The pectoralis major muscle, also known as the pec major, is the outermost chest muscle that sits over the ribcage to the side of the sternum. It is a broad muscle that is formed by two parts; the clavicular head that starts at the collar bone and the sternal head that starts from the breastbone (sternum) and the costal cartilage of the first 6 ribs. As the two parts of pectoralis major run towards their insertion, they converge and join to form a strong, flat tendon that attaches and inserts into the upper part of the upper arm bone (humerus).
The function of the pectoralis major muscle varies according to its different parts, and it plays an important role in shoulder movement and strength. The clavicular head has a role in raising the arm (flexion) and the sternal head helps to bring the arm back to the side of the body (extension) against resistance. Together they work to rotate the arm inwards and to bring the arm horizontally across the body (adduction).
Functionality of the pectoralis major is often improved through an increase is muscle size and strength (hypertrophy), which can be achieved by weight and strength training that involves pressing motions against resistance. Common examples include: press ups, bench and dumbbell press, cable punches and cross overs.
Injury to pectoralis major muscle is rare but can occur in healthy and active individuals, with the main site of the injury being the musculotendinous junction. Tears at the muscle belly are less common. The severity of pectoralis major injuries can range from small strains to partial, or even full, ruptures.
Ruptures of pectoralis major are most often seen in weight or power lifting but can also occur in sports such as boxing or wrestling. They are most often the result of a forceful muscle contraction where the musculotendinous junction is unable to tolerate the force produced, hence they are often seen during heavy bench press. The population that is most at risk of pectoralis major ruptures are men in their twenties to forties, with very small numbers of women being affected by this type of injury.
General lifestyle has an important role in tendon health and there are multiple lifestyle factors that could contribute to weakening of the tendon, making them more susceptible to tendon rupture. These factors can include smoking and alcohol abuse, type 2 diabetes, obesity, long term oral steroid use for medical conditions, and previous injury to the muscle.
The symptoms of a pectoralis major injury will vary depending on the extent of the injury, with minor symptoms associated with small tears, while more substantial symptoms are associated with large tears or ruptures. Ultrasound or MRI scans can be used to identify and grade the extent of the injury.
Small tears or muscle strains, where only a small portion of the muscle or tendon fibres are involved, will be characterised by a sudden acute pain at the chest and shoulder and only slight shoulder weakness. This type of injury can also have some bruising and swelling around the pectoralis major muscle and shoulder but should recover in a few days to a couple of weeks.
Higher grade tears or ruptures of the pectoralis are much more significant and easier to diagnose. A common symptom is a feeling of ripping at the shoulder while performing a maximal effort, this can be associated with an audible “pop” or “snap” and sudden weakness. It is normal for the pain to be minimal with a full rupture. This may be due to associated injury to the nerves around the muscle.
Bruising and swelling are common around the outer part of the chest and the front of the shoulder, and in ruptures there will be an obvious deformity as the muscle and tendon retract and pull away from the insertion at the upper arm. This deformity may present as a hollow or gap in the chest muscle and the nipple on the injured side can move towards the midline of the chest. There will be a loss of function at the arm and shoulder most notably significant weakness of the chest and shoulder.
Conservative management and graded rehabilitation are recommended for lower grade or partial ruptures, as well as in older or more sedentary individuals who might not respond favourably to surgical interventions.
High grade tears and complete ruptures need to be diagnosed early as these will often require surgical intervention. Delayed intervention can reduce the likelihood of successful surgery as the tendon and muscle can retract and become more difficult to repair.
Surgery for pectoralis major ruptures has been shown to be advantageous in regaining shoulder muscle strength when compared to conservatively managed ruptures. Following surgery there can be a lengthy period of rehabilitation that will focus on improving mobility and flexibility at the shoulder and assisting to regain strength so that a full return to sport and function can be facilitated.