(A) Classification 1. Support phase disorders The activities of the support phase of the lower extremities belong to the closed chain of motion, with the foot, ankle, knee, hip, pelvis, trunk, upper extremity, neck and head all involved in walking posture. Any change in the closed chain system will cause a change in the entire motor chain, and the distal weight-bearing axis (ankle joint) has the greatest effect on the overall posture. (1) Abnormalities of the supporting surfaces Inversion of the foot, valgus, simple ankle valgus and ankle valgus with valgus, simple ankle valgus and ankle valgus with valgus, toe flexion, and bunion dorsiflexion. (2) Limb instability Limb instability is caused by excessive dorsiflexion of the supporting ankle, flexion or hyperextension of the knee joint, inversion or valgus of the knee, and inversion or flexion of the hip joint due to muscle strength disorders or joint deformities. (3) Trunk instability Generally compensatory changes caused by abnormalities of hip, knee and ankle joints. 2.Swing phase disorder The swing phase belongs to the open chain movement, each joint can have relatively isolated postural changes, but often causes compensatory changes in the posture of the lower limb in the contralateral support phase; the proximal axis (hip joint) is the most affected. (1) Limb contouring disorder Drooping foot, knee stiffness, restricted hip flexion, and restricted hip internal retraction. (2) Limb travel disorder Knee stiffness, restricted hip flexion or restricted hip posterior extension on the opposite side, and hip inversion. (2) Common abnormal gait Abnormal gait can exist in isolation or in combination, constituting a complex clinical phenomenon. 1, foot inversion is the most common pathological gait, mostly seen in patients with upper motor neuron lesions, often combined with foot drop and toe curl flexion. When walking, the foot touches the ground mainly at the anterolateral edge of the foot, especially at the base of the fifth bone, often with pain in the weight-bearing area, leading to ankle instability, which in turn affects general balance. The early and middle phases of the brace phase result in limited anterior tibial movement due to impaired ankle dorsiflexion, which promotes knee hyperextension at the end of the brace phase to compensate for the lack of anterior tibial movement. As a result of knee hyperextension, the pedal release force is reduced, resulting in a significant decrease in joint work. In addition, compensatory flexion of the hip joint may also occur. The ability to contour the ground in the swing phase of the affected limb is reduced. Correction of foot pronation in patients with gait disorders is often the first element in improving gait. The muscles associated with clubfoot deformity include the anterior tibialis, posterior tibialis, long toe flexors, gastrocnemius, hallux valgus, bunions, and peroneus longus. The anterior tibial, posterior tibial, gastrocnemius and hallux valgus muscles are more commonly overactive, and overactivity of the bunions is also associated. 2, foot ectropion is common in children or young patients with immature skeletal development (e.g., cerebral palsy), manifested as a lateral tilt of the foot when walking, with the medial side of the foot touching the ground in the support phase, and may have a toe flexion deformity. It can lead to callus generation in the navicular area and pain in the medial side of the foot (first bone), which significantly affects weight-bearing in the supporting phase. The body weight falls mainly on the anteromedial side of the ankle during walking. Ankle dorsiflexion is often limited, again affecting anterior tibial movement and increasing valgus. Severe deformities may result in unequal leg lengths, heel spur joint pain and ankle instability. In the early support phase there may be knee hyperextension, lack of strength in the foot stirrups, and ankle flexion in the swing phase leading to impaired limb contouring (compensatory flexion of the knee and hip joints may occur). Dynamic electromyography can be seen: peroneus longus, peroneus shortus, long toe flexor, gastrocnemius, flounder muscle hyperactivity or spasm, anterior tibial muscle, posterior tibial muscle activity is reduced or muscle strength is decreased. 3.Foot drop Foot drop refers to insufficient dorsiflexion of the swing phase ankle joint, which often coexists with inversion or valgus of the foot and can lead to contouring disorders. The compensatory mechanisms include: increased ipsilateral flexion of the swing phase y, flexion of the knee, circular marching of the lower limbs, and tilting of the trunk to the opposite side. A common etiology is inactivity or abnormal activity phase of the anterior tibial muscles. Simple foot drop is mainly seen in spinal cord injury, pediatric anesthesia and peripheral nerve injury. 4, toe curl support phase toes remain flexed. Commonly seen in nerve injury, reflex sympathetic dystrophy, long-term braking and contracture. Often accompanied by foot drop and inversion. Patients complain of pain at the tip of the toe and the back of the toe joint when wearing shoes, with callus formation. Patients often shorten the stride length and support time of the affected limb, resulting in reduced propulsive phase strength of the foot. The muscles involved include the long toe flexors, long bunion extensors and flexors. The deformity is exacerbated by dorsiflexion of the ankle joint. Dynamic electromyography often reveals significantly prolonged activity of the long toe flexors and long bunion flexors, abnormally active gastrocnemius and hallux valgus muscles, and reduced activity of the long toe extensors. 5, bunion dorsiflexion Most often seen in patients with central nerve injury. Patients walk with dorsiflexion of the bunions in both the supporting and swing phases, often accompanied by foot drop and foot inversion. The patient complains of pain at the bunion and the first toe joint of the plantar aspect of the foot in the support phase. It is difficult to bear weight in the early and middle phases of the support phase, so the support phase on the affected side is often shortened, making the swing phase longer than the support phase, thus affecting the foot stirrup force at the end of the support phase or in the pre-swing phase. Dynamic electromyography may show overactive gastrocnemius muscles; the bunions in the swing phase are more active to compensate for foot drop, and the toe flexors are correspondingly less active; the tibialis anterior and tibialis posterior muscles may be less active, but they can also be active. Dynamic electromyography plays a key role in choosing the correct direction of treatment. The abnormality is mostly seen in both legs. 6. Knee collapse When the triceps (flounder dominant) muscles of the lower leg are weak, the tibia travels excessively anteriorly in the mid and late support phase, leading to ankle instability or a knee collapse gait. Patients present with premature knee flexion accompanied by shortened contralateral stride length and delayed ipsilateral foot advancement. If patients use increased quadriceps contraction to avoid premature knee flexion and stabilize the knee, this will result in delayed ipsilateral knee flexion at the end of the support phase and eventually lead to knee extensor overuse syndrome. Patients must use the upper extremity to support the knee joint in order to compensate when they are unable to maintain knee stability. The muscles involved include: gastrocnemius-fibularis and quadriceps. Quadriceps muscle electromyographic activity can be prolonged and overactive. 7. Knee stiffness The joint flexion angle in the late support phase and early swing phase is <40 degrees (normal is 60 degrees), while the hip flexion is delayed in both time and phase. Knee flexion in the swing phase is driven by hip flexion, and reduced hip flexion will reduce knee flexion, thereby reducing its swing phase moment, resulting in foot dragging. Patients often compensate in the swing phase by adopting a circle gait, lifting the hip as much as possible, or tiptoeing on the contralateral lower extremity (premature heel lift). Dynamic electromyography usually shows overactivity of the rectus femoris, intermediate femoris, internal femoris and external femoris, decreased activity of the iliopsoas muscle, and sometimes increased activity of the gluteus maximus and N cord muscles. Knee stiffness is exacerbated by the presence of clubfoot. Knee stiffness is commonly seen in patients with upper motor neuron lesions and ankle flexion or y-joint flexion deformities. Fixed knee orthoses and prostheses also cause the same gait. < p=""> 8. Knee hyperextension Knee hyperextension is common but is generally a compensatory change, most often seen early in the brace phase. Common triggers include: weakness of one knee leading to compensatory knee hyperextension on the opposite side; flexor spasm or contracture leading to knee hyperextension; use of knee hyperextension as a compensator during knee collapse gait; spasm of the knee extensor muscle in the support phase; and the line of gravity falling anterior to the center of the knee during trunk forward flexion, prompting posterior knee extension to maintain balance. 9. Knee flexion is less common and is usually caused by osteoarthritic deformities or lesions. The patient maintains a flexed knee position in both the support phase and the swing phase. Patients must use compensatory mechanisms to stabilize the knee joint during the brace phase. Dynamic electromyography of the N cord, quadriceps, gastrocnemius, and hallux valgus muscles often shows a more active medial head of the N cord than the lateral head, and the gastrocnemius is usually overactive, especially in the swing phase. Kinetic studies often show limited knee extension with increased hip flexion. 10. Hip hyperflexion is mainly manifested by hip flexion in the support phase, especially in the middle and late support phase. If the deformity is unilateral, the contralateral lower limb shows functional hyperextension and shortened stride length, while hip lift marching or trunk tilt is used to compensate for the contouring function of the swing phase. Dynamic electromyography commonly shows hyperactivity of the iliopsoas, rectus femoris, and internal hip retractors, while the hip extensors and paraspinatus muscles are diminished. Hip extensor weakness can lead to trunk instability and difficulty in y-joint posterior extension; knee extensor weakness and ankle flexion deformity can lead to extensor y-joint overuse syndrome, resulting in extensor y-joint weakness; secondary flexion deformity of the knee often occurs in hip hyperflexion, aggravating gait disturbance. Hip flexion and its secondary deformities not only affect gait, but also care, urination and defecation, and even wheelchair use in severe cases. Therefore, treatment can be used for patients who cannot walk in order to improve their quality of life and care. 11.Excessive hip inversion Excessive hip inversion is manifested as scissor gait, which is most common in patients with cerebral palsy and traumatic brain injury. In the swing phase, the hip joint is inwardly retracted, crossed with the opposite lower limb, and the step width or foot support surface is reduced, resulting in difficulty in balancing and affecting the ground contouring and forward movement of the limb in the swing phase. It also interferes with activities of daily living, such as dressing, hygiene, toileting and sexual life. The muscles involved include the hip adductors, hip abductors, iliopsoas, pubococcygeus, sutures, medial N cord and gluteus maximus. Spasm or overactivity of the adductor muscles, i.e. imbalance between the adductor and abductor muscle groups, is the main cause. 12, Hip flexion deficiency Flexor hip muscle weakness or hip extensor muscle spasm/contracture can cause y joint flexion deficiency, so that the limb cannot be effectively elevated in the swing phase, causing contouring disorders. Patients can compensate by external rotation of the y-joint, using contraction of the adductor muscles. Contralateral shoe elevation can compensate appropriately. 13, simple muscle weakness gait Simple peripheral nerve injury can lead to specific muscle weakness gait, including: (1) gluteus maximus gait The gluteus maximus is the main hip extension and spinal stabilizing muscle. It controls the center of gravity forward when the foot touches the ground. The N cord muscle can partially compensate for the gluteus maximus, but in peripheral nerve injury, the innervation of the N cord muscle and the gluteus maximus is often compromised simultaneously. (2) Gluteus medius gait The patient’s pelvis shifts more than 5 degrees downward toward the affected side in the early and mid-support phase, the hip joint is convex toward the affected side, and the patient develops compensatory scoliosis of the shoulder and waist to increase pelvic stability. The functional lower extremity on the affected side is relatively too long, so knee and ankle flexion increases in the swing phase to ensure ground contouring. (3) Hip flexor weakness gait The hip flexor is the main accelerator muscle in the swing phase, and its reduced muscle strength causes lack of power for limb travel in the swing phase, which is only compensated by the trunk swinging backward at the end of the support phase and suddenly forward in the early swing phase, and the gait length on the affected side is significantly shortened. (4) Quadriceps weakness gait The quadriceps is the main muscle that controls the stability of the knee joint. In the early support phase, quadriceps weakness makes it necessary to keep the knee joint in a hyperextended position, using the gluteus maximus to keep the proximal femur in position and the hallux valgus to keep the distal femur in position, thereby maintaining knee joint stability. Knee hyperextension results in anterior trunk flexion, creating an additional posterior knee moment. Prolonged exposure to this state will greatly increase knee ligament and joint capsule loading, leading to injury and pain. (5) Ankle dorsiflexor weak gait After the foot touches the ground, the support phase is shortened early and rapidly enters the middle of the support phase because the ankle joint cannot be controlled to flex. In severe cases, the patient develops foot drop in the swing phase, resulting in functional hyperextension of the lower extremity, often compensated by excessive hip flexion and knee flexion (upstep gait), while the early part of the support phase is preceded by full foot or forefoot contact with the ground. (6) Gastrocnemius/flounder muscle weak gait is characterized by impaired ankle dorsiflexion control, prolongation at the end of the support phase and reduced lower limb propulsion, resulting in delayed anterior pelvic motion and shortened stride length on the non-involved side, as well as increased knee flexion moment on the affected side, leading to knee flexion and knee collapse gait.