Bone properties of the humeral head and resistance to screw cutout

Modified-tension band suturing: 'the pulling the reins technique' - a technique for displaced proximal humeral fracture with medial column instability

Fractures of the proximal humerus with medial column instability are challenging and present an unacceptable rate of complications and reoperations. Despite good results reported with the use of locking plates and augmentation techniques using bone graft or a second plate, varus subsidence and fixation failure have been frequently reported. We describe the case of a patient presenting with a complex, multifragmentary proximal humerus fractures successfully treated with open anatomic reduction and internal fixation using a locking plate augmented with lateral traction using three bone anchors in the humerus head. After 18 months, the patient reported fully recovering the mobility and functionality of the operated shoulder. The use of bone anchors pulling the humeral in three different directions like three vectors applied from medial to lateral, posterior to anterior and lateral to anterior help to reduce the most important deformities (varus and retroversion) by applying the tension band principle. This is an interesting approach to avoid primary and secondary reduction loss of the proximal fractures of the humerus with postero-medial cortical defect. The procedure is a good alternative to be used in patients with failure or insufficiency of the medial wall and marked varus.

Screw placement in two different implants for proximal humeral fractures regarding regional differences in bone mineral density: An anatomical study

BACKGROUND

The aim of this study was to investigate proximal humerus plating regarding drill depth and over penetration of the glenohumeral joint and to find a relation between these findings and different areas of bone mineral density (BMD) in the humeral head.

MATERIAL & METHODS

The study sample involved 45 upper extremities from human adult cadavers. Two different plates (HOFER; PHILOS) were applied to the proximal humerus. Each hole was drilled until the respective participant thought to have placed the drill bit subchondral. Next, penetration of the far cortex was conducted to determine the residual bone stock. Additionally, the point of screw penetration of the far cortex was identified for each hole of the plates and allocated to five regions with different bone mineral density as described by Tingart et al.

RESULTS

The screw penetration rate and the residual bone stock were compared within the 5 BMD regions. A significantly thicker residual bone stock was found at the central region (SD ± 13.1 mm) than in the anterior region (SD ± 9.5 mm) and in the posterior region (SD ± 8.5 mm). The anterior region revealed a significantly higher penetration rate than the posterior region (p = 0.01) and the central region (p = 0.03).

CONCLUSION

The anterior region of the humeral head was associated with a higher over penetration rate of the far cortex into the glenohumeral joint and a decreased bone stock after subchondral drilling representing a reduced bone mineral density (BMD).

LEVEL OF EVIDENCE

Cadaver Study.

[Research progress on intra-articular screw penetration in proximal humeral fracture treated with locking plate]

Objective

To review the research progress on intra-articular screw penetration in proximal humeral fracture treated with locking plate.

Methods

The domestic and foreign literature about the proximal humeral fracture treated with locking plate was extensively reviewed. The incidence of screw penetration and risk factors were summarized from both primary and secondary screw penetrations, and the reasons of the intra-articular screw penetration and the technical solutions to avoid the penetration were analyzed.

Results

The incidence of intra-articular screw penetration is about 11%-30%, which includes primary and secondary screw penetrations. The primary screw penetration is related to improper operation, inaccurate measurement, and "Steinmetz solid" effect, which results in inadequate fluoroscopy and blind zone. The secondary screw penetration is related to the loss of reduction and varus, collapse, and necrosis of the humeral head. The risk factors for intra-articular screw penetration include the bone mass density, the fracture type, the quality of fracture reduction, the applied location, number, and length of the plate and screws, and whether medial column buttress is restored. Improved fracture reduction, understanding the geometric distribution of screws, good intraoperative fluoroscopy, and reconstruction of medial column buttress stability are the key points for success.

Conclusion

The risk of the intra-articular screw penetration in the proximal humeral fractures treated with locking plates is still high. Follow-up studies need to further clarify the cause and mechanism of screw penetration, and the risk factors that lead to screw penetration, in order to effectively prevent the occurrence of this complication.

Indications and results of osteosynthesis for proximal humerus fragility fractures in elderly patients

Proximal humerus fractures (PHF) are common injuries in the elderly population. Conservative treatment is indicated for undisplaced and stable fractures, which account for almost 80% of the cases. More complex fracture patterns might need surgery, with a wide variety of indication criteria and surgical techniques described in the literature. Surgical treatment should be reserved for patients in good clinical conditions, autonomous in daily living activities and able to adhere to postoperative rehabilitation protocols. In the elderly population with severe osteoporosis, cognitive impairment and clinical comorbidities, the risk of surgical failures is high. In these patients, the choice between surgical and conservative treatment, as well as for the type of procedure, is even more difficult, with no general consensus in the literature. Final indication is usually conditioned by surgeon’s experience and preference. Two independent reviewers (B.H and G.G) independently extracted studies on proximal humeral fractures. All selected studies were screened independently (B.H and G.G) based on title and abstract. Then the full text of any article that either judged potentially eligible was acquired and reviewed again. Any disagreement was resolved by discussing the full text manuscripts. Aim of the present paper is to review the literature about indications and results of osteosynthesis for proximal humerus fragility fractures in the elderly population.

Effect of screw thread length on stiffness of proximal humerus locking plate constructs: A finite element study

Plate-based treatment of proximal humerus fractures is associated with a high risk of complications such as screw perforation into glenohumeral joint. Smooth and threaded pegs were developed with the hope of minimising these risks. No consensus exists onto which threading profile achieves stiffest bone-plate construct. This study investigated the biomechanical effect of five percentages of threading on individual humeral head screws on a bone-plate construct. A finite element model simulating a two-part proximal humerus fracture treated with a Spatial Subchondral Support plate was developed and validated against in vitro biomechanical tests. The proportion of the humeral head screw length that was threaded was varied between 0%-100% in 25% increments. A 5-mm cantilever varus displacement was applied and the required load (F₅) was calculated. Full (100%) threading achieved the stiffest construct for all six screws. Fully threading all smooth pegs at once increased F₅ by 18%. Threading did not increase F₅ equally in all screws. Inferior three plate screws exhibited a larger increase in stiffness than superior three. Most of the mechanical benefits of threading in inferior three screws can be achieved by using threaded pegs (50% threading) while the superior three screws need to be fully threaded. In practice, the smooth surface profile may also offer additional mechanical benefits if implanted with longer lengths and larger diameters. Threading is an effective way of increasing the varus bending stiffness of proximal humerus plates constructs.

A Biomechanical and Structural Comparison of Articular Cartilage and Subchondral Bone of the Glenoid and Humeral Head

Background:

The underlying cause of glenohumeral arthritis is poorly understood. Glenohumeral arthrosis patterns have been classified and described, and differential contact stresses within the joint have been implicated as a cause of joint degeneration, but the intrinsic cause of degeneration patterns in the glenohumeral joint (GHJ) remains largely unknown.

Purpose/Hypothesis:

The purpose of this study was to assess morphological and mechanical differences in articular cartilage (AC) and subchondral bone (SCB) of the glenoid and humeral head in matched cadaveric specimens. We hypothesized that there would be significant zone-dependent differences between the intrinsic characteristics (AC thickness, SCB thickness, compressive forces) of the glenoid and humeral head.

Study Design:

Descriptive laboratory study.

Methods:

Ten human cadaveric GHJs (mean age, 60.2 years) were dissected to expose articular surfaces to facilitate biomechanical testing. A 2-mm and 6-mm osteochondral plug was harvested at 5 zones (central, anterior, posterior, inferior, superior) on the glenoid and humeral head (N = 200 plugs). Each 2-mm core was histologically sectioned and stained with hematoxylin and eosin. AC thickness measurements were taken using light microscopy. The 6-mm plugs were imaged using micro–computed tomography to measure SCB thickness. After imaging, AC specimens were removed from the SCB and tested in confined compression. The compressive aggregate modulus (H_A0), compressive stiffening coefficient (β), and compressive modulus at 16% strain (H_A0.16) and at 50% strain (H_A0.50) were calculated.

Results:

The overall AC thickness was significantly greater on the glenoid. The glenoid also had significantly thicker AC at the inferior, posterior, and superior zones as well as significantly higher SCB thickness overall and significantly greater SCB thickness at the anterior and central zones. The glenoid had significantly greater overall H_A0.50 and H_A0.50 values at the superior zone and had a significantly greater overall compressive stiffening coefficient (β).

Conclusion:

The glenoid had thicker AC, thicker SCB, and greater compressive stiffness at high strain.

Clinical Relevance:

These intrinsic differences may help better elucidate the cause of differential degeneration patterns between the glenoid and humeral head.

Biomechanical comparison of screw-based zoning of PHILOS and Fx proximal humerus plates

Background

Treatment of proximal humerus fractures with locking plates is associated with complications. We aimed to compare the biomechanical effects of removing screws and blade of a fixed angle locking plate and hybrid blade plate, on a two-part fracture model.

Methods

Forty-five synthetic humeri were divided into nine groups where four were implanted with a hybrid blade plate and the remaining with locking plate, to treat a two-part surgical neck fracture. Plates’ head screws and blades were divided into zones based on their distance from fracture site. Two groups acted as a control for each plate and the remaining seven had either a vacant zone or blade swapped with screws. For elastic cantilever bending, humeral head was fixed and the shaft was displaced 5 mm in extension, flexion, valgus and varus direction. Specimens were further loaded in varus direction to investigate their plastic behaviour.

Results

In both plates, removal of inferomedial screws or blade led to a significantly larger drop in varus construct stiffness than other zones. In blade plate, insertion of screws in place of blade significantly increased the mean extension, flexion valgus and varus bending stiffness (24.458%/16.623%/19.493%/14.137%). In locking plate, removal of screw zones proximal to the inferomedial screws reduced extension and flexion bending stiffness by 26–33%.

Conclusions

Although medial support improved varus stability, two inferomedial screws were more effective than blade. Proximal screws are important for extension and flexion. Mechanical consequences of screw removal should be considered when deciding the number and choice of screws and blade in clinic.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2185-5) contains supplementary material, which is available to authorized users.

Development and initial validation of a novel smoothed-particle hydrodynamics-based simulation model of trabecular bone penetration by metallic implants

A novel computational model of implant migration in trabecular bone was developed using smoothed-particle hydrodynamics (SPH), and an initial validation was performed via correlation with experimental data. Six fresh-frozen human cadaveric specimens measuring 10 × 10 × 20 mm were extracted from the proximal femurs of female donors (mean age of 82 years, range 75-90, BV/TV ratios between 17.88% and 30.49%). These specimens were then penetrated under axial loading to a depth of 10 mm with 5 mm diameter cylindrical indenters bearing either flat or sharp/conical tip designs similar to blunt and self-tapping cancellous screws, assigned in a random manner. SPH models were constructed based on microCT scans (17.33 µm) of the cadaveric specimens. Two initial specimens were used for calibration of material model parameters. The remaining four specimens were then simulated in silico using identical material model parameters. Peak forces varied between 92.0 and 365.0 N in the experiments, and 115.5-352.2 N in the SPH simulations. The concordance correlation coefficient between experimental and simulated pairs was 0.888, with a 95%CI of 0.8832-0.8926, a Pearson ρ (precision) value of 0.9396, and a bias correction factor Cb (accuracy) value of 0.945. Patterns of bone compaction were qualitatively similar; both experimental and simulated flat-tipped indenters produced dense regions of compacted material adjacent to the advancing face of the indenter, while sharp-tipped indenters deposited compacted material along their peripheries. Simulations based on SPH can produce accurate predictions of trabecular bone penetration that are useful for characterizing implant performance under high-strain loading conditions. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1114-1123, 2018.

A novel fracture mechanics model explaining the axial penetration of bone-like porous, compressible solids by various orthopaedic implant tips

Many features of orthopaedic implants have been previously examined regarding their influence on migration in trabecular bone under axial loading, with screw thread design being one of the most prominent examples. There has been comparatively little investigation, however, of the influence that implant tip design has on migration under axial loads. We present a novel fracture mechanics model that explains how differences in tip design affect the force required for axial penetration of porous, compressible solids similar to trabecular bone. Three tip designs were considered based on typical 5 mm diameter orthopaedic locking screws: flat and conical tip designs, as well as a novel elastomeric tip. Ten axial penetration trials were conducted for each tip design. In order to isolate the effect of tip design on axial migration from that of the threads, smooth steel rods were used. Tip designs were inserted into polyurethane foam commonly used to represent osteoporotic trabecular bone tissue (ASTM Type 10, 0.16 g/cc) to a depth of 10 mm at a rate of 2 mm/min, while force and position were recorded. At maximum depth, elastomeric tips were found to require the greatest force for axial migration (mean of 248.24 N, 95% Confidence Interval [CI]: 238.1-258.4 N), followed by conical tips (mean of 143.46 N, 95% CI: 142.1-144.9 N), and flat tips (mean of 113.88 N, 95% CI: 112.2-115.5 N). This experiment was repeated in cross-section while recording video of material compaction through a transparent window. Strain fields for each tip design were then generated from these videos using digital image correlation (DIC) software. A novel fracture mechanics model, combining the Griffith with porous material compaction, was developed to explain the performance differences observed between the three tip designs. This model predicted that steady-state stress would be roughly the same (~ 4 MPa) across all designs, a finding consistent with the experimental results. The model also suggested that crack formation and friction are negligible mechanisms of energy absorption during axial penetration of porous compressible solids similar to trabecular bone. Material compaction appears to be the dominant mechanism of energy absorption, regardless of tip design. The cross-sectional area of the compacted material formed during migration of the implant tip during axial penetration was shown to be a strong determinant of the force required for migration to occur (Pearson Coefficient = 0.902, p < .001). As such, implant tips designed to maximize the cross-sectional area of compacted material - such as the elastomeric and conical tips in the present study - may be useful in reducing excessive implant migration under axial loads in trabecular bone.

Complications Associated with Locking Plate of Proximal Humerus Fractures

Proximal humerus fractures constitute a significant percentage of fragility fractures. The growing use of locking plate has helped treat this problem, but at the same time has brought about complications. Past systematic reviews have documented these complications, however a large number of recent studies have been published since, reporting their own complication rates with different techniques. This study reviews the current complications associated with locking plate of proximal humerus fractures as well as methods to reduce them. A systematic review, following the PRISMA guidelines, was conducted in November 2013 and repeated in March 2015, using PubMed, Scopus, and Cochrane databases, to evaluate locking plate fixation (and complications) of traumatic proximal humerus fractures. Inclusion criteria included adults (>18 years), minimum of 12-month postoperative followup, articles within the last 5 years, and studies with >10 participants. Exclusion criteria included pathologic fractures, cadaveric studies, and nonhuman subjects. Eligible studies were graded using a quality scoring system. Articles with a minimum of 7/10 score were included and assessed regarding their level of evidence per the Journal of Bone and Joint Surgery and Centre for Evidence-Based Medicine guidelines. The initial query identified 51,206 articles from multiple databases. These records were thoroughly screened and resulted in 57 articles, consisting of seven Level 1, three Level 2, 10 Level 3, and 37 Level 4 studies, totaling 3422 proximal humerus fractures treated with locking plates. Intraarticular screw penetration was the most reported complication (9.5%), followed by varus collapse (6.8%), subacromial impingement (5.0%), avascular necrosis (4.6%), adhesive capsulitis (4.0%), nonunion (1.5%), and deep infection (1.4%). Reoperation occurred at a rate of 13.8%. Collapse at the fracture site contributed to a majority of the implant-related complications, which in turn were the main reasons for reoperation. The authors of these studies discussed different techniques that could be used to address these issues. Expanding use of locking plate in the proximal humerus fractures leads to improvements and advancements in surgical technique. Further research is necessary to outline indications to decrease complications, further.

Clinical outcomes and prognostic factors depending on implant design in the treatment of proximal humeral fractures: A retrospective study

PURPOSE

We aimed to examine the clinical outcomes of proximal humeral fractures treated with different intramedullary nail shapes.

METHODS

Thirty-seven patients were divided into two groups depending on the implant shape. We also defined F group as a subgroup of fracture classification.

RESULTS

In the F group, the flexion of the shoulder joint was significantly greater in S (mean, 134.6°) than in C groups (mean, 109°) (p = 0.04). The complication rate was significantly larger in the C group (p = 0.04).

CONCLUSIONS

Patients with one kind of fracture and who were treated with straight nails had better outcomes.

Prediction of stemless humeral implant micromotion during upper limb activities

BACKGROUND

Adequate primary stability is essential for the long term success of uncemented stemless shoulder implants. The goal of this study was to evaluate the micromotion of a stemless humeral implant during various upper limb activities.

METHODS

A finite element model was validated by reproducing experimental primary stability testing. Loading from an instrumented prosthesis representing a set of 29 upper limb activities were applied within the validated FE model. Peak micromotion and percentage area for different micromotion thresholds were considered.

FINDINGS

In all simulated activities, at least 99% of the implant surface experienced micromotion below 150μm. Micromotion depended strongly on loading with large discrepancies between upper limb activities. Carrying no external weight and keeping the arm at lower angles induced lower micromotion. Activities representative of demanding manual labor generally led to higher micromotion. Axilla crutches led to lower micromotion than forearm crutches. Micromotion increased when a wheelchair was used on slopes above 2% inclination.

INTERPRETATION

Micromotions below the 150μm threshold below which bone ingrowth occurs were measured over at least 99% of the implant surface for all simulated activities. Peak micromotion dependence on activity type demonstrates the need to consider physiologic in vivo loading and the full contact interface in primary stability evaluations. Focusing on activities with no hand weight and low arm motions during the rehabilitation period may enhance primary stability. For patients unable to walk without aids, axilla crutches and motorized wheelchairs might be more beneficial than forearm crutches and manual drive wheelchairs respectively.