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A B M P m e m b e r s ea r n F R E E C E h o u r s by rea d i n g t h i s i s s u e ! 67 to reveal the smooth, semi-translucent surface of the enveloping deep fascia of the limbs (crural fascia on the lower leg and antebrachial fascia on the forearm). Looking through the deep fascia, we can see the tendons that slide and glide underneath, looking like highways of silvery collagen ribbons traveling across the joints. The fascial bag is sheer and fairly easy to see through, but as it approaches the joint, it becomes thicker and denser. These areas of reinforcement, made of collagen fibers, are the retinacula. FUNCTIONAL IMPLICATIONS One of the biggest findings in fascia research from the past two decades is that deep fascia is richly innervated with sensory nerves. Specialized mechanoreceptors allow deep fascia to feel and sense tension, compression, and other physical stimuli. The presence of these nerve endings indicates that fascia is involved in nociception, motor coordination, and proprioception. Every stretch or movement pulls on the fascial fabric, which translates information to the brain. Discovering the retinacula to be completely continuous with deep fascia sheds new light on their possible function. Previously, retinacula's supportive role was thought to be primarily structural, keeping the tendons in place. Viewing retinacula as a continuous part of the deep fascia presents the possibility of it being supportive in a totally different way—through sensory perception. Based on location, they certainly are positioned to receive a lot of information from the joints. Could they play a role in proprioception? Researchers pulled out the microscopes to analyze retinacula up close. Viewing retinacula as a continuous part of the deep fascia presents the possibility of it being supportive in a totally different way—through sensory perception. Sensory, Not Just Structural Zooming in, fascia researcher Carla Stecco and her team explored retinacula's microanatomy. If the retinacula are involved in proprioception, nerves must be present. What they found was game-changing: Not only are retinacula innervated, but they are the most innervated deep fascia. 3 In addition, they found that retinacula have high concentrations of encapsulated nerve endings, like Ruffini's and Pacini's corpuscles, specialized structures that amplify the nerve's ability to detect particular stimuli. Based on their research, they concluded that retinacula are not "merely passive elements of stabilization, but a sort of specialization of the fascia to better perceive the movements of the foot and ankle as proprioceptive organs." 4 What Happens When There's an Injury? With the updated knowledge of retinacula's innervation and role in proprioception, researchers looked further into how retinacula could be involved in ankle injuries. Ankle sprains are one of the most common lower limb injuries, accounting for 10–15 percent of all sports injuries. 5 Ankle sprains often lead to more ankle sprains, chronic ankle instability, and lowered proprioception, which piqued the curiosity of fascia researchers. They examined ankles with a history of sprain but no ligament damage and found that though the ligaments were intact, the retinacula were thicker and had gaps in continuity and adhesions to the overlying subcutaneous layers. 6 Because of retinacula's innervation and role in proprioception, damage and alteration to them help explain the reduction in joint-position awareness, sensory-motor coordination, and increased risk for reinjury.