Protrusio acetabuli is the protrusion of the acetabulum into the pelvic cavity. With the medial movement of the acetabulum, the femoral head also shifts into the pelvis. Although the condition was first recognized in 1816, it was not until 120 years later that it was classified into primary (idiopathic) and secondary disease[1]. By today, a large number of conditions are known to cause secondary protrusio acetabuli [1]; the category of primary protrusio acetabuli is maintained for cases whose origins cannot be attributed to other diseases. As diagnostic techniques keep improving, the number of primary cases keeps decreasing [2].

Infections by gonoccous and echinococcus as well as tuberculosis were found early on to cause protrusio acetabuli. The main inflammatory conditions that cause protrusio acetabuli are rheumatoid arthritis [3], ankylosing spondylitis [4], psoriatic arthritis, acute idiopathic chondrolysis, and Reiter’s syndrome. A number of metabolic diseases are also associated with protrusio acetabuli. Among these are osteogenesis imperfecta, osteoporosis, hyperparathyroidism, and Paget’s disease. Some genetic ailments associated with protrusio acetabuli are sickle cell disease [5], trisomy 18, Ehlers-Danlos syndrome, and Marfan’s disease. Neoplastic disease and trauma to the bone, such as fractures, can also result in protrusio acetabuli [6].

Primary protrusio acetabuli is caused by deficiency or destruction of the bone structure or developmental abnormalities. It can be the source of osteoarthritis; senile patients with protrusio acetabuli almost always report with osteoarthritis [7]. Primary protrusio acetabuli is most frequently bilateral and affects women more than men. Several familial cases have been reported which were compatible with an autosomal dominant inheritance pattern [2]. Primary protrusio acetabuli showcases mainly with stiffness, limitation of movement, and possibly pain [2].

Workup has to start with a thorough history (including family history), and careful physical examination of the hip. Blood tests (such as complete blood count, the presence of C-reactive protein) and synovial biopsy will aid in the diagnosis. An anteroposterior radiogram is the most usual diagnostic tool, using plain radiography. Some investigators advocate the use of the false profile view, which reveals excessive cartilage destruction [8]. Magnetic resonance arthrography is useful for the detection of structural changes in the early stages of the disease.

In young patients, the condition is difficult to diagnose because the radiological signs are not characteristic. The difficulty also lies in differentiating protrusio acetabuli from acute idiopathic chondrolysis. With complaints of stiffness and pain – and with secondary causes, such as inflammation and trauma excluded –young people would be diagnosed with idiopathic chondrolysis if they display loss of joint space. If they also exhibit signs of an acetabular protrusion in addition to the loss of joint space, the diagnosis is protrusio acetabuli. Some investigators regard protrusio acetabuli and idiopathic chondrolysis as the same condition [9]; however, for various reasons, this view is not universally accepted. For example, idiopathic chondrolysis does not show a female preponderance [2].

A critical measurement for diagnosis deduced from radiographs is the center-edge angle of Wiberg [2], which is between 25 and 40 degrees in normal hips. An angle of more than 46 degrees indicates protrusio acetabuli. However, several authors find the angle measurement inadequate for diagnosis; for example, angles greater than 46 degrees can also be found in the general population [10]. Another important indication of protrusio acetabuli is the extent to which the medial wall of the acetabulum shifts medially in relation to the ilioischial line (Kohler’s line). Some investigators require the acetabular wall to reach the ilioischial line, while others call for the line to be crossed to establish the diagnosis. Yet another widely used criterion is the arrangement of the teardrop. Using the above criteria for diagnosis requires the careful centering of radiographic images. Other anatomical criteria can be used. A grading of the protrusion is provided by determination of the distance of the acetabulum from the upper margin of the superior pubic ramus [11].

Treatment for protrusio acetabuli depends on the severity of the condition and the underlying cause. Conservative management includes pain relief with medications, physical therapy to improve joint function, and lifestyle modifications. In severe cases, surgical intervention may be necessary. Options include osteotomy, which reshapes the hip joint, or total hip replacement.

The prognosis for protrusio acetabuli varies. With early diagnosis and appropriate management, many patients can maintain a good quality of life. However, if left untreated, the condition can lead to significant joint damage and disability. Surgical interventions generally have good outcomes, but the success depends on the patient's overall health and the extent of joint damage.

Protrusio acetabuli can be caused by a variety of factors. Congenital conditions like Marfan syndrome or osteogenesis imperfecta can predispose individuals to this condition. Acquired causes include trauma, inflammatory diseases like rheumatoid arthritis, and metabolic bone diseases such as Paget's disease. In some cases, the cause remains idiopathic, meaning it is unknown.

Protrusio acetabuli is relatively rare, with varying prevalence depending on the underlying cause. It can occur in both children and adults, but the etiology often differs. For instance, congenital forms are more common in younger individuals, while degenerative causes are seen in older adults. There is no significant gender predilection, although some underlying conditions may have gender biases.

The pathophysiology of protrusio acetabuli involves the inward displacement of the acetabulum into the pelvic cavity. This can result from weakening of the bone structure due to genetic, inflammatory, or metabolic factors. The altered biomechanics of the hip joint lead to increased stress and wear, contributing to pain and functional impairment.

Preventing protrusio acetabuli involves managing risk factors and underlying conditions. For those with genetic predispositions, regular monitoring and early intervention can help. Maintaining a healthy lifestyle, including weight management and regular exercise, can reduce the risk of joint degeneration. For inflammatory or metabolic causes, appropriate medical management is essential.

Protrusio acetabuli is a condition characterized by the inward displacement of the hip socket, leading to pain and limited mobility. It can result from various congenital, traumatic, or disease-related factors. Diagnosis involves imaging studies, and treatment ranges from conservative management to surgical intervention. Early detection and management are key to preventing joint damage and maintaining quality of life.

If you have been diagnosed with protrusio acetabuli, it's important to understand your condition and treatment options. This condition affects the hip joint, causing pain and movement limitations. Treatment may include medications, physical therapy, or surgery, depending on the severity. Regular follow-ups with your healthcare provider are crucial to monitor your condition and adjust treatment as needed. Maintaining a healthy lifestyle can also help manage symptoms and improve outcomes.

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