When Should You Be Wary Of Hypertrophic Bone Formation?

By Pamela M. Jensen, DPM

Post-surgical hypertrophic bone formation can be a frustrating problem. It has been identified at fracture, osteotomy and amputation sites. The majority of patients with hypertrophic bone formation are largely asymptomatic and practitioners often identify the condition via radiographs they get for other pathologies. However, those who are symptomatic often have a problematic non-healing wound at the site and can complain of pain, swelling or even decreased range of motion if a joint is involved.
Most of the literature addresses hypertrophic bone formation as a complication associated with acetabular fracture surgery, total hip arthroplasty and below/above knee amputations in children. Yet there is very little literature in the podiatric or orthopedic realm with regard to hypertrophic bone formation in the foot.
Armstrong, et. al., conducted a study of 92 consecutive diabetic patients that confirmed a 45 percent incidence of hypertrophic bone formation two years after patients underwent isolated partial ray amputations. They defined hypertrophic bone formation as bony regrowth of 3 mm or greater, which they noted at the site of a surgical resection or osteotomy of bone.1

What Studies Reveal About The Risk Factors
The etiology of hypertrophic bone formation is largely unknown. However, researchers have determined that surgical or traumatic manipulation of the bone can stimulate factors that may promote overgrowth.2 Known risk factors for hypertrophic bone formation include gender, the location of osteotomy and the type of instrumentation you use. In Armstrong’s study of patients with isolated partial ray amputations, there were some interesting findings in regard to the incidence rates of hypertrophic bone incidence.1
• Fifty-eight percent of male patients had hypertrophic bone.
• When the surgeons performed osteotomies distally to the surgical neck of the metatarsal, 34 percent of the patients had hypertrophic bone.
• When surgeons used manual bone cutting instrumentation, 74.2 percent of the patients experienced hypertrophic bone formation. When they used power instrumentation, 29.5 percent of the patients wound up with hypertrophic bone.1
Upon reviewing the literature, there is no evidence of hypertrophic bone formation in the healing of disarticulation procedures. This phenomenon of bony overgrowth has only been documented in procedures requiring an osteotomy. In addition, osteotomies in the metaphyseal region have a greater incidence of overgrowth.1,2

Looking at it on a microscopic level, you would notice that multi-potential fibroblasts are stimulated by an osteotomy. These fibroblasts produce osteoid, which eventually can result in hypertrophic bone formation. The periosteal layer of hypertrophic bone formation is different from the periosteal layer you would find in normal lamellar bone. Upon maturation, however, hypertrophic bone is histologically identical to normal lamellar bone.3,4 Researchers have also shown that overgrowth occurs from the medullary canal following amputations in young rabbits.5

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