Smith & Nephew RT-PLUS User manual

Text
Titel
Surgical Technique
“Intramedullary Application” *smith&nephew
RT-PLUS™
Modular Rotating Hinged

RT-PLUS™ Modular
Table of Contents
Introduction........................................................................... 3
Concept/Description............................................................. 4
Indications ............................................................................ 8
Contraindications.................................................................. 8
Case Study............................................................................ 9
Preoperative Planning ..........................................................10
Surgical Technique............................................................... 13
Postoperative Treatment ......................................................51
References.......................................................................... 52
Sterilization ......................................................................... 53
Implants .............................................................................. 54
Instrumentation................................................................... 60
Product Overview (Combination Tables)...............................74
Nota Bene
The technique description herein is made available to the healthcare
professional to illustrate the authors’ suggested treatment for the
uncomplicated procedure. In the final analysis, the preferred treatment
is that which addresses the needs of the patient.
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With the rising number of implantations we are increasingly
being confronted by cases which are difficult to treat and
which require the use of special prosthetic systems using a
higher degree of coupling. The RT-PLUS™ Modular prosthesis
has been designed to take this development into account.
It is a constrained rotating knee, the development of which
drew upon knowledge and experience gained from state-of-
the-art knee joint prosthesis.
The RT-PLUS Modular knee system is the modular version of
RT-PLUS and it represents a valuable addition to bicondylar
surface replacement.
The functional design allows extremely sparing resections.
The joint components features anatomical geometry, as it’s
also used today for bicondylar surface replacement cases.
The femoral and tibial components have the same stem
coupling and are anchored in the bone by stems made of
Ti6Al4V for cementless application and in CoCrMo for
cemented application. To compensate various femoral and/or
tibial bone defects, there are CoCrMo augmentation blocks
available.
Special attention was also paid to the development of a user-
friendly instrument set. This ensures that the prosthesis is
implanted securely and precisely.
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Introduction

The RT-PLUS™ Modular is a constrained rotating knee prosthesis for cemented implantation.
The prosthesis allows an internal/external rotation of approx. 10° each. This is locked by the
tibial-insert when extended. Due to the peg design, the prosthesis has the capability
of elongation, i.e., for distraction between the femoral and the tibial components. In an ext-
reme flexed position, the femoral component can lift off the tibial-insert, which reduces
the sagittal leverage forces that have an effect on the prosthesis stem in this load situation.
The implant allows sparing resections. The cut compatibility with the tricompartmental pros-
thesis TC-PLUS™ permits if necessary an intraoperative switchover from the resurfacing to
the constrained rotating knee.
The femoral and tibial components of RT-PLUS Modular are identical to those of RT-PLUS,
with the exception of the additional option to connect stems and augmentation blocks. The
tibial inserts are the same. As a result, the femoral and tibial components in both these
systems are entirely cross-compatible. All the stems of RT-PLUS Modular can be combined
with the femoral and tibial components of RT-PLUS Modular to suit requirements.
The implants are available in five sizes (corresponding to RT-PLUS sizes 2, 4, 6, 8 and 10).
Apart from size 2, the sizes can be combined with the next size up or down.
Note
RT-PLUS Modular requires condylar support for the femoral/tibial components. The forces
have to be absorbed by the condyles as well as by the stems.
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Concept/Description

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Femoral component
The femoral component is manufactured from
CoCrMo alloy and is asymmetrical.
The patellar groove is deeply hollowed out
and presents an anatomical oblique outline.
This feature offers improved patellar tracking
and leverage on the knee extensor appara-
tus.
The joint mechanism is contained in a narrow
box, the width of which is comparable to that
of a “posterior stabilized” implant. This allows
sparing bone resection, which reduces the
risk of femoral condyle fracture.
The rotation peg of 40 mm length provides
adequate security against dislocation, but
the components can nevertheless be easily
coupled. Because of the design of the con-
dyles, physiological “rollback” of 9 mm is
possible, which improves the flexion capa-
bility of the joint.
The joint mechanism has been designed in such way that all metal components (peg and
joint axis) interface with UHMW polyethylene to absorb the stress forces therefore prevent-
ing premature wear.
A modular stem connection allows the use of different stems to stabilize the femoral
component.
To compensate femoral bone defects, distal and/or posterior femoral augmentation blocks
can be fixed to the femoral component.
The femoral component is available in sizes 2, 4, 6, 8 and 10.
Please see the available sizes in the implant table (from page 54 ff).
Product Description

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Patellar component
The all-poly (UHMW polyethylene) patellar
component has a symmetrical biconcave
surface for better tracking.
Tibial insert
The simple and securely anchored tibial insert
is manufactured from UHMW polyethylene and
is available in three different heights of 8 mm,
11 mm and 14 mm, in order to restore the joint
height independent to the degree of tibial
bone substance loss.
The special design of the polyethylene insert
enables an easy coupling of the prosthesis,
for which only minimal distraction is required.
The minimum effective PE thickness in the load zone is 8mm. The selected manufacturing
method, the design (condyles) and the high-quality material combine to form the proven wear-
resistance of the insert.
The tibial inserts are identical to those in the RT-PLUS™ portfolio.
Tibial component
The symmetrical tibial component is manu-
factured from CoCrMo alloy.
In order to prevent polyethylene wear inside
the tibial component, the base plate is polished
on the inside and the insert is completely en-
closed along its entire circumference.
A modular stem connection allows the use of
different stems, which serve to stabilize the
tibial component.
To compensate tibial bone defects, proximal
tibial blocks can be fixed on the tibial compo-
nent.
The tibial component is available in sizes 2,
4, 6, 8 and 10.

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Femoral and tibial blocks
The femoral and tibial blocks are manufac-
tured from CoCrMo alloy.
In order to compensate different femoral and/
or tibial bone defects, there are distal femoral
blocks available in heights of 5 mm, 10 mm
and 15 mm, posterior femoral blocks in heights
of 5mm and 10 mm and proximal tibial blocks
in heights of 5 mm, 10 mm and 15 mm.
The same femoral blocks are used for the
medial as for the lateral condyle of the
femoral component. The same tibial blocks,
except height of 15 mm, are used for the
medial as for the lateral condyle of the
tibial component.
The blocks have to be assembled to the femoral and tibial components with screws and can
then be cemented on the tibia, respectively on the femur.
Cemented stem
The femoral and tibial components can be
intramedullary anchored in the bone by
cemented conical stems, made of forged
CoCrMo alloy.
Available in lengths 95 mm, 120 mm and
160 mm.
Cementless stems
The femoral and tibial components can also be
stabilized into the bone by using non cement-
ed cylindrical stems, made of extruded Ti6Al4V
alloy. These stems are not suitable for primary
anchorage; therefore, they are not designed for
osseointegration.
A wide stems range enables an optimum
adaptation to different indications. They are
available in various diameters ( Ø 10, Ø 12,
Ø 14, Ø 16, Ø 18 and Ø 20 mm) and lengths
(95 mm, 120 mm, 160 mm and 200mm) in order
to ensure optimum anchorage, even with a
variety of femoral or tibial geometries.
Please see the available sizes in the implant table (from page 54 ff).

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The principal preoperative planning factor is the correct diagnosis. It has to be determined
whether the bone and stability situation require the implantation of a constrained prosthesis.
The main indications for implantation of RT-PLUS™ Modular are:
• High-grade joint destruction with considerable loss of function and requirement for addi-
tional stabilization with longer stems and reconstruction of bone defects
•Severe joint instability that predictably cannot be corrected by suitable bone reconstruction
(bone grafts) or soft-tissue intervention
• Marked contractures and axial displacements of more than 15°–20°
• Failure after surface replacement (e.g., infection, loosening) – revision of a primary prosthesis
• Trauma – induced femoral or tibial fractures
• Due to the design, it is possible to switch with relatively little effort, even intraoperatively,
from the TC-PLUS™ knee system to the RT-PLUS™ Modular knee system, since the resections
and prosthesis sizes are matching
Contraindications
Contraindications are:
• Acute or chronic, local or systemic infections (or in the case of a corresponding anamnesis)
• Severe muscle, nerve or vascular diseases that endanger the affected extremity
• Lacking bone substance or inadequate bone quality that endangers a stable seating of the
prosthesis
• Severe adiposity
• All concomitant diseases that may endanger the function of the implant. These include in
particular extreme insufficiency of the knee extensor mechanism, which can lead to exces-
sive joint distortion; or severe adiposity, which can lead to a dorsal impingement, which may
uncouple the components. In these cases it may be advisable to use a coupled hinge or a
tumour prosthesis
• Patient hypersensitivities or allergies to the materials used
• Strenuous physical activity (e.g., competitive sports, hard physical work)
See also instructions on the package insert.
Indications

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Preoperative situation
Case Study
Patient with severe joint instability (varus gonarthrosis) as well as medial joint destruction.
Postoperative result
Immediately postoperative; functional and pain-free reconstruction with RT-PLUS™ Modular knee.

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A full-leg X-ray with the patient in the standing position is recommended for preoperative-
planning purposes. If this is not possible, an X-ray of the thigh, including the femoral head,
should be taken. The X-ray images of the knee joint at three levels should be available for
planning the surgery. A tangential patellar exposure, a frontal and a sagittal to the leg axis
exposure must be taken.
For preoperative planning there are X-ray tem-
plates available: with scale of 1.15:1 Lit. No. 1135
and with scale of 1:1 Lit. No. 1584 (see page
74). The lateral view of the condyles is deci-
sive. If these are no longer completely intact,
it is possible to switch to the condylar width.
In cases of doubt, the smaller implant should
be selected to prevent the prosthesis com-
ponents from protruding. In normal cases,
the size determination and the correct posi-
tioning of the prosthesis are controlled intra-
operatively with relevant instruments, and
planning may also be possible on the unre-
stored opposite side leg.
Note
The femoral and tibial component sizes can
all be combined with the next size up or
down (see product overview on page 76 ff).
This does not apply to combinations of sizes
2 and 4.
Large deviations of the femoral-neck angle as
well as severe deformities of femur and tibia
(e.g., posttraumatic axial deformities) must be
taken into consideration during surgical plan-
ning.
In rare cases of deformities away from the knee
joint that negatively influence the mechanical
leg axis, additional corrective osteotomies may
be indicated.
Preoperative Planning

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Planning of Surgery Using the Radiograph
A Anatomical femoral axis
B Anatomical tibial axis
C Mechanical leg axis
D Mechanical femoral axis
E Tibial resection depth (mm)
Valgus angle
Preop. Postop.
The following procedure is recommended for
the anterior-posterior whole leg imaging pro-
cess:
1. The femoral axis A (anatomical axis) is drawn
onto the radiograph.
2. A line is drawn from the femoral head to the
center of the knee (mechanical axis D) on the
radiograph.
3. The angle measured between the anatomical
and the mechanical axis = angle determines
the valgus angle.
4. The tibial axis B is drawn in and the tibial re-
section plane E is determined to avoid exces-
sive resection, especially where there are
defects.
5. The component sizes and resection depths
are determined preoperatively using the
X-ray templates (Lit. No. 1135 or 1584) in A/P
and the lateral planes.
6. The mechanical leg axis C should merge with
lines D and B after correction.
Postop.
Preop.

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Positioning of the patient for the surgery
Surgery is performed whilst the patient is
supine.
It is recommended that the blood supply be
partially blocked with the use of a tourniquet.
But this is not absolutely necessary.
The leg must be covered, so as to allow mo-
vement, and secured to the operating table
in such a way that the knee joint is brought
into a stable 90° flexion position. Most of the
surgical steps are performed in this position.
Surgical procedure
The skin incision can be a midline incision or
a parapatellar incision.
If there are scars from skin incisions made
during previous surgery, it is advisable to use
them for access in order to reduce the risk of
cutaneous blood flow disorders. Medial ar-
throtomy is recommended, or an approach
adapted to the pathological situation.
After the usual preparation (meniscus resec-
tion, removal of osteophytes and synovecto-
my if necessary), the cruciate ligaments
are sectioned and if necessary, the collateral
ligaments are removed close to the bone.
Surgical Technique

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It is important that the flexion and extension gaps are identical.
1. Distal femoral resection and optional distal
augment resection.
2. A/P femoral resections and optional posterior
augment resection.
3. Chamfer resections and cutting out of the
box. Remove residual posterior condyles if
present.
Note
To avoid the risk of a condyle fracture, we
recommend to prepare the box after tibial
preparation.
4.Tibial resection and optional augment
resection.
5. Patellar resection (optional).
Important
Only 1.0 mm saw blades must be used for all bone resections! See Lit. No. 1403 for corre-
sponding connection.
Overview of the Resections Sequences for Primary Application

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The bone resections are refreshed after extraction of the primary implants.
1. Distal femoral resection and optional distal
augment resection.
2. A/P femoral resections and optional posterior
augment resection.
3. Chamfer resections and cutting out of the
box. Remove residual posterior condyles if
present.
Note
To avoid the risk of a condyle fracture, we
recommend to prepare the box after tibial
preparation.
4. Tibial resection and optional augment
resection.
5. Patellar resection (optional).
Overview of the Resections Sequences for Revision Application

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Access: Please refer to the relevant surgical textbooks for the initial access to the knee.
Note
In addition to the bone resections, it is important to correct any ligament imbalance by
appropriate soft-tissue procedures. If necessary, a general release should be performed on
the side of the contracture prior to the bone resections.
The leg is flexed and any osteophytes on the femur and tibia should be removed. This
provides good exposure of the knee joint, which facilitates size determination.
Femoral size determination
By using the femoral sizer (2, 4, 6, 8 or 10)
the size is determined, sagittaly according to
the inside/outside contours as well as
ventrally according to the anterior/posterior
resections and the medial/lateral contours.
Note
The line in the sagittal view of the femoral sizer
shows the position of the femoral IM canal, i.e.,
the position of the stem.
Femur opening
The adjustable IM femoral drill guide is set to
the planned size of the femoral components
(size marking 2, 4, 6, 8 or 10) and inserted
under the quadriceps into the center of the
femur. The distal stop should be on the
medial condyle. Make sure that the gauge
is flat on the anterior femoral cortical bone in
the direction of the femoral axis.
Open the femoral IM canal with the
Ø 8 mm
IM drill.
Important
To ensure an optimal position of the femoral
drill guide on the condyles, gently tap the
M/L area, not the drill guide section of the
instrument.
Femoral Preparation

The Ø 8 mm IM rod is carefully inserted using
the modular handle to approximately the
isthmus of the femoral IM canal and removed
again. It is important to work carefully to pre-
vent excess pressure in the IM canal.
The femoral IM canal is opened further with
the
Ø 8/14 mm stepped drill. Note that the
drill is positioned at the entry point of the
femoral IM canal, previously determinated by
the IM drill. The drill direction is along the
femoral axis. Drill as far as the stop.
Note
The femoral IM canal, which determines the
implants stem position, must be opened
carefully (reference for the femoral position)
to prevent the development of a relative ex-
tension position (risk of notching) or flexion
position (projecting patella).
Preparing the femoral anchorage
Reamers are used carefully and in progres-
sive stages (starting with
Ø 10) to ream to the
required stem diameter and depth.
Notes
Reamers are available in diameter
Ø 10,
Ø 12, Ø 14, Ø 16, Ø 18 and Ø 20. The depth
indicator is on the reamer: observe the laser
markings (95, 120, 160 and 200).
When using cemented stems, the Ø 12 mm
reamer is used to drill to the desired depth
and the corresponding cementless trial stem
is used. The optional cemented trial stems
are only used with the trial components (not
with the instruments)!
The 200 mm length is only available in the
cementless version.
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