The sudden inability to fully bend your arm, known as elbow flexion, signals an underlying mechanical or biological problem. This restriction, often described as a hard block or deep stiffness, prevents the hand from reaching the face or the opposite shoulder, severely limiting daily function. The elbow joint is uniquely important for positioning the hand in space. Understanding the cause, whether a recent injury or a slowly developing condition, is the first step toward restoring mobility.
Understanding the Mechanics of Bending
Full elbow flexion relies on the precise interaction of three bones: the humerus, radius, and ulna, which form a modified hinge joint. As the elbow bends, the tip of the ulna (the coronoid process) must glide into a depression on the humerus (the coronoid fossa). This bony interaction allows the arm to achieve its maximum bend, typically around 140 to 150 degrees. The primary muscle driving this action is the biceps brachii, which attaches to the radius, but the deeper brachialis muscle also provides powerful flexion. Any interference with the joint’s bony structure or surrounding soft tissues will result in limited movement.
Sudden Restrictions Due to Injury or Trauma
A sudden, sharp restriction in the ability to bend the arm is frequently the result of an acute traumatic event causing a mechanical block. Fractures involving the radial head or the coronoid process of the ulna can cause immediate pain and physical obstruction. Shifting pieces of broken bone disrupt the smooth articulation required for the joint to close completely. Even after a successful elbow dislocation reduction, associated soft tissue damage and severe swelling can physically restrict the final degrees of flexion.
A sudden inability to flex can also be caused by severe soft tissue injuries. For example, a complete rupture of the distal biceps tendon immediately removes the main dynamic engine for bending the elbow, causing weakness and a visible defect in the arm. Furthermore, a significant hematoma (a collection of blood) within the joint capsule or surrounding muscles following impact can create a pressure-based restriction. In all these acute scenarios, the limited motion is immediate and often accompanied by severe pain and swelling, demanding prompt medical attention.
Gradual Stiffness from Long-Term Conditions
In contrast to sudden trauma, many causes of restricted flexion develop slowly over time due to changes in soft tissues or bone surfaces. One common long-term cause is post-traumatic stiffness, where the joint capsule and ligaments thicken and shorten following injury or surgery, known as capsular contracture. This scar tissue formation limits the joint’s ability to stretch and glide through its full range of motion. Another condition is osteoarthritis, where chronic wear and tear or previous trauma leads to the formation of abnormal bone growths called osteophytes.
These bony spurs typically form on the coronoid process and the olecranon, creating a physical barrier that prevents full flexion or extension. A more complex condition is heterotopic ossification, which involves the abnormal growth of mature bone within soft tissues, often after severe injury or head trauma. This new bone acts as a rigid block that physically tethers the joint and drastically limits movement. Chronic inflammatory conditions, like rheumatoid arthritis, can also cause persistent joint swelling and cartilage damage, leading to progressive stiffness.
When to Seek Medical Evaluation and Treatment Options
If the inability to bend your arm is sudden, accompanied by significant pain, visible deformity, or immediate weakness, seek prompt medical evaluation. A professional will perform a physical examination and typically order imaging, such as X-rays, to identify bony problems like fractures, dislocations, or the presence of osteophytes. A computed tomography (CT) scan or magnetic resonance imaging (MRI) may be used for a more detailed look at bone structure or to evaluate soft tissue damage, including ligament or tendon tears.
Treatment depends entirely on the underlying cause, often starting with conservative management for stiffness. Physical therapy is a mainstay, utilizing stretching and splinting techniques to slowly regain motion, often accompanied by non-steroidal anti-inflammatory drugs (NSAIDs) to manage pain and inflammation. If imaging reveals a clear mechanical block, such as a large osteophyte or scar tissue unresponsive to therapy, surgical intervention may be necessary. Procedures like arthrolysis, which involves releasing contracted soft tissues or removing bony obstructions, restore the functional arc of motion.