Review Question - QID 219901

A patient with HO formation 4 months after THA should be observed with repeat radiographs, as HO typically requires 6 to 18 months to mature following the surgery (Answer 1).

Symptomatic HO complicates approximately 7% of primary THA. Typically, pain improves within six months, and most patients do not require surgery. However, surgical excision may be necessary for symptomatic cases after the HO matures. Monitoring for HO maturation can be achieved through serum alkaline phosphatase levels, which are initially elevated but should normalize after maturation. Alternatively, a bone scan can be used to show decreased activity. To help prevent HO, indomethacin can be administered for six weeks postoperatively, or a single irradiation dose of 7-8 Gy can be effective.

Legosz et al. reviewed the diagnosis, prophylactic measures, and treatment of HO in the setting of THA. The cited risk factors for the development of HO after THA include hip ankylosis, male gender, and previous history of HO. Diagnosis is typically established with a single AP radiograph, and the Brooker classification can be utilized to grade severity. The most effective prophylactic treatment is radiation therapy or the administration of nonsteroidal anti-inflammatory drugs, with the prescribed regimens being 7 Gy and indomethacin, respectively. However, the definitive treatment for symptomatic HO after maturation is surgical excision or revision arthroplasty.

Iorio et al. also reviewed the risk factors, prevention, and treatment of HO after arthroplasty. This group states that patients at high risk for developing HO after THA include men with bilateral hypertrophic osteoarthritis, patients with a history of HO in either hip and patients with posttraumatic arthritis characterized by hypertrophic osteophytosis. Similarly, patients with ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis, Paget's disease, or unilateral hypertrophic osteoarthritis have a moderate risk of developing HO after THA. High-risk patients for developing HO after TKA include those with limited knee flexion, high lumbar bone mineral density, hypertrophic arthrosis, excessive periosteal trauma, anterior femur notching, and those requiring forced manipulation post-surgery. The authors conclude that preoperative radiation effectively prevents HO after THA, along with postoperative prophylactic drug regimens and single-dose radiation treatments. Without prophylaxis, HO recurrence after surgical excision is likely.

Cobb et al. reviewed the functional outcomes after the excision of HO in the setting of THA. Fifty-three cases of symptomatic HO were evaluated after THA to determine the impact of surgical excision without additional procedures. The mean follow-up was 3.5 years for range of motion and 7.8 years for radiographic assessment. Results showed a significant increase in range of motion: an average increase of 34 degrees in flexion, 22 degrees in abduction/adduction, and 21 degrees in rotation. However, patients who had surgery solely for pain did not experience complete symptom relief. Thus, while surgical excision improves functional outcomes, it does not guarantee pain relief.

Figures:
Figure A: This is an AP radiograph of a right THA demonstrating HO formation proximal to the greater trochanter, likely within gluteus minimus.
Figure B: This is a lateral radiograph of an elbow with distal humerus hardware in place and significant HO consolidation both anteriorly and posteriorly.
Figure C: This is an AP radiograph of a left shoulder with significant inferior HO formation, causing a pseudo arthrodesis of the shoulder.
Figure D: This is a lateral radiograph of a total knee arthroplasty with significant HO consolidation inferiorly, which can likely impede extension.
Figure E: This is an AP radiograph of a left THA with significant HO formation and likely a loose acetabular component.

Incorrect answers:
Answer 2: Significant HO 2 years status post traumatic brain injury is likely matured and should be excised if symptomatic and restrictive.
Answer 3: Significant HO 1 year after a complete spinal cord injury is likely matured and should be excised if compromising function.
Answer 4: Significant HO 1 year status post TKA with decreased activity on bone scan is indicative of maturation and can be excised.
Answer 5: Significant HO that is limiting range of motion 1-year status post THA should be excised.