Improved Clinical Outcomes With Dynamic, Force-Controlled, Gap-Balancing in Posterior-Stabilized Total Knee Arthroplasty.

BACKGROUND: Optimal soft-tissue management in total knee arthroplasty (TKA) may reduce symptomatic instability. We hypothesized that TKA outcomes using a computer-assisted dynamic ligament balancer that acquires medial and lateral gap sizes throughout the motion arc would show improved Knee Society Scores (KSS) compared to TKAs done with a traditional tensioner at 0 and 90°. We also sought to quantify the degree to which the planned femoral rotation chosen to optimize medio-lateral balance throughout the arc of motion deviated from the femoral rotation needed to achieve a rectangular flexion gap at 90° alone. METHODS: Baseline demographics, clinical outcomes, KSSs, and femoral rotations were compared in 100 consecutive, computer-assisted TKAs done with the balancer (balancer group) to the immediately prior 100 consecutive computer-assisted TKAs done without the balancer (control group). Minimum follow-up was 13 months and all patients had osteoarthritis. Mean knee motion did not differ preoperatively (110.1 ± 13.6° balancer, 110.4 ± 12.5° control, P = .44) or postoperatively (119.1 ± 10.3° balancer, 118.8 ± 10.9° control, P = .42). Tourniquet times did not differ (93.1 ± 13.0 minutes balancer, 90.7 ± 13.0 minutes control, P = .13). Postoperative length of stay differed (40.2 ± 20.9 hours balancer, 49.0 ± 18.3 hours control, P = .0009). There were 14 readmissions (7 balancer, 7 control), 11 adverse events (4 balancer, 7 control), and 3 manipulations (1 balancer, 2 control). The cohorts were compared using Student's t-tests, Shapiro-Wilk normalities, Wilcoxon rank-sums, and multivariable logistic regression analyses. RESULTS: Postoperative KSS improvements were higher in the balancer group (P < .0001). In multivariable regression analyses, the balancer group experienced 7 ± 2 point improvement in KSS Knee scores (P < .0001) and 4 ± 2 point improvement in KSS Function scores (P = .040) compared to the control group. CONCLUSIONS: The statistically and clinically significant improvements in postoperative KSS demonstrated in the balancer cohort are likely driven by improved stability throughout the motion arc. Further study is warranted to evaluate replicability by non-design surgeons.

Intraoperative knee kinematics measured by computer-assisted navigation and intraoperative ligament balance have the potential to predict postoperative knee kinematics.

This study was designed to analyze the effects of type of activity and cruciate ligament resection on knee kinematics and ligament balance after total knee arthroplasty (TKA), and to determine if intraoperative passive kinematics are associated with active kinematics. Fresh-frozen human cadaveric knees were examined. The knees were mounted on a quadriceps-driven simulator. Cruciate-retaining (CR-TKA) and posterior-substituting (PS-TKA) TKA was performed using a contemporary knee system. Active flexion (closed-kinetic chain [CKC] and open-kinetic-chain [OKC]) and passive flexion were analyzed by recording the knee kinematics using a specifically developed application of an imageless navigation system. An electronic ligament balancer was used to measure the tibiofemoral gap under constant distraction pressure. The femur rotated externally relative to the tibia during passive and active CKC flexion. The femur translated anteriorly from 10° to 50° of flexion after TKA. Beyond 50° of flexion, the femur translated posteriorly in all surgical conditions. The femoral location during active CKC flexion was posterior relative to that during active OKC. Femoral rotation and translation during passive knee flexion correlated significantly with that during active knee flexion. Posterior tilt of the electronic ligament balancer was greater with CR-TKA than with PS-TKA and correlated significantly with the anteroposterior position of the femur. Statement of Clinical Significance: Intraoperative knee kinematics measured by computer-assisted navigation and intraoperative ligament balance have the potential to predict postoperative knee kinematics.

Improved total knee arthroplasty pain outcome when joint gap targets are achieved throughout flexion.

PURPOSE: Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the definition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midflexion, and flexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout flexion. METHODS: 135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacrificing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90 N from 10°-90° flexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to define clinically relevant joint gap target thresholds in extension, midflexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets. RESULTS: Significant linear correlations were found throughout extension, midflexion, and flexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the final insert thickness in midflexion, and a medio-lateral imbalance of less than 1.5 mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisfied (median ∆ = 11.2, p = 0.002). CONCLUSION: Gap thresholds identified in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacrificing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed. LEVEL OF EVIDENCE: Level II.

What is the Effect of Posterior Osteophytes on Flexion and Extension Gaps in Total Knee Arthroplasty? A Cadaveric Study.

BACKGROUND: Posterior compartment knee osteophytes may pose a challenge in achieving soft-tissue balance during total knee arthroplasty (TKA). Obtaining symmetry of flexion and extension gaps involves balance of both bony and soft-tissue structures. We hypothesize that space-occupying posteromedial femoral osteophytes affect soft-tissue balance. METHODS: Five cadaveric limbs were acquired. Computed tomography scans were obtained to define the osseous contours. Three-dimensionally printed, specimen-specific synthetic posterior femoral osteophytes were fabricated in 10-mm and 15-mm sizes. TKAs were implanted. Medial and lateral compartment contact forces were measured during passive knee motion using pressure-sensing technology. For each specimen, trials were completed without osteophytes and with 10-mm and 15-mm osteophytes affixed to the posteromedial femoral condyle. Contact forces were obtained at full extension, 10°, 30°, 45°, 60°, and 90° of flexion. These were recorded across each specimen in each condition for three trials. Tukey post hoc tests were used with a repeated measures ANOVA for statistical data analysis. RESULTS: The presence of posteromedial osteophytes increased asymmetric loading from full extension to 45° of flexion, with statistically significant differences observed at full extension and 30°. A reduction in lateral compartment forces was noted. The 25%-75% bounds of variability in the contact force was less than 3.5 lbs. CONCLUSIONS: Posteromedial femoral osteophytes caused an asymmetric increase in medial contact forces from full extension continuing into mid-flexion. The soft-tissue imbalance created from these osteophytes supports their removal before performing ligament releases to obtain desired soft-tissue balancing during TKA.

Can a robot help a surgeon to predict a good total knee arthroplasty?

AIMS: Neither a surgeon's intraoperative impression nor the parameters of computer navigation have been shown to be predictive of the outcomes following total knee arthroplasty (TKA). The aim of this study was to determine whether a surgeon, with robotic assistance, can predict the outcome as assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) for pain (KPS), one year postoperatively, and establish what factors correlate with poor KOOS scores in a well-aligned and balanced TKA. METHODS: A total of 134 consecutive patients who underwent TKA using a dynamic ligament tensioning robotic system with a tibia first resection technique and a cruciate sacrificing ultracongruent TKA system were enrolled into a prospective study. Each TKA was graded based on the final mediolateral ligament balance at 10° and 90° of flexion: 1) < 1 mm difference in the thickness of the tibial insert and that which was planned (n = 75); 2) < 1 mm difference (n = 26); 3) between 1 mm to 2 mm difference (n = 26); and 4) > 2 mm difference (n = 7). The mean one-year KPS score for each grade of TKA was compared and the likelihood of achieving an KPS score of > 90 was calculated. Finally, the factors associated with lower KPS despite achieving a high-grade TKA (grade A and B) were analyzed. RESULTS: Patients with a grade of A or B TKA had significantly higher mean one-year KPS scores compared with those with C or D grades (p = 0.031). There was no difference in KPS scores in grade A or B TKAs, but 33% of these patients did not have a KPS score of > 90. While there was no correlation with age, sex, preoperative deformity, and preoperative KOOS and Patient-Reported Outcomes Measurement Information System (PROMIS) physical scores, patients with a KPS score of < 90, despite a grade A or B TKA, had lower PROMIS mental health scores compared with those with KPS scores of > 90 (54.1 vs 50.8; p = 0.043). Patients with grade A and B TKAs with KPS > 90 were significantly more likely to respond with "my expectations were too low", and with "the knee is performing better than expected" compared with patients with these grades of TKA who had a KPS score of < 90 (40% vs 22%; p = 0.004). CONCLUSION: A TKA balanced with robotic assistance to within 1 mm of difference between the medial and lateral sides in both flexion and extension had a higher KPS score one year postoperatively. Despite accurate ligament balance information, a robotic system could not guarantee excellent pain relief. Patient expectations and mental status also significantly affected the perceived success of TKA. Cite this article: Bone Joint J 2021;103-B(6 Supple A):67-73.

Patient-specific instrumentation combined with a new tool for gap balancing is useful in total knee replacement: a 3-year follow-up of a retrospective study.

OBJECTIVE: The purpose of this study was to determine whether the gap-balancing technique with patient-specific instrumentation (PSI) and a new balancing device in total knee arthroplasty (TKA) can improve knee function to a greater extent than can the measured resection technique. MATERIALS AND METHODS: Data from 150 patients who underwent TKA from August 2014 to June 2016 were studied retrospectively. The gap-balancing technique assisted by PSI and the new balancing device was used in 80 patients (82 knees), and the measured resection technique was used in 70 patients (70 knees). The surgical, imaging, and knee function data were compared. RESULTS: The gap-balancing technique assisted by PSI and the new balancing device was found to be feasible in all operated knees and reliable. In total, 150 patients (152 knees) of ages ranging from 52 to 78 years (mean 67 years) underwent TKA during the study period. The follow-up period ranged from 35 to 52 months (mean 45 months). Only one patient, who was included in the gap-balancing group, underwent a revision surgery at 2 years postoperatively due to infection. There were no differences in the incidence of anterior knee pain between the two groups. The mean flexion angle, KSS scores, and VAS scores did not significantly differ between the measured resection group and gap-balancing group at 12 weeks or 36 weeks postoperatively. The average joint line displacement was 1.3 ± 1.1 mm (range 0-3) proximally in the GB (gap-balancing) group and 1.2 ± 1.4 mm in the MR (measured-resection) group. No outliers >5 mm in either group were recorded. The mean leg axis deviation from the neutral mechanical axis was 1.8°±1.5° varus (range 0°-3°varus) versus the neutral mechanical axis in the GB group and 1.4°±1.2°(range 0°-3°)in the MR group. No outliers with >3° deviation in either group were recorded. CONCLUSIONS: The gap-balancing technique performed with the new balancing device and PSI can yield accurate femoral component alignment as well as outcomes similar to those of measured resection at 3 years. The new balancing device can be taken into consideration by surgeons who prefer performing the gap-balancing technique with PSI.

Small soft tissue tension changes do not affect patient-reported outcomes one year after primary TKA.

BACKGROUND: Adequate soft tissue tension and balance is paramount to achieve favourable outcomes of total knee arthroplasty (TKA). Implant manufacturers offer 1-mm liner increments to fine-tune ligament tension and balance. In this study, we assessed if soft tissue tension changes introduced by minimal changes in liner thicknesses affect early patient reported outcomes. METHODS: Eighty-nine patients undergoing 99 primary, elective TKAs by a single surgeon were included. After achieving adequate ligament balance, the first 50 knees received an insert that would allow 2-3 mm of medial and lateral opening (control group), whereas the last 49 received an insert which was 1 mm thicker, resulting in a slight increase in ligament tension (study group). Sensor technology was used to record compartmental loads. Knee Society Score (KSS), KOOS Jr., and ROM were recorded pre-operatively, six weeks, four and 12 months post-operatively. The Forgotten Joint Score (FJS) was administered four and 12 months post-operatively. RESULTS: No differences were observed in demographic variables, pre-operative outcome scores, and ROM measures between groups. Six weeks post-operatively, there was no statistically significant difference in the outcome variables. Four months post-operatively, statistically significant differences were only observed in KOOS Jr. (79 and 73.6; p = 0.05), and FJS (59.9 and 45.5; p < 0.01); all of which favoured the control group. There was no difference in the outcome variables at 12 months. CONCLUSION: Minor changes in soft tissue tension induced by 1-mm changes in liner thickness resulted in clinically meaningful differences favouring the control group four months post-operatively, but in no clinically noticeable differences 12 months post-operatively. It is possible that lower soft tissue tension may lead to transient improvement in patient-reported early outcomes.

The effects of soft tissue lateral release on the stability of the ligament complex of the knee.

PURPOSE: Valgus deformity presents a particular challenge in total knee arthroplasty. This condition regularly leads to contractures of the lateral capsular ligament complex and to overstretching of the medial ligamentous complex. Reconstruction of the knee joint kinematics and anatomy often requires lateral release. However, data on how such release weakens the stability of the knee are missing in the literature. This study investigated the effects of sequential lateral release on the collateral stability of the ligament complex of the knee in vitro. METHODS: Ten knee prostheses were implanted in 10 healthy cadaveric knee joints using a navigation device. Soft tissue lateral release consisted of five release steps, and stiffness and stability were determined at 0, 30, 60 and 90° flexion after each step. RESULTS: Soft tissue lateral release increasingly weakened the ligament complex of the lateral compartment. Because of the large muscular parts, the release of the iliotibial band and the M. popliteus had little effect on the stability of the lateral and medial compartment, but release of the lateral ligament significantly decreased the stability in the lateral compartment over the entire range of motion. Stability in the medial compartment was hardly affected. Conversely, further release of the posterolateral capsule and the posterior cruciate ligament led to the loss of stability in the lateral compartment only in deep flexion, whereas stability decreased significantly in the medial compartment. CONCLUSION: Our study shows for the first time the association between sequential lateral release and stability of the ligamentous complex of the knee. To maintain the stability, knee surgeons should avoid releasing the entire lateral collateral ligament, which would significantly decrease stability in the lateral compartment.

Bone resection for mechanically aligned total knee arthroplasty creates frequent gap modifications and imbalances.

PURPOSE: The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment (MA) technique for total knee arthroplasty (TKA). METHODS: MA bone resections were simulated on 1000 consecutive lower limb CT scans from patients undergoing TKA. Femoral rotation was aligned with either the surgical trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Imbalances in the extension space, flexion space, medial compartment and lateral compartment were calculated. RESULTS: Extension space imbalances (≥ 3 mm) occurred in 25% of varus and 54% of valgus knees and severe imbalances (≥ 5 mm) were present in up to 8% of varus and 19% of valgus knees. Higher flexion space imbalance rates were created with TEA versus PC (p < 0.001). Using TEA, only 49% of varus and 18% of valgus knees had < 3 mm of imbalance throughout the extension and flexion spaces, and medial and lateral compartments. CONCLUSION: A systematic use of the simulated measured resection MA technique for TKA leads to many cases with imbalance. Some imbalances may not be correctable surgically and may result in TKA instability. Modified versions of the MA technique or other alignment methods that better reproduce knee anatomies should be explored. LEVEL OF EVIDENCE: 2.

Weakening of the knee ligament complex due to sequential medial release in total knee arthroplasty.

PURPOSE: The purpose of this study was to investigate the effects of sequential medial release on the stiffness and collateral stability of the ligament complex of the knee. Irrespective of the implantation technique used, varus deformity frequently requires release of the capsular ligament complex. Yet, no data are available on how stiffness and stability of the knee ligament complex are weakened by such release. METHODS: After total knee arthroplasty, ten healthy Thiel-fixed knee joints were subjected to sequential medial release consisting of six release steps. After each step, stiffness and stability were determined at 0°, 30°, 60°, and 90°. RESULTS: Sequential medial release increasingly weakened the ligament complex. In extension, release of the anteromedial tibial sleeve 4 cm below the joint line already weakened the ligament complex by approximately 13%. Release 6 cm below the joint line reduced stiffness and stability by 15-20% over the entire range of motion. After detachment of the medial collateral ligament, stability was only about 60% of its initial value. CONCLUSION: Our study showed for the first time the association between medial release and stiffness and stability of the knee ligament complex. To maintain stability, vigorous detachment of the knee ligament complex should be avoided. Release of the anteromedial tibial sleeve already initiates loss of stability. The main stabiliser is the medial ligament, which should never be completely detached. LEVEL OF EVIDENCE: IV.

The Role of the Tourniquet and Patella Position on the Compartmental Loads During Sensor-Assisted Total Knee Arthroplasty.

BACKGROUND: An inflated tourniquet may diminish the natural excursion of the extensor mechanism and alter compartmental loads, affecting the surgeon's ability to accurately assess ligament balance during total knee arthroplasty (TKA). In addition, patella position (reduced, lateralized, or everted) has also been known to affect compartmental loads. This study used intraoperative sensing to assess how a combination of tourniquet inflation and patella position may affect medial and lateral compartmental loads during sensor-assisted TKA. METHODS: Fifty-six patients (13 men) with a mean age of 66 years (standard deviation, 8.66) and mean BMI of 31 kg/m2 (standard deviation, 6.66) undergoing primary cemented TKA for primary osteoarthritis were enrolled. After final prosthetic implantation, with the tourniquet inflated, medial and lateral compartment loads were obtained in the 10°, 45°, and 90° of flexion with the patella in reduced, lateralized, or everted positions. The tourniquet was deflated and this process repeated. Surgeons were blinded to the values as to not influence medial and lateral stressing of the knee. Linear regression was used to evaluate absolute loads. RESULTS: Tourniquet inflation did not significantly alter compartmental loads regardless of knee flexion or patella position. Lateral compartment loads significantly increased as the patella moved from the reduced, to the lateralized, to the everted position with the tourniquet inflated or deflated. CONCLUSION: Tourniquet inflation did not significantly alter compartmental loads during sensor-assisted TKA. However, irrespective of tourniquet use, a lateralized or everted patellar position significantly increased lateral compartment loads.

Variability in Elongation and Failure of the Medial Collateral Ligament After Pie-Crusting With 16- and 18-Gauge Needles.

BACKGROUND: In knee arthroplasty with preoperative varus deformity, medial collateral ligament (MCL) release may be needed to achieve balance. Pie-crusting allows for controlled release, but questions remain regarding its ability to obtain predictable results. We compared 16- vs18-gauge needle punctures and determined the number of punctures required to (1) lengthen the MCL by 1 mm and (2) cause ligament failure. METHODS: Thirteen knees were dissected, leaving the femur and tibia with an isolated MCL, and randomly assigned to 16- or 18-gauge groups. Initial stiffness was assessed by cycling the ligament to 300 N for 5 cycles. The selected needle was used to make 10 punctures centered over the area of greatest tension. Cyclic testing was repeated after each set of punctures. Changes in MCL length and stiffness were measured. This process was repeated until failure. RESULTS: No differences occurred between the 16- and 18-gauge groups in cross-sectional area, initial stiffness, number of punctures to lengthen the MCL by 1 mm, or number of punctures to failure. As the number of punctures increased, a linear increase in elongation and decrease in stiffness occurred. CONCLUSION: Needle size was not the influencing factor. Variability in number of punctures, regardless of needle size, to elongate or fail the MCL shows the difficulty in developing a reproducible pie-crusting technique. This suggests that a standard number of punctures do not achieve controlled MCL lengthening for all patients, but that the number of punctures needed can be calculated for an individual knee based on the initial elongation after 10 punctures.

Second-Generation Electronic Ligament Balancing for Knee Arthroplasty: A Cadaver Study.

BACKGROUND: Knee instability is emerging as a major complication after total knee arthroplasty (TKA), with ligament laxity and component alignment listed as important contributory factors. Knee balancing remains an art and is largely dependent on the surgeon's subjective "feel." The objectives were to measure the accuracy of an electronic balancing device to document the magnitude of correction in knee balance after soft-tissue releases and measure change in knee laxity after medial release. METHODS: The accuracy of a second-generation electronic ligament-balancing device was compared with that of 2 mechanical balancing instruments. TKA was performed in 12 cadaver knees. Soft-tissue balance was measured sequentially before TKA, after mounting a trial femoral component, after medial release, and after resecting the posterior cruciate ligament. Coronal laxity of the knee under a 10 Nm valgus moment was measured before and after medial release. RESULTS: The electronic balancing instrument was more accurate than mechanical instruments in measuring distracted gap and distraction force. On average, before TKA, the flexion gap was wider than the extension gap, and the medial gap was tighter than the lateral gap. Medial release increased the medial gap in flexion and increased passive knee valgus laxity. Posterior cruciate ligament release increased the tibiofemoral gap in both flexion and extension with a greater increase in the lateral gap. CONCLUSION: The second-generation electronic balancing device was significantly more accurate than mechanical instruments and could record knee balance over the entire range of flexion. More accurate soft-tissue balance may enhance outcomes after TKA.

Intraoperative load-sensing drives the level of constraint in primary total knee arthroplasty: Surgical technique and review of the literature.

Total knee arthroplasty is a traditional surgical procedure aimed to restore function and relief pain in patients with severe knee osteoarthritis. Recently, many medial pivot knee systems were deigned to replicate the normal knee kinematic: a highly congruent medial compartment and a less conforming lateral tibial plateau characterize these devices. A slightly asymmetric soft tissue balancing is mandatory using medial pivot designs to obtain a correct and physiological knee biomechanics leading good outcomes and long survival rates. This article describes a new surgical technique using a modern third generation TKA design combined with wireless load-sensor tibial trials to improve the correct knee load balancing with a minimal conformity of the polyethylene insert. The use of wireless load-sensing tibial trials has several benefits: it is an intraoperative, objective and dynamic tool allowing surgeons to optimize in real time soft tissue balancing. The meaning of a "truly balanced knee" is still a controversial issue in the current literature.

Stability of knee ligament complex of Thiel-embalmed cadaver compared to in vivo knee.

BACKGROUND: The first biomechanical evaluation of new implants is usually carried out with cadavers. Fixation of Thiel-embalmed cadavers is supposed to preserve the histological structure, colour and consistency of the tissue and has a low risk of infection and toxicity. However, the biomechanical properties of Thiel-fixated tissue are still unknown. The aim of this study was to quantify the effect of the Thiel-embalming method on the elastic properties of the ligament complex of the knee compared to in vivo knees during total knee arthroplasty. METHODS: The results of biomechanical tensile tests with 10 Thiel-embalmed knees were compared with the findings of 10 patients who underwent total knee arthroplasty with a standardised knee balancer at our department. We reconstructed the force-elongation curves of the medial and lateral ligament complex and calculated the stiffness in direct correlation with overall soft tissue stability in full extension and in 90° of flexion. RESULTS: All curves consisted of a non-linear part at the beginning and a linear part from about 80N onwards. In full extension, median stiffness in the cadavers was 26.6N/mm for the medial compartment and 31.6N/mm for the lateral compartment. The values for in vivo were 25.7N/mm for the medial compartment and 25.3N/mm for the lateral compartment (p=0.684 for the medial compartment and p=0.247 for the lateral compartment). In 90° of flexion, median stiffness in the cadaver group was 24.7N/mm for the medial compartment and 22.2N/mm for the lateral compartment. In vivo, median stiffness was 30.3N/mm for the medial compartment and 29.2N/mm for the lateral compartment (p=0.009 for the medial compartment and p=0.143 for the lateral compartment). CONCLUSION: Stiffness of the medial and lateral ligament complex in the knee was comparable between Thiel-embalmed cadavers and in vivo patients during total knee arthroplasty. Thiel fixation seems to preserve the soft tissue properties similar to those in vivo.

A Targeted Approach to Ligament Balancing Using Kinetic Sensors.

BACKGROUND: Currently, soft-tissue imbalance contributes to several of the foremost reasons for revision following primary TKA, including instability, stiffness, and aseptic loosening. In order to decrease the incidence of soft-tissue imbalance, intraoperative sensors were developed to provide real-time, quantitative load data within the knee. This study examines the intraoperative data of a group of multicenter patients to determine how targeted ligament releases affect intra-articular loading, and to understand which types of releases are necessary to achieve quantified ligament balance. METHODS: A group of 129 patients received sensor-assisted TKA, as part of a multicenter study. Medial and lateral loading data were collected pre-release, during any sequential releases, and post-release. All data were collected at 10°, 45°, and 90° during range of motion testing. Ligament release type, release technique type, and resultant loading were collected. RESULTS: Loading across the joint decreased, overall, and became more symmetrical after releases were performed. On average, between 2 and 3 corrections were made (up to 8) in order to achieve ligament balance. The ligament release type and subsequent quantified change in loading were in agreement with historical, qualified sources. CONCLUSION: Objective data from sensor output may assist surgeons in decreasing loading variability and, thereby, decreasing ligament imbalance and its associated complications.

The Impact of Mechanical and Restricted Kinematic Alignment on Knee Anatomy in Total Knee Arthroplasty.

BACKGROUND: Total knee arthroplasty (TKA), aiming at neutral mechanical alignment (MA), inevitably modifies the patient's native knee anatomy. Another option is kinematic alignment (KA), which aims to restore the original anatomy of the knee. The aim of this study was to evaluate the variations in lower limb anatomy of a patient population scheduled for TKA, and to assess the use of a restricted KA TKA protocol and compare the resulting anatomic modifications with the standard MA technique. METHODS: A total of 4884 knee computed tomography scans were analyzed from a database of patients undergoing TKA with patient-specific instrumentation. The lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and hip-knee-ankle angle (HKA) were measured. Bone resections were compared using a standard MA and a restricted KA aiming for independent tibial and femoral cuts of maximum ±5° deviation from the coronal mechanical axis and a resulting overall coronal HKA within ±3° of neutral. RESULTS: The mean preoperative MPTA was 2.9° varus, LDFA was 2.7° valgus, and overall HKA was 0.1° varus. Using our protocol, 2475 knees (51%) could have undergone KA without adjustment. To include 4062 cases (83%), mean corrections of 0.5° for MPTA and 0.3° for LDFA were needed, significantly less than with MA (3.3° for MPTA and 3.2° for LDFA; P < .001). CONCLUSION: The range of knee anatomy in patients scheduled for TKA is wide. MA leads to greater modifications of knee joint anatomy. To avoid reproducing extreme anatomy, the proposed restricted KA protocol provides an interesting hybrid option between MA and true KA.

Algorithmic pie-crusting of the medial collateral ligament guided by sensing technology affects the use of constrained inserts during total knee arthroplasty.

BACKGROUND: Intra-operative sensing technology is an alternative to standard techniques in total knee arthroplasty (TKA) for determining balance by providing quantitative analysis of loads and point of contact throughout a range of motion. We used intra-operative sensing (VERASENSE-OrthoSensor, Inc.) to examine pie-crusting release of the medial collateral ligament in knees with varus deformity (study group) in comparison to a control group where balance was obtained using a classic release technique and assessed using laminar spreaders, spacer blocks, manual stress, and a ruler. METHODS: The surgery was performed by a single surgeon utilizing measured resection and posterior-stabilized, cemented implants. Seventy-five study TKAs were matched 1:3 with 225 control TKAs. Outcome variables included the use of a constrained insert, functional- and knee-specific Knee Society score (KSS) at six weeks, four months, and one year post-operatively. Outcomes were analyzed in a multivariate model controlling for age, sex, BMI, and severity of deformity. RESULTS: The use of a constrained insert was significantly lower in the study group (5.3 vs. 13.8%; p = 0.049). The use of increased constraint was not significant between groups with increasing deformity. There was no difference in functional KSS and knee-specific KSS between groups at any follow-up interval. CONCLUSION: An algorithmic pie-crusting technique guided by intra-operative sensing is associated with decreased use of constrained inserts in TKA patients with a pre-operative varus deformity. This may cause a positive shift in value and cost savings.

How does total knee replacement technique influence polyethylene wear?

In knee prostheses, wear is inherent to the tribology of the imperfectly congruent surfaces, one in chromium-cobalt alloy, the other in polyethylene. It is a multifactorial phenomenon, involving the properties of the respective materials and implant design, but also implant functioning, as determined by the implantation technique. There are still dark corners in the implantation charge book, especially concerning minimal insert thickness, the adjustment of tibiofemoral alignment and ligament balance. A review of the literature revealed consensus regarding minimal insert thickness (8mm), tibiofemoral alignment (to be kept within 5° on either side of the neutral axis) and ligament balance (identical collateral ligament tension in both extension and flexion spaces). Finer adjustment seems desirable. Tibiofemoral alignment is probably customizable according to individual patient morphology and weight. The rotational alignment of the components should allow harmonious patellar engagement. Classic ligament balance rules underestimate sagittal laxity, which needs checking to prevent paradoxical movement accelerating polymer delamination. Navigation techniques or specific ancillaries can help optimize implant component alignment. Control of sagittal laxity may require specific adaptation, notably in the flexion space. Improved implantation technique could postpone wear onset until beyond the 10th or even 20th postoperative year, barring material failure for other reasons.

What Preoperative Radiographic Parameters Are Associated With Increased Medial Release in Total Knee Arthroplasty?

BACKGROUND: Preoperative varus deformity of the knee is a common malalignment in patients undergoing primary total knee arthroplasty (TKA). We are unaware of any studies that have correlated how various preoperative radiographic parameters can predict the amount of medial releases performed to achieve optimal coronal alignment and ligamentous balance. METHODS: A retrospective review was performed on 67 patients who required at least a medial tibial reduction osteotomy (MTRO) during primary TKA to achieve coronal balance. This patient population was matched 1:1 to another cohort of TKA patients by age, gender, and body mass index who did not require an MTRO. A radiographic evaluation was used to compare the 2 cohorts. RESULTS: Preoperatively, the MTRO cohort was noted to have significantly increased varus tibiofemoral (86.12° vs 93.43°), tibial articular surface (85.79° vs 87.54°), and medial tibial articular surface angles (75.22° vs 85.34°) compared to the control cohort. The MTRO cohort had 3.13 mm of medial tibial offset and 9.06 mm of lateral joint space opening and the control cohort had 0.09 mm and 4.07 mm, respectively. The medial tibial articular surface angle and lateral joint space widening were statistically associated with the MTRO cohort. The final tibiofemoral angle in the MTRO cohort was 92.43° and was 93.40° in the control cohort. CONCLUSION: The MTRO cohort was noted to have several preoperative radiographic parameters that were significantly different than the control cohort. However, the medial tibial articular surface angle and lateral joint space widening were the only radiographic parameters that were statistically associated with requiring an MTRO.