Geometric topology of multi-strand ACL graft constructs: A mechanical framework and exploratory clinical analysis

Hamstring graft preparation in anterior cruciate ligament (ACL) reconstruction varies widely, with strand number often determined by tendon length or surgeon preference. The influence of internal strand geometry on graft mechanical behaviour and postoperative stability remains poorly understood.

A geometric-mechanical framework was developed to characterize ACL graft constructs composed of two to six strands within a circular femoral tunnel. Spatial strand coordinates were used to derive four theoretical geometric descriptors: Symmetry Index (SI), effective polar moment of inertia (J_eff), Anisotropy Index (AI), and centroid displacement. Potential clinical relevance was explored in 162 patients undergoing primary ACL reconstruction with autologous hamstring grafts. Outcomes included anterior tibial translation, pivot-shift grade, and subjective IKDC score. Exploratory multivariable analyses adjusted for age, sex, pivoting sport participation, graft diameter, and follow-up duration.

Even-strand constructs, particularly four- and six-strand grafts, demonstrated greater symmetry, higher polar moment of inertia, and lower anisotropy. Odd-strand constructs showed greater centroid displacement and geometric asymmetry. Exploratory clinical analyses showed numerical associations between greater theoretical geometric symmetry and lower anterior laxity and residual pivot shift. These descriptors represent theoretical structural properties rather than direct measurements of biomechanical performance.

Internal graft topology may represent a structural characteristic influencing ACL graft behaviour beyond diameter alone. However, this hypothesis was not directly tested biomechanically or through in vivo topology measurements. The observed clinical associations are exploratory and hypothesis-generating. This geometric framework provides a conceptual basis for future biomechanical, computational, and clinical investigations of strand configuration.

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