A prospective randomised control trial comparing functional with mechanical axis alignment in total knee arthroplasty: study protocol for an investigator initiated trial

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.

Large multiplanar changes to native alignment have no apparent impact on clinical outcomes following total knee arthroplasty

PURPOSE

This study sought to examine if achieved postoperative alignment when compared to the native anatomy would lead to a difference in Patient Reported Outcome Measures (PROMs), and whether the achieved alignment could be broadly categorised by an accepted alignment strategy.

METHODS

A retrospective cohort study of prospectively collected data on patients undergoing single primary or bilateral simultaneous total knee arthroplasty (TKA) was carried out. CT scans were used to determine the mean change ("delta values") between the pre and postoperative; hip-knee-ankle angle, lateral distal femoral angle, medial proximal tibial angle and femoral implant rotation. Femoral implant flexion and tibial implant slope were measured postoperatively. The primary outcome was the relationship of the variables to the change in KOOS pain subscale after one year. The secondary outcome was the number of knees which could be categorised postoperatively to an alignment strategy, and the mean PROMs in each cohort.

RESULTS

A total of 296 knees in 261 patients were available for analysis. With regards to the primary outcome, the delta values for each variable did not demonstrate any association with the change in knee injury and osteoarthritis outcome score (KOOS) pain score. Approximately 46% of knees could not be categorised to an alignment strategy based on postoperatively measured alignment, with no significant difference between each cohort with regards to the change in KOOS Pain score.

CONCLUSION

Achieved alignment does not consistently match accepted alignment strategies, and appears to confer no benefit to clinical outcomes when the native anatomy is most closely approximated, nor results in poorer outcomes in outliers. This study highlights the importance of routine three dimensional pre and postoperative imaging in clinical practice and for the valid analysis of outcomes in studies on alignment.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Functional alignment is associated with increased incidence of pre-balance, reduced soft-tissue release, and post-operative pain compared to mechanical alignment in patients undergoing simultaneous bilateral robotic-assisted TKA

This study aimed to compare two alignment strategies in the same patient undergoing simultaneous bilateral robotic-assisted TKA (SB-RATKA): mechanical alignment (MA), the gold-standard, and functional alignment (FA), a balance-driven, personalized alignment strategy. The outcome measures included quantitative assessment of soft-tissue release, incidence of knee balance, and post-operative pain. This was a prospective, self-controlled, randomized-controlled trial involving 72 patients who underwent SB-RATKA using the MAKO® robotic system with comparable grades of deformity and pain in both knees. 65 patients were finally included with one alignment strategy done per knee, with the patients blinded to the strategy used. The study recorded the additional soft-tissue releases required, incidence of pre-balance, and daily post-operative VAS pain scores. The mean age of the study population was 57.95 years, with a female preponderance (N = 53, 81.6%). MA group had significantly more medial compartment tightness in both flexion (MA-15.6 ± 1.8; FA-17 ± 1.3) and extension (MA-14.9 ± 1.9; FA-17 ± 1.1) (p < 0.0001) compared to the FA group after dynamic balancing. 66% of knees in the FA group (N = 43) achieved pre-balance compared to 32.3% in the MA group (N = 21) (p < 0.0001). VAS scores showed a significant reduction in pain in the FA group up to 72 h post-surgery (p < 0.0001). The requirement for posteromedial release (PM), posterior capsular (PC) release, tibial reduction osteotomy (TRO), and superficial MCL pie crusting (sMCL) were significantly lower in FA (PM-22, PC-13, TRO-8, sMCL-2) compared to MA (PM-44, PC-29, TRO-18, sMCL-8). Functional alignment strategy consistently resulted in a higher incidence of knee balance with a significant reduction in soft-tissue releases and immediate post-operative pain when compared to MA in the same patient undergoing SB-RATKA. Therapeutic Level 1.

Navigated functional alignment total knee arthroplasty achieves reliable, reproducible and accurate results with high patient satisfaction

PURPOSE

The decision on which technique to perform a total knee arthroplasty (TKA) has become more complicated over the last decade. Perceived limitations of mechanical alignment (MA) and kinematic alignment (KA) have led to the development of the functional alignment (FA) philosophy. This study aims to report the 2-year results of an initial patient cohort in terms of revision rate, PROMs and complications for Computer Aided Surgery (CAS) Navigated FA TKA.

METHODS

This paper reports a single surgeon's outcomes of 165 consecutive CAS FA TKAs. The final follow-up was 24 months. Pre-operative and post-operative patient-reported outcome measures, WOMAC and KSS, and intra-operative CAS data, including alignment, kinematic curves, and gaps, are reported. Stress kinematic curves were analysed for correlation with CAS final alignment and CAS final alignment with radiographic long-leg alignment. Pre- and post-operative CPAK and knee phenotypes were recorded. Three different types of prostheses from two manufacturers were used, and outcomes were compared. Soft tissue releases, revision and complication data are also reported.

RESULTS

Mean pre-operative WOMAC was 48.8 and 1.2 at the time of the final follow-up. KSS was 48.8 and 93.7, respectively. Pre- and post-operative range of motion was 118.6° and 120.1°, respectively. Pre-operative and final kinematic curve prediction had an accuracy of 91.8%. CAS data pre-operative stress alignment and final alignment strongly correlate in extension and flexion, r = 0.926 and 0.856, p < 0.001. No statistical outcome difference was detected between the types of prostheses. 14.5% of patients required soft tissue release, with the lateral release (50%) and posterior capsule (29%) being the most common.

CONCLUSION

CAS FA TKA in this cohort proved to be a predictable, reliable, and reproducible technique with acceptable short-term revision rates and high PROMs. FA can account for extremes in individual patient bony morphology and achieve desired gap and kinematic targets with soft tissue releases required in only 14.5% of patients.

LEVEL OF EVIDENCE

IV (retrospective case series review).

Maintaining joint line obliquity optimizes outcomes of functional alignment in total knee arthroplasty in patients with constitutionally varus knees

INTRODUCTION

Functional alignment (FA) strives to balance the knee soft-tissue envelope during total knee arthroplasty (TKA) using implant alignment adjustments rather than soft-tissue releases. There is debate on how best to achieve FA. We compared minimum two-year outcomes between FA with a mechanical alignment plan [FA(m)] and FA with a kinematic alignment plan [FA(k)]. The null hypothesis was that there would be no difference in outcomes between FA(m) and FA(k).

METHODS

Prospective data was collected from 300 consecutive robotic assisted (RA) FA TKAs [135 FA(m) and 165 FA(k)]. Patient reported outcomes were obtained pre-operatively and two years post-operatively. The coronal plane alignment of the knee (CPAK) classification was used to classify knee alignment phenotypes.

RESULTS

Overall limb alignment was equivalent between groups. Final implant alignment was different between FA(m) and FA(k) groups, with FA(k) TKAs having higher tibial varus (P<0.01), higher femoral valgus (P<0.01), and higher joint line obliquity (P<0.01). Patients reported higher FJS-12 scores with FA(k) TKAs (79.4 versus 71.6, P=0.018), and greater range of motion (125 versus 121°; P=0.003). Patients who had constitutional varus reported the greatest improvement with FA(k) technique (FJS at minimum two years of 89 versus 65; P<0.001).

CONCLUSION

Utilizing an individualized alignment plan (FA(k)) led to a final implant position with greater joint line obliquity, yet the same overall limb alignment. This was associated with improved outcomes at two years post TKA in patients who had constitutional varus. Three-dimensional component position and joint line obliquity affect outcomes following TKA independent of coronal limb alignment.

Perioperative Essential Amino Acid Supplementation Facilitates Quadriceps Muscle Strength and Volume Recovery After TKA: A Double-Blinded Randomized Controlled Trial

BACKGROUND

Perioperative essential amino acid (EAA) supplementation suppresses lower-limb muscle atrophy and promotes functional improvement in the first 4 weeks after total knee arthroplasty (TKA). However, its effect on the recovery of muscle volume and strength in the intermediate term is unclear. The aim of this study was to evaluate the effect of perioperative EAA supplementation on the recovery of lower-limb muscle volume and strength in the 2 years after TKA.

METHODS

Sixty patients who underwent unilateral TKA for primary knee osteoarthritis were included in this double-blinded randomized controlled trial. After excluding dropouts, 26 patients assigned to the EAA group (9 g/day) and 26 assigned to the placebo group (powdered lactose, 9 g/day) were available for analysis. Patients received EAA supplementation or a placebo from 1 week prior to surgery to 2 weeks after it. The rectus femoris muscle area was measured using ultrasonography and quadriceps muscle strength was measured isometrically with a handheld dynamometer, preoperatively and periodically up to 2 years postoperatively. Knee pain, knee range of motion, functional mobility, and Knee Society Score 2011 subjective scores were measured at each time point. Perioperative management, except for supplementation, was identical in the 2 groups.

RESULTS

Taking the baseline as 100%, the mean values in the EAA and placebo groups were 134% ± 31% and 114% ± 27%, respectively, for the rectus femoris muscle area and 159% ± 54% and 125% ± 40% for the quadriceps muscle strength, respectively, at 2 years after surgery. The differences were significant (p < 0.05). Clinical outcomes were not significantly different between the 2 groups.

CONCLUSIONS

Perioperative EAA supplementation contributes to the recovery of rectus femoris muscle volume and quadriceps muscle strength in the 2 years after TKA. The EAA supplementation did not impact clinical outcomes.

LEVEL OF EVIDENCE

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

The language of knee alignment : updated definitions and considerations for reporting outcomes in total knee arthroplasty

Orthopaedic surgeons are currently faced with an overwhelming number of choices surrounding total knee arthroplasty (TKA), not only with the latest technologies and prostheses, but also fundamental decisions on alignment philosophies. From 'mechanical' to 'adjusted mechanical' to 'restricted kinematic' to 'unrestricted kinematic' - and how constitutional alignment relates to these - there is potential for ambiguity when thinking about and discussing such concepts. This annotation summarizes the various alignment strategies currently employed in TKA. It provides a clear framework and consistent language that will assist surgeons to compare confidently and contrast the concepts, while also discussing the latest opinions about alignment in TKA. Finally, it provides suggestions for applying consistent nomenclature to future research, especially as we explore the implications of 3D alignment patterns on patient outcomes.Cite this article: Bone Joint J 2023;105-B(2):102-108.

A prospective randomised controlled trial of mechanical axis with soft tissue release balancing vs functional alignment with bony resection balancing in total knee replacement-a study using Stryker Mako robotic arm-assisted technology

Background

Improving the functional outcome following total knee arthroplasty (TKA) by using different alignment techniques remains controversial. The surgical techniques and technologies used so far to obtain these alignments have all suffered from inaccuracies. The use of robotic technology to plan and execute the bony resection provides increased accuracy for these various alignment techniques and may determine which will deliver superior function. Functional alignment (FA) is a newer surgical technique that aims to position the prosthesis with respect to each patients’ specific bony anatomy whilst minimising disruption to the soft tissue envelope. This trial aims to compare the patient and surgical outcomes of FA to the current gold standard surgical technique, mechanical alignment (MA), under randomised and blinded conditions.

Methods

Patients with symptomatic knee osteoarthritis will be prospectively recruited. Following informed consent, 240 patients will be randomised to either a MA surgical technique (the control group) or a FA surgical technique (the intervention group) at a ratio of 4:1 using a random number generator. All patients will undergo computer tomography (CT) based robotic arm-assisted surgery to execute planned implant positioning and alignment with high levels of accuracy. The primary outcome is the forgotten joint score (FJS) at 2 years post-operation. Secondary outcome measures include patient reported outcome measures of post-operative rehabilitation, pain, function and satisfaction, as well as limb alignment, implant revisions and adverse events. Intention-to-treat and per-protocol population analysis will also be conducted. Standardisation of the surgical system and care pathways will minimise variation and assist in both patient and physiotherapist blinding. Ethical approval was obtained from the Northern B Health and Disability Ethics Committee (20/NTB/10).

Discussion

Currently, MA remains the gold standard in knee replacement due to proven outcomes and excellent long-term survivorship. There are many alternative alignment techniques in the literature, all with the goal of improving patient outcomes. This study is unique in that it leverages an advanced analytics tool to assist the surgeon in achieving balance. Both alignment techniques will be executed with high precision using the CT-based robotic arm-assisted surgery system which will minimise surgical variation. This trial design will help determine if FA delivers superior outcomes for patients.

Trial registration

Australia and New Zealand Clinical Trials Registry (ANZCTR), ACTRN12620000009910. Registered on 9 January 2020. ClinicalTrials.gov, NCT04600583. Registered on 29 September 2020.

Computer-Aided Surgery-Navigated, Functional Alignment Total Knee Arthroplasty: A Surgical Technique

The decision on which technique to use to perform a total knee arthroplasty has become much more complicated over the last decade. The shortfalls of mechanical alignment and kinematic alignment has led to the development of a new alignment philosophy, functional alignment. Functional alignment uses preoperative radiographic measurements, computer-aided surgery, and intraoperative assessment of balance, to leave the patient with the most “normal” knee kinematics achievable with minimal soft-tissue release. The purpose of this surgical technique article is to describe in detail the particular technique needed to achieve these alignment objectives.