Soft tissue laxity is highly variable in patients undergoing total knee arthroplasty.

BACKGROUND: One major goal of total knee arthroplasty (TKA) is to achieve balanced medial and lateral gaps in flexion and extension. While bone resections are planned by the surgeon, soft tissue laxity is largely intrinsic and patient-specific in the absence of additional soft tissue releases. We sought to determine the variability in soft tissue laxity in patients undergoing TKA. METHODS: We retrospectively reviewed 113 patients undergoing TKA. Data on preoperative knee deformity were collected. Data from a dynamic intraoperative stress examination were collected by a robotic tracking system to quantify maximal medial and lateral opening in flexion (85-95 degrees) and extension (-5-20 degrees). T-tests were used to assess the differences between continuous variables. RESULTS: A valgus stress opened the medial compartment a mean of 4.3 ± 2.3 mm (0.0-12.4 mm) in extension and 4.6 ± 2.3 mm (0.0-12.9 mm) in flexion. A varus stress opened the lateral compartment a mean of 5.4 ± 2.4 mm (0.3-12.6 mm) in extension and 6.2 ± 2.5 mm (0.0-13.4 mm) in flexion. The medial compartment of varus knees opened significantly more in response to valgus stress than valgus knees in both extension (5.2 mm vs. 2.6 mm; P < 0.0001) and flexion (5.4 mm vs 3.3 mm; P < 0.0001). The lateral compartment of valgus knees opened significantly more in response to varus stress than varus knees in both extension (6.7 mm vs. 4.8 mm; P < 0.0001) and flexion (7.4 mm vs. 5.8 mm; P = 0.0003). CONCLUSIONS: Soft tissue laxity is highly variable in patients undergoing TKA, contributing anywhere from 0-13 mm to the post-resection gap. Only a small part of this variability is predictable by preoperative deformity. These findings have implications for either measured-resection or gap-balancing techniques. LEVEL OF EVIDENCE: Level III.

A Simple Surgical Technique for Correction of Varus Deformity in Advanced Osteoarthritis of Knees by Medial Femoral Condylar Sliding Osteotomy-Description of Procedure and short term Outcome-A Prospective Study.

Background: Advanced osteoarthritis of knees with varus deformity consists of attenuation of lateral structures with contracture of the posteromedial structures and formation of medial osteophytes. The conventional step-wise medial and posteromedial release with measured resection may sometimes hinder achievement of perfectly balanced flexion and extension gaps with maintenance of flexion stability, without the use of a constrained prosthesis. Medial femoral epicondylar sliding osteotomy tailors the balancing to the need of the kinematics of the native knee and precludes the use of a constrained implant. Methods: 15 patients with Ahlbäck Grades III through V osteoarthritic changes at Howrah Orthopaedic Hospital were included in a prospective cohort case series with a minimum period of follow-up being 12 months. Physical examination, clinical questionnaire and radiographic evaluation were done post-operatively for objectification by functional Knee Society and Oxford Knee Scores respectively. Results and Analysis: The mean post-operative femorotibial angulation ameliorated to a value of 3.73 ± 1.58° from 18.67 ± 4.2° in the pre-operative stage. The mean overall Range of Motion of operated knee was 109.87 ± 6.86° with no residual frontal laxity and/or laxity in the coronal plane. The mean amount of resection of tibial plateau in patients with severe varus deformity was kept to a minimum, 6.56 mm from the least deficient portion of the lateral condyle. There were no complications as regards component loosening and/or surgical-site infection. Conclusion: The main objective of balancing a severely varus-afflicted knee is to preserve as much of the Medial Collateral Ligament as possible, to retain its check rein function and not jeopardise the stability. This is ensured by distalisation and posteriorizing the medial epicondyle by an incomplete osteotomy in addition to modest tibial resection fetching a non-isometric point of knee flexion. All osteotomies united by bony union and restoration of kinematic alignment. The limitation of this study however includes the lack of long-term results, such as late instability and polyethylene wear.

Robotic arthroplasty software training improves understanding of total knee arthroplasty alignment and balancing principles: a randomized controlled trial.

Understanding alignment and gap balancing in Total Knee Arthroplasty (TKA) can be challenging for trainee and experienced orthopedic surgeons. Traditional learning methods may not effectively translate to real-life scenarios. The advent of advanced technologies like robotic surgery and navigation systems has revolutionized intraoperative understanding of gap balancing techniques. This trial aims to investigate the effectiveness of robotic TKA planning software in educating trainees about alignment and ligament balancing. We hypothesize that a single session with the software will significantly enhance trainees' understanding of these techniques. This UK-based single-center, two-arm, group parallel randomized controlled trial was conducted during a national robotic arthroplasty symposium. It aims to evaluate the effect of robotic knee arthroplasty software training on understanding TKA alignment and gap balancing principles using Multiple Choice Questions (MCQs). The MCQ test was crafted based on established guidelines from a different institution with expert consensus in the field. Our study revealed that baseline knowledge of gap balancing and alignment principles was generally low among all participants. However, the intervention group, which received comprehensive robotic software training, demonstrated a significant improvement in their MCQ scores compared to the control group, which did not undergo the training. In conclusion, our study demonstrates that robotic arthroplasty software training significantly improves the understanding of TKA alignment and balancing principles among orthopedic trainees. Level of Evidence II.

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.

Surgeon-Applied Stress and a Ligament Tensor Instrument Provide a Similar Assessment of Preresection Flexion Laxity During Robotic Total Knee Arthroplasty.

Background: Robotic-assisted total knee arthroplasty (RA-TKA) allows surgeons to perform intraoperative soft tissue laxity assessments prior to bone resections and is used to alter resections to achieve gap balance. This study compared 2 techniques for flexion gap laxity assessment during RA-TKA. Methods: A prospective study of 50 primary RA-TKAs performed by a single surgeon was conducted between February and October 2023. Following full exposure, anterior tibial dislocation, and osteophyte removal, maximal medial and lateral compartment flexion laxity was quantified to the nearest 0.5 mm by the robotic system using a dynamic, surgeon-applied stress (SURGEON). This data was used to plan a balanced flexion gap by adjusting the femoral component size, rotation, and anterior-posterior translation. Flexion laxity was quantified again after distal femoral and proximal tibial resections using a ligament tensor instrument (TENSOR). These new data were used to plan for the same desired flexion gap using the same variables. Paired-samples t-tests and a simple linear regression were used for analysis. Results: Both methods produced near-identical recommendations for femoral component sizing (mean deviation 0.06 sizes, range -1 to +1 size; P = .569), rotation (deviation mean 1.0°, range -3.0° to +3.0°; P = .741), and anterior-posterior translation (deviation mean 0.13 mm, range -0.5 to +0.5 mm, P = .785). SURGEON femoral component rotation predicted TENSOR rotation (R2 = 0.157; 95% confidence interval = 0.124, 0.633; P = .004). Conclusions: Assessing flexion laxity with a surgeon-applied stress vs a ligament tensor produced near-identical laxity data in RA-TKA, suggesting surgeons may comfortably choose either technique as a reliable method. Level of Evidence: Level III.

Robotic-assisted differential total knee arthroplasty with patient-specific implants: surgical techniques and preliminary results.

OBJECTIVE: In total knee arthroplasty (TKA), achieving soft-tissue balance while retaining acceptable lower limb alignment is sometimes difficult and may lead to patient dissatisfaction. Theoretically, patient-specific implants can bring great benefits, while the lack of precise surgical tools may hinder the improvement of outcomes. The objective of this study was to illustrate surgical techniques and evaluate kinematics and early clinical outcomes of robotic-assisted TKA using patient-specific implants. METHODS: Based on preoperative CT scan, femoral and tibial components were 3D printed. Medial and lateral tibial liners were separate with different thicknesses, posterior slopes and conformity. TiRobot Recon Robot was used for surgery, and was armed with smart tools that quantify gap, force and femoral-tibial track. We collected data on demographics, intraoperative gap balance and femoral-tibial motion. In the follow-up, we evaluated the range of motion, Visual Analogue Scale (VAS), forgotten joint score (FJS), Knee injury and Osteoarthritis Outcome Score, Joint Replacement (KOOS, JR) score. Radiological data were also harvested. RESULTS: Fifteen patients (17 knees) were enrolled with a mean age of 64.6 ± 6.4 (53-76) years. In 5 knees, we used symmetric tibial liners, the rest were asymmetric. After surgery, the average alignment was 1.6 ± 2.0 (-3-5) degrees varus. The average follow-up lasted 6.7 ± 4.2 (1-14) months. The mean visual analogue scale was 0.8 ± 0.7 (0-2), FJS was 62.4 ± 25.3 (0-87), KOOS was 86.5 ± 9.4 (57-97). 11 patients were "very satisfied", 3 were "satisfied" with the result, and one patient was neutral due to restricted extension and unsatisfactory rehabilitation at five months' follow-up. CONCLUSIONS: With patient-specific implants and robotics, TKA could be performed by a mathematical way, which was dubbed a "differential" TKA. Intraoperative kinematics was excellent in terms of gap-force balancing and femoral-tibial relative motion. Preliminary clinical outcomes were overall satisfactory.

Maintaining the Physiological Lateral Flexion Gap in the Kinematically Aligned TKA Does Not Compromise Clinical Outcomes at One-Year Follow-Up.

Background: Instability is a common cause of (total knee arthroplasty) TKA failure, which can be prevented by achieving proper gap balance during surgery. There is no consensus on the ideal gap balance in TKA, and different alignment philosophies result in varying soft-tissue tightness. Traditional TKA aims for symmetric compartment balance, while kinematic alignment (KA) restores anatomy and accepts asymmetric flexion gaps. This study evaluated the impact of these philosophies on the flexion gap balance and clinical outcomes. Methods: A retrospective review of 167 patients who received true or restricted KA robotic-assisted TKA with at least one year of follow-up was conducted. The groups were based on intraoperative flexion gap differences: symmetric (0-1 mm) (n = 94) and asymmetric (2-5 mm) (n = 73). Results: Preoperative demographics and postoperative clinical and functional scores were compared. Both groups were similar in demographics and preoperative scores. True KA alignment was more likely to result in an asymmetric flexion gap, while restricted KA produced symmetric gaps. Conclusions: The study found no adverse effects from the physiological asymmetric flexion gap, with clinical and functional outcomes comparable to symmetric gaps. A 5 mm difference between the medial and lateral gap width did not negatively impact the outcomes. True KA more frequently results in a physiological asymmetric flexion gap.

Effect of Surgical Technique, Implant Design, and Time of Examination on Contact Kinematics: A Study of Bicruciate-Stabilized and Posterior-Stabilized Total Knee Arthroplasty.

BACKGROUND: Bicruciate-stabilized (BCS) total knee arthroplasty (TKA) designs attempt to approximate natural knee mechanics. Multiple surgical techniques, including gap balancing (GB) and measured resection (MR), have been developed to provide optimal implant positioning and soft-tissue balance. The goal of this study was to determine the effect of surgical technique on BCS TKA contact kinematics. Secondary goals included investigating the change of kinematics over time and comparing BCS TKA kinematics to a posterior-stabilized (PS) design. METHODS: The study included the BCS-GB, BCS-MR, and PS-MR groups. The BCS-GB and BCS-MR groups underwent weight-bearing radiostereometric analysis for multiple knee flexion angles at 3 months and 1 year postoperatively, whereas the PS-MR group was imaged at 1 year postoperatively. The medial and lateral contact kinematics were determined from implant poses. RESULTS: There were no differences in BCS TKA kinematics between the GB and MR techniques. There were differences in the mid-flexion ranges when comparing the 3-month and 1-year kinematics of the BCS design; however, they were less than 1.5 mm. Differences existed between the kinematics of the BCS and PS designs at all flexion angles for the medial condyle (P < .0006) and at 0° of flexion on the lateral condyle (P < .0001). CONCLUSIONS: Contact kinematics for a BCS design were similar for both surgical techniques, suggesting both are appropriate for this design. Small, likely clinically insignificant differences were found between 3-month and 1-year kinematics. The BCS TKA kinematics differed from the PS design; however, it is unclear whether these differences improve clinical outcomes.

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.

Constitutional alignment predicts medial ligament balancing in mechanically aligned total knee arthroplasty for varus knees.

PURPOSE: The aim of this study was to identify if constitutional alignment and preoperative radiologic parameters determined whether medial gap balancing was required in mechanically aligned total knee arthroplasty (TKA). METHODS: Two hundred and sixty three patients with 394 consecutive knees who underwent primary TKAs were retrospectively analysed in this study. Selective sequential multiple needle puncturing (MNP) was performed for medial ligament balancing when required. Constitutional alignment, which was determined using the Coronal Plane Alignment of the Knee (CPAK) classification, as well as preoperative and postoperative radiologic parameters was evaluated to identify factors which predicted the need for MNP. RESULTS: One hundred and fifty eight (40.1%) knees required medial ligament balancing with MNP. Patients who required MNP during surgery had significantly more constitutional varus, more varus preoperative mechanical Hip-Knee-Ankle angle (mHKA), smaller preoperative medial proximal tibial angle (MPTA) and a larger change in mHKA and MPTA after surgery than those who did not. Patients with constitutional varus also had a higher incidence of having had MNP to both anterior and posterior superficial medial collateral ligament (sMCL) fibres. There was no significant difference in preoperative lateral distal femoral angle (LDFA), posterior tibial slope (PTS) and varus-valgus difference (VVD) between groups. CONCLUSION: Ligament balancing using MNP was determined by constitutional alignment rather than medial soft tissue contracture. Patients with constitutional varus who had a larger medio-lateral gap difference in extension also had a higher incidence of having had MNP to both anterior and posterior sMCL fibres. LEVEL OF EVIDENCE: Retrospective comparative study, level IV.

Large Osteophytes over 10 mm at Posterior Medial Femoral Condyle Can Lead to Asymmetric Extension Gap Following Bony Resection in Robotic Arm-Assisted Total Knee Arthroplasty with Pre-Resection Gap Balancing.

Robotic arm-assisted total knee arthroplasty (TKA) involves a pre-resection gap balancing technique to obtain the desired gap. However, the expected gap may change owing to the soft-tissue release effect of unreachable osteophytes. This study evaluated the effect of unreachable osteophytes of the posterior medial femoral condyle on gap changes following bony resection. We retrospectively analysed 129 robotic arm-assisted TKAs performed for varus knee osteoarthritis. Knees were classified according to the size of osteophytes on the posterior medial femoral condyle using preoperative computed tomography measurement. After the removal of reachable osteophytes, the robotic system measured pre- and post-resection medial extension (ME), lateral extension (LE), medial flexion (MF), and lateral flexion (LF) gaps. No extension gap changes were observed for 25 (19.4%), and no flexion gap changes were observed 41 (31.8%) knees, following bone cuts. ME, LE, MF, and LF gaps increased with the osteophyte size (p < 0.05). For osteophytes <10 mm, all the gaps increased symmetrically. However, for osteophytes >10 mm, the ME gap increased asymmetrically more than LE, MF, and LF gaps (p < 0.05). The gap changes due to bony resection were correlated to the osteophyte sizes of the posterior medial femoral condyle. Surgeons should plan a slightly tight medial extension gap to attain the desired gaps for >10 mm osteophytes.

Patella scores are similar both with gap balancing and measured resection after total knee arthroplasty: a randomized single-centre study.

PURPOSE: The purpose of this prospective study was to compare femoral component rotation (FCR) values when adjusted with 'gap balancing' (GB) and 'measured resection' (MR) techniques following total knee arthroplasty (TKA). The study hypothesis was that the GB technique would be better on FCR than MR in TKA. METHODS: From a total of 93 unilateral TKAs performed between August 2019 and November 2020, the FCR values were adjusted by GB in 46 cases and MR in 47. Post-TKA magnetic resonance imaging (MRI) was applied for FCR assessment. Orthoroentgenograms and lateral knee radiographs were taken to determine the mechanical axis and posterior condylar offset (PCO) ratio, respectively. Both groups were compared radiologically. The Western Ontario and Mcmaster Universities Osteoarthritis Index (WOMAC), Knee Society Score (KSS), and Hospital for Special Surgery (HSS) patella scores were calculated and compared between the groups preoperatively and at the end of 6 months, and 1 and 2 years postoperatively. RESULTS: There was no difference between the groups in respect of the demographic data. The mean HSS patella score was 86.4 ± 4.1 in the GB group and 84.6 ± 3.8 in the MR group in the 2nd year (p = 0.047). A higher degree of external rotation in the FC was determined in the GB group [2.2° (1.7°-4.3°)] compared to the MR group [1.7° (0.8°-3.0°)] (p = 0.009). The postoperative increase in PCO ratio was higher in the GB group (p = 0.005). All other variables were similar in both groups. CONCLUSION: The results of this study showed that at the end of the 2nd year, the HSS patella scores were better, FCs were more externally rotated and PCO ratios were higher in TKAs using the GB technique. However, taking into account that the difference between the 2nd year HSS patella scores was too small to be considered clinically significant, it was shown that both the GB and MR techniques can be used for FCR in clinical practice without any hesitation.

Differences in joint line level and posterior condylar offset during total knee replacement with use of gap-balancing and measured resection techniques-matched cohort study.

BACKGROUND: Total knee replacement (TKR) is considered one of the most common elective orthopaedic procedures. The main focus of TKR is to offer patient's symptomatic relief from persistent knee pain. To achieve this it is crucial to restore joint biomechanics by performing proper bone cuts. Some surgeons favor the measured resection technique, others prefer gap balancing technique. The researchers of the presented study performed TKR using these two techniques. The aim of this study was to compare the postoperative change in joint line and posterior condylar offset after TKR with use of anatomic knee design implants between gap balancing and measured resection techniques. METHODS: Two hundred twenty-five X-rays of patients who underwent TKR performed by a single surgeon between 2020 and 2021 were analyzed. The first group of patients (101) was operated with the use of gap balancing technique and the second group (124) was operated with the use of measured resection technique. Patients included in the study were > 50 years of age, had confirmed primary knee osteoarthritis, underwent primary TKR with a PS (posterior stabilized) knee implants without patella resurfacing and had at least 15 degree flexion contracture. T-student test and U Mann-Whitney test were used in statistical analysis of results, according to the normality of distribution examined with the Shapiro-Wilk test. Post-hoc analysis was performed using the Dwass-Steel-Crichtlow-Fligner test (DSCF). RESULTS: The postoperative analysis showed a significantly elevated joint line level in the gap balancing group (-2.6 ± 4.1 vs -0.7 ± 4.8, p < 0.0005). In the gap balancing group significantly more patients had joint lines elevated > 2 mm comparing to measured resection technique. The difference between pre- and postoperative PCO (posterior condylar offset) and PCOR (posterior condylar offset ratio) results had no significant differences (100.8 ± 11.8 vs 101 ± 12.5, p > 0.05) between the groups. CONCLUSIONS: The results of the study suggest that when it comes to restoring joint line level measured resection technique seems to be superior in comparison to the gap balancing technique. What is more, results indicate measured resection is equal in terms of restoring posterior condylar offset to the gap balancing technique. TRIAL REGISTRATION: NCT04164147, date of registration: November 14, 2019.

Robotic-arm Assisted Total Knee Arthroplasty: the Relationship between Bone Resection, Gap Balancing and Resultant Implant Alignment.

Objectives: The primary aim was to assess the association between bone resection and the resultant flexion and extension gaps in the medial and lateral compartments of the knee when performing robotic-arm assisted total knee arthroplasty (rTKA). The secondary aims were to compare medial and lateral bone resections and the influence on limb alignment, and whether the amount of bone resection that resulted in equal gaps was predictable. Methods: A prospective study of 22 consecutive patients with a mean age of 66 years undergoing rTKA was conducted. The femoral component was mechanically aligned, and the alignment of the tibial component was adjusted (+/-3degrees of the mechanical axis) to obtain equal extension and flexion gaps. All knees underwent soft tissue balancing using sensor-guided technology. The final compartmental bone resection, gaps, and implant alignment were obtained from the robot data archive. Results: There was a correlation between bone resection and the resultant gap in the medial (r=0.433, p=0.044) and lateral (r=0.724, p<0.001) compartments of the knee. There were no differences in bone resection from the distal femur and posterior condyles in the medial (p=0.941) or lateral compartments (p=0.604) or for the resultant gaps (p=0.341 and p=0.542, respectively). There was more bone removed from the medial compartment compared to the lateral aspect: 0.9mm (p=0.005) in extension and 1.2mm (p=0.026) flexion. The differential bone resection changed the knee alignment by one degree of varus. There were no significant differences between the actual and predicted medial (difference 0.05, p=0.893) or lateral (difference 0.00, p=0.992) tibial bone resection. Conclusion: There was a direct association between bone resection and resultant compartment joint gap when using rTKA, which was predictable. Gap balancing was achieved when less bone was resected from the lateral compartment which resulted in an estimated one-degree varus alignment of the knee.

Gap Balancing Throughout the Arc of Motion With Navigated TKA and a Novel Force-Controlled Distractor: A Review of the First 273 Cases.

BACKGROUND: This study evaluated the ability to achieve the targeted soft-tissue balance in terms of medio-lateral (ML) laxity and gap values when using a computer-assisted orthopedic surgery (CAOS) system featuring an intra-articular force-controlled distractor and assessed learning curves associated with the adoption of this technology. METHODS: The first 273 cases using this technology were reported without exclusions comparing 1) final ML laxity and 2) final average gap to their predefined targets. For both parameters, the signed and unsigned differentials were reported. The linear mixed model was used to evaluate laxity curve differences between surgeons. A cumulative sum control chart (CUSUM) was applied to assess surgeon learning curves regarding surgical time. RESULTS: Both the average signed ML laxity and gap differentials were neutral throughout the full arc of motion. Both the average unsigned ML laxity and gap differentials were linear. Signature of ML laxity and gap differential curves tended to be surgeon-specific. The CUSUM analyses of surgical times demonstrated either a short learning curve or the absence of a discernible learning pattern for surgeons. CONCLUSION: Data from all users involved with the pilot release of the balancing device were considered to capture variability in familiarity with the technique and learning curve cases were included. A high ability to achieve targeted gap balance throughout the arc of motion using the proposed method was observed.

Component Rotation in Well-Functioning, Gap Balanced Total Knee Arthroplasty Without Navigation.

BACKGROUND: Malalignment of total knee arthroplasty (TKA) components is a potential cause of clinical failure following TKA. Since the goal of a gap balancing (GB) technique is equal flexion and extension gaps secondary to soft-tissue balancing, and not necessarily component alignment, variation in component placement may exist. Our purpose was (1) to evaluate precision of component alignment in well-functioning GB TKAs performed without the aid of navigation using computed tomographic evaluation and (2) to determine any relationship between femoral version and/or tibial torsion and TKA component positioning. METHODS: There were 93 well-functioning TKAs performed with an extension gap first GB technique with a minimum 2-year follow-up evaluated using computed tomography to assess component rotational alignment, as well as osseous femoral version and tibial torsion. Femoral and tibial rotational alignment was assessed by previously described methods. RESULTS: The mean Knee Society Score was 185.7 ± 21.7. The mean range of motion was 128.5 ± 7.8°. Femoral posterocondylar axis (relative to the transepicondylar axis) values ranged from -8.3 to 4.1° with a mean of -0.78 ± 2.7° (internal rotation). Mean tibial rotation was 17.2 ± 7.9° internal rotation relative to the tibial tubercle. No correlation was found between native femoral version and femoral component rotational alignment (Pearson's correlation coefficient, r, 0.007). Weak correlation was found between native tibial torsion and tibial component alignment (r = 0.24). CONCLUSION: Despite being only a secondary objective with the GB technique, most components evaluated were within the desired range of rotation. Alignment was not influenced by native osseous rotational geometry. LEVEL OF EVIDENCE: Level III, Retrospective Cohort Study.

How does the use of quantified gap-balancing affect component positioning and limb alignment in robotic total knee arthroplasty using functional alignment philosophy? A comparison of two robotic platforms.

PURPOSE: This study aimed to compare the effect of an image-based (MAKO) system using a gap-balancing technique with an imageless (OMNIbot) robotic tool utilising a femur-first measured resection technique. METHODS: A retrospective cohort study was performed on patients undergoing primary TKA with a functional alignment philosophy performed by a single surgeon using either the MAKO or OMNIbot robotic systems. In all cases, the surgeon's goal was to create a balanced knee and correct sagittal deformity (eliminate any fixed flexion deformity). Intra-operative data and patient-reported outcomes (PROMS) were compared. RESULTS: A total of 207 MAKO TKA and 298 OMNIbot TKAs were analysed. MAKO TKA patients were younger (67 vs 69, p=0.002) than OMNIbot patients. There were no other demographic or pre-operative alignment differences. Regarding implant positioning, in MAKO TKAs the femoral component was more externally rotated in relation to the posterior condylar axis (2.3° vs 0.1°, p<0.001), had less valgus femoral cuts (1.6° vs 2.7° valgus, p<0.001) and more varus tibial cuts (2.4° vs 1.9° varus, p<0.001), and had more bone resected compared to OMNIbot TKAs. OMNIbot cases were more likely to require tibial re-cuts than MAKO (15% vs 2%, p<0.001). There were no differences in femur recut rates, soft tissue releases, or rate of achieving target coronal and sagittal leg alignment between robotic systems. A subgroup analysis of 100 MAKO and 100 OMNIbot propensity-matched TKAs with 12-month follow-up showed no significant difference in OKS (42 vs 43, p=0.7) or OKS PASS scores (83% vs 91%, p=0.1). MAKO TKAs reported significantly better symptoms according to their KOOS symptoms score than patients that had OMNIbot TKAs (87 vs 82, p=0.02) with a higher proportion of KOOS PASS rates, at a slightly longer follow-up time (20 months vs 14 months, p<0.001). There were no other differences in PROMS. CONCLUSION: A gap-balanced technique with an image-based robotic system (MAKO) results in different implant positioning and bone resection and reduces tibial recuts compared to a femur-first measured resection technique with an imageless robotic system (OMNIbot). Both systems achieve equal coronal and sagittal deformity correction and good patient outcomes at short-term follow-ups irrespective of these differences.

Restricted Inverse Kinematic Alignment Better Restores the Native Joint Line Orientation While Achieving Similar Balance, Laxity, and Arithmetic Hip-Knee-Ankle Angle to Gap Balancing Total Knee Arthroplasty.

Background: Both restricted inverse kinematic alignment (iKA) and gap balancing aim for a balanced total knee arthroplasty by adjusting femoral component position based on ligamentous gaps. However, iKA targets a native tibial joint line vs resecting perpendicular to the mechanical axis. This study compares how these 2 techniques impact the balance and laxity throughout flexion and joint line obliquity (JLO), arithmetic hip-knee-ankle angle (aHKA), and the coronal plane alignment of the knee (CPAK). Methods: Two surgeons performed 75 robot-assisted iKA total knee arthroplasties. A digital joint tensioner collected laxity data throughout flexion before femoral resection. The femoral component position was determined using predictive gap-planning to optimize the balance throughout flexion. Planned gap balancing (pGB) simulations were performed for each case using neutral tibial resections. Mediolateral balance, laxity, and CPAK were compared among pGB, planned iKA (piKA), and final iKA. Results: Both piKA and pGB had similar mediolateral balance and laxity, with mean differences <0.4 mm. piKA had a lower mean absolute difference from native JLO than pGB (3 ± 2° vs 7 ± 4°, P < .001). aHKA was similar (P > .05) between pGB and piKA. piKA recreated a more native CPAK distribution, with types I-V being the most common ones, while most pGB knees were of type V, VII, and III. Final iKA and piKA had similar mediolateral balance and laxity, with a root-mean-square error <1.4 mm. Conclusions: Although balance, laxity, and aHKA were similar between piKA and pGB, piKA better restored native JLO and CPAK phenotypes. The neutral tibial resection moved most pGB knees into types V, VII, and III. Surgeons should appreciate how the alignment strategy affects knee phenotypes.

Gap balanced adjusted mechanical alignment versus measured resection mechanical alignment: a randomised controlled trial.

INTRODUCTION: Alignment goals in total knee replacement (TKR) is a topical subject. This study compares the short-term functional outcomes and patient reported outcome measures (PROMs) of two philosophies for knee arthroplasty alignment: measured resection (MR) and an individualised alignment philosophy, with the tibia mechanically aligned and an instrumented gap balancer (GB) to align the femur in both flexion and extension. PATIENTS AND METHODS: 94 knees were enrolled in this randomised controlled trial. The surgical protocol used a MR technique for mechanical alignment or a GB technique for individualised alignment. Primary outcome was quadriceps strength. Secondary outcomes included validated functional tests and PROMs as well as patient satisfaction. Outcomes were assessed pre-operatively, at 6 weeks, 3, 6 and 12 months post-operatively. RESULTS: At 12-month follow-up, there was no significant difference in the change from baseline mean quadriceps peak torque between the two groups (p = 0.988). Significant improvement in the change in range of motion (ROM) in the GB group compared to the MR group at 3 months (13° vs 6° p = 0.028) but this improvement was not significant at 1 year (20° vs 17° p = 0.21). The functional test of balance showed statistically significant improvement at 6 weeks (p = 0.03) in the GB group but this difference was not maintained. PROMs favoured the GB group, with the KOOS pain scoring statistically better (p ≤ 0.05) at 6 weeks, 3, 6 and 12 months. CONCLUSIONS: Individualised alignment philosophy utilising a GB technique did not demonstrate an improvement in the primary outcome measure quadriceps peak torque. Improvement was seen in the GB group in PROM pain scores that was significant, both statistically and clinically, out to at least 1 year. Gains that were seen in functional assessment with GB, although significant at some time points, were no longer significant at 1 year and no difference was seen in quads strength. Compared to a MR technique, the individualised GB technique appears to confer some improvement in pain, ROM and some functional tests following TKR in the short-term.

Comparison of the Imaging and Clinical Outcomes among the Measured Resection, Gap Balancing, and Hybrid Techniques in Primary Total Knee Arthroplasty.

OBJECTIVE: Although many studies have compared the measured resection (MR) technique to the gap balancing (GB) technique, few studies have investigated the hybrid technique. In this study, we compared imaging and clinical outcomes of the MR, GB, and hybrid techniques in primary total knee arthroplasty (TKA). METHODS: From January 2016 to January 2019, we conducted a retrospective study on 90 patients who underwent unilateral primary TKA; 30 received the MR technique, 30 received the GB technique, and 30 received the hybrid technique. Radiological outcomes, including joint line level, mechanical alignment of the lower limb, positions of the femoral and tibial components, and rotation of the femoral component, and clinical outcomes, including the visual analog scale score for pain, the Knee Society Score, and the range of motion, were assessed among the three groups. One-way analysis of variance and Dunnett's test were performed for normally distributed data. Kruskal-Wallis H test and Dunn-Bonferroni test were conducted for non-normally distributed data. RESULTS: No significant difference in the mechanical alignment (p = 0.151) and the positions of the tibial and femoral components (p = 0.230 for α angle, p = 0.517 for ß angle, p = 0.686 for femoral flexion angle, and p = 0.918 for tibial slope angle) was found among the three groups. No significant difference in the elevation of the joint line between the MR and the hybrid groups was found (2.1 ± 0.3 mm vs 2.1 ± 0.1 mm, p = 0.627), but the GB group (2.8 ± 0.2 mm) differed significantly from the other two groups (p < 0.001). Although rotation of the femoral component in the GB group was larger than that of the MR and hybrid groups, the difference was not significant (1.8° ± 0.2° vs 1.7° ± 0.3° vs. 1.7° ± 0.2°, p = 0.101). The clinical outcomes were not significantly different (p > 0.05), although the results in the hybrid group were slightly higher. CONCLUSION: The hybrid technique helped to restore the mechanical alignment of the lower limb and realize optimal positions of the femoral and tibial components without significant differences relative to the MR and GB techniques. The hybrid technique was more helpful for maintaining the original height of the joint line, which was similar to the MR technique. Additionally, although the improvement in the clinical outcomes in the hybrid group was slightly higher, it was not significantly different among the three groups.