SINGAPORE – In early 2025, Tan Boon Foo noticed a mild ache in his right shoulder. The 72-year-old retired tax consultant thought it was muscle pain that would go away after a couple of weeks.

However, the ache worsened. After two months, when he reached for a cup of coffee one day, he felt a jolt of stabbing pain.

“The pain was mild when I did things without stretching, but when I tried to reach out, I felt this stabbing pain and had to pull myself back,” he says.

Tan had frozen shoulder, or adhesive capsulitis, a condition that leads to prolonged stiffness and a reduced range of motion, which affects daily life.

He was unable to wash his hair or reach behind his back. Any activity that required stretching, even lifting his hand up, was painful.

He also could not put any weight on that shoulder. If he unconsciously turned onto his right side while sleeping, the pain would wake him up.

Physiotherapy is recommended for a frozen shoulder, but some patients, like Tan, are in too much discomfort to do the exercises needed to improve their range of motion.

A steroid injection gave him pain relief for up to a year. Being pain-free has motivated him to keep up mobility exercises that help him reach behind his back.

The only joint that freezes

Doctors know what happens inside a frozen shoulder, and who might be at risk of developing it. However, sometimes the shoulder just freezes without any obvious reason.

A frozen shoulder starts with inflammation of the shoulder joint capsule, or lining of the shoulder joint.

Consultant Luke Peter from Ng Teng Fong General Hospital’s division of shoulder and elbow surgery says that patients first feel pain because of this inflammation in the capsule.

As the inflammation wanes, cells begin to deposit more collagen in the capsule. The capsule thickens and tightens.