Horizontal and Multidirectional Single-Leg Hop Tests Predict Isokinetic Quadriceps and Hamstring Strengths After Anterior Cruciate Ligament Reconstruction

Background: After anterior cruciate ligament reconstruction (ACLR), isokinetic strength and single-leg hop tests (SLHT) are used to assess return to sport readiness. This study examined the relationships and predictive effects of isokinetic knee extension (Ex) and flexion (Flx) strength with 5 SLHTs at 6 to 8 months post-ACLR. Hypothesis: There would be significant correlation between knee Ex and Flx strengths on the operated side and 5 different SLHTs; SLHTs would significantly predict knee isokinetic Ex and Flx strength. Study Design: Cross-sectional study. Level of Evidence: Level 3. Methods: Fifty-one male participants underwent unilateral ACLR. Lysholm, International Knee Documentation Committee (IKDC), and Tegner scales were assessed preoperatively and 6 to 8 months postoperatively. At the same follow-up, isokinetic strength at 60°/s, 180°/s, and 240°/s and 5 SLHTs were tested on both limbs. Data were analyzed with paired t tests, Pearson correlations, Fisher’s exact test, and simple linear regression; limb symmetry index (LSI) cut-off was ≥85%. Results: Isokinetic strength and single-leg hop (SH), crossover hop, and medial side triple-hop (TH) distances did not differ significantly between limbs ( P > 0.05), whereas TH and 90° medial rotation hop distances were significantly shorter on the operated side ( P < 0.05). Participants’ Lysholm and IKDC scores improved significantly at 6 to 8 months post-ACLR ( P < 0.001), but Tegner activity level did not change significantly ( P > 0.05). High correlation was found between Ex strength at 60°/s and SH and TH distances on the operated side, and high-moderate correlations were found at 180°/s and 240°/s. Flx strengths showed a similar but slightly lower degree of correlation. Simple linear regression models revealed that especially SH and TH distances significantly predicted both Ex and Flx strengths (adjusted R 2 0.26-0.52; P < 0.001). Among the LSI values, only a significant correlation was found between 60°/s Ex and TH LSI ratio ( P = 0.01). Conclusion: The findings show that SH and TH tests were highly predictive of isokinetic knee strength after ACLR. Clinical Relevance: SLHTs after ACLR can be used as a practical and accessible complement to isokinetic measurements.