Is hamstrings-to-quadriceps torque ratio useful for predicting anterior cruciate ligament and hamstring injuries? A systematic and critical review

Abstract

Background: For the past 30 years, the hamstring (H)-to-quadriceps (Q) (H:Q) torque ratio has been considered an important index of muscle strength imbalance around the knee joint. The purpose of this systematic review was to examine the value of H:Q torque ratio as an independent risk factor for hamstring and anterior cruciate ligament (ACL) injuries.

Methods: Database searches were performed to identify all relevant articles in PubMed, MEDLINE, Cochrane Library, and Scopus. Prospective studies evaluating the conventional (concentric H:Q), functional (eccentric H: concentric Q), and mixed (eccentric H at 30°/s: concentric Q at 240°/s) H:Q ratios as risk factors for occurrence of hamstring muscle strain or ACL injury were considered. Risk of bias was assessed using the Quality In Prognosis Studies tool.

Results: Eighteen included studies reported 585 hamstrings injuries in 2945 participants, and 5 studies documented 128 ACL injuries in 2772 participants. Best evidence synthesis analysis indicated that there is very limited evidence that H:Q strength ratio is an independent risk factor for hamstring and ACL injury, and this was not different between various ratio types. Methodological limitations and limited evidence for ACL injuries and some ratio types might have influenced these results.

Conclusion: The H:Q ratio has limited value for the prediction of ACL and hamstring injuries. Monitoring strength imbalances along with other modifiable factors during the entire competitive season may provide a better understanding of the association between H:Q ratio and injury.

Keywords: ACL; Isokinetic; Prospective; Strains; Strength imbalance.

Graphical abstract

Fig. 1

Search flow diagram. ACL = anterior cruciate ligament; H:Q = hamstrings-to-quadriceps torque ratio.

Fig. 2

Risk of bias assessment.

Fig. 3

Mean conventional H:Q torque ratio values of Inj and Uinj groups reported by the studies included in this review. For all studies but that of Sugiura et al., 95%CI were estimated based on the reported means, SDs, and study sample sizes. Solid circle means injured and circle means uninjured. *p < 0.05, significant differences between groups. 95%CI = 95% confidence interval; ACL = anterior cruciate ligament; conc = concentric; ecc = eccentric; H:Q = hamstrings-to-quadriceps; Inj = injured; Uinj = uninjured.

Fig. 4

Mean (95%CIs) functional, mixed, and other type of H:Q torque ratio values of groups with (Inj) and without (Uinj) hamstring injury reported by the studies included in this review. For all studies but that of Sugiura et al., 95%CIs were estimated based on the reported means, SDs, and study sample sizes. Solid circle means injured and circle means uninjured. *p < 0.05, significant differences between groups. 95%CI = 95% confidence interval; H:Q = hamstrings-to-quadriceps; Inj = injured; L = left; R = right; Uinj = uninjured.