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Computational studies of total knee arthroplasty (TKA) often focus on either joint mechanics (kinematics and forces) or implant fixation mechanics. However, such disconnect between joint and fixation mechanics hinders our understanding of overall TKA biomechanical function by preventing identification of key relationships between these two levels of TKA mechanics. We developed a computational workflow to holistically assess TKA biomechanics by integrating musculoskeletal and finite element (FE) models. For our initial study using the workflow, we investigated how tibiofemoral contact mechanics affected the risk of failure due to debonding at the implant-cement interface using the four available subjects from the Grand Challenge Competitions to Predict In Vivo Knee Loads. We used a musculoskeletal model with a 12 degrees-of-freedom knee joint to simulate the stance phase of gait for each subject. The computed tibiofemoral joint forces at each node in contact were direct inputs to FE simulations of the same subjects. We found that the peak risk of failure did not coincide with the peak joint forces or the extreme tibiofemoral contact positions. Moreover, despite the consistency of joint forces across subjects, we observed important variability in the profile of the risk of failure during gait. Thus, by a combined evaluation of the joint and implant fixation mechanics of TKA, we could identify subject-specific effects of joint kinematics and forces on implant fixation that would otherwise have gone unnoticed. We intend to apply our workflow to evaluate the impact of implant alignment and design on TKA biomechanics.

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PURPOSE: A varus deformity (VD) of the lower limbs results in greater loading of the medial compartment of the knee joint (KJ), leading to its degenerative changes and, eventually, to progressive osteoarthritis (OA) of the joint. The aim of the study was to investigate the mid-term changes in gait biomechanics and clinical symptoms in patients with VD of KJ and OA before and six months after surgical correction. METHODS: The study enrolled 25 patients with medial OA of grade 2-3 according to Kellgren-Lawrence and a VD of > 3°, who underwent arthroscopic lavage and debridement of the knee joint followed by corrective osteotomy. The control group included 20 healthy adults. Clinical and biomechanical assessments were done twice: immediately prior to and six months after the surgical treatment. Biomechanical parameters of gait were recorded using an inertial sensor system. RESULTS: According to our findings, there was a statistically significant post-operative increase in the knee extension amplitude by 1.4° in female patients and an insignificant extension increase in male patients. The mean postoperative KOOS score was 66.7 points (46 to 91) in the patient group, 67.1 points (54 to 91) in males, and 59.5 points (46 to 64) in females. As early as six months after a valgus osteotomy, we already observed improved biomechanics of the KJ motions compared to pre-operative data. By that time, the swing flexion amplitude of the affected KJ had increased and became symmetrical, which had not been the case before surgery. We observed a total of three changes in the KJ kinematics after surgery: increased swing flexion amplitudes in both KJs, a decreased extension amplitude in the affected KJ, and increased first flexion amplitudes in both KJs. CONCLUSION: According to our study, the midterm outcomes after a valgus osteotomy showed clinical improvements based on the VAS and KOOS scores, which were however less pronounced than in similar studies with a longer assessment term after surgery. We also found a significant increase in the amplitude of joint extension, but only in females. As the function of the operated joint is concerned, valgus osteotomy restored the kinematics of walking movements to a nearly normal gait with increased first and second flexion amplitudes. The function of KJ becomes symmetric though the non-operative side. Thus, the healthy and functionally more capable side is copying the movement pattern of the affected side. Hence, the non-operative leg is functioning less efficiently than it is required by the walking pace.

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BACKGROUND: Many studies have shown that distal femoral sagittal morphological characteristics have a clear relationship with knee joint kinematics. The aim of this study was to determine the relationship between distal femoral sagittal morphological characteristics and noncontact anterior cruciate ligament (ACL) injury. METHODS: A retrospective case-control study of 148 patients was conducted. Two age- and sex-matched cohorts (each n = 74) were analysed: a noncontact ACL injury group and a control group. Several characteristics were compared between the two groups, including the lateral femoral posterior radius (LFPR), medial femoral posterior radius (MFPR), lateral height of the distal femur (LH), medial height of the distal femur (MH), lateral femoral anteroposterior diameter (LFAP), medial femoral anteroposterior diameter (MFAP), lateral femoral posterior radius ratio (LFPRR), and medial femoral posterior radius ratio (MFPRR). Receiver operating characteristic (ROC) analysis was used to evaluate the significance of the LFPRR and MFPRR in predicting ACL injury. RESULTS: Compared with patients in the control group, patients in the ACL injury group had an increased LFPR, MFPR, MFAP, LFPRR, and MFPRR. ROC analysis revealed that an increased LFPRR above 31.7% was associated with noncontact ACL injury, with a sensitivity of 78.4% and a specificity of 58.1%; additionally. an increased MFPRR above 33.4% was associated with noncontact ACL injury, with a sensitivity of 58.1% and a specificity of 70.3%. CONCLUSION: This study showed that increased LFPRR and increased MFPRR are risk factors for developing noncontact ACL injury. These data could thus help identify individuals susceptible to ACL injuries.

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Background: For total knee arthroplasty (TKA), the optimal rotational position of the femoral component is felt to be critically important. The current knee joint kinematics measurement technology is unable to identify the exact rotation axis of the knee joint, the main reasons being low measurement accuracy and insufficient three-dimensional data (2D-3D image matching technology). In order to improve the effect of TKA surgery, we proposed a knee joint kinematics measurement method, based on the MRI technology, and verified its measurement accuracy. We then employed this method to identify the personalized optimal rotation axis of the knee joint for TKA patients. Purposes: The purpose of the study was 1) to propose a method for measuring knee joint kinematics and verify its accuracy and 2) to propose a method for determining the optimal rotation axis of knee joint for TKA surgery, based on accurate kinematic measurement results. Materials and Methods: The experiment was divided into two parts: in vitro and in vivo. The purpose of the in vitro experiment was to verify the measurement accuracy of our method. We fixed two aquarium stones (approximately 10 cm * 10 cm * 10 cm in size, close to the size of the distal femur and proximal tibia) firmly on the fixed and moving arms of the goniometer/vernier caliper with glue and immersed the aquarium stones in the water to capture MRI images. The MRI images were then processed with MATLAB software, and the relative motion of the two aquarium stones was measured. The measurement accuracy of our method was verified via the scale reading of the moving arm on the goniometer/vernier caliper. In vivo, 36 healthy elderly participants (22 females, 14 males) were recruited from the local community; our method was then employed to measure the relative motion of the tibia and femur and to observe the rollback and screw home motion of the medial/lateral condyle of the femur, which was identified as specific kinematic features of the knee joint. Results: In vitro, all measurements were accurate to <1 mm and <1°. In vivo, all knee measurements showed rollback motion (the rollback distance of the medial femoral condyle was 18.1 ± 3.7 mm and that of the lateral condyle was 31.1 ± 7.3 mm) and screw home motion. Conclusion: In the application scenario of knee joint kinematics measurement, our method has an accuracy of <1° of rotation angle and <1 mm of translation for all reference points, and it can be employed to identify the most stable axis of the knee joint. Significance: Using our method to accumulate data on the knee rotation axis of more subjects to establish an average rotation axis of a given population may help in knee prosthesis design and reduce the patient dissatisfaction rate. Individually measuring the patient's rotation axis before TKA surgery and adjusting the prosthesis installation in TKA may further reduce the patient dissatisfaction rate, and automatic computer measurement may be realized in the future, but it is still time-consuming for now.

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Background and Objectives: Patients with Down syndrome have many orthopedic problems including flat foot. Insertion of an insole for a flat foot provides support to the medial longitudinal arch; thus, insole therapy is often used to treat a flat foot. However, the influence of an insole insertion on the knee joint kinematics for a patient with Down syndrome is unknown. This study aimed to elucidate the influence of an insole for a flat foot on the knee kinematics during gait for a patient with Down syndrome. Materials and Methods: The subject was a 22-year-old male with Down syndrome who had a flat foot. The knee joint angle during the gait was measured using a 3D motion capture system that consisted of eight infrared cameras. Results: The gait analysis demonstrated a reduction in the knee flexion angle during double knee action. The knee valgus and tibial internal rotation angles also decreased during the loading response phase while wearing shoes that contained the insole. Conclusions: As the angle of the knee joint decreased during the gait, it was considered that the stability of the knee joint improved by inserting the insole. In particular, there was a large difference in the tibial internal rotation angle when the insole was inserted. It is thus hypothesized that the insole contributes to the rotational stability of the knee joint. This study suggests that knee stability may improve and that gait becomes more stable when a Down syndrome patient with a flat foot wears an insole.

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PURPOSE: A functional test battery (FTB) has been proposed to evaluate the readiness of return to activity after ACLR. However, there is limited evidence documenting the usefulness of an FTB. Therefore, the purpose of the current investigation was to compare knee joint landing biomechanics asymmetry during double-leg jump landing (DLJL) and single-leg jump cutting (SLJC) between healthy females and ACLR females who pass (ACLR-pass) or fail (ACLR-fail) an FTB before and after the completion of a sustained exercise protocol. METHOD: Eighteen ACLR females (ten ACLR-pass and eight ACLR-fail) and twelve healthy females performed an FTB including The 2000 International Knee Documentation Committee Subjective Knee Evaluation Form, the Knee Outcome Survey Activities of Daily Living Scale, quadriceps strength, and single-leg hop tests. DLJL and SLJC knee joint biomechanics asymmetry were measured before and after exercise. RESULTS: During DLJL, there were significant main effects of group on peak anterior tibial shear force (ATSF) asymmetry [F(2,27) = 3.86, p < 0.05, [Formula: see text] = 0.214] and peak vertical ground reaction force (vGRF) asymmetry [F(2,27) = 3.34, p = 0.05, [Formula: see text] = 0.198]. During SLJC, there was a significant group main effect for peak ATSF asymmetry [F(2,27) = 3.494, p = 0.04, [Formula: see text] = 0.206]. CONCLUSION: ACLR-fail exhibited greater asymmetry in peak ATSF during DLJL and SLJC compared to healthy females. In addition, ACLR-pass exhibited greater asymmetry in peak ATSF and peak vGRF during DLJL and SLJC, respectively, compared to healthy females. However, ACLR-fail did not exhibit any significant differences in landing biomechanics asymmetry during either task compared with ACLR-pass. Furthermore, the completion of a sustained exercise protocol did not affect knee joint landing biomechanics asymmetry across groups. LEVEL OF EVIDENCE: II.

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Computational knee models that replicate the joint motion are important tools to discern difficult-to-measure functional joint biomechanics. Numerous knee kinematic models of different complexity, with either generic or subject-specific anatomy, have been presented and used to predict three-dimensional tibiofemoral (TFJ) and patellofemoral (PFJ) joint kinematics of cadavers or healthy adults, but not pediatric populations. The aims of this study were: (i) to develop subject-specific TFJ and PFJ kinematic models, with TFJ models having either rigid or extensible ligament constraints, for eight healthy pediatric participants and (ii) to validate the estimated joint and ligament kinematics against in vivo kinematics measured from magnetic resonance imaging (MRI) at four TFJ flexion angles. Three different TFJ models were created from MRIs and used to solve the TFJ kinematics: (i) 5-rigid-link parallel mechanism with rigid surface contact and isometric anterior cruciate (ACL), posterior cruciate (PCL) and medial collateral (MCL) ligaments (ΔLnull), (ii) 6-link parallel mechanism with minimized ACL, PCL, MCL and lateral collateral ligament (LCL) length changes (ΔLmin) and (iii) 6-link parallel mechanism with prescribed ACL, PCL, MCL and LCL length variations (ΔLmatch). Each model's geometrical parameters were optimized using a Multiple Objective Particle Swarm algorithm. When compared to MRI-measured data, ΔLnull and ΔLmatch performed the best, with average root mean square errors below 6.93° and 4.23 mm for TFJ and PFJ angles and displacements, respectively, and below 2.01 mm for ligament lengths (<4.32% ligament strain). Therefore, within these error ranges, ΔLnull and ΔLmatch can be used to estimate three-dimensional pediatric TFJ, PFJ and ligament kinematics and can be incorporated into lower-limb models to estimate joint kinematics and kinetics during dynamic tasks.

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Objective: To investigate the short-term effectiveness of total knee arthroplasty (TKA) assisted by three-dimensional (3D) printing osteotomy navigation template. Methods: A retrospective study was performed on 60 patients with osteoarthritis bewteen January 2016 and June 2017. Thirty cases underwent TKA assisted by 3D printing osteotomy navigation template (3D printing group) and 30 cases underwent the conventional TKA (conventional TKA group). There was no significant difference in gender, age, body mass index, surgical side, and disease duration between 2 groups ( P>0.05). The operation time, the pre- and post-operative hemoglobin values, the amount of drainage, the Hospital for Special Surgery (HSS) score and Knee Society Score (KSS) of knee joint before operation and at 3 months after operation were observed. And 6 freedom degrees of knee (the varus and valgus angle, the internal and external rotation angle, the antero-posterior displacement, the proximal-distal displacement, the flexion and extension angle, and the internal and external displacement) before operation and at 3 months after operation were recorded by Opti-Knee (the knee 3D motion analysis system). The values of 2 groups were compared with 30 healthy adults (<60 years). Results: The operation time was shorter in 3D printing group than that in conventional TKA group ( t=5.833， P=0.000). The hemoglobin values at 1 and 3 days after operation were higher in 3D printing group than those in conventional TKA group ( P<0.05). The amount of drainage was less in 3D printing group than that in conventional TKA group ( t=5.468， P=0.000). All patients were followed up 6-9 months (mean, 7.3 months). There was no significant difference in pre- and post-operative HSS score and KSS clinical score between 2 groups ( P>0.05). There was no significant difference in preoperative KSS function score between 2 groups ( P>0.05), but the KSS function score of 3D printing group at 3 months after operation was higher than that of conventional TKA group ( P<0.05). Before operation, the varus and valgus angle, the internal and external rotation angle, the antero-posterior displacement, the proximal-distal displacement of 3D printing group and conventional TKA group were larger than that of the healthy adults ( P<0.05); there was no significant difference in the flexion and extension angle and the internal and external displacement between 2 groups and healthy adults ( P>0.05). At 3 months after operation, compared with healthy adults, the varus and valgus angle of conventional TKA group was increased, the flexion and extension angle of conventional TKA group was decreased ( P<0.05); the proximal-distal displacement and the internal and external displacement of 2 groups were decreased ( P<0.05); there was no significant difference in other freedom degrees between groups ( P>0.05). No sign of prosthesis loosening was observed by X-ray examination. Conclusion: Compared with the traditional TKA, TKA assisted by the 3D printing osteotomy navigation template had such advantages as shorter operation time, less postoperative blood loss, and well postoperative recovery.

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BACKGROUND: Pain is a cardinal symptom of knee osteoarthritis (OA) and although conservative treatments such as exercise and diet related interventions can reduce pain, effects are modest and can be improved. Frontal plane knee joint motion has been associated with knee pain, and is suggested as a patient-specific characteristic on which to tailor interventions. RESEARCH QUESTION: Does the association between baseline frontal plane knee joint kinematics and pain-relief differ among overweight and obese people with knee OA who underwent an intervention from the Intensive Diet and Exercise for Arthritis (IDEA) clinical trial: diet-only, exercise-only, and combined diet and exercise intervention? METHODS: 323 participants with knee OA were included in the analysis (77% females; 66 ±â€¯6 years; 33.5 ±â€¯3.7 kg/m2). At baseline, frontal plane knee joint kinematics during walking were measured using 3-dimensional gait analysis and characterised as peak varus-valgus knee angle, peak varus-valgus excursion, and peak varus angular velocity. Pain was assessed at baseline and 18-month follow-up using the Western Ontario and McMaster Universities Osteoarthritis Index pain subscale. Linear regressions were performed unadjusted and adjusted for covariates to determine if the associations between baseline frontal plane knee joint kinematics and 18-month change in pain differed according to intervention. RESULTS: The interaction terms between the intervention and measures of frontal plane knee joint kinematics were not statistically significant (all P ≥ 0.05). SIGNIFICANCE: We found no evidence to suggest that 18-months of either exercise, diet, or a combination of diet and exercise could be more effective than the other to improve pain based on frontal plane measures of knee kinematics.

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Objective: To investigate the short-term effectiveness of total knee arthroplasty (TKA) assisted by three-dimensional (3D) printing osteotomy navigation template. Methods: A retrospective study was performed on 60 patients with osteoarthritis bewteen January 2016 and June 2017. Thirty cases underwent TKA assisted by 3D printing osteotomy navigation template (3D printing group) and 30 cases underwent the conventional TKA (conventional TKA group). There was no significant difference in gender, age, body mass index, surgical side, and disease duration between 2 groups ( P>0.05). The operation time, the pre- and post-operative hemoglobin values, the amount of drainage, the Hospital for Special Surgery (HSS) score and Knee Society Score (KSS) of knee joint before operation and at 3 months after operation were observed. And 6 freedom degrees of knee (the varus and valgus angle, the internal and external rotation angle, the antero-posterior displacement, the proximal-distal displacement, the flexion and extension angle, and the internal and external displacement) before operation and at 3 months after operation were recorded by Opti-Knee (the knee 3D motion analysis system). The values of 2 groups were compared with 30 healthy adults (0.05). There was no significant difference in preoperative KSS function score between 2 groups ( P>0.05), but the KSS function score of 3D printing group at 3 months after operation was higher than that of conventional TKA group ( P0.05). At 3 months after operation, compared with healthy adults, the varus and valgus angle of conventional TKA group was increased, the flexion and extension angle of conventional TKA group was decreased ( P0.05). No sign of prosthesis loosening was observed by X-ray examination. Conclusion: Compared with the traditional TKA, TKA assisted by the 3D printing osteotomy navigation template had such advantages as shorter operation time, less postoperative blood loss, and well postoperative recovery.

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INTRODUCTION: The aim of our study was to compare and contrast the effects of two types of mobile-bearing total knee arthroplasties (TKA), namely, the cruciate-retaining (CR) and posterior-stabilized (PS) TKAs, on clinical outcomes and in vivo kinematics during stair climbing. MATERIALS AND METHODS: The Press-Fit Condylar Sigma rotating platform was used for both CR and PS TKAs. Patient-reported outcomes were assessed using the 2011 Knee Society Score. Quadriceps muscle strength was evaluated by isokinetic dynamometry. In vivo kinematics were evaluated using periodic sagittal plane radiographic images obtained during stair climbing to quantify anteroposterior (AP) tibiofemoral translation, implant flexion and axial rotation angles using image-matching techniques. Outcomes were evaluated in 20 TKAs, which had been undergone with clinical success, including ten knees with CR types and ten knees with PS types. RESULTS: There were no significant differences between the CR and PS TKA groups (p > 0.05) in isometric extensor torque (1.0 ± 0.2 and 1.1 ± 0.6 N m/kg, respectively) or patient-reported score for stair climbing function (4.0 ± 0.5 and 3.8 ± 0.9, respectively). Both types of TKAs showed stable AP translation in the mid range of knee flexion and paradoxical translation in the low range of flexion, with limited rotation, during stair climbing. There were no significant differences between the CR and PS TKA groups (P > 0.05) in anterior translation from 80° to 40° of knee flexion (4.2 ± 1.2 and 3.5 ± 1.6 mm, respectively), posterior translation from 40° to 10° of knee flexion (2.3 ± 1.9 and 2.0 ± 1.5 mm, respectively), and total external rotation (2.8° ± 4.9° and 0.5° ± 5.0°, respectively). CONCLUSIONS: Both CR and PS types of rotating platform mobile-bearing TKAs provided reproducible knee joint kinematics during stair climbing and equivalent clinical outcomes. LEVEL OF EVIDENCE: IV.

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PURPOSE: Dynamic intraligamentary stabilization (DIS) has been introduced for the repair of acute anterior cruciate ligament (ACL) tears as an alternative to delayed reconstruction. The aim of the present study was to compare knee joint kinematics after DIS to those of the ACL-intact and ACL-deficient knee under simulated Lachman/KT-1000 and pivot-shift tests. We hypothesized that DIS provides knee joint kinematics equivalent to an intact ACL. METHODS: With the use of a robotic knee simulator, knee kinematics were determined in simulated Lachman/KT-1000 and pivot-shift tests at 0°, 15°, 30°, 60°, and 90° of flexion in eight cadaveric knees under the following conditions: (1) intact ACL, (2) ACL deficiency, (3) DIS with a preload of 60 N, and (4) DIS with a preload of 80 N. Statistical analyses were performed using two-factor repeated-measures analysis of variance. The significance level was set at a p value of <0.05. RESULTS: After DIS with a preload of either 60 N or 80 N, the anterior translation was significantly reduced in the simulated Lachman/KT-1000 and pivot-shift tests when compared to the ACL-deficient knee (p < 0.05). No significant differences were observed between the DIS reconstruction with a preload of 80 N and the intact ACL with regard to anterior laxity in either test. However, DIS with a preload of only 60 N was not able to restore knee joint kinematics to that of an intact knee in all degrees of flexion. CONCLUSION: DIS with a preload of 80 N restores knee joint kinematics comparable to that of an ACL-intact knee and is therefore capable of providing knee joint stability during ACL healing. DIS therefore provides a new technique for primary ACL repair with superior biomechanical properties in comparison with other techniques that have been described previously, although further clinical studies are required to determine its usefulness in clinical settings.

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BACKGROUND: Following anterior cruciate ligament (ACL) rupture, the knee becomes unstable with alterations in joint kinematics including anterior tibial displacement (ATD), and internal tibial rotation. Therapeutic exercises that promote faulty kinematics should be discouraged, especially early post-reconstruction, to avoid graft stretching and possibly longer-term osteoarthritis. Our study aimed to compare ATD and tibial rotation during two commonly prescribed exercises, namely: open kinetic chain (OKC) seated extension and closed kinetic chain (CKC) single leg wall squatting in ACL-deficient and healthy knees. METHODS: Eight ACL-deficient patients and eight healthy subjects matched for age, gender and sports history were assessed using Qualisys 3D-Motion Analysis System to track 17 infrared markers while performing a seated knee extension with 3kg weight and a unilateral wall squat. We developed a model to measure joint kinematics through 70° of knee flexion and extension. ANOVA and paired t-tests compared relative ATD and tibial rotation between exercises and groups at 10° increments of flexion and extension. RESULTS: We found increased ATD in the wall squat compared to the seated extension (p=0.049). There was no difference in ATD between the healthy and ACL-deficient knees but overall the tibia was significantly more internally rotated (p=0.003) in ACL-deficient knees, irrespective of the exercise, possibly interfering with the screw-home mechanism. CONCLUSIONS: CKC exercises, in particular wall squats, are not necessarily safer for patients with ACL-deficiency and possibly ACL-reconstruction; although generalization should only be made with appropriate caution. Clinicians require a detailed knowledge of the effect of exercise on knee joint kinematics.

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