Hi Toran, it’s an interesting and important question. Measurements of muscle size by MRI are costly and, as your paper suggests, might not necessarily provide the best indication of those likely to cope after ACL injury. There is a need therefore to identify more appropriate markers of the potential to cope with ADL and return to sport. With regards to the latter, we recently published some data in a young, healthy cohort of males concerning the relative ability of hamstrings and quadriceps to rapidly produce force during “explosive” isometric contractions (https://www.researchgate.net/publication/257814567_Longer_Electromechanical_Delay_Impairs_Hamstrings_Explosive_Force_versus_Quadriceps). We suggested that an explosive H/Q force ratio might provide a better indicator of the capacity for dynamic knee joint stabilisation than the more common ratio of maximum voluntary force or torque, because non-contact ACL injuries are thought to occur within 50 ms of planting the foot (Krosshaug et al. 2007), which is way before maximum force or torque is typically achieved (>300 ms). Interestingly, explosive H/Q force ratio was very low at 25 and 50 ms from activation onset (0-17%) and was much lower than the ratio of H/Q maximum voluntary force (56%). Furthermore, the inter-individual variability (coefficient of variation) in the explosive H/Q force ratio (50 ms, 98%) was much greater compared with the ratio of H/Q maximum voluntary force (11%). This wide variability in explosive H/Q force could indicate large differences between individuals in the capacity for rapid muscular stabilisation.

I would be keen to hear your thoughts on whether something like this, a relatively simple and inexpensive to set-up, test of isometric force production could be useful in evaluating function in the context of return to sport after injury or prior identification of those a risk of injury.

Article Longer Electromechanical Delay Impairs Hamstrings Explosive ...

I would hypothesize that tibial plateau geometry is an important factor. Javad Hashemi's work on this as a risk factor for injury is compelling.

Hamstring and quadriceps force, ratio, and rate of development are interesting, but to date have only been found to play a role in female athletes for prevention of ACL injury. At least that I'm aware of in the literature.

Currently, I think the best predictors are still hop tests, effusion, and global rating score for a quick in clinic assessment. However, return to sport must be done on a person by person basis depending on the individuals goals and likelihood for re-injury (graft type, age, body mass, are good predictors).

Tibial plateau geometry is interesting, but I have never had a patient that was interested in changing their bone shape to either avoid initial or secondary ACL injury. Therefore, this as a risk factor for possible interventions does not appear to be fruitful at this point.

Thoughts?

When this question first appeared back in the 1990's the people were called ACL dependent and ACL-Independent. At that time the literature advocated pre-surgical therapeutic intervention to restore normal gait, muscle function, and limit atrophy. Persons were classified as ACL dependent if they had multiple "giving way" episodes during the pre-surgical period that usually occurred with less and less perturbation. ACL Independent persons had few if any giving way episodes during the pre-surgical period and some would refuse surgery because of the good results with the pre-surgical exercise program.

In the early 2000's we discovered that the body had two different motor programs for extending the lower extremity based on limb dominance. When classifying limb dominance by which leg the person would kick a ball with, we found that the kicking leg had a quad dominant motor program, while the non-kicking leg had a hip/ankle dominant motor program. Therefore the leg that was injured had an effect on the outcome of the rehabilitation process, we found that if the dominant leg was injured it would adopt an non-dominant motor program (increased reliance on the hip and ankle musculature) while if the non-dominant leg was injured it was basically business as usual. We were the first to demonstrate the substitution of hip torques to compensate for the involved quads loss of torque producing capability. Since the publication a number of papers have demonstrated the persistent lack of quad strength in persons undergoing ACL reconstruction.

Attached is the article, you can find a few other abstracts along the same line as well as clinical presentations about the subject at my Research gate page.

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Article SIGNIFICANT SIDE-TO-SIDE DIFFERENCES IN JOINT MOMENTS DURING SQUATTING

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Conference Paper An evaluation of the return to activity criteria of a single...