The relationship between patella alta and crouch gait in cerebral palsy

The relationship between patella alta and crouch gait in cerebral palsy
1Orthopaedics, Texas A & M Health Science Center College of Medicine, Temple, TX;
2University of Texas Medical School at Houston, TX;
3 Shriners Hospital for Children, Houston, TX, USA.

Background/Objectives: Patella alta has been implicated in the etiology of crouch gait in individuals with cerebral palsy. Crouch gait can cause knee pain, decreased efficiency in ambulation and increased energy expenditure. Recently, surgical intervention to the patellar tendon has been used to decrease patella alta and reduce crouch gait. Although both patella alta and crouch gait are more common with increasing severity of spasticity, the specific correlation between crouch gait and patella alta is know. This study investigates the relationship of patella alta to dynamic knee position in ambulatory adolescents with cerebral palsy. The hypothesis of the study was that increased patella alta would be associated with more severe crouch gait.
Design: Retrospective cohort study.
Participants and setting: Fourty -four ambulatory individuals (87 limbs) with spastic cerebral palsy ages 15-19 years followed in a children’s orthopedic hospital were evaluated. Inclusion criteria were bilateral involvement (diplegia or quadriplegia), standing lateral knee radiographs performed after age 14 (to measure patella alta) and three-dimensional motion analysis (to measure crouch gait) completed after age 14.
Materials/Methods: Patella alta was determined by measuring standing lateral knee radiographs and calculating the ratio between the patellar tibial and femoral tibial distances: PT/FT using the method of koshino and sugimoto, 1989.Crouch gait was assessed by select sagittal plane knee parameters including degree of flexon at initial contact and loading minimum flexion during stance calculated from kinematic data collected with a three-dimensional vicon motion analysis system. Correlation between lateral radiograph ratios and knee kinematic parameters were performed using SPSS statistical software.
Results: Seventy-seven of 87(88.5%) evaluated knee had patella alta as defined by a patellar height index (PT/FT) greater than two standard deviations over published normative values. Knee position in varied widely among this patient population with 45% demonstrating knee flexion greater than 200 in stance and 21% demonstrating some degree of genu recurvatum in stance. Pearson correlation coefficients calculated for the PT/FT ratios and the knee kinematic values were all very small (knee flexion at initial contact: r = -0.071, knee flexion at loading: r = -0.064, minimum knee flexion in stance: r = 0.096, mean knee flexion in stance: r=0.044). None of these correlation coefficients between the degree of patella alta and knee position in stance.
Conclusions/Significance: Patella alta is a common radiographic finding in ambulatory individuals with cerebral palsy at skeletal maturity. The severity of the patella alta, however did not correlate with the severity of crouch gait as measured by motion analysis. These findings should be considered when recommending surgical treatment such as extensor mechanism shortening to treat patella alta.

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