No demonstrable benefit for coronal alignment outcomes in PSI knee arthroplasty: A systematic review and meta-analysis

The Role of 3D-Printed Patient-Specific Instrumentation in Total Knee Arthroplasty: A Literature Review

Total knee arthroplasty (TKA) is currently one of the most common orthopedic surgeries due to the ever-increasing average life expectancy. The constant need for effective and accurate techniques was contributed to the development of three-dimensional (3D) printing in that field, especially for patient-specific instrumentation (PSI) and custom-made implants fabrication. PSI may offer numerous benefits, such as resection accuracy, mechanical axis alignment, cost-effectiveness, and time economy. Nonetheless, the results of existing studies are controversial. For this purpose, a review article of the published articles was conducted to summarize the role of 3D-printed PSI in TKA.

Comparison of clinical outcomes of VISIONAIRE patient-specific instrumentation with conventional instrumentation in total knee arthroplasty: a systematic literature review and meta-analysis

INTRODUCTION

Malalignment and resulting complications are major challenges in total knee arthroplasty (TKA) which patient-specific instrumentation (PSI) is proposed to alleviate. Previous PSI meta-analyses of TKA outcomes typically do not differentiate between PSI systems and assess relatively few outcomes, so the value of their findings is limited. VISIONAIRE™ cutting guides (Smith + Nephew Inc., Memphis, TN, USA) is a PSI system based on preoperative magnetic resonance and X-ray imaging. A systematic literature review (SLR) and meta-analysis, focussed specifically on VISIONAIRE, were conducted to assess TKA accuracy, intraoperative outcomes, and postoperative outcomes, compared with conventional instrumentation (CI).

MATERIALS AND METHODS

The SLR was performed using PubMed, Embase, and Google Scholar databases to identify relevant studies published until March 2022. Depending on statistical heterogeneity, meta-analyses were performed for outcome measures with fixed effect (I2 < 50%) or random-effects models (I2 ≥ 50%). Dichotomous outcomes were reported as odds ratios and continuous outcomes were reported as mean differences. Descriptive analyses were performed for outcomes not amenable to meta-analysis.

RESULTS

Outcomes for VISIONAIRE versus CI were reported in 25 studies. Compared with CI, VISIONAIRE reduced odds of mechanical outliers by 40% (p < 0.0001), with no statistically significant differences in odds of overall coronal, sagittal, or rotational plane component outliers. VISIONAIRE improved surgical efficiency (operating room, turnover, and tourniquet times reduced by 7.3% (p = 0.02), 42% (p = 0.022), and 15.9% (p = 0.01), respectively), lowering the odds of blood transfusion by 53% (p = 0.01) and shortening patients' hospital stays (11.1% reduction; p < 0.0001). There were no significant differences between groups in incidence of postoperative complications and (descriptively analyzed) return-to-function outcomes.

CONCLUSION

Options for PSI in TKA differ substantially, and it is important to assess the outcomes of individual systems. The current findings suggest that VISIONAIRE guides can lead to improved alignment accuracy and surgical efficiency compared with CI, without compromising postoperative safety and return-to-function outcomes.

Comparison of accuracy for hip-knee-ankle (HKA) angle by X-ray and knee motion analysis system and the relationships between HKA and gait posture

BACKGROUND

The lower limb mechanical axis was used to assess the severity of knee osteoarthritis (KOA) with varus/valgus deformity and the accuracy of targeted lower limb alignment correction after operation by conventional X-rays. There are lots of parameters to assess the gait in elder patients such as velocity, stride length, step width and swing/stance ratio by knee joint movement analysis system. However, the correlation between the lower limb mechanical axis and gait parameters is not clear. This study is aimed at obtaining the accuracy of the lower limb mechanical axis by the knee joint movement analysis system and the correlation between the lower limb mechanical axis and gait parameters.

METHODS

We analysed 3D knee kinematics during ground gait of 99 patients with KOA and 80 patients 6 months after the operations with the vivo infrared navigation 3D portable knee joint movement analysis system (Opti-Knee®, Innomotion Inc, Shanghai, China). The HKA (Hip-Knee-Ankle) value was calculated and compared to X-ray findings.

RESULTS

HKA absolute variation after the operation was 0.83 ± 3.76°, which is lower than that before the operation (5.41 ± 6.20°, p = 0.001) and also lower than the entire cohort (3.36 ± 5.72). Throughout the cohort, a significant correlation with low coefficients (r = -0.19, p = 0.01) between HKA value and anterior-posterior displacement was found. In comparing the HKA values measured on the full-length alignment radiographs and 3D knee joint movement analysis system (Opti-Knee), there was a significant correlation with moderate to high coefficients (r = 0.784 to 0.976). The linear correlation analysis showed that there was a significant correlation between the values of HKA measured by X-ray and movement analysis system (R² = 0.90, p < 0.01).

CONCLUSIONS

Data with equivalent results as HKA, the 6DOF of the knee and ground gait data could be provided by infrared navigation based 3D portable knee joint movement analysis system comparing with the conventional X-rays. There is no significant effect of HKA on the kinematics of the partial knee joint.

Patient Specific Instruments and Patient Individual Implants—A Narrative Review

Joint arthroplasties are one of the most frequently performed standard operations worldwide. Patient individual instruments and patient individual implants represent an innovation that must prove its usefulness in further studies. However, promising results are emerging. Those implants seem to be a benefit especially in revision situations. Most experience is available in the field of knee and hip arthroplasty. Patient-specific instruments for the shoulder and upper ankle are much less common. Patient individual implants combine individual cutting blocks and implants, while patient individual instruments solely use individual cutting blocks in combination with off-the-shelf implants. This review summarizes the current data regarding the implantation of individual implants and the use of individual instruments.

Patient-specific instrumentation makes sense in total knee arthroplasty

INTRODUCTION

Patient-specific instrumentation (PSI) for total knee arthroplasty (TKA) surgery was initially developed to increase accuracy. The potential PSI benefits have expanded in the last decade, and other advantages have been published. However, different authors are critical of PSI and argue that the advantages are not such and do not compensate for the extra cost. This article aims to describe the recently published advantages and disadvantages of PSI.

AREAS COVERED

Narrative description of the latest publications related to PSI in accuracy, clinical and functional outcomes, operative time, efficiency, and other benefits.

EXPERT COMMENTARY

We have published high accuracy of the system, with a not clinically relevant loss of accuracy, significantly higher precision with PSI than with conventional instruments, and a high percentage of cases in the optimal range and similar to that obtained with computer-assisted navigation, greater imprecision for tibial slope, a significant blood loss reduction, and time consumption, an acceptable and non-significant increase in the cost per procedure and no difference in complications during hospital admission and at 90 days. We think that PSI will not follow the Scott Parabola and that it will continue to be a valuable type of device in some instances of TKA surgery.

Computed Tomography-Based Patient-Specific Instrumentation Loses Accuracy with Significant Varus Preoperative Misalignment

Patient-specific instrumentation (PSI) has been introduced to simplify and make total knee arthroplasty (TKA) surgery more precise, effective, and efficient. We performed this study to determine whether the postoperative coronal alignment is related to preoperative deformity when computed tomography (CT)-based PSI is used for TKA surgery, and how the PSI approach compares with deformity correction obtained with conventional instrumentation. We analyzed pre- and post-operative full length standing hip-knee-ankle (HKA) X-rays of the lower limb in both groups using a convention > 180 degrees for valgus alignment and < 180 degrees for varus alignment. For the PSI group, the mean (± SD) pre-operative HKA angle was 172.09 degrees varus (± 6.69 degrees) with a maximum varus alignment of 21.5 degrees (HKA 158.5) and a maximum valgus alignment of 14.0 degrees. The mean post-operative HKA was 179.43 degrees varus (± 2.32 degrees) with a maximum varus alignment of seven degrees and a maximum valgus alignment of six degrees. There has been a weak correlation among the values of the pre- and post-operative HKA angle. The adjusted odds ratio (aOR) of postoperative alignment outside the range of 180 ± 3 degrees was significantly higher with a preoperative varus misalignment of 15 degrees or more (aOR: 4.18; 95% confidence interval: 1.35-12.96; p = 0.013). In the control group (conventional instrumentation), this loss of accuracy occurs with preoperative misalignment of 10 degrees. Preoperative misalignment below 15 degrees appears to present minimal influence on postoperative alignment when a CT-based PSI system is used. The CT-based PSI tends to lose accuracy with preoperative varus misalignment over 15 degrees.

Comparative Study of Pinless Navigation System versus Conventional Instrumentation in Total Knee Arthroplasty

Backgroud

Optimal placement of the components and achieving a neutral mechanical axis are the main goals of total knee arthroplasty (TKA). Different computerised navigation systems are presently used for these purposes. This aim of this study was to compare the pinless navigation (PNA) TKA performed using iAssist with the conventional instrumented (CIN) TKA in terms of functional and radiological outcomes.

Methods

A total of 100 knees operated for TKA by a single surgeon were studied retrospectively for a period of 2 years. Weight-bearing postoperative radiographs of the knees along with scanograms of the lower limbs were used for measurements of component positioning, mechanical axis alignment, and number of outliers. Oxford knee scoring was used for functional analysis.

Results

No statistically significant difference was seen in the mean mechanical axis alignment (hip-knee-ankle angle), coronal alignment (α and β angles) and sagittal alignment (γ and δ angles) of the femoral and tibial components between the two groups. Though the percentage of outliers for mechanical axis alignment was lower in the PNA-TKA group than in the CIN-TKA group, the difference was not statistically significant (p = 0.73). The number of outliers for the femoral and tibial component positioning in coronal and sagittal planes was not statistically significantly different between the two groups. No statistically significant difference (p = 0.68) was noted between the two groups with respect to the Oxford Knee Score. The mean surgical time was greater in the PNA-TKA group by 11 minutes, which was statistically significantly longer (p = 0.018). Complications were seen in 6.89% of the cases in the CIN-TKA group, while none in the PNA-TKA group.

Conclusions

The accurate mechanical axis alignment and component positioning can be achieved with the conventional instrumentation, so the use of PNA system, which adds to the surgical cost, is questionable. Also, equally good short-term functional outcome can be achieved with the conventional instrumentation. The surgeon must be accustomed with the instrumentation of the PNA system, or it adds to the surgical time.

Patient-specific instrumentation (PSI) in total ankle arthroplasty: a systematic review

BACKGROUND

Patient-specific instrument (PSI) may theoretically make total ankle arthroplasty (TAA) more accurate. Several studies have reported the outcomes of PSI TAA. The aim of this study is to systematically review the literature of PSI TAA.

METHODS

PubMed, Embase, Web of Science, and Cochrane Library databases were systematically reviewed according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines for PSI TAA. The quality of the included studies was evaluated according to Methodological Index for Non-Randomized Studies (MINORS).

RESULT

Nine articles were ultimately included in the systematic review. The implant position and function outcome of TAA was similar between PSI and SI. Prediction accuracy of implant size remained great difference. PSI can shorten the operative time and fluoroscopy time. The quality of current studies on PSI TAA is insufficient to produce high-level evidence.

CONCLUSION

PSI can get similar implant position and clinical outcome in TAA compared to SI, but current evidence is not strong enough to evaluate PSI TAA.

Patientenspezifische Instrumentierung und Totalendoprothesen am Knie

Hintergrund

Die patientenspezifische Instrumentierung (PSI) ist eine vielversprechende neue Technologie in der orthopädischen Chirurgie, die das Ziel verfolgt, die Implantationstechnik der Knietotalendoprothese (Knie-TEP) im Vergleich zur konventionellen Instrumentierung zu vereinfachen und präziser zu machen. Ziel dieses Artikels ist es, Vorteile und Grenzen der PSI für die primäre Knie-TEP zu beschreiben.

Material und Methoden

Es erfolgte eine umfassende Literaturrecherche zum Thema PSI in der Knieprothetik hinsichtlich Evidenz für Planung, Präzision, klinische Ergebnisse, intraoperative Parameter sowie Kosten und Effizienz.

Ergebnisse

Die dreidimensionale Computertomographie (CT) weist in der präoperativen Planung der Knie-TEP eine höhere Genauigkeit auf als 2‑D-Röntgenaufnahmen. Die meisten Arbeiten postulierten keine signifikanten Effekte zugunsten der Genauigkeit der PSI gegenüber der Standard-Knie-TEP. Aber sie berichteten auch nicht, dass die Genauigkeit mit PSI schlechter sei. Hinsichtlich des klinischen Outcomes gibt es genügend Konsens unter den veröffentlichten Studien, um festzuhalten, dass es kurz- und mittelfristig keinen Unterschied zwischen Patienten gibt, die mit PSI oder konventioneller Technik operiert wurden. Eine große Metaanalyse konnte weder eine kürzere Operationszeit noch eine geringere Komplikationsrate für die PSI-Knie-TEP feststellen. Lediglich der intraoperative Blutverlust erwies sich als niedriger im Vergleich zur Standardtechnik, jedoch mit unveränderter Transfusionsrate. Kosteneffektivitätsanalysen lassen schlussfolgern, dass die PSI aktuell (noch) nicht kosteneffektiv ist.

Diskussion

Obwohl die aktuell vorliegenden Studienergebnisse die PSI-Technologie hinsichtlich vieler messbaren Kriterien nicht eindeutig von der Standardtechnik abheben, zeigt die PSI viele theoretische und praktische Vorteile.

Patient-Specific Instrumentation Accuracy Evaluated with 3D Virtual Models

There have been remarkable advances in knee replacement surgery over the last few decades. One of the concerns continues to be the accuracy in achieving the desired alignment. Patient-specific instrumentation (PSI) was developed to increase component placement accuracy, but the available evidence is not conclusive. Our study aimed to determine a PSI system’s three-dimensional accuracy on 3D virtual models obtained by post-operative computed tomography. We compared the angular placement values of 35 total knee arthroplasties (TKAs) operated within a year obtained with the planned ones, and we analyzed the possible relationships between alignment and patient-reported outcomes. The mean (SD) discrepancies measured by two experienced engineers to the planned values observed were 1.64° (1.3°) for the hip–knee–ankle angle, 1.45° (1.06°) for the supplementary angle of the femoral lateral distal angle, 1.44° (0.97°) for the proximal medial tibial angle, 2.28° (1.78°) for tibial slope, 0.64° (1.09°) for femoral sagittal flexion, and 1.42° (1.06°) for femoral rotation. Neither variables related to post-operative alignment nor the proportion of change between pre-and post-operative alignment influenced the patient-reported outcomes. The evaluated PSI system’s three-dimensional alignment analysis showed a statistically significant difference between the angular values planned and those obtained. However, we did not find a relevant effect size, and this slight discrepancy did not impact the clinical outcome.

Tibial tray rotation and posterior slope increase risk for outliers in coronal alignment

AIMS

The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation.

METHODS

We constructed a computer model of knee arthroplasty and used a virtual cutting guide to cut the tibia at 90° to the coronal plane. The virtual guide was rotated axially (15° medial to 15° lateral) and with posterior slopes (0° to 7°). To assess the effect of axial malrotation, we measured the coronal plane alignment of a tibial tray that was axially rotated (25° internal to 15° external), as viewed on a standard anteroposterior (AP) radiograph.

RESULTS

Axial rotation of the cutting guide induced a varus-valgus malalignment up to 1.8° (for 15° of axial rotation combined with 7° of posterior slope). Axial malrotation of tibial tray induced a substantially higher risk of coronal plane malalignment ranging from 1.9° valgus with 15° external rotation, to over 3° varus with 25° of internal rotation. Coronal alignment of the tibial cut changed by 0.07° per degree of axial rotation and 0.22° per degree of posterior slope (linear regression, R² > 0.99).

CONCLUSION

While the effect of axial malalignment has been studied, the impact on coronal alignment is not known. Our results indicate that the direction of the cutting guide and malalignment in axial rotation alter coronal plane alignment and can increase the incidence of outliers. Cite this article: Bone Joint J 2020;102-B(6 Supple A):43-48.

Different targets of mechanical alignment do not improve knee outcomes after TKA

BACKGROUND

Accurate alignment is a basic principle of TKA surgery, but achieving alignment within this target may not translate into superior outcomes after surgery.

PURPOSE

To assess if neutral TKA mechanical alignment was associated with superior knee outcomes and to examine the effect of various aspects of pre-operative and post-operative alignment on knee function.

METHODS

Analysis of a database of 444 TKA patients between June 2009 and October 2016. Knee outcomes (WOMAC, AKSS and knee range of motion) were collected before surgery and during follow-up at a minimum of six months.

RESULTS

Analysis included 444 TKA patients (62% female, mean age 66 years, mean follow-up 23 months). Deformity varied from 21° varus (mean = 7.9, SD = 2.8) to 17° valgus deformity (mean = 7.7, SD = 2.8). Pre-operatively, 101 (23%) knees were in native neutral mechanical alignment, while 278 (63%) were in varus and 65 (15%) were in valgus. Post-operatively, a group of 365 (82%) TKA were found to be in neutral mechanical alignment and a group of 79 (18%) TKA were noted to be 'Outliers' (17 [4%] TKA > 3° varus and 62 [14%] TKA > 3° valgus alignment). Restoration of the target of alignment of 0 ± 3° or 0 ± 1°, did not have better functional outcomes scores, range of motion or prosthesis longevity than those in the outlier range.

CONCLUSION

Neutral TKA alignment did not appear to be a significant contributing factor to the improvement in knee function in short-medium term follow-up.

Comparison of iASSIST Navigation System with Conventional Techniques in Total Knee Arthroplasty: A Systematic Review and Meta-Analysis of Radiographic and Clinical Outcomes

The iASSIST navigation system is a handheld accelerometer‐based navigation system that has been applied in clinical practice in recent five years. This meta‐analysis aimed to compare the radiographic and clinical outcomes of iASSIST navigation with conventional surgical techniques for patients undergoing total knee arthroplasty (TKA) and to compare the surgery time between an iASSIST group and a conventional treatment group. This systematic review and meta‐analysis included all comparative prospective and retrospective studies published in Pubmed, Embase, the Cochrane Central Register of Controlled Trials, the Web of Science and the CNKI databases over the past 20 years. Inclusion criteria were studies that compared the iASSIST navigation system with conventional TKA. The primary outcomes were mechanical axis (MA) and outliers, which means postoperative MA varus or valgus of more than 3°. Secondary outcomes were coronal femoral angle (CFA) and coronal tibial angle (CTA). Knee Society Score (KSS) was used to evaluate functional outcome. The Newcastle–Ottawa Scale (NOS) was used to assess the methodological quality of included studies. Eight studies involving 558 knees were included in this meta‐analysis. Of these, 275 patients used the iASSIST navigation system and 283 used conventional surgical techniques. A total of 5 studies were considered high quality and the other 3 were considered to be of moderate quality. The occurrence of malalignment of >3° in the iASSIST group was 13.3%, compared with 29.04% in the conventional group. Postoperative MA of the iASSIST group was significantly better than that of the conventional group (I² = 19%, OR = −0.92, 95% CI = −1.09 to −0.75, P < 0.00001). The iASSIST navigation system provided significantly increased accuracy in the coronal femoral angle (I² = 79%, OR = −0.88, 95% CI = −1.21 to −0.54, P < 0.00001) and the coronal tibial angle (I² = 34%, OR = 0.39, 95% CI = −0.48 to −0.30, P < 0.00001) compared with conventional techniques. However, the duration of surgery using the iASSIST procedure was longer and there was no significant difference in the short‐term KSS in the iASSIST group compared with the conventional group. We found that when pooling the data of included studies, the number of outliers was fewer in the iASSIST group, and compared with conventional TKA techniques, the iASSIST system significantly improved the accuracy of lower limb alignment but the duration of surgery was prolonged in addition to there being no apparent advantage in terms of short‐term functional score.

Postoperative mechanical alignment analysis of total knee replacement patients operated with 3D printed patient specific instruments: A Prospective Cohort Study

Objective

Total knee replacement (TKR) is a surgical treatment for final stage gonarthrosis. The lifespan of the prosthetic implants used in TKR surgery is a major interest for the orthopaedic research community.Previously, proper implant alignment of the implants has been advocated for longevity of the TKR surgery. Recently, patient-specific (PSI) instruments have been proposed to improve the mechanical alignment of the TKR by permitting better implant positioning over conventional TKR surgery. The aim of this study is to compare the mechanical alignment results of patients operated with PSIs and conventional instruments.

Methods

Two groups of 20 patients chosen in a quasi-random manner have been compared in this study. In the first group femoral distal and tibial osteotomies were made by a PSI which was produced by the patients' computed tomography scans. All osteotomies in the control group were made with the TKR set's routine instruments by conventional means. Patients' preoperative and postoperative mechanical femorotibal angles (mFTA), femoral coronal angles (FCA), tibial coronal angles (TCA) were measured and the number of outliers which showed more than 3° of malalignment were counted in both groups for comparison.

Results

The average postoperative mFTA was found to be 2.09° for the PSI group and in was found to be 2.84° for the control which was not statistically significant. The comparison of postoperative FCA and TCA also did not show significant difference between the groups. The number of outliers showing more than 3° of malalignment per group were found to be 1 out of 20 (5%) for the PSI group and 7 out of 20 (35%) for the control which was statistically significant.

Conclusion

In this study patient-specific instrumentation provided significantly better mechanical alignment compared to conventional TKR for the frequency of outlier cases with malalignment beyond 3°. PSI proved no significant difference when the groups were compared for mFTA, FCA and TCA. Our findings support that PSI may improve TKR alignment by improving the ratio of the outlier patients with marked malalignment.

Level of Evidence

Level III, Therapeutic Study.

A randomized controlled trial of tibial component migration with kinematic alignment using patient-specific instrumentation versus mechanical alignment using computer-assisted surgery in total knee arthroplasty

AIMS

Patient-specific instrumentation of total knee arthroplasty (TKA) is a technique permitting the targeting of individual kinematic alignment, but deviation from a neutral mechanical axis may have implications on implant fixation and therefore survivorship. The primary objective of this randomized controlled study was to compare the fixation of tibial components implanted with patient-specific instrumentation targeting kinematic alignment (KA+PSI) versus components placed using computer-assisted surgery targeting neutral mechanical alignment (MA+CAS). Tibial component migration measured by radiostereometric analysis was the primary outcome measure (compared longitudinally between groups and to published acceptable thresholds). Secondary outcome measures were inducible displacement after one year and patient-reported outcome measures (PROMS) over two years. The secondary objective was to assess the relationship between alignment and both tibial component migration and inducible displacement.

PATIENTS AND METHODS

A total of 47 patients due to undergo TKA were randomized to KA+PSI (n = 24) or MA+CAS (n = 23). In the KA+PSI group, there were 16 female and eight male patients with a mean age of 64 years (sd 8). In the MA+CAS group, there were 17 female and six male patients with a mean age of 63 years (sd 7). Surgery was performed using cemented, cruciate-retaining Triathlon total knees with patellar resurfacing, and patients were followed up for two years. The effect of alignment on tibial component migration and inducible displacement was analyzed irrespective of study group.

RESULTS

There was no difference over two years in longitudinal migration of the tibial component between the KA+PSI and MA+CAS groups (reaching median maximum total point motion migration at two years of 0.40 mm for the KA+PSI group and 0.37 mm for the MA+CAS group, p = 0.82; p = 0.68 adjusted for age, sex, and body mass index (BMI) for all follow-ups). Both groups had mean migrations below acceptable thresholds. There was no difference in inducible displacement (p = 0.34) or PROMS (p = 0.61 for the Oxford Knee Score) between groups. There was no correlation between alignment and tibial component migration or alignment and inducible displacement. These findings support non-neutral alignment as a viable option with this component, with no evidence that it compromises fixation.

CONCLUSION

Kinematic alignment using patient-specific instrumentation in TKA was associated with acceptable tibial component migration, indicating stable fixation. These results are supportive of future investigations of kinematic alignment. Cite this article: Bone Joint J 2019;101-B:929-940.

Patient-specific instrumentation in total knee arthroplasty

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Impact of Image-Derived Instrumentation on Total Knee Arthroplasty Revision Rates: An Analysis of 83,823 Procedures from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

Computer navigation and image-derived instrumentation (IDI) are technology-based methods developed to improve outcomes and potentially reduce revision total knee arthroplasty (TKA). IDI refers to the use of manufactured, patient-specific surgical jigs. Conflicting reports exist on IDI-associated improvements in outcomes. The primary aim of the current study was to compare the rates of revision among TKA cases in which components were initially implanted with use of IDI, computer navigation, or neither of these methods ("other" TKA). The secondary aim was to determine whether the outcomes of IDI differed for specific subgroups.

METHODS

Data were obtained from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) for the 3 TKA groups: IDI, computer-navigated, and other TKA. The study period was from the first IDI procedure recorded by the AOANJRR (April 2010) to December 31, 2016. The analysis was restricted to primary TKA cases undertaken for osteoarthritis and involving patellar resurfacing and the use of a cross-linked polyethylene insert. Subanalyses were performed to evaluate the effects of age, sex, implantation method, IDI manufacturer, prosthetic design, and prosthesis type on the rates of revision. Kaplan-Meier estimates of survivorship described the time to first revision. Hazard ratios (HRs, Cox proportional hazards models) with adjustment for age and sex were used to compare revision rates.

RESULTS

IDI was used in 5,486 primary TKA procedures. There was no significant difference among the groups in the cumulative percent revision (CPR) at 5 years: 3.3% (95% confidence interval [CI], 2.4% to 4.6%) for IDI, 2.4% (95% CI, 2.2% to 2.7%) for the computer-navigated group, and 2.5% (95% CI, 2.3% to 2.7%) for other TKA. Posterior-stabilized TKA with use of the IDI method had a significantly higher rate of revision at >3 months (HR, 1.45 [95% CI, 1.02 to 2.04]; p = 0.036), as did IDI TKA in the ≤65-year-old patient cohort (HR, 1.52 [95% CI, 1.10 to 2.09]; p = 0.010), compared with computer-navigated TKA. Patellar revision was significantly more likely in the IDI group.

CONCLUSIONS

IDI TKA demonstrated no overall difference in early to mid-term revision rates compared with standard implantation methods. However, elevated rates of revision were seen with posterior-stabilized TKA, in patients ≤65 years of age, and for patellar revision, meaning that this method should be used with some caution and requires further study.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Rotational component alignment in patient-specific total knee arthroplasty compared with conventional cutting instrument

BACKGROUND

Although many studies investigated the accuracy of customized cutting block (CCB), the data on rotational alignment are still lacking. The study aimed to assess whether CCB improved the component rotational position compared with conventional cutting instrument (CCI) using computed tomography scanning.

METHODS

Eighty-six of 102 total knee arthroplasties from the previous randomized study were analyzed. The outcomes were rotational position of the femoral and tibial components, frequency of outliers and intra-class correlation coefficient.

RESULTS

The mean femoral component rotation was not different between CCB versus CCI: 0.9° ± 0.8° versus 1.1° ± 1.1° (P = 0.29). Both groups had similar outlier frequencies: 2% (CCB) versus 2% (CCI) (P = 0.74). CCB had nearly 1° less mean tibial component deviation compared with CCI (P < 0.001): (1) dorsal tangent reference (DTR): 0.7° ± 0.8° versus 1.5° ± 1.0°, and (2) tibial trans-epicondylar reference (TTR): 0.5° ± 0.9° versus 1.4° ± 1.1°. Outlier frequencies were similar: (1) DTR: 0% CCB versus 5% CCI (P = 0.24), and (2) TTR: 5% in CCB versus 12% CCI (P = 0.20). Measurements based on tibial tubercle showed that CCB had ~ 1.4° less mean tibial component deviation compared with CCI: 0.3° ± 1.4° versus 1.7° ± 1.6° (P < 0.001) with a corresponding, less frequency of outliers: 0% versus 19% (P = 0.002). However, there was poor intra-observer reproducibility (0.61).

CONCLUSIONS

CCB did not improve femoral component rotational alignment compared with CCI nor affect outlier frequency, but it marginally improved the accuracy of tibial rotational alignment. The tibial tubercle reference point had poor intra-observer reproducibility.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

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

Computer navigation for total knee arthroplasty achieves better postoperative alignment compared to conventional and patient-specific instrumentation in a low-volume setting

BACKGROUND

Procedure volume is an important determinant of total knee arthroplasty (TKA) outcomes. We aimed to determine whether computer navigation or patient-specific instrumentation (PSI) would improve postoperative alignment in a low-volume setting.

HYPOTHESIS

PSI for TKA achieves better limb and implant alignment compared to conventional TKA and to computer navigated TKA.

MATERIALS AND METHODS

This is a retrospective cohort study of 385 primary TKAs (Women=59%. Mean age=67years. Mean BMI=30.1kg/m²), which were performed using conventional instrumentation (n=117; 30%), computer navigation (n=209; 54%), or patient-specific instrumentation (n=59; 15%) in a low-volume center (<50 TKAs/year). The risk of postoperative leg and implant mechanical alignment outliers in the coronal plane (>3° from neutral), average alignment and operation time were assessed.

RESULTS

The risk of postoperative mechanical alignment outliers (>3°) was reduced by 89% in the navigated group (4% outliers) compared to the conventional group (35%) (RR=0.11; p<0.0001). No significant improvement was observed in the PSI group (27%) (RR=0.91; p=0.772). The risk of postoperative femoral component coronal alignment outliers was reduced by 63% in the navigated group (11%) compared to the conventional group (31%) (RR=0.37; p=0.018). No significant reduction in outliers was observed in the PSI group (32%) (RR=1.08; p=0.816). There was a reduction in the risk of tibial component coronal malalignment of 66% in the navigated group (5%) compared to the conventional group (13%) (RR=0.33; p=0.070). There was a two-fold increase in the risk of tibial component alignment outliers in the PSI group (29%) (RR=1.94; p=0.110).

DISCUSSION

Computer navigation improved postoperative alignment in TKA. No evidence of improved alignment was seen with patient-specific instrumentation. The routine use of patient-specific instrumentation in low-volume centers is not supported by the currently available data.

TYPE OF STUDY

Retrospective cohort study. Level IV.

Conventional versus Smart Wireless Navigation in Total Knee Replacement: Similar Outcomes in a Randomized Prospective Study

Purpose  The development of new computer-assisted navigation technologies in total knee arthroplasty (TKA) has attracted great interest; however, the debate remains open as to the real reliability of these systems. We compared conventional TKA with last generation computer-navigated TKA to find out if navigation can reach better radiographic and clinical outcomes.

Methods  Twenty patients with tricompartmental knee osteoarthritis were prospectively selected for conventional TKA ( n  = 10) or last generation computer-navigated TKA ( n  = 10). Data regarding age, gender, operated side, and previous surgery were collected. All 20 patients received the same cemented posterior-stabilized TKA. The same surgical instrumentation, including alignment and cutting guides, was used for both the techniques. A single radiologist assessed mechanical alignment and tibial slope before and after surgery. A single orthopaedic surgeon performed clinical evaluation at 1 year after the surgery. Wilcoxon's test was used to compare the outcomes of the two groups. Statistical significance was set at p  < 0.05.

Results  No significant differences in mechanical axis or tibial slope was found between the two groups. The clinical outcome was equally good with both techniques. At a mean follow-up of 15.5 months (range, 13–25 months), all patients from both groups were generally satisfied with a full return to daily activities and without a significance difference between them.

Conclusion  Our data showed that clinical and radiological outcomes of TKA were not improved by the use of computer-assisted instruments, and that the elevated costs of the system are not warranted.

Level of Evidence  This is a Level II, randomized clinical trial.

Stability and alignment do not improve by using patient-specific instrumentation in total knee arthroplasty: a randomized controlled trial

PURPOSE

The primary aim of the study was to examine stability and alignment after total knee arthroplasty (TKA) using patient-specific instrumentation (PSI) and conventional instrumentation (CI). The hypothesis was that stability and alignment would be better using PSI than CI, 12 months postoperatively. The secondary aim included the evaluation of clinical outcomes after TKA.

METHODS

In this prospective randomized controlled trial, 42 patients with knee osteoarthritis received a Genesis II PS prosthesis with either PSI or CI. Patients visited the hospital preoperatively and postoperatively after 6 weeks and 3 and 12 months. To evaluate stability, varus-valgus laxity was determined in extension and flexion using stress radiographs 12 months postoperatively. Three months postoperatively, a long-leg radiograph and CT scan were obtained to measure hip-knee-ankle (HKA) alignment and component rotation. Furthermore, frontal and sagittal alignment of the components, the Knee Society Score, VAS Pain, VAS Satisfaction, Knee injury and Osteoarthritis Outcome score, Patella score (Kujala), University of California Los Angeles activity score, anterior-posterior laxity, (serious) adverse device-related events, and intraoperative complications were reported. The clinical outcomes were compared using independent t tests or non-parametric alternatives, and repeated measurements ANOVA with a significance level of p < 0.05.

RESULTS

No significant differences were found between the two groups regarding stability, HKA angle, and rotational alignment. In four patients, the PSI did not fit correctly on the tibia and/or femur requiring intraoperative modifications. Both groups improved significantly over time on all clinical outcomes, with no significant differences between the groups 12 months postoperatively. The PSI group showed less tibial slope than the patients in the CI group [PSI 2.6° versus CI 4.8° (p = 0.02)]. Finally, the PSI group more frequently received a thinner insert size than the CI group (p = 0.03).

CONCLUSIONS

Patients operated with PSI did not differ from CI in terms of stability and alignment. However, in the PSI group ligament releases were more often required intraoperatively. Furthermore, the two methods did not show different clinical results. It seems that the preoperative planning for the PSI facilitates more conservative bone cuts than CI, but whether this is clinically relevant should be investigated. Since PSI is more expensive and time consuming than CI, and does not outperform CI with regard to clinical results, we recommend to use CI.

LEVEL OF EVIDENCE

I.

Increased precision of coronal plane outcomes in robotic-assisted total knee arthroplasty: A systematic review and meta-analysis

BACKGROUND

Inaccuracy of component alignment in total knee arthroplasty adversely impacts outcomes. Robotic systems improve translation of pre-operative planning to intra-operative steps, theoretically resulting in greater accuracy and precision. In this study we systematically review literature data of alignment outcomes and apply meta-analysis methods to assess whether robotic-assisted knee arthroplasty provides superior outcomes when compared to conventional knee prostheses.

METHODS

A PRISMA compliant search comparing alignment outcomes in robotic vs conventional knee arthroplasty was performed. Primary outcome measures were; number of three degree outliers and mean deviation from a neutral post-operative mechanical axis.

RESULTS

In total, from five studies reporting upon 402 knees, a post-operative mechanical axis malalignment of >3° occurred in 1/181 (0.006%) of robotic knees, and 42/159 (26.4%) of conventional knees with a meta-analysis odds ratio of 0.04 (95% CI 0.01-0.14), p < 0.00001 favouring robotic-assisted instrumentation. Meta-analysis also demonstrated weighted mean differences of post-operative mechanical axis alignment to be significantly more accurate in the robotic knee group: mean difference -0.63 (95% CI: -1.18,-0.08), z = 2.25, p = 0.02. Sensitivity analysis with inclusion of only Level 1 studies showed similar findings.

CONCLUSIONS

This systematic review and meta-analysis demonstrates clear evidence of increased accuracy of alignment in robotic-assisted knee arthroplasty with specific regard to reconstituting a neutral mechanical axis and minimising number of outliers in the coronal plane. Further studies and long term data is required in order to conclude on survivorship and functional outcomes.

Three-dimensional analysis of accuracy of component positioning in total knee arthroplasty with patient specific and conventional instruments: A randomized controlled trial

BACKGROUND

Component malalignment remains a major concern in total knee arthroplasty (TKA). Patient-specific guides (PSG) were developed to increase accuracy of bone resections and component placement, but available evidence is contradictory. We assessed the accuracy of 3D component placement in TKA with PSG compared to conventional surgery using virtual 3D bone models.

METHODS

Fifty patients were randomly assigned to the PSG or conventional instrumentation group, 44 were finally analyzed. Preoperatively, MRI and CT scans were converted into virtual 3D models and a surgical plan was developed. Surgery was performed and changes in component sizing were recorded. Postoperative CT images were converted to 3D models and aligned to the planned, preoperative models and implant orientation. Differences between planned and postoperative implant orientations were calculated in 3D.

RESULTS

PSG allowed significantly more accurate varus/valgus placement for the femoral component (PSG: 0.14±1.47; control: 1.40±1.99; p<0.05), but more slope was introduced (PSG: 2.82±2.42; control: 0.90±2.28; p<0.05). Less variability in positioning accuracy for femoral flexion angle and tibial rotation was found with PSG, indicating a result closer to the planned position, but no significant differences in positioning accuracy were found. PSG allowed more accurate prediction of the femoral (PSG: 100%; control: 64%) and tibial (PSG: 79%; control 56%) component size.

CONCLUSION

PSG led to adequate component positioning accuracy compared to the pre-operative plan. For the femoral component, the positioning was significantly closer to the planned position in the coronal plane, a similar trend was observed for the sagittal plane. But, for the tibial component, significantly more slope was introduced. A better prediction of component sizing was found with PSG compared to conventional surgery.

Mapping of the anterior tibial profile to identify accurate reference points for sagittal alignment of tibial component in total knee arthroplasty

BACKGROUND

Although standard instrumentation is the procedure most frequently used to implant a Total Knee Arthroplasty (TKA), high rates of malalignment of tibial component are reported using this technique. Anatomical landmarks for sagittal alignment have been little investigated and the best reference axis, which parallels the mechanical axis, is yet to be established.

HYPOTHESIS

Mapping the Anterior Tibial Profile (ATP) may allow the identification of segmental zones of the ATP parallel to the mechanical axis which can be used to align the extramedullary rod.

METHODS

An intramedullary rod was positioned in line with the mechanical axis in 47 dried cadaveric tibiae. The rod was connected to a cutting jig and to an extramedullary rod. Digitalized images of lateral view radiographs were taken and the distance between the ATP and the extramedullary rod was measured at 10-mm intervals and at interpolated distances corresponding to every 2% of the tibial length.

RESULTS

Segmental portions of the ATP exhibit an alignment parallel to the mechanical axis between points located at 58% and 90% and at 62% and 88% of the tibial length. Points placed at 50% of tibial length and 5mm proximal to the ankle joint generate the longer axis parallel to the mechanical axis.

CONCLUSION

The orientation of sagittal tibial cut may be improved by aligning the extramedullary rod parallel to the ATP at definite points. Points placed at 50% of the tibial length and 5mm proximal to the ankle joint may be preferred since they generate the longer axis parallel to the mechanical axis and are more easily identified at surgery.

Postoperative alignment of TKA in patients with severe preoperative varus or valgus deformity: is there a difference between surgical techniques?

BACKGROUND

There have been conflicting studies published regarding the ability of various total knee arthroplasty (TKA) techniques to correct preoperative deformity. The purpose of this study was to compare the postoperative radiographic alignment in patients with severe preoperative coronal deformity (≥10° varus/valgus) who underwent three different TKA techniques; manual instrumentation (MAN), computer navigated instrumentation (NAV) and patient specific instrumentation (PSI).

METHODS

Patients, who received a TKA with a preoperative coronal deformity of ≥10° with available radiographs were included in this retrospective study. The groups were: MAN; n = 54, NAV; n = 52 and PSI; n = 53. The mechanical axis (varus / valgus) and the posterior tibial slope were measured and analysed using standing long leg- and lateral radiographs.

RESULTS

The overall mean postoperative varus / valgus deformity was 2.8° (range, 0 to 9.9; SD 2.3) and 2.5° (range, 0 to 14.7; SD 2.3), respectively. The overall outliers (>3°) represented 30.2% (48 /159) of cases and were distributed as followed: MAN group: 31.5%, NAV group: 34.6%, PSI group: 24.4%. No significant statistical differences were found between these groups. The distribution of the severe outliers (>5°) was 14.8% in the MAN group, 23% in the NAV group and 5.6% in the PSI group. The PSI group had significantly (p = 0.0108) fewer severe outliers compared to the NAV group while all other pairs were not statistically significant.

CONCLUSIONS

In severe varus / valgus deformity the three surgical techniques demonstrated similar postoperative radiographic alignment. However, in reducing severe outliers (> 5°) and in achieving the planned posterior tibial slope the PSI technique for TKA may be superior to computer navigation and the conventional technique. Further prospective studies are needed to determine which technique is the best regarding reducing outliers in patients with severe preoperative coronal deformity.

Efficacy of Patient-Specific Instruments in Total Knee Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

Patient-specific instrumentation (PSI) was introduced with the aim of making the procedure of total knee arthroplasty more accurate and efficient. The purpose of this study was to compare PSI and standard instrumentation in total knee arthroplasty with regard to radiographic and clinical outcomes as well as operative time and blood loss.

METHODS

A meta-analysis was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement. PubMed and Embase were searched from 2011 through 2015. We included randomized controlled trials and cohort studies that reported the effect of PSI on the aforementioned outcomes. The primary end point was deviation from the mechanical axis by >3°. Random and fixed-effect models were used for analysis.

RESULTS

A total of 44 studies, which included 2,866 knees that underwent surgery with PSI and 2,956 knees that underwent surgery with standard instrumentation, were evaluated. The risk of mechanical axis malalignment was significantly lower for PSI, with a pooled relative risk of 0.79 (p = 0.013). The risk of tibial sagittal-plane malalignment was higher for PSI than for standard instrumentation (relative risk = 1.32, p = 0.001), whereas the risk of femoral coronal-plane malalignment was significantly lower (relative risk = 0.74, p = 0.043). The risk of tibial coronal-plane malalignment was significantly higher for PSI only when employing fixed-effect meta-analysis (relative risk = 1.33, p = 0.042). Minor reductions in total operative time (-4.4 minutes, p = 0.002) and blood loss (-37.9 mL, p = 0.015) were noted for PSI.

CONCLUSIONS

PSI improves the accuracy of femoral component alignment and global mechanical alignment, but at the cost of an increased risk of outliers for the tibial component alignment. The impact of the increased probability of tibial component malalignment on implant longevity remains to be determined. Meta-analyses indicated significant differences with regard to operative time and blood loss in favor of PSI. However, these differences were minimal and, by themselves, not a substantial justification for routine use of the technology.

LEVEL OF EVIDENCE

Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

The early outcome of kinematic versus mechanical alignment in total knee arthroplasty: a prospective randomised control trial

AIMS

Our aim was to compare kinematic with mechanical alignment in total knee arthroplasty (TKA).

PATIENTS AND METHODS

We performed a prospective blinded randomised controlled trial to compare the functional outcome of patients undergoing TKA in mechanical alignment (MA) with those in kinematic alignment (KA). A total of 71 patients undergoing TKA were randomised to either kinematic (n = 36) or mechanical alignment (n = 35). Pre- and post-operative hip-knee-ankle radiographs were analysed. The knee injury and osteoarthritis outcome score (KOOS), American Knee Society Score, Short Form-36, Euro-Qol (EQ-5D), range of movement (ROM), two minute walk, and timed up and go tests were assessed pre-operatively and at six weeks, three and six months and one year post-operatively.

RESULTS

A total of 78% of the kinematically aligned group (28 patients) and 77% of the mechanically aligned group (27 patients) were within 3° of their pre-operative plan. There were no statistically significant differences in the mean KOOS (difference 1.3, 95% confidence interval (CI) -9.4 to 12.1, p = 0.80), EQ-5D (difference 0.8, 95% CI -7.9 to 9.6, p = 0.84), ROM (difference 0.1, 95% CI -6.0 to 6.1, p = 0.99), two minute distance tolerance (difference 20.0, 95% CI -52.8 to 92.8, p = 0.58), or timed up and go (difference 0.78, 95% CI -2.3 to 3.9, p = 0.62) between the groups at one year.

CONCLUSION

Kinematically aligned TKAs appear to have comparable short-term results to mechanically aligned TKAs with no significant differences in function one year post-operatively. Further research is required to see if any theoretical long-term functional benefits of kinematic alignment are realised or if there are any potential effects on implant survival. Cite this article: Bone Joint J 2016;98-B:1360-8.

Patient-specific instrumentation versus conventional instrumentation in total knee arthroplasty

PURPOSE

To compare patient-specific instrumentation (PSI) with conventional instrumentation in total knee arthroplasty (TKA) in terms of component alignment, operating time, and the learning curve required in a non-teaching hospital.

METHODS

Records of 33 men and 29 women aged 50 to 88 (mean, 71) years who underwent TKA for osteoarthritis using PSI (n=31) or conventional instrumentation (n=31) by a single surgeon were reviewed. The choice of instrumentation was made by the patient; the surgeon did not express any preference and had not used PSI before. All patients used the same cemented, cruciate-retaining system.

RESULTS

The PSI and conventional instrumentation groups were comparable in terms of age, body mass index (BMI), American Society of Anesthesiologists grade, pre- and post-operative haemoglobin level, and the need for blood transfusion. Compared with conventional instrumentation, PSI resulted in a smaller coronal femoral component angle (7.7º vs. 6.4º, p=0.003) and posterior tibial slope angle (6.4º vs. 3.2º, p=0.0001), and smaller variance of the respective angles (p=0.006 and p=0.003). In patients with a BMI ≥30, PSI still resulted in a smaller posterior tibial slope angle (5.8º vs. 3.1º, p=0.015) and variance of the angle (p=0.02). The mean tourniquet time was shorter in the PSI group in all patients (p=0.013) and in patients with BMI ≥30 kg/m2 (p=0.0008), and its variance was also smaller in the PSI group (p=0.0004). There was no learning curve required.

CONCLUSION

PSI was simple to use, with no learning curve required. It can be used in non-teaching hospitals and in patients with a high BMI and in cases where the use of an intramedullary alignment guide would be problematic due to previous femoral trauma.

Radiographic outcomes in the coronal plane with iASSIST™ versus optical navigation for total knee arthroplasty: A preliminary case-control study

BACKGROUND

The new navigation system iASSIST™ for total knee arthroplasty (TKA) relies on accelerometers and gyroscopes. The objective of this prospective study was to compare the accuracy of iASSIST™ to that of the conventional optical navigation system Navitrack™ by determining the rate of mechanical axis restoration (±3°), postoperative mean mechanical alignment, rate of adequate femoral and tibial component positioning, mean operative time, and occurrence of navigation-related adverse events.

HYPOTHESIS

The rate of mechanical axis restoration (±3°) is not lower with iASSIST™ than with the conventional navigation system Navitrack™.

MATERIAL AND METHODS

Of 40 patients who underwent primary TKA between October 2013 and March 2014, 20 had navigation using iASSIST™ and 20 using Navitrack™. Six months after TKA, an independent observer measured three parameters on coronal radiographs: the hip-knee-ankle angle (HKA), the mechanical lateral distal femoral angle (mLDFA), and the mechanical medial proximal tibial angle (mMPTA).

RESULTS

The two groups showed no significant differences for the rates of HKA restoration (P=0.3), adequate coronal positioning of the femoral component (P=0.12) and tibial component (P=0.12), or optimal success (P=0.09). Significant differences in favour of iASSIST™ were demonstrated for the values and angular deviations of the HKA (P=0.02) and mMPTA (P=0.01), whereas no significant difference was found for mLDFA. There were no significant differences regarding the mean operative time (P=0.06) or the occurrence of navigation-related adverse events (P=0.18).

DISCUSSION

The iASSIST™ system provides a neutral mechanical axis and optimal component position in the coronal plane in 95% of cases, indicating that it is as accurate as the optical navigation system Navitrack™.

LEVEL OF EVIDENCE

III, prospective case-control study.

Favourable rotational alignment outcomes in PSI knee arthroplasty: A Level 1 systematic review and meta-analysis

BACKGROUND

Implant malposition in total knee arthroplasty (TKA) often results in unsatisfactory outcomes. Rotational malalignment leads to impaired patellar tracking, stability and joint biomechanics. Patient-specific instrumentation aims to improve three-dimensional implant positioning while reducing overall costs of instrumentation.

METHODS

A PRISMA compliant search of all relevant literature between 2000 and 2014 was performed. The primary outcome of interest was deviation from a neutral femoral and tibial axial alignment of patient-specific instrumentation (PSI) vs conventional instrumentation. Femoral rotation was measured with reference to the transepicondylar axis. Tibial rotation was reported with reference to the anterior tibial tuberosity and a "best fit" with the anterior tibial cortex.

RESULTS

Six randomised studies met the inclusion criteria reporting on a total of 444 knees. Computed tomography (CT) based PSI systems were used exclusively in three studies, and two further studies in association with magnetic resonance imaging (MRI). MRI was used exclusively in one study. Mean femoral rotation in the conventional group was: -1.7 to 1.6° (vs -1.7 to 1° in the PSI group). Meta-analysis demonstrated a significant treatment effect favouring PSI with increased accuracy in "three-degree outliers" with femoral rotation: Z=2.07, P=0.04. A single study reported tibial rotational outcomes with no significant difference demonstrated in conventional instrumentation vs PSI.

CONCLUSIONS

This Level 1 meta-analysis demonstrates favourable femoral rotational alignment outcomes in PSI knee arthroplasty. Only limited data is available for tibial rotational outcomes. Further studies with standardised "gold-standard" measurement criteria are required to clarify tibial rotational outcomes in PSI TKA.

LEVEL OF EVIDENCE

1.

Poor reproducibility of the MRI measurement of distal femoral torsion

Recent publications on patient-specific instrumentation for total knee arthroplasty have reported considerable variability in the axial positioning of the cutting guides for the femoral component. These personalized cutting guides are manufactured based on bone shape data, generated from magnetic resonance imaging (MRI) or computed tomography (CT). The goal of this study was to compare the reproducibility and accuracy of distal femoral torsion (DFT) values measured using these two imaging modalities. We hypothesized that MRI does not reproducibly and consistently measure DFT and is not as accurate as CT scan.

METHODS

Anonymized radiology records from 54 patients that included MRI and CT scans of the knee were read in random order by two observers, on two separate occasions. These records were from patients being considered for a meniscal or osteochondral graft and who had their knee explored, but who had not undergone femoral or tibial surgery and were free of osteoarthritis. The DFT was estimated using the posterior condylar angle (PCA), using both its anatomical and surgical definitions. The intra- and inter-observer reproducibility of the MRI and the differences relative to CT scan measurements were analysed.

RESULTS

The average intra-observer difference for the MRI evaluation of the anatomical PCA was 0.8±1.2°; it was 0.4±0.9° for the surgical PCA. More than 1° difference from the average was found in 8 cases (14%) using the anatomical PCA measurement and 4 cases (7.4%) when using the surgical PCA (P=0.4). The intraclass correlation coefficients (ICCs) were 0.67 (95% CI: 0.33-0.85) and 0.74 (95% CI: 0.47-0.89) for the anatomical and surgical PCA, respectively. The average inter-observer difference for the MRI evaluation of the anatomical PCA was 1.6±1.4°; it was 1.5±1.0° for the surgical PCA. More than 1° difference from the average was found in 27 cases (50%) using the anatomical PCA measurement and 22 cases (40%) when using the surgical PCA (P=0.4). The ICCs were 0.31 (95% CI: 0.14-0.65) and 0.48 (95% CI: 0.06-0.75) for the anatomical and surgical PCA, respectively. The average differences between the CT and MRI measurements were 1.4±1.1° (0.2-5°) and 1.1±0.8° (0-3.6°) for the anatomical and surgical PCA, respectively. Greater than 1° difference between CT and MRI was found in 29 records (54%) for the anatomical PCA and in 18 records (33%) for the surgical PCA (P=0.03).

CONCLUSION

DFT measurement on MRI is more reproducible and consistent when using the surgical PCA. MRI measurements differed by more than 1° relative to CT measurements in more than one-third of cases.

CASE CONTROL STUDY

Level III.

Posterior tibial slope accuracy with patient-specific cutting guides during total knee arthroplasty: A preliminary study of 50 cases

BACKGROUND

Patient-specific cutting guides were recently introduced to facilitate total knee arthroplasty (TKA). Their accuracy in achieving optimal implant alignment remains controversial. The objective of this study was to evaluate postoperative radiographic outcomes of 50 TKA procedures with special attention to posterior tibial slope (PTS), which is difficult to control intraoperatively. We hypothesized that patient-specific cutting guides failed to consistently produce the planned PTS.

MATERIAL AND METHODS

The Signature™ patient-specific cutting guides (Biomet) developed from magnetic resonance imaging data were used in a prospective case-series of 50 TKAs. The target PTS was 2°. Standardised digitised radiographs were obtained postoperatively and evaluated by an independent reader. Reproducibility of the radiographic measurements was assessed on 20 cases. The posterior cortical line of the proximal tibia was chosen as the reference for PTS measurement. Inaccuracy was defined as an at least 2° difference in either direction compared to the target.

RESULTS

The implant PTS was within 2° of the target in 72% of knees. In the remaining 28%, PTS was either excessive (n=10; maximum, 9°) or reversed (n=4; maximum, -6°). The postoperative hip-knee-ankle angle was 0° ± 3° in 88% of knees, and the greatest deviation was 9° of varus.

CONCLUSION

These findings support our hypothesis that patient-specific instrumentation decreases PTS accuracy. They are consistent with recently published data. In contrast, patient-specific instrumentation provided accurate alignment in the coronal plane.