Radial Reference Points for Measuring Palmar Tilt and Ulnar Variance on Lateral Wrist Radiographs

A novel approach for three-dimensional evaluation of reduction morphology in distal radius fracture

BACKGROUND

Distal radius fractures are among the most common fractures, traditionally evaluated using two-dimensional (2D) parameters. These methods are unreliable in significantly displaced fractures, with discrepancies among evaluators. Recent advancements in imaging have introduced three-dimensional (3D) models, but standard parameters for 3D reduction morphology are not well established. This study aimed to develop a novel method for evaluating 3D reduction morphology based on the normal vector of a plane defined by anatomical reference points, comparing the reduction shape to the mirror image of the unaffected contralateral side.

METHODS

This retrospective case-control study included 27 patients (mean age 67.6 years) who underwent osteosynthesis with a volar locking plate for distal radius fractures. Preoperative and postoperative computed tomography (CT) scans of the affected and unaffected wrists were analyzed using 3D image analysis software. The 3D coordinates of three reference points; (1) radial styloid process, (2) sigmoid notch volar edge, and (3) sigmoid notch dorsal edge, were used to evaluate the reduction shape and compare it to the unaffected side mirror image. Correlations between vector angles in the coronal, sagittal, and axial planes and clinical outcomes, such as % total active motion (%TAM) and Mayo wrist scores, were analyzed.

RESULTS

The distances between the unaffected mirror image and postoperative image for the three reference points were 2.1 mm, 2.1 mm, and 2.7 mm, with barycenter differences of 1.7 mm. The postoperative plane areas consisted from three reference points were significantly larger in the postoperative image compared to the unaffected mirror image (203.4 mm² vs. 192.4 mm², P < 0.01). Correlation coefficients for vector angles in the yz-plane between unaffected mirror image and postoperative image were moderate (0.58, P < 0.05). Mild correlations were found between postoperative vector angles in the xy and xz planes and %TAM.

CONCLUSIONS

This novel 3D evaluation method provides a more comprehensive assessment of fracture reduction, particularly in the axial plane. While it demonstrates good reproducibility in coronal alignment, further refinement is needed for sagittal and axial alignments. This method could enhance surgical precision and improve clinical outcomes in distal radius fracture management.

CLINICAL TRIAL NUMBER

Not applicable.

An Evaluation of the Reliability of Manual Landmark Identification on 3D Segmented Wrists

BACKGROUND

Three-dimensional (3D) preoperative planning is increasingly used in orthopaedic surgery. Two-dimensional (2D) characterization of distal radial deformities remains inaccurate, and 3D planning requires a reliable reference frame at the wrist. We aim to evaluate the reliability of the determination of anatomical points placed manually on 3D models of the radius to determine which of those points allow reliable morphometric measurements.

METHODS

Twenty-three radial scans were reconstructed in 3D. Five operators specialized in the upper limb manually positioned 8 anatomical points on each model. One of the operators repeated the operation 6 times. The anatomical points were based on previously published 3D models used for radial inclination and dorsopalmar tilt measurements. The repeatability and reproducibility of the measurements derived using this manual landmarking were calculated using different measurement methods based on the identified points. An error of ≤2° was considered clinically acceptable.

RESULTS

This study of intraobserver and interobserver variability of the anatomic points allowed us to determine the least variable and most accurately defined points. The middle of the ulnar border of the radius, the radial styloid, and the midpoint of the ulnar incisura of the radius were the least variable. The palmar and dorsal ends of the ridge delineating the scaphoid and lunate facets were the most variable. Only 1 of the radial inclination measurement methods was clinically acceptable; the others had a repeatability and reproducibility limit of >2°, making those measurements clinically unacceptable.

CONCLUSIONS

The use of isolated points seems insufficient for the development of a wrist reference frame, especially for the purpose of measuring dorsopalmar tilt. If one concurs that an error of 2° is unacceptable for all distal radial measurements, then clinicians should avoid using 3D landmarked points, due to their unreliability, except for radial inclination measured using the radial styloid and the midpoint of the ulnar edge of the radius. A characterization of the wrist using 3D shapes that fit the articular surface of the radius should be considered.

LEVEL OF EVIDENCE

Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Ulnar variance in distal radial fractures: assessment and interpretation

We explored patterns of shortening of the distal radius and investigated the effect of displacement on 'ulnar variance' in 250 patients with distal radial fractures. A small number of patients (5%) had a fracture that resulted in true shortening. Thirty-two per cent had fractures that appeared short, but lateral radiographs revealed that the articular surface was tilted, with either the anterior or dorsal rim of the articular surface being proximal to the distal ulna but the other rim was distal to it. We recommend initial assessment of variance on lateral radiographs. If the anterior and dorsal rims of the distal radial articular surface are proximal to the distal ulna, then true shortening is present and lengthening and stabilization, to hold the radius distracted, should be considered. If only one rim is proximal to the distal ulna, then correction of the tilt will lessen the apparent positive variance.Level of evidence: IV.