Experimental study of a sheathed core bone plug in Bashti ACL reconstructive method

Bashti Bone Plug Technique (BBPT) is an implant-less surgical technique uses for Anterior Cruciate Ligament (ACL) reconstruction. The technique uses a core bone plug obtained the patient to secure the tendon graft. The authors previously shown the Bashti insertion technique needs and improvement as the core bone cut with very thin cutter and therefore the core bone has a small dimension different with its tunnel. When the tendon graft passes through the tunnel the core bone should be inserted back into the tunnel. Because of the small gap and high friction between the core bone, graft and tunnel, the insertion needs a considerable push force to insert the core bone into the tunnel. This may increase the risk of core bone's fracture during the insertion process. To reduce the risk of the fracture, the core bone was sheathed with a thin flexible cover. The sheath should provide a lower friction between the core bone at the time of insertion. The insertion also needs lower insertion force, and this reduces the risk of fracture. The sheath was designed considering its effect on the pull-out force. Although, the sheath should make the insertion easier but should not reduce the overall strength of the fixation. To examine the hypothesis of the study, a series of experimental test was performed using synthetic Sawbones as a model for human bone and bovine digital flexor tendons as graft tissues. The density of the Sawbones was correlated to the bone density of a young human. The core bone cover sheath was made of PVC and PTFE polymers with two different thicknesses. To insert the sheathed core bone, hand hammer and electrical hammer were used. Following the insertion, the structure was tested under a cyclical loading. Initially a preconditioning loading of 5-20 N for 10 cycles with 1 Hz frequency was applied to justify the setup. Then a cyclical loading of 40-120 sinusoidal loading for 100 cycles with 1 Hz frequency was applied. The cyclical test was immediately followed by a single cycle test to failure with a rate of 20 mm/s. The mechanical strength and stiffness in the PTFE sheath with 0.1 mm were 343.86 N and 114.62 N/mm and in the PVC sheath with similar thickness, 235.95 N and 93.36 N/mm. In the next step, the sheath with bigger mechanical properties was selected and compared with the 0.2 mm PTFE sheath. The ultimate result obtained for 0.2 mm PTFE sheath, were 420.02 N strength and 126.16 N/mm stiffness. It was noticed that, the inserted length of core bone inside the tunnel has a significant effect on the fixation strength. The best result will be expected when the core bone is fully inserted into the tunnel. Please note this paper originally written in Farsi language. The full paper is attached.