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

Biomechanical study of the fixation ability of the dorsal and volar locking plate for transverse metacarpal neck fractures

Metacarpal neck fracture is one of the most common types of hand fractures; the literature suggests that applying a bone plate on the dorsal side provides higher fixation strength than that provided by other fixation methods. However, bone plate fixation on the dorsal side may result in postoperative tendon adhesion. So far, no studies have investigated the fixation of metacarpal neck fractures on the volar side by using a bone plate. The objective of this study was to investigate the differences in the fixation results between bone plate fixation on the dorsal side and bone plate fixation on the volar side of the metacarpal in the case of a metacarpal neck fracture. A saw blade was used to create a transverse metacarpal neck fracture on 14 artificial metacarpal bone specimens. The specimens were divided into 2 groups depending on the fixation method: a volar locking plate (VLP) group and a dorsal locking plate (DLP) group. All specimens were subjected to a cantilever bending test on a material testing system, and a force-displacement curve was used to measure the yield force and stiffness, which served as an indicator of the fixation ability of the 2 fracture fixation methods. For the experimental results, the Mann-Whitney U test was used to compare the fixation abilities of the 2 fixation methods. In terms of yield force, the DLP group (266.9 ± 68.3 N) scored significantly higher than the VLP group (32.6 ± 2.7 N) (P < .05); expressed in terms of median, the DLP group scored 8.2 times higher than the VLP group. Similarly, in terms of stiffness, the DLP group (69.0 ± 13.4 N/mm, median ± interquartile range) scored significantly higher than the VLP group (12.9 ± 1.4 N/mm) (P < .05); expressed in terms of median, the DLP group scored 5.3 times higher than the VLP group. The fixation strength of volar bone plates is only about one-third of that of dorsal bone plates.

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.

Biomechanical Modeling of Connecting Intermetacarpal K-Wires in the Treatment of Metacarpal Shaft Fractures

BACKGROUND

Clinical series have been published using the configuration of 2 intercarpal Kirschner wires (K-wires) adjacent to the fracture being connected, but biomechanical analysis is lacking. The objective of this pilot biomechanical study was to model and compare the effects of externally connecting 2 intermetacarpal K-wires for the stabilization of transverse metacarpal shaft fractures. Our research hypothesis was that the connected constructs would be stiffer than the unconnected K-wires.

METHODS

A 3-dimensional computer-based model of small finger transverse metacarpal fracture stabilization was designed with 3 transverse 1.1 mm K-wires being anchored to the adjacent metacarpal. Three arrangements were tested: all 3 K-wires in parallel, the middle K-wire angled toward the proximal wire, and the middle angled K-wire being rigidly fixed to the proximal K-wire. The proximal wire was proximal to the fracture. A finite element analysis was performed by applying a cantilever force of 100 N at the head of the metacarpal. The metacarpal was considered to be uniform in composition with parameters typical for human bone. Kirschner wire parameters for stainless steel were used. Force (N) versus displacement was measured.

RESULTS

The configuration with the middle angled K-wire being rigidly fixed to the proximal K-wire showed greater stiffness (12 N/mm) than nonattached constructs. The connected construct was 2.3 times more stiff than the unattached parallel construct and 2.5 times more stiff than angling the middle K-wire without attachment.

CONCLUSIONS

In a computer model simulation, our results show that attaching 2 K-wires adjacent to the fracture provides more than twice the stiffness of unconnected K-wires.

Biomechanical comparison of intramedullary screw fixation, dorsal plating and K-wire fixation for stable metacarpal shaft fractures

We compared four methods of metacarpal shaft fixation: 2.2 mm intramedullary headless compression screw; 3.0 mm intramedullary headless compression screw; intramedullary K-wire fixation; and dorsal plate fixation. Transverse mid-diaphyseal fractures were created in 64 metacarpal sawbones and were assigned into four groups. Peak load to failure and stiffness were measured in cantilever bending and torsion. We found that dorsal plating had the highest peak load to failure. However, initial bending stiffness of the 3.0 mm intramedullary headless compression screw was higher than that of the dorsal plates. In torsion testing, dorsal plating had the highest peak torque, but there was no significant difference in torsional stiffness between the plate and intramedullary headless compression screw constructs. We concluded that intramedullary headless compression screw fixation is biomechanically superior to K-wires in cantilever bending and torsion; however, it is less stable than dorsal plating. In our study, the initial stability provided by K-wire fixation was sufficient to cope with expected loads in the early rehabilitation period, whereas dorsal plates and IHCS constructs provided stability far in excess of what is required.

Inter-relationships of Metacarpals 1 to 5, Regarding Their Length, Metaphyseal Midshaft Width, Articular Surface Area of Head and Base, Age, and Sex: A Cadaveric Study

Background: Metacarpal factures are common, comprising up to 50% of hand fractures. More work is needed to further our understanding of metacarpal anatomy to improve fixation techniques and reduce postoperative complications following surgical implants. The purpose of this anatomic study was to evaluate the length, midshaft metaphyseal width, and area of the articular surface of the head (AH) and base (AB) of metacarpals 1 to 5. Methods: This prospective study assessed measures from 17 cadavers at 1 institution's anatomy lab. The anatomic dimensions of the metacarpals in both the right and left hands were measured. Epidemiological data including sex and age at death were also collected. Results: In all, 29 hands were dissected for metacarpal anatomic measurements, for a total of 145 metacarpals. The second metacarpal was longest, at 69.58 mm. Multivariate analysis of variance revealed a significant effect of sex overall, with greater metacarpal dimensions in men. Increasing age was associated with decreasing dimensions, except for AH of metacarpal 1 (F = 3.43, P = .02) and AB of metacarpal 1 (F = 11.54, P < .001) and 4 (F = 4.21, P = .01). Multiple metacarpal dimensions were also significantly correlated with each other. Conclusion: Our data reveal further information regarding metacarpal dimensions of length, midshaft width, and AH and AB. The results allow for potential to improve surgical management through improving metacarpal implants, developing an optimal plate and screw design, techniques to better accommodate anatomical differences based on age and sex, reducing postoperative complications and improving the standard of care.

Bone plate fixation ability on the dorsal and lateral sides of a metacarpal shaft transverse fracture

Background

Metacarpal shaft fractures are a common hand trauma. The current surgical fixation options for such fractures include percutaneous Kirschner wire pinning and nonlocking and locking plate fixation. Although bone plate fixation, compared with Kirschner wire pinning, has superior fixation ability, a consensus has not been reached on whether the bone plate is better placed on the dorsal or lateral side.

Objective

The purpose of this study was to evaluate the fixation of locking and regular bone plates on the dorsal and lateral sides of a metacarpal shaft fracture.

Materials and methods

Thirty-five artificial metacarpal bones were used in the experiment. Metacarpal shaft fractures were created using a saw blade, which were then treated with four types of fixation as follows: (1) a locking plate with four locking bicortical screws on the dorsal side (LP_D); (2) a locking plate with four locking bicortical screws on the lateral side (LP_L); (3) a regular plate with four regular bicortical screws on the dorsal side (RP_D); (4) a regular plate with four regular bicortical screws on the lateral side (RP_D); and (5) two K-wires (KWs). All specimens were tested through cantilever bending tests on a material testing system. The maximum fracture force and stiffness of the five fixation types were determined based on the force–displacement data. The maximum fracture force and stiffness of the specimens with metacarpal shaft fractures were first analyzed using one-way analysis of variance and Tukey’s test.

Results

The maximum fracture force results of the five types of metacarpal shaft fracture were as follows: LP_D group (230.1 ± 22.8 N, mean ± SD) ≅ RP_D group (228.2 ± 13.4 N) > KW group (94.0 ± 17.4 N) > LP_L group (59.0 ± 7.9 N) ≅ RP_L group (44.5 ± 3.4 N). In addition, the stiffness results of the five types of metacarpal shaft fracture were as follows: LP_D group (68.7 ± 14.0 N/mm) > RP_D group (54.9 ± 3.2 N/mm) > KW group (20.7 ± 5.8 N/mm) ≅ LP_L group (10.6 ± 1.7 N/mm) ≅ RP_L group (9.4 ± 1.2 N/mm).

Conclusion

According to our results, the mechanical strength offered by lateral plate fixation of a metacarpal shaft fracture is so low that even KW fixation can offer relatively superior mechanical strength; this is regardless of whether a locking or nonlocking plate is used for lateral plate fixation. Such fixation can reduce the probability of extensor tendon adhesion. Nevertheless, our results indicated that when lateral plate fixation is used for fixating a metacarpal shaft fracture in a clinical setting, whether the mechanical strength offered by such fixation would be strong enough to support bone union remains questionable.

Comparative analysis of the effects of AO mini-plate and Kirschner wire pinning in the metacarpal fractures: A retrospective study

The aim of this study was to investigate the clinical effect of AO miniplate screw internal fixation and Kirschner wire (KW) in the treatment of metacarpal fractures.We retrospectively analyzed the clinical data of 590 metacarpal fracture patients admitted to our hospital from March 2016 to March 2019. Among them, 290 patients were treated with KWs; 300 were treated with AO microplate internal fixation. The clinical, radiological results, time of surgery, and complications were observed and compared between the 2 groups.The imaging characteristics and preoperative fracture types of the 2 groups were similar and comparable (P > .05). The operation time, length of hospital stay, and fracture healing time of AO group were shorter than those of KW group, and the differences were statistically significant (41.22 ± 7.23 vs 25.64 ± 6.29; 7.13 ± 2.38 vs 5.26 ± 1.71; 67.43 ± 22.01 vs 52.57 ± 17.46, P < .05). In addition, the incidence of postoperative complications in AO group was lower than that in KW group (8.3% vs 15.2%, P < .05). In terms of surgical knuckle extension, flexion, and total mobility (compared with the uninjured hand), patients in the AO plate group were significantly improved compared with patients in the KW group, and the difference was statistically significant (4 vs 10 degree; 19 vs 10 degree; 14 vs 29 degree, P < .05); The average degree of finger rotation deformity in AO plate group was significantly lower than that in KW group (1 vs 6 degree, P < .05). In terms of grip strength (compared with the healthy hand), the average grip strength of AO plate group was significantly higher than that of KW group (93% vs 83%, P < .05). Patients in the OA plate group had a lower Disabilities of the Arm, Shoulder and Hand score (P < .05).Compared with KW fixation, AO mini-plate and screw fixation for the metacarpal fracture has a better effect, which can effectively shorten the operation time and reduce the trauma to patients. It can provide patients with better stability and realize the early movement of the palm, promote fracture healing and joint function recovery; it can reduce the incidence of postoperative complications, which has certain safety. In addition, it can effectively reduce the risk of poor finger rotation.

Morphometric analysis of the second through fifth metacarpal through posteroanterior X-Rays

Over the past 10 years, metacarpal fractures have had an annual incidence of 13.6 per 10,000 individuals. Literature has not reviewed anatomical variations through radiographic imaging, which may play a role in reducing postoperative complications. The purpose of this study was to use radiographic imaging to provide a detailed anatomy of the second through fifth metacarpals. This retrospective study measured length, neck width, narrowest body width, and narrowest medullary canal width of the second through fifth metacarpals through the use of posteroanterior X-rays. Patients who were ≥18 years and received hand radiographs from January 2015 to July 2019 were included in this study. Those with acute injury or fracture of the metacarpal were excluded. Five hundred and seventy-two metacarpals were included in this study, with 143 metacarpals measured each for the second through fifth metacarpal. The second metacarpal had the largest measured length, neck width, and narrowest body width at 68.72, 12.34, and 8.74 mm, respectively. The fifth metacarpal had the greatest average medullary canal width at 4.15 mm. This is the largest study in literature to comprehensively examine the anatomical variation of the second through fifth metacarpals. The second metacarpal had greatest dimensions except for canal width, which was the fifth metacarpal. Men almost consistently had greater metacarpal size when compared to women, and age was associated with second and third metacarpal canal width. The increased knowledge of metacarpal anatomy may potentially lay the foundation of further improvement of metacarpal implants and potentially reduce postoperative complications. Clin. Anat., 33:1014-1018, 2020. © 2019 Wiley Periodicals, Inc.