Lumbosacral stability of consolidated anteroposterior fusion after instrumentation removal determined by roentgen stereophotogrammetric analysis and direct surgical exploration

Migration of the femoral component and clinical outcomes after total knee replacement: a narrative review

Loosening is considered as a main cause of implant failure in total knee replacement (TKR). Among the predictive signs of loosening, migration is the most investigated quantitative parameter. Several studies focused on the migration of the tibial component in TKR, while no reviews have been focused on the migration of the femoral component and its influence on patients' clinical outcomes. The aim of this narrative review was (1) to provide information about of the influence of migration in femoral component of TKR prostheses, (2) to assess how migration may affect patient clinical outcomes and (3) to present alternative solution to the standard cobalt-chrome prostheses. A database search was performed on PubMed Central® according to the PRISMA guidelines for studies about Cobalt-Chrome femoral component migration in people that underwent primary TKR published until May 2020. Overall, 18 articles matched the selection criteria and were included in the study. Few studies investigated the femoral component through the migration, and no clear migration causes emerged. The Roentgen Stereophotogrammetric Analysis has been mostly used to assess the migration for prognostic predictions. An annual migration of 0.10 mm seems compatible with good long-term performance and good clinical and functional outcomes. An alternative solution to cobalt-chrome prostheses is represented by femoral component in PEEK material, although no clinical evaluations have been carried out on humans yet. Further studies are needed to investigate the migration of the femoral component in relation to clinical outcomes and material used.

A phantom and cadaveric study of radiostereometric analysis in posterior cervical and lumbar spinal fusion

BACKGROUND CONTEXT

Detecting pseudarthrosis following spinal fusion is important for accurate diagnosis and treatment. Current diagnostic measures hold certain drawbacks. Radiostereometric analysis (RSA) is a radiographic technique with the capability to measure intervertebral segment changes and may be a novel way of assessing fusion.

PURPOSE

The purpose of this work was to measure the accuracy and precision of RSA in instrumented posterior cervical and lumbar spinal fusion for measuring intervertebral movement. Further, to gain surgical practice with RSA in spine and determine optimal bead placements.

STUDY DESIGN

Artificial bone and cadaveric spine models were used to simulate a 3-level cervical (C3-C6) and a 2-level (L4-S1) lumbosacral posterior spinal fusion to analyze bead placements and to measure RSA accuracy and precision.

METHODS

Preliminary RSA bead placements were planned and measured in the artificial model. Secondary bead placements were adjusted slightly in the cadaveric model to consider additional fusion scenarios. Bead spread, detectability, and stability were measured to determine optimal placements. Translational and rotational precision of both models were measured. Accuracy was measured in the artificial spine model. Model-based RSA software was used for analysis.

RESULTS

Optimal bead placements were found to be throughout the lateral mass of C3-C6 and in the spinous process, transverse process, and within the screw canal of L4-S1. Detectability was high among all segments. Spread was greater in L4-S1 than C3-C6 due to bead collinearity along the transverse axis of the cervical vertebrae. Translational and rotational RSA accuracy in cervical and lumbosacral regions ranged between 0.005 to 0.014 mm and 0.058 to 0.208°. Translational and rotational precision measured in the phantom models ranged 0.017 to 0.131 mm and 0.058 to 0.394° in C3-C6, and 0.086 to 0.191 mm and 0.200 to 0.369° in L4-S1. Translational and rotational precision measured in the cadaveric models ranged 0.054 to 0.548 mm and 0.148 to 1.386° in C3-C6, and 0.068 to 0.164 mm and 0.100 to 0.270° in L4-S1.

CONCLUSIONS

RSA was found to be a feasible radiographic technique in C3-C6 and L4-S1 spinal fusion when measured in artificial and cadaveric models. Optimal bead placements were determined. Bead spread was shown to be better throughout the lumbar region than the cervical region due to anatomical size variations. RSA accuracy and precision were within acceptable RSA criteria.

CLINICAL SIGNIFICANCE

The results from this work contribute to the accuracy, precision, and bead placements for studying RSA in cervical and lumbar spinal fusions. This work may further support the development of clinical studies to assess spinal fusion by evaluating postoperative intervertebral movement using RSA.

RSA in Spine: A Review

STUDY DESIGN

Systematic review of literature.

OBJECTIVES

This systematic review was conducted to investigate the accuracy of radiostereometric analysis (RSA), its assessment of spinal motion and disorders, and to investigate the limitations of this technique in spine assessment.

METHODS

Systematic review in all current literature to invesigate the role of RSA in spine.

RESULTS

The results of this review concluded that RSA is a very powerful tool to detect small changes between 2 rigid bodies such as a vertebral segment. The technique is described for animal and human studies for cervical and lumbar spine and can be used to analyze range of motion, inducible displacement, and fusion of segments. However, there are a few disadvantages with the technique; RSA percutaneous procedure needs to be performed to implant the markers (and cannot be used preoperatively), one needs a specific knowledge to handle data and interpret the results, and is relatively time consuming and expensive.

CONCLUSIONS

RSA should be looked at as a very powerful research instrument and there are many questions suitable for RSA studies.

Simulation of a Bead Placement Protocol for Follow-up of Thoracic Spinal Fusion Using Radiostereometric Analysis

STUDY DESIGN

Computer simulation to detect intervertebral motion enabling future follow-up of spinal fusions performed on patients with multilevel thoracic scoliosis.

OBJECTIVES

To propose a method using computer simulation to evaluate a radiostereometric analysis (RSA) marker placement protocol for visibility and redundancy and validate the performance of the developed RSA system in detecting intervertebral motion.

SUMMARY OF BACKGROUND DATA

Radiostereometric analysis is a stereo x-ray technique in which clusters of tantalum markers are implanted to label well-defined landmarks and measure the relative motion between rigid bodies.

METHODS

A model of the spine with the instrumentation and the RSA markers was developed. The vertebrae were aligned to mimic multilevel thoracic scoliosis after correction. The researchers performed virtual segment motion to validate the performance of the developed system. X-ray images were simulated and RSA was used to evaluate the proposed marker placement protocol and detect virtual motion. The authors performed a physical phantom study to evaluate marker visibility.

RESULTS

All markers were located and matched between simulations and the condition numbers were well below the recommended value of 100. Based on computer simulation, average translational accuracy was 0.14, 0.01, and 0.24 mm along the x, y, and z axes, respectively, and average rotational accuracy was 0.23°, 0.12°, and 0.11° about the x, y, and z axes, respectively. The translational and rotational precision of the simulated RSA system was generally high. The physical phantom study agreed with the computer simulation and validated marker visibility.

CONCLUSIONS

Computer simulation is a powerful tool that can be used to facilitate the development and refinement of an RSA system before its application in patients, particularly when the anatomy involved is complex. The proposed marker placement protocol yielded translational and rotational accuracy below the limits of clinical significance, which enables future follow-up of multilevel thoracic scoliosis with Lenke classification 1AN.

Guideline update for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 4: Radiographic assessment of fusion status

The ability to identify a successful arthrodesis is an essential element in the management of patients undergoing lumbar fusion procedures. The hypothetical gold standard of intraoperative exploration to identify, under direct observation, a solid arthrodesis is an impractical alternative. Therefore, radiographic assessment remains the most viable instrument to evaluate for a successful arthrodesis. Static radiographs, particularly in the presence of instrumentation, are not recommended. In the absence of spinal instrumentation, lack of motion on flexion-extension radiographs is highly suggestive of a successful fusion; however, motion observed at the treated levels does not necessarily predict pseudarthrosis. The degree of motion on dynamic views that would distinguish between a successful arthrodesis and pseudarthrosis has not been clearly defined. Computed tomography with fine-cut axial images and multiplanar views is recommended and appears to be the most sensitive for assessing fusion following instrumented posterolateral and anterior lumbar interbody fusions. For suspected symptomatic pseudarthrosis, a combination of techniques including static and dynamic radiographs as well as CT images is recommended as an option. Lack of facet fusion is considered to be more suggestive of a pseudarthrosis compared with absence of bridging posterolateral bone. Studies exploring additional noninvasive modalities of fusion assessment have demonstrated either poor potential, such as with 99mTc bone scans, or provide insufficient information to formulate a definitive recommendation.

A comparison of radiostereometric analysis and computed tomography for the assessment of lumbar spinal fusion in a sheep model

Study Design Prospective animal study.

Objective The aim of this animal study is to evaluate the accuracy of radiostereometric analysis (RSA) compared with computed tomographic (CT) scan in the assessment of spinal fusion after anterior lumbar interbody fusion (ALIF) using histology as a gold standard.

Methods Three non-adjacent ALIFs (L1–L2, L3–L4, and L5–L6) were performed in nine sheep. The sheep were divided into three groups of three sheep. All the animals were humanely killed immediately after having the last scheduled RSA. The lumbar spine was removed and in vitro fine cut CT and histopathology were performed.

Results Using histological assessment as the gold standard for assessing fusion, RSA demonstrated better results (100% sensitivity and 66.7% specificity; positive predictive value [PPV] = 27.3%, negative predictive value [NPV] =100.0%) compared with CT (66.7% sensitivity and 60.0% specificity [PPV = 16.7%, NPV = 93.8%]).

Conclusions RSA demonstrated higher sensitivity and specificity when compared with CT. Furthermore, RSA has the advantage of much lower radiation exposure compared with fine cut CT. Further studies are required to see if RSA remains superior to CT scan for the assessment spinal fusion in the clinical setting.

Lumbar intervertebral instability: a review

Intervertebral instability of the lumbar spine is thought to be a possible pathomechanical mechanism underlying low back pain and sciatica and is often an important factor in determining surgical indication for spinal fusion and decompression. Instability of the lumbar spine, however, remains a controversial and poorly understood topic. At present, much controversy exists regarding the proper definition of the condition, the best diagnostic methods, and the most efficacious treatment approaches. Clinical presentation is not specific, and the relationship between radiologic evidence of instability and its symptoms is controversial. Because of its simplicity, low expense, and pervasive availability, functional flexion-extension radiography is the most thoroughly studied and the most widely used method in the imaging diagnosis of lumbar intervertebral instability. In this article, we provide an overview of the current concepts of vertebral instability, focusing on degenerative lumbar intervertebral instability, and review the different imaging modalities most indicated in diagnosing vertebral instability.

Assessment of fragment micromotion in distal femur fracture fixation with RSA

To assess fragment micromotion in three fracture fixation constructs 18 composite femur models were sectioned to create AO-C3 fractures and fixed using the Less Invasive Stabilization System (LISS), Dynamic Condylar Screw (DCS), or the Condylar Buttress Plate (CBP). Tantalum beads were attached to each fracture fragment. The constructs were tested for permanent deformation after cyclical loading (amplitude = 242.2N) and elastic deformation during static loading with 490.5N. Radiographs were taken before loading and then after unloading to determine permanent deformation or during loading to determine elastic deformation. We used RSA to quantify the six degrees of freedom interfragmentary maximum total motion, strain, and stress. For maximum total motion the CBP had more permanent deformation and two failures, whereas the LISS underwent the greatest elastic deformation. LISS and CBP had the highest strain conditions in the fracture gap and LISS had the greatest stress movements between fragments, all of which exceeded the upper limits for bone healing. LISS and CBP may not be indicated for comminuted fractures due to the high degree of flexibility of the LISS, resulting in high stress and strain conditions and susceptibility to catastrophic failure and high strain conditions with the CBP.

The history and future of radiostereometric analysis

Roentgen stereophotogrammetry allows one to localize the position of an object in space using roentgen rays. For orthopaedic purposes it was developed 35 years ago by Göran Selvik, and since that time many investigators have refined the radiostereometric calculations and evaluative software. Many uses and mathematical algorithms have been developed, and advancements in computer programs and digital radiography continue to expand its capabilities. Despite these advances, improvements in the technical accuracy and type of kinematic analyses possible have been relatively modest. However, radiostereometric analysis is now easier and less time consuming to use, with a resolution in clinical practice almost equal to what could only previously be obtained under ideal laboratory conditions. The ability to measure skeletal and implant movements with high resolution in vivo images was an important progressive step for the orthopaedic community. Radiostereometric analysis has helped develop new fields in clinical orthopaedic research and continues to improve advancements in orthopaedic health care.

Loss of coronal correction following instrumentation removal in adolescent idiopathic scoliosis

STUDY DESIGN

Retrospective radiographic analysis of patients with adolescent idiopathic scoliosis (AIS) status after instrumentation removal.

OBJECTIVE

To evaluate the effect of instrumentation removal in surgically corrected AIS.

SUMMARY OF BACKGROUND DATA

Spinal instrumentation is occasionally removed for various reasons, most commonly for postoperative pain or infection, in surgically corrected AIS. The fate of instrumentation removal in adults has been previously reported with documented loss of sagittal alignment. However, to our knowledge, the long-term follow-up after instrumentation removal in AIS has not been reported.

METHODS

We retrospectively reviewed the preoperative, pre-instrumentation removal, postoperative following instrumentation removal, and latest follow-up radiographs of all patients with a primary diagnosis of AIS who underwent instrumentation removal after posterior spinal fusion. There were 21 patients (15 females, 6 males) from 2 institutions, at an average age of 14.8 years (range 9-19), who were originally treated between 1988 and 2002. Instrumentation removal occurred at an average of 2.4 years after surgery (range 8 months to 4 years, 2 months), with an average follow-up of 5.2 years (range 2-11). Fifteen patients underwent removal secondary to pain (2 of these with undetected infection) and 6 for known infection. Evaluation included coronal proximal thoracic, main thoracic, thoracolumbar/lumbar (TL/L), and sagittal T2-T5, T5-T12, T2-T12, T10-L2, T12-S1, and sagittal balance before surgery, before instrumentation removal, at immediate post-removal evaluation, and at latest follow-up.

RESULTS

There were 12 main thoracic curves (Lenke type 1), 6 double thoracic curves (Lenke type 2), and 3 double major curves (Lenke type 3) in the series. Average proximal thoracic curve was 19.7 degrees (range 5 degrees -35 degrees ), the main thoracic curve 63.3 (range 42 degrees -112 degrees ), and the TL-L curve averaged 31.4 degrees (range 17 degrees -53 degrees ). There was an immediate loss of approximately 4 degrees (range 0 degrees -8 degrees ) in the main thoracic curve and 6 degrees (range 1 degrees -15 degrees ) in the TL/L curve after removal, with continued settling of an additional 6 degrees (10 degrees total, P = 0.002) in the main thoracic curve, and 3 degrees in the TL/L curve (9 degrees total, P = 0.01). There was also a significant difference in the group that underwent instrumentation removal <2 years after surgery compared to >2 years (main thoracic curve 13 degrees vs. 7 degrees , P = 0.017; TL/L 11 degrees vs. 7 degrees , P = 0.036). There were no significant changes in sagittal curvature or sagittal balance in either group (P > 0.39).

CONCLUSIONS

Instrumentation removal in AIS is not always a benign process because the long-term follow-up of this cohort of patients shows a "settling" effect in the coronal plane of the main thoracic and TL/L curves after instrumentation removal. Interestingly, there was no change in the sagittal plane with time. Parents and patients should be counseled for this result when instrumentation removal is contemplated, and limited removal of focally symptomatic implants should be considered.

Comparing precision of distortion-compensated and stereophotogrammetric Roentgen analysis when monitoring fusion in the cervical spine

Two methods to measure sagittal plane segmental motion in the cervical spine are compared. Translational and rotational motion was measured in nine cervical motion segments of nine patients by distortion-compensated (DCRA) as well as by stereophotogrammetric Roentgen analysis (RSA). To compare measurement precision of the new DCRA protocol with the established RSA technique under realistic clinical conditions and to discuss advantages and disadvantages of both methods in clinical studies. RSA constitutes the most precise method available to assess segmental motion or to monitor fusion in the cervical spine. Due to the invasive nature of the procedure there is an interest in alternative, non-invasive protocols, based on conventional, lateral radiographic views. In nine patients, segmental motion of nine cervical segments with spinal surgery and fusion had previously been assessed from stereo views by RSA. From the archive radiographs, sagittal plane segmental motion was re-assessed by DCRA. Results for sagittal plane translational and rotational motion obtained by both methods are compared. With respect to RSA, sagittal plane rotation was determined by DCRA with an error of 2.4 degrees and a mean difference not significantly different from zero. Sagittal plane translation was determined by DCRA with an error of less than 0.78 mm and a mean difference not significantly different from zero. As two methods are compared, these errors represent the combined (propagated) errors of RSA and DCRA. Averaged over the cohort investigated, measurement of sagittal plane segmental motion exhibited no significant difference between DCRA and RSA.

Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 4: radiographic assessment of fusion

The assessment of fusion status with static plain radiography is accurate in approximately two thirds of patients treated with lumbar fusion when the radiographic results are compared with surgical exploration findings. Therefore, static plain radiography is not recommended as a stand-alone modality following lumbar fusion procedures. The addition of lateral flexion-extension radiography may improve accuracy because the lack of motion between fused lumbar segments on lateral views is highly suggestive of a solid fusion. Some degree of motion between segments may be present even when the spine has fused. The amount of motion allowable across fused segments is not clear, and the role of internal fixation in limiting motion has also not been adequately addressed. The addition of multiplanar CT scanning results in the detection of pseudarthrosis in some patients in whom fusion has been deemed successful based on plain radiographic criteria. Therefore, CT scanning may be more accurate in the determination of fusion status than plain radiography; however, a rigorous comparison of modern CT scanning and surgical exploration has not been performed. It appears that RSA is exquisitely sensitive for the detection of motion between vertebral bodies, and the loss of motion between treated vertebral segments does appear to indicate the presence of fusion. The modality, however, is invasive and not widely available. Furthermore, the only