Tibial Cartilage Damage and Deformation at Peak Displacement Compression During Simulated Landing Impact

Background: Structural changes of articular cartilage at the point of peak displacement compression during a landing impact are unknown.

Hypothesis: Extent of damage and deformation is significantly different for superficial, middle, and deep cartilage zones at peak displacement compression during simulated landing impact compared with after impact.

Study Design: Controlled laboratory study.

Methods: Explants were extracted from porcine tibial cartilages and divided into 3 test conditions: nonimpact control, impact and release, and impact and hold. Impact compression, with peak deformation of 2 mm, was applied based on a single 10-Hz haversine to simulate landing impact. For impact and release, explants were subjected to formalin fixation on removal of load after impact. For impact and hold, explants were immediately immersed in formalin with peak deformation maintained at 2 mm. After fixation, the explants underwent histology, whereby Mankin scores and cartilage thicknesses were obtained.

Results: Peak stresses of 9.8 to 28.1 MPa were noted during impact compression. For impact and release, substantial cartilage defects such as surface fraying and fissures were observed. For impact and hold, explants exhibited less severe matrix damage, such as superficial irregularities and tidemark disruption. Mankin scores were lower (indicating less damage; P < .05) in impact and hold than in impact and release condition. Superficial cartilage zone thickness was reduced ( P < .05) in both impact and hold and impact and release conditions, relative to nonimpact control.

Conclusion: Not only does the loading phase of impact compression play a role in introducing substantial damage and deformation to cartilage, the unloading phase contributes to overall cartilage damage by exacerbating fissure propagation from surface lesions.

Clinical Relevance: Imaging of clinical injuries may underestimate the magnitude of cartilage compression that occurred during injury. Cartilage tissue engineering scaffolds must be designed to cope with the effects of loading and unloading phases, especially at the superficial zone, so that the repair site can function as well as does the neighboring native cartilage.