Genu recurvatum is characterized by excessive extension of the knee at the tibiofemoral joint. It is a deformity of the lower limb, in which the knee bends backwards posteriorly. During an individuals gait analysis, common dysfunctions noticed include decreased stride length, cadence, velocity, and step length . There are a couple different classifications of genu recurvatum that can be looked at .
We will look at external rotary deformity recurvatum. It is identified by a triplanar foot deformity that involves the distal base of the lower leg to acquire a load-bearing stance that now has to sustain the forefoot in a position of adduction of the knee, and supination at the foot and plantar flexion at the ankle. The levers on the lower leg have become dysfunctional. When these forefoot and hind foot base levers are lost, it allows an external torque to be immediately transferred to the talocrural joint and also the knee joint. This dysfunction is more likely going to involve the deep longitudinal subsystem of the human body.
Muscles in this subsystem include the biceps femoris (hamstrings), peroneus longus, and tibialis anterior. These are all muscles surrounding the knee joint and play a role in maintaining the stability of the joint . During normal gait, just before heel strike, the biceps femoris muscle of the hamstring complex activates to eccentrically decelerate hip flexion and knee extension.
Weakness Of Hamstring
With genu recurvatum, the hamstring is not at the proper length-tension relationship to generate an adequate amount of force to propel movement. The hamstring is always in an extended position. This will make the muscle fibers not able to connect maximally because they will not be able to achieve the greatest degree of overlap .
This lack of muscle fiber connections means that the muscle is stimulated at lengths greater than or less than the optimal length, resulting in less than adequate tension that can be placed on the muscle. These length-tension relationships correlate with the concept of joint alignment. In any movement, the change in a joint angle can affect the amount of tension produced by the muscles that are around that joint and can also affect the kinetic chain movements of other joints and length-tension relationships of other muscles. With genu recurvatum, the knee joint is misaligned posteriorly, affecting the length-tension relationship between the hamstrings. When the muscle length is altered, the amount of tension that can be developed is far less than the amount of tension that needs to be developed for efficient movement.
Force couple relationships are also affected by genu recurvatum. Being that the specific amount of force that a muscle can produce depends on the muscle length-tension relationship (muscle fiber recruitment specifically), and muscle size, a muscle force couple relationship can be correlated to the length-tension relationship of that muscle as well.
A force couple is produced when muscles around a joint produce a synergistic motion to generate movement at a specific joint. In genu recurvatem, the muscles cannot be recruited efficiently to produce a force that is substantial enough to generate movement at the joint. This is why individuals with genu recurvatum cannot extend their knees more than 10 degrees . This means that not all the muscles around the knee joint are able to work together to produce a movement. This would make them unable to work in a proper force couple.
The human body moves more effective only when there are proper force-couple relationships . Ideally, the body needs to possess adequate length-tension relationships, force couple relationships, and proper arthrokinematics in order to operate effectively and efficiently for proper movement . If the body does not possess these things, then dysfunction and injury are most likely going to be produced. A couple injuries that can occur are ligament and muscle injury caused by soft tissue damage, meniscus injury, compression fractures caused by inappropriate forces, and structural damage of the knee and surrounding structures (ACL, MCL, PCL, LCL) .
A study by Shultz et al. looked at the relationship between anterior knee joint laxity and ACL injuries. Lower extremity knee alignment is believed to influence the weight distribution at the knee, which further leaves the knee joint vulnerable to greater stress and possible injury . “Anterior knee laxity defines the amount of displacement of the tibia relative to the femur where the primary restraint is the ACL” . If this laxity is greater than normal, then an ACL injury in a common risk factor during weight-bearing activities.
When the alignments of certain joints in the kinetic chain are misaligned, the tension placed on certain structures in increased significantly . The study also looked at genu recurvatum as a big predictor of anterior knee laxity. It did come out to be a positive predictor being that hyperextension of the knee joint can cause increased tibial torques and increase ACL tension forces on the joint . It was concluded that genu recurvatum, along with other misalignments, was a major predisposition of ACL injuries in both men and women .