Load Distribution in Dorsally-Angulated Distal Radius Deformity Using Finite Element Analysis

PURPOSE

The load axis of the carpals is located on the volar side of the normal distal radius. A volar lunate facet fracture (VLFF) is exposed to volar-shearing stress, which can cause volar displacement of the carpus. A previous biomechanical study reported that the load at the scaphoid fossa was located more dorsally and the pressure at the lunate fossa decreased in a dorsally-angulated model. However, the distal radius load distribution for various volar tilts remains unclear. We speculate that if the volar tilt decreases, the load distribution moves dorsally and decreases the stress on the VLFF. Therefore, we analyzed a dorsally-angulated distal radius model to evaluate changes in the load distribution using finite element analysis.

METHODS

A 3-dimensional finite element wrist model was developed using computed tomography images. The ligaments were modeled as tension-only spring elements. We considered the intact wrist model for a volar tilt of 15° and created 5 additional models for volar tilts of 10°, 5°, 0°, -5°, and -10°.

RESULTS

As the dorsal angulation increased, the stress distribution moved from volar to dorsal and from the lunate fossa toward the scaphoid fossa. The maximum stress on the volar lunate facet was reduced as volar tilt decreased. The maximum stress was higher on the lunate fossa for volar tilts from 15° to 5°. In contrast, the maximum stress was higher on the scaphoid fossa for volar tilts of ≤0°.

CONCLUSIONS

Load transmission moved from volar to dorsal and from the lunate fossa to the scaphoid fossa when the volar tilt decreased. Therefore, a decrease in the volar tilt would reduce the load on the VLFF.

CLINICAL RELEVANCE

This study provides surgeons accurate knowledge regarding load distribution of the distal radius for various volar tilts that could be helpful in treating patients with VLFFs.

Volar Lunate Facet Rim Fractures: K-I Classification and Technique

Background and Purpose  It is difficult to capture and safely support a small volar lunate facet (VLF) fragment and obtain sufficient initial fixation. The challenge in treating VLF rim fractures has resulted in various management options. The purpose of this study was to evaluate the clinical and radiological outcomes of a consecutive series of VLF rim fractures of the distal radius treated surgically and to report the Kondo-Imatani (K-I) classification of these fractures, using computed tomography (CT) images and surgical technique, which is termed the Plate buttress and Double tiered subchondral support (PD) technique. Patients and Methods  A retrospective review was conducted on 35 patients with VLF rim fractures that included postoperative clinical evaluations, CT images, and radiographs. Description of Technique  The PD technique to stabilize the VLF fragment with an anatomical and low-profile volar locking plate (VLP). Results  All fractures healed at the final follow-up; Mayo wrist performance score average was 81.7 points (45-100), and the quick disabilities of the arm, shoulder, and hand (quick-DASH) score average was 9.5 points (0-31.8), showing relatively good clinical results. Conclusion  VLF rim fragments are not amenable to standard VLP fixation. Unstable fixation may result in postoperative correction loss, aseptic necrosis, malunion, radiocarpal subluxation, and wrist dysfunction. This report described the K-I classification for VLF rim fractures of the distal radius and surgical technique, termed the PD technique, to stabilize the VLF rim fragment with an anatomical and low-profile VLP. Level of Evidence  This is a Level IV, case series study.

Classification and Management of Failed Fixation of the Volar Marginal Fragment in Distal Radius Fractures

Greater understanding of specific fracture patterns following distal radius fractures has arisen with the advent of volar plating. The volar marginal fragment (VMF) is a small peripheral piece of bone which is critical to carpal stability. Failure to achieve good fixation of the VMF can result in volar subluxation of the carpus and distal radioulnar joint instability. Due to its small, distal nature, this fragment can be easily missed and difficult to fix. Loss of reduction of the VMF following operative fixation presents specific challenges and surgical considerations dictated by patient characteristics and timing. Our goal of this review is to present a classification system for these failed VMFs which can help guide surgical treatment as well as expected outcomes.

Dorsal Wrist Extrinsic Carpal Ligament Injury Exacerbates Volar Radiocarpal Instability After Intra-Articular Distal Radius Fracture

Background: Volar radiocarpal instability is often seen after loss of fixation of volar lunate facet fragments. The pathogenesis of post-traumatic volar radiocarpal instability is poorly understood. The purpose of this study was to determine if injury to the dorsal wrist extrinsic carpal ligaments contributes to volar radiocarpal instability. Methods: Six matched pairs of cadaveric upper extremities were tested using a dynamic hand testing system. In group 1, the intact wrist, the wrist with a volar lunate facet fracture, and the fractured wrist after 500 cycles of grip were tested. In group 2, in addition to the intact and fractured wrist, the fractured wrist with the dorsal extrinsic carpal ligaments cut and the fractured wrist with the dorsal extrinsic carpal ligaments cut after 500 cycles of grip were also tested. Volar-dorsal displacement of the lunate was measured from 45° wrist flexion to 45° wrist extension in 22.5° increments with the wrist flexors/extensors loaded for each condition. Results: Volar lunate translation did not significantly increase after the volar lunate facet fracture alone, and was not evident to a significant extent until the dorsal wrist extrinsic carpal ligaments were cut. Further instability of the lunate occurred after grip cycling only with the dorsal extrinsic capsular ligaments cut. Conclusions: Injury to the dorsal wrist extrinsic carpal ligaments exacerbates volar radiocarpal instability. Unrecognized dorsal sided injury may be a contributing factor to why stable fixation of volar lunate facet fragments remains problematic after volar plating of intra-articular distal radius fractures with displaced volar lunate facet fragments.

The Sigmoid Notch View for Distal Radius Fractures

PURPOSE

This study defines the sigmoid notch view of the distal radius. Specifically, we tested the null hypothesis that there is no relationship between the subchondral stripe of bone seen on a sigmoid notch view of the distal radius and the articular surface of the sigmoid notch.

METHODS

We used 44 wrist specimens for anatomic and fluoroscopic analysis. We measured the articular depth of the sigmoid notch from its deepest point and classified the shape of the sigmoid notch. We then placed a radiopaque marker at the nadir of the articular surface and quantified the fluoroscopic depth of the sigmoid notch. A sigmoid notch view, which was a tangential fluoroscopic view of the volar and dorsal lips of the sigmoid notch, was obtained. The relationship of the articular surface to the stripe of subchondral bone seen on this view, called the sigmoid stripe, was determined.

RESULTS

Anatomic analysis revealed sigmoid notch types with proportions similar to those in previous descriptions. The marker for the articular surface was superimposed or just ulnar to the sigmoid stripe in all specimens. In flat face and ski slope notches, this was coincident with the volar and dorsal lips of the sigmoid notch. In C- and S-type notches, there was a measurable distance from the articular surface marker to the edges of the bone of the volar and dorsal lips of the sigmoid.

CONCLUSIONS

The articular surface marker at the nadir of the sigmoid notch is always coincident or ulnar to the sigmoid stripe in the sigmoid notch view.

CLINICAL RELEVANCE

Surgeons can use the sigmoid notch view as a reliable method to (1) evaluate the integrity of the articular surface, (2) ensure hardware is not placed in the distal radioulnar joint, and (3) guide placement of volar locking plates in the coronal plane.

Volar-Ulnar Approach for Fixation of the Volar Lunate Facet Fragment in Distal Radius Fractures: A Technical Tip

The volar Henry approach is most commonly used for surgical fixation of distal radius fractures. However, this approach is limited in achieving adequate exposure for the fixation of the volar-ulnar portion of the distal radius, rendering it difficult for the ideal placement of the fixation construct. We propose the use of the extensile volar-ulnar approach for fixation of distal radius fracture involving a small volar-ulnar fragment. This approach allows optimal reduction of the sigmoid notch and the volar lunate facet, which anatomically reduces both the radiocarpal joint and the sigmoid notch. In addition, extension of this approach may safely be performed if concomitant carpal tunnel release is necessary.

Volar plate fixation failure for volar shearing distal radius fractures with small lunate facet fragments

PURPOSE

To determine the percentage of AO B3 distal radius fractures that lose reduction after operative fixation and to see whether fracture morphology, patient factors, or fixation methods predict failure. We hypothesized that initial fracture displacement, amount of lunate facet available for fixation, plate position, and screw fixation would be significant risk factors for loss of reduction.

METHODS

A prospective, observational review was conducted of 51 patients (52 fractures) with AO B3 (volar shearing) distal radius fractures treated operatively between January 2007 and June 2012. We reviewed a prospective distal radius registry to determine demographic data, medical comorbidities, and physical examination findings. Radiographs were evaluated for AO classification, loss of reduction, length of volar cortex available for fixation, and adequacy of stabilization of the lunate facet fragment with a volar plate. Preoperative data were compared between patients who maintained radiographic alignment and those with loss of reduction. A multivariate logistic regression analysis was completed to determine significant predictors of loss of reduction.

RESULTS

Volar shearing fractures with separate scaphoid and lunate facet fragments (AO B3.3), preoperative lunate subsidence distance, and length of volar cortex available for fixation were significant predictors for loss of reduction; the latter was significant in multivariate analysis. Plate position and number of screws used to stabilize the lunate facet were not statistically different between groups.

CONCLUSIONS

Patients with AO B3.3 fractures with less than 15 mm of lunate facet available for fixation, or greater than 5 mm of initial lunate subsidence, are at risk for failure even if a volar plate is properly placed. In these cases, we recommend additional fixation to maintain reduction of the small volar lunate facet fracture fragments in the form of plate extensions, pins, wires, suture, wire forms, or mini screws.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic III.