in this video I will explain you what our alignment philosophies in total knee arthroplasty and more precisely how we restore the natural or constitutional alignment of the patient using the CPAK classification. When considering alignment in knee replacement it is important to realize what the natural alignment is in your patient and contrary to what we all have learned in the past this is not always zero degrees mechanical. What the normal alignment is in humans has been very thoroughly studied by us and we have published our findings in 2012 in this landmark publication in CORR and indeed contrary to what was thought before the natural alignment of the knee is not systematically zero for everybody it is on the contrary highly individual with a bell curve or gaussian distribution around an average of 1.3 degrees of varus with a standard deviation of 2.3 degrees meaning that 95 percent of knees are situated between 6 degrees of varus and three degrees of valgus and also meaning that an important fraction of the population approximately one-third has a natural alignment in varus and we have called that constitutional varus from the Latin word "constituere" which means building so how you were built or constructed after skeletal maturity and before any degeneration and axis deviation has taken place, that is your constitutional or natural alignment and in one third of the population that is in more or less significant varus now these patients with constitutional varus they pose a problem with standard mechanical alignment restoration to zero because when you do so you see that you run into a conflict with the soft tissues on the medial side. Cutting perpendicular to the mechanical access to the femur and the tibia then indeed leads to an asymmetric extension space where you can never get the rectangular prosthesis in between, unless you release, or stretch, or partially disrupt the medial collateral ligaments and the medial soft tissue sleeve which of course is a strange thing to do because it would mean that you correct a mistake by making another mistake. That is damaging the medial soft tissues in order to obtain a rectangular extension space. Now while we looked at the normal alignment distribution in healthy population we noted that amongst the individuals with constitutional varus there was another factor of variability within this group itself and that is the joint line orientation and that same variability we also noted in the neutral knees as well as in the group with constitutional valgus that same variability in joint line orientation was present and this observation led to the second landmark publication that was published by Dr Sam MC Dessi and Dr Darren Shan from Sydney Australia, Dr Bill Griffith Jones from the UK, Dr Harris from Australia and myself from Belgium in this publication we present the CPAK classification which is based on these two observations. That is the variability in the alignment as well as joint line orientation that is present in healthy or normal individuals. So this is the CPAK classification, it subdivides and classifies the different knee phenotypes into a matrix of nine different types depending on overall alignment and joint line orientation which are, as I explained, the two factors of importance. So the matrix has three columns and three rows. In the columns we see the overall alignment, in the rows the joint line orientation so in the first column we have the knees that are in varus alignment the second column the neutrally aligned knees and in the third column the knees that are in valgus alignment in the rows we have the joint line orientation in the first row we see the knees with apex distal joint line orientation, the second row the knees with a neutral joint line orientation, in the third row the knees with apex proximal joint line orientation. So any knee, any knee can be classified or positioned in one of these nine boxes and this can be by just visual assessment of the full-leg radiograph or more precisely by using two simple mathematical formulations the first formulation is MPTA minus LDFA, which defines the alignment and we call this the arithmetic hip knee angle so MPTA, the medial proximal tibial angle minus LDFA, the lateral distal femoral angle. When MPTA minus LDFA is negative in other words MPTA is smaller than LDFA than the knee is in varus alignment if MPTA minus LDFA is zero the leg is in neutral alignment if MPTA minus LDFA is positive the knee is in valgus alignment. The second formulation is MPTA plus LDFA. So the summation of both. This defines the joint line orientation when the summation is less than 180, the apex of the joint line orientation is distal, if the summation equals 180, the Joint line orientation is neutral, if the summation exceeds 180 the Joint line orientation is apex proximal so with these two formulations you can easily assess what type of knee you are confronted with where it sits in the matrix and what its natural alignment and joint line orientation is. In other words which CPAK type it is. Here you see some practical examples. Now it is interesting to note that in the normal Western European population where I live, our data show that most needs are located in CPAK one two three four and five categories in other words apex distal with overall varus or neutral alignment and by the way this work in the meantime has also been done in Japanese and other Asian populations. Which in general show almost exactly the same distribution as in our data. Now here you see a very interesting slide of arthritic patients. So patients with knee OA and what you note is that the distribution of the clouds, or dots, or patients is not so much different. It is a bit more spread because of the OA and also a bit more to the left because of the increasing varus during OA but overall it is pretty much the same most are CPAK one, two, three, four and five. So apex distal and overall varus or neutral alignment. So pretty much identical to the previous slide, the healthy patients and that is very logical because during the progression of OA, MPTA and LDFA only change in the very late stage of the process when bone erosion has occurred and until then what mainly progresses is JLCA, the joint line conversion angle which is caused by progressing cartilage wear and progressing ligament laxity on the convex site. So that means that MPTA and LDFA are very reliable parameters to judge what the original constitutional alignment and joint line orientation of the knee were and therefore this makes the CPAK classification a very reliable tool to determine though and to restore both constitutional alignment and Joint line orientation in the most optimal way during surgery. Now let's go back to the surgery as I have explained earlier if you restore mechanical alignment systematically in all of your patients to zero degrees, you regularly run into this conflict with the soft tissues because of an asymmetric or trapezoidal extension space for this reason some surgeons have suggested to cut parallel to the articular surfaces instead of perpendicular to the mechanical axis and they have called this kinematic alignment and as a matter of fact this is a good idea I believe, because it restores indeed the constitutional alignment and the CPAK type at least in the little deformed knee when there is not too much bone erosion. When there is however severe axis deviation or bone erosion, kinematic alignment becomes less reliable and even dangerous I believe the reason you can see here this is a moderate to severe varus knee if you perform kinematic alignment in this knee and you cut parallel to the jointline, you see that on the tibial side this would mean a resection in severe varus somewhere around 8 degrees or even more so in this case and if there is one thing that we have learned from the past that is that cutting the tibia in severe varus is a dangerous thing to do for two reasons one if you cut the tibia in varus this means that inevitably you will need to cut and position the femoral components in relative internal rotation otherwise you will never obtain a rectangular flexion space. Now if you position the femoral component in internal rotation this will of course negatively affect overall rotation of the legging extension and you will medialize the trochlea which provokes lateralized patellar tracking and the risk for lateral patellar dislocation. Secondly we have also learned from the past that a severe cut on the tibia especially when combined to overall varus of the leg increases the stress on the medial side of the knee both on the prosthesis and the underlying bone which may lead to accelerated implant wear or to migration or subsidence of the prosthesis or to persistent pain on the medial side of the knee and the tibia because of the increased bone stress. So instead of cutting the tibia here in severe varus it is in my opinion better to restore this knee to its constitutional status in other words to its original CPAK type which in this example if you do the calculations is a CPAK Type 4, meaning that the MPTA should ideally be restored to about 87 degrees I will come back to this in a few minutes when we discuss specifically what our strategy is for CPAK Type 4 knees and this brings us indeed to the essence or the core of our philosophy that these two restore the knee to its constitutional or natural alignment with help of the CPAK classification. So the first thing we do when we perform knee arthroplasty, is to evaluate thoroughly the pre-operative full leg radiographs and determine which CPAK type the knee is that we are going to operate and we use the two equations to do so MPTA minus LDFA to determine on Alignment MPTA plus LDFA for joint line orientation and based upon this we bring back the knee to its predecist or constitutional configuration so let's explain in detail how this works for each of the nine CPAK types so we start with CPAK type 1 which is a varus knee with apex distal joint line orientation and this represents 26 percent of all knee types so one in four knees are like this CPAK type 1. to be this type mpta minus LDFA is below -2 and MPTA plus LDFA is under 177 so it is like this varus apex distal here you see an example varus apex distal and this is typically how the knee looks like so 26 percent of all knees are like this but amongst the varus knees its proportion is 83 percent so most varus knees, 83 percent are CPAK's type 1. typical example coming in for surgery with an MPTA of 83 degrees LDFA of 91 degrees so 83 minus 91 is -8 so 8 degrees varus 83 plus 91 is 174 so apex distal what is our strategy in this type of knee restore MPTA to 87 degrees so correct the tibial varus to its constitutional state 87 degrees and bring LDFA to 89 so 1 degree valgus so 87 minus 89 is 2 degrees varus 87 plus 89 is 176 so apex distal so the knee is restored to its constitutional CPAK type varus apex distal in case there is remaining this balance with the soft tissues in this case residual tightness on the middle side I will increase LDFA gradually to a maximum of 92 degrees so increase the varus on the femur to a maximum of 2 degrees which is my upper restricted boundary typically this will be in a case with severe varus bowing of the femoral shaft and a varus hip configuration with a low neck shaft angle on the tibial side my restricted boundary for MPTA is 85 so never more than 5 degrees varus on the tibial side in total my overall restricted limit is 6 degrees virus overall so in other words MPTA 87 and LDFA 89 are my standard settings with some margin to adjust intraoperatively towards the maximal restricted boundaries in case the soft tissues would dictate so CPAK type 2 neutral alignment apex distal joint line orientation and this represents 39 percent of all knee types so almost 40 percent of all knees are like this CPAK type 2 MPTA minus LDFA is zero plus or minus 2 degrees and MPTA plus LDFA is under 177. so it is like this neutral alignment and apex distal an example and this is typically how the knee looks like so 39 of all knees are like this and amongst all neutral knees its proportion is 72 percent so most neutral knees have an apex distal joint line orientation 72 typical example coming in for surgery with an MPTA of 87 degrees LDFA of 87 degrees so 87 minus 87 is zero so neutral 87 plus 87 is 174 so apex distal what is our strategy here easy restore to MPTA 87 and LDFA 87 logical and straightforward, keep the knee into its CPAK box of type 2 neutral and apex distal joint line orientation CPAK type 3 valgus knee Apex distal jointline orientation 10 of all needs are like this CPAK type 3. MPTA minus LDFA is greater than plus two, so MPTA greater than LDFA and MPTA plus LDFA is below 177 valgus alignment apex distal an example and this is typically how the knee looks like so 10% of all knees are like this but amongst the valgus knees its proportion is 73 so most valgus knees, 70 percent are CPAK type 3 with an apex distal joint line orientation typical example coming in for surgery with an MPTA of 89 degrees so one degree varus LDFA of 82 degrees so important valgus on the femoral side so 89 minus 82 is plus 7 so 7 degrees of valgus 89 plus 82 is 171 so apex distal. What is our strategy in this type of knee, our strategy is keep MPTA at 89 degrees reduce the values on the femur from 82 to our more reasonable 87 degrees so 89 minus 87 is 2 degrees valgus remaining 89 plus 87 is 176 so apex distal joint line orientation in other words the knee is safely restored to its CPAK type preconstitution CPAK Type 4 varus knee neutral joint line orientation five percent of all needs are like this CPAK Type 4 MPTA minus LDFA is below -2 and MPTA plus LDFA is between 177 and 183 varus alignment, jointline neutral, an example, and this is typically how the knee looks like so five percent of all knees are like this and amongst varus knees 17 are like this so only one out of six varus knees are CPAK Type 4 with an apex neutral jointline orientation most varus knees are indeed type ones with apex distal joint orientation typical example coming in for surgery with an MPTA of 85 degrees an LDFA of 94 degrees so 85 minus 94 is -9 so 9 degrees of varus 85 Plus 94 is 179 so apex neutral what is our strategy in this type of name restore MPTA to 87 degrees so correct the table varus to 87 degrees and bring LDFA to 90 which is neutral so 87 minus 90 is 3 degrees of residual varus 87 Plus 90 is 177 so apex neutral so the knee is restored to its constitutional CPAK type varus and apex neutral also here similar to CPAK type one in case there is remaining this balance with the soft tissues usually residual tightness on the medial side, I will increase LDFA gradually to a maximum of 92 degrees which is my upper restricted boundary typically this will be in cases with severe varus bowing of the femoral shaft and a varus hip configuration with a low neck shaft angle on the tibial side my restricted boundary for MPTA is 85 degrees so I never give more than 5 degrees of varus on the tibial side in total my overall restricted limit is 6 degrees varus overall so in other words MPTA 87 and LDFA 90 are my standard settings for CPAK type 4. with some margin to adjust intraoperatively towards the maximal restricted boundaries in cases of tissues would dictate so CPAK type 5, neutral alignment, overall neutral joint line orientation. 15% of all knees are like this CPAK type 5 MPTA minus LDFA is zero plus or minus two degrees and MPTA plus LDFA is between 177 and 183 so neutral overall alignment and neutral joint line orientation an example so 15% of all knees are like this and amongst neutral aligned knees 28% are like this. So this type 5 is much less frequent than the CPAK type 2 neutral knees which are apex distal and represent 72 percent of neutrally aligned knees. Typical example of a CPAK type 5 coming in for surgery MPTA of 90 degrees LDFA of 90 degrees so 90 minus 90 is zero so neutral, 90 plus 90 is 180, so apex neutral what is our strategy here, restore MPTA to 90 and LDFA to 90 degrees, logical and straightforward but one caveat I don't want any over correction towards valgus not a single degree neither on the femur nether on the tibia I indeed never want post-operative valgus alignment unless the knee was in pre-operative valgus. I'm very strict on this so I would rather error towards slide varus if I'm not sure about my resection accuracy CPAK type 6 valgus knee, neutral joint line orientation only three percent of all knees are like this. CPAK type 6. MPTA minus LDFA is greater than plus two so MPTA is greater than LDFA and MPTA plus LDFA is between 177 and 183 valgus alignment joint line neutral. An example. So only three percent of all knees are like this and amongst the valgus knees 25% are like this so this type 6 is much less frequent than the CPAK type 3 valgus knees which are apex distal and which are the majority 72 percent of all valgus knees. Typical example of a CPAK type 6 scheduled for surgery. MPTA of 92 LDFA of 86 so 92 minus 86 is 6 degrees of valgus 92 plus 86 is 178 so joint line orientation neutral what is our strategy here restore MPTA to 90 degrees so decrease the valgus on the tibia to neutral and reduce the values on the femur to an LDFA of 88 degrees so 90 minus 88 is 2 degrees valgus remaining 90 plus 88 is 178 so neutral joint line restoration in other words the knee is nicely restored to its CPAK type 6 configuration CPAK type 7 various knee apex proximal joint line orientation is extremely rare only 1 in 500 knees are like this MPTA minus LDFA is below -2 and MPTA plus LDFA is greater than 183 varus apex proximal an example, extremely rare only 0.2 percent of all knees and only 0.6 percent of all varus knees are CPAK type 7. typical example of a CPAK type 7 scheduled for surgery MPTA of 90 degrees LDFA of 97 degrees so severe varus on the femur neutral on the tibia. MPTA minus LDFA 7 degrees of varus MPTA plus LDFA is 187 so apex proximal joint line orientation so what is our strategy in this type of knee, keep MPTA at 90 degrees restore LDFA to 93 degrees so MPTA minus LDFA is -3 so 3 degree overall varus MPTA plus LDFA is 183 so apex proximal in other words we reduce the varus on the femur to a more reasonable and safe degree restoring the knee safely back to its constitutional CPAK type 7. varus, apex proximal in case the soft tissues require more varus intra-operatively we do so on the tibia up to an MPTA of 87 as a restricted boundary CPAK type 8 neutral alignment overall apex proximal joint line orientation extremely extremely rare this is the configuration, neutral apex proximal joint line orientation and extremely rare actually this is the only one that I've seen in recent years and I don't recall having encounters a CPAK type 7 for knee arthroplasty so if you encounter a case for surgery please let me know because that will really be very exceptional like seeing a Tasmanian tiger your case would then probably look like this MPTA of 92 degrees LDFA of 92 degrees so varus on the femur valgus on the tibia MPTA minus LDFA is zero so neutral MPTA plus LDFA is 184, so Apex proximal joint line orientation so what is our strategy in this type of need as I explained we have not encountered in recent years a CPAK type 8 for surgery but probably our strategy would be to go for keeping the MPTA and LDFA as they are avoiding any error towards increasing valgus both on a tibia as well as on the femur because as I have explained before we do not want positioning a knee into valgus unless it was clearly in valgus prior to the surgery finally CPAK type 9 valgus knee apex proximal joint line orientation extremely rare, only one in 500 knees are like this MPTA minus LDFA greater than plus two and MPTA plus LDFA greater than 183. Valgus, apex proximal, an example so extremely rare only 0.2 percent of all knees and only 1.5 percent of all valgus knees are CPAK type 9. typical example of a CPAK type 9 is scheduled for surgery MPTA of 96 degrees LDFA of 92 degrees so severe valgus on the tibia some varus on the femur MPTA minus LDFA is plus 4 degrees so overall 4 degrees valgus MPTA plus LDFA is 188 so apex proximal joint line orientation what is our strategy here for type 9 restore MPTA to 92 LDFA to 90 degrees so reduce the volume of the tibia to a reasonable and safe 2 degrees and restore the femur to neutral so with this we have covered all CPAK types I hope that this explanation is of help to you in your further planning and execution of the surgery thank you for watching.