A biomechanical study comparing plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to cyclic loading

Biomechanical analysis of locking plates for fixation of metacarpal shaft fractures: A finite element analysis

BACKGROUND

There appears to be a paucity of knowledge about the biomechanics of locking plates for the fixation of metacarpal shaft fractures. A thorough understanding of the biomechanics of locking plates is needed to apply them correctly, optimize outcomes, and avoid complications. The purpose of this study is to investigate the biomechanics of the fixation of metacarpal fractures using locking plate-screw constructs with different numbers of screws.

HYPOTHESIS

The difference in the number of screws in the locking plate influenced the biomechanical outcome of the metacarpal fracture.

METHODS

Finite element models of third metacarpal fractures with locking plate-screw constructs were established, and the magnitude and distribution of their stresses and displacements were investigated when a vertical load of 100N was applied.

RESULTS

For the metacarpal fracture with a locking plate and screws, the stress in the metacarpal was largely shared by the plate-screw construct. For the plate-screw construct, the stress is concentrated in the area close to the fracture line, and the 6-screw Group has the lowest failure risk since it has the lowest plate stress and the second-lowest screw stress. The implant-bone construct with 8 screws has better biomechanical stability because of minimal displacement, but increased stress on both the metacarpal bone and the screws, leading to increased failure rates.

DISCUSSION

The stresses in the metacarpal were mostly shared by the plate-screw constructs and the screws closest to the fracture line were the most likely to break or loosen. For the implant-bone constructs, the locking plate with 2 screws was the most vulnerable to break or loosen, whereas the locking plate with 6 screws was the least likely to break or loosen. The implant-bone construct with 8 screws had better biomechanical stability, but the stresses in both the metacarpal and the screws were increased, which increased the risk of failure.

LEVEL OF EVIDENCE

IV, basic science study.

Comparison of Screw Quantity and Placement of Metacarpal Fracture Fixation: A Biomechanical Study

BACKGROUND

It is recommended to have 6 bicortical screws for plate fixation of long bone fractures; however, many metacarpal fractures do not allow 6 screws due to size limitations and proximity of crucial anatomical structures. The purpose of this biomechanical study was to determine whether the mechanical properties of a 4-screw nonlocking construct are noninferior to those of a 6-screw nonlocking construct.

METHODS

Metacarpal sawbones were used to simulate a midshaft, transverse fracture. Nonlocking bicortical screws were placed in the 6-hole plate, and the metacarpals were randomly assigned to 2 equal study groups: (1) 4 screws, 2 on either side of the fracture (4S); and (2) 6 screws, 3 on either side of the fracture (6S). The metacarpals were tested in a cyclic loading mode and load to failure in a cantilever bending mode.

RESULTS

Maximum deflection was significantly higher for 4S compared with 6S. Cyclic root mean square (RMS) was also significantly greater for 4S at 70 and 100 N. There were no statistically significant differences observed between the 2 constructs for maximum bending load, bending stiffness, and cyclic RMS at 40 N. The maximum bending load in 4S and 6S was 245.6 ± 37.9 N and 230.8 ± 41.9 N, respectively; 4S was noninferior and not superior to 6S. Noninferiority testing was inconclusive for bending stiffness.

CONCLUSIONS

A 4-screw bicortical nonlocking construct is noninferior to a 6-screw bicortical nonlocking construct for fixation of metacarpal fractures, which may be advantageous to minimize disruption of soft tissues while maintaining sufficient construct stability.

Comparison of low-profile locking plate fixation versus antegrade intramedullary nailing for unstable metacarpal shaft fractures--A prospective comparative study

BACKGROUND

The purpose of this study was to compare the effectiveness of mini-open antegrade intramedullary nailing (AIN) and open reduction and internal fixation (ORIF) using the low-profile locking plate for angulated metacarpal shaft fractures, through prospective comparative trial.

METHODS

Group 1 (mini-open AIN; 40 patients) and the other consecutive patients in group 2 (locking plate; 35 patients) who met our inclusion/exclusion criteria were investigated between January 2010 and December 2016. We compared radiological findings (e.g., union and residual angulation or shortening); clinical conditions (e.g., pain, measured on a visual analog scale (VAS), and Disabilities of the Arm, Shoulder, and Hand (DASH) scores); active range of motion (ROM); and grip strength.

RESULTS

Union was achieved in both groups without any major complications. The final angulation measurements were not significantly different (p = 0.402). The final VAS scores were not different (p = 0.868); however, the final DASH score was better in group 1 than in group 2 (p = 0.034). The plates were removed in 14 patients at 9.6 months postoperatively for various reasons. Mean ROM at the time of hardware removal in these 14 patients was significantly lower compared with the final ROM in groups 1 and 2 (non-removal patients). Final grip strengths recovered significantly more in group 1 than in group 2 (p = 0.029). Extension lag was found in four patients in group 2, and the mean amount was 15°; however, it was resolved by tenolysis during hardware removal.

CONCLUSIONS

Both mini-open AIN and low-profile plate fixation are excellent options for metacarpal shaft fractures without significant radiological or clinical problems; however, some clinical outcomes evaluated at least 2 years postoperatively, such as DASH scores and grip strength, were better in the AIN group than in the locking plate group. Plate removal was performed under anesthesia in some patients in the plate group for various reasons, and this may have caused the small differences in the final outcomes evaluated 2 years after surgery.

Comparing biomechanical strength of unicortical locking plate versus bicortical compression plate for transverse midshaft metacarpal fracture

PURPOSE

Metacarpal bone fractures constitute 10% of all fractures. Unstable metacarpal fractures require surgical intervention, which poses danger to flexor tendon either due to bicortical drilling or construct of the implant. Unicortical locking plate fixation may be the solution to preventing flexor tendon injury. Studies have compared locking and compression plates. However, in these studies, the biomechanical properties were tested using the static loading method. This study looks into cyclical loading that is more representative of in vivo conditions, particularly for early rehabilitation. We compared the biomechanical strength of the unicortical locking plate and bicortical compression plate system in a transverse metacarpal fracture, tested with cyclical loading and torsion.

METHOD

Twenty pieces of fourth-generation, biomechanical testing grade, left third metacarpal composite bones were used. Resin was used to create the holding block at both ends of the bone. An oscillating saw with 0.8 mm thick saw blade was used to osteotomize the metacarpal sawbones to create a midshaft transverse metacarpal fracture model. Ten pieces were fixed with a 2.0 mm titanium locking plate via unicortical screw purchase and 10 were fixed with a 2.0 mm, four holes, titanium dynamic compression plate, bicortical purchase of screws. They were subjected to cyclic load to failure testing three-point bending and torsion.

RESULTS

There were no significant difference in stiffness and cyclic three-point bending to failure between the unicortical locking plate group and the bicortical compression plate group. The bicortical compression plate group is stiffer and has a higher cyclic bending load to failure as compared to the unicortical locking plate group.

CONCLUSION

Unicortical locking plate fixation of metacarpal fracture can be reliably applied clinically to produce a strong and stable construct that allows early mobilization of the joints. This will not only reduce the complication rate of metacarpal plating, but also improve the functional outcome of the hand.

A biomechanical analysis of plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to 4-point bending and dynamical bending test

In the published literature there are controversial data to the biomechanical stability of monocortical comparing to the bicortical fixation of metacarpal fractures. The aim of this study was to compare the biomechanical stability of monocortical and bicortical locking osteosynthesis in quasi-static and dynamic 4-point bending tests of composite third metacarpal bone (4th Gen third metacarpal, Sawbones, Malmö, Sweden) fixed with 7-hole locking plate (XXS System, Biotech-Ortho, Wright, Memphis, TN). The tests to determine quasi-static yield and bending strength as well as fatigue strength were conducted in 4 groups of 10 samples after creating standardized mid-shaft transverse osteotomies using a diamont belt grinder (0.3 mm saw blade). The force applied was the dorsal apex loading, similar to the forces applied to metacarpals during normal finger flexion and extension.In the quasi-static testing, no plate breakage was observed in each group. All metacarpals broke at their thinnest part. The average bending strength of the bicortical samples (10.54 ± 0.998 Nm) was significantly higher comparing to the monocortical samples (8.57 ± 0.894 Nm) (P < .001).In the dynamic loading test, all constructs (8 monocortical samples and 7 bicortical) that failed broke at the osteotomy site and the average fatigue strength did not differ in both groups.Consequently, a unicortical plating method may provide adequate strength and stability to metacarpal fractures based on the results of the cyclical loading representative of in vivo loading.

Comparison of 2-Dimensional and 3-Dimensional Metacarpal Fracture Plating Constructs Under Cyclic Loading

PURPOSE

Metacarpal fractures are commonly treated by a variety of means including casting or open reduction internal fixation when unacceptable alignment is present following attempted closed reduction. Dorsal plating with either single-row 2-dimensional or double-row 3-dimensional plates has been proposed. This study's purpose was to determine if there are any differences in fixation construct stability under cyclic loading and subsequent load to failure between the lower profile 3-dimensional and the larger 2-dimensional plates in a metacarpal fracture gap sawbone model.

METHODS

Thirty metacarpal cortico-cancellous synthetic bones were cut with a 1.75-mm gap between the 2 fragments simulating mid-diaphyseal fracture comminution. Half of the metacarpals were plated with 2.0-mm locking 2-dimensional plates and half with 1.5-mm locking 3-dimensional plates. The plated metacarpals were mounted into a materials testing apparatus and cyclically loaded under cantilever bending for 2,000 cycles at 70 N, then 2,000 cycles at 120 N, and finally monotonically loaded to failure. Throughout testing, fracture gap sizes were measured, failure modes were recorded, and construct strength and stiffness values were calculated.

RESULTS

All 3-dimensional constructs survived both cyclic loading conditions. Ten (67%) 2-dimensional constructs survived both loading conditions, whereas 5 (33%) failed the 120-N loading at 1377 ± 363 cycles. When loaded to failure, the 3-dimensional constructs failed at 265 N ± 21 N, whereas the 2-dimensional constructs surviving cyclic loading failed at 190 N ± 17 N.

CONCLUSIONS

The shorter, thinner 3-dimensional metacarpal plates demonstrated increased resistance to failure in a cyclic loading model and increased load to failure compared with the relatively longer, thicker 2-dimensional metacarpal plates.

CLINICAL RELEVANCE

The lower-profile 3-dimensional metacarpal plate fixation demonstrated greater stability for early postoperative resistance than the thicker 2-dimensional fixation, whereas the smaller size and lower profile of the 3-dimensional plates potentially reduces soft tissue stripping, implant prominence, and risk of extensor tendon irritation.

Comparison of Dorsal Plate Fixation Versus Intramedullary Headless Screw Fixation of Unstable Metacarpal Shaft Fractures: A Biomechanical Study

Background: Recently, intramedullary headless screw (IMHS) has shown promise as an alternative to dorsal plate fixation of metacarpal fractures. The purpose of this study was to assess the biomechanical performance of IMHS versus plating. We hypothesized that IMHS fixation provides inferior stability to plating. Methods: Metacarpal fracture model with 3-mm of volar gapping in forty-four human cadaveric metacarpals was created. The specimens were divided into 5 groups: Group 1, 1.5-mm non-locking plate; Group 2, 1.5-mm locking plate; Group 3, 2.0-mm non-locking plate; Group 4, 2.0-mm locking plate; and Group 5, 2.4-mm short cannulated IMHS. A 4-point bending model was used to assess load-to failure (LTF) and stiffness. Results: Mean LTF was 364 ± 130 N for 1.5-mm non-locking plates, 218 ± 94 N for 1.5-mm locking plates, 421 ± 86 N for 2.0-mm non-locking plates, 351 ± 71 N for 2.0-mm locking plates, and 75 ± 20 N for IMHS. Mean stiffness was 91 ± 12 N/mm for 1.5-mm non-locking plates, 110 ± 77 N/mm for 1.5-mm locking plates, 94 ± 20 N/mm for 2.0-mm non-locking plates, 135 ± 16 N/mm for 2.0-mm locking plates, and 55 ± 15 N/mm for IMHS. IMHS demonstrated significantly lower LTF and stiffness than plates. Conclusions: IMHS fixation of unstable metacarpal shaft fractures offers less stability compared to plating when loaded in bending. The LTF and stiffness of IMHS versus plating of metacarpal shaft fractures has not been previously quantified. Our results reveal that IMHS fixation is less favorable biomechanically and should be carefully chosen in regards to fracture stability.

Stability of Unicortical versus Bicortical Metacarpal Fracture Internal Fixation Trial (SUBMIT): study protocol for a randomized controlled trial

BACKGROUND

Metacarpal fractures are common, accounting for 40 % of all hand injuries. The use of plates for the fixation of these fractures allows early aggressive hand therapy post-operatively, reducing post-operative stiffness. Traditionally, bicortical fixation is the standard practice, where both dorsal and palmar cortices of the metacarpal are drilled through, with screws engaging both cortices. Recent biomechanical studies have shown that unicortical fixation, where only the near cortex is drilled and engaged by the screw, results in no difference in stiffness, load to failure or failure mechanism, when compared with bicortical fixation. This trial aims to compare fracture union, complication rate and functional outcomes between unicortical and bicortical fixation for adults with displaced metacarpal fractures.

METHODS/DESIGN

All adults with displaced diaphyseal metacarpal fracture requiring plate fixation are potentially eligible to take part in this study. A total of 315 consenting patients will be randomly allocated to either unicortical or bicortical plate and screw fixation. The surgery will be performed in specialist hand trauma units across the UK. Data regarding fracture healing, hand function, quality of life, and complications will be collected at 2 weeks, 6 weeks and 6 months following surgery.

DISCUSSION

This pragmatic, prospective, multi-centre, randomized controlled trial is expected to deliver results in 2018.

TRIAL REGISTRATION

ISRCTN 18006607 . Registered on 19 Nov 2015.

Unicortical fixation of metacarpal fractures: is it strong enough?

Unicortical fixation has some practical and theoretical advantages over bicortical fixation. Questions have been raised to its adequacy for post-operative mobilization. We hypothesized that fixation using a plate and eight unicortical screws would be as strong as using a plate and four bicortical screws. A total of 40 unicortical and 40 bicortical fixations were compared using a cadaveric metacarpal model. Unicortical fixation was performed using an eight-hole parallel plate and bicortical fixation with a four-hole straight plate. Fixations were tested to failure using four-point bending load. The mean load to failure was 414 N SD 38(SE) for the unicortical group and 296 N SD 29(SE) for the bicortical group. Significant differences between these two constructs were observed. The mean stiffness of the fixation was higher for the bicortical group than the unicortical, although this difference did not reach significance. Unicortical fixation alone is sufficient to enable early post-operative mobilization in a live model.

Angular stable lateral plating is a valid alternative to conventional plate fixation in the proximal phalanx. A biomechanical study

BACKGROUND

Dorsal plating is commonly used in proximal phalanx fractures but it bears the risk of interfering with the extensor apparatus. In this study, dorsal and lateral plating fixation methods are compared to assess biomechanical differences using conventional 1.5mm non-locking plates and novel 1.3mm lateral locking plates.

METHODS

Twenty-four fresh frozen human cadaveric proximal phalanges were equally divided into four groups. An osteotomy was set at the proximal metaphyseal-diaphyseal junction and fixed with either dorsal (group A) or lateral (group B) plating using a 1.5mm non-locking plate, or lateral plating with a novel 1.3mm locking plate with bicortical (group C) or unicortical (group D) screws. The specimens were loaded in axial, dorsovolar and mediolateral direction to assess fixation stiffness followed by a cyclic destructive test in dorsovolar loading direction.

FINDINGS

Axial stiffness was highest in group D (mean 321.02, SEM 21.47N/mm) with a significant difference between groups D and B (P=0.033). Locking plates (groups C and D) were stiffer than non-locking plates under mediolateral loading (P=0.007), no significant differences were noted under dorsovolar loading. Furthermore, no significant differences were observed under cyclic loading to failure between any of the study groups.

INTERPRETATION

No considerable biomechanical advantage of using a conventional 1.5mm dorsal non-locking plate was identified over the novel 1.3mm lateral locking plate in the treatment of proximal phalanx fractures. Since the novel low-profile plate is less disruptive to the extensor mechanism, it should be considered as a valid alternative.

Biomechanical studies: science (f)or common sense?

INTRODUCTION

It is our impression that many biomechanical studies invest substantial resources studying the obvious: that more and larger metal is stronger. The purpose of this study is to evaluate if a subset of biomechanical studies comparing fixation constructs just document common sense.

METHODS

Using a web-based survey, 274 orthopaedic surgeons and 81 medical students predicted the results of 11 biomechanical studies comparing fracture fixation constructs (selected based on the authors' sense that the answer was obvious prior to performing the study). Sensitivity, specificity, and accuracy were calculated according to standard formulas. The agreement among the observers was calculated by using a multirater kappa, described by Siegel and Castellan.

RESULTS

The accuracy of predicting outcomes was 80% or greater for 10 of 11 studies. Accuracy was not influenced by level of experience (i.e., time in practice and medical students vs. surgeons). There were substantial differences in accuracy between observers from different regions. The overall categorical rating of inter-observer reliability according to Landis and Koch was moderate (κ=0.55; standard error (SE)=0.01).

CONCLUSION

The results of a subset of biomechanical studies comparing fracture fixation constructs can be predicted prior to doing the study. As these studies are time and resource intensive, one criterion for proceeding with a biomechanical study should be that the answer is not simply a matter of common sense.

Biomechanical analysis of the efficacy of locking plates during cyclic loading in metacarpal fractures

PURPOSE

To analyse the biomechanical characteristics of locking plates under cyclic loading compared to a nonlocking plate in a diaphyseal metacarpal fracture.

METHODS

Oblique diaphyseal shaft fractures in porcine metacarpal bones were created in a biomechanical fracture model. An anatomical reduction and stabilization with a nonlocking and a comparable locking plate in mono- or bicortical screw fixation followed. Under cyclic loading, the displacement, and in subsequent load-to-failure tests, the maximum load and stiffness were measured.

RESULTS

For the monocortical screw fixation of the locking plate, a similar displacement, maximum load, and stiffness could be demonstrated compared to the bicortical screw fixation of the nonlocking plate.

CONCLUSIONS

Locking plates in monocortical configuration may function as a useful alternative to the currently common treatment with bicortical fixations. Thereby, irritation of the flexor tendons would be avoided without compromising the stability, thus enabling the necessary early functional rehabilitation.

The biomechanics of fixation techniques for hand fractures

Multiple options are available for the fixation of metacarpal and phalangeal fractures; treatment options depend largely on the fracture characteristics, concomitant injuries, and surgeon preference. With an understanding of the options available and the biomechanics involved, appropriate treatment options may be chosen. Although plate and screw constructs provide the strongest fixation for these fractures, many other techniques provide adequate fixation and may be favored for reasons other than biomechanics.