Knee Replacement — the Prosthesis, the Operation and Recovery

Advancing age and genetic predisposition lead to conditions such as knee osteoarthritis. In some cases the classic treatment methods bear fruit, but in advanced stages surgery is recommended. Specifically, for problems of this kind, knee replacement surgery (total knee arthroplasty) is considered.

A knee prosthesis is a device that gives the patient the chance to regain mobility. It significantly reduces the pain caused by knee osteoarthritis by replacing the damaged articular cartilage. In essence, the femoral and tibial components are covered in metal, and the spacer between them in a special plastic that allows the knee to flex and extend.

The operation takes approximately 1–2 hours. Patients can most often walk with the aid of a frame from the day after surgery — it is a safe and effective procedure that eliminates pain and corrects deformity of the leg.

The anatomy of the knee

The anatomy of the knee consists broadly of 3 components: the lower end of the femur, the upper end of the tibia and the kneecap (patella). Where these 3 structures meet, the surfaces are covered by articular cartilage. The cartilage is smooth, protects the bones and allows them to move easily.

Then, between the femur and the tibia, there are 2 "C"-shaped structures called the menisci. They work by absorbing the shocks to which the knee joint is subjected.

If the knee is working healthily, all these parts work in harmony, allowing fluid movement. When a serious injury occurs, or a condition such as knee osteoarthritis, this harmony is disturbed and pain, reduced muscle strength and diminished mobility appear.

Types of knee prosthesis

There are two kinds of prosthesis: partial (also called unicompartmental) and total (also called tricompartmental). A partial prosthesis replaces only the affected parts of the knee, while a total prosthesis replaces the knee completely.

There is also another way of describing the types of knee prosthesis. Those based on the system for fixing to bone can be cemented or uncemented.

When a total knee replacement is recommended

Total knee replacement is suggested when it is established quite clearly that the patient is suffering from a condition such as knee osteoarthritis.

The key signs that may lead to the condition being suspected, and to the decision to operate, relate to constant knee pain and stiffness. This means interference with ordinary activities such as walking, climbing stairs, and getting in and out of a car. The pain increases more and more while walking, to the point where you feel the need for a stick or something to lean on.

Other symptoms can be knee pain that does not ease at rest, and deformity of the knee (the knee bowing inwards or outwards). Nor should we forget the signs that do not go away. If, despite conservative treatment such as anti-inflammatory medication, intra-articular injections and physiotherapy, there is no improvement, then surgery is recommended.

The knee replacement operation

One important point is that the patient receives various recommendations several weeks before the operation:

The first recommendation concerns medication. Where possible, stop aspirin 5 days before the operation. Anticoagulant treatments such as Plavix or Sintrom must be mentioned to the doctor from the outset, so that they can be stopped before the replacement surgery. Cardiac treatments are only altered following discussion with, and on the recommendation of, a cardiologist. The patient should give the specialist a list of all the medicines they take, the list being handed over at the pre-anaesthetic consultation.

Patients are asked not to eat or drink anything for 8 hours before the operation. The patient's knee is positioned so that the surgeon can easily reach all the ligaments. Anaesthesia is applied from the waist down and an incision of 15–20 cm is made. The damaged surfaces of the articular cartilage are removed along with a small part of the bone underneath. Once removed, metal implants are fitted that recreate the surface of the joint (most often they are cemented into the bone). A plastic spacer is added between the metal components to provide a smooth gliding surface. Before closing the incision, the surgeon will move the patient's knee gently to test the mobility of the prosthesis.

Recovery after knee replacement surgery

Rehabilitation is necessary after knee replacement surgery. The hospital stay generally lasts 2 days, and the patient is encouraged to walk with the aid of a frame from the day after the operation. Pain medication is personalised and adapted to each individual patient, and intravenous antibiotics are given for 24 hours after surgery.

Anticoagulant medication is also given for around 30 days after the operation. A physiotherapist will work with the patient daily and teach them how to walk safely and which movements they are allowed to make. Follow-up appointments with the doctor take place at 14 days, 45 days, 3 months, 6 months, 1 year and annually thereafter.

Rehabilitation exercises

The rehabilitation protocol is essential to the success of an operation of this kind. Rehabilitation exercises begin immediately after the procedure and are aimed in the first instance at strengthening the muscles around the prosthesis. Physiotherapy begins the day after surgery, where you will initially use passive mobilisation devices designed to help with gentle stretching and bending movements. The exercises include ankle flexion and extension, active extension of the knee, active flexion of the knee, and movements to restore balance. In general, the types of rehabilitation exercise are tailored to each patient's needs.

FAQ:

Q: How long does a knee replacement operation take?

A: The operation takes approximately 1–2 hours, and patients can most often walk with the aid of a frame from the day after surgery.

Q: When does the prosthesis need replacing?

A: Over time the prosthesis can wear, which creates the need for a revision prosthesis. Modern prostheses are extremely durable, but there is a chance that replacement will be needed after 15–20 years.

References:

Yvet Mooiweer, Martin Stevens - Being active with a total hip or knee prosthesis: a systematic review into physical activity and sports recommendations and interventions to improve physical activity behavior - European Review of Aging and Physical Activity

Insall J, Tria AJ, W N Scott - The total condylar knee prosthesis: the first 5 years - Clinical Orthopaedics and Related Research, 01 Nov 1979, (145):68-77

Ernesto C. Martinez-Villalpando, Hugh Herr- Agonist-antagonist active knee prosthesis: A preliminary study in level-ground walking - Journal of Rehabilitation Research & Development