Radiostereometric analysis in measurements of migration and inducible micromotion in intra-articular distal radius fractures treated with a volar plate

Biomechanical Stability of Diaphyseal Ulnar Shaft Fractures and Ulnar Shortening Osteotomies After Fixation

BACKGROUND

To determine the amount of micromotion during forearm rotation after diaphyseal ulnar shaft fracture or osteotomy.

METHODS

This was a biomechanical study using 7 paired-matched cadavers. The upper extremity was mounted in a custom rig and the forearm brought through full pronation and supination. A Hall effect sensor was placed at the fracture ends to measure micromotion for all tested conditions. There were 4 conditions tested: (1) intact ulnar shaft with plate to act as a control; (2) transverse fracture/osteotomy without stabilization; (3) fracture/osteotomy with cortical apposition stabilized with plate fixation; and (4) 50% comminuted fracture stabilized with plate.

RESULTS

There was a significantly greater amount of fracture site motion in the fracture/osteotomy model without stabilization compared with all other tested conditions (P < .001, .0001, .0003, respectively). The fracture/osteotomy site with cortical apposition and the comminuted fracture models showed no statistically significant differences in the amount of micromotion compared with each another (P = .952) or compared with the intact ulnar shaft (P = .997, .889, respectively).

CONCLUSIONS

There was no significant difference in the amount of motion between an intact ulnar shaft, an ulnar shaft fracture with cortical apposition stabilized with a plate, and a plated comminuted fracture. These findings may help surgeons decide on their type of postoperative immobilization in the setting of isolated ulnar shaft fractures or ulnar shaft osteotomies stabilized with plate fixation.

Dorsal Tilt of the Distal Radius Fracture Changes With Forearm Rotation When Measured on Radiographs

Purpose

This study examined the impact of pronation and supination on the reliability of the radiographically measured values of dorsal tilt, radial inclination (RI), and ulnar variance (UV) in cadaveric forearms with artificially created distal radius fractures.

Methods

We prepared 21 human cadaveric forearms (11 right and 10 left) for radiostereometric analysis (RSA) by insertion of tantalum markers. Distal radius fractures were created midway between the marker segments. Radiographs and RSA images were taken at different degrees of supination and pronation. The precise degree of forearm rotation was calculated using RSA software. Two observers (H.B.T. and T.T.) independently measured tilt, RI, and UV on all radiographs in a blinded and randomized fashion. Univariate linear regression analyses were used to determine the relationship between forearm rotation and the measured radiographic values.

Results

The radiographically measured value of tilt was significantly impacted by forearm rotation. Supinating or pronating the forearm by 10° decreased and increased, respectively, the radiographic value of dorsal tilt by approximately 3°.

Conclusions

This study showed that the positioning of the fractured forearm during the radiographic procedure significantly impacted subsequent radiographic measurements of tilt. Dorsal tilt measurements increased (ie, fracture displacement measured more dorsal) with pronation and decreased (ie, fracture displacement measured more toward neutral, with less dorsal tilt) with supination of the forearm. However, measurements of RI (p = 0.12 and p = 0.55 for observer 1 and 2) and UV (p = 0.34 and p = 0.17, observer 1 and 2) were not significantly impacted by rotation.

Clinical relevance

Treatment of a distal radius fracture is, at least to some extent, based on radiographic quantification of fracture deformity. Therefore, unreliable measurements may adversely influence clinical decision making.

Future modalities to assess fracture healing

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Radiostereometric Analysis of Stability and Inducible Micromotion After Locked Lateral Plating of Distal Femur Fractures

OBJECTIVES

To evaluate interfragmentary motion over 1 year after distal femoral fracture fixation using radiostereometric analysis (RSA). The secondary aim was to assess whether RSA data are consistent with diagnoses of nonunion.

DESIGN

Prospective cohort study.

SETTING

Level I urban trauma center.

PATIENTS

Sixteen patients between 22 and 89 years of age with distal femoral fracture (OTA/AO type 33).

INTERVENTION

All fractures were treated with a lateral locking plate, and tantalum markers were inserted into the main proximal and distal fracture fragments. RSA was performed at 2, 6, 12, 18, and 52 weeks postoperatively. Both unloaded and loaded RSA measurements were performed.

MAIN OUTCOME MEASUREMENTS

Unloaded fracture migration over time and inducible micromotion at the fracture site in the coronal plane were determined at each follow-up interval.

RESULTS

RSA precision in the coronal plane of interfragmentary motion over time and inducible micromotion were 1.2 and 0.9 mm in the coronal plane, respectively. Two cases required revision surgery for nonunion 1 year postoperatively. For cases of union, unloaded fracture migration stopped being detectable between 12 and 18 weeks, and inducible micromotion was no longer detectable by the 12-week visit. For cases of nonunion, both unloaded migration and inducible micromotion were detected throughout the study period.

CONCLUSIONS

RSA may be used to reliably assess distal femoral fracture healing. RSA revealed differences in cases of union and nonunion by 3 months and more consistently than traditional x-rays.

LEVEL OF EVIDENCE

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

Radiostereometric analysis of the initial stability of internally fixed femoral neck fractures under differential loading

We examined the feasibility of radiostereometric analysis (RSA) in the assessment of the initial stability of internally fixed femoral neck fractures. The study included 16 patients (mean age 73 years). During surgery, multiple RSA-beads were inserted on both sides of the fracture. Radiographs for RSA were taken in the supine position within the first 3 days and 6, 12, 24, and 52 weeks after surgery. To detect any inducible motion at the fracture-site, radiographs for RSA were taken with the patient resting or applying a load through the fracture. Fracture loading was achieved by the patient pressing the ipsilateral foot as much as tolerated on a force plate while providing a counterforce through both hands. Micromotion exceeding the precision values of RSA (≥0.3 mm for the translation vector and/or ≥1.2 degrees for the rotation vector) was considered significant. Permanent three-dimensional fracture-site displacement was also recorded. Voluntary loading induced fracture-site micromotion, which exhibited a dichotomous distribution. In patients with uncomplicated fracture union, inducible micromotion was detectable only at baseline-if at all. Conversely, fractures that developed a nonunion were characterized by the continuation of inducible micromotion beyond baseline. Permanent fracture-site displacement was, on average, nearly an order of magnitude greater than the inducible micromotion. Fracture unions were characterized by the cessation of permanent fracture-site displacement by 12 weeks. Nonunions presented as outliers in permanent fracture-site displacement. Large-scale studies are warranted to evaluate whether the detection of inducible micromotion beyond baseline could serve as an indicator of insufficient fixation stability. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society.

Trochanteric fracture-implant motion during healing - A radiostereometry (RSA) study

Cut-out complication remains a major unsolved problem in the treatment of trochanteric hip fractures. A better understanding of the three-dimensional fracture-implant motions is needed to enable further development of clinical strategies and countermeasures. The aim of this clinical study was to characterise and quantify three-dimensional motions between the implant and the bone and between the lag screw and nail of the Gamma nail. Radiostereometry Analysis (RSA) analysis was applied in 20 patients with trochanteric hip fractures treated with an intramedullary nail. The following three-dimensional motions were measured postoperatively, at 1 week, 3, 6 and 12 months: translations of the tip of the lag screw in the femoral head, motions of the lag screw in the nail, femoral head motions relative to the nail and nail movements in the femoral shaft. Cranial migration of the tip of the lag screw dominated over the other two translation components in the femoral head. In all fractures the lag screw slid laterally in the nail and the femoral head moved both laterally and inferiorly towards the nail. All femoral heads translated posteriorly relative to the nail, and rotations occurred in both directions with median values close to zero. The nail tended to retrovert in the femoral shaft. Adverse fracture-implant motions were detected in stable trochanteric hip fractures treated with intramedullary nails with high resolution. Therefore, RSA method can be used to evaluate new implant designs and clinical strategies, which aim to reduce cut-out complications. Future RSA studies should aim at more unstable fractures as these are more likely to fail with cut-out.

Secondary displacement of distal radius fractures treated by bridging external fixation

Loss of reduction remains an important problem after treatment of distal radius fractures, whatever the type of bone fixation. We assessed retrospectively the rate of secondary displacement after external fixation of distal radius fractures in order to identify possible risk factors for instability. We reviewed the pre-operative and serial post-operative radiographs of a retrospective series of 35 distal radius fractures treated by bridging external fixation. When classified according to the Société Française d'Orthopédie et Traumatologie (SOFCOT) criteria, the rate of secondary displacement was 48.5%. At final follow up, the reduction was anatomical in 12% and acceptable in 83%. There was malunion in 5%. The loss of reduction concerned primarily the distal radius palmar tilt and was moderate. No correlation was found with age, gender, type of fracture, degree of initial displacement, associated ulnar fracture, or seniority of the treating surgeon.