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3 Extrinsic Risk Factors for ACL Injury

As an athlete, playing on the perfect field like the professionals is a dream comes true. Throughout my career, I played on turf fields, grass fields and fields that were mostly potholes. Unfortunately, I have seen players end their careers playing on these bad fields. I was one of players that loved to play on grass. Playing on turf would get extremely hot and would hurt to fall on.

Injuries to the anterior cruciate ligament (ACL) of the knee are common in athletes. Injury rates as high as 2.8 and 3.2 injuries per 10,000 athletes. The goal of the research is to help identify those who are at increased risk of ACL injury so that an intervention can be targeted at them. 

3 Extrinsic Risk Factors for ACL Injury:

1. Weather

Weather conditions have been related to an increased risk of ACL injury. Wet and rainy weather may reduce the friction between the athlete’s shoe and playing surface. Studies have evaluated the effects of weather on ACL injury risk, as well as knee injury risk. There was an increased risk of ACL injury in hot weather in open stadiums versus cooler weather. This may be due to heat increasing the ligament extensibility.

2. Type and condition of playing surface

The type of playing surface can also play a huge part in ACL injuries. Studies suggest heat evaporation rates in the month before the match, as well as low rainfall in the year before, the match was associated with increased ACL tear rates. Recent studies have assessed ground variables such as grass type to the rate of ACL tears. ACL injury risk increased with higher level of play, northern venues, more evaporation, early season games, and stadiums using Bermuda grass turf. Researchers have hypothesized that less “trapping” of the cleat occurred less on rye grass than Bermuda..

3. Footwear

Everyone thinks shoes play a role in ACL injury rate and guess what, you’re right! These factors influence the shoe-surface interaction, which could be the cause of injury. Increased friction between the shoe e and the playing surface may be produced by many sources: the type and number of cleats, the design of the shoe itself, the type of grass, artificial grass or floor surface, and the weather (Balazs 2014). Cleat design creates the resistance between the foot and the ground, and the type of cleats affects ACL injury risk. Studies have shown that certain types of cleats produced significantly higher levels of resistance on the same surface. The cleat with the highest resistance (edge cleats) had longer irregular cleats placed at the periphery of the sole with a number of smaller pointed cleats positioned centrally. This cleat design was associated with a significantly higher ACL injury rate on various playing surfaces in comparison with the other designs, including systems with smaller and flatter cleats, fewer cleats, or rotating cleats.

COR works with many athletes recovery from ACL injury and those seeking ACL prevention programs. When rehabilitating from injury, progression and individualization are mandatory. If that means starting with mobility in the beginning, then that’s where we will begin. We want to have a safe recovery back into our sport so that there are no setbacks.


1. Balazs GC, Pavey GJ, Brelin AM, Pickett A, Keblish DJ, Rue JP. Risk of Anterior Cruciate Ligament Injury in Athletes on Synthetic Playing Surfaces: A Systematic Review. Am J Sports Med. 2014 Aug 27. 

Written by Chris Barber, CPT