Early compensatory and anticipatory postural adjustments following anterior cruciate ligament reconstruction

 Purpose = Early identification of postoperative neuromuscular deficits has been advocated to prevent muscle weakness and maximize functional outcomes following anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to investigate neuromechanical changes in compensatory and anticipatory postural adjustments, which play a major role in minimizing unpredictable and predictable disturbances, respectively, as early as 2 months after ACLR. Methods = Nine young male individuals who underwent ACLR with patellar tendon and nine age-matched healthy controls were exposed to two blocks of ten either unexpected or expected loading perturbations of the knee joint, while semi-reclined on a raised plinth. Amplitude and latency of postural responses in the vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF) muscles were determined by surface electromyography. Results = Latency of compensatory responses was higher in patients with ACLR than in healthy participants for VL (82 ± 15 vs 68 ± 10 ms, P < 0.05) and RF (81 ± 21 vs 63 ± 10 ms, P < 0.05). Amplitude of compensatory responses was 54 % lower in patients with ACLR than in healthy participants for VL (P < 0.05). Onset of anticipatory responses occurred earlier in patients with ACLR than in healthy participants for VL (−83 ± 45 vs −26 ± 21 ms, P < 0.05), RF (−59 ± 48 vs −10 ± 13 ms, P < 0.05) and BF (−72 ± 42 vs −12 ± 14 ms, P < 0.01). Conclusion = Patients with ACLR showed early abnormalities in compensatory and anticipatory postural adjustments, which may reflect the inability to quickly detect sudden changes in muscle length or to completely activate muscles surrounding the knee, and may be addressed by specific training interventions.