title: Humeral head resurfacing in central bone defects: in vitro stability of different implants with increasing defect size.
abstract: We examined the rotary motions of two distinct cementless surface replacement arthroplasties of the shoulder that were implanted on humeri with central spherical bone defects of 8%, 17%, and 37% of the head volume (n = 5 each). Rotary motions were measured under a cyclic torque application and translated into relative micromotions. Implant A with a perforated central crown had micromotions < 150 µm in all bony defects and during all simulated shoulder activities. Implant B with a central tapered tri-fin pin had no micromotions > 150 µm in defects of 0% and 8% during a strenuous activity like lifting 10 kg, but did exhibit micromotion > 150 µm in 40% of the experiments in defects of 17% and 37%, which could impair bony ingrowth. Implant B displayed a significant increase in micromotions for defects of 8% and 17% (p < 0.05). Our results suggest that implant A could be used without risk in spherical head defects up to 37% of volume, even in strenuous shoulder activities immediately after its implantation. Implant B, however, is recommended in spherical defects starting from 8% and only during light shoulder activities until bony integration of the implant has occurred.
authors.affiliation: Division of Shoulder/Elbow Surgery and Sports Medicine, Department of Orthopaedic Surgery, University Hospital Carl Gustav Carus Dresden, Fetscherstrasse 74, 01307 Dresden, Germany.
authors.forename: Philip
authors.initials: P
authors.lastname: Kasten
authors.forename: Christine
authors.initials: C
authors.lastname: Neubrech
authors.forename: Patric
authors.initials: P
authors.lastname: Raiss
authors.forename: Jan
authors.initials: J
authors.lastname: Nadorf
authors.forename: Markus
authors.initials: M
authors.lastname: Rickert
authors.forename: Eike
authors.initials: E
authors.lastname: Jakubowitz
mesh_terms: D000328:Adult; D000368:Aged; D019643:Arthroplasty, Replacement / Q000379:methods*; D015519:Bone Density; D006801:Humans; D058430:Humeral Head / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D019736:Prostheses and Implants; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012785:Shoulder Joint / Q000601:surgery*