Assessment of fluid ingress into the graft-host interface of osteochondral grafts and synthetic scaffolds under cyclic axial loading in a tibio-femoral model

This study developed an in vitro method to evaluate fluid ingress into the graft-host interface of osteochondral grafts and mimetic constructs and the risk of graft subsidence, using porcine and ovine tibio-femoral models, to investigate mechanisms associated with cyst development. Distal femurs were implanted with two osteochondral grafts or mimetic constructs. One was implanted axially with the loading direction at the point of initial contact of the femur and tibia (“loaded graft”); another on an unloaded portion of the opposite condyle (“unloaded graft”). During testing under a uniaxial cyclic loading regime, the specimens were housed in a contrast medium. Micro-CT scans taken before and after testing allowed the movement of the contrast fluid to be visualized. Fluid ingress was quantified by comparing the greyscale distribution across line profiles between the μCT scans. Ingress was calculated at six sites of interest: two at each graft site (“graft-host interface”, “graft centre”), one through “loaded host bone”, and one through “unloaded host bone”. Graft presence and loading were key factors to promote fluid ingress (p = 0.001). Fluid ingress at loaded graft-host interfaces relative to the unloaded host bone of porcine-in-porcine was 2.4 ± 8.9 mm, porcine-in-ovine was 9.9 ± 3.1 mm, and mimetic constructs-inporcine was 3.6 ± 3.8 mm. A mismatch in material properties between the graft and host bone promoted ingress, driven by host bone quality. Subchondral bone damage and fluid pooling below grafts was detectable from μCT images. Results indicate host bone quality should be considered when assessing a patient’s suitability for surgery.