Osteochondral resurfacing with a novel hydrogel implant: biomechanical analysis (SS-57)

Abstract

The development and clinical use of synthetic osteochondral implants would avoid complications and limitations related to donor site morbidity or allograft tissue. We evaluated loading patterns and contact pressures of femoral condyle osteochondral grafting with a novel hydrogel implant. Materials and Methods: Using a custom loading apparatus an 80 N load was applied for 120 s to the femoral condyles of 11 fresh swine knees. Contact pressure was measured with Fuji prescale superlow pressure sensitive film under 5 conditions: (1) intact articular surface; (2) surface with 10 mm diameter circular defect; (3) defect grafted with a 10 mm diameter hydrogel plug, with the plug 1.0 mm elevated above adjacent cartilage surface; (4) plug flush; (5) plug sunk 1.0 mm below surface. The relative height was confirmed at each stage with a digital micrometer. The implant is an organic polymer-based material with mechanical properties similar to articular cartilage and designed to undergo repeated loading. Fuji film was scanned and digitally analyzed using Scion image analysis software. Results: Peak contact pressures were significantly elevated by 21% after defect creation (9.60 to 11.64 kg/cm2, P < .01). Grafting with a hydrogel plug resulted in a significant (p < .001) reduction of contact pressures to 7.58 kg/cm2 when the plug was placed flush to the surrounding articular surface. A hydrogel plug implanted 1mm elevated with respect to the surrounding cartilage (6.28 kg/cm2) was also significantly (P < .001) less than the peak contact pressure of an empty defect. Contact pressures with the plug sunk 1 mm (10.30 kg/cm2) were also significantly (P < .001) lower than an empty defect, but were somewhat higher than intact cartilage (P = .054). Conclusions: Osteochondral resurfacing with a flush hydrogel implant produced loading patterns and contact pressures similar to those produced by the intact specimens. The implant successfully reduced the contact pressure elevations caused by an osteochondral defect. In addition, graft-surface incongruities of 1.0 mm still resulted in a significant decrease in contact pressure compared to the defect state. These findings suggest that clinical use of such an implant would result in near-normal articular cartilage contact pressures.