Surgery of DDH of femur
May. 11, 2020
Surgery of DDH of femur
When the center of the acetabulum has changed little,as with Crowe type I and type II dysplasias, femoral length is not problematic and the femoral reconstruction generally is straightforward. Small-diameter cemented or cementless stems generally are satisfactory. The femoral component must be placed in neutral or slight anteversion in relation to the axis of the knee joint. Marked anteversion of the femoral neck can be misleading when positioning the femoral component, and anterior instability may occur, particularly if the acetabular component has been placed in additional anteversion. Excessive femoral anteversion can be corrected with a modular cementless femoral component that can be rotated into any degree of version. This does not correct the posterior displacement of the greater trochanter, however, which may cause impingement in external rotation.
For Crowe type III and type IV hips, femoral length is more problematic. When the prosthetic socket has been placed in the true acetabulum, the femur must be translated distally several centimeters to reduce the prosthetic femoral head into the acetabulum. Often the tissues most limiting this distal translation are the hamstrings and rectus femoris rather than the abductors. In such cases, a femoral shortening osteotomy allows reduction of the femoral head into the true acetabulum without extensive soft tissue release. Osteotomy of the greater trochanter and resection of 2 to 3 cm from the proximal femoral metaphysis may be necessary to permit reduction of the joint without causing undue tension on the sciatic nerve or fracture of the femoral shaft (Fig. 3-77). The bone should be resected 0.5 cm at a time, and trial reductions are repeated until enough shortening is obtained to reduce the hip without undue soft tissue tension. The narrow canal and the resection of the metaphyseal flare of the femur often require the use of a component with a small, straight stem to ensure a proper fit and to allow space for an adequate cement mantle.
Sponseller and McBeath described a technique of subtrochanteric femoral shortening using the femoral component for intramedullary fixation. This approach allows Correction of excessive femoral anteversion along with the posterior displacement of the greater trochanter while avoiding trochanteric osteotomy and the potential for nonunion. The architecture of the proximal femoral metaphysis is preservedand the orientations of the greater trochanter and abductors are corrected to restore hip mechanics and prevent instability and limp. A standard stem design also can be used.Additionally, the level of the femoral osteotomy provides excellent exposure of the acetabulum if structural bone grafting is required (Fig. 3-78). The femur is provisionally prepared with reamers and broaches before the femoral osteotomy. The depth of reaming of the distal canal should take into account the length of the segment of femur that will be removed in the shortening. The osteotomy is made just distal to the lesser trochanter, and the two fragments areretracted anteriorly for acetabular preparation and implantation. A trial reduction is then carried out with the femoral osteotomy. The depth of reaming of the distal canal should take into account the length of the segment of femur that will be removed in the shortening. The osteotomy is made just distal to the lesser trochanter, and the two fragments are retracted anteriorly for acetabular preparation and implantation. A trial reduction is then carried out with the femoral component in the proximal fragment alone. Traction is applied to the distal femoral fragment, and the overlapping portion is resected from the distal fragment. Final preparation of the distal fragment is then carried out. A larger diameter stem may be required to obtain a tight fit after removing the segment from the femur. The two fragments are reduced, the proximal fragment is derotated to 10 to 15 degrees of anteversion, and the osteotomy site trimmed for optimal apposition. The final stem is implanted maintaining the proper rotation of the fragments as well as the implant. The stem must be rotationally stable within both fragments to ensure union. Prophylactic cerclage wiring of the distal fragment (or both fragments) helps prevent fractures since a very tight fit is required. The resected portion of femur can be bivalved and placed over the osteotomy as onlay grafts. Becker and Gustilo reported using a chevron-shaped osteotomy to improve rotational stability. A short oblique or step-cut osteotomy fixed with cerclage wires also provides greater rotational stability than a transverse osteotomy but adds a degreeof technical difficulty. We have used a modular stem with distal flutes to gain rotational stability with a transverse osteotomy, and union has been reliable (Fig. 3-79).
Note: this article comes from CAMPBELL’S OPERATIVE ORTHOPAEDICS by S. Terry Canale James H. Beaty.