I've noticed that a lot of magazines state that lat pulls behind the neck work the shoulders as opposed to what the training books and sources on the Internet say, which is that they work the back. Which is more accurate, or does that technique work both?
To perform a pull down behind the neck without any shoulder girdle and/or spinal compensation, an individual must posses the ability to achieve around 100-120 degrees of ACTIVE external shoulder rotation while abducted. When this ROM is lacking (as will be in the VAST majority of people), the force from the machine pulls the shoulder joint toward external rotation, which places large amounts of stress on the anterior shoulder capsule. You'll see this lack of ROM displayed in the individuals performing the exercise behind the neck as compensatory cervical and/or lumbar flexion.
One must take into account the functional anatomy of the situation. The lat attaches anteriorly on the superior portion of the humorous and then winds back, fans out and attaches into the thoraco lumbar fascia (low back). Hence, the lat does not run directly from top to bottom... it runs from top/front to bottom/back, at an angle. An attempt to pull straight down as in a behind the neck pull down to train the lats simply does not follow the lats fiber alignment, thereby not following the lats angle of pull! This would make the front of the neck pull down the more appropriate choice based on its anterior to posterior angle of motion. REMEMBER, A MUSCLE'S ABILITY TO PULL IS DICTATED BY ITS FIBER ALIGNMENT (I.E. ITS ORIGIN AND INSERTION), NOT BY THE MACHINE CHOSEN!
It should also be noted that in a standard lat pull down, the rear shoulder/upper back musculature is also heavily involved (posterior cuff, rear deltoids, mid/lower traps, rhomboids, teres major/minor).
All anatomy and mechanics aside, if the cable should happen to break while performing a BEHIND the neck pull down, the cervical damage could be severe. It's simply not worth the risk.