Adequate joint line restoration and good preliminary clinical outcomes after total knee arthroplasty using the Flexion First Balancer technique

Enhancing soft tissue balance: Evaluating robotic-assisted functional positioning in varus knees across flexion and extension with quantitative sensor-guided technology

PURPOSE

Functional implant positioning (FIP) for total knee arthroplasty (TKA) is an evolution of kinematic alignment based on preoperative CT scan and robotic-assisted technology. This study aimed to assess the ligament balancing of image-based robotic-assisted TKA in extension, mid-flexion and flexion with an FIP using intraoperative sensor-guided technology. The hypothesis was that image-based robotic-assisted TKA performed by FIP would achieve ligament balancing all along the arc of knee flexion.

METHODS

This prospective monocentric study included 47 consecutive patients with varus knees undergoing image-based robotic-assisted TKA performed with FIP. After robotic-assisted bone cuts, trial components were inserted, and soft tissue balance was assessed using sensor-guided technology at 10°, 45° and 90° of knee flexion. A mediolateral balanced knee was defined by an intercompartmental pressure difference (ICPD) ≤ 15 lbf and medial and lateral compartment pressure ≤60 lbf. The mean age was 71.6 years old ±6.7, the mean BMI was 29.0 kg/m2 ± 4.9 and the mean preoperative HKA was 174° ± 5 [159; 183].

RESULTS

The mean postoperative knee alignment was 177.0° ± 2.2° [172; 181]. There were 93.6% of balanced knees (n = 44) at 10 and 90° of knee flexion versus 76.6% (n = 36) at 45° of knee flexion with a significant difference (p = 0.014). Median ICPD at 10, 45 and 90° of knee flexion were, respectively, 7.0 (interquartile range [IQR]: 9), 11.0 (IQR: 9.5) and 8.0 (IQR: 9.0). Pairwise analyses revealed differences for ICPD at 45° versus ICPD at 10° (p = 0.003) and ICPD at 90° versus ICPD at 45° (p = 0.007).

CONCLUSION

FIP with an image-based robotic-assisted system allowed the restoration of a well-balanced knee at 10° and 90° of flexion in varus knees. Nevertheless, some discrepancies occurred in midflexion, and more work is needed to understand ligament behaviour all along the arc of knee flexion.

LEVEL OF EVIDENCE

Level II.

Balancing the flexion gap first in total knee arthroplasty leads to better preservation of posterior condylar offset resulting in better knee flexion

PURPOSE

The purpose of this study is to determine whether the flexion first balancing technique, developed in an attempt to solve the dissatisfaction due to instability in total knee arthroplasties, leads to better restoration of joint line height and medial posterior condylar offset. This might result in better knee flexion, compared to the classic extension first gap balancing technique. The secondary objective is to show non-inferiority of the flexion first balancing technique in terms of clinical outcomes as measured by the Patient Reported Outcome Measurements.

METHODS

A cohort of 40 patients (46 knee replacements) operated using the flexion first balancing technique was retrospectively analyzed and compared with a cohort of 51 patients (52 knee replacements) operated using the classic gap balancing technique. Radiographic analysis of the coronal alignment, joint line height and posterior condylar offset was performed. Clinical and functional outcome data were analyzed pre- and postoperatively and compared between both groups. The two sample t test, Mann-Whitney U test, Chi-square test and a linear mixed model were used for performing statistical analyses, after normality analyses were executed.

RESULTS

Radiologic evaluation showed a decrease in posterior condylar offset using the classic gap balancing technique (p = 0.040) versus no change using the flexion first balancing technique (p = n.s.). No statistically significant differences were noted for joint line height and coronal alignment. Using the flexion first balancer technique leads to a greater postoperative range of motion with deeper flexion (p = 0.002) and a better Knee injury and Osteoarthritis Outcome Score (KOOS) (p = 0.025).

CONCLUSION

The Flexion First Balancing technique is a valid and safe technique for TKA, resulting in better preservation of PCO with consequently greater postoperative flexion and better KOOS scores.

LEVEL OF EVIDENCE

III.

Use of a Spacer Block Tool for Assessment of Joint Line Position during Revision Total Knee Arthroplasty

There is a tendency of orthopaedic surgeons to elevate joint line (JL) in revision total knee arthroplasty (RTKA). Here, we ascertain the use of the spacer block tool (SBT) to determine JL more accurately for less experienced RTKA surgeons. To perform more precise restoration of JL, an SBT with markers was developed and produced using computer software and three-dimensional printers. The study was planned prospectively to include patients who received either condylar constrained or rotating hinge RTKA between January 2016 and December 2019. To determine JL, distance from fibular head (FH), adductor tubercle (AT), and medial epicondyle (ME) were measured on contralateral knee preoperative radiographs and on operated knee postoperative radiographs. Patients were randomized and grouped according to the technique of JL reconstruction. In Group 1, conventional methods by evaluating aforementioned landmarks and preoperative contralateral knee measurements were used to determine JL, whereas in Group 2, the SBT was used. The main outcome measure was the JL change in revised knee postoperatively in contrast to contralateral knee to compare effective restoration of JL between the groups. Twenty-five patients in Group 1 (3 males, 22 females, 72 years, body mass index [BMI] 32.04 ± 4.45) and 20 patients (7 males, 13 females, 74 years, BMI 30.12 ± 5.02) in Group 2 were included in the study. JL measurements for the whole group were FH-JL = 18.3 ± 3.8 mm, AT-JL = 45.8 ± 4.6 mm, and ME-JL = 27.1 ± 2.8 mm preoperatively, and FH-JL = 20.7 ± 4.2 mm, AT-JL = 43.4 ± 5.2 mm, and ME-JL = 24.7 ± 3.1 mm postoperatively. JL level differences in reference to FH, AT, and ME in Group 1 were 3.6 ± 3.1, 3.6 ± 3.5, and 3.4 ± 3.1 mm, respectively, and in Group 2 were 1.0 ± .0.9, 1.3 ± 1.3, and 1.1 ± 1.3 mm, respectively. There were statistically significant differences between the two groups in JL changes referenced to all of the specific landmarks (p < 0.05). The use of the SBT helped restore JL effectively in our cohort of RTKA patients. Therefore, this tool may become a useful and inexpensive gadget for less experienced and low-volume RTKA surgeons.

Reliability of the posterior condylar offset

The posterior condylar offset (PCO) has been proposed as a determinant of a postoperative range of motion after total knee arthroplasty, although there is no consensus. This study aimed to demonstrate the error introduced by forcing the femoral rotation to overlap both condyles for the "true" lateral X-ray projection for the PCO measurement. We hypothesize that the angular discrepancy between the posterior femoral cortical reference plane and the posterior condylar axis plane due to rotation invalidates the acquisition of reliable measurements on X-rays. We have measured the PCO in 50 "true" lateral X-rays and compared it with the medial and lateral condyles PCO's assessed on a computed tomography-scan-based three-dimensional (3D) model of each knee. PCO based on the 3D imaging differed significantly between the medial (25.8 ± 3.67 mm) and lateral (16.59 ± 2.92 mm) condyle. Three-dimensional PCO values differ significantly from those determined in the radiographic studies. Also, the mean values of the medial and lateral condyle PCO measurements differed significantly (p < 0.001) with all PCO measurements on radiographs. We have identified a difference between the posterior cortical plane and the posterior condylar axis projections, both on the axial plane with a mean value of 11.23° ± 3.64°. Our data show an interplane discrepancy angle between the posterior femoral diaphyseal cortical and the posterior condylar axis plane (due to the femur's necessary rotation to overlap both condyles) may invalidate the 2D X-ray PCO assessment as a reliable measurement.

The effect of restored medial knee anatomy in total knee arthroplasty with the flexion first balancer technique on mid-flexion laxity and functional outcome

Background

The Flexion First Balancer (FFB) technique for total knee arthroplasty (TKA) was developed to maintain the isometry of the medial collateral ligament (MCL) by restoring the medial anatomy of the knee. Inability to correct MCL isometry could hypothetically result in an increased mid-flexion laxity. The aim of the current study was to evaluate if the FFB technique results in improved functional outcome and less mid-flexion laxity compared to Measured Resection (MR).

Methods

A cross-sectional study was performed comparing 27 FFB patients with 28 MR patients. Groups were matched for age, gender, BMI and ASA classification. All patient received the cruciate retained type, Vanguard Complete Knee System (Biomet Orthopedics, Warsaw, IN, USA). Stress X-rays of the knee with 30 degrees of flexion were made to assess varus-valgus laxity. Furthermore, three tests were conducted to asses functional outcome: a 6 min walk test, a stair climb test and quadriceps peak force measurements. Mean follow-up was respectively 2.6 (SD 0.4) and 3.9 years (SD 0.2).

Results

The MR group showed a postoperative elevation in joint line in contrast to the FFB group, the mean difference between the two groups was 3 mm (p < 0.001). No differences in total laxity between the two groups was found. The FFB group showed a higher quadriceps peak force (1.67 (SD 0.55) N/BMI) in comparison with the MR group (1.38 (SD 0.48) N/BMI) (p < 0.05). All other outcome parameters were comparable between the two groups (p: n.s.). Correlation analysis showed a moderate negative correlation between joint line elevation and quadriceps peak force (r = − 0.29, p < 0.05).

Conclusion

The FFB technique did not lead to less coronal laxity in the mid-flexion range compared to MR. Although peak quadriceps force was significantly higher for the FFB group no clinically relevant benefits could be identified for the patients with regards to functional outcome. Therefore, minor deviations in joint line seems to have no effect on functional outcome after TKA.

Trial registration

ISRCTN, ISRCTN85351296. Registered 23 april 2021 - Retrospectively registered, https://www.isrctn.com/ISRCTN85351296

Three-year clinical and radiological results of a cruciate-retaining type of the knee prosthesis with anatomical geometry developed in Japan

Background

The FINE total knee was developed in Japan and clinical use began in 2001. It has unique design features, including an oblique 3^o femorotibial joint line that reproduces anatomical geometry. Although 20 years have passed since the FINE knee was clinically used for the first time in Japan, a formal clinical evaluation including patient-reported and radiographic outcomes has not been undertaken.

Methods

A total of 175 consecutive primary cruciate-retaining (CR)-FINE total knee arthroplasties (TKAs) at our hospital between February 2015 and March 2017 were included in this study. Three years postoperatively, range of motion (ROM), Knee Society Score (KSS), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Forgotten Joint Score (FJS) were recorded and compared with preoperative scores. Radiographic analyses including mechanical alignment, component alignment, and incidence of radiolucent lines also were undertaken based on the radiographs 3 years postoperatively.

Results

One-hundred twenty-two knees (70%) were available for 3-year follow-up data using KOOS, except for the sports subscale. Postoperative KOOS-symptom, −pain and -ADL were > 85 points, but KOOS-sports, −QOL and FJS were less satisfactory. ROM, KSS and all the subscales of KOOS were significantly improved compared with preoperative scores. Postoperative mean FJS was 66 and was significantly correlated with all the subscales of KOOS, but not with postoperative ROM. Radiolucent lines ≧1 mm wide were detected in five knees (4.1%). There were no major complications needing revision surgeries.

Conclusions

Patient-reported outcomes (PROs) for symptoms, pain and ADL after the CR-FINE TKA were generally improved, but those for sports, QOL and FJS were improved less. The incidence of radiolucent lines was rare but detected around the femoral components. With the mid- to long-term follow-up, improvements of surgical technique will be necessary to achieve better PROs from patients receiving the FINE knee.

3D-surface scan based validated new measurement technique of femoral joint line reconstruction in total knee arthroplasty

Purpose

This study aimed to validate a new joint line measurement technique in total knee arthroplasty for separated assessment of the medial and lateral femoral joint line alteration with 3D-surface scan technology. Separate assessment of the medial and lateral joint line alteration may improve TKA alignment assessment regarding to joint line restoration in kinematic alignment and use of robotic-assisted TKA surgery.

Methods

The medial and lateral joint line difference after TKA implantation on an artificial bone model was analyzed and compared with a 3D-scan and full femoral radiographs pre- and postoperatively. Radiographic analysis included the perpendicular distance between the most distal point of the medial and lateral condyle and the reproduced preoperative lateral distal femoral angle (LDFA). For evaluation of validity and reliability, radiographs were captured initially with true anteroposterior view and subsequently with combined flexion and rotation malpositioning. Reliability of the introduced measurement technique in between three observers was tested with intraclass correlation coefficient (ICC).

Results

Radiographic measurement showed a mean difference of 0.9 mm on the medial side and 0.6 mm on the lateral side when compared to the 3D-surface scan measurement. The reliability of measurement accuracy was ≤ 1 mm in x-rays with < 10° flexion error regardless to malrotation in these images. The ICC test showed very good reliability for the medial joint line evaluation and good reliability for lateral joint line evaluation (ICC 0.92, ICC 0.86 respectively).

Conclusion

The new introduced joint line measurement method showed a sufficient reliability, accuracy and precision. It provides separated information about medial and lateral joint line alteration in TKA surgery in absolute values.

Level of evidence

V - Experimental Study

Flexion First Balancer: description of new technique in TKA to reproduce joint line and pre-disease mechanical alignment

A considerable proportion of patients (19%) are dissatisfied after total knee arthroplasty (TKA). Possible factors contributing to this dissatisfaction are decreased posterior condylar offset (PCO) with subsequent joint line elevation, leading to mid-flexion instability. Secondly, the pre-disease mechanical alignment is changed into a neutral alignment. The Flexion First Balancer was developed to avoid these problems. This technique aims to maintain MCL isometry by restoring medial PCO and medial joint line to its pre-disease level. Also, to reconstruct the pre-disease mechanical alignment by adjusting the distal femoral angle. In this study we provide a detailed technical overview of the Flexion First Balancer technique.