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Chapter 9178provide a good alternative rehabilitation modality to enhance compliance among some patients.Understanding the effects of ACL injuryRupture of the ACL leads to an onset of several events that include biological, mechanical, neuromuscular and psychological factors. The biological aspect is demonstrated by several cascades which involve the release of inflammatory markers (CRP and lubricin) at the time of injury.5While the level of the inflammatory markers drop over the course of the first four weeks, serum proteins that indicate increased cartilage metabolism (proteoglycans) actually seem to increase over the same period, which may indicate an adaption of the cartilage biosynthesis in the presence of mechanical instability.Over 50% of patients with a traumatic hemarthrosis have an ACL rupture,26so one might say that hemarthrosis is pathognomonic for the presence of ACL rupture. Even though that might be a bold statement, the presence of a hemarthrosis may initiate the cascade mentioned above. On the other hand, hemarthrosis also leads to stiffening of the knee capsule.27This stiffening can be regarded as a protective strategy to oppose the mechanical instability caused by the rupture of the ACL.Also, the ACL contains mechanoreceptors and proprioceptive receptors.31Transection of the ACL leads to altered afferent neurological pathways to the central nervous system. It is shown that sensory nerves located in the knee capsule play an important role in preventing the acutely unstable knee from rapid breakdown, probably by influencing protective muscular reflexes.25 It is suggested that after ACL injury the central nervous system relies more on visual feedback and spatial awareness, as the biomechanical feedback is disturbed.30 Those parts of the brain responsible for visual processing (posterior inferior temporal gyrus), motor control (presupplementary motor area), and pain and sensory control (somatosensory area) are more active in patients after ACL injury.19 This indicates that the central nervous system is shifting to alternative pathways to regain knee stability.Mark Zee.indd 178 03-01-2024 08:56