Preemptive analgesia with nonsteroidal anti-inflammatory drugs, intravenous
prophylactic antibiotics, and spinal or general anesthesia are all part of
routine perioperative management of the patient. A side-support is placed at
the level of the tourniquet, and a sandbag is placed to allow the knee to be
positioned in 90° of flexion. The limb is cleaned and draped in a standard
aseptic manner.
The infrared camera is placed directly opposite the involved limb, and the
computer monitor is adjacent to the camera
(Fig. 1). Ci knee essential
version-2.0 software (DePuy/BrainLab, Feldkirchen, Germany) is used. This can
be adapted to the individual surgeon's preference for implant type and
bone-cut sequence. We use a cemented cruciate-retaining knee prosthesis and
prefer that the tibial cut be performed first. We use the so-called
gap-balancing method for femoral positioning and rotation. It is also
possible, for surgeons who prefer to do so, to choose the measured resection
technique for femoral bone cuts and to rotate the femur according to osseous
landmarks such as the anteroposterior axis, the epicondylar axis, or the
posterior condyles.
The tourniquet is inflated, the knee is flexed to 90°, and the osseous
landmarks are palpated (Fig.
2). A midline skin incision is made from 2 cm proximal to the
superior pole of the patella to 2 cm distal to the joint line, just medial to
the tibial tubercle. Sharp dissection through Scarpa's fascia is performed to
raise a medial subfascial skin flap and expose the quadriceps tendon. This is
followed by an arthrotomy placed 2 mm lateral to the medial edge of the
quadriceps tendon, commencing 2 to 3 cm proximal to the superior pole of the
patella and extending medially around the patella to the medial edge of the
patellar ligament (Fig. 3).
The knee is then extended, and a medial release is performed to gain
exposure. The patellar ligament and the lateral aspect of the capsule are
freed from Gerdy's tubercle. The knee is placed in 75° of flexion, and
osteophytes are removed from the medial femoral and tibial condyles. This
progressive removal of osteophytes decreases the tension on the extensor
mechanism and allows easier lateral subluxation of the patella. A curved
osteotome is placed at the level of the joint and is passed subperiosteally in
a posteromedial direction to complete the release. The patella is then
subluxated laterally and is held with a curved Hohmann retractor
(Fig. 4). The anterior cruciate
ligament is transected, and another curved Hohmann retractor is placed behind
the posteromedial border of the tibia, which is then externally rotated and
translated anteriorly. This further reduces tension on the extensor mechanism
and allows further subluxation of the patella. The menisci and part of the
infrapatellar fat pad are sharply excised to expose enough of the tibial
surface for computer registration.
Stab incisions are made over the distal third of the femur and the midpart
of the tibia. Two 3.5-mm partially threaded pins are inserted unicortically
into both the tibia and the femur. Reference arrays are placed so that they
are easily detected by the infrared camera
(Fig. 5). The computer is then
able to rapidly triangulate the location of the arrays that are rigidly fixed
to bone in real time, with a position accuracy of 0.5 mm. Registration
involves providing information to the computer regarding the individual
patient's osseous anatomy for the process of surgical navigation.
Computer registration is started with confirmation of the center of the
hip. This is identified by circumduction of the hip with a gradually enlarging
circular motion while an assistant anchors the pelvis. The knee is placed in
75° of flexion, the patella is subluxated laterally, and the tibial
surface is exposed with two curved Hohmann retractors. The centers of the
distal part of the femur (just above the intercondylar notch) and the proximal
part of the tibia (the center of the anterior cruciate origin) are identified.
The medial and lateral malleoli are then registered to determine the center of
the ankle. From this information, the mechanical axes of the femur, tibia, and
lower limb are determined. Following this, the osseous landmarks on the
surface of the tibial plateau are registered along with the anteroposterior
axis of the tibia. The computer calculates an optimal proximal tibial cut,
which is depicted as an illustrated line on a three-dimensional knee model on
the monitor. This line is perpendicular to the mechanical axis with a default
depth of 8 mm from the lowest point on the least-damaged tibial plateau to
allow for the minimum thickness of a tibial insert. In the case of a varus
knee, this would be the lateral tibial plateau. The default posterior tibial
slope is 3° according to the manufacturer's recommendation. The
plane-verifier is inserted into the cutting slot of the extramedullary tibial
jig. This allows the computer to register the direction of the cutting slot,
and thus a saw cut is made with use of the slot, which is illustrated as
another line on the knee model. The surgeon then adjusts the tibial jig while
watching the monitor to superimpose the cutting-block line onto the
computer-calculated line on the knee model. This so-called navigation is
performed in both the coronal and the sagittal plane. Once the position of the
jig is satisfactory, it is held in place with pins, and the navigated proximal
tibial cut is performed with the oscillating saw
(Fig. 6). The accuracy of the
cut is verified with use of the plane-verifier, with acceptance of up to
1° of variance in any plane (Fig.
7).
Following the tibial bone cut, the patella is subluxated farther, the
distal part of the femur is digitized, and a bone model is generated. A
low-profile soft-tissue tensioner is then inserted; this provides an equal
medial and lateral distraction force of 23 N. Soft-tissue releases are then
performed to achieve a neutral mechanical axis in extension as visualized on
the computer monitor; the bone gap is stored in the computer (Figs.
8, 9, and
10). The knee is brought into
90° of flexion with the tissue tensioner in place; the patella is
relocated, and this bone gap is stored in the computer (Figs.
11 and
12). This follows the
principles of the gap-balancing technique, with which the knee is first
balanced in extension. Then, flexion gap balance is achieved by the
anteroposterior positioning and appropriate rotation of the femoral component.
It is crucial that the soft-tissue releases be completed so that the knee is
well balanced before the bone gaps are recorded. The computer software uses
this information to provide an optimum femoral anteroposterior size,
proximal-distal position, and rotation along with a suggested tibial insert
thickness to achieve equal and rectangular gaps in extension and flexion
(Fig. 13). The default femoral
rotation is parallel to the cut tibial surface at 90°. Osseous landmarks
such as the epicondylar axis can be used to determine the rotation should the
surgeon prefer this, and manual adjustments to the plan are possible at this
stage (Fig. 14). The planned
distal femoral bone cut (performed at 15° of knee flexion) and anterior
femoral bone cut (performed at 70° of knee flexion) are navigated with the
aid of fine-tuning femoral jigs developed for computer-aided surgery
(Figs. 15 and 16). Once again,
the accuracy of each bone cut is verified, and variances of 1° and 1 mm
are accepted (Figs. 17 and
18). The advantage of this
technique is that the bone gaps are balanced before any femoral bone cuts are
made and no recutting of the bone is necessary once the planned resections are
decided.
With the spacer block of appropriate thickness inserted in both full
extension and 90° of flexion, the stability of the knee and the alignment
of the lower limb are assessed with respect to the mechanical axis and are
confirmed with the aid of the computer-generated models
(Fig. 19). The amount of
medial and lateral opening, in millimeters, with respective valgus and varus
stress can be determined at this stage. If this is satisfactory, then no more
trials are required. Further soft-tissue releases can be performed at this
stage if the surgeon chooses to do so, and these are followed by a repeat
assessment of the gap balance with use of the spacer blocks or the trial
prosthesis.
A low-profile femoral finishing block of appropriate size is placed, and
the final femoral bone cuts are completed
(Fig. 20). A lamina spreader
is used with the knee in flexion to assist in clearing the posterior space of
meniscal remnants and posterior femoral osteophytes.
With the completion of the bone cuts, eversion of the patella is easier in
extension and the patella can be resurfaced at this stage
(Fig. 21). The tibia is then
subluxated anteriorly, and the entire surface is exposed with the aid of
curved Hohmann retractors. Preparation for insertion of the keel and stem is
then performed (Fig. 22).
A cocktail of morphine, bupivacaine with epinephrine, triamcinolone, and
vancomycin is then injected into the posterior part of the capsule and the
quadriceps muscle, and pulsatile lavage is performed to remove debris from the
bone surfaces.
The cement is pressurized into the bone, the tibial component is inserted,
and all excess cement is removed. Visualization around the entire tibial
surface is possible with balanced Hohmann retraction
(Fig. 23). The femoral
component and then the patellar implant are cemented with use of a single
batch of cement (Fig. 24).
Computer screenshots of the limb alignment are made with the knee in full
extension, 90° of flexion, and full flexion (Figs.
25 and
26). We do not use a drain.
The reference arrays are removed, and the knee joint is closed in separate
layers. The tourniquet is released at the end of skin closure and after
application of a pressure bandage. Administration of low-molecular-weight
heparin is started twelve hours after the surgery. The standard physical
therapy regimen is started the day after the operation.
Preoperative and one-month postoperative radiographs of an illustrative
case are presented in Figures 27-A,
27-B, 27-C,
27-D.
CRITICAL CONCEPTSINDICATIONS:Genu varum of any degree.Genu valgum of <15°. (Computer navigation can be used for more
severe deformities, but it is difficult to perform an adequate lateral release
through a minimally invasive approach.)Abnormal tibial or femoral bowing.An inability to use a femoral intramedullary guide because of retained
implants or severe femoral deformity.CONTRAINDICATIONS:Revision total knee arthroplasty.Active knee infection.A body mass index of >30 kg/m2. (Computer navigation is very
useful for obese patients to determine the alignment and the position of the
prosthesis, but the minimally invasive approach becomes exceedingly difficult
with increasing subcutaneous fat.)Genu valgum of >15°.Patella baja. (This condition makes it difficult to subluxate the patella
adequately during the minimally invasive approach.)An ankylosed hip in which it is difficult to establish the center of hip
rotation.Retained implants that require removal through extended incisions.PITFALLS:Proper positioning of the reference arrays is crucial for ease of surgery.
They should be placed away from the operative site so as not to hinder the
surgery. The pins should be placed unicortically in order to minimize the risk
of fracture.Implantation of the femoral component may be difficult as the extensor
mechanism is under greatest tension with the knee in extreme flexion and
patellar subluxation may be limited. This may lead to malpositioning. If
needed, extension of the quadriceps incision is performed to improve exposure
under these circumstances.AUTHOR UPDATE:The computer software has been upgraded to allow split registration of the
tibia first and then the femur to permit more accurate femoral bone
digitization. We use the low-profile tensor sensor to aid in gap balancing. We
reviewed the clinical results of the original study patients at two years and
found them to be the same in the group treated with computer-assisted
minimally invasive total knee arthroplasty and the group treated with standard
total knee arthroplasty. No radiographic signs of implant migration or
loosening were noted in either group at two years.
CRITICAL CONCEPTS
INDICATIONS:
Genu varum of any degree.Genu valgum of <15°. (Computer navigation can be used for more
severe deformities, but it is difficult to perform an adequate lateral release
through a minimally invasive approach.)Abnormal tibial or femoral bowing.An inability to use a femoral intramedullary guide because of retained
implants or severe femoral deformity.
Genu varum of any degree.
Genu valgum of <15°. (Computer navigation can be used for more
severe deformities, but it is difficult to perform an adequate lateral release
through a minimally invasive approach.)
Abnormal tibial or femoral bowing.
An inability to use a femoral intramedullary guide because of retained
implants or severe femoral deformity.
CONTRAINDICATIONS:
Revision total knee arthroplasty.Active knee infection.A body mass index of >30 kg/m2. (Computer navigation is very
useful for obese patients to determine the alignment and the position of the
prosthesis, but the minimally invasive approach becomes exceedingly difficult
with increasing subcutaneous fat.)Genu valgum of >15°.Patella baja. (This condition makes it difficult to subluxate the patella
adequately during the minimally invasive approach.)An ankylosed hip in which it is difficult to establish the center of hip
rotation.Retained implants that require removal through extended incisions.
Revision total knee arthroplasty.
Active knee infection.
A body mass index of >30 kg/m2. (Computer navigation is very
useful for obese patients to determine the alignment and the position of the
prosthesis, but the minimally invasive approach becomes exceedingly difficult
with increasing subcutaneous fat.)
Genu valgum of >15°.
Patella baja. (This condition makes it difficult to subluxate the patella
adequately during the minimally invasive approach.)
An ankylosed hip in which it is difficult to establish the center of hip
rotation.
Retained implants that require removal through extended incisions.
PITFALLS:
Proper positioning of the reference arrays is crucial for ease of surgery.
They should be placed away from the operative site so as not to hinder the
surgery. The pins should be placed unicortically in order to minimize the risk
of fracture.Implantation of the femoral component may be difficult as the extensor
mechanism is under greatest tension with the knee in extreme flexion and
patellar subluxation may be limited. This may lead to malpositioning. If
needed, extension of the quadriceps incision is performed to improve exposure
under these circumstances.
Proper positioning of the reference arrays is crucial for ease of surgery.
They should be placed away from the operative site so as not to hinder the
surgery. The pins should be placed unicortically in order to minimize the risk
of fracture.
Implantation of the femoral component may be difficult as the extensor
mechanism is under greatest tension with the knee in extreme flexion and
patellar subluxation may be limited. This may lead to malpositioning. If
needed, extension of the quadriceps incision is performed to improve exposure
under these circumstances.
AUTHOR UPDATE:
The computer software has been upgraded to allow split registration of the
tibia first and then the femur to permit more accurate femoral bone
digitization. We use the low-profile tensor sensor to aid in gap balancing. We
reviewed the clinical results of the original study patients at two years and
found them to be the same in the group treated with computer-assisted
minimally invasive total knee arthroplasty and the group treated with standard
total knee arthroplasty. No radiographic signs of implant migration or
loosening were noted in either group at two years.