Assessment of fragment micromotion in distal femur fracture fixation with RSA

Three-dimensional computed tomography mapping techniques in the morphometric analysis of AO/OTA 33A and 33C distal femoral fractures: a retrospective single-center study

Purpose: Complex distal femoral fractures involve a challenging set of considerations that must be known to provide optimal management. This study aimed to determine the location and frequency of fracture lines and comminution zones in AO/OTA types 33A and 33C distal femoral fractures using three-dimensional computed tomography mapping. Methods: Seventy-four consecutive eligible patients were included. Fracture fragments for each patient were reconstructed, virtually reduced, and adjusted to match the distal femoral template. Then, all fracture lines and comminuted areas were extracted in transparent mode, and corresponding heat maps were constructed. Finally, these maps, along with the quantitative analysis findings of the counts and volumes of each fragment, were used to summarize the characteristics of the fractures. Results: Thirty-four females and 40 males [average age, 58 years (range, 18-92 years)] presented with a distal femoral fracture. There were 53 AO/OTA type 33A fractures, and 21 AO/OTA type 33C fractures. These two patterns differed significantly on fracture fragment count, comminuted zone fracture fragment count, and mean comminuted zone fracture fragment volume (p < 0.05). Most of the fracture line heat zones were in the femoral epiphysis, intercondylar notch of the femur, and patellofemoral joint. The comminuted area heat regions were mostly found on the lateral, anterior, and posterior femoral diaphysis, with less involvement on the medial side. Conclusion: Our findings may serve as a guide for the surgical approach selection of complex distal femur fractures, the placement strategy of the internal fixation, and the optimization of the osteotomy plan for biomechanical studies.

Using a Traction Table for Fracture Reduction during Minimally Invasive Plate Osteosynthesis (MIPO) of Distal Femoral Fractures Provides Anatomical Alignment

INTRODUCTION

Fracture reduction and fixation of distal femur fractures are technically demanding. Postoperative malalignment is still commonly reported after minimally invasive plate osteosynthesis (MIPO). We evaluated the postoperative alignment after MIPO using a traction table with a dedicated femoral support.

METHODS

The study included 32 patients aged 65 years or older with distal femur fractures of all AO/OTA types 32 (c) and 33 (except 33 B3 and C3) and peri-implant fractures with stable implants. Internal fixation was achieved with MIPO using a bridge-plating construct. Bilateral computed tomography (CT) scans of the entire femur were performed postoperatively, and measurements of the uninjured contralateral side defined anatomical alignment. Due to incomplete CT scans or excessively distorted femoral anatomy, seven patients were excluded from analyses.

RESULTS

Fracture reduction and fixation on the traction table provided excellent postoperative alignment. Only one of the 25 patients had a rotational malalignment of more than 15° (18°).

CONCLUSIONS

The surgical setup for MIPO of distal femur fractures on a traction table with a dedicated femoral support facilitated reduction and fixation, resulting in a low rate of postoperative malalignment, despite a high rate of peri-implant fractures, and could be recommended for surgical treatment of distal femur fractures.

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.

Preliminary testing of a novel bilateral plating technique for treating periprosthetic fractures of the distal femur

BACKGROUND

Current stabilization methods for periprosthetic fractures of the distal femur are inadequate in achieving fracture fixation, with complication rates as high as 29%. A major contributor to poor outcomes is that these methods rely only on screw purchase in the bone to maintain fracture reduction. We designed, manufactured and evaluated a novel plating method that utilizes the femoral prosthesis to enhance stability for treatment of distal femoral periprosthetic fractures.

METHODS

Medial and lateral plates were designed and manufactured based on geometry of a synthetic femur and femoral prosthesis. The two plates were linked via a compression screw and a small tab on each plate that inserted into pre-existing slots on the prosthesis. Mechanical tests (500N compression or 250N anterior directed cantilever bending), were performed on synthetic femurs with simple transverse fractures (3mm gap) just superior to the distal femoral prosthesis that were stabilized using either the prototype plates or a single lateral plate. Translational movements of the fracture site during loading were measured using 3D motion tracking.

FINDINGS

With the single lateral plate, the distal fragment experienced a resultant displacement of 0.40mm under cantilever bending and 0.61mm under compression (13% and 20% respectively of fracture gap width). With the bilateral plates, fracture gap motion was significantly reduced to 0.13mm under bending and compression (4.3% of the fracture gap).

INTERPRETATION

Our results indicate that a bilateral plating method is capable of improving stabilization of periprosthetic fractures compared to the traditional lateral plating technique.

Internal fixators: a safe option for managing distal femur fractures?

OBJECTIVE:

Evaluate safety and reliability of internal fixator for the treatment of intra-articular and periarticular distal femur fractures.

METHODS:

Retrospective data evaluation of 28 patients with 29 fractures fixed with internal fixator was performed. There was a predominance of male patients (53.5%), with 52% of open wound fractures, 76% of AO33C type fractures, and a mean follow up of 21.3 months. Time of fracture healing, mechanical axis deviation, rate of infection and postoperative complications were registered.

RESULTS:

Healing rate was 93% in this sample, with an average time of 5.5 months. Twenty-seven percent of patients ended up with mechanical axis deviation, mostly resulting from poor primary intra-operative reduction. There were two cases of implant loosening; two implant breakage, and three patients presented stiff knee. No case of infection was observed. Healing rate in this study was comparable with current literature; there was a high degree of angular deviation, especially in the coronal plane.

CONCLUSION:

Internal fixators are a breakthrough in the treatment of knee fractures, but its use does not preclude application of principles of anatomical articular reduction and mechanical axis restoration.

Level of Evidence II, Retrospective Study.

Periprosthetic supracondylar femoral fractures above total knee arthroplasty: comparison of the locking and non-locking plating methods

PURPOSE

The purpose of this study was to compare the results and complications of periprosthetic supracondylar femoral fracture treatment using locking or non-locking plates.

METHODS

A locking compression plate was used in 14 patients, and a non-locking condylar buttress plate was used in 19 patients. There were no significant differences in the demographic data between the two groups. The primary healing rate and bone union time were compared. The Knee Society knee score and range of motion (ROM) were reviewed. The femorotibial angle and α and γ angles were measured using the Knee Society radiological evaluation method. The clinical and radiographic results, complications, and additional surgeries were compared between the two groups.

RESULTS

Thirteen of 14 locking plating patients and 11 of 19 non-locking plating patients healed without any additional surgeries. There were no differences in the average bone union time, knee score, or ROM between the two groups. The alignment and position of the implants were better without a loss in the reduction angle of >3° in the locking plating group compared with the non-locking plating group. Locking plate fixation reduced the incidence of overall complications, non-union, malunion, loss of reduction, and additional surgeries compared with non-locking plate fixation.

CONCLUSION

Fixation of periprosthetic supracondylar femoral fractures with a locking plate provided satisfactory results with a low risk of complications and additional surgeries compared with fixation with a non-locking plate.

LEVEL OF EVIDENCE

III.

Biomechanical methods for the assessment of fracture repair

The progress of fracture healing is directly related to an increasing stiffness and strength of the healing fracture. Similarly the weight bearing capacity of a bone directly relates to the mechanical stability of the fracture. Therefore, assessing the progress of fracture repair can be based on the measurement of the mechanical stability of the healing fracture. However, fracture stability is difficult to assess directly due to various obstacles of which shielding of the mechanical properties by the fracture fixation construct is the most relevant one. Several assessment methods have been proposed to overcome these obstacles and to obtain some sort of mechanical surrogate describing the stability of the fracture. The most direct method is the measurement of the flexibility of a fracture under a given external load, which comprises the challenge of accurately measuring the deformation of the bone. Alternative approaches include the measurement of load share between implant and bone by internal or by external sensors. A direct 3 dimensional measurement of bone displacement is provided by radiostereometric analysis which can assess fracture migration and can detect fracture movement under load. More indirect mechanical methods induce cyclic perturbations within the bone and measure the response as a function of healing time. At lower frequencies the perturbations are induced in the form of vibration and at higher frequencies in the form of ultrasonic waves. Both methods provide surrogates for the mechanical properties at the fracture site. Although biomechanical properties of a healing fracture provide a direct and clinically relevant measure for fracture healing, their application will in the near future be limited to clinical studies or research settings.

Radio-opaque bioactive glass markers for radiostereometric analysis

The objective of the study was to test the hypothesis that resorbable radio-opaque bioactive glass markers can be used in radiostereometric analysis (RSA). Cones made from (1) bioactive glass 1-06 with 2.5 wt.% BaSO(4), (2) glass 1-06 with 10 wt.% BaSO(4), (3) glass 1-06 without any additives and (4) nearly inert glass were created. The in vitro surface reactivity, as a surrogate of bioactivity, was analyzed using a simulated body fluid (SBF) immersion test. The in vivo performance was evaluated in the rat femur using biomechanical testing as well as histological and microcomputed tomography analysis of marker incorporation into bone. A phantom model RSA study using a porcine radius with a soft tissue envelope was carried out to determine the accuracy and precision of spherical markers for the measurement of fracture micromotion. SBF immersion studies and bone implantation studies showed that the addition of BaSO(4) slightly reduced surface reactivity in vitro and the bone-bonding properties of the bioactive glass in vivo. In the simulated RSA study with the selected resorbable marker composition (bioactive glass with 10 wt.% BaSO(4)), the accuracy of translation and rotation measurements in the longitudinal axis was +/-51 microm and +/-0.87 degrees , respectively. The precision of translation and rotation measurements in the longitudinal axis were 9 microm and 0.18 degrees , respectively. Bioactive glass markers with BaSO(4) additive appear to have adequate bone-bonding properties for marker stability and sufficient radio-opacity for RSA, but further preclinical comparison studies with tantalum markers are necessary.

Differentially loaded radiostereometric analysis to monitor fracture stiffness: a feasibility study

Inability to accurately and objectively assess the mechanical properties of healing fractures in vivo hampers clinical fracture management and research. We describe a method to monitor fracture stiffness during healing in a clinical research setting by detecting changes in fracture displacement using radiostereometric analysis and simultaneously measuring applied axial loads. A method was developed for load application, positioning of the patient, and radiographic setup to establish the technique of differentially loaded radiostereometric analysis (DLRSA). A DLRSA examination consists of radiostereometric analysis radiographs taken without load (preload), under different increments of load, and without load (postload). Six patients with distal femur fractures had DLRSA examinations at 6, 12, 18, and 26 weeks postoperatively. The DLRSA method was feasible in a clinical setting. The method provides objective and quantifiable data for internally fixed fractures and may be used in clinical research as a tool to monitor the in vivo stiffness of healing femoral fractures managed with nonrigid internal fixation.

Correlation of radiostereometric measured cervical range of motion with clinical radiographic findings after anterior cervical discectomy and fusion

STUDY DESIGN

Prospective clinical study.

OBJECTIVE

To evaluate the correlation between clinical radiographic findings and sagittal range of motion (ROM) measured using radiostereometric analysis (RSA) after anterior cervical discectomy and fusion (ACDF).

SUMMARY OF BACKGROUND DATA

Evaluation of fusion after ACDF continues to be difficult. Radiographic films including flexion/extension views are routinely used for this purpose. Unfortunately, routine radiographs are insensitive in demonstrating pseudarthrosis. RSA is an accurate technique that can be used in evaluation of segmental motion in vivo and can potentially be used in evaluation of spinal fusion.

METHODS

Sixteen patients who underwent multi-level ACDF were enrolled in this study. The procedure was performed in the routine fashion; cervical plates were utilized in each case. Intraoperatively, 3 to 5 tantalum beads were inserted into each vertebral body. At the 1-year follow-up period, sagittal ROM of the operated segments was measured with RSA. In addition, each segment was clinically evaluated for evidence of radiographic fusion by using a 3-point grading system (fused, uncertain, pseudarthrosis) and by measuring the interspinous widening on flexion/extension films. The correlation between the radiographic findings and RSA measured sagittal ROM was evaluated.

RESULTS

Fourteen 2-level and two 3-level procedures representing 31 motion segments were analyzed. The average sagittal ROM of all segments as measured by RSA was 1.3 +/- 1.4 degrees . The sagittal ROM of the segments with less than 2 mm of interspinous widening on clinical flexion/extension radiographs was measured at 1.1 degrees +/- 1.0 degrees with RSA, whereas the sagittal ROM of the segments with greater than 2 mm of interspinous widening was measured at 3.4 degrees +/- 2.9 degrees ; a significant correlation was noted between the 2-point grading method and the sagittal ROM (Pearson coefficient, r = 0.504, P = 0.004). Using the 3-point grading system, there were 20 levels graded as fused (0.8 degrees +/- 0.9 degrees ), 6 levels were graded as uncertain (1.7 degrees +/- 1.0 degrees ), and 4 levels were graded as pseudarthrosis (3.5 degrees +/- 2.7 degrees ). The pseudarthrosis group showed significantly greater motion than the fusion group (P = 0.005); a significant correlation was noted between the 3-point grading method and the sagittal ROM (Pearson coefficient, r = 0.561, P = 0.001).

CONCLUSION

In this study, we evaluated the utility of RSA in evaluating segmental motion after ACDF and demonstrated a significant difference between segments that demonstrated radiographic evidence of fusion when compared with segments that demonstrated evidence of pseudarthrosis. RSA appears to be a quantitative technique capable of assisting in the evaluation of fusion.

Mechanotransduction and fracture repair

Fracture-healing is regulated in part by mechanical factors. Study of the processes by which the mechanical environment of a fracture modulates healing can yield new strategies for the treatment of bone injuries. This article focuses on several key unanswered questions in the study of mechanotransduction and fracture repair. These questions concern identifying the mechanical stimuli that promote bone-healing, defining the mechanisms that are involved in this process, and examining the potential for cross-talk between investigations of mechanotransduction in bone-healing and in healing of other mesenchymally derived tissues. Several approaches to obtain accurate estimates of the mechanical stimuli present within a fracture callus are proposed, and our current understanding of the mechanotransduction processes involved in bone-healing is reviewed. Further study of mechanotransduction mechanisms is needed in order to identify those that are most critical and active during the various phases of fracture repair. A better understanding of the effect of mechanical factors on bone-healing will also benefit the study of healing, regeneration, and engineering of other skeletal tissues.