Estimated reading time: 6 minutes
Hello friends, this is Dr. Ashish Taneja. So today I welcome you to the conceptual orthopedics arthroplasty course my talk for today will be about solving various knee and mainly focus on the surgical steps. So the various deformities can be of two types, it can be intra-articular which can be because of cartilage or bone loss, tibia vera, stress fractures, malunion or non-union of the intra-articular fractures of the tibial condyle.
There can be another component to the various deformities as well like extra-articular deformities which can be because of tibial fractures, femoral bowing or tibial bowing, some stress fracture or a prior osteotomy. So we have to solve both these components together. Through our knee replacement surgery, our focus will be mainly on the intra-articular deformity because that is something which we can correct through our knee replacement surgery.
Extra-articular often times do not need surgery per se but if there are severe deformities which are deforming the biomechanics then we may need to correct the extra-articular deformity as well. So how do you see what is intra-articular and what is extra-articular? You have to understand your angles, have to start drawing angles. So the intra-articular deformity is the angle between the femoral joint line, this one and the tibial joint line.
So this is your intra-articular deformity which is mainly because of the cartilage and bone loss here in the middle compartment. For extra-articular or total deformity you will have to have a scanogram with you. Through scanogram you will draw your mechanical axis of the femur and tibia and the fungal between the two which is your total various deformity of the limb.
If your intra-articular component is less as compared to total deformity suppose this is 15 degrees and this is 22 degrees that means there is 7 degree component of the extra-articular deformity as well which will not be corrected by your knee replacement.
So whenever your total deformity is more than the intra-articular deformity you would suspect an extra-articular component as well. In our scenario, especially in Indian settings, there are a lot of patients who come with tibial and femoral bowing that will contribute to the extra-articular deformities but again mostly we do not focus on these deformities unless they are very very substantial.
So how do you classify these deformities? Various deformities has been classified by Thienpont and Parvizi into three main types intra-articular which can be a reducible deformity in early stages can be an antromedial OA or a postomedial OA. You have to understand clearly that till the ACL is intact it starts with antromedial OA. The sequence of deformity always starts with an antromedial OA then the ACL gets damaged and the disease progresses to posterior.
So antromedial OA with ACL intact second will be postmedial OA with deficient ACL. These deformities usually are reducible. The middle compartment deformities are reducible.
You can just do a valvular stress and the deformity corrects because the MCL is not tight. However, when the MCL becomes tight it becomes a fixed deformity. It can be without lateral instability or with lateral instability.
When in the beginning it is just the MCL tightness but when the deformity progresses the LCL becomes latched. That is when it becomes a lateral unstable knee as well. This is the intra-articular deformity.
Then we have the metaphyseal deformity. The metaphyseal deformity is within five centimetres of joint 9 both on the femur and tibial side. So you will see that the wear is extending to the metaphyseal region.
There is tibia or femur wear that is happening. That is a metaphyseal deformity and diaphyseal deformity will be beyond five centimeters away from joint 9. It can be tibial, femoral or both. This is how it is.
This can be an antromedial deformity with intact ACL. This is the intra-articular deformity with postmedial involvement with deficient ACL. How do we say it’s a postmedial involvement? It is this region.
When the wear is in the postmedial aspect then we say that the ACL is now damaged and the disease has progressed to the posterior aspect as well. Then we have the fixed deformities. The fixed wear is without lateral laxity and finally, we have the metaphyseal or the diaphyseal deformities which are within five centimetres or more than five centimetres away from the joint line.
So till there it is metaphyseal and beyond this it is diaphyseal and then there can be some previous osteotomies which will be a part of metaphyseal deformities again. These are deformities, these are osteotomies which are old heel osteotomies or old fractures which will cause a metaphyseal varus deformity. Now for the varus knee, we have to understand the structures causing wearers.
Structures can be static or dynamic. So in the static structures we have the superficial MCL, deep MCL, we have the posterior oblique ligament, PCL and posterior capsule. For dynamic we have the pes anserine tendons and semimembranosus tendon.
The muscular part is the dynamic stabilizer on the medial side and the other structures like ligaments capsule and PCL will be the static components on the medial side. So these structures are mainly responsible for causing wearers. So the MCL, the POL, the posterior oblique ligament, the semimembranosus tendon, and the pes tendons, are all the tendons and muscles that are dynamic remaining are static.
You have to understand one rule regarding the release. Whenever we release the anterior structures right here then we will affect the flexion gap. When we release the posterior structures we will mainly affect the extension gap.
So this is what you have to understand. Anterior release of the medial structures will help in opening the flexion medial gap and release of posterior structures on the medial side will help in releasing the medial extension gap. This is what you should be remembering.
As we discussed, the release of anterior structures will always increase the flexion gap while the release of posterior structures like POL, and semimembranosus will increase the extension gap. Oftentimes the varus knee will always have a flexion contracture as well and by releasing PCL we will increase the flexion gap. So this is what you should be remembering.
Release of anterior structures helps in improving the flexion medial gap. Releasing of posterior structures helps in releasing the medial extension gap and PCL will help in improving the flexion gap. So this is a diagram which clearly states, this is the flowchart which states the effect of structures.
You will see most of the medial structures affect the extension gap.
