Comparison of 3 different methods to analyze ankle plantarflexor stiffness in children with spastic diplegia cerebral palsy.

OBJECTIVE To compare 3 different methods of measuring plantarflexor stiffness in children with spastic diplegia cerebral palsy (CP) and children without disability. DESIGN Case-control study. SETTING Human performance laboratory. PARTICIPANTS A retrospective analysis was conducted with children with spastic diplegia (n=121; mean age, 8.4y) and children with typical development (TD) (n=48; mean age, 9.7y). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES An isokinetic dynamometer was used to measure ankle plantarflexor stiffness at 10°/s using 3 methods: (1) end-range method, which applied a linear slope to the end of the torque-angle curve; (2) set-range method, which applied a linear slope from 30° to 10° plantarflexion; and (3) a linear method, which applied a slope only to the linear portion of the curve. RESULTS Two-way analysis of variance revealed significant main effects for group and stiffness method. The end-range method showed no significant difference between groups for plantarflexor stiffness (P=.62), the set-range method showed the CP group with 120% greater stiffness than the TD group (P<.046), and the linear method showed the CP group with 35% greater stiffness than the TD group (P<.001). CONCLUSIONS The linear method appeared to resolve the issues with the previous methods; applying a linear slope to a nonlinear curve or applying a linear slope to the same range of motion for each child regardless of their range limitations. It is clear that children with CP have limited range of motion; therefore, stiffness occurs earlier in the range than would be expected for a typically developing child. Using the linear method, children with CP were 35% stiffer in the ankle plantarflexors than typically developing peers.

[1]  R. J. Johns,et al.  Relative importance of various tissues in joint stiffness , 1962 .

[2]  Richard L Lieber,et al.  Structural and mechanical alterations in spastic skeletal muscle. , 2005, Developmental medicine and child neurology.

[3]  Martina Krüger,et al.  Fibre type‐specific increase in passive muscle tension in spinal cord‐injured subjects with spasticity , 2006, The Journal of physiology.

[4]  R. Palisano,et al.  Development and reliability of a system to classify gross motor function in children with cerebral palsy , 1997, Developmental medicine and child neurology.

[5]  J Harlaar,et al.  Measurement of impaired muscle function of the gastrocnemius, soleus, and tibialis anterior muscles in spastic hemiplegia: a preliminary study. , 1998, Journal of rehabilitation research and development.

[6]  Relation between spasticity and strength in individuals with spastic diplegic cerebral palsy , 2002 .

[7]  T Sinkjaer,et al.  Passive, intrinsic and reflex-mediated stiffness in the ankle extensors of hemiparetic patients. , 1994, Brain : a journal of neurology.

[8]  R. Lieber,et al.  Inferior mechanical properties of spastic muscle bundles due to hypertrophic but compromised extracellular matrix material , 2003, Muscle & nerve.

[9]  S. Delp.  What causes increased muscle stiffness in cerebral palsy? , 2003, Muscle & nerve.

[10]  Muscle stiffness and strength and their relation to hand function in children with hemiplegic cerebral palsy. , 2006, Developmental medicine and child neurology.

[11]  M. Abel,et al.  Spasticity versus strength in cerebral palsy: relationships among involuntary resistance, voluntary torque, and motor function , 2001, European journal of neurology.

[12]  R. Kearney,et al.  Identification of intrinsic and reflex ankle stiffness components in stroke patients , 2005, Experimental Brain Research.

[13]  R. Shepherd,et al.  Mechanical properties of the plantarflexor musculotendinous unit during passive dorsiflexion in children with cerebral palsy compared with typically developing children , 2010, Developmental medicine and child neurology.

[14]  Richard L Lieber,et al.  Spastic muscle cells are shorter and stiffer than normal cells , 2003, Muscle & nerve.

[15]  Overstretching of sarcomeres may not cause cerebral palsy muscle contracture , 2004, Journal of orthopaedic research : official publication of the Orthopaedic Research Society.

[16]  W. Rymer,et al.  Muscle and reflex changes with varying joint angle in hemiparetic stroke , 2008, Journal of NeuroEngineering and Rehabilitation.

[17]  J. Engsberg,et al.  Ankle spasticity and strength in children with spastic diplegic cerebral palsy , 2000, Developmental medicine and child neurology.

[18]  R. Gajdosik,et al.  A stretching program increases the dynamic passive length and passive resistive properties of the calf muscle-tendon unit of unconditioned younger women , 2007, European Journal of Applied Physiology.