Biomechanical comparison of different pin configurations during percutaneous pinning for the treatment of proximal humeral fractures

The effect of different pin configurations on cyclic stability in pediatric proximal humerus fracture fixation: A Sawbones model study

BACKGROUND

In sawbones with proximal humerus fracture model, three different fixation configurations, Parallel-Straight K-wires, Cross-Straight K-wires and Palm-Tree Method, were biomechanically compared.

METHODS

A total of 36 anatomical pediatric humerus sawbones models were used. They were divided into three equal groups; parallel fixation with straight K-wires (Group PS), cross fixation with straight K-wires (Group CS), and Palm-Tree Method (Group PT). Models were tested in abduction and torsional at a speed of 0.5 mm/s and a 0-5 mm displacement range. Loading (N) and Stiffness (N/mm) data were calculated and compared statistically.

RESULTS

Group PS was significantly higher than the other two groups in abduction bending cyclic load values (P<0.001). It was also significantly higher in Group CS than in Group PT (P < 0.001). No significant differences were detected between the three different fixation groups' cyclic torsional load values (p < 0.05).

CONCLUSION

The parallel configuration with straight K-wires will provide a more stable fixation than the cross configuration with straight or Palm-Tree Method in pediatric proximal humeral sawbones fracture modeling.

Digital analysis of external fixation area of proximal humerus fractures in elderly patients

Introduction

The purpose is based on anatomical basis, combined with three-dimensional measurement, to guide the clinical repositioning of proximal humeral fractures, select the appropriate pin entry point and angle, and simulate surgery.

Methods

11 fresh cadaveric specimens were collected, the distance of the marked points around the shoulder joint was measured anatomically, and the vertical distance between the inferior border of the acromion and the superior border of the axillary nerve, the vertical distance between the apex of the humeral head and the superior border of the axillary nerve, the vertical distance between the inferior border of the acromion and the superior border of the anterior rotator humeral artery, and the vertical distance between the apex of the humeral head and the superior border of the anterior rotator humeral artery were marked on the 3D model based on the anatomical data to find the relative safety zone for pin placement.

Results

Contralateral data can be used to guide the repositioning and fixation of that side of the proximal humerus fracture, and uniform data cannot be used between male and female patients. For lateral pining, the distance of the inferior border of the acromion from the axillary nerve (5.90 ± 0.43) cm, range (5.3-6.9) cm, was selected for pining along the medial axis of the humeral head, close to the medial cervical cortex, and the pining angle was measured in the coronal plane (42.84 ± 2.45)°, range (37.02° ~ 46.31°), and in the sagittal plane (28.24 ± 2.25)°, range (19.22° ~ 28.51°). The pin was advanced laterally in front of the same level of the lateral approach point to form a cross-fixed support with the lateral pin, and the pin angle was measured in the coronal plane (36.14 ± 1.75)°, range (30.32° ~ 39.61°), and in the sagittal plane (28.64 ± 1.37)°, range (22.82° ~ 32.11°). Two pins were taken at the greater humeral tuberosity for fixation, with the proximal pin at an angle (159.26 ± 1.98) to the coronal surface of the humeral stem, range (155.79° ~ 165.08°), and the sagittal angle (161.76 ± 2.15)°, with the pin end between the superior surface of the humeral talus and the inferior surface of the humeral talus. The distal needle of the greater humeral tuberosity was parallel to the proximal approach trajectory, and the needle end was on the inferior surface of the humeral talus.

Conclusion

Based on the anatomical data, we can accurately identify the corresponding bony structures of the proximal humerus and mark the location of the pin on the 3D model for pin placement, which is simple and practical to meet the relevant individual parameters.

Nail Versus Plate: A Biomechanical Comparison of a Locking Plate Versus an Intramedullary Nail With an Angular Stable Locking System in a Shoulder Simulator With Active Muscle Forces Using a Two-Part Fracture Model

OBJECTIVES

To compare a locking compression plate versus an intramedullary nail with an angular stable locking system (ASLS) using a 2-part fracture model in a shoulder test bench.

METHODS

Twelve fresh frozen humeri were used for biomechanical testing in a shoulder simulator. A 2-part fracture model, with and without medial cortical support, was used to compare the locking plate and a nail with an ASLS. The varus impaction, varus per cycle motion, tilt, and tilt per cycle were analyzed.

RESULTS

No significant differences for the resulting forces in the glenoid fossa were evaluated. The stable fracture model showed no significant differences for the 2 groups. The median varus impaction was -0.96 degrees (range -0.55 to -4.26 degrees) in the plate group and 0.5 degrees (range -3.06 to 0.98 degrees) in the nail group, after 500 cycles of cyclic loading in the unstable fracture model. The plate group showed a significantly higher median varus impaction per cycle motion and median varus impaction at the 200th, 300th, and 400th cycle of physiological loading.

CONCLUSIONS

The intramedullary nail with the ASLS could be an alternative for patients suffering from osteoporosis and comorbidities.

Minimally invasive fixation with modified palm tree technique for proximal humerus fractures: Outcomes in a series of 132 patients

INTRODUCTION

Various surgical techniques and implants are available for surgical treatment of significantly displaced proximal humerus fractures. We describe a minimally invasive technique using 3 curved wires, inserted in a retrograde fashion into the humeral head. These are aimed to diverge within the humeral head to provide three separate 3-point fixations to achieve good stability. We present the results of proximal humerus fractures managed with the modified palm tree technique.

METHODS

A retrospective analysis of data collected prospectively including demographics, radiographs, clinical outcomes, complications and revision surgery for patients treated with the palm tree technique was performed.

RESULTS

Between 1998 and 2017, 132 patients underwent fixation with this technique. Average age was 61.8 years. Fifty-Eight fractures were 2 part, 46 were three part and 28 were four part. Average follow up was 26 months. In three to four part fractures, a bone graft substitute block was used behind the humeral head fragment for structural support. There were 11 early revisions (8.3%). In 7 cases the fixation failed early and was revised to other implants like angular & locking plates (4), hemiarthroplasties (2) and reverse arthroplasty (1). In 4 cases the construct was revised to achieve better positioning of the wires. From the 125 remaining patients, 120 achieved union(96.8%). There were 3 painless fibrous non-unions and 2 painful non-unions requiring revision. The mean final Constant score was 75.5 and subjective shoulder value was 7.8/10. Nine patients (6.8%) developed avascular necrosis of the humeral head of which three patients were revised later to an arthroplasty.

CONCLUSION

This technique is a simple, minimally invasive technique which can be used for two, three and four part fractures with good functional outcomes and high union rates. No metalwork remains in the proximal humerus should another procedure like arthroplasty be required in case of avascular necrosis of the humeral head or fracture sequela.

Reusing cadaveric humeri for fracture testing after testing simulated rotator cuff tendon repairs

The financial cost of using human tissues in biomedical testing and surgical reconstruction is predicted to increase at a rate that is disproportionately greater than other materials used in biomechanical testing. Our first hypothesis is that cadaveric proximal humeri that had undergone monotonic failure testing of simulated rotator cuff repairs would not differ in ultimate fracture loads or in energy absorbed to fracture when compared to controls (i.e., bones without cuff repairs). Our second hypothesis is that there can be substantial cost savings if these cadaveric proximal humeri, with simulated cuff repairs, can be re-used for fracture testing. Results of fracture tests (conducted in a backwards fall configuration) and cost analysis support both hypotheses. Hence, the bones that had undergone monotonic failure tests of various rotator cuff repair techniques can be re-used in fracture tests because their load-carrying capacity is not significantly reduced.

Biomechanical Measurements of Stiffness and Strength for Five Types of Whole Human and Artificial Humeri

The human humerus is the third largest longbone and experiences 2–3% of all fractures. Yet, almost no data exist on its intact biomechanical properties, thus preventing researchers from obtaining a full understanding of humerus behavior during injury and after being repaired with fracture plates and nails. The aim of this experimental study was to compare the biomechanical stiffness and strength of “gold standard” fresh-frozen humeri to a variety of humerus models. A series of five types of intact whole humeri were obtained: human fresh-frozen (n = 19); human embalmed (n = 18); human dried (n = 15); artificial “normal” (n = 12); and artificial “osteoporotic” (n = 12). Humeri were tested under “real world” clinical loading modes for shear stiffness, torsional stiffness, cantilever bending stiffness, and cantilever bending strength. After removing geometric effects, fresh-frozen results were 585.8 ± 181.5 N/mm2 (normalized shear stiffness); 3.1 ± 1.1 N/(mm2 deg) (normalized torsional stiffness); 850.8 ± 347.9 N/mm2 (normalized cantilever stiffness); and 8.3 ± 2.7 N/mm2 (normalized cantilever strength). Compared to fresh-frozen values, statistical equivalence (p ≥ 0.05) was obtained for all four test modes (embalmed humeri), 1 of 4 test modes (dried humeri), 1 of 4 test modes (artificial “normal” humeri), and 1 of 4 test modes (artificial “osteoporotic” humeri). Age and bone mineral density versus experimental results had Pearson linear correlations ranging from R = −0.57 to 0.80. About 77% of human humeri failed via a transverse or oblique distal shaft fracture, whilst 88% of artificial humeri failed with a mixed transverse + oblique fracture. To date, this is the most comprehensive study on the biomechanics of intact human and artificial humeri and can assist researchers to choose an alternate humerus model that can substitute for fresh-frozen humeri.

Biomechanical comparison of an angular stable plate with augmented and non-augmented screws in a newly developed shoulder test bench

BACKGROUND

The proximal humeral fracture is one of the most common fractures. Although there are a number of treatment options available, the clinical outcomes in geriatric patients are still unsatisfactory. Therefore, the aim of this study was to investigate the biomechanical behaviour of an angular stable plate with either augmented or non-augmented screws using two different fracture models in a shoulder test bench with active muscle forces.

METHODS

Six paired fresh-frozen humeri were loaded into a shoulder test bench simulating ab- and adduction between 15 and 45° induced by active muscle forces. The bone mineral density was measured by a quantitative CT. A two-part fracture model (stable and an unstable) was used to investigate the different biomechanical behaviours of the PHILOS plate, either utilising cannulated screws, allowing in situ augmentation, or without utilising augmented screws. Four screws were augmented with 0.5ml PMMA cement.

FINDINGS

The in vitro-measured resulting forces in the glenoid fossa were comparable to the in vivo forces generated in shoulder arthroplasties. Under stable conditions, the per cycle motion and varus impaction tilting showed no significant difference. In the unstable state, the augmented group showed a maximum of 0.81° per cycle motion and a maximum varus impaction of -1.46° compared to the non-augmented maximum of 2.31° per cycle motion and maximum varus impaction of -4.26° (P<0.05).

INTERPRETATION

In an unstable fracture model under dynamic testing conditions, augmentation leads to a decreased per cycle motion and varus impaction of the humeral head.

Results of the percutaneous pinning of proximal humerus fractures with a modified palm tree technique

PURPOSE

Many techniques are available for closed reduction and percutaneous fixation of proximal humeral fractures. The palm tree technique was described by Kapandji in 1989. In that technique three curved wires are inserted through one hole at the V-shaped insertion of the deltoid muscle. It is a good technique but it has some disadvantages. In this study we introduced some modifications for the technique, and we evaluated the clinical results of the modified technique in treatment of 18 cases.

METHODS

Eighteen patients with displaced proximal humeral fractures were treated by closed reduction and percutaneous fixation with the palm tree technique after minor modifications. The age of the patients ranged from 38 to 75 years with an average of 56 years. Eleven were females and seven were males. The fractures were two-part in 13 cases and three-part fractures in five cases.

RESULTS

The average time of healing was seven weeks. The follow-up period ranged from 14 months to 39 months with an average of 22 months. The Constant score ranged from 45 to 88 with a mean of 73. The results were satisfactory in 77% and unsatisfactory in 23% of the cases. The complications included pin tract infection in two cases, intraarticular wire migration in one case, skin necrosis around the wires in three cases and malunion with varus deformity in one case. No cases were complicated by neurovascular injury, loss of fixation or avascular necrosis of the humeral head.

CONCLUSIONS

The palm tree technique is a good method for fixation of proximal humeral fractures. It produces good grip in both of the proximal and distal fragments and allows for early joint movements. Our modifications allow for easy insertion of the wires, increase the stability of fixation and minimize the risk of complications.

Biomechanical evaluation of 3-part proximal humerus fractures: a cadaveric study

Proximal humerus fractures occur frequently, and treatment remains controversial. This study compares stiffness in axial loading for 3 methods of fixation (locking compression plate, standard (nonlocking) proximal humerus plate, and blade plate) in a 3-part proximal humerus fracture model. Twelve paired proximal humeri were obtained from embalmed human cadavers and separated into 3 groups. Osteotomies of the surgical neck and greater tuberosity were created to simulate a 3-part proximal humerus fracture. After fixation, constructs were axially loaded in 20 degrees of abduction for 200 cycles in an Instron materials testing machine (Norwood, Massachusetts). The blade plate (mean, 146.87+/-28.9 N/mm) demonstrated 29% more mean stiffness than the standard plate (mean, 113.0+/-22.3 N/mm; P=.19). The locking compression plate (mean, 130.71+/-39.2 N/mm) exhibited 15% greater stiffness compared to the standard plate in our 3-part model (P=.58). The blade plate demonstrated 12% greater stiffness than the locking compression plate (P=.64). There was no significant difference in mean stiffness between the fixed-angle devices and the standard plate. Future in vitro and clinical studies of plate devices for proximal humerus fractures would be worthwhile to determine the benefits and limitations of various implants for specific types of fractures, including clinical performance and cost of care.

Percutaneous fixation of proximal humerus fractures

Closed reduction and percutaneous fixation is a viable treatment option for displaced two-part, three-part, and valgus-impacted four-part proximal humerus fractures. Despite biomechanical studies demonstrating inferior stability compared with plate and intramedullary nail constructs, percutaneous fixation offers a minimally invasive approach with potential clinical advantages. Decreased scarring, improved cosmesis, and lower rates of avascular necrosis have been reported. Potential complications include pin migration, infection, avascular necrosis, neurovascular injury, and malunion. Clinical outcomes have been comparable with conventional techniques, with studies reporting approximately 70% good to excellent results.