Substantial Braking Force of Anterior Tibial Translation Induces the Spontaneous Healing of Murine Anterior Cruciate Ligament

Purpose of this studyThe anterior cruciate ligament (ACL) has been believed to have a low spontaneous healing capacity; growing evidence has suggested that ACL could heal spontaneously. While the healed ACL has reduced mechanical properties and incomplete tissue maturation, the mechanisms underlying these problems remain unknown. We aimed to elucidate the effect of mechanical stresses during the early phase of spontaneous ACL healing. Materials and MethodsMale and female C57BL/6 mice were subjected to ACL rupture and randomly classified into three groups: Tight-CATT; tightly controlled anterior tibial translation (ATT), Loose-CATT; loosely controlled ATT and mild increasing mechanical stress compared to Tight-CATT, and ACL-Rupture (ACL-R) group; not controlled ATT. Mice were sacrificed and analyzed immediately after injury and at 4 and 8 weeks. We evaluated the effect of controlling the braking force of the ATT of each knee, the success rate of the ACL healing, collagen maturation, COL1A1 expression in the healed ACL, and the mechanical properties of the healed ACL. ResultsThe Tight-CATT group showed a higher success rate of ACL healing than the Loose-CATT group at 4 and 8 weeks. However, collagen maturation and the mechanical properties of healed ACL did not differ between the Tight-CATT and Loose-CATT groups. ConclusionOur results suggested that loose ATT braking immediately after injury is a negative factor for the healing of the completely ruptured ACL, and that it may be necessary to apply higher mechanical stress in the later stages to achieve greater healing.