Under normal circumstances, the stability of the knee is maintained by the surrounding bony structures, ligaments, joint capsule and muscle tissue. Knee hyperextension exists in hemiplegic patients after stroke and is caused by insufficient muscle strength of the affected lower limb, decreased balance and coordination, the emergence of primitive movement patterns and incorrect exercise patterns, and once it occurs, it is difficult to correct.
According to statistics, about 75% of stroke patients have lower limb dysfunction, and knee hyperextension is a common phenomenon in rehabilitation training, especially in patients in the posterior phase of rehabilitation in the community. Because this poor gait affects the patient’s ability to walk, knee hyperextension will have to be taken seriously to improve the quality of life of stroke patients.
Knee hyperextension is also known as knee dystocia or knee dorsiflexion deformity, also known as “trivial knee” phenomenon, which means that during walking or standing, the lower limb on the affected side is hyperextended (knee extension angle greater than 5°) during the support period, the body weight is shifted back, the affected hip is hyperextended and the body tends to lean back.
1. Causes of post-stroke knee hyperextension
It is widely believed that post-stroke knee extension is a result of weak quadriceps muscle strength, which cannot fully support the weight; weak flexor muscle strength, which cannot maintain the normal flexion angle of the knee joint during the support period; quadriceps muscle spasm, which prevents the knee joint from mild flexion, etc. Methods.
1.1, quadriceps muscle strength is weak, not enough to support the weight When standing or walking because of the affected leg in the support phase of knee extension instability, the patient often tilted forward the upper body compensation method, so that the body weight up to the front of the knee joint, passive straightening of the knee joint to increase its stability, it leads to the occurrence of knee hyperextension.
1.2. Weak muscle strength of the knee flexors (N cord muscle) cannot maintain mild knee flexion of 0° to 15° during the support period.
1.3, emergence of primitive movement pattern High spasm of quadriceps muscle causes hyperextension of the knee joint and inability to actively flex, combined with weakness of ankle dorsiflexion or foot drop due to spasm of gastrocnemius muscle, forcing a hemiplegic gait of the affected limb.
The proprioceptive nerve impulses from the musculoskeletal and tendon organs around the knee are transmitted to the spinal cord by Ⅰa fibers, which directly excite the motor neurons of the muscle and inhibit the activity of the antagonist muscles through the activity of inhibitory interneurons, so that the active and antagonist muscles cooperate and restrain each other to complete coordinated movements. When there is cross-inhibition of the affected limb due to proprioceptive impairment, the patient cannot easily obtain accurate position perception of the affected knee and cannot inhibit excessive quadriceps muscle tone, resulting in dysfunction in the coordination of knee flexion and extension and knee hyperextension.
As for the essential cause of knee hyperextension, there is still no clear report in the literature.
2. Training program for knee hyperextension after stroke
2.1. Resisted muscle strength training
2.1.1. Early separation and resistance exercise training Since knee hyperextension is difficult to correct once it occurs, prevention is particularly important. For patients within 3 weeks of stroke, the lower extremity rehabilitation treatment was carried out gradually and early, including normal position placement, hip extension, knee flexion, weight-bearing of the affected limb and knee flexion control from 0° to 15°, etc. The training intensity was 1 time/d, 40-60 min/time, 5 times/week, and the total course of treatment was 6 months. The results showed that the incidence of knee hyperextension in the rehabilitation group was significantly lower than that in the control group without rehabilitation training (p<0.01), and the treatment significant rate was significantly higher than that in the control group (p<0.05).
In stroke patients with a disease duration of less than 2 weeks, with muscle strength of lower limbs <2 levels, and unable to stand, the rehabilitation group underwent early knee stability training (including training to promote the recovery of deep sensation in the knee joint, such as distraction and compression of the affected lower limb, and training to strengthen the muscles of quadriceps, N cord and anterior tibial muscles, together with medium-frequency electrical therapy), and then performed standing training after the muscle strength of the affected lower limb reached 3 levels. After 3 months of treatment, the incidence of knee hyperextension in the rehabilitation group was significantly lower than that in the control group which only underwent conventional training.
For patients who could walk independently after stroke and had knee instability without sensory cognitive impairment, maximum centripetal isotonic knee flexion and terminal isometric resistance training of the N cord muscle was performed under the suppression of upper limb and trunk muscle spasm, each resistance lasted 10s, and each 2 exercises were repeated for 20min at an interval of 30s. The treatment course was 60 days. The isometric muscle strength test showed that the knee flexion/extension muscle strength ratio on the affected side was significantly higher than that before treatment at all angular speeds, i.e., the N cord muscle strength was increased and the knee stability was improved.
2.1.3. Strengthen the anterior tibial muscle Using biofeedback, let the patient actively do ankle dorsiflexion training, and through visual feedback, make the patient keep working toward a high threshold to achieve the effect of active exercise. If there is no biofeedback, medium frequency electrical stimulation can be used to stimulate the anterior tibial muscle and increase weight-bearing training.
2.2.Acupuncture method
2.2.1, milli-needle flying method Take 50mm milli-needle, and stab the milli-needle obliquely into Yanglingquan, Fuzhong, Zhizhong, and Chengshan, and perform acupuncture for two minutes at each point once a day for 15 days as a course of treatment, with a 3-day rest, for a total of 2 courses of treatment. As shown in the electromyographic H-reflex, the wave amplitude of knee hyperextension spasm outbreak was reduced, the time duration was shortened, the outbreak frequency was significantly reduced, and the latency rate was reduced after treatment using the milli-needle flying method, and the difference was very significant compared with that before treatment.
2.2.2, acupuncture with rehabilitation technology treatment Take No. 30 1. 5 inch stainless steel needle, select Liangqiu, Blood Sea, Foot Sanli, Yanglingquan, all straight stab; middle calf nose upward oblique stab, flat tonic and flat diarrhea technique. After obtaining the Qi, the G6805 electro-acupuncture instrument was connected, the sparse and dense wave was selected, the power was as much as the patient could tolerate, the needles were kept for 1 h, 1 time/day, 10 times a course of treatment, together with the rehabilitation training based on the control of knee flexion within the range of 0° to 15°. The results showed that the total effective rate of knee hyperextension treatment was 98% in 52 stroke patients.
2.3. Lower limb orthosis If there is no serious knee deep sensory disorder after stroke, the formation of knee hyperextension can be mostly prevented by early formal rehabilitation training. Once formed and after the rehabilitation treatment is not satisfactory, there are reports of cases where orthoses have to be used.
It has been proposed to use a long lower limb orthosis to control the angle of the knee and ankle joints, and a knee hinge to keep the knee joint in a mildly flexed position of 10° to 20° to inhibit knee hyperextension; it has also been proposed to use a long lower limb orthosis early in hemiplegia to promote the postural response of the patient from the onset, prevent muscle atrophy, and strengthen the muscle strength of the healthy lower limb. It is widely believed that the use of AFOs that prevent plantarflexion of the ankle joint is effective in preventing knee hyperextension when the stroke patient stands.
2.4. For deficits in proprioception in stroke patients, early joint distraction and compression are preferred to promote recovery; if proprioception is lost, therapists can enhance their functional gait training or compensate using visual and auditory compensation, such as a biofeedback device with a limb load indicator that prompts the patient when the foot touches the ground, providing information on the strength of muscle contraction during intensive training.
Knee hyperextension severely affects the walking ability of stroke patients and is an urgent issue to be addressed in order to improve their quality of life. At present, studies on knee hyperextension after stroke have not clearly reported its essential causes. As far as the existing summary is concerned, the causes of knee hyperextension after stroke can be divided into weak lower limb muscles, primitive motor patterns, and lower limb proprioceptive deficits, and the causes of above ankle proprioceptive deficits and weak quadriceps muscles are particularly prominent.
Most of the targeted rehabilitation treatment methods also advocate gradual progress, early promotion of detachment movement, restoration of proprioception, when the lower limb muscle strength is sufficient to support the weight and the lower limb detachment movement, followed by standing and walking training, avoid premature standing and walking before the lower limb muscle strength reaches level 3 (Lovett muscle strength 6 grade method); if the patient has already appeared knee hyperextension phenomenon and no improvement by rehabilitation training, then can Choose the appropriate lower limb orthosis to correct the gait.