What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study

High Rate of Undetected Infections in Failed Osteosynthesis of Pertrochanteric Fractures

OBJECTIVE

The objective of this study was to assess the incidence of infection in patients with cutout after proximal femur fracture (PFF) osteosynthesis.

METHODS

DESIGN

Retrospective cohort study.

SETTING

Third-level trauma center.

PATIENT SELECTION CRITERIA

Patients presenting with a cutout following PFF (OTA/AO 31A) osteosynthesis, between January 2007 and December 2020.

OUTCOME MEASUREMENTS AND COMPARISONS

The primary outcome was infection according to the European Bone and Joint Infection Society criteria.

RESULTS

Sixty-seven patients presenting with a cutout were included, with mean age of 83.3 years (range 63-96), and 51 (76.1%) were women. Of all cases, 16 (24.7%) presented a concomitant infection. The presence of concomitant infection was suspected preoperatively in only 3 of the cases. A subgroup analysis was performed between the cases with infection and those without infection, the groups being comparable in terms of demographic data and postoperative radiological criteria. Patients with underlying infection had a higher rate of surgical wound complication (56.3% vs. 22%, P = 0.014) and higher rates of leukocytosis (11.560 vs. 7.890, P = 0.023).

CONCLUSION

Faced with a cutout after osteosynthesis of a PFF, underlying infection should be considered as a possible etiological factor.

LEVEL OF EVIDENCE

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

A novel model of locking plate and locking spongious screw: a biomechanical in vitro comparison study with classical locking plate

BACKGROUND

Locking plates are commonly used for the fixation of comminuted, periprosthetic and osteoporotic bone fractures. These plates are secured to the bone with screws, creating a stable connection with fixed angle between the plate and the screws. In this biomechanical in vitro study, our aim is to evaluate and compare the novel locking plate-locking spongious screw model with FDA approved classical locking plate.

METHODS

Sawbone PCF-15 osteoporotic bone model was utilized to simulate osteoporotic bone conditions. Two screws were used to attach both the classical locking plate and the novel locking plate-locking spongious screw model to these bone models. The attachment strength of the screws to the bone blocks was measured by pull-out tests.

RESULTS

Novel locking plate-locking spongious screw model exhibited an 84.38% stronger attachment to the osteoporotic bone model compared to the current locking plate model.

CONCLUSIONS

In conclusion, one of the important problems in the locking plates which is the high Pull-out risk of the locking spongious screws can been resolved with our proposed new model and has a chance of having a better purchase especially in osteoporotic bones.

Proximal femoral bionic nail-a novel internal fixation system for the treatment of femoral neck fractures: a finite element analysis

Introduction: Currently, cannulated screws (CSs) and dynamic hip screws (DHSs) are widely used for the treatment of femoral neck fractures, but the postoperative complications associated with these internal fixations remain high. In response to this challenge, our team proposes a new approach involving triangular-supported fixation and the development of the proximal femoral bionic nail (PFBN). The primary objective of this study is to investigate the biomechanical differences among CSs, DHSs, and the PFBN in their capacity to stabilize femoral neck fractures. Methods: A normal proximal femur model was constructed according to the CT data of a normal healthy adult. A femoral neck fracture model was constructed and fixed with CSs, DHSs, and the PFBN to simulate the fracture fixation model. Abaqus 6.14 software was used to compare the biomechanical characters of the three fracture fixation models. Results: The maximum stresses and displacements of the normal proximal femur were 45.35 MPa and 2.83 mm, respectively. Under axial loading, the PFBN was more effective than DHSs and CSs in improving the stress concentration of the internal fixation and reducing the peak values of von Mises stress, maximum principal stress, and minimum principal stress. The PFBN fixation model exhibits superior overall and fracture section stability in comparison to both the DHS fixation model and the CS fixation model under axial loading. Notably, the maximum stress and peak displacement of the PFBN and bone were lower than those of the DHS and CS fixation models under bending and torsional loading. Conclusion: The PFBN shows considerable improvement in reducing stress concentration, propagating stress, and enhancing the overall stability in the femoral neck fracture fixation model compared to DHSs and CSs. These enhancements more closely correspond to the tissue structure and biomechanical characteristics of the proximal femur, demonstrating that the PFBN has great potential for therapeutic purposes in treating femoral neck fractures.

Medial helical versus straight lateral plating of distal femoral fractures-a biomechanical comparative study

BACKGROUND

Distal femoral fractures are commonly treated with lateral straight plates. However, the lateral approach may not always be desirable, and 180°-helical plates may be an alternative.

AIM

To investigate the biomechanical competence of 180°-helical plating versus standard straight lateral plating of unstable fractures at the distal femur.

METHODS

Twelve left artificial femora were instrumented with a 15-hole Locking Compression Plate-Distal Femur, using either 180°-helical plates (group 1) or conventional straight lateral plates (group 2). An unstable distal femoral fracture AO/OTA 33-A3.3 was simulated. All specimens were biomechanically tested under quasi-static and progressively increasing combined cyclic axial and torsional loading in internal rotation until failure.

FINDINGS

Initial axial stiffness (N/mm) was significantly higher in group 1 (185.6 ± 50.1) compared to group 2 (56.0 ± 14.4), p < 0.001. Group 1 demonstrated significantly higher initial interfragmentary flexion (°) and significantly lower initial varus/valgus deformation (°) under 500 N static axial compression versus group 2 (2.76 ± 1.02 versus 0.87 ± 0.77 and 4.08 ± 1.49 versus 6.60 ± 0.47), p ≤ 0.005. Shear displacement (mm) under 6 Nm static torsion was significantly higher in group 1 versus group 2 in both internal (1.23 ± 0.28 versus 0.40 ± 0.42) and external (1.21 ± 0.40 versus 0.57 ± 0.33) rotation, p ≤ 0.013. Cycles to failure and failure load (N) (clinical/catastrophic) were significantly higher in group 1 (12,484 ± 2116/13,752 ± 1518 and 1748.4 ± 211.6/1875.2 ± 151.8) compared to group 2 (7853 ± 1262/9727 ± 836 and 1285.3 ± 126.2/1472.7 ± 83.6), p ≤ 0.001.

INTERPRETATION

Although 180°-helical plating using a pre-contoured standard straight lateral plate was associated with higher shear and flexion movements, it demonstrated improved initial axial stability and resistance against varus/valgus deformation compared to straight lateral plating. Moreover, the helical plates were associated with significantly higher endurance to failure. From a biomechanical perspective, 180°-helical plating may be considered as a valuable alternative to standard straight lateral plating of unstable distal femoral fractures.

Is augmented femoral lateral plating with helically shaped medial plates biomechanically advantageous over straight medial plates?

Dual plating of comminuted distal femoral fractures allows for early patient mobilization. An additional helically shaped medial plate avoids the medial vital structures of the thigh. The aim of this study is to investigate the biomechanical competence of an augmented lateral locking compression plate distal femur (LCP-DF) using an additional straight versus a helically shaped medial LCP of the same length. Ten pairs of human cadaveric femora were instrumented with a lateral anatomical 15-hole LCP-DF. Following, they were pairwise instrumented with either an additional medial straight 14-hole LCP (group 1) or a 90°-helical shape LCP (group 2). All specimens were biomechanically tested under quasi-static and progressively increasing combined cyclic axial and torsional loading until failure. Initial interfragmentary axial displacement and flexion under static compression were significantly smaller in group 1 (0.11 ± 0.12 mm and 0.21 ± 0.10°) versus group 2 (0.31 ± 0.14 mm and 0.68 ± 0.16°), p ≤ 0.007. Initial varus deformation under static compression remained not significantly different between group 1 (0.57 ± 0.23°) and group 2 (0.75 ± 0.34°), p = 0.085. Flexion movements during dynamic loading were significantly bigger in group 2 (2.51 ± 0.54°) versus group 1 (1.63 ± 1.28°), p = 0.015; however, no significant differences were observed in terms of varus, internal rotation, and axial and shear displacements between the groups, p ≥ 0.204. Cycles to failure and load at failure were higher in group 2 (25,172 ± 6376 and 3017 ± 638 N) compared to group 1 (22,277 ± 4576 and 2728 ± 458 N) with no significant differences between them, p = 0.195. From a biomechanical perspective, helical double plating may be considered a useful alternative to straight double plating, demonstrating ameliorated damping capacities during flexion deformation and safer application as the medial neurovascular structures of the thigh are avoided.

Morbidity and Mortality Analysis in the Treatment of Intertrochanteric Hip Fracture with Two Fixation Systems: Dynamic Hip Screw (DHS) or Trochanteric Fixation Nail Advance (TFNA)

BACKGROUND

The aim of this study was to compare the clinical outcomes, complications, and mortality of patients with intertrochanteric hip fracture treated with dynamic hip screw (DHS) vs. trochanteric fixation nail advance (TFNA).

METHODS

We evaluated 152 patients with intertrochanteric fractures concerning age, sex, comorbidity, Charlson Index, preoperative gait, OTA/AO classification, time from fracture to surgery, blood loss, amount of blood replacement, changes in gait, full weight-bearing at hospital discharge, complications, and mortality. The final indicators encompassed the adverse effects linked to implants, postoperative complications, clinical healing or bone healing duration, and functional score.

RESULTS

The study included a total of 152 patients, out of which 78 (51%) received DHS treatment and 74 (49%) received TFNA treatment. The results of this study show that the TFNA group demonstrated superiority (p < 0.001). However, it should be noted that the TFNA group had a higher frequency of the most unstable fractures (AO 31 A3, p < 0.005). Full weight-bearing at discharge also decreased in patients with more unstable fractures (p = 0.005) and severe dementia (p = 0.027). Mortality was higher in the DHS group; however, a longer time from diagnosis to surgery was also observed in this group (p < 0.005).

CONCLUSIONS

The TFNA group has shown a higher success rate in achieving full weight-bearing at hospital discharge when treating trochanteric hip fractures. This makes it the preferred choice for treating unstable fractures in this region of the hip. Additionally, it is important to note that a longer time to surgery is associated with increased mortality in patients with hip fractures.

[Research progress in biomechanics of common internal fixation for femoral neck fracture]

OBJECTIVE

To summarize the characteristics and biomechanical research progress of common internal fixation for femoral neck fractures in recent years, so as to provide reference to clinical treatment of femoral neck fracture.

METHODS

The domestic and foreign relevant literature on biomechanics of internal fixation of femoral neck fracture in recent years was reviewed, and the biomechanical research progress was summarized.

RESULTS

Among the internal fixations currently used in the treatment of femoral neck fractures, three cannulated screws can provide sliding compression at the end of the fracture, but the shear resistance is weak, and the risk of long-term internal fixation failure is high; dynamic hip screw and proximal femoral locking plate have excellent angle stability and overall strength; medial buttress plate can transform vertical shear force into compressive stress to promote fracture healing and produce a certain anti-rotation effect; femoral neck system can support the fracture in multi-axial direction, with excellent anti-rotation and anti-shortening properties; and cephalomedullary nails have high overall strength and failure load. Different internal fixations have their own indications due to differences in structure and biomechanics.

CONCLUSION

At present, there is no detailed standard guidance of internal fixation selection. Clinically, the appropriate treatment should be selected according to the fracture types of patients.

The utility of reverse distal femur locking compression plate in minimally invasive osteosynthesis for type C subtrochanteric fractures of the femur: technical description and a clinical series of 50 cases

BACKGROUND

Establishing fracture consolidation and avoiding postoperative complications of comminuted subtrochanteric fractures of the femur are technically challenging. The authors delineated a technical description of minimally invasive plate osteosynthesis (MIPO) by using a reverse distal femur locking compression plate (LCP-DF) and retrospectively reviewed the outcomes of these particular fractures.

METHODS

Fifty patients with 51 type C subtrochanteric fractures of the femur were operated on by MIPO and reverse LCP-DF fixation. The collected data included postoperative complications, union times, and clinical outcomes.

RESULTS

All fractures were united with a mean union time of 19.4 weeks (range 16-22). Regarding postoperative complications, asymptomatic valgus angulation occurred in five patients and trochanteric pain in six. According to Harris hip score, nine patients were determined to be excellent, 36 to be good and five to be fair.

CONCLUSION

MIPO by reverse LCP-DF is reliable and effective for type C subtrochanteric fractures of the femur particularly in situations where intramedullary nailing is not feasible.

Effect of cyclic loading on the stability of screws placed in the locking plates used to bridge segmental bone defects

The objective of this study was to evaluate the ex vivo effect of cyclic loading on the stability of screws placed in locking plates used to bridge segmental bone defects. The primary interface stability was assessed using peak reverse torque. Eighteen, 8-hole stainless-steel 4.5 mm locking plates and 4.0-mm self-tapping locking-head screws were used to stabilize 40-mm segmental defects in goat tibiae. Treatment groups included control constructs without cyclic loading (n = 6) and constructs tested to 5000 (n = 6) and 10,000 cycles (n = 6) of 600 N compressive axial loading. The insertion of all screws was standardized to 400 N-cm insertion torque. Peak reverse torque was measured immediately after screw placement (control), or after the completion of the respective loading cycles. The difference between treatment groups was compared using univariate analysis of variance. The analysis revealed a significant difference in peak reverse torque of the screws among the treatment groups (p = .000). The mean reverse torque values equaled 343.5 ± 18.3 N-cm for non-cycled controls, 303.3 ± 25.9 and 296.0 ± 42.9 N-cm after 5000 and 10,000 cycles, respectively. Among all treatment groups, screws placed in the distal bone segment tended to have lesser peak reverse torque reduction than those placed in the proximal segment and the difference was proportional to the number of cycles (p = .562; p = .255; p = .013 in control, and after 5000 and 10,000 cycles, respectively). Cyclic loading may have a negative effect on the primary stability of screws placed in locking plate constructs used to bridge segmental bone defects and could contribute to the risk of screw loosening.

Intramedullary versus extramedullary fixation in the treatment of subtrochanteric femur fractures: A comprehensive systematic review and meta-analysis

OBJECTIVE

This meta-analysis aimed to compare the clinical outcomes of intramedullary fixation with the extramedullary fixation in the surgical management of subtrochanteric fractures by analyzing relevant randomized controlled trials (RCTs) and retrospective cohort studies (RCSs).

METHODS

The PubMed, Embase, Cochrane Library, Wanfang database, and Chinese National Knowledge Infrastructure (CNKI) were searched from their inception till June 29, 2020. Two reviewers extracted the data, including operation time, intraoperative blood loss, fluoroscopy time, length of stay, union time, nonunion rate, infection rate, implant failure rate, reoperation rate, Harris hip score, and mortality rate. The Cochrane risk-of-bias tool and the Newcastle-Ottawa quality assessment scale were used to evaluate the methodological quality of RCTs and RCSs, respectively. Statistical heterogeneity was quantitatively evaluated with the I2 statistic.

RESULTS

There were no significant differences in operation time, intraoperative blood loss, average length of stay in hospital, infection rate, implant failure rate, Harris hip scores, and mortality rate. Intramedullary nail could achieve shorter union time (MD=-1.77, 95% CI -3.40~-0.14, p=0.03), lower nonunion rate (RR=0.36, 95%CI 0.14~0.97, p=0.04), and reoperation rate (RR=0.46, 95% CI 0.24~0.89, p=0.02) than extramedullary fixations. The subgroup analysis indicated that intramedullary nail was superior than extramedullary fixations in operation time, reoperation rate, and Harris hip scores in the ≥60-year subgroup. However, the intraoperative blood loss in intramedullary nail group was significantly higher than that of extramedullary fixation group in the <60-year subgroup.

CONCLUSION

The results of this study have revealed that intramedullary fixation can confer shorter union time, lower nonunion, and reoperation rates compared with extramedullary fixations. Therefore, intramedullary fixation should be considered as the first selection for the treatment of patients with subtrochanteric fractures.

LEVEL OF EVIDENCE

Level II, Therapeutic study.

How Do the Locking Screws Lock? A Micro-CT Study of 3.5-mm Locking Screw Mechanism

OBJECTIVE

 To quantify the amount of the screw head thread and the plate hole thread connection in two 3.5 mm locking plates: Locking Compression Plate (LCP) and Polyaxial Locking System (PLS).

MATERIALS AND METHODS

 A micro - CT scan of a screw head - plate hole connection was performed pre- and post destructive tests. Tests were performed on bone surrogates in a fracture gap model. The 3.5 LCP and 3.5 PLS plates, with 3 perpendicular screws per segment were used in a destructive static test. The 3.5 PLS plates with mono- and polyaxial screws were compared in a cyclic fatigue tests in two orthogonal directions. Pre - and post - test scan datasets were compared. Each dataset was converted into serial images depicting sections cut orthogonally to locking screw axis. The amount of engagement was detected through automated image postprocessing.

RESULTS

 The mean amount of the thread connection for the LCP was 28.85% before and 18.55% after destructive static test. The mean amount of the connection for the PLS was 16.20% before and 14.55% after destructive static test. When inserted monoaxially, the mean amount of the connection for the PLS screws was 14.4% before and 19.24% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate thickness was 2.99% before and 2.08% after destructive cyclic test. The mean amount of the connection for the polyaxial inserted PLS screws when loaded against plate width was 3.36% before and 3.93% after destructive cyclic test. The 3D visualization of the thread connection showed that the initial interface points between screw head and plate hole are different for both LCP and PLS after the destructive testing. Depending on the type of applied force, there was either loss or increase of the contact.

CLINICAL RELEVANCE

 Micro-CT offers news possibilities in locking implant investigation. It might be helpful in better understanding the nature of locking mechanism and prediction of possible mode of failure in different systems.

Secondary Perforation Risk in Plate Osteosynthesis of Unstable Proximal Humerus Fractures: A Biomechanical Investigation of the Effect of Screw Length

Secondary perforation of screws into the joint surface is a commonly reported mechanical fixation failure mode in locked plating of proximal humerus fractures (PHF). This study investigated the influence that screws tip to joint distance (TJD) has on the biomechanical risk of secondary screw perforation and the stability of PHF. Ten pairs of cadaveric proximal humeri with a wide range of bone mineral density were used. Each specimen was osteotomized and instrumented with the PHILOS plate, simulating a highly unstable 3-part fracture. Bones were randomized into a long screw group (LSG) with 4 mm TJD, or a short screw group (SSG) with 8 mm TJD. A custom biomechanical setup was used to test the samples to failure cyclically with a constant valley load and an increasing ramp. The number of cycles to the initial screw loosening event was significantly higher for the LSG (mean ± standard deviation: 17,532 ± 6,458) compared with the SSG (11,102 ± 5,440) (p < 0.01). The mode of failure during testing was lateral-inferior displacement combined with varus collapse, with calcar screws perforating first. The number of cycles to failure event for LSG (27,849 ± 5,648) was not significantly different compared with SSG (28,782 ± 7,307) (p = 0.50). Screws that purchase closer to the joint had better initial stability and resistance against loosening. Placing longer screws, within limits dictated by the surgical guide, is expected to decrease the risk of secondary perforation failures in unstable PHF. These findings require clinical corroboration. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2625-2633, 2019.

Biomechanics of Femoral Neck Fractures and Implications for Fixation

Fractures of the femoral neck can occur in young healthy individuals due to high loads occurring during motor vehicle accidents, impacts, or falls. Failure forces are lower if impacts occur sideways onto the greater trochanter as compared with vertical loading of the hip. Bone density, bone geometry, and thickness of cortical bone at the femoral neck contribute to its mechanical strength. Femoral neck fractures in young adults require accurate reduction and stable internal fixation. The available techniques for fracture fixation at the femoral neck (cannulated screws, hip screw systems, proximal femur plates, and cephallomedullary nails) are reviewed with respect to their competence to provide biomechanical stability. Mechanically unstable fractures require a load-bearing implant, such as hip screws, with antirotational screws or intramedullary nails. Subcapital or transcervical fracture patterns and noncomminuted fractures enable load sharing and can be securely fixed with cannulated screws or solitary hip screw systems without compromising fixation stability.

Comparison of Intra- and Extramedullary Implants in Treatment of Unstable Intertrochanteric Fractures

INTRODUCTION

Comparison was made of the clinical and radiological results of the surgical treatments of proximal femoral nail (PFN), dynamic hip screw (DHS) or proximal femoral locking compression plate (PF-LCP) in patients with AO 31A2.2/2.3 unstable intertrochanteric femoral fracture(ITF).

METHODS

Evaluation was made of a total of 91 patients in respect of age, gender, time from fracture to surgery, operating time, amount of blood replacement, total hospitalisation, follow-up period, time to full weight-bearing, time to union, complications and Harris hip scores(HHS).

RESULTS

A statistically significant difference was determined between the groups in respect of perioperative operating time, blood replacement and hospitalisation period with the values of the PFN group seen to be superior to those of the other two groups (p < 0.001). No significant difference was determined beween the DHS and PFN groups in respect of time to union and in the long-term HHS, both groups were seen to be superior to the PF-LCP group (p < 0.001). Full weight-bearing was statistically significantly earlier in the PFN group (p < 0.001). The numbers of implant failures was statistically significantly higher in the PF-LCP group (p < 0.001).

CONCLUSION

The new generation intra-medullar nails are easy to apply and have more successful clinical results compared to extra-medullar implants in the treatment of A2 unstable ITF. Due to the high rates of implant failure, PF-LCP should not be preferred in these fractures.

Epidemiology, treatment and mortality of trochanteric and subtrochanteric hip fractures: data from the Swedish fracture register

BACKGROUND

Hip fractures are a major worldwide public health problem and includes two main types of fractures: the intracapsular (cervical) and the extracapsular (trochanteric and subtrochanteric) fractures. The aim of this study on patients with trochanteric and subtrochanteric hip fractures was to describe the epidemiology, treatment and outcome in terms of mortality within the context of a large register study.

METHODS

A descriptive epidemiological register study including patients registered in the national Swedish Fracture Register from January 2014 to December 2016. Inclusion criteria were all primary surgically treated traumatic non-pathological trochanteric and subtrochanteric femoral fractures in patients aged 18 years and above. Individual patient data (age, gender, injury location, injury cause, fracture type, treatment and timing of surgery) were retrieved from the register database. Mortality data was obtained via linkage to the Swedish Death Register.

RESULTS

A total of 10,548 consecutive patients were identified and included in the study. The mean (±SD) age for all patients was 82 ± 11 years and the majority of the patients were females (69%). Most of the fractures were caused by a fall at the same level (83%) at the patients' accommodation (75%). Fractures were classified using the AO/OTA classification as 31-A1 in 29%, as 31-A2 in 49% and as 31-A3 in 22% of the cases. The most commonly used implant was a short antegrade intramedullary nail (42%), followed by a plate with sliding hip screw (37%). With increasing fracture complexity, the proportion of intramedullary nails was increasing, and also the use of long versus short nails. The majority of the patients were operated within 36 h (90%). There was a higher mortality at 30 days and 1 year for males, and for all those who were delayed to surgery > 36 h.

CONCLUSION

Safety measures to prevent fall at elderly patient's accommodation might be a way to reduce the number of trochanteric and subtrochanteric hip fractures. Surgery as soon as possible without delay should be considered to reduce the mortality rate. The selection of surgical methods depends on the fracture complexity.

High failure rate of proximal femoral locking plates in fixation of trochanteric fractures

Background

The aim of this study was to report our previous results of treatments for trochanteric fractures with proximal femoral locking plates (PFLP) and to analyze the underlying mechanisms and possible risk factors associated with the high failure rate of this technique.

Methods

From January 2010 to October 2014, 273 consecutive patients with trochanteric femoral fractures were identified, and 95 patients (with 97 fractures) ultimately met the inclusion criteria. Clinical records regarding demographic features and intraoperative data including total incision length, operation time, blood loss, and failures detected in radiographs were documented and assessed. The collected data were analyzed with SPSS 19.0 software.

Results

The stable group (AO/OTA 31 A1 and A2.1) had less blood loss than the unstable group (AO/OTA 31 A2.2, A2.3, and A3). The ultimate failure rate was 36% in 97 fractures. The obvious complications in this study included nonunion in 7 (7.2%) fractures, implant breakage in 4 (4.1%) fractures, varus deformity in 34 (35%) fractures, and loosening of the proximal femoral screw in 21 (21.6%) fractures. Six patients received reoperations. The total failure rate in the stable group was 17% and was 50% in the unstable group. In patients greater than 60 years old in the unstable group, the failure rate was 60.5%.

Conclusions

High failure rates of PFLP were observed in patients with trochanteric fracture, especially in patients who were greater than 60 years old with unstable fracture types. PFLP was not an appropriate treatment for trochanteric fractures.

Why and how do locking plates fail?

Locking plates have led to important changes in bone fracture management, allowing flexible biological fracture fixation based on the principle of an internal fixator. The technique has its indications and limitations. Most of the typical failure patterns arise from basic technical errors. Types of locking plates, material properties and the general principles of locking plate applications are reviewed together with their misapplication.

Biomechanical Analysis of the Proximal Femoral Locking Compression Plate: Do Quality of Reduction and Screw Orientation Influence Construct Stability?

OBJECTIVES

To investigate biomechanically in a human cadaveric model the failure modes of the proximal femoral locking compression plate and explore the underlying mechanism.

METHODS

Twenty-four fresh-frozen paired human cadaveric femora with simulated unstable intertrochanteric fractures (AO/OTA 31-A3.3) were assigned to 4 groups with 6 specimens each for plating with proximal femoral locking compression plate. The groups differed in the quality of fracture reduction and plating fashion of the first and second proximal screws as follows: (1) anatomic reduction with on-axis screw placement; (2) anatomic reduction with off-axis screw placement; (3) malreduction with on-axis screw placement; (4) malreduction with off-axis screw placement. The specimens were tested until failure using a protocol with combined axial and torsional loading. Mechanical failure was defined as abrupt change in machine load-displacement data. Clinical failure was defined as 5 degrees varus tilting of the femoral head as captured with optical motion tracking.

RESULTS

Initial axial stiffness (in N/mm) in groups 1 to 4 was 213.6 ± 65.0, 209.5 ± 134.0, 128.3 ± 16.6, and 106.3 ± 47.4, respectively. Numbers of cycles to clinical and mechanical failure were 16,642 ± 10,468 and 8695 ± 1462 in group 1, 14,076 ± 3032 and 7449 ± 5663 in group 2, 8800 ± 8584 and 4497 ± 2336 in group 3, and 9709 ± 3894 and 5279 ± 4119 in group 4. Significantly higher stiffness and numbers of cycles to both clinical and mechanical failure were detected in group 1 in comparison with group 3, P ≤ 0.044.

CONCLUSIONS

Generally, malreduction led to significantly earlier construct failure. The observed failures were cut-out of the proximal screws in the femoral head, followed by either screw bending, screw loosening, or screw fracture. Proper placement of the proximal screws in anatomically reduced fractures led to significantly higher construct stability. Our data also indicate that once the screws are placed off-axis (>5 degrees), the benefit of an anatomic reduction is lost.

Locking Cap Designs Improve Fatigue Properties of Polyaxial Screws in Upper Extremity Applications

OBJECTIVES

This study sought to examine fatigue characteristics of 2 polyaxial locking screw designs: locking cap (LC) and cross-threaded (CT). The goal was to compare LC and CT implants at 0, 10, and 15 degrees of angulation to determine the effect of locking mechanism on screw-plate interface failure. The hypothesis was that LC implants would have superior fatigue properties in comparison to CT designs and that increased angulation of the screw would have a negative impact on the fatigue life of CT implants, but would not have any effect on LC implants.

METHODS

A total of 72 screws were tested in 4 upper extremity implants. Implants were subjected to cyclic shear loads and subsequent ramp to failure. Performance characteristics were statistically compared using nonparametric statistical methods.

RESULTS

Fatigue testing demonstrated that LC designs were consistently able to sustain a significantly higher number of cyclic loads than CT designs. There were no significant differences in the number of cycles sustained by LC designs because of changes in screw angle, but CT implants exhibited decreases in screw stability with increasing angulation.

CONCLUSIONS

Likely because of the spherical screw head geometry, LC fatigue characteristics are not influenced by the orientation of the screw relative to the plate. Application of an LC in the operating room requires additional time, but provides significantly more robust fixation of the screw, especially at oblique angles to the plate and provides a more predictable and consistent biomechanical result.

Management of unstable pertrochanteric fractures with proximal femoral locking compression plates and affect of neck-shaft angle on functional outcomes

BACKGROUND

Management of unstable pertrochanteric fractures remains a challenge with various implant choices. Intramedullary devices are usually preferred for the management of the unstable fractures. When nailing is unsuitable for the configuration of the fracture extra medullary procedures are preferred. PFLCP is a contact limited implant that allows multiple angularly stable fixations with preserving more bone stock after implantation as an extramedullary implant. There are only a few reports in the literature about the osteosynthesis of unstable trochanteric fractures with proximal femoral locking compression plates and their results are conflicting. In the present study we aimed to evaluate the functional and radiological outcomes of proksimal femoral locking compression plates in open reduction and internal fixation of AO/OTA 31A2-2 and 3 fractures.

METHODS

Patients older than 18 years of age with a minimum follow-up time of 1 year matching the inclusion criteria retrospectively evaluated. Patients' demographics, Singh index, intra and post-operative data, mobilization and union time gathered from the patients' files. Baumgaertner modified criteria of fracture reduction was used to assess the post-operative reduction quality. Early and last follow-up radiographs were used to evaluate malunion and change in neck- shaft angle. Final clinical outcome was assessed using the Harris Hip scoring system.

RESULTS

18 male and 13 female patients with the mean age of 74 (46-88) met the inclusion criteria. Reduction quality according to Baumgaertner modified criteria was good in 25 patients and acceptable in 6. Mean union time was 21.53 ± 4.18 weeks. There was neither non-union nor malunion. The mean neck-shaft angle change was -3.1° ± 2.16°. The mean HHS was 77.90 ± 4.84 and there was no significance in HHS according to reduction quality and change in neck-shaft angle (p = 0.385, p = 0.0059). HHS was negatively correlated with age, mobilization time and, longer union time (p < 0.05). There was no correlation between Singh index and reduction quality (p = 0.865). Singh index was only correlated with the patient's age (p = 0.000, rho = -0.595). There were 2 infections and, 2 backing of the proximal screws.

CONCLUSION

Even though PFLCP is not the first choice in management of unstable pertrochanteric fractures, it must be kept in mind as an alternative to the other conventional plates and intramedullary implants with the properties of an increased stability by multiaxial screw locking and the results are satisfactory when appropriate settlement achieved.

Clinical outcome of conventional versus biological fixation of subtrochanteric fractures by proximal femoral locked plate

INTRODUCTION

Surgical fixation is the standard management of the subtrochanteric fractures. Proximal femoral locked plating (PF-LCP) provides a strong construct for fixation with a high success rate. However, some studies reported implant failure due to loss of the postero-medial bone support and recommended an anatomical reduction. Other studies reported excellent to good results with indirect (biological) fixation without anatomical reduction. In this study, we reviewed the short-term clinical results of PF-LCP fixation for subtrochanteric fractures using both conventional and biological fixation.

MATERIALS AND METHODS

Forty six patients (34 males and 12 females) with comminuted subtrochanteric fractures were included aged between 18 and 74 (mean 44.3 years). They were treated in a single-blind random manner by either conventional (open, direct) or biological (indirect) reduction method and internal fixation with PF-LCP. Intra-operative variables including; duration of surgery, blood loss, fluoroscopy time and any complications were recorded. Post-operative differences including; duration of healing, implant failure, complications and the final clinical outcome by Harris Hip Score (HHS) were documented.

RESULTS

44 cases continued to the final follow-up (23 of the open fixation group and 21 of the biological fixation group). Patients of open group demonstrated greater blood loss (756±151 vs. 260±39ml; P<0.0001), longer operative times (129±16.9 vs. 91±8min; P<0.0001) and incisions (s) length (20.4±3 vs. 13.4±1cm; P<0.0001). More patients needed blood transfusion in open group (11 patients vs. six in closed group; P<0.0001). Patients of biological group demonstrated longer fluoroscopy time (80.9±7.3 vs. 47.2±5.8sec.; P<0.0001). For each group, one case of implant failure was recorded. Low patient compliance was a detrimental factor for the implant failure in both cases. No much difference was demonstrated for the healing rate (open group; 18.3±3.7 vs. biological group16.5±4 weeks; P<0.058) and for the functional outcome (open group; excellent/good: 54%/37%, biological group; excellent/good: 57%/33%; P=0.766).

CONCLUSION

PF-LCP provided a strong construct for fixation of the comminuted subtrochanteric fractures either by open or biological techniques. Low patient compliance is an influential factor for implant failure in both types.

Head-locking durability of fixed and variable angle locking screws under repetitive loading

Polyaxial locking screws are increasingly applied in fracture fixation. To investigate the durability of the head-locking mechanism, the removal torque of variable angle (VA) and fixed angle (FA) stainless steel and titanium locking screws was investigated without and after a cyclic loading test. Stainless steel (St) and titanium (Ti) 2.4 mm orthogonally inserted FA screws and 2.4 mm VA screws inserted in different inclinations (0°-15°) (n = 6 per group) were locked at 0.8 Nm. Removal torque was determined without (W) and after (A) cyclic loading (sinusoidal load, 5 Hz, constant amplitude of 25 N, up to 10'000 cycles, or failure). Significant differences in-between the groups were detected by Student's t-test (p < 0.05). Except VA Ti in 0deg and FA, all groups exhibited a drop in removal torque below the insertion torque without and after cyclic testing. The removal torque was (St: FA W:0.81 Nm ± 0.04 A:0.72Nm ± 0.04; VA0deg W:0.73 Nm ± 0.04 A:0.65 Nm ± 0.05; VA15deg W:0.51 Nm ± 0.05 A:0.50 Nm ± 0.08; Ti: FA W:0.82 Nm ± 0.03 A:0.70 Nm ± 0.04; VA0deg W:0.80 Nm ± 0.02 A:0.72 Nm ± 0.05; VA15deg W:0.55 Nm ± 0.03 A:0.54 Nm ± 0.06). In all groups, the removal torque after cyclic testing did not drop below 16% of the removal torque without cyclic testing. No head loosening was observed after cyclic testing. Stainless steel and titanium 2.4 mm fixed and variable angle locking screws provide a stable and lasting head-locking mechanism. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:949-952, 2016.

Locked plating versus cephalomedullary nailing of unstable intertrochanteric femur fractures

BACKGROUND

Proximal femur locking plates (PFLP) have received increased attention as an alternative for the treatment of proximal femur fractures. However, recent clinical data on these implants has raised concern about higher than expected failure rates.

QUESTION/PURPOSE

The purpose of the present study was to compare outcomes of unstable pertrochanteric femur fractures (AO/OTA 31A3) treated at a level-1 trauma center using either PFLP or cephalomedullary nailing (CMN).

PATIENTS AND METHODS

Sixty-two patients (31 PFLP and 31 CMN, 55 % female, average age 63 years, range 21-94) with 64 OTA 31A3 fractures (32 PFLP and 32 CMN) treated between 2003 and 2007 were retrospectively reviewed. No differences were found with regard to gender, BMI, diabetes and time to surgery.

RESULTS

One patient (5 %) in the CMN group underwent a reoperation (debridement with hardware removal), while eight PFLP patients (25 %) did (two debridements, two hardware removals, four nonunion repairs). One mechanical failure (5 %) occurred in the CMN group and 12 (38 %) in the PFLP group (p = 0.007). One nonunion (5 %) was observed in the CMN group, while 6 (19 %) occurred in the PFLP group.

CONCLUSION

A higher rate of reoperation and mechanical failure can be expected for unstable intertrochanteric femur fracture when treated with PFLP than with CMN.

Increased Fracture Collapse after Intertrochanteric Fractures Treated by the Dynamic Hip Screw Adversely Affects Walking Ability but Not Survival

In osteoporotic hip fractures, fracture collapse is deliberately allowed by commonly used implants to improve dynamic contact and healing. The muscle lever arm is, however, compromised by shortening. We evaluated a cohort of 361 patients with AO/OTA 31.A1 or 31.A2 intertrochanteric fracture treated by the dynamic hip screw (DHS) who had a minimal follow-up of 3 months and an average follow-up of 14.6 months and long term survival data. The amount of fracture collapse and shortening due to sliding of the DHS was determined at the latest follow-up and graded as minimal (<1 cm), moderate (1-2 cm), or severe (>2 cm). With increased severity of collapse, more patients were unable to maintain their premorbid walking function (minimal collapse = 34.2%, moderate = 33.3%, severe = 62.8%, and p = 0.028). Based on ordinal regression of risk factors, increased fracture collapse was significantly and independently related to increasing age (p = 0.037), female sex (p = 0.024), A2 fracture class (p = 0.010), increased operative duration (p = 0.011), poor reduction quality (p = 0.000), and suboptimal tip-apex distance of >25 mm (p = 0.050). Patients who had better outcome in terms of walking function were independently predicted by younger age (p = 0.036), higher MMSE marks (p = 0.000), higher MBI marks (p = 0.010), better premorbid walking status (p = 0.000), less fracture collapse (p = 0.011), and optimal lag screw position in centre-centre or centre-inferior position (p = 0.020). According to Kaplan-Meier analysis, fracture collapse had no association with mortality from 2.4 to 7.6 years after surgery. In conclusion, increased fracture collapse after fixation of geriatric intertrochanteric fractures adversely affected walking but not survival.