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

Restoration of anatomical knee phenotype is associated with improved postoperative clinical outcomes after total knee arthroplasty

BACKGROUND

A comprehensive assessment of knee phenotypes is crucial for optimizing surgical realignment strategies in total knee arthroplasty (TKA). This study aimed to investigate the relationship between the restoration of preoperative phenotypes, such as joint line orientation (JLO) and alignment, and clinical outcomes following TKA.

METHODS

A retrospective review was performed on the records of 1052 primary osteoarthritic knees that underwent mechanically aligned (MA) TKA between March 2016 and October 2021. Patient-reported outcome measures (PROMs) were assessed preoperatively and at 2 years postoperatively. Patients were categorized according to the coronal plane alignment of the knee (CPAK) classification system, which incorporates the arithmetic hip-knee-ankle angle (aHKA) as an indicator of constitutional alignment and JLO. Clinical outcomes were compared between patients whose knee phenotype was maintained and those in whom it was not restored.

RESULTS

Among osteoarthritic knees, the majority (59.4%) were classified as CPAK type I (varus aHKA, apex distal JLO) preoperatively. Using mechanical axis techniques, the native phenotype was restored in 127 (12.1%) of the 1052 cases. These patients demonstrated significantly better postoperative clinical outcomes, as measured by WOMAC function and Forgotten Joint Scores (FJS), compared with the non-restored group (P < 0.05). When alignment was adjusted through detailed analyses of patients with maintained alignment between preoperative and latest follow up assessments, the significant differences in WOMAC function and FJS outcomes between restored JLO and non-restored JLO groups persisted (all P < 0.05). No significant association was observed between the restoration of aHKA and clinical outcomes.

CONCLUSION

The restoration of the anatomical knee phenotype, particularly JLO, is associated with improved postoperative PROMs, notably in functional outcomes, following TKA. These findings underscore the clinical importance of prioritizing preoperative JLO for optimizing surgical outcomes, rather than focusing exclusively on overall limb alignment.

Distribution of coronal plane alignment of the knee and functional knee phenotype classification in the Thai arthritic population and correlation with other Asian populations

PURPOSE

The Coronal Plane Alignment of the Knee (CPAK) and Functional Knee Phenotype (FKP) classification system categorize knee phenotypes into subtypes. It has been proposed that maintaining constitutional knee alignment in knee arthroplasty may enhance outcomes. Therefore, this study aimed to examine the phenotypic distribution in a Thai population using the CPAK and FKP classifications and its correlation with other Asian populations.

METHODS

This retrospective cohort study included 509 patients who underwent knee arthroplasty. Long-leg standing weight-bearing radiographs were used to categorize patients according to the CPAK (arithmetic hip-knee-ankle angle [aHKA], joint-line obliquity [JLO]) and FKP (hip-knee-ankle angle [HKA], femoral mechanical angle [FMA], and tibial mechanical angle [TMA]) classification system.

RESULTS

The most common CPAK distribution was type I (49.3%), followed by type II (20.6%) and type IV (11.0%). In males, CPAK Types I and II were the most common, similar to females; however, males had a significantly higher rate of Type I than females (58.8% vs. 46.5%, p = 0.049). The most frequent FKP was VARHKA6°VARFMA3°VARTMA3° (10%), VARHKA3°VARFMA3°NEUTMA0° (7.7%), and NEUHKA0°NEUFMA0°NEUTMA0° (7.1%). Thai arthritic knees predominantly exhibited apex distal JLO with constitutional varus alignment, consistent with findings from other Asian populations. There were no significant differences in CPAK distribution between TKA and UKA patients; however, aHKA and lateral distal femoral angle were significantly different between groups.

CONCLUSION

The Thai arthritic population demonstrates a significant trend toward apex distal JLO and varus alignment, aligning with findings from other Asian populations, which aids in the personalization of knee arthroplasty approaches.

Comparative effects of mechanical and functional alignment in bilateral robotic total knee arthroplasty: a randomized controlled trial

BACKGROUND

Functional alignment (FA) in total knee arthroplasty (TKA) can achieve soft tissue balance by fine-tuning adjustments of bony resections and component alignment with less soft tissue release. However, joint line orientation relative to the floor in the knee and ankle after TKA is not well studied.

METHODS

A randomized-controlled trial was performed in 30 patients with robotic-assisted bilateral TKA using FA and mechanical alignment (MA) in the same patient. The outcome measures were as follows: (1) standing radiographic knee and ankle alignment; (2) clinical outcomes at 1, 3 and 6 months postoperatively (including forgotten joint score (FJS), KOOS, knee range of motion); (3) patient satisfaction score; and (4) soft tissue release.

RESULTS

Postoperative hip-knee-ankle angles between the FA and MA groups were similar (2.4° versus 2.4°, P = 0.952). Knee joint line orientation was significantly more parallel to the floor in the FA group (3.0° versus 4.7°, P < 0.001). There was no significant difference in ankle joint line orientation relative to the floor in the FA and MA groups (91.0° versus 92.4°, P = 0.099 for tibial plafond inclination and 92.5° versus 93.2°, P = 0.564 for talar dome inclination). However, in knees with preoperative varus with apex distal joint line orientation (coronal plane alignment of the knee (CPAK) classification type I), FA significantly achieved a more parallel knee and ankle joint line orientation relative to the floor (3.1° versus 5.1°, P = 0.002 for knee and 91.0° versus 93.5°, P = 0.028 for tibial plafond inclination). FA can obtain a balanced knee with significantly lower posteromedial releases (23.3% versus 76.7%, P < 0.001), with no superficial MCL release needed (0% versus 6.67%, P < 0.01). The FA group achieved significantly higher FJS at 3 months (53.3 versus 46.0, P = 0.015) and 6 months (67.8 versus 57.8, P < 0.001) with a higher patient satisfaction score (79.2 versus 84.3, P = 0.001).

CONCLUSION

Functional alignment can control the overall lower limb alignment similarly to mechanical alignment, with a knee joint line more parallel to the floor. Additionally, the ankle joint line was more parallel in knees with CPAK type I. FA can also provide a more balanced knee with less soft tissue release, a higher functional score, and greater patient satisfaction compared to mechanical alignment.

Is limb overcorrection following total knee arthroplasty compromising functional outcome?

Purpose

Many patients remain unsatisfied after total knee arthroplasty (TKA). Personalized alignment strategies have gained popularity in the search to improve patient satisfaction and function. This study aimed to examine the impact of limb overcorrection in the coronal plane on patient satisfaction and functional outcome. The secondary aim was to investigate how a change in knee phenotype following TKA affects clinical outcome.

Methods

A retrospective matched case-control study was designed between patients with limb overcorrection (N = 37) and a control group (N = 104). Mean follow-up was 68 months. Satisfaction and function were compared by means of the new 2011 Knee Society Score (KSS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS). Radiological evaluation was performed on weight-bearing full-leg radiographs. Overcorrection was defined as a mechanical HKA (mHKA) angle of 2° or more and opposite to the preoperative alignment. The control group consisted of TKAs that were corrected to neutral or left in slight undercorrection. Finally, component alignment (lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA)) and Coronal Plane Alignment of the knee (CPAK) phenotypes were evaluated.

Results

The overcorrection group performed better than the control group in terms of KSS subscores satisfaction and functional activities, total KSS score, all KOOS subcategories, and total KOOS score. Subdivision of the control group into a neutral and undercorrection group, and the overcorrection group into mild and severe overcorrection, revealed similar findings.A chance in knee phenotype as per aHKA, JLO or CPAK did not result in worse clinical outcomes.

Conclusion

Accidental limb overcorrection after TKA does not result in inferior clinical outcomes or patient satisfaction at midterm follow-up.The present study could not identify an optimal coronal alignment target. This suggests that coronal alignment as a predictor of patient satisfaction and function is likely less important than previously believed.

Level of evidence

Level III, retrospective case-control study.

Change of CPAK class does not affect functional outcomes in robotic arm-assisted total knee arthroplasty performed with functional alignment

PURPOSE

The purpose of this study was to assess the impact of post-operative coronal plane alignment of the knee (CPAK) class change on functional outcomes and determine the rate and type of CPAK class change after image-based robotic arm-assisted (RA)-total knee arthroplasty (TKA) performed with functional alignment (FA) at two different centres.

METHODS

The present retrospective, observational, multicentre study included 201 patients treated with RA-TKA between October 2020 and April 2022 at two different centres. The radiographic CPAK classification was adapted using CT images to achieve pre- and post-operative knee categorization into CPAK classes. At a minimum of 1 year post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and surveyed about their post-operative satisfaction level using a 5-level Likert scale (5-LLS).

RESULTS

The most common preoperative overall CPAK classes were: Types II, I, III, IV and V. Implant positioning after RA-TKA with FA within the alignment boundaries, determined distribution in the CPAK classification, predominantly maintaining classes I, II, IV, and V. No statistically significant FJS-12 differences were detected between subjects who maintained and changed their preoperative CPAK class. The mean 5-LLS for satisfaction in patients where the preoperative CPAK class was maintained intraoperatively was 4.4 ± 1.1 (range = 1-5), while subjects having the CPAK class changed had a mean 5-LLS of 4.4 ± SD 1.0 (range 1-5).

CONCLUSION

In the setting of image-based RA-TKA with FA, CPAK can be changed within a 'functional safe-zone', without compromising functional outcomes. Good functional outcomes are the result of a stable and balanced knee with soft-tissue preservation, regardless of the maintenance of the preoperative CPAK class.

LEVEL OF EVIDENCE

Level III.

Tibial Components Placed in Constitutional Varus Alignment in Primary Total Knee Arthroplasty: A 5-Year Survivorship Analysis

BACKGROUND

Placing tibial components in varus alignment has been controversial due to concerns of loosening and subsequent revision. The purpose of this study was to compare 5-year survivorship of tibial components placed in 3° or greater of varus alignment versus neutral mechanical alignment (nMA).

METHODS

This was a retrospective matched cohort study of 530 patients with 265 patients who underwent primary robotic-assisted total knee arthroplasty (TKA) with tibial components intentionally placed in varus matched to a control group of 265 patients who underwent TKA using manual instrumentation with tibial components placed in nMA. Both cementless and cemented implants were used in both groups. There was no difference between groups with respect to patient sex or age. There were 100 and 87.5% of patients who had a minimum 5-year follow-up in the tibial varus and nMA groups, respectively. Outcomes included survivorship, complications, revisions, and patient-reported outcome measures.

RESULTS

All-cause survivorship at 5 years postoperatively was 98% in the group with constitutional tibial varus and 96% in the nMA group (P = 0.12). There were no cases of aseptic loosening in the group with tibial component varus. There were five patients who required revision in the varus group versus 14 in the nMA group (P = 0.02). There was a significant difference in nonrevision intervention for stiffness between the two groups in favor of the varus group (three versus 14, P = 0.003).

CONCLUSIONS

Similar survivorship was demonstrated at a mid-term 5-year follow-up between patients undergoing primary TKA using a functional alternative alignment concept with tibial components intentionally placed in 3° or greater of varus compared to nMA. Tibial components placed in constitutional or anatomic varus, in an attempt to restore the native oblique joint line along with well-balanced gaps, demonstrated 98% survivorship at 5 years.

Chronic pain at 1-year following knee arthroplasty is associated with a worse joint-specific function and health-related quality of life

PURPOSE

The purpose of this study was to identify independent variables associated with chronic pain (CP) at 1 year following knee arthroplasty (KA) and whether this influenced functional outcomes.

METHODS

This retrospective study was conducted over a 2-year period and included 2588 patients with completed Oxford knee score (OKS) and EuroQol (EQ)-five domains (5D) preoperatively and at 1 and 2 years postoperatively. The OKS pain component score was used to define patients with CP (≤14 points). The mean age was 70.0 (range 34-94) years and there were 1553 (60.0%) females.

RESULTS

There were 322 (12.4%) patients with CP at 1 year. A worse preoperative EQ-5D (p = 0.025), EQ-visual analogue scale (VAS) (p = 0.005) and OKS questions relating to washing (p = 0.010), limping (p = 0.007), kneeling (p = 0.003) and night pain (p = 0.004) were independently associated with risk of CP. However, the preoperative OKS (area under the curve [AUC]: 72.0, p < 0.001) and EQ-5D score (AUC: 70.1, p < 0.001) were the most reliable predictors, with threshold values of <18-points and <0.300 being predictive of CP, respectively. Of those with CP at 1 year, 231 were followed up at 2 years, of which 92 (39.8%) had resolution of their CP. A worse response to OKS question 11 (ability to shop) and EQ-5D (p = 0.028) at 1 year was independently associated with persistent CP. Patients with CP had significantly (p < 0.001) worse OKS, EQ-5D and EQ-VAS at 1 year compared to those without. However, for those that had resolution of their CP at 2 years, their outcomes were clinically equal to those that did not have CP at 1 year.

CONCLUSION

One in eight patients had CP at 1 year following surgery, which was associated with clinically worse knee-specific outcomes and quality of life. However, by 2 years, two in five patients had resolution of their CP and had functional outcomes clinically equal to those without CP at 1 year. The risk factors identified could be used to inform patients of their risk for CP and the potential for resolution.

LEVEL OF EVIDENCE

Level III retrospective study.

Effect of tibia-first, restricted functional alignment technique on gap width changes, and component positioning in robotic arm-assisted total knee arthroplasty

PURPOSE

This study aims to quantitatively assess the predictability of post-resection gap dimensions and the attainment of balanced gaps using robotic arm-assisted total knee arthroplasty (TKA).

METHODS

This retrospective cohort study included 100 consecutive patients who underwent robotic arm-assisted TKA for knee osteoarthritis using a restricted functional alignment (FA) technique. Tibial cuts were performed based on preoperative tibial anatomy within predefined boundaries, followed by femoral component adjustments according to tensioned soft tissues to optimise gap balance. The primary outcome was the proportion of balanced gaps, defined as differential laxities of ≤2 mm, across extension, flexion, lateral, and medial gap measurements. Ligament balancing in lateral and medial compartments was assessed using a robotic system at 10° and 90° flexion to evaluate if restricted FA facilitated a balanced knee. Secondary outcomes included implant alignment, resection depth, and patient-reported outcome measures (PROMs).

RESULTS

Significant increases in both lateral and medial gaps at 10° and 90° flexion were observed following tibial and femoral bone resections (p < 0.001). At extension, average gap changes were 0.9 mm (lateral) and 1.6 mm (medial) after tibial cuts, and 0.5 mm (lateral) and 1.2 mm (medial) after femoral cuts. At 90° flexion, changes were 0.3 mm (lateral) and 1.7 mm (medial) following tibial cuts, and 1.0 mm (lateral) and 1.4 mm (medial) after femoral cuts. Despite these variations, the tibia-first, gap-balancing technique achieved overall balance in 98% of gap measurements. The tibial component was placed at an average of 2.1° varus, while the femoral component was positioned at 0.3° varus and 1.3° external rotation relative to the surgical transepicondylar axis. Significant improvements in PROMs were noted between preoperative and one-year postoperative evaluations (all p < 0.05).

CONCLUSIONS

The tibia-first, restricted FA technique achieved a well-balanced knee in 98% of cases, despite inconsistent gap increments observed between initial assessments and post-resection.

LEVEL OF EVIDENCE

Therapeutic Level IV.

Preoperative Predictors Associated With Postoperative Chronic Knee Pain Following Total Knee Arthroplasty and the Effect on Patient Reported Outcomes at 6-Months

AIM

The aim was to identify independent variables associated with chronic knee pain (CKP) 6 months after knee arthroplasty (KA) and to determine whether CKP influenced improvement in patient reported outcomes measures (PROMs).

METHODS

A retrospective study was conducted over an 8-year period and included 3310 patients with completed PROMs at 6 months postoperatively; with a mean age of 69.9 (standard deviation 9.3) and 1823 (55.1%) were females. The Oxford knee score (OKS) pain component score was used to define patients with CKP (≤ 14 points) at 6 months.

RESULTS

There were 551 (16.6%) patients with CKP. Gender (p < 0.001), BMI (p = 0.025), preoperative EQ-5D (p = 0.010) and pain VAS (p < 0.001) as well as questions 2: washing (p = 0.006), 8: night pain (p = 0.001), 10: stability (p = 0.008) and 11: shopping (p = 0.047) of the OKS were independently associated CKP. The pre-operative OKS total score (p = 0.542) was not independently associated with CKP. The risk of CKP was shown to vary from 3.0% to 30.5% when discriminatory threshold values were used in the pre-operative responses to questions 2, 8, 10 and 11 of the OKS. Patients with CKP had significantly (p < 0.001) worse 6-month OKS, EQ-5D, EQ-VAS, and pain VAS scores and improvements in scores relative to preoperative baseline that were potentially not clinically meaningful (OKS mean difference 2.6, 95% CI 2.1-3.2). Those with CKP were significantly less likely to be satisfied with their KA (odds ratio 0.076, p < 0.001): only 231 (42.9%) patients with CKP were satisfied.

CONCLUSIONS

Approximately one-in-six (16.6%) patients had CKP at 6 months following KA, which was associated with significantly worse PROMs and lower satisfaction. Preoperative responses to four (2, 8, 10 and 11) of the pre-operative OKS questions were independently associated with CKP. These questions could be used to inform patients of their risk of CKP (3.0%-30.5%) following KA and potentially with expectation modification this may improve their PROMs.

LEVEL OF EVIDENCE

Retrospective study, Level III.

The John N. Insall Award: Functional Versus Mechanical Alignment in Total Knee Arthroplasty: A Randomized Controlled Trial

BACKGROUND

Mechanical alignment (MA) in total knee arthroplasty is regarded as a gold standard; however, some patients report dissatisfaction postsurgery. Functional alignment (FA) is a potential alternative, integrating kinematic alignment (KA) principles with preresection bone balancing within defined boundaries. The use of FA aims to improve outcomes by restoring native joint lines and optimizing soft-tissue balance. However, comparative evidence is limited.

METHODS

This prospective, randomized controlled trial compared MA (n = 121) and FA (n = 123) in robotic-assisted total knee arthroplasty. For MA, components were positioned perpendicular to the limb mechanical axis, with soft-tissue releases to achieve balance. For FA, initial virtual component positioning was used to match native knee anatomy, with adjustments for soft-tissue balance before bone cuts. The primary outcome was the forgotten joint score (FJS). Outcomes were compared with a mixed-model analysis of variance.

RESULTS

At the 2-year follow-up, the mean FJS was comparable (MA: 64.4 ± 30.1 versus FA: 70.1 ± 25.6, P = 0.10). The MA cases had more soft-tissue releases than FA (65 versus 16%, P < 0.001). Compared to MA patients, FA patients had higher Knee Injury and Osteoarthritis Outcome (KOOS) Symptoms (86.6 ± 12.9 versus 82.5 ± 14.0, P = 0.01) and KOOS-Quality of Life scores (76.1 ± 20.3 versus 70.7 ± 22.7, P = 0.03). More FA patients "would recommend" the procedure (94 versus 82%, P < 0.01). For patients who had preoperative Coronal Plane Alignment of the Knee Type I, FA had higher FJS (71.3 ± 24.8 versus 56.8 ± 31.6, P = 0.02) and KOOS-Quality of Life (76.4 ± 21.7 versus 64.2 ± 19.2, P = 0.02) than MA. No other differences were seen in patient-reported outcomes (Oxford Knee Score, KOOS, EuroQol-5 Dimensions, Pain Visual Analog Scale), clinical outcomes (length of stay, functional physio tests), reoperations, or implant survivorship (FA: 1 versus MA: 0 revisions).

CONCLUSIONS

While FA required fewer soft-tissue releases compared to mechanical alignment, at 2 years patient-reported and clinical outcomes were similar. The use of FA may provide improved outcomes for a specific subgroup of patients based on their preoperative alignment.

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.

A Workflow-Efficient Approach to Pre- and Post-Operative Assessment of Weight-Bearing Three-Dimensional Knee Kinematics

BACKGROUND

Knee kinematics during daily activities reflect disease severity preoperatively and are associated with clinical outcomes after total knee arthroplasty (TKA). It is widely believed that measured kinematics would be useful for preoperative planning and postoperative assessment. Despite decades-long interest in measuring three-dimensional (3D) knee kinematics, no methods are available for routine, practical clinical examinations. We report a clinically practical method utilizing machine-learning-enhanced software and upgraded C-arm fluoroscopy for the accurate and time-efficient measurement of pre-TKA and post-TKA 3D dynamic knee kinematics.

METHODS

Using a common C-arm with an upgraded detector and software, we performed an 8-s horizontal sweeping pulsed fluoroscopic scan of the weight-bearing knee joint. The patient's knee was then imaged using pulsed C-arm fluoroscopy while performing standing, kneeling, squatting, stair, chair, and gait motion activities. We used limited-arc cone-beam reconstruction methods to create 3D models of the femur and tibia/fibula bones with implants, which can then be used to perform model-image registration to quantify the 3D knee kinematics.

RESULTS

The proposed protocol can be accomplished by an individual radiology technician in ten minutes and does not require additional equipment beyond a step and stool. The image analysis can be performed by a computer onboard the upgraded c-arm or in the cloud, before loading the examination results into the Picture Archiving and Communication System and Electronic Medical Record systems.

CONCLUSIONS

Weight-bearing kinematics affects knee function pre- and post-TKA. It has long been exclusively the domain of researchers to make such measurements. We present an approach that leverages common, but digitally upgraded, imaging hardware and software to implement an efficient examination protocol for accurately assessing 3D knee kinematics. With these capabilities, it will be possible to include dynamic 3D knee kinematics as a component of the routine clinical workup for patients who have diseased or replaced knees.

Gap Balancing Technique With Functional Alignment in Total Knee Arthroplasty Using the Cuvis Joint Robotic System: Surgical Technique and Functional Outcome

Introduction The application of robotic technologies in total knee arthroplasty (TKA) has widely grown in the past few years. The preoperative CT (computed tomography) scan planning of the knee along with the quantitative soft tissue information recorded and assessed by the robot can be utilized in achieving functional alignment and aid in gap balancing. Gap tension is an important factor influencing the clinical outcome after TKA. This paper describes our technique for gap balancing and functional alignment using a fully autonomous Cuvis joint robotic system. Methods A total of 624 knees underwent primary TKA using Cuvis robotic assistance in the time period between November 2023 to April 2024. A total of 360 patients that included 100 males and 260 females were included in the study. All the surgeries were performed by the same surgeon and the same posterior-stabilized (PS)-design prosthesis was implanted. The medial and lateral gaps were balanced using our technique intraoperatively. The patients were followed up at one, three, and six months duration postoperatively, and their knee functional outcomes were analyzed using the Oxford Knee Score (OKS). Results A total of 360 patients with a mean age of 64.36 were part of this study. The study shows significant improvement in knee function post surgery. The average preoperative OKS recorded was 15.82, which improved at the postoperative sixth-month follow-up to a mean value of 42.07. There were no patients with poor results as per OKS scores, and no patients required any revision procedures. Conclusion The gap balancing technique with functional knee alignment using the Cuvis joint robotic system improved short-term outcomes, with balanced gaps, controlled alignment, and preserved soft tissue tension. No complications were reported, but further long-term, multicenter studies are needed for definitive conclusions.

Outcomes following functionally aligned total knee arthroplasty in severe varus deformity

Introduction

Total knee arthroplasty (TKA) in severe varus deformity still remains a challenge. Alternative alignment TKA aims to improve outcomes and satisfaction. The purpose of this study is to report on the outcomes of a functionally aligned TKA in severe varus deformity.

Methods

This is a retrospective review of single surgeon series. 92 patients with a varus deformity of >15⁰ on varus stress underwent a functionally aligned, TKA (Stryker Triathlon, Mahwah, New Jersey, USA) between 2016 and 2022. A control group, matched for age, gender and body mass index (BMI) from the same period was also identified with mild varus deformity (<10⁰). Intra-operative robotic data collected included gap measurements, bone resection depths, alignment, and rate of soft tissue releases. Clinical outcome data was collected as part of the prospective registry which included patient reported outcome measures (Forgotten Joint Score 12, Oxford Knee Score and Knee Injury and Osteoarthritis Outcome Score Joint Replacement), pain Visual analogue score (VAS), patient satisfaction and range of motion. We reported a minimum follow-up of 12 months.

Results

Medial soft tissue release was performed in 7.6 % of patients in the severe varus group. No soft tissue release was required in the control group. 96.7 % of TKAs achieved coronal balance in extension within 1 mm in the severe varus group. The varus stressed Hip knee ankle angle (HKA) was corrected by 8.5⁰ (95 % CI -9.4 to -7.6, p < 0.001). Patients in both group achieved excellent clinical outcomes scores and satisfaction (Severe varus: 91.9 % vs control: 92.7 %) at the final follow-up.

Conclusion

Patient with severe varus deformity (>15⁰) undergoing a functionally aligned TKA achieve a well-balanced TKA with excellent clinical outcomes and small rates of soft tissue release.

Functional alignment minimizes changes to joint line obliquity in robotic-assisted total knee arthroplasty: a CT analysis of functional versus kinematic alignment in 2,116 knees using the Coronal Plane Alignment of the Knee (CPAK) classification

Aims

Functional alignment (FA) in total knee arthroplasty (TKA) aims to achieve balanced gaps by adjusting implant positioning while minimizing changes to constitutional joint line obliquity (JLO). Although FA uses kinematic alignment (KA) as a starting point, the final implant positions can vary significantly between these two approaches. This study used the Coronal Plane Alignment of the Knee (CPAK) classification to compare differences between KA and final FA positions.

Methods

A retrospective analysis compared pre-resection and post-implantation alignments in 2,116 robotic-assisted FA TKAs. The lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured to determine the arithmetic hip-knee-ankle angle (aHKA = MPTA - LDFA), JLO (JLO = MPTA + LDFA), and CPAK type. The primary outcome was the proportion of knees that varied ≤ 2° for aHKA and ≤ 3° for JLO from their KA to FA positions, and direction and magnitude of those changes per CPAK phenotype. Secondary outcomes included proportion of knees that maintained their CPAK phenotype, and differences between sexes.

Results

Overall, 71.6% had an aHKA change ≤ 2°, and 87.0% a JLO change ≤ 3°. Mean aHKA changed from -1.1° (SD 2.8°) in KA to -1.9° (SD 2.3°) in FA (mean difference (MD) -0.83 (SD 2.0); p < 0.001). Mean JLO changed from 173.9° (SD 3.0°) in KA to 174.2° (SD 2.6°) in FA (MD 0.38 (SD 2.3); p < 0.001). CPAK type was maintained in 58.1% of knees, with the proportion highest for Types I (73.9%), II (61.1%), and IV (51.2%). In valgus knees, 67.5% of Type III and 71.7% of Type VI were shifted to neutral phenotypes. There was minimal change to constitutional JLO across all CPAK types (MDs -2.0° to 1.2°).

Conclusion

Functional alignment may alter CPAK type, but does not significantly change JLO. A kinematic starting point minimizes changes to native anatomy, while final position with FA provides an optimally balanced TKA.

Alignment Strategies in Total Knee Arthroplasty: The Rise and Role of Enabling Technology

Total knee arthroplasty (TKA) remains the gold standard surgical care for end-stage knee arthritis. Since its inception, TKA has seen many transformative factors with advances in material properties, implant design, and fixation. Improvements in implant longevity has culminated in TKA being recognized as one of modern medicine's most successful surgical procedures. Patient satisfaction, however, remains a significant challenge. Recent studies report that patient satisfaction with current implants and techniques remains at 80 to 90%, suggesting that up to one in five patients remain dissatisfied with their procedure. A balanced knee, defined as equal medial and lateral gaps in knee extension and flexion, is a desired outcome in TKA. This has been shown to be associated with improved clinical outcomes. Given the poor rate of surgeon-defined balance, intraoperative knee balance can be confirmed with objective load data using sensor-embedded smart inserts or by measuring gaps using computer-assisted or robotic platforms. Currently, there is no consensus on the correct alignment or laxity targets for individualized alignment strategies in TKA, and further research in this area is required to answer this. Tremendous advances in our understanding of knee anatomy and kinematics have come to light in the recent past, and these insights have spawned interest in alternative alignment techniques in TKA. More recently, an appreciation of individual knee phenotypes and associated classification systems have provided a platform and the scientific justification behind these contemporary alignment strategies. Paired with enabling technologies, it is becoming an accepted paradigm that surgeons have the ability to select a desired alignment target when undertaking an individualized alignment strategy in TKA and execute the surgery with a high degree of precision. It is hoped that this may reduce the rate of dissatisfaction following TKA and improve clinical outcomes. This review article provides an overview of the concepts of knee phenotypes, current alignment strategies in TKA, and the emerging benefits of enabling technologies.

Restoring the Preoperative Phenotype According to the Coronal Plane Alignment of the Knee Classification After Total Knee Arthroplasty Leads to Better Functional Results

BACKGROUND

Mechanical alignment after total knee arthroplasty (TKA) is still widely used in the surgical community, but the alignment finally obtained by conventional techniques remains uncertain. The recent Coronal Plane Alignment of the Knee (CPAK) classification distinguishes 9 knee phenotypes according to constitutional alignment and joint line obliquity (JLO). The aim of this study was to assess the phenotypes of osteoarthritic patients before and after TKA using mechanical alignment and to analyze the influence of CPAK restoration on functional outcomes.

METHODS

This retrospective multicenter study included 178 TKAs with a minimum follow-up of 2 years. Patients were operated on using a conventional technique with the goal of neutral mechanical alignment. The CPAK grade (1 to 9), considering the arithmetic Hip-Knee-Ankle angle (aHKA) and the JLO, was determined before and after TKA. Functional results were assessed using the following patient-reported outcome measures: Knee Injury and Osteoarthritis Outcome Score, the Simple Knee Value, and the Forgotten Joint Score.

RESULTS

A true neutral mechanical alignment was obtained in only 37.1%. Isolated restoration of JLO was found in 31.4%, and isolated restoration of the aHKA in 44.9%. Exact restoration of the CPAK phenotype was found in 14.6%. Restoration of the CPAK grade was associated with an improvement in the "daily living": 79.2 ± 5.3 versus 62.5 ± 2.3 (R2 = 0.05, P < .05) and "Quality of life" Knee Injury and Osteoarthritis Outcome Score subscales: 73.8 ± 5.0 versus 62.9 ± 2.2 (R2 = 0.02, P < .05).

CONCLUSIONS

This study shows that few neutral mechanical alignments are finally obtained after TKA by conventional technique. A major number of patients present a postoperative modification of their constitutional phenotype. Functional results at 2 years of follow-up appear to be improved by the restoration of the CPAK phenotype, JLO, and aHKA.

LEVEL OF CLINICAL ART EVIDENCE

III, Retrospective Cohort Study.

Joint-line obliquity angle is significantly affected by hip abduction and adduction: A simulated analysis

PURPOSE

Different methods for quantifying joint-line obliquity (JLO) have been described, including joint-line obliquity angle (JLOA), Mikulicz joint-line angle (MJLA) and medial proximal tibial angle (MPTA). The goal of the present study was to quantify the variation of JLOA based on the position of the hip. The hypothesis of our study is that JLO is significantly influenced by the abduction/adduction of the limb, unlike MJLA.

METHODS

One hundred long-leg-weightbearing X-rays were used. At time 0 and after 30 days, two observers performed different measurements, including (1) distance between pubic symphysis and center of the femoral head, (2) distance between center of the femoral head and center of the ankle joint, (3) distance between center of the ankle and medial malleolus, (4) hip-knee-ankle angle, (5) MPTA, (6) lateral distal femoral angle, (7) joint-line congruency angle, (8) JLOA, (9) MJL and (10) angle between Mikulicz line and line perpendicular to the ground. The changes of the JLOA based on the position of the hip (abducted, neutral, bipedal stance adduction and monopodal stance adduction) were calculated with trigonometric formulas and with simulation on an orthopaedic planning digital software.

RESULTS

The JLOA change between adducted and abducted positions was on average 12.8° (SD 0.9 mm). The MJL did not vary significantly based on hip position.

CONCLUSIONS

The adduction/abduction of the lower limb has a considerable impact on JLOA. Methods like MJLA which are not affected by hip position should be preferred for JLO evaluation.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Considerations of morphometry and phenotypes in modern knee arthroplasty

As advancements in total knee arthroplasty progress at an exciting pace, two areas are of special interest, as they directly impact implant design and surgical decision making. Knee morphometry considers the three-dimensional shape of the articulating surfaces within the knee joint, and knee phenotyping provides the ability to categorize alignment into practical groupings that can be used in both clinical and research settings. This annotation discusses the details of these concepts, and the ways in which they are helping us better understand the individual subtleties of each patient's knee.

The current role of CT in total knee arthroplasty

Advanced 3D imaging and CT-based navigation have emerged as valuable tools to use in total knee arthroplasty (TKA), for both preoperative planning and the intraoperative execution of different philosophies of alignment. Preoperative planning using CT-based 3D imaging enables more accurate prediction of the size of components, enhancing surgical workflow and optimizing the precision of the positioning of components. Surgeons can assess alignment, osteophytes, and arthritic changes better. These scans provide improved insights into the patellofemoral joint and facilitate tibial sizing and the evaluation of implant-bone contact area in cementless TKA. Preoperative CT imaging is also required for the development of patient-specific instrumentation cutting guides, aiming to reduce intraoperative blood loss and improve the surgical technique in complex cases. Intraoperative CT-based navigation and haptic guidance facilitates precise execution of the preoperative plan, aiming for optimal positioning of the components and accurate alignment, as determined by the surgeon's philosophy. It also helps reduce iatrogenic injury to the periarticular soft-tissue structures with subsequent reduction in the local and systemic inflammatory response, enhancing early outcomes. Despite the increased costs and radiation exposure associated with CT-based navigation, these many benefits have facilitated the adoption of imaged based robotic surgery into routine practice. Further research on ultra-low-dose CT scans and exploration of the possible translation of the use of 3D imaging into improved clinical outcomes are required to justify its broader implementation.

A new gap balancing technique with functional alignment in total knee arthroplasty using the MAKO robotic arm system: a preliminary study

BACKGROUND

Gap tension is an important factor influencing the clinical outcomes of total knee arthroplasty (TKA). Traditional mechanical alignment (MA) places importance on neutral alignment and often requires additional soft tissue releases, which may be related to patient dissatisfaction. Conversely, the functional alignment requires less soft tissue release to achieve gap balance. Conventional gap tension instruments present several shortcomings in practice. The aim of this study is to introduce a new gap balancing technique with FA using the modified spacer-based gap tool and the MAKO robotic arm system.

METHODS

A total of 22 consecutive patients underwent primary TKA using the MAKO robotic arm system. The gap tension was assessed and adjusted with the modified spacer-based gap tool during the operation. Patient satisfaction was evaluated post-operatively with a 5-point Likert scale. Clinical outcomes including lower limb alignment, Knee Society Score (KSS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC) were recorded before surgery, 3 months and 1 year after surgery.

RESULTS

The range of motion (ROM) was significantly increased (p < 0.001) and no patients presented flexion contracture after the surgery. KSS and WOMAC score were significantly improved at 3 months and 1 year follow-up (p < 0.001 for all). During the surgery, the adjusted tibial cut showed more varus than planned and the adjusted femoral cut presented more external rotation than planned (p < 0.05 for both). The final hip-knee-ankle angle (HKA) was also more varus than planned (p < 0.05).

CONCLUSIONS

This kind of spacer-based gap balancing technique accompanied with the MAKO robotic arm system could promise controlled lower limb alignment and improved functional outcomes after TKA.

Total Knee Arthroplasty Kinematics Predict Patient-Reported Outcome Measures: Implications for Clinical Kinematic Examinations

BACKGROUND

A core tenet of total knee arthroplasty (TKA) is that achieving more natural kinematics will lead to superior patient outcomes. Yet this relationship has not been proven for large representative cohorts of TKA patients because accurately measuring 3-dimensional TKA kinematics is time-consuming and expensive. But advanced imaging systems and machine learning-enhanced analysis software will soon make it practical to measure knee kinematics preoperatively and postoperatively in the clinic using radiographic methods. The purpose of this study was to assess the reported relationships between TKA kinematics and outcomes and distill those findings into a proposal for a clinically practical protocol for a clinical kinematic exam.

METHODS

This study reviewed the recent literature relating TKA kinematics to patient outcomes. There were 10 studies that reported statistical associations between TKA kinematics and patient outcome scores utilizing a range of functional activities. We stratified these activities by the complexity of the radiographic examination to create a proposed examination protocol, and we generated a list of requirements and characteristics for a practical TKA clinical kinematic examination.

RESULTS

Given considerations for a clinically practical kinematic exam, including equipment, time and other resources, we propose 3 exam levels. With basic radiographs, we suggest studying single-leg stance in extension, lunge or squat, and kneeling. For fluoroscopic systems with X-ray pulses up to 20 ms, we propose chair-rise or stair ascent to provide additional dynamic information. For fluoroscopic systems with X-ray pulses of less than 10 ms, we propose rapid open-chain knee flexion-extension to simulate the highly dynamic swing phase of gait.

CONCLUSIONS

It is our hope that this proposed examination protocol spurs discussion and debate so that there can be a consensus approach to clinical examination of knee and TKA kinematics when the rapidly advancing hardware and software capabilities are in place to do so.

Large angular correction of arithmetic coronal alignment is associated with residual lateral laxity after total knee arthroplasty in varus knees for Japanese patients

Purpose

One of the most common types of coronal plane alignment of the knee (CPAK) is type I, which is characterised by varus alignment and apex distal joint line obliquity. The purpose of this study was to evaluate the association of changes in arithmetic hip-knee-ankle angle (aHKA) with both postoperative joint laxity and patient-reported outcome measures (PROMs) in patients with CPAK type I following mechanical alignment (MA) total knee arthroplasty (TKA).

Methods

Of 111 consecutive knees in 92 patients with osteoarthritis who underwent primary TKA, 80 knees (72.0%) with CPAK type I phenotype preoperatively were evaluated. All TKAs were performed to achieve neutral MA by a medial stabilising gap balancing technique. Pre- to postoperative change in aHKA was defined as ΔaHKA. The 80 CPAK type I knees were divided into a larger ΔaHKA group (>7°) and a smaller ΔaHKA group (≤7°). PROMs, including the Knee Society Score and Forgotten Joint Score-12, were assessed before and 2 years after surgery. Pre- and postoperative joint laxity was assessed using a Telos arthrometer.

Results

Twenty-two knees showed a larger ΔaHKA, and postoperative lateral joint laxity in varus stress was significantly greater in these patients than in those with a smaller ΔaHKA (6.8° vs. 4.5°, p = 0.006). There were no significant differences between the groups in PROMs (p = n.s.).

Conclusions

Postoperative lateral laxity was associated with larger aHKA changes than smaller aHKA changes in CPAK type I knees after TKA. However, no statistically significant differences in PROMs were found according to the amount of change in aHKA.

Level of Evidence

Level III.

A comprehensive analysis of the pre- and postoperative responses to each of the 12 Oxford knee score questions one year following knee arthroplasty

AIMS

To assess the pre- and postoperative responses to each of the 12 individual Oxford Knee Score (OKS) questions and percentages of those that were better, same or worse after primary knee arthroplasty (KA).

METHODS

A single centre retrospective cohort study conducted over a 24-month period which included 3259 patients with completed OKS preoperatively and 1-year after KA. There were 1286 males and 1973 females, with an overall mean age of 70.0 (range 34-94). The mean scores for each question of the OKS were compared between baseline and 1-year. The percentage of patients who reported better, the same or worse postoperative symptoms for each question were calculated and represented on a heatmap.

RESULTS

There were significant (p < 0.001) improvements in all 12 questions, all of which demonstrated moderate (Q2, Q7) or large effect sizes. Improvements in individual question responses varied. Symptoms of pain and limping demonstrated the greatest improvement, with 86% of patients enjoying a positive change in their symptoms. Despite this improvement 1067 (41.4%) continued to have mild to severe pain in their knee, and 442 (17.3%) patients limped often to all the time when walking postoperatively. Whereas other questions that did not improve to the same extent for example washing and drying only improved in 53% of patients but only 347 (13.5%) had moderate/extreme trouble or found it impossible to do this postoperatively. Preoperatively four questions (Q1, Q6, Q7, Q8) demonstrated floor effects, postoperatively all questions apart from question 7 (kneeling) demonstrated ceiling effects.

CONCLUSION

The mean improvement and outcome at 1-year for each of the 12 questions varied according to the patient's preoperative response. As a clinical tool, the heatmap (improvement, same and worse) will enable communication to patients about their potential change in their knee specific symptoms according to their preoperative responses.

LEVEL OF EVIDENCE

Retrospective study, Level III.

Not all knees are the same

The aim of mechanical alignment in total knee arthroplasty is to align all knees into a fixed neutral position, even though not all knees are the same. As a result, mechanical alignment often alters a patient's constitutional alignment and joint line obliquity, resulting in soft-tissue imbalance. This annotation provides an overview of how the Coronal Plane Alignment of the Knee (CPAK) classification can be used to predict imbalance with mechanical alignment, and then offers practical guidance for bone balancing, minimizing the need for soft-tissue releases.

Radiologic Assessment of Knee Phenotypes Based on the Coronal Plane Alignment of the Knee Classification in a Korean Population

Background

The Coronal Plane Alignment of the Knee (CPAK) classification system has been developed as a comprehensive system that describes 9 coronal plane phenotypes based on constitutional limb alignment and joint line obliquity (JLO). Due to the characteristics of Asian populations, which show more varus and wider distribution in lower limb alignment than other populations, modification of the boundaries of the arithmetic hip-knee-ankle angle (aHKA) and JLO should be considered. The purpose of this study was to determine the knee phenotype in a Korean population based on the original CPAK and modified CPAK classification systems.

Methods

We reviewed prospectively collected data of 500 healthy and 500 osteoarthritic knees between 2021 and 2023 using radiographic analysis and divided them based on the modified CPAK classification system by widening the neutral boundaries of the aHKA to 0° ± 3° and using the actual JLO as a new variable. Using long-leg standing weight-bearing radiographs, 6 radiographic parameters were measured to evaluate the CPAK type: the mechanical HKA angle, medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), aHKA, JLO, and actual JLO.

Results

From 2 cohorts of 1,000 knees, the frequency distribution representing all CPAK types was different between the healthy and arthritic groups. The most common categories were type II (38.2%) in the healthy group and type I (53.8%) in the arthritic group based on the original CPAK classification. The left and upward shift in the distribution of knee phenotypes in the original classification was corrected evenly after re-establishing the boundaries of a neutral aHKA and the actual JLO. According to the modified CPAK classification system, the most common categories were type II (35.2%) in the healthy group and type I (38.0%) in the arthritic group.

Conclusions

Although the modified CPAK classification corrected the uneven distribution seen when applying the original classification system in a Korean population, the most common category was type I in Korean patients with osteoarthritic knees in both classification systems. Furthermore, there were different frequencies of knee phenotypes among healthy and arthritic knees.

Calipered kinematic alignment restored the arithmetic hip-knee-ankle angle, achieved high satisfaction and improved clinical outcomes

PURPOSE

The purpose of this study was to determine whether unrestricted calipered kinematic alignment (KA), coupled with a medial-stabilised (MS) implant system, can reproduce the patient's constitutional alignment as per the arithmetic hip-knee-ankle (aHKA) and improve clinical outcomes.

METHODS

One-hundred and ninety-three patients received total knee arthroplasty by the senior author. To determine whether the constitutional alignment was achieved, the postoperative hip-knee-ankle (HKA) alignment was compared against the aHKA. Range of motion (ROM) was determined preoperative and postoperatively at 6 months and 2 years by measuring the active flexion and extension. Patient-Reported Outcomes Measures (PROMs) including Oxford Knee Score (OKS), Knee Injury and Osteoarthritis Outcome Score (KOOS), Forgotten Joint Score (FJS) and Visual Analogue Scale for Satisfaction were also completed. The Sports and Recreation component of KOOS was used to assess the patient's ability to return to sports and daily activities.

RESULTS

There was a strong correlation between postoperative HKA and aHKA (r = 0.7, p < 0.05). There was a significant improvement in both extension and flexion seen from as early as 6 months postoperatively, with a mean flexion of 123° ± 11° and extension of 1° ± 3° at 2 years. PROMs had significant improvements with a mean score of 42.8 ± 6.0 for the OKS and all KOOS subscales consisting of Symptoms (88.0 ± 11.7), Pain (91.4 ± 11.6), Activities of Daily Living (91.1 ± 12.4), Sports (76.8 ± 22.1) and Quality of Life (83.0 ± 19.1). The FJS had significant improvements from 6 months to 2 years of 19.9 (p < 0.05), with a mean score of 69.2 ± 26.6 at 2 years. Ninety-three percent (180 patients) were classified as 'satisfied' at the 2-year timepoint. The KOOS Sports component was completed by 64% (124 patients), whereby the mean age was younger than the noncompliant patients (67.7 ± 9.4 vs. 71.7 ± 8.2 years).

CONCLUSION

Unrestricted calipered KA can result in an alignment that closely resembles the patient's constitutional alignment, as per the aHKA. This resulted in improved knee ROM and patient satisfaction, as well as assisting younger patients to return to sports and daily activities.

LEVEL OF EVIDENCE

Level IV.

Functionally aligned total knee arthroplasty: A lateral flexion laxity up to 6 mm is safe!

PURPOSE

Loose flexion gaps are associated with poor functional outcomes and instability in total knee arthroplasty (TKA). The effect of a trapezoidal flexion gap in a functionally aligned TKA remains unknown. The aim of this study was to investigate the effect of a larger lateral flexion gap in a robotic-assisted (RA), functionally aligned (FA) and cruciate-retaining (CR) TKA on clinical outcomes.

METHODS

Data from 527 TKA in 478 patients from 2018 to 2020 were collected. All patients underwent an RA (MAKO, Stryker), FA and CR TKA. Gap measurements were collected intraoperatively. Patient-reported outcome measures (PROMs), pain Visual analogue score (VAS) and range of motion were collected postoperatively. Patients were also asked about the ease of stair ascent and descent and kneeling on a 5-point scale. The minimum follow-up was 2 years. Patients were stratified into three groups based on lateral flexion laxity.

RESULTS

At 2 years postoperatively, the group with a looser gap (3-6 mm) had higher mean PROMs when compared with the group with a gap of 2-3 mm. There were no differences detected in any other outcomes at 2 years. A total of 70.9% of patients in the group with a 3-6 mm gap reported being able to walk down a flight of stairs 'easily', compared with 56.7% in the 2-3 mm group and 54% in the <2 mm group (p = 0.04).

CONCLUSION

The study shows that a loose lateral flexion gap in functionally aligned CR TKA does not adversely affect outcomes in the short term.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Patient sex and race are associated with differences in coronal plane alignment classification in native arthritic knees

Purpose: The purpose of this study was to evaluate associations between demographics and Coronal Plane Alignment of the Knee (CPAK) classification in pre-surgical TKA patients. Methods: This is a retrospective study of 1167 patients with knee osteoarthritis who underwent TKA. CPAK categories I-IX were determined by arithmetic mechanical hip-knee-ankle angle and joint line obliquity measurements from pre-operative bone length radiographs. Patient age, sex, body mass index (BMI) and race were collected. Chi-square test of independence and adjusted Pearson's residuals evaluated associations between CPAK classification and demographics. Results: There was a significant association between CPAK phenotypes I-IX and patient sex (X2 = 5.8, p < 0.01). A positive association was found between both men and CPAK phenotype I, and women and CPAK phenotype VII. A positive association was found between African American patients and CPAK phenotype III and a negative association was found between African American patients and CPAK phenotype I (X2 =14.8, p-value = 0.01). There was no association between age and BMI with CPAK phenotypes (n.s.). Conclusion: These results indicate that there are unidentified sex and race differences that exist in the CPAK classification of native arthritic knees. Patient characteristics play a significant role in determining patient knee phenotypes. Further research should investigate whether these characteristics warrant inclusion in pre-operative preparations, aiming to enhance the personalization of arthroplasty procedures.

Restoration of constitutional alignment optimizes outcomes of computer navigated total knee arthroplasty: a prospective randomized controlled trial

PURPOSE

The value of computer navigation in total knee arthroplasty (TKA) for arthritic knees continues to be debated. The purpose of this study was to evaluate the value of navigated TKA associated with updated alignment philosophy.

METHODS

This prospective randomized controlled trial enrolled 38 consecutive patients (76 knees) and were randomly assigned to both groups. The demographic data and perioperative data were recorded. The coronal plane alignment of the knee (CPAK) classification was used to classify knee alignment phenotypes. Radiographic outcomes were measured and subgroup analysis was further performed. Clinical outcomes were evaluated using patient-reported outcome measures (PROMs). Surgery-related complications were recorded.

RESULTS

The distribution of CPAK phenotypes following constitutional aligned TKA was equivalent to the native cohort, whereas the mechanical aligned TKA dramatically altered the phenotype distribution from type I and type II to type V and type IV. Final implant positioning was different between groups, with constitutional aligned TKA having larger cTCA (P = .004), joint line obliquity (P = .006), joint line distance (P = .033) and smaller sFCA (P = .013). Subgroup analysis showed higher actual accuracy of component positioning was achieved in navigated TKA, especially in knees with deformity of > 10° (P < .05). Patients reported higher HSS score at three months postoperatively in constitutional aligned group (P = .002). One patient in navigated group suffered femoral pin site fracture caused by a minor trauma.

CONCLUSION

Computer navigated TKA allows for restoration of constitutional alignment and minimizes soft tissue release, which when compared to mechanical alignment may be associated with superior early outcomes.

Tibia-first, gap-balanced patient-specific alignment technique achieves well-balanced gaps in 90% of cases by rebuilding bony anatomy within boundaries

PURPOSE

Patient-specific alignment (PSA) technique tries to achieve balanced gaps and simultaneously rebuild the individual bony phenotype. The hypothesis was: PSA technique achieves balanced knees in a high percentage with more anatomical resections than adjusted mechanical alignment (AMA).

METHODS

Three hundred sixty-seven patients underwent navigated total knee arthroplasty (TKA) with a tibia-first gap-balanced PSA technique. Resection boundaries for medial proximal tibia angle (MPTA) of 86-92°, mechanical lateral distal femoral angle (mLDFA) of 86-92°, and hip-knee-ankle angle (HKA) of 175-185° were defined. Preoperative and intraoperative parameters of HKA, MPTA, mLDFA, and gap widths were recorded. Depending on the coronal deformity, the patients were divided into three groups: varus HKA < 178°; straight 178-182° and valgus HKA > 182°. The stability was analysed by assessing the difference between medial and lateral extension and flexion gaps as well as between flexion and extension gaps. All PSA measurements were compared with data from a previously published AMA series.

RESULTS

PSA achieved balanced gaps in extension, flexion and between flexion/extension in over 90% of cases, being similar to AMA. In PSA, MPTA and mLDFA were restored within 1°, except in extreme varus (MPTA difference 2°) and valgus knees (mLDFA difference 3°). This was caused by the defined boundaries of the alignment technique. This individualised reconstruction led to significantly more anatomical resections of all tibia and femur resections.

CONCLUSION

A tibia-first, gap-balanced PSA technique achieves balanced joints in more than 90% of cases. By maintaining preoperative MPTA and mLDFA to a high extent, far more anatomical resections, compared to AMA were performed. Future studies need to be conducted to investigate whether those promising intraoperative results correlate with postoperative patient outcomes and whether patients outside the 5° corridor have higher failure rates.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Correction of Coronal Deformity and Intercompartmental Imbalance through Bone Resection

This review discusses the correction of coronal deformity and intercompartmental imbalance through bone resection in total knee arthroplasty (TKA). To achieve functional knee balance, coronal, rotational, and sagittal alignment are critical to successful patient outcomes. Though variations in coronal alignment are debated as a correlate to positive results, advancements in utilizing implant position, alignment, and soft tissue balance to improve patient outcomes and function are an evolving discussion. This study draws upon existing literature, clinical studies, and surgical techniques related to TKA, including advancements in navigation and robotics. The study highlights the importance of individualized alignment strategies for varus and valgus knees. While mechanical neutral alignment has shown excellent long-term data, reevaluating the anatomic recreation of the patient's joint line obliquity is now being studied extensively. Sensor data and navigation systems contribute to improved outcomes and patient satisfaction. The evolution of navigation and robotics has led surgeons to achieve their target angles consistently and accurately; now, the discussion is around the most effective alignment targets. The classification of various phenotypes assists in the proposed starting points for implant position, but soft tissue tension is required in the input data to achieve global balance and stable motion. Each approach's advantages and limitations are considered. In conclusion, achieving optimal coronal alignment, joint line obliquity, and soft tissue balance is crucial for successful TKA outcomes. Personalized alignment philosophies, supported by three-dimensional data and sensor technology, are evolving to minimize critical errors and enhance functional results. Robotic assistance and future advancements in artificial intelligence and machine learning hold promise for further improving TKA outcomes in the quest for soft tissue stabilization.

Functional positioning principles for image-based robotic-assisted TKA achieved a higher Forgotten Joint Score at 1 year compared to conventional TKA with restricted kinematic alignment

PURPOSE

Few comparative studies assessed the current concept of individualised alignment for total knee arthroplasty (TKA) and their outcomes at mid-term. This study aimed to evaluate the functional outcomes at 1 year of primary TKA performed with a functional positioning technique based on an image-based robotic-assisted system, compared to conventional TKA performed with a restricted kinematic alignment technique.

METHODS

This retrospective comparative study included 100 primary TKAs performed with functional positioning principles using an image-based robotic-assisted system. A control group included 100 primary TKAs with the same posterior-stabilised implant as the robotic group but performed with manual instrumentation and restricted kinematic alignment technique. In the robotic group, the mean age was 69.2 years old ± 7.9; the mean body mass index was 29.7 kg/m2 ± 4.6. The demographic characteristics were similar between both groups. Kujala score, Forgotten Joint Score (FJS), Knee Society Score (KSS) knee and KSS function were collected 12 months postoperatively. Normally distributed continuous variables were compared using the Student t test. For non-normally distributed continuous variables, the Mann-Whitney test was used.

RESULTS

FJS was significantly higher in the robotic group (76.3 ± 13 vs. 68.6 ± 16.9 in the conventional group; p = 0.026). At a 1-year follow-up, there was no significant difference in the KSS knee and KSS function scores and the Kujala score between both groups. The mean KSS knee score was 90.8 ± 11.4 in the robotic group versus 89.4 ± 9.6 in the conventional group (p = 0.082). The mean KSS function score was 91.4 ± 12.3 versus 91.3 ± 12.6, respectively (p = 0.778).

CONCLUSION

Functional positioning principles using an image-based robotic-assisted system achieved a higher Forgotten Joint Score 1 year after TKA compared to restricted kinematic alignment. Personalised alignment and implant positioning are interesting paths to improve the functional outcomes after TKA.

LEVEL OF EVIDENCE

III.