Overview
Humero-ulnar synostosis (unilateral) is a very rare skeletal condition in which the humerus (the upper arm bone) and the ulna (one of the two forearm bones) are fused together on one side of the body. This fusion occurs at or near the elbow joint, which means the affected elbow cannot bend or straighten normally. The term 'OBSOLETE' in the official disease name indicates that this specific classification has been retired or merged into a broader category in medical databases, but the condition itself — a bony fusion between the humerus and ulna on one side — still exists as a recognized finding. This condition is typically present from birth, as the fusion develops during fetal development when the bones of the arm fail to separate properly. The main symptom is limited or absent movement at the affected elbow. The arm may be fixed in a bent or straight position, which can make everyday tasks like feeding, dressing, and reaching more difficult. Because only one side is affected, the other arm usually functions normally, which helps compensate. Treatment is generally supportive and may include physical therapy, occupational therapy, and in some cases surgery to try to improve the position or function of the affected arm. The overall treatment landscape is limited because bony fusions are difficult to correct surgically without risking complications. Adaptive devices and strategies can help individuals manage daily activities. The condition does not typically affect lifespan or other organ systems.
Also known as:
Key symptoms:
Inability to bend or straighten the elbow on one sideStiffness of the affected elbow jointLimited range of motion in one armDifficulty with tasks requiring two handsThe affected arm may appear shorter or positioned differentlyDifficulty reaching the mouth or face with the affected armTrouble with self-care activities like dressing or eating
Variable
Can be inherited in different ways depending on the underlying gene
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for OBSOLETE: Humero-ulnar synostosis, unilateral.
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Specialists
View all specialists →No specialists are currently listed for OBSOLETE: Humero-ulnar synostosis, unilateral.
Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to OBSOLETE: Humero-ulnar synostosis, unilateral.
Community
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
Rare disease caregiving can be isolating. Connect with counseling and peer support.
Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.What position is my child's elbow fused in, and how does that affect function?,Is surgery an option to improve the position of the arm, and what are the risks?,Should we pursue genetic testing to check for any underlying syndrome?,What type of occupational therapy would be most helpful?,Are there adaptive devices that can help with daily activities?,Will this condition affect my child's growth or development in other ways?,How often should we schedule follow-up appointments?
Common questions about OBSOLETE: Humero-ulnar synostosis, unilateral
What is OBSOLETE: Humero-ulnar synostosis, unilateral?
Humero-ulnar synostosis (unilateral) is a very rare skeletal condition in which the humerus (the upper arm bone) and the ulna (one of the two forearm bones) are fused together on one side of the body. This fusion occurs at or near the elbow joint, which means the affected elbow cannot bend or straighten normally. The term 'OBSOLETE' in the official disease name indicates that this specific classification has been retired or merged into a broader category in medical databases, but the condition itself — a bony fusion between the humerus and ulna on one side — still exists as a recognized findin
At what age does OBSOLETE: Humero-ulnar synostosis, unilateral typically begin?
Typical onset of OBSOLETE: Humero-ulnar synostosis, unilateral is neonatal. Age of onset can vary across affected individuals.