Athletics are at the root of American culture: sports teach young children teamwork, provide teenagers and young adults with passion and identity, and as one grows older, serve as an active hobby. Sports steal the hearts and time of Americans everywhere, yet it only takes an awkward landing on the court, a sharp cut across the field, or a sudden collision for America’s favorite pastime to become dangerous. Sudden movements requiring quick directional changes can cause the ACL to become severely stretched, torn, or even ruptured (1). The ACL is one of the two ligaments that connect the femur to the tibia, keeping the knee joint secure (1). An estimated 200,000 ACL tears are reported annually in the United States; however, for an injury that occurs quite frequently, it can be permanently incapacitating (7). 

Functional movement following an ACL injury or tear can cause persistent osteoarthritis of the knee, in which the cartilage protecting one’s bones degrades with time (4).  Osteoarthritis is marked by intense joint pain and stiffness, limited flexibility, and tenderness following pressure, all of which can prevent one from comfortably participating in moderate physical activities. When ACLs are torn, the trauma from the injury alters the knee’s loading patterns both in stillness and in movement.  As a result, the knee cartilage experiences increased force, causing it to deteriorate (4). A study reported in the Clinical Journal of Sports Medicine reported that posttraumatic osteoarthritis followed ACL injury in 87% of reported patients. Even after undergoing nonsurgical ACL treatment, 56% of patients reported severe osteoarthritis 17-20 years after injury (4). To compare, osteoarthritis occurs in about 19.2% of adults above 45 with no history of ACL injury, according to the Framingham Osteoarthritis Study (4). 

Both partial and complete ACL tears can also cause early onset joint degradation. Partial ACL tears are a bit more forgiving; after three months of recovery and rehabilitation, joint degradation may only be marked by mild instability symptoms (2,6). On the other hand, complete ACL rupture increases anterior pressure on the tibia while limiting the valgus rotational motion of the knee. With time, these disruptions limit the rotational flexibility of the knee and cause specific knee tissue to break down due to excessive stress (6). It is estimated that without ACL reconstruction, this joint damage can age the knee by 30 years. However, reconstructive surgery requires the joint to once again undergo distress, resulting in inflammation due to excess cytokine activity (4). In short, ACL injury threatens joint stability both with or without surgical treatment.

Living with these conditions is not only physically burdensome but also increases the probability of future reinjuries, especially in young athletes.  A study reported by the British Journal of Sports Medicine evaluated 106 patients who participated in popular “Level 1” contact sports, such as basketball or football, that had recently recovered from an ACL injury (5). Using the Knee Outcome Survey-Activities of Daily Living Scale to evaluate knee function, they found that athletes who had continued to play their sport were 4.32 times more likely to suffer reinjury than those who stopped participating in athletics after their injury (5). Moreover, undergoing just one ACL injury makes athletes incredibly prone to further injury even after surgical treatment. 

ACL reconstruction may improve the physical mobility of the injured knee; however, it cannot fully prevent joint damage or restore full mobility (3). A study published in the Current Reviews in Musculoskeletal Medicine reported that while ACL reconstruction helps prevent knee cartilage and meniscus damage, 85% of reconstructed knees exhibit abnormal tibial motion in comparison to knees that have never undergone ACL injury (3). Therefore, ACL injury-induced damage can be alleviated, yet not fully prevented, with treatment. 

ACL injury leaves patients with chronic pain, reduced functional mobility, and a high risk for further injury that cannot be fully recovered with treatment. It’s incredibly clear: just one ACL injury is one too many. In response to a national increase of ACL injuries, specifically in adolescents, Esurgi saw a need for a low-cost screening and prevention device. Thus, the Joint Spy was established. Esurgi’s Joint Spy is a wearable device that provides real-time biofeedback on knee-joint motion during athletic activity. Esurgi helps identify high-risk individuals so that they may develop safe movement strategies before a potential ACL injury can occur, thus avoiding these long term consequences.


1. ACL Injury: Does It Require Surgery? – OrthoInfo – AAOS. (n.d.). Retrieved January 04, 2021, from

2. ACL Surgery: Rebuilding A Torn Anterior Cruciate Ligament. (n.d.). Retrieved January 04, 2021, from

3. Cheung, E. C., Dilallo, M., Feeley, B. T., & Lansdown, D. A. (2020). Osteoarthritis and ACL Reconstruction—Myths and Risks. Current Reviews in Musculoskeletal Medicine, 13(1), 115-122. doi:10.1007/s12178-019-09596-w

4. Friel, N. A., & Chu, C. R. (2013). The Role of ACL Injury in the Development of Posttraumatic Knee Osteoarthritis. Clinics in Sports Medicine, 32(1), 1-12. doi:10.1016/j.csm.2012.08.017

5. Grindem, H., Snyder-Mackler, L., Moksnes, H., Engebretsen, L., & Risberg, M. A. (2016). Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: The Delaware-Oslo ACL cohort study. British Journal of Sports Medicine, 50(13), 804-808. doi:10.1136/bjsports-2016-096031

6. Øiestad, B. E., Engebretsen, L., Storheim, K., & Risberg, M. A. (2009). Winner of the 2008 Systematic Review Competition: Knee Osteoarthritis after Anterior Cruciate Ligament Injury. The American Journal of Sports Medicine, 37(7), 1434-1443. doi:10.1177/0363546509338827

7. You’ve torn your ACL. Now what? (2020). Retrieved January 04, 2021, from Harvard Health Publishing site: