When walking after hemiplegia, many people experience “knee hyperextension”, which is a lack of knee flexion in the affected leg and a knee that is extended too far. Knee hyperextension is very common, but is usually a compensatory change, and there are several common causes of knee hyperextension.
1, severe imbalance between extensor muscle strength and flexor muscle strength, i.e., too little flexor muscle strength.
2, excessive tension in the knee extensor muscle
3, weakness of the knee extensor muscle.
4, excessive tension of the triceps calf muscle / i.e. foot drop, passive inability to cross the neutral position.
5, May be related to hip joint control Li Shao-ling, Department of Physical Therapy, Sichuan Province Eighty-one Rehabilitation Center
6, compensatory knee hyperextension caused by triceps spasm or Achilles tendon contracture
7. Knee hyperextension caused by too strong knee extension device
8, Hip flexion contracture, posterior pelvic rotation, or weak gluteus maximus posterior extension can cause hyperextension of the knee.
9, Trunk control has an effect on knee hyperextension
10. Weak quadriceps muscle strength is also a cause of knee hyperextension
11, weakness of one knee joint leading to compensatory knee hyperextension on the opposite side
12. flexor spasm or contracture leading to knee hyperextension
13, the use of compensatory knee hyperextension during collapsed knee gait.
14, spasm of the supporting phase knee extensors.
15, the line of gravity falls in front of the center of the knee during trunk forward flexion, prompting posterior extension of the knee to maintain balance
16, compensatory knee hyperextension due to Achilles tendon contracture
Knee hyperextension in patients with cerebral palsy usually results in three conditions.
One, is that the ankle joint does not reach a functional position and the knee hyperextends compensatingly.
Second, there is inadequate knee control due to insufficient knee muscle strength or ligamentous laxity.
Third, the hip joint muscle strength is too high or insufficient to cause the body weight to shift forward or backward, the whole body weight does not fall on the load-bearing line, the knee and ankle joint appear to compensate to maintain body balance.
There are many reasons for knee hyperextension.
1, anterior knee paralysis or low muscle strength due to quadriceps paralysis or low muscle strength, weakened N cord muscle, knee joint instability in the straight position, forced to walk in the posterior extension position when carrying weight. It is common in ataxia type and hypotonia type cerebral palsy.
2.Posterior knee paralysis or hypotonia, paralysis or hypotonia of the N cord muscle and triceps calf muscle, posterior knee relaxation including joint capsule and ligament, etc. causing knee dystocia. It is commonly seen in spastic and hypotonic cerebral palsy.
3. Poor muscle selective motor control of the quadriceps and N cord muscles of the knee joint, lack of simultaneous contraction, resulting in knee instability, mainly seen in the tardive dyskinesia type of cerebral palsy.
4, support phase knee extension muscle spasm quadriceps muscle hypertonia especially rectus femoris, resulting in standing or support phase stiffness, in forward trunk flexion, the line of gravity falls in front of the knee joint, prompting the knee joint posterior extension to maintain balance. It is common in spastic and tonic cerebral palsy.
5.Plantar flexor spasm or contracture causes knee hyperextension due to triceps calf muscle spasm or contracture makes the gravity line fall in front of the knee joint and compensates to form knee anteversion, common in spastic cerebral palsy.
6. Knee proprioceptive disorder, poor knee control, in order to increase joint stability, the knee joint is locked in the posterior extension position and knee anteversion occurs, mainly seen in ataxic cerebral palsy.
In addition, long-term flexion deformity of the knee joint leads to patellar ligament relaxation, and knee hyperextension occurs when the N cord muscle is released, which is also a common cause of knee hyperextension in cerebral palsy.
”Knee hyperextension can cause excessive wear and tear on the knee joint over time, resulting in deformity. This can be corrected by walking with the affected leg on the ground heel first and then consciously bending the knee before raising the foot to walk forward. However, the easiest way to solve the problem is to wear a knee brace, preferably cotton and thicker, on the affected leg.
The knee flexion training method is as follows
Sit on a slightly higher chair, with your legs hanging in the air, and fling the affected leg back and forth. When the lower leg is thrown backwards to its highest position, try to hold it in the air and then throw it forward again. When the lower leg can continue to hang for a minute or two, then do the exercise with the affected foot on the ground and knee backward flexion and extension. If the knee can be flexed and extended backwards more than 90 degrees, the training score will be perfect.
When standing and doing some activities, consider padding the back of the standing frame a little higher so that the knee joint is slightly bent, or pushing it forward a little, or putting some towels behind the knee joint. Be sure to wear orthopedic shoes when training in the standing position to increase muscle strength training. If the quadriceps weakness is caused, you should strengthen the quadriceps muscle strength and do quadriceps resistance exercises.