1Mayo Clinic, Rochester, Minnesota 2Tissue Engineering, Regeneration, and Repair Program, Hospital for Special Surgery, New York, NY.
J Bone Joint Surg Am. 2017 Aug 16;99(16):1382-1391. doi: 10.2106/JBJS.17.00133.
Following anterior cruciate ligament (ACL) reconstruction, the mechanical loading of the tissues has a significant impact on tendon-to-bone healing. The purpose of this study was to determine the effect of the timing of the initiation of mechanical loading on healing of a tendon graft in a bone tunnel.
ACL reconstruction using a flexor tendon autograft was performed in 56 mice randomized to 4 groups with differing times to initiation of postoperative mechanical loading: (1) immediate, (2) 5 days, (3) 10 days, or (4) 21 days following surgery. An external fixator was placed across the knee at the time of surgery and removed when mechanical loading was scheduled to commence. Following removal of the external fixator, animals were permitted free, unrestricted cage activity. All mice were killed on postoperative day 28, and tendon-to-bone healing was assessed by biomechanical testing, microcomputed tomography (micro-CT), and histological analysis.
The mean failure force (and standard deviation) of the reconstructed ACL at the time of sacrifice was highest for Group 2 (3.29 ± 0.68 N) compared with Groups 1, 3, and 4 (p = 0.008). Micro-CT bone volume fraction was greatest for Group 2 in the femoral tunnel (p = 0.001), tibial tunnel (p = 0.063), and both bones (p < 0.001). Similarly, histological analysis demonstrated a narrower scar tissue interface and increased direct contact at the tendon-bone interface (p = 0.012) for Group 2.
Following ACL reconstruction, a defined period of immobilization without weight-bearing appears to improve biomechanical strength of the healing tendon-bone interface, while prolonged periods without mechanical load and motion decrease the ultimate load to failure in this murine model.
The ideal period of restricted weight-bearing and motion following ACL reconstruction remains undefined. In a murine model, improved healing was noted for animals immobilized for a brief period of 5 days. This work may serve as an initial step in determining the ideal time period in a clinical population.
在前交叉韧带（ACL）重建后，组织的机械加载对肌腱-骨愈合有重大影响。本研究的目的是确定启动机械加载的时机对骨隧道中肌腱移植物愈合的影响。
56 只小鼠随机分为 4 组，每组在术后不同时间开始机械加载：（1）立即，（2）术后 5 天，（3）术后 10 天，或（4）术后 21 天。手术时在膝关节上放置外固定器，当计划开始机械加载时将其移除。移除外固定器后，动物可以自由、不受限制地在笼子中活动。所有小鼠均在术后第 28 天处死，通过生物力学测试、微计算机断层扫描（micro-CT）和组织学分析评估肌腱-骨愈合情况。
在处死时，重建 ACL 的平均失效力（及标准差）以第 2 组最高（3.29 ± 0.68 N），与第 1、3 和 4 组相比（p = 0.008）。micro-CT 骨体积分数在股骨隧道（p = 0.001）、胫骨隧道（p = 0.063）和双骨中以第 2 组最高（p < 0.001）。同样，组织学分析显示第 2 组肌腱-骨界面的瘢痕组织界面更窄，直接接触增加（p = 0.012）。
在 ACL 重建后，一段时间的固定而不承受体重似乎可以提高愈合肌腱-骨界面的生物力学强度，而长时间没有机械负荷和运动则会降低该鼠模型中最终失效负荷。
ACL 重建后限制负重和运动的理想时间仍未确定。在鼠模型中，固定 5 天的短时间内观察到愈合改善。这项工作可能是确定临床人群理想时间的初步步骤。
