Unicompartmental Knee Replacement (UKR)

Unicompartmental knee replacement (UKR), also known as partial knee replacement, is a minimally invasive surgical procedure in which only the damaged compartment of the knee is replaced or resurfaced with an implant. The knee can be divided into three compartments: the medial compartment (on the inner side of the knee), the lateral compartment (on the outer side of the knee), and the patellofemoral compartment (in the front of the knee between the kneecap and the thigh bone). 

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This procedure is an alternative to total knee replacement for patients whose disease is limited to just a single compartment of the knee. Partial knee replacement is done through a smaller incision, and patients usually spend much less time in the hospital and return to normal activities sooner than total knee replacement patients.

In unicompartmental knee replacement, only one area of the knee is resurfaced. (orthoinfo.aaos.org)

The popularity and concepts behind unicompartmental knee arthroplasty dramatically altered with the onset of minimally invasive surgery. This occurred in the early 1990s due to the work of Dr John Repicci. Using the Repicci minimally-invasive technique, it became possible to implant a resurfacing unicompartmental knee replacement as a day procedure. 

A/Prof Woodgate started doing this procedure in January 1999, and about one-third of patients are discharged within 24 hours. This requires a thorough preoperative education program and intense postoperative pain management protocol. Satisfaction rate is approximately 90% and expected or projected survivorship of the implant is approximately 7-10 years. The annual revision rate of unicompartmental knee replacements is approximately 3%, which translates to a survivorship of 70% by 10 years.

The implant currently used by A/Prof Woodgate is called a GRU unicompartmental knee replacement, which is a modification of the original Repicci prosthesis, but has a wider femoral component for better surface coverage and a slightly wider and deeper tibial plastic component. Minimal bone is removed for implantation, making it easier for conversion to a total knee replacement in the future if necessary. 

Unicompartmental knee replacement provides the opportunity of improved quality of life to a patient with single compartment bone-on-bone knee arthritis, utilising a fairly straightforward procedure, and with expectations of relief for approximately 10 years. It is, however, unlikely to be a “forever” solution, and is best considered as a pre-total knee replacement operation and a way of buying time without the necessity of going through major surgery. Unicompartmental knee implants are reported to feel far more natural than total knee replacements because there is less disruption involved with the surgery and usually far greater range of motion and function. The operation is best performed early in the arthritic disease process rather than late before other compartments of the knee become involved.

Disease Overview

Arthritis is inflammation of a joint resulting in pain, swelling, and stiffness. Osteoarthritis is the commonest form of knee arthritis in which the joint cartilage gradually wears away, and Ii most often affects older people. In a normal knee joint, articular (hyaline) cartilage allows for smooth movement of the joint, whereas in an arthritic knee the cartilage wears away and becomes thinner or completely absent. In addition, the bones become thicker around the edges of the joint forming  “spurs”. All of these factors can cause pain and restricted range of motion in the joint.

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(Left) Osteoarthritis that is limited to the medial compartment. (Right) This x-ray shows severe osteoarthritis with "bone-on-bone" degeneration in the medial compartment (arrow).

Causes of Knee Arthritis

The exact cause is unknown, however there are a number of factors that are commonly associated with the onset of arthritis, including:

• Injury or trauma to the joint
• Fractures of the knee joint surfaces
• Increased body weight
• Repetitive overuse
• Joint infection (septic arthritis)
• Inflammation of the joint, e.g. rheumatoid arthritis
• Connective tissue disorders, such as systemic lupus erythematosus.

Symptoms and Diagnosis

Knee arthritis can cause pain, which may increase after activities such as walking, stair climbing, or kneeling.  There may be associated joint stiffness, and swelling. Knee deformities such as knock-knees, bow-legs, and flexion contractures may also occur. Knee osteoarthritis is diagnosed by a thorough medical history, physical examination, and X-rays (which show a narrowing of the joint space in the affected arthritic compartment).  Occasionally, MRI scans are ordered to confirm the other knee compartments are uninvolved.

Candidates for Surgery

Knee replacement surgery is recommended when the osteoarthritis has advanced and nonsurgical treatment options are no providing relief of symptoms.

Arthritis must be limited to one compartment of the knee in order to be a candidate for unicompartmental knee replacement. In addition, you may not be eligible for the procedure if any of the following are present:

• Inflammatory arthritis
• Significant knee stiffness
• Ligament damage

Advantages of the Partial Knee

The advantages of partial knee replacement over total knee replacement include:

• Smaller incision
• Less bone removed
• Less blood loss
• Less risk of infection, bleeding and wound problems
• Rapid return to normal knee function
• Less postoperative pain
• Shorter hospital stay, potentially day only procedure
• Allows for future treatment options (revision)
• Feels more like a natural knee
• Minimal disturbance to normal knee function
• Less disruption to lifestyle.

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An advantage of partial knee replacement over total knee replacement is that healthy parts of the knee are preserved, which helps to maintain more "natural" function of the knee.

Disadvantages of Partial Knee Replacement

The disadvantages of partial knee replacement compared with total knee replacement include:

• Slightly less predictable pain relief in some patients
• Potential need for more surgery. For example, a total knee replacement may be necessary in the future if progressive arthritis develops in the parts of the knee that have not been replaced.
• Approximately 20% incidence of pes bursitis (inflammation of the small fluid-filled sac around the tendons on the inner aspect of the upper tibia) – this can occasionally be quite recalcitrant.

Prior to Surgery

A/Prof Woodgate’s rooms will provide an instruction booklet, which includes information on the procedure and the post-operative programme. You will contacted on the day prior to surgery and informed of your admission time for the day of your surgery, and you will be advised of a time from which you need to stop eating and drinking. Previous advice will have been provided with regard to any medications you may be taking.  The anaesthetist for the surgery will also contact you to discuss your medical history, medications, and the type of anaesthesia to be used, as well as the post-operative pain management. 

In your preparations for the surgery, you should plan to bring the following items:

• Pension / Medicare / Veteran’s affairs cards /Health insurance details
• X-rays
• All regular medications
• Toiletries needed if staying overnight
• Clothing (loose fitting)

Day of Surgery

At your allocated time, you will be admitted to the preoperative area, and the nursing staff will prepare you for the procedure.

• The nurse will ask some questions and record baseline observations (temperature, pulse, blood pressure).
• You will be asked about any allergies that you may have.
• You will be provided with some special clothing to put on.
• Compression stockings (TED stockings) will be fitted - these help to prevent blood clots forming in the legs and reduce swelling. One will be applied to the leg not being operated on.  You will need to apply the other stocking to your operated leg on day 3 when your dressing is removed.
• A/Prof Woodgate will see you in the pre-op area and confirm your consent, answer any questions, and mark the leg to be operated on.
• You may be given some light anaesthesia or sedation prior to being transferred to the operating theatre.

Surgical procedure

A partial knee replacement operation typically takes about 2 hours. During the surgery, a small incision (arthroscopy portal) is made over the knee and an arthroscope is inserted to allow inspection of the whole knee and to confirm the other compartments are not involved. Once satisfied that the arthritis is isolated to a single compartment, this incision is enlarged to expose the relevant (medial or lateral) compartment involved. The damaged part of the meniscus is removed.  Residual cartilage and minimal bone is removed and the surfaces of the femur (thigh bone) and tibia (shin bone) are shaped and prepared with a high-speed burr. The plastic component is placed into the freshly prepared area on the tibia, and is secured with bone cement. The new metal femoral component is similarly impacted and fixed in place using bone cement. Once the cement has cured, the knee is taken through a range of motion. The muscles and tendons are then repaired and the incision is closed in layers, and dressings are applied. A knee immobilizer (splint) is placed over the dressing. The general anaesthetic is reversed, and you are then transferred to the recovery unit. In recovery, you will be closely monitored and given any pain relief you require. The duration of your stay in the recovery room is variable, and you will be observed until you recover from the anaesthetic, that is, you will be rousable, comfortable and your observations stable.

After the Procedure

Depending on individual circumstances you may be discharged home 4-6 hours after surgery, or you may have been planned to stay for 1-3 nights in the Hospital. Most patients benefit from having someone at home to assist for the first few days if they are going home on the day of surgery, and these patients will require someone to pick them up to take them home after the procedure.

Under the dressing, you will have a local anaesthetic catheter and pump, which has been inserted by the anaesthetist.  The Painbuster pain management system consists of a small round pump filled with local anaesthetic medication, which is attached to a small catheter (tube) that has been inserted by the anaesthetist adjacent to the femoral nerve in the groin region. The pump automatically delivers the anaesthetic medication at a continual slow flow rate. The pump will be inside a small black carry bag that can be easily transported during walking. It is not necessary to squeeze the pump as the balloon deflates as the anaesthetic medication is delivered automatically to the tissues. The Painbuster should be removed with your dressings on day 3. The catheter is very small and will be painless to remove at home. To remove the painbuster if you are at home, carefully pull the catheter out in the same direction as it enters your skin. There may be a small amount of discharge from the exit point, and this is normal. A gauze dressing or bandaid should be placed over the site.

You will also have a wound drain, which collects any local bleeding from the wound for a couple of hours after the operation.  This drain will be removed before you go home for the day-surgery patients, or on day 1 post-op for those staying in hospital.

Discharge Procedures for the Same Day Surgery Patients

• You will be able to leave the Hospital 4 to 6 hours after your operation.
• You must have someone to collect you from the Hospital and take you home.
• You will be given medication to take home and it is very important to take this medication as prescribed, and this will include regular Panadol, Targin and/or Endone, and anti-inflammatory medication if these can be tolerated.
• You will also receive a dressing pack and instructions will be given on how to change your dressing on day 3 - The thigh to toe dressing needs to remain intact until day 3. 
• The knee immobiliser splint should be worn when walking until the dressing is removed on day 3.
• If showering, you will need to keep your leg dressing dry.  A garbage bag and tape is used for keeping the dressing dry and waterproof.

Day 1 and 2 after surgery

• Remember to rest and elevate the leg.
• Continue to take the analgesic medication at the prescribed regular intervals.
• Keep to a normal diet and drink plenty of fluids - this will help in the healing process and to maintain normal bowel function, though aperients may be needed (e.g. Coloxyl with Senna).
• When mobilising use your knee splint and crutches.  Full weight bearing on the operative leg as tolerated is encouraged.
• You will need to commence your leg exercises a minimum of 4-5 times / day.  (See exercise notes)
• Continue to wear the compression (TED) stocking on the non-operated leg.
• Apply ice packs to the knee for about 20 minutes every 2-4 hours.

Day 3 after surgery

• Follow your pain protocol sheet for the first 48 hours after surgery
• Mobilisation should be easier by day 3 and you may no longer require the knee splint
• Continue with your knee exercises - These are best done about 30 minutes after taking your pain medication
• You may now remove the post-operative bulky thigh-knee dressing, and throw away the crepe bandaging
• The painbuster can be removed from the groin region, and the site covered with a gauze dressing or a bandaid. 
• You may shower and then re-apply both long leg compression (TED) stockings
• Continue using an ice pack for 20 minutes at least 4 times a day with your leg elevated above the level of your heart.

Those patients who have been admitted to hospital will usually be discharged on day 3.

Your Wound Dressing

• The Duoderm or Comfeel dressing is water resistant and may be left intact for showering - Please remove the TED stockings for showering (this is an ideal time to wash or rinse the TED stockings as they dry very quickly).
• It is normal for the Duoderm dressing to become soft and squishy if there is any oozing from the wound, and this will appear as an opaque-looking fluid.
• If the Duoderm dressing lifts off or rolls up or down, replace it with a clean spare dressing pack and leave it intact until your follow-up review.

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Day 4 onwards

• You will need to continue with pain medications as necessary and as prescribed.
• Rest/elevation and ice packs 20 minutes 4 times/day.
• Wearing of both long compression (TED) stockings.
• Showering as normal.
• When sitting elevate your leg on a stool.
• Exercising the knee as instructed.

Day 10

• At or around day 10 post surgery. you will need to see by A/Prof Woodgate for you initial follow-up in rooms.
• You will need to have a postoperative x-ray on the same day, and may be advised to visit the physiotherapist to assist with regaining knee movement.

General Information and Expectations

• Bruising around the thigh/knee area is not uncommon and may be a result of the tourniquet used during the surgery, as well as the surgery itself.  It may extend down the leg as far as the foot, but it usually resolved within 10 to 14 days.
• Some swelling and warmth generally around the knee should be expected following surgery.
• If increased redness, swelling or fever develop, contact A/Prof Woodgate as soon as possible, or the Hospital (if after hours).
• For approximately 2 weeks after surgery, activity levels are usually limited, though you will be able to walk independently and use bathroom and kitchen facilities.
• After 2 weeks, most patients may be able to engage in moderate activities such as climbing stairs. Returning to driving should be discussed with A/Prof Woodgate as this depends on return of movement and requirement for analgesia.
• Within 6 weeks, most patients have resumed of normal activities, though kneeling should be avoided.
• Complete surgical healing takes months.  During this time, some swelling and discomfort is normal and should be manageable with the prescribed or simple analgesic medications.
• After this time, the knee tissues start to soften and become more natural feeling.
• Occasional patients may require an injection of cortisone (after 12 weeks) to relieve tissue soreness due to surgery and readjustment of the knee, especially around the medial (inner) aspect of the tibia.
• Most patients may have a small area of numbness on the lateral (outer) aspect of the incision, and this may or may not resolve over time.

Exercises after Unicompartmental Knee Replacement

It is important to maintain a good balance of rest and exercise following knee surgery to reduce stiffness and obtain maximum function of your knee - too much activity will produce increased swelling and/or pain; too little activity could prolong your recovery and/or limit your knee mobility. Take as much weight on the leg as possible. The knee splint is worn until day 3. Immediately after surgery commence your circulation exercises (as shown by the physiotherapist).

The following leg exercises commence from day 1, as pain permits, but must commence by day 3. Aim to perform a minimum of 4-5 times a day with 10-20 repetitions for each exercise:

1. Straight leg raise

• Lie on your back with the non-operative leg bent so the foot rests on the bed.
• Straighten the knee on your operative leg.
• Lift your leg approximately 15-30cms off the bed.
• Keep the knee straight for 5 seconds.
• Slowly lower to the bed. 

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2. Terminal knee extension (supine)

Lie on you back with a thick rolled up towel under your thigh.

Pull your toes and ankle towards you; lift your heel off the bed until the knee is straight, hold for 5 seconds, and then relax.

Your thigh should remain resting on the towel throughout.

Repeat 10 times.

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Once the dressings are lightened and the splint removed on day 3, knee bending exercises may then commence.

3. Knee flexion seated

• Sit on the edge of a table or chair, and lift the lower leg out until the knee is straight.
• Then bend the leg as far as possible underneath the table or chair.
• Maintain this stretched position with the knee bent for 10-20 seconds, and then relax.

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4. Knee flexion lying

• Lie on your stomach with both legs straight.
• Bend the knee of the operated leg,, and you will feel the stretch in the front of the thigh.
• Do not lift the hips off the bed.

A physiotherapist can advise you on an exercise program to follow for 4 to 6 months to help maintain range of motion and restore your strength and conditioning. You may perform exercises such as walking, swimming and bike riding, but high impact activities such as jogging should be avoided.  A waterproof dressing will usually be needed for about 4-6 weeks when undertaking hydrotherapy.

Risks and Complications

As with any surgical procedure, there are risks and complications involved with partial knee replacement, and these can include:

• Knee stiffness
• Blood clots (DVT or deep vein thrombosis) 
• Infection – This may be superficial in the skin or deep in the wound or knee itself, and may occur early or late.  A/Prof Woodgate routinely uses two separate antibiotics to prevent infection at the time of the procedure, and will continue for 24 hours post surgery
• Injury to nerves or vessels - Although it rarely happens, nerves or blood vessels may be injured or stretched during the procedure. Most patients will have minor sensory skin numbness to the outer side of the surgical incision.
• Ongoing pain unrelieved by the knee surgery.
• Risks of anaesthesia
• Need for additional surgery, especially if the arthritic process progresses in the remaining compartments of the knee.

• Plastic liner wear
• Loosening of the implant.
• Patella (kneecap) dislocation or subluxation.

Medications and Knee Surgery

Many tablets and medications can cause excessive bleeding at operation, interfere with healing, or increase risks of infection. You should provide a list to A/Prof Woodgate of all medications (prescribed and non-prescription) including any herbal supplements that you take, and discuss those which may need to be ceased prior to surgery.  This is particularly important for some of the cardiac (heart) blood thinning agents (such as Asasantin, Clopidogrel, Iscover, Persantin, Plavix, Eliquis, Xarelto, Pradaxa, and Warfarin) as well as some herbal medications (such as Fish Oil, Krill Oil, Arnica, and Turmeric). 

If there is any doubt or confusion about any medication that may need to be stopped, please contact A/Prof Woodgate for advice.