Definition

Hip dysplasia, also named acetabular dysplasia or shallow hip pocket, is a malformation of the ball and socket forming the hip joint that interferes with the normal function of the hip.

Pathology

Developmental hip dysplasia is a congenital condition leading to the abnormal growth of the hip joint. It may involve the femoral head, the acetabulum and surrounding soft tissues.

Depending on the case, the acetabulum (socket) may be too shallow, underdeveloped or the tendons of the hip joint too loose, thus failing to keep the femoral head firmly into the acetabulum. Hip dysplasia is the most common orthopaedic problem in newborns with a higher frequency on the left hip and bilateral in 20% of the cases.

The pathology can be diagnosed at childhood, adolescence and early adulthood. Early treatment is paramount to prevent long-term complications such as recurrent hip subluxation (partial exit) or full dislocation (the femoral head exits completely from the acetabulum) and later osteoarthritic degeneration of the joint in 20-40% of patients eventually requiring a hip replacement surgery. A late dysplasia in adolescents is less severe due to the mechanical stability of the joint, which is easily reduced.

Classification

A hip dysplasia is classified as:

Dislocated defined as Ortolani positive or negative depending on whether it is reducible or irreducible

Dislocatable Barlow-positive

Subluxatable Barlow-suggestive

Crowe Classification is used to assess the severity of adult developmental dysplasia of the hip:

Grade 1: less than 50% subluxation

Grade 2: between 50% to 75% subluxation

Grade 3: between 75% to 100% subluxation

Grade 4: over 100% subluxation

Causes

The causes underlying the hip dysplasia are not known as it mostly develops in utero. Thus far these are the most common factors predisposing to this condition:

In utero and post-birth malposition of the baby

Early instability of the hip joint causing dysplasia

Acquired dysplasia in swaddling infants (wrapping infants in blankets)

Risk factors

A hip dysplasia has a congenital aetiology and occurs most commonly in:

Females (6:1 vs males)

Family history

First born child

Breech position at birth (buttocks appearing first in the birth canal)

Twin pregnancy

Symptoms

The symptoms for a congenital hip dysplasia are often difficult to detect in newborns. There are signs that may suggestive of this pathology such as one leg appearing shorter, excessive skin folds on the inner thigh, different range of movement between the hips. In older children walking on the tiptoes of one side, walking with a limp or a waddle may be symptoms of a unilateral or bilateral hip dysplasia, respectively. In older individuals pain and limp, together with clicking and popping noises during activity are the most frequent symptoms.

Treatment

Nonoperative treatment

When the femoral head is not entirely fitting into the underdeveloped acetabulum of a baby, conservative treatment aims at keeping it in place to allow for a full growth of the socket.

In a baby under 6 months this is achieved with the use of a Pavlik harness for 6-8 weeks, which keeps the legs spread with hips flexed. The correct positioning of the two elements will favour the growth of the acetabulum. In older babies a rigid hip, spica cast, is used possibly supported by a metal bar between the legs. Other devices include braces and splints that may be used after surgery.

In adults conservative treatment is implemented with mild dysplasia or when the joint is too arthritic for surgery. Life style changes are recommended to reduce pain and delay arthritis of the joint:

Weight loss

Joint injections

Targeted physical therapy

Cycling or swimming instead of high impact sports (running and basketball) to reduce stress on the hips.

Surgical treatment

In some cases the abnormal anatomy of the hip joint is corrected with surgical reconstruction. This is usually performed in adolescent and adult patients. Different methods are available:

Open reduction and spica casting: below 18 months (after failure of Pavlik harness treatment)

Open reduction and femoral osteotomy: between 2 and 4 years (abnormal femur development)

Open reduction and pelvic osteotomy: above 2 years, more frequent in children over 4 years and adults (acetabulum malformation).

In the last scenario, surgery aims at widening the incomplete, small acetabulum with a peri-acetabular osteotomy (partial bone removal) or Ganz treatment, thus preserving own bones without the use of prosthesis. This treatment reduces pain, restores function and prevents or delays a hip replacement.

Surgical procedure for total hip replacement includes:

An incision is cut along the lateral hip and the muscles gently separated

The hip is dislocated and the femoral head is resected

The acetabulum is enlarged to accommodate for the insertion of prosthesis

The concave artificial acetabulum is fixed to the pelvis sometimes with screws

The prosthesis of the femur is introduced in the bone cavity and ;connected to the artificial acetabulum

Joint replacement surgery: arthroplasty

When hip dysplasia has severely compromised the integrity of the joint cartilage, a hip replacement or arthroplasty may be necessary. With this method the damaged bones are firstly removed and then replaced with artificial prostheses.  

Complications

After conservative or surgical treatment of hip dysplasia the child undergoes multiple follow-ups to monitor the growth of the hip joint with proper anatomical positioning and function. Similarly, an adult patient will be monitored to evaluate the stability of the hip and the occurrence of further degenerative changes.

Complications are:

Osteonecrosis (bone death) can occur in both types of treatment

Infection post-surgery

Deep vein thrombosis (DVT) and pulmonary embolism “ following surgery in adult patients

Blood loss - this can occur during or after surgery