Unicompartmental (Partial) Knee Replacement
When is this procedure indicated?
In order to proceed with the implantation of a monocompartmental knee prosthesis, it is necessary to meet the following requirements:
- remaining 2 intact compartments or with minimal non-symptomatic arthrosis;
- intact cruciate and collateral ligaments;
- ROM > 90 degrees;
- contracture in flexion < 5 degrees, tibial bone defect less than 10 mm.
There is no defined limit for coronal deformity and patient weight. In case of bicompartmental damage with intact ligaments, it is possible to perform a bicompartmental replacement by associating two small implants (monocompartmental prosthesis + femorotulae, medial + lateral monocompartmental prosthesis). In rare cases, in young and active patients, it is possible to perform a monocompartimental prosthesis + ACL reconstruction.
How is it performed?
Total knee replacement surgery is usually performed under epidural anesthesia (in which only the lower body is insensitive to pain) + sedation. The procedure can be divided into:
surgical access, usually a medial para-patellar incision and subsequent midvastus or subvastus approach (between the vastus medialis femoris fibers or below the muscular belly of the quadriceps femoris);
removal of damaged osteo-cartilage components;
implantation of trial prosthetic components;
verification of the restoration of the pre-pathological articular anatomical characteristics and stability tests;
implantation of the definitive prosthetic components;
post-operative radiological control.
The patient can walk, with the aid of Canadian canes and physiotherapy staff, as early as the first 6h after operation. Physiokinesitherapy begins on the day of surgery, and includes: active and passive progressive and complete joint recovery, global strengthening exercises of the lower limbs and exercises for selective strengthening of the quadriceps bilaterally, walking training, training to climb / descend stairs, joint stretching.
Full recovery and resumption of normal activities occurs after about 1 month. Normal activities include the practice of certain sports, while those in which sudden movements and bumps are not expected. Therefore, soccer, skiing, horseback riding, rugby, etc. are strongly discouraged.
Although it is for all intents and purposes a major surgery, the single-compartment knee replacement procedure is considered safe. However, some complications are possible, though in rare cases (less than 1% in total in our case series). These risks are usually increased if the patient has prior diseases that complicate the overall clinical picture.
There are general medical complications due to the anesthetic procedure (cardiovascular and cerebrovascular events, pneumonia) and general complications of surgery (hemorrhage, nerve injury, peri-articular soft tissue injury, early infection (increased risk related to the implant), and lower extremity venous thrombosis (increased risk).
The specific complications of prosthetic replacement surgery are intra-operative periprosthetic fractures, hypercorrection of the implant, persistent pain, persistent or recurrent swelling.
After the convalescent period, the patient is usually able to return to a completely normal life. In some cases, however, it's good to know that there may be long-term consequences that can lead to revision surgery.
Implanted components are destined to wear out: in optimal conditions they have a life span of more than 15 years, but there are several factors that can lead to premature wear (overuse, overweight).
The other compartments of the knee may develop an arthritic condition requiring prosthetic replacement.
The implant may not osseointegrate optimally and may loosen from the operation site.The prosthesis is a foreign body implanted in the human body and can promote the development of bacterial colonies on its surface: infections can start from anywhere and reach the prosthetic component through the blood.
Although prosthetic replacement surgery can accurately restore pre-arthritic anatomical relationships, some patients may complain of instability or persistent stiffness and pain unresponsive to conservative treatment.
In all these cases, a total revision of the implanted prosthesis may be necessary.