Hip Dysplasia

Adam Hart

Daniel J. Berry

Key Concepts

Hip dysplasia entails a spectrum of deformity, which must be evaluated preoperatively and addressed at the time of surgery.
- The acetabulum is shallow, typically deficient anteriorly and superiorly, and may have additional bone loss or erosion from a subluxated femoral head.
- The femur often, but not always, has excessive anteversion and may also have posterior overhang of the greater trochanter, coxa valga, and a narrow canal (especially in the medial-lateral plane).
Goals of surgery include:
- In most cases, restore the hip’s true center of rotation thereby improving the abductor lever arm and locomotive kinematics and minimizing joint reactive forces.
- Implant an acetabular component that is supported as well as possible by host bone and that gains good long-term fixation (typically with an uncemented implant).
- Select an appropriate femoral implant that accommodates the patient’s anatomy and provides sufficient hip stability.
- Minimize complications, chiefly overlengthening and traction injury on the sciatic nerve, loosening of the acetabular or femoral components, and nonunion of an osteotomy.
The Crowe classification system subdivides dysplastic hips by the level of hip subluxation (Figure 15.1) and provides a practical framework by which the surgeon can systematically assess, plan, and execute the reconstruction.
- Crowe 1 (Figure 15.2A): An uncemented acetabular component in the true acetabular region with slight medialization and a cemented or uncemented stem based on patient age, bone quality, and bone geometry.
- Crowe 2-3 (Figure 15.2B and C): An uncemented component at or near the true acetabular region, if necessary with autograft augmentation or high hip center or component medialization. A cemented or uncemented stem based on patient age and bone geometry.
- Crowe 4 (Figure 15.2D): An extra-small uncemented acetabular component in the true acetabular region with an uncemented stem and usually shortening subtrochanteric osteotomy (refer to Chapter 16).

Sterile Instruments and Implants

Perioperative: Consider having intraoperative electromyography (EMG) monitoring for the sciatic nerve (if potentially lengthening more than 3 cm or 10% the length of the femur), cell saver and tranexamic acid, Foley catheterization, general anesthesia without paralysis or spinal anesthesia, and intraoperative fluoroscopy or radiography as needed.

Implants: Uncemented acetabular components with multiple screw holes and available in small diameters (in addition to small-diameter femoral heads). Femoral components that can best
accommodate the patient’s anatomy such as a monolithic conical or modular stem with a proximally coated triangle and distal fluted body versus a small cemented stem. Uncemented fixation is typically preferred in younger patients (Figure 15.3).

Figure 15.1 ▪ Crowe classification: draw the inter-teardrop line (A), then take the ratio of (B/C) to determine percent dislocation: I for 0 to 50%, II for 50 to 75%, III for 75 to 100%, and IV for >100%. If the femoral heads are significantly deformed, one can use the pelvic height (D/5) to approximate (C). Used with permission of Mayo Foundation for Medical Education and Research. All rights reserved.

Extras: High-speed burr with 6.5-mm round tip, 4.5-mm screws, and cables or cerclage wires.

Surgical Approaches

Anterolateral or posterolateral based on surgeon preference.
When femoral shortening is required, there are 2 options:
- A transtrochanteric approach with sequential proximal femoral resection provides excellent exposure but has the disadvantage of advancing the trochanter onto a progressively narrow and tubular proximal femur. There is a high risk of trochanteric nonunion with this technique.
- Combining an anterolateral or posterolateral approach with a subtrochanteric osteotomy (this is the authors’ preferred technique and is discussed in detail in Chapter 16).

Figure 15.2 ▪ Radiographic examples of dysplastic hips with Crowe 1 (A), 2 (B), 3 (C), and 4 (D) classification.

Figure 15.3 ▪ Select the femoral component that best accommodates the patient’s anatomy and bone quality. Options include proximally coated tapered (A), fully porous coated cylindrical (B), modular (C), fluted tapered (D), and cemented (E) stems.

Preoperative Planning

Review the radiographs and template the implants to determine:
- The amount of lengthening that would occur if the cup and stem are placed at the desired location (generally, a shortening osteotomy should be considered for anticipated lengthening greater than 3 cm).
- Access bone defects superiorly and available bone medially to estimate the size of the acetabular component.
- Ensure the availability of femoral components that are adequately suited for the patient’s anatomy (canal diameter and proximal femoral morphology).
Special considerations for patients with bilateral hip dysplasia:
- Given that most patients will require a period of partial weight bearing after surgery, simultaneous bilateral hip replacements are not recommended.
- If both sides are of similar severity, stage the procedures and start with the most symptomatic side. Any bone removed (e.g., the femoral head) from the first hip may be conserved (frozen) for the second hip.