Summary: Lack of initial mechanical stability of cementless prostheses may be responsible for fibrous tissue fixation of prosthetic components to bone. TO study the influence of micromovements on bony ingrowth into titanium alloy (Ti) and hydroxyapatite (HA)-coated implants, a loaded unstable device producing movements of 500 pm during each gait cycle was developed. Mechanically stable implants served as controls. The implants were inserted into the weight-bearing regions of all four femoral condyles in each of seven mature dogs. Histological analysis after 4 weeks of implantation showed a fibrous tissue membrane surrounding both Ti and HA-coated implants subjected to micromovements, whereas variable amounts of bony ingrowth were obtained in mechanically stable implants. The pushout test showed that the shear strength of unstable Ti and HA implants was significantly reduced as compared with the corresponding mechanically stable implants (p < 0.01). However, shear strength values of unstable HA-coated implants were significantly greater than those of unstable 'l'i implants (p < 0.01) and comparable to those of stable Ti implants. The greatest shear strength was obtained with stable HA-coated implants, which was threefold stronger as compared with the stable Ti implants (p < 0.001). Quantitative determination of bony ingrowth agreed with the mechanical test except for the stronger anchorage of unstable HA implants as compared with unstable Ti implants, where no difference in bony ingrowth was found. Unstable HA-coated implants were surrounded by a fibrous membrane containing islands of fibrocartilage with higher collagen concentration, whereas fibrous connective tissue with lower collagen concentration was predominant around unstable Ti implants. In conclusion, micromovements between bone and implant inhibited bony ingrowth and led to the development of a fibrous membrane. The presence of iibrocartilage and a higher collagen concentration in the fibrous membrane may be responsible for the increased shear strength of unstable HA implants. Mechanically stable implants with HA coating had the strongest anchorage and the greatest amount of bony ingrowth. Key Words: Bone ingrowth-Fibrous membraneHydroxyapatite-Micromotion-Porous ingrowth-Titanium. Porous coated prostheses were designed to obtain permanent fixation by ingrowth of bone into the porous implant surface. However, recent histological analyses of cementless tibia1 components (1 1,16) and total hip replacements (10,12) retrieved 285

Background Giant cell tumors of bone rarely metastasize but often recur locally after surgery. There is limited knowledge about the risk of recurrence related to different types of treatment.Patients and methods We analyzed factors affecting the local recurrence rate in 294 patients with giant cell tumors of the extremities using prospectively collected material from 13 centers. The median follow-up time was 5 (0.2-18) years.Results A local recurrence was diagnosed in 57 of 294 patients (19%). The overall 5-year local recurrence rate was 0.22. Univariate analysis identified young age and intralesional surgery to be associated with a higher risk of recurrence. Based on multivariate analysis, the relative risk was 2.4-fold for intralesional surgery compared to more extensive operative methods. There was no correlation between tumor size, tumor extension, sex of the patient, tumor location, or fracture at diagnosis and outcome. In the subgroup of 200 patients treated with intralesional surgery, the method of filling (cement or bone) was known for 194 patients and was statistically highly significant in favor of the use of cement.Interpretation Intralesional surgery should be the first choice in most giant cell tumors, even in the presence of a pathological fracture. After thorough evacuation, the cavity should be filled with cement.

Mathematics Subject Classification (2010) IntroductionLet k be a field and let D be a k-linear algebraic triangulated category with split idempotents. Let be the suspension functor of D and let s be a 2-spherical object of D, that is, the morphism space D(s, i s) is k for i = 0 and i = 2 and vanishes otherwise. Assume that s classically generates D, that is, each object of D can be built from s using (de)suspensions, direct sums, direct summands, and distinguished triangles.It was proved in [15, thm. 2.1] that D is uniquely determined by these properties. As we will explain, D is a good candidate for a cluster category of Dynkin type A ∞ . For instance, we show that there is a bijection between the cluster tilting subcategories of D and certain triangulations of the ∞-gon.We use this to give an example of a subcategory A which is weak cluster tilting, that is, satisfies A = ( −1 A ) ⊥ = ⊥ ( A ), but fails to be functorially finite. Perpendicular

No abstract

A semi-dualizing module over a commutative noetherian ring A is a finitely generated module C with RHom A (C, C) A in the derived category D(A).We show how each such module gives rise to three new homological dimensions which we call C-Gorenstein projective, C-Gorenstein injective, and C-Gorenstein flat dimension, and investigate the properties of these dimensions.