Extract
Patients with an above-the-knee amputation often experience poor socket fit, which may become more problematic with minor weight changes, sweating, and skin problems. In 1999, the first author began using a transcutaneous, press-fit distal femoral intramedullary device with the distal, external portion serving as a hard point for attachment of an above-the-knee prosthesis (Fig. 1). The implant is placed in a retrograde fashion as a first stage, and approximately six to eight weeks later this is followed by stomatization, in which the distal aspect of the implant is exposed and an extension is added for fixation of the above-the-knee prosthesis. Thirty-seven patients underwent the procedure between 1999 and December 2009. The indications for surgery were persistent difficulties with the socket of an above-the-knee prosthesis after an above-the-knee amputation; the amputations had typically followed trauma but in some cases were for surgical treatment of a malignant tumor.
Patients with an above-the-knee amputation often experience poor socket fit, which may become more problematic with minor weight changes, sweating, and skin problems. In 1999, the first author began using a transcutaneous, press-fit distal femoral intramedullary device with the distal, external portion serving as a hard point for attachment of an above-the-knee prosthesis (Fig. 1). The implant is placed in a retrograde fashion as a first stage, and approximately six to eight weeks later this is followed by stomatization, in which the distal aspect of the implant is exposed and an extension is added for fixation of the above-the-knee prosthesis. Thirty-seven patients underwent the procedure between 1999 and December 2009. The indications for surgery were persistent difficulties with the socket of an above-the-knee prosthesis after an above-the-knee amputation; the amputations had typically followed trauma but in some cases were for surgical treatment of a malignant tumor.
Source of Funding
There was no external funding source for this investigation.
Brånemark in Sweden is credited with the idea of a percutaneous, osteointegrated prosthesis, which has been successful in dental implantation. In 1997, Brånemark performed the first procedure with a transcutaneous femoral intramedullary prosthesis, which was a 12-cm screw-type device for a patient who had undergone an above-the-knee amputation1. In 1999, ESKA Implants (Lubeck, Germany) produced the Endo-Exo-Femurprosthesis, which was first implanted into the femoral canal of a young man who had lost a leg in a motorcycle accident. Since then, the device has undergone design improvements, and by late 2009 it had been implanted in thirty-seven patients in Lubeck, Germany. The device is a modular, noncemented device that fits within the medullary canal of the femur and has a hard-point attachment that exits through the skin (Fig. 2).
There are two principal challenges with a transcutaneous femoral prosthesis of this type. First, with a bone-guided, soft-tissue-perforating femoral prosthesis, there has to be secure and durable fixation of the prosthetic shaft in the medullary canal of the femur. Second, there must be reliable shielding of the endoprosthesis against possible ascending infections arising from the dermal interface.
Stable fixation and osteointegration has been demonstrated with the spongiosa metal interface utilized on the stems. This interface provides a porous surface for bone ingrowth. This same surface has been utilized with hip prostheses with good results.
The dermal interface is achieved by performing the procedure in two stages, with the first stage consisting of a primary, closed procedure with the stump closed. The stoma is created six to eight weeks later, which allows the stump to heal with a solid seal around the prosthesis after tissue swelling has subsided.
Preoperative planning requires careful evaluation of the amputation stump, including scars or burns. Radiographs are used to determine the length and diameter of intramedullary implant needed. A computed tomography scan is helpful for determining the necessary implant size and limb length. Bone transport with distraction osteogenesis has been used successfully in some cases to obtain the necessary 12 to 15 cm of distal femur needed for the implant-stem placement (Fig. 3).
To minimize stump difficulties and soft-tissue problems, the operation is divided into two separate surgical procedures. The first stage involves reaming the femoral canal in a retrograde fashion. A tight press-fit is achieved with the spongiosa metal surface of the intramedullary component of the implant. The stump may also be debulked or scars can be revised at this point, and the stump incision is closed over the capped internal prosthesis (Figs. 4-A and 4-B).
Approximately six to eight weeks after the implantation of the endoprosthesis, when the wounds are well healed, the second procedure is done to create the stoma and attach the transdermal coupler (Figs. 5-A, 5-B, and 5-C). This is usually done as an outpatient procedure. The sharp cutter is passed percutaneously over the guide, producing a circular skin incision with a diameter that is intentionally larger than the coupler diameter. The coupler connects to a prosthetic leg. A quick-disconnect coupler can be used if desired, and essentially any type of external prosthesis may be utilized (Fig. 6).
Once the coupler is attached, the skin heals around it in a few days. The skin will epithelialize around the stoma channel from the outer skin margin, and connective tissue will fill in the gap down to the femoral cortex, in a manner similar to how a dental implant heals. The silicone device shown in Figures 6 and 7 is to hold the gauze but is not essential. Partial weight-bearing can begin as early as two or three weeks after the stoma procedure (Fig. 7). Full weight-bearing and a secure gait can be achieved four to six weeks after the stoma procedure, if the patient has no other medical issues.
At the time of reporting, thirty-nine Endo-Exo-Femurprosthesis devices had been implanted in thirty-seven patients in Lubeck, Germany. Exclusion criteria for use of this technique included diabetes, arteriosclerosis, mental disease, chemotherapy, pregnancy, skeletal immaturity, and infection. Additionally, patients needed to have problems with their current standard-socket above-the-knee prosthesis to be a candidate. Since many patients have good results with traditional-socket prostheses, these individuals were excluded from consideration for this surgery.
The demographics of the thirty-seven patients are detailed in Table I. Thirty of the thirty-seven patients were male. The ages ranged from seventeen to sixty-nine years and averaged forty-four years at the time of implantation; the average age at the time of the initial amputation was thirty-three years. Trauma was the principal reason for the original amputation (in thirty of the thirty-seven patients). Four patients underwent the amputation for treatment of a malignant tumor and three, for other reasons, including a previous infection at the site of a total knee arthroplasty and other failed surgical procedures. Two of the thirty-seven patients underwent bilateral implantation of an Endo-Exo-Femurprosthesis after bilateral above-the-knee amputation.
The outcomes were generally good, although, as expected, complications tended to be more common in association with the procedures done early in the series. The outcomes are detailed in Table II. Twenty of the thirty-seven patients underwent one or more revisions, with four undergoing removal of the implant. One implant was removed because of intramedullary infection, two removals were due to chronic soft-tissue problems at the dermal interface, and one was due to failure of the implant seven years after its insertion. Two of the four patients with a removal had successful reimplantation at a later date. Two patients underwent revision for subsequent pertrochanteric fracture. Fourteen of the thirty-seven patients underwent minor revisions because of problems at the stoma, with twelve of the fourteen undergoing exchange of the coupler as a result of soft-tissue problems or irritation. This problem was dramatically decreased later in the series by the use of smoothly polished couplers instead of rough textured couplers (Figs. 8-A and 8-B).
Thirty-five of the thirty-seven patients stated that they would choose to have this surgical procedure again under similar circumstances. The majority of patients have found the combination of the Endo-Exo-Femurprosthesis and a prosthetic leg to be very practical and comfortable (Fig. 9).
A number of lessons have been learned as the endo-exo technique has evolved over the past ten years. Initial implant designs were smaller, and only the first intramedullary component in the thirty-seven patients in this series failed as a result of fatigue fracture (at seven years after implantation); after this, the diameter of the intramedullary stem was increased. Current designs also include the option of utilizing a bracket distally to reduce bending moments.
With the initial designs, the transdermal coupler had a porous surface, but hypergranulation tissue sometimes appeared and was uncomfortable and occasionally necessitated soft-tissue debridement procedures. In these cases, replacing the coupler with a smoothly polished surface resolved these issues and has dramatically diminished soft-tissue problems and minor superficial infections. The devices in recent years have all included a smoothly polished coupler instead of a rough-surface coupler. Additionally, in the early procedures, the diameter of the stoma was the same as or slightly smaller than the coupler diameter. The procedure now allows sharp dissection of a stoma with a diameter that is slightly larger than that of the implant, which promotes epithelialization. Some patients have begun to engage in activities that they previously could not perform, such as diving and swimming.
Future directions for the use of this endo-exo technique include applying it for individuals with a tibial or humeral amputation. The majority of patients with a below-the-knee amputation have very good results with traditional prostheses, but a patient who was considering elective above-the-knee amputation because of persistent soft-tissue problems successfully underwent the first implantation of a tibial endo-exo prosthesis in May 2009 and had good results at one year. In October 2009, a combined endo-exo total knee implant was utilized, with preservation of knee motion. More long-term study is needed, but early results of this technique are promising.
Endo-Exo-Femurprosthesis devices were implanted over a ten-year period, with good results, in thirty-seven patients for whom a traditional-socket-type above-the-knee prosthesis had presented difficulties. It is especially useful for active, healthy people with a posttraumatic amputation and provides secure osteointegration with a low rate of deep intramedullary infection (one in thirty-seven patients). Additionally, it appears to lead to improved gait and comparatively less energy consumption, although these outcomes need to be quantified with additional studies.
Soft-tissue problems at the stoma can be an issue, but these complications have decreased with recent modifications of the technique, particularly the use of a smoothly polished coupler and a larger circular incision. Also, these soft-tissue problems usually resolve with local wound care and usually do not lead to an intramedullary infection of the bone. As the technique has evolved, this two-stage surgical procedure now presents a good alternative for management of patients with difficulties related to the prosthetic socket after an above-the-knee amputation.
Brånemark
R;
Brånemark
PI;
Rydevik
B;
Myers
RR. Osseointegration in skeletal reconstruction and rehabilitation: a review. J Rehabil Res Dev.
2001;38:175-81. [PubMed]