Total Knee Arthroplasty procedure also known as Total Knee Replacement (TKR) surgery is surgery performed by a joint replacement surgeon on a patient suffering from severe arthritis like Osteoarthritis (condition of wear and tear of joints causing inflammation and pain) or sometimes Rheumatoid Arthritis.

The dimensions of total knee arthroplasty procedure changes basis patient’s condition, need and surgeon’s preference. There are different steps involved in the procedure:

Pre-Operative Planning Full-length extremity X-ray is obtained and mechanical & anatomical axes are identified. The X-ray gives prima fascia glimpse to a surgeon about the condition of a patient. Radiographic templates are overloaded on X-ray film to estimate appropriate size of prosthesis, thus templating is an important part of pre-operative planning of Total Knee Arthroplasty procedure.

Templating is excellent at predicting the size of primary prostheses to one size, or to two possibilities, one larger or smaller than the right dimension. This decreases the need for a wide range of extensive and less used stock to be kept on site and permits a surgeon to order the right amount of necessary sizes on table. Use of templates is totally a surgeon’s preference.

Surgery:  All pre-surgery patient preparation like draping etc are completed

Step 1 Knee Incision: – A surgeon makes an incision across front of patient’s knee to access patella (Kneecap). In traditional knee replacement the incision is around 8-10 inches while in MIS (minimally invasive surgery) it’s about 4-6 inches long. Surgeon will have his own preference in terms of approaches to follow. There are three approaches

1.       Medial parapatellar

2.      Mid Vastus,

3.       Sub Vastus.

Medial parapatellar is most commonly used approach.             

Step 2  Exposure by sidelining patella: – Once knee is open a surgeon pushes patella on the lateral side (away from body) to obtain comprehensive exposure of a knee to perform next steps.

Step 3 Preparing the tibia (shinbone)-Preparation of tibia (shinbone) or femur (thighbone) first is entirely a surgeon’s preference. Most of the surgeons prefer tibia preparation first while doing total knee arthroplasty procedure.

Surgeon puts special instruments on tibia platue (demaged part) as shown in figure 1, then he or she performs precise cuts also called measured resection with the help of saw blade as shown in figure 2

Tibial broaching is step of creating a space for keel of tibia. While implanting final tibia, the keel gets fit in this space along with cement to impart fixation to tibia

Step 4 Femur (Thighbone) preparation:- In femur preparation, first of all a surgeon reams femoral canal to find anatomical axis (figure 3), then a specialized instrument assembly is put over femur base condoyles (bottom area of femur) – (Figure 4), with this a surgeon tries to align cuts to gain natural alignment of knee (get and align valgus angle between mechanical and anatomical axes). Because of deformity there is change in the angle; normal angle is around 6 degree. The main objective of total knee arthroplasty procedure is to restore natural alignment to achieve natural feel of artificial joint

Post this surgeon performs distal (bottom) cut of femur (figure 5), with this damaged part are cut away.

Further to get few additional cuts, a sizer is placed over distal (bottom) part. Once the size is ascertained, same size cutting jig is placed over it to get additional 4 cuts namely; 1 anterior, 1 posterior and 2 chamfer cuts. Once all 5 cuts are in place, femur component fits over a femur.

Step 5 Extension and flexion gap confirmation Surgeon checks whether desired extension and flexion gap is achieved or not.  This is done with the help of special instrument called spacer (Figure 5).

If required, a surgeon may choose to resect more bone in order to achieve desired gap.

Step 6  Trialing  Post cuts the femoral and tibial trial implants along with trial polyethylene are placed over cuts and alignment, expected knee movements in extension and flexion are checked (figure 6). If surgeon feels the need of additional bone cut, he may choose to do the same.

Step 6 Tibial component implantation If surgeon is happy with the alignment then he removes trial implants and proceeds with final implantation of tibial component called tibial tray (figure 7) which is implanted over tibia with the help of bone cement. Bone cement gives good fixation. A plastic polyethylene (medical grade plastic) is placed over a tibia which acts like a cushion similar to that of meniscus between femur and tibia (figure 8).

Step 7 Femoral component implantation After trialing, if surgeon is happy with the alignment, expected knee movements then he or she proceed with final implantation of femoral component with the help of femoral impactor (figure 9) and cement it over femur.

Step 8 Patella preparation Patella is flattened and resurfaced with additional plastic component in order to ensure proper fit of new artificial knee assembly.  Patella resurfacing is totally depends on surgeon’s preference and patella’s condition. A portion of patella is resected and plastic component is cemented over it. Patella movement over joint is of paramount importance as it plays major part in extensor mechanism. With deformity and new implants in the joint the dimension around patella changes, hence it needs the attention as patella would be tracking against metallic femoral component. Faulty alignment at and around patella may cause instable patellofemoral joint, subluxation and compromised or disrupted extensor mechanism of knee. 

Step 9 Finalizing total knee arthroplasty procedure:-A surgeon bends and flexes the knee to ensure proper alignment, sizing, placement, position and working of implants. To complete the procedure, the surgeon closes the incision with stitches or staples. A patient will be shifted to general ward and will be on the way to recovery .Discharge and physiotherapy course follows total knee arthroplasty procedure.

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