Divergence from the Normative Gait-Development Trajectory: A Multidomain Model of Gait Divergence in Hemiplegic (Unilateral) and Diplegic (Bilateral) Spastic Cerebral Palsy

Background/Objective: Gait symmetry in children is increasingly understood as a development-dependent continuum rather than a fixed endpoint. This narrative review extends that framework into a multidomain model of gait divergence in cerebral palsy (CP), asking whether asymmetry in hemiplegic and diplegic CP fails to reach the normative curve or diverges from it in phenotype-specific ways that cannot be captured by a single index. Methods: Literature was identified through a semantic search (Elicit; April–August 2026) supplemented by gap-directed searches, yielding 50 references, synthesized across four domains—interlimb symmetry, kinematic deviation, neuromuscular/coordination control, and functional balance/postural control—drawing predominantly on cross-sectional and cross-study evidence, with fewer longitudinal and intervention studies. Results: Hemiplegic CP shows lateralized divergence with compensatory changes in the nominally unaffected limb and partial improvement in asymmetry over time. Diplegic CP frequently shows preserved or near-normal left–right symmetry coexisting with progressive, growth-linked deterioration in sagittal-plane impairments hidden beneath a stable global gait score, alongside a more coupled, less variable coordination strategy not matched by comparable neuromuscular maturation; whether this coupling explains the preserved symmetry remains an untested hypothesis. These domains do not move in parallel across phenotypes; therefore, no single metric is sufficient. Conclusions: Because the hemiplegia–diplegia contrast is currently better supported as a cross-sectional distinction than as evidence of differing longitudinal slopes, we propose a provisional, non-summative Trajectory Divergence Framework—without numerical scoring—as a hypothesis-generating structure for future multi-domain monitoring, identifying the absence of longitudinal, multi-domain, multi-phenotype cohorts as the principal evidence gap in the field.