The immediate effect of navigation on implant accuracy in primary mini-invasive unicompartmental knee arthroplasty

Comparison of computer-assisted navigated technology and conventional technology in unicompartmental knee arthroplasty: a meta-analysis

Background

Though unicompartmental knee arthroplasty (UKA) is a useful procedure to treat knee osteoarthritis, it remains a great controversial point as to if navigated systems are able to achieve better accuracy of limb alignment and greater clinic results. Current meta-analysis was conducted to explore if better clinical outcomes and radiographic outcomes could be acquired in the navigated system when compared with conventional procedures.

Methods

We identified studies in the online databases, including Medline, Embase, the Cochrane Library and Web of Science before May 2021. The PRISMA guidelines in this report were strictly followed. Our research was completed via Review Manager 5.4 software.

Results

Fourteen articles were included, involving 852 knees. The present meta-analysis displayed that the navigated system had remarkably improved outcomes in inliers of mechanical axis (MA) (P < 0.01), MA in the Kennedy's central zone (Zone C) (P = 0.04), inliers of the coronal femoral component (P < 0.01), inliers of the coronal tibial component (P = 0.005), inliers of the sagittal femoral component (P = 0.03), inliers of the sagittal tibial component (P = 0.002) and Range Of Motion (ROM) (P = 0.04). No significant differences were observed in Oxford Knee Score (OKS) (P = 0.15), American Knee Society Knee Score (KSS score) (P = 0.61) and postoperative complications (P = 0.73) between these 2 groups. Regarding operating time, the navigated group was 10.63 min longer in contrast to the traditional group.

Conclusion

Based on our research, the navigated system provided better radiographic outcomes and no significant difference in the risk of complications with longer surgical time than the conventional techniques. But no significant differences were found in functional outcomes. Because the included studies were small samples and short-term follow-up, high-quality RCTs with large patients and sufficient follow-up are required to identify the long-term effect of the navigated system.

Navigated Unicompartmental Knee Arthroplasty: A Different Perspective

Backgroud

Anteromedial osteoarthritis is a recognized indication for unicompartmental knee arthroplasty (UKA). Favorable postoperative outcomes largely depend on proper patient selection, correct implant positioning, and limb alignment. Computer navigation has a proven value over conventional systems in reducing mechanical errors in total knee arthroplasty (TKA). However, the lack of strong evidence impedes the universal use of computer navigation technology in UKA. Therefore, this study was proposed to investigate the accuracy of component positioning and limb alignment in computer navigated UKA and to observe the role of navigation in proper patient selection.

Methods

A total of 50 knees (38 patients) underwent computer navigated UKA between 2016 and 2018. All operations were performed by the senior surgeon using the same navigation system and implant type. The navigation system was used as a tool to aid patient selection: knees with preoperative residual varus > 5° on valgus stress and hyperextension > 10° were switched to navigated TKA. We measured the accuracy of component placement in sagittal and coronal planes on postoperative radiographs. Functional outcomes were also evaluated at the final follow-up (a minimum of 16 months).

Results

Nine patients had tibia vara and 14 patients had preoperative hyperextension deformity. We observed coronal outliers for the tibial component in 12% knees and for the femoral component in 10% knees. We also observed sagittal outliers for the tibial component in 14% knees and for the femoral component in 6% knees. There was a significant improvement in the functional score at the final follow-up. On multiple linear regression, no difference was found in functional scores of knees with or without tibia vara (p = 0.16) and with or without hyperextension (p = 0.25).

Conclusions

Our study further validates the role of computer navigation in desirable implant positioning and limb alignment. We encourage use of computer-assisted navigation as a tool for patient selection, as it allows intraoperative dynamic goniometry and provides real-time kinematic behavior of the knee to obviate pitfalls such as significant residual varus angulation and hyperextension that predispose early failure of UKA.

Navigation und Robotik in der Knieendoprothetik

Hintergrund

Die Langlebigkeit einer Knieprothese hängt von der korrekten Ausrichtung der Prothesenkomponenten und der mechanischen Achse des Beins sowie einer optimalen Weichteilbalancierung ab. Um dieses Ziel präziser und sicherer zu erreichen, wurde die computerassistierte Chirurgie entwickelt. Ziel dieses Artikels ist es, die Navigation und Robotik zu bewerten und die aktuellen Ergebnisse zu diskutieren.

Methode

Umfassende Literaturrecherche in der Datenbank PubMed und dem Suchdienst Google Scholar.

Ergebnisse

Die computerassistierte Chirurgie führt zu einer präziseren Ausrichtung der mechanischen Beinachse und der Positionierung der Prothesenkomponenten. Trotzdem sind die klinischen Ergebnisse zur Kniefunktion und die Resultate der patientenbezogenen Fragebögen (PROMs) kontrovers. Sie zeigen, wie für die Überlebensrate, keinen signifikanten Unterschied zur konventionellen Technik. Hohe Anschaffungs- und Unterhaltskosten limitieren zudem die Verbreitung dieser Systeme.

Schlussfolgerung

Momentan bietet die bildgestützte Navigation dem Chirurgen bei gewissen Operationsschritten eine wertvolle Unterstützung für ein präziseres und sichereres Arbeiten. Trotzdem sind Langzeitstudien zur Kniefunktion, zu den PROMs, zur Überlebensrate dringend erforderlich. In der Robotik zeigen nur kurzfristige Ergebnisse ähnliche Trends wie bei der Navigation. Die Robotiksysteme müssen und werden sich weiterentwickeln, um den Anforderungen der Nutzer und Patienten zu entsprechen (Kosten, Größe, Programmierung).

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.

External rotation of the tibial component should be avoided in lateral unicompartmental knee arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) leads to good clinical outcomes for isolated lateral osteoarthritis. However, the impact of the tibial component position on postoperative outcomes in lateral UKA is yet to be determined.

PURPOSE

This study investigated the influence of tibial component malposition on clinical outcomes in lateral UKA.

MATERIALS

This was a retrospective study of 50 knees (mean age 73.5 years) who underwent lateral UKA between September 2013 and January 2019. The Oxford Knee Score (OKS), Knee Society Score - Knee (KSSK), and Knee Society Score - Function (KSSF) were evaluated. The coronal alignment, posterior slope of tibial component, tibial component rotation relative to Akagi's line (angle α), and femoral anteroposterior (AP) axis (angle β) were measured postoperatively. The average follow up period was 2.3 (range, 1-4.9) years.

RESULTS

Clinical scores were significantly improved after lateral UKA. The mean coronal alignment was 0.9° ± 3.2° varus (range, 9.1° varus to 5.5° valgus), the mean posterior slope was 6.8° ± 3.8° (range, 0.8° to 14.8°). The mean α and β angles, were 4.1° ± 5.8° (range, -9.7° to 16.5°) and 6.7° ± 7.1° (range, -7.0° to 20.5°) external rotation. The angle α had significant negative correlations with postoperative OKS (r = -0.36), KSSK (r = -0.28), and KSSF (r = -0.39), and angle β had significant negative correlations with postoperative OKS (r = -0.34) and KSSK (r = -0.46).

CONCLUSION

Excessive external rotation of the tibial component could negatively influence the postoperative outcomes of lateral UKA.

Robot-Assisted Unicompartmental Knee Arthroplasty: Increasing Surgical Accuracy? A Cadaveric Study

Unicompartmental knee arthroplasty (UKA) represents 10% of knee arthroplasties. Advantages are better functional results, quicker recovery, shorter hospitalization time, and lower blood loss, among others. However, revision rates are larger than total knee arthroplasty. Among the most important factors that explain this are the implant position and alignment, and the correct surgical indication. Greater accuracy in the implant placement may improve clinical results and increase the rate of implant survival. The objective of this study is to evaluate the precision of the Navio robot-assisted system in the position and alignment of medial UKA compared with the conventional technique. This is an experimental pilot study. Twenty-six cadaveric models were randomized into 2 groups: Robot-Assisted surgery (R) and Conventional Surgery (C). Radiological study was performed pre- and post-surgery, evaluating the medial distal femoral angle (MDFA), medial proximal tibial angle (MPTA), tibial slope, tibiofemoral angle (TFA), sagittal femoral angle (SFA), and size of the femoral and tibial components. The main result measurement was the change in postoperative angulation. The results of this study are MDFA median of 1.07° (0.19-4.5) for group R and 0.12° (0.03-10.4) with a significant difference in variances; a Welch t-test of p = 0.013; and an MPTA of 1.28° (0.05-5.87) for R and 1.3°(0.08-14.1) for C with significantly different variances (p = 0.0064). Size of the femoral component has a difference of p < 0.05 between groups. No differences for dispersion of TFA nor for the size of the tibial component were observed. In conclusion, using robot-assisted UKA allows for greater accuracy in the positioning of the implants and in the prediction of the size of the femoral component.

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.

Improved implant alignment accuracy with an accelerometer-based portable navigation system in medial unicompartmental knee arthroplasty

PURPOSE

This study aimed to examine the accuracy of tibial implant alignment using an accelerometer-based portable navigation system in unicompartmental knee arthroplasty (UKA).

METHODS

This retrospective matched case-control study reviewed 51 UKAs performed using an accelerometer-based portable navigation system, matched with 51 UKAs performed using conventional extramedullary rods. Coronal alignment and posterior slope of the tibial implant were measured on postoperative radiographs, and differences from preoperative planning were examined. Outliers and accuracy of tibial implant alignment were compared between the portable navigation and conventional groups using Fisher's exact test and Mann-Whitney U test, respectively.

RESULTS

In the portable navigation group, 100% of the implants were aligned within 3.0° of both target coronal and sagittal implant alignment. In the conventional group, 76.5% and 88.2% of the implants were within 3.0° of both target coronal and sagittal implant alignment. Statistical analysis revealed that outliers of coronal and sagittal alignment were significantly less in the portable navigation group than in the conventional group (P < 0.05). In addition, the absolute value difference between postoperative measurement and preoperative planning of both coronal and sagittal alignment was significantly smaller in the portable navigation group than in the conventional group (P < 0.05).

CONCLUSION

The portable navigation system improved the accuracy of tibial implant alignment in UKA. We found that 100% of the implants were aligned within 3.0° of both target coronal and sagittal implant alignment. The portable navigation system decreased the outliers of tibial coronal and sagittal alignment.

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Dependence of knee range of motion on the alignment of femoral and tibial components after medial unicompartmental knee arthroplasty

INTRODUCTION

This study evaluated the relationship between postoperative knee flexion angles and the position of femoral and tibial components in unicompartmental knee arthroplasty (UKA).

MATERIALS AND METHODS

Eighteen patients (a total of 22 knees: three men, four knees; 15 females, 18 knees) who underwent navigation-assisted UKA were included. Pre- and postoperative computed tomography images were applied on 3D software, which were matched and used to calculate the position of femoral and tibial components. Correspondingly, we investigated the relationship between the knee range of motion (ROM) at 1-year postoperative follow-up and the position of femoral and tibial components.

RESULTS

At 1-year post-UKA, the knee flexion angle was associated with the posterior flexion angle of tibial components. This particular angle was significantly greater in the group with equal or greater postoperative knee ROM compared to preoperative ROM (5.2 ± 2.1°) than in the group with less postoperative knee ROM compared to preoperative ROM (2.6 ± 1.6°, p < 0.01). There was no significant difference between both groups in the femoral component position, preoperative posterior slope of the medial tibial plateau, change in the pre- to postoperative posterior tibial slope, and postoperative knee society score.

CONCLUSION

The posterior flexion angle of the tibial component affected the improvement/deterioration of the postsurgery knee flexion angle in navigation-assisted UKA. For improved outcomes after UKA using navigation systems, surgeons should aim to achieve a 5° to 8° posterior flexion angle of the tibial component.

The Impact of Coronal Alignment on Revision in Medial Fixed-Bearing Unicompartmental Knee Arthroplasty

BACKGROUND

To better define the optimal alignment target for medial fixed-bearing unicompartmental knee arthroplasty (UKA), this study compares the postoperative mechanical alignment of well-functioning UKAs against 2 groups of failed UKAs, including revisions for progression of lateral compartment osteoarthritis ("Progression") and revisions for aseptic loosening or subsidence ("Loosening").

METHODS

From our prospective institutional database of 3351 medial fixed-bearing UKAs performed since 2000, we identified 37 UKAs revised for Progression and 61 UKAs revised for Loosening. Each of these revision cohorts was matched based on age at surgery, gender, body mass index, and postoperative range of motion with unrevised UKAs that had at least 10 years of follow-up and a Knee Society Score of 70 or greater without subtracting points for alignment ("Success" groups). Postoperative alignment was quantified by the hip-knee-ankle (HKA) angle measured on long-leg alignment radiographs.

RESULTS

The mean HKA angle at 4-month follow-up for the Progression group was 0.3° ± 3.6° of valgus compared to 4.4° ± 2.6° of varus for the matched Success group (P < 0.001). For the Loosening group, the mean HKA angle was 6.1° ± 3.1° of varus versus 4.0° ± 2.7° of varus for the matched Success group (P < 0.001).

CONCLUSIONS

Patients with well-functioning UKAs at 10 years exhibited mild varus mechanical alignment of approximately 4°, whereas patients revised for progression of osteoarthritis averaged more valgus and those revised for loosening or subsidence averaged more varus. The optimal mechanical alignment for medial fixed-bearing UKA survival with contemporary polyethylene is likely slight varus.

Effect of Computer Navigation on Complication Rates Following Unicompartmental Knee Arthroplasty

BACKGROUND

We evaluated whether the complication and revision rates of unicompartmental knee arthroplasty (UKA) performed with intraoperative computer-based navigation differ from standard UKAs performed without intraoperative computer-based navigation.

METHODS

A Medicare database containing administrative claims data from 2005 to 2014 was queried. Patients who underwent a single UKA and had a minimum of 2 years of follow-up were included in the study. Data from 1025 UKAs performed with navigation were compared against 9228 age and gender-matched UKAs performed without it. Postoperative complications were identified using International Classification of Diseases, Ninth Revision, codes and evaluated at 30 days, 90 days, and 2 years.

RESULTS

Orthopedic complications after UKA are rare, and the use of navigation did not affect the rate of conversion to total knee arthroplasty at 2-year follow-up (3.8% in navigated UKAs vs 4.7% in standard UKAs, P = .218). There were also no significant differences in the rates of knee arthrotomy at 2-year follow-up (1.3% in navigated UKAs vs 1.6% in standard UKAs, P = .379). The rates of deep vein thrombosis at 90-day follow-up did not significantly differ between the 2 groups (1.4% in navigated UKAs vs 2.0% in standard UKAs, P = .157).

CONCLUSION

This is one of the first studies to use a large cohort to compare outcomes in computer-assisted surgery-UKA against standard UKAs without navigation. The results, particularly that there was not a difference in the rate of conversion to total knee arthroplasty, are directly relevant to clinical decision-making when surgeons are considering employing navigation during UKA.

Gait comparison of unicompartmental knee arthroplasty and total knee arthroplasty during level walking

This meta-analysis compared the gait patterns of unicompartmental knee arthroplasty (UKA) patients and total knee arthroplasty (TKA) patients during level walking by evaluating the kinetics, kinematics, and spatiotemporal parameters. Studies were included in the meta-analysis if they assessed the vertical ground reaction force (GRF), joint moment at stance, flexion at initial contact, flexion at swing, overall range of motion (ROM), coronal knee angle at stance, walking speed, cadence, and stride length in UKA patients or TKA patients. Seven non-randomized studies met the criteria for inclusion in this meta-analysis. UKA patients and TKA patients were similar in terms of vertical GRF (95% CI: -0.36 to 0.20; P = 0.60), joint moment (95% CI: -0.55 to 0.63; P = 0.90), kinematic outcomes (95% CI: -0.72 to 1.02; P = 0.74), walking speed (95% CI: -0.27 to 0.81; P = 0.32), and cadence (95% CI: -0.14 to 0.68; P = 0.20). In contrast, the stride length (95% CI: 0.01 to 0.80; P = 0.04) differed significantly between groups. Subgroup analyses revealed that the pooled data were similar between the groups: 1st maximum (heel strike), -0.18 BW (P = 0.53); 1st minimum (mid-stance), -0.43 BW (P = 0.08); and 2nd maximum (toe off), -0.03 BW (P = 0.87). On gait analysis, there were no significant differences in vertical GRF, joint moment at stance, overall kinematics, walking speed, or cadence between UKA patients and TKA patients during level walking. However, the TKA group had significantly shorter stride length than UKA patients. Although the comparison was inconclusive in determining which types of knee arthroplasty offered the closest approximation to normal gait, we consider it important to provide better rehabilitation programs to reduce the abnormal stride length in TKA patients compared to UKA patients.

The influence of different sets of surgical instrumentation in Oxford UKA on bearing size and component position

INTRODUCTION

The Oxford unicompartmental knee arthroplasty (OUKA) has been proven to be an effective treatment for anteromedial osteoarthritis of the knee joint. New instrumentation has been introduced to improve the reproducibility of implant positioning and to minimize bone loss during tibial resection (Oxford Microplasty; Zimmer Biomet, Warsaw, Indiana, USA).

METHODS

To assess the effect of the new instrumentation, we retrospectively evaluated the postoperative radiographs and surgical records of 300 OUKAs in three consecutive cohorts of patients. The first cohort consists of the first 100 minimal invasive implantations of the OUKA using the conventional phase III instrumentation, the second cohort consists of the 100 most recent minimal invasive OUKA with the conventional phase III instrumentation and the third cohort consists of the first 100 minimal invasive OUKA using the new Oxford Microplasty instrumentation.

RESULTS

Mean bearing thickness was statistically significant and lower in OUKA with use of the updated instrumentation than with the conventional instrumentation (p = 0.01 and p = 0.04). Additionally, statistically significant and more femoral components were aligned within the accepted range of tolerance in both the coronal and the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group A (p = 0.029 and p = 0.038) and in the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group B (p = 0.002).

CONCLUSION

The new modified instrumentation seems to be an effective tool to reduce the risk of malalignment of the femoral component in the coronal and in the sagittal plane compared to the conventional phase III instrumentation. Furthermore, the instrumentation is also effective in determining an adequate level of tibial resection and thus avoiding unnecessary bone loss.

Superior femoral component alignment can be achieved with Oxford microplasty instrumentation after minimally invasive unicompartmental knee arthroplasty

PURPOSE

Oxford microplasty (MP) instrumentation has been developed to facilitate the reproducible and consistent performance of minimally invasive unicompartmental knee arthroplasty (MI-UKA) operation. The aim of this study was to compare the clinical and radiographic results of two groups of patients implanted using either a conventional instrumentation technique or an MP technique.

METHODS

A prospective cohort study of 108 knees in 108 patients who underwent an MI-UKA procedure using either conventionally instrumented UKA (CI-UKA) (52 knees of 52 patients) or MP-assisted UKA (MP-UKA) (56 knees of 56 patients). The clinical assessment included the Oxford Knee Score (OKS), the Knee Society Score (KSS), a visual analogue scale (VAS) for pain, and range of motion (ROM). Complications were also recorded.

RESULTS

No significant differences were observed between the two groups regarding OKS, KSS, VAS, and ROM. There were also no significant differences in terms of mechanical limb alignment and tibia implant alignment. However, the MP-UKA group showed significantly more accurate positioning of the femoral component than the CI-UKA group. Additionally, the MP-UKA group had more femoral prostheses implanted in the "satisfactory" range and fewer "outliers" than the CI-UKA group. No significant difference in complications was noted between the two groups.

CONCLUSION

This study suggested that compared with CI-UKA, MP-UKA provides significant improvements in increasing the accuracy of sagittal and coronal implantation of the femoral component and in reducing the numbers of outliers for femoral prosthetic alignment. It is advocated that the MP system should be considered when MI-UKA is performed.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

Patient-specific positioning guides do not consistently achieve the planned implant position in UKA

PURPOSE

To investigate whether the intended preoperative planning corresponded with the postoperative component position after medial UKA using patient-specific positioning guides (PSPGs).

METHODS

Twenty-five consecutive UKAs performed with the PSPG technique (Signature™) were included. Two independent observers performed postoperative CT measurements. The preoperative angles for the femoral component were defined in the frontal plane as 0°. In the first eight cases, a femoral component with single peg was inserted, and the flexion of the femoral component was set to 5°. In the last 17 cases, a twin-peg component was used and flexion set to 10°. In the axial plane, the femoral component was on average set at 2.5° internal rotation. The preoperative tibial component angles in the frontal and axial plane were defined as 0° and in the sagittal plane as 4° in flexion.

RESULTS

The postoperative femoral component angles were on average 0.8° of valgus (SD 3.2, range 12.2° valgus to 5.1° varus, n.s., CI -2.1 to 0.6), 5.0° of flexion (SD 3.9, range 10.2° flexion to 6.0° extension, p = 0.001, CI -5.3 to -1.5) and 4.0° of internal rotation (SD 1.7, range 1.4° to 6.9° int.rot., p < 0.001, CI -4.7 to -3.4). The tibial component angles were on average 3.0° of varus (SD 1.9, range 1.3° valgus to 6.8° varus, p < 0.001, CI 2.2 to 3.8), 3.2° of flexion (SD 2.4°, 6.7° flex to 1.8° ext, n.s., CI -0.2 to 1.7) and 2.7° of internal rotation (SD 7.0, range 16.6° int.rot. to 10.7° ext.rot., n.s., CI -5.6 to 0.2).

CONCLUSION

This study showed no agreement between preoperative planning and postoperative component alignment (p < 0.05) for the femoral component angle in sagittal and axial plane and for the tibial component angle in the coronal plane. Although the results did not show significant difference for the tibial component angle in the axial plane, a considerable range of the component angles was found varying from 17° internal to 11° external rotation. This study suggests that the use of PSPGs for UKA does not lead to consistent component position.

LEVEL OF EVIDENCE

IV.

Superior alignment but no difference in clinical outcome after minimally invasive computer-assisted unicompartmental knee arthroplasty (MICA-UKA)

PURPOSE

Variety of clinical trials have been published comparing the alignment of MICA-UKA with MI-UKA. However, to the best of our knowledge, no published study has showed whether radiological alignment by MICA-UKA has influence on the clinical results. The present study was conducted to compare the short-term results of MICA-UKA with MI-UKA. It was hypothesized that better alignment as well as clinical results was achieved by MICA-UKA as compared to MI-UKA.

METHODS

The clinical and radiological results of 87 subjects who underwent primary UKA using either minimally invasive and computer-assisted technique (45 patients Group A) or minimally invasive technique (42 patients, Group B) were reported. Knee Society scores (KSSs), Knee Society functional scores (KSFSs), range of motion (ROM), and radiographic results were assessed and reported preoperatively and at 24-month follow-up. Total blood loss, operative time, and length of skin incision were compared.

RESULTS

The accuracy of the implantations in relation to the coronal mechanical axis in Group A was significantly superior to that of Group B (P = 0.033). The femoral rotational profile revealed the prosthesis in Group A that was implanted with significantly less internal rotation than Group B (P = 0.025). Clinical results, with regard to ROMs and KSSs, as well as KSFSs were equally good in both the groups. The average blood loss in patients of Group A was significantly reduced as compared to patients of Group B. No significant difference was detected in terms of operative time or length of skin incision.

CONCLUSIONS

It is suggested that MICA-UKA improves the implant alignment without increasing clinical results versus MI-UKA. We advocate that computer navigation should be considered when minimally invasive unicompartmental knee arthroplasty is performed.

LEVEL OF EVIDENCE

Therapeutic study, Level II.

Does 3-Dimensional In Vivo Component Rotation Affect Clinical Outcomes in Unicompartmental Knee Arthroplasty?

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an effective treatment for single-compartment osteoarthritis. Limited studies have examined the relationship between component rotation and functional outcomes, with no existing consensus to guide "optimal" UKA component rotation. Our study aims to study the effect of 3-dimensional (3D) in vivo UKA component axial rotation on functional outcomes by determining (1) how much component axial rotation variability exists in UKA? and (2) does 3D in vivo UKA component axial rotation affect functional outcomes?

METHODS

Sixty-six UKAs from 58 consecutive patients (36 male [62.1%], age 63.7 ± 9.2 years, body mass index 28.2 ± 4.9 kg/m(2), and mean follow-up time 49.2 months) were imaged in weight-bearing standing position using biplanar radiography. We performed multiple comparisons to analyze the relationship between 3D UKA component alignment and European Quality of Life - 5 Dimensions (EQ-5D), UCLA activity score, and Knee Injury and Osteoarthritis Outcome Scores.

RESULTS

Significant improvements in EQ-5D, EQ-5D (United States adjusted), and Knee Injury and Osteoarthritis Outcome Scores (Sport/Rec) scores were noted postoperatively. However, high variability in 3D UKA femoral (6.2° ± 6.5°) and tibial (4.6° ± 6.4°) component positioning was observed. A trend toward better outcome scores in lower angles of femoral (<2.7° external rotation [ER]) and tibial (2.7° ER to 2.4° internal rotation [IR]) component rotation was noted, with better functional scores observed at mean femoral and tibial rotation angles of 3° ER to 3° IR.

CONCLUSION

Patients with UKA femoral and/or tibial component rotation angles within 3° ER to 3° IR of neutral component alignment reported better functional outcomes. Surgeons should be cognizant of the high variability noted in UKA component axial rotation and its potential correlation with functional scores.

Computerised navigation of unicondylar knee prostheses: from primary implantation to revision to total knee arthroplasty

AIM

Computerized navigation of unicondylar knee arthroplasties (UKA) is not a widespread technique. The lifespan of a UKA depends on the quality of its implantation. We know that overcorrection leads to a rapid extension of the osteoarthritis to the opposite side of the knee and undercorrection to a rapid loosening or wear of the prosthesis. Because of these difficulties and following a long experience with navigation of total knee arthroplasties (TKA) and osteotomies around the knee, we began using navigation for revisions to TKA in 2003 and for UKAs in 2008. The aim of this work is to present, firstly, the axial alignment of 79 medial and 19 lateral computer-assisted UKAs and, secondly, the axial alignment of 23 computer-assisted UKA revisions to TKA.

METHODS

In all the cases we used the Orthopilot^® device (BBraun-Aesculap, Tuttlingen, Germany), which is a non image-based navigation system.

RESULTS

For medial prostheses, the main objective was to obtain a post-operative HKA angle of 177° ± 2°, i.e. an under correction of 1-5°. This objective was met in 88.5 % of the cases. For lateral prostheses, the main objective was to achieve a post-operative HKA angle of 183° ± 2°, i.e. also an under correction of 1-5°. This objective was met in 84 % of the cases (3 cases at 186° and no cases of over correction). Regarding UKA revisions, the main objective was to ensure an HKA angle of 180° ± 3°. This was met in 92.4 % of the cases.

CONCLUSION

As for TKA and osteotomies, computerized navigation of UKAs and UKA revisions allows the pre-operative goal to be met easily.

Is tibial cut navigation alone sufficient in medial unicompartmental knee arthroplasty? Continuous series of fifty nine procedures

PURPOSE

Our purpose was to assess medial unicompartmental knee arthroplasty with navigation alone for the tibial cut and limb alignment. We hypothesised that this technique could be used routinely in practice.

METHODS

Outcome measures were tibial cut orientation and residual varus. Six-month post-operative radiographs of 59 knees were assessed.

RESULTS

Tibial cut orientation was within 2° of planned in 70.2 and 76.3 % of knees in the coronal and sagittal planes, respectively (49.1 % in both), within 4° in 91.2 and 91.5 %, respectively (82.5 % in both). All coronal-plane errors were in varus. Excessive planed tibial slope was at risk of excessive varus of the tibial cut. The hip-knee-ankle angle was ≤179° in 81.4 % and the mechanical axis through Kennedy Zone 2 in 59.3 % of knees. Risk factors for inadequate varus were pre-operative hip-knee-ankle angle >176° and strictly articular varus.

CONCLUSIONS

Our results are not as good as previously reported with this technique, but taking into account the factors of failure identified, we could enhance the results.

Three-Dimensional Imaging Analysis of Unicompartmental Knee Arthroplasty Evaluated in Standing Position: Component Alignment and In Vivo Articular Contact

BACKGROUND

Component malalignment in unicompartmental knee arthroplasty (UKA) has been associated with contact stress concentration and poor clinical outcomes. However, there is a paucity of data regarding UKA component alignment and in vivo articular contact in weight-bearing position. This study aims to (1) quantify three-dimensional UKA component alignment and (2) evaluate the association between the component alignment and in vivo articular contact in standing position.

METHODS

Seventy-seven UKAs in 68 consecutive patients were imaged in standing position using a biplanar X-ray imaging acquisition system. The UKA models were imported into a virtual imaging environment and registered with component silhouette on X-ray image for determination of component position and contact location. Anatomic bony landmarks of the lower limb were digitized for quantification of the bone alignment.

RESULTS

The femoral component (FC) showed 1.6° ± 3.3° valgus, 6.5° ± 6.4° external rotation, and 2.4° ± 4.6° flexion. The tibial component (TC) showed 3.9° ± 4.5° varus, 4.4° ± 6.7° internal rotation, and 10.1° ± 4.6° tibial slope. The average contact point was located medially and posteriorly by 7.8 ± 7.6% and 0.7 ± 7.7% of TC dimensions to its center. Multiple regression analysis identified FC flexion as a significant variable affecting UKA anterior and/or posterior contact position (R = 0.549, P < .001).

CONCLUSION

This study demonstrated the highest variability of UKA component positioning in axial plane rotation for FC and TC. The association between FC flexion and anterior contact position suggests accurate implant positioning may be important in optimizing in vivo UKA contact behavior. Further studies are required to gain understanding of the influence of axial rotation variability on in vivo UKA contact kinematics during functional activities.

Comparison of Outcome and Survival After Unicompartmental Knee Arthroplasty Between Navigation and Conventional Techniques With an Average 9-Year Follow-Up

BACKGROUND

Unicompartmental knee arthroplasty(UKA) has become a treatment of choice for many patients with isolated unicomparmental arthritis due to its specific advantages over total knee arthroplasty, but few studies have compared conventional and navigational UKA with similar instrumentation on mid- to long-term results. We investigated whether the use of imageless navigation can improve implant positioning and clinical outcomes of UKA at a long-term follow-up compared to the conventional technique.

METHODS

We prospectively studied clinical and radiological results in 68 patients with an average age of 64.0 years (range, 50 to 81 years) who received UKA between January 2003 and December 2005 using the conventional or navigational technique. Clinical evaluations were performed preoperatively and the last follow-up included knee range of motion, Hospital for Special Surgery (HSS) scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores and Visual Analogue Scale (VAS) pain score. For radiologic evaluation, the mechanical alignment of the lower limb was measured using mechanical femoro-tibial angle (mFTA) and Kennedy protocol.

RESULTS

After an average 9-year follow-up (range, 7.4 to 10.8 years), the navigation group showed better coronal alignments of the components, fewer radiological outliers and better clinical scores, but similar estimated 10-year prosthesis survival rates.

CONCLUSION

This study indicates that the use of navigation significantly contributes to the desired mechanical axis and improved component placement as compared to the conventional technique.

LEVEL OF EVIDENCE

Prospective comparative study, Level III.

Inaccurate rotational component position in image-free navigated unicompartmental knee arthroplasty

Background/Objective

The success of unicompartmental knee arthroplasty (UKA) is highly dependent on the accuracy of component and leg alignment. Computer-assisted surgery is gaining popularity in total knee arthroplasty with numerous studies reporting improved accuracy and decreased variability in implant position and postoperative limb alignment compared with conventional techniques. However, literature evaluating the accuracy of computer-navigated UKA is limited. Therefore, this study aimed to investigate the accuracy of component positions in navigated UKA using a three-dimensional (3D) image-matching system. To the best of our knowledge, this study is the first to evaluate the accuracy of implant-placement position in UKA using 3D image-matching systems.

Methods

Twenty-three knees in 22 patients (9 men, 13 women) underwent computer-assisted UKA performed by a senior surgeon from 2011 to 2013. All surgeries were performed with measured resection techniques using an image-free-navigation system. We recorded the coronal, sagittal, and rotational bone-resection angles towards the mechanical axis in the distal femur and proximal tibia using image-free navigation intraoperatively. The coronal, sagittal, and rotational alignments of the femoral and tibial components were also measured using the 3D image-matching system, and the accuracy of the navigated UKA was evaluated. The rotational alignment of the femur and tibia was defined as surgical epicondylar axis and Akagi's line, and a deviation over 3° from the AA was defined as an outlier.

Results

We observed coronal outliers for the femoral component in four of the 23 patients, and for the tibial component in three of the 23 patients. We also observed sagittal outliers for the femoral component in five of 23 patients, and for the tibial component in three of the 23 patients. Twenty-two tibial components were placed in external rotation relative to the rotational reference line.

Conclusion

In both coronal and sagittal alignments, there were a definite proportion of outliers. The ratio of outliers in rotational alignment was especially higher than that in coronal and sagittal alignments. In UKA, the identification of bony landmarks is difficult because of the small operation field. Therefore, careful surface mapping of particular bony landmarks is necessary, and it is not enough to use image-free navigation system in UKA.

High accuracy in knee alignment and implant placement in unicompartmental medial knee replacement when using patient-specific instrumentation

PURPOSE

The influence of patient-specific instrumentations on the accuracy of unicompartmental medial knee replacement remains unclear. The goal of this study was to examine the ability of patient-specific instrumentation to accurately reproduce postoperatively what the surgeon had planned preoperatively.

METHODS

Twenty consecutive patients (20 knees) who suffered from isolated unicompartmental medial osteoarthritis of the knee and underwent medial knee replacement using newly introduced magnetic resonance imaging-based patient-specific instrumentation were assessed. This assessment recorded the following parameters: (1) the planned and the postoperative mechanical axis acquired through long-leg AP view radiographies; (2) the planned and the postoperative tibial slope acquired by means of standard AP and lateral view radiographies; and (3) the postoperative fit of the implanted components to the bone in coronal and sagittal planes. The hypothesis of the study was that there was no statistically significant difference between postoperative results and preoperatively planned values.

RESULTS

The study showed that (1) the difference between the postoperative mechanical axis (mean 1.9° varus ± 1.2° SD) and the planned mechanical axis (mean 1.8° varus ± 1.2° SD) was not statistically significant; (2) the difference between the postoperative tibial slope (mean 5.2° ± 0.6° SD) and the planned tibial slope (mean 5.4° ± 0.6° SD) was statistically significant (p = 0.008); and (3) the postoperative component fit to bone in the coronal and sagittal planes was accurate in all cases; nevertheless, in one knee, all components were implanted one size smaller than preoperatively planned. Moreover, in two additional cases, one size thinner and one size thicker of the polyethylene insert were used.

CONCLUSIONS

This study suggests that overall patient-specific instrumentation was highly accurate in reproducing postoperatively what the surgeon had planned preoperatively in terms of mechanical axis, tibial slope and component fit to bone.

LEVEL OF EVIDENCE

IV.

Minor varus alignment provides better results than neutral alignment in medial UKA

INTRODUCTION

Few data exist regarding the outcome and survivorship of medial UKA in patients with minor varus alignment. The purpose of this study was therefore to analyse the clinical results of medial UKA implanted with no more than 7° of varus, and to verify whether there was a relationship between limb alignment and overall outcomes.

MATERIAL AND METHODS

One hundred and twenty five medial fixed-bearing UKAs with no more than 7° of varus were retrospectively analysed. The varus/valgus inclination and thickness of the bone cuts were performed relating to the proximal tibial epiphyseal axis. Patients were assessed with the IKS scores and range of knee motion. The subjects were classified into three groups according to the postoperative femoro-tibial mechanical alignment angle (group A: -2° to 1°; group B: 2° to 4°; group C: 5° to 7°).

RESULTS

The mean follow-up was 7.6years (range, 3.5-9.3). IKS knee scores increased proportionally with increasing varus according to a linear relationship (p≪0.01). Additionally, IKS knee scores were significantly higher in group B and still higher in group C if compared to those in group A (p=0.003). Finally, a significantly higher frequency of IKS function scores>90 points in subjects with femoro-tibial mechanical alignment angle≥4° was found (p=0.009).

CONCLUSIONS

Minor varus alignment does not compromise the mid- to long-term outcome of a medial UKA, and gives better results compared to neutral or close-to-neutral alignment.

LEVEL OF EVIDENCE

IV - Retrospective case series study.

Robotic guidance does not improve component position or short-term outcome in medial unicompartmental knee arthroplasty

We performed a retrospective review in a matched group of patients on the use of robotic-assisted UKA implantation versus UKA performed using standard operative techniques to assess differences between procedures. While both techniques resulted in reproducible and excellent outcomes with low complication rates, the results demonstrate little to no clinical or radiographic difference in outcomes between cohorts. Average operative time differed significantly with, and average of 20 minutes greater in, the robotic-assisted UKA group (P=0.010). Our minimal clinical and radiographic differences lend to the argument that it is difficult to justify the routine use of expensive robotic techniques for standard medial UKA surgery, especially in a well-trained, high-volume surgeon. Further surgical, clinical and economical study of this technology is necessary.

Improved accuracy in computer-assisted unicondylar knee arthroplasty: a meta-analysis

PURPOSE

Inaccurate implantation rates of up to 30 % have been reported in cases using the conventional technique for implantation of a unicompartmental knee arthroplasty. Navigation should permit a more precise implantation, and several studies have investigated its role, albeit with a limited number of patients and inconsistent results. The aim of this meta-analysis was to compare risks of unsatisfactory outcomes in patients with navigated and conventional technique.

METHODS

An electronic search was performed, and ten studies were eligible and included in the meta-analysis, with a total of 258 prostheses implanted with the navigated technique and 295 with the conventional one. The following items were analysed: radiological positioning of the femoral and the tibial component in the AP and lateral view, radiological analysis of the tibiofemoral mechanical axis and the difference in operating time between the two groups. Relative risks (RR) were calculated from the reported percentages of implants outside the optimal ranges defined by the manufacturers or the study groups. Natural logarithms of the relative risks were pooled by means of random effects models.

RESULTS

For all the analysed radiological parameters, the RR of measurements outside the optimal ranges were less than 1 in the navigation group suggesting a reduction in the risk of outliers with navigation. The average operating time in the navigated group was 15.4 min (95 % CI: 10.2-20.6) longer than in the conventional group.

CONCLUSION

The meta-analysis shows that the use of navigation systems in UKA leads to a more precise component position. Whether the more accurate position in UKA results in a better clinical outcome or long-term survival is yet unknown. Nevertheless, as a precise implant position appears to be beneficial, the use of navigation should be recommended for UKA. The limits defined by the manufacturers for an optimal positioning are not consistent.

Patient-specific instruments: industry's innovation with a surgeon's interest

PURPOSE

The aim of this study was (1) to survey the orthopaedic companies about the volume of patient-specific instruments (PSI) used in Europe and worldwide; (2) to survey a group of knee arthroplasty surgeons on their acceptance of PSI and finally; (3) to survey a medico-legal expert on PSI-related issues.

METHODS

Seven orthopaedic implant manufacturers were contacted to obtain their sales figures (in volume) of PSI in Europe and worldwide for the 2011 and 2012 period. During the Open Meeting of the Belgian Knee Society, a survey by a direct voting system was submitted to a selection of knee surgeons. Finally, a number of medico-legal 'PSI-related' questions were submitted to an adult reconstruction surgeon/legal expert.

RESULTS

The total volume, for all contacted companies, of PSI in Europe for 2012 was 17,515 total knee arthroplasty (TKA) and 82,556 TKA worldwide. Biomet (Warsaw, USA) was the number one in volume, both in Europe as worldwide with their Signature system. Biomet represented 27 % of the market share in PSI worldwide. Stryker preferred not to reply to the survey because of the FDA class 1 recall on ShapeMatch cutting guides. Eighty per cent of the Belgian knee surgeons expressed a great interest in PSI and especially, for 58 % of them, if it would increase their surgical accuracy. They valued it even more in unicompartmental arthroplasty, and 55 % was ready to use single-use instruments. Surprisingly, 47 % of surgeons thought it was the company's responsibility if something goes wrong with a PSI-assisted case. The medico-legal expert concluded that PSI is a complex process that exposes surgeons to new risks in case of failure and stated that companies should not produce surgical guides without validation of the planning by the surgeon.

CONCLUSION

Patient-specific instruments is of great interest if it can proof to increase the surgical accuracy in knee arthroplasty to the level surgeons are expecting and if in the same time it would make the surgical process more efficient.

LEVEL OF EVIDENCE

V.

Achievements during the Bone and Joint Decade 2000-2010

Musculoskeletal diseases continue to produce major disability around the world. Advances in therapy - particularly for the inflammatory diseases - have the potential to eradicate the inflammation and thus prevent joint destruction. Surgical advances include minimally invasive and computer-assisted robotic surgery, and advances in arthroscopic surgery. The development of new musculoskeletal tissues - tendons, cartilage and bone using nanotechnology and stem cells - has the potential to revolutionise the way we approach these chronic destructive diseases as well as major trauma. With the rapid increase in these conditions with an ageing population, new models of care will need to be developed to ensure that the right care is delivered at the right time by the most appropriately trained health professional and at a reasonable cost. The Bone and Joint Decade has played a significant role in focussing researchers, clinicians and health educators on these diseases and also in drawing them to the attention of Governments around the globe. While there is still much to be done, the journey has commenced and will continue into the future with education, research and service delivery into these important conditions being further enhanced.

Implant and limb alignment outcomes for conventional and navigated unicompartmental knee arthroplasty

Accurate implant positioning and restoration of lower limb alignment are major requirements for successful long-term results in unicompartmental knee arthroplasty (UKA). Alignment accuracy was compared between navigated-UKA (nUKA) and conventional-UKA (cUKA) groups using a retrospective matched case-control study (n=129, 58 nUKA, 71 cUKA). Mechanical axis (MA), hip-knee-ankle angle (HKA°), coronal implant alignment, and tibial implant posterior slope were measured. No statistically significant difference was observed when comparing MA, HKA° or coronal implant alignment (p>0.05). Statistical significance was seen with tibial component posterior slope (p=0.04, nUKA 4.2°, cUKA 2.9°); and between intra-operative navigationally determined HKA° and post-operative whole-leg standing (WLS) film HKA°. Navigation does not significantly improve UKA alignment compared to conventional methods. Further studies are needed to justify the use of this technology in UKA.

Deviation between navigated and final 3-dimensional implant position in mini-invasive unicompartmental knee arthroplasty: a pilot study in 13 patients

BACKGROUND AND PURPOSE

Unicompartmental knee arthroplasty (UKA) is an established method of treating isolated gonartrosis. Modern techniques such as computer-assisted surgery (CAS) and minimally invasive surgery (MIS) are attractive complementary methods to UKA. However, the positioning of the components remains a concern. Thus, we performed a prospective study to assess whether there was deviation between the navigated implant position and the final implant position.

PATIENTS AND METHODS

We performed UKA with MIS and CAS in 13 patients. By comparing intraoperative navigation data with postoperative computed tomography (CT) measurements, we calculated the deviation between the computer-assisted implant position and the final 3-D implant position of the femoral and tibial components.

RESULTS

The computer-assisted placement of the femoral and tibial component showed adequate position and consistent results regarding flexion-extension and varus-valgus. However, regarding rotation there was a large variation and 6 of 10 patients were outside the target range for both the femoral component and the tibial component.

INTERPRETATION

Difficulties in assessing anatomical landmarks with the CAS in combination with MIS might be a reason for the poor rotational alignment of the components.

Navigation of the tibial plateau alone appears to be sufficient in computer-assisted unicompartmental knee arthroplasty

PURPOSE

The aim of this study was to present our technique to implant unicompartmental knee arthroplasty (UKA) using navigation and to give our first results regarding the accuracy of the device.

METHODS

A total of 33 patients with medial femorotibial osteoarthritis (31) or avascular necrosis (2) were included in this study. The mean preoperative hip-knee-ankle (HKA) angle was 172.7 ± 2.2° (range 167-177°) and the preoperative planning aimed to reach an HKA angle between 175 and 179° (177 ± 2°), a tibial varus at 3 ± 1°, which means a tibial mechanical angle (TMA) close to 87 ± 1°, and posterior tibial slope at 3 ± 2°. In all cases, we used the OrthoPilot® device with dedicated software allowing us to navigate only the tibial plateau.

RESULTS

The preoperative plan was reached in 93.9 % of cases for HKA angle, 84.8 % for TMA and 100 % for the posterior slope.

CONCLUSIONS

Unicompartmental knee navigation is reliable. The navigation of only the tibial bone cut is a reasonable option as has been shown in this study. Its role is invaluable in the positioning of mobile-bearing UKA, where the risk of overcorrection should not be underestimated.

Navigation in minimally invasive unicompartmental knee arthroplasty has no advantage in comparison to a conventional minimally invasive implantation

INTRODUCTION

Minimally invasive implantation of unicompartmental knee prostheses can shorten rehabilitation time and lead to better functional results than conventional implantation. Exact positioning of the implant should be achieved, as this is a factor for the long-term survival of the prosthesis, although malpositioning can result due to the poor intraoperative view when using the minimally invasive approach. Navigation of the unicompartmental prosthesis could lead to a better implant positioning without losing the advantages of a minimally invasive approach.

MATERIALS AND METHODS

The same unicondylar knee prosthesis was implanted in a total of 40 patients, of whom 20 were implanted using navigation (kinematic navigation) and 20 using a conventional technique. The operating time was assessed in both groups. The orientation of the tibial and femoral implants was assessed radiologically postoperatively. We analysed these results according to the optimal positioning range proposed by the manufacturer. Furthermore, we examined the clinical results with the knee society score (KSS).

RESULTS

A good positioning of the prosthesis was observed in both techniques with only 11% of the radiologic measurements out of the proposed optimal range in each group. The operating time was significantly longer in the navigation group (17 min). The KSS did not differ between both groups at a follow-up of 16 resp. 18 months (navigated group: 184 points, conventional group: 178 points).

CONCLUSIONS

Navigation did not lead to a better positioning of the prosthesis than the conventional method and the operating time was longer. The clinical results were similar in both groups. The navigation may be a useful help for surgeons performing less unicompartmental knee arthroplasty using a minimally invasive approach.

Quantification of the difference between 3D CT and plain radiograph for measurement of the position of medial unicompartmental knee replacements

The aim of this study was to quantify the differences in measurements obtained from 3D Computed Tomography and plain radiograph, for the positioning of the tibial component of the Oxford unicompartmental knee replacement. Post-operative 3D Computed Tomography data and plain radiographs (long antero-posterior (AP) and short lateral) were obtained for 28 knees of patients who had undergone medial unicompartmental knee replacement. Parameters of the orientation/positioning of the tibial component: Varus/valgus, posterior tibial slope and rotation were measured with both modalities. Bland-Altman plots were used to calculate the 1.96 standard deviation limits of agreement (LOA) between imaging modalities. Intra class correlation was used to assess inter-method and inter-rater reliability (>0.81 = very good reliability). Radiographs were less reliable in all parameters, when compared with 3D CT (intra class correlation coefficients: tibial rotation 0.94 vs 0.96, varus/valgus 0.76 vs 0.94, and posterior tibial slope 0.82 vs 0.92). The LOA were -4.9° to 3.4° for varus/valgus (bias -0.7°, one third >3° different); -4.9° to 0.1° for posterior tibial slope (bias -2.4°, one third >3° different); and -20.6° to 16.1° for rotation (bias -2.2°, one third >10° different). There was some disagreement between measurement by 3D Computed Tomography and plain radiograph for all three parameters of tibial component orientation, especially tibial rotation. This will be particularly relevant to research into the relationship between the accuracy of implant positioning/orientation and patient satisfaction/implant survival rates. This method offers a more reliable standard for the reporting of knee arthroplasty.

Evaluation of implant position and knee alignment after patient-specific unicompartmental knee arthroplasty

Implant positioning and knee alignment are two primary goals of successful unicompartmental knee arthroplasty. This prospective study outlines the radiographic results following 32 patient-specific unicompartmental medial resurfacing knee arthroplasties. By means of standardized pre- and postoperative radiographs of the knee in strictly AP and lateral view, AP weight bearing long leg images as well as preoperative CT-based planning drawings an analysis of implant positioning and leg axis correction was performed.The mean preoperative coronal femoro-tibial angle was corrected from 7° to 1° (p<0.001). The preoperative medial proximal tibial angle of 87° was corrected to 89° (p<0.001). The preoperative tibial slope of 5° could be maintained. The extent of the dorsal femoral cut was equivalent to the desired value of 5mm given by the CT-based planning guide. The mean accuracy of the tibial component fit was 0mm in antero-posterior and +1mm in medio-lateral projection. Patient-specific fixed bearing unicompartmental knee arthroplasty can restore leg axis reliably, obtain a medial proximal tibial angle of 90°, avoid an implant mal-positioning and ensure maximal tibial coverage.

Nanoimaging and neurological surgery

Over 32 million surgical procedures are performed in the United States each year. Increasingly, image guidance is used in order to aid in the surgical localization of pathology, minimization of incisions, and improvement of surgical intervention outcomes. A variety of imaging modalities using different portions of the electromagnetic spectrum are used in neurological surgery. These include wavelengths used in ultrasonography, optical, infrared, ionizing radiation, and magnetic resonance. The use of currently available image-guidance tools for neurological surgery is reviewed. Advances in nanoparticulates and their integration into the neurosurgical operating room environment are discussed.

The accuracy of acquisition of an imageless computer-assisted system and its implication for knee arthroplasty

The majority of the current computer-assisted systems (CAS) for knee prosthetic surgery require the acquisition of points using a tracker detected by an infrared camera. Two types of measurements are then essential: angles and distances. The goal of this study was to evaluate the accuracy of the data obtained during computer-assisted surgery using an in vitro protocol. Two models were developed to locate precisely both points (120 acquisitions) and distance measurements (144 acquisitions) and angles (170 acquisitions) with an image-free CAS using an infrared optical camera. For validation, a precise coordinate 3D measurement device was used to assess the accuracy of CAS acquisitions. The points, distances and angles had a mean error respectively of 0.638 mm (0.244 mm to 0.931 mm), 0.355 mm (0.001 mm to 1.338 mm) and 0.39° (0.06° to 0.69°). For all these acquisitions, the mean error was statistically less than 1mm or 1° (p<0.001). By using a 3D measurement system, it was possible to determine the accuracy of the data obtained with the navigation system. The precision assessed at less than 1mm or 1° corresponds with the accuracy needed in knee arthroplasty and with the use of CAS as a measurement tool. Variability in computer-assisted navigation may be more likely related to other aspects of the procedure such as bony landmark acquisition, tolerance of saw blades and cutting jigs than the accuracy of the imageless CAS itself.

The long-term benefit of computer-assisted surgical navigation in unicompartmental knee arthroplasty

We reviewed the outcomes of 30 consecutive primary unicompartmental knee arthroplasties (UKA) performed by a single surgeon for medial compartmental osteoarthritis. Fifteen Allegretto knees were implanted without computer navigation and 15 EIUS knees were implanted with navigation. We compared the survivorship, radiological and clinical outcomes of the two groups at an average of 8.9 years and 6.9 years respectively. The patients were assessed clinically using the Oxford Knee Score (OKS) and radiologically using long-leg weightbearing films and non-weightbearing computed tomography alignment measurements. The overall survivorship was 86.7% at 9 years. A higher proportion of navigated knees were well aligned with a more reproducible position and malaligned knees tended to have a less favourable OKS. However, we found no statistically significant difference in survivorship, clinical outcome and radiological alignment between the two groups.

Accuracy of implantation during computer-assisted minimally invasive Oxford unicompartmental knee arthroplasty: a comparison with a conventional instrumented technique

The prognosis of unicompartmental knee arthroplasty (UKA) is strongly associated with the accuracy of the component alignment. To determine the accuracy of navigated UKA during primary minimally invasive Oxford UKA, twenty-nine knees of 29 consecutive patients (Group A) implanted using conventional instrumented UKA were followed by 23 knees of 17 consecutive patients (Group B) implanted by navigation assisted UKA and radiological results regarding alignments of the femorotibial mechanical axis, femur, and tibial component were compared in the two groups. Assessments of mechanical limb alignment revealed statistically significant increases in mechanical limb alignment post-operatively in both groups (p=0.0 for both). In terms of component alignment, Group B had more prostheses implanted in the satisfactory range (> ± 3° from the targeted values) for the femoral and tibial components than Group A. There were no significant differences in the rate of prosthesis implanted within the range of radiographic alignment variations for the coronal implantation of either femoral or tibial components in both groups. (Radiographic alignment variation; coronal orientation of femoral components 90 ± 10°, sagittal orientation of femoral components 90 ± 5°, coronal orientation of tibial components from 10° varus to 5° valgus, sagittal orientation of tibial components from 7° of posterior tibial flexion to 5° of anterior tibial flexion). However, significant increases in the accuracies of sagittal implantation of femoral and tibial components were observed in Group B versus Group A. Our data suggest that navigated implantation improves the accuracy of the radiological implantation of the Oxford UKA prosthesis without increasing complications versus conventional UKA.

Effect of preoperative deformity on postoperative leg axis in total knee arthroplasty: a prospective randomized study

Computer-assisted surgery-total knee arthroplasty (CAS-TKA) has been suggested to afford greater precision than conventional TKA; however, it is unclear whether this is influenced by preoperative angular deformity. This prospective study was conducted to determine the effect of preoperative angular deformity on the postoperative mechanical axis. Sixty patients underwent stage bilateral TKA; CAS-TKA was performed on one side and conventional TKA on the other side. It was demonstrated that severity of preoperative angular deformity affected the resulting alignment in conventional TKA, but not in CAS-TKA. The mechanical axis of the leg was within 3° of the planned axis in 83% of CAS-TKA but only 32% of conventional TKA cases when the preoperative angular deformity was >12° (P < 0.01). When the preoperative angular deformity was <12°, the mechanical axis of the leg was within 3° of the planned axis in 90% of CAS-TKA but only 69% of conventional TKA (P < 0.025). This study thus concluded that the resulting alignment in conventional TKA is influenced by large preoperative angular deformity. Consistent results in alignment can be achieved with CAS-TKA, though preoperative angular deformity still played a role in predicting the postoperative mechanical axis. CAS-TKA achieves better postoperative alignment than conventional TKA in both severe and mild preoperative angular deformity.

Sagittal flexion angle of the femoral component in unicompartmental knee arthroplasty: is it same for both medial and lateral UKAs?

The flexion of the femoral component in the sagittal plane in unicompartmental knee arthroplasty (UKA) was analyzed radiographically in this study. Thirty medial and 30 lateral UKAs were included. The sagittal flexion angles were measured both relative to the posterior femoral cortex and midline sagittal distal femoral axis. Both of the measurement methods revealed that the femoral components were inserted in a significantly more flexed fashion in the medial UKA group. Neither preoperative nor postoperative tibial slope did have any significant effect on the sagittal flexion angle. To the best of our knowledge, this is the first study demonstrating an angular difference in the sagittal flexion of the femoral components between medial and lateral UKAs.

Scientific evidence for the use of modern unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty as a surgical treatment for monocompartmental knee arthritis remains a controversial procedure with questions surrounding the benefits and survivorship of the procedure versus osteotomies or total knee arthroplasties. The authors, by examining the complete body of literature for scientific evidence concerning the procedure, will describe the history of usage of these prostheses, their rationale for usage, modern devices and their results, and why they may have advantages as a treatment modality for monocompartmental knee arthritis. Outcomes of current unicompartmental designs will be presented and evaluated to determine which aspects of the design and patient selection technique are associated with success or failure. Commonly asked questions regarding the use of these devices will be addressed. The authors will also describe some potential modifications that might affect the use of these components in the future, including minimally invasive procedures and robotics, and how these devices may change over the next 5 years.

The future of surgical orthopaedics of the knee

Over the past two decades, orthopaedics has gone through major changes, principally in the surgical treatment options for articular defects of the knee. This paper explores the advantages and shortcomings of the current surgical treatment modalities for cartilaginous defects in the knee. Emphasis is placed on current techniques in knee arthroplasty, including a view on the future of orthopaedic knee surgery.

Reliability of leg alignment using the OrthoPilot system depends on knee position: a cadaveric study

Despite the increase in clinical use of navigation systems in total knee arthroplasty, few studies have focused on the reproducibility of these systems. The aim of the present study was to assess the influence of knee position and observer experience on intra- and inter-observer agreement in limb alignment assessment with the OrthoPilot system. Limb alignment in the coronal plane and extension range of the knee were assessed in four embalmed cadaveric specimens by five independent observers and measurements were repeated four times to determine intra- and inter-observer agreement, expressed as intraclass correlation coefficients (ICCs). Additionally, navigation results were compared against figures from conventional measurement of leg alignment (ground truth). Intra- and inter-observer agreements were excellent for assessing the extension range (ICC, 0.97 and 0.95) and the coronal femuro-tibial axis in knee extension (ICC, 0.92 and 0.88) but were generally worse in knee flexion (ICC, 0.62 and 0.55). There was an increased tendency of intraobserver errors in observers with less clinical experience. Mean correlation with conventional measurements was fair (Spearman's rho 0.61). The OrthoPilot system showed excellent reproducibility for assessment of extension range and coronal limb alignment. However, assessments of coronal limb alignment in flexion were prone to error and caution should be taken when relying on these measurements.