Your OS and probably your physios if you asked them as well will say the same - don't do full squats, they are not necessary and will damage your knee.

Full squats such as you describe are a tremendous strain on a healthy uninjured knee. Your knee is no longer uninjured, even if it has been repaired. These types of squats are just not good for your knee which it is why it feels "wrong".  The way in which the joint works has been altered for ever as a reconstruction can never exactly copy the original uninjured joint movement.

By all means have full flex and use the standing heel to backside stretch for your quads as part of your warm-up and stretching routine. But doing a loaded full squat will result in damage to the meniscus and articular cartilage surfaces in your knee as the joint, even with the best of surgical placement, no longer works as it originally did.

I have been repeatedly told over the years that the squats that I have to do as part of my training routine should not exceed 90° weight loaded. I use loaded held squats as part of my strength building exercise for skiing but I only go to a maximum of 90°. In skiing we are even more likely to unintentionally do a loaded squat to greater than 90° which is why there are so many busted ACLs in skiing and snow sports in general.

You have full flex, I can't see how a fully weighted squat is part of the every day movement in a football match. Work on plyiometrics especially explosive changes of direction for the strength work and make sure your hamstring/quads strength is balanced.

Sue 

Your OS and probably your physios if you asked them as well will say the same - don't do full squats, they are not necessary and will damage your knee.

Full squats such as you describe are a tremendous strain on a healthy uninjured knee. Your knee is no longer uninjured, even if it has been repaired. These types of squats are just not good for your knee which it is why it feels "wrong".  The way in which the joint works has been altered for ever as a reconstruction can never exactly copy the original uninjured joint movement.

By all means have full flex and use the standing heel to backside stretch for your quads as part of your warm-up and stretching routine. But doing a loaded full squat will result in damage to the meniscus and articular cartilage surfaces in your knee as the joint, even with the best of surgical placement, no longer works as it originally did.

I have been repeatedly told over the years that the squats that I have to do as part of my training routine should not exceed 90° weight loaded. I use loaded held squats as part of my strength building exercise for skiing but I only go to a maximum of 90°. In skiing we are even more likely to unintentionally do a loaded squat to greater than 90° which is why there are so many busted ACLs in skiing and snow sports in general.

You have full flex, I can't see how a fully weighted squat is part of the every day movement in a football match. Work on plyiometrics especially explosive changes of direction for the strength work and make sure your hamstring/quads strength is balanced.

Sue 

Oh boy, I get so tired of hearing these silly myths about full squats.  There is absolutely no high quality evidence showing that full squats "should not exceed 90 degrees" and this is just a myth that is perpetuated by people who don't know how to execute a proper squat.  Aside from the first few months following surgery, my OS and PT put no such restrictions on squatting for me and said to go right ahead with deep squatting after the 5 month mark. 

Deep squats are something we do from the time we can walk (watch what toddlers do all the time), and are critical to fully activating and developing the glutes, hamstrings and hip flexors, which are especially important for athletes.  There's a reason you see sprinters, football players, soccer players, etc. doing heavy weight training with full depth squats (hip below patella - ass to ground isn't necessary); it's because they build strength, power and explosiveness, and glutes & hammies are a key part of that.  Properly executed deep squats are in fact very good for your knees and overall knee stability.  There are data to suggest that deep squatting is actually very beneficial to knee stability:  (http://www.nsca-lift.org/HotTopic/download/Squat%20Depth.pdf) {link is Work and Family Safe}

"Subsequent research, however, has refuted Klein's findings, showing no correlation between deep squatting and injury risk (Meyers, 1971; Steiner et al., 1986; Panariello et al., 1994). In fact, there is some evidence that those who perform deep squats have increased stability of the knee joint. In a study using a knee ligament arthrometer to test nine measures knee stability, Chandler, et al. (1989) found that male powerlifters, many of them elite class, demonstrated significantly tighter joint capsules on anterior drawer compared to controls. Moreover, both the powerlifters as well as a group of competitive weight lifters were significantly tighter on the quadriceps active drawer at 90 degrees of knee flexion than control subjects.

Contrary to Klein's hypothesis, ACL and PCL forces have been shown to diminish at high degrees of knee flexion. Peak ACL forces occur between 15 to 30 degrees of flexion, decreasing significantly at 60 degrees and leveling off thereafter at higher flexion angles (Sakane, et al., 1997; Li, et al., 1999; Kanamori, et al., 2000). PCL forces rise consistently with every flexion angle beyond 30 degrees of knee flexion, peaking at approximately 90 degrees, and declining significantly thereafter (Li, Zayonz, Most, et al., 2004). Beyond 120 degrees, PCL forces are minimal (Markolf, et al., 1996)."

As you can see, full depth squats actually put very little load on the ACL, though people with PCL issues or recons should obviously be more careful about deep squats.  As for the issue with menisci and articular surfaces, while the loads are potentially higher, this is addressed as well in the above article:

"The greatest risk for injury during deep squatting would theoretically be to the menisci and articular cartilage (Escamilla, 2001; Li, Zayontz, Most, et al., 2004). Tibiofemoral compressive forces have been shown to peak at 130 degrees of knee flexion (Nisell and Ekholm, 1986) where the menisci and articular cartilage bear significant amounts of stress. Deep squats also may increase susceptibility to patellofemoral degeneration given the high amount of patellofemoral stress that arises from contact of underside of the patella with articulating aspect of femur during high flexion (Escamilla, et al., 2001). However, there is little evidence to show a cause-effect relationship implicating an increased squat depth with injury to these structures in healthy subjects."

Now, with all that said, you must make sure to execute the full-depth squat properly, which means you need to:

a) Turn your toes about 30 degrees outward to align with your knee caps,
b) make sure that your knees don't slide forward much past your toes during the squat, and
a) make sure that your butt comes back and down during the squat with your weight concentrated in your heels.

Here is a great video to show you how to do a proper full-depth front squat: http://www.youtube.com/watch?v=dehR3d6NuQE

Lastly, while plyometrics are great, most people cannot properly incorporate plyometrics into a training program without having a good strength base first.  Plyos place a considerably higher amount of stress on joints, bones, ligaments, etc. so you can't just leap into that without a good solid base of strength.  The recommendations I've seen (http://www.nsca-lift.org/perform/articles/060502.pdf) are that someone considering plyos should be able to squat 1-2X their own bodyweight before starting plyos.  This may not be necessary for someone who is well coordinated and is doing low intensity plyos, but in general is a good guideline.

Please stop perpetuating the myth that full-depth squats are bad.  It's simply not true.  The reason people wrongly advise that full squats "will damage your knee" is because they are watching people do them incorrectly.  Doing full squats incorrectly may damage your knees (and other parts of your body), but doing them correctly is quite good for them.

@gizzardio - that seems odd to me that the joint would slip out of place when sitting on your heels.  Have your OS and PT done a Lachman or Pivot test on your knee to see if the ACL is still intact?

sherwooa and your qualifications are?

I take notice of my trained therapists, sports physicians and fellow coaches before any weirdo on the internet! As an experienced physical education teacher and high level sports coach, I can safely say I do know what I am doing. The reconstructed knee is never the same as an uninjured one and has to be treated differently. Full bum to heel squats, particularly weighted ones, put undue stress on a joint that has already lost elasticity and where the bio-mechanics of the movements will never be the same as pre-injury.

<Sigh>  Sad, but typical Internet forum behavior.  Can't cite any actual evidence for your claims, so you resort to ad hominem attacks.  I'm sure that you think that gym teachers know everything (LOL), but just because you teach gym and coach a few skiers doesn't make you the be-all and end-all when it comes to knowledge about training or, more specifically, training for all athletes.  And just because a few therapist and coach friends of yours follow the same "conventional wisdom" doesn't mean it's right.  Doctors follow certain practices for years before evidence demonstrates that what they are doing is wrong.  My wife is a physician at one of the world's leading research institutions and constantly notes incorrect treatments being done by community physicians in outlying hospitals based on past beliefs and "conventional wisdom".  The bottom line is that evidence is king, so unless you can cite some high quality clinical evidence demonstrating the full squats are harmful to reconstructed knees, then your statements are pure conjecture, and the people you associate with are just perpetuating myths that have been around since the 60's. 

Secondly, I never said one has to necessarily do full "bum to heel" squats.  I said "full depth squats" which means at least hip below patella.  90 degree squats do not activate the glute fully, which is ineffective for anything but quadricep training.  You may be a gym teacher, but clearly you lack depth in your knowledge about what muscles are necessary for athletics, and for many life activities in general.

Lastly, not that it matters, but if you want to talk about qualifications, fine.  I played college lacrosse at a Division 1 University, where I worked with top strength and conditioning coaches.  I continue to play in a high level men's club league along with many amateur and professional players, coaches, and strength and conditioning professionals.  I also play with at least two sports orthopods, one of whom has recovered from his own ACL recon.  I have done my fair share of coaching in lacrosse myself, and I am a Level 1 certified Crossfit trainer.  Finally, I am an avid reader on the subject of strength and conditioning and, since I have access to Pubmed, I also read many of the journal articles related to training and injuries.  I know that doesn't make me a gym teacher, but...

LOL.  Exactly the response I expected.  No evidence, no data.  Just avoidance. 

Folks, do your own research on the topic and you'll find there's nothing to support Kaputt's claims.