Computer modeling of the pathomechanics of spastic hip dislocation in children.

Spastic muscles about the hip cause subluxation, dislocation, and lead to acetabular dysplasia. Spastic hip disease occurs when the muscles about the hip exert forces that are too high or in the wrong direction or both. To determine the role of the hip forces in the progression of spastic hip disease and the effect of both muscle-lengthening and bony reconstructive surgeries, a computerized mathematical model of a spastic hip joint was created. The magnitude and direction of the forces of spastic hips undergoing surgery were analyzed preoperatively and postoperatively to determine which procedure is best suited for the treatment of spastic hip disease. The muscle-lengthening procedures included (a) the adductor longus, (b) the psoas, iliacus, gracilis, adductor brevis, and adductor longus, and (3) the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus. The bony reconstructive and muscle-lengthening procedures included (a) lengthening the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing femoral neck anteversion from 45 to 10 degrees , (b) lengthening of the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing neck-shaft angle from 165 to 135 degrees , and (c) lengthening of the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing femoral neck anteversion from 45 to 10 degrees and neck-shaft angle from 165 to 135 degrees . Results show that a child with spastic hip disease has a hip-force magnitude 3 times that of the a child with a normal hip in the normal physiologic position. Based on this mathematical model the best to normalize the magnitude of the hip-joint reaction force, the muscles to be lengthened should include the psoas, iliacus, gracilis, adductor brevis, and the adductor longus. To normalize the direction of the hip force, the extremity should be positioned in the normal physiologic position. The impact of decreasing the femoral anteversion or femoral neck-shaft angle or both had little additional effect on the direction or magnitude of hip forces.

[1]  A P Cosgrove,et al.  BOTULINUM TOXIN IN THE MANAGEMENT OF THE LOWER LIMB IN CEREBRAL PALSY , 1994, Developmental medicine and child neurology.

[2]  F. Miller,et al.  Reconstruction of the dysplastic spastic hip with peri-ilial pelvic and femoral osteotomy followed by immediate mobilization. , 1997, Journal of pediatric orthopedics.

[3]  C. K. Lee,et al.  Assessment of Complex Hip Deformity Using Three‐Dimensional CT Image , 1991, Journal of pediatric orthopedics.

[4]  Michael R. Pierrynowski,et al.  A physiological model for the evaluation of muscular forces in human locomotion: theoretical aspects , 1985 .

[5]  I. Paul,et al.  The biomechanics of congenital dislocated hips and their treatment. , 1974, Clinical orthopaedics and related research.

[6]  E E Bleck,et al.  Management of the lower extremities in children who have cerebral palsy. , 1990, The Journal of bone and joint surgery. American volume.

[7]  K. An,et al.  Incorporation of muscle architecture into the muscle length-tension relationship. , 1989, Journal of biomechanics.

[8]  A Seireg,et al.  A mathematical model for evaluation of forces in lower extremeties of the musculo-skeletal system. , 1973, Journal of biomechanics.

[9]  E. Bleck.  The hip in cerebral palsy. , 1980, The Orthopedic clinics of North America.

[10]  E. Bleck,et al.  PREVENTION OF SPASTIC PARALYTIC DISLOCATION OF THE HIP , 1985, Developmental medicine and child neurology.

[11]  M. Rang,et al.  Adductor Release in Nonambulant Children with Cerebral Palsy , 1985, Journal of pediatric orthopedics.

[12]  F. Miller,et al.  Soft-tissue release for spastic hip subluxation in cerebral palsy. , 1997, Journal of pediatric orthopedics.

[13]  A Huson,et al.  A model study of muscle forces and joint-force direction in normal and dysplastic neonatal hips. , 1989, Journal of biomechanics.

[14]  W. Sharrard,et al.  Surgical prophylaxis of subluxation and dislocation of the hip in cerebral palsy. , 1975, The Journal of bone and joint surgery. British volume.