The inability to fully straighten the arm, known medically as a loss of terminal elbow extension, is a common problem. The elbow is a hinge joint where the humerus (upper arm bone) meets the ulna and radius (forearm bones), allowing for both bending and rotation. Full extension is achieved when the bony projection of the ulna, called the olecranon, seats into the olecranon fossa groove on the back of the humerus. When this movement is blocked, the restriction can stem from issues with the bones, the cartilage, or the surrounding soft tissues. The cause can range from a sudden, severe injury to a gradual process of wear.
Acute Injuries Limiting Extension
A sudden inability to straighten the arm often points to an acute, traumatic event that has physically disrupted the joint’s structure. Elbow dislocations are a frequent cause, occurring when the forearm bones are forced out of alignment relative to the humerus. This displacement creates an immediate mechanical block, making full extension impossible. The trauma is often severe enough to tear the surrounding ligaments.
Fractures around the joint also commonly cause an extension deficit. A displaced fracture of the radial head or the olecranon can leave bone fragments or a misaligned joint surface that prevents the arm from reaching a straight position. Even without a full dislocation, intense swelling and bleeding within the joint capsule (hemarthrosis) following a fracture can create enough internal pressure to mechanically limit movement. These acute injuries demand rapid medical attention to realign the joint and stabilize broken bones, minimizing the risk of long-term stiffness.
Chronic Conditions Causing Stiffness
In contrast to acute trauma, some conditions cause a gradual loss of elbow extension over time. Different forms of arthritis, which involve the degradation of the joint’s smooth cartilage lining, are primary culprits. Osteoarthritis, or “wear-and-tear” arthritis, leads to the loss of this protective cushioning, resulting in increased friction between the bones.
The body attempts to stabilize the joint by producing new bone growths called osteophytes, or bone spurs, particularly in the olecranon fossa. These bony spurs act as mechanical obstructions, filling the space where the olecranon needs to recess for full extension, thereby blocking movement. Rheumatoid arthritis, an inflammatory autoimmune disease, also contributes to stiffness by causing chronic joint inflammation (synovitis) and eventual erosion of the bone and cartilage. The persistent inflammation causes the joint capsule to thicken and contract, which further restricts the total range of motion.
Additionally, loose bodies—small fragments of bone or cartilage—can float within the joint fluid and occasionally get wedged between the joint surfaces, leading to sudden, temporary mechanical locking.
Soft Tissue and Muscle Contractures
The limitation can stem from a shortening of the non-skeletal structures surrounding the joint. The joint capsule, a fibrous sac enclosing the elbow, can become thickened and tight in a condition called capsular contracture. This frequently follows prolonged immobilization after an injury or surgery, causing the capsule to scar and lose its natural elasticity. The resulting fibrosis of the anterior joint compartment specifically restricts the ability to straighten the arm.
Another soft tissue cause is heterotopic ossification (HO), which is the pathological formation of new bone in soft tissues, such as within the muscle or ligaments. HO is a common complication after severe trauma, burns, or certain neurological injuries. It creates a rigid, bony block outside the joint that tethers and restricts movement. Furthermore, general scar tissue within the flexor muscles and connective tissues around the elbow can shorten the tissues enough to prevent complete extension.
Necessary Steps for Diagnosis and Treatment
If you notice a sudden or progressive inability to straighten your arm, seeking a professional medical evaluation is the first step. A physician, often an orthopedic specialist, will begin with a physical examination to assess the active range of motion and determine whether the restriction is a soft tissue limitation or a hard, bony block. Imaging studies are then used to visualize the internal structures of the elbow.
Standard X-rays are the initial tool to detect fractures, dislocations, bone spurs (osteophytes), heterotopic ossification, or loose bodies. Further imaging, such as a computed tomography (CT) scan, may be used to identify the exact cause of a bony blockage. Treatment depends on the cause. Conservative approaches like physical therapy and splinting are recommended first to gently stretch contracted soft tissues. For limitations caused by a clear mechanical obstruction, such as large bone spurs or extensive heterotopic ossification, surgery may be required to remove the blockage and release the joint capsule.