Objective and sensitive assessment of cartilage repair outcomes lacks suitable
methods. This study investigated the feasibility of 3D ultrasound
biomicroscopy (UBM) to quantify cartilage repair outcomes volumetrically and
their correlation with established classification systems. 32 sheep underwent
bilateral treatment of a focal cartilage defect. One or two years post-
operatively the repair outcomes were assessed and scored macroscopically
(Outerbridge, ICRS-CRA), by magnetic resonance imaging (MRI, MOCART), and
histopathology (O'Driscoll, ICRS-I and ICRS-II). The UBM data were acquired
after MRI and used to reconstruct the shape of the initial cartilage layer,
enabling the estimation of the initial cartilage thickness and defect volume
as well as volumetric parameters for defect filling, repair tissue, bone loss
and bone overgrowth. The quantification of the repair outcomes revealed high
variations in the initial thickness of the cartilage layer, indicating the
need for cartilage thickness estimation before creating a defect. Furthermore,
highly significant correlations were found for the defect filling estimated
from UBM to the established classification systems. 3D visualisation of the
repair regions showed highly variable morphology within single samples. This
raises the question as to whether macroscopic, MRI and histopathological
scoring provide sufficient reliability. The biases of the individual methods
will be discussed within this context. UBM was shown to be a feasible tool to
evaluate cartilage repair outcomes, whereby the most important objective
parameter is the defect filling. Translation of UBM into arthroscopic or
transcutaneous ultrasound examinations would allow non-destructive and
objective follow-up of individual patients and better comparison between the
results of clinical trials
