Personalisation and customisation in total knee arthroplasty: the paradox of custom knee implants

Excellent results of restricted kinematic alignment total knee arthroplasty at a minimum of 10 years of follow-up

PURPOSE

While restricted kinematic alignment (rKA) total knee arthroplasty (TKA) with cemented implants has been shown to provide a similar survivorship rate to mechanical alignment (MA) in the short term, no studies have reported on the long-term survivorship and function.

METHODS

One hundred four consecutive cemented cruciate retaining TKAs implanted using computer navigation and following the rKA principles proposed by Vendittoli were reviewed at a minimum of 10 years after surgery. Implant revisions, reoperations and clinical outcomes were assessed using knee injury and osteoarthritis outcome score (KOOS), forgotten joint score (FJS), patients' satisfaction and joint perception questionnaires. Radiographs were analyzed to identify signs of osteolysis and implant loosening.

RESULTS

Implant survivorship was 99.0% at a mean follow-up of 11.3 years (range: 10.3-12.9) with one early revision for instability. Patients perceived their TKA as natural or artificial without limitation in 50.0% of cases, and 95.3% were satisfied or very satisfied with their TKA. The mean FJS was 67.6 (range: 0-100). The mean KOOS were as follows: pain 84.7 (range: 38-100), symptoms 85.5 (range: 46-100), function in daily activities 82.6 (range: 40-100), function in sport and recreation 35.2 (range: 0-100) and quality of life 79.1 (range: 0-100). No radiological evidence of implant aseptic loosening or osteolysis was identified.

CONCLUSION

Cemented TKA implanted with the rKA alignment protocol demonstrated excellent long-term implant survivorship and is a safe alternative to MA to improve patient function and satisfaction.

LEVEL OF EVIDENCE

IV, continuous case series with no comparison group.

Custom total knee arthroplasty with personalised alignment showed better 2-year functional outcome compared to off-the-shelf arthroplasty

PURPOSE

Customised individually made (CIM) total knee arthroplasty (TKA) with personalised alignment is relatively new and evidence is limited. The aim of this study was to compare patient-reported outcome measures between CIM and off-the-shelf (OTS) TKA patients in a matched-pair analysis with a 2-year follow-up.

METHODS

In this single-centre, prospective cohort study, propensity score matching was performed on 51 CIM and 51 OTS TKA. Data were measured at baseline, at 4 months, 1 and 2 years and included the Forgotten Joint Score (FJS-12), the High Activity Arthroplasty Score (HAAS), the Knee injury and Osteoarthritis Outcome Score (KOOS), the EQ-5D-3L, the EQ-Visual Analogue Scale, satisfaction, overall knee improvement, willingness to undergo the surgery again and the Knee Society Score.

RESULTS

At 2 years follow-up, the FJS-12 (77 vs. 67, p = .058), HAAS (13 vs. 11, p < .001), KOOS daily living (92 vs. 86, p = .029), KOOS sport (76 vs. 65, p = .019), KOOS quality of life (81 vs. 71, p = .028) and the EQ-5D (.95 vs. .90, p = .030) were higher for CIM TKA compared to OTS TKA. Satisfaction rate was 92% for CIM TKA and 84% for OTS TKA (p = .357). Most patients reported an improvement in the overall knee state (94% CIM and 90% OTS, p = .487) and almost all patients would undergo the surgery again (96% CIM and 98% OTS, p = .999).

CONCLUSION

The current study found that CIM TKA patients had better functional outcomes at 2 years. Patient satisfaction was high and not statistically significantly different from OTS TKA patients.

LEVEL OF EVIDENCE

Level II prospective cohort study.

Individualised compared to off-the-shelf total knee arthroplasty results in lower and less variable patellar tilt

PURPOSE

The purpose of this study was to compare postoperative patellar tilt at 4 months follow-up in a consecutive series of randomised patients that received individualised or off-the-shelf (OTS) primary total knee arthroplasty (TKA). The hypothesis was that patellar tilt would be lower and less variable in patients who received individualised TKA compared to patients who received OTS TKA.

METHODS

A consecutive series of 385 patients randomised (1:1) to receive either OTS TKA or individualised TKA were analysed. Pre- and postoperative radiographs at 4 months were obtained of weight-bearing long leg, anterior-posterior and lateral knee views and a skyline view at 30° of flexion. Postoperative patellar tilt was measured between the anterior femoral line and patellar resection surface (β) and the anterior femoral line and mediolateral patellar axis (σ). Postoperative patellar tilt (absolute value) was compared between the individualised and OTS TKA groups based on preoperative phenotypes of their femoral mechanical angle, tibial mechanical angle and hip-knee-ankle angle. Variability in postoperative patellar tilt was compared using the 95% confidence intervals (CIs).

RESULTS

Comparisons of baseline patient characteristics revealed no difference between the individualised and OTS TKA groups. Comparison of absolute postoperative patellar tilt revealed significant differences between individualised and OTS TKA (|β|, 1.0° ± 1.0° and 2.5° ± 2.2°, respectively, p < 0.001; |σ|, 1.7° ± 1.6° and 2.8° ± 2.3°, respectively, p < 0.001). The 95% CI of postoperative patellar tilt (|β|) was narrower in patients that received individualised compared to OTS TKA (0.0° to 3.8° and 0.1° to 8.3°, respectively), irrespective of their preoperative phenotype.

CONCLUSION

Patients who underwent individualised TKA had lower and less variable postoperative patellar tilt than those with OTS TKA, irrespective of preoperative phenotype. Individualised TKA allows the decoupling of the tibiofemoral and patellofemoral joints, replicating anatomical trochlear orientation and improving patellar tilt, which could facilitate better clinical outcomes.

CLINICAL TRIAL REGISTRATION

This study constitutes a part of a larger registered randomised controlled trial comparing patient satisfaction following OTS versus individualised TKA (NCT04460989).

LEVEL OF EVIDENCE

Level II.

Navigating the Divide: A Comprehensive Review of the Mechanical and Anatomical Axis Approaches in Total Knee Replacement

This comprehensive review explores the mechanical and anatomical axis approaches in total knee replacement (TKR) surgery, addressing the ongoing debate within the orthopedic community. Emphasizing the significance of TKR in alleviating knee-related disorders, this review underscores the pivotal role of accurate alignment in achieving optimal surgical outcomes. The purpose is to navigate the divide between the well-established mechanical axis approach, focusing on a straight-line alignment, and the anatomical axis approach, aligning with natural knee landmarks. The analysis delves into the advantages, disadvantages, and clinical implications of each approach, offering a nuanced perspective on their efficacy. The conclusion emphasizes a patient-centric approach, recommending the adoption of hybrid strategies and the incorporation of emerging technologies for enhanced precision. The future of TKR aligns with personalized medicine, leveraging advancements in computer-assisted navigation, robotics, and patient-specific implants. Ongoing professional development and interdisciplinary collaboration are crucial for surgeons, and as the field evolves, innovations in artificial intelligence, imaging, and 3D printing are expected to shape the trajectory of TKR alignment approaches.

Ten Flaws of Systematic Mechanical Alignment Total Knee Arthroplasty

Mechanical alignment (MA) and its tenets have been considered essential for total knee arthroplasty (TKA) success since they were introduced in 1973. However, over time, there have been colossal advances in our knowledge and understanding of the anatomy and kinematics of the knee, as well as in surgical precision and implants. However, the MA systematic principles of prosthetic arthroplasty and implant position related to the lower-extremity mechanical axis, have only recently been called into question. The high rates of dissatisfaction and residual pain reported after MA TKA prompted this questioning, and that leaves plenty of room for improvement. Despite the general consensus that there is great variability between patients' anatomy, it is still the norm to carry out a systematic operation that does not consider individual variations. Evolving to a more personalized arthroplasty surgery was proposed as a rational and reasonable option to improve patient outcomes. Transitioning to a personalized TKA approach requires questioning and even disregarding certain MA TKA principles. Based on current knowledge, we can state that certain principles are erroneous or unfounded. The aim of this narrative review was to discuss and challenge 10 previously accepted, yet we believe, flawed, principles of MA, and to present an alternative concept, which is rooted in personalized TKA techniques.

Validating a Novel 2D to 3D Knee Reconstruction Method on Preoperative Total Knee Arthroplasty Patient Anatomies

BACKGROUND

As advanced technology continues to evolve, incorporating robotics into surgical procedures has become imperative for precision and accuracy in preoperative planning. Nevertheless, the integration of three-dimensional (3D) imaging into these processes presents both financial considerations and potential patient safety concerns. This study aims to assess the accuracy of a novel 2D-to-3D knee reconstruction solution, RSIP XPlan.ai™ (RSIP Vision, Jerusalem, Israel), on preoperative total knee arthroplasty (TKA) patient anatomies.

METHODS

Accuracy was calculated by measuring the Root Mean Square Error (RMSE) between X-ray-based 3D bone models generated by the algorithm and corresponding CT bone segmentations (distances of each mesh vertex to the closest vertex in the second mesh). The RMSE was computed globally for each bone, locally for eight clinically relevant bony landmark regions, and along simulated bone cut contours. In addition, the accuracies of three anatomical axes were assessed by comparing angular deviations to inter- and intra-observer baseline values.

RESULTS

The global RMSE was 0.93 ± 0.25 mm for the femur and 0.88 ± 0.14 mm for the tibia. Local RMSE values for bony landmark regions were 0.51 ± 0.33 mm for the five femoral landmarks and 0.47 ± 0.17 mm for the three tibial landmarks. The RMSE along simulated cut contours was 0.75 ± 0.35 mm for the distal femur cut and 0.63 ± 0.27 mm for the proximal tibial cut. Anatomical axial average angular deviations were 1.89° for the trans epicondylar axis (with an inter- and intra-observer baseline of 1.43°), 1.78° for the posterior condylar axis (with a baseline of 1.71°), and 2.82° (with a baseline of 2.56°) for the medial-lateral transverse axis.

CONCLUSIONS

The study findings demonstrate promising results regarding the accuracy of XPlan.ai™ in reconstructing 3D bone models from plain-film X-rays. The observed accuracy on real-world TKA patient anatomies in anatomically relevant regions, including bony landmarks, cut contours, and axes, suggests the potential utility of this method in various clinical scenarios. Further validation studies on larger cohorts are warranted to fully assess the reliability and generalizability of our results. Nonetheless, our findings lay the groundwork for potential advancements in future robotic arthroplasty technologies, with XPlan.ai™ offering a promising alternative to conventional CT scans in certain clinical contexts.

Definition of normal, neutral, deviant and aberrant coronal knee alignment for total knee arthroplasty

PURPOSE

One of the most pertinent questions in total knee arthroplasty (TKA) is: what could be considered normal coronal alignment? This study aims to define normal, neutral, deviant and aberrant coronal alignment using large data from a computed tomography (CT)-scan database and previously published phenotypes.

METHODS

Coronal alignment parameters from 11,191 knee osteoarthritis (OA) patients were measured based on three dimensional reconstructed CT data using a validated planning software. Based on these measurements, patients' coronal alignment was phenotyped according to the functional knee phenotype concept. These phenotypes represent an alignment variation of the overall hip knee ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA). Each phenotype is defined by a specific mean and covers a range of ±1.5° from this mean. Coronal alignment is classified as normal, neutral, deviant and aberrant based on distribution frequency. Mean values and distribution among the phenotypes are presented and compared between two populations (OA patients in this study and non-OA patients from a previously published study).

RESULTS

The arithmetic HKA (aHKA), combined normalised data of FMA and TMA, showed that 36.0% of knees were neutral within ±1 SD from the mean in both angles, 44.3% had either a TMA or a FMA within ±1-2 SD (normally aligned), 15.3% of the patients were deviant within ±2-3 SD and only 4.4% of them had an aberrant alignment (±3-4 SD in 3.4% and >4 SD in 1.0% of the patients respectively). However, combining the normalised data of HKA, FMA and TMA, 15.4% of patients were neutral in all three angles, 39.7% were at least normal, 27.7% had at least one deviant angle and 17.2% had at least one aberrant angle. For HKA, the males exhibited 1° varus and females were neutral. For FMA, the females exhibited 0.7° more valgus in mean than males and grew 1.8° per category (males grew 2.1° per category). For TMA, the males exhibited 1.3° more varus than females and both grew 2.3° and 2.4° (females) per category. Normal coronal alignment was 179.2° ± 2.8-5.6° (males) and 180.5 > ± 2.8-5.6° (females) for HKA, 93.1 > ± 2.1-4.2° (males) and 93.8 > ± 1.8-3.6° (females) for FMA and 86.7 > ± 2.3-4.6° (males) and 88 > ± 2.4-4.8° (females) for TMA. This means HKA 6.4 varus or 4.8° valgus (males) or 5.1° varus to 6.1° valgus was considered normal. For FMA HKA 1.1 varus or 7.3° valgus (males) or 0.2° valgus to 7.4° valgus was considered normal. For TMA HKA 7.9 varus or 1.3° valgus (males) or 6.8° varus to 2.8° valgus was considered normal. Aberrant coronal alignment started from 179.2° ± 8.4° (males) and 180.5 > ± 8.4° (females) for HKA, 93.1 > ± 6.3° (males) 93.8 > ± 5.4° (females) for FMA and 86.7 > ± 6.9° (males) and 88 > ± 7.2° (females) for TMA. This means HKA > 9.2° varus or 7.6° valgus (males) or 7.9° varus to 8.9° valgus was considered aberrant.

CONCLUSION

Definitions of neutrality, normality, deviance as well as aberrance for coronal alignment in TKA were proposed in this study according to their distribution frequencies. This can be seen as an important first step towards a safe transition from the conventional one-size-fits-all to a more personalised coronal alignment target. There should be further definitions combining bony alignment, joint surfaces' morphology, soft tissue laxities and joint kinematics.

LEVEL OF EVIDENCE

III.

Five or more gender- and size-diverse customizations of distal femur prostheses are needed to improve fit for Chinese knees

PURPOSE

Mismatch between partial imported prostheses and Chinese anatomy affects the clinical outcome of the procedure. The purpose of this study was to measure the anatomical dimensions of Chinese distal femurs to provide guidance for the design of more compatible distal femoral prostheses.

METHODS

A total of 406 healthy distal femurs were reconstructed and measured. Consistency of these measurements and differences in sides, gender, and populations were examined. Parameter correlations were analyzed, and pairs with strong correlations underwent linear regression analysis. The design of distal femoral prostheses was referenced from the results of K-means and hierarchical clustering analysis.

RESULTS

Ten parameters were measured, including the trans-epicondylar axis, width of the distal femur (ML), anteroposterior diameter of the distal femur (AP), etc. The intra-class correlation coefficient ranged from 0.795 to 0.999 for intra-observer consistency, and from 0.796 to 0.998 for inter-observer consistency. Males exhibited significantly larger parameters than females, except for the posterior condylar angle (all P values < 0.05). Compared to other populations, substantial differences were observed for most parameters, such as ML, AP, width of lateral femoral condyle, etc. (all P values < 0.05). Clustering analysis suggested that distal femoral prostheses should include at least five sizes to adequately accommodate the sampled population. ML sizes for males were 68, 70, 83, 73, and 89 mm, and for females 64, 65, 71, 67, and 77 mm. AP sizes for males were 56, 60, 60, 64, and 64 mm, and for females 48, 52, 54, 57, and 58 mm.

CONCLUSIONS

Chinese distal femur morphology, as analyzed using 3D techniques, varies significantly between genders and when compared with international data. For improved patient fit, the creation of five or more distal femur prostheses, diversified by gender and size and informed by the associated morphological parameters, is recommended.

LEVEL OF EVIDENCE

IV.