Stability of small pegs for cementless implant fixation. Issue 12 (23rd May 2017)

• Record Type: Journal Article
• Authors: Geraldes, Diogo M.; Hansen, Ulrich; Jeffers, Jonathan; Amis, Andrew A.
• Is Part Of: Journal of orthopaedic research. Volume 35:Issue 12(2017)
• Page Start: 2765
• Page End: 2772
• Publication Date: 2017-05-23
• Subjects: cementless implant fixation -- interference fit -- press‐fit -- shoulder -- glenoid; Orthopedics -- Periodicals; Musculoskeletal system -- Periodicals; 616.7
• DOI: 10.1002/jor.23572
• Languages: English
• ISSNs: 0736-0266

Abstract

ABSTRACT: Most glenoid implants rely on large centrally located fixation features to avoid perforation of the glenoid vault in its peripheral regions. Upon revision of such components there may not be enough bone left for the reinsertion of an anatomical prosthesis. Multiple press‐fit small pegs would allow for less bone resection and strong anchoring in the stiffer and denser peripheral subchondral bone. This study assessed the fixation characteristics, measured as the push‐in ( P in ) and pull‐out ( P out ) forces, and spring‐back, measured as the elastic displacement immediately after insertion, for five different small press‐fitted peg configurations manufactured out of UHMWPE cylinders (5 mm diameter and length). A total of 16 specimens for each configuration were tested in two types of solid bone substitute: Hard (40 PCF, 0.64 g/cm 3, worst‐case scenario of P in ) and soft (15 PCF, 0.24 g/cm 3, worst‐case scenario of spring‐back and P out ). Two different diametric interference‐fits were studied. Geometries with lower stiffness fins (large length to width aspect ratio) were the best performing designs in terms of primary fixation stability. They required the lowest force to fully seat, meaning they are less damaging to the bone during implantation, while providing the highest P out / P in ratio, indicating that when implanted they provide the strongest anchoring for the glenoid component. It is highlighted that drilling of chamfered holes could minimize spring‐back displacements. These findings are relevant for the design of implants press‐fitted pegs because primary fixation has been shown to be an important factor in achieving osseointegration and longevity of secondary fixation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2765–2772, 2017. Abstract : The fixation characteristics for five different UHMWPE small press‐fitted peg configurations were assessed. 16 specimens for each configuration were tested in two types of solid bone substitute representing soft and hard bone and two diametric interference‐fits. Geometries with lower stiffness with high aspect ratios fins were the best performing designs in terms of primary fixation stability. They required the lowest force to fully seat, they are less damaging to the bone and provided the strongest anchoring. It is highlighted that drilling of chamfered holes could improve implant sitting.