Exostosis: Symptoms, Types, Causes and Treatment

Exostosis—a term that may sound unfamiliar to many—refers to the abnormal formation of new bone on top of existing bone. While it is often benign, exostosis can have a significant impact on daily life, depending on its location, size, and growth rate. From mild discomfort to severe pain or movement restrictions, understanding exostosis is crucial for early recognition and management. In this article, we'll explore exostosis in depth, looking at its symptoms, types, causes, and treatment options with evidence-based insights.

Symptoms of Exostosis

Exostosis can often fly under the radar, especially in its early stages. Many people may not notice any signs until the growth becomes large enough to interfere with normal activities or structures nearby. However, when symptoms do occur, they can be varied, depending on the location and type of exostosis.

Symptom	Description	Typical Sites	Source(s)
Pain	Aching, sharp, or radiating pain	Limbs, ribs, feet, ear canal	1,8,11
Movement Limit	Reduced joint or limb mobility	Forearm, shoulder, ankle	1,4,10
Nerve/Soft Tissue Impingement	Numbness, tingling, snapping sensation	Forearm, shoulder	1,4
Deformity	Visible or palpable lump, nail change	Toes, hands, ribs, oral cavity	9,13,6
Functional Impact	Difficulty walking, using hands, or hearing loss	Feet, hands, ear canal	9,12,11

Table 1: Key Symptoms

Overview of Symptoms

Exostoses often present asymptomatically until they reach a size or position that causes problems. Some of the typical manifestations include:

• Pain and Discomfort: This is the most common complaint, especially if the exostosis presses against nerves, tendons, or other sensitive tissues. Pain can be sharp, aching, or radiate along a limb. In some cases, pain may mimic other conditions, such as radial tunnel syndrome when the posterior interosseous nerve is affected in the forearm 1.

• Movement Limitation: When exostoses are near joints, they can restrict motion. For instance, impingement in the shoulder (thrower's exostosis) or forearm can lead to limited rotation or general stiffness 1,4.

• Nerve and Tendon Impingement: Exostoses can press on nerves, causing sensations like tingling, numbness, or "snapping" during movement, as reported with exostoses near the distal biceps tendon 1.

• Visible Deformity: Some exostoses, such as those on the ribs, toes, or oral cavity, may be seen or felt as hard lumps. Subungual (under the nail) exostoses can lead to nail deformity or onychodystrophy 9,13,6.

• Functional Impact: Depending on their location, exostoses can interfere with walking, hand function, or even hearing, particularly in the case of exostoses in the external auditory canal (commonly seen in surfers) 12,11.

Symptom Progression and Complications

• Asymptomatic Period: Many exostoses remain undetected for years, only becoming symptomatic when they grow or shift.
• Secondary Symptoms: Complications like bursitis, vessel entrapment, or hemothorax (in chest wall exostoses) can develop 8.
• Long-term Impact: Chronic pain, joint deformity, or even malignant transformation (rarely, 2–5% in hereditary cases) are possible 3,7.

Types of Exostosis

Not all exostoses are created equal. Their classification depends on origin, location, and underlying causes. Some are isolated and benign, while others are part of hereditary syndromes.

Type	Description	Common Sites	Source(s)
Osteochondroma	Cartilage-capped bony outgrowth	Long bones, ribs	2,3,8
Hereditary Multiple Exostoses (HME)	Multiple exostoses, genetic basis	Limbs, ribs, pelvis	2,3,5
Subungual Exostosis	Bone spur under the toenail	Toes, especially big toe	9
Buccal/Lingual Oral Exostosis	Bony protrusions in oral cavity	Jaw (mandible, maxilla)	6
Thrower’s (Bennett) Exostosis	Bony growth due to repetitive motion	Shoulder (glenoid)	4
External Auditory Canal Exostosis	Bony growth in ear canal (often from cold water)	Ear canal	12
Calcaneal Exostosis	Bony spur on heel bone	Heel (calcaneus)	11
Costal Exostosis	Bony growth on ribs	Ribs	8,13

Table 2: Common Types of Exostosis

Osteochondroma: The Classic Exostosis

Osteochondroma is the most common type and is characterized by a cartilage-capped bony projection. These typically develop near the growth plates of long bones like the femur, tibia, and humerus, but can also affect the ribs and other skeletal sites 2,3,8.

Hereditary Multiple Exostoses (HME)

HME is a genetic disorder where multiple osteochondromas appear throughout the skeleton. These exostoses can lead to bone deformities, growth disturbances, and, in rare cases, malignant transformation into chondrosarcoma 2,3,5.

Subungual and Oral Exostoses

• Subungual Exostosis: Affects the toes, particularly under the big toenail, often causing pain and nail deformity 9.
• Buccal/Lingual Oral Exostosis: These are benign bony growths on the inside of the jaw (mandible or maxilla), possibly related to dental stress or genetics 6.

Sports- and Activity-Related Exostoses

• Thrower’s/Bennett Lesion: Seen in athletes who perform repetitive overhead movements, leading to bony outgrowths on the shoulder's glenoid 4.
• External Auditory Canal Exostosis ("Surfer’s Ear"): Results from repeated exposure to cold water, leading to bone growth that can obstruct the ear canal 12.
• Calcaneal Exostosis (Haglund’s Deformity): A bony enlargement of the heel affecting the Achilles tendon area, often due to repetitive stress 11.

Other Rare Forms

• Costal Exostosis: Bony growths on the ribs can cause unique symptoms like chest pain, hiccups, or even hemothorax if they impinge on internal organs 8,13.

Causes of Exostosis

Exostosis formation is a multifactorial process, involving genetic, environmental, and mechanical factors. Understanding these causes can help in both prevention and targeted treatment.

Cause	Mechanism/Description	Associated Types	Source(s)
Genetic	Mutations in EXT1/EXT2 genes; inherited	HME, osteochondromas	2,3,5,7
Environmental	Repetitive trauma, cold exposure, infection	Ear canal, oral exostosis	12,6
Mechanical	Chronic stress, occlusal wear, overuse	Oral, heel, shoulder exostosis	4,6,11
Somatic Mutation	Spontaneous gene mutation in local tissue	Solitary osteochondroma	5
Developmental	Growth plate disorders	Costal, long bone exostoses	8

Table 3: Causes of Exostosis

Genetic Factors

• EXT1 and EXT2 Genes: The majority of hereditary multiple exostoses are caused by mutations in these genes, which are responsible for the synthesis of heparan sulfate. Disruption leads to abnormal signaling in growth plates, resulting in exostosis formation 2,3,5,7.
• Inheritance: HME is classically autosomal dominant, with about 80% of affected individuals having a family history 3.

Environmental and Mechanical Factors

• Repetitive Trauma and Stress: Activities causing repeated stress or injury to bone can stimulate exostosis formation. For instance, surfers often develop ear canal exostosis from frequent cold water exposure, while athletes can develop shoulder or heel exostosis from repetitive motion or pressure 12,4,11.
• Dental and Oral Stress: Chronic occlusal stress, periodontal disease, and temporomandibular joint (TMJ) pathology have been linked to exostosis in the jaw and mouth 6.

Somatic Mutations and Developmental Abnormalities

• Somatic Mutations: Solitary exostoses can result from a spontaneous mutation in EXT1 in a single location, rather than being inherited 5.
• Growth Plate Disorders: Abnormalities in growth plate development can result in protrusions of bone, as seen in costal (rib) exostoses 8.

Treatment of Exostosis

Treatment strategies for exostosis range from conservative management to surgical intervention. The choice depends on the type, location, symptoms, and risk of complications.

Treatment	Indication	Outcomes/Considerations	Source(s)
Observation	Asymptomatic, non-progressive cases	No intervention needed	8
Physical Therapy	Mild symptoms, functional impact	Can improve motion, reduce pain	4,11
Medication	Pain or inflammation	Symptomatic relief	11
Surgical Excision	Symptomatic, progressive, or complicated	High success, but risk of recurrence or complications	1,9,11,12
Endoscopic Surgery	Minimally invasive option	Less morbidity, quicker recovery	11
Orthopedic Reconstruction	Severe deformities, children with HME	Correction of deformity, improved function	10

Table 4: Exostosis Treatments

When to Treat?

• Observation: Many exostoses, especially if asymptomatic, do not require treatment. Regular monitoring may be enough 8.
• Conservative Management: Physical therapy, activity modification, and pain control are first-line treatments for minor symptoms or when surgery poses a high risk 4,11.

Surgical Intervention

• Indications: Surgery is recommended when exostoses cause significant pain, restrict movement, impinge on nerves or tendons, or present a risk of complications (e.g., hemothorax, nail deformity, hearing loss) 1,8,9,12.
• Techniques:
  • Open Excision: Standard for accessible locations, such as the toes or forearm 1,9.
  • Endoscopic/Minimally Invasive Surgery: Increasingly favored for heel (calcaneal) exostosis, providing better outcomes and less morbidity 11.
  • Orthopedic Reconstruction: In cases of severe deformity, especially in children with HME, reconstructive surgery may be necessary to correct bone alignment and function 10.

Special Cases

• Subungual Exostosis: Complete marginal excision with careful nail bed management yields high satisfaction and low recurrence 9.
• Ear Canal Exostosis: Surgery is reserved for advanced cases or when hearing is affected, with attention to preserving surrounding tissues to minimize complications 12.
• Shoulder (Thrower’s Exostosis): Surgery is considered only after nonoperative management fails, as return to sport is not guaranteed and recovery may be prolonged 4.

Risks and Outcomes

• Recurrence: While recurrence is relatively rare after complete excision, it can occur, especially if the underlying cause is not addressed 9.
• Complications: Vary by site and procedure, but can include infection, nerve injury, deformity, and, in rare cases, malignant transformation (especially in hereditary cases) 3,7,12.

Conclusion

Exostosis is a complex skeletal condition that can range from an incidental finding to a source of significant discomfort or disability. Understanding its symptoms, types, causes, and treatment options is essential for effective management and prevention of complications.

Key Takeaways:

• Exostosis may cause pain, deformity, or movement restriction, but can also be asymptomatic for years.
• Types of exostosis include isolated osteochondromas, hereditary multiple exostoses (HME), subungual, oral, and activity-related forms.
• Causes are multifactorial—ranging from genetic mutations (EXT1/EXT2) to environmental and mechanical factors like trauma, cold exposure, or repetitive stress.
• Treatment depends on symptoms and severity. While many cases require only observation, surgery is often needed for functional impairment or complications.
• Advances in surgical techniques, especially minimally invasive approaches, have improved outcomes for many patients.

Staying informed and seeking early medical advice when new bone lumps or unexplained discomfort arise can make a significant difference in the management and quality of life for those affected by exostosis.