No radiological and clinical advantages with patient-specific positioning guides in total knee replacement

Enhancing Surgical Efficiency and Radiological Outcomes Through Advances in Patient-Specific Instrument Design

Background/Objectives: Patient-specific instrumentation (PSI) in total knee arthroplasty (TKA) uses preoperative three-dimensional imaging to create cutting blocks tailored to patient anatomy. However, there is debate regarding the additional benefits of PSI in terms of improved alignment or functional outcomes compared to using conventional instruments. Although PSI design has undergone continuous development, the improvements have not been incorporated. Therefore, the aim of this study was to compare the surgical time and radiological outcomes between advanced-design PSI and conventional instruments. Methods: We conducted a retrospective review of 328 patients who underwent primary TKAs using PSI for osteoarthritis and compared them with 328 matched patients who underwent TKA performed with conventional instruments during the same period (March 2023 to August 2024). We compared the surgical time and component alignment between the advanced-design PSI group and the conventional instrument group. Results: The average surgical time was significantly shorter in the advanced-design PSI group (47.6 ± 12.4 min) compared to the conventional instrument group (59.2 ± 14.2 min, p < 0.05). The advanced PSI design group had a significantly lower occurrence of outliers in hip-knee-ankle alignment (7%) compared to the conventional instrument group (36.3%). This trend was also observed in femoral coronal alignment, tibial coronal alignment, and femoral sagittal alignment. Conclusions: The use of advanced-design PSI demonstrated significantly reduced surgical time and improved alignment compared to conventional instruments. This highlights that proper design is a key factor for PSI to achieve superior biomechanical effects. Our study shows that advanced-design PSI technology has the potential to replace conventional instruments in TKA, though further research is required to determine its clinical outcomes and economic benefits.

The efficacy and safety of patient-specific instrumentation in primary total knee replacement: a systematic review and meta-analysis

INTRODUCTION

Patient-specific instrumentation (PSI) for primary total knee arthroplasty (TKA) surgery has been shown to increase accuracy of component positioning. However, it is unclear whether this also translates to actual benefits for patients in terms of better outcomes (efficacy) or less complications such as revisions (safety). We therefore systematically reviewed the literature to determine the efficacy and safety of PSI in primary TKA.

METHODS

Randomized controlled trials comparing PSI to non-PSI in primary TKA were included. A random effects model was used with meta-regression in case of heterogeneity.

RESULTS

Forty-three studies were included with a total of 1816 TKA in the PSI group and 1887 TKA in the control group. There were no clinically relevant differences between the PSI-group and non-PSI group regarding all outcomes. There was considerable heterogeneity: meta-regression analyses showed that the year the study was published was an important effect modifier. Early publications tended to show a positive effect for PSI compared to non-PSI TKA, whereas later studies found the opposite.

CONCLUSION

Based on evidence of moderate certainty, our study suggested that there were no clinically relevant differences in efficacy and safety between patients treated with PSI TKA and patients treated with non-PSI TKA.

Functional outcomes in patient specific instrumentation vs. conventional instrumentation for total knee arthroplasty; a systematic review and meta-analysis of prospective studies

Background

Total Knee Arthroplasty (TKA) is an established surgical option for knee osteoarthritis (OA). There are varying perceptions of the most suitable surgical technique for making bone cuts in TKA. Conventional Instrumentation (CI) uses generic cutting guides (extra- and intra-medullary) for TKA; however, patient specific instrumentation (PSI) has become a popular alternative amongst surgeons.

Methods

A literature search of electronic databases Embase, Medline and registry platform portals was conducted on the 16^th May 2021. The search was performed using a predesigned search strategy. Eligible studies were critically appraised for methodological quality. The primary outcome measure was Knee Society Function Score. Functional scores were also collected for the secondary outcome measures: Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Visual Analog Scale (VAS) for pain. Review Manager 5.3 was used for all data synthesis and analysis.

Results

There is no conclusive evidence in the literature to suggest that PSI or CI instrumentation is better for functional outcomes. 23 studies were identified for inclusion in this study. Twenty-two studies (18 randomised controlled trials and 4 prospective studies) were included in the meta analysis, with a total of 2277 total knee arthroplasties. There were 1154 PSI TKA and 1123 CI TKA. The majority of outcomes at 3-months, 6-months and 12 show no statistical difference. There was statistical significance at 24 months in favour of PSI group for KSS function (mean difference 4.36, 95% confidence interval 1.83–6.89). The mean difference did not exceed the MCID of 6.4. KSS knee scores demonstrated statistical significance at 24 months (mean difference 2.37, 95% confidence interval (CI) 0.42—4.31), with a MCID of 5.9. WOMAC scores were found to be statistically significant favouring PSI group at 12 months (mean difference -3.47, 95% confidence interval (CI) -6.57- -0.36) and 24 months (mean difference -0.65, 95% confidence interval (CI) -1.28—-0.03), with high level of bias noted in the studies and a MCID of 10.

Conclusions

This meta-analysis of level 1 and level 2 evidence shows there is no clinical difference when comparing PSI and CI KSS function scores for TKA at definitive post operative time points (3 months, 6 months, 12 months and 24 months). Within the secondary outcomes for this study, there was no clinical difference between PSI and CI for TKA. Although there was no clinical difference between PSI and CI for TKA, there was statistical significance noted at 24 months in favour of PSI compared to CI for TKA when considering KSS function, KSS knee scores and WOMAC scores. Studies included in this meta-analysis were of limited cohort size and prospective studies were prone to methodological bias. The current literature is limited and insufficiently robust to make explicit conclusions and therefore further high-powered robust RCTs are required at specific time points.

Minimum 5-Year Outcomes of a Multicenter, Prospective, Randomized Control Trial Assessing Clinical and Radiological Outcomes of Patient-Specific Instrumentation in Total Knee Arthroplasty

BACKGROUND

Patient-specific instrumentation (PSI) was developed to produce more accurate alignment of components and consequently improve clinical outcomes when used in total knee arthroplasty. We compare radiological accuracy and clinical outcomes at a minimum of 5-year follow-up between patients randomized to undergo total knee arthroplasty performed using PSI or traditional cutting block techniques.

METHODS

This multicenter, randomized control trial included patients blinded to the technique 1used. Outcome measures were coronal alignment measured radiologically, Euroqol-5D, Oxford knee score, and International Knee Society Score measured at 1- and 5-year follow-up.

RESULTS

At a minimum 5-year follow-up, there were 38 knees in the PSI group and 39 in the conventional instrumentation group for analysis. Baseline demographics and clinical outcome scores were matched between groups. Overall, there was no significant difference in the coronal femoral angle (P = .59), coronal tibial angle (P = .37), tibiofemoral angle (P = .99), sagittal femoral angle (P = .34), or the posterior tibia slope (P = .12) between knees implanted using PSI and those implanted with traditional cutting blocks. On the measurement of coronal alignment, intraobserver reliability tests demonstrated substantial agreement (k = 0.64). Clinical outcomes at both 1-year and 5-year follow-up demonstrated statistically significant and clinically relevant improvement in scores from baseline in both groups, but no difference could be detected between the Euroqol-5D (P = .78), Oxford knee score (P = .24), or International Knee Society Score (P = .86) between the 2 groups.

CONCLUSION

This study has shown no additional benefit to PSI in terms of improved alignment or functional outcomes at minimum 5-year follow-up over traditional techniques.

Fragility Index as a Measure of Randomized Clinical Trial Quality in Adult Reconstruction: A Systematic Review

Background

The Fragility Index (FI) and Reverse Fragility Index are powerful tools to supplement the P value in evaluation of randomized clinical trial (RCT) outcomes. These metrics are defined as the number of patients needed to change the significance level of an outcome. The purpose of this study was to calculate these metrics for published RCTs in total joint arthroplasty (TJA).

Methods

We performed a systematic review of RCTs in TJA over the last decade. For each study, we calculated the FI (for statistically significant outcomes) or Reverse Fragility Index (for nonstatistically significant outcomes) for all dichotomous, categorical outcomes. We also used the Pearson correlation coefficient to evaluate publication-level variables.

Results

We included 104 studies with 473 outcomes; 92 were significant, and 381 were nonstatistically significant. The median FI was 6 overall and 4 and 7 for significant and nonsignificant outcomes, respectively. There was a positive correlation between FI and sample size (R = 0.14, P = .002) and between FI and P values (R = 0.197, P = .000012).

Conclusions

This study is the largest evaluation of FI in orthopedics literature to date. We found a median FI that was comparable to or higher than FIs calculated in other orthopedic subspecialties. Although the mean and median FIs were greater than the 2 recommended by the American Academy of Orthopaedic Surgeons Clinical Practice Guidelines to demonstrate strong evidence, a large percentage of studies have an FI < 2. This suggests that the TJA literature is on par or slightly better than other subspecialties, but improvements must be made.

Level of Evidence

Level I; Systematic Review.

Fewer femoral rotational outliers produced with CT- than with MRI-based patient-specific instrumentation in total knee arthroplasty

PURPOSE

Previous studies comparing the surgical accuracy between computed tomography (CT)- and magnetic resonance imaging (MRI)-based patient-specific instrumentation (PSI) methods have produced contradictory results. The aim of this study was to determine which is the more reliable imaging method (CT versus MRI) for patient-specific total knee arthroplasty (TKA). CT-based PSI is hypothesised to have an advantage regarding the number of outliers.

METHODS

A total of 22 randomised controlled trials (RCTs), including 1749 TKA cases, were eligible for the meta-analysis. RCTs, systematic reviews and meta-analyses on this topic published in databases before September 2018 were identified by a literature search. The primary outcome was the number of lower extremities with greater than 3° of difference in alignment angles between the postoperative outcomes and target outcomes. The parameters calculated from the meta-analysis included risk ratios (RRs) and 95% confidence intervals (CIs). Additionally, the publication bias and heterogeneity of the studies were assessed.

RESULTS

The risk of femoral rotational outliers in the PSI group (RR = 0.48; 95% CI 0.24-0.98) was significantly reduced. Furthermore, subgroup analysis showed that the accuracy in the CT-based PSI group was significantly higher than that in the MRI-based CSI group (RR = 0.31; 95% CI 0.10-0.92).

CONCLUSION

This meta-analysis shows that when performing TKA with PSI, preoperative CT is beneficial for the production of the PSI, resulting in a significantly lower proportion of outliers in femoral rotational alignment. CT should be the preferred choice for imaging when performing TKA surgery with PSI to obtain better femoral rotational alignment.

LEVEL OF EVIDENCE

Therapeutic study (systematic review and meta-analysis), Level I.

Patient-Specific or Conventional Instrumentations: A Meta-analysis of Randomized Controlled Trials

Objective

To conduct a meta-analysis of randomized controlled trials (RCTs) to compare knee arthroplasty with patient-specific instrumentation (PSI) with the conventional instrumentation (CI).

Methods

RCTs were selected in PubMed and Embase from 2012 to 2018. Key data extracted included malalignment of mechanical axis, blood loss, surgical time, Oxford Knee Score (OKS), Knee Society Score (KSS), length of stay, and complications. Subgroup analysis was also performed regarding different PSI systems and different image processing methods.

Results

29 RCTs with 2487 knees were eligible for the meta-analysis. Results showed that PSI did not improve the alignment of the mechanical axis compared with CI, but MRI-based PSI and Visionaire-specific PSI decrease the risk of malalignment significantly (P = 0.04 and P = 0.04 and P = 0.04 and P = 0.04 and P = 0.04 and

Conclusion

PSI reduced the blood loss and improved KSS. MRI-based PSI reduced operative time and risk of malalignment of mechanical axis compared with CT-based PSI. Moreover, Visionaire-specific PSI achieves better alignment result of the mechanical axis than other systems.

Clinical outcomes of two-stage total knee arthroplasty using articulating cement spacer in patients with infected arthritic knee: A comparison with arthroscopic surgery

BACKGROUND

The aim of this study was to compare the functional outcomes and recurrence rate of infection between patients who underwent arthroscopic surgery and two-stage total knee arthroplasty (TKA) for infected arthritic knees.

METHODS

A retrospective analysis was conducted on 52 patients (52 knees) with advanced knee joint arthritis who underwent arthroscopic surgery or two-stage TKA using articulating cement spacer (ACS) for knee joint infection between January 2009 and November 2013. Of the 52 patients (52 knees), 38 and 14 patients underwent arthroscopic surgery (AS group) and two-stage TKA using ACS (ACS-TKA group), respectively. Patient-reported outcomes (Knee Injury and Osteoarthritis Outcome Score (KOOS) and EuroQol-Visual Analog Scales (EQ-VAS)); range of motion; and recurrence rate of infection were evaluated.

RESULTS

Recurrence of infection was observed in 7/38 patients who underwent arthroscopic surgery, all of whom received two-stage TKA using ACS. Regarding the functional outcomes of the ACS-TKA group obtained before conversion to TKA and those of the AS group obtained six months after arthroscopic surgery, the former group had better outcomes for KOOS pain, KOOS activities of daily living, KOOS quality of life, and EQ-VAS. Regarding the functional outcomes of the ACS-TKA group obtained during the last follow-up and after conversion to TKA and those of the AS group who underwent TKA after arthroscopic surgery, no significant between-group differences were observed. The infection recurrence rate was higher in the AS than in the ACS-TKA group.

CONCLUSIONS

Considering infection control and functional outcomes, two-stage TKA using ACS can be an effective alternative treatment for patients with infected arthritic knees.

Total knee arthroplasty using patient-specific instrumentation for osteoarthritis of the knee: a meta-analysis

BACKGROUND

Total knee arthroplasty using patient-specific instrumentation (TKA-PSI), which are disposable cutting block guides generated to fit each patient's 3-dimensional knee anatomy, has been developed to treat patients with end-stage osteoarthritis of the knee. Surrogate markers such as radiographic malalignment have been well investigated, however, patient-important outcomes are not well examined to elucidate the efficacy of TKA-PSI. The aim of this review is to determine if TKA-PSI improves patient-reported outcome measures (PROM), surgery time, blood loss, transfusion and complications (e.g. surgical site infection, deep venous thrombosis, and revision TKA).

METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and ongoing clinical trials. For PROMs, surgery time, blood loss, and transfusion rate, we included randomized controlled trials (RCT) comparing TKA-PSI and standard TKA to treat osteoarthritis of the knee. For complications, we also included non-randomized comparative studies (non-RCT).

RESULTS

This review includes 38 studies, 24 of which were RCT and 14 of which were non-RCT. These included a total of 3487 patients. The predominant population in the included studies highly reflected the general population, with 62% being female, aged over 60 and having end-stage osteoarthritis of the knee. TKA-PSI did not improve PROMs as compared to standard TKA for less than 1-year (mean difference 0.48, 95% confidence interval (CI) -1.92-0.97 in the Oxford knee score, mean 3-month follow-up) and for 1-year or more (mean difference 0.25, 95%CI - 4.39-4.89 in the WOMAC score, mean 29-month follow-up). TKA-PSI did not reduce surgery time (mean difference - 3.09 min, 95%CI -6.73-0.55). TKA-PSI decreased blood loss with a small effect size corresponding to a 0.4 g/dl hemoglobin decrease (95%CI 0.18-0.88), but did not decrease transfusion rate (risk difference - 0.04, 95%CI -0.09-0.01). TKA-PSI did not reduce complication rates (risk difference 0.00, 95%CI - 0.01-0.01 in the composite outcome).

CONCLUSIONS

TKA-PSI does not improve patient-reported outcome measures, surgery time, and complication rates as compared to standard TKA. TKA-PSI decreases blood loss with a small effect, which is not enough to reduce transfusion rate.

Accuracy of patient-specific instrumentation in shoulder arthroplasty: a systematic review and meta-analysis

Background

There has been significant recent emphasis on the use of patient-specific instrumentation (PSI) in shoulder arthroplasty. However, clinical data are lacking to support the increased time and expense associated with PSI. Our purposes were to determine whether PSI significantly improves implantation accuracy during total shoulder arthroplasty (TSA) and to analyze available techniques and correlation with clinical outcomes. We hypothesized that PSI may improve glenoid component position radiographically but without correlation with clinical outcomes.

Methods

The MEDLINE, Scopus, Embase, and Cochrane Library databases were queried. Included articles reported use of any preoperative or intraoperative PSI techniques, models, or guides to assist with TSA prosthesis implantation. The primary outcomes were mean deviation from the preoperative plan in version (in degrees), inclination (in degrees), and entry-point offset on the glenoid (in millimeters).

Results

Among the included articles, 518 TSA procedures (352 anatomic and 166 reverse) were performed. The mean postoperative errors in both version and inclination angles were 5° or less in 20 articles (90.9%) using PSI. Meta-analysis revealed no statistically significant differences in version error (P > .999, I ² = 64.6%), inclination error (P = .702, I ² = 82.2%), or positional offset (P = .777, I ² = 85.7%) between PSI and standard instrumentation. No data regarding patient-reported outcome measures, range of motion, strength, or glenoid component loosening and longevity were reported.

Conclusions

Meta-analysis revealed no significant differences in accuracy between PSI and standard instrumentation. Although PSI may possess the potential to improve TSA techniques, further investigations regarding long-term clinical outcomes, impact on operating room time, and cost-effectiveness are warranted before PSI can be routinely recommended over conventional instrumentation.

Agreement in component size between preoperative measurement, navigation and final implant in total knee replacement

Background

One of the possible causes of dissatisfaction reported by many patients after total knee replacement (TKR) is the lack of agreement between component size and bone structure. To avoid this complication and facilitate the procedure, preoperative planning with digitized templates is recommended. Surgical navigation indicates the best position and the most adequate size of arthroplasty and may therefore replace preoperative radiographic measurement. The objective of the study was to check agreement between the sizes of TKR components measured before surgery with digitized templates, the size recommended by the navigation and sizes actually implanted.

Methods

In 103 patients scheduled for TKR, preoperative full-limb radiography was performed to measure the mechanical and anatomical axes of the limb, femur and tibia. The most adequate size of the femoral and tibial components was planned by superimposing digitized templates. The size recommended in navigation and the size of the finally implanted components were also recorded.

Results

A high level of agreement was found between the sizes of femoral and tibial components measured by X-rays and in navigation (0.750 and 0.772, respectively) (intraclass correlation and Cronbach's alpha). Agreement between the sizes recommended by X-rays and navigation and those finally implanted was 0.886 for the femur and 0.891 for the tibia. Agreement levels were not different in cases with prior deformities of limb axis.

Conclusions

The high level of agreement found in component sizes between radiographic measurement with digitized templates and navigation suggests that preoperative X-ray measurement is not needed when navigation is used for placement of implants during TKR.

The translational potential of this article

Computer-assisted surgery may avoid preoperative measurement with templates in TKR.

Patient-Specific Instrumentation Does Not Affect Rotational Alignment of the Femoral Component and Perioperative Blood Loss in Total Knee Arthroplasty: A Prospective, Randomized, Controlled Trial

BACKGROUND

Proposed aims of patient-specific instrumentation (PSI) for total knee arthroplasty (TKA) are to improve accuracy of component alignment, while reducing blood loss and surgical time. The primary goal of this prospective, randomized, controlled, clinical trial is to verify whether PSI improves the rotational alignment of the femoral component in comparison to conventionally implanted TKA.

METHODS

One-hundred thirty-three consecutive patients were assessed for eligibility. Block randomization was performed to allocated patients in the treatment (PSI) or control group. During hospital stay, surgical times were recorded, and total blood volume loss and estimated red blood cell were calculated. Two months after surgery, a computed tomography of the knee was obtained to measure femoral component rotation to the transepicondylar axis and tibial component slope.

RESULTS

Sixty-nine patients were enrolled. PSI did neither result in a significant improvement in femoral component rotation nor result in a reduction of outliers, as compared with conventional instrumentation. No significant improvement in terms of tibial slope, blood loss, total surgical time, and ischemia time could be identified. The number of tibial recuts required in the PSI group was significantly higher than in the control group (P = .0003).

CONCLUSION

PSI does not improve the accuracy of femoral component rotation in TKA in comparison to conventional instrumentation. Moreover, PSI did not appear to influence any of the other variables investigated as secondary goals by this study. The results of this study do not support its routine use during standard TKA.

LEVEL OF EVIDENCE

Level I, randomized, controlled trial.

Patient-specific instrumentation in total knee arthroplasty

INTRODUCTION

Total knee arthroplasty (TKA) is one of the most commonly performed orthopedic procedures. During the past decade, patient-specific instrumentation (PSI) has been commercially introduced in order to simplify and make TKA surgery more effective, precise and efficient than conventional mechanical instrumentation (CI) and computer-assisted surgery (CAS). Nevertheless, there are critical arguments against PSI for routine use. The aim of the current manuscript is to describe advantages and limitations of PSI for primary TKA.

AREAS COVERED

By means of a description of the available literature different aspects are discussed (accuracy, clinical and functional outcomes, operative time, blood loss, efficiency and costs).

EXPERT OPINION

Most publications do not claim a significant increase in PSI accuracy over CI, but they also do not postulate PSIs accuracy is worse either. Regarding clinical aspects, PSI did not appear to give any advantage over standard techniques although, equally, it did not appear to show any disadvantages. PSI seems to reduce operative time, could reduce perioperative blood loss and provides logistical benefits in the operation room. Further studies will be required to more thoroughly assess all the advantages and disadvantages of this promising technology as an alternative to CI and CAS.

Patient-specific instrumentation improved axial alignment of the femoral component, operative time and perioperative blood loss after total knee arthroplasty

PURPOSE

The purpose of the present study was to compare patient-specific instrumentation (PSI) with standard instrumentation (SI) in patients undergoing total knee arthroplasty (TKA). PSI is hypothesized to have advantages with respect to component alignment; number of outliers (defined as alignment > 3° from the target alignment); operative time; perioperative blood loss; and length of hospital stay. This new surgical technique is expected to exhibit superior performance.

METHODS

A total of 23 randomized controlled trials (RCTs) involving 2058 knees that compared the clinical outcomes of TKA between PSI and SI were included in the present analysis; these RCTs were identified via a literature search of the PubMed, Embase, and Cochrane Library databases through March 1, 2018. The outcomes of interest included coronal, sagittal and axial component alignment (presented as the angle of deviation from the transcondylar line); number of outliers; operative time; perioperative blood loss; and length of hospital stay.

RESULTS

There was a significant difference in postoperative femoral axial alignment between PSI and SI patients (95% CI - 0.71 to - 0.21, p = 0.0004, I² = 48%). PSI resulted in approximately 0.4° less deviation from the transcondylar line than SI. Based on our results, PSI reduced operative time by a mean of 7 min compared with SI (95% CI - 10.95 to - 3.75, p < 0.0001, I² = 78%). According to the included literature, PSI reduced perioperative blood loss by approximately 90 ml compared with SI (95% CI - 146.65 to - 20.18, p = 0.01, I² = 74%). We did not find any differences between PSI and SI with respect to any other parameters.

CONCLUSIONS

PSI has advantages in axial alignment of the femoral component, operative time, and perioperative blood loss relative to SI. No significant differences were found between PSI and SI with respect to alignment of the remaining components, number of outliers, or length of hospital stay.

LEVEL OF EVIDENCE

Therapeutic study (systematic review and meta-analysis), Level I.

A 2-year RSA study of the Vanguard CR total knee system: A randomized controlled trial comparing patient-specific positioning guides with conventional technique

Background and purpose - There is some concern regarding the revision rate of the Vanguard CR TKA in 1 registry, and the literature is ambiguous about the efficacy of patient-specific positioning guides (PSPGs). The objective of this study was to investigate the stability of the cemented Vanguard CR Total Knee using 2 different surgical techniques. Our hypothesis was that there is no difference in migration when implanting the Vanguard CR with either PSPGs or conventional technique. We hereby present a randomized controlled trial of 2-year follow-up with radiostereometric analysis (RSA). Patients and methods - 40 TKAs were performed between 2011 and 2013 with either PSPGs or the conventional technique and 22 of these were investigated with RSA. Results - The PSPG (8 knees) and the conventional (14 knees) groups had a mean maximum total point motion (MTPM) (95% CI) of 0.83 (0.48-1.18) vs. 0.70 (0.43-0.97) mm, 1.03 (0.60-1.43) vs. 0.86 (0.53-1.19), and 1.46 (1.07-1.85) vs. 0.80 (0.52-1.43) at 3, 12, and 24 months respectively (p = 0.1). 5 implants had either an MTPM >1.6 mm at 12 months and/or a migration of more than 0.2 mm between 1- and 2-year follow-ups. 2 of these also had a peripheral subsidence of more than 0.6 mm at 2 years. Interpretation - 5 implants (3 in the PSPG group) were found to be at risk of later aseptic loosening. The PSPG group continuously migrated between 12 and 24 months. The conventional group had an initial high migration between postoperative and 3 months, but seemed more stable after 1 year. Although the difference was not statistically significant, we think the migration in the PSPG group is of some concern.