When Should You Be Wary Of Hypertrophic Bone Formation?

By Pamela M. Jensen, DPM

Review The Diagnostic Indicators For Hypertrophic Bone
You’ve achieved normal amputation stump healing without spur formation when there is cortical bone density across the end of a mature bony stump. On the other hand, hypertrophic bone formation of a stump will show osteopenia and periosteal spurs but no cortical bone density across the medullary canal. Researchers have shown that this growth occurs from the medullary canal.6 The resulting ossification, which is evident on plain film radiographs, occurs approximately one to three months after surgery.4,7,8
When sensate patients have hypertrophic bone following an osteotomy, they will often have symptoms of pain, swelling and erythema. You may also notice a progressive stiffness and decreased range of joint motion during the postoperative period.4 Non-sensate patients will have similar clinical signs (with the exception of pain). Also be aware that these patients are at higher risk from complications, such as plantar ulceration, following a mid-metatarsal amputation. In a study at the University of Texas Health Science Center at San Antonio (UTHSCSA), patients were approximately eight times more likely to reulcerate at the site of ray amputation in the bony overgrowth group.1
In your differential diagnosis, researchers say you should check for post-op infection with osteomyelitis, exuberant periosteal bone formation, heterotopic bone formation and tumor.4 When evaluating non-sensate diabetic patients, you should also include acute Charcot in your differential diagnosis.

At UTHSCSA, we have noted many of the patients who develop hypertrophic bone following a partial foot amputation will also develop a non-healing wound at this site. There is often copious serous drainage from these wounds but cultures and biopsies are negative for soft tissue or bone infection.

Essential Tips On Treatment
We often manage these patients by emphasizing offloading, local care and hyperbaric oxygen but many require revisional amputation. If you suspect hypertrophic bone, you should pursue radiographic evaluation. Findings may include poorly defined radiodense areas without trabecular patterns. These areas of suspect bone enlarge and are continuous with the underlying bone in the form of irregular outgrowths and trabecular architecture. Ossification can occur at some distance from the joint and become attached to the subadjacent bone, forming an exostoses.4
You should reserve treatment for symptomatic cases of pain or recurrent ulceration. Be aware that excising immature bone is associated with a high degree of recurrence in addition to disturbing the periosteum that may control the degree of bone remodeling.1,6 Bone scans are advocated in the literature to determine bone activity. You should not consider surgical intervention until there is substantially decreased uptake.3 When it comes to prophylaxis for heterotropic bone formers, you may include etidronate disodium (Didronel).
You should give etidronate disodium in a dose of 20 mg/kg for one month prior to surgery and three months following the procedure. Researchers have shown that this regimen reduces the formation of hypertrophic bone.6
However, studies have failed to prove the efficacy of etidronate disodium in the treatment of ectopic bone formation secondary to myositis ossificans progressiva.2 A study has revealed that irradiation with 2,000 rads decreases the formation of heterotopic bone if you administer it early in the treatment course.6 Attempts to cap the end of amputations with a variety of metallic, silastic and other synthetic materials have not been consistently successful in eliminating bony overgrowth.6 Many advocate addressing the periosteum when considering any revisional procedure. Some propose using 1 to 2 cm of periosteal stripping while others suggest that you keep the protective envelope intact. This is clearly an area that is worthy of further research.

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