Poland syndrome is a condition present from birth in which part or all of a major chest muscle is missing on one side of the body. The hallmark feature is an absent or underdeveloped pectoralis major, the large fan-shaped muscle that connects the upper arm to the breastbone. The condition ranges from barely noticeable to quite visible, and it can involve the hand, ribs, and other soft tissues on the same side of the body.
What the Condition Looks Like
The most consistent feature is a missing section of the pectoralis major, specifically the portion that normally runs from the upper arm to the sternum. This creates an asymmetry in the chest that may be subtle or pronounced depending on how much muscle tissue is absent. In some people, additional muscles on the affected side of the torso, chest wall, shoulder, or side are also missing or underdeveloped.
Rib abnormalities sometimes accompany the muscle differences. Ribs on the affected side can be shortened, and with less fat beneath the skin in that area, the remaining ribs may be more visible than usual. The forearm bones on the affected side can also be slightly shorter, though this is often difficult to detect without direct measurement.
Hand differences on the same side are a well-known part of the condition. These can range from mild webbing between fingers to noticeably shortened fingers. Not everyone with Poland syndrome has hand involvement, but when it appears, it always occurs on the same side as the chest abnormality.
What Causes It
Poland syndrome occurs randomly. It is not inherited, and no specific gene mutation has been identified. Nearly all cases are sporadic, meaning they appear in families with no prior history of the condition.
The most widely accepted explanation is called the subclavian artery supply disruption sequence. During roughly the sixth to seventh week of pregnancy, the embryo’s aortic arch is transforming into the arterial system. If something, likely a brief period of reduced oxygen, interrupts blood flow through the subclavian artery or its branches on one side, the tissues that depend on that blood supply don’t develop fully. Because the subclavian artery feeds the chest wall, shoulder, arm, and hand, a disruption at this stage can affect all of those structures on the same side.
This vascular theory explains why the condition is always one-sided and why the chest and hand are so often affected together: they share the same blood supply during that critical window of development.
Who Gets Poland Syndrome
Estimates place the incidence at roughly 1 in 20,000 to 1 in 30,000 births, though milder cases likely go undiagnosed, so the true number may be higher. It affects males about two to three times more often than females. The right side of the body is involved more frequently than the left, for reasons that aren’t fully understood.
Effects on Strength and Daily Life
Missing the pectoralis major doesn’t prevent people from using their arm, but it does create measurable differences in specific movements. Long-term studies using strength testing devices have found significant deficits in shoulder internal rotation (the twisting motion you’d use to throw a ball) and horizontal adduction and abduction (bringing the arm across the chest or pulling it back). People with associated hand differences also show reduced grip strength and pinch strength.
In everyday life and at work, most people with Poland syndrome report relatively low levels of disability. The limitations become more noticeable during activities that demand high upper-body dexterity: competitive sports, weight training, and playing musical instruments tend to highlight the strength asymmetry more than routine tasks do.
Rare Internal Associations
In uncommon cases, particularly when the condition involves the left side and significant rib defects, the heart may sit slightly to the right side of the chest instead of the left. This is called dextrocardia. An important distinction: when dextrocardia occurs as part of Poland syndrome, the heart itself is structurally normal. It’s simply positioned differently because of the rib and chest wall abnormalities rather than because of a cardiac defect.
Lung herniation, where lung tissue pushes through gaps in missing ribs, is rare and has been reported in about 9% of cases with rib involvement. In severe instances, the missing ribs can cause paradoxical breathing movements, where part of the chest wall moves inward during inhalation instead of outward. When rib defects are significant enough to leave the heart and lungs unprotected, surgical repair using rib grafts may be needed early in life.
How It’s Diagnosed
Many mild cases aren’t recognized until adolescence or adulthood, when the chest asymmetry becomes more apparent with physical development. In more obvious presentations, the condition is identified in infancy. Diagnosis is primarily clinical, based on the visible absence of the chest muscle, sometimes combined with hand differences on the same side. Imaging of the chest and hands can confirm the extent of missing muscle and any rib or bone abnormalities.
Surgical and Reconstructive Options
Treatment is tailored to what’s affected and how much it bothers the individual. Many people with mild Poland syndrome choose no treatment at all.
For those who want to address the chest asymmetry, one well-established approach involves transferring the latissimus dorsi, a large back muscle, to the front of the chest. This muscle is relocated from its normal attachment at the upper arm to recreate the missing chest contour and the anterior axillary fold (the front crease of the armpit, which is absent when the pectoralis is missing). This procedure can be performed through a single small incision hidden in the mid-armpit area. In women, a breast implant can be placed beneath the transferred muscle to restore breast volume and symmetry.
Although breast reconstruction typically waits until physical maturity, recreating the axillary fold at a younger age can make a meaningful difference in a child’s body image and self-confidence by restoring a more symmetrical chest appearance.
Custom Implants Using 3D Modeling
For patients who want to correct the chest contour without a muscle transfer, custom silicone implants designed with three-dimensional computer modeling have become an increasingly refined option. Before 2007, these implants were made from plaster molds of the patient’s chest. Since then, 3D scanning and computer-aided design have allowed surgeons to create precisely fitted implants that match the deficit. One surgical center that has treated 129 patients for Poland syndrome reported that these custom implants produced significant improvements in both appearance and quality of life, with consistent patient satisfaction. The procedure is considered relatively straightforward and reliable compared to more complex reconstructive surgeries.