Journal of Biomechanics 36 (2003) 1203–1208 Short Communication Short-term load bearing capacity of osteochondral autografts implanted by the mosaicplasty technique: an in vitro porcine model R.A. Whiteside a, *, J.T. Bryant a , R.P. Jakob b , P. Mainil-Varlet c , U.P. Wyss a,d a Department of Mechanical Engineering, Queen’s University, Kingston, Ont., Canada K7L 3N6 b Kantonsspital Freiburg, Switzerland c Institute of Pathology, University of Bern, Bern, Switzerland d Centerpulse Orthopedics Ltd., Winterthur, Switzerland Accepted 12 March 2003 Abstract Articular surface congruency and graft stability are considered essential factors in the success of osteochondral grafting; however, quantitative measures of short-term load bearing capacity of grafts implanted by the mosaicplasty technique have not been reported. The purpose of this study was to develop a live tissue in vitro model to examine short-term fixation strength of mosaicplasty autografts immediately after and 1 week following graft implantation. Cylindrical osteochondral autografts were implanted in vitro by the mosaicplasty technique on five pairs of porcine femoral condyles within one and a half hours of animal sacrifice. Immediately following the surgical procedure, graft push-in and pull-out strength tests as well as indentation tests to determine modulus of the surrounding cancellous bone were performed on half of the specimens from the distal femurs of each animal. The remaining specimens, matched for location in the contralateral leg, were incubated in culture medium for 7 days prior to performing the same set of mechanical tests. Averaged push-in and pull-out graft fixation strength decreased 44% from 135.7 to 75.5N over the 7-day period, while no change in modulus was detected in the surrounding cancellous bone. These in vitro results demonstrate a substantial deterioration of short-term fixation strength of mosaicplasty grafts from the immediate post-operative state. Such a reduction in short-term graft load bearing capacity may pose a threat to the surgically established articular surface congruency and blood vessels formed during the early stages of the healing response. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Osteochondral; Graft; Fixation; Press-fit; Mosaicplasty 1. Introduction It is well documented that articular cartilage is unable to heal partial-thickness lesions and that full-thickness lesions including subchondral bone most often produce fibrocartilage scar tissue inappropriate for full weight bearing (Chu et al., 1999; Hunziker, 1999; Marcacci et al., 1999; Buckwalter and Mankin, 1997, 1998). Several treatment options exist for focal lesions of the articular surface; however, none have exhibited consis- tent long-term success (Hasler et al., 1999; Hunziker, 1999; Kish et al., 1999; Buckwalter and Mankin, 1998; Oates et al., 1995). Osteochondral mosaicplasty is a surgical technique designed to repair focal lesions using several cylindrical osteochondral grafts harvested from lesser load-bearing regions of the knee. Results of clinical studies involving the use of mosaicplasty to repair focal defects have been promising (Bobic, 1999; Hangody et al., 1998). The mosaicplasty technique has also been successfully employed to reattach loose osteochondral fragments in cases of osteochondritis dissecans of the knee (Berlet et al., 1999) and may prove to be a suitable method for attachment of sheets of autologous bio-engineered cartilage due to its ability to provide initial fixation and load-bearing capacity (Mainil-Varlet et al., 2001). The mosaicplasty technique takes advantage of the healing capability of live cancellous bone to anchor osteochondral graft tissue. A successful result exhibits long-term graft fixation capable of full weight bearing as ARTICLE IN PRESS *Corresponding author. Tel.: +1-613-533-2579; fax: +1-613-533- 6489. E-mail address: whitesid@me.queensu.ca (R.A. Whiteside). 0021-9290/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0021-9290(03)00115-5