Experimental autologous osteochondral plug transfer in the treatment of focal chondral defects: magnetic resonance imaging signs of technical success in sheep.
OBJECTIVE
To describe the magnetic resonance imaging (MRI) signs of technically successful osteochondral plug transfer and to correlate the findings with histology using the Mankin score.


METHODS
The study was done in a prospective animal experiment: 11 adult black-head sheep underwent surgical treatment with osteochondral plug transfer of a knee joint. The animals were killed 6 months later and MRI of the joints was done immediately. MRI was applied with a 1.5T MR scanner using a spin-echo (SE) T1-weighted, turbo spin-echo (TSE) T2-weighted with spectral fat suppression and a fat-suppressed 3D-spoiled gradient echo (GRE) sequence (manufacturer's acronym: FLASH) (TR 50.0 ms, TE 11.0 ms, flip 35 degrees). After MRI, all knee joints were dissected and a biopsy of the plug and the adjacent cartilage was taken. Classification of the cartilage biopsies was carried out in accordance with a modified Mankin score.


RESULTS
Cartilage repairs with a hypointense cartilage signal in the FLASH 3D sequence were correlated with poor histological results (lower Mankin score). Histologically, the regions of cartilage with a hypointense signal showed a fibrocartilage-like repair tissue. Hyaline cartilage with well-defined layers had the same signal intensity in the FLASH sequence relative to adjacent hyaline cartilage. There were two plugs with a surface defect, graded as Outerbridge grade 1 in MRI and histology. Both had a poor outcome in the histologic Mankin score. Grade 2-4 lesions were not observed in the MRI study nor in the histologic study.


CONCLUSIONS
MRI is a useful non-invasive tool for evaluating the morphologic status of osteochondral plug transfers. A good postoperative result of the cartilage repair was found histologically if an isointense cartilage signal of the graft was documented in the FLASH 3D sequence, and the graft had good congruity with the articular surface without defects.
Uhl
M
M
Department of Diagnostic Radiology, University Hospital Freiburg, Freiburg, Germany. UHL@MRS1.UKL.uni-freiburg.de
Lahm
A
A
Bley
T A
TA
Haberstroh
J
J
Mrosek
E
E
Ghanem
N
N
Erggelet
C
C
D000818:Animals; D002356:Cartilage / Q000637:transplantation*; D002358:Cartilage, Articular / Q000473:pathology* / Q000601:surgery*; D020219:Chondrogenesis; D004195:Disease Models, Animal; D017352:Echo-Planar Imaging; D005269:Femur / Q000637:transplantation*; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000473:pathology* / Q000601:surgery*; D012756:Sheep; D014182:Transplantation, Autologous