A scoping review of human skeletal kinematics research using biplane radiography

Biplane radiography has emerged as the gold standard for accurately measuring in vivo skeletal kinematics during physiological loading. The purpose of this scoping review was to map the extent, range, and nature of biplane radiography research on humans from 2004 through 2022. A literature search was performed using the terms biplane radiography, dual fluoroscopy, dynamic stereo X-ray, and biplane videoradiography. All articles referenced in included publications were also assessed for inclusion. A secondary search was then performed using the names of the most frequently appearing principal investigators among included papers. A total of 379 manuscripts were identified and included. The first studies published in 2004 focused on the native knee, followed by studies of the ankle joint complex in 2006, the shoulder in 2007, and the spine in 2008. Nearly half (180, 47.5%) of all manuscripts investigated knee kinematics. The average number of publications increased from 21.6 per year from 2012 to 2017 to 34.6 per year from 2017 to 2022. The average number of participants per study was 16, with a range from 1 to 101. A total of 90.2% of studies featured cohorts of 30 or less. The most prolific research groups for each joint were: Mass General Hospital (lumbar spine and knee), Henry Ford Hospital (shoulder), the University of Utah (ankle and hip), The University of Pittsburgh (cervical spine), and Brown University (hand/wrist/elbow). Future advancements in biplane radiography research are dependent upon increased availability of these imaging systems, standardization of data collection protocols, and the development of automated approaches to expedite data processing.

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.

Mid-Term Migration Behavior of an Uncemented Proximally Anchored Straight Stem-A Retrospective EBRA Migration Analysis

BACKGROUND

Aseptic loosening is one of the most-common causes of the failure of cementless stems. Einzel Bild Röntgen Analyse-Femoral Component Analysis (EBRA-FCA) allows the diagnosis of stem migration, which can be considered a factor in predicting implant survival. The current study aimed to present the migration behavior of a tapered proximally anchored straight stem.

METHODS

This retrospective study reviewed all consecutive patients who received a cementless CBC straight stem (Mathys AG, Bettlach, Switzerland) between 2005 and 2019. We analyzed the migration pattern using the EBRA-FCA software and reviewed their medical histories. In addition, periprosthetic radiolucency was rated according to the Gruen zones and femoral configuration according to Dorr.

RESULTS

A total of 333 stems in 332 patients (female 191; male 141) met our inclusion criteria. The mean age at surgery was 63 (range 21-87) years. Migration analysis by EBRA-FCA showed a mean subsidence of 1.6 mm at final follow-up at 96 months with a maximum noted mean subsidence of 2.0 mm at 72 and 84 months. Dorr Type A showed a tendency of less subsidence than did Dorr Type B and was statistically significant at 6 (p = 0.0396) and 72 months (p = 0.0127). The body mass index (BMI) and increased subsidence were not found to correlate (p > 0.05). For this cohort, the overall femoral revision-free rate was 95.2% and the revision-free rate for aseptic loosening was 99.1%.

CONCLUSIONS

The results showed migration behavior in cementless stems with initial increased migration and subsequent secondary stabilization, suggesting an excellent long-term outcome. Stem migration of this tapered proximally anchored stem might be lower in Dorr Type A than in Dorr Type B femurs without being statistically significant at all time points.

A randomized controlled trial comparing two-year postoperative femoral and tibial migration of a new and an established cementless rotating platform total knee arthroplasty

AIMS

The primary aim of this study was to compare the migration of the femoral and tibial components of the cementless rotating platform Attune and Low Contact Stress (LCS) total knee arthroplasty (TKA) designs, two years postoperatively, using radiostereometric analysis (RSA) in order to assess the risk of the development of aseptic loosening. A secondary aim was to compare clinical and patient-reported outcome measures (PROMs) between the designs.

METHODS

A total of 61 TKAs were analyzed in this randomized clinical RSA trial. RSA examinations were performed one day and three, six, 12, and 24 months postoperatively. The maximal total point motion (MPTM), translations, and rotations of the components were analyzed. PROMs and clinical data were collected preoperatively and at six weeks and three, six, 12, and 24 months postoperatively. Linear mixed effect modelling was used for statistical analyses.

RESULTS

The mean MTPM two years postoperatively (95% confidence interval (CI)) of the Attune femoral component (0.92 mm (0.75 to 1.11)) differed significantly from that of the LCS TKA (1.72 mm (1.47 to 2.00), p < 0.001). The Attune femoral component subsided, tilted (anteroposteriorly), and rotated (internal-external) significantly less. The mean tibial MTPM two years postoperatively did not differ significantly, being 1.11 mm (0.94 to 1.30) and 1.17 mm (0.99 to 1.36, p = 0.447) for the Attune and LCS components, respectively. The rate of migration in the second postoperative year was negligible for the femoral and tibial components of both designs. The mean pain-at-rest (numerical rating scale (NRS)-rest) in the Attune group was significantly less compared with that in the LCS group during the entire follow-up period. At three months postoperatively, the Knee injury and Osteoarthritis Outcome Physical Function Shortform score, the Oxford Knee Score, and the NRS-activity scores were significantly better in the Attune group.

CONCLUSION

The mean MTPM of the femoral components of the cementless rotating platform Attune was significantly less compared with that of the LCS design. This was reflected mainly in significantly less subsidence, posterior tilting, and internal rotation. The mean tibial MTPMs were not significantly different. During the second postoperative year, the components of both designs stabilized and low risks for the development of aseptic loosening are expected.Cite this article: Bone Joint J 2023;105-B(2):148-157.

EBRA Migration Analysis of a Modular, Distally Fixed Stem in Hip Revision Arthroplasty: A Clinical and Radiological Study

Background: Massive osteolysis of the proximal femur makes stem revision a challenging procedure. EBRA-FCA provides the opportunity to determine stem migration, which is considered a predictive factor for implant survival. In this study, we aimed to analyze the migration behavior of a modular, distally fixed reconstruction prosthesis. Methods: Applying a retrospective study design, we reviewed all consecutive patients who received a cementless MP reconstruction prosthesis (Waldemar Link GmbH & Co. KG, Hamburg, Germany) at our Department between 2005 and 2019. We reviewed medical histories and performed radiological measurements using EBRA-FCA software. Results: A total of 67 stems in 62 patients (female 26; male 36) fulfilled our inclusion criteria. Mean age at surgery was 68.0 (range 38.7−88.44) years. EBRA migration analysis showed a median subsidence of 1.6 mm (range 0.0−20.6) at 24 months. The angle between stem and femur axis was 0.3° (range 0.0°−2.9°) at final follow-up. No correlation between body mass index and increased subsidence was found (p > 0.05). Overall revision-free rate amounted to 92.5% and revision-free rate for aseptic loosening to 98.5%. Furthermore, no case of material breakage was detected. Conclusions: In summary, the MP reconstruction prosthesis showed low subsidence and reduction in the migration rate over the investigated follow-up. Based on this, the modular stem can be considered as a good therapy option in challenging stem revisions offering various options to address the individual anatomical situation.

An efficient hybrid method for 3D to 2D medical image registration

Purpose

The purpose of this paper is to present a method for registration of 3D computed tomography to 2D single-plane fluoroscopy knee images to provide 3D motion information for knee joints. This 3D kinematic information has unique utility for examining joint kinematics in conditions such as ligament injury, osteoarthritis and after joint replacement.

Methods

We proposed a non-invasive rigid body image registration method which is based on two different multimodal similarity measures. This hybrid registration method helps to achieve a trade-off among different challenges including, time complexity and accuracy.

Results

We performed a number of experiments to evaluate the performance of the proposed method. The experimental results show that the proposed method is as accurate as one of the most recent registration methods while it is several times faster than that method.

Conclusion

The proposed method is a non-invasive, fast and accurate registration method, which can provide 3D information for knee joint kinematic measurements. This information can be very helpful in improving the accuracy of diagnosis and providing targeted treatment.

Surface wear in a custom manufactured temporomandibular joint prosthesis

The wear of a novel temporomandibular joint (TMJ) prosthesis was evaluated in an animal model. The prosthesis consisted of an additively manufactured titanium alloy (Ti₆Al₄V) mandibular condyle and glenoid fossa created through selective laser melting, with a machined vitamin E‐enriched ultra‐high molecular weight polyethylene (UHMWPE) surface attached to the fossa. Thirteen TMJ prosthesis were implanted in sheep, six of which had condylar heads coated with HadSat® diamond‐like carbon (H‐DLC). Euthanasia took place after 288 days, equaling 22 years of human mastication. Linear and volumetric wear analysis of the fossa was performed by optical scanning. The condylar head surfaces were assessed by scanning electron and confocal laser microscopy. The average linear UHMWPE wear, when combined with the coated condyle, was 0.67 ± 0.28 mm (range: 0.34–1.15 mm), not significantly differing (p = .3765, t‐test) from the non‐coated combination average (0.88 ± 0.41 mm; range: 0.28–1.48 mm). The respective mean volumetric wear volumes were 25.29 ± 11.43 mm³ and 45.85 ± 22.01 mm³, not significantly differing (p = .1448, t‐test). Analysis of the coated condylar surface produced a mean Ra of 0.12 ± 0.04 μm and Sa of 0.69 ± 0.07 μm. The non‐coated condylar surface measured a mean Ra of 0.28 ± 0.17 μm and Sa of 2.40 ± 2.08 μm. Both Sa (p = .0083, Mann–Whitney U test) and Ra (p = .0182, Mann–Whitney U test), differed significantly. The prosthesis exhibits acceptable wear resistance and addition of the H‐DLC‐coating significantly improved long‐term condylar surface smoothness.

Accuracy of virtual 3-dimensional cephalometric images constructed with 2-dimensional cephalograms using the biplanar radiography principle

Purpose

The purpose of this study was to evaluate the accuracy of virtual 3-dimensional (3D) cephalograms constructed using the principle of biplanar radiography by comparing them with cone-beam computed tomography(CBCT) images.

Materials and Methods

Thirty orthodontic patients were enrolled in this study. Frontal and lateral cephalograms were obtained with the use of a head posture aligner and reconstructed into 3D cephalograms using biplanar radiography software. Thirty-four measurements representing the height, width, depth, and oblique distance were computed in 3 dimensions, and compared with the measurements from the 3D images obtained by CBCT, using the paired t-test and Bland-Altman analysis.

Results

Comparison of height, width, depth, and oblique measurements showed no statistically significant differences between the measurements obtained from 3D cephalograms and those from CBCT images (P>0.05). Bland-Altman plots also showed high agreement between the 3D cephalograms and CBCT images.

Conclusion

Accurate 3D cephalograms can be constructed using the principle of biplanar radiography if frontal and lateral cephalograms can be obtained with a head posture aligner. Three-dimensional cephalograms generated using biplanar radiography can replace CBCT images taken for diagnostic purposes.

Upconversion Spectral Rulers for Transcutaneous Displacement Measurements

We describe a method to measure micron to millimeter displacement through tissue using an upconversion spectral ruler. Measuring stiffness (displacement under load) in muscles, bones, ligaments, and tendons is important for studying and monitoring healing of injuries. Optical displacement measurements are useful because they are sensitive and noninvasive. Optical measurements through tissue must use spectral rather than imaging approaches because optical scattering in the tissue blurs the image with a point spread function typically around the depth of the tissue. Additionally, the optical measurement should have low background and minimal intensity dependence. Previously, we demonstrated a spectral encoder using either X-ray luminescence or fluorescence, but the X-ray luminescence required an expensive X-ray source and used ionizing radiation, while the fluorescence sensor suffered from interference from autofluorescence. Here, we used upconversion, which can be provided with a simple fiber-coupled spectrometer with essentially autofluorescence-free signals. The upconversion phosphors provide a low background signal, and the use of closely spaced spectral peaks minimizes spectral distortion from the tissue. The small displacement noise level (precision) through tissue was 2 µm when using a microscope-coupled spectrometer to collect light. We also showed proof of principle for measuring strain on a tendon mimic. The approach provides a simple method to study biomechanics using implantable sensors.

Outcome and EBRA migration analysis of a reconstruction cage in acetabular revision arthroplasty: a clinical and radiological study

PURPOSE

Restoration cages and bone allografts have been proposed to manage severe acetabular bone defects. We aimed to investigate the migration behaviour of a restoration cup and impacted allograft bone in severe acetabular defects with Einzel-Bild-Röntgen-Analyse (EBRA).

METHODS

Applying a retrospective study design, 64 cases treated between 2009 and 2016 were reviewed. We determined the preoperative Charlson Comorbidity Index (CCI), pre- to postoperative WOMAC score, blood loss and functional outcome. From preoperative x rays, the acetabular deficiencies were classified according to Paprosky. Cup migration analyses were performed with EBRA.

RESULTS

Mean age at surgery was 73 (range: 38-93) years. According to the classification by Paprosky et al., 50% (n = 32) of our patients showed a type III B and 28.1% (n = 18) a type III A defect. Radiological follow-up for migration analysis was 35 (range: 4-95) months. Migration analysis showed a mean cup migration of 0.7 mm (range: 5.7-9.6) medial and 1.8 mm (range: 1.7-12.6) cranial.

CONCLUSION

In conclusion, acetabular restoration cages in combination with bone impaction grafting showed a low revision rate at a mean follow-up of 35 months. Mean cup migration revealed low rates after 2 years and suggested a stable postoperative implant position.

Fast and automatic periacetabular osteotomy fragment pose estimation using intraoperatively implanted fiducials and single-view fluoroscopy

Accurate and consistent mental interpretation of fluoroscopy to determine the position and orientation of acetabular bone fragments in 3D space is difficult. We propose a computer assisted approach that uses a single fluoroscopic view and quickly reports the pose of an acetabular fragment without any user input or initialization. Intraoperatively, but prior to any osteotomies, two constellations of metallic ball-bearings (BBs) are injected into the wing of a patient's ilium and lateral superior pubic ramus. One constellation is located on the expected acetabular fragment, and the other is located on the remaining, larger, pelvis fragment. The 3D locations of each BB are reconstructed using three fluoroscopic views and 2D/3D registrations to a preoperative CT scan of the pelvis. The relative pose of the fragment is established by estimating the movement of the two BB constellations using a single fluoroscopic view taken after osteotomy and fragment relocation. BB detection and inter-view correspondences are automatically computed throughout the processing pipeline. The proposed method was evaluated on a multitude of fluoroscopic images collected from six cadaveric surgeries performed bilaterally on three specimens. Mean fragment rotation error was 2.4 ± 1.0 degrees, mean translation error was 2.1 ± 0.6 mm, and mean 3D lateral center edge angle error was 1.0 ± 0.5 degrees. The average runtime of the single-view pose estimation was 0.7 ± 0.2 s. The proposed method demonstrates accuracy similar to other state of the art systems which require optical tracking systems or multiple-view 2D/3D registrations with manual input. The errors reported on fragment poses and lateral center edge angles are within the margins required for accurate intraoperative evaluation of femoral head coverage.

Minimum ten-year follow-up of a randomized trial comparing acetabular component fixation of two porous in-growth surfaces using radiosteriometric analysis

Aims

To compare the in vivo long-term fixation achieved by two acetabular components with different porous ingrowth surfaces using radiostereometric analysis (RSA).

Methods

This was a minimum ten-year follow-up of a prospective randomized trial of 62 hips with two different porous ingrowth acetabular components. RSA exams had previously been acquired through two years of follow-up. Patients returned for RSA examination at a minimum of ten years. In addition, radiological appearance of these acetabular components was analyzed, and patient-reported outcome measures (PROMs) obtained.

Results

In all, 15 hips were available at ten years. There was no statistically significant difference in PROMS between the two groups; PROMs were improved at ten years compared to preoperative scores. Conventional radiological assessment revealed well-fixed components. There was minimal movement for both porous surfaces in translation (X, Y, Z, 3D translation in mm (median and interquartile range (IQR)), StikTite (Smith and Nephew, Memphis, Tennessee, USA): 0.03 (1.08), 0.12 (0.7), 0.003 (2.3), 0.37 (0.30), and Roughcoat (Smith and Nephew): -0.6 (0.59),–0.1 (0.49), 0.1 (1.12), 0.48 (0.38)), and rotation (X, Y, Z rotation in degrees (median and IQR), (Stiktite: -0.4 (3), 0.28 (2), -0.2 (1), and Roughcoat: - 0.4 (1),–0.1 (1), 0.2 (2)). There was no statistically significant difference between the two cohorts (p-value for X, Y, Z, 3D translation - 0.54, 0.46, 0.87, 0.55 and for X, Y, Z rotation - 0.41, 0.23, 0.23 respectively) at ten years. There was significant correlation between two years and ten years 3D translation for all components (r = 0.81(p =< 0.001)).

Conclusion

Both porous ingrowth surfaces demonstrated excellent fixation on plain radiographs and with RSA at ten years. Short-term RSA data are good predictors for long-term migration data.

J-curve design total knee arthroplasty: the posterior stabilized shows wider medial pivot compared to the cruciate retaining during chair raising

PURPOSE

Which total knee arthroplasty (TKA) design represents the better solution to restore a correct knee biomechanics is still debated. The aim of this study was to compare posterior stabilized (PS) and cruciate retaining (CR) version of the same TKA design (femoral component with an anatomic sagittal radius-J-curve design) by the use of dynamic Roentgen stereophotogrammetric analysis (RSA). The hypothesis was that the two models influence differently in vivo knee kinematic.

METHODS

A cohort of 16 randomly selected patients was evaluated 9 months after surgery: Zimmer PERSONA® was implanted, eight with CR design and eight with PS design. The kinematic evaluations were performed using a Dynamic RSA (BI-STAND DRX 2) developed in our Institute, during the execution of the sit-to-stand motor task. The motion parameters were obtained using the Grood and Suntay decomposition and the low-point kinematics methods.

RESULTS

PS TKA lateral femoral compartment had a wider anterior translation (17 ± 2 mm) than the medial one (11 ± 2 mm), while the two compartments of CR TKA showed a similar anterior translation (medial: 9 ± 2 mm/lateral: 11 ± 2 mm). T test for comparison between CR and PS TKA of antero-posterior translation showed a statistically significant difference (p < 0.05) in the flexion range between 15° and 40°. The CR prosthesis did not anteriorly translate during flexion. The PS design translated anteriorly showing a roll-forward mechanism during extension from 80° to 18° of flexion and a posterior translation from 18° to 0°. The same significant differences (p < 0.05) between the PS and CR groups were found comparing the low-point positions of the femoral condyles in the range of flexion between 25° and 40° for the medial compartment and between 15° and 25° for the lateral compartment.

CONCLUSIONS

Dynamic RSA was able to investigate for the first time in vivo the kinematic behaviour of PS and CR version of the same TKA J-curve design. PS type showed a medial pivot during sit-to-stand motion task, while the CR type showed a cylindrical movement. Further studies are needed to evaluate the impact of different TKA designs on clinical results.

LEVEL OF EVIDENCE

IV.

Wear measurements with use of radiostereometric analysis in total hip arthroplasty with obscured femoral head

Radiostereometric analysis (RSA) has evolved as gold standard in the evaluation of wear and especially as regards novel hip implant materials. However, several cup shell materials and articulation types used in total hip arthroplasty (THA) cannot be studied due to poor radiographic visibility of the femoral head (FH). We addressed this problem with use of a point transfer function in the RSA software to indirectly measure FH translations with use of stem markers. In a base examination, the stem marker segment and cup center, as an approximation for the FH center position, were mathematically coupled. Thereafter, in subsequent examinations, we used the point transfer function to calculate FH positions from stem marker positions. To determine the variance of the difference of directly and indirectly measured FH positions, four stem marker configurations were studied in THAs with radiographically visible FHs. For the axis with least variance we also compared directly and indirectly measured translation up to 7 years. Finally, we applied the method in a ceramic-on-ceramic (COC) articulation and measured proximal translation up to 7 years and also estimated precision. Vertical translations had the smallest variation between measured and calculated FH position. Directly and indirectly measured vertical FH translation correlated well but indirect measurements had increased variance. Proximal steady-state penetration rate in uncemented COC THA was -0.003 (SD 0.021) mm/year with 99% precision along the vertical axis measuring 0.34 mm. The point transfer function can be used to measure proximal FH penetration, but with less precision than direct RSA.

Validation and application of dynamic biplane radiography to study in vivo ankle joint kinematics during high-demand activities

Ankle ligament injuries are the most common musculoskeletal injury in physically active populations. Failure to restore native kinematics post-injury often leads to long-term consequences including chronic instability and arthritis. Using traditional motion capture, it is difficult to distinguish independent motions of the tibiotalar and subtalar joints to assess the effects of injury, surgical repair, and rehabilitation on ankle joint complex (AJC) kinematics. Therefore, the aims of this study were to determine the accuracy of dynamic biplane radiography for determining in vivo AJC kinematics and arthrokinematics, and to identify sport-related movements that require the largest AJC range of motion (ROM) during support. Two subjects had three to five 1.0 mm diameter tantalum beads implanted into the tibia, fibula, talus, and calcaneus during lateral ankle ligament repair. Six months after surgery, the subjects executed seven movements while biplane radiographs were collected. Bone motion was tracked using radiostereophotogrammetric analysis (RSA) as a "gold standard", and compared to a volumetric CT model-based tracking algorithm that matched digitally reconstructed radiographs to the original biplane radiographs. Over all movements, the average tibiotalar, subtalar and tibiofibular RMS errors were 0.5 mm ± 0.2 mm, 0.8 mm ± 0.5 mm and 0.8 mm ± 0.3 mm in translation and 1.4° ± 0.4°, 1.5° ± 0.5° and 1.7° ± 0.6° in rotation, respectively. Tibiotalar joint space was determined with an average precision of 0.5 mm. ROM results indicate that jumping and a forward-to-backward push-off movement are the best of the seven sport-related movements evaluated for eliciting full ROM kinematics.

Similar patient positioning: A key factor in follow-up studies when using model-based radiostereometric analysis of the hip

INTRODUCTION

Despite protocols, patients are not positioned exactly alike at radiostereometric (RSA) follow-up examinations, and it is unknown how much variation is tolerable. We report precision for optimal and extreme position differences from a phantom hip-study, and clinical precision of hip-RSA.

METHODS

A femoral stem with 3 bead-towers was fixed in a saw bone with bone-markers (phantom), and series of RSA examinations within optimal (5 × 5 cm and 5°) and extreme (20 × 30 cm and 30°) phantom positions were obtained. Double-examination RSA of 12 patients with the same femoral stem type were analyzed. Both model-based (CAD) and marker-based (MM) analysis was used. Precision was reported as standard deviation of differences.

RESULTS

Precision for translations in the optimal and extreme phantom position were below 0.06 mm and 0.02 mm for MM analysis, and below 0.05 mm and 0.18 mm for CAD analysis, respectively. Precision for rotations in the optimal and extreme phantom rotation were below 0.18° and 0.26° for MM analysis, and below 0.34° and 0.52° for CAD analysis, respectively. Clinical precision was 0.29 mm and 0.44° for MM analysis, and 0.40 mm and 1.59° for CAD analysis.

CONCLUSION

Extreme differences in patient position during RSA examination negatively affects precision, and CAD model-analysis was more sensitive than MM analysis. Longitudinal translation and rotation about the long stem-axis are the effect parameters which are most affected by position and rotation changes, and also the best indicators of implant loosening.

IMPLICATIONS FOR PRACTICE

Based on our research, we recommend that similar patient positioning between follow-up RSA examinations is debated and prioritized.

New design total knee arthroplasty shows medial pivoting movement under weight-bearing conditions

PURPOSE

To assess, using model-based dynamic radiostereometric analysis (RSA), the biomechanical behaviour of a new design posterior-stabilized (PS) fixed-bearing (FB) total knee arthroplasty (TKA) in vivo while patients performing two common motor tasks. The hypothesis was that model-based dynamic RSA is able to detect different behaviour of the implant under weight-bearing and non-weight-bearing conditions.

METHODS

A cohort of 15 non-consecutive patients was evaluated by dynamic RSA 9 months after TKA implantation. The mean age of patients was 73.4 (65-72) years. The kinematic evaluations were performed using an RSA device (BI-STAND DRX 2) developed in our Institute. The patients were asked to perform two active motor tasks: sit-to-stand in weight-bearing condition; range of motion (ROM) while sitting on the chair. The motion parameters were evaluated using the Grood and Suntay decomposition and the low-point kinematics methods.

RESULTS

The dynamic RSA evaluation showed a significant difference (p < 0.05) between the biomechanical behaviour of the prosthesis during the two motor tasks. When subjected to the patient weight (in the sit-to-stand) the low point of the medial compartment had a shorter motion (5.7 ± 0.2 mm) than the lateral (11.0 ± 0.2 mm). This realizes a medial pivot motion as in the normal knee. In the ROM task, where the patient had no weight on the prosthesis, this difference was not present: the medial compartment had a displacement of 12.7 ± 0.2 mm, while the lateral had 17.3 ± 0.2 mm.

CONCLUSIONS

Model-based RSA proved to be an effective tool for the evaluation of TKA biomechanics. In particular, it was able to determine that the fixed-bearing posterior-stabilized TKA design evaluated in this study showed a medial pivoting movement under weight-bearing conditions that was not present when load was not applied. Under loading conditions what drives the pattern of movement is the prosthetic design itself. By the systematic use of this study protocol future comparisons among different implants could be performed, thus contributing significantly to the improvement of TKA design.

LEVEL OF EVIDENCE

IV.

Accuracy of three-dimensional cephalograms generated using a biplanar imaging system

Objective

Biplanar imaging systems allow for simultaneous acquisition of lateral and frontal cephalograms. The purpose of this study was to compare measurements recorded on three-dimensional (3D) cephalograms constructed from two-dimensional conventional radiographs and biplanar radiographs generated using a new biplanar imaging system with those recorded on cone-beam computed tomography (CBCT)-generated cephalograms in order to evaluate the accuracy of the 3D cephalograms generated using the biplanar imaging system.

Methods

Three sets of lateral and frontal radiographs of 15 human dry skulls with prominent facial asymmetry were obtained using conventional radiography, the biplanar imaging system, and CBCT. To minimize errors in the construction of 3D cephalograms, fiducial markers were attached to anatomical landmarks prior to the acquisition of radiographs. Using the 3D Ceph™ program, 3D cephalograms were constructed from the images obtained using the biplanar imaging system (3D ceph_biplanar), conventional radiography (3D ceph_conv), and CBCT (3D ceph_cbct). A total of 34 measurements were obtained compared among the three image sets using paired t-tests and Bland-Altman plotting.

Results

There were no statistically significant differences between the 3D ceph_biplanar and 3D ceph_cbct measurements. In addition, with the exception of one measurement, there were no significant differences between the 3D ceph_cbct and 3D ceph_conv measurements. However, the values obtained from 3D ceph_conv showed larger deviations than those obtained from 3D ceph_biplanar.

Conclusions

The results of this study suggest that the new biplanar imaging system enables the construction of accurate 3D cephalograms and could be a useful alternative to conventional radiography.

Correct Assessment of Acetabular Component Orientation in Total Hip Arthroplasty From Plane Radiographs

BACKGROUND

Correct positioning of the cup is an important factor in total hip arthroplasty. Assessing its position from a plain anteroposterior pelvic radiograph is known to be hampered by systemic errors. This study focuses on developing a correction method to adjust for these potential sources of error and to eliminate them based on a 3D geometric analysis.

METHODS

Computed tomography scans of 113 (66 male, 47 female) pelvices were reconstructed and virtually projected onto a plain radiograph with varying rotational and translational positions. Thus cup inclination and anteversion as measured on a 2D-radiograph and in the 3D environment were correlated. Projected offset of the symphysis from the mid-sacrum served as a mean to measure pelvic right/left-rotation. Pelvic tilt was determined from the projected height of the contour of the small pelvis. Correction formulas were verified by projecting a gimbal-mounted artificial pelvis with a cup implanted in a known position.

RESULTS

We found gender-specific formulas that correct for malrotated and off-centered radiographs. Applying these formulas cup inclination was assessed as close as 1.3° (±1.90°) to the true 3D value and cup anteversion as close as 1° (±1.91°) although deviations between directly measured plain values and corrected values rose up to 18°.

CONCLUSION

Inherent effects of central projection and malrotations due to pelvic tilt, pelvic rotation, and noncentered radiographs are corrected. Evaluation of radiographic inclination and anteversion of acetabular cups from plain 2D-radiographs show improved precision. Real values are approached better than 1.3° when applying our correction formulas.

Radiostereometric analysis using clinical radiographic views: Validation with model-based radiostereometric analysis for the knee

Radiostereometric analysis is a sophisticated radiographic technique with high measurement accuracy. In order to improve the accessibility of radiostereometric analysis for clinical use, a modified radiostereometric analysis procedure has been previously proposed that enables clinical radiographic views to be used for radiostereometric analysis. It has been successfully validated for its application to the hip wear study with the conventional bead-based radiostereometric analysis environment using computed radiography. In this study, we describe the implementation and validation of this technique for the knee study with the model-based radiostereometric analysis environment using digital radiography. A knee-joint phantom with 6 degrees of freedom was examined, and the bias and repeatability/reproducibility of the modified radiostereometric analysis approach were investigated following the newly updated ASTM recommendations. The bias parameters (mean ± 95% confidence interval) ranged from 0.008 ± 0.003 mm to 0.027 ± 0.006 mm for translation and from 0.014° ± 0.007° to 0.040° ± 0.020° for rotation. The repeatability standard deviation ranged from 0.004 to 0.020 mm for translation and from 0.005° to 0.015° for rotation. The 95% repeatability limit ranged from 0.011 to 0.055 mm for translation and from 0.014° to 0.041° for rotation. The reproducibility standard deviation ranged from 0.004 to 0.023 mm for translation and from 0.006° to 0.040° for rotation. The 95% reproducibility limit ranged from 0.012 to 0.063 mm for translation and from 0.016° to 0.112° for rotation. The modified procedure allows routine clinical radiographs to be used for radiostereometric analysis, which provides the possibility of adding quantitative measurements to current patient registries.

In vivo validation of patellofemoral kinematics during overground gait and stair ascent

BACKGROUND

The patellofemoral (PF) joint is a common site for non-specific anterior knee pain. The pathophysiology of patellofemoral pain may be related to abnormal motion of the patella relative to the femur, leading to increased stress at the patellofemoral joint. Patellofemoral motion cannot be accurately measured using conventional motion capture.

RESEARCH QUESTION

The aim of this study was to determine the accuracy of a biplane radiography system for measuring in vivo PF motion during walking and stair ascent.

METHODS

Four subjects had three 1.0 mm diameter tantalum beads implanted into the patella. Participants performed three trials each of over ground walking and stair ascent while biplane radiographs were collected at 100 Hz. Patella motion was tracked using radiostereophotogrammetric analysis (RSA) as a "gold standard", and compared to a volumetric CT model-based tracking algorithm that matched digitally reconstructed radiographs to the original biplane radiographs.

RESULTS

The average RMS difference between the RSA and model-based tracking was 0.41 mm and 1.97° when there was no obstruction from the contralateral leg. These differences increased by 34% and 40%, respectively, when the patella was at least partially obstructed by the contralateral leg. The average RMS difference in patellofemoral joint space between tracking methods was 0.9 mm or less.

SIGNIFICANCE

Previous validations of biplane radiographic systems have estimated tracking accuracy by moving cadaveric knees through simulated motions. These validations were unable to replicate in vivo kinematics, including patella motion due to muscle activation, and failed to assess the imaging and tracking challenges related to contralateral limb obstruction. By replicating the muscle contraction, movement velocity, joint range of motion, and obstruction of the patella by the contralateral limb, the present study provides a realistic estimate of patellofemoral tracking accuracy for future in vivo studies.

Radiostereometric analysis using clinical radiographic views: Development of a universal calibration object

Radiostereometric analysis (RSA) is a highly accurate technique used to provide three-dimensional (3D) measurements of orthopaedic implant migration for clinical research applications, yet its implementation in routine clinical examinations has been limited. Previous studies have introduced a modified RSA procedure that separates the calibration examinations from the patient examinations, allowing routine clinical radiographs to be analyzed using RSA. However, in order to calibrate the wide range of clinical views, a new calibration object is required. In this study, a universal, isotropic calibration object was designed to calibrate any pair of radiographic views used in the clinic for RSA. A numerical simulation technique was used to design the calibration object, followed by a phantom validation test of a prototype to verify the performance of the novel object, and to compare the measurement reliability to the conventional calibration cage. The 3D bias for the modified calibration method using the new calibration object was 0.032 ± 0.006 mm, the 3D repeatability standard deviation was 0.015 mm, and the 3D repeatability limit was 0.042 mm. Although statistical differences were present between the universal calibration object and the conventional cage, the differences were considered to be not clinically meaningful. The 3D bias and repeatability values obtained using the universal calibration object were well under the threshold acceptable for RSA, therefore it was successfully validated. The universal calibration object will help further the adoption of RSA into a more routine practice, providing the opportunity to generate quantitative databases on joint replacement performance.

Maxillary and Mandibular Displacement in Hemifacial Microsomia: A Longitudinal Roentgen Stereometric Study of 21 Patients with the Aid of Metallic Implants

Objective

To record maxillary and mandibular displacement with articular growth and in response to bimaxillary surgical repositioning in patients with hemifacial microsomia (HFM) and to observe ipsilateral corpus/ramus growth in severely affected children.

Design

Prospective roentgen stereometric analysis (mean age 7 years 10 months to 18 years 0 months) and retrospective profile and panoramic roentgenograms. Mean total observation period was 9 years 1 month.

Setting

Department of Plastic and Reconstructive Surgery, Malmö University Hospital (Malmö, Sweden).

Patients

Twenty-one patients consecutively diagnosed from 1976 through 1988 with HMF, five of whom had bimaxillary surgery.

Interventions

Surgery was performed at the Department of Plastic and Reconstructive Surgery. Implants were inserted at the initial reconstructive surgical procedure under general anesthesia. Roentgen examinations were performed in connection with continued clinical evaluations and treatment.

Main Outcome Measures

Stereo roentgenograms were digitized at the Department of Orthopedic Surgery, Malmö University Hospital (Malmö, Sweden).

Results

Displacement of the jaws with articular growth and in response to bimaxillary surgical repositioning varied interindividually with no apparent common pattern. Relapse displacement occurred several years after bimaxillary surgery. Mandibular growth changes were found in the corpus/ramus area and alveolar process on the affected side.

Conclusions

A marked interindividual variability of maxillary and mandibular displacement indicates that the relevance of statistical analysis of HFM growth data may be questioned. We would suggest that precise and accurate longitudinal recordings of growth and response to surgery in individual HFM patients be more appropriate.

Quantification of intervertebral displacement with a novel MRI-based modeling technique: Assessing measurement bias and reliability with a porcine spine model

The purpose of this study was to develop a novel magnetic resonance imaging (MRI)-based modeling technique for measuring intervertebral displacements. Here, we present the measurement bias and reliability of the developmental work using a porcine spine model. Porcine lumbar vertebral segments were fitted in a custom-built apparatus placed within an externally calibrated imaging volume of an open-MRI scanner. The apparatus allowed movement of the vertebrae through pre-assigned magnitudes of sagittal and coronal translation and rotation. The induced displacements were imaged with static (T₁) and fast dynamic (2D HYCE S) pulse sequences. These images were imported into animation software, in which these images formed a background 'scene'. Three-dimensional models of vertebrae were created using static axial scans from the specimen and then transferred into the animation environment. In the animation environment, the user manually moved the models (rotoscoping) to perform model-to-'scene' matching to fit the models to their image silhouettes and assigned anatomical joint axes to the motion-segments. The animation protocol quantified the experimental translation and rotation displacements between the vertebral models. Accuracy of the technique was calculated as 'bias' using a linear mixed effects model, average percentage error and root mean square errors. Between-session reliability was examined by computing intra-class correlation coefficients (ICC) and the coefficient of variations (CV). For translation trials, a constant bias (β₀) of 0.35 (±0.11) mm was detected for the 2D HYCE S sequence (p=0.01). The model did not demonstrate significant additional bias with each mm increase in experimental translation (β₁Displacement=0.01mm; p=0.69). Using the T₁ sequence for the same assessments did not significantly change the bias (p>0.05). ICC values for the T₁ and 2D HYCE S pulse sequences were 0.98 and 0.97, respectively. For rotation trials, a constant bias (β₀) of 0.62 (±0.12)° was detected for the 2D HYCE S sequence (p<0.01). The model also demonstrated an additional bias (β₁Displacement) of 0.05° with each degree increase in the experimental rotation (p<0.01). Using T₁ sequence for the same assessments did not significantly change the bias (p>0.05). ICC values for the T₁ and 2D HYCE S pulse sequences were recorded 0.97 and 0.91, respectively. This novel quasi-static approach to quantifying intervertebral relationship demonstrates a reasonable degree of accuracy and reliability using the model-to-image matching technique with both static and dynamic sequences in a porcine model. Future work is required to explore multi-planar assessment of real-time spine motion and to examine the reliability of our approach in humans.

Investigation of imaging magnification in radiostereometric analysis

Radiostereometric analysis is a highly accurate imaging technique. A recent advance in radiostereometric analysis is the use of flat panel digital radiography, which provides the opportunity for quick analysis using radiostereometric analysis. However, such a setup is expensive. Using large cassettes for small joints could minimize the cost. In this article, we investigated the influence of cassette size for small joint examinations with a biplanar radiostereometric analysis setup. Our results indicated that there is no significant difference in the precision when using large cassettes over small cassettes, whether or not imaging magnification is applied.

Radiostereometric analysis using clinical radiographic views: Validation measuring total hip replacement wear

Radiostereometric analysis (RSA) is a stereo X-ray technique used in clinical research studies to evaluate micro-motion and wear of orthopaedic implants within bone. While highly accurate and precise, its adoption has been limited due to technical requirements such as the need for implanted marker beads and radiograph view angles determined by a calibration cage. We propose a new technique that separates the calibration procedure from the patient examination, enabling clinical radiograph views to be used for RSA measurements. The concept of a reference plate was adapted to establish the link between calibration procedure and patient examination procedure for cassette radiography, which may not be necessary for digital radiography. A hip wear phantom was used to validate this technique by comparing the error and repeatability of the novel procedure with that of conventional RSA. Femoral head penetration was measured versus the acetabular cup (head/cup) and marker beads in the acetabular liner (head/liner). Conventional RSA had lower inferior-superior average error (p = 0.03 for head/cup) while the modified RSA had lower anterior-posterior average error (p = 0.01). Average error was greater but not significantly so for the medial-lateral (p = 0.06) and 3D (p = 0.97) measurements. The head/liner method had lower average errors (p < 0.0001) for both procedures, but did not affect repeatability, which was similar between techniques. The novel procedure's average error and repeatability was therefore, similar to conventional RSA. This new technique could be applied to any joint with two clinical radiograph view angles pending further validation in subjects. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1521-1528, 2016.

Cementless total knee arthroplasty

As the number of younger and more active patients treated with total knee arthroplasty (TKA) continues to increase, consideration of better fixation as a means of improving implant longevity is required. Cemented TKA remains the reference standard with the largest body of evidence and the longest follow-up to support its use. However, cementless TKA, may offer the opportunity of a more bone-sparing procedure with long lasting biological fixation to the bone. We undertook a review of the literature examining advances of cementless TKA and the reported results.

Cite this article: Bone Joint J 2016;98-B:867–73.

Development of a morphology-based modeling technique for tracking solid-body displacements: examining the reliability of a potential MRI-only approach for joint kinematics assessment

Background

Single or biplanar video radiography and Roentgen stereophotogrammetry (RSA) techniques used for the assessment of in-vivo joint kinematics involves application of ionizing radiation, which is a limitation for clinical research involving human subjects. To overcome this limitation, our long-term goal is to develop a magnetic resonance imaging (MRI)-only, three dimensional (3-D) modeling technique that permits dynamic imaging of joint motion in humans. Here, we present our initial findings, as well as reliability data, for an MRI-only protocol and modeling technique.

Methods

We developed a morphology-based motion-analysis technique that uses MRI of custom-built solid-body objects to animate and quantify experimental displacements between them. The technique involved four major steps. First, the imaging volume was calibrated using a custom-built grid. Second, 3-D models were segmented from axial scans of two custom-built solid-body cubes. Third, these cubes were positioned at pre-determined relative displacements (translation and rotation) in the magnetic resonance coil and scanned with a T₁ and a fast contrast-enhanced pulse sequences. The digital imaging and communications in medicine (DICOM) images were then processed for animation. The fourth step involved importing these processed images into an animation software, where they were displayed as background scenes. In the same step, 3-D models of the cubes were imported into the animation software, where the user manipulated the models to match their outlines in the scene (rotoscoping) and registered the models into an anatomical joint system. Measurements of displacements obtained from two different rotoscoping sessions were tested for reliability using coefficient of variations (CV), intraclass correlation coefficients (ICC), Bland-Altman plots, and Limits of Agreement analyses.

Results

Between-session reliability was high for both the T₁ and the contrast-enhanced sequences. Specifically, the average CVs for translation were 4.31 % and 5.26 % for the two pulse sequences, respectively, while the ICCs were 0.99 for both. For rotation measures, the CVs were 3.19 % and 2.44 % for the two pulse sequences with the ICCs being 0.98 and 0.97, respectively. A novel biplanar imaging approach also yielded high reliability with mean CVs of 2.66 % and 3.39 % for translation in the x- and z-planes, respectively, and ICCs of 0.97 in both planes.

Conclusions

This work provides basic proof-of-concept for a reliable marker-less non-ionizing-radiation-based quasi-dynamic motion quantification technique that can potentially be developed into a tool for real-time joint kinematics analysis.

Assessment of accuracy and precision of 3D reconstruction of unicompartmental knee arthroplasty in upright position using biplanar radiography

This study aimed to evaluate the precision and accuracy of 3D reconstruction of UKA component position, contact location and lower limb alignment in standing position using biplanar radiograph. Two human specimens with 4 medial UKAs were implanted with beads for radiostereometric analysis (RSA). The specimens were frozen in standing position and CT-scanned to obtain relative positions between the beads, bones and UKA components. The specimens were then imaged using biplanar radiograph (EOS). The positions of the femur, tibia, UKA components and UKA contact locations were obtained using RSA- and EOS-based techniques. Intraclass correlation coefficient (ICC) was calculated for inter-observer reliability of the EOS technique. The average (standard deviation) of the differences between two techniques in translations and rotations were less than 0.18 (0.29) mm and 0.39° (0.66°) for UKA components. The root-mean-square-errors (RMSE) of contact location along the anterior/posterior and medial/lateral directions were 0.84mm and 0.30mm. The RMSEs of the knee rotations were less than 1.70°. The ICCs for the EOS-based segmental orientations between two raters were larger than 0.98. The results suggest the EOS-based 3D reconstruction technique can precisely determine component position, contact location and lower limb alignment for UKA patients in weight-bearing standing position.

Stem Migration and Fretting Corrosion of the Antirotation Pin in the K2/Apex Hip System

BACKGROUND

Many exchangeable neck hip systems have been withdrawn because of fretting corrosion at the neck/stem coupling.

METHOD

Our prospective randomized study evaluating stem stability (Roentgen stereophotogrammetric analysis, dual-energy x-ray absorptiometry) and clinical outcomes between the K2/Apex hip systems was ceased early because of a withdrawal of the stems which had an unfavorably high early revision rate reported in the Australian Orthopaedic Association National Joint Registry (9.3% at 3 years).

RESULTS

At 2 years, there are no clinical differences between the stems. Roentgen stereophotogrammetric analysis has identified a high proportion of potentially concerning subsidence and retroversion in both groups, more marked in the K2 stem, although mostly in asymptomatic patients. Dual-energy x-ray absorptiometry has shown similar bone density around the stems. Retrieval analysis of 3 study patients showed fretting corrosion of the antirotation pin and aseptic lymphocyte-dominated vasculitis-associated lesion, with no relationship to bearing type or size. Analysis of 7 further nonstudy K2/Apex stems confirmed similar corrosion.

CONCLUSION

This study shows potentially concerning subsidence of both stems and is the first to describe corrosion at the neck-stem interface and a relationship to metal-related pathology.

Radiostereometric migration analysis of the Lubinus SP II hip stem: 59 hips followed for 2 years

The aim of this prospective study was to analyze the migration pattern of the Lubinus SP II hip stem and to evaluate the clinical results. Fifty-nine patients were followed for 2 years. Translational and rotational micromotion of the implant was measured by radiostereometric analysis (RSA) and the Harris hip score (HHS), and the Charnley classification was used to assess the clinical outcome. Although there was a very small, but statistically significant, distal migration of 0.04±0.83 mm, the prosthesis was found stable at 2 years of follow-up. The main migration in this direction took place between 6 months and 1 year. Maximum total point motion (MTPM) showed a mean of 0.99±0.69 mm. Good clinical outcome with HHS results of 42±11 before and 79±16 at 2 years after surgery was observed. The Charnley classification showed increasing additional impairments in the 2-year interval, which is likely to influence the HHS results of future follow-ups. The migration values measured in the present study are far below the thresholds considered clinically relevant in literature. Thus, the conclusion can be drawn that the implant is not at risk for early aseptic loosening. Long-term RSA is required to assess possible late migration.

Early controlled tension improves the material properties of healing human achilles tendons after ruptures: a randomized trial

BACKGROUND

Weightbearing in a fixed brace after acute Achilles tendon ruptures does not necessarily lead to mechanical tension in the tendon. Early motion has a positive effect on the clinical outcome, but it is not clear if this is because of effects on tendon strength or unspecific effects. The aim of this study was to examine if tensional loading leads to an improvement in the mechanical properties of the healing Achilles tendon.

HYPOTHESIS

The elastic modulus of the tendon callus is increased by early tensional loading.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

Thirty-five patients with an acute Achilles tendon rupture were recruited consecutively. They underwent surgery with a single suture and received metal markers in the distal and proximal parts of the tendon. After surgery, the patients were randomized to either cast immobilization for 7 weeks or tensional loading. The latter group wore a cast for 2 weeks and then a removable foam walker boot for 5 weeks. They were instructed to remove the boot twice daily and push a special training pedal to produce a predetermined, gradually increasing tensional load on the healing tendon. At 7, 19, and 52 weeks postoperatively, the patients were investigated with roentgen stereophotogrammetric analysis under different loading conditions and computed tomography. The collected data allowed calculation of the modulus of elasticity. At 52 weeks, the clinical outcome was also examined using the Achilles tendon Total Rupture Score (ATRS) and the heel-raise index.

RESULTS

The elastic modulus at 19 and 52 weeks was higher in the tensional loading group. There was no significant difference in the ATRS or heel-raise index at 52 weeks. As in previous studies, there was a significant correlation between the modulus at 7 weeks and the heel-raise index at 52 weeks. There were no signs of tendon elongation.

CONCLUSION

Early tensional loading improves the mechanical properties of the healing Achilles tendon.

Three-dimensional evaluation of cyclic displacement in single-row and double-row rotator cuff reconstructions under static external rotation

BACKGROUND

The double-row suture bridge repair was recently introduced and has demonstrated superior biomechanical results and higher yield load compared with the traditional double-row technique. It therefore seemed reasonable to compare this second generation of double-row constructs to the modified single-row double mattress reconstruction.

HYPOTHESIS

The repair technique, initial tear size, and tendon subregion will have a significant effect on 3-dimensional (3D) cyclic displacement under additional static external rotation of a modified single-row compared with a double-row rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

Rotator cuff tears (small to medium: 25 mm; medium to large: 35 mm) were created in 24 human cadaveric shoulders. Rotator cuff repairs were performed as modified single-row or double-row repairs, and cyclic loading (10-60 N, 10-100 N) was applied under 20° of external rotation. Radiostereometric analysis was used to calculate cyclic displacement in the anteroposterior (x), craniocaudal (y), and mediolateral (z) planes with a focus on the repair constructs and the initial tear size. Moreover, differences in cyclic displacement of the anterior compared with the posterior tendon subregions were calculated.

RESULTS

Significantly lower cyclic displacement was seen in small to medium tears for the single-row compared with double-row repair at 60 and 100 N in the x plane (P = .001) and y plane (P = .001). The results were similar in medium to large tears at 100 N in the x plane (P = .004). Comparison of 25-mm versus 35-mm tears did not show any statistically significant differences for the single-row repairs. In the double-row repairs, lower gap formation was found for the 35-mm tears (P ≤ .05). Comparison of the anterior versus posterior tendon subregions revealed a trend toward higher anterior gap formation, although this was statistically not significant.

CONCLUSION

The tested single-row reconstruction achieved superior results in 3D cyclic displacement to the tested double-row repair. Extension of the initial rupture size did not have a negative effect on the biomechanical results of the tested constructs.

CLINICAL RELEVANCE

Single-row repairs with modified suture configurations provide comparable biomechanical strength to double-row repairs. Furthermore, as increased gap formation in the early postoperative period might lead to failure of the construct, a strong anterior fixation and restricted external rotation protocol might be considered in rotator cuff repairs to avoid this problem.

Excessive distal migration of fiber-mesh coated femoral stems

BACKGROUND

The surface texture, localization, and magnitude of the surface material applied to the femoral stem can facilitate bone ingrowth and influence the survival of total hip arthroplasties. Clinical and radiographic studies have shown superior bone ingrowth in proximally porous-coated stems with a diaphyseal grit-blasted surface in comparison to a smooth diaphyseal surface. Surface textures-especially porous surface material-have been suggested to have a sealing effect against migration of polyethylene debris along the implant-bone interface and to reduce the inflammatory response, leading to a prolonged implant survival.

PATIENTS AND METHODS

Between 2004 and 2006, we conducted a randomized, controlled trial (RCT) involving 50 patients with non-inflammatory arthritis. They received either a distally tapered, extended coated stem or a straight, proximally coated stem. During surgery, tantalum markers were inserted into the greater and lesser trochanter. Implant migration was evaluated at 3, 12, and 24 months postoperatively by radiostereometric analysis. The primary endpoint was stem migration 2 years after surgery.

RESULTS

All femoral components in both groups showed pronounced distal translation, with the highest rate of translation occurring between 0 and 3 months. After 2 years, the mean distal translation was 2.67 (95% CI: -3.93 to -1.42) mm for the tapered, extended coated stem and 1.80 (-2.45 to -1.15) mm for the straight, proximally coated stem. Half of the tapered, extended coated stems and two-thirds of the straight, proximally coated stems had migrated more than 1 mm. No difference between the 2 stems could be seen with regard to translation or rotation at any time point. After 2 years, 2 hips have been reoperated due to mechanical loosening of the stem.

INTERPRETATION

An excessive amount of migration of both stem types was seen 2 years postoperatively. It is of vital importance to follow this patient cohort since radiostereometric analysis is known to be predictive of late implant failure, especially in this study where pronounced early migration was observed. We recommend longer follow-up of both stem types.

Comparison of trabecular metal cups and titanium fiber-mesh cups in primary hip arthroplasty: a randomized RSA and bone mineral densitometry study of 50 hips

BACKGROUND

Trabecular metal has shown promising results in experimental studies of bone ingrowth. Several clinical studies support these results. However, until now, no randomized clinical radiostereometric analysis (RSA) studies have been published. In this randomized RSA trial, we compared a new acetabular cup with a surface made of tantalum trabecular metal and a cup with a titanium fiber-mesh surface.

PATIENTS AND METHODS

Between 2004 and 2006, we operated 60 patients with noninflammatory hip arthritis. The patients were randomized to receive either an uncemented cup with a titanium fiber-mesh surface (Trilogy cup) or a cup with a trabecular tantalum surface (Monoblock cup). After 2 years, 50 patients had completed the study. The primary endpoint was cup migration within the first 2 years after surgery; the secondary endpoints were change in bone mineral density and Harris hip score at 3 months.

RESULTS

Both cup types showed excellent fixation. RSA revealed minimal translation and rotation at 2 years. There was no statistically significant difference between the cup types with regard to translation. However, less rotation along the transverse axis was seen in the trabecular metal cups than in the fiber mesh cups: mean -0.01º (95% CI: -0.11 to 0.12) for trabecular metal cups and -0.60º (-0.72 to -0.48) for fiber-mesh cups (p = 0.04). The degree of periprosthetic bone loss was similar between the cup types in any of the regions of interest at 2 years of follow-up. 3 months postoperatively, we found a similar increase in Harris hip score in both groups: from around 50 to over 90.

INTERPRETATION

We found promising early results concerning fixation of trabecular metal components to the acetabular host bone. However, we recommend a longer observation period to evaluate the outcome of this new cup design.

Validation of a noninvasive technique to precisely measure in vivo three-dimensional cervical spine movement

STUDY DESIGN

In vivo validation during functional loading.

OBJECTIVE

To determine the accuracy and repeatability of a model-based tracking technique that combines subject-specific computed tomographic (CT) models and high-speed biplane x-ray images to measure three-dimensional (3D) in vivo cervical spine motion.

SUMMARY OF BACKGROUND DATA

Accurate 3D spine motion is difficult to obtain in vivo during physiological loading because of the inability to directly attach measurement equipment to individual vertebrae. Previous measurement systems were limited by two-dimensional (2D) results and/or their need for manual identification of anatomical landmarks, precipitating unreliable and inaccurate results. All previous techniques lack the ability to capture true 3D motion during dynamic functional loading.

METHODS

Three subjects had 1.0-mm-diameter tantalum beads implanted into their fused and adjacent vertebrae during anterior cervical discectomy and fusion surgery. High-resolution CT scans were obtained after surgery and used to create subject-specific 3D models of each cervical vertebra. Biplane x-ray images were collected at 30 frames per second while the subjects performed flexion/extension and axial rotation movements 6 months after surgery. Individual bone motion, intervertebral kinematics, and arthrokinematics derived from dynamic radiostereophotogrammetric analysis served as a gold standard to evaluate the accuracy of the model-based tracking technique.

RESULTS

Individual bones were tracked with an average precision of 0.19 and 0.33 mm in nonfused and fused bones, respectively. Precision in measuring 3D joint kinematics in fused and adjacent segments averaged 0.4 mm for translations and 1.1° for rotations, while anterior and posterior disc height above and below the fusion were measured with a precision ranging between 0.2 and 0.4 mm. The variability in 3D joint kinematics associated with tracking the same trial repeatedly was 0.02 mm in translation and 0.06° in rotation.

CONCLUSION

The 3D cervical spine motion can be precisely measured in vivo with submillimeter accuracy during functional loading without the need for bead implantation. Fusion instrumentation did not diminish the accuracy of kinematic and arthrokinematic results. The semiautomated model-based tracking technique has excellent repeatability.

Autologous platelets have no effect on the healing of human achilles tendon ruptures: a randomized single-blind study

BACKGROUND

Animal studies have shown that local application of platelet-rich plasma (PRP) stimulates tendon repair. Preliminary results from a retrospective case series have shown faster return to sports.

HYPOTHESIS

Autologous PRP stimulates healing of acute Achilles tendon ruptures.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

Thirty patients were recruited consecutively. During surgery, tantalum beads were implanted in the Achilles tendon proximal and distal to the rupture. Before skin suture, randomization was performed, and 16 patients were injected with 10 mL PRP (10 times higher platelet concentration than peripheral blood) whereas 14 were not. With 3-dimensional radiographs (roentgen stereophotogrammetric analysis; RSA), the distance between the beads was measured at 7, 19, and 52 weeks while the patient resisted different dorsal flexion moments over the ankle joint, thereby estimating tendon strain per load. An estimate of elasticity modulus was calculated using callus dimensions from computed tomography. At 1 year, functional outcome was evaluated, including the heel raise index and Achilles Tendon Total Rupture Score. The primary effect variables were elasticity modulus at 7 weeks and heel raise index at 1 year.

RESULTS

The mechanical variables showed a large degree of variation between patients that could not be explained by measuring error. No significant group differences in elasticity modulus could be shown. There was no significant difference in heel raise index. The Achilles Tendon Total Rupture Score was lower in the PRP group, suggesting a detrimental effect. There was a correlation between the elasticity modulus at 7 and 19 weeks and the heel raise index at 52 weeks.

CONCLUSION

The results suggest that PRP is not useful for treatment of Achilles tendon ruptures. The variation in elasticity modulus provides biologically relevant information, although it is unclear how early biomechanics is connected to late clinical results.

Migration of the humeral component of the Souter-Strathclyde elbow prosthesis

Mechanical loosening which begins with early-onset migration of the prosthesis is the major reason for failure of the Souter-Strathclyde elbow replacement. In a prospective study of 18 Souter-Strathclyde replacements we evaluated the patterns of migration using roentgen stereophotogrammetric analysis. We had previously reported the short-term results after a follow-up of two years which we have now extended to a mean follow-up of 8.2 years (1 to 11.3). Migration was assessed along the co-ordinal axes and overall micromovement was expressed as the maximum total point movement. The alignment of the prosthesis and the presence of radiolucent lines were examined on conventional standardised radiographs.

All the humeral components showed increased and variable patterns of migration at the extended follow-up and four humeral components were revised. The maximum total point movement at two years in the revised prostheses was 1.8 mm (sd 1.0) and in the non-revised 0.7 mm (sd 0.5, p = 0.01). Most humeral components migrated into external rotation resulting in an anterior and varus tilt. The ulnar components remained stable.

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.

Mechanical properties during healing of Achilles tendon ruptures to predict final outcome: a pilot Roentgen stereophotogrammetric analysis in 10 patients

Background

There are presently few methods described for in vivo monitoring of the mechanics of healing human tendon ruptures, and no methods for prediction of clinical outcome. We tested if Roentgen stereophotogrammetric analysis (RSA) can be used to follow the restoration of mechanical properties during healing of ruptured Achilles tendons, and if early measurements can predict clinical results.

Methods

Achilles tendon repair was studied with RSA in 10 patients with a total rupture. Tantalum beads were implanted in conjunction with surgical repair. The patients were evaluated at 6, 12 and 18 weeks, and after 1 year. RSA was performed with two different mechanical loadings, and the strain induced by increasing load was measured. The transverse area was determined by ultrasound. CT scan at 12 weeks confirmed that the tantalum beads were located within the tendons. Functional testing was done after 1 year. A heel raise index was chosen as primary clinical outcome variable.

Results

The strain was median 0.90, 0.32 and 0.14 percent per 100 N tendon force at 6 weeks, 18 weeks and one year respectively. The error of measurement was 0.04 percent units at 18 weeks. There was a large variation between patients, which appears to reflect biological variation. From 6 to 18 weeks, there was a negative correlation between increase in transverse area and increase in material properties, suggesting that healing is regulated at the organ level, to maximize stiffness. Modulus of elasticity during this time correlated with a heel raise index at one year (Rho = 0.76; p = 0.02).

Conclusion

We conclude that the RSA method might have potential for comparing different treatments of Achilles tendon ruptures.

Measurement of laxity in the anterior cruciate ligament-deficient knee: A comparison of three different methods in vitro

The aim of this study was to compare in-vitro measurements of anteroposterior laxity in the anterior cruciate ligament (ACL)-deficient knee using three different methods: an Instron materials-testing machine, then a KT-2000 arthrometer, and finally by Roentgen stereophotogrammetric analysis (RSA). Eight ACL-deficient human cadaver knees were used. Total displacement was measured between 90 N anterior and 90 N posterior tibiofemoral drawer forces at both 20° and 90° knee flexion. Laxity ranged from 11.5 to 27.6 mm at 20° and from 8.7 to 23.9 mm at 90°. A statistically significant difference was not found between the mean RSA and KT-2000 measurements. However, the mean Instron measurements of laxity were significantly (3-4 mm) higher than both RSA and KT-2000 measurements. The clinical methods of RSA and the KT-2000 measurements agreed well but appeared to underestimate tibiofemoral anteroposterior laxity compared with the materials-testing machine. These findings may be helpful in the future comparison of different studies.

The ProDisc-C prosthesis: clinical and radiological experience 1 year after surgery

STUDY DESIGN

This is a prospective randomized and controlled study, approved by the local ethical committee of Saarland (Germany).

OBJECTIVE

The aim of the current study was to analyze segmental motion following artificial disc replacement using disc prosthesis over 1 year. A second aim was to compare both segmental motion as well as clinical result to the current gold standard (anterior cervical discectomy and fusion [ACDF]).

SUMMARY OF BACKGROUND DATA

ACDF may be considered to be the gold standard for treatment of symptomatic degenerative disc disease within the cervical spine. However, fusion may result in progressive degeneration of the adjacent segments. Therefore, disc arthroplasty has been introduced. Among these, artificial disc replacement seems to be promising. However, segmental motion should be preserved. This, again, is very difficult to judge and has not yet been proven.

METHODS

A total of 49 patients with cervical disc herniation were enrolled and assigned to either study group (receiving a disc prosthesis) or control group (receiving ACDF, using a cage with bone graft and an anterior plate). Roentgen stereometric analysis (RSA) was used to quantify intervertebral motion immediately as well as 3, 6, 12, 24, and 52 weeks after surgery. Also, clinical results were judged using visual analog scale and neuro-examination at even RSA follow-up.

RESULTS

Cervical spine segmental motion decreased over time in the presence of disc prosthesis or fusion device. However, the loss segmental motion is significantly higher in the fusion group, when looked at 3, 6, 12, 24, and 52 weeks after surgery. We observed significant pain reduction in neck and arm after surgery, without significant difference between both groups.

CONCLUSION

Cervical spine disc prosthesis remains cervical spine segmental motion within the first 1 year after surgery. The clinical results are the same when compared with the early results following ACDF.

Disc replacement using Pro-Disc C versus fusion: a prospective randomised and controlled radiographic and clinical study

Anterior cervical discectomy and fusion (ACDF) may be considered to be the gold standard for treatment of symptomatic degenerative disc disease within the cervical spine. However, fusion of the segment may result in progressive degeneration of the adjacent segments. Therefore, dynamic stabilization procedures have been introduced. Among these, artificial disc replacement by disc prosthesis seems to be promising. However, to be so, segmental motion must be preserved. This, again, is very difficult to judge and has not yet been proven. The aim of the current study was to first analyse the segmental motion following artificial disc replacement using a disc prosthesis. A second aim was to compare both segmental motion as well as clinical result to the current gold standard (ACDF). This is a prospective controlled study. Twenty-five patients with cervical disc herniation were enrolled and assigned to either study group (receiving a disc prosthesis) or control group (receiving ACDF, using a cage with bone graft and an anterior plate.) Radiostereometric analysis was used to quantify intervertebral motion immediately as well as 3, 6, 12 and 24 weeks postoperatively. Further, clinical results were judged using visual analogue scale and neuro-examination. Cervical spine segmental motion decreased over time in the presence of disc prosthesis or ACDF. However, the loss of segmental motion is significantly higher in the ACDF group, when looked at 3, 6, 12 and 24 weeks after surgery. We observed significant pain reduction in neck and arm postoperatively, without significant difference between both groups (P > 0.05). Cervical spine disc prosthesis preserves cervical spine segmental motion within the first 6 months after surgery. The clinical results are the same when compared to the early results following ACDF.

Dynamic function of the ACL-reconstructed knee during running

Little is known about the three-dimensional behavior of the anterior cruciate ligament (ACL) reconstructed knee during dynamic, functional loading, or how dynamic knee function changes over time in the reconstructed knee. We hypothesized dynamic, in vivo function of the ACL-reconstructed knee is different from the contralateral, uninjured knee and changes over time. We measured knee kinematics for 16 subjects during downhill running 5 and 12 months after ACL reconstruction (bone-patellar tendon-bone or quadrupled hamstring tendon with interference screw fixation) using a 250 frame per second stereoradiographic system. We used repeated-measures ANOVA to ascertain whether there were differences between the uninjured and reconstructed limbs and over time. We found no differences in anterior tibial translation between limbs, but reconstructed knees were more externally rotated and in more adduction (varus) during the stance phase of running. Anterior tibial translation increased from 5 to 12 months after surgery in the reconstructed knees. Anterior cruciate ligament reconstruction failed to restore normal rotational knee kinematics during dynamic, functional loading and some degradation of graft function occurred over time. These abnormal motions may contribute to long-term joint degeneration associated with ACL injury and reconstruction.

The distal tibiofibular syndesmosis during passive foot flexion. RSA-based study on intact, ligament injured and screw fixed cadaver specimens

INTRODUCTION

The aim of the study was to investigate the kinematics of the distal tibiofibular syndesmosis in intact and ligament injured ankles and to assess how effective is the syndesmotic screw in restraining mortise width variations during passive foot flexion.

MATERIALS AND METHODS

The trials were carried out on seven fresh frozen cadaver specimens. The distal tibiofibular syndesmosis widening was investigated using Roentgen stereophotogrammetric analysis, in intact and ligament injured ankles and after the fixation of the syndesmotic screw. The AO-ASIF recommendations were followed for screw implant.

RESULTS

Injury to the syndesmotic and deltoid ligaments of the ankle did not result in a significant variation of the syndesmosis behavior during passive foot flexion. The 4.5-mm diameter cortical screw used in this study proved effective in restraining mortise width variation during foot flexion. The recorded mortise widening in the flexion arc extending from the neutral to the maximally dorsiflexed position was negligible in intact and ligament injured joints.

CONCLUSION

The result does not endorse the recommendation of placing the foot in full dorsal flexion during screw implantation. The choice of screw fixation as a treatment for ankle syndesmosis disruption should be carefully evaluated.