Underappreciated Factors to Consider in Revision Anterior Cruciate Ligament Reconstruction: A Current Concepts Review

Nagelli CV and Hewett TE. Should return to sport be delayed until two years after anterior cruciate ligament reconstruction? Biological and functional considerations. Sports Med. 2017 Feb;47(2):221-232. doi: 10.1007/s40279-016-0584-z.

This is the editor's interpretation of a review paper published in the orthopaedic literature in 2018 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original just click through the link above.

In this paper the authors review the long term literature relating to failure of anterior cruciate ligament (ACL) reconstruction in athletes returning to sport within two years of the reconstructive surgery. They find that such studies reveal a high risk of a second injury, both to the original reconstruction and even to the cruciate ligament on the other side, with several factors implicated. Younger athletes are at particularly high risk, especially those under 20 years of age, and in such an age group the risk of a second ACL injury if returning to sport within a year is 15 times higher that a healthy athlete with no past history of injury.

The authors conclude that there is a significant impact, in patients who have already had an ACL reconstruction, of returning to sport too early, and that there is a disproportionately high risk when returning before two years has elapsed. 


Factors involved in healing after ACL reconstruction

They suggest that the evidence does not support the 'accelerated rehabilitation' programme, and that the joint needs this two years of time to allow the graft to heal properly, and let the range of motion return fully and let the biology of the knee to return to normal.

  • The cells in the graft need to repopulate and proliferate, and blood vessels and nerves need to grow in to restore the native properties of the ligament. In addition they point out that the graft needs to mature via a process of assimilation and re-ligamentisation to fully restore its integrity.
  • In addition, one needs to be aware that in the original injury it is likely that other structures were damaged at the same time as the ACL, such as the bone and the articular cartilage, and these need also to have time to return as far as possible to normal. MRI studies show that the more severe bone bruises may still not be fully healed a year after the original injury. Bone scan studies have showed that the bone mineral density may take up to 24 months to recover to normal levels.
  • Dynamic joint stability and position sense are normally controlled by special sensory nerve fibres and receptors within the native ligament, as well as their communication with the neighbouring musculature. These are all disrupted with ACL reconstruction, and the nerves never full recover. Patients will find themselves with deficiencies in 'proprioception' and need to compensate via re-education of the sensory structures on the outside of the joint, and this process tends to be slow.
  • Functional recovery needs to include the resolution of any effusion in the knee, restoration of range of motion and restoration of quadriceps muscle strength and activation. The literature suggests that full quadriceps strength may nor be restored for several months and even years after ACL reconstruction.
  • Residual neuromuscular and biomechanical deficits of the hip and trunk, as revealed by gait analysis, may also require specific functional training before sports are resumed. Special units may offer dynamic assessments during sports-specific exercises.


The authors conclude that "the recovery of baseline knee health and function should be a fundamental requisite prior to returning to sport following ACLR".