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Effects of Resumption of Loading on Stress-Shielded Autografts After Augmentation Procedures

An Experimental Study

Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Sapporo

Kazunori Yasuda, MD, DcMedSci

Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Sapporo

Kozaburo Hayashi, PhD

Department of Mechanical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka, Japan

Noritaka Yamamoto, PhD

Department of Mechanical Engineering, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka, Japan

Kiyoshi Kaneda, MD, DcMedSci

Department of Orthopaedic Surgery, Hokkaido University School of Medicine, Sapporo

An experiment was conducted to verify if resumption of loading (restressing) on autografts after augmentation procedures can recover the mechanical properties of the grafts that were deteriorated by complete stress shielding. One hundred ten Japanese White rabbits were used. After the patellar tendon in each right knee was frozen in situ, tension applied to the tendon was released for an interval in 80 rabbits. These 80 animals were divided into four groups of 20 rabbits. The patellar tendons in these groups were completely shielded from stress for 1, 2, 3, and 6 weeks, respectively. From each group, rabbits were sacrificed immediately before restressing (N = 5), and after 3 (N = 5), 6 (N = 5), and 12 (N = 5) weeks of restressing. The remaining 30 rabbits underwent sham operations. The results showed that complete stress shielding markedly de creased tensile strength of the patellar tendon. How ever, if restressing was applied within 3 weeks of com plete stress shielding, the once-reduced strength gradually increased to the level of the sham-operated tendons by 12 weeks after the onset of restressing. Restressing applied after 6 weeks of complete stress shielding also increased the strength of the tendon; however, it reached only 65% the strength of the sham- operated tendons at 12 weeks after restressing. The timing to apply stress to grafts should be carefully determined for optimal recovery.

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