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Genu Recurvatum: Anatomy and Biomechanics of Genu Recurvatum in DancersResearch Paper

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Anatomy and Biomechanics of Genu Recurvatum in Dancers

In the world of dance, flexibility and grace may be everything, but they both come at a price. Dancers are continually predisposed to muscle injuries and imbalances due to the repetitive motions associated with dance routines. They have often utilized these dysfunctions to perform aesthetically beautiful and highly trained movements - one example being genu recurvatum, a posture where the knees often appear to bend backwards when an individual is standing. According to the National Center for Biotechnology Information, NCBI (2015), genu recurvatum, also referred to as knee hyperextension, is often a consequence of inadequate control over the knee joint, which may be caused by weak muscles, improper positioning of the joints and functionally defective tonus. Although genu recurvatum may have negative consequences to knee structures, many professional dance schools often prefer dancers with this condition with claims that it makes the lines look nicer and also makes the routines breathtaking. Dancers who are able to hyperextend their knees are also hyper-mobile, which means that aside from the knees, their range of motion can also extend across many other joints. However, genu recurvatum is a double edged sword and it may make dancers appear elegant and graceful, but it poses great risks to their overall health. This text presents the anatomy and biomechanics of genu recurvatum and takes a look at how it affects dancers' muscles, postures and alignment, as well as their dancing techniques.

Genu recurvatum

Genu recurvatum is a deformity that mostly occurs in the knee joint and makes the knee curve backwards. It is a position of the tibiofemoral joint, where the range of motion often occurs beyond zero or neutral degrees of extension. Based on these degrees of extension, it is often divided into two: acquired pathological and constitutional physiological. In acquired genu recurvatum, the range of motion is usually unilateral, which means it is more than fifteen degrees, while in constitutional genu recurvatum it is less than 15 degrees, hence symmetric. Genu recurvatum can also be defined in terms of the radiographic relationship between the femur and the tibia where it is classified as simple hyperextension, anterior subluxation, or anterior dislocation (Graham, 2007). The knee is said to be dislocated if the tibia is displaced on the front of the femur and if longitudinal contact is maintained. However, if there is no joint displacement, then it is a clear case of hyperextension.

The causes of genu recurvatum

Genu recurvatum is more common in females than males and when it is not caused by knee injury, it can be caused by joint laxity, poor postural habits and weaknesses of the muscles surrounding the knee. Speck (2014) also states that some of the major causes of the disorder are laxity of the knee ligaments, unstable knee joints from injuries, quadraricep weakness, and misalignments of the tibia and the femur. Connective tissue disorders also contribute to joint hypermobility problems, which aggravate the disorder. These include: benign hyper-mobile joint syndrome, marfan syndrome, Ehlers-Danlos syndrome, and osteogenesis imperfect disease. Fish and Kosta (1998) state that hip extensor weakness, limb length discrepancies, and plantarflexion contracture also cause genu recurvatum. They go on to explain that the genesis of this deformity may be influenced by postural adjustments that are developed to prevent anterior knee collapse and to achieve stability of the limbs.

The muscles

The muscles associated with condition include: the quadriceps femoris popliteus and gastrocnemius muscles, whose weakness is one causative factor of the condition. The popliteus muscle is stressed in an individual who portrays genu recurvatum (Loudon, Goist and Loudon, 1998). This muscle is in charge of unlocking the knee during extension and flexion by rotating the tibia on the femur and in an individual with the condition, it will not prevent the impingement of the back horn of the lateral meniscus by drawing it backwards. The biceps femoris muscle, which provides stability in the posterolateral conmpartment of the knee, is also affected (Loudon, Goist and Loudon, 1998). Another is the semimembranous muscle, which is attached to the lateral facet and supports the medial condyle of the tibia. This muscle is not able to provide the expansion required to reinforce the posteromedial corner of the knee capsule. In summary, the muscles that are weakened are those that facilitate extension and those that are essential in providing support in the posterior structures of the knee: the semimembranous, biceps femoris, gastrocnemius, and poplietus muscles.

Biomechanics

Biochemically, the knee joint is one of the largest joints of the human skeletal system and it is also the most complex (Fish and Costa, 1998). The surfaces of the femur have asymmetrical design, which help in joint stability and complex joint motions. Any movement at the ankle joint and the hip has an influence on the mechanics of the knee joint (Loudon, Goist and Loudon, 1998). During the movement of joint surfaces, the femur often glides posteriorly and moves anteriorly upon the fixed tibia. Loudon, Goist and Loudon also state that rotations of the tibia and the femur often occur near terminal extension because the lateral femoral condyle rolls continually. In the case of genu recurvatum, the femur is not able to roll anteriorly; instead, it tilts forward and creates anterior compression between the tibia and the femur. Moreover, hyperextension is not limited by bony contact in a healthy knee as often witnessed in the elbows. Rather, soft tissue structures are the ones that check hyperextension (Loudon, Goist and Loudon, 1998). In a normal standing posture, the vector force is often behind the knee and unless quadriceps contract, further knee flexion is often evident. Genu recurvatum, however, sees the axis of the thigh inclined posteriorly, and in the process, the ground reaction force is placed anterior to the knee. In such a case, quadriceps muscle activity is not necessary because posterior structures are stretched and the knee joint becomes stabilized (Loudon, Goist and Loudon, 1998).

How genu recurvatum affects dancers' posture, alignment and techniques

In the dance arena, sometimes dancers attempt to maintain stability by hanging onto ligamental constraints instead of using normal muscular control. Individuals with genu recurvatum, therefore, stress the posterior structure of their knees. In ballet for example, slight genu recurvatum is desirable because there is more anterior placement of the upper body and the trunk, which shifts the dancer's center of gravity at the front of the knee and produces a gentler S-curve line, a much preferred line on point, instead of a straight line (Shrader, 1996). However, the dancers often experience pain along the medial side on the patella and the knee, often without any particular injury. The reason for this is that genu recurvatum places tension anteriorly on the patella and dances often push the knee back in order to support their weight.

Genu recurvatum is sometimes also attributed more to dances that are associated with less activity in the quadriceps, than in dancers who stand with their knees bent. In fact, Shrader (1996) reports that a study conducted revealed that at peak season, relative quadriceps torque that was measured for male ballet dancers was 98% of the weight measure that had been predicated, and for female ballet dancers, it was only 77%. This explains why females are often susceptible to pain related to genu recurvatum, as a result of decreased quadriceps strength. The development of strong inclined fibers of the quadriceps is essential in medial tracking of dancers' patella. Therefore, dancers are bound to experience pain and discomfort from genu recurvatum due to weak and over stretched adductors, rotational and lateral forces on the patella, and an increased compression. Shrader (1996) also states that excessive practice and a tight iliotibial band also predispose dancers to genu recurvatum.

The biomechanics of genu recurvatum also interfere with some aspects of dancers' techniques. For instance, during the loading response in foot movements, dancers with the disorder transfer their body weight from the femur to the tibia directly, without the required absorption of muscle energy and the cushioning that is provided by a flexed knee. What follows is a decrease in the cadence, step length, velocity, and stride length, which cause the dancers to experience pain in the posterolateral ligamentous structures and the medial tibiofemoral joint. Sometimes, routines may involve landing from a jump on a knee that is extended or blows to the proximal tibia, causing genu recurvatum in the process. Tight Achilles tendons and repetitive jumps are other factors in dancers that may further aggravate genu recurvatum because they cause the dancer's weight to fall behind the calf muscles and the heel and they have to work harder to maintain their balance (Shrader, 1996).

How genu recurvatum can be treated - a strengthening program

Speck (2014) suggests that the best approach to dealing with genu recurvatum is to build overall motor control and strength, with more emphasis being put on muscle balance. Fish and Costa (1998) also state that individuals with the disorder should be rehabilitated using gait training, muscle control, proprioception training… [END OF PREVIEW]

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