Review Question - QID 218204

This patient presents with clinical and radiographic evidence of heterotopic ossification (HO) after undergoing a total hip replacement (THA). At this time, the HO should be allowed to mature (or assessed for maturity) and, given his current symptoms, basic laboratory evaluation should be sought to ensure he does not have an underlying periprosthetic joint infection.

Heterotopic ossification (HO) is a common radiographic finding within the first year after total hip arthroplasty (THA). The degree of severity reported is classically based on radiographic findings via the Brooker classification system (Illustration A). Most cases are inconsequentially asymptomatic and seldom cause pain or limitations in range of motion (i.e. Brooker I/II). However, approximately 15% may develop clinically significant stiffness affecting activities of daily living (i.e. Brooker III/IV). The best treatment is prevention, particularly for patients with known risk factors (i.e. ankylosing spondylitis, history of HO at other sites, history of traumatic brain injury, etc.). The postoperative use of nonsteroidal anti-inflammatory medications and/or perioperative administration of 700-800 cGy of radiation to the surrounding area are the mainstay of prophylactic treatment options. However, once formed, clinically significant HO can only be treated with surgical excision. In general, an HO maturation assessment should be obtained before excision as time to maturation varies widely in the literature. This can be performed via serial radiographs over multiple months with unchanged findings or by normal uptake on a bone scan. The patient's serum alkaline phosphatase level, elevated during active stages of HO, should normalize once maturation is complete. However, serum alkaline phosphatase is nonspecific and should be taken into account as one portion of the clinical decision-making. In any case of persistent pain after THA, underlying periprosthetic joint infection should be ruled out as a potential etiology.

Purcell and Lachiewicz provided a comprehensive review article regarding the management of heterotopic ossification after modern THA. The authors currently endorse HO-specific prophylaxis treatment for patients with bilateral hypertrophic osteoarthritis of the hips, unilateral osteoarthritis with diffuse idiopathic skeletal hyperostosis (DISH) of the lumbar spine, ankylosing spondylitis, and any patient with heterotopic bone formation after a contralateral hip surgical procedure. The authors conclude that a preoperative CT scan should be employed to aid in determining the degree of bony resection required, plan for the most appropriate implants needed, and delineate the location of key neurovascular structures.

Legosz and colleagues provided a similar review of HO after THA. The authors discuss that many different NSAIDs have been recommended for HO prevention, however, they all appear to have equivalent efficiency. The authors highlight the importance of ensuring HO maturation before excision utilizing a bone scan. They conclude that if HO excision is required, it is imperative to utilize NSAIDs and radiation therapy together to prevent recurrence after HO excision.

Cobb and colleagues performed a retrospective review of their case series involving 53 patients who underwent heterotopic ossification excision after the primary surgery of THA. At a 3.5-year follow-up, the authors reported a significantly increased hip range of motion in patients at a mean added 34 degrees of flexion, 22 degrees of abduction/adduction, and 21 degrees of rotation arc. They also reported that worse outcomes occurred in patients who underwent HO excision for pain alone as the indication rather than restricted range of motion. The authors concluded that HO excision results in significantly improved functional outcomes but cannot be expected to predictably alleviate pain.

Figures A and B demonstrate this patient’s 6-month post-operative radiographic findings demonstrating Brooker grade II HO formation. Illustration A demonstrates the Brooker classification system.

Incorrect Answers:
Answer 2&3: Both of these prophylactic treatments are considered appropriate for HO prevention. However, both are ineffective if used in a delayed manner once HO has formed. The only treatment for HO once it is formed is surgical excision.
Answer 4: As with other areas of HO within the body, there is a high recurrence if it is excised before maturity. As discussed, HO maturity should be confirmed before performing excision.
Answer 5: When performing HO excision, the risks and benefits of partial versus attempted full excision must be weighed. Careful dissection is necessary to avoid iatrogenic injury to surrounding soft tissue and neurovascular structures, particularly soft tissue stabilizers and the sciatic nerve. It is prudent to have constrained liners available as resultant instability after excision is common.