Creep behavior of human knee joint determined with high-speed biplanar video-radiography and finite element simulation.

Creep and relaxation of knee cartilage and meniscus have been extensively studied at the tissue level with constitutive laws well established. At the joint level, however, both experimental and model studies have been focused on either elastic or kinematic responses of the knee, where the time-dependent response is typically neglected for simplicity. The objectives of this study were to quantify the in-vivo creep behavior of human knee joints produced by the cartilaginous tissues and to use the relevant data to validate a previously proposed poromechanical model. Two participants with no history of leg injury volunteered for 3T magnetic resonance imaging (MRI) of their unloaded right knees and for biplanar video-radiography (BVR) of the same knees during standing on an instrumented treadmill for 10 min. Approximately 550 temporal data points were obtained for the in-vivo displacement of the right femur relative to the tibia of the knee. Models of the bones and soft tissues were derived from the MRI. The bone models were used to reconstruct the 3D bone kinematics measured using BVR. Ground reaction forces were simultaneously recorded for the right leg, which were used as input for the subject-specific finite element knee models. Cartilaginous tissues were modeled as fluid-saturated fibril-reinforced materials. In-vivo creep of the knee was experimentally observed for both participants, i.e., the joint displacement increased with time while the reaction forces at the foot were approximately constant. The creep displacements obtained from the finite element models compared well with the experimental data when the tissue properties were calibrated (Pearson correlation coefficient = 0.99). The results showed the capacity of the poromechanical knee model to capture the creep response of the joint. The combined experimental and model study may be used to understand the fluid-pressure load support and contact mechanics of the joint using material properties calibrated from the displacement data, which enhance the fidelity of model results.

Associations of hamstring and triceps surae muscle spasticity and stance phase gait kinematics in children with spastic diplegic cerebral palsy.

Clinical decisions on interventions to improve function in children with cerebral palsy (CP) are based, in part, on hypothesized interactions amongst physical signs of CP and functional deficits. However, a knowledge gap exists regarding associations between spasticity and gait function. This study quantified associations of hamstring and triceps surae spasticity with hip, knee and ankle CP gait patterns. This is a cohort study of children and adolescents [n = 51; 31 male; 20 female; spastic diplegia; Gross Motor Function Classification System I (n = 23) and II (n = 28)] who participated in a clinical consult including gait (Motion Analysis, USA) and modified Tardieu scale (MTS) testing (hamstrings, triceps surae). Shape-based clustering was performed on stance phase sagittal hip, knee and ankle patterns using z-normalized and non-normalized data. Linear regression (R, v3.5.0, R Core Team, Austria) was conducted to assess associations between MTS measures and data clusters (α = 0.05). Shape-clustering revealed two hip and three knee and ankle clusters for z-normalized and non-normalized data. Significant associations of hamstring spasticity and joint patterns were observed for z-normalized knee clusters (CKnee A p = 0.002; CKnee B p = 0.006) and interactions amongst non-normalized hip and knee clusters (CHipA:CKnee B p = 0.033). Trends were observed for soleus spasticity and gastrocnemius range of motion angle and non-normalized ankle clusters (CAnkle B p = 0.051; CAnkle B p = 0.053 respectively). Significant associations of early knee extension and hamstring spasticity, observed using shape-clustering of z-normalized data, provide unique information that may inform the identification of individuals most likely to benefit from spasticity management and targets for spasticity management assessment.

Alterations in lower limb multimuscle activation patterns during stair climbing in female total knee arthroplasty patients.

Total knee arthroplasty (TKA) patients commonly experience neuromuscular adaptations that may affect stair climbing competence. This study identified multimuscle pattern (MMP) changes in postoperative female TKA patients during stair climbing with a support vector machine (SVM). It was hypothesized that TKA patients adopt temporal and spectral muscle activation characteristics indicative of muscle atrophy and cocontraction strategies. Nineteen female subjects [10 unilateral sex-specific TKAs, 62.2 ± 8.6 yr, body mass index (BMI) 28.2 ± 5.4 kg/m(2); 9 healthy control subjects, 61.4 ± 7.4 yr, BMI 25.6 ± 2.4 kg/m(2)] were recruited. Surface electromyograms (EMGs) were obtained for seven lower limb muscles of the affected limb of TKA subjects and a randomly assigned limb for control subjects during stair climbing. Stance phase (±30%) EMG data were wavelet transformed and normalized to total power. Data across all muscles were combined to form MMPs and analyzed with a SVM. Statistical analysis was performed with binomial tests, independent group t-tests, or independent group Mann-Whitney U-tests in SPSS (P < 0.05). SVM results indicated significantly altered muscle activation patterns in the TKA group for biceps femoris (recognition rate 84.2%), semitendinosus (recognition rate 73.7%), gastrocnemius (recognition rate 68.4%), and tibialis anterior (recognition rate 68.4%). Further analysis identified no significant differences in spectral activation characteristics between groups. Temporal adaptations, indicative of cocontraction strategies, were, however, evident in TKA MMPs. This approach may provide a valuable tool for clinical neuromuscular function assessment and rehabilitation monitoring.

Multi-muscle activation strategies during walking in female post-operative total joint replacement patients.

Dynamic knee joint function requires coordinated multi-muscle activation patterns (MMP) that may be adversely affected by total knee arthroplasty (TKA). This study identified MMP changes in post-operative female TKA patients using a Support Vector Machine (SVM). It was hypothesised that TKA patients can successfully be classified and display significant alterations in temporal and spectral muscle activation characteristics. 19 female subjects (10 unilateral gender-specific TKA, 62.2±8.6yrs, BMI 28.2±5.4; and 9 healthy controls, 61.4±7.4yrs, BMI 25.6±2.4) were recruited. Surface electromyograms (EMG) were obtained for 7 lower limb muscles during walking. Stance phase (±30%) EMG data were processed using a wavelet transform and normalized to total power. Data across all muscles were combined to form MMPs and analyzed using a SVM. Recognition rates for all subjects were computed for MMPs and individual muscles. A binomial test was used to establish statistical significance (p<0.05). The results supported the hypothesis indicating significantly altered muscle activations for vastus medialis (recognition rate ∼68.4%) and biceps femoris (recognition rate ∼73.7%). Further analysis identified distinct between group differences across temporal, spectral and intensity domains. Application of a combined SVM and MMP approach may be beneficial for the future assessment of post-surgical dynamic muscle function.

Severe combined immunodeficiency in Brazil: management, prognosis, and BCG-associated complications.

BACKGROUND: Severe combined immunodeficiency (SCID) is one of the most severe forms of primary immunodeficiency. The objectives of this study were to analyze the diagnosis, treatment, and prognosis of SCID in Brazil and to document the impact of BCG vaccine. METHODS: We actively searched for cases by contacting all Brazilian referral centers. RESULTS: We contacted 23 centers and 70 patients from 65 families. Patients were born between 1996 and 2011, and 49 (70%) were male. More than half (39) of the diagnoses were made after 2006. Mean age at diagnosis declined from 9.7 to 6.1 months (P = .058) before and after 2000, respectively, and mean delay in diagnosis decreased from 7.9 to 4.2 months (P = .009). Most patients (60/70) were vaccinated with BCG before the diagnosis, 39 of 60 (65%) had complications related to BCG vaccine, and the complication was disseminated in 29 of 39 (74.3%). Less than half of the patients (30, 42.9%) underwent hematopoietic stem cell transplantation (HSCT). Half of the patients died (35, 50%), and 23 of these patients had not undergone HSCT. Disseminated BCG was the cause of death, either alone or in association with other causes, in 9 of 31 cases (29%, no data for 4 cases). CONCLUSIONS: In Brazil, diagnosis of SCID has improved over the last decade, both in terms of the number of cases and age at diagnosis, although a much higher number of cases had been expected. Mortality is higher than in developed countries. Complications of BCG vaccine are an important warning sign for the presence of SCID and account for significant morbidity during disease progression.