Women's Football Hub

Author Carolyn Kent, Lecturer in Physiotherapy, University of Cumbria

Editor Dr Anne Leung, PT, DPT. Arcadia University, Department of Physical Therapy.

The ACL is one of the major ligaments in the knee and it connects the shin bone to the thigh bone (1). If you’re involved in football, you’ll probably know that we have a real problem with anterior cruciate ligament (ACL) tears in football. The data has shown since the 1990’s that females are 3-6 times more likely to tear their ACL than boys (2). There’s even data showing they may be up to 8 times more likely to sustain this injury (3)(4). In the recent 2024 UEFA elite club injury study ACL injuries were found to be the injury with the biggest time loss for female players (5).

ACL Reconstruction (ACL-R)

ACL-R is a common surgical procedure for female football players and the three graft options that are commonly used are bone patellar tendon bone (BPTB), hamstring, and bone quadriceps tendon grafts (6). BPTB has historically been considered the gold standard for ACL-R (7). The addition of a lateral extra-articular tenodesis (LET) to the ACL reconstruction is showing early potential to decrease re-tear rates by preventing excessive rotational movements (8). However, it should be noted that surgery with a graft from your own body is not the only option, you can use a graft from another person, some people choose synthetic grafts and some people do not require surgery at all (9).

Rehabilitation of the quadriceps after ACL-R

The failure of the quadriceps to perform adequately is common after ACL-R and has been shown to happen in both the operated leg and the non-operated leg. The performance deficit is worse in females and also takes longer to recover in those who have has a BPTB graft (10)(11)(12) Some of this quadriceps deficit appears to be related to the nervous system and is called arthrogenic muscle inhibition (AMI) (13). The neural system also shows sex related differences in the corticospinal tract (the pathway for the nerve signal from the brain to the quadriceps), post ACL-R with females, resulting in females showing reduced quadriceps performance compared to male counterparts (14). More detail on graft type considerations and post operative rehabilitation for clinicians can be found here.

The LSI and OKC’s

Comparing quadriceps function between the operated leg and the non-operated leg is done via the limb symmetry index (LSI). It is calculated by dividing the score of the operated leg by the non operated leg then multiplying this by 100 to get a percentage (15).

Operated limb/non operated limb x 100 = LSI %

So, you could use an athletes score from a quads extension machine to compare their operated vs non-operated limb. An athlete should aim to have a minimal LSI of 90%. However, this alone is not enough to return an athlete to play, and it should be noted that LSI’s have been shown to overestimate a patient’s knee function (16). This is another reason why the athlete’s return to the field should be based on a multitude of tests and not time.

On the subject of quads extension machines let’s bust the very outdated theory that open kinetic chain (OKC) quads exercises (the kind where you sit and then straighten your knee, either with no weight at all or you put a bar or a weight across/around the bottom of your shin bone) are unsafe. There are papers that clearly state that open kinetic chain exercises are safe in early rehabilitation and low loads to the point of failure can be utilised (17). These exercises are especially safe at the angle of 90-40 degrees (18). As the athlete progresses more load should be added and at least 60-70% of their 1RM advised (17).

So, it’s all about quads?

No, it’s not. They are an essential part of returning an athlete to the field after ACL-R. As some studies have shown that female athletes have a significantly lower rate of return to sport than male counterparts 65 v 75% (19). Strengthening the quadriceps to ensure we are building a foundation upon which activities like running, cutting and jumping can be built upon is essential. Finally, getting the quads to above 90% on the LSI significantly reduces knee re-injury rate (20).

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References

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