If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Treatment of large osseous defects remains a difficult surgical challenge. Autografts and allografts have been known to undergo late collapse, because these options are not specifically designed to withstand the high loads of the foot and ankle. The inability to achieve the correct shape for reconstruction further limits their application. Large osseous defects will result during salvage after failed Lapidus bunionectomy, explantation of failed total ankle replacements, and nonunion of Evans calcaneal osteotomy. Each of 3 patients received a 4WEB custom 3-dimensional (3D) titanium truss implant (Patient Specific Custom Implant; 4WEB Medical, Inc., Frisco, TX) for reconstruction. The mean follow-up period was 17.33 ± 3.51 months. Significant improvement was seen in pain, with a successful return to activities of daily living. The 12-month postoperative computed tomography findings demonstrated incorporation of the implant to the surrounding cortical and cancellous bone. No signs of delayed complications, such as stress shielding or implant failure, were found. This is the first case series to describe the use of a custom 3D-printed titanium truss implant to successfully contribute to reconstruction in the setting of failed elective foot and ankle surgery. This technology might play an important role in limb salvage of osseous defects that would otherwise require bone block arthrodesis with structural allograft or autograft bone.
Treatment of large osseous defects continues to be a clinical challenge for foot and ankle surgeons. Reconstruction of these injuries has been described after posttraumatic defects, avascular necrosis, severe pilon fracture, hindfoot and ankle nonunion, Charcot neuroarthropathy, failed total ankle arthroplasty, and osseous tumors (
). Despite advances in reconstruction techniques, complication rates have remained high, with subsequent amputation rates of 19% in patients with revision surgery (
). Reconstruction of large osseous defects has traditionally required the use of a structural graft to fill the void and maintain height, length, and desired correction (
). Autografts or allografts are sources of structural grafts to fill the defect space and promote consolidation. However, both structural bone graft options have associated disadvantages, including high rates of nonunion, graft infection, donor site morbidity, recalcitrant pain, and limb length discrepancies (
Tibio-talo-calcaneal arthrodesis with retrograde compression intramedullary nail fixation for salvage of failed total ankle replacement: a systematic review.
Autografts have largely been associated with donor site morbidity, a longer hospital stay, limited quantity, and concerns for quality in a compromised host (
). Allografts and autografts have been shown to undergo late collapse and structural failure, leading to either less satisfying results or failure of the procedure. Furthermore, these options are limited by an inability to achieve the precise anatomic shape for reconstruction according to the shape of the osseous defect (
). These grafting techniques are also not specifically designed to withstand the high loads and forces found in the foot and ankle, which predisposes these techniques to graft collapse (
). Thus, a grafting option with improved structural integrity and the ability to accommodate internal fixation is needed.
Additive manufacturing, commonly referred to as 3-dimensional (3D) printing, is the process of creating a predefined object by precise deposition of materials in a layer-by-layer fashion (
). 3D printing allows implants to be tailored to each patient's pathoanatomy. The conception of patient-specific implants was first introduced in the cutting guide instrumentation in total knee replacements (
). The theoretical advantage of 3D printing is the seemingly limitless customizability in size, shape, and fixation options, thus opening a new frontier for reconstruction in patients previously relegated to complex limb salvage efforts or amputation. To the best of our knowledge, the present report is the first to describe the versatile and durable application of a custom 3D-printed truss implant (Patient Specific Custom Implant; 4WEB Medical, Inc., Frisco, TX) for the treatment of large osseous defects in the foot and ankle with >1 year of follow-up.
Patients and Methods
An institutional review board approved the study, and all study participants provided informed consent before study enrollment. A retrospective medical record review of 3 consecutive patients in whom elective foot and ankle surgery had failed was undertaken. The patients had undergone radiography of the foot pre- and postoperatively. Multiple debridements, intravenous antibiotics, bone cultures, and an antibiotic cement spacer with external fixation were used to assist in the eradication of infection, if present. Once the culture and biopsy results were negative, the wound was deemed clean and ready for reconstruction. All 3 patients were counseled preoperatively regarding their reconstructive options. They were given the choice of a structural autograft or allograft or the 3D-printed titanium truss implant. Each patient had consented for use of a custom-designed, patient-specific 3D-printed titanium truss cage by 4WEB Medical (4WEB Medical, Inc.) in conjunction with additional internal fixation. The patients were sent for a preoperative computed tomography (CT) scan for preoperative planning. Once the CT images of the patient's pathoanatomy were available, the manufacturer initiated the design team, which involves management and design engineers. The surgeon is invited to provide recommendations for fixation desires. Once a design has been reached, a schematic is sent to the surgeon with hardware projections and dimensions. If screws are to traverse the implant, those can be sent to the company ahead of time so the exact measurement can be used. Supplemental hardware such as trial-sizing implants, trial implant replica, and directional guides are also designed at this time. Once the surgeon has approved the implant, the implant is manufactured and shipped to the healthcare institution for final inspection by the surgeon. Finally, the implant is sterilized before implantation.
The preoperative diagnosis was failed total ankle replacement, septic nonunion Lapidus bunionectomy, and nonunion Evans calcaneal osteotomy in 1 patient each. All 3 patients underwent an implant protocol with a preoperative wash the night before and the morning of surgery. All the patients were given a popliteal nerve block before induction. The patients were brought to the operating room and placed in the supine position with a thigh tourniquet. General anesthesia was obtained. The lower extremity was scrubbed in the operating room before the formal preparation. The choice of bone graft was by surgeon preference. In 1 case, the distal one third of the fibula was excised and morcelized for an autograft. This was mixed with bone marrow aspirate from the proximal tibia and then packed into the truss cage. One patient underwent reamer-irrigator-aspirator bone graft harvest of the ipsilateral femur. The guidewire was placed in the greater trochanter and entry reaming performed. A size 13 reamer was used to procure the graft, which was packed into the truss cage before implantation. Dissection was continued down through scar tissue until the osseous defect was visualized. The edges were debrided to bleeding margins with the tourniquet released. The trial implant spacers (4WEB Medical, Inc.) for the cage were inserted into the bony defect in accordance with the preoperative surgical plan and adjusted to obtain the proper alignment and positioning. With the trial implant in the patient, the appropriate guidewires for internal fixation were inserted, followed by cannulated overdrilling or reaming. The cage was filled with the autograft and inserted into the final defect. Once the planned internal fixation had been placed, adequate hemostasis was achieved. The wound was closed with 2-0 absorbable and nonabsorbable suture. A well-padded splint was placed in neutral alignment. No drains were used.
The sutures were removed at 3 weeks, followed by application of a short leg cast, with the patient kept non-weightbearing. At 3 months postoperatively, the patients were allowed to weight bear with 50% body weight in a walking cast or boot. The patients were advanced as tolerated through physical therapy. A 12-month postoperative CT scan was obtained of each patient.
Results
Successful limb salvage of large osseous defects occurred in the setting of a failed total ankle arthroplasty, septic nonunion of Lapidus bunionectomy, and nonunion of Evans calcaneal osteotomy. All 3 patients were treated from August 2015 to September 2016. The mean cubic volume of the custom implants measured 26.9 × 46.8 × 27.2 mm. The patient demographic data, failed index procedure, implant characteristics, fixation methods, and limb salvage are presented in the Table.
TablePatient demographics, failed index procedure, implant characteristics, fixation methods, and limb salvage
Variable
Patient Number
1
2
3
Age (y)
38
29
64
Gender
Female
Female
Female
Failed procedure
Total ankle replacement implant failure
Evans calcaneal osteotomy, septic nonunion
Lapidus bunionectomy, septic nonunion
Dimensions (mm)
Height
NA
NA
Overall
25.4
Superiorly
43.8 × 35.5
Inferiorly
43.8 × 44.6
Length
NA
Overall
24.5
70
Anteriorly
18.5 × 25.6
14.5 × 13.5
Posteriorly
24.4 × 27.0
28.7 × 19.5
Orthobiologics
Trinity ELITE DBM (Orthofix, Lewisville, TX) and autogenous fibular bone graft
5 mL Paragon V92 MSCs (Paragon28 Inc., Englewood, CO) and 40 mL of BMA from right tibia
Trinity ELITE DBM (Orthofix) and 40 mL of bone graft major from left femur by reamer-irrigator-aspirator
Follow-up (mo)
21
14
17
Limb salvage
Yes
Yes
Yes
Complications
Superficial wound dehiscence
None
None
Fixation
13 × 200-mm retrograde nail with 6 interlocking screws (Orthofix)
7.0-mm screw (Paragon28 Inc.)
6.5-mm beaming screw with two 4.0-mm interlocking screws (Wright Medical Technologies, Memphis, TN)
Abbreviations: BMA, bone marrow aspirate; MSCs, mesenchymal stem cells; NA, not applicable.
Of the 3 patients, 2 (66%) healed uneventfully and 1 (33%) developed a postoperative complication. The patient who had experienced a postoperative complication had previously undergone total ankle replacement, with skin compromise over the anterior ankle. This was successfully treated with local wound care and oral antibiotics. All 3 patients (100%) were able to ambulate without pain at 12 weeks and were fitted for a custom orthotic or brace. No clinical evidence was seen of impending skin breakdown, infection, or nonunion at the 12-week follow-up visit in any of the 3 patients (100%). The 6-month postoperative CT scan demonstrated >50% osseous integration of the implant and the supplemental bone graft within the implant itself. No early signs of subsidence, implant collapse, or loss of correction were seen at a mean follow-up point of 17.33 ± 3.51 months.
Discussion
Large osseous defects are difficult for foot and ankle surgeons to treat. Judicious investigation should be first undertaken to ensure appropriate neurovascular status and eradication of any infection. The published data regarding management of segmental bone loss involves the use of autografts and allografts in isolation or with the aid of orthobiologics (
). The iliac crest autograft is considered the reference standard for bone block arthrodesis. It has a relatively low cost and high osteoinductive potential; however, it has been associated with donor site morbidity in 73.3% of cases (
) reported on a cohort of 32 patients (100%) who had undergone distraction calcaneocuboid arthrodesis using an autogenous iliac crest graft. Of their 32 patients, 16 (50%) experienced either osteolysis or collapse of the graft (
). The use of an Allograft eliminates donor site morbidity but carries the risk of disease transmission and late collapse. The incidence of nonunion has been reported to be greater with allografts. McGarvey and Braly (
) reported a greater incidence of nonunion with allograft bone than with autogenous iliac crest for triple arthrodesis. Therefore, autografts and allografts, although proven beneficial, have been known to undergo late collapse, leading to structural failure. Also, their use can be limited by the ability to truly achieve the correct shape for reconstruction according to the shape of the osseous defect. Synthetic grafts and bone substitutes have also been used to assist surgeons in treating osseous defects (
). However, these ancillary options, similar to autografts and allografts, are not specifically designed to withstand the high loads and forces found in the foot and ankle.
Tantalum is a porous metal that provides a rapid and efficient source of soft tissue attachment (
) reported on the use of a porous tantalum trabecular metal implant (Zimmer, Warsaw, IN) for ankle arthrodesis after failed ankle replacement in 2 patients and posttraumatic ankle arthritis in 1 patient. All 3 patients reported improvement in pain and functional outcome on questionnaires and proceeded to fusion at a mean of 3 months (
) reported on a series of 18 patients (100%) who had undergone subtalar bone block arthrodesis with porous tantalum implants (Zimmer). They reported that all 18 patients (100%) had achieved fusion at a mean final follow-up period of 17.7 months (
). Additionally, tantalum metal spacers might need to be modified intraoperatively using a high-speed burr or saw, which could compromise the implant's ability to integrate with the host bone (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). These allow for a mechanically robust construct that resists the load-bearing forces of the foot and ankle. The truss configuration acts as a lattice for bone grafting procedures such as autograft and allograft bone chips or combined with the Masquelet technique (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). Therefore, the custom 3D truss design has the potential for successful union rates without concern for late collapse or subsidence. The patient-specific 3D printing of the truss implant (4WEB Medical, Inc.) allows for precise shape configuration that obviates intraoperative modification and, thus, the possibility of jeopardizing its structural integrity. Although the design of the truss construct is theoretically stronger than that of porous tantalum, no biomechanical studies have compared the load failures of these 2 metallic spacers.
The design of the implant must consider a number of critical factors to ensure a favorable outcome. These include the mechanical, anatomic, and functional aspects that are unique to each case (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). The 3D configuration of the implant must be designed to allow it to be successfully implanted through the planned surgical exposure, cognizant of the constraints imposed by the local anatomy and previous implants (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). Inherent stability is provided by the titanium struts, which are rough and therefore assist in resisting torsional forces. To enhance rotation stability, miniature spikes or “cleats” can be added to the struts. These will provide not only torsional resistance but also resistance against shear (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). Once the general size, shape, and contours of the implant have been configured to closely match the defect, one must consider how to provide stability. The implant can be created to allow the fixation to traverse the implant itself. Fixation can include retrograde nails, plates, or screws or a combination thereof. Compression should be achieved across the device. The truss functions to provide a side of compression and tension, which potentiates bone growth.
In our series, the original preoperative planning was carried through in the intraoperative setting. An intramedullary retrograde nail (Orthofix, Lewisville, TX) was used in the patient with failed ankle arthroplasty to stabilize the truss component as osseointegration occurred between the implant and host. In the patients with the failed Lapidus bunionectomy (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13) and Evans calcaneal osteotomy (Fig. 14, Fig. 15, Fig. 16), the truss implants were designed to accommodate screw fixation. Plates were considered in the preoperative planning; however, ultimately, this type of fixation was not incorporated into the final design of the implants. Owing to the local pathoanatomy and previous soft tissue compromise, plates would have increased the likelihood of becoming a source of prominence and impingement. Additionally, the junction of the titanium truss and plates creates a concentrated stress point, resulting in the potential for hardware failure (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
). If plates are to be used, the plate should span the entire titanium truss component to minimize this stress point and adequate soft tissue should be available to cover the implant and plate (
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
Fig. 5Radiograph after debridement of nonviable soft tissue and bone with application of antibiotic cement spacer and monorail external fixator. The bone was debrided to clinical bleeding bone.
Fig. 8(A) Side, (B) anteroposterior, and (C) plantar views of the preoperative computer model of the patient-specific 3-dimensional printed truss implant (4WEB Medical, Inc.) depicting the planned placement of 6.5-mm beaming screw with two 4.0-mm interlocking screws.
Fig. 9(A) Diagram of the computer model implant geometry showing the measurements and architecture with the open truss design. (B) Clinical photograph of the truss implant before implantation. Shown with permission.
Fig. 10Intraoperative photograph showing final implantation of the truss implant with definitive fixation and filled with femoral autograft (reamer-irrigator-aspirator). Shown with permission.
Fig. 13(A) Sagittal and (B) transverse computed tomography cuts adjacent to the implant showing successful fusion of the medial column, with bone formation through and around the truss implant.
Fig. 15(A) Anteroposterior, (B) medial oblique, and (C) lateral radiographs at the 12-month follow-up visit showing maintenance of correction and position.
Fig. 16(A) Sagittal and (B) axial computed tomography images at the 12-month follow-up visit showing osseointegration of the implant, fixation, and host bone.
). Owing to the unique nature of each patient, the published data have been limited to case reports. To the best of our knowledge, the present study is the first report of a small case series of patients to demonstrate successful limb salvage after a variety of failed elective procedures. Furthermore, we have illustrated the vast potential of this technology because it can treat osseous defects of varying sizes, shapes, and orientations. The current data highlight the concerns regarding the rate of union and maintenance of correction with autografts and allografts. In the present series, our patients did not experience nonunion, loss of correction, subsidence, or collapse of the graft. We attribute this finding to the mechanical strength of the truss implant and the coefficient of friction of its highly textured surface. The advantage of 3D printing is the seemingly limitless customizability in size, shape, and fixation options, opening a new frontier for reconstruction in patients previously relegated to complex limb salvage efforts or amputation.
Our pilot study had certain limitations. First, our group of patients was small. Second, CT imaging of the foot and ankle postoperatively was somewhat obscured by artifact, making precise assessment of bone ingrowth difficult. Third, the long-term results are unknown. Large and comparative clinical trials are required to assess the efficacy of this treatment strategy by comparing it with the use of autogenous or allograft structural bone grafts. Further research is needed to determine the mechanical strength of the implant compared with the traditional structural graft options and other metallic implant spacers. The question also remains whether this technology is a cost-effective method. A preoperative CT scan is required to adequately design the implant, in addition to the costs for manufacturing and permanent fixation. These limitations might be cost-prohibitive in many healthcare systems. Therefore, this technology might not be widely accessible. However when available, the truss implant (4WEB Medical, Inc.) appears promising and might be appropriate in select cases. Finally, we did not define the exact measurements and dimensions of the osseous defect that qualify as “large.” Rather, our definition of a “large osseous defect” was determined by the need for a structural bone graft to maintain anatomic length.
In conclusion, the results of the present case series suggest that the patient-specific 3D printed titanium truss scaffold can be used as part of the treatment strategy for large osseous defects of the foot and ankle. The availability of this technology has brought a new option with the potential for significant benefit compared with the classic treatment. Our indication for the 3D printed titanium truss scaffold is for salvage of anticipated osseous defects after any serial debridements that would otherwise require bone block arthrodesis with a structural allograft or autograft bone. We experienced an acceptable complication rate, and all 3 patients achieved a stable arthrodesis. The initial correction was maintained, and the functional outcomes were satisfactory.
References
Masquelet A.C.
Fitoussi F.
Begue T.
Muller G.P.
Reconstruction of the long bones by the induced membrane and spongy auto-graft.
Ann Chir Plast Esthet.2000; 45 (in French): 346-353
Tibio-talo-calcaneal arthrodesis with retrograde compression intramedullary nail fixation for salvage of failed total ankle replacement: a systematic review.
Putting 3 modelling and 3D printing into practice: virtual surgery and preoperative planning to reonstruct complex post-traumatic skeletal deformities and defects.
30487-8&id=yjfas52514-fig-0001.jpg){kind=link}
30487-8&id=yjfas52514-fig-0002.jpg){kind=link}
30487-8&id=yjfas52514-fig-0003.jpg){kind=link}
30487-8&id=yjfas52514-fig-0004.jpg){kind=link}
30487-8&id=yjfas52514-fig-0005.jpg){kind=link}
30487-8&id=yjfas52514-fig-0006.jpg){kind=link}
30487-8&id=yjfas52514-fig-0007.jpg){kind=link}
30487-8&id=yjfas52514-fig-0008.jpg){kind=link}
30487-8&id=yjfas52514-fig-0009.jpg){kind=link}
30487-8&id=yjfas52514-fig-0010.jpg){kind=link}
30487-8&id=yjfas52514-fig-0011.jpg){kind=link}
30487-8&id=yjfas52514-fig-0012.jpg){kind=link}
30487-8&id=yjfas52514-fig-0013.jpg){kind=link}
30487-8&id=yjfas52514-fig-0014.jpg){kind=link}
30487-8&id=yjfas52514-fig-0015.jpg){kind=link}
30487-8&id=yjfas52514-fig-0016.jpg){kind=link}