Muscle strength in HSPers is decreased in most of the muscles of the leg, and muscle stiffness is increased. Muscle weakness is worse the further down the leg you go.
Muscle weakness in all the major leg muscles has been found in this study to be a significant limiting factor affecting walking in people with HSP. Muscle stiffness is the other important factor identified.
These findings contradict other reports that weakness is not a limiting factor in HSP, but are in line with what some physiotherapists are reporting in their assessments of HSP patients.
Different factors impact on walking in people with HSP, compared for example, with people who have cerebral palsy, despite spasticity being a common factor in both conditions. The results suggest that clinicians should assess and target both muscle strength and stiffness in people with HSP.
This study investigated the relationship in HSPers between muscle strength, stiffness (the tension felt in the muscles when the limb is moved by the therapist, with the participant relaxed) and spasticity, and difficulties bending the knee when walking. To do this, they compared the walking patterns, strength, spasticity and muscle stiffness in 20 people with HSP to 18 unimpaired people.
When they analysed the data they found muscle strength in HSPers is decreased in most of the muscles of the leg, and muscle stiffness is increased, especially in the calf muscles. The major muscles used to lift the foot are located on the front of the lower leg. These are 50% weaker in HSPers. Difficulty lifting the foot is exaggerated by stiffness in the calf muscles, which are 35% stiffer in HSPers. As well as the stiffness, HSPers’ calf muscles are also weaker. The thigh muscles of HSPers were also found to be stiffer.
While muscle spasticity was noted in people with HSP, they reported that this was not related to changes in the way that the knee moved when stepping. Instead they reported that less knee flexion (bending) during the ‘swing phase’ (when stepping forward) was associated with stiffness in the thigh muscles, and decreased strength in the calf muscles affecting the push-off before the leg swings forward.
Glossary (click on diagrams to enlarge)
paresis = weakness
knee flexion = the bend at the knee of the trailing leg during walking
knee flexors = muscles at the back of the thigh
knee extension = the straightening of the front leg as it swings through in walking
knee extensors = muscles at the front of the thigh
dorsiflexion = upward movement of the foot
dorsiflexors = muscles on the front of the leg below the knee
plantarflexion = downward movement of the foot
plantarflexors = calf muscles
People with Hereditary and Sporadic Spastic Parapresis (SP) walk with a stiff legged gait characterised by a lack of knee flexion.
We investigated the relationship between lower limb strength and stiffness and knee flexion during swing phase while walking in 20 people with SP and 18 matched controls.
Maximal isometric strength was measured using a dynamometer. Passive stiffness and spasticity was assessed during motor-driven slow (5°/s) and fast (60°/s) stretches at the ankle and knee while the subject was relaxed or preactivating the muscle. Walking was assessed using 3D motion analysis.
Isometric muscle strength was decreased in people with SP with over a 50% reduction in strength being found in the ankle dorsiflexors. Passive stiffness, assessed during slow stretches, was 35% higher in the plantarflexors in people with SP (P<0.05). Faster stretches induced large stretch evoked muscle activity and over a 110% increase in stiffness at the ankle and knee in people with SP reflecting the presence of spasticity (P<0.05). However, stretch reflex size and stiffness was similar between the groups following identical stretches of the pre-activated muscle (P>0.05). Lower knee flexion during swing phase was associated with reduced knee flexion velocity at the end of stance phase which in turn was associated with reduced plantarflexor strength and increased passive stiffness in the knee extensors.
The relative importance of muscle paresis and passive stiffness in limiting walking in SP suggests that these impairments should be the target of future therapies.
Gait Posture. 2012 Feb;35(2):266-71. Epub 2011 Nov 1.
Muscle paresis and passive stiffness: key determinants in limiting function in Hereditary and Sporadic Spastic Paraparesis.
School of Health Professions, Peninsula Allied Health Centre, University of Plymouth, Derriford Road, PL6 8BH, UK.