The influence of screw length on predicted cut-out failures for proximal humeral fracture fixations predicted by finite element simulations

Intramedullary versus locking plate fixation for proximal humerus fractures: indications and technical considerations

Background

The incidence of proximal humerus fractures (PHFs) continues to increase with an aging population, and intramedullary nailing (IMN) and locking plate fixation are two commonly employed techniques for the surgical management of PHF. However, the optimal fixation method can be a source of ongoing controversy. Some influencing factors include the extent of humeral head involvement, fracture complexity, patient age, and surgeon preference. There are many studies that provide a mix of data either when comparing the two techniques or analyzing them in isolation. The aim of this review is to further elucidate the indications and technical considerations involved specifically in IMN vs. locking plate fixation for PHF to further aid orthopedic surgeons when choosing surgical management.

Methods

A narrative approach was chosen for this review allowing for a comprehensive review of literature, including recent findings pertaining to the comparison of management options for PHF. A comprehensive literature search was conducted using the PubMed, Embase, and Cochrane Library databases. The inclusion criteria involved studies that discussed "proximal humerus fracture" and either "intramedullary nail" or "locking plate fixation."

Results

Complications such as avascular necrosis, hardware failure, additional surgical interventions, infection, fracture redisplacement, rotator cuff rupture, and nonunion did not show significant differences between the two groups. Newer generation humeral nails have minimized early complications. As both techniques undergo further refinement and utilization when specifically indicated, functional outcomes, potential complications, and postoperative pain continue to be improved.

Conclusion

The available evidence suggests that both intramedullary nails and locking plates can effectively restore shoulder function in the treatment of displaced proximal humeral fractures, with unclear superiority of either method. The choice of technique should be tailored to patient factors such as fracture type, age, bone quality, and functional expectations. Surgeon experience also plays a role. While certain presentations may exhibit trends that favor one fixation, no specific technique can be universally recommended. Both IMN and LP have shown comparable and satisfactory outcomes, and the final fixation method chosen should take into account the unique characteristics of each patient.

Morphology and novel classification of proximal humeral fractures

Background: The morphology of proximal humeral fractures (PHFs) is complex, and the fixation and selection of implants need to be guided by the fracture type and classification, which requires an accurate understanding of the fracture line. This study had three purposes. 1) Define and analyze the fracture lines and morphological features of all types PHFs by three-dimensional (3D) mapping technology. 2) Determine the osteotomy position of the biomechanical model of the PHFs according to the fracture heat map. 3) Based on the analysis of the pathological morphology and distribution of a large number of consecutive cases of PHFs, propose a novel classification of PHFs. Methods: We retrospectively collected 220 cases of PHFs and generated a 3D fracture map and heat map based on computed tomography (CT) imaging. Through analysis of the fracture morphology of the 220 PHFs, a novel classification was proposed. The primary criterion for staging was the continuity between the humeral head and the greater tuberosity and lesser tuberosity, and the secondary criterion was the relationship between the humeral head segment and the humeral shaft. Results: The fracture line was primarily found around the metaphyseal zone of region of the surgical neck, with the most extensive distribution being below the larger tuberosity and on the posterior medial side of the epiphysis. We suggest that the osteotomy gap should be immediately (approximately 5-10 mm) below the lower edge of the articular surface. The most common type of fracture was type I3 (33 cases, 15.0%), followed by type IV3 fracture (23 cases, 10.4%), and type III2 fracture (22 cases, 10.0%). Interobserver and intraobserver reliability analysis for the fracture classification revealed a k value (95% confidence interval) of 0.639 (0.57-0.71) and 0.841, P < 0.01, respectively. Conclusion: In this study, the fracture line and morphological characteristics of PHFs were clarified in detail by 3D mapping technique. In addition, a new classification method was proposed by analysis of the morphological characteristics of 220 PHFs, A two-part fracture model for PHFs is also proposed.

Pre-operative virtual three-dimensional planning for proximal humerus fractures: A proof-of-concept study

Purpose

To (1) evaluate surgeon agreement on plating features (position and screw length) in virtual 3D planning software, (2) describe outcomes (fracture reduction, plate position, malpositioning of calcar screws and screw lengths) of plate fixations planned with routine pre-operative assessment (2D- and 3D CT imaging) and those planned with dedicated virtual 3D software of the same proximal humerus fracture.

Methods

Fourteen proximal humerus fractures were retrospectively reduced and fixed with virtual planning software by eight attending orthopaedic surgeons and compared to the true surgical fixation with post-operative computed tomography (CT) scans. Reduction differences were quantified using CT micromotion analysis.

Results

Intraclass correlation for screw lengths was 0.97 (95% CI: 0.96-0.98) and 0.90 (95% CI: 0.79-0.96) for plate position. Mean difference in total fracture rotation of the head between the virtual and conventional group was 22.0°. Plate position in the virtual planning group was 3.2 mm more proximal. There were no differences in inferomedial quadrant calcar screw positioning and, apart from the superior posterior converging screw, no significant differences in screw lengths.

Conclusion

Reproducibility on plate position and screw length with virtual planning software is adequate. Apart from fracture reduction, virtual planning yielded similar plate positions, screw malpositioning rates and lengths compared to routine pre-operative assessment.

Effect of different constraining boundary conditions on simulated femoral stresses and strains during gait

Finite element analysis (FEA) is commonly used in orthopaedic research to estimate localised tissue stresses and strains. A variety of boundary conditions have been proposed for isolated femur analysis, but it remains unclear how these assumed constraints influence FEA predictions of bone biomechanics. This study compared the femoral head deflection (FHD), stresses, and strains elicited under four commonly used boundary conditions (fixed knee, mid-shaft constraint, springs, and isostatic methods) and benchmarked these mechanics against the gold standard inertia relief method for normal and pathological femurs (extreme anteversion and retroversion, coxa vara, and coxa valga). Simulations were performed for the stance phase of walking with the applied femoral loading determined from patient-specific neuromusculoskeletal models. Due to unrealistic biomechanics observed for the commonly used boundary conditions, we propose a novel biomechanical constraint method to generate physiological femur biomechanics. The biomechanical method yielded FHD (< 1 mm), strains (approaching 1000 µε), and stresses (< 60 MPa), which were consistent with physiological observations and similar to predictions from the inertia relief method (average coefficient of determination = 0.97, average normalized root mean square error = 0.17). Our results highlight the superior performance of the biomechanical method compared to current methods of constraint for  both healthy and pathological femurs.

Preventing secondary screw perforation following proximal humerus fracture after locking plate fixation: a new clinical prognostic risk stratification model

INTRODUCTION

After locking plate (LP) fixation, secondary screw perforation (SSP) is the most common complication in proximal humerus fracture (PHF). SSP is the main cause of glenoid destruction and always leads to reoperation. This study aimed to identify independent risk parameters for SSP and establish an individualized risk prognostic model to facilitate its clinical management.

METHODS

We retrospectively reviewed the medical information of patients with PHF who underwent open reduction and internal LP fixation at one medical center (n = 289) between June 2013 and June 2021. Uni- and multivariate regression analyses identified the independent risk factors. A novel nomogram was formulated based on the final independent risk factors for predicting the risk of SSP. We performed internal validation through concordance indices (C-index) and calibration curves. To implement the clinical use of the model, we performed decision curve analyses (DCA) and risk stratification according to the optimal cutoff value.

RESULTS

A total of 232 patients who met the inclusion criteria were enrolled. The incidence of SSP was 21.98% at the last follow-up. We found that fracture type (odds ratio [OR], 3.111; 95% confidence interval [CI], 1.223-7.914; P = 0.017), postoperative neck-shaft angle (OR, 4.270; 95% CI 1.622-11.239; P = 0.003), the absence of calcar screws (OR, 3.962; 95% CI 1.753-8.955; P = 0.003), and non-medial metaphyseal support (OR,7.066; 95% CI 2.747-18.174; P = 0.000) were independent predictors of SSP. Based on these variables, we developed a nomogram that showed good discrimination (C-index = 0.815). The predicted values of the new model were in good agreement with the actual values demonstrated by the calibration curve. Furthermore, the model's DCA and risk stratification (cutoff = 140 points) showed significantly higher clinical benefits.

CONCLUSIONS

We developed and validated a visual and personalized nomogram that could predict the individual risk of SSP and provide a decision basis for surgeons to create the most optional management plan. However, future prospective and externally validated design studies are warranted to verify our model's efficacy.

Biomechanical design optimization of proximal humerus locked plates: A review

BACKGROUND

Proximal humerus locked plates (PHLPs) are widely used for fracture surgery. Yet, non-union, malunion, infection, avascular necrosis, screw cut-out (i.e., perforation), fixation failure, and re-operation occur. Most biomechanical investigators compare a specific PHLP configuration to other implants like non-locked plates, nails, wires, and arthroplasties. However, it is unknown whether the PHLP configuration is biomechanically optimal according to some well-known biomechanical criteria. Therefore, this is the first review of the systematic optimization of plate and/or screw design variables for improved PHLP biomechanical performance.

METHODS

The PubMed website was searched for papers using the terms "proximal humerus" or "shoulder" plus "biomechanics/biomechanical" plus "locked/locking plates". PHLP papers were included if they were (a) optimization studies that systematically varied plate and screw variables to determine their influence on PHLP's biomechanical performance; (b) focused on plate and screw variables rather than augmentation techniques (i.e., extra implants, bone struts, or cement); (c) published after the year 2000 signaling the commercial availability of locked plate technology; and (d) written in English.

RESULTS

The 41 eligible papers involved experimental testing and/or finite element modeling. Plate variables investigated by these papers were geometry, material, and/or position, while screw variables studied were number, distribution, angle, size, and/or threads. Numerical outcomes given by these papers included stiffness, strength, fracture motion, bone and implant stress, and/or the number of loading cycles to failure. But, no paper fully optimized any plate or screw variable for a PHLP by simultaneously applying four well-established biomechanical criteria: (a) allow controlled fracture motion for early callus generation; (b) reduce bone and implant stress below the material's ultimate stress to prevent failure; (c) maintain sufficient bone-plate interface stress to reduce bone resorption (i.e., stress shielding); and (d) increase the number of loading cycles before failure for a clinically beneficial lifespan (i.e., fatigue life). Finally, this review made suggestions for future work, identified clinical implications, and assessed the quality of the papers reviewed.

CONCLUSIONS

Applying biomechanical optimization criteria can assist biomedical engineers in designing or evaluating PHLPs, so orthopaedic surgeons can have superior PHLP constructs for clinical use.

Treatment of Metaphyseal Defects in Plated Proximal Humerus Fractures with a New Augmentation Technique-A Biomechanical Cadaveric Study

Background and Objectives: Unstable proximal humerus fractures (PHFs) with metaphyseal defects-weakening the osteosynthesis construct-are challenging to treat. A new augmentation technique of plated complex PHFs with metaphyseal defects was recently introduced in the clinical practice. This biomechanical study aimed to analyze the stability of plated unstable PHFs augmented via implementation of this technique versus no augmentation. Materials and Methods: Three-part AO/OTA 11-B1.1 unstable PHFs with metaphyseal defects were created in sixteen paired human cadaveric humeri (average donor age 76 years, range 66-92 years), pairwise assigned to two groups for locked plate fixation with identical implant configuration. In one of the groups, six-milliliter polymethylmethacrylate bone cement with medium viscosity (seven minutes after mixing) was placed manually through the lateral window in the defect of the humerus head after its anatomical reduction to the shaft and prior to the anatomical reduction of the greater tuberosity fragment. All specimens were tested biomechanically in a 25° adduction, applying progressively increasing cyclic loading at 2 Hz until failure. Interfragmentary movements were monitored by motion tracking and X-ray imaging. Results: Initial stiffness was not significantly different between the groups, p = 0.467. Varus deformation of the humerus head fragment, fracture displacement at the medial humerus head aspect, and proximal screw migration and cut-out were significantly smaller in the augmented group after 2000, 4000, 6000, 8000 and 10,000 cycles, p ≤ 0.019. Cycles to 5° varus deformation of the humerus head fragment-set as a clinically relevant failure criterion-and failure load were significantly higher in the augmented group, p = 0.018. Conclusions: From a biomechanical standpoint, augmentation with polymethylmethacrylate bone cement placed in the metaphyseal humerus head defect of plated unstable PHFs considerably enhances fixation stability and can reduce the risk of postoperative complications.

Proximal humeral fractures treated with a low-profile plate with enhanced fixation properties

BACKGROUND

Our purpose was to evaluate the clinical and radiographic outcomes of proximal humeral fractures treated with a new generation plating system and compare results with a meta-analysis of recent literature.

METHODS

Between 2014 and 2017, 93 patients (18 males, 75 females) with proximal humerus fractures were treated with open reduction and internal fixation (ORIF) using a Pantera® Plate. These low-profile plates are anatomically shaped and include "cross-elements" that form a three-dimensional scaffold in bone to enhance fixation stability. According to Neer classification, there were 24 two-part fractures, 49 three-part fractures and 20 four-part fractures (4 with dislocated heads). X-rays and Constant Shoulder Scores (CSS) were used to evaluate healing, complications, and clinical outcomes. Results were compared with a meta-analysis of similar studies reported in literature over the last 10 years.

RESULTS

Eighty-three patients with a minimum follow-up of 2 years had a mean CSS of 72 (53-90) graded as excellent for 23 patients (28%), good for 35 (42%), fair for 14 (17%), and poor for 11 (13%). Fractures healed without complication in 75 (91%) patients. Eight (9%) complications were observed, i.e., three avascular necrosis of the humeral head, one case of implant loosening, two cases of subacromial impingement and two superficial infections. There was no significant correlation between Neer fracture stage and patient outcome (p = 0.257). Compared to the literature, this method had a lower complication grade (p = 0.03), though it did not significantly differ in its clinical outcomes (p = 0.08).

CONCLUSIONS

The investigated plating system includes design features that can potentially increase utility for ORIF of proximal humeral fractures. While the complication profile was signficantly less than reported in the literature for standard proximal humerus plates, clinical outcomes were similar. Further studies will be required to better understand the role of plate design on treatment of these challenging fractures.

LEVEL OF EVIDENCE

IV, therapeutic study.

Deterioration of the fixation segment's stress distribution and the strength reduction of screw holding position together cause screw loosening in ALSR fixed OLIF patients with poor BMD

The vertebral body's Hounsfield unit (HU) value can credibly reflect patients' bone mineral density (BMD). Given that poor bone-screw integration initially triggers screw loosening and regional differences in BMD and strength in the vertebral body exist, HU in screw holding planes should better predict screw loosening. According to the stress shielding effect, the stress distribution changes in the fixation segment with BMD reduction should be related to screw loosening, but this has not been identified. We retrospectively collected the radiographic and demographic data of 56 patients treated by single-level oblique lumbar interbody fusion (OLIF) with anterior lateral single rod (ALSR) screw fixation. BMD was identified by measuring HU values in vertebral bodies and screw holding planes. Regression analyses identified independent risk factors for cranial and caudal screw loosening separately. Meanwhile, OLIF with ALSR fixation was numerically simulated; the elastic modulus of bony structures was adjusted to simulate different grades of BMD reduction. Stress distribution changes were judged by computing stress distribution in screws, bone-screw interfaces, and cancellous bones in the fixation segment. The results showed that HU reduction in vertebral bodies and screw holding planes were independent risk factors for screw loosening. The predictive performance of screw holding plane HU is better than the mean HU of vertebral bodies. Cranial screws suffer a higher risk of screw loosening, but HU was not significantly different between cranial and caudal sides. The poor BMD led to stress concentrations on both the screw and bone-screw interfaces. Biomechanical deterioration was more severe in the cranial screws than in the caudal screws. Additionally, lower stress can also be observed in fixation segments' cancellous bone. Therefore, a higher proportion of ALSR load transmission triggers stress concentration on the screw and bone-screw interfaces in patients with poor BMD. This, together with decreased bony strength in the screw holding position, contributes to screw loosening in osteoporotic patients biomechanically. The trajectory optimization of ALSR screws based on preoperative HU measurement and regular anti-osteoporosis therapy may effectively reduce the risk of screw loosening.

Locking Plates With Computationally Enhanced Screw Trajectories Provide Superior Biomechanical Fixation Stability of Complex Proximal Humerus Fractures

Joint-preserving surgical treatment of complex unstable proximal humerus fractures remains challenging, with high failure rates even following state-of-the-art locked plating. Enhancement of implants could help improve outcomes. By overcoming limitations of conventional biomechanical testing, finite element (FE) analysis enables design optimization but requires stringent validation. This study aimed to computationally enhance the design of an existing locking plate to provide superior fixation stability and evaluate the benefit experimentally in a matched-pair fashion. Further aims were the evaluation of instrumentation accuracy and its potential influence on the specimen-specific predictive ability of FE. Screw trajectories of an existing commercial plate were adjusted to reduce the predicted cyclic cut-out failure risk and define the enhanced (EH) implant design based on results of a previous parametric FE study using 19 left proximal humerus models (Set A). Superiority of EH versus the original (OG) design was tested using nine pairs of human proximal humeri (N = 18, Set B). Specimen-specific CT-based virtual preoperative planning defined osteotomies replicating a complex 3-part fracture and fixation with a locking plate using six screws. Bone specimens were prepared, osteotomized and instrumented according to the preoperative plan via a standardized procedure utilizing 3D-printed guides. Cut-out failure of OG and EH implant designs was compared in paired groups with both FE analysis and cyclic biomechanical testing. The computationally enhanced implant configuration achieved significantly more cycles to cut-out failure compared to the standard OG design (p &lt; 0.01), confirming the significantly lower peri-implant bone strain predicted by FE for the EH versus OG groups (p &lt; 0.001). The magnitude of instrumentation inaccuracies was small but had a significant effect on the predicted failure risk (p &lt; 0.01). The sample-specific FE predictions strongly correlated with the experimental results (R2 = 0.70) when incorporating instrumentation inaccuracies. These findings demonstrate the power and validity of FE simulations in improving implant designs towards superior fixation stability of proximal humerus fractures. Computational optimization could be performed involving further implant features and help decrease failure rates. The results underline the importance of accurate surgical execution of implant fixations and the need for high consistency in validation studies.

Factors influencing surgical management of proximal humerus fractures: do shoulder and trauma surgeons differ?

BACKGROUND

Proximal humerus fractures (PHFs) are managed with open reduction and internal fixation (ORIF), hemiarthroplasty (HA), reverse shoulder arthroplasty (RSA), or nonoperatively. Given the mixed results in the literature, the optimal treatment is unclear to surgeons. The purpose of this study was to survey orthopedic shoulder and trauma surgeons to identify the patient- and fracture-related characteristics that influence surgical decision-making.

METHODS

We distributed a 23-question closed-response email survey to members of the American Shoulder and Elbow Surgeons and Orthopaedic Trauma Association. Questions posed to respondents included demographics, surgical planning, indications for ORIF and arthroplasty, and the use of surgical augmentation with ORIF. Numerical and multiple-choice responses were compared between shoulder and trauma surgeons using unpaired t-tests and χ² tests, respectively.

RESULTS

Respondents included 172 shoulder and 78 trauma surgeons. When surgery is indicated, most shoulder and trauma surgeons treat 2-part (69%) and 3-part (53%) PHFs with ORIF. Indications for managing PHFs with arthroplasty instead of ORIF include an intra-articular fracture (82%), bone quality (76%), age (72%), and previous rotator cuff dysfunction (70%). In patients older than 50 years, 90% of respondents cited a head-split fracture as an indication for arthroplasty. Both shoulder and trauma surgeons preferred RSA for treating PHFs presenting with a head-split fracture in an elderly patient (94%), pre-existing rotator cuff tear (84%), and pre-existing glenohumeral arthritis with an intact cuff (75%). Similarly, both groups preferred ORIF for PHFs in young patients with a fracture dislocation (94%). In contrast, although most trauma surgeons preferred to manage PHFs in low functioning patients with a significantly displaced fracture or nonreconstructable injury nonoperatively (84% and 86%, respectively), shoulder surgeons preferred either RSA (44% and 46%, respectively) or nonoperative treatment (54% and 49%, respectively) (P < .001). Similarly, although trauma surgeons preferred to manage PHFs in young patients with a head-split fracture or limited humeral head subchondral bone with ORIF (98% and 87%, respectively), shoulder surgeons preferred either ORIF (54% and 62%, respectively) or HA (43% and 34%, respectively) (P < .001).

CONCLUSIONS

ORIF and HA are preferred for treating simple PHFs in young patients with good bone quality or fracture dislocations, whereas RSA and nonoperative management are preferred for complex fractures in elderly patients with poor bone quality, rotator cuff dysfunction, or osteoarthritis. The preferred management differed between shoulder and trauma surgeons for half of the common PHF presentations, highlighting the need for future research.

[Cement augmentation and bone graft substitutes-Materials and biomechanics]

BACKGROUND

Materials with different characteristics are used for cement augmentation and as bone graft substitutes.

OBJECTIVE

Cement augmentation and bone graft substitutes are the subject of current research. The evaluation of new knowledge allows its specific application.

MATERIAL AND METHODS

Selective literature search and outline of experimental research results on cement augmentation and bone graft substitutes.

RESULTS

Augmentation and bone graft substitutes are essential components of current trauma surgical procedures. Despite intensive research all materials have specific disadvantages. Cement augmentation of implants enhances not only the anchorage but also influences the failure mode.

CONCLUSION

Cement augmentation has large potential especially in osteoporotic bone. In load-bearing regions acrylic-based cements remain the standard of choice. Ceramic cements are preferred in non-load-bearing areas. Their combination with resorbable metals offers still largely unexplored potential. Virtual biomechanics can help improve the targeted application of cement augmentation.

The Mismatch Between Bony Endplates and Grafted Bone Increases Screw Loosening Risk for OLIF Patients With ALSR Fixation Biomechanically

The mismatch between bony endplates (BEPs) and grafted bone (GB) triggers several complications biomechanically. However, no published study has identified whether this factor increases the risk of screw loosening by deteriorating the local stress levels. This study aimed to illustrate the biomechanical effects of the mismatch between BEP and GB and the related risk of screw loosening. In this study, radiographic and demographic data of 56 patients treated by single segment oblique lumbar interbody fusion (OLIF) with anterior lateral single rod (ALSR) fixation were collected retrospectively, and the match sufficiency between BEP and GB was measured and presented as the grafted bony occupancy rate (GBOR). Data in patients with and without screw loosening were compared; regression analyses identified independent risk factors. OLIF with different GBORs was simulated in a previously constructed and validated lumbosacral model, and biomechanical indicators related to screw loosening were computed in surgical models. The radiographic review and numerical simulations showed that the coronal plane’s GBOR was significantly lower in screw loosening patients both in the cranial and caudal vertebral bodies; the decrease in the coronal plane’s GBOR has been proven to be an independent risk factor for screw loosening. In addition, numerical mechanical simulations showed that the poor match between BEP and GB will lead to stress concentration on both screws and bone-screw interfaces. Therefore, we can conclude that the mismatch between the BEP and GB will increase the risk of screw loosening by deteriorating local stress levels, and the increase in the GBOR by modifying the OLIF cage’s design may be an effective method to optimize the patient’s prognosis.

How can medial support for proximal humeral fractures be achieved when positioning of regular calcar screws is challenging? Slotting and off-axis fixation strategies

BACKGROUND

Achieving medial support for proximal humeral fractures (PHFs) by regular calcar screw positioning is challenging when the humeral head is small or locking plates are placed distally, as there are unable inserted calcar screws into the humeral head. We aimed to investigate the suitability of the 2 strategies, slotting calcar screw (SCS) and off-axis calcar screw (OCS), to achieve medial support for PHFs.

METHODS

Regular calcar screw (RCS), SCS, OCS, and noncalcar screw (NCS) were tested via mechanical experiments and finite element analysis (FEA), using synthetic bones for biomechanical comparisons. All PHFs treated in our hospital from March 2017 to March 2019 were reviewed. The patients were divided into 3 groups based on the calcar screw fixation: RCS, SCS, and OCS. The postoperative varus collapse (neck-shaft angle changed to less than 120°) and Disabilities of the Arm, Shoulder and Hand (DASH) scores were recorded.

RESULTS

The properties of RCS, SCS, and OCS against the torsion and varus force were superior to those of NCS, whereas the stiffness of SCS, OCS, and RCS were similar. FEA predicted lower peri-screw strains in the OCS and SCS than in the RCS, indicating a lower risk of cut-out. Patients (n = 125; 75 female, 50 male) aged 55.9 ± 13.0 years were evaluated. Compared with the RCS (5/55), varus collapse incidences were not significantly higher following SCS (0/29, P = .094) or OCS (3/41, P = .756), and neither were DASH scores (P = .867 and .736, respectively).

CONCLUSIONS

This study is a preliminary study demonstrating that the SCS and OCS fixation strategies could be useful alternatives when regular calcar fixation is not possible using the plate at hand.

One size may not fit all: patient-specific computational optimization of locking plates for improved proximal humerus fracture fixation

BACKGROUND

Optimal treatment options for proximal humerus fractures (PHFs) are still debated because of persisting high fixation failure rates experienced with locking plates. Optimization of the implants and development of patient-specific designs may help improve the primary fixation stability of PHFs and reduce the rate of mechanical failures. Optimizing the screw orientations in locking plates has shown promising results; however, the potential benefit of subject-specific designs has not been explored yet. The purpose of this study was to evaluate by means of finite element (FE) analyses whether subject-specific optimization of the screw orientations in a fixed-angle locking plate can reduce the predicted cutout failure risk in unstable 3-part fractures.

METHODS

FE models of 19 low-density proximal humeri were generated from high-resolution computed tomographic images using a previously developed and validated computational osteosynthesis framework. The specimens were virtually osteotomized to simulate unstable malreduced 3-part fractures and fixed with the PHILOS plates using 6 proximal locking screws. The average principal compressive strain in cylindrical bone regions around the screw tips-a biomechanically validated surrogate for the risk of cyclic screw cutout failure-was defined as the main outcome measure. The angles of the 6 proximal locking screws were optimized via parametric analysis for each humerus individually, resulting in subject-specific screw orientations (SSO). The average peri-implant strains of the SSO were statistically compared with the previously reported cohort-specific (CSO) and original PHILOS screw orientations (PSO) for females vs. males.

RESULTS

The optimized SSO significantly reduced the peri-screw bone strain vs. CSO (6.8% ± 4.0%, P = .006) and PSO (25.24% ± 7.93%, P < .001), indicating lower cutout risk for subject-specific configurations. The benefits of SSO vs. PSO were significantly higher for women than men.

CONCLUSION

The findings of this study suggest that subject-specific optimization of the locking screw orientations could lead to lower cutout risk and improved PHF fixation. These computer simulation results require biomechanical and clinical corroboration. Further studies are needed to evaluate whether the potential benefit in stability could justify the increased efforts related to implementation of individualized implants. Nevertheless, computational exploration of the biomechanical factors influencing the outcome of fracture fixations could help better understand the fixation failures and reduce their incidence.

Finite Element Analysis of Fracture Fixation

PURPOSE OF REVIEW

Fracture fixation aims to provide stability and promote healing, but remains challenging in unstable and osteoporotic fractures with increased risk of construct failure and nonunion. The first part of this article reviews the clinical motivation behind finite element analysis of fracture fixation, its strengths and weaknesses, how models are developed and validated, and how outputs are typically interpreted. The second part reviews recent modeling studies of the femur and proximal humerus, areas with particular relevance to fragility fractures.

RECENT FINDINGS

There is some consensus in the literature around how certain modeling aspects are pragmatically formulated, including bone and implant geometries, meshing, material properties, interactions, and loads and boundary conditions. Studies most often focus on predicted implant stress, bone strain surrounding screws, or interfragmentary displacements. However, most models are not rigorously validated. With refined modeling methods, improved validation efforts, and large-scale systematic analyses, finite element analysis is poised to advance the understanding of fracture fixation failure, enable optimization of implant designs, and improve surgical guidance.

Principles of Locking Plate Fixation of Proximal Humerus Fractures

Proximal humerus fractures are common, particularly in elderly patients and those with osteopenia or osteoporosis. Although nonsurgical management results in satisfactory outcomes for most patients, surgical treatment is indicated in select cases. Despite an increasing trend toward arthroplasty, open reduction and internal fixation of proximal humerus fractures can still provide excellent clinical outcomes. Proper technique for internal fixation of the proximal humerus requires an understanding of osseous and neurovascular anatomy. In particular, understanding reliable regions of biomechanically superior bone can help prevent failure of fixation. Biomechanical studies have shown that locked plating of proximal humerus fractures provides stable fixation. Cadaveric and finite element models underscore the importance of screw placement in the posteromedial metaphysis. When medial column support is challenging to obtain, or when bone quality is poor, augmentation with bone autograft, allograft, and/or synthetic composites can improve the biomechanics of internal fixation constructs. The purpose of this review is to outline the anatomic, biologic, and biomechanical principles of plate fixation for proximal humerus fractures to provide evidence-based recommendations for optimizing fixation and preventing fixation failure.

Generic Implant Positioning Technology Based on Hole Projections in X-Ray Images

Implant placement plays a key role in trauma and orthopedics. In this paper, a generic technological concept for implant positioning assistance is outlined. The system utilizes conventional radiographic devices for imaging and tracking and embeds into surgical workflows without the need for complex navigation equipment. It is based on feature extraction from cylindrical hole-projections in X-ray images for determining spatial alignment of implant and anatomy. Basic performance of a prototype system was experimentally verified in terms of tracking accuracy and robustness under varying conditions. In a second step, the system was developed into a set of application modules, each serving a pressing clinical need: Plating of the proximal humerus, cephalic nail and dynamic hip-screw placement, general anatomic plating, distal nail interlocking with adjustment of femoral anteversion and corrective osteotomies. Module prototypes were tested according to their degree of maturity from feasibility assessment in wet-labs to clinical handling tests. Orientation tracking of reference objects yielded an accuracy and precision of 0.1±0.71 deg (mean±standard deviation) with a maximum error of 4.68 deg at unfavorable conditions. This base-performance translated, e.g., into a precision of ±1.2 mm (standard deviation) screw-tip to joint distance at proximal humerus plating, or into a precision of lag screw positioning in the femoral head of ±0.6 mm in craniocaudal and ±1.6 mm in anterioposterior direction. The concept revealed strong potential to improve surgical outcomes in a broad range of orthopedic applications due to its generic and simplistic nature. Comprehensive validation activities must follow for clinical introduction.

Overdrilling increases the risk of screw perforation in locked plating of complex proximal humeral fractures - A biomechanical cadaveric study

Locked plating of proximal humerus fractures (PHF) is associated with high failure rates (15-37%). Secondary screw perforation is a prominent mode of failure for PHF and typically requires reoperation. The anatomical fracture reduction is an essential factor to prevent fixation failure. However, recent studies indicate that the risk of secondary screw perforation may increase if the articular surface is perforated during predrilling of the screw boreholes (overdrilling). This study aimed to determine whether overdrilling increases the risk of secondary screw perforation in unstable PHF. Nine pairs of human cadaveric proximal humeri were osteotomized to simulate a malreduced and highly unstable 3-part fracture (AO/OTA 11 B1.1), followed by their assignment to two study groups for overdrilling or accurate predrilling in paired design, and fixation with a locking plate. Overdrilling was defined by drilling the calcar screw's boreholes through the articular surface. All humeri were cyclically loaded to screw perforation failure. Number of cycles to initial screw loosening and final perforation failure were analysed. The accurately predrilled group revealed a significantly higher number of cycles to both initial screw loosening (p < 0.01) and final screw perforation failure (p = 0.02), compared to the overdrilled one. This is the first study reporting that drilling to the correct depth significantly increases endurance until screw perforation failure during cyclic loading after locked plating in a highly unstable PHF model. Prevention of overdrilling the boreholes could help reduce failure rates of locked plating. Future work should investigate the prevalence and consequences of overdrilling in clinics.

Role of Additional Inferomedial Supporting Screws in Osteoporotic 3-Part Proximal Humerus Fracture: Finite Element Analysis

INTRODUCTION

Importance of inferomedial supporting screws in preventing varus collapse has been investigated for the proximal humerus fracture. However, few studies reported the results of osteoporotic complex fracture. This study aimed to demonstrate the stress distribution pattern, particularly in osteoporotic 3-part proximal humerus fractures involving greater tuberosity (GT) with different screw configurations.

MATERIALS AND METHODS

Using the computed tomography (CT) images of 2 patients, who had osteoporosis and the other had normal bone density, 3-part fractures involving the GT, without medial support were reconstructed. To reflect the osteoporosis or real bone density, Hounsfield unit of CT scans were utilized. A force of 200 N was applied in 30° varus direction. The proximal screws were set in 2 ways: 6 screws without inferomedial supporting screws and 9 screws with inferomedial supporting screws. Qualitative and quantitative analysis of internal stress distribution were performed.

RESULTS

The most proximal part area near humeral head vertex and near the 1st screw's passage and tip had more stress concentrated in osteoporotic 3-part fractures. The stress distribution around the proximal screws was found near the GT fracture line and its lateral side, where the local max values located. Inferomedial supporting screws decreased these effects by changing the points to medial side from the GT. The ratio in osteoporotic bone model decreased to that in normal bone model when inferomedial supporting screws were applied (normal bone, 2.97%-1.30%; osteoporosis bone, 4.76%-1.71%).

CONCLUSIONS

In osteoporotic 3-part proximal humerus fracture, the stress distribution was concentrated on the area near the humeral vertex, 1st row screw tips, and lateral side region from the GT fracture line. Moreover, inferomedial supporting screws ensured that the stress distribution is similar to that in normal bone setting, particularly in osteoporotic condition.

Cement augmentation of calcar screws may provide the greatest reduction in predicted screw cut-out risk for proximal humerus plating based on validated parametric computational modelling: Augmenting proximal humerus fracture plating

Aims

Fixation of osteoporotic proximal humerus fractures remains challenging even with state-of-the-art locking plates. Despite the demonstrated biomechanical benefit of screw tip augmentation with bone cement, the clinical findings have remained unclear, potentially as the optimal augmentation combinations are unknown. The aim of this study was to systematically evaluate the biomechanical benefits of the augmentation options in a humeral locking plate using finite element analysis (FEA).

Methods

A total of 64 cement augmentation configurations were analyzed using six screws of a locking plate to virtually fix unstable three-part fractures in 24 low-density proximal humerus models under three physiological loading cases (4,608 simulations). The biomechanical benefit of augmentation was evaluated through an established FEA methodology using the average peri-screw bone strain as a validated predictor of cyclic cut-out failure.

Results

The biomechanical benefit was already significant with a single cemented screw and increased with the number of augmented screws, but the configuration was highly influential. The best two-screw (mean 23%, SD 3% reduction) and the worst four-screw (mean 22%, SD 5%) combinations performed similarly. The largest benefits were achieved with augmenting screws purchasing into the calcar and having posteriorly located tips. Local bone mineral density was not directly related to the improvement.

Conclusion

The number and configuration of cemented screws strongly determined how augmentation can alleviate the predicted risk of cut-out failure. Screws purchasing in the calcar and posterior humeral head regions may be prioritized. Although requiring clinical corroborations, these findings may explain the controversial results of previous clinical studies not controlling the choices of screw augmentation.

Does cement augmentation of the screws in angular stable plating for proximal humerus fractures influence the radiological outcome: a retrospective assessment

BACKGROUND

Screw-tip augmentation in angular stable plating offers new possibilities for the treatment of complex proximal humerus fractures. This retrospective analysis was performed to evaluate the radiological outcome of proximal humerus fractures treated with angular stable plates and additional screw-tip cement augmentation in patients over the age of 60.

MATERIALS AND METHODS

A retrospective single centre analysis was conducted from June 2013 to December 2016. The minimum follow-up time was set to 6 months after surgery. Anatomical reduction and fixation were evaluated in respect to reattached tuberosities to the head fragment and the adequate restoration of the calcar area not showing any valgus or varus malalignment. Complete fracture healing was determined 3 months after surgery. Any failures such as secondary displacement, primary screw perforation, intraarticular cement leakage and avascular necrosis of the humeral head with concomitant screw cut-out were assessed.

RESULTS

In total, 24 patients (21 females; 3 males) at a median age of 77.5 (62-96) years were included. Five 2-part, twelve 3-part and seven 4-part fractures were detected. The measured median BMD value of 23 patients was 78.4 mg/cm³ (38.8-136.9 mg/cm³). Anatomical reduction was achieved in 50% of the patients. In most cases, the A level screws and the B1 screw were augmented with bone cement by a median of 7 (5-9) head screws used. Postoperative varus displacement was not detected in any of the patients. One patient (4.2%) sustained an early secondary displacement. Intraarticular cement leakage was detected in 3 patients (2 head-split fractures). Avascular necrosis of the humeral head was observed in 4 patients (16.7%). Revision surgery was necessary in four cases, using hemiarthroplasty twice and reverse shoulder arthroplasty the other two times.

CONCLUSION

Screw-tip augmentation in angular stable plating for proximal humerus fracture treatment showed a low secondary displacement rate of 4.2% in patients suffering from poor bone quality. Nevertheless, the occurrence of avascular necrosis of the humeral head with mainly severe fracture patterns observed in this study was higher compared to previously reported results in the literature. Cement augmentation in head-split fractures is not recommended, considering the high risk of an intraarticular cement leakage.

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.