Articular cartilage in adults has limited ability for self-repair. Some met
hods devised to augment the natural healing response stimulate some regener
ation, but the repair is often incomplete and lacks durability. Hyaluronan-
based polymers were tested for their ability to enhance the natural healing
response. It is hypothesized that hyaluronan-based polymers recreate an em
bryonic-like milieu where host progenitor cells can regenerate the damaged
articular surface and underlying bone. Osteochondral defects were made on t
he femoral condyles of 4-month-old rabbits and were left empty or filled wi
th hyaluronan-based polymers. The polymers tested were ACP sponge, made of
crosslinked hyaluronan, and HYAFF-11 sponge, made of benzylated hyaluronan.
The rabbits were killed 4 and 12 weeks after surgery, and the condyles wer
e processed for histology. All 12-week defects were scored with a 29-point
scale, and the scores were compared with a Kruskall-Wallis analysis of vari
ance on ranks. Untreated defects filled with bone tissue up to or beyond th
e tidemark, and the noncalcified surface layer varied from fibrous to hyali
ne-like tissue. Four weeks after surgery, defects treated with ACP exhibite
d bone filling to the level of the tidemark and the surface layer was compo
sed of hyaline-like cartilage well integrated with the adjacent cartilage.
At 12 weeks, the specimens had bone beyond the tidemark that was covered wi
th a thin layer of hyaline cartilage. Four weeks after surgery, defects tre
ated with HYAFF-11 contained a rim of chondrogenic cells at the interface o
f the implant and the host tissue. In general, the: 12-week defects exhibit
ed good bone fill and the surface was mainly hy aline cartilage. Treated de
fects received significantly higher scores than untreated defects (p < 0.05
), and ACP-treated defects scored significantly higher than HYAFF-11-treate
d defects (p < 0.05). The introduction of these hyaluronan-based polymers i
nto defects provides an appropriate scaffolding and favorable microenvironm
ent for the reparative process. Further work is required to fully assess th
e long-term outcome of defects treated with these polymers.