The knee consists of a hinge joint where the thigh bone (femur) articulates with the shin bone (tibia). There is also a kneecap bone (patellar) which also articulates with the thigh bone (femur), where it essentially goes up and down a groove as the knee moves from extension to flexion.
These three bones are covered in articular cartilage, and when arthritis occurs, this articular cartilage is worn out, resulting in bone on bone contact.
This can be in any one or combination of the three compartments, and hence we have options to replace either 1, 2 or 3 compartments in knee replacement surgery which can be customised to the patient.

A knee joint is very different to a hip joint, and hence, when one looks at the medical literature, one will see the outcomes are different and that there is a higher dissatisfaction rate with knee replacements than there is with hip replacements. This is because of the far more complex anatomy present within a knee. So when replacing a hip joint, we are essentially trying to look at two main parameters, the femoral head centre and the acetabular cup centre and matching these up with implants.

When undertaking knee replacement surgery, there are many more factors to consider. These include radiuses of curvature and relation to the medial femoral condyle, the lateral femoral condyle, how the kneecap moves up and down through the groove, the alignment of the leg, both looking from the front and the side, the rotation when looking through the knee not only the femur but the tibia. In addition, we have to take into account the centres of the hip joint, the knee joint and the ankle joint; the list goes on. Every person has completely different anatomy. Therefore, expecting one of only eight implant sizes that only consider a few of these anatomic parameters is unlikely to recreate that patient’s anatomy exactly. Therefore, there will be abnormalities in the reconstruction, and those abnormalities are consequently felt by the patient, who is undoubtedly dissatisfied and unhappy with the replaced knee.

For some, it can be catastrophic with continuing persisting pain forever and a situation where they are worse off than they started. For others, it may be the inability to get back to sporting activities.

Given this great variation in anatomical parameters, a 3D CT scan will allow us to see all of these parameters and, therefore, create a customised implant for that patient. This now means we are recreating anatomy, and with that anatomy comes accuracy. An implant that now feels more natural to the patient and will allow them to get back to activities they want to, including sporting activities, which is the aim for most.

Patients usually attend on the day of surgery in the morning. They must be starved of food for 6 hours prior to surgery at the minimum. In addition, they will be starved of clear drinks for 2 hours before the beginning of surgery.

Surgery is undertaken ideally under low dose spinal anaesthesia and either sedation or general anaesthetic. We have found this gives the best results. The surgery takes approximately 1 hour and 15 minutes but can vary, and I believe it takes as long as it takes for me to do an excellent job; these times can be longer or shorter. All patients will have a 3D plan; I would have discussed and gone through the 3D plan in great detail with the representative from the company prior to surgery. We have the ability to make corrections at a millimetric level during surgery if we make slight changes to the plan. I utilise a mini invasive muscle sparing approach which results in a smaller scar and faster recovery.

COVID also plays a role, and currently, we would like patients to have been free from COVID infection for several weeks prior to surgery (these dates and times are changing according to various government and health guidelines).

This is not the issue of spreading COVID; it is more the issue of the medical health status of the patient should they catch COVID during the time of a surgical procedure, given they will be slightly immunocompromised. Their ability to fight off a significant COVID infection would be lessened. Dates are set for surgery well in advance.

After surgery, the patient will go to recovery and then back to their room. Usually, the spinal wears off within a matter of hours, and we will mobilise the patient that day if timing and anaesthesia allow.

Their expected hospital stay is 2-3 days. Post-operatively, we like to use a cold compression ice machine (Gameready); this can reduce swelling and, therefore, discomfort and has greatly benefited patients with significant knee surgery. We advise them to use this for at least one month, but most patients like it so much that they normally use it for two months.

As part of the investigation process, we will be able to see what is damaged in the knee. Usually, by the time most patients present, they have worn out 2 or 3 compartments and usually, the decision is to replace the entire joint.

This means we do one surgery that covers all bases and allow that patient to get back to activity with no requirement for any further surgery. However, in younger, more active patients where we know they have an intact anterior cruciate ligament and a pristine usually lateral compartment, then we have an option to replace just two compartments, given we are expecting the patellofemoral compartment to be worn or alternatively, if it is only worn within one compartment at the medial or lateral or patellofemoral then again we have 3D planning. So we have customised implants that allow us to replace that compartment only and enable them to get back to their activities.

Driving can be undertaken when an emergency stop can be performed as well as taking emergency evasion action and also to have an acceptable brake reaction time. I would expect this to be 4 – 6 weeks after surgery. It is important that the therapist undertakes an assessment to make sure that a patient is able to achieve this.

We advise patients not to fly for six weeks after knee replacement surgery. This is because they have had a lower limb surgery, and there is an increased deep vein thrombosis risk. They will be provided with anticoagulation for the first two weeks after surgery and are expected to take this, even though they may well feel fully mobile.

We expect patients to be in physiotherapy within the first week of surgery. They should be attending 1-2 times per week for the first 6-8 weeks and then once per week for the next 6-8 weeks and then once per fortnight for the following 6-8 weeks and then once a month thereafter.

The physiotherapy programme will lead to a strength and conditioning programme. It is important that the joint is not just exercised, but it also involves a certain degree of manual work. The muscles that are being worked are becoming tight and, therefore, need to be loosened. Early on, we advise increasing walking distances, ideally 10% increments at a time.

One can get onto a static bike and start doing work on a bike again to increase the range of motion with low resistance and a higher saddle height.

Swimming is also possible after knee replacement surgery. One must consider accessing a pool and how that is undertaken; we advise starting with a front crawl, but then there is no reason why patients cannot move on to breaststroke, but this should be after at least six weeks.