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Biomechanics I Dr. Noha Elserty Pathological gait Quadriceps muscle weakness Normally, during early stance as weight is being shifted onto the stance leg (loading response), the line of force falls behind the knee...

Biomechanics I Dr. Noha Elserty Pathological gait Quadriceps muscle weakness Normally, during early stance as weight is being shifted onto the stance leg (loading response), the line of force falls behind the knee requiring quad contraction to prevent buckling of knee. With quadriceps weakness, there is inability to counteract the flexion moment which will further leads to instability at heel strike, high tendency for excessive knee flexion and decrease in shock absorption abilities during loading response. Compensation: the main compensation is the action of hip extensors and ankle planter flexors to pull the femur and tibia posteriorly which results in knee extension. Patient leans forward at trunk, causing COG to be shifted forward so line of force falls anterior to knee, forcing it into extension. 1 Biomechanics I Dr. Noha Elserty N.B. if both quadriceps and the gluteus maximus are paralyzed, a patient may compensate by pushing femur posteriorly with his hand at the initial contact and loading response. The arm support trunk and prevent hip flexion and thrusts knee into extension. After long run of compensation, it leads to fatigue and degeneration of ligaments that support knee. Inadequate dorsiflexion control The dorsiflexors are active at two different times during the gait cycle, so inadequate dorsiflexion control may give rise to two different gait abnormalities. During loading response, the dorsiflexors resist the external plantarflexion moment, thus permitting the foot to be lowered to the ground gently. If they are weak, the foot is lowered abruptly in a foot slap. The dorsiflexors are also active during the swing phase, when they are used to raise the foot and achieve ground clearance. Failure to raise the foot sufficiently during initial swing may cause toe drag. Both problems are best observed from the side of the subject. Inadequate dorsiflexion control may result from weakness or paralysis of the anterior tibial muscles or from these muscles being overpowered by spasticity of the triceps surae. 2 Biomechanics I Dr. Noha Elserty Abnormal foot contact The foot may be abnormally loaded so that the weight is primarily borne on only one of its four quadrants. Loading of the heel occurs in the deformity known as talipes calcaneus (also known as pes calcaneus), where the forefoot is pulled up into extreme dorsiflexion, usually as a result of muscle imbalance, such as results from spasticity of the anterior tibial muscles or weakness of the triceps surae. Except in mild cases, weight is never taken by the forefoot and the stance phase duration is reduced. The reduced stance phase duration on the affected side reduces the swing phase duration on the opposite side, which in turn reduces the overall stride length. In the deformity known as talipes equinus (or pes equinus), the forefoot is fixed in plantarflexion, usually through spasticity of the plantarflexors. In a mild equinus deformity, the foot may be placed onto the ground flat; in more severe cases the heel never contacts the ground at all and initial contact is made by the metatarsal heads, in a gait pattern known as primary toestrike. 3 Biomechanics I Dr. Noha Elserty Excessive medial contact occurs in a number of foot deformities. Weakness of the inverters or spasticity of the evertors will cause the medial side of the foot to drop and to take most of the weight. In pes valgus, the medial arch is lowered, permitting weight bearing on the medial border of the foot. Increased medial foot contact may also be due to a valgus deformity of the knee, accompanied by an increased walking base. Excessive lateral foot contact may also result from foot deformity, when the medial border of the foot is elevated or the lateral border depressed, by spasticity or weakness. The foot deformity known as talipes equinovarus combines equinus with varus, producing a curved foot where all the load is borne by the outer border of the forefoot. Although the term club foot may be applied to any foot deformity, it is most commonly applied to talipes equinovarus. 4 Biomechanics I Dr. Noha Elserty Insufficient push off In normal walking, weight is borne on the forefoot during the ‘push off ’ in pre- swing. In the gait pattern known as insufficient push off, the weight is taken primarily on the heel and there is no push off phase, the whole foot being lifted off the ground at once. It is best observed from the side. The main cause of insufficient push off is a problem with the triceps surae or Achilles tendon, which prevents adequate weight bearing on the forefoot. Rupture of the Achilles tendon and weakness of the soleus and gastrocnemius are typical causes. Weakness or paralysis of the intrinsic muscles of the foot may also prevent the foot from taking load through the forefoot. Insufficient push off may also result from any foot deformity, if the anatomy is so distorted that it prevents normal forefoot loading. A calcaneus deformity obviously makes it impossible to put any significant load on the forefoot. Another important cause of insufficient push off is pain under the forefoot, if the amount of pain is affected by the degree of loading (as it usually is). This may occur in metatarsalgia and also when arthritis affects the metatarsophalangeal joints. 5 Biomechanics I Dr. Noha Elserty Abnormal walking base The walking base is usually in the range 50‒130 cm. In pathological gait it may be either increased or decreased beyond this range. While ideally determined by actual measurement, changes in the walking base may be estimated by eye, preferably from behind the subject. An increased walking base may be caused by any deformity, such as an abducted hip or valgus knee, which causes the feet to be placed on the ground wider apart than usual. A consequence of an increased walking base is that increased lateral movement of the trunk is required to maintain balance. The other important cause of an increased walking base is instability and a fear of falling, the feet being placed wide apart to increase the area of support. This gait abnormality is likely to be present when there is a deficiency in the sensation or proprioception of the legs, so that the subject is not quite sure where the feet are, relative to the trunk. It is also used in cerebellar ataxia, to increase the level of security in an uncoordinated gait pattern. Another effective way to improve stability is to walk with one or two canes. A narrow walking base usually results from an adduction deformity at the hip or a varus deformity at the knee. Hip adduction may cause the swing phase leg to cross the midline, in a gait pattern known as scissoring, which is commonly seen in cerebral palsy. In milder cases, the swing phase leg is able to pass the stance phase leg, but then moves across in front of it. Rhythmic disturbances Gait disorders may include abnormalities in the timing of the gait cycle. Two types of rhythmic disturbance can be identified: an asymmetric rhythmic disturbance shows a difference in the gait timing between the two legs; an irregular rhythmic 6 Biomechanics I Dr. Noha Elserty disturbance shows differences between one stride and the next. Rhythmic disturbances are best observed from the side and may also be audible. An antalgic gait pattern is specifically a gait modification which reduces the amount of pain a person is experiencing. The term is usually applied to a rhythmic disturbance, in which as short a time as possible is spent on the painful limb and a correspondingly longer time is spent on the pain-free side. The pattern is asymmetrical between the two legs but is generally regular from one cycle to the next. A marked difference in leg length between the two sides may also produce a regular gait asymmetry of this type, as may a number of other differences between the two sides, such as joint contractures or ankylosis. Irregular gait rhythmic disturbances, where the timing alters from one step to the next, are seen in a number of neurological conditions. In particular, cerebellar ataxia leads to loss of the ‘pattern generator’, responsible for a regular, coordinated sequence of footsteps. Loss of sensation or proprioception may also cause an irregular arrhythmia, due to a general uncertainty about limb position and orientation. Other gait abnormalities A number of other gait abnormalities may be observed, either alone or in combination with some of the gait patterns described above. They include: 1. Abnormal movements, for example intention tremors and athetoid movements 2. Abnormal attitude or movements of the upper limb, including a failure to swing the arms 3. Abnormal attitude or movements of the head and neck 4. Rapid fatigue. 7