Mid-range Flexion Research Articles

Assessment of the Acute Effects of Wearable Sensor Derived Auditory Biofeedback on Gross Lumbar Proprioception

Lower back disorders (LBDs) affect a large proportion of the population, and treatment for LBDs have been shifting toward individualized, patient-centered approaches. LBDs are typically associated with poor proprioception. Therefore, there has been a recent uptake in the utilization of wearable sensors that can administer biofeedback in various industrial, clinical, and performance-based settings to improve lumbar proprioception. The aim of this study was to investigate whether wearable sensor-derived acute auditory biofeedback can be used to improve measures of gross lumbar proprioception. To assess this, healthy participants completed an active target repositioning protocol, followed by a training period where lumbar-spine posture referenced auditory feedback was provided for select targets. Target re-matching abilities were captured before and after acute auditory biofeedback training to extract measures related to accuracy and precision across spine flexion targets (i.e., 20%, 40%, 60%, 80% maximum). Results suggest a heterogenous response to proprioceptive training whereby certain individuals and spine flexion targets experienced positive effects (i.e., improved accuracy and precision). Specifically, results suggest that mid-range flexion targets (i.e., 40-60% maximum flexion) benefited most from the acute auditory feedback training. Further, individuals with poorer repositioning abilities in the pre-training assessment showed the greatest improvements from the auditory feedback training.

Tibiofemoral articulation and axial tibial rotation of the knee after a cruciate retaining total knee arthroplasty

PurposeNumerous research has reported that total knee arthroplasty (TKA) cannot reproduce axial tibial rotations of normal knees. The objective of this study was to measure the tibiofemoral articular contact motions and axial tibial rotations of TKA knees to investigate the mechanism causing the knee kinematics change of after TKAs.MethodsEleven patients with unilateral cruciate retaining (CR) TKA were tested for measurements of knee motion during a weight-bearing flexion from 0° to 105° using an imaging technique. The tibiofemoral contact kinematics were determined using the contact points on medial and lateral surfaces of the tibia and femoral condyles. Axial tibial rotations were calculated using the differences between the medial and lateral articulation distances on the femoral condyles and tibial surfaces at each flexion interval of 15°.ResultsOn femoral condyles, articular contact distances are consistently longer on the medial than on the lateral sides (p < 0.05) up to 60° of flexion, corresponding to internal tibial rotations (e.g., 1.3° ± 1.0° at 15–30° interval). On tibial surfaces, the articular contact point on the medial side moved more posteriorly than on the lateral side at low flexion angles, corresponding to external tibial rotations (e.g., −1.4° ± 1.8° at 15–30° interval); and more anteriorly than on the lateral sides at mid-range flexion, corresponding to internal tibial rotations (e.g., 0.8° ± 1.7° at 45–60° interval). At higher flexion, articular motions on both femoral condyles and tibial surfaces caused minimal changes in tibial rotations.ConclusionsThese results indicate that the axial tibial rotations of these TKA knees were mainly attributed to asymmetric articulations on the medial and lateral femoral condyles and tibial surfaces. The data can help understand the mechanisms causing axial tibial rotations of TKA knees and help improve implant designs for restoration of normal knee kinematics.

Medial-pivot total knee arthroplasty enhances tibiofemoral axial rotation stability in weight-bearing mid-range flexion compared to posterior-stabilised system.

Total knee arthroplasty (TKA) stands as a primary intervention for severe knee ailments, yet concerns remain regarding postoperative patient satisfaction and flexion instability. This study aims to evaluate the in-vivo kinematics of medial-pivot (MP) and posterior-stabilised (PS) designs during step-up activity, in comparison to the kinematics of the nonoperated contralateral knee. Sixteen patients with PS-TKA and 14 with MP-TKA were retrospectively examined. Clinical outcomes were assessed using patient-completed questionnaires. Motion during step-up was captured using a dual fluoroscopic system. Statistical analysis was applied to evaluate the in-vivo tibiofemoral six-degree-of-freedom kinematics and articular contact positions between the two groups. Despite being older, patients in the MP group reported higher postoperative subjective scores for weight-bearing functional activities. The axial rotation centres of MP-TKA located on the medial tibial plateau exhibited less variance compared to PS-TKA and contralateral knees. Compared to the contralateral knee (contralateral to medial-pivot [C-MP] or contralateral to posterior-stabilised [C-PS]), the MP group exhibited limited range of motion in terms of anteroposterior translation (MP: 3.6 ± 1.3 mm vs. C-MP: 7.4 ± 2.5 mm, p < 0.01) and axial rotation (MP: 6.6 ± 1.9° vs. C-MP: 10.3 ± 4.9°, p = 0.02), as well as in the PS group for anteroposterior translation (PS: 3.9 ± 1.7 mm vs. C-PS: 7.2 ± 3.7 mm, p < 0.01). The MP group with better postoperative ratings demonstrated a more stable MP axial rotation pattern during step-up activity compared to the PS group, underscoring the pivotal role of prosthetic design in optimising postoperative rehabilitation and functional recovery. Level III.

Medial Soft Tissue-Preserving Technique Impact on Sagittal Stability in Bi-cruciate Stabilized Total Knee Arthroplasty.

Sagittal stability in total knee arthroplasty is achieved through complex processes enabled by prosthetic design and intraoperative soft tissue balancing. This study investigated the effects of preserving medial soft tissue on sagittal stability in bicruciate stabilized total knee arthroplasty (BCS TKA). This retrospective study included 110 patients who underwent primary BCS TKA. The patients were divided into two groups: 44 TKAs were performed releasing medial soft tissue (CON group), and 66 TKAs were performed preserving medial soft tissue (MP group). We assessed joint laxity using tensor device and anteroposterior translation immediately after surgery using the arthrometer at 30° knee flexion. Propensity score matching (PSM) was performed according to preoperative demographic and intraoperative medial joint laxity, and further comparisons between the two groups were performed. After PSM analysis, medial joint laxity in the mid-flexion range tended to be smaller in the MP group than in the CONT group, with a significant difference at 60 degrees (CON group: - 0.2 ± 0.9mm, MP group: 0.8 ± 1.3mm, P < 0.05). Anteroposterior translation was significantly different between the two cohorts (CON group: 11.6 ± 2.5mm, MP group: 8.0 ± 3.1mm, P < 0.001). This study demonstrated the effects of preserving medial soft tissue on postoperative sagittal stability in BCS TKA. We concluded that this surgical procedure enhances postoperative sagittal stability in the mid-flexion range in BCS TKA.

Excessive flexed position of the femoral component causes abnormal kinematics and joint contact/ ligament forces in total knee arthroplasty

Poor clinical outcomes are reported in excessive flexion of the femoral component in total knee arthroplasty (TKA), but their mechanisms have not yet been elucidated. This study aimed to investigate the biomechanical effect of flexion of the femoral component. Cruciate-substituting (CS) and posterior-stabilised (PS) TKA were reproduced in a computer simulation. The femoral component was then flexed from 0° to 10° with anterior reference, keeping the implant size and the extension gap. Knee kinematics, joint contact, and ligament forces were evaluated in deep-knee-bend activity. When the femoral component was flexed 10° in CS TKA, paradoxical anterior translation of the medial compartment was observed at mid-flexion. The PS implant was best stabilised with a 4° flexion model in mid-flexion range. The medial compartment contact force and the medial collateral ligament (MCL) force increased with the flexion of the implant. There were no remarkable changes in the patellofemoral contact force or quadriceps in either implant. In conclusions, excessive flexion of the femoral component yielded abnormal kinematics and contact/ligament forces. Avoiding excessive flexion and maintaining mild flexion of the femoral component would provide better kinematics and biomechanical effects in CS and PS TKA.

Medial stability and lateral flexibility of the collateral ligaments during mid-range flexion in medial-pivot total knee arthroplasty patients demonstrates favorable postoperative outcomes.

The objectives of the present study were to investigate the length change in different bundles of the superficial medial collateral ligament (sMCL) and lateral collateral ligament (LCL) during lunge, and to evaluate their association with Knee Society Score (KSS) following medial-pivot total knee arthroplasty (MP-TKA). Patients with unilateral MP-TKA knees performed a bilateral single-leg lunge under dual fluoroscopy surveillance to determine the in-vivo six degrees-of-freedom knee kinematics. The contralateral non-operated knees were used as the control group. The attachment sites of the sMCL and LCL were marked to calculate the 3D wrapping length. The sMCL and LCL were divided into anterior, intermediate, and posterior portions (aMCL, iMCL, pMCL, aLCL, iLCL, pLCL). Correlations between lengths/elongation rate of ligament bundles from full extension to 100° flexion and the KSS were examined. The sMCL and LCL demonstrated relative stability in length at low flexion, but sMCL length decreased whereas LCL increased with further flexion on operated knees. The sMCL length increased at low flexion and remained stable with further flexion, while the LCL length decreased with flexion on the contralateral non-operated knees. The lengths of aMCL, iMCL, and pMCL showed moderate (0.5 < r < 0.7, p < 0.05) negative correlations with the KSS, and the lengths of aLCL, iLCL, and pLCL were positively correlated with the KSS at mid flexion on operated knees (p < 0.05). The elongation rates of aLCL, iLCL, and pLCL were negatively correlated with the KSS at high flexion on operated knees (p < 0.05). However, no significant correlations between the length of different bundles of sMCL or LCL with KSS were found on contralateral non-operated knees. The elongation pattern of sMCL/LCL on MP-TKA knees showed differences with contralateral non-operated knees. The sMCL is tense at low to middle flexion and relaxed at high flexion, while LCL is relaxed at low to middle flexion and tense at high flexion following MP-TKA. Medial stability and proper lateral flexibility during mid flexion were associated with favorable postoperative outcomes in MP-TKA patients. In contrast, lateral relaxation at deep flexion should be avoided when applying soft-tissue balancing in MP-TKA. Level III.

Difference in implant design affects midflexion rotational laxity in cruciate-retaining total knee arthroplasty: a computer navigation study

PurposeThis study aimed to compare midflexion rotational laxity between two different design concept models of cruciate-retaining total knee arthroplasty: symmetrical surface design of neutral joint line obliquity and asymmetrical surface design of varus joint line obliquity.MethodsSixty-three knees that underwent cruciate-retaining total knee arthroplasty were evaluated. Manual maximum passive rotational stress without acceleration was applied to the knees under navigation monitoring. Pre-operative and post-operative internal and external rotational angles were measured at 30°, 45°, 60°, and 90° knee flexion.ResultsThe post-operative internal rotational laxity was significantly increased compared with pre-operative levels at 30°, 45°, 60°, and 90° flexion among all subjects (mean 9.7° vs 11.1°, 10.6° vs 11.6°, 11.2° vs 12.9°, and 13.2° vs 14.9°; p = 0.01, 0.04, 0.001, and 0.008, respectively). The post-operative external rotational laxity was significantly decreased compared to pre-operative levels at 30°, 45°, 60°, and 90° flexion among all subjects (mean 10.8° vs 6.8°, 12.5° vs 9.4°, 12.8° vs 10.0°, and 11.3° vs 9.5°; p < 0.0001, < 0.0001, < 0.0001, and 0.0008, respectively). The post-operative total rotational laxity significantly decreased, compared with pre-operative levels, at 30° and 45° flexion among all subjects (mean 20.4° vs 17.9°, and 23.1° vs 21.1°; p = 0.002 and 0.04, respectively). The post-operative total rotational laxity was significantly smaller in asymmetrically designed total knee arthroplasty than in symmetrically designed total knee arthroplasty at 30°, 45°, and 60° flexion (mean 19.3° vs 15.8°, 22.8° vs 18.7°, and 24.4° vs 20.8°; p = 0.03, 0.03, and 0.02, respectively), whereas no significant difference was observed at 90° flexion.ConclusionCompared to symmetrical surface design, asymmetrical surface design resulted in lower rotational laxity at the midflexion range in cruciate-retaining total knee arthroplasty.Level of evidenceIII.

Effect of posterior capsular release on intraoperative joint gap mismatch in the mid-flexion range during posterior-stabilized total knee arthroplasty

IntroductionIntraoperative mismatch between extension and mid-flexion joint gaps remains a critical issue in posterior-stabilized total knee arthroplasty (PS-TKA). Posterior capsular release has been found to increase the extension joint gap. However, there is still a lack of robust evidence for the effect of posterior capsular release on the mid-flexion joint gap. The purpose of the present study was to quantify the effect of posterior capsular release on the intraoperative joint gap from extension through 45° mid-flexion to flexion and to clarify how this procedure might affect the improvement of gap mismatch in the mid-flexion 45° range. Materials and methodsIn total, 38 consecutive cases of primary PS-TKA were reviewed. The center, medial, and lateral component gaps from extension to flexion were measured with a tensor device before and after posterior capsular release. The minimal detectable change for joint gap measurement was calculated using two methods, error variance and intra-observer intraclass correlation coefficients. Pre- and post-release joint gap differences were assessed using the paired t-test. ResultsMinimal detectable change was found to be 0.59 mm. At 0° and 10° of flexion, the post-release center, medial, and lateral component gaps were significantly greater than at pre-release. At 45° and 90° and maximum flexion, there were no joint gap differences exceeding the minimal detectable change. The joint gap mismatches between 0° and 10°, and 45°, 90° and maximum flexion were significantly smaller at post-release than those at pre-release with the change values exceeding the minimal detectable change (P < 0.05). ConclusionPosterior capsular release significantly decreased both joint gap mismatch between extension and 45° mid-flexion, and extension and flexion, showing clinical usefulness in PS-TKA.

Restoration of the Joint Line Configuration Reproduces Native Mid-Flexion Biomechanics after Total Knee Arthroplasty: A Matched-Pair Cadaveric Study.

Background: Recent evidence supports that restoration of the pre-arthritic condition via total knee arthroplasty (TKA) is associated with improved post-TKA performance and patient satisfaction. However, whether the restored pre-arthritic joint line simulates the native mid-flexion biomechanics remains unclear. Objective: We performed a matched-pair cadaveric study to explore whether restoration of the joint line via kinematically aligned (KA) TKA reproduced native knee biomechanics more accurately than the altered joint line associated with mechanically aligned (MA) TKA. Methods: Sixteen fresh-frozen cadaveric knees (eight pairs) were affixed onto a customized knee-squatting simulator for measurement of femoral rollback and medial collateral ligament (MCL) strain during mid-flexion. One knee from each cadaver was randomly designated to the KA TKA group (with the joint line restored to the pre-arthritic condition) and the other to the MA TKA group (with the joint line perpendicular to the mechanical axis). Optical markers were attached to all knees and rollback was analyzed using motion capture cameras. A video extensometer measured real-time variations in MCL strain. The kinematics and MCL strain prior to and following TKA were measured for all specimens. Results: KA TKA was better for restoring the knee kinematics to the native condition than MA TKA. The mid-flexion femoral rollback and axial rotation after KA TKA were consistently comparable to those of the native knee. Meanwhile, those of MA TKA were similar only at ≤40° of flexion. Furthermore, KA TKA better restored the mid-flexion MCL strain to that of the native knee than MA TKA. Over the entire mid-flexion range, the MCL strain of KA TKA and native knees were similar, while the strains of MA TKA knees were more than twice those of native knees at >20° of flexion. Conclusions: The restored joint line after KA TKA effectively reproduced the native mid-flexion rollback and MCL strain, whereas the altered joint line after MA TKA did not. Our findings may explain why patients who undergo KA TKA experience superior outcomes and more natural knee sensations during daily activities than those treated via MA TKA.

In vivo kinematic comparison of medial pivot total knee arthroplasty in weight-bearing and non-weight-bearing deep knee bending

BackgroundThis study aimed to determine the kinematics of medial pivot total knee arthroplasty by comparing weight-bearing and non-weight-bearing deep knee bending and to evaluate the effect of the weight-bearing state on the kinematics. MethodsThe kinematics of 19 knees were investigated under fluoroscopy during squatting (weight-bearing) and active-assisted knee bending (non-weight-bearing) using two- to three-dimensional registration technique. Accordingly, range of motion, anteroposterior translation for the medial and lateral low contact points, axial rotation of the femoral component relative to the tibial component and kinematic pathway were evaluated. FindingsThere was no difference in range of motion between the two states. The medial anteroposterior translation showed no significant movement with no anterior translation in both the weight-bearing and non-weight-bearing from 0° to 90° of flexion. Regarding the lateral anteroposterior translation, a posterior translation was observed during weight-bearing, whereas a slight anterior translation from 0° to 30° of flexion and subsequent posterior translation were found in the non-weight-bearing. Femoral external rotation was observed in the weight-bearing, whereas femoral internal rotation was seen from 0° to 30° of flexion and subsequent femoral external rotation was observed in the non-weight-bearing. The kinematic pathway showed medial pivot motion and subsequent bicondylar rollback in the weight-bearing, whereas only medial pivot motion was observed in the non-weight-bearing. InterpretationThe medial anteroposterior translation of the femur during deep knee bending showed no anterior motion in the two states. The lateral anteroposterior translation and femoral rotation were different in the mid-flexion range between the two states.

Intraoperative Load Sensing in Total Knee Arthroplasty Leads to a Functional but Not Clinical Difference: A Comparative, Gait Analysis Evaluation.

Introduction: Although Total Knee Arthroplasty (TKA) is a successful procedure, a significant number of patients are still unsatisfied, reporting instability at the mid-flexion range (Mid-Flexion Instability-MFI). To avoid this complication, many innovations, including load sensors (LS), have been introduced. The intraoperative use of LS may facilitate the balance of the knee during the entire range of motion to avoid MFI postoperatively. The objective of this study was to perform a Gait Analysis (GA) evaluation of a series of patients who underwent primary TKA using a single LS technology. Methods: The authors matched and compared two groups of patients treated with the same posterior stabilized TKA design. In Group A, 10 knees were intraoperatively balanced with LS technology, while 10 knees (Group B) underwent standard TKA. The correct TKA alignment was preoperatively determined aiming for a mechanical alignment. Clinical evaluation was performed according to the WOMAC, Knee Society Score (KSS) and Forgotten Joint Score, while functional evaluation was performed using a state-of-the-art GA platform. Results: We reported excellent clinical results in both groups without any statistical difference in patient reported outcome measurements (PROMs); from a functional standpoint, several GA space–time parameters were closer to normal in the sensor group when compared to the standard group, but a statistically significant difference was not reached. Conclusions: Gait Analysis represents a valid method to evaluate TKA kinematics. This study, with its limitations, showed that pressure sensitive technology represents a valid aid for surgeons aiming to improve the postoperative stability of TKA; however, other factors (i.e., level of intra-articular constraint and alignment) may play a major role in reproducing the normal knee biomechanics.

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

BackgroundThe Flexion First Balancer (FFB) technique for total knee arthroplasty (TKA) was developed to maintain the isometry of the medial collateral ligament (MCL) by restoring the medial anatomy of the knee. Inability to correct MCL isometry could hypothetically result in an increased mid-flexion laxity. The aim of the current study was to evaluate if the FFB technique results in improved functional outcome and less mid-flexion laxity compared to Measured Resection (MR).MethodsA cross-sectional study was performed comparing 27 FFB patients with 28 MR patients. Groups were matched for age, gender, BMI and ASA classification. All patient received the cruciate retained type, Vanguard Complete Knee System (Biomet Orthopedics, Warsaw, IN, USA). Stress X-rays of the knee with 30 degrees of flexion were made to assess varus-valgus laxity. Furthermore, three tests were conducted to asses functional outcome: a 6 min walk test, a stair climb test and quadriceps peak force measurements. Mean follow-up was respectively 2.6 (SD 0.4) and 3.9 years (SD 0.2).ResultsThe MR group showed a postoperative elevation in joint line in contrast to the FFB group, the mean difference between the two groups was 3 mm (p < 0.001). No differences in total laxity between the two groups was found. The FFB group showed a higher quadriceps peak force (1.67 (SD 0.55) N/BMI) in comparison with the MR group (1.38 (SD 0.48) N/BMI) (p < 0.05). All other outcome parameters were comparable between the two groups (p: n.s.). Correlation analysis showed a moderate negative correlation between joint line elevation and quadriceps peak force (r = − 0.29, p < 0.05).ConclusionThe FFB technique did not lead to less coronal laxity in the mid-flexion range compared to MR. Although peak quadriceps force was significantly higher for the FFB group no clinically relevant benefits could be identified for the patients with regards to functional outcome. Therefore, minor deviations in joint line seems to have no effect on functional outcome after TKA.Trial registrationISRCTN, ISRCTN85351296. Registered 23 april 2021 - Retrospectively registered, https://www.isrctn.com/ISRCTN85351296

Intraoperative Assessment of Gap Balancing in Total Knee Arthroplasty Using Navigation with Joint Stability Graphs.

The purpose of this study was to assess continuous gaps in the replaced knee throughout the full range of motion (ROM) after total knee arthroplasty (TKA) using a joint stability graph, and to analyze the gap laxity in the mid-flexion range. Ninety-three TKAs were performed using imageless navigation with a joint stability graph. While positioning guides for each respective cut, the surgeon can safely preview the resection's impact for the resulting joint gaps and control the soft tissue balance at the knee flexion of 0° (extension) and 90° (flexion). The gaps between the femoral component and insert were evaluated throughout the full ROM using the joint stability graph. The mechanical axis (MA) and change of joint line height were radiographically evaluated. Posthoc power analyses using a significant α value of 0.05 were performed on the proportion of the mid-flexion instability as a primary outcome to determine whether the sample had sufficient power. The power was determined to be sufficient (100%). The flexion-extension gap differences in each medial and lateral compartment and the mediolateral gap differences in flexion and extension were all ≤3 mm. None of the knees had mid-flexion instability, which is defined by a peak mid-flexion gap that is 3 mm greater than the smaller value of flexion or extension gap. The average MA was well corrected from varus 11.4° to varus 1.0° postoperatively. The proportion of postoperative well-aligned knees (MA ≤ 3°) was 87.1%. The joint line height was well preserved (14.7 vs. 14.8 mm, p = 0.751). The joint stability graph in TKA using the navigation can effectively evaluate the continuous gap throughout the ROM, including the mid-flexion range. Mid-flexion instability was uncommon in primary TKAs with appropriate alignment and proper preservation of the joint line. The Level of evidence for the study is IV.

Influence of surgical factors on patient satisfaction after bi\u2010cruciate stabilized total knee arthroplasty: retrospective examination using multiple regression analysis

BackgroundOne of the causes of dissatisfaction following total knee arthroplasty (TKA) is abnormal knee kinematics. A newly designed bi-cruciate stabilized (BCS) TKA system has been developed to produce close-to-normal kinematics because of its anatomic tibiofemoral articular geometry and cam-post mechanism. Although BCS TKA is expected to improve patient satisfaction, no reports have described the appropriate technique or soft tissue handling required to achieve excellent satisfaction with BCS TKA. This study is to identify intraoperative surgical predictors of patient satisfaction after BCS TKA.MethodsWe studied 104 knees with primary varus knee osteoarthritis that underwent BCS TKA with a navigation system retrospectively. Surgical parameters including coronal, sagittal and axial alignment and joint laxity in each compartment that affected patient satisfaction was evaluated. Satisfaction score was evaluated with use of the 2011 Knee Society Scoring system. The multivariate regression analysis included age, gender, body mass index and intraoperative parameters that correlated with satisfaction scores in the univariate analysis (P < 0.05). The current study focused on the patient satisfaction score at 1 year postoperatively and didn’t evaluate the long term clinical results nor survivorship.ResultsThe postoperative satisfaction score was 28.6 ± 8.1. Multivariate analysis showed that medial joint laxity at 30° flexion (P = 0.003), tibial excessive external rotation alignment (P = 0,009) and tibial varus alignment (P = 0.029) were predictors of poor satisfaction score.ConclusionsWhen performing BCS TKA, surgeons should pay attention to maintaining proper stability of the medial compartment at mid flexion range and should avoid tibial varus and excessive external rotational alignment.

Anatomy and Biomechanics of the Posterior Cruciate Ligament.

Posterior cruciate ligament (PCL) injuries are often encountered in the setting of other knee pathology and sometimes in isolation. A thorough understanding of the native PCL anatomy is crucial in the successful treatment of these injuries. The PCL consists of two independent bundles that function in a codominant relationship to perform the primary role of resisting posterior tibial translation relative to the femur. A secondary role of the PCL is to provide rotatory stability. The anterolateral (AL) bundle has a more vertical orientation when compared with the posteromedial (PM) bundle. The AL bundle has a more anterior origin than the PM bundle on the lateral wall of the medial femoral condyle. The tibial insertion of AL bundle on the PCL facet is medial and anterior to the PM bundle. The AL and PM bundles are 12-mm apart at the center of the femoral origins, while the tibial insertions are more tightly grouped. The different spatial orientation of the two bundles and large distance between the femoral centers is responsible for the codominance of the PCL bundles. The AL bundle is the dominant restraint to posterior tibial translation throughout midrange flexion, while the PM bundle is the primary restraint in extension and deep flexion. Biomechanical testing has shown independent reconstruction of the two bundles that better reproduces native knee biomechanics, while significant differences in clinical outcomes remain to be seen. Stress X-rays may play an important role in clinical decision-making process for operative versus nonoperative management of isolated PCL injuries. Strong understanding of PCL anatomy and biomechanics can aid surgical management.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee.

To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion. Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee. At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation. The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs. Level IV.

Bi-cruciate substituting total knee arthroplasty provides varus–valgus stability throughout the midflexion range

BackgroundProper soft tissue balance is crucial for a successful clinical outcome after total knee arthroplasty (TKA). Bi-cruciate substituting (BCS)-TKA has been developed to more closely approximate normal knee characteristics. The purpose of the present study was to evaluate midflexion laxity before and after BCS-TKA using a navigation system, and assess the correlation between intraoperative laxity and the maximum flexion angle after surgery. MethodsFifty-one knees in 46 patients with osteoarthritis replaced with BCS prosthesis were assessed. Manual mild passive internal–external rotational and varus–valgus stress was applied to the knees, and the maximum total laxity was measured automatically by a navigation system before and after TKA. The correlations with the range of motion (ROM) were evaluated using Spearman's correlation coefficients (ρ). ResultsInternal–external stress assessment revealed no statistically significant difference at each flexion angle before and after BCS-TKA. In contrast, the varus–valgus stress assessment revealed that BCS-TKA had significantly decreased varus–valgus laxity from preoperative levels at 20–120° flexion angles. Furthermore, the maximum flexion angle at six months after surgery significantly correlated with the intraoperative laxity at deep flexion range. ConclusionBCS-TKA stabilized varus–valgus laxity to better than preoperative levels at midflexion range.

Posterior tibial slope impacts intraoperatively measured mid-flexion anteroposterior kinematics during cruciate-retaining total knee arthroplasty

Posterior tibial slope (PTS) for cruciate-retaining (CR) total knee arthroplasty (TKA) is usually pre-determined by the surgeon. Limited information is available comparing different choices of PTS on the kinematics of the CR TKA, independent of the balancing of the extension gap. This study hypothesized that with the same balanced extension gap, the choice of PTS significantly impacts the intraoperatively measured kinematics of CR TKA. Navigated CR TKAs were performed on seven fresh-frozen cadavers with healthy knees and intact posterior cruciate ligament (PCL). A custom designed tibial baseplate was implanted to allow in situ modification of the PTS, which altered the flexion gap but maintained the extension gap. Knee kinematics were measured by performing passive range of motion (ROM) tests from full extension to 120° of flexion on the intact knee and CR TKAs with four different PTSs (1°, 4°, 7°, and 10°). The measured kinematics were compared across test conditions to assess the impact of PTS. With a consistent extension gap, the change of PTS had significant impact on the anteroposterior (AP) kinematics of the CR TKA knees in mid-flexion range (45°-90°), but not so much for the high-flexion range (90°-120°). No considerable impacts were found on internal/external (I/E) rotation and hip-knee-ankle (HKA) angle. However, the findings on the individual basis suggested the impact of PTS on I/E rotation and HKA angle may be patient-specific. The data suggested that the choice of PTS had the greatest impact on the mid-flexion AP translation among the intraoperatively measured kinematics. This impact may be considered while making surgical decisions in the context of APkinematics. When using a tibial component designed with "center" pivoting PTS, a surgeon may be able to fine tune the PTS to achieve proper mid-flexion APstability.

Joint Gap in Mid-Flexion Is Not a Predictor of Postoperative Flexion Angle After Total Knee Arthroplasty

BackgroundPostoperative knee flexion angle is one of the most important outcomes of total knee arthroplasty (TKA). Intraoperative ligament balancing may affect the postoperative range of motion of the knee. However, the relationship between intraoperative ligament balancing and postoperative flexion angle was still controversial. The purpose of this study was to determine whether intraoperative joint gap affects postoperative knee flexion angle or not. MethodsProspective multicenter study of 246 knees with varus osteoarthritis undergoing a posterior–stabilized, mobile-bearing TKA was performed. The joint gap before implantation and after implantation was measured. The joint gap after implantation was measured using a specially designed tensor device with the same shape of a total knee prosthesis at 0°, 30°, 60°, 90°, 120°, and 145° of flexion with the reduction of the patellofemoral joint. Stepwise multiple regression analysis was conducted to determine the predictors of the flexion angle of the knee after the operation. ResultsPredictors were identified in the following 3 categories: (1) preoperative flexion angle, (2) intraoperative flexion angle, and (3) joint gap looseness at 120° of flexion (joint gap after implantation at 120° of flexion − joint gap after implantation at 0° of flexion) (R = 0.472, P < .01). ConclusionFlexion angle after TKA was not affected by the flexion joint gap looseness before implantation and the joint gap looseness after implantation from 30° to 90° of flexion. Surgeons should notice that joint gap looseness in mid-flexion range did not increase the postoperative knee flexion angle.

Varus\u2013valgus stability at 90\xb0 flexion correlates with the stability at midflexion range more widely than that at 0\xb0 extension in posterior-stabilized total knee arthroplasty

IntroductionMidflexion stability can potentially improve the outcome of total knee arthroplasty (TKA). The purpose of this study was to evaluate the correlation between varus–valgus stability at 0° of extension and 90° of flexion and that at the midflexion range in posterior-stabilized (PS)-TKA.Materials and methodsForty-three knees that underwent PS-TKA were evaluated. Manual mild passive varus–valgus stress was applied to the knees, and the postoperative maximum varus–valgus stability was measured every 10° throughout range of motion, using a navigation system. Correlations between the stability at 0°, 90° of flexion, and that at each midflexion angle were evaluated using Spearman’s correlation coefficients.ResultsThe stability of 0° modestly correlated with that of 10°–20°, but it did not significantly correlate with that of 30°–80°. However, the stability of 90° strongly correlated with that of 60°–80°, modestly correlated with that of 40°–50°, weakly correlated with that of 20°–30°, and did not correlate with that of 10°.ConclusionsThe present study confirmed the importance of acquiring stability at 90° flexion to achieve midflexion stability in PS-TKA. However, initial flexion stability did not strongly correlate with the stability at either 0° or 90°. Our findings can provide useful information for understanding varus–valgus stability throughout the range of motion in PS-TKA. Attention to soft tissue balancing is necessary to stabilize a knee at the initial flexion range in PS-TKA.