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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5241_Библиотеки_им_академика_М_И_Перельмана.pdf
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tibial orientation at 90° exion are the combination of KA, which resurfaces the
patient’s pre-arthritic knee without releasing ligaments, and an insert with a medial
1:1 ball-in-socket and a lateral at articular surface along with PCL retention.
A. J. Nedopil et al.
Denition andAdvantages ofKinematically Aligned Total
Knee Arthroplasty
Kinematically aligned (KA) total knee arthroplasty resurfaces the patient’s prearthritic knee to restore the articular surfaces, limb alignment, and joint line obliquity. Using components that restore the articular surface geometry and soft tissue
constraints of the native knee, these steps align the knee’s three kinematic axes with
the axes of the femoral and tibial components [1–3]. Resurfacing the pre-arthritic
knee retains the native resting lengths of the collateral ligaments and the posterior
cruciate ligament (PCL), thus eliminating the need for their release [4].
The high long-term implant survival rates at 7, 13, and 16years after KA TKA
are comparable to or higher than survival rates after mechanically aligned TKA
[5–7]. Furthermore, radio-stereometric analysis (RSA) of tibial baseplate migration
after unrestricted kinematically aligned TKA with posterior cruciate ligament
(PCL) retaining components has shown that the risk of tibial baseplate loosening at
1 and 2years is low and comparable to or less than mechanically aligned TKA, even
up to 9° of varus alignment [8–10]. The high Forgotten Joint Scores (FJS) and
Oxford Knee Scores (OKS) and the restoration of native knee medial and lateral
tibial compartment forces can encourage surgeons to explore the advantages of
resurfacing the patient’s pre-arthritic knee, thus avoiding costly and time- consuming
physical therapy, and enabling early functional recovery [1, 11–17].
Performing theKA TKA Surgical Technique While Preserving
thePCL withManual Instruments andCaliper Measurements
Offers Greater Accuracy than Robotics
Because KA resurfaces the knee by matching the resection thickness of the distal
and posterior femoral condyles to the thickness of the femoral component, KA TKA
is a surgery based on millimeter measurements and not angular measurements.
10 Kinematic Approach
119
Surgical Steps forResurfacing thePre-Arthritic Femur
withManual Instruments andFour Caliper Measurements
The surgeon relies on four caliper measurements of the femoral resections to verify
that the femoral component resurfaces the patient’s pre-arthritic articular surface
(Fig.10.1). After inspection of the distal and posterior femoral condyles, partially
worn cartilage is removed to expose subchondral bone. Worn cartilage is compensated with augments that reduce the thickness of the resected condyle by 2mm [18]
(Fig.10.2). After the caliper measurement of the resected condyle, each femoral
resection is corrected so that its thickness equals that of the condyle of the femoral
component after compensating 2mm for cartilage loss and 1mm for the kerf made
by the saw blade to limit deviations from the pre-arthritic distal and posterior femoral articular surfaces to within 0±0.5mm [19].
Accuracy withManual Instruments
Two studies that used manual instruments to perform KA TKA reported that the
most inaccurate distal and posterior medial femoral resections deviated from
0.9mm over-resection to a −1.5mm under-resection [20, 21]. These studies also
reported the effect of surgeons’ experience and the learning curve of performing KA
TKA accurately, which was negligible. Three studies that used robotic instrumentation to perform mechanically aligned TKA reported the most inaccurate distal and
posterior medial femoral resections deviated from a 2.3 mm over-resection to a
−0.9mm under-resection [22–24]. These deviations due to inaccuracy can be dev-
astating because 1mm or more over-resections from the medial pre-arthritic femoral articular surface worsen the FJS (100 best, 0 worst) and OKS (48 best, 0 worst)
by a minimum of 31 and 7 points [25].
Surgical Steps forResurfacing thePre-Arthritic Tibia
withManual Instruments andFour Caliper Measurements
To set the proximal tibia parallel to the patient’s pre-arthritic varus-valgus (V-V)
orientation and medial tibial slope, the surgeon rst sets the tibial resection guide
8mm distal to the tibial articular surface and parallel to its V-V orientation after
visually compensating for cartilage and bone wear. Next, they set an angle wing,
inserted through the tibial guide’s medial slot, parallel to the patient’s pre-arthritic
slope. When stabilizing the tibial resection guide to the bone the surgeon adjusts the
I-E orientation of the guide to match the anterior-posterior axis of the oval-shaped
lateral tibial plateau. After performing the proximal tibial resection, two caliper
measurements verify that the tibial resection sets the tibial component’s V-V
120
A. J. Nedopil et al.
Fig. 10.1 The image shows the intraoperative verication worksheet the surgeon completes for
each kinematically aligned total knee arthroplasty. It includes the patient number, surgeon name,
sex, age, BMI, date of surgery, right or left knee, type of primary deformity (varus, valgus, or patellofemoral), condition of ACL and PCL, target thickness of femoral resections, initial and corrected
caliper-measured thickness of each femoral and tibial resection, and the implanted component sizes
10 Kinematic Approach
121
Fig. 10.2 The composite of images shows the manual instruments used to make the distal and
posterior femoral resections. The features include an offset distal referencing guide with two holes
(orange squares) for compression screws (upper left and right), a posterior referencing guide set at
0° with small, medium, and large width posterior feet with two holes (orange squares) for compression screws and removable shims to compensate for 2mm of distal and posterior cartilage
wear (lower left), and a washer, available in 1 and 2mm (shown) thicknesses, to correct for an
over-resection of wear (lower left), and a washer, available in 1 and 2mm (shown) thicknesses, to
correct for an over-resection of a distal femoral condyle (lower right)
orientation, and the inspection of the medial tibial resection in conjunction with two
caliper measurements veries that the tibial resection matches the patient’s prearthritic slope. When necessary, differences between the medial and lateral thicknesses of the tibial resection are ne-tuned by recutting the tibia to correct the
difference. Equalization of these two thicknesses is the initial verication that the
V-V orientation of the tibial resection is correct. When necessary, differences
between the medial anterior and posterior thicknesses are ne-tuned by recutting
the tibia to correct the difference, which sets the posterior slope [26].
122
A. J. Nedopil et al.
Protecting thePCL by Inserting aPin Anterior tothePCL Fossa
To maintain the PCL’s integrity, the surgeon can drill a pin anterior to the PCL fossa,
which blocks the saw from posterior translation. To verify the PCL’s integrity, the
surgeon should ex the knee to 90°, inspect, and palpate the PCL to conrm its
maintained tension (Fig.10.3).
Three Surgical Steps forBalancing theKA TKA that Use
aSpacer Block andtheInsert Goniometer
At 90° exion, the surgeon chooses the spacer block thickness that restores a medial
pivot. They insert the spacer block between the posterior femoral condyles and the
proximal tibia and gently pivot the spacer block at its handle. If the spacer block
pivots medially, i.e., the medial portion of the spacer block is pinched between the
medial condyle and tibia while its lateral portion translates anteriorly posteriorly,
the surgeon extends the knee to examine the extension space. If the spacer block
pivots laterally or centrally, the surgeon increases the thickness of the spacer block
until a medial pivot is restored. They then proceed to examine the extension space
using the same spacer block thickness.
At full extension, the surgeon conrms that the spacer block thickness restores a
rectangular extension space. They apply a V-V moment to the knee and look for
lift- off of the medial and lateral femoral and tibial resection from the spacer block.
Insert Goniometer
Medial 1:1 Ball-In-
Socket
Articular Surface
0˚
Screw-Home
Tibial Screw-Home (Extension)
Fig. 10.3 The composite of a right knee with valgus deformity demonstrates an additional technique to preserve the PCL’s insertion when resecting the proximal tibia (left) and the conrmatory
step to ensure its integrity (right)
Axis of Rotation
-15˚
Internal
Orientation
Lateral Flat
Articular Surface
90˚ Flexion
10 Kinematic Approach
123
The tibial resection is ne-tuned by removing additional tibia until the extension
space becomes rectangular [27]. The surgeon refrains from releasing collateral ligaments and the PCL.Hence, when a KA TKA appears too tight, the surgeon readjusts the tibial resection so that the tibial component’s orientation resurfaces the
knee’s pre-arthritic articulation.
The nal step of balancing the KA TKA occurs with trial components at full
extension and 90° exion. The surgeon uses the insert goniometer to determine the
optimal insert thickness after matching an anatomically shaped tibial baseplate to
the tibial resection surface [28, 29]. The design of the insert goniometer consists of
markings in front of the medial compartment that are calibrated to the axis of rotation and dene the orientation of the insert in relation to the femoral component.
The insert goniometer measures tibial orientation relative to a reference line, laser
etched vertically on the center of the trial femoral component’s medial condyle.
Combining an angular scale on the medial insert and a vertical line on the medial
femoral condyle enables the surgeon to measure tibial orientation in extension and
at 90° exion intraoperatively during passive knee positioning (Fig.10.4).
The surgeon selects the ideal insert thickness by observing changes between different insert thicknesses in the external orientation of the tibia in extension and
internal tibial orientation in 90° exion as measured by an insert goniometer. The
surgeon records the extension and exion tibial orientations for each insert
Right Knee with Valgus Deformity
A pin (cyan arrow), inserted
anterior to the PCL insertion,
protects the PCL
Fig. 10.4 The composite shows left trial components, which measure the tibial internal-external
orientations relative to the femur in extension and at 90° exion. The markings in the front of the
insert’s medial compartment are calibrated to the axis of rotation within the medial socket (top).
The intersection of the vertical line along the femoral component’s medial condyle with the insert’s
markings denes the tibial orientation, which measured 0° in extension (bottom left) and −15°
internal at 90° exion (bottom right)
Inspection and palpation of the
PCL (framed by cyan lines)
confirms its integrity
124
thickness. The optimal thickness is the insert that provides the greatest orientations
in extension and/or 90° exion [28].
A. J. Nedopil et al.
Restoring ACL Stability Requires aMedial 1:1 Ball-in-Socket
Insert Conformity toRestore aMedial Pivot
The kinematics of the knee in the axial plane during extension largely depend on the
intact anterior cruciate ligament (ACL) and the geometry of the articular surfaces
[30, 31]. During knee exion-extension, the medial femoral condyle is a sphere
(=ball) that rotates on the medial tibial plateau and the medial meniscus (=socket)
to produce a combination of exion-extension and I-E rotation [31]. Because the
medial condyle hardly translates from anterior to posterior during a exion motion,
the medial compartment of the knee is analogous to a constrained ball-in-socket
joint. The ACL aids in the medial condyle’s anterior-posterior (A-P) stability. The
stable position of the medial condyle contributes to the isometry of the medial collateral ligament (MCL) during range of motion [32]. A medial 1:1 ball-in-socket
insert conformity restores the stable position of the femoral component’s medial
condyle during gait, downhill walking, and stair descent in contrast to lowconforming PCL retaining or posterior stabilized insert conformities [33, 34]. In
vivo uoroscopic evaluation of KA TKA with PCL retention and a 1:1 ball-insocket insert conformity reported restoration of close to native tibiofemoral kinematics. In contrast, a low-conforming PCL retaining insert exhibits a loss of a
medial pivot indicative of abnormal tibiofemoral kinematics [1, 35]. Restoring a
native medial pivot with a 1:1 medial ball-in-socket insert conformity improves
patient-reported outcomes when implanted with KA principles [12, 36].
Restoring I-E Tibial Rotation Requires anIntact PCL,
aMedial 1:1 Ball-In-Socket Insert withaLateral Flat
Articular Surface that Mimics theMorphology
oftheNative Knee
Tibial External Orientation inExtension Tightens theLateral
Collateral Ligament
While the medial femoral condyle does not translate, the lateral condyle exes but
also translates from anterior to posterior during a exion motion. The convex shape
of the lateral tibial plateau and the mobile lateral meniscus permit this coupled
motion of the lateral condyle. The coupling of a stable medial condyle with a lateral
condyle that translates from anterior to posterior during exion translates into internal tibial rotation during exion. The anterior position of the lateral condyle (i.e.,
10 Kinematic Approach
external tibial orientation) during knee extension increases the distance between the
lateral collateral ligament’s femoral origin and its insertion on the bula head, thus
tightening the lateral collateral ligament (LCL) [32]. Hence, the external tibial rotation during terminal knee extension (=screw-home) is essential to tension the LCL
and to restore a rectangular extension space.
125
Tibial Internal Orientation at 90° Flexion Reduces theQ-Angle
As the native knee exes, the PCL tension drives the tibia’s internal rotation. This,
in turn, reduces the Q-angle and optimizes the tension in the retinacular ligaments,
which enables optimal patellofemoral tracking during knee exion [37–39]. Ideally,
a TKA should restore this native tibial internal orientation at 90° exion, promoting
patellofemoral tracking. As the native knee moves from extension to 90° exion, the
tibia internally rotates by an average of 17°–18° [37, 40–42].
PCL Retention Promotes Internal Tibial Rotation During Flexion
A well-known consequence of PCL excision is an increased exion space laxity,
which is inconsistent and unpredictable between knees [43–45]. In addition, PCL
excision causes a loss of about half of the internal tibial rotation from extension to
90° exion [39]. Trying to compensate for the loss of internal tibial rotation by
reducing the posterior slope does not solve the problem [46]. In a cadaveric study,
four surgeons performed a KA TKA with a medial ball-in-socket and lateral at
tibial articular design. Before and after PCL excision, they compared the internalexternal orientation of the tibia in extension and at 90° exion. With retention of the
PCL, the mean internal tibial orientation was 15°, whereas with excision of the
PCL, the mean internal tibial orientation decreased to 7°. This implies that retention
of the PCL helped the prosthetic knee achieve mean internal tibial orientation (15°)
that was comparable to the native knee (18°) (Fig.10.5). The loss of PCL-driven
internal tibial rotation can, in turn, predispose the knee to patella maltracking and
anterior knee pain.
126
A. J. Nedopil et al.
Right KA TKA with 1:1 Medial Ball-in-Socket
and Lateral Flat Articular Surface
a
25
20
15
10
5
0
Internal Tibial Rotation from
Extension to 90˚ Flexion (˚)
Fig. 10.5 The bar chart illustrates the difference in internal tibial rotation during cadaveric KA
TKA, which occurs from a exion motion from 0° to 90°, before (a) and after PCL excision (b),
which caused a loss of about half of the internal tibial rotation
KA TKA with PCL Retention (A)
KA TKA with PCL Excision (B)
15
b
7
An Insert withMedial 1:1 Ball-In-Socket Conformity
andaLateral Flat Articular Surface Restores I-E
Tibial Rotation
The sagittal plane conformity of the insert on the medial side determines passive
knee kinematics. Medial Stabilized (MS) inserts from different manufacturers have
varying levels of spherical conformity in the medial compartment. A study of 21
patients undergoing caliper-veried KA TKA with PCL retention compared the
degree of internal tibial rotation between inserts with a 1:1 medial ball-in-socket or
spherical conformity and one with a less than spherical medial ball-in-socket conformity. Both inserts had an identical lateral at articular surface [47]. The mean
tibial orientation for both insert conformities was similar in extension. In 90° and
120° exion, the 1:1 ball-in-socket conformity demonstrated 2° and 3° more internal tibial orientation, respectively (Fig.10.6). Inserts with less than spherical conformity allow the tibia to move anteriorly, thereby reducing the tension in the
PCL.PCL tension is required for optimal internal tibial rotation. However, whether
this minor increase in internal tibial rotation is clinically relevant remains to be seen.
An equally important condition for restoring native knee kinematics, in addition
to a medial 1:1 ball-in-socket conformity, is the sagittal plane geometry of the lateral compartment of the insert. Posterior stabilized (PS), cruciate retaining (CR),
10 Kinematic Approach
127
a
b
c
KA TKA with 1:1 medial ball-in-socket conformity (A)
KA TKA with less than spherical medial conformity (B and C)
25
20
15
10
5
0
Internal Tibial Rotation from
Extension to 90˚ Flexion (˚)
Fig. 10.6 The bar chart illustrates the difference in PCL-driven internal tibial rotation during KA
TKA, which occurs during a exion motion from 0° to 90° and 120°, between an insert with a
lateral at articular surface and a 1:1 medial ball-in-socket conformity (a) and a less than spherical
medial conformity (b and c). The insert with less than spherical medial conformity reduces internal
tibial rotation by 2° to 3°
19
17
90˚ 120˚
Knee Flexion Angle
23
20
and ultra-congruent (UC) insert geometries that have an anterolateral and posterolateral rim cause a mechanical stop of the tibial screw-home during knee extension
and block internal tibial rotation during knee exion. A study quantitated the reduction in tibial rotation caused by an anterolateral and posterolateral rim. Two surgeons treated 23 patients undergoing KA with PCL retention [48]. They determined
the difference in tibial rotation between inserts with a lateral at articulation surface
(F), low-congruent (LC), and ultra-congruent (UC) inserts. Compared to the lateral
at surface, the LC and UC surfaces decreased the magnitude of tibial rotation by
reducing the external tibial orientation in extension and internal tibial orientation at
90° exion (Fig.10.7). Thus, a medial ball-in-socket insert with a lateral at articular surface allows the PCL to drive tibial rotation during knee extension and exion.
This axial plane motion is less likely with other insert geometries with lateral concavities, where the posterolateral rim functions as a “chock-block” [39].