The primary aim of this study was to evaluate the effects of ACL injury on neuromuscular function in elite alpine ski racers, and to monitor skiersthroughout the return to sport transition. In Chapter 2 a narrative review of the literature was performed on ACL injury, ACL re-injury, and return to sport after ACL injury in ski racing.

In Chapter 3, a new test of inter-limb functional asymmetry was used to evaluate alpine ski racers with/without ACL reconstruction (ACLR). Despite a full return to competition, ACLR ski racers demonstrated elevated inter-limb functional asymmetries that were correlated with lower limb muscle mass asymmetry.

In Chapter 4, hamstring/quadriceps strength ratios were measured in ski racers with/without ACLR. ACLR ski racers displayed significant hamstring/quadriceps strength deficits in the ACLR limb compared to the contralateral limb and the limb average of non-injured skiers.

In Chapter 5, the functional lower-limb asymmetry test introduced in Chapter 3 was used to evaluate the acute effects of a fatiguing jump protocol on asymmetry and hamstring/quadriceps muscle activity in ski racers with/without ACLR. The ACLR skiers displayed systematic inter-limb functional asymmetries. ACLR skiers displayed reduced quadriceps muscle activity at takeoffin the surgical limb. Both the ACLR group and non-injured controls became quadriceps dominant with fatigue. Quadriceps muscle activity increased while hamstring muscle activity decreased. Notably, this was found in the pre-landing phase. In Chapter 6, primary ACLR operative reports from 28 skiers were analyzed to evaluate the associated pathology including multi-ligament injury, meniscal tears and chondral lesions. Operative reports from future surgeries were analyzed to evaluate the injury progression. At the time of primary ACLR, there was a higher proportion of chondral lesions in the lateral compartment compared to the medial compartment, and complex meniscal tears compared to one-dimensional tears. At the time point of future surgery, a significant proportion of skiers showed a worsening of chondral lesions, including half of the skiers presenting with Grade 3 or Grade 4 lesions. Functional asymmetry was also evaluated at various time points following primary ACLR. Nearly two years were required for functional asymmetry indices to reach values comparable to those of non-injured ski racers.