Background Meeting specific objective discharge criteria after ACL reconstruction (ACLR) or delaying return to sport (RTS) until nine months post ACLR decreases the risk of re-injury.

Objective Compare plantar forces during running in two groups of soccer players: cases (5–10 months post ACLR) vs controls (no history of ACLR).We also undertook within subjects comparison (injured vs uninjured limb). Players were arbitrarily divided into two groups (≥9 months post ACLR or <9 months post ACLR) and peak plantar forces and symmetry across different running speeds compared.

Design Case-control study.

Setting Elite male soccer players.

Participants Sixteen football players (age 26±4 yrs, weight 74±6 kg, height 178±6 cm) post ACLR on completion of criteria based rehabilitation and 16 uninjured players (28±4 yrs, 77±9 kg, 179±6 cm) were recruited.

Interventions In-shoe plantar force measured (Novel PedarX) while running on a treadmill at 12,14, and 16 km/h.

Main Outcome Measurements Peak plantar forces of the injured and uninjured limbs in athletes <9 months post-ACLR and those ≥9 months ACLR were compared. Negative vales indicate relatively lower peak forces on the injured leg. Normative data was collected in uninjured players for comparison (N=16).

Results Increasing asymmetry for peak plantar force was demonstrated at all running speeds in athletes <9 months post ACLR (n=11) compared to athletes ≥9 months (n=5). Increasing asymmetry was seen with increasing running speed and peaked at 16 km/h −32±11% asymmetry compared to −6±8%; ES=−2.8, p<0.01. Controls showed substantially less asymmetry at each running speed than <9 months ACLR players: 16 km/h (3.8±3% peak plantar force limb asymmetry).

Conclusions Relative unloading of the ACLR limb is marked at higher running speeds for athletes <9 months post ACLR despite having completed all functional criteria required to permit return to play. These preliminary findings may help add further objective criteria to guide RTS following ACLR.