The mechanical stability of extra-articular distal radius fractures with respect to the number of screws securing the distal fragment

Implant cost variation in surgically treated distal radius fractures

Aims & objectives

The purpose of this study was to evaluate for cost variation in distal radius fractures (DRFs) treated with a volar locking plate (VLP) and to identify key factors that affect the total construct cost.

Materials & methods

A retrospective case series was conducted for a single healthcare system. A total of 140 patients with a DRF treated with a VLP from May 2014 to December 2021 were identified. Patients were excluded for polytrauma, open fractures, and skeletal immaturity.

Results

Most patients were female (n = 120, 85.7%) and were on average 59 ± 13.7 years old. Patients most often injured their dominant hand (n = 75, 53.6%) and presented with an AO/OTA 23C fracture (n = 93, 66.4%). Twenty-two surgeons were included with fellowship training in hand or trauma and orthopaedic or plastic surgery residency. Orthopaedic hand-trained surgeons treated the highest proportion of 23C fractures (69.8%). Ninety patients (64.3%) were treated at a surgery center. The average cost was $1289.67 ± $215.32 (range: $857.83-$2156.95). The most expensive fixation constructs used a variable angle locking screw ($1316.75 ± $264.99) or a multidirectional threaded peg ($1321.67 ± $192.94). Multivariable regression analysis revealed none of the study variables to be significant contributors to construct cost (all p-values >0.27).

Conclusions

Surgically treated DRFs with a VLP demonstrated similar total implant costs regardless of fracture pattern, surgeon specialty, or treatment facility. Contrary to previous literature, VLPs showed minimal cost variation, although some surgeons were able to decrease the overall cost by reducing the number of screws used.

Towards optimization of volar plate fixations of distal radius fractures: Using finite element analyses to reduce the number of screws

BACKGROUND

Using fewer distal screws in volar plate fixation of distal radius fractures could reduce treatment costs and complications. However, there is currently no consensus on the ideal screw configuration, likely due to experimental limitations and its subject-specific nature. In this study, finite element analysis was used to investigate (1) if reducing the number of screws is biomechanically feasible and (2) if an optimal screw configuration is subject-specific.

METHODS

Validated subject-specific finite element models of 16 human radii with extra articular distal radius fractures and volar plate fixation with six distal screws were used as a baseline. 41 additional configurations with three to six distal screws were simulated for each subject. Axial stiffness and peri-implant strains around the distal screws were evaluated. Subject-specific optimum configurations were determined using a lower bound for the axial stiffness and minimizing peri-implant strains.

FINDINGS

Even using three distal screws led to only minor deterioration of the biomechanical properties in the best configuration (axial stiffness: -11.2%, peri-implant strains: -35.0%), but a considerable deterioration in the worst configuration (axial stiffness: -46.2%, peri-implant strains: +112.4%). The optimization showed that the ideal screw configuration is subject-specific and on average 1.9 screws could be saved based on the herein used optimization criterion.

INTERPRETATION

This study highlights that not only how many, but which screws are used in volar plate fixation of distal radius fractures is critical. Using a patient-specific selection of distal screws bears potential to save costs and reduce complications.

Early loss of fixation after surgical treatment of distal radius fractures: Does the number of screws matter?

Fixation methods in distal radius fractures has been studied biomechanically, but studies evaluating clinical correlation of that data are lacking. We hypothesize that the use of unthreaded pegs and decreased screw number would correlate with an early failure of fixation. There were 50 operatively treated distal radius fractures with initial post-operative radiographs that demonstrated loss of fixation. An age, BMI, and fracture-type matched cohort of 50 non-failed distal radius fractures was used for comparison. The average number of distal screws in the failed fixation group was 5.3 compared to 4.8 in the group with no loss of fixation (p = 0.07). The average number of proximal shaft screws used in the failed fixation group was 3.2 compared to 3.2 in the control group (p = 0.60). There was no difference between the use of pegs in either group. There was a significant difference between distal screw number between constructs that failed from distal screw pullout as compared to the control group, 5.6 vs. 4.8 (p = 0.0001). In conclusion, there was no difference in the number of proximal screws used in distal radius fractures that demonstrated loss of early fixation. Additionally, having more than five screws in the distal fragment had a higher rate of failure from distal screw pullout, however this was likely confounded by the more severe intra-articular fractures that had additional fixation applied in an attempt to increase stability. Finally, using smooth pegs or screws in the distal fragment made no difference in loss of fixation.

Biomechanical Comparison of Titanium Locking Fragment-Specific and Volar Locking Plates for AO B1 and B2 Fractures of the Distal Radius

PURPOSE

This biomechanical study compared the stability of volar locking plates (VLPs) and locking fragment-specific (LFS) dorsal and radial styloid plates for the fixation of dorsal (AO 23-B2) and radial styloid (AO 23-B1) shear fractures of the distal radius, respectively.

METHODS

Two groups of 6 composite radii were fixed with a VLP or an LFS dorsal plate over a simulated dorsal shear fracture. Two additional groups of 6 radii received the same VLP or an LFS radial plate to fix a radial styloid fracture. Each plated radius was tested under cyclic axial compression by a servohydraulic testing machine that recorded axial displacement per cycle. Construct stiffness was calculated from the slope of the force-displacement curve.

RESULTS

In the dorsal shear fracture model, the dorsal LFS plate exhibited less displacement than the VLP (0.32 ± 0.04 vs 0.43 ± 0.07 mm, respectively) and showed greater average stiffness (645 ± 64 vs 433 ± 88 N/mm, respectively). Plate type was responsible for 53.1% of the variation in displacement and 68.6% of the variation in stiffness. In the radial styloid fracture model, variations due to number of cycles elapsed and plate type were similar for displacement and stiffness in both groups. The average stiffness during cyclical nondestructive testing was 566 ± 45 and 573 ± 60 N/mm for VLP and LFS radial plating groups, respectively.

CONCLUSIONS

For AO 23-B2 (dorsal rim) fractures, the dorsal LFS plates exhibited significantly less displacement and greater stiffness in axial loading than VLPs. For AO 23-B1 (radial styloid) fractures, the VLP displayed similar displacement and stiffness to the radial LFS plates.

CLINICAL RELEVANCE

All constructs tested could be expected to withstand axial compressive forces typical of early postoperative rehabilitation.

Biomechanical considerations for strategies to improve outcomes following volar plating of distal radius fractures

This article is a systematic review of the recent published literature on the biomechanics of volar locking plate fixation of distal radius fractures. PUBMED/MEDLINE and EMBASE databases were searched on 13th Sep 2018. Biomechanical papers on volar locking plate fixation of distal radius fractures since 2010 were included. Papers were analysed and included studies were appraised by the author using the validated quality assessment GRADE tool. The search revealed 456 papers between January 2010 and the present day whose abstracts were reviewed for relevance and 21 papers were included for full paper review. The aim of this systematic review was to evaluate the evidence to determine the surgical techniques and strategies that are associated with the best biomechanical outcomes of volar plating for distal radius fractures. Review of the literature revealed that it was not necessary to fill all available distal locking screws, there was little evidence to support the use of 2 rows of screws distally over 1 row. Screws of 75% length of the distal cortex are sufficient to withstand standard postoperative regimes in extrarticular fractures. The was a paucity of evidence to conclude multidirectional locking plates were superior to fixed angle plates or that one brand of plate was superior to another.

Evaluation of Factors Driving Cost Variation for Distal Radius Fracture Open Reduction Internal Fixation

PURPOSE

Distal radius fracture open reduction and internal fixation (ORIF) represents a considerable cost burden to the health care system. We aimed to elucidate demographic-, injury-, and treatment-specific factors influencing surgical encounter costs for distal radius ORIF.

METHODS

We retrospectively reviewed adult patients treated with isolated distal radius ORIF between November 2014 and October 2016 at a single tertiary academic medical center. Using our institution's information technology value tools-which allow for comprehensive payment and cost data collection and analysis on an item-level basis-we determined relative costs (RC) for each factor potentially influencing total direct costs (TDC) for distal radius ORIF using univariate and multivariable gamma regression analyses.

RESULTS

Of the included 108 patients, implants and facility utilization costs were responsible for 48.3% and 37.9% of TDC, respectively. Factors associated with increased TDC include plate manufacturer (RC 1.52 for the most vs least expensive manufacturer), number of screws (RC 1.03 per screw) and distal radius plates used (RC 1.67 per additional plate), surgery setting (RC 1.32 for main hospital vs ambulatory surgery center), treating service (RC 1.40 for trauma vs hand surgeons), and surgical time (RC 1.04 for every 10 min of additional surgical time). Open fracture was associated with increased costs (RC 1.55 vs closed fracture), whereas other estimates of fracture severity were nonsignificant. In the multivariable model controlling for injury-specific factors, variables including implant manufacturer, and number of distal radius plates and screws used, remained as significant drivers of TDC.

CONCLUSIONS

Substantial variations in surgical direct costs for distal radius ORIF exist, and implant choice is the predominant driver. Cost reductions may be expected through judicious use of additional plates and screws, if hospital systems use bargaining power to reduce implant costs, and by efficiently completing surgeries.

CLINICAL RELEVANCE

This study identifies modifiable factors that may lead to cost reduction for distal radius ORIF.

Damage in a Distal Radius Fracture Model Treated With Locked Volar Plating After Simulated Postoperative Loading

PURPOSE

"Damage" is an engineering term defining a period between a state of material perfection and the onset of crack initiation. Clinically, it is a loss of fixation due to microstructural breakdown, indirectly measured as a reduction of stiffness of the bone-implant construct, normalized by the cross-sectional area and length of the bone. The purpose of this study was to characterize damage in a cadaver model of extra-articular distal radius fracture with dorsal comminution treated using 2-column volar distal radius plates.

METHODS

Ten matched distal radii were randomly divided into 2 groups: group I specimens were treated with a volar distal radius plate with an independent, 2-tiered scaffold design; group II specimens (contralateral limbs) were treated with a volar plate with a single-head design for enhanced ulnar buttressing. Specimens were cyclically loaded to simulate a 6-month postoperative load-bearing period. We report damage after a defined protocol of cyclical loading and load to failure simulating a fall on an outstretched hand.

RESULTS

Group II specimens experienced more damage under cyclic loading conditions than group I specimens. Group I specimens were stiffer than group II specimens under load-to-failure conditions. Ultimate force at failure in group I and group II specimens was not different. Specimens failed by plate bending (group I, n = 6/10; group II, n = 2/10) and fracture of the lunate facet (group I, n = 4/10; group II, n = 8/10).

CONCLUSIONS

Group I specimens had less screw cutout at the lunate facet than group II specimens under cyclic loading as indicated by lower damage measures and fewer facet fractures during load-to-failure testing. The overall strength of the construct is not affected by plate design.

CLINICAL RELEVANCE

Microstructural damage or a loss of fixation due to an overly rigid volar plate design may cause malunion or nonunion of fracture fragments and lead to bone-implant instability.

[Biomechanics of distal radius fractures : Basics principles and GPS treatment strategy for locking plate osteosynthesis]

Fractures of the distal radius are most commonly caused by hyperextension injuries of the wrist. Tensile forces and force vectors, strength of impact, bone strength and soft tissue tension create individually different fracture patterns. Metaphyseal comminution, loss of cortical support, ligament avulsion and shear fragments are defining parameters for fracture instability. The dislocation of the articular fragment follows the force vectors of the extrinsic forearm muscles bridging the joint. The goal-plan-standardized (GPS) treatment strategy has proven to be helpful in choosing the ideal individual treatment. It is based on individual patient demands on wrist function and an analysis of fracture instability in computed tomography (CT) scans. The "goal" is a realistic expectation assessed by patient and surgeon. The "plan" includes a benefit-risk analysis and selection of an appropriate treatment modality. The "standardized treatment" of surgical and follow-up treatment is based on biomechanical knowledge. Locking plate osteosynthesis aims to neutralize dislocating force vectors and to allow early active mobility. Unidirectional instability can be indirectly neutralized by palmar locking plate systems. A multidirectional instability can be addressed by multiple plating following the column theory. Distal shear and avulsion fractures may require a fragment-specific osteosynthesis approach.

Pearls and Pitfalls of the Volar Locking Plating for Distal Radius Fractures

Volar locking plate fixation has been widely accepted method for the treatment of unstable distal radius fractures. Although the results of volar locking plate fixation are encouraging, it may cause implant-related complications such as flexor or extensor tendon injuries. In depth understanding of anatomy of the distal radius is mandatory in order to obtain adequate fixation of the fracture fragments and to avoid these complications. This article will review the anatomic characteristics of the distal radius because selecting proper implant and positioning of the plate is closely related to the volar surface anatomy of the distal radius. The number and the length of distal locking screws are also important to provide adequate fixation strength to maintain fracture fixation. We will discuss the pros and cons of the variable-angle locking plate, which was introduced in an effort to provide surgeons with more freedom for fixation. Finally, we will discuss about correcting radial length and volar tilt by using eccentric drill holes and distal locking first technique.

Optimal Positioning for Volar Plate Fixation of a Distal Radius Fracture: Determining the Distal Dorsal Cortical Distance

Distal radius fractures are currently among the most common fractures of the musculoskeletal system. With a population that is living longer, being more active, and the increasing incidence of osteoporosis, these injuries will continue to become increasingly prevalent. When operative fixation is indicated, the volar locking plate has recently become the treatment of choice. However, despite its success, suboptimal position of the volar locking plate can still result in radiographic loss of reduction. The distal dorsal cortical distance is being introduced as an intraoperative radiographic tool to help optimize plate position and minimize late loss of fracture reduction.

The influence of bone density and anisotropy in finite element models of distal radius fracture osteosynthesis: Evaluations and comparison to experiments

Continuum-level finite element (FE) models can be used to analyze and improve osteosynthesis procedures for distal radius fractures (DRF) from a biomechanical point of view. However, previous models oversimplified the bone material and lacked thorough experimental validation. The goal of this study was to assess the influence of local bone density and anisotropy in FE models of DRF osteosynthesis for predictions of axial stiffness, implant plate stresses, and screw loads. Experiments and FE analysis were conducted in 25 fresh frozen cadaveric radii with DRFs treated by volar locking plate osteosynthesis. Specimen specific geometries were captured using clinical quantitative CT (QCT) scans of the prepared samples. Local bone material properties were computed based on high resolution CT (HR-pQCT) scans of the intact radii. The axial stiffness and individual screw loads were evaluated in FE models, with (1) orthotropic inhomogeneous (OrthoInhom), (2) isotropic inhomogeneous (IsoInhom), and (3) isotropic homogeneous (IsoHom) bone material and compared to the experimental axial stiffness and screw-plate interface failures. FE simulated and experimental axial stiffness correlated significantly (p<0.0001) for all three model types. The coefficient of determination was similar for OrthoInhom (R(2)=0.807) and IsoInhom (R(2)=0.816) models but considerably lower for IsoHom models (R(2)=0.500). The peak screw loads were in qualitative agreement with experimental screw-plate interface failure. Individual loads and implant plate stresses of IsoHom models differed significantly (p<0.05) from OrthoInhom and IsoInhom models. In conclusion, including local bone density in FE models of DRF osteosynthesis is essential whereas local bone anisotropy hardly effects the models׳ predictive abilities.

The influence of distal screw length on the primary stability of volar plate osteosynthesis--a biomechanical study

Background

Extensor tendon irritation is one of the most common complications following volar locking plate osteosynthesis (VLPO) for distal radius fractures. It is most likely caused by distal screws protruding the dorsal cortex. Shorter distal screws could avoid this, yet the influence of distal screw length on the primary stability in VLPO is unknown. The aim of this study was to compare 75 to 100 % distal screw lengths in VLPO.

Methods

A biomechanical study was conducted on 11 paired fresh-frozen radii. HRpQCT scans were performed to assess bone mineral density (BMD) and bone mineral content (BMC). The specimens were randomized pair-wise into two groups: 100 % (group A) and 75 % (group B) unicortical distal screw lengths. A validated fracture model for extra-articular distal radius fractures (AO-23 A3) was used. Polyaxial volar locking plates were mounted, and distal screws was inserted using a drill guide block. For group A, the distal screw tips were intended to be flush or just short of the dorsal cortex. In group B, a target screw length of 75 % was calculated. The specimens were tested to failure using a displacement-controlled axial compression test. Primary biomechanical stability was assessed by stiffness, elastic limit, and maximum force as well as with residual tilt, which quantified plastic deformation.

Results

Nine specimens were tested successfully. BMD and BMC did not differ between the two groups. The mean distal screw length of group A was 21.7 ± 2.6 mm (range: 16 to 26 mm), for group B 16.9 ± 1.9 mm (range: 12 to 20 mm). Distal screws in group B were on average 5.6 ± 0.9 mm (range: 3 to 7 mm) shorter than measured. No significant differences were found for stiffness (706 ± 103 N/mm vs. 660 ± 124 N/mm), elastic limit (177 ± 25 N vs. 167 ± 36 N), maximum force (493 ± 139 N vs. 471 ± 149 N), or residual tilt (7.3° ± 0.7° vs. 7.1° ± 1.3°).

Conclusion

The 75 % distal screw length in VLPO provides similar primary stability to 100 % unicortical screw length. This study, for the first time, provides the biomechanical basis to choose distal screws significantly shorter then measured.

Electronic supplementary material

The online version of this article (doi:10.1186/s13018-015-0283-8) contains supplementary material, which is available to authorized users.

Can the use of variable-angle volar locking plates compensate for suboptimal plate positioning in unstable distal radius fractures? A biomechanical study

OBJECTIVE

To compare the biomechanical stability under load-to-failure conditions of optimally placed fixed-angle volar locking plates versus suboptimally placed variable-angle volar locking plates in unstable, intraarticular distal radius fractures.

METHODS

A Melone type 1 (AO 23-C3) fracture was created in 25 sawbone radii and plated with either a fixed-angle or variable-angle Synthes plate with identical profile. Four plate positions were tested: distal ulnar (DU, positioned distally to obtain subchondral support and ulnar to hold the lunate facet fragments), distal radial (DR, 3 mm radial to DU), proximal ulnar (PU, 3 mm proximal to DU), and proximal radial (PR, 3 mm proximal and 3 mm radial to DU). The specimens were loaded until failure as defined by a 2-mm displacement of any fracture fragment. The fixed-angle plates were tested in the DU position, whereas the variable-angle plates were tested in all 4 positions.

RESULTS

The dorsal lunate fragment was the first to fail in every group followed by the radial styloid and volar lunate fragments, respectively. Load-to-failure, from greatest to least, occurred at the DR (278 ± 56 N), PR (277 ± 68 N), DU fixed-angle (277 ± 68 N), DU variable-angle (236 ± 31 N), and PU (202 ± 75 N) positions, respectively. Rigidity was calculated using the slope of the dorsal lunate force-displacement curve before failure (at loads 100-150 N). Rigidity was greatest at the PU position (126 ± 60 N/mm) followed by PR (125 ± 30 N/mm), DU fixed-angle (125 ± 25 N/mm), DR (122 ± 66 N/mm), and DU variable-angle (101 ± 35) positions, respectively. Univariate analysis of rigidity and load-to-failure was not significantly different between groups.

CONCLUSIONS

In this experimental model, variable-angle screws provided a leeway of 3 mm in both the sagittal and coronal directions without sacrificing construct strength, which may considerably facilitate fixation of these difficult fractures.