TKA - TOTAL KNEE ARTHROPLASTY ( Total Knee Replacement )

 

Total knee replacement has been practiced since the 1960s , but the complexities of the knee joint began to be understood in the 1980s , because of this , TKA  initially was not as successful as it is in the new century . However, over the last 20 years, dramatic advances in the  design modifications that appear to be durable. Significant advances have occurred in the type and quality of the metals, polyethylene, and more recently, ceramics used in the prosthesis manufacturing process, leading to improved durability . As with most procedures  in modern medicine, more and more patients are receiving the benefits of total knee arthroplasty (TKA) .

History of the Procedure

1 - Fergusson reported a resection arthroplasty of the knee for arthritis in the 1860s .

2 -  Verneuil is thought to have performed the first interposition arthroplasty using joint capsule. Other tissues were subsequently tried, including skin, muscle, fascia, fat, and even pig bladder.

3 - The first artificial implants were tried in the 1940s as molds fitted to the femoral condyles following similar designs in the hip.

4 - Combined femoral and tibial articular surface replacements appeared in the 1950s as simple hinges. These implants failed to account for the complexities of knee motion and consequently had high failure rates from aseptic loosening.

5 - Gunston importantly recognized that the knee does not rotate on a single axis like a hinge, but rather the femoral condyles roll and glide on the tibia with multiple instant centres of rotation. His polycentric knee replacement had early success with its improved kinematics over hinged implants but was unsuccessful because of inadequate fixation of the prosthesis to bone.

6 - The total condylar prosthesis was designed by Insall at the Hospital for Special Surgery in 1973. This prosthesis concentrated on mechanics and did not try to reproduce normal knee motion. In 1993, Ranawat et al reported a rate of survivorship of 94% at 15 years of follow-up, which is the most impressive reported to date. The component was subsequently altered to artificially introduce normal kinematics to improve range of motion of the component. At the same time, a prosthesis with more natural kinematics was developed at the Hospital for Special Surgery, relying on the retained cruciate ligaments to provide knee motion.

7 - The argument as to whether knee ligaments should be preserved or sacrificed continues to this day. Long-term follow-up studies do not show any significant differences, although gait appears to be less abnormal if ligaments are preserved, especially when walking up and down stairs. One theoretical way of incorporating normal kinematics and maximal conformity is with mobile tibial bearings. Current midterm follow-up studies of these prostheses have so far shown encouraging results.

Frequency

Approximately 130,000 knee replacements are performed every year in the United States.

Etiology

Osteoarthritis ( OA ) is disease of synovial joints , characterized by degeneration process . this disease is present in 40% of people more than 40 years old , but 50% of them are symptomatic , Osteoarthritis can be primary or secondary . secondary OA is due to mechanical derangements of the joints ( meniscal injury , ligamentous injury ), fractures , infection , RA , Gout , hemophilia , pigmented villonodular synovitis , steroid-induced ,  avascular necrosis,  and bone dysplasias ,  the primary OA is idiopathic  .

Pathophysiology

The cause of primary OA is unknown , it may represents a problem in chondrocytes repair . The cartilage in OA joints has water concentration more than normal jounts , it has abnormal type 2 collagen too . it has also high levels of cathepsins and interleukin-1 . the synovium has some changes too , that includes synoviocytes hyperplasia , increased leukocytes concentration , neovascularisation , and increased vessles permeability .

Clinical

Pain is the Dominant symptom in the osteoarthritic patient . pain starts in the weight bearing phase and at the end stage of OA , pain is constant , and not reliefed by rest. And when the patiens has night pain , we must consider his complain as disabling , and at that time we must pay urgent  attention for him . Quantifying the patient’s pain may be simply scaled  as ( mild , moderate , severe ) or Numericaly scaled ( from 1 to 10 ) . 

other symptoms are like stiffness , swelling , locking , and giving way . some patients may have considerable alterations in there social life  , sexual activity , sleep , exhaustion , and sometimes depression .

INDICATIONS  of  TKA

 1 - The primary indication for TKA is to relieve pain caused by severe arthritis. Pain which is significant , disabling  and distressing at night  .

2 -  dysfunction of the knee causing reduction in the patient's quality of life , is another main indication .

3 - Correction of knee deformity is another indication  but not primary indication .

* Radiological  findings must correlate with a clinical impression of knee arthritis .

**Failure of all conservative treatment methods before considering surgery, is a must .

RELEVANT ANATOMY

The knee moves on 6 axis , 3 are translations ( antero-posterior , medio-lateral, and infero-superior ) , and 3 are rotations ( Flexion-extension  , abduction- adduction , and internal-external rotation ) . these movements are a result of the shape of the articular surfaces and the direction of the 4 major ligaments ( ACL , PCL , MCL , LCL ) .

The flexion extension of the knee joint is combined of rolling and sliding , and it is called rollback , which allows more degrees of flexion .

The asymmetry between the medial and lateral femoral condyles ( the lateral is bigger ) , causes the screw home mechanism , which is locking the joint into extension .

The MCL resists valgus and external rotation  , and the LCL resists varus and internal rotaion .

The ACL  primarily resists anterior displacement of the tiba , and it also resists varus and valgus especially if the MCL and LCL are torn .

The PCL mainly allows rollback of the femoral condyl , and resists posterior displacement of the tibia in full flexion .

The patella works as a pulley , transmitting the force of the quadriceps to the femur and the patellar tendon . its motion is kind of sliding and gliding .

The mechanical axis of the lower extremity , is an imaginary line starts from the center of the hip . to the center of the ankle , passes through the middle of the knee , and through this line the weight of the body passes . This mechanical axis is disturbed when the patient has deformity in the knee , and must be corrected during total knee arthroplasty .

CONTRAINDICATIONS

Absolute contraindications of TKA : 1-  active knee infection .  2 – extensor mechanism dysfunction .  3 – severe vascular diseases . 4 – recurvatum deformity due to muscle weakness .

Relative contraindications  : 1 - medical conditions . 2- skin lesions at the site of surgery. 3 – neuropathic joint .

TREATMENT

Medical therapy

The treatment of OA is initially  non operative  ,  and includes simple analgesics , NSAIDS , intra-articular viscusupplementation injections ( e.g.  Hyalgan , crespine gel )  , joint aspiration and steroid injection , walking aids , activity modification , knee rehabilitation and occupational therapy .

Surgical therapy

Many surgical procedures can be done for the patients with osteoarthritis , like arthroscopic debridement which some times indicated when there is mechanical symptoms , high tibial osteotomy can be done when the patient has varus deformity and stable joint and medial compartment involvement .  arthrodesis of the knee joint can be considered in some young patients when there is chronic sepsis . unicompartmental arthroplasty can be done in elderly patiens who has unicompartment involvement and are notobese .

The aim of TKA is to resurface the damaged tibiofemoral joint surfaces , with a metal components and a low friction polyethylene bearing .

Preoperative workup

Good preoperative workup , and identification and optimization of the patient conditions prior to surgery , will reduce the peri and post operative complications including the mortality rate .

Examination of the patient should include examining the skin at the site of the knee , esp. for any scar or skin lesions , presense of bursitis , or vascular disease .

Examination of the ligaments as that may affect the choose of the prosthesis .

We must examine the patient for any radiating pain from the spine or the hip .

Assessment of the social situation of the patient is important to arrange his post opearative rehabilitation program .

Lab Studies

Preoperative lab. evaluation :

CBC , FBS , ESR , CRP , PT , aPTT , urine analysis , urea and electrolytes.

Radiological Studies

Radiographic views of the knee include the following: Standing AP view , Lateral view , Patellofemoral (skyline) view , and Long leg radiographs to assess malalignment . these views are Helpful for preoperative planning .

Routine chest XRay is not a routine  screening tool, but it is indicated if the patient has any cardiopulmonary complain.

Other Tests

ECG for older patients ,or patients with cardiac complains history . MRI and BMD are done when indicated , but are not done as routine .

The patient must fully understand the risks and possible complications of the procedure . they should have all medical conditions optimized before surgery , and be free of any activeinfection . tow unites of blood must be ready for perioperative infusion , either from the blood bank or as predonated blood .

Choosing the type of anesthesia , general or regional , is discussed with the patient with some input from the surgical team , although cardiovascular outcome , and mortality rates show no difference between general and regional anesthesia , but epidural anesthesia have been shown to develop fewer DVT . another good benefit of epidural anesthesia is avoiding the need of excessive opiums by keeping the catheter for about 72 hours .

Antibiotics and antithrobtics must be given prior to surgery to reduce the rate of infection and DVT .

Intraoperative details

·         A thigh tourniquet is used to help in surgical procedure , but it must be avoided in patients with vascular diseases , or patients with history of DVT .

·         Prevention of contamination is vital , and that is by meticulous attention to sterility and using laminar  flow theature .

·         Anterior approach is usually used , although some use lateral or subvastus approache .

·         Intra-articular soft tissue and osteophytes must be cleaned .

·         Bone cuts of the distal femur must be done perpendicular to the mechanical axis of the femur , by using intramedulary alignment system .

·         Bone cuts of the proximal tibia should be done perpendicular to the axis of the tibia , using intra or extra articular alignment rods .

·         When there is deformity , the contracted ligaments around the knee must be released in a step-wise fashion to balance the soft tissue .

·         Patellofemoral tracking must be assessed with trial components  , and if the patella is severly diseased it can be resurfaced by a button .

·         Bone cement is used to fix the components in place , and in non cemented system , press fit gives the short term fixation , and bone ingrowth gives the long term fixation of the system .

·         Mechanical anti thromboembolic devices ( stockings , foot pumps ) are used intraoperatively .

Postoperative details

·         Strict observation for 24 hours .

·         Adequate hydration .

·         Adequate analgesia provided by continuation of epidural catheter , or by intravenous analgesia pump .

·         Knee motion with CPM machine supervised by physiotherapist .

·         Cryotherapy to reduce swelling and pain .

·         Drains removed within 24 hours .

·         Walking in the 2^nd P.O. day .

·         Discharge of the patient is only after checking the wound , the knee flexion is 90 , and the patient is considered to be safe at home .

·         Anti thrombolytic agent must continue for about 5 weeks.

·         Outpatient review is in 3 weeks , 6 weeks , and 12 weeks , and follow up at 6 monthes , 1 year , 2 years , 5 years , 10 years  .

COMPLICATIONS

Thromboembolism

Predisposing factors which increase the incidence of DVT are age more than 40 , female sex , history of DVT , obesity , varicose veins , smoking , DM , and coronary heart disease . incidence of DVT after total hip arthroplasty without prophylaxis is more than 40% , and the risk of the fatal PE is around 0.1-1% .

Methods of prophylaxis of DVT which consists  of antithrombotic agents , intaoperative foot pumps , epidural , stockings , adequate hydration , and early mobilization .

Infection

Factors which increase the incidence of infection after TKA are , RA , skin breakdown , previous knee surgery , obesity , DM , renal failure , malignancy , and concomitant UTI or chest infection .

Prophylaxis of infection includes  : preoperative examination to execlude any site of infection , in the operating room , decreasing the traffic , use of laminar flow ,body exhaust systems ,  prophylactic antibioptics , and meticulous surgery . all help in reducing incidence of infection to less than 1% .

Patellofemoral complications

That includes instability of the patellofemoral joint , patellar fracture , patellar component failure , patellar clunk syndrome , and extensor tendon rupture .

Neurovascular complications

Artery thrombosis after TKA is very rare ( 0.03-0.1 ) but usually results in amputation .

Peroneal nerve palsy is the most commonly reported  nerve palsy after TKA , esp. when there is valgus and flexion deformities which can be seen more in RA . most of the patiens recover completely or partially .

Periprosthetic fractures

Rare complication , more seen in the femoral supracondylar  area in RA patients , osteoporotic patients , and revision arthroplasty patients .

Aseptic loosening

This is the ultimate failure of the TKA , and it occurs in 5-10% of patients in 10-15 years ,  and if it is accompanied with bone loss or bone osteolysis , it leads to catastrophy .

Arthrofibrosis

Excessive scar tissue formation , causing limitation of motion . the etiology is unknown , and the treatment is conservative , includes NSAIDS , physiotherapy , and some times manipulation under GA and CPM therapy and in rare cases scar excision .

OUTCOME AND PROGNOSIS