Patient choice – are there weight limits when using ex-fix?
External fixation (ex-fix) is often used as an adjunct to internal fixation when correcting rocker bottom flat foot due to Charcot arthropathy. The reason that ex-fix is used is that the frame, or ex-fix device, can be used to carry weight thereby offloading the internal fixation. With the use of an ex-fix device, patients are able to ambulate earlier which reduces many of the post-op complications in this high-risk population of patients. The ex-fix device is also used to protect the internal fixation from excessive load-bearing and potential failure.
Lower extremity reconstruction with ex-fix enables off-loading of the foot by applying body weight to the various types of pins anchored directly in the tibia, talus (ankle bone) and calcaneus (heel bone). When these pins are loaded with weight-bearing, they apply sheer force to the bone. When using ex-fix in patients with higher BMI, how much sheer force can the bone tolerate?
I performed a Charcot reconstruction 3 weeks ago on a patient with a body mass index of 79 (450 lbs/5’3” tall). In my initial interview with this patient, I recommended below the knee amputation. A second opinion concurred with my recommendation but the patient wanted to attempt limb salvage. Due to her size, she was a poor candidate for reconstruction with internal fixation alone. I opted for combined internal fixation and ex-fix with primary load applied by the frame to half-pins in the tibia.
To date, the patient has done well with weight-bearing limited to 25-50% of full weight. Wounds appear healthy with no issues. This patient will be in her ex-fix for four months.
What are the weight limitations of lower extremity ex-fix?
When considering ex-fix in Charcot reconstruction, BMI needs to be considered. A review of the literature shows no papers that discuss BMI in use of lower extremity ex-fix. With a BMI of 79, we certainly are testing the limits.