A 50 year-old-housewife recently came with the complaints of difficulty in walking due to inward angulation of her knee joints. Her knee joints used to collapse with every step. Her walking distance was significantly reduced and she experienced difficulty in completing household chores.
She was diagnosed with having arthritis in only the inner part of the knee joint; but her anatomy and alignment was well preserved. As the patient was young (less than 60-years-old) and the disease was only limited to the one compartment of the knee, she was prescribed unicompartmental knee replacement. Surgery was done with a minimally invasive technique.
Explaining the technique, Dr Pradeep Moonot, says, “The joint was exposed through a small incision (3 inch), the diseased condylar (round prominence at the bone end) surfaces were excised and after adequate preparations, a unicondylar femoral (thigh bone) and tibial (bone from knee to ankle) component was fixed. The beauty of this implant lies in its floating meniscus with increased durability and dependability. This polyethylene component moves with movement of femoral condyle and continues to change its weight bearing axis.
After operation, the lady started weight bearing exercise and was able to walk comfortably the next day itself.
On the third day after the surgery, the patient was able to walk independently more than 50 metres or to the washroom unassisted. She had minimal pain and swelling of the knee joint because of the minimal invasive nature of the surgery. She did not require any blood transfusion or physiotherapy post operatively.
Without losing her ACL (which is crucial for her movement arc), her varus deformity, which was 10 degree, was corrected and her pain vanished.
What is Unicompartmental arthritis?
When any one of the three compartments of the knee is affected, it is referred to as unicompartmental arthritis. A knee joint is divided into three compartments — medial (inside), lateral (outside) and the Patellofemoral (kneecap joint). In most of the cases, only the medial or lateral compartment is affected, unlike arthritis where it affects all three of them. If diagnosed at an early stage, it can be treated with medication, but when the symptoms have crossed the extreme stage, surgery is the only option left.
Full knee replacement has been the most common and the conventional method for treating arthritic knee. This is useful and necessary only when all the three compartments are involved, and can prove to be a disadvantage in case of unicompartmental arthritis.
But when the problem is limited to just one of the knee compartments, there are options to replacement.
How is it diagnosed?
An orthopaedic surgeon and a sports medicine specialist need to perform physical examination along with the help of imaging technique like X-rays. This will help in evaluating the degree of deformation and the alignment of the knee which indicates the uneven load distribution across the joint. The details of each compartment are obtained through an imaging technique that includes joint space narrowing, bone spur formation, and increased density of the bone adjacent to the overloaded compartment.
A history of pain limited to the medial compartment with swelling in the joint and stiffness is suggestive enough to visit the doctor.
What is unicompartmental knee replacement?
Unicompartmental knee replacement is a very successful procedure in young arthritics where the disease is confined to the medial compartment of the knee. Added advantage of the procedure is that the knee can still be converted to a full replacement if for any reason a revision surgery is envisaged. The polyethylene articular insert is mobile and hence allowed to freely float on top of the tibial base which absorbs the sheer stress and protects the bone interface. As it is mobile, the design can be customised conforming to the curve of the femur to spread the weight bearing capacity evenly thereby reducing its wear and stress.
What are the treatment options?
The surgeon takes the decision whether to opt for surgical treatment or to continue with medication depending upon the age, degree of symptoms, history of other diseases and the patient’s activity level.
l Injections: Corticosteroid injections decrease the inflammation and relieve the associated pain, which lasts for upto six months. These contain natural components of the joint fluid that helps to lubricate and absorb shock to protect the damaged cartilage.
Bracing: These are known as off loader braces, which help in correcting the malalignment of the knee and distribute the weight evenly across the joint.
- Articular Cartilage Restoration Procedures: Surgical procedures are required to restore the articular cartilage as it does not heal on its own.
- Osteotomy: A wedge of bone is cut out from either tibia or femur to adjust the angulation to straighten the knee. This relieves the uneven distribution of the weight across the joint and prevents progression.
- Total knee replacement: This involves all the three compartments. The surgeon removes the damaged cartilage from the femur and tibia and replaces it with metal and plastic.
- Unicompartmental knee replacement: Unlike the total knee replacement, this procedure is minimally invasive and replaces only the damaged portion of the joint.
Why is unicompartmental replacement preferable?
The main advantage of the unicompartmental knee replacement is that it preserves the ACL which is a crucial ligament for movement and knee stability unlike total knee replacement where it is sacrificed. As this follows the minimal incision approach, a faster recovery, rehabilitation and quick return to full fledged activities is seen in all patients. Because the ligaments are kept intact, the patient feels the replaced portion of the knee as a natural part itself.