Biomechanical studies: science (f)or common sense?

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.

Biomechanically superior treatments do not translate into improved outcomes in randomized controlled trials

PURPOSE

Significant time and resources are devoted to conducting orthopaedic biomechanics research; however, it is not known how these studies relate to their subsequent clinical studies. The purpose of the present study was to determine whether biomechanically superior treatments were associated with improved clinical outcomes as determined by analogous randomized controlled trials (RCTs).

METHODS

A systematic review was conducted to find RCTs that tested a research question based on a prior biomechanical study. PubMed and SCOPUS databases were queried for orthopaedic randomized controlled trials, and full text articles were reviewed to find RCTs which cited biomechanical studies with analogous comparison groups. A random-effects multi-level logistic regression model was conducted examining the association between RCT outcome and biomechanics outcome, adjusting for multiple outcomes nested within study.

RESULTS

In total, 20,261 articles were reviewed yielding 21 RCTs citing a total of 43 analogous biomechanical studies. In 7 instances (16.2%), the RCT and a cited biomechanical study showed concordant results (i.e. the superior treatment in the RCT was also the superior construct in the biomechanical study). RCT outcome was not associated with biomechanical outcome (β = -1.50, standard error = 0.78, p = .05).

CONCLUSION

This study assessed 21 orthopaedic RCTs with 43 corresponding biomechanical studies and found no association between superior biomechanical properties of a given orthopaedic treatment and improved clinical outcomes. Favourable biomechanical properties alone should not be the primary reason for selecting one treatment over another. Furthermore, RCTs based on biomechanical studies should be carefully designed to maximize the chance of providing clinically relevant insights.

Forces acting on the clavicle during shoulder abduction, forward humeral flexion and activities of daily living

BACKGROUND

The forces acting on the human clavicle in vivo are difficult if not impossible to measure. The goal of this study is to quantify the forces acting on the human clavicle during shoulder abduction, forward humeral elevation and three activities of daily living using the Delft Shoulder and Elbow Model.

METHODS

The Delft Shoulder and Elbow Model and a computed tomography scan of a clavicle were used to calculate the forces and moments acting on the entire clavicle and on three planes within the middle third of the clavicle during the simulated movements.

FINDINGS

The largest resultant force simulated across the clavicle was 126 N during abduction. Maximum resultant moments of 2.4 Nm were identified during both abduction and forward humeral elevation. The highest forces in the middle third of the clavicle were of a compressive nature along the longitudinal axis of the clavicle, increasing to 97 N during forward humeral elevation and 91 N during abduction. Forces in opposite direction along the y-axis were identified on either side of the conoid ligament. The three simulated activities of daily living had similar ranges of forces and moments irrespective of the sagittal plane in which these activities were performed.

INTERPRETATION

Peak forces occurred at different locations on the middle third of the clavicle during different movements. The results create an understanding of the forces and their distribution across the clavicle during activities of daily living. These data may be helpful in the development of clavicular fixation devices.

LEVEL OF EVIDENCE

Biomechanical study.

Biomechanical comparison between solid and cannulated intramedullary devices for midshaft clavicle fixation

Background

A method of closed reduction and internal fixation with cannulated screws was proposed as a surgical treatment of midshaft clavicle fractures. However, there are no mechanical studies about the cannulated screw used in the fixation of midshaft clavicle fracture. We conducted this study to compare the construct bending stiffness of a fixation midshaft clavicle fracture with a Knowles pin, cannulated screw and reconstruction plate. In addition, purchase lengths of both intramedullary devices were measured.

Methods

After transverse osteotomy over the midpoint for fracture simulation, eighteen synthetic clavicles were assigned to 3 groups and fixed with reconstruction plate, Knowles pin or cannulated screw. Purchase length was defined as the engaged length of the intramedullary portion of the two intramedullary devices Stiffness, yield load and maximum load of the cantilever bending test were calculated of each tested synthetic bones.

Results

The Knowles pin group had a significantly longer average intramedullary purchase length compared with that of the cannulated screw group. The construct stiffness in the reconstruction plate group (5.6 ± 0.9 N/mm) was higher than that of the intramedullary devices; the Knowles pin group (3.1 ± 0.6 N/mm) provided a greater construct stiffness than did the cannulated screw group (1.7 ± 0.4 N/mm) (p = 0.007). The cannulated screw group had the lowest yield and maximum load compared with the reconstruction plate and Knowles pin groups. Both the reconstruction plate and Knowles pin failed at the implant-bone interface. However, the cannulated screw group failed at the osteotomy site with broken implants.

Conclusion

This study suggests that fixation of midshaft clavicle fractures with cannulated screws may lead to early failure due to inadequate mechanical strength. Ideal intramedullary clavicle devices should supply adequate intramedullary purchase lengths and mechanical strength.

Surgical fixation of midshaft clavicle fractures: A systematic review of biomechanical studies

PURPOSE

Surgical treatment of displaced midshaft clavicle fractures requires a decision between plate fixation and intramedullary (IM) fixation. Numerous studies report on the biomechanical properties of various repair constructs. The goal of this systematic review was to provide an overview of studies describing the biomechanical properties of the most commonly used surgical fixations of midshaft clavicle fractures. Additionally, we aimed to translate these biomechanical results into clinically relevant conclusions.

METHODS

A computer-aided search of the EMBASE and PudMed/MEDLINE databases was conducted. Studies included for review compared biomechanical properties of plate fixation with IM fixation and superiorly positioned plates with anteroinferiorly positioned plates for midshaft clavicle fractures.

RESULTS

Fifteen studies were eligible for inclusion. Plate fixation seemed to form a more robust construct than IM fixation in terms of stiffness and failure loading. The remaining clavicle was stronger after removal of the IM device than after removal of the plate. Superior plating of transverse fractures generally seemed to provide greater stiffness and strength during bending loads than anteroinferior plating did. The absence of cortical alignment in wedge and comminuted fractures directly influenced the fixation stability for both IM fixation and plate fixation, regardless of location.

CONCLUSION

Each type of fracture fixation has biomechanical advantages and disadvantages. However, exact thresholds of stiffness for inducing healing and failure strength to withstand refractures are unknown. The clinical relevance of the biomechanical studies may be arguable. Since none of the studies investigate the effect of tissue adaptation over time they should be interpreted with caution.

Reliability of classification for post-traumatic ankle osteoarthritis

PURPOSE

The purpose of this study was to identify the most reliable classification system for clinical outcome studies to categorize post-traumatic-fracture-osteoarthritis.

METHODS

A total of 118 orthopaedic surgeons and residents-gathered in the Ankle Platform Study Collaborative Science of Variation Group-evaluated 128 anteroposterior and lateral radiographs of patients after a bi- or trimalleolar ankle fracture on a Web-based platform in order to rate post-traumatic osteoarthritis according to the classification systems coined by (1) van Dijk, (2) Kellgren, and (3) Takakura. Reliability was evaluated with the use of the Siegel and Castellan's multirater kappa measure. Differences between classification systems were compared using the two-sample Z-test.

RESULTS

Interobserver agreement of surgeons who participated in the survey was fair for the van Dijk osteoarthritis scale (k = 0.24), and poor for the Takakura (k = 0.19) and the Kellgren systems (k = 0.18) according to the categorical rating of Landis and Koch. This difference in one categorical rating was found to be significant (p < 0.001, CI 0.046-0.053) with the high numbers of observers and cases available.

CONCLUSIONS

This study documents fair interobserver agreement for the van Dijk osteoarthritis scale, and poor interobserver agreement for the Takakura and Kellgren osteoarthritis classification systems. Because of the low interobserver agreement for the van Dijk, Kellgren, and Takakura classification systems, those systems cannot be used for clinical decision-making.

LEVEL OF EVIDENCE

Development of diagnostic criteria on basis of consecutive patients, Level II.

6-week radiographs unsuitable for diagnosis of suspected scaphoid fractures

INTRODUCTION

Six week follow-up radiographs are a common reference standard for the diagnosis of suspected scaphoid fractures. The main purpose of this study was to evaluate the interobserver reliability and diagnostic performance characteristics of 6-weeks radiographs for the detection of scaphoid fractures. In addition, two online techniques for evaluating radiographs were compared.

MATERIALS AND METHODS

A total of 81 orthopedic surgeons affiliated with the Science of Variation Group assessed initial and 6-week scaphoid-specific radiographs of a consecutive series of 34 patients with suspected scaphoid fractures. They were randomized in two groups for evaluation, one used a standard website showing JPEG files and one a more sophisticated image viewer (DICOM). The goal was to identify the presence or absence of a (consolidated) scaphoid fracture. Interobserver reliability was calculated using the multirater kappa measure. Diagnostic performance characteristics were calculated according to standard formulas with CT and MRI upon presentation in the emergency department as reference standards.

RESULTS

The interobserver agreement of 6-week radiographs for the diagnosis of scaphoid fractures was slight for both JPEG and DICOM (k = 0.15 and k = 0.14, respectively). The sensitivity (range 42-79 %) and negative predictive value (range 79-94 %) were significantly higher using a DICOM viewer compared to JPEG images. There were no differences in specificity (range 53-59 %), accuracy (range 53-58 %), and positive predictive value (range 14-26 %) between the groups.

CONCLUSIONS

Due to low agreement between observers for the recognition of scaphoid fractures and poor diagnostic performance, 6-week radiographs are not adequate for evaluating suspected scaphoid fractures. The online evaluation of radiographs using a DICOM viewer seem to improve diagnostic performance characteristics compared to static JPEG images and future reliability and diagnostic studies should account for variation due to the method of delivering medical images.

LEVEL OF EVIDENCE

Diagnostic level II.

Osteochondritis dissecans of the humeral capitellum: reliability of four classification systems using radiographs and computed tomography

BACKGROUND

The radiographic appearance of osteochondritis dissecans (OCD) of the humeral capitellum varies according to the stage of the lesion. It is important to evaluate the stage of OCD lesion carefully to guide treatment. We compared the interobserver reliability of currently used classification systems for OCD of the humeral capitellum to identify the most reliable classification system.

METHODS

Thirty-two musculoskeletal radiologists and orthopaedic surgeons specialized in elbow surgery from several countries evaluated anteroposterior and lateral radiographs and corresponding computed tomography (CT) scans of 22 patients to classify the stage of OCD of the humeral capitellum according to the classification systems developed by (1) Minami, (2) Berndt and Harty, (3) Ferkel and Sgaglione, and (4) Anderson on a Web-based study platform including a Digital Imaging and Communications in Medicine viewer. Magnetic resonance imaging was not evaluated as part of this study. We measured agreement among observers using the Siegel and Castellan multirater κ.

RESULTS

All OCD classification systems, except for Berndt and Harty, which had poor agreement among observers (κ = 0.20), had fair interobserver agreement: κ was 0.27 for the Minami, 0.23 for Anderson, and 0.22 for Ferkel and Sgaglione classifications. The Minami Classification was significantly more reliable than the other classifications (P < .001).

CONCLUSIONS

The Minami Classification was the most reliable for classifying different stages of OCD of the humeral capitellum. However, it is unclear whether radiographic evidence of OCD of the humeral capitellum, as categorized by the Minami Classification, guides treatment in clinical practice as a result of this fair agreement.