Before Advanced Therapies, Hip Pain Common in SMA, Study Finds

New research is shedding light on the problem of hip pain among non-ambulatory people with spinal muscular atrophy (SMA) types I and II.

The study—which was performed prior to the widespread use of disease-modifying therapies (DMTs)—found hip pain is especially prevalent in type II SMA, though in most cases the pain did not lead to the decision to undergo invasive intervention. The study was published in the journal JBJS Open Access.

SMA, a genetic disease marked by severe motor dysfunction, is categorized based on the age of diagnosis and the highest level of motor function achieved. Patients with type I or type II SMA are never able to stand or walk, though patients with type II SMA can sit upright without aid. The disease is caused by a mutation of the survival motor neuron 1 (SMN1) gene. People with SMA have variable numbers of the SMN2 gene, which produces low levels of SMN protein.

Investigators including corresponding author Matthew A. Halanski, MD, of the University of Wisconsin-Madison and the Children’s Hospital and Medical Center of Omaha, noted that the development of DMTs in recent years has led to new hope for patients, because the therapies appear to be able to improve motor function and extend life expectancy, though the authors added that the effect of the therapies on orthopedic manifestations of the disease are not yet well understood.

Halanski and colleagues noted that scoliosis and hip subluxation or dislocation have historically been common problems for people with SMA. Spinal deformities can be meaningfully addressed with spinal fusion or growing rods, but the investigators said the question of how to treat hip pain has been more controversial.

In the new study, which was performed at American Family Children’s Hospital, in Madison, the investigators wanted to understand the prevalence of hip pain in people with type I and II SMA. They said that in the previous 2 decades, their SMA strategy had been to focus on aggressive medical management of the disease and the spinal deformities associated with it, while only symptomatically treating hip pain.

Halanski and colleagues looked back at medical records of 72 people with type I and type II SMA (33 and 39 patients, respectively) from the years 1993 to 2017. They sought out subjective reports of hip pain, along with any treatments provided for the pain. They also used radiographs to assess hip instability and spinal deformity.

What they found was that a significant number of patients experienced hip pain, though it varied by type and by the number of SMN2 copies the patient had. Half of patients with type II SMA (49%) reported hip pain, compared with 12% of patients with type I SMA. Seventeen percent of patients with 2 copies of SMN2 reported hip pain, but 53% of patients with 3 copies said the same. Only 2 patients had 4 copies of the gene, and one of those patients had hip pain.

“Nearly all patients had abnormal findings on hip radiographs made at the onset of pain or at the latest follow-up; however, no patient with type- I and 18% of those with type-II SMA had pain that was severe enough to undergo invasive intervention,” Halanski and colleagues said.

Most patients who underwent invasive intervention reported alleviation of pain, but only one patient said the pain went away completely.

The authors said they did not find an association between the type of spinal procedure a patient underwent and the risk of needing invasive hip treatment, nor did the age of the patient at the time of the spinal procedure affect the risk. They therefore said that patient symptoms, rather than radiography, might be a more effective tool to direct patient care.

Though care of SMA patients has changed dramatically in the age of DMTs, Halanski and colleagues said this retrospective study should prove highly valuable as a control demonstrating spinal and hip pathology without the use of the new therapies.

“As these DMTs are potentially life-saving, withholding such treatments to prospectively evaluate their effects on orthopedic outcomes is unethical,” they wrote. “Thus, despite the limitations of the current study, the data presented will be extremely useful as a control, in monitoring the effects that these treatments have on the prevalence of spine and hip pathology.”

Reference

Hanna RB, Nahm N, Bent MA, et al. Hip pain in nonambulatory children with type-I or II spinal muscular atrophy. JB JS Open Access. 2022;7(3):e22.00011. doi:10.2106/JBJS.OA.22.00011