A novel test reliably captures hip and knee kinematics and kinetics during unanticipated/anticipated diagonal hops in individuals with anterior cruciate ligament reconstruction

A comparison of three methods for establishing an ACL reference length in vivo

As anterior cruciate ligament (ACL) injuries are highly prevalent among active individuals, it is vital to better understand the loading conditions which lead to injury. One method for doing so is through measurement of dynamic, in vivo ACL strain. To measure strain, it is necessary to normalize elongation of the ACL to a 'reference length' which corresponds to the point at which the ligament transitions from being unloaded to carrying tension. The purpose of this study was to compare the length of the ACL in three different positions to evaluate their utility for establishing a reference (or zero-strain) length of the ACL. ACL reference length was determined using three different methods for each of ten healthy participants. Using magnetic resonance and biplanar radiographic imaging techniques, we measured the length of the ACL during supine resting, quiet standing, and anterior/posterior (AP) drawer testing. During the AP drawer testing, the slack-taut transition point was defined as the inflection point of the AP translation vs ACL elongation curve. There was good consistency between the three ACL length measurements (ICC=0.80). Differences in mean ACL length between the three methods were within 1 mm. While determining the precise zero-strain length of the ACL in vivo remains a challenge, the reference positions utilized in this study produce consistent measurements of ACL length. These findings are important because reliable measurements of in vivo ACL strain have the potential to serve as indicators of propensity for injury.

Thigh muscle co-contraction patterns in individuals with anterior cruciate ligament reconstruction, athletes and controls during a novel double-hop test

Efficient neuromuscular coordination of the thigh muscles is crucial in maintaining dynamic knee stability and thus reducing anterior cruciate ligament (ACL) injury/re-injury risk. This cross-sectional study measured electromyographic (EMG) thigh muscle co-contraction patterns during a novel one-leg double-hop test among individuals with ACL reconstruction (ACLR; n = 34), elite athletes (n = 22) and controls (n = 24). Participants performed a forward hop followed by a 45° unanticipated diagonal hop either in a medial (UMDH) or lateral direction (ULDH). Medial and lateral quadriceps and hamstrings EMG were recorded for one leg (injured/non-dominant). Quadriceps-to-Hamstring (Q:H) ratio, lateral and medial Q:H co-contraction indices (CCIs), and medial-to-lateral Q:H co-contraction ratio (CCR; a ratio of CCIs) were calculated for three phases (100 ms prior to landing, initial contact [IC] and deceleration phases) of landing. We found greater activity of the quadriceps than the hamstrings during the IC and deceleration phases of UMDH/ULDH across groups. However, higher co-contraction of medial rather than lateral thigh muscles during the deceleration phase of landing was found; if such co-contraction patterns cause knee adduction, a putative mechanism to decrease ACL injury risk, during the deceleration phase of landing across groups warrants further investigation.

Acute effects of a neuromuscular warm-up on potential re-injury risk factors associated with unanticipated jump landings after anterior cruciate ligament reconstruction: A crossover trial

OBJECTIVE

To investigate acute effects of a single bout of football specific neuromuscular injury preventive warm-up on potential anterior cruciate ligament (ACL) re-injury risk factors during anticipated and unanticipated jump-landings.

DESIGN

Crossover.

METHODS

Fourteen participants (mean ± SD age, 23.4 ± 4.1 years) 6-24 months after ACL reconstruction performed the Prevent Injury and Enhance Performance (PEP) and bicycle ergometer warm-up in a randomised sequence. Washout phase was one week. Countermovement jumps with anticipated and unanticipated single-leg-landings were assessed. Decision-making quality was measured using landing error count.

RESULTS

No carry-over effects occurred (p > 0.05). The unanticipated task produced significantly higher peak ground reaction forces (Δ+4%, F₍₁₁₎ = 3.46, p < 0.001, eta² = 0.21) after PEP warm-up compared to ergometer warm-up. A lower number of decision (Δ+12%, F ₍₅₎ = 17.1, p < 0.001, eta² = 0.57) and cumulated (Δ+15%, F ₍₃₎ = 17.2, p < 0.001, eta² = 0.57) errors were recorded during the unanticipated condition following PEP compared to ergometer warm-up.

CONCLUSIONS

Evaluating unanticipated jump-landing ability prior to return to sports clearance may provide information on potential re-injury risk factors. PEP warm-up may be superior to bicycle ergometer warm-up at improving unanticipated decision-making quality among athletes cleared to return to sports.