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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4479_Библиотеки_им_академика_М_И_Перельмана.pdf
Patient-Specific Implants
andProsthetics
DavidA.Rengifo, AlexanderP.Simko, andRajaSawhney
Introduction andHistory
Major facial defects are typically repaired with autologous reconstructive techniques. There are situations, however, where prosthetic rehabilitation is preferable
as a primary or complementary reconstruction method for facial defects. The
advancement of technologies in imaging and biocompatible materials has allowed
patient-specic implants and prostheses to become an integral part of facial reconstructive surgery. By providing a synthetic replacement of traumatic, ablative, or
congenital defects, the transformative role of these prosthetics can provide a robust
combination of function and aesthetics.
Initially, the historical breakthroughs in prosthetics were limited to biomaterials.
The earliest prosthetics were largely composed of shells and animal xenografts;
however, extensive use and experience with these materials showed poor integration
and high infection rates. Rapid improvement and utilization of implants and prosthetics began during the world wars of the twentieth century. Advancements in antibiotics and anesthesia meant patients surviving what were once mortal injuries.
These patients presented with morbid injuries, requiring surgeons to expand the
reconstructive armamentarium. Materials such as plaster, latex, leather, silver, and
steel gained popularity and were used for several decades. Most of these options
failed to maintain relevance due to their inherent characteristics. Issues with longevity, heat conduction, tensile strength, biocompatibility, and radio-opacity limited
4
D. A. Rengifo (*) · R. Sawhney
Department of Otolaryngology, Head and Neck Surgery, University of Florida,
Gainesville, FL, USA
e-mail: David.Rengifo@ent.u.edu
A. P. Simko
University of Florida School of Medicine, Gainesville, FL, USA
e-mail: ap.simko@u.edu
© The Author(s), under exclusive license to Springer Nature
Switzerland AG 2024
F. Sokoya, A. G. Vincent (eds.), Manual of Head and Neck Reconstruction,
https://doi.org/10.1007/978-3-031-65999-7_4
43
44
D. A. Rengifo et al.
their long-term viability. Modern materials are increasingly clinically inert and can
be molded, stretched, or color-matched to the defect being repaired. The development of osteointegration with titanium was another major step in implant development. Prior methods of implant retention included mechanical anchoring or
adhesives which led to frequent dislocation and repetitive need for replacement.
Beyond the biomaterials, traditional methods of prostheses fabrication relied on
highly skilled crafting that was both labor intensive and time consuming. The process relied on patients attending multiple clinic appointments and waiting weeks to
months before a successful implant was created. Improvement in imaging modalities allows the rapid importation of patient data directly into the modeling environment. Technological advancements including computer-assisted presurgical
planning and three-dimensional printing have made facial prosthetics more accessible and a wider variety of materials to be incorporated into the fabrication process.
Fundamental Concepts ofProsthetics andImplants
In general, a prosthetic is a synthetic replacement which restores the cosmesis of the
anatomical defect. An implant typically refers to an object that is osteointegrated
and supportive in nature. That said, the terms are often used interchangeably, and
further confounding the matter, some reconstructive materials can be both.
Multiple factors must be considered when determining the ideal reconstructive
solution of an area. These include surgical requirements, limitations, and potential
outcomes as well the patient’s short-term and long-term desires. Reconstruction
using an autograft is typically the ideal option for larger defects and advanced
reconstructions; however, this option may not align with the patient’s goals due to
the extent of surgery, cost, or recovery time. Prosthetics and implants can often be a
better reconstructive option by providing the patient with better cosmetic results
while decreasing the operative risks. This may be especially true in certain patient
populations including the elderly and those with signicant comorbidities. Patients
with highly nuanced anatomical defects which would require numerous reconstructive surgeries such as total nasal defects or those defects that are poorly mimicked
by autografts including reconstruction after orbital exenteration often prefer prosthetics. Also, patients requiring long-term surveillance after cancer extirpation often
benet from a temporary prosthesis when interacting with society.
Successful implantation and prosthetic utilization rely heavily on their method
for anchoring them in place and are impacted by anatomical, mechanical, and material variations. Early retention systems included eyeglasses, adhesives, or anatomical undercuts. Drawbacks to these systems included low durability, failure in
patients with active lifestyles, skin irritations and allergic reactions, as well as difcult prosthetic positioning. Innovations in osteointegration have brought great
advances in retention systems.
4 Patient-Specic Implants andProsthetics
45
Implant Materials
Several materials are used currently in facial reconstruction thanks in part to scientic and production advancements. Each has its advantages and limitations.
Porous high-density polyethylene (PHDPE) is made of simple carbon chains
and commonly used for many soft tissue implants. Its favorable characteristics
include ease of molding and radiolucency on imaging. Porous polyethylene is also
highly biocompatible by inducing broblast ingrowth and eventual bony incorporation, which add to its stability. It has also been shown to have reduced risk of infections and increased vascular ingrowth. Porous polyethylene has been used
extensively for the repair of orbital wall and lid defects, nasal implants, and auricular reconstruction. The material’s ability to incorporate tissue can make it difcult
to remove, if revisions are needed.
Polyether ether ketone (PEEK) is another polymer that is popular in both neurosurgical and facial reconstructions. It is quite strong, highly biocompatible, stable
with temperature changes, and lightweight. PEEK is especially popular as a patientspecic implant (PSI) that is prefabricated using three-dimensional technology. The
material can be altered intra-operatively allowing the correction of slight discrepancies between surgical plan and patient anatomy. PEEK can be used in conjunction
with titanium and can tolerate the placement of plates in screws to hold it in place.
Its biggest limitation is its lack of bio-integration which can increase the risk of
dislodgement.
Lastly, titanium has long been a popular implant for a myriad of reasons. It is
relatively inexpensive, and it is easy to alter its shape. It offers excellent tensile
strength, especially against compressive forces. The implant has long been used in
conjunction with other autografts and allografts and is usually the choice when
placing free bone grafts or PEEK implants. It also limits heat conduction and is
markedly more radiolucent when compared to other metals. Drawbacks to titanium
include its reliance on surrounding bone stock for xation. Titanium can also have
a relatively high extrusion rate.
Patient-Specific Implant Planning andPlacement
Patient-specic implants (PSIs) created with CT imaging have gained a widespread
acceptance. Improvements in product precision and manufacturing time as well as
decreased cost have been at the heart of its spike in utilization. To create a PSI, the
surgical team uploads the patient’s CT scan data to the engineering team of the
company producing the implant. Next, the surgeon and engineer review the imaging
and discuss logistics. These include determining the best surgical approaches for
placement as well as the material that will be chosen based on various merits. Next,
the size and shape of the implant are determined. Smaller implants can be created as
a single piece. Larger implants or those reconstructing several abutting anatomical
subunits, maybe designed in multiple sections, can be united during implantation.
This can be an incredibly important consideration when trying to navigate and place
46
the PSI under the soft tissue. The placement of implants in the virtual space becomes
exponentially more difcult once the constraints of soft tissue are in place. Beyond
the creation of the implant, patient-specic cut guides can be designed and manufactured. These guides can be used to remove the unwanted bone and to pre-drill
screw holes for the implant so that it sits exactly as planned. The guides can be
placed and xated intraoperatively and then removed after the desired cuts and
holes are made. Additionally, the creation of a manufactured skeletal model can be
benecial. It can be used to reassess the defect area as well as to conrm correct
implant position. The turnaround time for the production of the implants, once the
plan is approved, is progressively becoming streamlined, though depending on multiple factors can still take a few weeks. There is also a learning curve when rst
using PSI intraoperatively, and extra surgical time for their incorporation should be
worked into the equation. The addition of neuro-navigation, rigid endoscopy, and
intra-operative imaging are valuable tools in verifying a proper placement of guides
and implants which with practice can reduce surgical time signicantly.
D. A. Rengifo et al.
Prosthetic Materials
The prosthetics of the early twentieth century were largely composed from latex
rubber. As materials progressed, acrylic resin, silicone, methacrylate, and polyurethane elastomers were introduced [1]. As noted previously, the ideal prosthetic
should be aesthetically pleasing, durable, nonirritating, and retentive. The most
popular material utilized for prosthetics is silicone due to its clinically inert characteristics and soft texture. Silicone is the preferred choice for soft tissue implants due
to its excellent color and texture match to surrounding tissues (Fig.4.1). It retains
body temperature without distortion, and it can be stretched so thin as to appear
transparent.
Prosthetic Placement
The choice for osteointegrated versus adhesive prosthetics depends on the patientspecic defect and site. Prosthetics that attach to an implant generally have better
stability and show less skin irritation. Adhesive prosthesis may not last as long when
compared to the implant-attached prosthetics. A larger defect is best reconstructed
with osteointegrated implants, as they will hold the prosthetic more securely in
place [2]. Issues with osteointegrated prosthetics include poor bone stock, extrusion, especially in radiated bone, and the need for more surgical procedures when
compared to those prosthetics that are secured by adhesives [3]. They are also often
expensive and may be uncovered by insurance.
4 Patient-Specic Implants andProsthetics
47
Fig. 4.1 An example of a silicone nasal prosthetic in place. Note that the removal of the majority
of the native nasal anatomy allows for the ideal size and placement of the prosthetic
Site-Specific Considerations
Auricular Reconstruction
Traditional auricular reconstruction can be achieved both with implants and prosthetics. Though not an absolute, most auricular implants occur in the pediatric population, while older patients tend to favor prosthetics. Several goals must be kept in
mind when considering ear reconstruction. Cosmetic appearance and facial symmetry are the principal goals of reconstruction. Children with microtia often suffer
48
D. A. Rengifo et al.
signicant psychological repercussions due to social ridicule, and therefore expedited reconstruction can be important [4]. For patients who wear glasses, a reconstruction of the auricle also provides a functional advantage for support. In situations
where the hearing loss is associated with microtia, reconstruction serves to restore
acoustic function. The literature pertaining to a two-stage porous polyethylene
implant reconstruction combined with bone-anchored hearing aid notes better
results in both aesthetics and hearing outcomes in comparison to autologous rib
reconstruction and atresiaplasty [5].
Auricular Alloplastic Implant Reconstruction
In the early 1990s, auricular implants were mainly fabricated from nonbiologic
silastic ear implants. This material resulted in an early capsule formation and a poor
vascular framework for overlying tissue aps and grafts, resulting in high extrusion
rates [5]. Currently, porous polyethylene is frequently used for auricular reconstruction, partially due to its reduced extrusion rates. The skeletal framework of the
porous polyethylene implants is made of two parts: the helical rim and the ear base
and is usually created as a PSI.It can be implanted as a single- or two-stage procedure and does not necessitate overnight hospital stay. When done in two stages, the
second procedure occurs around 3 months after the initial surgery and involves
minor revisions including improving auricle projection, lobule transposition, tragal
reconstruction, or deepening of the concha. Successful implantation heavily relies
on the recipient tissues. A large, well-vascularized soft tissue envelope is the main
determinant of successful implantation..
Indications for porous polyethylene auricular reconstruction include microtia
patients, especially those who failed autologous reconstruction, as well as patients
who have suffered from auricular trauma or resection due to malignancy.
Contraindications to implant reconstruction include compromised temporoparietal
aps due to congenital anomalies, trauma, malignancy, history of radiation, infection, or previous harvest.
As part of the preoperative planning, the contralateral ear is typically used as a
guide to shape the implant. If a normal contralateral ear is not available, as may be
the case for microtia, the implant can be constructed from a template of a parent’s
ear. Positioning of the implant in relation to the lateral canthus and nasal ala is
important and varies depending on patient age.
The description that follows focuses on younger pediatric patients and should be
supplemented with other sources based on individual patient parameters.
Perioperatively, patients usually receive prophylactic intravenous antibiotics. Most
surgeons will elect for the patients to receive a weight-appropriate dose of cephalexin or clindamycin; however, it is important to note that several large clinical trials
have not shown results to conrm clinical advantage to prophylactic antibiotics in
auricular reconstruction [4]. It is also recommended to soak the implant in an antibiotic solution prior to placement. Prior to making incisions, the supercial temporal artery branches can be traced using Doppler to prepare for the temporoparietal
4 Patient-Specic Implants andProsthetics
49
fascial (TPF) ap. It is also important to mark the path of the frontal branch of the
facial nerve.
The TPF ap is then raised initially by making a Y-incision, where the bottom tail
sits at the superior edge of the intended helix and the anterior extent placed 10cm
superior to the intended helical rim. The posterior tail of this incision is made at
5cm posterior to the intended helical rim. The ap is then raised, beginning anteriorly, with dissection carried just supercial to the deep temporalis fascia. The anterior border is separated from the deep temporal fascia to the anterior branch of the
supercial temporal artery. If the anterior aspect of the ap is encroaching into the
path of the frontal branch of the facial nerve, only the lower portion fed by the anterior branch of the supercial temporal artery is included. The posterior border of the
ap is then incised and raised with the intent to include subgaleal fascia, as this will
add bulkier soft tissue coverage and decrease the risk of implant extrusion. Lastly,
the raised ap is delivered through the inferior temporal incision by transecting the
remaining anterior, posterior, and distal edges. After harvesting the ap, vestigial
cartilage should be removed to maximize the t of the implant; however, a portion
can be banked subcutaneously and be used later for a second-stage procedure that
includes tragal reconstruction [5]. Then, two bulb suction drains are inserted in the
lateral neck.
At this point of the surgery, the surgeon may make last-minute adjustments to the
implant if necessary. Ear assembly is started by delivering the TPF ap, and then the
construct is placed in the ideal position. The TPF ap is laid over, and suction is
applied. The ap should shrink wrap over the implant to achieve contour. Sutures
may not be necessary to x the framework into place as soft tissue suction is usually
enough. At this point, a full thickness skin graft may be harvested to provide further
coverage. Usually, the contralateral non-hair bearing retro auricular skin is used for
the anterior and lateral surfaces of the implant. Other full thickness graft donor sites
may include the abdominal wall or groin; however, the darker pigmentation in these
areas can be a disadvantage, unless placed posteriorly to the implant, to provide a
natural shadow [5]. Absorbable sutures are then used to x the skin grafts over the
TPF ap. Molded silicone putty, or prep sponges, are placed to prevent swelling
without excessive compression on the reconstruction, and a protective cup is placed
over the reconstructed ear.
Suction drains should be removed 5 to 7days postoperatively. If used, the silicone mold or sponges are generally removed 7 to 10days postoperatively. The plastic ear protective cup should be kept on for 2 to 4weeks after surgery [5].
Postoperative complications pertaining to porous-polyethene auricular reconstruction are generally divided by time frame after surgery. The most common acute
complications are the formation of hematoma and ap loss. A hematoma can be
drained in the clinic setting as needed. Flap loss most commonly happens in the rst
5 to 7days after surgery and may be rst noticed at the rst postoperative dressing
change in clinic [4]. The accepted treatment course for this ap loss is returning to
the operating room for the removal of the implant and debridement. After allowing
for appropriate healing, an ipsilateral occipital fascial ap or contralateral free TPF
ap can be used as salvage options [3].
50
D. A. Rengifo et al.
Subacute postoperative complications include implant extrusion and infection
[6]. If the exposure or extrusion is limited without any evidence of infection, local
tissue can be raised to maintain a good seal. If the implant exposure is less than 1
cm, this defect may heal by secondary intention. In cases of subtotal extrusions, the
implant should be removed, and granulation tissue should be debrided. A new
implant should be placed as soon as possible to take advantage of the preserved ear
and soft tissue architecture constructed in the initial surgery [7]. Risk of implant
extrusions and exposure may increase in patients with prior atresiaplasty, as this can
lead to increased scarring and poorly perfused periauricular skin [6].
Postoperative implant infections are usually due to implant extrusion or exposure. The infected site is treated on the basis of severity. If the infection is mild or
limited, antibiotic treatment and close observation of any implant exposure are recommended. In more severe infection, aggressive debridement and surgical site
washouts are necessary. If frank purulence is encountered, complete removal of the
implant is recommended [6].
Long-term complications of alloplastic auricular reconstruction are usually due
to fracture of the implant. Treatment recommendations include removal of the damaged implant and immediate replacement with a newly constructed framework [6].
Trauma experienced in the long-term setting can also damage the overlying TPF
ap and skin grafts. Additional complications include hair growth of the skin enveloping the implant, local alopecia at the donor site, as well as poor texture and color
match of tissue coverage. Recent literature shows overall implantation exposure
rates to be less than 10%, fractures rate of 3%, and overall complication rate
of 6% [6].
Alloplastic reconstruction provides a reasonable size match with the contralateral ear and good denition of the conchal bowl, helical rim, and antihelical fold.
Validated questionnaires in the literature have shown over 75% improvement in
quality of life in patients who underwent porous polyethylene implant reconstruction, with nearly 73% of adults and 85% of children noting satisfaction with their
aesthetic results [6].
Auricular Prosthetics
As previously discussed, auricular reconstruction is complex and difcult. Auricular
prosthesis provides satisfactory results in most patients with several studies showing aesthetic satisfaction in nearly 90% of patients who have chosen this option [8].
Silicone continues to be the most used material for auricular prosthesis, as it is
malleable, which results in anatomically precise framework, providing excellent
color and texture matching (Fig.4.2). While adhesive attachment remains popular,
osteointegrated implants have gained signicant popularity as this retention system
requires less maintenance and provides more stability. In comparison to autologous
reconstruction, alloplastic implant reconstruction has signicantly less morbidity
due to fewer surgeries as well as due to a lack of donor-site morbidity. Similar to
4 Patient-Specic Implants andProsthetics
51
Fig. 4.2 Example of the recipient site before and after placement of silicone auricular implant
alloplastic auricular reconstruction, reconstruction can be performed as early as
4years of age.
The issues with auricular prosthetics are the same as with most facial prosthetics.
Daily cleaning of the prosthetic-associated implants and the recipient site is necessary to maximize benets and avoid infections. Additionally, daily activity exposes
the prosthetic to general wear and tear and the risk of dislodgement [8].
In general, the major indications for the need of a prosthetic ear include auricular
loss due to trauma, oncologic defects, and congenital abnormalities. Aggressive
tumors involving the auricle require large resections and are frequently followed by
radiotherapy, which will affect the local tissue vascularity and stability, thereby limiting the possibility for autologous or alloplastic reconstruction. While a history of
radiation to the recipient site can increase complication risks in prosthetic
52
D. A. Rengifo et al.
reconstruction, it is not a contraindication for an ear prosthetic. Several studies have
shown excellent outcomes in radiated patients when the implant placement of
implant is delayed by 6 to 12months after radiation therapy [9]. Congenital abnormalities such as microtia or partial auricular congenital abnormalities, especially
relating to patients with prior reconstructive failures or lack of healthy tissue in the
temporal bone region, have shown excellent aesthetic results after prosthesis
reconstruction.
There are few absolute contraindications for a prosthetic. These include a compromised bony framework such as osteitis or osteomyelitis of the mastoid bone or a
temporal bone that is thinner than 2.5mm which will not support the construct. In
this scenario, the use of adhesives may be an option. The discussion regarding the
daily maintenance of the prosthetic and retention systems must be done with the
patients and family, as a lack of hygiene can signicantly increase the risk of infection of the implant, tissue reactions, and overall prosthetic failure. Lastly, some
studies have shown signicantly high risk of infection and extrusion of implants in
patients who have been exposed to radiation and continue to use tobacco products.
Prior to the placement of bone-anchored prosthesis, a careful evaluation must
be performed of the skin and subcutaneous tissue in the auriculotemporal area,
with attention given to potential recurrent tumors, scars, and brosis. If hair is
present, it must be permanently removed prior to surgery, as hair follicles may
increase the risk of implant infection. Many surgeons opt for laser hair removal in
these cases. Alternatively, hair roots may be removed while thinning the subcutaneous tissue in surgery. A dedicated CT scan of the temporal bones without contrast should be obtained preoperatively to evaluate for appropriate bone thickness
and to evaluate any changes caused by prior therapies or congenital abnormalities.
A team-based approach with the anaplastologist involved in manufacturing the
prosthetic can be benecial. They can assist the surgeon in determining which
anatomic structures can assist or hinder optimal implant placement. Often, to optimize prosthetic placement, it is benecial to remove all remnants of the auricle
except the tragus, as it helps with the skin-to-prosthetic match and soft tissue
transition. Leaving excess tissue may not provide the patient with the best cosmetic outcome due to difculty with color matching and a more visible transition
from prosthetic to native auricle.
Most surgeons perform prosthetic reconstruction in two stages, often under local
anesthesia. The rst stage involves the placement of titanium bone implants which
requires raising a skin ap in the auricular temporal area. Perioperative antibiotics
are not indicated but may be considered in diabetic patients or those with radiated
tissues. The skin is incised, and dissection is carried deep to the periosteum. A ap
is raised in the subperiosteal plane until the adequate sites of implant placement are
reached. The ideal site for implants is 20mm from the center of the external auditory meatus at the 8 and 11 o’clock positions. Usually, two implants are placed into
the bone; however, literature suggests placing a third “sleeper” implant in case of
implant failure. The initial holes are drilled to a depth of 3mm. If there is no dural
contact at the initial depth, one can proceed to 4mm of depth to maximize load support. The implants are then introduced at a torque speed of 40 to 50 newton meters