Recurvatum of the Knee in Cerebral Palsy: A Review

Abstract

Recurvatum is defined as hyperextension of the knee in the stance phase of gait. Recurvatum knee is a naturally occurring common gait deviation in those with cerebral palsy, along with crouch knee, jump knee, and stiff knee gaits. Early and late recurvatum occur in the first and second halves of stance. Early recurvatum is associated with dynamic calf contraction that raises the heel and pushes the knee into hyperextension as the forefoot contacts the floor. Late recurvatum occurs after the foot is already flat on the floor. As the body weight comes forward over the foot, the tibia stops its forward motion too early as the ankle comes to its range-of-motion limit. The advancing body then moves forward over a hyperextending knee. Surgical hamstring lengthening can have recurvatum as a side effect. There are several strategies to decrease this risk. Medial hamstring lengthening may be safer than combined medial and lateral lengthening. The concept here is that less lengthening or less aggressive lengthening means less recurvatum risk. However, combined medial and lateral lengthening can be reasonably safe from the risk of causing recurvatum if the knee is showing enough preoperative flexion in stance to warrant the increased surgery. More flexion in stance relates to less risk, while less flexion in stance relates to more risk. Knee flexion in stance can be measured. This is done by measuring knee flexion at initial contact and knee flexion in stance in a gait lab or with stop-action video. If there is minimal knee flexion in stance, hamstring lengthening might not be advisable, even if the hamstrings are tight on popliteal angle testing. There are other factors that contribute to recurvatum risk, such as knee hyperextension on static exam, equinus contracture, and jump knee gait. For treatment of recurvatum, the mainstay is the use of ankle foot orthoses set in dorsiflexion. Surgical equinus correction in those with early stance recurvatum can be effective but it is not likely to be effective in those with late stance recurvatum.

Keywords: ankle-foot orthosis; cerebral palsy; gait; hamstring surgery; knee; knee-ankle-foot orthosis; recurvatum; stance.

Figure 1. Early stance recurvatum.

(A) The gait cycle starts with initial contact of the right foot. Both feet are in equinus. (B) As the body weight transfers to the right leg, the right ankle is still in equinus. The right knee extends sooner than normal in response to the plantar flexion-knee extension couple. (C) The right knee is already in recurvatum by the time mid-stance is reached. (D) As the left leg swings forward, the right knee continues in recurvatum. (E) As the left foot contacts the floor and starts bearing weight, the right knee starts to flex as the hip flexes. (F) The gait cycle ends as the right foot lifts off the floor. Without weightbearing, the recurvatum resolves.

Figure 2. Late stance recurvatum.

(A) The gait cycle starts with initial contact of the right foot. The left heel will start to rise only after the right foot has made secure contact and has started to accept weight. (B) Weight continues to shift to the right leg. (C) At mid-stance, the tibia is planted on the floor through a rigid ankle. The tibia is blocked from moving forward. (D) As the body weight continues forward over the fixed tibia, the knee hyperextends. (E) While the left leg swings forward and makes initial contact, the right forefoot and heel remain planted. Normally, the right heel would be rising at this point. (F) The right heel rises only after the left foot has made full contact and started to accept weight.