studying fixation methods or conditions (such as bone healing) that are difficult to study in vivo or in vitro. However, a few issues still remain and are highlighted.

INTERPRETATION

The increased use of computational studies in investigating periprosthetic femoral fracture fixation techniques has proven valuable. Existing protocols for testing periprosthetic femoral fracture fixation need to be standardised in order to make more direct and conclusive comparisons between studies. A consensus on the 'optimum' treatment method for periprosthetic femoral fracture fixation needs to be achieved.

Biomechanical considerations in the design of patient-specific fixation plates for the distal radius

Use of patient-specific fixation plates is promising in corrective osteotomy of the distal radius. So far, custom plates were mostly shaped to closely fit onto the bone surface and ensure accurate positioning of bone segments, however, without considering the biomechanical needs for bone healing. In this study, we investigated how custom plates can be optimized to stimulate callus formation under daily loading conditions. We calculated implant stress distributions, axial screw forces, and interfragmentary strains via finite element analysis (FEA) and compared these parameters for a corrective distal radius osteotomy model fixated by standard and custom plates. We then evaluated these parameters in a modified custom plate design with alternative screw configuration, plate size, and thickness on 5 radii models. Compared to initial design, in the modified custom plate, the maximum stress was reduced, especially under torsional load (- 31%). Under bending load, implants with 1.9-mm thickness induced an average strain (median = 2.14%, IQR = 0.2) in the recommended range (2-10%) to promote callus formation. Optimizing the plate shape, width, and thickness in order to keep the fixation stable while guaranteeing sufficient strain to enhance callus formation can be considered as a design criteria for future, less invasive, custom distal radius plates. Graphical abstract ᅟ.

Bone plate-screw constructs for osteosynthesis – recommendations for standardized mechanical torsion and bending tests

This paper follows up on a recent systematic review of test methods and parameters for biomechanical testing of bone plates and it is the first study that contains recommendations for standardized mechanical testing of bone plate-screw constructs for osteosynthesis. Following the testing philosophy of ASTM F382 and ISO 9585, we have developed standardized quasi-static and dynamic testing methods for straight linear and anatomically shaped plates, including locked type and conventional systems. The test specification comprises torsion and bending tests along the implant axis and therefore modifies and extends the methods proposed by ASTM F382. We present specific test setups in order to determine product-specific characteristics of the mechanical construct, consisting of the bone plate with corresponding screws (such as construct stiffness, yield strength, ultimate strength and fatigue properties) under the condition that it is rigidly fixed to “healthy bone”. We also address specific testing requirements that are important for the purpose of standardization, such as the positioning of the construct for testing or the number of screws in the diaphysis and metaphysis. Finally, we define the outcome parameters and associated failure criteria related to quasi-static and dynamic testing for comparative purposes. This paper does not intend to replace biomechanical testing of those devices under physiological loading conditions.

Biomechanical Analysis Using FEA and Experiments of Metal Plate and Bone Strut Repair of a Femur Midshaft Segmental Defect

This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional “high stiffness” femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern “low stiffness” femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone.

Early Comparative Outcomes of Carbon Fiber-Reinforced Polymer Plate in the Fixation of Distal Femur Fractures

OBJECTIVE

To evaluate the early clinical results of distal femur fractures treated with carbon fiber-reinforced polyetheretherketone (CFR-PEEK) plates compared with stainless steel (SS) lateral locking plates.

DESIGN

Retrospective comparative cohort study.

SETTING

ACS Level I trauma center.

PATIENTS/PARTICIPANTS

Twenty-two patients (11 SS, 11 CFR-PEEK) with closed distal femur fractures treated by a single surgeon over a 6-year period.

MAIN OUTCOME MEASUREMENTS

Nonunion, hardware failure, reoperation, time to full weight-bearing, and time union were assessed.

RESULTS

The CFR-PEEK cohort was on average older (71 vs. 57 years, P = 0.03) and more likely to have diabetes (P = 0.02). Nonunion was diagnosed in 4/11 (36%) patients in the SS group and 1/11 (9%) patients in the CFR-PEEK group (P = 0.12). Hardware failure occurred in 2 SS patients (18%) compared with none in the CFR-PEEK group (P = 0.14). Time to full weight-bearing was similar between groups, occurring at 9.9 and 12.4 weeks in the CFR-PEEK and SS groups, respectively (P = 0.23). Time to radiographic union averaged 12.4 weeks in the SS group and 18.7 weeks in the CFR-PEEK group (P = 0.26). There were 4 reoperations in the SS group and 1 in the CFR-PEEK group (P = 0.12).

CONCLUSIONS

CFR-PEEK plates show encouraging short-term results in the treatment of distal femur fractures with a comparable nonunion, reoperation, and hardware failure rates to those treated with SS plates. This data suggest that CFR-PEEK plates may be a viable alternative to SS plates in fixation of these fractures.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Biomechanical Testing of a 3-Hole Versus a 4-Hole Sliding Hip Screw in the Presence of a Retrograde Intramedullary Nail for Ipsilateral Intertrochanteric and Femur Shaft Fractures

OBJECTIVE

The goal of this study was to compare a 3-hole versus a 4-hole sliding hip screw (SHS) in the presence of a retrograde intramedullary (RIM) nail for fixing intertrochanteric and comminuted midshaft femur fractures.

METHODS

Mechanical tests were performed on 10 matched pairs of human cadaveric femurs that were osteotomized and then fixed using a 3-hole SHS versus the traditional "gold standard" 4-hole SHS in the presence of an RIM nail.

RESULTS

Data showed no differences between the 3-hole SHS with RIM nail versus 4-hole SHS with RIM nail for stiffness (281 ± 127 vs. 260 ± 118 N/mm, P = 0.76), clinical failure at 10 mm of hip displacement (2014 ± 363 vs. 2134 ± 614 N, P = 0.52), or ultimate mechanical failure (3476 ± 776 vs. 3669 ± 755 N, P = 0.12).

CONCLUSIONS

For this fracture pattern, a 3-hole SHS with RIM nail may be a suitable surgical alternative to the traditional "gold standard" method because it provides the same biomechanical properties while potentially reducing surgical time, blood loss, and hardware used.

In-vivo stiffness assessment of distal femur fracture locked plating constructs

BACKGROUND

The purpose of this study was to design and validate a novel stiffness-measuring device using locked plating of distal femur fractures as a model.

METHODS

All patients underwent a laterally-based approach, with a bridging locked construct after indirect reduction. A custom and calibrated intraoperative stiffness device was applied and the stiffness of the construct was blindly recorded. Fourteen of twenty-seven patients enrolled with distal femur fractures (AO/OTA 33A and 33C) completed the study. Correlations between stiffness and callus formation, working length, working length/plate length ratio, number of distal locking screws, and fracture pattern were explored.

FINDINGS

Callus and modified radiographic union scale in tibias scores as a linear function of stiffness did not correlate (R2 = 0.06 and 0.07, respectively). Construct working length and working length to plate length ratio did not correlate to stiffness (R2 = 0.18 and 0.16 respectively). A combined delayed and nonunion rate was 14%. Lower extremity measure scores were not statistically different when comparing delayed and nonunion with healed fractures.

INTERPRETATION

The lack of correlation may have been due to the mechanical properties of the plate itself and its large contribution to the overall stiffness of the construct. To our knowledge, clinically relevant stiffness has not been described and this study may provide some estimates. This methodology and these preliminary findings may lay the groundwork for further investigations into this prevalent clinical problem. Other parameters not investigated may play a key role such as body mass index and bone mineral density.

LEVEL OF EVIDENCE

Diagnostic/Prognostic Level II.

Minimally invasive plate osteosynthesis with locking compression plate in patients with Vancouver type B1 periprosthetic femoral fractures

BACKGROUND

Periprosthetic femoral fractures (PFF) following total hip arthroplasty (THA) remain one of the most challenging complications to address. Although the principal treatment modalities for Vancouver type B1 fractures are open reduction and internal fixation (ORIF), surgeons have not yet reached a consensus on the optimal method for reduction and fixation. We therefore investigated whether minimally invasive plate osteosynthesis (MIPO) using locking compression plate (LCP) would lead to favorable outcomes for patients with Vancouver type B1 PFFs. In addition, we also compared the outcomes of patients treated with MIPO to those treated with ORIF.

METHOD

We retrospectively evaluated the clinical and radiographic outcomes of a series of 21 Vancouver type B1 PFFs treated with MIPO and LCP between February 2011 and February 2017. The mean duration of follow-up was 33.8 months. We also compared outcomes of these patients to those of patients with 19 Vancouver type B1 fractures treated with ORIF between April 2006 and December 2011.

RESULTS

Fracture healing without complications was achieved in 20 (95.2%) out of 21 cases in the MIPO group and in 14 (87.5%) out of 16 cases in the ORIF group. There was one case of fixation failure with stem subsidence in the MIPO group. In the ORIF group, there were 2 nonunion with metal failure. Operation time was significantly shorter and intraoperative blood loss was significantly less in the MIPO group compared to the ORIF group. However, there were no significant differences in frequency of transfusion, time-to-union, walking abilities, modified Harris hip score, or complications.

CONCLUSION

The radiological and clinical outcomes of MIPO using LCP in patients with Vancouver type B1 PFFs were shown not to be inferior to ORIF and resulted in fewer intraoperative complications than ORIF. If care is taken regarding the stability of femoral implant and optimal surgical techniques, MIPO may be a recommended option in the treatment of Vancouver type B1 periprosthetic fracture.

Pre-operative planning for fracture fixation using locking plates: device configuration and other considerations

Most locked plating failures are due to inappropriate device configuration for the fracture pattern. Several studies cite screw positioning variables such as the number and spacing of screws as responsible for occurrences of locking plate breakage, screw loosening, and peri-prosthetic re-fracture. It is also widely accepted that inappropriate device stiffness can inhibit or delay healing. Careful preoperative planning is therefore critical if these failures are to be prevented. This study examines several variables which need to be considered when optimising a locking plate fixation device for fracture treatment including: material selection; screw placement; the effect of the fracture pattern; and the bone-plate offset. We demonstrate that device selection is not straight-forward as many of the variables influence one-another and an identically configured device can perform very differently depending upon the fracture pattern. Finally, we summarise the influence of some of the key parameters and the influence this can have on the fracture healing environment and the stresses within the plate in a flowchart.

Evolution of plate design and material composition

The evolution of plate fixation of fracture was accompanied by advances in metallurgy and improvement in understanding of the requirements for successful fracture healing. Locked internal fixation minimizes biologic damage and when used in conjunction with minimally invasive approaches may optimize fracture healing. Some current metal locked plate constructs may actually be too stiff, and various methods including screw modification, plate hole modification, and changes in plate material composition may provide a solution to optimize fracture healing. This paper reviews the evolution of plate design and describes the early clinical experience with the use of carbon fibre reinforced reinforced polyetheretherketone composite plates.

Clinical Management of Osteoporotic Fractures

PURPOSE OF REVIEW

This review examines recent literature regarding the clinical management of fragility fractures, provides insight into new practice patterns, and discusses controversies in current management.

RECENT FINDINGS

There are declining rates of osteoporosis management following initial fragility fracture. Management of osteoporotic fractures via a multidisciplinary team reduces secondary fracture incidence and improves overall osteoporotic care. Anabolic agents (abaloparatide and teriparatide) are effective adjuvants to fracture repair, and have shown positive results in cases of re-fracture in spite of medical management (i.e., bisphosphonates). For AO 31-A1 and A2 intertrochanteric hip fractures (non-reverse obliquity), no clinical advantage of intramedullary fixation over the sliding hip screw (SHS) has been proven; SHS is more cost-effective. As fragility fracture incidence continues to rise, orthopedic surgeons must play a more central role in the care of osteoporotic patients. Initiation of pharmacologic intervention is key to preventing subsequent fragility fractures, and may play a supportive role in initial fracture healing. While the media bombards patients with complications of medical therapy (atypical femur fractures, osteonecrosis of jaw, myocardial infarction), providers need to understand and communicate the low incidence of these complications compared with consequences of not initiating medical therapy.

[Current status and progress of clinical research on distal femoral fractures]

Objective

To investigate current status and latest progress of clinical research on distal femoral fractures.

Methods

The related literature was extensively reviewed to summarize the trend of the researches and their clinical application in the treatment of distal femoral fractures.

Results

Distal femoral fractures are likely to occur in young people who suffer from high-energy damage and the elderly with osteoporosis, which is always comminuted and unstable fractures, and often involved in the articular surface and combined with serious soft tissue injury. Therefore, the treatment faces many challenges. External fixation is now used as a temporary means of controlling injury. The vast majority of patients are feasible to internal fixation, including plates system and intramedullary nail system. Different internal fixator also has its own characteristics, such as double plates can strengthen the medial support of the femur, less invasive stabilization system protects the blood supply of fractures, distal cortial locking plate is theoretically more fit for the requirements of bone healing, retrograde intramedullary nail can resist varus and valgus.

Conclusion

The treatment of distal femoral fractures should be based on the type of fracture and the characteristics of internal fixators.

Ex vivo cyclic mechanical behaviour of 2.4 mm locking plates compared with 2.4 mm limited contact plates in a cadaveric diaphyseal gap model

Objectives: To compare the mechanical properties of locking compression plate (LCP) and limited contact dynamic compression plate (LC-DCP) constructs in an experimental model of comminuted fracture of the canine femur during eccentric cyclic loading.

Methods: A 20 mm mid-diaphyseal gap was created in eighteen canine femora. A 10-hole, 2.4 mm stainless steel plate (LCP or LC-DCP) was applied with three bicortical screws in each bone fragment. Eccentric cyclic loadings were applied at 10 Hertz for 610,000 cycles. Quasistatic loading / unloading cycles were applied at 0 and 10,000 cycles, and then every 50,000 cycles. Structural stiffness was calculated as the slope of the linear portion of the load-displacement curves during quasistatic loading / unloading cycles.

Results: No bone failure or screw loosening occurred. Two of the nine LCP constructs failed by plate breakage during fatigue testing, whereas no gross failure occurred with the LC-DCP constructs. The mean first stiffness of the LCP constructs over the course of testing was 24.0% lower than that of constructs stabilized by LC-DCP. Construct stiffness increased in some specimens during testing, presumably due to changes in boneplate contact. The first stiffness of LC-DCP constructs decreased by 19.4% and that of locked constructs by 34.3% during the cycling period. A biphasic stiffness profile was observed: the second stiffness was significantly greater than the first stiffness in both groups, which allowed progressive stabilization at elevated load levels.

Clinical significance: Because LCP are not compressed to the bone, they may have a longer working length across a fracture, and thus be less stiff. However, this may cause them to be more susceptible to fatigue failure if healing is delayed.

Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices

Objectives

Secondary fracture healing is strongly influenced by the stiffness of the bone-fixator system. Biomechanical tests are extensively used to investigate stiffness and strength of fixation devices. The stiffness values reported in the literature for locked plating, however, vary by three orders of magnitude. The aim of this study was to examine the influence that the method of restraint and load application has on the stiffness produced, the strain distribution within the bone, and the stresses in the implant for locking plate constructs.

Methods

Synthetic composite bones were used to evaluate experimentally the influence of four different methods of loading and restraining specimens, all used in recent previous studies. Two plate types and three screw arrangements were also evaluated for each loading scenario. Computational models were also developed and validated using the experimental tests.

Results

The method of loading was found to affect the gap stiffness strongly (by up to six times) but also the magnitude of the plate stress and the location and magnitude of strains at the bone-screw interface.

Conclusions

This study demonstrates that the method of loading is responsible for much of the difference in reported stiffness values in the literature. It also shows that previous contradictory findings, such as the influence of working length and very large differences in failure loads, can be readily explained by the choice of loading condition.

Cite this article: A. MacLeod, A. H. R. W. Simpson, P. Pankaj. Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices. Bone Joint Res 2018;7:111–120. DOI: 10.1302/2046-3758.71.BJR-2017-0074.R2.

Proximal Screw Configuration Alters Peak Plate Strain Without Changing Construct Stiffness in Comminuted Supracondylar Femur Fractures

OBJECTIVES

Assess the effect of proximal screw configuration on the strain in lateral plating of a simulated comminuted supracondylar femur fracture.

METHODS

Fractures were simulated in 12 synthetic femurs by removing a 200-mm section of bone, located 60 mm from the intercondylar fossa and repaired using a 16-hole locked lateral plate instrumented with 8 uniaxial strain gauges. Three proximal screw type configurations were evaluated: (1) 4 nonlocking screws, (2) 4 locking screws, and (3) a hybrid configuration of 2 nonlocking screws flanked by a locking screw at each end of the proximal fragment. Each screw type was compared for 2 working lengths (∼90 and 160 mm). The longer working length was created by removing the proximal screw closest to the fracture gap. Testing consisted of a vertical load (500 N) applied to the head of femur. Configurations were compared using plate strain, construct stiffness, and fracture gap displacement as outcome measures.

RESULTS

Plate strain immediately above the fracture gap was reduced with nonlocking screws compared with the other screw types. Plate strains were reduced around the fracture gap with the longer working length but increased for the nonlocking construct at the location of the removed screw. Construct stiffness was not altered by screw type or working length. An increase in fracture gap displacement was only evident in shear translation with the longer working length.

CONCLUSIONS

Plate strain in lateral plating of supracondylar femur fractures is decreased using nonlocking screws proximal to the fracture. Increasing the working length reduces plate strains over the working length yet should be cautioned because of increased interfragmentary shear motion.

Comparison of 4 Methods for Dynamization of Locking Plates: Differences in the Amount and Type of Fracture Motion

BACKGROUND

Decreasing the stiffness of locked plating constructs can promote natural fracture healing by controlled dynamization of the fracture. This biomechanical study compared the effect of 4 different stiffness reduction methods on interfragmentary motion by measuring axial motion and shear motion at the fracture site.

METHODS

Distal femur locking plates were applied to bridge a metadiaphyseal fracture in femur surrogates. A locked construct with a short-bridge span served as the nondynamized control group (LOCKED). Four different methods for stiffness reduction were evaluated: replacing diaphyseal locking screws with nonlocked screws (NONLOCKED); bridge dynamization (BRIDGE) with 2 empty screw holes proximal to the fracture; screw dynamization with far cortical locking (FCL) screws; and plate dynamization with active locking plates (ACTIVE). Construct stiffness, axial motion, and shear motion at the fracture site were measured to characterize each dynamization methods.

RESULTS

Compared with LOCKED control constructs, NONLOCKED constructs had a similar stiffness (P = 0.08), axial motion (P = 0.07), and shear motion (P = 0.97). BRIDGE constructs reduced stiffness by 45% compared with LOCKED constructs (P < 0.001), but interfragmentary motion was dominated by shear. Compared with LOCKED constructs, FCL and ACTIVE constructs reduced stiffness by 62% (P < 0.001) and 75% (P < 0.001), respectively, and significantly increased axial motion, but not shear motion.

CONCLUSIONS

In a surrogate model of a distal femur fracture, replacing locked with nonlocked diaphyseal screws does not significantly decrease construct stiffness and does not enhance interfragmentary motion. A longer bridge span primarily increases shear motion, not axial motion. The use of FCL screws or active plating delivers axial dynamization without introducing shear motion.

Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness

Objectives

External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF).

Methods

A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness.

Results

The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171).

There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed.

Conclusion

Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness.

Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216–223. DOI: 10.1302/2046-3758.64.2000470.

Metaphyseal locking plate as an external fixator for open tibial fracture: Clinical outcomes and biomechanical assessment

OBJECTIVE

This study aimed to evaluate the outcome of using a metaphyseal locking plate as a definitive external fixator for treating open tibial fractures based on biomechanical experiments and analysis of clinical results.

METHODS

A metaphyseal locking plate was used as an external fixator in 54 open tibial fractures in 52 patients. The mean follow-up was 38 months (range, 20-52 months). Moreover, static axial compression and torsional tests were performed to evaluate the strength of the fixation techniques.

RESULTS

The average fracture healing time was 34.5 weeks (range, 12-78 weeks). At 4 weeks postoperatively and at the final follow-up, the average Hospital for Special Surgery knee score was 85 (range, 81-100) and 94 (range, 88-100), respectively, and the American Orthopaedic Foot and Ankle Society score was 88 (range, 80-100) and 96 (range, 90-100), respectively. Based on the static test result, the axial stiffness was significantly different among groups (p=0.002), whereas the torsional stiffness showed no significant difference (p=0.068).

CONCLUSIONS

Clinical outcomes show that the use of locking plate as a definitive external fixator is an alternative choice for tibial fractures after obtaining appropriate fracture reduction. However, external locked plating constructs were not as strong as standard locked plating constructs. Therefore, the use of external locked plating constructs as a definitive treatment warrants further biomechanical study for construct strength improvement.

A Concert between Biology and Biomechanics: The Influence of the Mechanical Environment on Bone Healing

In order to achieve consistent and predictable fracture healing, a broad spectrum of growth factors are required to interact with one another in a highly organized response. Critically important, the mechanical environment around the fracture site will significantly influence the way bone heals, or if it heals at all. The role of the various biological factors, the timing, and spatial relationship of their introduction, and how the mechanical environment orchestrates this activity, are all crucial aspects to consider. This review will synthesize decades of work and the acquired knowledge that has been used to develop new treatments and technologies for the regeneration and healing of bone. Moreover, it will discuss the current state of the art in experimental and clinical studies concerning the application of these mechano-biological principles to enhance bone healing, by controlling the mechanical environment under which bone regeneration takes place. This includes everything from the basic principles of fracture healing, to the influence of mechanical forces on bone regeneration, and how this knowledge has influenced current clinical practice. Finally, it will examine the efforts now being made for the integration of this research together with the findings of complementary studies in biology, tissue engineering, and regenerative medicine. By bringing together these diverse disciplines in a cohesive manner, the potential exists to enhance fracture healing and ultimately improve clinical outcomes.

Dynamic Fixation of Humeral Shaft Fractures Using Active Locking Plates: A Prospective Observational Study

BACKGROUND

Rigid locked plating constructs can suppress fracture healing by inhibiting interfragmentary motion required to stimulate natural bone healing by callus formation. Dynamic fixation with active locking plates reduces construct stiffness, enables controlled interfragmentary motion, and has been shown to induce faster and stronger bone healing in vivo compared to rigid locking plates. This prospective observational study represents the first clinical use of active locking plates. It documents our early clinical experience with active plates for stabilization of humeral shaft fractures to assess their durability and understand potential complications.

METHODS

Eleven consecutive patients with humeral shaft fractures (AO/OTA types 12 A-C) were prospectively enrolled at a level I and a level II trauma center. Fractures were stabilized by using active locking plates without supplemental bone graft or bone morphogenic proteins. The screw holes of active locking plates are elastically suspended in elastomer envelopes inside the plate, enabling up to 1.5 mm of controlled interfragmentary motion. Progression of fracture healing and integrity of implant fixation was assessed radiographically at 3, 6, 12, and 24 weeks post surgery. Patient-reported functional outcome measures were obtained at 6, 12, and 24 weeks post surgery. The primary endpoint of this study was plate durability in absence of plate bending or breakage, or failure of the elastically suspended locking hole mechanism. Secondary endpoints included fracture healing, complications requiring revision surgery, and functional outcome scores.

RESULTS

The eleven patients had six simple AO/ OTA type 12A fractures, three wedge type 12B fractures, and two comminuted type 12C fracture, including one open fracture. All active locking plates endured the 6-month loading period without any signs of fatigue or failure. Ten of eleven fractures healed at 10.9 ± 5.2 weeks, as evident by bridging callus and pain-free function. One fracture required revision surgery 37 weeks post surgery due to late fixation failure at the screwbone interface in the presence of a atrophic delayed union. The average Disability of the Arm, Shoulder and Hand (DASH) score improved from 31 ± 22 at week 6 to 13 ± 15 by week 24, approaching that of the normal, healthy population (DASH = 10.1). By week 12, the difference between Constant shoulder scores, expressed as the difference between the affected and contralateral arm (8 ± 8), was considered excellent. By week 24, the SF-12 physical health score (44 ± 9) and mental health score (48 ± 11) approached the mean value of 50 that represents the norm for the general U.S. population.

CONCLUSION

Absence of failure of the plate and locking holes suggests that dynamic fixation of humeral shaft fractures with active plates provides safe and effective fixation. Moreover, early callus bridging and excellent functional outcome scores suggest that dynamic fixation with active locking plates may promote increased fracture healing over standard locked plating.

History of internal fixation with plates (part 2): new developments after World War II; compressing plates and locked plates

The first techniques of operative fracture with plates were developed in the 19th century. In fact, at the beginning these methods consisted of an open reduction of the fracture usually followed by a very unstable fixation. As a consequence, the fracture had to be opened with a real risk of (sometimes lethal) infection, and due to unstable fixation, protection with a cast was often necessary. During the period between World Wars I and II, plates for fracture fixation developed with great variety. It became increasingly recognised that, because a fracture of a long bone normally heals with minimal resorption at the bone ends, this may result in slight shortening and collapse, so a very rigid plate might prevent such collapse. However, as a consequence, delayed healing was observed unless the patient was lucky enough to have the plate break. One way of dealing with this was to use a slotted plate in which the screws could move axially, but the really important advance was recognition of the role of compression. After the first description of compression by Danis with a "coapteur", Bagby and Müller with the AO improved the technique of compression. The classic dynamic compression plates from the 1970s were the key to a very rigid fixation, leading to primary bone healing. Nevertheless, the use of strong plates resulted in delayed union and the osteoporosis, cancellous bone, comminution, and/or pathological bone resulted in some failures due to insufficient stability. Finally, new devices represented by locking plates increased the stability, contributing to the principles of a more biological osteosynthesis while giving enough stability to allow immediate full weight bearing in some patients.

Finite Element-Derived Surrogate Models of Locked Plate Fracture Fixation Biomechanics

Internal fixation of bone fractures using plates and screws involves many choices-implant type, material, sizes, and geometric configuration-made by the surgeon. These decisions can be important for providing adequate stability to promote healing and prevent implant mechanical failure. The purpose of this study was to develop mathematical models of the relationships between fracture fixation construct parameters and resulting 3D biomechanics, based on parametric computer simulations. Finite element models of hundreds of different locked plate fixation constructs for midshaft diaphyseal fractures were systematically assembled using custom algorithms, and axial, torsional, and bending loadings were simulated. Multivariate regression was used to fit response surface polynomial equations relating fixation design parameters to outputs including maximum implant stresses, axial and shear strain at the fracture site, and construct stiffness. Surrogate models with as little as three regressors showed good fitting (R ² = 0.62-0.97). Inner working length was the strongest predictor of maximum plate and screw stresses, and a variety of quadratic and interaction terms influenced resulting biomechanics. The framework presented in this study can be applied to additional types of bone fractures to provide clinicians and implant designers with clinical insight, surgical optimization, and a comprehensive mathematical description of biomechanics.

Mechanical Construct Characteristics Predisposing to Non-union After Locked Lateral Plating of Distal Femur Fractures

OBJECTIVES

To identify discrete construct characteristics related to overall construct rigidity that may be independent predictors of nonunion after lateral locked plate (LLP) fixation of distal femur fractures.

DESIGN

Retrospective case-control study.

SETTING

Three level-1 urban trauma centers.

PATIENTS/PARTICIPANTS

Two hundred and seventy-one supracondylar femoral fractures treated with LLP at 3 affiliated level 1 urban trauma centers between August 2004 and December 2010.

METHODS

Nonunion was defined as a secondary procedure for poor healing. Construct variables included: (1) combined plate design and material variable, (2) Plate length, (3) # screws proximal to fracture, (4) total screw density (TSD), (5) proximal screw density (PSD), (6) presence of a screw crossing the main fracture, and (7) rigidity score multivariable analysis was performed using logistic regression to identify independent risk factors for nonunion.

INTERVENTION

LLP fixation.

MAIN OUTCOME MEASURE

Nonunion.

RESULTS

Nonunion rate was 13.3% (n = 36). There was a significant association between plate design/material and nonunion with 41% of stainless constructs and 10% of titanium constructs resulting in a nonunion (P < 0.001). Rigidity scores reached significance (P = 0.001) with constructs resulting in a nonunion having higher scores. No significant univariate differences with respect to number of proximal screws, plate length, total screw density, or proximal screw density were observed between healed fractures and those with nonunion. Results of the multivariate analysis confirmed that the primary significant independent predictor of nonunion was plate design/material (odds ratio, 6.8; 95% CI, 2.9-16.1; P < 0.001).

CONCLUSIONS

When treating distal femur fractures with LLP, combined plate design and material variable has a highly significant influence on the risk of nonunion independent of any other construct variable.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Application of Far Cortical Locking Technology in Periprosthetic Femoral Fracture Fixation: A Biomechanical Study

BACKGROUND

Lack of fracture movement could be a potential cause of periprosthetic femoral fracture (PFF) fixation failures. This study aimed to test whether the use of distal far cortical locking screws reduces the overall stiffness of PFF fixations and allows an increase in fracture movement compared to standard locking screws while retaining the overall strength of the PFF fixations.

METHODS

Twelve laboratory models of Vancouver type B1 PFFs were developed. In all specimens, the proximal screw fixations were similar, whereas in 6 specimens, distal locking screws were used, and in the other six specimens, far cortical locking screws. The overall stiffness, fracture movement, and pattern of strain distribution on the plate were measured in stable and unstable fractures under anatomic 1-legged stance. Specimens with unstable fracture were loaded to failure.

RESULTS

No statistical difference was found between the stiffness and fracture movement of the two groups in stable fractures. In the unstable fractures, the overall stiffness and fracture movement of the locking group was significantly higher and lower than the far cortical group, respectively. Maximum principal strain on the plate was consistently lower in the far cortical group, and there was no significant difference between the failure loads of the 2 groups.

CONCLUSION

The results indicate that far cortical locking screws can reduce the overall effective stiffness of the locking plates and increase the fracture movement while maintaining the overall strength of the PFF fixation construct. However, in unstable fractures, alternative fixation methods, for example, long stem revision might be a better option.

Dynamic Stabilization with Active Locking Plates Delivers Faster, Stronger, and More Symmetric Fracture-Healing

BACKGROUND

Axial dynamization of fractures can promote healing, and overly stiff fixation can suppress healing. A novel technology, termed active plating, provides controlled axial dynamization by the elastic suspension of locking holes within the plate. This prospective, controlled animal study evaluated the effect of active plates on fracture-healing in an established ovine osteotomy model. We hypothesized that symmetric axial dynamization with active plates stimulates circumferential callus and delivers faster and stronger healing relative to standard locking plates.

METHODS

Twelve sheep were randomly assigned to receive a standard locking plate or an active locking plate for stabilization of a 3-mm tibial osteotomy gap. The only difference between plates was that locking holes of active plates were elastically suspended, allowing up to 1.5 mm of axial motion at the fracture. Fracture-healing was analyzed weekly on radiographs. After sacrifice at nine weeks postoperatively, callus volume and distribution were assessed by computed tomography. Finally, to determine their strength, healed tibiae and contralateral tibiae were tested in torsion until failure.

RESULTS

At each follow-up, the active locking plate group had more callus (p < 0.001) than the standard locking plate group. At postoperative week 6, all active locking plate group specimens had bridging callus at the three visible cortices. In standard locking plate group specimens, only 50% of these cortices had bridged. Computed tomography demonstrated that all active locking plate group specimens and one of the six standard locking plate group specimens had developed circumferential callus. Torsion tests after plate removal demonstrated that active locking plate group specimens recovered 81% of their native strength and were 399% stronger than standard locking plate group specimens (p < 0.001), which had recovered only 17% of their native strength. All active locking plate group specimens failed by spiral fracture outside the callus zone, but standard locking plate group specimens fractured through the osteotomy gap.

CONCLUSIONS

Symmetric axial dynamization with active locking plates stimulates circumferential callus and yields faster and stronger healing than standard locking plates.

CLINICAL RELEVANCE

The stimulatory effect of controlled motion on fracture-healing by active locking plates has the potential to reduce healing complications and to shorten the time to return to function.

A novel adjustable dynamic plate for treatment of long bone fractures: An in vitro biomechanical study

INTRODUCTION

Locking compression plate (LCP) system was designed to provide bone stability and to enhance bone healing. However, implant failure, nonunion and instability are still frequently encountered complications. The purpose of this study was to assess and compare the biomechanical characteristics of a novel adjustable dynamic plate (ADP) with the commonly used LCP.

MATERIALS AND METHODS

Twelve 4th generation composite artificial femoral bones were used. Transverse fracture was created in all bones, 6 femurs were fixated using the novel ADP, whereas the other 6 femurs were fixated using the traditional LCP. All samples had undergone a non-destructive repetitive different forces (axial compression, bending and torsion), to evaluate the biomechanical differences between the two plating systems.

RESULTS

Under axial load the mean stiffness value was 439.0 N/mm for the ADP and 158.9 N/mm for the LCP, ADP showed a statistically significant stiffness value than LCP with a P value of 0.004. There was no significant difference in flexion/extension bending strain values between ADP and LCP. However LCP provided significantly stiffer fixation in medial and lateral bending tests than ADP (P = 0.037) and (P = 0.016) respectively. But no significant difference was detected between the two plating system in the applied torsional stress.

CONCLUSION

These results do not show any significant biomechanical difference in the applied torsional and bending stresses between LCP and ADP. However the remarkably increased persistent compression effect of the ADP created a considerable stress on fracture edges which may accelerate bone healing.

Biomechanical Concepts for Fracture Fixation

Application of the correct fixation construct is critical for fracture healing and long-term stability; however, it is a complex issue with numerous significant factors. This review describes a number of common fracture types and evaluates their currently available fracture fixation constructs. In the setting of complex elbow instability, stable fixation or radial head replacement with an appropriately sized implant in conjunction with ligamentous repair is required to restore stability. For unstable sacral fractures with vertical or multiplanar instabilities, "standard" iliosacral screw fixation is not sufficient. Periprosthetic femur fractures, in particular Vancouver B1 fractures, have increased stability when using 90/90 fixation versus a single locking plate. Far cortical locking combines the concept of dynamization with locked plating to achieve superior healing of a distal femur fracture. Finally, there is no ideal construct for syndesmotic fracture stabilization; however, these fractures should be fixed using a device that allows for sufficient motion in the syndesmosis. In general, orthopaedic surgeons should select a fracture fixation construct that restores stability and promotes healing at the fracture site, while reducing the potential for fixation failure.

Drilling the near cortex with elongated figure-of-8 holes to reduce the stiffness of a locking compression plate construct

PURPOSE

To compare the stiffness of locking compression plate (LCP) constructs with or without drilling the near cortex with elongated figure-of-8 holes.

METHODS

24 synthetic bones were sawn to create a 10-mm gap and were fixed with a 9-hole 4.5-mm narrow LCP. In 12 bones, the near cortex of the adjacent holes to the LCP holes was drilled to create elongated figure-of-8 holes before screw insertion. The stiffness of LCP constructs under axial loading or 4-point bending was assessed by (1) dynamic quasi-physiological testing for fatigue strength, (2) quasi-static testing for stiffness, and (3) testing for absolute strength to failure.

RESULTS

None of the 24 constructs had subcatastrophic or catastrophic failure after 10 000 cycles of fatigue loading (p=1.000). The axial stiffness reduced by 16% from 613±62 to 517±44 N/mm (p=0.012) in the case group, whereas the bending stiffness was 16±1 Nm2 in both groups (p=1.000). The maximum axial load to catastrophic failure was 1596±84 N for the control group and 1627±48 N for the case group (p=0.486), whereas the maximum bending moment to catastrophic failure was 79±12 and 80±10 Nm, respectively (p=0.919).

CONCLUSION

Drilling the near cortex with elongated figure-of-8 holes reduces the axial stiffness of the LCP construct, without compromising its bending stiffness or strength.

Reducing Fracture Risk Adjacent to a Plate With an Angulated Locked End Screw

OBJECTIVES

Locking screws often are used in the treatment of osteoporotic fractures. Studies show that locking screws can increase bone stresses at the plate end, which increases the possibility of peri-implant fracture. This study evaluates whether the technique used to insert the end screw is related to the fracture tolerance adjacent to the plate.

METHODS

Twelve groups of plate constructs were evaluated using a fibular diaphyseal surrogate with mechanical properties similar to osteoporotic bone. All inboard screws were nonlocked with only the end screw fixation differing among groups. The end screws were inserted either perpendicularly to the plate or at an angle of 30 degrees for 6- and 12-hole plates. For both orientations, the end screws were inserted nonlocked, locked, or by a locked overdrilling technique, resulting in 6 groups per plate length. The perpendicular nonlocked screws represented a control group. The constructs were tested to failure in 4-point bending to determine peak load, failure energy, and stiffness.

RESULTS

All constructs failed by peri-implant fracture along a plane through the 2 cortical holes of the end screw. Compared with the control group, an angulated locked screw at the plate end significantly increased the peak bending moment and energy required to produce a fracture for both plate lengths (6-hole, P = 0.008, P < 0.001; 12-hole, P = 0.006, P < 0.001).

CONCLUSIONS

The use of an angulated locked end screw may enhance the resistance of osteoporotic bone to peri-implant fractures caused by bending forces.

A Biomechanical Comparison of Locking Versus Conventional Plate Fixation for Distal Fibula Fractures in Trimalleolar Ankle Injuries

Previous biomechanical studies have advocated the use of locking plates for isolated distal fibula fractures in osteoporotic bone. Complex rotational ankle injuries involve an increased number of fractures, which can result in instability, potentially requiring the same fixed angle properties afforded by locking plates. However, the mechanical indication for locking plate technology has not been tested in this fracture model. The purpose of the present study was to compare the biomechanical properties of locking and conventional plate fixation for distal fibula fractures in trimalleolar ankle injuries. Fourteen (7 matched pairs) fresh-frozen cadaver leg specimens were used. The bone mineral density of each was obtained using dual x-ray absorptiometry scans. The fracture model simulated an OTA 44-B3.3 fracture. The syndesmosis was not disrupted. Each fracture was fixated in the same fashion, except for the distal fibula plate construct: locking (n = 7) and one-third tubular (n = 7). The specimens underwent axial and torsional cyclic loading, followed by torsional loading to failure. No statistically significant differences were found between the locking and conventional plate constructs during both fatigue and torque to failure testing (p > .05). Our specimen bone mineral density averages did not represent poor bone quality. The clinical implication of the present study is that distal fibular locking plates do not provide a mechanical advantage for trimalleolar ankle injuries in individuals with normal bone density and in the absence of fracture comminution.

Role of Appositional Screw Fixation in Minimally Invasive Plate Osteosynthesis for Distal Tibial Fracture

OBJECTIVES

To determine the effect of interfragmentary appositional (gap-closing) screw fixation in minimally invasive plate osteosynthesis (MIPO) for distal tibial fractures on the clinical and radiologic results.

DESIGN

Prospective nonrandomized study.

SETTING

Level I trauma center.

PATIENTS

Sixty patients who were diagnosed as distal metadiaphyseal oblique or spiral tibial fracture without displaced articular fragment.

INTERVENTION

Thirty patients (group A) of the 60 patients were treated with MIPO without appositional screw fixation, and the other 30 (group B) were treated with the screw.

MAIN OUTCOME MEASUREMENTS

Radiologic union, clinical union, clinical functional score [American Orthopaedic Foot and Ankle Society (AOFAS) score], and complications.

RESULTS

The time for initial callus formation and radiologic union was significantly longer in group A than those in group B (76.8 vs. 58.0 days, P = 0.044; 409 vs. 258.7 days, P = 0.002, respectively). The rate of clinical union during 1 year was significantly higher in group B than in group A (P = 0.0063). Four nonunion patients in group A achieved bone union after placement of an additional bone graft. None of the patients in group B diagnosed with delayed union or nonunion (P < 0.001). None of the patients of both groups had malreduction, skin problems, or infection. Overall, the AOFAS score did not significantly differ between groups A and B (85.4 vs. 87.0, P = 0.43).

CONCLUSIONS

The use of additional interfragmentary appositional screw fixation in distal tibia MIPO for the fixation of oblique or spiral fracture promoted callus formation and union rate compared with MIPO without appositional screw fixation.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Dynamic locking plates provide symmetric axial dynamization to stimulate fracture healing

Axial dynamization of an osteosynthesis construct can promote fracture healing. This biomechanical study evaluated a novel dynamic locking plate that derives symmetric axial dynamization by elastic suspension of locking holes within the plate. Standard locked and dynamic plating constructs were tested in a diaphyseal bridge-plating model of the femoral diaphysis to determine the amount and symmetry of interfragmentary motion under axial loading, and to assess construct stiffness under axial loading, torsion, and bending. Subsequently, constructs were loaded until failure to determine construct strength and failure modes. Finally, strength tests were repeated in osteoporotic bone surrogates. One body-weight axial loading of standard locked constructs produced asymmetric interfragmentary motion that was over three times smaller at the near cortex (0.1 ± 0.01 mm) than at the far cortex (0.32 ± 0.02 mm). Compared to standard locked constructs, dynamic plating constructs enhanced motion by 0.32 mm at the near cortex and by 0.33 mm at the far cortex and yielded a 77% lower axial stiffness (p < 0.001). Dynamic plating constructs were at least as strong as standard locked constructs under all test conditions. In conclusion, dynamic locking plates symmetrically enhance interfragmentary motion, deliver controlled axial dynamization, and are at least comparable in strength to standard locked constructs. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1218-1225, 2015.

Retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunion following failed locked plating

PURPOSE

To review the outcome of retrograde locked nailing for aseptic supracondylar femoral nonunions following failed locked plating.

METHODS

Records of 20 men and 4 women aged 20 to 57 (mean, 39) years who underwent retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunion following failed locked plating were reviewed. There were 20 closed and 4 open Gustilo type II or IIIA fractures secondary to motor vehicle accidents (n=21) or falls (n=3). Patients had undergone one to 3 operations. The mean time from injury to the present revision surgery was 1.3 years. No patient had a flexion contracture. The locked plate was removed and replaced with a retrograde dynamic locked nail (with or without buttress plate augmentation) followed by bone grafting.

RESULTS

17 men and 4 women were followed up for a mean of 3.4 years. The rest were lost to follow-up. The 21 patients achieved bone union after a mean of 4.3 months. The mean maximal knee flexion improved from 97.1º to 107.6º (p=0.03). Knee function was excellent in one, good in 15, and fair in 5 knees. The fair outcome was due to extension contracture, varus knee deformity, or knee pain. There were 3 malunions with varus deformity of 7º, 8º, and 9º each. No patient had deep infection causing a nonunion. All 21 patients could walk without aids.

CONCLUSION

Retrograde locked intramedullary nailing for aseptic supracondylar femoral nonunions following failed locked plating achieved a high union rate.