Accurate implant fit and leg alignment after cruciate-retaining patient-specific total knee arthroplasty

Robotic-assisted differential total knee arthroplasty with patient-specific implants: surgical techniques and preliminary results

OBJECTIVE

In total knee arthroplasty (TKA), achieving soft-tissue balance while retaining acceptable lower limb alignment is sometimes difficult and may lead to patient dissatisfaction. Theoretically, patient-specific implants can bring great benefits, while the lack of precise surgical tools may hinder the improvement of outcomes. The objective of this study was to illustrate surgical techniques and evaluate kinematics and early clinical outcomes of robotic-assisted TKA using patient-specific implants.

METHODS

Based on preoperative CT scan, femoral and tibial components were 3D printed. Medial and lateral tibial liners were separate with different thicknesses, posterior slopes and conformity. TiRobot Recon Robot was used for surgery, and was armed with smart tools that quantify gap, force and femoral-tibial track. We collected data on demographics, intraoperative gap balance and femoral-tibial motion. In the follow-up, we evaluated the range of motion, Visual Analogue Scale (VAS), forgotten joint score (FJS), Knee injury and Osteoarthritis Outcome Score, Joint Replacement (KOOS, JR) score. Radiological data were also harvested.

RESULTS

Fifteen patients (17 knees) were enrolled with a mean age of 64.6 ± 6.4 (53-76) years. In 5 knees, we used symmetric tibial liners, the rest were asymmetric. After surgery, the average alignment was 1.6 ± 2.0 (-3-5) degrees varus. The average follow-up lasted 6.7 ± 4.2 (1-14) months. The mean visual analogue scale was 0.8 ± 0.7 (0-2), FJS was 62.4 ± 25.3 (0-87), KOOS was 86.5 ± 9.4 (57-97). 11 patients were "very satisfied", 3 were "satisfied" with the result, and one patient was neutral due to restricted extension and unsatisfactory rehabilitation at five months' follow-up.

CONCLUSIONS

With patient-specific implants and robotics, TKA could be performed by a mathematical way, which was dubbed a "differential" TKA. Intraoperative kinematics was excellent in terms of gap-force balancing and femoral-tibial relative motion. Preliminary clinical outcomes were overall satisfactory.

No clinical advantage with customized individually made implants over conventional off-the-shelf implants in total knee arthroplasty: a systematic review and meta-analysis

INTRODUCTION

Total knee arthroplasty (TKA) can be performed with either conventional off-the-shelf (OTS) or customized individually-made (CIM) implants. The evidence for CIM implants is limited and variable, and the aim of this review was to compare clinical and radiological outcomes between CIM and OTS implants.

METHODS

A systematic review and meta-analysis were conducted in accordance with PRISMA guidelines. Studies reporting on clinical, radiological, or alignment outcomes for CIM and OTS implants were selected. The studies were appraised using the Methodical index for non-randomized studies tool.

RESULTS

Twenty-three studies fulfilled the inclusion criteria. The studies comprised 2856 CIM and 1877 OTS TKAs. Revision rate was higher with CIM (5.9%) compared to OTS (3.7%) implants [OR 1.23(95% CI 0.69-2.18)]. Manipulation under anesthesia (MUA) was higher in CIM (2.2%) compared to OTS (1.1%) group [OR 2.95(95% CI 0.95-9.13)] and complications rate was higher in CIM (5%) vs. OTS (4.5%) [OR 1.45(95% CI 0.53-3.96)] but neither reached statistical significance. Length of stay was significantly shorter in CIM group 2.9 days vs. 3.5 days [MD - 0.51(95% CI - 0.82 to - 0.20)]. Knee Society Score showed no difference between CIM and OTS groups for Knee 90.5 vs. 90.6 [MD - 0.27(95% CI - 4.27 to 3.73)] and Function 86.1 vs. 83.1 [MD 1.51(95% CI - 3.69 to 6.70)].

CONCLUSION

CIM implants in TKA have theoretical benefits over OTS prostheses. However, in this present review, CIM implants were associated with higher revisions, MUA, and overall complication rates. There was no difference in outcome score and CIM implants did not improve overall target alignment; however, more CIM TKAs were found to be in the HKA target zone compared to OTS TKAs. The findings of this review do not support the general utilization of CIM over OTS implants in TKA.

A review of the design, manufacture, and outcomes of custom total joint replacement implants available in the United States

Custom total joint replacement (TJA) implants, specifically designed and manufactured for each patient, have emerged as surgeons seek to improve functional outcomes of primary total joint replacement, as well as treat patients with complex primary deformities, bone defects, and revision surgeries. The purpose of this review is to present the various custom total hip and knee arthroplasty implants available in the United States for primary and revision cases, so that surgeons can understand the design considerations and manufacturing processes of custom implants, as well as their performance compared to standard implants.

Patient specific implants versus conventional implants in primary total knee arthroplasty: No significant difference in patient reported outcomes at 5 years

Background

Patient specific implants (PSI) represent a novel innovation aimed to improve patient satisfaction and function after total knee arthroplasty (TKA); however, longitudinal patient reported outcome measures (PROMs) for PSI are not well described. We sought to primarily evaluate PROMs of patients undergoing TKA with either PSI or off-the-shelf (OTS) implants at mid-term follow-up.

Methods

A retrospective review was performed on a prospectively collected cohort of 43 primary, cruciate-retaining TKAs performed with PSI (n = 23) and OTS implants (n = 20) by a single surgeon. Patient demographics, operative characteristics, range of motion (ROM) return, reoperations, and outcomes [Patient-Reported Outcomes Measurement Information System (PROMIS) T-score, Knee Injury and Osteoarthritis outcome score (KOOS), and Knee Society Score-Function (KSS-F)] were compared. Mean follow-up was 5 years.

Results

TKA performed with either PSI and OTS implants demonstrated no difference in obtaining ROM by 3 months (extension 3° short of full extension vs. 0°, p = 0.16) or flexion (114° vs. 115°, p = 0.99) and final ROM was identical [0° extension to 120° flexion (p = 1)]. Although not significant (p = 0.42), 5 (22%) PSI TKA and 2 (10%) OTS implant patients required manipulation under anesthesia. KSS-F and PROMIS T-scores were higher in the PSI versus OTS TKA patients, respectively (90 vs. 73, p = 0.002; 51.6 vs. 44.5, p = 0.01). However, after multivariable analysis, none of these continuous outcome measures were significantly different (p = 0.28 for KSS and p = 0.45 for PROMIS T-score) between the groups.

Conclusion

In a series of TKAs performed with PSI, no difference existed in postoperative ROM, reoperations, or patient-reported outcomes compared to OTS implants at 5 years. Surgeons may utilize the equivocal midterm results during TKA preoperative patient discussion of implant technologies.

Applying machine learning methods to enable automatic customisation of knee replacement implants from CT data

The aim of this study was to develop an automated pipeline capable of designing custom total knee replacement implants from CT scans. The developed pipeline firstly utilised a series of machine learning methods including classification, object detection, and image segmentation models, to extract geometrical information from inputted DICOM files. Statistical shape models then used the information to create femur and tibia 3D surface model predictions which were ultimately used by computer aided design scripts to generate customised implant designs. The developed pipeline was trained and tested using CT scan images, along with segmented 3D models, obtained for 98 Korean Asian subjects. The performance of the pipeline was tested computationally by virtually fitting outputted implant designs with 'ground truth' 3D models for each test subject's bones. This demonstrated the pipeline was capable of repeatably producing highly accurate designs, and its performance was not impacted by subject sex, height, age, or knee side. In conclusion, a robust, accurate and automatic, CT-based total knee replacement customisation pipeline was shown to be feasible and could afford significant time and cost advantages over conventional methods. The pipeline framework could also be adapted to enable customisation of other medical implants.

A computational design of experiments based method for evaluation of off-the-shelf total knee replacement implants

A methodology to explore the design space of off-the-shelf total knee replacement implant designs is outlined. Generic femur component and tibia plate designs were scaled to thousands of sizes and virtually fitted to 244 test subjects. Various implant designs and sizing requirements between genders and ethnicities were evaluated. 5 sizes optimised via the methodology produced a good global fit for most subjects. However, clinically significant over/underhang was present in 19% of subjects for tibia plates and 25% for femur components, reducing to 11/20% with 8 sizes. The analysis highlighted subtly better fit performance was obtained using sizes with unequal spacing.

The Impact of Total Knee Replacement with a Customized Cruciate-Retaining Implant Design on Patient-Reported and Functional Outcomes

Purpose: To treat patients with tricompartimental knee osteoarthritis (OA), a customized cruciate-retaining total knee arthroplasty (CCR-TKA) system can be used, including both individualized instrumentation and implants. The objective of this monocentric cohort study was to analyze patient-reported and functional outcomes in a series of patients implanted with the second generation of this customized implant. Methods: At our arthroplasty center, we prospectively recruited a cohort of patients with tricompartmental gonarthrosis to be treated with total knee replacement (TKA) using a customized cruciate-retaining (CCR) implant design. Inclusion criteria for patients comprised the presence of intact posterior cruciate and collateral ligaments and a knee deformity that was restricted to <15° varus, valgus, or flexion contracture. Patients were assessed for their range of motion (ROM), Knee Society Score (KSS), Western Ontario and McMaster University osteoarthritis index (WOMAC), and short form (SF)-12 physical and mental scores, preoperatively, at 3 and 6 months, as well as at 1, 2, 3, and 5 years of follow-up (FU) postoperatively. Results: The average age of the patient population was 64 years (range: 40–81), the average BMI was 31 (range: 23–42), and in total, 28 female and 45 male patients were included. Implant survivorship was 97.5% (one septic loosening) at an average follow-up of 2.5 years. The KSS knee and function scores improved significantly (p < 0.001) from, respectively, 41 and 53 at the pre-operative visit, to 92 and 86, respectively, at the 5-year post-operative time point. The SF-12 Physical and Mental scores significantly (p < 0.001) improved from the pre-operative values of 28 and 50, to 50 and 53 at the 5-year FU, respectively. Patients experienced significant improvements in their overall knee range of motion, from 106° at the preoperative visit to 122°, on average, 5 years postoperatively. The total WOMAC score significantly (p < 0.001) improved from 49.1 preoperatively to 11.4 postoperatively at 5-year FU. Conclusions: Although there was no comparison to other implants within this study, patients reported high overall satisfaction and improvement in functional outcomes within the first year from surgery, which continued over the following years. These mid-term results are excellent compared with those reported in the current literature. Comparative long-term studies with this device are needed. Level of evidence 3b (individual case–control study).

Custom TKA: what to expect and where do we stand today?

INTRODUCTION

The concept of custom total knee arthroplasty (TKA) is explored with specific attention to current limitations. Arguments in favor of custom TKA are the anatomic and functional variability we encounter in our patients. The biggest conceptual challenge is to marry the need for correction of deformity with the ambition to stay as close as possible to original anatomy.

MATERIALS AND METHODS

A Pubmed search was performed on the following terms: 'patient specific implant', 'custom made implant', 'custom implant', 'total knee arthroplasty' and 'total knee replacement'. These studies were evaluated for the following intra- and post-operative variables: blood loss, hospital stay, range of motion, patient-reported outcome measures, limb and implant alignment, implant fit, tibiofemoral kinematics, complications and revision rates.

RESULTS

Out of 1117 studies found with the initial search, a total of 17 articles were included in the final analysis. In eight out of the 17 (47%) studies, either the research was commercially funded or one of the authors had a conflict of interest related to the work. 11 out of 17 studies included a control group in their study setup. Of those studies that included a control group, both superior and inferior results compared to off-the-shelf implants have been reported.

CONCLUSION

Custom knee implants are the next step in matching the geometric features of the prosthesis to the anatomy of the individual patient, after several iterations that added asymmetry and sizes in the existing implants. Several companies have proven that it is feasible to produce these implants in a safe way. An overview of current literature reveals the lack of strong methodological studies that prove the value of this new technology. Custom knee implants face conceptual and practical difficulties, some of which might be overcome with technological advances, such as robotics and artificial intelligence.

No significant difference in early clinical outcomes of custom versus off-the-shelf total knee arthroplasty: a systematic review and meta-analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to collect, synthesise and critically appraise findings of clinical studies that report outcomes of custom total knee arthroplasty (TKA). The hypothesis was that, compared to off-the-shelf (OTS) TKA, custom TKA would yield better surgical, clinical and radiographic outcomes.

METHODS

This systematic review and meta-analysis was performed in accordance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). On 8 February 2021, two authors independently searched and screened articles using MEDLINE®, Embase® and the Cochrane Library without restriction on date of publication. Findings from eligible articles were narratively synthesised and tabulated, and when ≥ 3 comparative studies reported the same outcome, results were pooled and summarised in forest plots. Quality assessments of the studies were done according to the guidelines of the Joanna Briggs Institute (JBI) Checklists.

RESULTS

A total of 15 articles were eligible for data extraction, of which 9 were case-control studies reporting on 929 custom versus 998 OTS TKA, 5 were case series reporting on results of 587 custom TKA, and 1 was a cross-sectional study reporting on results of 44 custom versus 132 OTS TKA. Five studies that compared early revision rates found the overall effect in favour of OTS TKA (odds ratio (OR), 0.4; p = n.s.) but the result did not reach statistical significance. Four studies found no statistically significant difference in KSS knee (standardised mean difference (SMD), - 0.10; p = n.s.) and function (SMD, 0.03; p = n.s.), and five studies found no statistically significant difference in range of motion (SMD, 0.02; p = n.s.). One study that compared bone-implant fit between custom and three OTS tibial components found no overhang but revealed under-coverage of up to 18% in knees with custom tibial baseplates.

CONCLUSION

Custom TKA demonstrated no significant benefits compared to OTS TKA in terms of pooled clinical outcomes, but had considerably higher early revision rates. The findings of the present systematic review and meta-analysis suggest the need for studies with better comparable groups and standardisation of reporting outcomes amongst studies, that could increase the quality of evidence and enable pooling of results in future meta-analyses.

LEVEL OF EVIDENCE

Level IV.

Comparison of Postoperative Coronal Leg Alignment in Customized Individually Made and Conventional Total Knee Arthroplasty

Neutral coronal leg alignment is known to be important for postoperative outcome in total knee arthroplasty (TKA). Customized individually made implants (CIM) instrumented with patient-specific cutting guides are an innovation aiming to increase the precision and reliability of implant positioning and reconstruction of leg alignment. We aimed to compare reconstruction of the hip–knee–ankle angle (HKA) of the novel CIM system iTotal™ CR G2 (ConforMIS Inc.) to a matched cohort of the off-the-shelf (OTS) knee replacement system Vanguard™ CR (Zimmer Biomet). Retrospective analysis of postoperative coronal full-leg weight-bearing radiographs of 562 TKA (283 CIM TKA, 279 OTS TKA) was conducted. Via a medical planning software, HKA and rotation of the leg were measured in postoperative radiographs. HKA was then adjusted for rotational error, and 180° ± 3° varus/valgus was defined as the target zone HKA. Corrected postoperative HKA in the CIM group was 179.0° ± 2.8° and 179.2° ± 3.1° in the OTS group (p = 0.34). The rate of outliers, outside of the ±3° target zone, was equal in both groups (32.9%). Our analysis showed that TKA using patient-specific cutting guides and implants and OTS TKA implanted with conventional instrumentation resulted in equally satisfying restoration of the coronal leg alignment with less scattering in the CIM group.

Patient-Specific Implants for Focal Cartilage Lesions in The Knee: Implant Survivorship Analysis up to Seven Years Post-Implantation

In the quest for increased surgical precision and improved joint kinematics, Computer-Assisted Orthopedic Surgery (CAOS) shows promising results for both total and partial joint replacement. In the knee, computer-assisted joint design can now be applied to the treatment of younger patients suffering pain and restriction of activity due to focal defects in their femoral articular cartilage. By taking MRI scans of the affected knee and digitally segmenting these scans, we can identify and map focal defects in cartilage and bone. Metallic implants matched to the defect can be fabricated, and guide instrumentation to ensure proper implant alignment and depth of recession in the surrounding cartilage can be designed from segmented MRI scans. Beginning in 2012, a series of 682 patient-specific implants were designed based on MRI analysis of femoral cartilage focal defects, and implanted in 612 knees. A Kaplan-Meier analysis found a cumulative survivorship of 96% at 7-year follow-up from the first implantation. Fourteen (2.3%) of these implants required revision due to disease progression, incorrect implant positioning, and inadequate lesion coverage at the time of surgery. These survivorship data compare favorably with all other modes of treatment for femoral focal cartilage lesions and support the use of patient-specific implants designed from segmented MRI scans in these cases.