science

Hip dislocation

Hip dislocation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Hip dislocation rather than just read about it. In short: A hip dislocation refers to a condition in which the thighbone (femur) separates from the hip bone (pelvis). Specifically it is when the ball–shaped head of the femur (femoral head) separates from its cup–shaped socket in the hip bone, known as the acetabulum.

Key takeaways

Hip dislocation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hip dislocation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hip dislocation from memory before moving on to harder problems.

Reference excerpt

A hip dislocation refers to a condition in which the thighbone (femur) separates from the hip bone (pelvis). Specifically it is when the ball–shaped head of the femur (femoral head) separates from its cup–shaped socket in the hip bone, known as the acetabulum. The joint of the femur and pelvis (hip joint) is very stable, secured by both bony and soft-tissue constraints. With that, dislocation would require significant force which typically results from significant trauma such as from a motor vehicle collision or from a fall from elevation. Hip dislocations can also occur following a hip replacement or from a developmental abnormality known as hip dysplasia. Hip dislocations are classified by fracture association and by the positioning of the dislocated femoral head. A posteriorly positioned head is the most common dislocation type. Hip dislocations are a medical emergency, requiring prompt placement of the femoral head back into the acetabulum (reduction). This reduction of the femoral head back into the hip socket is typically done under sedation and without surgery, through maneuvers including traction on the thighbone in line with the dislocation. If this is unsuccessful or if there is an associated fracture in need of repair, surgery is required. It often takes 2–3 months for a dislocated hip to fully heal, and it can take even longer depending on associated injuries such as fracture. Typically, people with hip dislocations present with severe pain and an inability to move the affected leg. Diagnosis is made by physical exam and plain X-rays of the hips. A CT scan is recommended following reduction to rule out complications. Complications include osteonecrosis, femoral head fractures, and posttraumatic osteoarthritis. Males are affected more often than females. Traumatic dislocations occurs most commonly in those 16 to 40 years old. Half of all hip dislocations are accompanied by a fracture. The condition was first described in the medical press in the early 1800s.

Classifications Dislocations are categorized as simple if there is no associated fracture, and complex if there is. In addition, hip dislocations are classified depending on the location of the head of the femur as follows:

Posterior dislocation Posterior dislocations is when the femoral head lies posteriorly after dislocation. It is the most common pattern of dislocation accounting for 90% of hip dislocations, and those with an associated fracture are categorized by the Thompson and Epstein classification system, the Stewart and Milford classification system, and the Pipkin system (when associated with femoral head fractures).

Anterior dislocation Anterior dislocations is when the femoral head lies anteriorly after dislocation. Anterior dislocations are subdivided into two types being inferior (obturator) dislocation and superior (iliac or pubic) dislocation. There is also a Thompson and Epstein classification system for anterior hip dislocations. To note, Central dislocation is an outdated term for displacement of the femoral head towards the body's center into a fractured acetabulum and is no longer used. Moreover, the term "congenital" dislocation is no longer recommended, except for very rare conditions, in which there is a "teratologic" fixed dislocation location present at birth.

Signs and symptoms The affected leg is usually extremely painful, precluding weight-bearing and movement. Nerve injuries also can accompany dislocations, necessitating careful neurovascular examination. Deformity is also present, which is based on concomitant injuries and the type of dislocation:

Posterior dislocation For posterior dislocation, the affected limb will be in a position of flexion, adduction, and internal rotation. This is to say, the affected leg will be bent upwards at the hip, while being shifted and pointed towards the middle of the body. Sciatic nerve injury is also present in 8%-20% of cases, conferring numbness and weakness to aspects of the lower leg.

Anterior dislocation For anterior dislocation, the affected limb will be in a position of abduction and external rotation. The degree of flexion depends on whether it is a superior or inferior dislocation, with the former resulting in hip extension and the latter, hip flexion. This is to say that with superior and inferior anterior dislocations, the affected leg will be bent at the hip backwards and upwards respectively, while being shifted and pointed away from the body. Femoral nerve palsies can also be present, conferring leg numbness and weakness, however are uncommon.

Mechanism

Functional anatomy The hip joint includes the articulation of the spherical femoral head (of femur) and the concave acetabulum (of pelvis). It forms a ball-and-socket joint that is encased by an articular capsule, reinforced and stabilized by muscle, tendon, and ligaments. Even so, the joint is quite flexible in movement, allowing three degrees of freedom. Major ligaments conferring stability to the hip joint include the iliofemoral ligament, the ischiofemoral ligament, the pubofemoral ligament, and the ligament of the head of the femur. The former three ligaments form the zona orbicularis or annular ligament which encases the femoral neck, stabilizing the joint capsule. The strength of a healthy hip, reinforced and stabilized by the aforementioned structures can withstand over 1000 lbs. of force.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Hip dislocation

Start with the simplest possible case. Write down what Hip dislocation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hip dislocation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hip dislocation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hip dislocation

In research: Hip dislocation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hip dislocation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hip dislocation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Congenital disorders of musculoskeletal system, Dislocations, sprains and strains, so understanding it makes those chapters shorter.
In everyday life: Look for Hip dislocation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Hip dislocation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hip dislocation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hip dislocation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hip dislocation in simple terms?

Why does Hip dislocation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hip dislocation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hip dislocation.