Radiographically evident heterotopic ossification (HO) around the hip and knee is an important clinical finding that must be carefully considered before any anticipated surgery.

Both extrinsic (head injuries, cerebrovascular accidents, burns, ankylosing spondylitis, etc.) and intrinsic factors (injury to the abductor musculature and extensor mechanism, surgical approach, retained bone debris, and hemorrhage, etc.) contribute to the overall risk of HO.

Patients who have previously formed heterotopic bone in the past are more likely to do so again and potentially to a greater extent after revision surgery.

Once heterotopic bone is present on radiographs, nonoperative measures are ineffective at impeding progression of the ectopic bone formation.

HO after joint arthroplasty most often manifests as ectopic bone in the abductor musculature in the hip and along the anterior femur adjacent to the extensor mechanism in the knee (Figures 42.1A-D and 42.2).

Although isolated heterotopic bone excision is rarely performed, the primary indication is severe restriction in functional range of motion (ROM). Pain is not an indication for isolated excision of HO (Figure 42.3A-C).

Excision of ectopic bone should not be performed before radiographic maturation of the heterotopic bone. Three-dimensional imaging with CT scan before surgery can define the exact location of HO and help with preoperative planning.

Surgery through ectopic bone is associated with considerable blood loss. Coagulopathies should be corrected and anticoagulants stopped before surgery.

External beam irradiation and nonsteroidal anti-inflammatory medications (NSAIDs) have proven extremely effective in reducing and altogether preventing severe HO in high-risk patients after revision surgery. Most surgeons prefer NSAIDs for prevention of HO in moderate-risk patients and external beam radiation in patients at high risk (such as when symptomatic HO is being excised).

Routine hip retractors

Blunt elevators

Osteotomes

Bone wax

Autologous blood recovery system

Hip: The patient is placed in a lateral decubitus position, which allows for a more extensile exposure if needed.

Knee: The patient is supine with an ipsilateral bump under the pelvis and tourniquet placed proximally around the thigh.

Draping should allow for adequate access for any extensile approach.

Hip: The preferred approach of the authors in the majority of revision total hip arthroplasty is an extensile posterior approach. However, the operative approach for HO excision should be tailored to the location of the HO. The goal is effective HO excision and preservation of muscle tissue to the degree possible.

The skin incision is dictated partly by previous incisions but should be based on the planned operative approach.

In cases with extensive heterotopic bone present, and when wide exposure is needed for complex femoral or acetabular reconstruction, a trochanteric osteotomy can be performed both for exposure purposes and to help protect and maintain the remaining abductor musculature.

Knee: The preferred approach for the authors is an extensile medial parapatellar approach.

The skin incision is dictated by the previous incisions, but ideally the most lateral usable incision is chosen. If there is any concern for wound issues, there should be a low threshold to involve our plastic surgery colleagues in helping plan the skin incision and to prepare for any subsequent soft tissue procedure that may be required.

Preoperative orthogonal radiographs (anteroposterior [AP] and lateral) of the involved joint are critical for the appropriate surgical planning.

Brooker et al classification of HO around the hip based on the AP pelvic radiograph is the most commonly used classification system for Hip HO (Table 42.1 and Figure 42.4):