Patient-specific Instrumentation System Research Articles

Accuracy of patient-specific instrumentation for implant positioning in custom-made total ankle arthroplasty.

This retrospective radiological analysis aimed to assess the accuracy of implant positioning in patients with ankle arthritis undergoing custom-made total ankle arthroplasty (TAA) with patient-specific instrumentation (PSI) compared with preoperative planning. Patients who underwent custom-made TAA with PSI from January 2018 to March 2023 were retrospectively evaluated, focusing on the tibial anterior surface (TAS) angle, tibial lateral surface (TLS) angleand tibiotalar ratio (TTR). Additionally, data regarding the time from the preoperative computed tomography (CT) scan to surgery, associated proceduresand complications were recorded. No associated procedures were performed, and only one intraoperative complication, an iatrogenic lateral malleolar fracture, was recorded. In the coronal plane, custom-made TAA with PSI consistently achieved precise positioning of prosthetic components, even in cases with significant preoperative deformities or bone deficits. However, a statistically significant deviation from the planned values was observed in the sagittal plane (p = 0.007). A notable correlation was identified between the time elapsed from the preoperative CT scan to surgery and the deviation from the planned to the actual postoperative TAS angle (p < 0.001). This study underscores the efficacy of PSI systems in achieving precise positioning in the coronal plane, in accordance with preoperative planning. In contrast, sagittal plane positioning did not demonstrate the same level of accuracy, as evidenced by a statistically significant difference between the planned and postoperative TLS values. Nevertheless, all measurements remained within the recommended range according to the existing literature. Level IV.

Flexion contracture can cause component mismatch in the Prophecy® preoperative patient-specific instrumentation for Evolution® medial-pivot knee system.

Patient-specific instrumentation (PSI) systems are used to conduct total knee arthroplasty. PSI reduces operative time, is less invasive and easier to use, and minimizes the risk of errors by providing precise measurements and reducing operating room turnover time. However, a study on the accuracy of Prophecy Evolution PSI (Microport Inc., Arlington, TN, USA) reported that 94% were below the error margin of 1.5mm and 90% had error margins of 1mm. This study aimed to evaluate the accuracy of the Prophecy Evolution PSI system in terms of the thickness of "total" bony resection required to achieve adequate extension/flexion gaps and the component match ratio between preoperative planning and actual component size inserted. Comparisons were made between the sizes of femoral and tibial components planned with PSI and those inserted. The primary outcome was the average preoperative range of motion with and without matched femoral/tibial components. The study further analyzed the proportions of cases in which both the femoral and tibial components matched, neither matched, and only one of the femoral or tibial components matched. The ratio of the same sizes between the PSI planning and those inserted was 50.8% (33 patients) for both the femoral and tibial components. For the femoral component alone, the ratio was 84.6% (55 patients), and for the tibial component, it was 58.4% (38 patients). A receiver-operating characteristic curve analysis indicated that flexion contracture greater than 20° was a significant prognostic factor for the PSI component match group versus the mismatch group. Flexion contracture may cause PSI mismatch. Notably, flexion contracture greater than 20° was a significant risk factor for the PSI component match group versus the mismatch group. During preoperative planning for a patient with flexion contracture, surgeons should prepare for the possibility of inserting an undersized tibial component.

Development and Validation of an Artificial Intelligence Preoperative Planning and Patient-Specific Instrumentation System for Total Knee Arthroplasty.

Accurate preoperative planning for total knee arthroplasty (TKA) is crucial. Computed tomography (CT)-based preoperative planning offers more comprehensive information and can also be used to design patient-specific instrumentation (PSI), but it requires well-reconstructed and segmented images, and the process is complex and time-consuming. This study aimed to develop an artificial intelligence (AI) preoperative planning and PSI system for TKA and to validate its time savings and accuracy in clinical applications. The 3D-UNet and modified HRNet neural network structures were used to develop the AI preoperative planning and PSI system (AIJOINT). Forty-two patients who were scheduled for TKA underwent both AI and manual CT processing and planning for component sizing, 20 of whom had their PSIs designed and applied intraoperatively. The time consumed and the size and orientation of the postoperative component were recorded. The Dice similarity coefficient (DSC) and loss function indicated excellent performance of the neural network structure in CT image segmentation. AIJOINT was faster than conventional methods for CT segmentation (3.74 ± 0.82 vs. 128.88 ± 17.31 min, p < 0.05) and PSI design (35.10 ± 3.98 vs. 159.52 ± 17.14 min, p < 0.05) without increasing the time for size planning. The accuracy of AIJOINT in planning the size of both femoral and tibial components was 92.9%, while the accuracy of the conventional method in planning the size of the femoral and tibial components was 42.9% and 47.6%, respectively (p < 0.05). In addition, AI-based PSI improved the accuracy of the hip-knee-ankle angle and reduced postoperative blood loss (p < 0.05). AIJOINT significantly reduces the time needed for CT processing and PSI design without increasing the time for size planning, accurately predicts the component size, and improves the accuracy of lower limb alignment in TKA patients, providing a meaningful supplement to the application of AI in orthopaedics.

Accuracy of a Patient-Specific Total Ankle Arthroplasty Instrumentation.

Total ankle arthroplasty (TAA) is a preferred surgical option for end-stage ankle osteoarthritis; however, it is a demanding procedure with a higher historical rate of revision compared with ankle fusion. Patient-specific instrumentation (PSI) has been introduced to optimize prosthesis alignment and theoretically overall improve TAA outcomes. The goal of this study is to report on the experience and surgical outcomes of one implant with specific evaluation of the accuracy and reproducibility of the system with respect to prosthesis alignment and prediction of implant size. A retrospective, multicentered study involving 4 foot and ankle fellowship-trained orthopaedic surgeon's patients undergoing TAA between January 1, 2015, and December 31, 2018, using the PROPHECY PSI system. 80 TAA procedures were performed. On average the postoperative tibial component alignment was 89.9 (range, 86.1-96.5) degrees in the coronal plane, with a mean sagittal alignment of 88.1 (range, 81.3-96.7) degrees. The mean deviation from neutral sagittal alignment improved from 4.9 ± 3.9 degrees preoperatively to 2.7 ± 1.7 degrees postoperatively, whereas the mean coronal alignment improved from 3.3 ± 2.5 degrees to 1.3 ± 1.1 degrees. The PSI software correctly determined the tibial implant size in 70 patients (89%). Prediction of talar implant sizing was less accurate than the tibial component, with 56 patients (71%) using the predicted sized implant. The overall implant survival at a mean follow-up of 45 months (range, 27-76) was 97.5%. We found that this PSI system accurately and reliably assisted in implant total ankle prosthesis positioning within a clinically acceptable margin and without significant outliers. Prediction of implant size was not as accurate as component orientation. Level III, retrospective study.

Effectiveness and Accuracy of a Patient-Specific Instrumentation System for Total Hip Arthroplasty.

Traditional total hip arthroplasty (THA) is often performed by visual inspection due to the lack of reliable reference, which results in inappropriate position of prosthesis and poor outcomes. This study attempts to introduce a novel patient-specific instrumentation (PSI) system and assess its effectiveness and accuracy compared with freehand operation and robot system through bone model experiments. Equally divide 30 sawbone models into the freehand group, PSI group, and robot group. Ten sets of prosthesis parameters were randomly generated as planning, and the three groups underwent simulated THA depending on these parameters. After the placement of the femoral prosthesis, the acetabular anteversion plan was adjusted in the PSI and robot groups so that the combined anteversion was maintained before and after adjustment. After the surgery, the actual prosthesis parameters of all bone models were measured and analyzed statistically. No statistically significant difference was found in femoral anteversion error among the three groups (p=0.951). The errors of acetabular cup anteversion, acetabular cup abduction, and combined anteversion in PSI group were 3.92° (2.94°, 4.62°), 5.65° (4.63°, 6.70°), and 3.93° (2.94°, 4.62°), respectively, which were significantly smaller than those in the freehand group [11.84° (9.92°, 13.87°), 13.54° (9.81°, 15.21°), 16.04° (8.18°, 19.25°), respectively, p < 0.05], but significantly larger than those in the robot group [1.34° (0.98°, 1.70°), 1.80° (1°, 2.02°), 1.34° (0.98°, 1.70°), respectively, p < 0.05]. Compared with the traditional freehand operation, the patient-specific instrumentation system is feasible in total hip arthroplasty because it improves the accuracy of prosthesis placement. In addition, the rapid measurement of intraoperative femoral prosthesis parameters can help surgeons optimize preoperative planning.

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

IntroductionMalalignment 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 methodsThe 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.ResultsOutcomes 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.ConclusionOptions 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.

Accuracy of a patient-specific instrumentation for coronal plane alignment of an anatomic alignment total knee arthroplasty system: A radiographic study.

Patient-individualised anatomic alignment in total knee arthroplasty (TKA) requires exact positioning of the tibial and femoral components. Patient-specific instrumentation (PSI) may be advantageous for implantation. However, the role of PSI in the instrumentation of such knee designs has not been investigated. The aim of this study was to investigate the accuracy of a PSI system designed for patient-individualised anatomic alignment. Fifty-four patients from a single centre were consecutively enrolled in this study. Patient-specific femoral and tibial cutting guides were manufactured using 3D models from computed tomography (CT) scans. All patients received an anatomic TKA implant design through an extension gap first technique. Postoperative radiography was taken, and implant component alignment and leg alignment were compared to the preoperative planning. Thirty-four patients were evaluable. Mean differences between planned angles values obtained from CT scans and the measured radiographic values were small and not significantly different from zero. Implantation of an anatomic knee design that allows individual component alignment using PSI is feasible. The percentage of component misalignment in the coronal plane was remarkably low. Whether this leads to clinical benefits requires further verification.

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.

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

Objective To conduct a meta-analysis of randomized controlled trials (RCTs) to compare knee arthroplasty with patient-specific instrumentation (PSI) with the conventional instrumentation (CI). Methods RCTs were selected in PubMed and Embase from 2012 to 2018. Key data extracted included malalignment of mechanical axis, blood loss, surgical time, Oxford Knee Score (OKS), Knee Society Score (KSS), length of stay, and complications. Subgroup analysis was also performed regarding different PSI systems and different image processing methods. Results 29 RCTs with 2487 knees were eligible for the meta-analysis. Results showed that PSI did not improve the alignment of the mechanical axis compared with CI, but MRI-based PSI and Visionaire-specific PSI decrease the risk of malalignment significantly (P = 0.04 and P = 0.04 and P = 0.04 and P = 0.04 and P = 0.04 and Conclusion PSI reduced the blood loss and improved KSS. MRI-based PSI reduced operative time and risk of malalignment of mechanical axis compared with CT-based PSI. Moreover, Visionaire-specific PSI achieves better alignment result of the mechanical axis than other systems.

The Accuracy of Alignment Determined by Patient-Specific Instrumentation System in Total Knee Arthroplasty.

PurposeThe aim of this study is to assess the accuracy of alignment determined by patient-specific instrumentation system in total knee arthroplasty (TKA).Materials and MethodsTwenty-seven TKAs using patient-specific instrument were reviewed. The intraoperative pin location determined by the patient-specific guide was recorded using imageless navigation software. Data recorded included tibial coronal alignment and posterior slope, femoral coronal alignment and sagittal alignment, and transepicondylar axis. A discrepancy within ±3° in each plane was considered an acceptable result.ResultsOn the tibia, an acceptable alignment was obtained in 24 (88.1%) in the coronal plane and 21 (77.8%) in the sagittal plane. On the femur, a satisfactory alignment was obtained in 25 (92.6%) in the coronal plane and 24 (88.1%) in the sagittal plane. Based on the transepicondylar axis, a satisfactory alignment was obtained in 23 (85.1%).ConclusionsSatisfactory alignment was obtained in more than 85% of each plane of the femur and in the coronal plane of the tibia and relative to the transepicondylar axis. Sufficeint experience and precise preoperative planning are required to improve the accuracy of sagittal alignment of the tibia.

Outcome of kinematic alignment using patient-specific instrumentation versus mechanical alignment in TKA: a meta-analysis and subgroup analysis of randomised trials.

Kinematic alignment (KA) in total knee arthroplasty (TKA) matches component position to the pre-arthritic anatomy of an individual patient, with the aim of improving functional outcomes. Recent randomised controlled trials (RCTs) comparing KA to traditional neutral mechanical alignment (MA) have been mixed. This collaborative study combined raw data from RCTs, aiming to compare functional outcomes between KA using patient-specific instrumentation (PSI) and MA, and whether any patient subgroups may benefit more from KA technique. A literature search in PubMed, EMBASE and Cochrane databases identified four randomised controlled trials comparing patients undergoing TKA using PSI-KA and MA. Unpublished data including Western Ontario McMaster Universities Arthritis Index (WOMAC) and Knee Society Score (KSS) were obtained from study authors. Meta-analysis compared MA to KA change (post-op minus pre-op) scores. Subgroup-analysis on KA patients looked for subgroups more likely to benefit from KA and the impact of PSI accuracy. Meta-analyses of change scores in 229 KA patients versus 229 MA patients were no different from WOMAC (mean difference 3.4; 95% confidence interval - 0.5 to 7.3), KSS function (1.3, - 3.9 to 6.4) or KSS combined (7.2, - 0.8 to 15.2). A small advantage was seen for KSS pain in the KA group (3.6, 95% CI 0.2-7.1). Subgroup-analysis showed no difference between varus, valgus and neutral pre-operative alignment groups, and those who did and did not achieve KA plans. Pain-free patients at 1-year were more likely to achieve KA plans. Patient-reported outcome scores following TKA using PSI-KA are similar to MA. No identifiable subgroups benefited more from KA, and long-term results remain unknown. Inaccuracy of the PSI system used in KA patients could potentially affect outcome.

Patient-Specific Guides/Instrumentation in Shoulder Arthroplasty.

Optimal outcomes following total shoulder arthroplasty TSA and reverse shoulder arthroplasty RSA are dependent on proper implant position. Multiple cadaver studies have demonstrated improved accuracy of implant positioning with use of patient-specific guides/instrumentation compared to traditional methods. At this time, there are 3 commercially available single use patient-specific instrumentation systems and 1 commercially available reusable patient-specific instrumentation system. Currently though, there are no studies comparing the clinical outcomes of patient-specific guides to those of traditional methods of glenoid placement, and limited research has been done comparing the accuracy of each system's 3-dimensional planning software. Future work is necessary to elucidate the ideal indications for the use of patient-specific guides and instrumentation, but it is likely, particularly in the setting of advanced glenoid deformity, that these systems will improve a surgeon's ability to put the implant in the best position possible.

Predicted osteotomy planes are accurate when using patient-specific instrumentation for total knee arthroplasty in cadavers: a descriptive analysis

PurposeMalalignment of implants is a major source of failure during total knee arthroplasty. To achieve more accurate 3D planning and execution of the osteotomy cuts during surgery, the Signature (Biomet, Warsaw) patient-specific instrumentation (PSI) was used to produce pin guides for the positioning of the osteotomy blocks by means of computer-aided manufacture based on CT scan images. The research question of this study is: what is the transfer accuracy of osteotomy planes predicted by the Signature PSI system for preoperative 3D planning and intraoperative block-guided pin placement to perform total knee arthroplasty procedures?MethodsThe transfer accuracy achieved by using the Signature PSI system was evaluated by comparing the osteotomy planes predicted preoperatively with the osteotomy planes seen intraoperatively in human cadaveric legs. Outcomes were measured in terms of translational and rotational errors (varus, valgus, flexion, extension and axial rotation) for both tibia and femur osteotomies.ResultsAverage translational errors between the osteotomy planes predicted using the Signature system and the actual osteotomy planes achieved was 0.8 mm (± 0.5 mm) for the tibia and 0.7 mm (± 4.0 mm) for the femur. Average rotational errors in relation to predicted and achieved osteotomy planes were 0.1° (± 1.2°) of varus and 0.4° (± 1.7°) of anterior slope (extension) for the tibia, and 2.8° (± 2.0°) of varus and 0.9° (± 2.7°) of flexion and 1.4° (± 2.2°) of external rotation for the femur.ConclusionThe similarity between osteotomy planes predicted using the Signature system and osteotomy planes actually achieved was excellent for the tibia although some discrepancies were seen for the femur. The use of 3D system techniques in TKA surgery can provide accurate intraoperative guidance, especially for patients with deformed bone, tailored to individual patients and ensure better placement of the implant.

Alignment Accuracy and Cost-Savings Threshold of Patient-Specific Instrumentation In Total Ankle Replacements

Category: Ankle Arthritis Introduction/Purpose: Traditional intraoperative referencing for total ankle replacements (TAR) involves multiple steps and fluoroscopic guidance to determine mechanical alignment. Recent adoption of patient-specific instrumentation (PSI) allows for referencing to be determined preoperatively, resulting in less steps and potentially decreased operative time. We hypothesize that usage of PSI will result in decreased operating room time that offsets the additional cost of PSI as compared to standard referencing (SR). Additionally, we aim to demonstrate similar postoperative radiographic alignment between PSI and SR. Methods: Between 2014 and 2015, 87 patients undergoing TAR were enrolled in a prospectively collected TAR database. Patients were divided into cohorts based on PSI versus SR and operative times were reviewed. Radiographic alignment parameters were retrospectively measured at 6 weeks postoperatively. Time-driven activity-based costing (TDABC) was utilized to derive direct costs. Cost versus operative time-savings were examined via two-way sensitivity analysis to determine cost-saving thresholds for PSI applicable to a range of institution types. Cost-saving thresholds defined the price of PSI below which PSI is cost-saving. Results: A total of 35 PSI and 52 SR cases were evaluated with no significant differences identified in patient characteristics. Operative time from incision to completion of casting in cases without adjunct procedures was 127 minutes with PSI and 161 minutes with SR (p &lt; 0.05). PSI demonstrated similar postoperative accuracy to SR in coronal tibial-plafond alignment (1.1° vs. 0.3° varus, p=0.06) and tibial component sagittal alignment (0.7° vs. 0.9° plantarflexion, p=0.14). TDABC methodology estimated a PSI cost-savings threshold range at our institution of $863 - $1,026 below which PSI pricing will provide net cost-savings. Two-way sensitivity analysis generated a globally applicable cost-savings threshold model based on institution-specific costs and surgeon-specific time-savings. Conclusion: This study demonstrates equivalent post-operative TAR alignment with PSI and SR referencing systems but with a significant decrease in operative time with PSI. Based on TDABC and associated sensitivity analysis, a cost-savings threshold of $863 - $1,026 is identified for PSI pricing at our institution below which PSI is less costly than SR. Similar internal cost accounting may benefit healthcare systems for identifying cost drivers and obtaining leverage during price negotiations.

Short-stemmed arthroplasty with glenoid preoperative planning

Total shoulder arthroplasty implant design, instrumentation, and outcomes continue to evolve; however, accurate glenoid placement remains a challenge especially in cases of glenoid deformity. Knowledge that malpositioning of the glenoid can lead to inferior outcomes and glenoid component loosening has led to the development of patient specific instrumentation (PSI). The ideal PSI system should be consistent, reliable, cost-effective, reusable, and robust enough to withstand applied stress during difficult exposures. In addition, short-stemmed humeral components appear to offer several advantages over the traditional length stems.

Determining the Cost-Savings Threshold and Alignment Accuracy of Patient-Specific Instrumentation in Total Ankle Replacements.

Traditional intraoperative referencing for total ankle replacements (TARs) involves multiple steps and fluoroscopic guidance to determine mechanical alignment. Recent adoption of patient-specific instrumentation (PSI) allows for referencing to be determined preoperatively, resulting in less steps and potentially decreased operative time. We hypothesized that usage of PSI would result in decreased operating room time that would offset the additional cost of PSI compared with standard referencing (SR). In addition, we aimed to compare postoperative radiographic alignment between PSI and SR. Between August 2014 and September 2015, 87 patients undergoing TAR were enrolled in a prospectively collected TAR database. Patients were divided into cohorts based on PSI vs SR, and operative times were reviewed. Radiographic alignment parameters were retrospectively measured at 6 weeks postoperatively. Time-driven activity-based costing (TDABC) was used to derive direct costs. Cost vs operative time-savings were examined via 2-way sensitivity analysis to determine cost-saving thresholds for PSI applicable to a range of institution types. Cost-saving thresholds defined the price of PSI below which PSI would be cost-saving. A total of 35 PSI and 52 SR cases were evaluated with no significant differences identified in patient characteristics. Operative time from incision to completion of casting in cases without adjunct procedures was 127 minutes with PSI and 161 minutes with SR ( P < .05). PSI demonstrated similar postoperative accuracy to SR in coronal tibial-plafond alignment (1.1 vs 0.3 degrees varus, P = .06), tibial-plafond alignment (0.3 ± 2.1 vs 1.1 ± 2.1 degrees varus, P = .06), and tibial component sagittal alignment (0.7 vs 0.9 degrees plantarflexion, P = .14). The TDABC method estimated a PSI cost-savings threshold range at our institution of $863 below which PSI pricing would provide net cost-savings. Two-way sensitivity analysis generated a globally applicable cost-savings threshold model based on institution-specific costs and surgeon-specific time-savings. This study demonstrated equivalent postoperative TAR alignment with PSI and SR referencing systems but with a significant decrease in operative time with PSI. Based on TDABC and associated sensitivity analysis, a cost-savings threshold of $863 was identified for PSI pricing at our institution below which PSI was less costly than SR. Similar internal cost accounting may benefit health care systems for identifying cost drivers and obtaining leverage during price negotiations. Level III, therapeutic study.

A novel integrated patient specific instrumentation system and its application for total knee arthroplasty

Objective To study the accuracy of preoperative planning and postoperative satisfaction of prosthesis position by applying the personal surgical cutting guide (PSCG) to total knee arthroscopy (TKA) based on 3D printing technique. Methods In this randomized study, 20 patients were selected from August 2014 to October 2015, who were randomly divided into two groups. In PSCG group, 4 males and 6 females were enrolled, with a mean age of 70.9±6.69 (from 59 to 78) years. In conventional instrumentation group, 2 males and 8 females were enrolled, with a mean age of 69.9±6.35 (from 58 to 77) years. The conventional instrumentation group was treated with conventional TKA, while the PSCG group was treated with personal surgical cutting guides. Then the knee valgus angle of patients, the angle between prosthesis components on the coronal and the sagittal plane of two groups were evaluated. Subsequently the correlation of the actual osteotomy amount, the valgus angle, caster angle, external rotation angle between intra- and preoperative planning were compared in the PSCG group. Results Compared with the ideal value of each angle, the mean deviation of the hip-knee-ankle angle 0.77°±0.51°, frontal femoral component angle 0.37°± 0.53° and frontal tibial component angle 0.11°±0.24° showed statistically significant difference between two groups (P 0.05). The actual osteotomy amount, the valgus angle, caster angle, external rotation angle correlated well between intra- and preoperative planning (t=-2.547, 3.864, 0.537, -0.040, -1.290,P >0.05). Conclusion TKA assisted by PSCG can make lower extremity alignment and accuracy of prosthesis implantation more accurate compared with conventional TKA, especially in hip-knee-ankle angle, frontal femoral component angle and frontal tibial component angle. Key words: Arthroplasty, replacement, knee; Individuality; Imaging, three-dimensional

Reply to the Letter to the Editor: The John Insall Award: No Functional Benefit After Unicompartmental Knee Arthroplasty Performed With Patient-specific Instrumentation: A Randomized Trial.

W e would like to thank Logishetty and colleagues for their enthusiastic evaluation and alternative interpretation of our work. Indeed, our department has been a fervent supporter of unicompartmental knee arthoplasty (UKA) for many years [2, 3]. We also have been involved in several trials of patientspecific instrumentation (PSI) on both UKA and TKA in the last several years [1, 5, 6], highlighting the frequency of outliers, the proportion of PSI procedures that needed to be aborted or modified during surgery, as well as the additional costs incurred by the new technology both directly and in terms of the surgeon’s time. We initially hypothesized [4] that PSI could be a useful tool for UKA, particularly to improve the tibial cut. Therefore, we decided to evaluate PSI-UKA in the setting of a randomized controlled trial highlighting the frequency of outliers, the proportion of PSI procedures that needed to be aborted or modified during surgery, as well as the additional costs incurred by the new technology both directly and in terms of the surgeon’s time, but did not succeed in demonstrating any clinical or radiological differences 1 year after surgery between PSI and conventional UKA [4]. As pointed out by Logishetty and colleagues, this might be related to the experience in UKA of the two surgeons. However, our analysis is different because in three cases (10%) the same two UKA-trained surgeons had to perform a recut of the tibial plateau due to insufficient bone resection with the PSI system [4]. It is important to recognize that less-experienced surgeons might have ignored or missed this slight bonecut difference conducing to potential mechanical axis modifications, and so the contention of Logishetty and (RE: Ollivier M, Parratte S, Lunebourg A, Viehweger E, Argenson JN. The John Insall Award: No functional benefit after unicompartmental knee arthroplasty performed with patient-specific instrumentation: A randomized trial. [Published online ahead of print March 20, 2015]. Clin Orthop Relat Res. DOI: 10.1007/ s11999-015-4259-0). The authors certify that they, or any members of their immediate families, have no funding or commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons. M. Ollivier MD, S. Parratte MD, PhD, A. Lunebourg MD, J.-N. Argenson MD, PhD (&) Department of Orthopedics and Traumatology, Institute for Locomotion, St Marguerite Hospital, Aix-Marseille University, 270 Boulevard Sainte Marguerite, 13274 Marseille, France e-mail: jean-noel.argenson@ap-hm.fr Reply to the Letter to the Editor Published online: 15 October 2015 The Association of Bone and Joint Surgeons1 2015

Computerised tomography vs magnetic resonance imaging for modeling of patient-specific instrumentation in total knee arthroplasty.

To summarise and compare currently available evidence regarding accuracy of pre-operative imaging, which is one of the key choices for surgeons contemplating patient-specific instrumentation (PSI) surgery. The MEDLINE and EMBASE medical literature databases were searched, from January 1990 to December 2013, to identify relevant studies. The data from several clinical studies was assimilated to allow appreciation and comparison of the accuracy of each modality. The overall accuracy of each modality was calculated as proportion of outliers > 3% in the coronal plane of both computerised tomography (CT) or magnetic resonance imaging (MRI). Seven clinical studies matched our inclusion criteria for comparison and were included in our study for statistical analysis. Three of these reported series using MRI and four with CT. Overall percentage of outliers > 3% in patients with CT-based PSI systems was 12.5% vs 16.9% for MRI-based systems. These results were not statistically significant. Although many studies have been undertaken to determine the ideal pre-operative imaging modality, conclusions remain speculative in the absence of long term data. Ultimately, information regarding accuracy of CT and MRI will be the main determining factor. Increased accuracy of pre-operative imaging could result in longer-term savings, and reduced accumulated dose of radiation by eliminating the need for post-operative imaging and revision surgery.

Coronal alignment in total knee replacement: historical review, contemporary analysis, and future direction.

Substantial healthcare resources have been devoted to computer navigation and patient-specific instrumentation systems that improve the reproducibility with which neutral mechanical alignment can be achieved following total knee replacement (TKR). This choice of alignment is based on the long-held tenet that the alignment of the limb post-operatively should be within 3° of a neutral mechanical axis. Several recent studies have demonstrated no significant difference in survivorship when comparing well aligned versus malaligned TKRs. Our aim was to review the anatomical alignment of the knee, the historical and contemporary data on a neutral mechanical axis in TKR, and the feasibility of kinematically-aligned TKRs. Review of the literature suggests that a neutral mechanical axis remains the optimal guide to alignment.