The human (Homo sapien-sapiens, modern anatomical cognitive human, created 50,000-70,000 years ago) knee evolved
• for primarily forward and limited backward locomotion,
• when in pursuit of food and reproduction.
• The ligaments, supporting the knee for human locomotion, evolved like the brake pads on a Ford 150 truck,
• evolved to prevent the stress and torques of misdirection,
• unlike the crab, that evolved with multiple legs for sideways locomotion, rather than multiple knee ligaments, for the same basic needs and sustainability.
• Like the Ford 150’s brake pads, there are just so many times the brakes can be intensely applied during misdirection before the pads are worn-out, damaged thin, malform and malfunction.
• The human female evolved with an additional locomotion consideration i.e. human childbirth after reproduction. Female pelvic, hip and knee anatomy are different than males.
• Thus the female knee ligament anatomy incurs additional stresses and torques at different angles, due in part to different pelvic, hip and knee anatomy, than the males’ brake pads, or ligaments. The human female has additional misdirection prevention and reproduction evolution.
• Human sideways pursuit for food and reproduction and pursuit during basketball play is not fundamental Homo sapien-sapiens’ locomotion.
• Repetitive sideways, back-and-forth sliding misdirection locomotion is normal for crabs, aka octopods (subphylum Crustacea, 8 legs, 2 hands, with lobsters, crayfish, shrimp, Brachyura covered with an exoskeleton).
• Crabs don’t have brake pads or knee ligaments that readily wear-out and malfucntion.
• Humans, particularly female, have ligaments or brake pads in their knees that readily weaken when overused and misused from too much side-to-side slide and man-to-man defense drills, often way before the season for season play begins.
• Humans are more apt to catch their pursuit, when the hunting season begins when they are mindful, disciplined, use alternate locomotion techniques, jave proper rest and nutrition and proper coaching instruction.
• So, after a while, humans evolved and developed tools like traps and nets in order to pursue prey and food.
• Basletball players should use more traps and nets to defend their opponents. Zone defenses and less overuse and over training during practice and play are recommended examples.
• There are an estimated, outrageous 350,000 ACL (over 1 million every 3 years) reconstructions (ACLRs) performed annually in the USA
• Many athlete overuse inujries are due to improper, win-at-all-cost coaching. Imporved education is recommended.
• “Training errors are the most common cause of overuse injuries. There are also technical, biomechanical and individual factors. Proper technique is critical in avoiding overuse injuries.
• “Most overuse injuries can be prevented with proper training and common sense.” [Matthew J. Matava, MD AMERICAN ORTHOPAEDIC SOCIETY FOR SPORTS MEDICINE (AOSSM) SPORTS TIPS: OVERUSE INJURIES www.sportsmed.org.]
• “About 50% of all sports injuries are secondary to overuse  and approximately 2X acute injury frequency . OI (Overuse Injuries) examples are tendinopathies, stress fractures, compartment syndrome (rhabdomyolysis mbmsrmd), shin splints and many other lower extremity injuries. A mismatch between overload time and recovery time causes OTS (Over Training Syndrome) and OI.
• Rapid increases in training without adequate recovery time may cause a “Global Overtraining Syndrome’’ when the entire body is affected from depression to other physical injuries.[Overuse injuries: tendinopathies, stress fractures, compartment syndrome, and shin splints Robert P. Wilder, MD, FACSM*, Shikha Sethi, MDDepartment of Physical Medicine and Rehabilitation, The University of Virginia, 545 Ray C. Hunt Drive, Suite 240, P.O. Box 801004, Charlottesville, VA 22908-1004, USA Clin Sports Med 23 (2004) 55– 81]
• Tommy Johns Elbow and surgery are other examples of overuse injuries.
• Please see Tommy Johns Elbow Epidemic. The link follows: http://www.cappaa.com/tommy-johns-elbow-epidemic
• Injury statistcs for sports programs should be important questions when athletes are recruited and begin selecting coaches and sports programs in which to join and participate. Athletes dedicate their SRE (Sports, Recreation and Exercise)careers, health and well being to coaches and their SRE programs.
• Humans have evolved from gathering food and reproduction to and beyond the ‘olympic ideal’ to adults, who are disabled to work for life secondary to intensive, OIs and OTSs participations that resulted in unnecessary chronic, lifelong injuries.
• Please see the difference in Accidental and non-Accidental Children’s Sports Injuries:
• Please see Overuse Injuries and Over Training Syndrome: http://www.cappaa.com/overuse-injuries-and-overtraining-syndrome
• Please see Overuse Signs and Symptoms: http://www.cappaa.com/overuse-signs-and-symptoms
The research of Harvard anthropologist Daniel Lieberman and University of Utah biologist Dennis Bramble defined modern anatomical Homo sapien running locomotion.
“They jointly proposed in a 2004 paper that human beings are superlatively endowed by evolution to ‘go long’. Our long-striding legs are packed with springlike tendons, muscles, and ligaments that enable us to briefly store elastic energy as we come down on a foot and then recoil to help propel us forward. Tellingly, the most important of these springs, our big, strong Achilles tendons, aren’t found in early human precursors such as Australopithecus—it seems that the high-end tendons evolved along with other adaptations for distance running in the genus Homo when it appeared on the African savannah about 2 million years ago.”
“Homo sapien inherited large leg and foot joints from those ancestors, which spread out high forces that must be absorbed when running. To help ensure stability on two legs, we have big gluteus maximus muscles. Our clever torsos are designed to “counter-rotate” versus the hips as we run, also aiding stability. Homo sapien have an unusually large percentage of fatigue-resistant, slow-twitch muscle fibers, which make for long running endurance rather than speed. By contrast, most animals are geared for sprinting short distances because they’re either predators that chase short distances or prey that run away short distances, and their muscles thus have much higher percentages of fast-twitch fibers than we Homo sapien.
“But what most sets we Homo sapien apart as runners is that we’re really cool—down efficiently. We are champion sweaters and can dissipate body heat faster than any other large mammal.”
“In sum, you might say we were born to run. But you also might just as well say we ran to be born.” [All Men Can’t Jump
Why nearly every sport except long-distance running is fundamentally absurd, by David Stipp, June 4, 2012, Sports Nut]
“> ACL Injury Prevention: What Does Research Tell Us?
Please see the publication for the complete report and References [Nessler T, Denney L, Sampley J. ACL Injury Prevention: What Does Research Tell Us? Current Reviews in Musculoskeletal Medicine. 2017;10(3):281-288. doi:10.1007/s12178-017-9416-5]
Although the incidence of anterior cruciate ligament (ACL) injury is unknown
, it is estimated that 350,000 ACL reconstructions (ACLRs) are performed annually in the USA
. Despite surgical repair, approximately 79% of those individuals develop knee osteoarthritis (OA) and 20% suffer re-injury within 2 years . The risk of re-injury and developing arthritis has become an economic burden and overall concern in the athletic arena
. Athletic ACL injury rates are increasing
 in both D1 career athletes
 and youth athletes
. One in four youths who suffer an ACL injury will suffer a second ACL injury in their athletic career
. Athletes who suffer a knee injury prior to participation in D1 career have an eightfold increased risk of suffering another knee injury during their D1 career and spend 50% more time on the disabled list (DL)
. Despite the ongoing research to identify contributing factors to potential knee injury in athletes, injury continues to occur and intervention and prevention models fail. As a result, knee injury (specifically ACL) has a large impact on future athletic performance.
An accurate functional assessment tool and intervention are needed to curb this injury trend and identify factors that predispose athletes to injury.
Functional Anatomy and Biomechanics of the Knee
The ACL, extending from the lateral femoral condyle to the crest of the anterior medial aspect of the tibia, contributes to knee stability via passive restraint. The orientation and direction of the bands of the ACL act as a biomechanical restraint for rotation as well as limiting anterior translation of the tibia on the femur . The combination of active muscle contraction with precise neuromuscular timing assists with knee stability during running, jumping, and cutting or pivoting maneuvers. Any alteration in the biomechanics or muscular control of the knee increases the risk of ACL injury.
Structural features of the knee that increase risk of injury to the ACL include intercondylar notch size as well as the integrity of the menisci. These factors, although only modifiable via surgery, should be recognized as potential causes of ACL injury. The intercondylar notch of the femur, especially in females, can be a structural risk if too narrow, resulting in compromised space for the ACL during rotation. The depth and integrity of the menisci assist condylar motion as the femur maintains contact during loaded motions such as flexion and rotation. A meniscus tear can alter the translation of the femoral condyles on the tibia and place added stress to the ACL during cutting or jumping maneuvers . Other passive restraints such as joint capsule and ligamentous structures (i.e., collateral ligaments) control dynamic motion and assist with knee stability. Injury to any passive restraint in the knee may compromise the biomechanical function of the knee and increase injury risk to the ACL. It should be noted that tibial slope has been identified as a potential structural risk factor in ACL injury as well.
Dynamic and modifiable biomechanics of the knee such as hyperextension, excessive valgus, or abduction moments attribute to ACL stress. Stress on the ACL is the greatest with internal tibial torsion near full knee extension . Cadaveric studies assist in further understanding the biomechanics of the knee by providing positions of the knee where the ACL is under stress. The ACL resists rotational forces at 10 and 30° knee flexion in cadaveric specimens and less at greater degrees of flexion such as 50–90° [10, 11]. However, dynamic muscular influences such as quadriceps dominance during sustained flexion activities causes anterior translation of the femur on the tibia and could predispose the ACL to stress [12,13,14•]. Effective co-contraction of the hamstrings and quadriceps has been postulated to assist in preventing the magnitude of anterior displacement that may occur with flexion activities such as cutting and landing from a jump [12, 15]. Double-limb or single-limb landing with an extended knee combined with abduction moments provides the greatest force to the ACL [14•,15•,16] (Fig. (Fig.1).1). As the knee accelerates into a valgus position, stress increases on the ACL. Additionally, poor muscular control results in improper knee alignment and increased anterior-posterior translation or rotary shear forces. This shear force and excessive rotary laxity can result in meniscus tears and injury to the ACL.
Injury to the ACL occurs during dynamic activities that primarily involve cutting and pivoting and can occur during landing after a jump. Competitive and recreational athletes between the ages of 15 and 25 are at the greatest risk of injury. The majority (80%) of the injuries are non-contact, and therefore, the mechanisms are modifiable [3, 17–19]. Female athletes are at risk four to six times greater than their male counterparts [20–22]. Female high school athletes had a ninefold increase injury risk and fivefold in collegiate sports  and those that competed at a higher level of play had a five times higher risk than their male counterpart . Sports that require high dynamic loading of the knee and report a high incidence of injury include soccer, volleyball, handball, and basketball.
Associated consequences for both athletes and military personnel who suffer an ACL injury include time on disabled list or loss of duty time, increased risk of another injury, and development of OA [25–27]. Unique to the military, females were not more susceptible to primary ACL injury when compared to male personnel. Overall, prior knee injury in all military personnel contributed to risk of another knee injury and prior hip injury increased risk of specific ACL injury . Re-injury in the athletic population occurs in one of four youths, and ACL graft rupture was higher in male athletes following repair when compared to female athletes who had ACLR [7, 29]. A 12-year follow-up study was conducted on 221 individuals post-ACLR and detected chondral defects (64%) and patellofemoral OA (26%) indicating continued degeneration of the knee joint and adjunct joints . Holm et al. (2012)  conducted a 10-year follow-up on 57 patients who had ACLR, and 79% had developed OA. Despite surgical intervention, individuals who suffered ACL injury developed OA and reduced function .
Excessive adduction moment at the knee in the frontal plane increases injury risk to the ACL [31, 32]. Landing from a drop jump and cutting maneuvers in sports are correlated with increased adduction moment at the knee. The drop jump may be performed with single leg or double leg while the cutting involves a single limb. Therefore, the kinematics and kinetics are different for each of these activities . A single-leg technique, such as the sidestep cutting maneuver, those with poor mechanics demonstrate six times the amount of frontal plane adduction moment when compared to the drop jump . The amount of frontal plane adduction moment can be reduced or controlled to decrease the risk of injury to the ACL [35•], and analysis of single-leg motion should be included as an assessment in sports injury prevention.
Fatigue and Single Limb Testing
Fatigue has been related to increase risk of injury in the athletic population . Athletes demonstrate increased motion in both the sagittal plane and frontal plane accompanied by greater ground reaction forces when fatigued . The hip and knee internal rotation increased with fatigue creating a valgus force at the knee  and ground reaction forces increased with a single-limb hop . The combined increased ground reaction force and valgus at the knee predisposes the ACL to injury.
Trunk position and hip motion strongly influence knee control during single limb and cutting motions [40•]. Decreases in trunk and hip strength and endurance result in larger center of mass (COM) displacement in athletics . Increased control of trunk and hip sagittal and frontal motions reduces COM displacement and frontal plane motion at the knee [41, 42]. This improvement in COM has been directly correlated to improvements in pitching mechanics  and decreased injury rates in major league baseball players . Targeted training to the hip and trunk has been shown to improve frontal plane motion at the knee and improvements in athletic performance measures .
Limb Symmetry Index
The standard of practice for assessing an athlete’s ability to return to play is to assess their affected limb in comparison to their unaffected limb or to assess their limb symmetry index (LSI). LSI is a percentile measurement comparing the limb symmetry of the affected side to the unaffected side. Figure Figure22 shows the calculation for LSI .The LSI has been utilized as a quantitative measure to determine the strength and performance of an athlete prior to return to sport [46–48]. Non-injured athletes have a LSI of 90–95% , while individuals who suffer an ACL injury rarely reach greater than 90% LSI post reconstruction . Although this has been primarily tested in an open kinetic chain, closed kinetic chain testing has been shown to be a better predictor of true limb symmetry [51–55].
Lateral Displacement of the Pelvis During Squatting Motion
The squatting motion is an essential movement for the development of lower extremity strength, endurance, and the explosive power associated with sports. Variations in weight distribution during this motion will impact joint and ligamentous loading, soft tissue and ligamentous strain , and influence asymmetry in strength development. Lateral displacement of the pelvis occurs during a squatting motion results in altered force distribution and joint forces [57•]. Peak ground reaction force has been calculated up to 3–6 times body weight during sporting activities . A lateral shift of the pelvis with the increased ground reaction force alters distribution of loads through the lower limb, ligamentous structures, and lumbar spine and increases the likelihood of ligamentous and soft tissue injury, such as ACL injuries . The altered length tension relationship of the musculature during training with poor mechanics leads to decreased force production. However, with proper education and rehabilitation, correction of lateral displacement of the pelvis is correlated with improved vertical jump height and sprint speed . <”
Please see the publication for the complete report and References [Nessler T, Denney L, Sampley J. ACL Injury Prevention: What Does Research Tell Us? Current Reviews in Musculoskeletal Medicine. 2017;10(3):281-288]