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Background: During total hip arthroplasty (THA), medialisation of the cup decreases the lever arm of body weight and is considered to be beneficial. Theoretically it should be compensated by an equivalent increase of the femoral offset in order to maintain global offset. Goal of the study: We investigated via a numerical model the forces on each bundle of the abductor muscles and the loading forces at the head-cup interface. We compared THA with and without medialisation of the cup and with and without restoration of the global offset. Method: A digital finite element model of the hip joint with THA was constructed. Monopodal weight-bearing was simulated with the cup positioned so that the hip centre of rotation was left unchanged. Forces in the abductors and pressure on the prosthetic head were measured and then compared with three other configurations: 1. Medialisation of the cup by 5 to 15mm with reproduction of the native femoral offset or; 2. with an increased femoral offset compensating for the cup medialisation and; 3. no medialisation of the cup with a femoral offset increased. Results: Medialisation of the cup decreased stresses on the head-cup interface and on the abductor muscles, even when the global offset was not restored. Anatomical placement of the cup did not give the best results. The optimal outcome in terms of stress was observed when the cup was medialised but global offset restored. Any increase of global offset significantly increases the length and the tension in the anterior bundles of the abductor muscles. [ABSTRACT FROM AUTHOR]

Background: The posterolateral corner of the knee consists of static and dynamic stabilizing structures. Knee injuries often include the posterolateral structures. The popliteus muscle-tendon unit is known as the major dynamic stabilizer of the posterolateral corner.Hypothesis: The dynamic stabilization of the posterolateral structures of the knee via the popliteus muscle-tendon unit during a squatting exercise follows a constant activation pattern.Study Design: Controlled laboratory study.Methods: Within the pilot study, 6 volunteers performed 2 exercises to verify the electrode position scheme and to analyze crosstalk. In the main study 2 static exercises (standing and standing with knees flexed 90°) and 2 dynamic exercises (isolated popliteus muscle activation and squats) were recorded in 17 volunteers. Electromyograms were obtained of the popliteus, medial and lateral gastrocnemius, and quadriceps muscles. Knee angle-related muscle activity was recorded.Results: In the pilot study it was assumed that the chosen electrode position allowed selective measurement of popliteus muscle activity. In the main study the mean popliteus onset angle was 43° ± 14° of flexion; activity lasted through the reversal point of the squat to 58° ± 21° of flexion during extension movement. Popliteus activity during all testing cycles revealed that the activity in the standing position is the smallest. The highest activity was recorded during the squat and the popliteus muscle-tendon unit exercise.Conclusion: This study demonstrates an activation pattern of the popliteus muscle-tendon unit with high interindividual differences in the onset angles. A constant activation during the reversal phase of the squatting exercise could be observed.Clinical Relevance: Reconstructive procedures of the posterolateral structures often include reconstruction of the popliteus muscle-tendon unit. Reconstructive procedures are usually done in a static manner, thus not addressing the dynamic stabilizing structure in a true functional way. The findings of the current study may be a useful contribution to the ongoing discussion of this topic. [ABSTRACT FROM AUTHOR]

The evaluation of hip abductor strength is useful in assessing of the outcome of hip surgery. Hand-held dynamometers are available, but they are less reliable in assessing hip abductor strength than some other muscle groups. We describe a new device designed to measure hip abductor strength, which is practical in a clinical setting. A system of constraints, pads and reference points was devised to make force measurements as little examiner-dependent as possible. Reproducibility was assessed in a controlled setting. The abductor strength of ten healthy young subjects (average age 28 years) was tested twice on each side by two independent examiners. Tests were performed in a supine position, eliminating the influence of gravity and examiner intervention. The results indicated high reproducibility, the maximal measurement uncertainty being within 1 N. Intra-class correlation coefficients ranged from 0.85-0.98 for intra-rater reproducibility, and 0.81-0.96 for inter-rater reporoducibility. The coefficient of variation was lower than 10%. The device described may be suitable for routine clinical assessment of patients after hip surgery. [ABSTRACT FROM AUTHOR]

Loss of muscle mass after stroke has implications for strength and functional ability and may also contribute to impaired glucose metabolism. Therefore, prevention of muscle loss is desirable. Before interventions to prevent loss of muscle can be designed and evaluated, the expected rate, magnitude and timing of muscle loss need to be understood. A systematic search was undertaken to identify all studies that investigated changes in skeletal muscle mass, volume or cross-sectional area in people after stroke. Studies that used either direct measures of muscle size (computer tomography, magnetic resonance imaging or ultrasound) or measures of lean tissue mass (dual X-ray absorptiometry) were included. Fourteen trials were found and the results were pooled for differences in lean tissue mass between the paretic and the nonparetic leg and arm as well as differences in the midthigh cross-sectional area. In individuals at least 6-month poststroke, there was significantly less lean tissue mass in the paretic compared with the nonparetic lower limb (MD 342·3 g, 95% confidence interval 247·0–437·6 g) and upper limb (MD 239·9 g, 95% confidence interval 181·7–298·2 g), and significantly less midthigh muscle cross-sectional area (MD 15·4 cm2, 95% confidence interval 13·8–16·9 cm2). There were insufficient data to pool with regard to change in muscle mass over time. There is a significant difference in the regional muscle mass in the paretic vs. the nonparetic limb in individuals greater than 6-months poststroke but little is known about how early and how quickly changes in muscle mass occur. [ABSTRACT FROM AUTHOR]