Biomechanics of Distal Radius Fractures





Key Points





  • The ideal classification meets three objectives: to describe the lesion, to guide treatment choice, and to predict the functional outcome.




    • An example of such is the Patient Accident Fracture (PAF) classification as it allows an exhaustive analysis that also puts into perspective patient and mechanism of injury characteristics.




  • An altered anatomy of the distal radius leads to biomechanical disorders such as altered load transfer, decreased joint amplitudes, carpal instability, stiffness, or instability of the distal radioulnar joint.




    • An important example of this is the fragmented discontinuity of the volar intermediate column—also referred to as the critical corner—with high risk of biomechanical construct failure when inadequately fixated.




  • The most recent biomechanical works on anterior plate osteosynthesis can be summarized by variable angulation plates with 3 to 4 unicortical epiphyseal locking screws in a single row, with 2 or 3 bicortical diaphyseal screws.



Importance of the Problem


Based on the knowledge of the anatomical “key points” of the distal radius, it is possible to classify the fracture in order to guide the treatment and explain the subsequent functional prognosis to the patient. It is also essential to know the biomechanical factors applied to distal radius fractures (DRF), which influence the decision of the type of treatment envisaged.



Panel 1: Case Scenario 1


A 72-year-old woman who fell directly on her left arm sustained an open DRF with an anterior displacement. How can this DRF best be classified? And based on biomechanical principles of DRFs, which type and configuration of osteosynthesis would be most adequate for this osteopenic fracture? ( Fig. 1 )




Fig. 1


Open comminuted articular DRF.



Panel 1: Case Scenario 2


A 51 year-old women was brought the emergency department with multiple fractures after sustaining a motor cycle accident. Her radiographs and reconstructed CT body scan of the left wrist show a displaced volar rim fragment of the distal radius ( Fig. 2 ). From a biomechanical point of view, what type of plate fixation would be most adequate for this type of fracture: a standard distal radius plate or a volar rim plate?




Fig. 2


Radiographs showing a displaced volar rim fragment of the distal radius.

(Courtesy of Benjamin Degeorge.)



Current Opinion


Advanced knowledge of distal radius biomechanics is mandatory to choose the adequate treatment strategy, whether operative or conservative. Multiple risk factors of fracture instability and fixation construct failure have been identified and should be considered during decision-making.


Finding the Evidence





  • Cochrane search: Distal Radius Fracture biomechanics



  • Pubmed (Medline): distal radius fracture*[tiab] AND biomechanic*[tiab]



  • Bibliography of eligible articles



  • Articles that were not in the English or French language were excluded.



Findings


Biomechanical studies of distal radius fractures are numerous. It is important to take into consideration that some in vitro studies are limited by the use of synthetic bone, or postulate boundary conditions that are different from one team to another, raising the question of the validity of comparing them with each other (strong heterogeneity bias). Finally, some biomechanically validated hypotheses still lack validation or clinical relevance. The emergence of new tools such as finite element models should not make us forget that these numerical models must be validated in vitro before valid conclusions can be drawn.


Classification: Why and Which One?


Energy and Fracture


There is no “typical DRF” but an injury spectrum, a consequence of hyperextension. Pechlaner reported the results of a cadaveric study in which 63 forearms were used in machine hyperextension. Depending on the position of the first row during the impact, the pressures applied on the articular surface of the radius will generate fractures rather dorsal, central, or palmar. In each of the three localizations, there is an increasing injury severity with pure metaphyseal fractures, followed by epiphyseal metaphysis (articular resection) and finally with dislocation. The most common form was the articular and metaphyseal form with dorsal displacement. In two-thirds of cases there were associated injuries at the level of the triangular complex (with or without avulsion of the ulnar styloid) or interosseous ligaments. This work legitimizes Laulan’s work and the MEU classification ( Fig. 3 ). Some particular lesions have been identified and are often described as specific entities: the fracture with a Die Punch fragment (postero-medial fragment) described by Scheck in 1962, and the radial styloid fracture (Chauffeur’s fracture).




Fig. 3


MEU classification of Laulan. Each fracture is composed of the three associated injury components: M etaphyseal involvement, E piphyseal joint involvement, (distal radio-) U lnar joint involvement.


The “Best” Classification


The large number of classifications published over time did not allow one of them to become a relevant management tool. Classifications are closely linked to an era and a type of treatment. The ideal classification must meet three objectives: to describe the injury , to guide decision-making , and to reliably predict the functional outcome .


Unfortunately, none of the classifications fulfill the three conditions defined above. Most only take into account the fractures of the radius, and on the radius only few parameters differ from one classification to another.


In addition, intra- and interobserver reliability are often poor and objectify the limits of these classifications where the observer has cannot readily “box” the fracture. Using both AP and lateral views, the AO classification was moderately reproducible in an interobserver and weakly in an intraobserver reliability analysis. Only type A (extraarticular), B (intraarticular partial) and C (intraarticular) of AO was reproducible. Using a scanner to complete the analysis, the AO classification lost any interobserver reproducibility. Similarly, the Frykman, Melone, and Mayo Clinic classifications were unreliable, both intra- and interobserver. Moreover, several studies have shown the lack of prognostic interest of these classifications, proving that the criteria studied are not the right ones to describe the fracture. After 5 years, the AO and Frykman classifications did not predict the clinical course of 652 patients. Older’s classification, tested on 633 patients, was also insufficient in terms of prognosis. Lenoble’s study also found no prognostic value in Castaing, Frykman, Gartland, Older, Lindström, and Jenkins’ classifications. The so-called universal classification proposed by Cooney tries to propose a therapeutic strategy but its recently tested validity remains debatable. Thus, the classifications studied are neither reproducible nor prognostic. Their usefulness is hence questionable. And more than a classification, a system of description of the injuries must prevail to compare the fractures. That of Laulan is validated and allows to “tidy up” in all cases the fracture of the radius. This classification describes the fracture with sufficient intra- and interobserver reproducibility to become a useful tool for treatment and functional prognosis. It consists in the description of three parameters allowing to know if the fracture is “serious” or not, each parameter having been validated as related to the prognosis. Metaphysis (comminution), epiphysis (articular fracture) and ulna involvement are different in each fracture, but each fracture case is a combination of these three parameters ( Figs. 3 and 4 ).




Analysis of the metaphyseal component (presence of comminution and/or corticospongious impaction at the metaphysis level):




  • M 0: absent metaphyseal line, and.



  • M 1: simple metaphyseal line, without comminution.



  • M 2: metaphyseal trait displaced with localized comminution. Comminution is less than hemicircumference (postero-external scale).



  • M 3: metaphyseal line with comminution of at least one hemicircumference (all the posterior cortical with respect for the opposite hemicircumference (anteromedial console allowing a reduction).



  • M 4: metaphyseal line with circumferential comminution. The instability after reduction is multidirectional.



The parameter “prime” is assigned to the parameter M if the metaphyseal line ends definitively in the distal radioulnar joint.




Analysis of the epiphyseal component of the fracture (presence of articular features with or without displacement).




  • E 0: absent joint line and.



  • E 1: articular line (s), not displaced.



  • E 2: articular fragment (s) displaced by shearing. There is no subchondral embedding component. The displacement concerns only a part of the articular surface with one or two epiphyseal fragments (radial styloid fracture, volar rim fracture, etc.)



  • E 3: articular fragment (s) displaced by localized compression. There is subchondral depression localized to a part of the articular surface which can involve up to three fragments.



  • E 4: articular fragments displaced by extended compression. Subchondral depression involves almost the entire articular surface with a bursting appearance. The small size of the fragments prevents their reduction and/or fixation.





Analysis of the ulnar line, according to its location and its displacement:




  • U 0: absence of ulnar fracture.



  • U 1: nondisplaced fracture of the ulnar styloid (distal or proximal).



  • U 2: displaced fracture of the ulnar styloid (distal or proximal).



  • U 3: metaphysio-diaphyseal ulnar fracture (+/− styloid).



  • U 4: metaphysio-epiphyseal ulnar fracture (+/− styloid).





Fig. 4


MEU classification of Laulan.


Fracture Analysis by the PAF System (Patient, Accident, Fracture)


The “analysis method” presented for the first time at the French Orthopaedic Society (SOFCOT) by Herzberg and Dumontier, then modified and improved by Herzberg, is a simple way of understanding the DRF in order to identify and therefore to treat all injuries without forgetting them ( Fig. 5 ). This is a list of essential elements whose anatomy is to be restored because it is related to the functional prognosis. There are four specific parameters of the distal radius (radial inclination, volar tilt, articular impaction, and the shortening of the radius by metaphyseal compression) as well as intracarpal and distal radioulnar (RUD) joint injury. The three parameters of the MEU classification finally become part of it ( Fig. 4 ). This “checklist” is filled out using a standard emergency radiographic assessment consisting of anteroposterior (AP), lateral and oblique views. These allow to analyze the presence and importance of a posteromedial fragment. In the event of a high-energy fracture, a CT scan will analyze all articular injuries at the radiocarpal level and at the radioulnar level. Intraoperatively, under anesthesia radiographs under traction allow a better analysis (especially comminution) and often relativize large displacement. In two thirds of cases they provided information to the operator that make him modify his strategy. In this analysis, arthroscopy is an additional tool to complete the assessment, in a contemporary way to fixation. Ligament and osteocartilaginous injuries will be perfectly visualized. With regard to ligamentous injuries, their high frequency contrasts with the small number of patients who secondarily require ligament repair. As Laulan showed, at the level of the interosseous ligaments (scapholunate), ligamentous injury is not synonymous with incompetence of the structure and therefore synonymous with repair. In a 1-year radiographic prospective study, 43% of dissociative intracarpal ligamentous injuries were diagnosed but these ligamentous injuries were not found to influence the functional result at 1 year. With regard to osteochondral injuries, in articular fractures in patients with high functional demands, arthroscopy remains a modern tool for the visualization and optimal fixation of inaccessible fragments. But seeing and better understanding intraarticular injuries does not mean that they always can or should be fixed.


Mar 15, 2021 | Posted by in RHEUMATOLOGY | Comments Off on Biomechanics of Distal Radius Fractures
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