Thoughts on ACL injuries

[msf22b]

Apologies if this has been brought up earlier but my experience in the dance world had me thinking that I had not heard a lot about ACL injuries in dancers, especially females.

My anecdotal memories were confirmed by the following study (and others).
Is there some knowledge that can be gained from this?
http://www.ncbi.nlm.nih.gov/pubmed/18753681

Incidence of anterior cruciate ligament injuries among elite ballet and modern dancers: a 5-year prospective study.
Liederbach M1, Dilgen FE, Rose DJ.
Author information

Abstract
BACKGROUND:
Ballet and modern dance are jump-intensive activities, but little is known about the incidence of anterior cruciate ligament (ACL) injuries among dancers.

HYPOTHESIS:
Rigorous jump and balance training has been shown in some prospective studies to significantly reduce ACL injury rates among athletes. Dancers advance to the professional level only after having achieved virtuosic jump and balance technique. Therefore, dancers on the elite level may be at relatively low risk for ACL injury.

STUDY DESIGN:
Descriptive epidemiology study.

METHODS:
Dance exposure, injuries, and injury conditions were systematically recorded at 4 dance organizations over 5 years. Select neuromuscular and psychometric variables were compared between and within ACL-injured and noninjured dancers.

RESULTS:
Of 298 dancers, 12 experienced an ACL injury over the 5-year period. The incidence of ACL injury was 0.009 per 1000 exposures. Landing from a jump onto 1 leg was the mechanism of injury in 92% of cases. Incidence was not statistically different between gender or dance groups, although women modern dancers had a 3 to 5 times greater relative risk than women ballet dancers and men dancers. No difference between ACL-injured and noninjured dancers emerged with regard to race, oral contraceptive use, or select musculoskeletal measures.

CONCLUSION:
Dancers suffer considerably fewer ACL injuries than athletes participating in team ball sports. The training dancers undertake to perfect lower extremity alignment, jump, and balance skills may serve to protect them against ACL injury. Anterior cruciate ligament injuries happened most often late in the day and season, suggesting an effect of fatigue.

 

[VAMike23]

Interesting - I would be further interested to know if the study breaks down the mechanics of the typical "exposure" in any of the dance forms.

In sports, the athlete is often attempting a big-time lateral deceleration while wearing cleats (turf) or rubber-soled shoes (gym floor) with serious grip. My impression from watching some dance (not a lot) is that they are not stopping as suddenly and with so much lateral deceleration or overall violence, at least not as often--particularly since their shoes are going to slide a little bit on the dance floor.

Also, athletes will often mix in a change of direction to go along with the rapid deceleration, so you have some torquing going on as well. Many of the jumps in the dance world seem to be more about height than about jump-stopping on a dead run, although I'm sure they do plenty of more challenging jumps as well where twisting is involved.

I'm not saying the study didn't cover these things - I don't know. But it would be important to know more.

 

[msf22b]

I'm not saying the study didn't cover these things - I don't know. But it would be important to know more.

I haven't gone into the issue in detail, wanted to bring this to everyone's attention early.
The issue has been looked into, other published studies are available. just google.
One might guess that the more rigorous ballet training (compared to Modern) is the cause of a smaller incidence.
Wouldn't it be something if routine bar exercises are the difference.

 

[UcMiami]

The thing with dance is generally all movements are choreographed and rehearsed so their are no 'surprise' movements involved and no contact not also choreographed. Most of the rehearsal starts at slow speed and only once the moves are set are they done at real speed. I would say that greatly reduces the comparable values in the study. The whole idea of dance is to be in complete control of your movements at all times, in contact sport that is impossible and in 'non-contact' sport you are still reacting instantaneously to a changing environment and pushing the physical envelope.
In ballet the choreography tends to be the stringing together of individual movements and positions that have been set for centuries - there are of course new variations on the old and new combinations that may add stresses, but 95+% of the individual positions/movements are historically 'safe'.
I can understand that modern dance would exhibit a higher level of potential risk since the idea of 'modern' is to throw away the old strictures of ballet and free the movements of the body - modern dance choreographers are often stretching the physical limits of balance, stretch, and movement and often experiment with physically impossible movements that have to be altered to become possible. (I have been in early rehearsals where dancers have said - nope, can't do that!) But again even at those limits the process is a slow experimentation and a setting of the movements before they are taken to 'live' speed.
The one area of dance that is different and potentially more hazardous than most sports movements are lifts which bring into play greater heights than a body can reach on its own leading to greater potential impacts on landing. It also requires coordination between two (or more) dancers which adds a level of 'surprise' to the movement should that coordination be off. I suspect a study of injuries in general in dance would show that on a percentage basis lifts had a much higher risk involved (though a lower actual number since they are a relatively small percentage of total dance movements.)
The other issue with sport vs. dance is that most sports involve high speed movement of the whole body - there is very little time in dance where the dancers are moving as fast as they physically can from point a to point b. Speed adds greater momentum and greater stresses to all joints. And as mentioned above the act of stopping or being stopped becomes much more stressful to the body.
The footwear issue is a good point too, though dancers often use rosin on their shoes or bare feet to improve the friction and most performance dance floors are also a rubberized surface that has a higher friction coefficient than wood.
Finally most dance floors are 'sprung' (in effect 'floating') to specifically soften impacts and most performance floors are a special material so even if the stage is not sprung the surface is a softer impact surface than straight wood. Most basketball courts are wood laid on concrete.

 

[UcMiami]

I haven't gone into the issue in detail, wanted to bring this to everyone's attention early.
The issue has been looked into, other published studies are available. just google.
One might guess that the more rigorous ballet training (compared to Modern) is the cause of a smaller incidence.
Wouldn't it be something if routine bar exercises are the difference.

Generally all dancers do bar exercises as part of their daily routines - as i posted in my long reply above, I think the difference is in the 'experimental' nature of modern vs. ballet - always trying to find new ways for the body to move - new positions and new movements.