High Hip Dysplasia

Key Concepts

In high hip dislocation the femoral head is in a false acetabulum superior to the true acetabulum (Figure 16.1A).
The goal is to place the acetabular component in the true acetabulum; this is where the best acetabular bone is, and it optimizes hip biomechanics. The true acetabulum is small, so small components are needed, including small-diameter femoral head sizes.
Once the acetabular component is placed in the true acetabulum, reduction of the hip is difficult, and the sciatic nerve is at risk for stretch injury, unless further measures are taken.
The most common modern method of achieving safe reduction is shortening subtrochanteric osteotomy (Figure 16.1B and C). Other methods including (1) greater trochanteric osteotomy along with proximal femoral shortening and (2) prolonged skeletal traction without shortening have been described but have drawbacks and are less commonly used today.
Different subtrochanteric osteotomy configurations have been described, but a transverse osteotomy is the simplest, allows both shortening and rotational correction, and can be fixed rigidly by the implant if implants that provide rotational fixation of the proximal and distal fragments of bone are chosen (Figure 16.2).
The femoral bone typically has a small diameter; therefore, small-diameter implants need to be available (see Figure 16.1).
Most patients are young, so uncemented implants are preferred, particularly because they work well in conjunction with subtrochanteric osteotomy.

Sterile Instruments and Implants

Routine hip retractors
Narrow (1-cm) ribbon retractors
Large pointed bone reduction forceps
Serrated bone reduction forceps
Large and small oscillating saws
Power burr
Cerclage cables
Uncemented acetabular component components (with instrumentation): include very-small-diameter cups down to 40 mm or below.
Uncemented femoral components (and instrumentation) that have a proximal triangle for fixation of the proximal fragment and also have flutes, sharp corners, or extensive porous coating to provide firm rotational control of the distal fragment.

Positioning

Lateral decubitus position.
Drape to allow access to proximal pelvis and entire femur.
If desired affix sciatic nerve monitoring equipment to limb before draping.

Figure 16.1 ▪ A, Radiograph of patient with high hip dislocation. Note the characteristic findings of high hip center in false acetabulum, small but preserved true acetabulum, and small femoral bone diameter. B, Postoperative radiograph after total hip arthroplasty with concomitant shortening subtrochanteric femoral osteotomy. C, Five years postoperatively after osteotomy healing.

Surgical Approaches

Posterior approach to the hip is preferred (the abductor attachments and vascular supply to the proximal femoral fragment is left undisturbed). Anterolateral approaches also are acceptable.
Femur at level of the osteotomy will be exposed by elevating a small section of vastus lateralis from femur.

Preoperative Planning

Know patient’s preoperative leg length discrepancy.
Template cup size and position.

Template femoral component size.

Figure 16.2 ▪ A, Radiograph of patient with high hip dislocation. B, Radiograph immediately after total hip arthroplasty with shortening subtrochanteric osteotomy. C, Radiograph after osteotomy healing.

Figure 16.3 ▪ A, Templating showing the amount of leg lengthening that would occur without femoral shortening. The templating allows calculation of the desired amount of shortening and also of the location of the osteotomy (below the flare of the proximal prosthesis but allowing for sufficient distal fixation). B, Templating allows calculation of the desired level of the proximal osteotomy. It should be below the proximal flare of the prosthesis, but allow for sufficient distal fixation of the osteotomy by the implant. C, After exposure of the hip and false acetabulum, and femoral neck osteotomy, ream and proximally prepare the proximal femur. D, Perform the transverse osteotomy at the preplanned level. E, Translate the femur anteriorly to expose the true acetabulum. F, Insert the cup into the true acetabulum. G, Perform trial reduction with the trial only in the proximal fragment. H, Traction on the limb provides estimate of the amount of subtrochanteric shortening required and should be correlated with the preoperative plan. I, The distal osteotomy is performed. J, The subtracted osteotomy fragment is kept vascular and split longitudinally with a saw. K, Trial reduction of hip and osteotomy. L, The osteotomy is trimmed as needed to perfect bone apposition. M, Placement of the real implants. N, Use of vascular strut to provide extra fixation and healing potential.

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