Total Knee Replacement (TKR)

Arthritis of the knee affects many patients from an early age. Normal activities of daily living require a wide range of motion and stability from the knee, a major weight bearing joint. The demands of patients in the 21st century have increased and many patients participate in sport into their 7 or 8th decades.

Improvement in Total Knee Replacement (TKR) prosthesis designs and materials provide excellent outcomes and enables many patients to return to pain free activity of daily living.

Only the patient themselves can determine when they have endured enough, exhausted all the conservative options and is ready for a TKR.

Basics of knee anatomy


The knee can be divided in 3 separate compartments: medial compartment, lateral compartment and patella-femoral joint. These 3 separate compartments are interlinked and share the same capsule and synovial fluid. That is why inflammatory arthritis affects all 3 compartments, but chondral lesions or osteoarthritis can only affects 1 of the 3 compartments.


The knee depends on ligaments for stability joint as it is not a ball and socket joint.


Alignment, in the frontal plain, can vary widely in patients. Varus alignment (bandy legs) lead to increased load on the medial compartment and valgus ( knock knees) on the lateral compartment.


The patella-femoral joint is a complex joint with the thickest cartilage in the body on the patella and small contact area on trochlea. Alignment on the patella-femoral joint is more complex than just frontal plain alignment.


Indications for Total Knee Replacements

Osteoarthritis of the knee with pain affecting activities of daily living that does not to respond to conservative treatment any more.

Only the patient themselves can determine when they have endured enough, exhausted all the conservative options and is ready for a TKR.


Conservative treatment options

The knee lends itself to several different conservative options due to different reasons. It is therefore that a myriad of treatment options exist.


Physical adjustments;


  • Adjustments of lifestyle activities and sports
  • Knee braces and unloader braces
  • Heat and ice treatments
  • Low impact sports like cycling, swimming and aqua -aerobics

Medical and pharmaceutical adjustments;


  • Glucosamine and chondroitin supplements
  • Non-steroidal anti-inflammatory medication
  • Different natural medications
  • Synthetic hyaluronic acid intra-articular injections
  • Platelet rich plasma infiltrations

Arthroscopic procedures


  • Removal of loose chondral cartilage
  • Meniscectomies
  • Microfracture
  • Autograft Chondral implants (OATS/Mosaiecplasty)
  • Autologous Chondral cell transplants (MACI/ACI)
  • Synthetic chondral membranes
  • Meniscus allografts and scaffolds

Surgical realignment procedures


  • Patellar realignment, elevations and distalisation
  • Tibial and femoral realignment osteotomies

Surgical partial knee replacements


  • Resurfacing/hemi-cap
  • Patella replacement/arthroplasty
  • Unicompartmental medial or lateral knee replacements

Partial Knee replacments

In 25% of patients that require knee replacement surgery, only one of the 3 compartments is involved and the other 2 compartments spared. In those cases unicompartemental knee replacement will not only give excellent short term results but also better mobility and need smaller revision procedures when the other compartments start to fail. Partial knee replacements seem very inviting, but surgeons must adhere to strict guidelines and prerequisites, otherwise these procedures will fail early and that in itself defeats the object of partial knee replacement.


Medial unicompartemental knee replacements

This procedure was pioneered in Oxford and with proven excellent long-term results in patients with anteromedial osteoarthritis and no underlying ligamentous instability. The key to the procedure is adherence to the pre-conditions and indications to achieve long-term survival of the implant.


Lateral unicompartmental knee replacements

The incidence of osteoarthritis confirmed the lateral compartment is much less patellofemoral or medial compartment osteoarthritis. In this very small selected group of patients, the results with the unicompartmental replacement seem also very good.


Patello-Femoral replacements

Replacement of the patella femoral joint have not delivered the same long term results as medial and lateral compartment replacements. In cases where this common condition has rendered the patient impaired, there are a number of prosthetic designs with reasonable medium term results.At least it can be followed in unsuccessful cases by a primary total knee replacement.


Total Knee replacement designs

Total knee replacement give excellent long term results in most studies and joint registers with better than 90% 10 year survival. Ironically TKR unfortunately very seldom become a forgotten joint.

The reason for that is possibly because of average maximum flexion of 120ᴼ , loss ofproprioception or slight paradoxically movement in deep flexion. Many different approaches in design adjustments of new prosthesis have tried to address the detail that would guarantee deeper flexion and more natural feeling knee. At this stage there is not much to choose between cruciate retained, mobile bearing, cemented or cementless , medial pivot, patella resurfacing , gap balanced or measured resection or posterior stabilised prosthesis. As long as the surgeon provides a stable replacement through full range of motion the patient will should have excellent function for activities of daily living and low impact sports and hobbies.


Enhanced recovery protocols

Soft tissue healing after TKR is important for longevity of the prosthesis, but early mobilisation also plays an important role in prevention of complications. The advantage of early mobilisation is less pain and lower risk of deep vein thrombosis. The enhanced recovery protocol is multidisciplinary approach to early safe mobilisation and decreased hospital stay. It involves the anaesthetist, physiotherapists and all the nursing staff. By adjusting pain medication, patients’ mobilization is started the same day as the operation.


Complications


Deep vein thrombosis (DVT)

There is a risk for a DVT in primary TKR procedures.Prevention of DVT is important and depends on good hydration, early mobilisation, foot pumps, and chemical trombo-prophylaxis ( low molecular weight heparin, factor 10 antagonists and Vitamin K antagonists).


Infections

There is always a risk of infections with major procedures and despite advances in prevention and antibiotics, it remains a concern. Prevention is still the best way of cure. For that reason the patient is investigated for any possible source of infection. Intra-operatively the principles that we adhere to prevent infections is laminar flow operating theatres, prophylactic antibiotics, accurate and precise surgical techniques, prevention of haematomas ( collection of blood in operating sites) and special care with barrier nursing. Superficial infections can be treated effectively with antibiotics, but deep chronic infection might need revision of the prosthesis.


Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) is a chronic pain condition most often affecting one of the limbs (arms, legs, hands, or feet), usually after an injury, trauma or trauma to that limb. CRPS is believed to be caused by malfunction of the peripheral and central nervous systems. It can occur after TKR, although rare. It is important that it is diagnosed early and pain modulation treatment is started early for resolution of this potentially debilitating condition.


Frequently asked questions


Can both knees replacement be done simultaneously?

In fit and healthy patients 2 simultaneous knee replacements can be done safely. The advantages are less time off from work, only 1 anaesthetic and theatre cost saving. In patients with underlying medical conditions and the elderly there is a higher incidence of systemic complications and in those cases doing the replacements separately is a wise decision. Sometimes medical aids will have a cap on prosthesis benefits and that will preclude bilateral procedures.

What will my limitations be after TKR?

Only a small percentage of patients will be able to do a full squat post- TKR. Patients will not be able to participate in high impact sports like, jogging, jumping, squash, snowboarding, kite boarding, wake boarding and surfing. Patients that are skilled in Alpine skiing, tennis, body boarding and windsurfing will be able to their previous sports as social participants and must be expect to compete at a lower level.

How long after the TKR can I return to drive a motor vehicle?

Depending on each surgeon’s approach and experience and soft tissue must be allowed, but a general rule is that 4-6 weeks after a TKR should be a safe period to return to driving motor vehicles.

Minimally invasive procedures a fad or a must have?

The length of the surgical scar is less important than the alignment and tissue tension in determining long term outcomes. TKR, although a very successful procedure, still carries a risk and often specialised observation in the immediate post-operative period can prevent complications. Cosmetics are important, but should not be more important than the patient’s health or long term outcomes.

What is the best replacement for me?

It depends on your age, demands and bone morphology. The best is to choose a surgeon that you trust, who does a reasonable amount of total knee replacements and is available if there are any post- surgery hick-ups. Let the surgeon choose the prosthesis after all the pros and cons have been discussed.

What is Computerised Assisted Surgery (CAS) and Patient Specific Instrumentation (PSI)

There was a time in the evolution of total knee replacements when correct anatomical alignment of the prosthesis was thought to increase the longevity of the prosthesis. CAS and PSI was developed to improve alignment of the implanted prosthesis. Both these 2 technologies are available but improved implant materials ( cross linked high density polyethylene) and instrumentation have made them less crucial for better surgical outcomes. CAS leads to added cost, longer theatre time and increased risk for complications. PSI can decrease the theatre time, but MRI or CT scan needs to be done, which adds to the cost.There are still very specific indications for this technology in patients with previous implants for femoral or tibial fractures or serious malalignment caused by previous fractures.

When is the right time for a TKR?

All underlying causes for cartilage wear, inflammatory causes, metabolic (gout), instability and alignment must be treated first. Once all other treatment options, chronic pain medication and anti –inflammatory medications have been exhausted the patient can start investigating the option of a TKR or partial knee replacement. The patient will know when the time has come that he or she is ready.



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