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

Validation for the effect of intra-exposure patient motion on the assessment of radiostereometric implant migration in a tibial component phantom study

BACKGROUND

An increasing number of radiostereometry (RSA) research studies have long-term follow-up implant migration outcomes, which show ascending curves of implant migration with occasionally decreasing migration. After scrutinizing images and RSA scenes related to the alternating curves, we suppose that intra-exposure patient motion may contribute to that. The main purposes of this in vitro study were 1) to identify whether the patient motion in different directions could result in the inaccurate assessment of implant migration, and 2) to figure out which direction(s) accounted for the alternating curves.

HYPOTHESIS

It was hypothesized that the assessments of implant migration would be less precise and accurate than they could be when patient motion occurred, and such motion would contribute to the alternating curves of radiostereometric implant migration.

MATERIALS AND METHODS

A customized phantom, assembled with a tibial component, was designed for simulating intra-exposure patient motion during follow-up RSA examinations. Two different Roentgen tubes were used as the current standard of radiology departments. Radiographs were acquired in a uniplanar technical arrangement. Two defined protocols were conducted: one is to simulate implant migration outcomes at post-op, the early stage (6months), and the later stage (2 to 10years) ; during the later stage, the other is to mimic patient motion by phantom motion in the medial-lateral (x), distal-proximal (y), and anterior-posterior (z) axes.

RESULTS

Phantom motion could result in the inaccurate assessment of implant migration, and translations along the medial-lateral (x) axis were the most influenced by patient motion. Motion along the medial-lateral (x) axis could account for the curves with decreasing migration.

DISCUSSION

Our assessments of implant migration may be less precise and accurate than they could be when intra-exposure patient motion occurs. We probably neglect the importance of 100% simultaneous exposures, and the influence of patient motion on RSA accuracy and data reliability, due to the difficulty in detecting patient (micro)motion. Electronically synchronized exposures of two paired Roentgen tubes are 100% simultaneous for image acquisition, and they are thus highly recommended for the assessment of implant migration in RSA.

TYPE OF STUDY AND LEVEL OF PROOF

not applicable.

No benefit of the trochanteric stabilizing plate on loss of fracture reduction in AO/OTA 31-A2 trochanteric fractures

Aims

Despite limited clinical scientific backing, an additional trochanteric stabilizing plate (TSP) has been advocated when treating unstable trochanteric fractures with a sliding hip screw (SHS). We aimed to explore whether the TSP would result in less post operative fracture motion, compared to SHS alone.

Methods

Overall, 31 patients with AO/OTA 31-A2 trochanteric fractures were randomized to either a SHS alone or a SHS with an additional TSP. To compare postoperative fracture motion, radiostereometric analysis (RSA) was performed before and after weightbearing, and then at four, eight, 12, 26, and 52 weeks. With the "after weightbearing" images as baseline, we calculated translations and rotations, including shortening and medialization of the femoral shaft.

Results

Similar migration profiles were observed in all directions during the course of healing. At one year, eight patients in the SHS group and 12 patients in the TSP group were available for analysis, finding a clinically non-relevant, and statistically non-significant, difference in total translation of 1 mm (95% confidence interval -4.7 to 2.9) in favour of the TSP group. In line with the migration data, no significant differences in clinical outcomes were found.

Conclusion

The TSP did not influence the course of healing or postoperative fracture motion compared to SHS alone. Based on our results, routine use of the TSP in AO/OTA 31-A2 trochanteric fractures cannot be recommended. The TSP has been shown, in biomechanical studies, to increase stability in sliding hip screw constructs in both unstable and intermediate stable trochanteric fractures, but the clinical evidence is limited. This study showed no advantage of the TSP in unstable (AO 31-A2) fractures in elderly patients when fracture movement was evaluated with radiostereometric analysis.

Postoperative Rotation Deformity of Head-Neck Fragments in Unstable Intertrochanteric Fractures Fixed with Intramedullary Nails

BACKGROUND

Our purpose was to quantify the postoperative rotation deformity (RD) after osteosynthesis of unstable intertrochanteric fractures (ITFx) using 3D-CT / image processing software, and to clarify the clinical meaning of RD.

METHODS

Forty-six consecutive patients with unstable intertrochanteric fractures were enrolled in this study. All were fixed with Gamma 3 Trochanteric nail and RC Lag Screw® (Stryker). We performed 3D-CT evaluations for the rotational deformity of head-neck fragments, the medial cortex support (MCS) between main fragments and bone healing at 3 months postoperatively.

RESULTS

The RD was significantly larger in the patients without the MCS (5.1 ± 4.0°, N = 9) than those with the MCS (2.4 ± 2.6°, N = 37) (P = 0.006*). Delayed healing (N=3) was observed in patients without the MCS, and the association between RD and delayed healing was significant (P = 0.003*, cut-off value 6.4°, sensitivity 100% and specificity 90.7%, AUC 0.91).

CONCLUSIONS

This study proposed a novel method of measuring postoperative RD. Lack of MCS may lead to RD and consequent delayed healing in unstable ITFx fixed with intramedullary nails.

No effect of hydroxyapatite-coated sliding hip screw threads on screw migration in the femoral head/neck of pertrochanteric fractures: a randomized controlled trial using radiostereometric analysis

INTRODUCTION

Cut-out is the most frequently reported mechanical failure of internal fixation of pertrochanteric fractures. The purpose of this study was to examine if hydroxyapatite-coated screw thread on a sliding hip screw (SHS) could reduce screw migration within the femoral head in patients with stable pertrochanteric fractures.

MATERIALS AND METHODS

In a double-blinded randomized controlled study, 37 patients at mean age 78 (range 56-96), with pertrochanteric fracture (Evans I, II, IV) received surgery with a SHS with a hydroxyapatite-coated or a non-coated lag screw thread. Radiostereometry and standard radiographs were obtained 1 day, 6 weeks, 3- and 6 months post-operatively to evaluate screw and fracture migration and fracture reposition. The two groups were combined to describe fracture migration.

RESULTS

There was similar and small screw migration in the femoral head between the two groups at 6 weeks, 3- and 6 months (p > 0.12). Fracture migration occurred predominantly in the first 6 weeks, where fracture impaction was 5.95 mm (CI 95% 2.87 to 9.04) and anterior rotation of the femoral head was -2.94° (CI 95% - 5.22 to - 0.66). Migration of the fracture (total translation) correlated to the post-operative fracture reposition (p = 0.002), but not significantly to screw migration (p = 0.09). Neither screw total translation (rho 0.06, p = 0.79) nor fracture total translation (rho 0.04, p = 0.77) correlated with bone mineral density.

CONCLUSION

There was no clinical benefit of hydroxyapatite coating on lag screw migration in this patient cohort. Migration of the pertrochanteric fractures was higher with poor fracture reposition but fractures generally stabilized after 6 weeks follow-up. The study was registered at ClinicalTrials.gov (NCT05677061).

LEVEL OF EVIDENCE II

Patient-blinded prospective randomized study. Trial registration number The study was registered at ClinicalTrials.gov (NCT05677061).

Assessment of Bone Healing: Opportunities to Improve the Standard of Care

➤ Bone healing is commonly evaluated by clinical examination and serial radiographic evaluation. Physicians should be mindful that personal and cultural differences in pain perception may affect the clinical examination. Radiographic assessment, even with the Radiographic Union Score, is qualitative, with limited interobserver agreement.➤ Physicians may use serial clinical and radiographical examinations to assess bone healing in most patients, but in ambiguous and complicated cases, they may require other methods to provide assistance in decision-making.➤ In complicated instances, clinically available biomarkers, ultrasound, and magnetic resonance imaging may determine initial callus development. Quantitative computed tomography and finite element analysis can estimate bone strength in later callus consolidation phases.➤ As a future direction, quantitative rigidity assessments for bone healing may help patients to return to function earlier by increasing a clinician's confidence in successful progressive healing.

Trajectory of bolt and length of plate in femoral neck system determine the stability of femur neck fracture and risk of subsequent subtrochanteric fracture : a finite element analysis

BACKGROUND

This study aimed to analyze the differences in the stability of fractures, stress distribution around the distal-most screw according to the length of the plate and the trajectory of the bolt in Pauwels type III femoral neck fracture using the femoral neck system (FNS).

METHODS

Finite element models of Pauwels type III femoral neck fractures were established with surgical variations in the trajectory of the bolt (central, inferior, valgus, and varus) and length of the lateral plate (1- and 2-hole plate). The models were subsequently subjected to normal walking and stair-climbing loads.

RESULTS

The screw-holding cortical bone in subtrochanter in the model with a 2-hole plate and the bolt in the inferior trajectory and the models with 1-hole or 2-hole plate and the bolt in valgus trajectory had shown greater maximum principal strain than the models with central or varus trajectories. The gap and sliding distance on the fracture surface were larger with inferior or varus trajectories of the bolt and smaller with the valgus trajectory of the bolt under both loads, compared to those of the central trajectory.

CONCLUSION

For the fixation of Pauwels type III femoral neck fracture, the trajectory of the FNS bolt and the length of the plate affect the mechanical stability of the fracture and the strain of cortical bone around the distal-most screw. The surgical target should stay on the central trajectory of the bolt and the 2-hole plate's mechanical benefits did not exceed the risk.

How Do Classic (Static) RSA and Patient Motion Artifacts Affect the Assessment of Migration of a TKA Tibial Component? An In Vitro Study

BACKGROUND

Classic (static) Roentgen stereophotogrammetric analysis (RSA) is the current gold standard to assess, in vivo, the migration of total joint arthroplasty components. To prevent potential patient motion artifacts during the acquisition of paired radiostereometric images, images must be taken by simultaneously firing both X-ray tubes. However, the influence of nonsynchronized RSA paired images or patient motion artifacts on the precision of RSA and the assessment of implant migration is not well understood.

QUESTIONS/PURPOSES

We assessed (1) the effect of possible patient motion on the precision of RSA and (2) apparent differences in implant migration among axes (in-plane and out-of-plane translations and in-plane and out-of-plane rotations) of possible motion artifacts.

METHODS

Radiographs of two tibial knee arthroplasty components, each fixed in two bone-implant models as a customized phantom, were taken in a uniplanar measurement setup. We evaluated both model-based (implant models from reversed engineering) and marker-based (additional attached implant markers) RSA approaches. Between the simulated reference and follow-up examinations, we used one of the bone-implant models to simulate patient motion and the other to simulate no patient motion in parallel. Two defined protocols were followed for each of the bone-implant models: no-motion and simulated motion protocols. RSA image pairs were analyzed using a model-based RSA software package (MBRSA 4.1, RSA core ). Precision was calculated through repeat examinations, and migration of the two components was assessed for comparison of the components with each other. Measurements were taken along the medial-lateral and posterior-anterior axes for translations and around the cranial-caudal axis for rotations. The maximum total point motion was measured for comparison between the two components.

RESULTS

The effect of simulated patient motion was generally small, except in the cranial-caudal axis, but the induced imprecision associated with motion was larger in model-based RSA than it was in marker-based RSA. The mean ± standard deviation values of precision in model-based RSA were 0.035 ± 0.015 mm, 0.045 ± 0.014 mm, and 0.049 ± 0.036 mm greater than those in marker-based RSA, in accordance with the simulated motion protocol in translations along the medial-lateral axis (0.018 ± 0.004 mm; p = 0.01), along the posterior-anterior axis (0.018 ± 0.007 mm; p = 0.003), and rotations around the cranial-caudal axis (0.017 ± 0.006 mm; p = 0.02). Apparent differences in implant migration were the greatest for the maximum total point motion. The maximum total point motion increased from 0.038 ± 0.007 mm for the no-motion protocol to 1.684 ± 0.038 mm (p < 0.001) for the simulated motion protocol in marker-based RSA, and from 0.101 ± 0.027 mm for the no-motion protocol to 1.973 ± 0.442 mm (p < 0.001) for the simulated motion protocol in model-based RSA, and was the worst-case scenario regarding patient motion artifacts.

CONCLUSION

Patient motion exceeding 1 mm or 1° on nonsynchronized RSA images affects measurement errors regarding the detection of migration of a tibial component. In clinical RSA studies, the effect of patient motion on the assessment of implant migration should be of particular concern, even if clinical RSA systems have acceptable precision. Specially trained radiographers are crucial for correctly acquiring radiographs, especially when simultaneous radiography exposures are not electronically automated. In general, RSA requires synchronized image acquisition, and this should be the state-of-the-art.

CLINICAL RELEVANCE

In clinical RSA studies, precision assessed by repeat examinations may not be reliable using the current standards that are widely used in radiology departments. When assessing implant migration for reliability, comparison of the maximum total point motion between the tested (simulated motion) implant and baseline (no-motion) implant, as in this study, is advocated because of the accurate detection of patient motion artifacts.

Accuracy of radiostereometric analysis using a motorized Roentgen system in a pilot study for clinical simulation

Radiostereometric analysis (RSA) is routinely implemented with two paired Roentgen tubes for three-dimensional (3D) implant migration measurements. A conventional set-up of one stationary tube and one mobile could be time-consuming. Utilizing two customized ceiling-mounted tubes is normally associated with investment costs. Thus, a pilot set-up of a motorized system (single Roentgen source) for radiostereometric image acquisition may be a time-saving and space-efficient alternative. RSA using the motorized system is feasible in this study as a non-synchronized image acquisition technique, however, patient motion may occur and influence the assessment of implant migration. The phantom study aimed to assess accuracy of RSA using the motorized Roentgen system in this in vitro study. Accuracy values of translations and rotations were ±0.29 mm and ±0.48° for the single Roentgen source RSA set-up and ±0.26 mm and ±0.48° for the conventional RSA set-up. This study was also performed to simulate potential patient motion during exposure intervals between paired image acquisition. RSA using the motorized system is able to implement RSA with acceptable accuracy. In general, RSA with synchronized image acquisition is the gold standard to access in vivo implant migration with the highest accuracy. Patient motion exists in non-synchronized image acquisition techniques and results in RSA-related motion artifacts. Then we introduced what RSA-related motion artifacts are. The uniplanar calibration cage applied in the study has a few fiducial and control markers, and some of the markers were occluded in radiographs. Whereas, the number of markers in the calibration cage is correlated with accuracy of 3D implant reconstruction.

Finite-Element Analysis of a Novel Cephalomedullary Nail for Restricted Sliding to Reduce Risk of Implant Failure in Unstable Intertrochanteric Fractures

Objective

How to restrict sliding of cephalomedullary nail and rigid reconstruct medial support for unstable intertrochanteric fractures remains a challenge. This study aims to explore the feasibility of a novel cephalomedullary nail for restriction sliding and reconstruction of medial femoral support to prevent failure in unstable trochanteric fractures through finite element analysis.

Methods

The DICOM files of a unilateral femur spiral computed tomography (CT) scans from a elderly female were converted into STL files, and the most common clinical trochanteric fracture model with the absence of medial support, AO/OTA 31‐A2.3 was simulated by removing the posterior medial femur. The model of a novel medial sustain nail (MSN‐II) and a widely used nail (proximal femoral nail anti‐rotation PFNA‐II) were modeled according to the manufacturer‐provided engineering drawing. Different loads were applied to the femoral head to simulate the postoperative weight bearing gait. The sliding distance of helical blade in femoral neck, maximum stress of femur and nail, displacement of proximal fragment were analyzed to revealing the mechanical stability of unstable trochanteric fracture stabilized by different implant.

Results

The sliding distance of helical blade in the femoral neck, the maximum stress on the femur and nail, the displacement of proximal fragment in MSN‐II under 2100N axial load were 0.65 mm, 689 MPa, 1271 MPa, 16.84 mm respectively, while that were 1.43 mm, 720.8 MPa, 1444 MPa, 18.18 mm, respectively in PFNA‐II. The difference between the two groups was statistically significant (P < 0.05) and the stress was mainly distributed in medial distal side of nail but helical blade and the proximal aperture for the nail in MSN‐II. Compared to PFNA‐II, MSN‐II demonstrates biomechanical merit against femur medialization, cut‐out and coax varus.

Conclusion

The sliding distance of helical blade in femoral neck, the maximum stress on the femur and nail, and the displacement of proximal fragment of MSN‐II were less than those of PFNA‐II in the treatment of unstable intertrochanteric fractures. Therefore MSN‐II has better stability than PFNA‐II and it may have the potential to avoid femur medialization and cut out. It might be an option in unstable trochanteric fracture because of its superiority in restricted sliding and medial support reconstruction.

Cement augmentation of internal fixation for trochanteric fracture: a systematic review and meta-analysis

PURPOSE

This study aimed to determine the efficacy and safety of cement augmentation for internally fixed trochanteric fractures through a systematic review and meta-analysis of randomized controlled trials (RCTs).

METHODS

We searched the MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov databases to identify RCTs, published until July 2020 that examined the effects of cement augmentation of internal fixation of trochanteric fractures. The primary outcomes were reoperation and Parker Mobility Score, whereas the secondary outcomes were 1-year mortality rate, EuroQol 5 Dimension, fixation failures, and adverse events. We conducted meta-analyses of the outcome measures using the random-effects models. We evaluated the certainty of evidence based on the Cochrane risk-of-bias tool and the Grading of Recommendations, Assessment, Development, and Evaluation approach.

RESULTS

We included three RCTs (326 participants). No significant effect was observed in favor of cement augmentation on all these outcomes. The certainty of evidence for fixation failures was very low and that for the other outcomes was low. The overall risk of bias for each outcome was high or of some concern in all included studies.

CONCLUSIONS

The effect of cement augmentation of internal fixation of trochanteric fractures was uncertain for the clinical outcomes due to the low certainty of evidence. Further RCTs with a low risk of selection bias may present convincing conclusions on the efficacy and safety of cement augmentation.

LEVEL OF EVIDENCE

Level 1.

Postoperative computed tomography assessment of anteromedial cortex reduction is a predictor for reoperation after intramedullary nail fixation for pertrochanteric fractures

PURPOSE

Postoperative radiographs are routinely used to assess fracture reduction following intramedullary nail fixation for pertrochanteric fractures, even though computed tomography (CT) is a superior modality. We aimed to determine the association between reduction quality assessed by CT and rates of reoperation and to evaluate the association of reoperation and reduction quality according to the assessment modality (plain radiographs vs. CT).

METHODS

A retrospective analysis of 299 consecutive patients treated with intramedullary nail fixation for pertrochanteric fractures was conducted. Fracture reduction measured by postoperative radiographs and CT was categorized as anatomical type, extramedullary type, or intramedullary type. Postoperative data for analysis included reduction status, tip-apex distance (TAD), screw position in the femoral head, sliding distance, and conditions associated with reoperation.

RESULTS

Of the 299 patients included with a mean age of 83.1 ± 8.2 years, there were six patients who required reoperation (2.0%). According to the CT assessments, there were 42 intramedullary reductions (14.0%). Patients with a non-intramedullary reduction based on postoperative CT images were significantly more likely to have proper placement of the screw, a reduced TAD, a reduced sliding distance, and a lower reoperation rate than those with an intramedullary reduction (P < 0.05). The reduction quality assessed by postoperative CT was significantly associated with reoperation (95% CI, 1.45-29.31).

CONCLUSIONS

Intramedullary reduction assessed by CT was associated with reoperation. The reduction quality based on CT findings was more predictive for reoperation than that from plain radiographs.

Case series and finite element analysis of PFNA combined with cerclage wire for treatment of subtrochanteric fracture of femur

Objective

To retrospectively analyze the clinical efficacy of PFNA combined with a cerclage wire in the treatment of 52 patients with unstable subtrochanteric fracture of the femur and to analyze the biomechanical effect of ligature on a fracture model.

Methods

In this study, 52 patients with unstable subtrochanteric fractures were treated in our orthopedic trauma center from June 2013 to July 2018. The Seinsheimer type IV fracture model was established using the patient’s CT data, and the joint surface of the distal femoral condyle and the external condyle were restrained. The femoral head was used as the loading point, and a force of 500 N was applied vertically along the long axis of the femoral shaft.

Results

All 52 patients were followed up for 12 to 37 months, with an average of 18.07 ± 4.38 months. According to the Sanders hip function score, 28 cases were excellent (55–60 points), 22 cases were good (45–54 points), and 2 cases were poor (35–44 points), with an excellent and good rate of 96.15%. Postoperative deep vein thrombosis occurred in 3 cases, and fracture nonunion occurred in 1 case. No infection, loose fracture of internal fixation or hip varus deformity occurred. The finite element analysis indicated that the displacement of the whole model decreased slightly and the relative sliding of the fracture block decreased, but the maximum stress of the femur increased after the addition of the cerclage wire.

Conclusion

The treatment of unstable subtrochanteric fracture of the femur with PFNA combined with cerclage wire has the advantages of simple operation, satisfactory reduction of fracture, stable fixation, and good recovery of limb function. The finite element analysis suggested that the biomechanical strength fixation was enhanced after the addition of cerclage wire. However, the local stress concentration of the tie may increase the risk of failure.

Assessment of fracture healing in orthopaedic trauma

Fracture healing is a complex physiologic process, relying on the crucial interplay between biological and mechanical factors. It is generally assessed using imaging modalities, including conventional radiology, CT, MRI and ultrasound (US), based on the fracture and patient features. Although these techniques are routinely used in orthopaedic clinical practice, unfortunately, they do not provide any information about the biomechanical status of the fracture site. Therefore, in recent years, several non-invasive techniques have been proposed to assess bone healing using ultrasonic wave propagation, changes in electrical properties of bones and callus stiffness measurement. Moreover, different research groups are currently developing smart orthopaedic implants (plates, intramedullary nails and external fixators), able to provide information about the fracture healing process. These devices could significantly improve orthopaedic and trauma clinical practice in the future and, at the same time, reduce patients' exposure to X-rays. This study aims to define the role of traditional imaging techniques and emerging technologies in the assessment of the fracture healing process.

Imaging Modalities to Assess Fracture Healing

PURPOSE OF REVIEW

This review discusses imaging modalities for fracture repair assessment, with an emphasis on pragmatic clinical and translational use, best practices for implementation, and challenges and opportunities for continuing research.

RECENT FINDINGS

Semiquantitative radiographic union scoring remains the clinical gold standard, but has questionable reliability as a surrogate indicator of structural bone healing, particularly in early-stage, complex, or compromised healing scenarios. Alternatively, computed tomography (CT) scanning enables quantitative assessment of callus morphometry and mechanics through the use of patient-specific finite-element models. Dual-energy X-ray absorptiometry (DXA) scanning and radiostereometric analysis (RSA) are also quantitative, but technically challenging. Nonionizing magnetic resonance (MR) and ultrasound imaging are of high interest, but require development to enable quantification of 3D mineralized structures. Emerging image-based methods for quantitative assessment of bone healing may transform clinical research design by displacing binary outcomes classification (union/nonunion) and ultimately enhance clinical care by enabling early nonunion detection.