The Ertl technique of creating a distal tibiofibular bone bridge during the performance of a transtibial amputation has very strong supporters. The most ardent proponents claim that patients can bear weight through the terminal end of the amputation stump without discomfort. More moderate supporters of the technique suggest that the bone bridge allows the fibula to more fully participate in weight-bearing, by creating an enhanced stable platform. This enhanced platform allows dissipation of weight-bearing over a larger surface area, making weight-bearing more comfortable and efficient1-7
. The information used to claim both of these potential benefits is based on Level-V experience and the observations of experienced clinicians treating amputees.
This investigation was undertaken in an attempt to provide objective outcome data to address whether distal tibiofibular bone-bridging provides a real, or simply a perceived, benefit. All of the bone-bridge procedures in this study were performed by a single experienced amputation surgeon, and all of the prostheses were constructed by the same experienced certified prosthetist.
It is interesting to note that all of the patients who underwent revision surgery with the creation of a bone bridge had had a subjectively poor-quality soft-tissue envelope observed preoperatively by both the surgeon and the prosthetist. Some of the perceived benefit to these patients may have been secondary to the improved soft-tissue envelope obtained at surgery12
. In spite of these apparent improvements, the patients did not demonstrate improved PEQ scores as compared with those of similar patients who had undergone traditional surgery by the same surgeon and similar prosthetic fitting.
The data derived from this investigation lead to more questions than answers. The normal foot is a unique organ of weight-bearing. It allows prepositioning of a stable platform and a unique durable plantar soft-tissue envelope to act as a shock-absorber at initial loading (heel-strike) and a stable “starting block” at terminal stance (push-off). When an amputation stump is fashioned into a terminal weight-bearing organ, it is composed of only two bones and no motion segments and its soft-tissue covering is not as durable as the sole of the foot. The patient bears weight in a prosthesis composed of durable materials that, in concert with the tissues of the amputation stump, must attempt to recreate functional weight-bearing. It is too simplistic to suggest, without taking into account both the characteristics of the weight-bearing osseous platform and the encasing soft-tissue envelope, that simply fusing the two bones together distally will allow an individual with a transtibial amputation to accomplish efficient weight-bearing within a prosthetic socket.
This investigation had several methodological shortcomings. The numbers of patients were small. The control and Brazilian populations were historic, not concurrent, and there was no attempt to match for age, activity level, or disease. There is also no way to determine if, by excluding patients with chronic pain or other disability, we were setting an unobtainable standard.
Much of our current appreciation of the method of weight-bearing within a prosthetic socket is based on clinical observation. Many of our finite-element-analysis models are based on clinical observation without the support of objectively measured data15
. We also do not fully understand the unique relationship between the osseous platform and the surrounding soft-tissue envelope. The data gleaned from this investigation suggest that more information is needed about the science of residual limb-prosthetic socket loading and about the gait of amputees before we can fully appreciate the potential benefit of distal tibiofibular bone-bridging. The American bone-bridge group did not appear to fare any better than the patients in whom the same experienced amputation surgeon created a reasonable platform without a bone bridge as well as a well-constructed soft-tissue envelope. The apparently better outcomes in the Brazilian group may be culturally biased, with the possibility that these individuals had lower expectations regarding their status following the amputation surgery and rehabilitation. The information gained from this investigation suggests that more objective data on weight-bearing with a prosthesis are needed before bone-bridging can be recommended as a standard component of transtibial amputation.