Flexion Laxity Research Articles

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

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) andcruciate-retaining (CR) TKA on clinical outcomes. Data from 527 TKA in 478 patients from 2018 to 2020 werecollected. All patients underwent an RA (MAKO, Stryker), FA andCR 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. 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). The study shows that a loose lateral flexion gap in functionally aligned CR TKA does not adversely affect outcomes in the short term. Level III, retrospective cohort study.

Lateral Laxity in Flexion Influences Patient-Reported Outcome After Total Knee Arthroplasty

IntroductionSlight lateral laxity exists in normal knee especially in flexion. The lateral laxity in flexion has possibility to affect the outcome after total knee arthroplasty (TKA).PurposeThe purpose of this study was to determine how intraoperative laxity in flexion affects patient-reported outcome after total knee arthroplasty.MethodsWe retrospectively analysed 98 knees with osteoarthritis that underwent total knee arthroplasty. After bone resection, ligament imbalance and joint component gaps were measured using an offset-type tensor while applying a 40-lb joint distraction force at 0° and 90° of knee flexion. The lateral laxity in flexion was determined by subtracting polyethylene insert thickness from the lateral gap at 90°. All patients were divided into three groups: ≤ 2 mm (A), 2–5 mm (B), and > 5 mm (C). One year after surgery, patients were asked to fill out questionnaires using the new Knee Society Score after examination outside the consultation room.ResultsThe mean intraoperative lateral laxities at 90° were − 0.2 ± 2.1 mm, 3.5 ± 0.7 mm, and 6.7 ± 1.9 mm in groups A, B, and C, respectively. The symptom score of group C was significantly lower than those of groups A or B. There were no significant differences in terms of satisfaction or the expectation and activity scores among all groups. There were no significant differences in terms of alignment after total knee arthroplasty among all groups.ConclusionsExcessive lateral laxity possibly resulted in worse patient-reported outcomes. However, slight lateral laxity of 2–5 mm might have no effect on patient-reported outcome and this slight varus imbalance could be acceptable. Altogether, our findings would lead to avoidance of excessive medial release in soft tissue balancing.

Laxity, Balance, and Alignment of a Simulated Kinematic Alignment Total Knee Arthroplasty.

Kinematic alignment (KA) and related personalized alignment strategies in total knee arthroplasty (TKA) target restoration of native joint line obliquity and alignment. In practice, deviations from exact restoration of the prearthritic joint surface are tolerated for either the femur or tibia to achieve ligamentous balance. It remains unknown what laxity, balance, and alignment would result if a pure resurfacing of both femur and tibia were performed in a KA TKA technique. We used data from 382 robot-assisted TKA performed with a digital joint tensioner to simulate TKA with a pure resurfacing KA technique for both femur and tibia. All knees had the posterior cruciate ligament retained. Knees were subdivided into 4 groups based on preoperative coronal alignment: valgus, neutral, varus, and high varus. Medial and lateral laxity in extension and flexion, balance in extension and flexion, and coronal plane alignment were compared between groups using analysis of variance testing. In simulated pure resurfacing KA TKA across a range of preoperative coronal plane deformities, only 11%-31% of knees would have mediolateral extension ligament balance within ±1 mm, and 20%-41% would have a medial flexion gap that is looser than the lateral flexion gap. Over 45% of knees would have coronal hip-knee-ankle angle >3 degrees from mechanical neutral. In simulations of pure resurfacing KA TKA, there was wide variability in the resulting laxity and alignment outcomes. Most knees had alignment and balance outcomes outside of normally accepted ranges. Techniques that deviate from pure resurfacing in order to achieve balance appear favorable.

Evaluation of anterior translation in total knee arthroplasty utilizing stress radiographs

BackgroundFlexion instability is a common cause for revision after total knee arthroplasty (TKA); however, little objective criteria exist to determine excessive laxity in flexion. This study sought to determine the reliability of stress radiographs for flexion laxity using manual stress as well as a commercially available flexion stress device, with the hypothesis that a commercially available force device would provide increased translation compared to manual stress, and radiographic measurements would be reproducible.MethodsTen patients who previously underwent TKA with non-hinged components were prospectively and consecutively enrolled at a single center to undergo stress radiographs. Three lateral radiographs with the knee at 90° of flexion were obtained for each patient: rest, commercial stress device at 150N, and manual stress. Calibrated radiographs were evaluated by two raters, and inter-rater and intra-rater reliability were determined using intraclass correlation coefficients (ICC).ResultsTen patients (seven female) with mean age 72 (range 55–82) years and average duration from surgery 36 (range 12–96) months were evaluated. The commercial stress device provided significantly less anterior translation than manual stress (− 0.3 mm vs. 3.9 mm; p < 0.01). Two patients reported pain with use of the stress device. Inter-observer reliability of measurements was good for commercial stress (ICC = 0.86) and excellent for manual stress (ICC = 0.94). Eighty-five percent of measurements were within 1 mm between observers. Intra-observer reliability of measurements was good to excellent for both the stress device and manual stress.ConclusionsLateral stress radiographs may assist in the objective evaluation of flexion instability. A commercially available product provided less translation than manual stress; however, measurements were reliable and reproducible between observers. Further research is required to correlate translation with stress radiographs to patient outcomes following revision arthroplasty.

The effect of posterior tibial slope on anteroposterior stability in posterior cruciate retaining total knee arthroplasty

BackgroundIt has been suggested that the posterior tibial slope (PTS) plays an important role in increasing the anteroposterior stability following total knee arthroplasty. Although the relationship between the PTS and the flexion range has been investigated many times, studies on the relationship between PTS and anterior-posterior stability are limited. The primary aim of this study was to investigate the relationship and effects of PTS on anteroposterior stability in posterior cruciate retainer total knee arthroplasty.Methods154 primary TKAs were identified retrospectively to analyze the any association between PTS and anteroposterior laxity following posterior cruciate-retaining total knee arthroplasty in the overall study populations. Anteroposterior displacement was measured at the final follow-up based on the following two procedures: KT-1000 arthrometer and sagittal drawer radiographic images. In addition, the relationship between PTS and functional scores-ROM was examined.ResultsThere was no correlation between patients’ posterior tibial slope and postoperative VAS (r: -0.060, p:0.544), WOMAC (r:0.037, p:0.709), KSS (r: -0.073, p:0.455). In addition, there was no significant correlation between postoperative knee ROM and postoperative PTS (r:0.159, p:0.106). Moreover, no correlation was found between KT-1000 arthrometer and 20 degrees AP translation with PTS. There was a negative correlation between PTS and 70 degrees AP translation (r: -0.281, p:0.008).ConclusionsThis study aimed to clarify the association between instability and AP laxity in flexion of implanted knees, and to determine what degree of AP laxity results of instability. A fundamental finding of this study was that; the optimum TS angle to increase anterior-posterior stability after total knee arthroplasty is between ≥ 4 to < 6 degrees, we also proved that there is no relationship between stability and patient satisfaction.

Avoiding Lateral Laxity in Robotic Arm-Assisted Total Knee Arthroplasty-A Surgical Technique Describing a New Method of Gap Capture and Balancing Strategy.

Optimal flexion-extension gap balancing is an important factor in outcomes after total knee arthroplasty. Knees with varus deformities are commonly associated with a greater degree of lateral laxity both in extension and flexion. Residual lateral laxity could be encountered by surgeons during component trialling after robotic-assisted total knee arthroplasty (RATKA), necessitating additional medial soft tissue release for a thicker insert. This study describes a new technique of gap assessment during RATKA and we propose a functional alignment based balancing strategy to avoid residual lateral laxity. This surgical technique was prospectively employed in 105 patients undergoing primary MAKO® (Stryker, Kalamazoo, Michigan) RATKA for osteoarthritis of the knee with varus deformity, between January 2021 and July 2021. Patients included had an initial lateral extension laxity of more than 24mm. Surgical data points collected consisted of characterization of the laxity profile of the knee using the medial and lateral extension and flexion initial gap captures, final gap captures after dynamic balancing with a functional alignment strategy, and residual lateral extension gap laxity in millimeters at the end of implantation. The mean initial lateral extension gap was 25.76mm (standard deviation [SD]=1.47) and the mean lateral flexion gap was 24.4mm (SD=1.94). Balance was achieved in all the patients with a 9 or 11mm insert, with a mean residual lateral laxity of 0.51mm (SD=0.73, range 0-2mm). The majority of patients (n=66, 62.85%) had zero lateral laxity at the end of final implantation while 24 patients (22.8%) had 1mm of residual lateral laxity. Residual lateral joint laxity can be avoided consistently and predictably in RATKA cases with initial gap capture of up to 30mm in lateral extension and flexion with this new technique of gap capture and employing various steps of balancing strategy described.

PREOPERATIVE MEDIAL LAXITY IN MIDFLEXION AND FLEXION CORRELATES WITH POORER KOOS-12 FUNCTION SCORES PRIOR TO TKA

Preoperative ligament laxity can be characterized intraoperatively using digital robotic tensioners. Understanding how preoperative knee joint laxity affects preoperative and early post-operative patient reported outcomes (PROMs) may aid surgeons in tailoring intra-operative balance and laxity to optimize outcomes for specific patients.This study aims to determine if preoperative ligament laxity is associated with PROMs, and if laxity thresholds impact PROMs during early post-operative recovery.106 patients were retrospectively reviewed. BMI was 31±7kg/m2. Mean age was 67±8 years. 69% were female. Medial and lateral knee joint laxity was measured intraoperatively using a digital robotic ligament tensioning device after a preliminary tibial resection.Linear regressions between laxity and KOOS12-function were performed in extension (10°), midflexion (45°), and flexion (90°) at preoperative, 6-week, and 3-month time points. Patients were separated into two laxity groups: ≥7 mm laxity and &lt;7 mm laxity. Student's t-tests determined significant differences between laxity groups for KOOS12-function scores at all time points.Correlations were found between preoperative KOOS12-function and medial laxity in midflexion (p&lt;0.001) and flexion (p&lt;0.01). Patients with &lt;7 mm of medial laxity had greater preoperative KOOS12-function scores compared to patients with ≥7 mm of medial laxity in extension (46.8±18.2 vs. 29.5±15.6, p&lt;0.05), midflexion (48.4±17.8 vs. 32±16.1, p&lt;0.001), and flexion (47.7±18.3 vs. 32.6±14.7, p&lt;0.01). No differences in KOOS12-function scores were observed between medial laxity groups at 6-weeks or 3-months. All knees had &lt;5 mm of medial laxity postoperatively. No correlations were found between lateral laxity and KOOS12-function.Patients with preoperative medial laxity ≥7 mm had lower preoperative PROMs scores compared to patients with &lt;7 mm of medial laxity. No differences in PROMs were observed between laxity groups at 6 weeks or 3 months. Patients with excessive preoperative joint laxity achieve similar PROMs scores to those without excessive laxity after undergoing gap balancing TKA.

Functional Alignment Philosophy in Total Knee Arthroplasty—Rationale and Technique for the Valgus Morphotype Using an Image Based Robotic Platform and Individualized Planning

Functional alignment (FA) is a novel philosophy to deliver a total knee arthroplasty (TKA) that respects individual bony and soft tissue phenotypes within defined limitations. The purpose of this paper is to describe the rationale and technique of FA in the valgus morphotype with the use of an image-based robotic-platform. For the valgus phenotype the principles are personalized pre-operative planning, reconstitution of native coronal alignment without residual varus or valgus of more than 3°, restoration of dynamic sagittal alignment within 5° of neutral, implant sizing to match anatomy, and achievement of defined soft tissue laxity in extension and flexion through implant manipulation within the defined boundaries. An individualized plan is created from pre-operative imaging. Next, a reproducible and quantifiable assessment of soft tissue laxity is performed in extension and flexion. Implant positioning is then manipulated in all three planes if necessary to achieve target gap measurements and a final limb position within a defined coronal and sagittal range. FA is a novel TKA technique that aims to restore constitutional bony alignment and balance the laxity of the soft tissues by placing and sizing implants in a manner that respects variations in individual anatomy and soft tissues within defined limits.

Potential for femoral size optimization for off-the-shelf implants: A CT derived implant database analysis.

In total knee arthroplasty, the femoral implant size is chosen mainly based on the femoral anteroposterior (AP) height and mediolateral (ML) width. This choice often is a compromise, due to limited size availability. Inadequate AP fit is expected to alter flexion laxity and thus knee function. Inadequate ML fit entails underhang or overhang, which is linked to worse clinical outcomes. Hence, we aimed to find implant size distributions, which maximize population coverage, and to evaluate the sensitivity regarding error bounds and the number of implant sizes for a database of 85,143 cases. All patients in the database have been provided with a patient-specific implant in the past. For a subset of 1049 cases, three-dimensional preoperative bone surface models were available. These were used to validate whether the implant dimensions were representative of the bone dimensions. Particle Swarm Optimization was used for optimizing the implant size distribution. The deviations between implant and bone measures in the subset were found to be clinically irrelevant. Therefore, the full database of 85,143 cases was used for further analyses. A higher sensitivity of the population coverage regarding the error bounds compared to the number of implant sizes was found. For an exemplary setup of 12 optimized implant sizes and error bounds of ±1.5 mm for AP and ±3 mm for ML, a population coverage of almost 85% was achieved. In contrast, even with 30 implant sizes, a full population coverage could not be reached. Hence, remaining cases should be provided with patient-specific implants.

Association of a Wider Medial Gap (Medial Laxity) in Flexion with Self-Reported Knee Instability After Medial-Pivot Total Knee Arthroplasty

Background: Medial-pivot total knee arthroplasty (TKA) is designed with high articular conformity in the medial compartment in order to achieve stability. The subjective outcome of patients has been reported to be good postoperatively; however, the association between the objective and subjective knee stability and the influence of subjective stability on the overall outcomes of TKA remained unknown. Our hypothesis was that postoperative flexion joint-gap imbalance could affect subjective knee instability following TKA in medial-pivot prostheses. The purpose of this study was to analyze the association between the joint gap in flexion and subjective knee instability and between subjective knee instability and outcomes following medial-pivot TKA. Methods: A total of 769 patients who underwent primary TKA with use of medial-pivot prostheses were enrolled. Clinical outcomes included knee range of motion, Knee Society Score-2011 (KSS-2011), Forgotten Joint Score-12 (FJS-12), patient-reported subjective knee instability, and axial knee radiography to assess flexion joint-gap balance measured at the final follow-up. Clinical outcomes were compared between patients with and without subjective knee instability. Moreover, associated factors were analyzed for postoperative subjective knee instability. Results: Overall, 177 patients (23%) reported experiencing postoperative subjective knee instability. Knee flexion (p = 0.04); KSS-2011 symptom (p&lt;0.001), satisfaction (p&lt;0.001), expectation (p=0.008), and activity (p&lt;0.001) subscales; and FJS-12 (p &lt; 0.001) were significantly worse in patients with subjective knee instability. The KSS-2011 subjective score differences were greater than the minimal clinically important difference. Older age at the time of surgery (odds ratio, 1.04; p = 0.04) and a wider postoperative joint gap in flexion on the medial side (odds ratio, 1.21; p = 0.001) were significant risk factors for subjective knee instability. A gap angle of −2.9° (i.e., medial laxity) was the threshold to predict postoperative knee instability (sensitivity, 0.29; specificity, 0.91). Conclusions: Postoperative flexion joint-gap laxity on the medial side following medial-pivot TKA affected the patient-reported subjective knee instability scores. Postoperative KSS-2011 subjective scores following medial-pivot TKA were poorer in patients with subjective knee instability. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Inter-Rater Reliability of Clinical Testing for Laxity After Knee Arthroplasty

BackgroundThe clinical examination for laxity has been considered a mainstay in evaluation of the painful knee arthroplasty, especially for the diagnosis of instability. More than 10 mm of anterior-posterior (AP) translation in flexion has been described as important in the diagnosis of flexion instability. The inter-observer reliability of varus/valgus and AP laxity testing has not been tested. MethodsTen subjects with prior to total knee arthroplasty (TKA) were examined by 4 fellowship-trained orthopedic knee arthroplasty surgeons. Each surgeon evaluated each subject in random order and was blinded to the results of the other surgeons. Each surgeon performed an anterior drawer test at 30 and 90 degrees of flexion and graded the instability as 0-5 mm, 5-10 mm or >10 mm. Varus-valgus testing was also graded. Motion capture was used during the examination to determine the joint position and estimate joint reaction force during the examination. ResultsInter-rater reliability (IRR) was poor at 30 and 90 degrees for both the subjective rater score and the measured AP laxity in flexion (k = 018-0.22). Varus-valgus testing similarly had poor reliability. Force applied by the rater also had poor IRR. ConclusionClinical testing of knee laxity after TKA has poor reliability between surgeons using motion analysis. It is unclear if this is from differences in examiner technique or from differences in pain or quadriceps function of the subjects. Instability after TKA should not be diagnosed strictly by clinical testing and should involve a complete clinical assessment of the patient.

Impact of intra-operative predictive ligament balance on post-operative balance and patient outcome in TKA: a prospective multicenter study.

New technologies exist which may assist surgeons to better predict final intra-operative joint balance. Our objectives were to compare the impact of (1) a predictive digital joint tensioning tool on intra-operative joint balance; and (2) joint balance and flexion joint laxity on patient-reported outcomes. Two-hundred Eighty patients received posterior cruciate ligament sacrificing TKA with ultra-congruent tibial inserts using a robotic-assisted navigation platform. Patients were divided into those in which a Predictive Plan with a digital joint-tensioning device was used (PP) and those in which it was not (NPP), in all cases final post-operative joint gaps were collected immediately before final implantation. Demographics and KOOS were collected pre-operatively. KOOS, complications and satisfaction were collected at 3, 6 and 12months post-operatively. Optimal balance difference between PP and NPP was defined and compared using area-under-the-curve analysis (AUC). Outcomes were then compared according to the results from the AUC. AUC analysis yielded a balance threshold of 1.5mm, in which the PP group achieved a higher rate of balance throughout flexion compared to the NPP group: extension: 83 vs 52%; Midflexion: 82 vs 55%; Flexion 89 vs 68%; Flexion to Extension 80 vs 49%; p ≤ 0.003. Higher KOOS scores were observed in knees balanced within 1.5mm across all sub-scores at various time points, however, differences did not exceed the minimum clinically important difference (MCID). Patients with > 1.5mm flexion laxity medially or laterally had an increased likelihood of 2.2 (1.1-4.4) and 2.5 (1.3-4.8), respectively, for failing to achieve the Patient Acceptable Symptom State for KOOS Pain at 12months. Patient satisfaction was high in both the PP and NPP groups (97.4 and 94.7%, respectively). Use of a predictive joint tensioning tool improved the final balance in TKA. Improved outcomes were found in balanced knees; however, this improvement did not achieve the MCID, suggesting further studies may be required to define optimal balance targets. Limiting medial and lateral flexion laxity resulted in an increased likelihood of achieving the Patient Acceptable Symptom State for KOOS Pain.

Satisfactory mid- to long-term outcomes of TKA aligned using conventional instrumentation for flexion gap balancing with minimal soft tissue release.

To describe a technique for flexion gap management in total knee arthroplasty (TKA) using conventional instrumentation with minimal soft tissue release, by aligning the femoral component to restore close-to-native posterior condylar angle (PCA). The hypothesis was that this technique renders consistent outcomes, regardless the preoperative deformity or intraoperative parameters. In a consecutive series of 152 TKAs, the femoral component was rotated to restore anatomic PCA of 2° ± 2° and the flexion gap was balanced with a final lateral flexion laxity of 1-3mm. Patients were assessed using the Knee Society Score (KSS), the Oxford Knee Score (OKS) and University of California Los Angeles (UCLA) activity score at a minimum follow-up of 4years. Uni- and multivariable analyses were performed to determine associations between clinical scores and patient demographics, PCA, laxity, pre- and postoperative hip-knee-ankle (HKA) angle, and preoperative femoral mechanical angle (FMA) and tibial mechanical angle (TMA). Intraoperative measurements indicated a target PCA of 2.9° ± 1.0° (range 0°-6°) with a final lateral flexion laxity of 1.5 ± 0.6mm (range 0-3). The target PCA was achieved in 145 knees (95%) and the desired final lateral flexion laxity was achieved in 151 knees (99.3%). There were no significant differences in postoperative clinical outcomes between knees within the target PCA range and outliers. KSS function decreased with age and preoperative HKA angle, and was lower for women, while KSS satisfaction improved with follow-up. OKS increased with target PCA and follow-up, decreased with preoperative TMA, was lower for women and better for knees with resurfaced patellae. UCLA activity decreased with age, preoperative HKA angle and BMI, and was lower for women. In this consecutive series of 152 TKAs performed with minimal ligament release, the target PCA and final lateral flexion laxity were simultaneously achieved in 95% of knees. At a minimum follow-up of 4years, adequate clinical scores and patient satisfaction were achieved, even in knees outside the target PCA range. IV.

Functional Flexion Instability After Rotating-Platform Total Knee Arthroplasty.

We sought to define "at risk" loading conditions associated with rotating-platform total knee arthroplasty (TKA-RP) implants that predispose to insert subluxation and spinout and to quantify tolerances for flexion-extension gap asymmetry and laxity in order to prevent these adverse events. Biomechanical testing was performed on 6 fresh-frozen cadaveric limbs with a TKA-RP implant with use of a gap-balancing technique, followed by sequential femoral component revision with variable-thickness polyethylene inserts to systematically represent 5 flexion-extension mismatch and asymmetry conditions. Each configuration was subjected to mechanical loading at 0°, 30°, and 60°. Rotational displacement of the insert on the tibial baseplate, lateral compartment separation, and insert concavity depth were measured with use of a digital caliper. Yield torque, a surrogate for ease of insert rotation and escape of the femoral component, was calculated with use of custom MATLAB code. Design-intended insert rotation decreased with increasing knee flexion angles in each loading configuration. Likewise, yield torque increased with increasing joint flexion and decreased with increasing joint laxity in all testing configurations. Insert instability and femoral condyle displacement were reproduced in positions of increasing knee flexion and asymmetrical flexion gap laxity. The depth of lateral polyethylene insert concavity determined femoral condylar capture and defined a narrow tolerance of <2 mm in the smallest implant sizes for flexion gap asymmetry leading to rotational insert instability. Decreased femoral-tibial articular surface conformity with increasing knee flexion and asymmetrical flexion gap laxity enable paradoxical motion of the femoral component on the upper insert surface rather than the undersurface, as designed. Mobile-bearing TKA-RP is a technically demanding procedure requiring a snug symmetrical flexion gap. As little as 2 mm of asymmetrical lateral flexion laxity can result in decreased conformity, condyle liftoff, and insert subluxation. Flexion beyond 30° decreases bearing surface contact area and predisposes to reduced insert rotation and mechanical malfunction.

The effect of anterior cruciate ligament resection on knee biomechanics.

The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA). This prospective study included 140 patients with symptomatic knee osteoarthritis undergoing primary robotic-arm assisted TKA. All operative procedures were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess study outcomes pre- and post-ACL resection with knee extension and 90° knee flexion. This study included 76 males (54.3%) and 64 females (45.7%) with a mean age of 64.1 years (SD 6.8) at time of surgery. Mean preoperative hip-knee-ankle deformity was 6.1° varus (SD 4.6° varus). ACL resection increased the mean extension gap significantly more than the flexion gap in the medial (mean 1.2 mm (SD 1.0) versus mean 0.2 mm (SD 0.7) respectively; p < 0.001) and lateral (mean 1.1 mm (SD 0.9) versus mean 0.2 mm (SD 0.6) respectively; p < 0.001) compartments. The mean gap differences following ACL resection did not create any significant mediolateral soft tissue laxity in extension (gap difference: mean 0.1 mm (SD 2.4); p = 0.89) or flexion (gap difference: mean 0.2 mm (SD 3.1); p = 0.40). ACL resection did not significantly affect maximum knee extension (change in maximum knee extension = mean 0.2° (SD 0.7°); p = 0.23) or fixed flexion deformity (mean 4.2° (SD 3.2°) pre-ACL release versus mean 3.9° (SD 3.7°) post-ACL release; p = 0.61). ACL resection did not significantly affect overall limb alignment (change in alignment = mean 0.2° valgus (SD 1.0° valgus; p = 0.11). ACL resection creates flexion-extension mismatch by increasing the extension gap more than the flexion gap. However, gap differences following ACL resection do not create any mediolateral soft tissue laxity in extension or flexion. ACL resection does not affect maximum knee extension or overall limb alignment. Cite this article: Bone Joint J 2020;102-B(4):442-448.

Retrieval Analysis of Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty and Correlations to Laxity and Wear

BackgroundTotal knee arthroplasty (TKA) with posterior-stabilized (PS) or posterior cruciate-retaining (CR) implants has high success rates and survivorship. However, it is uncertain how laxity and constraint are associated with long-term polyethylene wear under physiological conditions. MethodsTo answer this question, we measured the laxity patterns of 47 harvested cadaver specimens with primary TKAs in a custom knee-testing machine at full extension and at 30°, 60°, and 90° of flexion. The wear patterns of the tibial inserts were assessed using a semiquantitative method which is a modified approach of that proposed by Hood et al in 1983. ResultsStatistical analysis found that the PS TKA cohort had a statistically significant increase in varus laxity at 60° and 90° of flexion, as well as total coronal laxity at 60° of flexion when compared to the CR cohort. Furthermore, analysis demonstrated a significant correlation between increased PS coronal laxity and increased tibial wear, a trend that was not seen in the CR specimens. ConclusionOur findings suggest that greater laxity in flexion after primary TKA may increase the wear realized over time and that PS TKAs may be more susceptible due to the loss of support the PCL affords to the flexion space. Whether a CR or PS TKA is used, surgeons need to avoid the pitfalls that may create greater flexion laxity during the procedure to optimize long-term polyethylene wear.

Intraoperative physiological lateral laxity in extension and flexion for varus knees did not affect short-term clinical outcomes and patient satisfaction.

Medial release during total knee arthroplasty (TKA) is used to correct ligament imbalance in knees with varus deformity. However, questions remain on whether residual ligament imbalance would be related to inferior clinical results. The purposes of the present study were to measure the intraoperative joint gap and to evaluate the effect of intraoperative soft tissue condition on the new Knee Society Score (KSS 2011) at 2-year follow-up, without the maneuver of additional medial release to correct the asymmetrical gap balance. Varus-valgus gap angle and joint gap were measured using a tensor device without medial release for 100 knees with preoperative varus deformity. The knees were categorized according to the varus-valgus gap angle and the laxity. The preoperative and postoperative clinical outcomes using KSS 2011 were compared between the groups. The average varus-valgus angles had a residual imbalance of 2.8° varus and 1.3° varus in extension and flexion, respectively. In comparison, according to varus-valgus joint gap angle and knee laxity in extension and flexion, no significant differences were found in postoperative range of motion and subscale of KSS 2011 among the groups. Intraoperative asymmetrical joint gap and physiological laxity do not affect early clinical results after TKA. III.

Difficult primary total knee arthroplasty in varus knees - A case series study

Introduction: Common indications for total knee arthroplasty (TKA) underwent in our hospital were severe grade osteoarthritis of the knee. The etiological factors are idiopathic, post-traumatic injury sequel, postinflammatory sequel, and metabolic conditions like gout and pseudogout. The risk factors include obesity, intraarticular fractures, and meniscal injuries. Materials and Methods: Study participants: A total of 12 cases were analyzed. Three of them were male and 9 were female. Four of them underwent cruciate-retaining and 8 cruciate sacrificing procedures. Discussion: The stability of the knee is a complex issue. The deformity and osteophytes affect the ligaments unequally because of different degrees of tightness or laxity in flexion and extension. We found that the most common difficulty arises in primary TKA was due to the medial tibial bony defect. The defects were secured with a graft fixed to the medial tibial condyle with or without utilizing screws. Physiotherapy was started from the next postoperative day onward. Conclusion: The TKA posed three challenges (1) Instability (2) Difficulty in soft-tissue balancing (3) The longevity of tibial tray. These three challenges were overcome by building the defect using bone graft.

Posterior cruciate ligament resection in total knee arthroplasty: the effect on flexion-extension gaps, mediolateral laxity, and fixed flexion deformity.

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA). This prospective study included 110 patients with symptomatic osteoarthritis of the knee undergoing primary robot-assisted PS TKA. All operations were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess gaps before and after PCL resection in extension and 90° knee flexion. Measurements were made after excision of the anterior cruciate ligament and prior to bone resection. There were 54 men (49.1%) and 56 women (50.9%) with a mean age of 68 years (sd 6.2) at the time of surgery. The mean preoperative hip-knee-ankle deformity was 4.1° varus (sd 3.4). PCL resection increased the mean flexion gap significantly more than the extension gap in the medial (2.4 mm (sd 1.5) vs 1.3 mm (sd 1.0); p < 0.001) and lateral (3.3 mm (sd 1.6) vs 1.2 mm (sd 0.9); p < 0.01) compartments. The mean gap differences after PCL resection created significant mediolateral laxity in flexion (gap difference: 1.1 mm (sd 2.5); p < 0.001) but not in extension (gap difference: 0.1 mm (sd 2.1); p = 0.51). PCL resection significantly improved the mean FFD (6.3° (sd 4.4) preoperatively vs 3.1° (sd 1.5) postoperatively; p < 0.001). There was a strong positive correlation between the preoperative FFD and change in FFD following PCL resection (Pearson's correlation coefficient = 0.81; p < 0.001). PCL resection did not significantly affect limb alignment (mean change in alignment: 0.2° valgus (sd 1.2); p = 0.60). PCL resection creates flexion-extension mismatch by increasing the flexion gap more than the extension gap. The increase in the lateral flexion gap is greater than the increase in the medial flexion gap, which creates mediolateral laxity in flexion. Improvements in FFD following PCL resection are dependent on the degree of deformity before PCL resection. Cite this article: Bone Joint J 2019;101-B:1230-1237.

The Effect of Femoral Cutting Jig Design on Restoration of Femoral Offset in Posterior-Referenced Total Knee Arthroplasty.

Femoral component sizing and rotation in total knee arthroplasty (TKA) affects patellofemoral tracking and tibiofemoral mechanics. Posterior referencing is said to optimize restoration of posterior condylar offset. However, it typically allows the surgeon to select 3° to 5° of external rotation to the posterior condylar axis, inevitably changing the offset of one or both condyles. The axis about which external rotation occurs varies between the jigs of various TKA systems. The location of this axis can result in a medial, central, or lateral reference point for posterior offset restoration. Variations in jig design will result in varying posterior offset changes at the same jig setting, with differential effects on balance between the flexion and extension gaps. Using identical Sawbones in a controlled laboratory setting, 9 TKA instrumentation systems were examined. Two systems referenced medially, 1 referenced laterally, and 6 referenced centrally. The authors measured distal and posterior resections in both 3° and 5° of external rotation to the posterior condylar axis. They calculated changes in both distal and posterior joint lines using resection measurements and implant specifications. Posterior resection thicknesses were greatest with instruments that referenced laterally and least with instruments that referenced medially. With increasing external rotation, instruments that referenced off the lateral femoral condyle introduced the greatest mismatch between the distal and posterior joint lines, as compared with instruments that referenced centrally or medially. Surgeons should be aware that laterally referencing systems can differentially restore distal and posterior joint lines at higher settings of femoral external rotation, potentially introducing incongruity between flexion and extension gaps if the posterior slope of the tibia is maintained. This may be particularly problematic if flexion laxity is increased by posterior cruciate ligament sacrifice. [Orthopedics. 2019; 42(6):316-322.].