The impact of patient-specific instrumentation on unicompartmental knee arthroplasty: a prospective randomised controlled study

The efficacy and safety of patient-specific instrumentation versus conventional instrumentation for unicompartmental knee arthroplasty: Evidence from a meta-analysis

BACKGROUND

The aim of this study was to compare the efficacy and safety of patient-specific instrumentation (PSI) and conventional instrumentation (CI) for unicompartmental knee arthroplasty. Our hypothesis was that the PSI would be superior to CI in improving implant positioning and clinical function.

METHODS

We searched electronic databases (PubMed, Web of Science, Embase, and Cochrane) to identify relevant studies published before July 1, 2023 that met our inclusion criteria. The identified reports at least included one of the following outcome variables: coronal component alignment, sagittal component alignment, number of outliers, hip-knee-ankle angle, postoperative complications, operative time and knee joint functional evaluation. For dichotomous variables, we calculated the risk ratio and its 95% confidence interval (CI). For continuous variables, we calculated the mean difference (MD) and its 95% CI. Heterogeneity of the included studies was assessed using the standard chi-square test. Meta-analyses were performed using RevMan 5.4. software. The meta-analysis was registered with PROSPERO (No. CRD42023454160).

RESULTS

A total of 9 articles were included in the analysis, consisting of 4 randomized controlled trials and 5 cohort studies. The study population comprised 494 patients, with 262 in the PSI group and 232 in the CI group. Our findings demonstrate that the PSI group exhibits superior tibial component coronal alignment compared to the CI group (MD = -0.66, 95% CI: -1.21 to -0.12, P = .02). Conversely, the CI group demonstrates better femoral component coronal alignment than the PSI group (MD = 0.89, 95% CI: 0.17-1.60, P = .01). No significant between 2 groups differences were observed in tibial component sagittal alignment, femoral component sagittal alignment, tibial coronal axis outliers, tibial sagittal axis outliers, femoral coronal axis outliers, femoral sagittal axis outliers, postoperative complications, operative time, hip-knee-ankle angle, and postoperative knee joint function score.

CONCLUSIONS

Our study findings suggest that the PSI confer an advantage in achieving superior tibial component coronal alignment, whereas the CI associated with better femoral component coronal alignment. However, no significant differences were observed between the groups in terms of other parameters. Future studies with larger sample sizes are needed to validate these findings.

Computed tomography-based patient-specific cutting guides used for positioning of the femoral component of implants during unicompartmental knee arthroplasty: a cadaver study

BACKGROUND

To investigate whether patient-specific instrumentation (PSI) improves the femoral component positioning of implants during unicompartmental knee arthroplasty (UKA) using cadaver bone models.

METHODS

Fifty adult cadaveric femoral bone specimens collected from February 2016-2018, were randomized to receive medial UKA with a PSI guide (n = 25) or conventional instrumentation (CI) (n = 25). Standard anteroposterior and lateral view radiographs were obtained postoperatively to assess the coronal and sagittal positioning of the femoral prostheses, respectively. The osteotomy time was recorded to assess the convenience of PSI in guiding osteotomy.

RESULTS

Osteotomy time significantly shortened in the PSI group (3.12 ± 0.65 versus 4.33 ± 0.73 min, p < 0.001). There was a significant difference in the postoperative coronal alignment of the femoral component between the PSI and CI groups (varus/valgus angle: 1.43 ± 0.93° vs. 2.65 ± 1.50°, p = 0.001). The prevalence of outliers in coronal alignment was lower in the PSI than the CI group (2/25, 8% vs. 9/25, 36%). Sagittal posterior slope angle of the femoral component was significantly different between the two groups (8.80 ± 0.65° and 6.29 ± 1.88° in the CI and PSI groups, respectively, p < 0.001). The malalignment rate of the femoral component in the sagittal plane was 60% in the CI group, whereas no positioning deviation was observed in the PSI group.

CONCLUSION

This study used a cadaver model to support the fact that CT-based PSI shows an advantage over CI in optimizing implant positioning for UKAs.

Combined Edge Loss UNet for Optimized Segmentation in Total Knee Arthroplasty Preoperative Planning

Bone segmentation and 3D reconstruction are crucial for total knee arthroplasty (TKA) surgical planning with Personalized Surgical Instruments (PSIs). Traditional semi-automatic approaches are time-consuming and operator-dependent, although they provide reliable outcomes. Moreover, the recent expansion of artificial intelligence (AI) tools towards various medical domains is transforming modern healthcare. Accordingly, this study introduces an automated AI-based pipeline to replace the current operator-based tibia and femur 3D reconstruction procedure enhancing TKA preoperative planning. Leveraging an 822 CT image dataset, a novel patch-based method and an improved segmentation label generation algorithm were coupled to a Combined Edge Loss UNet (CEL-UNet), a novel CNN architecture featuring an additional decoding branch to boost the bone boundary segmentation. Root Mean Squared Errors and Hausdorff distances compared the predicted surfaces to the reference bones showing median and interquartile values of 0.26 (0.19-0.36) mm and 0.24 (0.18-0.32) mm, and of 1.06 (0.73-2.15) mm and 1.43 (0.82-2.86) mm for the tibia and femur, respectively, outperforming previous results of our group, state-of-the-art, and UNet models. A feasibility analysis for a PSI-based surgical plan revealed sub-millimetric distance errors and sub-angular alignment uncertainties in the PSI contact areas and the two cutting planes. Finally, operational environment testing underscored the pipeline's efficiency. More than half of the processed cases complied with the PSI prototyping requirements, reducing the overall time from 35 min to 13.1 s, while the remaining ones underwent a manual refinement step to achieve such PSI requirements, performing the procedure four to eleven times faster than the manufacturer standards. To conclude, this research advocates the need for real-world applicability and optimization of AI solutions in orthopedic surgical practice.

Comparative efficacy of the different cutting guides in unicompartmental knee arthroplasty: A systematic-review and network meta-analysis

BACKGROUND

Several cutting guides including conventional, navigation, patient specific instrumentation (PSI) and robotic are currently used in unicompartmental knee arthroplasty (UKA). A network meta-analysis was conducted to compare the most widely used cutting guides regarding the improvement of radiological, functional outcomes and the rate of complications.

METHODS

Randomised controlled trials (RCTs) comparing UKA cutting guides were searched in electronic databases, major orthopaedics journals, and oral communications in major orthopaedics meetings, until May 1st, 2022. The primary outcomes were the rate of outliers for the tibial and femoral components in the frontal plane, KSS score and the complication rate.

RESULTS

Eighteen RCTs involving 1562 patients with 1564 UKA were included Regarding the prosthetic components' positions, we found a significant increase of the outliers rate using PSI for the femoral component, compared to robotic surgery (risk ratio 0.00 [95% CI 0.00 to 0.55]) and navigated surgery (risk ratio 305.1 [95% CI 1.50 to 1,27e + 07]). We didn't emphasize any difference regarding the tibial component's position, the KSS value at 24 months postoperatively, and the complication rate. Regarding secondary outcomes, robotics provided a better precision in bone cuts in the sagittal plane for the tibial component and the lower limb alignment. No other differences were observed.

CONCLUSION

In the light of these results, the robot seems to be the most precise cutting instrument to perform UKA. However, this did not demonstrate any difference in functional or clinical outcome. The cost of this technology can be a major economic brake, especially in surgical centers that do not have an exclusive prosthetic activity. Further outcome and survivorship data is needed to recommend one cutting instrument over the other.

Robotic-Assisted versus Manual Unicompartmental Knee Arthroplasty: Contemporary Systematic Review and Meta-analysis of Early Functional Outcomes

Robotic-assisted unicompartmental knee arthroplasty (RA-UKA) aims to improve accuracy of component placement. Studies have shown improvement in radiographic positioning/alignment with RA-UKA but have not addressed clinical outcome measures (COMs). The purpose of this study was to determine if RA-UKA is associated with improved early revision rates and functional outcome scores (FOS) compared with manual UKA. A systematic review of all English language articles from 1999 to 2019 on RA-UKA using Medline, EMBASE, Scopus, and Web of Science databases identified 277 studies. Seven (three randomized controlled trials) met inclusion criteria. Revision rates/FOS were aggregated for RA-UKA and manual UKA; a forest plot was constructed utilizing inverse variance/Mantel-Haenszel fixed-effects meta-analysis. The seven articles included a total of 363 RA-UKA patients and 425 manual UKA patients. Mean age was 66 ± 3.5 and 65 ± 4.0 years, and mean body mass index (BMI) was 26.8 ± 2.1 and 27.1 ± 1.5 kg/m², respectively. Mean follow-up was 25.5 months (4.5-48) and 29.1 months (4.5-48) for RA-UKA and manual UKA, respectively. At latest follow-up, RA-UKA patients showed a 26% ± 12 improvement in COMs versus 24% ± 12 improvement for manual UKA patients (p = 0.6). The revision rate was 3% for both groups (p = 0.8); however, a meta-analysis of RCTs showed no difference. Robotic and manual UKAs offer comparable improvements in pain, FOS, and revision rates. The effects of follow-up duration, ceiling effects of COMs, and surgeon experience remain unknown. Future studies comparing robotic versus manual UKAs with longer term follow-up may inform further benefits of each, with respect to component durability, alignment, and functional improvement.

New instrumentation system for cementless mobile-bearing unicompartmental knee arthroplasty improves surgical performance particularly for trainees

BACKGROUND

Mobile-bearing medial-unicompartmental knee arthroplasty (mUKA) has a documented learning curve. New instrumentation has been designed with the aim of reducing the technical challenges of this procedure. The primary aim of this study was to evaluate the technical performance of mUKA using new (Microplasty) versus older (Phase III) instrumentation, performed by expert surgeons and trainees. Secondary aims were to evaluate functional outcome and mid-term survivorship.

METHODS

A time-based comparative cohort study was performed between 2009 and 2015 at a high-volume centre. 273 patients (273 knees, 49.5% female) of mean age 67.8 (standard deviation 10.1) years underwent mUKA. 153 (56.0%) procedures used Microplasty instruments and 120 procedures (44.0%) used Phase III instruments.

RESULTS

Non-optimal bearing usage was less frequent with Microplasty than Phase III instruments (24 knees [15.7%] versus 33 knees [27.5%], p = 0.024), with differences due to improved trainee performance. Femoral component sagittal alignment outliers were less frequent with Microplasty, but this was not statistically significant (9 knees [5.9%] versus 13 knees [10.8%], p = 0.18). Post-operative Oxford Knee Scores (OKS) were better with Microplasty (median 42 points [interquartile range 38-44]) compared to Phase III (median 39.5 points [IQR 33-44]), which was statistically significant (p = 0.023), but not clinically meaningful. The overall 5-year Kaplan-Meier (KM) survival estimate was 99.3% (95% CI 97.0-99.8%), with no differences between Microplasty and Phase III instrumentation.

CONCLUSIONS

New instrumentation improved the reliability of the proximal tibial resection in trainees. Further research is warranted to investigate whether Microplasty instrumentation shortens the learning curve for medial UKA.

What is the evidence for clinical use of advanced technology in unicompartmental knee arthroplasty?

BACKGROUND

With an aim of improving prosthesis survivorship of unicompartmental knee arthroplasty (UKA), use of computer-assisted technologies (CATs) such as robotics, has been on the rise to reduce intraoperative errors in surgical technique. In light of recent influx of CATs in the UKA, a review of these innovations will help providers to understand their clinical utility.

METHOD

A systematic literature search was performed following Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines.

RESULTS

Among 19 studies comparing robot-assisted UKA with conventional UKA, only 32% were randomized control trials, 47% reported minimum mean follow-up of 2 years, and 21% evaluated prosthesis survival. Similar results were obtained for navigation-assisted UKA and UKA performed with patient-specific instrumentation.

CONCLUSION

While CATs seem to reduce the surgical errors in UKA, the evidence on the efficacy of any of the studied CATs to improve survivorship remains limited and there are issues related to cost-effectiveness, learning curve, and increase in operating time.

Comparing clinical and radiographic outcomes of robotic-assisted, computer-navigated and conventional unicompartmental knee arthroplasty: A network meta-analysis of randomized controlled trials

Introduction

The purpose was to compare robotic assisted (RA), computer navigated (CN), and conventional UKA techniques.

Methods

Databases were queried for data on study characteristics, UKA systems, complications, and tibiofemoral alignment.

Results

Four RA and six CN RCTs were identified. No significant differences were found in operative time, tibiofemoral alignment, and reoperation rates when comparing RA or CN to conventional UKA. RA UKA resulted in a significantly lower risk of complications compared to conventional UKA.

Conclusions

RA UKA results in fewer complications than conventional UKA with a clinically significant increase in operative time. All groups were similar in remaining evaluated parameters.

[Focal femoral resurfacing and unicompartmental knee replacement : Between osteotomy and total knee replacement]

Unicompartmental knee arthroplasty, especially for both femorotibial compartments of the knee, is an established partly joint-saving treatment option for osteoarthritis of the knee if the disease is limited to one compartment. Even smaller implants or resurfacing of the patellofemoral joint have been shown-in smaller patient collectives-to have the potential to yield good clinical results.

Radiological outcomes following manual and robotic-assisted unicompartmental knee arthroplasty

Aims

The purpose of this study was to compare the radiological outcomes of manual versus robotic-assisted medial unicompartmental knee arthroplasty (UKA).

Methods

Postoperative radiological outcomes from 86 consecutive robotic-assisted UKAs (RAUKA group) from a single academic centre were retrospectively reviewed and compared to 253 manual UKAs (MUKA group) drawn from a prior study at our institution. Femoral coronal and sagittal angles (FCA, FSA), tibial coronal and sagittal angles (TCA, TSA), and implant overhang were radiologically measured to identify outliers.

Results

When assessing the accuracy of RAUKAs, 91.6% of all alignment measurements and 99.2% of all overhang measurements were within the target range. All alignment and overhang targets were simultaneously met in 68.6% of RAUKAs. When comparing radiological outcomes between the RAUKA and MUKA groups, statistically significant differences were identified for combined outliers in FCA (2.3% vs 12.6%; p = 0.006), FSA (17.4% vs 50.2%; p < 0.001), TCA (5.8% vs 41.5%; p < 0.001), and TSA (8.1% vs 18.6%; p = 0.023), as well as anterior (0.0% vs 4.7%; p = 0.042), posterior (1.2% vs 13.4%; p = 0.001), and medial (1.2% vs 14.2%; p < 0.001) overhang outliers.

Conclusion

Robotic system navigation decreases alignment and overhang outliers compared to manual UKA. Given the association between component placement errors and revision in UKA, this strong significant improvement in accuracy may improve implant survival.

Level of Evidence: III

Cite this article: Bone Jt Open 2021;2-3:191–197.

[New technologies (robotics, custom-made) in unicondylar knee arthroplasty-pro]

BACKGROUND

Unicondylar knee arthroplasty offers the advantage that partial degenerative changes can be addressed with partial prosthetic solutions, thus preserving as much of the native joint as possible, including the cruciate ligaments. On the other hand, the number of revisions is still higher than for total knee endoprosthetics. In the literature, the causes mentioned are insufficient fit of the components as well as surgical errors. The use of new technologies to achieve a better fit and higher surgical precision and reproducibility, therefore, represents a promising approach.

INDIVIDUAL ENDOPROSTHETICS

Individual endoprosthetics offers the advantage that the prosthesis is adapted to the individual anatomy of each patient and not the patient's anatomy to the prosthesis, as is the case with standard prostheses. This allows for an optimal fit of the prosthesis while avoiding excessive bone resections and soft tissue releases.

ROBOTICS

The use of robotics in endoprosthetics makes it easier to correctly perform bone resections and align components. This ensures high and reproducible precision even for surgeons with lower case numbers. Studies on individual unicondylar endoprosthetics and robotics are reporting promising results. However, long-term results of high-quality randomized studies must be awaited in order to make a scientifically sound statement.

Coronal Alignment of Fixed-Bearing Unicompartmental Knee Arthroplasty Femoral Component May Affect Long-Term Clinical Outcomes

BACKGROUND

This study aims to investigate the clinical effects of femoral component coronal alignment in a cohort of fixed-bearing unicompartmental knee arthroplasty with clinical and radiological follow-up of 10 years.

METHODS

Prospectively collected registry data of 264 consecutive, cemented, primary fixed-bearing medial unicompartmental knee arthroplasties performed at a single institution from 2004 to 2007 were reviewed. Femoral component coronal angle (FCCA), tibial component coronal angle, and hip-knee-ankle angle were measured on postoperative radiographs. Patients were grouped into acceptable (AG ≤ 3°) and outlier (OG > 3°) groups according to absolute FCCA. Clinical assessment at 6-month, 2-year, and 10-year follow-up was performed using Knee Society Knee and Function Scores, Oxford Knee Score (OKS), and Short Form-36. Fulfillment of expectations, satisfaction, and implant survivorship was recorded.

RESULTS

There was no significant difference in demographics, tibial component coronal angle, hip-knee-ankle angle, and sagittal parameters in both groups. The OG had poorer OKS at 10 years and a larger deterioration from 2 to 10 years compared to AG (P = .02). Increase in FCCA was associated with deterioration in 2-year OKS (adjusted ß = 0.23, P = .01), 10-year OKS (adjusted ß = 0.26, P = .03), and 2-year Short Form-36 physical component score (adjusted ß = -0.44, P = .01). Expectation fulfillment at 2 years was lower in the OG vs the AG (88% vs 100%, P = .03). Both groups had similar 10-year survivorship (99% vs 98%, P = .65).

CONCLUSIONS

FCCA may affect long-term clinical outcomes, but not short-term clinical outcomes nor 10-year survivorship. Given similar limb alignment, coronal and sagittal component positioning, a larger FCCA was associated with poorer outcomes at 10-year follow-up.

Patient-specific instrument for unicompartmental knee arthroplasty does not reduce the outliers in alignment or improve postoperative function: a meta-analysis and systematic review

BACKGROUND

Unsatisfactory alignment in unicompartmental knee arthroplasty (UKA) is one potential cause of postoperative failure. Patient-specific instruments (PSIs) are designed to improve the alignment of the prostheses, but the effect of PSIs on the alignment or clinical outcome is controversial and lacks validated evidence. We conducted a meta-analysis and systematic review to determine the effect of PSIs on UKA outcomes for the first time.

MATERIALS AND METHODS

A systematic literature search in MEDLINE, EMBASE, CNKI (Chinese database) and Cochrane Central Register of Controlled Trials (up to June 2019) was performed to collect studies that compared PSIs with conventional instruments. Two reviewers independently screened all the records on the basis of inclusion and exclusion criteria. Quality assessments with Cochrane's quality assessment tool or Newcastle-Ottawa scale (NOS) were conducted, the data were extracted, and statistical analyses were completed.

RESULTS

Ten studies with 444 knees were included. The meta-analysis confirmed that PSIs contributed to reduced errors in the alignment of the femoral compartment in the sagittal plane (mean difference = - 2.53, CI [- 3.14, - 1.99], P < 0.01) and the tibial compartment in both the coronal (mean difference = - 0.97, CI [- 1.44, - 0.49], P < 0.01) and the sagittal plane (mean difference = - 1.29, CI [- 1.81, - 0.76], P < 0.01). One study supported that PSIs reduced outliers in inexperienced surgeons; however, all studies investigating PSIs among experienced surgeons suggested that PSIs cannot reduce the percentage of outliers. There was no significant difference in the postoperative score (mean difference = - 0.06, CI [- 0.36, 0.23], P = 0.68) or rate of complications (RR = 1.02, CI [0.15, 6.79], P = 0.99) between PSIs and conventional instruments.

CONCLUSION

The findings of this study suggest PSIs could not reduce the percentage of outliers in UKA patients for experts, and postoperative scores and complication rates are not improved by PSIs, compared with conventional instruments. Based on this meta-analysis and systematic review, no practical benefit to UKAs in experts was detected in PSIs. The findings of this study also suggest that PSIs improved alignment of UKA and might be beneficial to inexperienced surgeons, but it is still unclear whether this improvement is clinically significant and the evidence of inexperienced surgeons is limited. Therefore, more high-quality RCTs are need to be carried out in the future.

Patient-specific instrumentation does not improve tibial component coronal alignment for medial UKA compared to conventional instrumentation

Background

Patient-specific instrumentation (PSI) may potentially improve unicompartmental knee arthroplasty (UKA) implant positioning and alignment. The purpose of this study was to compare early radiographic coronal alignment of medial UKA performed using PSI versus conventional instrumentation (CI) for tibial resections.

Methods

A consecutive series of 47 knees (47 patients) received medial UKA, with the tibial resections performed using CI (first 22 knees) or PSI (next 25 knees), while femoral resections were performed with CI in both groups. The target mechanical medial proximal tibial angle (mMPTA) was 87° ± 3°, and the target hip-knee-ankle (HKA) angle was 177° ± 2°. The postoperative mMPTA and HKA were evaluated from postoperative radiographs at a follow-up of 2 months.

Results

Differences in postoperative mMPTA (p = 0.509) and HKA (p = 0.298) between the two groups were not statistically significant. For the mMPTA target, 24% of knees in the PSI group (85.6° ± 2.1°) and 32% of the CI group (85.0° ± 3.6°) were outliers. For the HKA target, 44% of knees in the PSI group (176.3° ± 2.8°) and 18% of the CI group (177.1° ± 2.3°) were outliers. Considering the two criteria simultaneously, 60% of knees in the PSI group and 45% of knees in the CI group were outside the target zone (p = 0.324), whereas 28% of knees in the PSI group and 41% of knees in the CI group were outside the target zone by more than 1° (p = 0.357).

Conclusions

The results of the present study revealed no statistically significant difference in radiographic coronal alignment of UKA performed using PSI versus CI for tibial resections.

Influence of patient selection, component positioning and surgeon's caseload on the outcome of unicompartmental knee arthroplasty

BACKGROUND

Implant malpositioning, low surgical caseload, and improper patient selection have been identified as essential factors, which could negatively affect the longevity of unicompartmental knee arthroplasty (UKA). The aim of the current study was to evaluate the impact of the surgeon's caseload on patient selection, component positioning, as well as component survivorship and functional outcomes following a PSI-UKA.

METHODS

A total of 125 patient-specific instrumented (PSI) UKA were included. One hundred and two cases were treated by a high-volume surgeon (usage 40%) and 23 cases by a low-volume surgeon (< 10 cases/year, usage 34%). Preoperative UIS, as well as the postoperative clinical and radiologic outcome, were assessed retrospectively.

RESULTS

Irrespective of the surgeon's UKA caseload, PSI allowed good accuracy in component positioning (p > 0.05). The high-volume surgeon had a more strict indication for UKA with 89% showing a UIS > 25 (considered a good indication) compared to 70% for the low-volume surgeon (p = 0.016). The low-volume surgeon achieved worse results regarding functional outcome (p < 0.05) and a tendency toward an increased risk for UKA failure (p = 0.11) compared to the high-volume surgeon.

CONCLUSION

Due to potential selection errors, mostly connected to a low UKA-caseload, low-volume UKA surgeons might achieve worse outcomes. Very strict indications for UKA might be recommended in low-volume surgeons to achieve excellent clinical outcomes following a UKA.

How should we evaluate robotics in the operating theatre?

The application of robotics in the operating theatre for knee arthroplasty remains controversial. As with all new technology, the introduction of new systems might be associated with a learning curve. However, guidelines on how to assess the introduction of robotics in the operating theatre are lacking. This systematic review aims to evaluate the current evidence on the learning curve of robot-assisted knee arthroplasty. An extensive literature search of PubMed, Medline, Embase, Web of Science, and Cochrane Library was conducted. Randomized controlled trials, comparative studies, and cohort studies were included. Outcomes assessed included: time required for surgery, stress levels of the surgical team, complications in regard to surgical experience level or time needed for surgery, size prediction of preoperative templating, and alignment according to the number of knee arthroplasties performed. A total of 11 studies met the inclusion criteria. Most were of medium to low quality. The operating time of robot-assisted total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) is associated with a learning curve of between six to 20 cases and six to 36 cases respectively. Surgical team stress levels show a learning curve of seven cases in TKA and six cases for UKA. Experience with the robotic systems did not influence implant positioning, preoperative planning, and postoperative complications. Robot-assisted TKA and UKA is associated with a learning curve regarding operating time and surgical team stress levels. Future evaluation of robotics in the operating theatre should include detailed measurement of the various aspects of the total operating time, including total robotic time and time needed for preoperative planning. The prior experience of the surgical team should also be evaluated and reported.

Cite this article: Bone Joint J 2020;102-B(4):407–413.

Midterm clinical and radiographic outcomes of 115 consecutive patient-specific unicompartmental knee arthroplasties

BACKGROUND

Poor implant positioning has been identified as a factor in early failure of unicompartmental knee arthroplasty. The aim of this study was to report the accuracy of component positioning, and midterm clinical, functional and radiological outcomes following patient-specific instrumented (PSI) unicompartmental knee arthroplasty (UKA).

METHODS

A total of 115 PSI-UKA were included. The primary outcomes were UKA survival, complication, and failure rates. Tibial implant positioning was determined using plain radiographs. Functional assessment included Oxford Knee Score (OKS), Forgotten Joint Score (FJS), patient satisfaction, and range of motion (ROM).

RESULTS

The survival rate of PSI-UKA was 92% after a mean follow-up of 55 months. The complication and failure rate was 13% and eight percent, respectively. The tibial component was accurately implanted in the desired frontal and sagittal alignment with a minor deviation of 0.3° (SD 1.9°) and 0.4° (SD 2.6°) to the preoperative planning. OKS increased from 24 (SD eight) points to 44 (SD six). FJS was 87 (SD 23) and 89.6% of all patients reported to be satisfied at the final follow-up. Patient satisfaction was negatively correlated with patients' age (p < 0.05).

CONCLUSION

Excellent accuracy regarding component placement in UKA can be achieved with PSI. However, despite excellent survivorship and clinical outcomes, these data indicate that the PSI system is not superior to conventional UKA implantation methods.

Unicompartmental knee arthroplasty: Current indications, technical issues and results

An age younger than 60 years, a body weight of 180 lb (82 kg) or more, performing heavy work, having chondrocalcinosis and having exposed bone in the patellofemoral (PF) joint are not contraindications for unicompartmental knee arthroplasty (UKA).Severe wear of the lateral facet of the PF joint with bone loss and grooving is a contraindication for UKA.Medial UKA should only be performed in cases of severe osteoarthritis (OA) as shown in pre-operative X-rays, with medial bone-on-bone contact and a medial/lateral ratio of < 20%.The post-operative results of UKA are generally good. Medium-term and long-term studies have reported acceptable results at 10 years, with implant survival greater than 95% for UKAs performed for medial OA or osteonecrosis and for lateral UKA, especially when fixed-bearing implants are used.When all implant-related re-operations are considered, the 10-year survival rate is 94%, and the 15-year survival rate is 91%.Aseptic loosening is the principal failure mechanism in the first few years in mobile-bearing implants, whereas OA progression causes most failures in later years in fixed-bearing implants.The overall complication rate and the comprehensive re-operation rate are comparable in both mobile bearings and fixed bearings.The survival likelihood of the all-polyethylene UKA implant is similar to that of metal-backed modular designs for UKA.Notable cost savings of approximately 50% can be achieved with an outpatient UKA surgery protocol. Outpatient surgery for UKA is efficacious and safe, with satisfactory clinical results thus far. Cite this article: EFORT Open Rev 2018;3:363-373. DOI: 10.1302/2058-5241.3.170048.

The femoral component alignment resulting from spacer block technique is not worse than after intramedullary guided technique in medial unicompartimental knee arthroplasty

PURPOSE

Although the spacer block technique has been recommended for the implantation of unicompartmental knee arthroplasty (UKA), there is still a lack of data concerning the resulting component positioning.

METHODS

This retrospective study included 193 consecutive patients who had undergone medial UKA using the spacer technique. On the basis of the postoperative long standing radiographs, the coronal component alignment was determined in relation to the mechanical axes and the sagittal component alignment in relation to the anatomical axes of the tibia and femur. The coronal alignment of the femoral component was determined through post hoc 3D planning with the CAD data projected onto the radiograph.

RESULTS

The angle of the tibial component was on the average 2.3° ± 2.8° in varus, the femoral component on the average 2.6° ± 3.7° in varus. Only 4 implants (2%) were outside an assumed tolerance range of 10° varus-10° valgus. A tilting from the femoral to the tibial component of more than 10° was observed in 8 cases (4%). A valgus positioning of the tibial component was followed by a valgus alignment of the femoral component (R = - 0.194, p = 0.007). An increased posterior slope of the tibial component led to an extended positioning of the femoral component (R = - 0.230, p = 0.001).

CONCLUSIONS

The spacer block technique produces results comparable to the intramedullary guided technique. However, the precision is low and outlier frequent. Due to the possibility of transferring a tibial malalignment to a femoral malalignment, even greater attention should be paid to the precision of tibial resection.

Do patient-specific instruments (PSI) for UKA allow non-expert surgeons to achieve the same saw cut accuracy as expert surgeons?

INTRODUCTION

High-volume unicompartmental knee arthroplasty (UKA) surgeons have lower revision rates, in part due to improved intra-operative component alignment. This study set out to determine whether PSI might allow non-expert surgeons to achieve the same level of accuracy as expert surgeons.

MATERIALS AND METHODS

Thirty-four surgical trainees with no prior experience of UKA, and four high-volume UKA surgeons were asked to perform the tibial saw cuts for a medial UKA in a sawbone model using both conventional and patient-specific instrumentation (PSI) with the aim of achieving a specified pre-operative plan. Half the participants in each group started with conventional instrumentation, and half with PSI. CT scans of the 76 cut sawbones were then segmented and reliably orientated in space, before saw cut position in the sagittal, coronal and axial planes was measured, and compared to the pre-operative plan.

RESULTS

The compound error (absolute error in the coronal, sagittal and axial planes combined) for experts using conventional instruments was significantly less than that of the trainees (11.6°±4.0° v 7.7° ±2.3º, p = 0.029). PSI improved trainee accuracy to the same level as experts using conventional instruments (compound error 5.5° ±3.4º v 7.7° ±2.3º, p = 0.396) and patient-specific instruments (compound error 5.5° ±3.4º v 7.3° ±4.1º, p = 0.3). PSI did not improve the accuracy of high-volume surgeons (p = 0.3).

CONCLUSIONS

In a sawbone model, PSI allowed inexperienced surgeons to achieve more accurate saw cuts, equivalent to expert surgeons, and thus has the potential to reduce revision rates. The next test will be to determine whether these results can be replicated in a clinical trial.