DDH is a relatively common hip joint disease. In patients with DDH, the acetabular articular surface presents with varying degrees of narrowing and tilt, and the center of the hip joint gradually shifts outward and upward to form a false socket. The femoral head is small and flat. The trunk Angle of the femoral neck is enlarged, presenting a deformity of valgus hip. The anterior inclination of the femur increases and the position of the greater trochanter shifts to the rear. The soft tissue around the hip joint is structurally altered due to dislocation. The capsule becomes thick and elongated. Gluteus medius muscle development is poor, walk line presents level. The adductor and iliopsoas muscles become shortened. The relative shortening of the peripheral vessels and nerves of the hip joint makes it vulnerable to injury during surgery [1, 2, 6].
Crowe typing is commonly used in patients with DDH. For Crowe Ⅰ ~ Ⅱ type patients, conventional THA can be applied to achieve good clinical effect. But for Ⅲ ~ Ⅳ type patients, acetabulum obviously stunted growth. The iliac crest lateral femoral head impinges on the cortical region of the bone and produces some reactive bone, causing the femoral head to impingle the iliac crest into a false acetabulum. In patients with high dislocation, the femoral head is completely dislocated and moved upwards. Acetabular development is relatively shallow and difficult to find and Limb shortening on affected side. In common THA, acetabular prostheses may be unstable due to an external and upper acetabular defect. If the limb lengthens by more than 4cm during total hip replacement, the sciatic nerve may be injured due to the pull [7].
Acetabular reconstruction is often used for acetabular defects. The commonly used methods [7–9] are as follows. ⑴ Reconstruction of true acetabulum with autologous femoral head grafting ⑵ Reconstruction of the acetabulum in the pseudoacetabulum. ⑶ endoplasty of true acetabulum. Reconstruction of the real socket restores the anatomical center of the hip joint and restores limb length and abductor function, and studies have shown that the wear rate of the real socket prosthesis is lower, so it is generally accepted. During the operation, because it is the use of their own femoral head materials, materials are convenient, but relatively speaking for the surgical personnel technical requirements are higher [10–12]. In our research, patients with high dislocation and combined with acetabular defect, bone grafting in true acetabular position was used to construct the cover. The length of the limbs of the patients recovered after surgery, and the abduction function of the affected hip recovered well. X-ray showed no bone absorption around the prosthesis, which achieved good clinical results (Fig. 1).
For Crowe Ⅳ type patients, due to the complete dislocation of the femoral head and shortening of the affected limb, the sciatic nerve never reached its normal length. When doing orthopaedic surgery, if the limb is prolonged too much, it is easy to cause serious consequences of nerve injury. Therefore, osteotomy is often needed. Meanwhile, shortened femur osteotomy can also correct the unequal length of lower limbs and also make the shortened abductor muscle restored to its normal length and angle [13, 14]. However, femur osteotomy also has a series of disadvantages [13, 15, 16]. ⑴ Patients with increased trauma, increased blood loss, prolonged operation time. ⑵ The osteotomy is difficult to fix, and the internal fixation is unstable and easy to break. ⑶ There is a risk of nonunion in the osteotomy, increased postoperative pain and delayed recovery. It has been reported that the rate of bone nonunion after femoral shortening osteotomy is up to 8%~29%. Flanagin et al [17] used postoperative traction combined with delayed reduction to treat Crowe Ⅳ DDH without femoral osteotomy and obtained good results. Some studies have also reported that there is no need for femoral osteotomy, and the treatment of DDH with high dislocation by direct pry and bar reduction has also achieved good results [18–20]. According to the report, we think that although the omitted problem because of femoral bone cutting operation difficulties, but also exist in dislocation and postoperative complications of nerve injury remains, such as postoperative nerve palsy ratio as high as 13% and the bone is not correct because no femoral rotation of knee valgus walking to claudication, so we will not be respected [21]. At present, the main surgical methods of femoral osteotomy are shortened subtrochanteric osteotomy, including oblique, "Z" shape, transverse shape and so on [22–27]. Oblique and z-shaped osteotomies increase the contact area of bone surface, so the bone healing is faster after osteotomy. However, it is not easy to rotate after osteotomy, so correcting the femoral pronation is more difficult. Transverse osteotomy can be performed multiple times and it is easy to correct the Angle of foretilt of femur through rotation. The disadvantage is poor anti-rotation stability, which is often solved by auxiliary fixation [6]. Howie et al [28] reported cemented Total Hip Arthroplasty With Subtrochanteric Osteotomy in Dysplastic Hips. They applied subtrochanteric transverse osteotomy to correct the femoral rotation and assisted monocortical screw plate fixation, and achieved good results. We also used THA with "Z" shape subtrochanteric osteotomy to treat Crowe Ⅳ DDH before, which not only restored the length of the limb, maximally restored the abductor function of the affected hip, but also reduced the postoperative sciatic nerve injury to a minimum. The osteotomy of the patient recovered ideally after surgery, and achieved good clinical results (Fig. 2). However, our experience is that this osteotomy method is relatively complicated, it is difficult to correct the anterior tilt of the femur during surgery, and it is not easy to place it when auxiliary internal fixation is selected after osteotomy, so we gradually adopt the method of transverse subtrochanteric osteotomy.
Reported in recent years, application of Wagner Cone prosthetic treatment of hip dysplasia has made great progress, but there are many scholars believe that Wagner Cone prosthesis is more suitable for application in Crowe Ⅱ ~ Ⅲ type patients, with small femoral bone marrow cavity isthmus and large anterior inclination of femur but does not need to osteotomy [29–31]. However, for patients with a femoral rake Angle greater than 40°, it is very difficult to correct the femoral rake Angle change by using Wagner Cone intraoperatively through excessive rotation of the femoral shaft, which is likely to cause fracture of the proximal femur. This has been demonstrated in our previous operations in patients with high dislocation. During the operation, we found that it was difficult to correct more than 40° forward tilt of the femur, so femur osteotomy had to be performed. Meanwhile, the distal fixation of the prosthesis was not reliable and auxiliary fixation had to be performed at the same time (Fig. 3). It has also been reported that the combined prosthesis with adjustable anterior inclination (S – ROM prosthesis) can be used to adjust the size of the anterior inclination of the femoral neck by means of osteotomy under the femoral trochanter [32, 33]. At the same time, there are also reports that the modular femur component may cause fracture risk at the link of the prosthesis due to fretting, corrosion and other reasons [34, 35].
We used THA with a common prosthesis and transverse subtrochanteric osteotomy with a monocortex locking plate for internal fixation. We first placed the acetabular prosthesis. After that, femur lateral medullating was performed until the femur lateral prosthesis size was selected. Because of the thin development of femur and the narrow femoral marrow cavity in DDH patients, preligated wire can be used to avoid the splitting of proximal femur during reaming. Even if we used the method to prevent prefixation wire during femoral reaming, the splitting of femoral marrow cavity during reaming occurred in patients with a smaller femoral marrow cavity. After the removal of the prosthesis, the femur was amputated with a pendulum saw about 2cm from the subtrochanteric. The length of the osteotomy could be reduced by pulling down after inserting the femoral side prosthesis to determine the length of the limb extension. The overlapping part is the osteotomy length, which is generally 2cm. After osteotomy, the femoral lateral prosthesis was repositioned with reamedullary reamulation. At this time, the anterior inclination of the femoral neck was corrected according to the position of the patient's patella. We have to be careful that there is no rotation of the femur. After the femoral prosthesis is placed, the monocortical locking plate is placed on the external posterior or anterior lateral side of the femur for screw fixation. Early on, we had a lack of experience in placing plates on the tension side of the femur, the pure lateral side (Fig. 4). Because of the presence of the femoral medullary cavity prosthesis, we can only apply the monocorcortical locking screw for fixation, so the plate fixation is not very strong. We dare not let the patient carry on the load of the affected limb too early to prevent the rotation of the prosthesis. Later, we put the plate on the posterior or anterior side of the femur. In these two positions, we can place a double-layer cortical screw in the position of the proximal greater trochanter of the femur, so that the plate can be fixed more firmly. We generally ensure that one bicortical screw is placed in the proximal femur, two or three bicortical screws are placed in the distal end of the prosthesis, and the rest are monocortical screws. It is advisable that the length should not touch the prosthesis in the femoral medullary cavity. In this way, we can ensure adequate support and secure fixation at the osteotomy (Fig. 5). Meanwhile, bone mud generated by acetabular grinding can be implanted into the osteotomy to promote fracture healing. Based on this approach, we can allow patients to perform early load bearing on the affected limb to promote compression healing of the osteotomy fracture end. Of course, the orthopedic operation of subtrochanteric osteotomy requires relatively high technical level of doctors, because they need very rich experience in anatomical and surgical techniques. Meanwhile, the operation of osteotomy and internal fixation theoretically increases the risk of non-healing of the osteotomy of patients. Our experience is that our technique can minimize the complications of vascular and nerve injury caused by limb lengthening as long as the patient is carefully and reasonably planned before operation, precise operation during operation, and well-coordinated rehabilitation guidance after operation. We did not encounter similar complications in postoperative follow-up. Only 1 patient experienced dislocation one week after the operation because of bad posture. All patients who accepted THA with transverse subtrochanteric osteotomy and monocortical locking plate achieved good clinical results. Because we only use a normal prosthesis and a single cortical locking plate, we call it simple prosthesis, simple technique.
In summary, due to the complexity of the local anatomy of patients with DDH, THA has become relatively complex and has a relatively high number of complications. However, as long as the preoperative perfect imaging examination, the development of a reasonable surgical program, the correct intraoperative operation, including the balance of abductor muscle, soft tissue release, reconstruction of acetabular defects, the correct treatment of the femoral side, and the ideal postoperative rehabilitation and exercise, the patient will be able to obtain good clinical results.