Multiple Osteochondromas (MO), also known as Multiple Cartilaginous Exostoses, is an autosomal dominant skeletal disorder with an incidence of approximately 1 in 50,000 in Western populations. Most cases are associated with pathogenic variants in the EXT1 and EXT2 genes, which lead to a systemic reduction of heparan sulfate, causing abnormalities in bone growth and other physiological processes.

Symptoms typically appear in childhood and include the development of bony protrusions often associated with pain due to compression of muscles and nerves. Patients are generally shorter than average and may experience dislocations, subluxations, reduced motor function, and skeletal deformities such as genu valgum, limb asymmetry, and scoliosis. The most severe complication is malignant transformation into chondrosarcoma, occurring in 0.5-5% of adult patients. Diagnosis is mainly based on imaging techniques (X-ray, CT, MRI, ultrasound) and is confirmed by the presence of at least two osteochondromas after excluding other conditions.

Following diagnosis, patients or their caregivers often raise questions regarding disease progression, the number and type of surgical interventions required, and differences between pediatric and adult surgical approaches. This retrospective observational cohort study aims to characterize the number and types of surgical procedures performed in MO patients at a European referral center, the Rizzoli Orthopaedic Institute.

Multiple Osteochondromas (MO, OMIM: 133700, 133701), also known as Multiple Cartilaginous Exostoses, represent an autosomal dominant skeletal dysplasia with an incidence in the Western population of approximately 1 in 50,000. The pathogenic variants identified in the majority of patients involve the EXT1 (OMIM: 608177) and EXT2 (OMIM: 608210) genes. Pathogenic mutations in these genes cause a systemic reduction of the polysaccharide heparan sulfate, leading to abnormalities in bone growth and in several physiological processes.

The first symptoms of the disease are observed in childhood, with the appearance of bony protrusions often associated with pain due to the pressure exerted by the osteochondroma on muscles and nerves. Furthermore, patients affected by MO, who are generally shorter than average, experience dislocations and subluxations, reduced motor abilities, as well as deformities such as genu valgum, limb length discrepancy, and scoliosis. The most severe complication is the malignant transformation of osteochondroma into chondrosarcoma, which occurs in 0.5-5% of adult patients. Clinical diagnosis is therefore primarily based on radiological imaging (X-rays, CT, MRI, ultrasound), with confirmation in the presence of at least two osteochondromas and after exclusion of other possible diagnoses.

At the time the diagnosis is communicated to the patient, numerous questions arise. The affected individual (or their guardian, in the case of minors) may ask about the clinical course of the disease or the number of surgical procedures they may need to undergo. Additional questions concern the type of surgical intervention and, given the progressive nature of the disease, surgery performed in children differs from that in adults. The present study (a retrospective observational cohort study) aims to characterize the number and type of surgical procedures performed in cases of MO at a European referral center such as the Rizzoli Orthopaedic Institute (IOR).

Inclusion Criteria:

• Patients diagnosed with multiple osteochondromas who underwent surgery at the IOR between January 1, 2012, and February 28, 2025.
• Patients of both sexes, regardless of age.

Exclusion Criteria:

- Patients with conditions that are part of the differential diagnosis for the condition under study, such as enchondromatosis and solitary exostosis.

Patients with multiple osteochondromas who underwent surgery at the Rizzoli Orthopedic Institute