Osteochondral resurfacing implantation angle is more important than implant material stiffness

Abstract

Osteochondral resurfacing implants are a promising treatment for focal cartilage defects. Several implant-factors may affect the clinical outcome of this treatment, such as the implant material stiffness and the accuracy of implant placement, known to be challenging. In general, softer implants are expected to be more accommodating for implant misalignment than stiffer implants, and motion is expected to increase effects from implant misalignment and stiffness. 3D finite element models of cartilage/cartilage contact were employed in which implantation angle (0°, 5°, 10°) and implant material stiffness (E = 5 MPa, 100 MPa, 2 GPa) were varied. A creep loading (0.6 MPa) was simulated, followed by a sliding motion. Creep loading resulted in low maximum collagen strains of 2.5% in the intact case compared to 11.7% with an empty defect. Implants mostly positively affected collagen strains, deviatoric strains, and hydrostatic pressures in the adjacent cartilage, but these effects were superior for correct alignment (0°). The main effect of implant misalignment was bulging of opposing cartilage tissue into the gap caused by the misalignment. This increased collagen strains and hydrostatic pressures. Deviatoric strains were increased adjacent to the gap. Subsequent sliding initially increased strains for a stiff, misaligned implant, but generally sliding decreased strains. In conclusion, implants can decrease the detrimental effect of defects, but correct implant alignment is crucial, more than implant material stiffness. Implant misalignment causes a gap, causing potentially damaging cartilage deformation during prolonged loading, for example, standing, even for soft implants. Mild motion may positively affect the cartilage. © 2018 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 9999:1-12, 2018.

A partial hemi-resurfacing preliminary study of a novel magnetic resonance imaging compatible polyetheretherketone mini-prosthesis for focal osteochondral defects

“…However, according to a previous research, partial articular resurfacing surgery has a certain positive significance for joint function and local cartilage [ 15 ]. The mini-prosthesis relieves shear and friction forces around cartilages, thereby avoiding further cartilage damage [ 15 ].…”

“…However, according to a previous research, partial articular resurfacing surgery has a certain positive significance for joint function and local cartilage [ 15 ]. The mini-prosthesis relieves shear and friction forces around cartilages, thereby avoiding further cartilage damage [ 15 ]. Some factors, including the hardness of the material, surface lubrication characteristics, biocompatibility of the material, and inflammatory properties of ions or small particles released by the material, have potential negative effects on cartilages and their microenvironment [ [15] , [16] , [17] , [18] ].…”

In vitro and in vivo study on the osseointegration of BCP‐coated versus uncoated nondegradable thermoplastic polyurethane focal knee resurfacing implants

“…Bionate® 75D (Sh) is the highest stiffness medical grade TPU and could potentially be used as a bone‐substitute (Geary, Birkinshaw, & Jones, 2008). An osteochondral implant fully composed of TPU has the potential to overcome the typical drawbacks of metal‐based implants, as it is MRI‐compatible and theoretically would not lead to excessive stress in opposing cartilage (Heuijerjans, Wilson, Ito, & van Donkelaar, 2018; Kanca et al, 2018). Polymers however, pose specific challenges when implanted in bone.…”

The performance of resurfacing implants for focal cartilage defects depends on the degenerative condition of the opposing cartilage

“…For instance, in an in vivo study, Martinez-Carranza et al, 2016 showed that damage to the opposing cartilage appears to be sensitive to implant position (Martinez-Carranza et al, 2016). Heuijerjans et al (2018) demonstrated using a computational approach, that softer materials such as PCU may be preferred when implant positioning is suboptimal. (Heuijerjans et al, 2018).…”

“…Heuijerjans et al (2018) demonstrated using a computational approach, that softer materials such as PCU may be preferred when implant positioning is suboptimal. (Heuijerjans et al, 2018). Another advantage of PCU implants over metal is that they can be imaged with MRI, the main orthopaedic imaging modality for cartilage defects.…”