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.
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.
A hip dysplasia is classified as:
Dislocated is defined as Ortolani positive or negative depending on whether it is reducible or irreducible
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
Intra-articular fracture extends to the wrist joint (or articulation)
Extra-articular fracture is located outside of the wrist joint
Open fracture when bone fragments perforate the skin
Comminuted fracture when the bone breaks into multiple fragments
Non-displaced when the anatomical alignment of the bone is maintained or displaced when the bone fragments move apart.
Melone’s classification describes the characteristics of intra-articular fractures of the radius:
i Stable fracture
ii Unstable "die-punch"
iii "Spike" fracture
iv Split fracture
v Explosion injuries
These fractures are divided into:
Anterior pillar (not weight bearing part of joint)
Posterior pillar (often associated with dislocation of the hip including the weight bearing part of joint)
Comminuted involving both column type
Sacral / coccygeal fractures
The sacrum is a triangular-shaped bone formed by 5 fused vertebrae, which provide a posterior wall to the pelvic ring. At each side of the sacrum, the ala structures articulate with the ilium bones forming the sacro-iliac joints. Sacral fractures are usually parallel to the spine and can involve the ala. Less frequently sacral fractures may display an “H” shape, including a transversal fracture uniting both sides of the sacrum. Three zones are described where sacral fractures can occur that are along vertical lines relative to the alignment of the foramina. Sacral fractures may result in sacral instability and require treatment via sacroplasty (injection of bone glue into the fracture). Surgery is necessary in case of associated neurological symptoms.
Fractures of the coccyx involve the tailbone, the terminal portion of the spine situated below the sacrum formed by 3 to 5 fused vertebrae. Coccyx fractures occur when falling on a seated position. They are more common in elderly women and seldom require surgical treatment.
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)
A hip dysplasia has a congenital aetiology and occurs most commonly in:
Females (6:1 vs males)
First born child
Breech position at birth (buttocks appearing first in the birth canal)
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.
In Western countries newborns undergo a routine ultrasound examination of the hip at 6 months to assess abnormalities of the joint and monitor changes with passive movements.
During clinical examination in older children/adults the physician will test the movement of the hip joint, audible clicking and popping sounds, leg length discrepancy, pelvic obliquity, lumbar lordosis, and toe walking.
A hip displacement may be diagnosed at later check-ups when the child is a few months/years old. If a dysplasia is suspected with clinical examination and ultrasound, the X-ray of the hip is recommended. In adults the severity of a hip dysplasia is evaluated by measuring the socket depth on an X-ray image. MRI is useful to determine the condition of the cartilage and labrum that may be degenerated due to joint misalignment as well as provide diagnosis on the type of displacement (upwards displacement wears out faster).
For clinical examination of newborns under 3 months various procedures are used and named after the orthopaedic surgeons who developed:
Barlow: dislocates the hip by adduction and depression of the flexed femur
Ortolani: reduces a dislocated hip by elevation and abduction of the flexed femur
Galeazzi: limb length discrepancy due to a unilateral dislocated hip; with hip and knee flexed at 90º the femur is shorter on the dislocated side
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:
Targeted physical therapy
Cycling or swimming instead of high impact sports (running and basketball) to reduce stress on the hips.
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.
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
Deep vein thrombosis (DVT) and pulmonary embolism – following surgery in adult patients
Blood loss - this can occur during or after surgery
Physical therapy consists in gentle movements of the hip and stretching exercises that keep the joint lubricated to protect the cartilage and increase blood flow. Exercise is also useful to strengthen the surrounding muscles in support of the hip joint (abduction and external rotation).
After surgery in adults the use of crutches, a walking stick may be necessary during the first weeks up to 12 months after arthroplasty.
Physiotherapy post surgery includes:
Exercise to strengthen quadriceps, hamstrings and gluteal muscles
Guided return to activity
Use of walking devices
Weight loss in overweighed patients
A hip dysplasia cannot be prevented as it is a congenital condition, however early diagnosis and treatment in newborns and young adults may avoid the detrimental consequences of this pathology. This includes a number of life style changes that reduce stress on the joint and prevent bone degeneration. Once the diagnosis is done, regular follow-ups will help in monitoring the progress of the hip condition. Pregnant women with previous hip surgery may require childbirth via Caesarean section. In babies wrong posture in swaddling may be detrimental to the development of the hips. The use of wide diapers, called “abduction pants” may aid proper hip growth in the first months of life.