Dynamic changes of intervertebral discs and multifidus muscles before and after spontaneous resorption of lumbar disc herniation: a longitudinal paired MRI study

The lower back is a complex machine built from stacked bones, cushioned by soft pads called intervertebral discs, and held steady by a network of muscles. When one of these discs slips out of place, pressing against a nerve, it causes the sharp, radiating pain known as a herniated disc. For decades, doctors have watched these slipped discs shrink or disappear on their own without surgery, a process called spontaneous resorption. This natural healing is driven by the body's immune system, which sends cells to clean up the escaped disc material. However, a lingering question has puzzled clinicians: when the painful lump vanishes, does the underlying damage to the spine itself get repaired? Does the disc return to a healthy state, and do the surrounding muscles, which often weaken from pain and inactivity, recover their strength? Understanding the difference between the disappearance of the pain-causing lump and the actual health of the spine is crucial for predicting whether a patient will remain pain-free or suffer from chronic back issues later in life.

A team of researchers at the Gansu Provincial Hospital of Traditional Chinese Medicine set out to answer this by tracking the same patients over time. They studied 58 individuals who had successfully avoided surgery because their herniated discs naturally reduced in size by at least 30 percent after receiving standard conservative care. The team took detailed magnetic resonance images of these patients' lower backs at the start of their treatment and again six to twelve months later. By comparing these paired images, they could see exactly what changed inside the body as the herniation resolved. They focused on two specific things: the health of the disc itself, measured by how much water it held, and the condition of the multifidus muscles, which run along the spine and are vital for stability. These muscles often become infiltrated with fat when they are not used properly due to pain, a sign of secondary injury.

The study revealed a surprising split in how the body heals. When the herniated disc material shrank, the disc itself did not get better. In fact, the researchers found that the natural degeneration of the disc continued to progress, even as the painful lump disappeared. The disc remained dehydrated and worn, showing no sign of reversing its primary damage. This suggests that the body's cleanup crew can remove the loose, painful tissue floating in the spinal canal, but it cannot fix the aging, dry, and damaged disc that remains in place. The researchers observed that this lack of improvement in the disc's health happened regardless of whether the herniation shrank a little or a lot.

In contrast, the muscles surrounding the spine showed a very different story. As the herniated disc shrank and the pressure on the nerves eased, the fatty infiltration in the multifidus muscles decreased significantly. The muscles appeared to recover, shedding the excess fat that had accumulated during the period of pain and inactivity. The more the herniation shrank, the more the muscles improved. Patients whose herniations reduced by more than half saw a much greater recovery in their muscle health compared to those with only a modest reduction. This indicates that the muscle damage was a reversible reaction to the nerve compression, and once the compression was gone, the muscles could begin to heal.

These findings suggest that looking only at the size of the herniated lump is not enough to judge a patient's long-term future. A shrinking herniation is a good sign for immediate pain relief, but it does not mean the spine has been restored to a healthy state. The disc remains degenerated, and the risk of future back problems persists. However, the recovery of the muscles is a positive indicator that the body is responding well to the relief of pressure. The researchers propose that doctors should use a combination of these two measurements—the state of the disc and the condition of the muscles—to get a complete picture of a patient's prognosis. This approach allows for a more accurate prediction of long-term function and helps in designing better, personalized rehabilitation plans for those recovering from back pain without surgery.