Acetabular dysplasia is also known as an unstable hip joint. It is characterized by a mismatch between the femoral head and the acetabulum, with the acetabulum not adequately covering the femoral head.
Although acetabular dysplasia is present in infancy, it is mostly asymptomatic. As age increases, painless hip dysfunction can gradually appear, and by adulthood, hip pain can occur due to the development of osteoarthritis. Patients with deformation of the femoral head and patients with subluxation develop osteoarthritis earlier due to stress concentration. The disease is mostly missed or improperly treated in adolescence and is seen in adulthood secondary to osteoarthritis, with hip pain and difficulty walking.
Early surgery not only relieves or eliminates symptoms, but also reduces the occurrence and progression of osteoarthritis. However, because there are very few objective criteria to assist in determining surgical procedures and a lack of rigorous surgical indications, it is difficult to select treatment options for young patients with mild symptoms and moderate dysplasia, causing clinicians to hesitate and delay surgery. Therefore, a detailed understanding of the etiology, mechanisms and treatment principles of this disease will undoubtedly guide clinicians.
Acetabular dysplasia is mainly due to a mismatch between the stresses acting on the joint and the properties of the tissues that counteract the stresses, which can cause abnormal acetabular development due to excessive or inappropriate stresses. Thus, the following structural or force malfunctions can cause acetabular dysplasia.
1, due to congenital defects, i.e. abnormal hip obliquity, shallow flat acetabulum, large anterior tilt angle due to lack of a strong fulcrum for the femoral head, and straightened neck stem angle.
2, ischemic femoral head necrosis in childhood, slipped femoral head epiphysis, hip exostosis or hip inversion.
3, lameness caused by improper treatment of osteoarthritic disease on the diseased side, resulting in acetabular dysplasia on the healthy side.
4, one side of the hip dysplasia causes the contralateral limb to be relatively longer, causing the area of the femoral head covered by the acetabulum to decrease and gradually develop into acetabular dysplasia.
According to the degree of acetabular adaptation through the Colemanl method acetabular dysplasia is divided into 4 types:
1. non-spherical adaptation: occurs in early childhood with femoral arteriosclerosis (AVN) of the femoral head, which may be a comorbidity of Legg-Calve-Perthes disease or congenital hip disorders treated with deformation of the femoral head, and the acetabulum is also deformed to accommodate the femoral head.
2. non-spherical maladaptation: AVN occurring in children with advanced femoral head deformation but the acetabulum remains spherical.
3, spherical adaptation: general state of the hip joint, the acetabulum and the femoral head are spherical and have the same radius.
4, spherical maladaptation: the radius of the acetabulum exceeds the radius of the femoral head.
In congenital and neuromuscular developmental anomalies, subluxation causes destruction of the cartilage rim on the lateral side of the acetabulum, the femoral head moves slowly upward and outward, the radius of the curve around the acetabulum increases, thus becoming a sourdough fossa, the femoral head and acetabulum are spherical, but the radius of the curve of the acetabulum is large.
If this progression is not corrected and still continues, the femoral head will further flatten and cause non-spherical maladjustment. Preoperative spiral CT and 3D reconstruction can display the acetabulum and femoral head morphology in multiple directions and in three dimensions, which is an important guide for the classification of the hip joint and the selection of an appropriate surgical plan. The forces acting on the hip joint are divided into four types: tensile stress, compressive stress, bending stress, and shear stress. The body’s center of gravity is transferred downward to the hip joint through the center of the pelvis, and the force on each hip joint is about 1/3 of the body weight.
When standing on one foot, the femoral head of the hip on the standing side is used as the fulcrum to establish a lever-like balance system. Due to the shift of the center of gravity, the pelvis is tilted and has the effect of rotating inward with the hip joint as the center, in order to maintain the balance, the abductor muscle needs to be tense and play the role of resistance, at this time, it can be calculated that the force on the hip joint is about 2-7 times of the body weight, and the forces acting on the hip joint are human gravity, abductor muscle force and iliotibial bundle muscle force, etc.
Surgical treatment methods can be divided into the following categories: interposition capsule arthroplasty, redirection osteotomy, periarticular osteotomy, and artificial joint replacement. The four treatments can also be applied in combination.
1. Interposition capsule arthroplasty: It is a joint capsule mosaic between the re-formed socket cap and the femoral head, and undergoes tissue degeneration into fibrocartilage. This includes Chiari inward displacement osteotomy and acetabular capsulotomy, which extends the joint by extending the distal end of the osteotomy centrally to provide a fibrocartilaginous joint to correct acetabular dysplasia and alter the mechanical properties of the hip joint.
The inward displacement of the joint allows for a shorter lever arm with an inward shift of the center of gravity, which in turn reduces joint loading. The acetabular cap can be used in conjunction with other acetabular procedures and so provides the ability to correct severe developmental abnormalities. The cap is a bone graft placed above the acetabular capsule to provide an interpositional capsule arthroplasty. A tipped iliac flap is chiseled immediately above the acetabular rim and pressed down to cover the upper and posterior femoral head, and then an iliac bone block is taken from the anterior superior iliac spine and embedded in the gap between the down-turned flap and the iliac bone.
2, reorientation osteotomy: change the relative direction and position between the acetabulum and the hip bone, reposition the existing acetabular articular cartilage to increase the load bearing area, including Salter pelvic osteotomy, Kalamchi, Hall, Sutherland, Steel and other osteotomy. salter pelvic osteotomy is to rotate the acetabulum forward and downward with the femoral head as the center Hall osteotomy uses a trapezoidal wedge to increase the height of the ilium, and this method effectively increases the limb on the operated side.
Lance described a peri-articular lip osteotomy including the acetabular rim to increase coverage and adaptability. the Wiberg procedure was performed to fill the acetabulum with fragmented bone after undermining it.
Pemberton described a pericapsular osteotomy in which the center of iliac rotation is in the “Y” cartilage, rotating the outer superior acetabular rim downward and forward to provide better coverage of the femoral head and altering the acetabular shape by reducing the radius of the acetabular ring. The complete spherical periacetabular osteotomy was described by Eppright as a “dial” osteotomy and was rarely used because of the high technical requirements. The acetabulum is rotated in all directions to increase the acetabular coverage of the femoral head.
In 2004, the China-Japan Friendship Hospital of Jilin University introduced a modified periacetabular osteotomy to treat acetabular dysplasia, with the advantage that the method is simpler.
4, artificial hip joint replacement: artificial hip joint replacement includes total hip joint replacement treatment and total hip joint surface replacement treatment. The most critical problem of hip dysplasia is the inadequate coverage of the acetabulum on the femoral head and the poor correspondence of the joint surface. The acetabular condition is the main basis for selecting the type of acetabular prosthesis. Therefore, the appropriate acetabular prosthesis should be used for the artificial total hip arthroplasty of patients with different degrees of acetabular dysplasia in order to obtain better results and reduce complications.
The hip joint is painful at rest, which is aggravated by claudication, combined with serious osteoarthritis, and the joint function is obviously restricted. The pathology is that most of the articular cartilage is destroyed, the subchondral bone is exposed, the joint space is narrowed or disappeared, the osteosclerosis is more serious, accompanied by cystic changes, and a large number of bone redundancies are formed at the acetabular rim, and the femoral head is flattened or even collapsed. The most suitable treatment option is total hip replacement.
Reconstruction of the center of rotation of the hip joint in the true socket position restores the normal anatomical relationship of the joint, provides good coverage of the acetabular prosthesis, and improves the tone and muscle strength of the abductor muscles. Compared with ordinary total hip replacement, total hip surface replacement does not remove the femoral neck, does not destroy the medullary cavity of the upper femur, is less traumatic, preserves the natural shape of the femoral neck, maintains the normal biomechanical characteristics of the hip joint, and does not produce stress masking of the proximal femur.
Choice of treatment method
Acetabular dysplasia will lead to osteoarthritis, and patients may experience hip pain and limited hip motion. The surgical approach may improve or stop the degenerative process of the hip joint. Surgery should increase the weight-bearing surface and decrease the weight-bearing capacity of the joint from a biomechanical point of view. In order to make a rational choice of treatment, it is necessary to understand the pathological anatomy and to consider some of the surgical aspects, in addition to the patient’s requirements, the surgeon’s experience and skill.
By comparing different parameters of pelvic plain films, the hip joint is evaluated and appropriate treatment is selected to correct acetabular dysplasia and to distribute the stresses on the hip joint so that the adaptation of the hip joint is maintained or improved. Try to extend the articular surface of the hip joint with hyaline cartilage, because hyaline cartilage can provide better tolerance than fibrocartilage.
1. In practice Chiari pelvic osteotomy and acetabular capsulotomy are more effective methods. The main indications for Chiari pelvic osteotomy therapy are that the joint is displaced within 1-1.5 cm of its normal size, and that the joint is displaced beyond 1.5 cm. The Chiari pelvic osteotomy is combined with a cap to improve joint adaptation and to avoid excessive central extension. In case of excessive inward displacement or excessive inclination of the osteotomy cut, the strength of the abductor muscle is reduced and the balance of the hip joint is affected. However, these 2 types of treatment apply fibrocartilage to extend the joint and are not as durable as hyaline cartilage.
Capsulotomy is useful in the teenage years for all types of developmental anomalies and is a practical procedure because of the ease with which it can be combined with other procedures and its inherent safety. When performing periacetabular osteotomy for older children, the iliac epiphysis and the muscles and ligaments attached to it should be preserved intact in order to ensure normal development of the affected iliac bone and blood flow to the iliac epiphysis.
2.Salter pelvic osteotomy and other redirected osteotomy can be performed in adolescent patients with CE (central marginal angle) angle greater than 15°. Redirected osteotomy is particularly indicated when there is a congenital developmental anomaly with spherical maladjustment and insufficient acetabular coverage due to misorientation. Redirected osteotomy should be avoided in the presence of non-spherical adaptation, which will be replaced by non-spherical maladjustment.
3. For patients with an acetabular angle greater than 40°, the Pemberton periarticular osteotomy is preferable to the Salter pelvic osteotomy. The periarticular osteotomy lengthens the iliac bone less than the Salter pelvic osteotomy, so the pressure on the increased socket head is less. The periacetabular rotational osteotomy extends the articular surface with hyaline cartilage. In patients with abnormal hip development and previous surgery, the periacetabular osteotomy described by Ganz et al. can be applied when the hip joint is spherically adapted, and this procedure is a more general and successful treatment. Further evidence that periacetabular osteotomy can be performed in patients with abnormal hip development and previous surgery is provided by the long-term follow-up results of Trumble et al. The long-term follow-up rate after periacetabular osteotomy is 80%, and the remaining patients have to undergo arthroplasty due to aggravation of symptoms or failure of surgery.
4, hip dysplasia secondary to osteoarthritis, joint structure has been destroyed, there is joint pain with dysfunction, through other surgical methods can not relieve the pain of patients, consider artificial hip arthroplasty.
5. In childhood, pain is not common, and the pain endured is limping, so the focus is on function. In adolescence and early adulthood, function and appearance are very important.