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Myositis ossificans (MO) also known as heterotopic ossification is the formation of bone in soft tissue. The most commonly affected soft tissue are muscles that have been injured or traumatized. During a total hip replacement, muscles are often cut in order to remove the old hip and put the new one in. Calcifications form at the site of the injured muscle.
Pain, tenderness, and swelling are common. Muscle atrophy and loss of joint motion can also occur. The most significant risk factor has already been mentioned: trauma. Myositis ossificans is less likely to occur after a total disc replacement (TDR).
The reason for this is because muscles are damaged or cut during the TDR. The iliopsoas (hip flexor muscle) has to be moved out of the way with a retractor but it is not split or removed.
If you develop MO after a total hip replacement, this does not put you at increased risk of the same condition after every operation. The type of procedure is really the key factor.
Studies show that about four per cent of patients with a TDR develop ossification but it doesn't seem to affect motion or pain. The only way to know it is present is by looking at an X-ray.
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