The Kinematic Alignment Technique for Total Knee Arthroplasty
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The kinematic alignment technique (KA) for total knee arthroplasty (TKA) is a surgical technique recently developed that aims to anatomically position and kinematically align total knee components . The kinematic implantation aims to resurface the knee joint by removing a cartilage and bone thickness equivalent to the implant thickness and where the knee implants are aligned on the knee kinematic axes that dictate motion of the patella and tibia around the distal femoral epiphysis [2–4]. Similar to unicompartmental knee replacement, kinematically aligning total knee components restores the constitutional knee joint line orientation and the physiological knee laxity without the need for soft-tissue release  (Fig. 16.1).
Kinematic alignment (KA) is a relatively new surgical technique for implanting total knee components.
The vast majority of patients are eligible for a kinematic implantation, and this may be achieved with most primary implant designs.
Kinematically aligning the femoral component is relatively easy and straightforward; following this first step, the kinematic tibial implant positioning is made reproducible by a combination of measured resection and ligament referencing techniques. As the surgical technique is not demanding and complex cases are rare, the KA technique is overall reliable.
KA implantation results in high prosthetic joint function, in a large range of preoperative deformity, and whether the postoperative alignment of the tibial component, knee and limb is in the varus and valgus outlier range of mechanical alignment criteria.
Due to an improvement in knee biomechanics, it is expected that component lifespan will also be improved. A prospective study of 222 successive unselected KATKAs has reported excellent implant survival at 10-year follow-up. Nevertheless, long-term outcomes of KA patients still need to be defined.
In the event of severe constitutional limb deformity, kinematic component positioning may be adjusted in order to reduce the limb deformity and hopefully improve prosthetic biomechanics. This defines the restricted kinematic alignment concept.
Development of new implant designs adapted to KA implantation needs to be undertaken.
16.1.1 What Is It? The Concept
16.1.2 Why Has This New Surgical Technique Been Developed? The Rationale
The KA technique for TKA has been developed following the observations that mechanically aligned (MA) TKAs are affected by residual complications that have not been solved by technology, and the rationale for the MA technique is being challenged.
Frequent prosthetic overstuffing of the distal lateral femoral condyle  which leads to abnormal stretching of the lateral retinaculum ligament during knee flexion.
Frequent, uncorrectable collateral ligament imbalance when performed with a measured resection technique (approximately 40% imbalance ≥2 mm) [11, 12] or gap-balancing (knee flexion gap tighter than physiological)  techniques.
The first pillar of the MA technique is to align knee components systematically, perpendicular to femoral and tibial mechanical axes. In fact, a bulk of evidence now suggests that knee kinematics is dictated by three main axes (Fig. 16.2) , and the cylindrical (or trans-condylar) axis is the one upon which the tibia effectively rotates around the femur from 10° to 120° of knee flexion .
The second pillar of the MA technique is the assumption that generating a neutrally aligned knee when standing creates a biomechanically friendly knee component environment that would persist even during gait. By reducing the prosthetic joint reaction force, this would optimise the lifespan of the components. In fact, many studies have now challenged this dogma, after having found that static standing limb alignment (hip knee ankle (HKA) angle) poorly predicts the risk of long-term MA-TKA failure [21, 22]. This may be due to the fact the HKA angle is a dynamic (or functional) value that changes when weight bearing  and walking  and that only partly predicts the knee adduction moment [24, 25] and the medial femoro-tibial joint reaction force .
The last pillar of the MA technique is the assumption that generating rectangular and identical extension and flexion gaps would be clinically beneficial. However, some recent studies suggest that preserving the physiological ligament laxity difference between the medial and lateral compartments and between the flexion and extension spaces may in fact be clinically advantageous .
16.1.3 What Are the Intended Benefits?
By aiming for a more physiological and more reproducible implantation, the KA technique aims to improve prosthetic knee function, patient satisfaction and component lifespan, compared to conventional techniques for knee replacement. The anatomic knee reconstruction has been shown to be clinically beneficial  by means of the generation of a close to physiological peri-prosthetic soft-tissue tension [29, 30] and prosthetic knee biomechanics [31, 32, 33, 34]. Interestingly, the kinetic aspect of a KA-TKA may also be advantageous (reduced prosthetic joint reaction force) compared to MA [31, 33, 34]. Those functional and biomechanical advantages with KA would hopefully contribute to counter the raising burden of revision in patients who are having joint replacement younger, with higher demands and expectations, and a longer life expectancy [7, 8].
16.2 Planning a Kinematic Implantation
16.2.1 Which Patient Can Be Kinematically Implanted?
Primary replacements requiring revision knee implants to treat a deficient knee soft-tissue envelope (e.g. MCL stretching and severe valgus knee) or severe bone loss are not eligible for KA. This is due to the design of revision implants, where the stem-implant angle dictates the implant orientation (often 6° for femur and 0° for tibia).
There is currently no evidence that osteoarthritic knees that require a primary replacement with sliding components lead to the preclusion of a surgeon using KA. Out of 219 consecutive unselected KA-TKAs prospectively followed for 10 years, prosthetic knees resulting in varus or valgus limb alignment (>3°) performed similarly as the ones neutrally aligned knees. Only three aseptic revisions (1.6%) were observed and were related to technical error in component positioning . Similarly, the fact that only 13 cases of patella instability were reported out of 3212 consecutive KA-TKAs indicates that the vast majority of patella-femoral joints and axial femoro-tibial rotations may be safely reproduced when kinematically implanting total knee components .
The safe range for frontal kinematically positioned total knee components is yet to be determined . This explains why some authors use KA unless the patient is an outlier, with excessive deviation from the average constitutional knee anatomy [37, 38]. In this event, those authors would adjust the kinematic components positioning, by slightly deviating from the native anatomy, in order to fit an arbitrarily defined, range of component positioning and limb alignment [37, 38]. This defines the concept of restricted kinematic alignment, best illustrated by the Montreal protocol (see Chap. 17) [37, 38]. The outlier constitutional knee/limb anatomies must not be confused with extra-articular deformities resulting from trauma (e.g. femoral diaphysis malunion), which are not physiological. These more often need to be corrected with an additional osteotomy at the time of TKA (one stage) or before (two stages) the TKA.
Similarly, the safe range for axially kinematically positioned total knee components is unknown . Kinematically implanting patients having an antecedent of patella instability (osteoarthritic knee type 5; Table 16.1) may seem unreasonable as reproducing a poor anatomy (e.g. excessive Q angle or trochlea groove-tibial tuberosity distance) may lead to failure. As stated above, with solely 13 cases of patella instability out of 3212 consecutive unselected KA-TKAs , the vast majority of patella-femoral joint anatomies and axial femoro-tibial rotations may, apparently, be safely reproduced.
Table illustrating different types of knee that make a kinematic implantation simple, complex or not indicated
None of the criteria defining the types 2, 3, 4, 5, 6
>5° constitutional varus
>5° constitutional valgus
Severe bone loss
Antecedent of patella instability
Deficient soft-tissue envelope
KA or ‘KA + realignment osteotomy’ or rKA
KA (unless revision implant needed)
±lateral retinaculum release and VMO plasty
±extensor mechanism realignment
Constrained implants needed, KA technique not indicated
16.2.2 Which Implant Design May Be Kinematically Implanted?
It is likely that the majority of traditional primary implant designs (symmetrical sliding designs) available on the market such as medial pivot and cruciate(s) retaining or substituting designs may be suitable for a kinematic implantation. As kinematic prosthetic implantation aims to restore close to physiological knee kinematics, implant designs that promote unconstrained, physiological femoro-tibial kinematics and that preserve or replicate cruciate ligament(s) function are probably the most sensible for use. For this reason, kinematic implantations have traditionally been reported with fixed bearing cruciate-retaining implant designs [35, 36, 37, 39, 40, 41, 42]. Nevertheless, successful kinematic implantation with mobile bearing postero-stabilised implant design has also been reported . After having used cruciate-retaining and postero-stabilised designs, the author (CR) is now performing kinematic implantation with a medial pivot TKA component design . By offering anteroposterior stability (substitution of both cruciate ligaments and medial meniscus) and medial implant congruency (ball in socket), medial pivot TKA design may be clinically advantageous by providing improved knee stability and reduced linear polyethylene wear. There is no study having compared the value of the multiple implant designs when kinematically positioned. Further research is therefore needed.
Asymmetric components with built-in joint line obliquity (e.g. Journey™, Genesis™—Smith & Nephew), because of asymmetry in the thicknesses of their medial and lateral compartments, are specifically designed for mechanical implantation (thus creating the effect of an anatomical alignment - see Fig. 16.1) and are inappropriate for kinematic alignment.
16.2.3 Which Instrumentation to use?
Conventional gap-balancing techniques, serving to define the femoral axial rotation, are inappropriate for KA. This is because a kinematic femoral component is always implanted parallel to the posterior condylar line (neutral rotation) in order to be adequately aligned with the cylindrical (trans-condylar) axis. This is easily achieved with a posterior referencing resection guide.
KA can be performed manually [45, 46] or with the use of assistive technology [35, 37, 39, 40, 41, 43]. Successful implantations have been reported using measured-resection manual instrumentation (Chap. 24) [45, 46], navigation systems (Chap. 26) [37, 43] and personalized cutting guide (Chap. 25) [35, 39, 40, 41, 42]. A modified gap-balancing technique for performing the tibial cut is also being assessed .
16.2.4 Resurface the Patella or Not?
There is unfortunately no evidence to help with this choice. As MA and KA implantations significantly differ from each other, the evidence accumulated for the former technique can’t be translated to the latter one.
MA frequently generates lateral femoral condyle prosthetic overstuffing that affects the patella balance (lateral retinaculum stretching) and biomechanics (lateral patella tilt/shift and increased lateral facet joint reaction force) when flexing the knee  and is sometimes responsible for MA-TKA failures [35, 36, 42]. In contrast, this significant alteration of the lateral femoral condyle anatomy does not occur when knee components are KA [11, 51, 52] and probably explains the more physiological patella biomechanics [33, 34] and the rare anterior knee pain [42, 53] and patella instability [35, 36] after KA-TKA. The improved patella environment after KA-TKA, relative to MA-TKA, may have a protective effect on it, whether it has been replaced or not. This would hopefully be clinically beneficial by reducing the risk of patella-femoral joint-related complications [35, 36, 42].
16.2.5 Recognising a Complex Case for KA Implantation
As KA and MA implantation significantly differ, both techniques are complex in different situations. A classification of the most frequent conditions that would make KA-TKA complex is illustrated in Table 16.1.
In contrast to MA, the frontal limb deformity is generally not a source of technical complexity with the KA technique [11, 12, 29, 30]. This is because the anatomical joint reconstruction given by KA reliably restores the physiological knee soft-tissue balance whatever the constitutional limb alignment of the patient [11, 12, 29, 30]. Therefore, constitutional frontal limb deformity does not add surgical complexity unless considered excessive and needing attenuation (restricted KA) or correction (additional osteotomy before or at the time of the KA-TKA). While arbitrarily defined by some authors [37, 38], the optimal deformity threshold is yet to be scientifically defined.
Patients with patella maltracking and/or a previous history of patella-femoral instability may need additional surgical correction (e.g. MPFL reconstruction, tibial tuberosity mobilisation) at the time of KA-TKA in order to optimise the patella tracking. Also, because the lateral retinaculum is often retracted in these cases, performing a lateral para-patellar arthrotomy, in addition to a plasty of the lateral retinaculum (Keblish style), may be advisable.
16.3 Key-Points for Performing a Kinematic Implantation
Kinematic alignment (KA) and mechanical (MA) alignment are two different techniques for implanting knee components that only have in common the sagittal positioning of the femoral component
Femoral component positioning
Follows distal femoral bowing
Follows distal femoral bowing
Parallel to the distal femoral joint line (considering articular surface wear)
Systematic and perpendicular to the femoral mechanical axis
Parallel to the posterior condylar line
Always measured resection and posterior referencing techniques for a compromise done only on the trochlear offset
External rotation relative to the posterior condylar line. Measured resection or gap-balancing techniques. Posterior or anterior referencing techniques for a compromise done either on the flexion gap or on the trochlear offset, respectively
Centred on the notch
Tibial component positioning
Parallel to the proximal tibial joint line (considering the wear)
Systematic and perpendicular to the tibial mechanical axis
Parallel to the medial plateau slope
Systematic and varies between 2° and 7° relative to the sagittal tibia mechanical axis
Parallel to lateral plateau long-axis
Towards the medial third of the anterior tibial tuberosity
None—close or physiological knee laxity automatically restored after bone cuts
Frequent for creating identical rectangular flexion and extension gaps
Rarely—only in case of preoperative abnormal patella tracking with retracted lateral retinaculum ligament
Often performed to palliate the frequent prosthetic overstuffing of the lateral femoral condyle
First, always estimate the individual physiological knee laxity and amount of bone loss before performing any bone cuts, by varus/valgus stressing the knee throughout the knee range of motion (Fig. 16.5).
Second, always check the quality of the bone resection with a calliper (Fig. 16.3). The expected thickness of the bone cut is easily calculated by deducting 1 mm from the implant thickness for the saw blade (kerf) thickness and by estimating the amount of articular surface wear. The cartilage thickness is frequently approximately 2 mm on the distal and posterior parts of the femoral condyles .
Last, unless using technological assistance, perform an economical tibial cut on the worn side (Fig. 16.7) as the amount of bone loss is difficult to estimate precisely and it is easy to secondarily refine the tibia cut by using user-friendly KA-dedicated recut guides (Figs. 16.4 and 16.7).
16.4 Current Evidence
The KA technique has been developed for trying to reduce the high proportions of dissatisfaction  and residual complications [7, 8, 10] that traditionally affect MA-TKA and are probably as a result of non-physiological (neglecting of unique individual knee anatomy and laxity) [5, 11, 14, 31, 33, 34] and unreliable (high rate of uncorrectable collateral ligament imbalance) [11, 12] implantation. Studies having assessed the value of KA-TKA have flourished over the last years, and the promises seem to have been met.
The KA technique generates high prosthetic knee function and a more natural feeling. Seven studies have compared KA and MA patients at short term (1–2 years), including five randomised controlled trials [39, 40, 41, 42, 58] and two matched case-control study [32, 43]. All have reported better functional scores for KA patients, while this was statistically significant for only five studies [32, 41, 42, 43, 58]. In addition, a national multicentre survey in the USA found KA patients to be three times more likely to report their knee to feel “normal” . Faster recovery for KA patients [40, 59], reduced risk of anterior knee pain [42, 53] and similar failure rates [39, 40, 41, 42, 43, 53, 58] were other interesting findings from those comparative studies. Three meta-analyses [28, 60, 61] concluded the superiority of the KA technique in terms of prosthetic function and recovery time, with a similar low failure rate. High functional scores have been shown to persist 10 years after implantation, with no difference between different groups of limb alignment (varus >3°, neutral, valgus >3°) . The faster recovery of KA patients could be the consequence of a more physiological and soft-tissue-friendly prosthetic knee implantation. This superiority is even more emphasised when the excellent clinical outcomes for KA patients were achieved despite the use of recently recalled Otismed™ cutting guides [39, 40, 41, 42, 53] and by surgeons likely in their learning curve for the KA technique. In contrast, MA implantations, which were often found to be inferior to KA implantation, were performed by surgeons familiar with the technique and sometimes using navigation assistance [39, 43, 58].
With short-term data, KA prostheses rarely failed. The early complication rates (initial 1–2 years after implantation) were reported to be similar between KA and MA patients [39, 40, 41, 42, 43, 53, 58]. The 10-year aseptic revision rate has been reported at 1.6% with 1 tibial component loosening and 2 patella recurrent instabilities out of 219 consecutive unselected KA-TKAs . There were no differences between varus, neutral and valgus groups of limb alignment . Also, only 13 cases of patella instability were reported out of 3212 consecutive kinematically implanted prosthetic knee patients during a 9-year period . KA implantation, therefore, results in high implant survival at 10 years regardless of the level of preoperative deformity and whether the postoperative alignment of the tibial component, knee and limb are varus and valgus outlier ranges according to MA criteria.
The KA technique is reliable as it accurately kinematically positions the knee components [46, 49, 50]. Studies have demonstrated that KA components with manual instrumentation is highly reproducible for both femoral [46, 49] and tibial [46, 50] components. Also, the KA technique has been shown to properly restore physiological knee laxity [29, 30].
The KA technique is more physiological as it is generating close to native biomechanics. Many studies have shown that the femoro-tibial [31, 32, 62] and patellofemoral [33, 34] KA prosthetic kinematics and kinetics (or biomechanics) more closely resemble those of the native knee, when compared to mechanically aligned TKA. Interestingly, it seems that kinematic implantation may also be kinetically more advantageous than mechanical implantation by better aligning the knee joint line parallel to the ground in situations of weight bearing [48, 63], leading to reduced deleterious shear stress on the bearing surfaces and component fixation interface. KA alignment also reduces the joint reaction forces at the lateral patella-femoral facet [33, 34] and through the medial femoro-tibial compartment . The improved patellofemoral kinetics [33, 34] may be explained by the prosthetic trochlea anatomy in the kinematically positioned femoral component being closer to the native trochlea groove alignment [52, 64]. The improved tibio-femoral kinetics  may be explained by the more physiological gait pattern after KA implantation that results in a lower knee adduction lever arm and, subsequently, a reduced knee adduction moment, despite the fact that lower limbs were slightly more varus . This is not surprising when one realises that the frontal limb alignment (HKA angle) is a dynamic value [23, 24] that has been shown to poorly predict the knee adduction moment [24, 25] and the medial femoro-tibial joint reaction force . The likely biomechanical advantage conferred to KA prosthesis may explain the very low rate of component failure that has been observed after KA .
16.5 Specific Component Designs for Kinematic Implantation?
Kinematically positioning contemporary knee components enables the restoration of the femoro-tibial joint line 3D orientation [46, 49], but it fails to accurately reproduce the individual trochlea anatomy [51, 52, 64]. This poor trochlea reconstruction is related to the fact that kinematic positioning of monoblock femoral components focuses on the reconstruction of the femoro-tibial joint line, with no possibility to fine-tune the prosthetic groove orientation. While this poor prosthetic trochlea anatomical reconstruction has not been responsible for catastrophic failure [5, 35, 36], it may nonetheless hinder optimal clinical outcomes of KA prosthetic knee. Some trochlea anatomy variations may therefore benefit from a more personalized reconstruction.
New modular femoral component designs offer the possibility to intraoperatively fine-tune the groove orientation/radius and trochlea stuffing (Fig. 16.9).
New monoblock femoral component designs displaying various trochlea anatomies. The cost-effectiveness of the last two options may be questioned considering the current economic trend.
KA-TKA is a surgical technique that may help better reproduce physiological knee function without the need for soft-tissue release. The vast majority of osteoarthritic patients are eligible for a KA-TKA. Because the surgical technique is not demanding and complex cases are rare, KA is reliable for most patients. KA implantation results in favourable implant survival and function at 10 years in a wide range of preoperative anatomies. Because the whole knee biomechanic environment is improved, it is hoped that component lifespan will also be improved. In the event of severe constitutional limb deformity, the kinematic component positioning may need to be adjusted in order to better suit the actual prosthetic fixation and bearing limitations; this defines the restricted KA concept. Long-term outcomes of KA patients still need to be defined. New TKA component designs that better match patients’ knee anatomy and help replicate native knee kinematics may need consideration.
16.7 Case Illustration
A 66-year-old patient presented with painful, bilateral, severely degenerated knees. In the left knee, the patient had a correctable 10° to 15° varus deformity and a varus trust when walking. The knee range of motion was normal.
Before performing any bone cuts on the left knee, the medial and lateral femoro-tibial laxities were assessed (Fig. 16.5), and an abnormal severe medial laxity was observed in full extension (Fig. 16.5b).
At 6 months follow-up, the patient was pain-free with an Oxford Knee Score at 42 and a satisfaction at 95/100.
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