Methods

Nine patients who were diagnosed and treated for chronic fungal PJIs after TKA in a single center from January 2001 to December 2016 were enrolled. Two-stage exchange arthroplasty was performed. During the 1st stage resection arthroplasty, amphotericin-impregnated cement spacer was inserted for all patients. Systemic antifungal medication was used during the interval between two stage operations. Patients were followed up for more than 2 years after exchange arthroplasty and their medical records were reviewed.

Methods

A surrogate consisting of the lower limb with overlying soft tissue was developed to simulate THR performed via a 10cm incision using the posterior approach. The surrogate was modified to match the resistance of the body to retraction of the incision, mobilization of the femur and hammering of the implanted femoral component. An instrumented femoral stem (SL PLUS) was surgically implanted into the bone after attachment of 3 miniature accelerometers (Dytran Inc) in an orthogonal array to the proximal surface of the prosthesis. A 32mm cobalt chrome femoral head was mounted on the trunnion (12/14 taper, machined) of the femoral stem. 15 Board-certified and trainee surgeons replicated their surgical technique in exposing the femur and impacting the modular head on the tapered trunnion. Impaction was performed using an instrumented hammer (5000 Lbf Dytran impact hammer) that provided measurements of the magnitude and temporal variation of the impact force. The components of force acting along the axis aof the neck and in the AP and ML directions were continuously samples using the accelerometers.

Methods

Four patient-specific scapular geometries were developed from CT data in 3D Slicer using a semi-automatic threshold technique. A generic glenoid component including the baseplate, a lateralization spacer, and four fixation screws was modelled as a monoblock. Screws were simplified as 4.5 mm diameter cylinders. The glenoid of each scapula was virtually reamed after which the glenoid component was placed. Models were meshed with quadratic tetrahedral elements with an edge length of 1.3 mm.

The baseplate and lateralization spacer were assigned titanium material properties (E = 113.8 GPa and ν = 0.34). Screws were also assigned titanium material properties with a corrected elastic modulus (56.7 GPa) to account for omitted thread geometry. Cortical bone was assigned an elastic modulus of 17.5 GPa and Poisson's ratio of 0.3. Cancellous bone material properties in the region of the glenoid were assigned on an element-by-element basis using previously established equations to convert Hounsfield Units from the CT data to density and subsequently to elastic modulus [1].

Fixed displacement boundary conditions were applied to the medial border of each scapula. Contact was simulated as frictional (μ = 0.8) between bone and screws and frictionless between bone and baseplate/spacer. Compressive and superiorly-oriented shear loads of 686 N were applied to the baseplate/spacer. Lateralization of the COR up to 16 mm was simulated by applying the shear load further from the glenoid surface in 4 mm increments (Fig. 1A). All lateralization levels were simulated with four and two (superior and inferior) fixation screws.

Absolute micromotion of the baseplate/spacer with respect to the glenoid surface was averaged across the back surface of the spacer and normalized to the baseline configuration considered to be 0 mm lateralization and four fixation screws. Adduction ROM was measured as the angle between the glenoid surface and the humeral stem when impingement of the humeral cup occurred (Fig. 1B).