Background Resistant organisms are difficult to eradicate in infected total knee arthroplasty. While most surgeons use antibiotic-impregnated cement in these revisions, the delivery of the drug in adequate doses is limited in penetration and duration. Direct infusion is an alternate technique. Questions/purposes We asked whether single-stage revision and direct antibiotic infusion for infected TKA would control infection in patients with methicillin-resistant Staphylococcus aureus (MRSA) infections.

An investigation is presented of the response of a three-degree-of-freedom system with quadratic nonlinearities and the autoparametric resonances w 3 ~ 2w 2 and w 2 ~ 2~o~ to a harmonic excitation of the third mode, where the ~o,,, are the linear natural frequencies of the system. The method of multiple scales is used to determine six first-order nonlinear ordinary differential equations that govern the time variation of the amplitudes and phases of the interacting modes. The fixed points of these equations are obtained and their stability is determined. For certain parameter values, the fixed points are found to lose stability due to Hopf bifurcations and consequently the system exhibits amplitude-and phase-modulated motions. Regions where the amplitudes and phases display periodic, quasiperiodic, and chaotic time variations and hence regions where the overall system motion is periodically, quasiperiodically, and chaotically modulated are determined. Using various numerical simulations, we investigated nonperiodic solutions of the modulation equations using the amplitude F of the excitation as a control parameter. As the excitation amplitude F is increased, the fixed points of the modulation equations exhibit an instability due to a Hopf bifurcation, leading to limit-cycle solutions of the modulation equations. As F is increased further, the limit cycle undergoes a period-doubling bifurcation followed by a secondary Hopf bifurcation, resulting in either a two-period quasiperiodic or a phase-locked solution. As F is increased further, there is a torus breakdown and the solution of the modulation equations becomes chaotic, resulting in a chaotically modulated motion of the system.

We evaluated the results of an operative technique used in five patients (five hips) to reconstruct the greater trochanter with a gluteus maximus flap transfer during revision total hip arthroplasty. We exposed the hip through a posterior approach that split the gluteus maximus in its midsubstance. We then raised a flap from the posterior portion of the gluteus muscle that was elevated proximally to create a triangular muscle flap. The flap was sewn into the gap between the greater trochanter and lateral cortex of the femur and secured to the inner surface of the anterior capsule of the hip. With the hip abducted 10 degrees to 15 degrees, the edges of the gluteus maximus were closed over the flap and the greater trochanter. We compared the results of these patients with those of five patients (five hips) who had the trochanter left unrepaired and those of four patients (four hips) who had excision of the greater trochanter and suture closure of the intervening gap. The flap group had less pain, lower incidence of limp and Trendelenburg sign, and less need for support than the other two groups, but range of motion decreased.

In this work the nonlinear localized modes of an n-degree-of-freedom (DOF) nonlinear cyclic system are examined by the averaging method of multiple scales. The set of nonlinear algebraic equations describing the localized modes is derived and is subsequently solved for systems with various numbers of DOF. It is shown that nonlinear localized modes exist only for small values of the ratio (k/μ), where k is the linear coupling stiffness and μ is the coefficient of the grounding stiffness nonlinearity. As (k/μ) increases the branches of localized modes become nonlocalized and either bifurcate from “extended” antisymmetric modes in inverse, “multiple” Hamiltonian pitchfork bifurcations (for systems with even-DOF), or reach certain limiting values for large values of(k/μ) (for systems with odd-DOF). Motion confinement due to nonlinear mode localization is demonstrated by examining the responses of weakly coupled, perfectly periodic cyclic systems caused by external impulses. Finally, the implications of nonlinear mode localization on the active or passive vibration isolation of such structures are discussed.