The elbow functions primarily as a hinge joint, connecting the humerus of the upper arm with the radius and ulna of the forearm. Its core movement involves flexion and extension, with full extension, or terminal extension, typically reaching zero degrees or occasionally a few degrees beyond. The inability to fully straighten the arm is a common symptom that restricts the hand’s ability to reach, push, and perform essential daily actions like dressing or self-care. This loss of motion, known as an extension deficit, can occur suddenly due to trauma or develop gradually over time, pointing to distinct underlying causes.
Acute Injuries and Mechanical Blockage
A sudden, complete inability to extend the elbow often signals a mechanical blockage from an acute traumatic event. A displaced olecranon fracture, for instance, involves a break in the bony prominence at the back of the elbow where the triceps muscle attaches. This structural failure disrupts the extensor mechanism, making it impossible to actively straighten the arm against gravity. The pull of the triceps muscle can further separate the bone fragments, causing a clear, immediate loss of function.
Another cause of immediate blockage is the presence of loose bodies—fragments of bone or cartilage floating within the joint space. These fragments, often created during a traumatic injury, can physically jam the joint, causing a sensation of “locking” that prevents the smooth glide required for full extension.
Acute trauma can also lead to an intra-articular hematoma, a collection of blood pooling inside the joint capsule. This rapid accumulation of fluid drastically increases the internal pressure, mechanically restricting movement. The intense pressure causes severe pain, prompting the body to protectively guard the elbow in a flexed position.
Chronic Conditions Causing Gradual Stiffness
Conditions that develop slowly result in a stiff elbow, defined by a progressive loss of terminal extension over time. Osteoarthritis, a wear-and-tear process, leads to the formation of bone spurs, or osteophytes, particularly at the tip of the olecranon and coronoid process. As the arm attempts to straighten, the olecranon tip impacts the humerus in the olecranon fossa, and these bony growths physically collide, creating a structural impediment to full extension.
Long-term stiffness, or contracture, can be caused by the development of scar tissue and thickening of the joint capsule and ligaments. This post-traumatic contracture often follows an initial injury or prolonged immobilization, leading to a reduction in the joint’s internal volume. The soft tissue surrounding the joint becomes pathologically dense and shortened, restricting the elbow’s ability to stretch into a straight position.
A challenging form of contracture is heterotopic ossification, where new, abnormal bone forms in soft tissues, such as muscles and tendons. This ectopic bone develops in response to severe trauma or burns and acts as a dense, physical block, sometimes locking the elbow at a fixed angle and preventing terminal extension.
How Inflammation and Pain Restrict Movement
Not all extension deficits are due to a hard structural block; some result from fluid accumulation or the body’s protective pain response. Olecranon bursitis, often called “student’s elbow,” involves inflammation of the fluid-filled sac over the bony point of the elbow, producing excess fluid and visible swelling.
The physical presence of this swollen bursa restricts the final degrees of extension as the fluid sac is compressed against the bone during straightening. Similarly, triceps tendonitis—irritation of the large extensor tendon—causes pain at the back of the elbow when extending the arm against resistance.
This localized pain triggers an involuntary reaction called muscle guarding, where the surrounding flexor muscles (like the biceps) spasm or tighten. The body subconsciously prevents the painful movement by contracting the opposing muscle group, creating a soft tissue barrier that limits the ability to achieve full, comfortable extension.
Diagnosis and Management Options
A sudden, painful loss of elbow extension, especially following an injury, requires urgent medical evaluation to rule out acute fracture or dislocation. The initial diagnostic step involves X-rays, which are effective for identifying bony issues such as fractures, loose bodies, and osteophytes. If a detailed view of the complex bony anatomy is necessary, such as for operative planning, a Computed Tomography (CT) scan provides superior three-dimensional detail.
For diagnosing soft tissue causes like ligament tears, tendonitis, or joint capsule thickening, Magnetic Resonance Imaging (MRI) provides detailed images of non-bony structures. Non-surgical management for stiffness often begins with physical therapy and splinting, utilizing static progressive splints to gently stretch contracted soft tissues. If conservative treatment fails, surgical options are considered, depending on the cause of the restriction.
Surgical intervention includes arthroscopic debridement, a minimally invasive procedure to remove bone spurs and loose bodies blocking movement. For chronic stiffness caused by thickened soft tissue, a capsulectomy involves releasing or excising the contracted joint capsule. In cases of complex fractures or heterotopic ossification, open surgery may be necessary to realign bone fragments or remove large blocks of abnormal bone, followed by immediate rehabilitation.