Polyaxial versus uniaxial volar locking plate for distal radial fractures

Biomechanical analysis of a novel screw system with a variable locking angle in mandible angle fractures

Locking plates nowadays represent an important treatment in bone trauma and bone healing due to its strong biomechanical properties. The purpose of this study was to both computationally and experimentally validate a novel screw locking system by comparing it to another locking system from state-of-the-art and to apply it in an environment of a fractured mandible. FEA was used to test both systems prior to experimental tests. The systems were locked in the plate holes at 0°, 10°, 15°, and 20°. Cyclic bending tests and push-out tests were performed in order to determine the stiffness and push-out forces of both locking systems. Finally, newly designed locking system was implemented in mandibular angle fracture. Control locking system was biomechanically superior in push-out test, but with no greater significance. In contrast, the new locking system showed greater stiffness by 17.3% at the deflection angle of 20° in cyclic tests, with lower values for other deflection angles. Similar values were displayed in fractured mandible angle environment. Greater stiffness of the new locking system in cyclic loading tests, together with polyaxiallity of the new locking screw, could lead to easier application and improved biomechanical stability of the mandible angle fractures.

Volar locking plate fixation for distal radius fractures: did variable-angle plates make difference?

Purpose

Two different locking plate designs are now being used for volar plating of the distal radius fractures based on the freedom of screw direction; the fixed-angle, and the variable-angle (polyaxial) plates. We investigated the clinical and radiographic outcomes of both designs.

Methods

We reviewed 96 patients with 113 unstable distal radius fractures that were operated on with volar locking plates. The patients’ mean age was 41 years. Fixed-angle volar locking plates were utilized in 65 fractures and variable-angle volar locking plates in 48 fractures through modified Henry approach or extended carpal tunnel approach. Full clinical and radiographic evaluation was done for all patients with a mean follow-up of 14 months.

Results

All patients had acceptable clinical and radiographic parameters. The overall functional results (Mayo score, Quick Disability of Arm, Shoulder, and Hand (Q-DASH) score, Range of motion (ROM), and grip strength) were in favor of the variable-angle plate. The radiographic parameters were better with the variable-angle group. The variable-angle group recorded less operative time but more mean image intensifier exposure time. There were two cases of flexor tendon rupture with the fixed-angle group. Fixation with the fixed-angle system needed K-wire augmentation more than the variable-angle group. There was a positive correlation between hand dominance and the final score.

Conclusion

Distal radius volar locking plates yield satisfactory results comparable among different designs. In our series, the variable-angle system showed slightly better function and radiographic outcomes. Supplementary K-wires were needed more frequently with the fixed-angle system.

Comparative study between fixed-angle and polyaxial screws in distal radius fixation with two volar locking plates

INTRODUCTION

When treating a distal radius fracture with a volar locking plate (VLP), numerous plate-screw designs are available. To date, there is not a screw fastening system with a clear superiority among the others.

HYPOTESIS

Fixed-angle screws are superior to polyaxial screws in distal radius VLP fixation with respect to screw protrusion and reduction preservation.

MATERIAL AND METHODS

A prospective cohort study based on eighty patients was performed. The first forty patients were treated by polyaxial VLP (PA group) were the next forty by a fixed-angle VLP (FA group). Fixation was performed by the flexor carpi radialis approach. Screws were placed 2mm shorter than actual measurement and intraoperative AP, lateral and tilt wrist views were done routinely. A computed tomography (CT) was conducted searching for screw protrusion. Loss of reduction was calculated from the difference between post-operative x-rays values and those at the 6-month follow-up. The total follow-up was 12 months with no losses.

RESULTS

Postoperative CT detected dorsal screw protrusion in 17 patients in PA group and 16 patients in FA group that intraoperative radiographs were assumed as correct (p=0.48). The mean invasion of dorsal cortex was of 2.2mm (1-7mm) for PA group and 2.6mm (1-5mm) for FA group (p=0.70). As from those protruding screws, the mean size was registered founding that fixed-angle screws had protrusions with shorter screws 20 vs. 22mm (p<0.05). Intraarticular screw protrusion was registered in 3 and 2 patients respectively (p>1.0). Experienced loss of reduction in volar tilt (p=0.42), radial inclination (p=0.75) and ulnar variance (p=0.83) were equivalent in both groups while a better preservation of the radial height in the PA group was observed (p<0.05).

DISCUSSIONS

In terms of screw protrusion rate, both fastening systems where similar. However, fixed-angle group invaded the dorsal cortex with shorter screws. Polyaxial screws were associated with a better preservation of the radial height. Finally, this study reinforces the idea that dorsal and articular screw protrusion is more frequent than we expected.

LEVEL OF EVIDENCE

II; therapeutic, prospective cohort study.

A Prospective Randomized Comparison of Variable-Angle and Fixed-Angle Volar Locking Plating for Intra-Articular Distal Radius Fractures

PURPOSE

To compare clinical and radiographic outcomes of using a variable-angle volar locking plate (VAVLP) with those of using a fixed-angle volar locking plate (FAVLP) for treating unstable intra-articular fractures of the distal radius.

METHODS

One hundred twenty patients with unstable intra-articular fractures of the distal radius were randomized to open reduction and internal fixation with a VAVLP (n = 60) or an FAVLP (n = 60). Supplementary methods (eg., Kirschner wire fixation) were required in 4 patients with a VAVLP and 9 with an FAVLP. Clinical outcomes were evaluated at 6 weeks, 3 months, 6 months, and 1 year after surgery. Posteroanterior and lateral radiographs were used to measure standard radiographic parameters before surgery, in the immediate postoperative period, and at 1 year. Plate prominence and articular congruity were quantified using computed tomography at 6 months.

RESULTS

There were no significant differences in any clinical outcome between the groups at any follow-up time. Volar tilt was significantly greater in patients treated with a FAVLP in the immediate postoperative period (8° vs 6°) and at 1 year (8° vs 5°). Although significant differences were not found in articular gap or stepoff between the 2 plates, the distal and volar prominence of the VAVLP was significantly greater than that of the FAVLP at 6 months. Significantly more patients treated with a VAVLP had a complication (38% vs 19%). However, most secondary surgeries were performed for hardware removal, and no patients from either group had complex regional pain syndrome or tendon rupture.

CONCLUSIONS

Patients with intra-articular distal radius fractures can expect good functional and radiographic outcomes with VAVLP or FAVLP fixation. The VAVLP may be more prone to technical errors, leading to complications, whereas the FAVLP is more likely to require supplementary fixation.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic I.

Hidden blood loss and its possible risk factors in cervical open-door laminoplasty

Objectives

To evaluate hidden blood loss (HBL) and its possible risk factors among patients following expansive open-door laminoplasty (EOLP) for multilevel, cervical spondylotic myelopathy.

Methods

This was a retrospective analysis of data from patients over 18 years of age who underwent posterior cervical EOLP (from C3-C6) in our department from January 2017 to July 2018. HBL was calculated by deducting the observed perioperative blood loss from the calculated total blood loss (TBL) based on the fall in haematocrit level.

Results

45 patients (35 men and 10 women) were identified. Mean ± SD HBL was 337.2 ± 187.8 ml, which was 46.8% of the total perioperative blood loss (705.2 ± 269.6 ml). Twenty-three patients developed postoperative anaemia. Posterior cervical soft tissue was positively correlated with both TBL and hidden blood loss (HBL) and hypertension was positively correlated with TBL.

Conclusions

HBL following cervical EOLP was significant and should be recognised as a detrimental factor to patient safety during the perioperative period, especially in patients with thick posterior cervical soft tissue.

A biomechanical comparison of four fixed-angle dorsal plates in a finite element model of dorsally-unstable radius fracture

PURPOSE

To compare the finite element models of two different composite radius fracture patterns, reduced and stabilised with four different fixed-angle dorsal plates during axial, dorsal and volar loading conditions.

METHODS

Eight different plastic models representing four AO/ASIF type 23-A3 distal radius fractures and four AO/ASIF 23-C2 distal radius fractures were obtained and fixed each with 1 of 4 methods: a standard dorsal non-anatomical fixed angle T-plate (3.5mm Dorsal T-plate, Synthes), anatomical fixed-angle double plates (2.4mm LCP Dorsal Distal Radius, Synthes), anatomical fixed angle T-plate (2.4mm Acu-Loc Dorsal Plate, Acumed) or anatomical variable-angle dorsal T-plate (3.5mm, Dorsal Plate, Zrinski). Composite radius with plate and screws were scanned with a 3D optical scanner and later processed in Abaqus Software to generate the finite element model. All models were axially loaded at 3 points (centrally, volarly and dorsally) with 50 N forces to avoid the appearance of plastic deformations of the models. Total displacements at the end of the bone and the stresses in the bones and plates were determined and compared.

RESULTS

Maximal von Mises stress in bone for 3-part fracture models was very similar to that in 2-part fracture models. The biggest difference between models and the largest displacements were seen during volar loading. The stresses in all models were the highest above the fracture gap. The best performance in all parameters tested was with the Zrinski plate and the most modest results were with the Synthes T-plate.

CONCLUSION

There was no significant difference between 2-part (AO/ASIF type 23-A3) and 3-part (AO/ASIF 23-C2) fracture models. Maximal stresses in the plates appeared above the fracture gap; therefore, it is worth considering the development of plates without screw holes above the gap.

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.

Initial stability of a new cementless fixation method of a tibial component with polyaxial locking screws: a biomechanical in vitro examination

INTRODUCTION

Cementless fixation of the tibial component is critical as reduced initial stability leads to implant failure. In this experimental in vitro study, a new fixation method of the tibial component using polyaxial locking screws is evaluated using Roentgen stereophotogrammetric analysis (RSA).

MATERIALS AND METHODS

A special prototype of a tibial component with four polyaxial locking screws was tested on 10 fresh-frozen human tibia specimens. The components were tested with an axial load of 2000 N for 10,000 cycles. Radiographs in two views were performed before loading, after 1000 and after 10,000 cycles, respectively. Besides rotation and translation along the x-, y-, and z-axes, endpoints for RSA were maximum subsidence (MaxSub), maximum lift off (MaxLiftOff) and maximum total point motion (MTPM).

RESULTS

MaxSub increased from -0.5 mm (SD = 0.2) after 1000 cycles to -0.9 mm (SD = 1.1). MaxLiftOff was 0.1 mm after 1000 cycles and did not increase after 10,000 cycles. The MTPM was 0.7 mm (SD = 0.3) after 1000 cycles and 1.1 mm (SD = 1.1) after 10,000 cycles. Two out of nine implants showed an MTPM ≥ 1.0 mm after 10,000 cycles.

CONCLUSIONS

Polyaxial locking screws can potentially improve the initial stability of tibial components. The results of this study indicate that the use of such screws in total knee arthroplasty may be of interest in the future. Further experimental and clinical investigation is needed.