When individuals experience unexplained hip pain, instability, or a noticeable limp, clinicians often use specific physical assessments to identify the underlying cause. These evaluations are designed to observe how the body’s stabilizing muscles and joints function under stress, particularly during movements that mimic daily activities like walking. The “one leg test” is a straightforward, non-invasive method used to check the strength and efficiency of the muscles responsible for keeping the pelvis level during single-leg support. Understanding this specific test provides valuable insight into how doctors assess functional limitations in the hip, which can be related to conditions like joint degeneration. This assessment helps pinpoint the source of a patient’s difficulty before determining a diagnosis or treatment plan.
The Medical Name and Function of the Test
The clinical assessment commonly known as the “one leg test” is medically termed the Trendelenburg Sign or Trendelenburg Test. This sign is named after the German surgeon Friedrich Trendelenburg, who first described it in the late 19th century as a way to evaluate hip function. Its primary function is to assess the integrity and strength of the hip abductor muscles, which are the main stabilizers of the pelvis. Specifically, the test targets the gluteus medius and gluteus minimus muscles, which attach from the pelvis to the top of the thigh bone, or femur.
These muscles are innervated by the superior gluteal nerve and must contract powerfully to prevent the pelvis from dropping when the opposite foot is lifted off the ground. The action of the abductors on the standing leg is crucial for maintaining a level pelvis and a stable center of gravity during the stance phase of walking. When these muscles are weakened or dysfunctional, the test will reveal a mechanical failure. Evaluating this function is a fundamental part of a comprehensive orthopedic examination.
Step-by-Step Procedure
The Trendelenburg Test is performed with the patient standing upright, often with the clinician observing from directly behind to clearly see the pelvic landmarks. The patient is first asked to stand unsupported on one leg, with the foot of the opposite leg lifted off the ground. To ensure the correct muscle group is isolated, the lifted leg is typically flexed slightly at the hip and knee, maintaining the stance for up to 30 seconds if possible.
The patient may be allowed to lightly hold onto a stable surface for balance, but they must not use the support to unload their hip. The examiner watches the level of the iliac crests, which are the bony prominences at the top of the pelvis, on both sides. This visual comparison allows the clinician to determine if the pelvis remains horizontal or if one side drops relative to the other.
Interpreting Positive and Negative Results
The interpretation of the Trendelenburg Test relies on observing the movement of the pelvis on the side of the lifted, unsupported leg. A “negative” result is observed when the pelvis remains level or even slightly elevates on the side of the lifted leg. This outcome indicates that the hip abductor muscles on the standing leg are strong enough to contract effectively and maintain a stable, horizontal pelvic position. A negative test suggests that the primary issue is not due to significant abductor muscle weakness.
Conversely, a “positive” Trendelenburg sign occurs when the pelvis visibly drops downward on the side of the lifted leg. This dropping motion signals a failure of the abductor muscles on the stance leg to generate the necessary force to stabilize the pelvis. The mechanical reason for this drop is that the weakened gluteus medius and minimus on the supporting side cannot counteract the torque created by the body’s weight acting on the unsupported side. A positive sign is a direct indicator of hip abductor muscle weakness, dysfunction, or pain inhibition on the side of the standing leg.
Clinical Relevance to Hip Arthritis
A positive Trendelenburg Sign is frequently noted in patients experiencing hip osteoarthritis, though the test itself does not diagnose the joint condition. The functional limitation indicated by the positive sign is an abductor muscle weakness, which can be a direct consequence of the arthritic process. Pain, joint space narrowing, and bony changes within the hip joint alter the biomechanics of the hip, leading to changes in gait and muscle function. This can cause the gluteal muscles to become inhibited or atrophy over time because the patient naturally favors the painful leg, reducing the load and subsequent use of those stabilizing muscles.
Furthermore, the pain from the degenerated joint can reflexively inhibit the firing of the gluteus medius and minimus, even if the muscle tissue itself is initially healthy. This pain-induced weakness contributes to a positive test result, creating a vicious cycle of instability and further joint stress. While the test is useful for identifying this functional impairment, a positive sign can also occur with nerve damage or other hip pathologies. Therefore, a positive Trendelenburg Sign is considered a piece of evidence highlighting a functional deficit often associated with the progression of hip arthritis, necessitating further diagnostic imaging for a definitive diagnosis.