Computed Tomography and In Vivo 9.4 Tesla Magnetic Resonance
Imaging as a Comprehensive Tool to Assess Variably Healed 6 and 52
Week Osteochondral Knee Defects
+1 Menendez, M I; 1Powell, K A; 1 Carlton, M; 1 Bertone, A L
+1 The Ohio State University, Columbus, Ohio
[email protected]
INTRODUCTION: Experimentally-created full-thickness
osteochondral defects are commonly used to study healing of bone
and cartilage in vivo. Frequently used animal models include small
animals such as rabbits1, guinea pigs and rats. Quantifying bone
and cartilage, particularly serially in live small animals, is a
challenge to obtain high resolution within a reasonable acquisition
time and to have confidence in the location of the defect once
healed. The goal of our study was to use high resolution imaging
modalities individually, and in combination, to assess bone,
cartilage and meniscus in healing rabbit knee defects. METHODS: The
study protocol was approved by The Ohio State University IACUC.
Osteochondral defects had been drilled (3mm diameter, 5 mm depth)
bilaterally on the medial and lateral condyles of the distal femur
of each rabbit and assigned a variety of protocols, including
injection with viral vectors encoding for bone morphogenetic
proteins (BMP-2 and BMP-6). These treatments resulted in a range of
bone and cartilage healing within the core of the drill hole,
permitting imaging development and validation over a diversity of
extent and type of repair tissue. Under general anesthesia at 52
weeks of healing, 10 rabbit distal femurs (n=20) were scanned in a
Bruker BioSpec 94/30 (Bruker BioSpin, Germany) scanner using a 40
mm rat brain surface coil in a 154 mm quadrature volume resonator.
Parameters and coils were adjusted to maximize the resolution of
the soft tissues (cartilage and meniscus) or bone in the images.
Immediately after euthanasia and harvest of distal femurs, µCT was
performed at 6 weeks (n=10) and 52 weeks (n=10) of healing using an
InveonTM system (Siemens, Erlangen Germany). Outcome µCT
measurements included Bone Mineral Density (BMD; mg/cm3), Bone
Mineral Content (BMC; mg), Bone Volume (BV; cm3) and Tissue Volume
(TV; cm3). In addition, a subjective visual core for extent and
severity of surface irregularity of defects in the µCT 3D
reconstructions and the gross specimens was performed (Fig 1). For
52 weeks data, isotropic data sets at a spatial resolution of 0.02
mm were obtained and down sampled to a resolution of 0.08 mm for
automated spatial registration and comparison to the MSME MRI data
sets.
RESULTS: Micro-computed Tomography: On µCT, bone cores had
greater amount and density of bone at 52 weeks than 6 weeks.
(Figure 2) At 6 weeks, there were no significant differences in
BMD, BMC, BV and TV among the defects. As expected, at 52 weeks,
the µCT confirmed a greater BMD, BMC and BV (p
