The Rotator Cuff: What It Is, and How It Works
November 30, 2016

Many people first become acquainted with the rotator cuff due to an injury, and indeed it’s one of the more common physical complaints reported by athletes and non-athletes alike. To better understand the root causes of these issues, it’s necessary to learn a little about the rotator cuff itself.

The first thing to note is that the rotator cuff is not in fact a single entity, but rather four muscles operating in conjunction with one another to ensure that the shoulder joint remains in place in its socket. It works alongside the biceps – specifically the long head – which, while not part of the rotator cuff, is nonetheless essential to its function. The tendons of the rotator cuff all attach in the front of the shoulder to the humerus.

There are four muscles in the rotator cuff. In no specific order, they are:

  • Infraspinatus. Located fully on the rear side of the shoulder, the infraspinatus is typically one of the weaker muscles in the rotator cuff. Its primary function is to support the outward – or “external” – rotation of the rotator cuff.
  • Teres Minor. The teres minor works in tandem with the infraspinatus to rotate the humerus externally, and to prevent the head of the humerus from sliding upwards when the arm is abducted.
  • Supraspinatus. As the name implies, the supraspinatus sits directly atop the scapula, known as the “shoulder blade” in common parlance. A relatively small muscle, it is separated from the infraspinatus by the spine of the scapula. The supraspinatus is notorious for being not only the most commonly injured of the four muscles of the rotator cuff, but also the muscle most liable to succumb to tendinitis.
  • Subscapularis. The subscapularis is located immediately opposite the infraspinatus, being found on the very front of the scapula. Accordingly, it is responsible for inward rotations of the humerus.

Long Head of the Biceps

While this is not, as noted previously, one of the constituent muscles of the rotator cuff, it does attach to a crucial piece of cartilage within the shoulder known as the “labrum”. It is due to this attachment with the long head of the biceps – and its function in moving the shoulder forwards – that it is susceptible to tear along with the labrum.

The Collective Function of the Muscles of the Rotator Cuff

The shoulder is a joint particularly susceptible to injury due to its shallow socket, which results in an unusual degree of mobility. This mobility comes at a price, however. While the shallowness of the joint offers an increased range of motion, it also means that the head of the humerus can easily move from the center of the socket. The likelihood of a dislocation is further increased when the shoulder is rotated in such a way that the arm is at or above shoulder height.

Assessment and Treatment of Shoulder Injuries

It is important to note first that not all shoulder injuries directly involve the rotator cuff, and that it is thus important to seek professional advice to determine the exact nature and cause of any injuries or pain in the shoulder area. Similarly, increasing strength in the joint is not a solution to every ailment, with everything from anti-inflammatory medication to surgical procedures being recommended depending on the type or severity of the injury. A consultation with an expert can help ensure that you take the necessary steps – surgical or otherwise – to both treat existing injuries, and to decrease the likelihood of future tears, dislocations or other injuries to the rotator cuff.