Two-Stage Revision for a Chronic Prosthetic Infection of a Megaprosthesis
Keywords: Limb salvage; Megaprosthesis; Infection; antibiotic spacer; Two-stage revision.
Limb salvage procedures for high-grade sarcomas have become the standard of care in many patients undergoing operative resection. Studies have continued to show that limb salvage procedures provide disease-free intervals similar to amputations [1,2], and most patients achieve a good functional outcome [2,3]. While these results have been encouraging, the use of an endoprosthesis for limb salvage procedures poses its own set of difficulties. Implants have a limited lifespan in an oftentimes young patient population. Combine this with the risk of periprosthetic fractures and infections, and reoperation rates remain a real problem in these patients. Infection is a serious and unfortunately common problem, with rates being reported with the use of a megaprosthesis ranging from 3-31% . Following an infection, the ability to perform a staged limb salvage revision procedure has been directly correlated with the condition of the surrounding soft tissues . The patient described in this case report is an example of such a case where a novel technique was utilized to preserve the soft-tissue envelope around a megaprosthesis, thus allowing for a successful 2-stage revision.
The patient is a 33-year-old Hispanic female with an extensive 20-year orthopedic history beginning at the age of 13 when she was diagnosed with an osteosarcoma of her left distal femur. An expandable prosthesis was surgically placed, which was subsequently replaced with a rotating hinge tumor prosthesis. Since that time, the patient has had 2 additional revisions due to a loosening of the prosthesis. Most recently, while out of the country, she fell and suffered a hemarthrosis, which led to the suggestion that she should have immediate surgery. A lateral parapatellar arthrotomy resulted in surgical drainage and removal or portions of the hardware. The patient presented to the emergency department of our facility with complaints of pain and swelling about the knee following 2 hyperflexion injuries over the last 2 months following her last surgery (Figure 1). No complaints of fever, chills, nausea, or vomiting were noted at the time. Lab results revealed a white blood cell count of 8,100 x 109/L, a C-reactive protein of 16.8 mg/L, and erythrocyte sedimentation rate of 53 mm/hour. A physical exam showed passive range of motion ranging from full extension to 45 degrees of flexion.
The previous extensile left lateral parapatellar approach was again utilized. After careful dissection, the distal femur prosthesis was encountered and was circumferentially dissected. Purulence was noticed over the proximal portion of the distal femur component. Once circumferential dissection was achieved around the proximal tibia, the hinge was disarticulated. The proximal junction of the distal femur modular component was disarticulated using a standard spreader device.
The patient presented is an example of the challenge that is often presented with treating osteosarcomas with limb salvage procedures. Multiple revision surgeries had been performed prior to the described operation, thus already compromising arguably the most important component of a 2-stage revision—the soft tissue envelope. This is a common occurrence among patients treated with megaendoprostheses with the average reoperation rate for these patients being reported at 2.6 procedures. However, with the use of a custom molded antibiotic spacer in this case, the difficulty level in performing the second stage of the revision was made significantly less.
Following the administration of long-term IV antibiotics, the patient returned to the OR for the second stage of her revision. The antibiotic spacer was removed and a new prosthesis was implanted. A medial release of the quadriceps musculature was utilized, thus allowing lateral excursion of the soft tissues and ultimately a loose closure. At the time of this paper, the patient had 2-year follow-up with infection control, and no evidence of hardware complications or soft-tissue breakdown (Figure 7).
This case demonstrates some of the unique complexities in treating high-grade sarcomas with limb salvage procedures. Owing to the high complication and reoperation rates associated with such operations, one must be prepared to deal with these situations as they arise. In the specific case of an infected megaprosthesis where a 2-stage operation is required, the surgeon could consider using the previous implant as a mold for the antibiotic spacer to ensure adequate spacing. Using bone cement, this is a quick and simple technique to provide a close match to the native prosthesis. By doing so, the soft tissue envelope is preserved, which has been shown to be an important aspect in limb salvage revision surgeries. REFERENCES
 Simon MA, Aschliman MA, Thomas N, Mankin HJ. Limb-salvage treatment versus amputation for osteosarcoma of the distal end of the femur. J Bone Joint Surg Am. 1986;68(9):1331-7.
 Rougraff BT, Simon MA, Kneisl JS, Greenberg DB, Mankin HJ. Limb salvage compared with amputation for osteosarcoma of the distal end of the femur. A long term oncological, functional, and quality-of-life study. J Bone Joint Surg Am. 1994;76(5):649-56.
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