Subchondral bone remodeling: comparing nanofracture with microfracture. An ovine in vivo study.
OBJECTIVE
microfracture, providing direct stimulation of chondrogenic mesenchymal stem cells (MSCs) in the subchondral bone, remains the most frequently used primary cartilage repair technique. However, the newly formed type I collagen-rich fibrocartilaginous tissue has poor biomechanical properties and a tendency to degenerate. To overcome these limitations the nanofracture technique was introduced. Our purpose was to compare subchondral bone remodeling 6 months after microfracture versus nanofracture (subchondral needling) treatment in an ovine model.


METHODS
full-thickness chondral lesions were created in the load-bearing area of the medial femoral condyles in four adult sheep. Each animal was then treated on one side with microfracture and on the contralateral side with nanofracture. Subchondral bone remodeling was assessed by micro-CT using a Bruker(®) SKYSCAN and CTVOX 2.7 software (Bruker Corp., Billerica, MA, USA) for image reconstruction; trabecular bone density measurements were performed through a color-representation structure thickness analysis.


RESULTS
at the six-month endpoint, the microfracture-treated samples showed limited perforation depth and cone-shaped channels with large diameters at the joint surface. The channel walls displayed a high degree of regularity with significant trabecular bone compaction leading to a sealing effect with limited communication with the surrounding trabecular canals. Condyles treated with nanofracture showed channels characterized by greater depth and smaller diameters and natural irregularities of the channel walls, absence of trabecular compaction around the perforation, remarkable communication with trabecular canals, and neo-trabecular remodeling inside the channels.


CONCLUSIONS
nanofracture is an effective and innovative repair technique allowing deeper perforation into subchondral bone with less trabecular fragmentation and compaction when compared to microfracture; it results in better restoration of the normal subchondral bone architecture at six months.


CONCLUSIONS
our data support the use of smaller-diameter and deeper subchondral bone perforation for MSC stimulation; this technique may prove to be an attractive alternative to standard microfracture procedures.
Orthopaedic and Traumatology Unit, Hospital San Francesco, Nuoro, Italy.
Pietro
P
Zedde
Orthopaedic and Traumatology Unit, Hospital San Francesco, Nuoro, Italy.
Sebastiano
S
Cudoni
Orthopaedic Department, University of Sassari, Italy.
Giacomo
G
Giachetti
Department of Veterinary Medicine, University of Sassari, Italy.
Maria Lucia
ML
Manunta
Department of Veterinary Medicine, University of Sassari, Italy.
Gerolamo
G
Masala
Polcoming Department, University of Sassari, Italy.
Antonio
A
Brunetti
Orthopaedic Department, University of Sassari, Italy.
Andrea Fabio
AF
Manunta
mesenchymal stem cell stimulation; micro-CT; microfracture; nanofracture; ovine; subchondral bone