Background
Despite remarkable advances in vascularized composite allotransplantation (VCA) over the past 2 decades, there has been general resistance to embrace the notion of lower extremity allotransplantation One of the principal concerns raised is the potential tissue burden associated with lower extremity allotransplantation; however, no formal studies to assess the anticipated volume of biological substrate to be transferred in lower extremity VCA has been performed to date.
Methods
We performed volumetric analyses of 10 patients' lower extremities utilizing DICOM data from standard lower extremity CT scans and Vitrea Enterprise Suite 674 software For each patient, standard 3D renderings of the lower extremities were generated and segmented into discrete tissue phases based on Hounsfield units Volumetric assessment were then made of each lower extremity at both the below knee (BK) level and above knee (AK) level Similar volumetric analyses were performed on a single patient's upper extremity CT scan to use as reference.
Results
Ten patients' lower extremity CT scans were analyzed. Mean patient age was 52±7 years, with mean BMI of 29 ± 4 and a 50:50 male:female gender split Volumetric analyses at the BK level were: total 2660 ± 676cc, muscle 1369 ± 307cc, fat 859 ± 387, bone 432 ± 79cc; at the AK level: total 7483 ± 1731cc, muscle 3632 ± 768cc, fat 2940 ± 1203cc, bone 921 ± 159cc By comparison, a full upper extremity control demonstrated the following volumetric results: total 2968cc, muscle 2005cc, fat 629cc, bone 334cc Approximate matching of a subset of the lower extremity patient analyses to the upper extremity control revealed that a unilateral BK transplant would involve transfer of 90% of the total tissue volume of a full upper extremity, while a unilateral AK transplant would involve transfer of 252% of the total tissue volume of the same.
Conclusions
In the case of BK level transplants, anticipated tissue transfer will likely be less than that already performed successfully in high upper extremity transplant procedures AK level transplants, however, will entail a higher level of tissue burden than what has previously been witnessed in VCA cases reported worldwide, and may require special considerations to mitigate the likely metabolic impact of larger scale ischemia-reperfusion injury and immunologic load.