Functional analysis of cases of tumor endoprostheses with deep infection around the knee: a multi institutional study by the Japanese Musculoskeletal Oncology Group (JMOG).
BACKGROUND
Although intensive studies have been conducted to clarify the incidence, risks, and management methods of deep infection of tumor endoprostheses, limited data have been published in respect of the impact of such deep infection on the function of the corresponding limb.


METHODS
Clinical data of 125 patients (infection group 57, control group 68) with malignant bone and soft tissue tumors around the knee enrolled with the Japanese Musculoskeletal Oncology Group were collected. We analyzed the impact of deep infection of tumor endoprostheses on the limb salvage status together with that on the function of the salvaged limb. The definition of deep infection was based on the recommendations of the Centers for Disease Control and Prevention. The functional evaluation was based on the functional classification system established by the International Society of Limb Salvage and the Musculoskeletal Tumor Society.


RESULTS
Infection together with extracapsular resection was demonstrated to be a risk factor for late amputation. There were no significant differences in the functional scores for "pain," "support," "walking," or "gait" between the infection and control groups. The risk factors identified for a loss of score for "functional activities" were deep infection, age, duration of operation, and extracapsular resection. The infection group also showed a significant lower score loss in "emotion". As for the overall functional scores, the risk factors identified for lower scores were deep infection and age. The mean scores for the infection group and control group were 19.3 (64.3 %) and 21.6 (72 %), respectively. Although the difference was confirmed to be statistically significant, the actual difference was only 2.3 (10.6 % reduction).


CONCLUSIONS
Infection was a major risk factor for late amputation. Limbs salvaged by management of deep infection may show loss of function; however, the impact may be limited.