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

BACKGROUND

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

HYPOTHESIS

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

MATERIALS AND METHODS

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

RESULTS

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

DISCUSSION

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

TYPE OF STUDY AND LEVEL OF PROOF

not applicable.

Influence of marker-selection method in radiostereometric analysis of total knee arthroplasty on tibial baseplate migration patterns: a secondary analysis of a randomized controlled trial with 5-year follow-up

BACKGROUND AND PURPOSE

 Different marker-selection methods are applied to represent implant and tibial segments in radiostereometric analysis (RSA) studies of total knee arthroplasty (TKA). Either a consistent set of markers throughout subsequent RSA examinations ("consistent-marker method") is used or all available markers at each follow-up ("all-marker method"). The aim of this secondary analysis was to compare marker-selection methods on individual and group level TKA migration results.

METHODS

 Data from a randomized RSA study with 72 patients was included. Tibial baseplate migration was evaluated at 3 months, 1, 2, and 5 years postoperatively with both marker-selection methods. Additionally, migration was calculated using 5 fictive points, either plotted based on the consistent set of markers or all available markers.

RESULTS

 Migration could be calculated with both marker-selection methods for 248 examinations. The same prosthesis and bone markers (n = 136), different prosthesis markers (n = 71), different bone markers (n = 21), or different prosthesis and bone markers (n = 20) were used. The mean difference in maximum total point motion (MTPM) between all examinations was 0.02 mm, 95% confidence interval -0.26 to 0.31 mm. 5 implants were classified as continuously migrating with the consistent-marker method versus 6 implants (same 5 plus one additional implant) with the all-marker method. Using fictive points, fewer implants were classified as continuously migrating in both marker-selection methods. Differences between TKA groups in mean MTPM were comparable with both marker-selection methods, also when fictive points were used.

CONCLUSION

 Estimated group differences in mean MTPM were similar between marker-selection methods, but individual migration results differed. The latter has implications when classifying implants for estimated risk of future loosening.

Stable fixation of an ultra-short femoral neck-preserving hip prosthesis: a 5-year RSA, DXA, and clinical prospective outcome study of 48 patients

BACKGROUND AND PURPOSE

We previously showed promising primary stability and preservation of bone stock with the ultra-short neck-loading hip implant in total hip arthroplasty (THA). The aim of this study was to evaluate clinical outcome, implant stability, and bone mineral density (BMD).

METHODS

50 patients were treated with the ultra-short neck Primoris hip implant at baseline and 48 were available for evaluation at 5-year follow-up. 5 different patient-reported outcome measures (PROMs) including hip-specific scores, disease-specific and generic quality of life outcome measures, and an activity score were used. Furthermore, implant stability using radiostereometric analysis (RSA) and assessment of periprosthetic BMD using dual-energy X-ray absorptiometry (DXA) were applied.

RESULTS

By 1-year follow-up, all PROMs showed improvements and remained high at 5-year follow-up. After initial distal translation (subsidence) and negative rotation around the z-axis (varus tilt) the implant showed stable fixation at 5-year follow-up with no further migration beyond 12 months. In the regions of interest (ROI) 3 and 4, BMD remained stable. In ROI 2, further bone loss of 12% was found at 5-year follow-up.

CONCLUSION

Clinical outcome including PROMs was satisfying throughout the 5-year follow-up period. The hip implant remains stable with both bone preservation and loss 5 years after surgery.

Migration and clinical outcomes of a novel cementless hydroxyapatite-coated titanium acetabular shell: two-year follow-up of a randomized controlled trial using radiostereometric analysis

Aims

The objective of this study was to compare the two-year migration and clinical outcomes of a new cementless hydroxyapatite (HA)-coated titanium acetabular shell with its previous version, which shared the same geometrical design but a different manufacturing process for applying the titanium surface.

Methods

Overall, 87 patients undergoing total hip arthroplasty (THA) were randomized to either a Trident II HA or Trident HA shell, each cementless with clusterholes and HA-coating. All components were used in combination with a cemented Exeter V40 femoral stem. Implant migration was measured using radiostereometric analysis (RSA), with radiographs taken within two days of surgery (baseline), and at three, 12, and 24 months postoperatively. Proximal acetabular component migration was the primary outcome measure. Clinical scores and patient-reported outcome measures (PROMs) were collected at each follow-up.

Results

Mean proximal migrations at three, 12, and 24 months were 0.08 mm (95% confidence interval (CI) 0.03 to 0.14), 0.11 mm (95% CI 0.06 to 0.16), and 0.14 mm (95% CI 0.09 to 0.20), respectively, in the Trident II HA group, versus 0.11 mm (95% CI 0.06 to 0.16), 0.12 mm (95% CI 0.07 to 0.17), and 0.14 mm (95% CI 0.09 to 0.19) in the Trident HA group (p = 0.875). No significant differences in translations or rotations between the two designs were found in any other direction. Clinical scores and PROMs were comparable between groups, except for an initially greater postoperative improvement in Hip disability and Osteoarthritis Outcome Symptoms score in the Trident HA group (p = 0.033).

Conclusion

The Trident II clusterhole HA shell has comparable migration with its predecessor, the Trident hemispherical HA cluster shell, suggesting a similar risk of long-term aseptic loosening.

Acetabular cup fixation with and without screws following primary total hip arthroplasty: migration evaluated by radiostereometric analysis

BACKGROUND

Early cup migration after total hip arthroplasty (THA) is correlated to late revision due to aseptic loosening. However, the use of screws for increased cup stability remains unclear and debated. The purpose of this study is to assess acetabular migration between cups fixated with and without the use of screws.

METHODS

Patients underwent primary THA using either a direct anterior (DA) or a direct lateral (DL) approach. The DA surgeon routinely supplemented cup fixation with 1 or 2 screws while the DL surgeon used no screws. At 7 follow-up visits up to 2 years post operation, patients underwent radiostereometric analysis (RSA) imaging for implant migration tracking. The primary outcome was defined as proximal cup migration measured with model-based RSA.

RESULTS

68 patients were assessed up to 2 years post operation, n = 43 received screws and n = 25 did not. The use of screws had a significant effect on cup migration (p = 0.018). From 2 weeks to 2 years post operation, the total mean migration was 0.403 ± 0.681 mm and 0.129 ± 0.272 mm (p = 0.319) for cups with and without screws, respectively. The number of screws used also had a significant impact, with cups fixated with 1 screw migrating more than cups fixated with 2 (p = 0.013, mean difference 0.712 mm).

CONCLUSIONS

Acetabular cups fixated with only 1 screw resulted in greater migration than cups with no screws or 2 screws, though the mean magnitude was well under the 1.0 mm threshold for unacceptable migration. However, 3 of the 24 patients who received only 1 screw exceeded the 1.0 mm threshold for unacceptable migration. Ultimately, the results of this study show that the use of 2 screws to supplement cup fixation can provide good implant stability that is equivalent to a secure press-fit component with no screws.Clinical trial registration: ClinicalTrials.gov (NCT03558217).

State of the Art in Radiostereometric Analysis for Tibial Baseplate Migration and Future Research Directions

Radiostereometric analysis (RSA) measures movement (migration) of a baseplate relative to the underlying tibia after total knee arthroplasty (TKA) and has been used extensively to evaluate safety of new implant designs and/or surgical techniques regarding baseplate loosening. Because RSA is a complex methodology which involves various choices that researchers make, including whether to use marker-based or model-based methods, which migration metric to report, how to relate short-term migrations to long-term risk, and how these choices impact error, the objectives of this review were to: (1) lay out a comprehensive structure illustrating the multiple components/considerations for RSA and their interrelations, (2) review components of the structure using the latest RSA literature, and (3) use the preceding review as a context for identifying future areas of study. The components to be reviewed were structured using the following topics: type of RSA, migration metrics, sources of error, studies/reports of error, stability limits, and studies of error in stability limits. Based on the current RSA literature and knowledge gaps which exist, the following future research directions were identified: (1) revising the ISO standard to require reporting of clinical measurement error (bias) and recommending use of a local baseplate coordinate system, (2) identifying the migration metric and associated threshold most predictive of baseplate loosening for individual patients, (3) creating a method for data sharing to improve individual patient diagnostics, and (4) determining an appropriate stability limit for model-based RSA for group stability and individual patient diagnostics.

Staged Revision Hip Arthroplasty With Femoral Impaction Bone Grafting for Prosthetic Joint Infections: Radiostereometric Analyses and Clinical Outcomes at Minimum 5-Year Follow-Up

BACKGROUND

There are ongoing concerns regarding the use of bone graft following prosthetic joint infection and subsequent implant subsidence. The aim of this study was to determine whether the use of a cemented stem combined with femoral impaction bone grafting (FIBG) at second stage revision for infection results in stable femoral stem fixation, determined by accurate methods, and good clinical results.

METHODS

A prospective cohort of 29 patients underwent staged revision total hip arthroplasty for infection using an interval prosthesis followed by FIBG at the final reconstruction. The mean follow-up was 89 months (range, 8 to 167 months). Femoral implant subsidence was measured with radiostereometric analysis. Clinical outcomes included the Harris Hip Score, Harris Pain score and Société Internationale de Chirurgie Orthopédique et de Traumatologie activity scores.

RESULTS

At 2-years follow-up the median stem subsidence relative to femur was -1.36 mm (range, -0.31 to -4.98), while the cement subsidence relative to femur was -0.05 mm (range, 0.36 to -0.73). At 5-years follow-up, the median stem subsidence relative to femur was -1.89 mm (range, -0.27 to -6.35), while the cement subsidence relative to femur was -0.06 mm (range, 0.44 to -0.55). There were 25 patients who were confirmed infection-free after the second stage revision with FIBG. The median Harris Hip Score improved from 51 pre-operatively to 79 at 5 years (P = .0130), and Harris Pain score from 20 to 40 (P = .0038).

CONCLUSIONS

Stable femoral component fixation can be achieved with FIBG when reconstructing the femur after revision for infection without compromising infection cure rates and patient-reported outcomes.

A low-dose biplanar X-ray imager has RSA level precision in total knee arthroplasty

BACKGROUND AND PURPOSE

The low radiation biplanar X-ray imager (EOS imaging, Paris, France) scans patients in a weight-bearing position, provides calibrated images, and limits radiation, an asset for serial radiostereometric analysis (RSA) studies. RSA in vivo precision values have not been published for this type of imaging system, thus the goal of this study was to assess the precision of RSA in vivo utilizing a low radiation biplanar imager.

PATIENTS AND METHODS

At a mean of 5 years post-surgery (range 1.4-7.5 years), 15 total knee arthroplasty (TKA) participants (mean age 67 years at the time of imaging, 12 female, 3 male) with RSA markers implanted during index surgery were scanned twice at the same visit in the EOS imager. Precision of marker-based analysis was calculated by comparing the position of the implant relative to the underlying bone between the 2 examinations.

RESULTS

The 95% limit of precision was 0.11, 0.04, and 0.15 mm along the x, y, and z axes, respectively and 0.15°, 0.20°, and 0.14° around the same axes.

CONCLUSION

This precision study has shown an in vivo RSA precision of ≤ 0.15 mm and ≤ 0.20°, well within published uniplanar values for conventional arthroplasty RSA, with the added benefit of weight-bearing imaging, a lower radiation dose, and without the need for a reference object during the scan.

Wider translations and rotations in posterior-stabilised mobile-bearing total knee arthroplasty compared to fixed-bearing both implanted with mechanical alignment: a dynamic RSA study

PURPOSE

The purpose of this study was to investigate the in vivo kinematics of the same femoral design mechanically aligned posterior-stabilised (PS) total knee arthroplasty (TKA) with either fixed-bearing (FB) or mobile-bearing (MB) inlay, implanted by the same surgeon, using model-based dynamic radiostereometric analysis (RSA). The hypothesis of the present study was that the MB design would show wider axial rotation than the FB design, without affecting the clinical outcomes.

MATERIALS AND METHODS

A cohort of 21 non-randomised patients (21 DePuy Attune PS-FB) was evaluated by dynamic RSA analysis at a minimum 9-month follow-up, while performing differently demanding daily living activities such as sit to stand (STS) and deep knee lunge (DKL). Kinematic data were compared with those of a cohort of 22 patients implanted with the same prosthetic design but with MB inlay. Anterior-posterior (AP) translations, varus-valgus (VV) and internal-external (IE) rotations of the femoral component with respect to the tibial baseplate were investigated. Translation of medial and lateral compartment was analysed using the low point method according to Freeman et al. Questionnaires to calculate objective and subjective clinical scores were administered preoperatively and during follow-up visit by the same investigator.

RESULTS

The FB TKA design showed lower AP translation during STS (6.8 ± 3.3 mm in FB vs 9.9 ± 3.7 mm in MB, p = 0.006*), lower VV rotation (1.9 ± 0.8° in FB vs 5.3 ± 3.3° in MB, p = 0.005) and lower IE rotation (2.8 ± 1.1° in FB vs 9.5 ± 4.3° in MB, p = 0.001) during DKL than the mobile-bearing TKA design. Posterior-stabilised FB group showed significant lower translation of the low point of the medial compartment than the MB group (p = 0.008). The percentage of patients performing medial pivot in the FB group was higher compared to MB group in the examined motor tasks. No significant differences in post-operative range of motion (117° ± 16° for FB group and 124° ± 13° for MB group) and in clinical outcomes emerged between the two cohort.

CONCLUSIONS

The FB and MB designs differed in AP translations, VV rotations and IE rotations of the femoral component with respect to the tibial component in STS and DKL. Furthermore, FB cohort reported a significant higher percentage of medial pivot with respect to MB cohort. Despite this, no differences in clinical outcomes were detected between groups. Both designs showed stable kinematics and represent a viable option in primary TKA.

LEVEL OF EVIDENCE

Prospective cohort study, II.

Comparison of two hydroxyapatite-coated femoral components: a randomized clinical trial using radiostereometric analysis

Aims

The primary aim of this trial was to compare the subsidence of two similar hydroxyapatite-coated titanium femoral components from different manufacturers. Secondary aims were to compare rotational migration (anteversion/retroversion and varus/valgus tilt) and patient-reported outcome measures between both femoral components.

Methods

Patients were randomized to receive one of the two femoral components (Avenir or Corail) during their primary total hip arthroplasty between August 2018 and September 2020. Radiostereometric analysis examinations at six, 12, and 24 months were used to assess the migration of each implanted femoral component compared to a baseline assessment. Patient-reported outcome measures were also recorded for these same timepoints. Overall, 50 patients were enrolled (62% male (n = 31), with a mean age of 65.7 years (SD 7.3), and mean BMI of 30.2 kg/m2 (SD 5.2)).

Results

The two-year subsidence was similar for Avenir (-0.018 mm (95% confidence interval (CI) -0.053 to 0.018) and Corail (0.000 mm (95% CI -0.027 to 0.026; p = 0.428). Both anteversion/retroversion (Avenir 0.139° (95% CI -0.204 to 0.481°); Corail -0.196° (95% CI -0.445 to 0.053°; p = 0.110) and varus/valgus tilt (Avenir -0.024° (95% CI -0.077 to 0.028); Corail -0.049° (95% CI -0.098 to 0.000°; p = 0.473) were not statistically significantly different. After two years, patients reported similar improvements in EuroQol five-dimension five-level health questionnaire (Avenir 0.22 (SD 0.2); Corail 0.22 (SD 0.18); p = 0.965) and other outcomes scores. Patient satisfaction on a five-point Likert scale was also similar between both groups after two years (Avenir 1.38 (SD 0.88); Corail 1.33 (SD 0.57); p = 0.846).

Conclusion

The performance of both femoral components was similar in terms of stability and patient outcomes.

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE II

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

A Radiostereometric Analysis of Tendon Migration After Arthroscopic and Mini-Open Biceps Tenodesis: Interference Screw Versus Single Suture Anchor Fixation

BACKGROUND

Studies suggest that similar clinical results are achieved via arthroscopic and open biceps tenodesis (BT) techniques.

PURPOSE

To quantify the postoperative migration of the BT construct between arthroscopic suprapectoral BT (ASPBT) and open subpectoral BT (OSPBT) techniques via interference screw (IS) or single-suture suture anchor (SSSA) fixation using radiostereometric analysis.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Distal migration of the biceps tendon after OSPBT with a polyetheretherketone IS, OSPBT with 1 SSSA, ASPBT with polyetheretherketone IS, and ASPBT with 2 SSSAs was measured prospectively. Patients with symptomatic biceps tendinopathy and preoperative patient-reported outcome measures (PROMs) including Constant-Murley subjective, Single Assessment Numeric Evaluation, or Patient-Reported Outcomes Measurement Information System-Upper Extremity scores were included. A tantalum bead was sutured on the proximal end of the long head of the biceps tendon before fixation of tendon tissue. Anteroposterior radiographs were performed immediately postoperatively, at 1 week, and at 3 months. Bead migration was measured, and preoperative PROMs were compared with those at latest follow-up.

RESULTS

Of 115 patients, 94 (82%) were available for final follow-up. IS fixation yielded the least tendon migration with no difference between the open and arthroscopic approaches (4.31 vs 5.04 mm; P = .70). Fixation with 1 suture anchor demonstrated significantly greater migration than that achieved with an IS at both 1 week (6.47 vs 0.1 mm, 6.47 vs 1.75 mm, P < .001;) and 3 months (14.76 vs 4.31 mm, 14.76 vs 5.04 mm, P < .001) postoperatively. Two-suture anchor fixation yielded significantly greater migration than IS fixation at 1 week (7.02 vs 0.1 mm, P < .001; 7.02 vs 1.75 mm, P = .003) but not 3 months postoperatively (8.06 vs 4.31 mm, P = .10; 8.06 vs 5.04 mm, P = .07). Four patients with suture anchor fixation (3 patients in the OSPBT 1 SSSA group, 9.4%, and 1 patient in the ASPBT 2 SSSAs group, 3.8%) developed a Popeye deformity, whereas no Popeye deformities occurred in the IS groups. Mean 3-month bead migration in patients with and without a Popeye deformity was 60.8 and 11.2 mm, respectively (P < .0001). PROMs did not differ among groups at final follow-up.

CONCLUSION

Interference screw fixation yielded the least tendon migration whether achieved arthroscopically or open. The available data indicated that fixation with 1 SSSA but not 2 SSSAs resulted in significantly greater migration than that achieved with an IS. Despite variations in tendon migration, PROMs were similar among all groups. When SSSAs are used, tendon migration may be minimized by using ≥2 anchors.

Surgical approach had minor association with femoral stem migration in total hip arthroplasty: radiostereometric analysis of 61 patients after 5-year follow-up

BACKGROUND AND PURPOSE

Total hip arthroplasty (THA) is usually performed using 1 of 3 surgical approaches: direct lateral (DLA), posterior (PA), or anterior (AA). AA is different from DLA and PA owing to limited intraoperative visibility of the femoral canal. This could affect stem positioning and therefore migration. We aimed to perform an exploratory radiostereometric analysis (RSA) study with 3 groups for surgical approach assessing stem migration up to 5 years postoperatively.

PATIENTS AND METHODS

61 patients with unilateral osteoarthritis of the hip were included. 21 patients were allocated to the DLA, 20 to the PA, and 20 to the AA group. All patients received an uncemented, collarless, double-tapered, fully hydroxyapatite-coated Profemur Gladiator stem. Migration was measured with model-based RSA. Baseline RSA was on day 1 postoperatively. The follow-ups were at day 8, at 5 weeks, and at 3, 6, 12, 24, and 60 months after surgery. Generalized linear mixed models were used to analyze maximum total point motion (MTPM) migrations.

RESULTS

Group mean differences in MTPM were 0.4 mm (95% confidence interval [CI] -1.5 to 2.4) for DLA vs. PA, 1.1 mm (CI -1.0 to 3.3) for AA vs. DLA, and 1.6 mm (CI -0.8 to 3.9) for AA vs. PA, when adjusted for sex and age as covariates. 2 stems in the AA group had excessive early migration. For all stems the migrations occurred mainly within 5-week follow-up and then stabilized.

CONCLUSION

At 5-year follow-up, there were no statistically significant differences in stem migration associated with the 3 surgical approaches used in this study.

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

BACKGROUND

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

QUESTIONS/PURPOSES

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

METHODS

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

RESULTS

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

CONCLUSION

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

CLINICAL RELEVANCE

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

Migration pattern of cemented Exeter short stem in Dorr type A femurs. A prospective radiostereometry study with 2-year follow-up

INTRODUCTION

The Exeter short stem (ESS) is 25 mm shorter than the standard length v40 Exeter stem (Stryker) and intended for a narrow femoral diaphysis. The purpose of the study was to evaluate the migration pattern of the cemented ESS.

MATERIAL AND METHOD

In a prospective single-center cohort study, 23 patients (21 female) mean age 78 (range 70-89) with hip osteoarthritis and Dorr Type A femurs were included. Preoperative DXA was used to group patients into normal (> - 1) and low (< - 1) T-score. Components were the collarless polished double-tapered Exeter short stem type N°1 L125. Patients were followed for 2 years with model-based RSA (stem migration), regular hip radiographs (stem position and cementation quality), Oxford Hip Score (OHS) and VAS pain.

RESULTS

At 2-year follow-up, the stems subsided 1.48 mm (CI 95% 1.69; 1.26) and retroverted 0.45° (CI 95% 0.01; 0.88). From 12 to 24 months, stem subsidence was 0.18 mm (CI 95% 0.1; 0.25) (p = 0.001) and retroversion was - 0.04° (CI 95% - 0.27; 0.18) (p = 0.70). T-score and stem subsidence correlated (rho = 0.48; p = 0.025) and patients with normal T-score (n = 7) had 0.42 mm (CI 95% - 0.01; 0.85) less subsidence as compared to patients with low T-score (n = 15) (p = 0.054). Stems in varus position (n = 9) subsided 1.7 mm (CI 95% 1.35; 2.05) compared to 1.33 mm (CI 95% 1.05; 1.60) for stems in neutral position (n = 13) (p = 0.07). Postoperative cementation quality did not influence 2-year stem migration. OHS improved to 40.7 (CI 95% 36.8; 44.7) and VAS pain at rest and activity decreased to 5 mm and 10 mm, respectively (p < 0.001).

CONCLUSION

The 2-year migration pattern of the cemented ESS was similar to reports for the cemented standard length Exeter stem. Low preoperative T-score and varus stem-position showed a tendency for higher stem migration and should be studied as risk factors for failure in larger studies of cemented polished stems.

Dynamic Radiographs Are Unreliable to Assess Arthrodesis Following Cervical Fusion: A Modeled Radiostereometric Analysis of Cervical Motion

STUDY DESIGN

In vitro study.

OBJECTIVE

The purpose of the present study was to utilize an idealized cervical spine model to determine whether the parallax effect or changes in the position of the spine relative to the x-ray generator influence intervertebral motion parameters on dynamic cervical spine radiographs.

SUMMARY OF BACKGROUND DATA

The utility of flexion-extension radiographs in clinical practice remains in question due to poor reliability of the parameters utilized to measure motion.

MATERIALS AND METHODS

A cervical spine model with tantalum beads inserted into the tip of each spinous process was utilized to measure interspinous process distance (IPD) on plain radiographs. The model was then manipulated to alter the generator angle and generator distance, and the IPD was measured. The impact of individual and combined changes in these parameters on IPD was assessed. Multivariate analysis was performed to identify independent drivers of variability in IPD measurements.

RESULTS

Isolated changes in the generator distance and generator angle and combined changes in these parameters led to significant changes in the measured IPD at each intervertebral level in neutral, flexion, and extension, which, in many instances, exceeded an absolute change of >1 mm or >2 mm. Multivariate analysis revealed that generator distance and generator angle are both independent factors impacting IPD measurements that have an additive effect.

CONCLUSIONS

In an idealized cervical spine model, small clinically feasible changes in spine position relative to the x-ray generator produced substantial variability in IPD measurements, with absolute changes that often exceeded established cutoffs for determining the presence of pathologic motion across a fused segment. This study further reinforces that motion assessment on dynamic radiographs is not a reliable method for determining the presence of an arthrodesis unless these sources of variability can be consistently eliminated.

LEVEL OF EVIDENCE

3.

Highly Crosslinked Polyethylene Liners Have Negligible Wear at 10 Years: A Radiostereometric Analysis Study

BACKGROUND

The introduction of crosslinked ultra-high molecular weight polyethylene (XLPE) acetabular liners has been very successful, with decreased wear and reduction in the rates of revision hip arthroplasties. XLPE is the preferred articulation for most surgeons; however, there are concerns about the long-term performance of XLPE liners created with different manufacturing processes, which may lead to time-dependent failure, including accelerated wear, after several years.

QUESTIONS/PURPOSES

(1) What is the amount and rate of wear during the first 10 years using radiostereometric analysis (RSA) measurements of patients who had THAs that included a second-generation XLPE bearing? (2) Does the rate of wear change after 5 years in situ?

METHODS

This is a brief follow-up of a previous RSA study. In that study, we prospectively enrolled 21 patients with osteoarthritis who underwent primary cementless THA with an XLPE acetabular liner (three cycles of 3Mrad annealed) and 32-mm articulation. That group represented 44% of the 48 THAs performed by the surgeon at the hospital where RSA was available; 16 had cemented hips, leaving 32 who were invited to participate in this study. Of those, 11 lived rurally and declined to participate, leaving 21 patients who were included in the initial study. Since then, three patients died, one developed dementia and could not participate, and one had revision THA for reasons other than wear, leaving 16 patients available for analysis at 10 years. Tantalum markers were inserted during surgery, and all patients had RSA radiographs taken at 1 week, 6 months, and 1, 2, 5, and 10 years postoperatively. Femoral head penetration into the acetabular component was measured with RSA, including bedding-in during the first year and annual wear thereafter.

RESULTS

The median medial, proximal, anterior, two-dimensional (2D), and three-dimensional (3D) wear rates between 1 and 10 years were -0.001, 0.004, -0.012, 0.000, and 0.002 mm/year, respectively. No patient in this cohort had a proximal or 2D wear rate greater than 0.025 mm/year. The median proximal wear rate between 5 and 10 years (0.002 mm/year) was not greater than wear at 1 to 5 years (0.004 mm/year).

CONCLUSION

Femoral head penetration in this second-generation XLPE liner remained very low at 10 years and accelerated wear after 5 years in situ did not occur. Concerns about late-onset wear from oxidation of irradiated-annealed XLPE were not observed. The low level of wear remains encouraging for the future clinical performance of this material.

LEVEL OF EVIDENCE

Level II, therapeutic study.

Vitamin E infused highly cross-linked cemented cups in total hip arthroplasty show good wear pattern and stabilize satisfactorily: a randomized, controlled RSA trial with 5-year follow-up

Background and purpose - Vitamin E infused highly cross-linked polyethylene (VEPE) was introduced in order to enhance oxidative resistance in highly cross-linked polyethylene cups in total hip arthroplasty (THA). We have, with a follow-up of 5 years, evaluated wear characteristics of 2 identically designed cemented cups with the only difference being the material, VEPE or ultra-high molecular weight polyethylene (UHMWPE). Furthermore, we report cup migration and clinical outcome. Patients and methods - 48 patients with primary osteoarthritis were randomized to either UHMWPE or VEPE cups. Patients were followed with radiostereometric analysis (RSA) from the first postoperative day, at 3 months, 1, 2, and 5 years as well as with hip-specific outcome questionnaires. Results - At 3 months the mean proximal head penetration for UHMWPE was 0.07 mm (95% CI 0.03-0.11) and for VEPE 0.06 mm (-0.01 to 0.13). Thereafter, there was a continuous annual wear of 0.08 mm/year, up to 0.46 mm (0.36-0.57) at 5 years, for the UHMWPE cup. The VEPE cup showed low annual wear of 0.01 mm/year, up to 0.09 mm (0.02-0.16) at 5 years. In the first 3 months the UHMWPE cup migrated cranially 0.08 mm (0.03-0.13) whereas the VEPE cup migrated 0.17 mm (0.10-0.24), Thereafter, they showed similar migration patterns with stabilization between 2 and 5 years up to 0.21 mm (0.04-0.39) and 0.24 mm (0.13-0.36) respectively. The HOOS remained good up to 5 years, and no cup was revised. Interpretation - Compared with otherwise identical UHMWPE cups the cemented VEPE cup shows statistically significant reduction of wear up to 5 years and both cup types stabilize well with good clinical outcome.

Continuous periprosthetic bone loss but preserved stability for a collum femoris-preserving stem: follow-up of a prospective cohort study of 21 patients with dualenergy X-ray absorptiometry and radiostereometric analysis with minimum 8 years of follow-up

Background and purpose - We previously described a decrease in bone mineral density (BMD) in the calcar region 2 years after insertion of the collum femoris-preserving (CFP) stem, but the implants were stable. Now we have examined the long-term changes in periprosthetic BMD and stability of the CFP stem. Patients and methods - We conducted a minimum 8-year follow-up of 21 patients from our original investigation. We examined periprosthetic BMD by dual-energy X-ray absorptiometry (DEXA) and implant stability by radiostereometric analysis (RSA). Results - Between 2 and 8 years 1 stem was revised due to aseptic loosening. Between 2 and 8 years we found a 14% (95% confidence interval [CI] 9-19) reduction in BMD in Gruen zone 6 and 17% (CI 6-28) in Gruen zone 7. From baseline the reduction in BMD was 30% (CI 23-36) in Gruen zone 6, 39% (CI 31-47) in Gruen zone 7, and 19% (CI 14-23) in Gruen zone 2. Between 2 and 8 years, RSA (n = 17) showed a mean translation along the stem axis of 0.02mm (CI -0.02 to 0.06) and a mean rotation around the stem axis of 0.08° (CI -0.26 to 0.41). From baseline mean subsidence was 0.07 mm (CI -0.16 to 0.03) and mean rotation around the stem axis was 0.23° (CI -0.23 to 0.68) at 8 years. Interpretation - There was continuous loss of proximomedial BMD at 8 years while the CFP stem remained stable. Proximal periprosthetic bone loss cannot be prevented by this stem.

Preoperative BMD does not influence femoral stem subsidence of uncemented THA when the femoral T-score is > -2.5

Background and purpose - It is believed that in uncemented primary total hip arthroplasty (THA) the anchorage of the stem is dependent on the level of bone mineral density (BMD) of the femoral bone. This is one of the reasons for the widely accepted agreement that a cemented solution should be selected for people with osteoporosis or age > 75 years. We evaluated whether preoperative BMD of the femur bone is related to femoral stem migration in uncemented THA.Patients and methods - We enrolled 62 patients (mean age 64 years (range 49-74), 34 males) scheduled for an uncemented THA. Before surgery we undertook DEXA scans of the proximal femur including calculation of the T- and Z-scores for the femoral neck. Evaluation of stem migration by radiostereometric analysis (RSA) was performed with 24 months of follow-up. In 56 patients both preoperative DEXA data and RSA data were available with 24 months of follow-up.Results - None of the patients had a T-score below -2.5. We found no statistically significant relationship between preoperative BMD and femoral stem subsidence after 3 or 24 months. When comparing the average femoral stem subsidence between 2 groups with T-score > -1 and T-score ≤ -1, respectively, we found no statistically significant difference after either 3 or 24 months when measured with RSA.Interpretation - In a cohort of people ≤ 75 years of age and with local femur T-score > -2.5 we found no relationship between preoperative BMD and postoperative femoral stem subsidence of a cementless THA.

Effect of symmetrical restoration for the migration of uncemented total hip arthroplasty: a randomized RSA study with 75 patients and 5-year follow-up

BACKGROUND

Inferior placement of a femoral stem is predictive for early loosening and failure, but does restoration of the original hip anatomy benefit the function and survival of a total hip replacement?

METHODS

Seventy-five patients with primary unilateral hip osteoarthritis operated with an uncemented anatomical stem were randomized for either standard or modular stems. We used 50 ABG II stems with modular necks and 25 standard stems (control group). We measured the symmetry in hip anatomy between healthy and operated side. The anatomical restoration variables were anteversion, global offset, and femoral offset/acetabular offset (FO/AO) quota. We performed measurements using a CT-based 3D templating and measuring software. Migratory behavior of the stems was then measured postoperatively with repeated radiostereometry (RSA) examinations over 5 years.

RESULTS

Both stem types showed an early (within 3 months) good stabilization after an initial slight rotation into retroversion and subsidence. There were no significant differences in RSA migration between modular and standard stems. Postoperative anteversion and FO/AO quota had no impact on stem migration. The standard stem tended to result in insufficient global offset (GO), whereas the modular stem did not.

CONCLUSIONS

The modular stem gave good symmetrical anatomical restoration and, like the standard version, a benign migratory behavior. Anteversion, GO, and FO/AO quota had no significant impact on stem migration. It therefore seems to be of no importance whether we choose a modular or a standard stem with regard to postoperative stem migration for this stem type. We overestimated the effect anatomical parameters have on stem movement; hence, we believe the study to be underpowered.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01512550. Registered 19 January 2012-retrospectively registered.

Imaging Modalities to Assess Fracture Healing

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Calibration of Stereo Radiography System for Radiostereometric Analysis Application

This paper describes a new alternative to conventional radiography system currently used for radiostereometric analysis studies. Instead of using two non-calibrated X-ray sources with a cumbersome calibration cage, we propose to use the biplanar radiography EOS system. Its fixed configuration provides a preliminary calibration and a much simpler acquisition protocol. A flexible and accurate calibration method is presented to optimize EOS default calibration using a simple object and a self-calibration method. To validate our system, we calculate the 3D reconstruction error of a known object. Results showed an accuracy of 70±11μm and 0.05±0.02° for translation and rotation respectively, and an average epipolar error of 23±03μm.

Uncemented or cemented femoral components work equally well in total knee arthroplasty

PURPOSE

To study the pattern of migration and clinical results up to 10 years of uncemented versus cemented fixation of the femoral component in total knee arthroplasty.

METHODS

Randomized controlled trial was conducted of 41 patients (23 women, 18 men) under the age of 60 years using radiostereometric analysis.

RESULTS

About two-thirds of the cemented implants and half of the uncemented implants stabilized between 2 and 10 years, while the remainder displayed a small annual increase of maximum total point motion of 0.09-0.10 mm/year. At 10 years there were no statistically significant differences in migration or clinical results between the groups.

CONCLUSION

Uncemented fixation with titanium fiber mesh coating of the femoral component in total knee arthroplasty works equally as well as cemented fixation up to 10 years. An annual migration of 0.1 mm seems compatible with excellent long-term performance.

LEVEL OF EVIDENCE

I.

Total knee replacement: intraoperative and postoperative kinematic assessment

BACKGROUND AND AIM

The main goals of the total knee arthroplasty (TKA) is to reduce the perceived pain and  restore knee mobility and function in case of osteoarthritic knees joints. Literature shows how the three major causes of TKA failures are related to wear, loosening and instability and this is due to a problem of imbalance and malalignment. Intraoperative and postoperative kinematics analysis could be of benefit for improving surgery outcome. The aim of the present paper is to give an overview of the two set-up with the highest accuracy for intraoperative and postoperative TKA kinematics evaluation, currently in use at Istituto Ortopedico Rizzoli. Introperative and Postoperative Evaluation: For intraoperative evaluation it has been presented a navigation system with a specifically developed software, while for the postoperative it has been presented the roentgen stereophotogrammetric analysis (RSA). The navigation system consists in a laptop connected with an optoelectronic localizer (Polaris, Northern Digital Inc, Canada).  Two reference arrays with passive optical markers and a marked probe are used to localize the knee joint in the 3D space and track the joint kinematics. The RSA is a radiographic technique used in orthopaedic field for measuring micromotion at bone/prosthesis interface or for joint kinematics evaluation. The RSA uses two X-ray sources synchronized with two digital flat-panels.

CONCLUSIONS

The present paper shows that using the navigation system allows the surgeon to easily perform kinematic and alignment evaluation during TKA surgery while the RSA allows a quantitative evaluation of the joint kinematics during the recovery time.

No Difference in Periprosthetic Bone Loss and Fixation Between a Standard-Length Stem and a Shorter Version in Cementless Total Hip Arthroplasty. A Randomized Controlled Trial

BACKGROUND

Cementless femoral stems in total hip arthroplasty provide dependable clinical and radiographic results in the treatment of osteoarthritis. Stem length might affect the preservation of proximal bone stock and stability. We hypothesized that a shorter stem decreases proximal bone loss without affecting implant stability.

METHODS

We randomly assigned 60 patients aged between 50 and 70 years to either a standard cementless femoral stem or a 35-mm shorter version. Patients were followed with dual-energy X-ray absorptiometry, radiostereometric analysis, Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index score, and clinical follow-up at 3, 6, 12, and 24 months. The trial is registered on ClinicalTrials.gov/.

RESULTS

After 24 months, short stems had on average 3.8% (95% confidence interval, 1.2%-8.9%) more bone loss in zone 1 compared to standard stems (P = .14). In zone 7, the bone loss was on average 6.5% (95% confidence interval, 6.6%-19.7%) higher compared to standard stems (P = .33). After 24 months, standard stems had migrated 0.93 mm (range, 0.25-4.66 mm) and short stems 0.93 mm (range, 0.17-2.96 mm; Student t-test after log transformation, P = .3). Patient-reported outcome measures were similar in both groups. One patient in the standard stem group was diagnosed with infection, one with a posterior dislocation, and one with a deep venous thrombosis. No stems were revised.

CONCLUSION

There were no statistically significant differences in periprosthetic bone loss or fixation between the stems at 24 months.

Reconstructing the anterolateral ligament does not decrease rotational knee laxity in ACL-reconstructed knees

PURPOSE

Little is known about the anterolateral ligament's (ALL) influence on knee laxity. The purpose of this study was to investigate rotational knee laxity against a pure axial rotational stress using radiostereometric analysis (RSA) after cutting and reconstructing both the anterior cruciate ligament (ACL) and the ALL.

METHODS

Eight human donor legs were positioned and stereoradiographically recorded at 0°, 30° and 60° of knee flexion using a motorised fixture, while an internally rotating force of 4 Nm was applied to the foot. Anterior-posterior and rotational laxity were investigated for knees with intact ligaments and compared with those observed after successive ACL and ALL resection and reconstruction.

RESULTS

After cutting the ALL in ACL-deficient knees, the internal rotation was increased in all three knee flexion angles, 0° (p = 0.04), 30° (p = 0.03) and 60° (p < 0.01) by 1.0°, 1.6° and 2.5°, respectively. However, no decrease in laxity was found after reconstructing the ALL in ACL-reconstructed knees.

CONCLUSIONS

The ALL was confirmed as a stabiliser of internal rotation in ACL-deficient knees. However, reconstructing the ALL using a gracilis autograft tendon did not decrease the internal rotation laxity in the ACL-reconstructed knee. Based on the results of this study, we do not recommend reconstructing the ALL in ACL-reconstructed knees to decrease internal knee laxity.

Early Subsidence Predicts Failure of a Cemented Femoral Stem With Minor Design Changes

BACKGROUND

Radiostereometry (RSA) measurements of early micromotion can predict later failure in hip and knee prostheses. In hip implants, RSA has been particularly helpful in the evaluation of composite-beam stem designs. The Spectron EF Primary stem (Smith & Nephew, London, UK) has shown inferior performance compared with its predecessors in both clinical studies and registry reports. Early RSA studies have shown somewhat greater subsidence for the Spectron EF Primary stem compared with the earlier Spectron EF, but still within boundaries considered to be safe.

QUESTIONS/PURPOSES

Our primary research question was whether stem subsidence and rotation for this stem design measured with RSA at 2 years can predict later stem failure. A secondary question was whether high femoral stem offset and small stem sizes, both features specific to the Spectron EF Primary stem compared with its predecessors, are associated with stem failure rate.

METHODS

Two hundred forty-seven hips (209 patients with median age 63 years [range, 29-80 years], 65% female, and 77% primary osteoarthritis) with a valid RSA examination at 2 years were selected from four different RSA studies (totaling 279 hips in 236 patients) in our department. The studies were primarily aimed at evaluating cup fixation, bone cement, and polyethylene types. All study patients received a cemented Spectron EF Primary stem. The selected hips had complete followup until stem failure, death, or the end of the followup period. Stem failure was defined as revision of a loose femoral stem or radiological failure with significant osteolysis in Gruen zones 2 to 6. Cox regression analyses were performed to evaluate if stem subsidence and rotation after 2 years, adjusted for age, sex, stem size, standard/high stem offset, and conventional/highly crosslinked polyethylene, could predict later clinical aseptic failure of the stem. We identified 32 stem failures (27 revisions, five radiological failures) at 14 years median followup (range, 3-18 years). Ten-year stem survival was 94% (95% confidence interval [CI], 90%-96%).

RESULTS

Stem subsidence at 2 years (adjusted hazard ratio [HR], 6.0; 95% CI, 2.5-15; p < 0.001) and retrotorsion of the stem (adjusted HR, 1.7; 95% CI, 1.1-2.5; p = 0.018) were associated with later stem failure. Further risk factors were male sex (subsidence analysis HR, 6.9; p > 0.001), use of the two smallest stem sizes (HRsize 1, 8.0; p > 0.001, HRsize 2, 1 [reference], HRsize 3+, 0.06; p = 0.035), and the high offset option (HR, 3.1; p = 0.005).

CONCLUSIONS

Stem subsidence and retrotorsion at 2 years can predict later failure in the Spectron EF Primary stem, consistent with earlier findings on composite-beam cemented stems. Small stem size and high-offset stems comprise the main group of underperforming stems. We recommend that premarket small-scale RSA studies be performed after any design change to a THA femoral component, because even seemingly minor design changes may unexpectedly result in inferior performance.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Migration and head penetration of Vitamin-E diffused cemented polyethylene cup compared to standard cemented cup in total hip arthroplasty: study protocol for a randomised, double-blind, controlled trial (E1 HIP)

INTRODUCTION

In vitro, Vitamin-E-diffused, highly cross-linked polyethylene (PE) has been shown to have superior wear resistance and improved mechanical properties when compared to those of standard highly cross-linked PE liners used in total hip arthroplasty (THA). The aim of the study is to evaluate the safety of a new cemented acetabular cup with Vitamin-E-doped PE regarding migration, head penetration and clinical results.

METHODS AND ANALYSIS

In this single-centre, double-blinded, randomised controlled trial, we will include 50 patients with primary hip osteoarthritis scheduled for THA and randomise them in a 1:1 ratio to a cemented cup with either argon gas-sterilised PE (control group) or Vitamin-E-diffused PE (vitamin-e group). All patients and the assessor of the primary outcome will be blinded and the same uncemented stem will be used for all participants. The primary end point will be proximal migration of the cup at 2 years after surgery measured with radiostereometry. Secondary end points include proximal migration at other follow-ups, total migration, femoral head penetration, clinical outcome scores and hip-related complications. Patients will be followed up at 3 months and at 1, 2, 5 and 10 years postoperatively.

RESULTS

Results will be analysed using 95% CIs for the effect size. A regression model will also be used to adjust for stratification factors.

ETHICS AND DISSEMINATION

The ethical committee at Karolinska Institutet has approved the study. The first results from the study will be disseminated to the medical community via presentations and publications in relevant medical journals when the last patient included has been followed up for 2 years.

TRIAL REGISTRATION NUMBER

NCT02254980.

Effects of exercise therapy for the treatment of symptomatic full-thickness supraspinatus tears on in vivo glenohumeral kinematics

BACKGROUND

The high incidence of rotator cuff disease combined with high failure rates for nonoperative treatment of full-thickness rotator cuff tears underlines the importance of improving nonoperative management of rotator cuff tears. The study objective was to assess changes in in vivo glenohumeral kinematics of patients with a symptomatic full-thickness supraspinatus tear before and after a 12-week exercise therapy program. It was hypothesized that successful exercise therapy would result in improved kinematics (smaller translations and increased subacromial space).

MATERIALS AND METHODS

Five patients were recruited for the study and underwent dynamic stereoradiography analysis before and after a 12-week exercise therapy protocol to measure changes in glenohumeral joint translations and subacromial space during coronal plane abduction. Strength and patient-reported outcomes (American Shoulder and Elbow Surgeons; Disabilities of the Arm, Shoulder and Hand; Western Ontario Rotator Cuff Index) were also evaluated.

RESULTS

After therapy, no subject went on to receive surgery. It was found that the contact path length of the humerus translating on the surface of the glenoid was reduced by 29% from 67.2% ± 36.9% glenoid height to 43.1% ± 26.9% glenoid height (P = .036) after therapy. Minimum acromiohumeral distance showed a small increase from 0.9 ± 0.6 mm to 1.3 ± 0.8 mm (P = .079). Significant improvements in strength and patient-reported outcomes were also observed (P < .05).

CONCLUSIONS

Successful exercise therapy for treatment of small full-thickness supraspinatus tears results in improvements in glenohumeral joint kinematics and patient-reported outcomes through increases in rotator cuff muscle strength and joint stability. This study may enable identification of prognostic factors that predict the response of a patient with a rotator cuff tear to exercise therapy.

Development and validation of an automated and marker-free CT-based spatial analysis method (CTSA) for assessment of femoral hip implant migration: In vitro accuracy and precision comparable to that of radiostereometric analysis (RSA)

BACKGROUND AND PURPOSE

We developed a marker-free automated CT-based spatial analysis (CTSA) method to detect stem-bone migration in consecutive CT datasets and assessed the accuracy and precision in vitro. Our aim was to demonstrate that in vitro accuracy and precision of CTSA is comparable to that of radiostereometric analysis (RSA).

MATERIAL AND METHODS

Stem and bone were segmented in 2 CT datasets and both were registered pairwise. The resulting rigid transformations were compared and transferred to an anatomically sound coordinate system, taking the stem as reference. This resulted in 3 translation parameters and 3 rotation parameters describing the relative amount of stem-bone displacement, and it allowed calculation of the point of maximal stem migration. Accuracy was evaluated in 39 comparisons by imposing known stem migration on a stem-bone model. Precision was estimated in 20 comparisons based on a zero-migration model, and in 5 patients without stem loosening.

RESULTS

Limits of the 95% tolerance intervals (TIs) for accuracy did not exceed 0.28 mm for translations and 0.20° for rotations (largest standard deviation of the signed error (SD(SE)): 0.081 mm and 0.057°). In vitro, limits of the 95% TI for precision in a clinically relevant setting (8 comparisons) were below 0.09 mm and 0.14° (largest SD(SE): 0.012 mm and 0.020°). In patients, the precision was lower, but acceptable, and dependent on CT scan resolution.

INTERPRETATION

CTSA allows detection of stem-bone migration with an accuracy and precision comparable to that of RSA. It could be valuable for evaluation of subtle stem loosening in clinical practice.

Radiostereometric and Radiographic Analysis of Glenoid Component Motion After Total Shoulder Arthroplasty

Aseptic glenoid component loosening is a common cause of total shoulder arthroplasty (TSA) failure, but early detection is difficult because pain often appears late and radiolucent lines are of uncertain significance. This study sought to answer the following questions: (1) What types of glenoid component motion may be observed during the first 3 years following implantation?; (2) Is the appearance of radiolucent lines around the glenoid component a reliable indicator of component motion?; and (3) Are clinical outcomes correlated with early glenoid component motion within the first 3 years after TSA? Eleven patients (mean age, 60.6 years) underwent TSA using a cemented, all-polyethylene glenoid component with tantalum bead implantation. Clinical outcomes (American Shoulder and Elbow Surgeons [ASES] score, visual analog scale [VAS] pain score, and range of motion) were compared pre- and postoperatively, and radiolucencies were graded according to the criteria of Lazarus et al. Patients were evaluated using radiostereometric analysis at 6 months and 1, 2, and 3 years postoperatively to measure component micromotion in translation and rotation. At a mean follow-up of 50.2 months, mean ASES score had improved from 30.3 to 81.3 (P<.001), mean VAS pain score had improved from 8 to 1 (P<.001), active forward flexion had improved from 109° to 155° (P=.001), active external rotation had improved from 28° to 54° (P=.003), and internal rotation had improved from the level of the sacrum to L3 (P=.002). Radiolucencies were detected around none of the components at 1 year, 6 components at 2 years, and 5 components at 3 years, and these radiolucencies were mostly found around components that experienced high levels of rotational motion.

Tibial component alignment and risk of loosening in unicompartmental knee arthroplasty: a radiographic and radiostereometric study

PURPOSE

Unicompartmental knee arthroplasty (UKA) has shown a higher rate of revision compared with total knee arthroplasty. The success of UKA depends on prosthesis component alignment, fixation and soft tissue integrity. The tibial cut is the crucial surgical step. The hypothesis of the present study is that tibial component malalignment is correlated with its risk of loosening in UKA.

METHODS

This study was performed in twenty-three patients undergoing primary cemented unicompartmental knee arthroplasties. Translations and rotations of the tibial component and the maximum total point motion (MTPM) were measured using radiostereometric analysis at 3, 6, 12 and 24 months. Standard radiological evaluations were also performed immediately before and after surgery. Varus/valgus and posterior slope of the tibial component and tibial-femoral axes were correlated with radiostereometric micro-motion. A survival analysis was also performed at an average of 5.9 years by contacting patients by phone.

RESULTS

Varus alignment of the tibial component was significantly correlated with MTPM, anterior tibial sinking, varus rotation and anterior and medial translations from radiostereometry. The posterior slope of the tibial component was correlated with external rotation. The survival rate at an average of 5.9 years was 89%. The two patients who underwent revision presented a tibial component varus angle of 10° for both.

CONCLUSIONS

There is correlation between varus orientation of the tibial component and MTPM from radiostereometry in unicompartmental knee arthroplasties. Particularly, a misalignment in varus larger than 5° could lead to risk of loosening the tibial component.

LEVEL OF EVIDENCE

Prognostic studies-retrospective study, Level II.

Measuring polyethylene wear in total knee arthroplasty by RSA: differences between weight-bearing and non-weight-bearing positioning

Measuring the minimum-joint-space-width (mJSW) in total knee arthroplasty (TKA) in Roentgen stereophotogrammetric analysis (RSA) provides valuable information on polyethylene wear, a leading cause for TKA failure. Most existing studies use non-weight-bearing (NWB) patient positioning. The latter may compromise mJSW measurements due to knee laxity with subsequent non-contact between the TKA components. We investigated the difference in mJSW between weight-bearing (WB) and NWB images and the association with mediolateral (ML) knee stability. At one-year follow-up, 23 TKAs were included from an ongoing RSA study, and ML stability was evaluated. For each examination, the mJSW and femoral-tibial contact locations were measured. A linear regression model was used to analyze the association between the mJSW difference (NWB-WB) with the ML stability and contact locations. The mean mJSW difference was 0.28 mm medially and 0.20 mm laterally. Four TKAs had medium (5-9°) and 19 TKAs had high (<5°) ML stability. A higher mJSW difference was found for TKAs with medium stability (0.36 mm, P = 0.01). In conclusion, mJSW measurements in existing (NWB) RSA studies are influenced by knee laxity, but may still provide information on wear progression based on TKA with high ML stability. A direct comparison of mJSW measurements from WB and NWB data is not possible.

Low wear of a second-generation highly crosslinked polyethylene liner: a 5-year radiostereometric analysis study

BACKGROUND

A sequentially irradiated and annealed, second-generation highly crosslinked polyethylene (XLPE) liner was introduced clinically in 2005 to reduce in vivo oxidation. This liner design has also been shown to reduce wear in vitro when compared with conventional and first-generation crosslinked liners. To date, there is only one study reporting an in vivo wear rate of this liner at 5 years' followup. However, that study used measurements made from plain radiographs, which have limited sensitivity, particularly when monitoring very low amounts of wear.

QUESTIONS/PURPOSES

What is the amount and direction of wear at 5 years using radiostereometric analysis (RSA) in patients who had THAs that included second-generation XLPE?

METHODS

We prospectively reviewed 21 patients who underwent primary cementless THA with the same design of XLPE acetabular liner and 32-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographs at 1 week, 6 months, and 1, 2, and 5 years postoperatively. Femoral head penetration within the acetabular component was measured with UmRSA(®) software. One patient died and two had incomplete radiographs leaving 18 radiographic series for analysis.

RESULTS

The mean amounts of proximal, two-dimensional, and three-dimensional head penetration between 1 week and 5 years were 0.018, 0.071, and 0.149 mm, respectively. The mean proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 5 years were all less than 0.001 mm/year with no patient recording a wear rate of more than 0.040 mm/year.

CONCLUSIONS

The head penetration of a second-generation XLPE liner remained low at 5 years and the wear rate calculated after the first year was low in all directions. This low level of wear remains encouraging for the future clinical performance of this material.

Early migration of the cemented tibial component of unicompartmental knee arthroplasty: a radiostereometry study

PURPOSE

Unicompartmental knee arthroplasty has good clinical results but high revision rates. A unicompartmental knee arthroplasty design features an all-polyethylene and conforming tibial component, and we hypothesized that this may put at risk its fixation. Implant-to-bone micromotion was measured together with relevant clinical outcomes.

METHODS

The migration of the tibial component in twenty patients was measured at 3, 6, 12 and 24 months, using standard radiostereometry, along with the relevant clinical outcomes using the IKS scoring system.

RESULTS

The eighteen arthroplasties at 24 months were found successful, with very good functional (mean 87.7; SD 15.4) and knee scores (mean 94.8; SD 10.1). The means and the standard deviations of the maximum total point motion (MTPM) for the four follow-ups were, respectively, as small as 0.4 ± 0.1 mm, 0.6 ± 0.2 mm, 0.6 ± 0.3 mm and 0.7 ± 0.3 mm, an average over all patients but one. In this knee, these were 1.6, 2.1, 2.4 and 2.2 mm, therefore not at high risk of aseptic loosening according to the literature. Only one knee was found at this risk, having the MTPM from 12 to 24 months of 0.5 mm, and the component moving and sinking medially, and rising laterally.

CONCLUSION

At 2-year follow-up, a successful implant-to-bone fixation can be achieved in conforming all-polyethylene cemented tibial component together with excellent clinical outcomes.

Expectations and outcome of a scientifically developed hip prosthesis in 170 hips with a follow-up of 5-12 years

Roentgen stereophotogrammetric analysis (RSA) is commonly used to assess prosthetic stability as a predictor of the long-term clinical outcome of new total hip systems. Although the RSA technique is very accurate, it may not be trivial to interpret migration rates into clinical outcome, as critical migration rates depend heavily on the design of the prosthesis. In the present study we describe the clinical results of the Scientific Hip Prosthesis (SHP), which had unexpectedly high migration values in a clinical RSA study. We evaluated the clinical results of a single surgeon study consisting of 170 hips with a follow-up of 5-12 years (mean: 83 years). The survival rate was 98.8% at ten years for aseptic loosening of the stem. This study therefore indicates that a prosthetic design may function clinically rather well although relatively high migration rates have been reported. The prediction of clinical survival of new prosthetic components remains a challenging task and the interpretation of migration rates with new designs should be considered with much caution.

The early migration of a partially cemented fluted pegged glenoid component using radiostereometric analysis

BACKGROUND

Radiostereometric analysis measures the position of rigid bodies in 3 dimensions with very high precision and can be used to measure early micromotion of glenoid implants.

MATERIALS AND METHODS

Radiostereometric analysis was used to measure migration of 11 partially cemented fluted pegged glenoid components in patients with osteoarthritis who underwent shoulder arthroplasty during a 2-year period. Patients were evaluated using the American Shoulder and Elbow Surgeons (ASES) and Constant scores and by a computed tomography (CT) scan at the 2-year follow-up.

RESULTS

Migration patterns could be classified into 2 groups: The first group showed little if any migration, the second group rotated by 4° or more as early as 3 months after operation. The maximum total point motion reached up to 2 mm by the 6-month follow-up. At 12 months, the 2 groups could be identified by the presence or absence of focal lucency around the central peg. At the end of 2 years, CT scans were able to classify the same 2 migration patterns by the presence or absence of osseointegration around the cementless central peg of the glenoid implant. The clinical effect of the absence of osseointegration in this novel glenoid component is unknown because both groups had similar clinical results at 2 years.

CONCLUSION

Rapid early migration associated with focal lucency and absence of osseointegration was observed in 6 of 11 components. We postulate that lack of initial fixation leads to early movement of the glenoid component and failure of osseointegration.

Fixation of the fully hydroxyapatite-coated Corail stem implanted due to femoral neck fracture: 38 patients followed for 2 years with RSA and DEXA

BACKGROUND

Today, dislocated femoral neck fractures are commonly treated with a cemented hip arthroplasty. However, cementing of the femoral component may lead to adverse effects and even death. Uncemented stems may lower these risks and hydroxyapatite (HA) coating may enhance integration, but prosthetic stability and clinical outcome in patients with osteoporotic bone have not been fully explored. We therefore studied fixation and clinical outcome in patients who had had a femoral neck fracture and who had received a fully HA-coated stem prosthesis.

PATIENTS AND METHODS

50 patients with a dislocated femoral neck fracture were operated with the fully HA-coated Corail total or hemiarthroplasty. 38 patients, mean age 81 (70-96) years, were followed for 24 months with conventional radiographs, RSA, DEXA, and for clinical outcome.

RESULTS

31 of the 38 implants moved statistically significantly up to 3 months, mainly distally, mean 2.7 mm (max. 20 mm (SD 4.3)), and rotated into retroversion mean 3.3º (-1.8 to 17) (SD 4.3) and then appeared to stabilize. Distal stem migration was more pronounced if the stem was deemed to be too small. There was no correlation between BMD and stem migration. The migration did not result in any clinically adverse effects.

INTERPRETATION

The fully hydroxyapatite-coated Corail stem migrates during the first 3 months, but clinical outcome appears to be good, without any adverse events.

The effects of different weight-bearing regimes on press-fit cup stability: a randomised study with five years of follow-up using radiostereometry

PURPOSE

There is little evidence to support immediate weight bearing after uncemented total hip arthroplasty (THA).

METHODS

Thirty-seven patients with unilateral osteoarthritis of the hip received a press-fit cup. Cup stability was assessed with radiostereometry (RSA) over five years. Patients were randomised to immediate full weight bearing, or partial weight bearing for three months.

RESULTS

At five years, we found no difference in micro-motion as assessed with radiostereometry. Numerically, there was more proximal translation and increased inclination with immediate weight bearing, but these values barely exceeded the precision limit for the method. Pooled data for the two groups revealed translations of 0.1-0.3 mm and rotations of 0.2-0.3° over the five year follow-up period.

CONCLUSIONS

We found no adverse effects of immediate weight bearing after THA in relation to stability of these press-fit cups. Early mobilisation might have other advantages.