Developmental dysplasia of the hip (DDH) is a dynamic developmental disorder that causes hip dysfunction due to congenital dysplasia of the acetabulum, proximal femoral deformity, adaptive soft tissue contracture, and biomechanical changes. Total hip arthroplasty (THA) is one of the main methods for the treatment of DDH, which can relieve the tension of soft tissue, restore the rotation center and stability of hip joint, and improve the deformity of lower limbs. Compared with Crowe type Ⅰ ~ Ⅲ DDH patients, the anteroposterior diameter of the acetabulum is smaller and shallower, and the variation of the anteversion angle is greater; the femoral head dysplasia even disappears, the femoral anteversion angle is greater, the greater trochanter is posterior, and the anteroposterior diameter of the femur is greater than the left and right diameter [1-2];Compared with the normal femur, the intramedullary parameters changed greatly, especially the medullary cavity near the lesser trochanter level was significantly narrowed [3]; long-term hip dislocation led to more serious local soft tissue contracture, resulting in difficulty in hip reduction [4]. Therefore, the establishment of stable hip joint structure and the recovery of bone loss have become one of the difficulties in surgery.
1. Why need a revision surgery?
The primary reason for revision after initial THA in Crowe type Ⅳ DDH is aseptic loosening of the prosthesis.In addition, periprosthetic infection, periprosthetic fracture, osteolysis, bone loss and prosthesis fracture and instability are also common causes of revision.。
2 Bone defect classification
The acetabular and femoral side of Crowe type Ⅳ DDH patients are often accompanied by a certain degree of bone defect during revision, and the residual bone mass and defect of acetabular and proximal femur can be measured by X-ray and CT before revision.At present, the most commonly used clinical bone defect classification standard is Paprosky classification, and the acetabular and femoral bone defect classification in this classification standard is summarized.
2.1 Paprosky's acetabular classification
Bone defect classification can not only indicate the degree of bone loss, but also reflect the stability of the implanted acetabular prosthesis [5-6], so as to select the appropriate acetabular side prosthesis and components.Paprosky classification is based on imaging findings to analyze the direction and degree of acetabular cup displacement, to judge the degree of acetabular bone landmark destruction, and to determine the degree of bone defect on the acetabular side, which can be divided into three types.Type ⅰ: a small amount and limited bone loss around the acetabulum, which can still maintain the original shape and structure of the acetabulum.Type Ⅱ: slight displacement of the upper medial, upper lateral and medial acetabulum, but the anterior and posterior columns of the acetabulum are well maintained, and the acetabulum still has some stability, but the bone defect needs some special components or Cage to repair and reconstruct.Type III: The acetabulum has a large number of annular bone loss, the center of the hip joint moves up severely (> 3 cm) [7-8], and even bone discontinuity or pelvic instability, which is the most serious type of bone defect on the acetabular side. Acetabular reconstruction and restoration of the center of rotation directly affect the success or failure of revision surgery.See Figure 1.
2.2 Paprosky's classification of femoral side
The Paprosky classification of the femoral side is based on the extent of bone defect in the proximal and distal isthmus of the femur, including the location of bone defect, the extent of proximal residual bone, the length of isthmus and its distal residual supporting bone, and is divided into three types.Type Ⅰ and Ⅱ: mild to moderate to severe proximal metaphyseal bone defect, which is easy to deal with during revision.Type III: severe proximal defect, but the femoral shaft bone remains intact, depending on whether the length of remaining bone mass at the isthmus of the femur reaches 4 cm [9].
3 Reconstruction of the acetabulum
Because of the structural deformities of Crowe type Ⅳ DDH patients and a series of complications after the first replacement, most of the revision prostheses can not achieve the initial stability of the joint, adequate bone coverage or improve the morphological deformities.
3.1 Application of biological fixed cup
When there is a Paprosky type II or above bone defect in the acetabulum and the ordinary standard biological hemispherical acetabular cup can not provide stable fixation, a large acetabular cup prosthesis (Jumbo cup) can be used to increase the contact area with the bone around the acetabulum and increase the attachment point, so as to achieve long-term stability.
3.2 Bone grafting
Impacted bone graft is a commonly used bone defect repair technique in clinic. For patients with small acetabular bone defect, impaction bone graft or prosthesis such as reinforcing ring, metal block and Cage can be used to restore bone mass, ingrow blood vessels, shape bone and improve bone reserve at the acetabular bone defect, so as to achieve the purpose of long-term stability of prosthesis [10].
3.3 Application of metal augments
At the same time, the contact area between the bone tissue at the defect site and the metal block is increased, which can promote bone ingrowth.The metal blocks have different shapes and sizes, and can be inosculated with the bone defect part to the greatest extent by selecting a proper metal block.Tantalum block and bone trabecular metal prosthesis have good biological characteristics and friction coefficient, and the use of metal block to repair bone defects can also increase the acetabular cup containment and enhance stability.
3.4 Application of cage & three-wings cups
There is less bone in the medial wall and anterior column of Crowe type Ⅳ DDH patients, and some patients have a large range of bone defects during revision surgery, resulting in acetabular discontinuity, and the acetabular cup can not be effectively fixed during revision, so Cage or three-wing acetabular cup can be used for acetabulum reconstruction at this time.
3.5 3D printing technology
In patients with Paprosky type Ⅲ bone defects, the acetabulum is not continuous due to massive bone loss, which leads to pelvic instability and difficulty in acetabular prosthesis implantation. 3D printing technology can be used to make a three-dimensional model of the patient's pelvis, through which the operator can intuitively understand the anatomical defects of the acetabulum, understand the local anatomical structure and the scope of the defect, better plan before operation, select appropriate components to repair the defect, or use 3D printing technology to prepare special prosthetic components to maximize the recovery of hip support, mobility and stability.
4 Reconstruction of the femoral side
4.1 Surgical difficulties
。Femoral deformity in DDH patients changed with the degree of hip dislocation.Among them, Crowe type IV is characterized by high dislocation of the hip joint, the most serious changes in the morphology and function of the proximal femur, and the high incidence of coxa vara and valgus [11-12]. When the femoral component of DDH patients is loose and accompanied by cavity and segmental bone loss, the revision of the femoral side is challenging.Such as implant removal, preservation of bone mass, reconstruction of proximal femur, selection of appropriate prosthesis implantation and stabilization have become the difficulties of femoral revision surgery [13].
4.2 Precautions for operation
There may be osteosclerosis in the proximal femur and narrow medullary cavity of Crowe type Ⅳ DDH patients during revision surgery. When taking out the biological femoral stem prosthesis, the sclerotic bone tissue and fibrous tissue wrapped in the proximal femur should be removed as far as possible, and the prosthesis should be fully exposed and the bone-prosthesis interface should be separated to minimize iatrogenic bone loss.To prevent the occurrence of cortical perforation and fracture, and to avoid blindly injecting the prosthesis [14-15].The success or failure of revision surgery depends on the preoperative and intraoperative evaluation of the degree of proximal femoral bone defect, the design, selection and fixation of implanted prosthesis, and the judgment of the quality of residual bone reserve.
4.3 How to choose the correct stem?
The modular modular prosthesis is often used in the revision surgery of Crowe Ⅳ DDH patients.The segmental modular prosthesis can better meet the actual needs of the patient's femur, the distal femoral stem can achieve adaptive stability, and the proximal cuff can effectively prevent postoperative osteolysis and fixation loosening.For Crowe Ⅳ DDH revision surgery, the femoral prosthesis should be selected according to the patient's femoral defect, so as to achieve femoral reconstruction and maintain the stability of the prosthesis as the primary purpose.
5 How to choose the liner?
At present, the prosthesis lining commonly used in surgery includes metal-metal interface, metal-polyethylene interface, ceramic-polyethylene interface and ceramic-ceramic interface [7,11].Polyethylene material is the main type of choice at present. At present, highly cross-linked polyethylene lining has gradually replaced the traditional polyethylene lining, which has high wear resistance, reduces osteolysis and wear between prostheses after operation, and is conducive to maintaining long-term prognosis [16].Most patients with Crowe type Ⅳ DDH were young when they underwent primary THA, and they had a large amount of daily activities. Considering the bone defect caused by wear particles during revision and the difficulty of revision, ceramic lining should be selected as far as possible during primary THA or revision. If it is impossible to select due to size limitation, highly crosslinked polyethylene lining can be selected [17].O as to prolong the service life of the prosthesis and reduce the number of revision operations.
6 Conclusion
。Aseptic loosening of the prosthesis is the most common cause of revision after the initial THA for Crowe type Ⅳ DDH. Repeated dislocation of the joint, bone defect, infection, nonunion at the osteotomy site, and prosthesis fracture may also lead to revision surgery.Hip joint reconstruction and femoral prosthesis implantation are the main difficulties in revision surgery for such patients, which need comprehensive and accurate preoperative assessment and measurement, taking full account of the patient's anatomical deformity, bone defect degree and possible intraoperative conditions.It is worth noting that bone defect is still the most important problem in revision surgery for Crowe type IV DDH patients. Although Cage technology, modular components and customized prosthesis have been proved to have good early and medium-term efficacy at this stage, the long-term survival rate still needs to be further clarified.With the continuous development of artificial intelligence technology in the medical field, personalized prosthesis components will also provide more options for the revision of such patients.
References
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Post time: Apr-16-2024