Ten Flaws of Systematic Mechanical Alignment Total Knee Arthroplasty

Matrix stiffness in osteoarthritis: from mechanism introduction to biomaterial-based therapies

Osteoarthritis (OA), the most prevalent joint disorder associated with aging, is characterized by impaired extracellular matrix (ECM) synthesis and the degradation of articular cartilage. It is influenced by various factors, including aging and mechanical stress (such as traumatic injury). Increasing evidence suggests that alterations in cartilage stiffness occur during OA progression, particularly at its onset. This review comprehensively examines how aging and mechanical stress contribute to ECM stiffening, a precursor to irreversible cartilage degradation. We also discuss how increased matrix stiffness disrupts the homeostatic balance between chondrocyte catabolism and anabolism and the mechanotransduction pathways involved in cartilage stiffening. Furthermore, the potential of cartilage engineering to target the stiffness of synthetic materials is explored as a promising approach to advancing cartilage repair and regeneration in OA. A deeper understanding of this research area may not only lead to more innovative strategies for early OA detection and diagnosis but also offer novel insights into OA treatment and prognosis.

Does robotic surgical assistant (ROSA) functionally aligned TKA lead to higher satisfaction than conventional mechanically aligned TKA: A propensity-matched pair analysis

Objectives

Total knee arthroplasty (TKA) is the established treatment for severe knee osteoarthritis, with robotic-assisted TKA (rTKA) proposed to enhance surgical precision and potentially improve outcomes. This study investigates whether functionally-aligned rTKA using the ROSA Knee System results in superior functional outcomes and patient satisfaction compared to conventional mechanically aligned TKA (mTKA).

Methods

We conducted a retrospective, propensity-score matched cohort study including 154 patients (46 rTKA, 108 mTKA) who underwent primary TKA by a single surgeon from October 2020 to October 2023. Functionally-aligned (FA) rTKA was performed using the ROSA Knee System. Patients were assessed using the Short-Form 36 (SF36), Knee Society Knee Score (KSKS), Knee Society Function Score (KSFS), and Oxford Knee Score (OKS) preoperatively and at 6 months postoperatively. Immediate postoperative outcomes such as pain at rest and movement, ambulation distance, and range of motion were measured. Statistical analysis evaluated results at a 95 % confidence interval, with significance at P < 0.05.

Results

No significant differences were observed in immediate postoperative pain at rest (P = 0.988), pain during movement (P = 0.634), ambulation distance (P = 0.243), and range of motion (P = 0.752) between the groups. At 6 months, there were no significant differences between rTKA and mTKA in achieving the minimal clinically important difference for SF36 (P = 0.996), KSKS (P = 0.150), KSFS (P = 0.091), and OKS (P = 0.949). No significant differences were noted for satisfaction levels (P = 0.315) and fulfilled expectations (P = 0.557) between both groups.

Conclusions

At 6 months postoperatively, FA rTKA demonstrated equivalent outcomes and satisfaction levels compared to mTKA. Future research should focus on examining longer-term follow-up outcomes, quantifying gap balance in MA mTKA to allow direct comparison with rTKA and studying alternative personalised alignment rTKA strategies to enhance patient outcomes.

Distribution of phenotypes of coronal plane alignment of the knees and functional phenotypes in the healthy young Iranian population: A cross-sectional study

Purpose

The functional phenotypes and the coronal plane alignment knee (CPAK) classification have recently been introduced. This study aimed to describe the phenotypes of normal knees in the healthy young Iranian population based on these systems.

Methods

This cross-sectional study included 402 knees in 201 healthy young adults. Phenotypes were reported using hip-knee-ankle (HKA) angle, femoral mechanical angle (FMA) and tibial mechanical angle (TMA) for functional phenotypes and joint line obliquity (JLO) and arithmetic HKA (aHKA) for CPAK classification. Also, a distinct combination of knee alignment parameters (HKA, FMA and TMA) that reflects the functional alignment characteristics of the knee, as described by Hirschmann, was used. Statistical analysis was performed using the Student's t test.

Results

The mean HKA, FMA and TMA were 176.03 ± 3.01°, 92.01 ± 2.77° and 86.52 ± 2.73°, respectively. All angles of female participants were significantly more varied compared to men (p < 0.05). The most common phenotypes were VAR(Varus)HKA3°, NEU(Neutral)TMA0° and NEUFMA0°. The distribution of the 10 most common functional phenotypes was not significantly different between men and women (p = 0.201). The most common CPAK types were type I (33.6%), II (26.6%) and III (16.7%), and types VII, VIII and IX were rarely seen (2.0% overall). The distribution of CPAK phenotypes significantly differed between men and women (p = 0.015), and CPAK type III was more frequently seen in women. Clinically, the predominance of varus phenotypes and the sex-specific differences observed underscore the importance of tailoring surgical alignment strategies to individual anatomy.

Conclusion

In conclusion, our study reveals that knee alignment in the healthy Iranian population tends to exhibit neutral or mild varus characteristics, with significant differences between men and women. These findings suggest that ethnicity may play a role in the natural alignment of the knee, which has important implications for surgical planning and outcomes.

Level of Evidence

Level III.

The Mark Coventry Award: Does Matching the Native Coronal Plane Alignment of the Knee Improve Outcomes in Primary Total Knee Arthroplasty?

BACKGROUND

The coronal plane alignment of the knee (CPAK) classification system was developed to assess personalized alignment strategies, such as kinematic alignment, in total knee arthroplasty (TKA). However, CPAK has not been studied with regard to patient-reported outcome measures (PROMs). This study evaluated whether incidentally matching a patient's native preoperative CPAK classification with TKA implant position meaningfully impacted postoperative PROMs.

METHODS

A retrospective review of 2,427 primary TKAs was performed. Knees were classified using the CPAK classification on standardized preoperative and postoperative short-leg radiographs using a five-degree adjustment for the lateral distal femoral angle based on available literature. Surgeries were performed using adjusted mechanical alignment strategies with a three-degree boundary. Patients who had a matching preoperative and postoperative CPAK were compared to all other combinations. Modern PROMs and clinically important differences were analyzed utilizing univariate and multivariate analyses.

RESULTS

There were 94.5% of native knees classified as CPAK I to III, like published CPAK distributions. The distribution of postoperative CPAK classification was significantly different, with 25.6% of TKAs classified as CPAK I to III (P < 0.001), and only 11.5% (N = 266) of postoperative CPAK matched the native preoperative classification. The CPAK was not associated with preoperative (P ≥ 0.208) or postoperative PROMs (P ≥ 0.085), except CPAK I had significantly higher preoperative pain with level walking compared to CPAK III only (P = 0.027). Patients who had matching preoperative and postoperative CPAK classes demonstrated no difference in PROMs at a median of 24 months of follow-up (P ≥ 0.143). Statistical power was ≥93.9%.

CONCLUSIONS

Study results demonstrate that matching a patient's native knee coronal alignment classified by CPAK was not predictive of PROMs. This supports prior research that suggests TKA outcomes are multifactorial and related to complex interactions between implant position in three dimensions as well as soft-tissue balance and kinematics.

LEVEL OF EVIDENCE

III.

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

Level IV, continuous case series with no comparison group.

Mechanically aligned total knee arthroplasty does not yield uniform outcomes across all coronal plane alignment of the knee (CPAK) phenotypes

PURPOSE

Patient dissatisfaction rates following total knee arthroplasty (TKA) reported in the literature reach 20%. The optimal coronal alignment is still under debate. The aim of this retrospective study was to compare clinical outcomes in different coronal plane alignment of the knee (CPAK) phenotypes undergoing mechanically aligned (MA) TKA. The hypothesis was that knees with preoperative varus arithmetic hip-knee-ankle angle (aHKA) would achieve inferior clinical outcomes after surgery compared to other aHKA categories. Additionally, another objective was to assess CPAK phenotypes distribution in the study population.

METHODS

A retrospective selection was made of 180 patients who underwent MA TKA from April 2021 to December 2022, with a 1-year follow-up. Coronal knee alignment was classified according to the CPAK classification. Clinical outcome evaluations were measured using the Knee Society Score (KSS), Oxford Knee Score (OKS), Short Form Survey 12 and Forgotten Joint Score (FJS). Differences in clinical outcomes were considered statistically significant with a p value <0 .05.

RESULTS

Patients with varus aHKA achieved significantly inferior outcomes at final follow-up compared to other aHKA categories in KSS pt. 1 (79.7 ± 17.2 vs. 85.6 ± 14.7; p = 0.028), OKS (39.2 ± 9.2 vs. 42.2 ± 7.2; p = 0.019) and FJS (75.4 ± 31.0 vs. 87.4 ± 22.9; p =0 .003). The most common aHKA category was the varus category (39%). The most common CPAK phenotypes were apex distal Types I (23.9%), II (22.8%) and III (13.3%).

CONCLUSION

MA TKA does not yield uniform outcomes across all CPAK phenotypes. Varus aHKA category shows significantly inferior results at final follow-up. The most prevalent CPAK categories are varus aHKA and apex distal JLO, with phenotypes I, II and III being the most common. However, their gender distribution varies significantly.

LEVEL OF EVIDENCE

Level IV.

The Restoration of the Prearthritic Joint Line Does Not Guarantee the Natural Knee Kinematics: A Gait Analysis Evaluation Following Primary Total Knee Arthroplasty

Background

Unrestricted kinematic alignment (uKA) in total knee arthroplasty (TKA) has the theoretical advantage of reproducing patients' constitutional alignment and restoring the pre-arthritic joint line position and obliquity. However, modifications of the original uKA technique have been proposed due to the potential risk of mechanical failure and instability. Given the significant variability in soft tissue behavior within the same bony morphology group, uKA pure knee resurfacing could be occasionally detrimental. This study aimed to kinematically compare the outcomes of uKA TKA with those of a robotic-assisted KA TKA technique based on specific soft-tissue boundaries.

Methods

In this retrospective gait analysis study, 24 TKA patients and 12 healthy controls were recruited. Inclusion criteria were a 9-month minimum follow-up from successfully, primary medial-pivot or medially-congruent TKA performed for isolated degenerative joint disease. Preoperatively, patients were randomly assigned to two surgical groups: A) uKA (#12) and B) robot-assisted (#12), KA (hybrid-kinematic) with boundaries (±3° from hip-knee-ankle neutral axis) and a slight intercompartmental gap asymmetry (max 2 mm lateral-opening). The gait analysis was performed using instrumented treadmills equipped with 3D cameras.

Results

Sagittal knee kinematic data: during the early-stance phase of gait, the uKA group showed a less consistent weight-acceptance phase and a less efficient transition between the first knee-flexion peak and mid-stance-extension plateau with respect to the hybrid-kinematic alignment group. Spatiotemporal and overall gait quality data: no significant differences were found between the two TKA groups regarding walking speed (P = .51) and step length (P = .8534). Control group patients walked more efficiently compared to TKA groups, showing inferior trunk flexion and inferior variation in step length (P < .0001).

Conclusions

This study showed that restoring the pre-arthritic joint line, as advocated by surgeons following the uKA philosophy, does not guarantee a closer-to-normal knee kinematics.

Inverse kinematic total knee arthroplasty using conventional instrumentation restores constitutional coronal alignment

PURPOSE

Restricted inverse kinematic alignment (iKA) is a contemporary alignment strategy for total knee arthroplasty (TKA), commonly performed with robotic assistance. While superior clinical results are reported for kinematic-type alignment strategies, registry data indicate no survivorship benefit for navigation or robotic assistance. This study aimed to determine the efficacy of an instrumented, restricted iKA technique for achieving patient-specific alignment.

METHODS

Seventy-nine patients undergoing 84 TKAs (five bilateral procedures) using an iKA technique were included for preoperative and postoperative lower limb alignment analysis. The mean age was 66.5 (range: 43-82) with 33 male and 51 female patients. Artificial intelligence was employed for radiographic measurements. Alignment profiles were classified using the Coronal Plane Alignment of the Knee (CPAK) system. Preoperative and postoperative alignment profiles were compared with subanalyses for preoperative valgus, neutral and varus profiles.

RESULTS

The mean joint-line convergence angle (JLCA) reduced from 2.5° to -0.1° postoperatively. The mean lateral distal femoral angle (LDFA) remained unchanged postoperatively, while the mean medial proximal tibial angle (MPTA) increased by 2.5° (p = 0.001). By preservation of the LDFA and restoration of the MPTA, the mean hip knee ankle angle (HKA) moved through 3.5° varus to 1.2° valgus. The CPAK system was used to visually depict changes in alignment profiles for preoperative valgus, neutral and varus knees; with 63% of patients observing an interval change in classification.

CONCLUSION

Encouraged by the latest evidence supporting both conventional instrumentation and kinematic-type TKA strategies, this study describes how a restricted, conventionally instrumented iKA technique may be utilised to restore constitutional lower limb alignment.

LEVEL OF EVIDENCE

Level III.

The effect of different alignment strategies on trochlear orientation after total knee arthroplasty

PURPOSE

When planning and delivering total knee arthroplasty (TKA), there are multiple coronal alignment strategies such as functional alignment (FA), kinematic alignment (KA), mechanical and adjusted mechanical alignment (MA, aMA). Recent three-dimensional and robotic-assisted surgery (RAS) studies have demonstrated that KA potentially better restores the trochlear anatomy than MA. The purpose of this study was to compare the restoration of the native trochlear orientation in patients undergoing RAS TKA using four different alignment strategies. It was hypothesised that FA would result in the lowest number of outliers.

METHODS

This is a prospective study of 200 patients undergoing RAS-TKA with a single implant. All patients were analysed for MA and KA prebalancing, and 157 patients received aMA and 43 patients FA with intraoperative balancing. Preoperative transverse computed tomography scans were used to determine the posterior condylar axis (PCA), lateral trochlear inclination (LTI) angle, sulcus angle (SA) and anterior trochlear line (ATL) angle. Implant measurements were obtained using a photographic analysis. Intraoperative software data combined with implant data and preoperative measurements were used to calculate the differences. Outliers were defined as ≥3° of alteration. Trochlea dysplasia was defined as LTI < 12°.

RESULTS

Native transepicondylar PCA had a median of 2°, LTI 18°, SA 137°, ATL 4°. LTI outliers were observed in 47%-60% of cases, with KA < FA < aMA < MA. For ATL, the range of outliers was 40.5%-85%, KA < FA < aMA < MA. SA produced 81% of outliers. Of all median angle values, only LTI when using KA was not significantly altered compared to the native knee.

CONCLUSION

There is a significant alteration of trochlear orientation after TKA, regardless of the alignment strategy used. KA produced the lowest, but a substantial, number of outliers. The uniform design of implants causes the surgeon to compromise on balance in flexion versus trochlear position. The clinical relevance of this compromise requires further clinical investigations.

LEVEL OF EVIDENCE

Level II, prospective cohort study.

Robotic Assisted TKA achieves adjusted mechanical alignment targets more consistently compared to manual TKA without improving outcomes

Introduction

Robotic total knee arthroplasty (rTKA), with its purported advantages of more accurate alignment, greater functional outcomes and patient satisfaction, is gaining popularity in patients undergoing TKA. The purpose of our study was to compare these parameters along with gait pattern and kneeling ability in a cohort of patients who underwent simultaneous TKA with manual instrumentation (mTKA) and rTKA in contralateral knees at a 1-year follow-up.

Methods

This was a retrospective review of 135 consecutive patients who underwent simultaneous bilateral TKA using robotic assistance on one side and manual instrumentation on the contralateral side between January 2022 and June 2022. The target alignment in both cohorts was adjusted mechanical. Patients were followed up at 3, 6 and 12 months to assess and compare alignment, range of motion (ROM) and patient-reported outcome measures (PROM) data. Gait parameters and kneeling ability were assessed at 1-year follow-up.

Results

While adjusted mechanical alignment was achieved in all rTKA patients, we recorded five outliers (≥3° with relation to 180° HKA axis) in the mTKA cohort (three varus and two valgus). There were no significant differences between both cohorts with regards to ROM, PROM scores, gait analysis parameters and kneeling ability at 1-year follow-up.

Conclusion

rTKA helps in achieving the adjusted mechanical alignment more consistently than mTKA. This, however, does not contribute to better functional outcomes and patient satisfaction at 1-year follow-up.

Level of Evidence

Level III.

Conventionally instrumented inverse kinematic alignment for total knee arthroplasty: How is it done?

Purpose

For primary total knee arthroplasty (TKA), there is an increasing trend towards patient-specific alignment strategies such as kinematic alignment (KA) and inverse kinematic alignment (iKA), which by restoring native joint mechanics may yield higher patient satisfaction rates. Second, the most recent Australian joint registry report describes favourable revision rates for conventionally instrumented TKA compared to technology-assisted techniques such as those using navigation, robotics or custom-cutting blocks. The aim of this technique article is to describe in detail a surgical technique for TKA that: (1) utilises the principles of iKA and (2) uses conventionally instrumented guided resections thereby avoiding the use of navigation, robotics or custom blocks.

Methods

A TKA technique is described, whereby inverse kinematic principles are utilised and patient-specific alignment is achieved. Additionally, the patellofemoral compartment of the knee is restored to the native patellofemoral joint line. The sequenced technical note provided may be utilised for cemented or cementless components; cruciate retaining or sacrificing designs and for fixed or rotating platforms.

Results

An uncomplicated, robust and reproducible technique for TKA is described.

Discussion

Knee arthroplasty surgeons may wish to harness the emerging benefits of both a conventionally instrumented technique and a patient-specific alignment strategy.

Level of Evidence

Level V.

Tibia-first, gap-balanced patient-specific alignment restores bony phenotypes and joint line obliquity in a great majority of varus and straight knees and normalises valgus and severe varus deformities

PURPOSE

The present study focuses on testing the capability of a restricted tibia-first, gap-balanced patient-specific alignment technique (PSA) to restore bony morphology and phenotypes.

METHODS

Three-hundred and sixty-seven patients were treated with navigated total knee arthroplasty and tibia-first gap-balanced PSA technique. Boundaries for medial proximal tibial angle were 86°-92°, mechanical lateral distal femoral angle 86°-92°, and hip-knee-ankle angle 175°-183°. Knees were classified by coronal plane alignment of the knee (CPAK), with subsequent analyses comparing pre- and postoperative distributions. Phenotype classification within CPAK groups assessed pre- and postoperative distributions.

RESULTS

Preoperatively, the largest CPAK group was type II (30.8%), followed by type I (20.5%) and type V (17.8%). Postoperatively, type II remained the largest group (39%), followed by type V (30%). All groups with varus/valgus deformities (I, III, IV and VI) became smaller. While in straight legs (II, IV), the CPAK was restored in more than 70%-75%, in varus groups (I, IV) in 40%-50% and in valgus (III and VI) in 5%-18%. The joint line obliquity remained the same in the majority of knees (straight >75%; varus 63%-80%; valgus VI 95%), with the exception of CPAK III (40%). The phenotype analysis showed for straight legs a phenotype restoration of 85%, for varus 94% and for valgus 37%. Joint line convergence angle was reduced significantly in all groups from 1.8°-4.3° preoperatively to 0.6°-1.2° postoperatively.

CONCLUSION

PSA restores bony phenotypes and joint line obliquity in the majority of straight and varus knees, while most of the valgus and extreme varus knees are normalised.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.