Unicompartmental prosthesis: the answer to gonarthrosis

Unicompartmental prosthesis: the answer to gonarthrosis

Publication date: 10-08-2022

Updated on: 28-04-2023

Topic: Orthopedics

Estimated reading time: 1 min

There are many people who are significantly affected by gonarthrosis, or knee osteoarthritis. It is a degenerative disease that begins with joint inflammation (arthritis) which increasingly thins the layers of articular cartilage.

As a result of the degenerative process, bones of the knees, devoid of cartilage, begin to rub against each other when moving. Degenerative knee arthritis leads to a significant deterioration in the quality of life, to the point that gonarthrosis can be defined as a disabling disease.

Today the best solution to gonarthrosis is the unicompartmental prosthesis about which we spoke to Dr. Michele Massaro, Director of the OPRAM center at the Istituto Ortopedico Galeazzi in Milan and the Policlinico San Pietro in Bergamo, expert in minimally invasive hip and knee arthroplasty.

“In my activity as a surgeon I apply the unicompartmental prosthesis in about 70% of the cases of gonarthrosis. Only in the remaining 30%, however, I suggest total prosthesis”, says the expert.

What is the unicompartmental knee prosthesis?

During the degenerative process due to osteoarthritis, the cartilage that protects the bones from rubbing gradually thins.

“In most cases cartilage thinning occurs in only one sector so a unicompartmental prosthesis is recommended. This is a minimally invasive ntervention in which only the damaged part of the knee is replaced with a small implant”, explains the specialist.

In this case, we mean a partial replacement of the knee in one of its three joints:

  • femororotubular: it is located in the front part of the knee, between the patella and the femur;
  • medial femorotibial: it is included in the inner part of the knee;
  • lateral femorotibial: resides in the external part of the joint.

By replacing only a part of the knee, thus avoiding a total joint replacement, the surgery will be less invasive and the patient will have much faster recovery times.

What the intervention consists of?

“Manipulations are carried out in the damaged compartment to reconstruct the damaged parts with an implant made of an alloy of titanium and very high density polyethylene. Thanks to these ultra-modern and technological materials it is possible to recreate the native shape of the knee. Thus, preserving healthy cartilage, bones and ligaments.

With this type of intervention very satisfactory results are obtained in the majority of cases. The success rate of unicompartmental knee replacement is, in fact, very high and let us reach:

  • faster recovery,
  • minor blood loss,
  • fewer painful symptoms after surgery.

Single compartment endoprosthesis as such has no disadvantages. However, if the arthrosis has spread to other parts of the knee, a unicompartmental knee replacement will only partially alleviate the situation. The choice of the type of intervention should be made by the orthopedist, who should best assess the individual case of each patient”, continues Dr. Michele Massaro.

Who can undergo the surgery?

Although osteoarthritis has developed in only one compartment of the knee, not all patients are suitable for this type of surgery.

“There are patients who are afflicted by chronic inflammatory rheumatic arthrosis for which we do not recommend this type of intervention, as well as in cases of high stiffness of the knee and of damaged ligaments. The ideal patient for this type of surgery must be carefully selected on the basis of all necessary medical exams.”

The orthopedic evaluation

A fundamental basis for any intervention is thorough assessment by a competent orthopedic surgeon.

“The orthopedic specialist must first evaluate patient's medical history, considering his/her general health. Subsequently orthopedist also measures pain level and the degree of functionality of the knee:

  • if pain is concentrated on only one of the affected parts (external, internal or anterior) the patient may be a candidate for the unicompartmental knee replacement;
  • if pain occurs in all parts of the knee, a total joint replacement would probably be more appropriate”.

After identifying the area affected by pain, the orthopedist performs a physical examination to assess mobility of the knee and condition of the ligaments. In the case of fragility or injury of the ligaments and a high degree of knee stiffness, most likely a total knee prosthesis will be suggested.

Once the orthopedist has an idea of ​​the functionality of the knee, it is necessary to perform an initial diagnostic examination through X-rays, in order to assess the extent of the damage present. Some cases prompt surgeons to also request a more in-depth diagnostic investigation through an MRI, in order to assess the condition of cartilage and ligaments.

Intervention step by step

In addition to using a minimally invasive method, we also strive to reduce time that the patient will have to spend in the hospital and for which ultra-fast procedures have been developed.

Hospitalization is carried out on the day of the surgery. Anesthesia is performed by administering low doses of opiates to ensure faster recovery.

The intervention itself usually lasts less than 1 hour and does not consist of particularly traumatic procedures. During the surgery a robot is used to position the implant more precisely and, therefore, to reach a higher level of joint functionality after recovery.

An incision is made in the anterior part of the knee joint, through which the state of the ligaments and parts of the knee is analyzed, and the unicompartmental replacement is confirmed 'on site'.

That is, if the diagnosis is confirmed at the beginning of the intervention, doctors proceed with the partial replacement of the knee joint. Otherwise, the plan may be changed and a total knee replacement may be performed. This possibility will be discussed with the patient before the operation to obtain his consent.

“I always choose the best treatment for the patient, possibly not resorting to surgery. When the need for surgery arises, I try to be as minimally invasive as possible and use a robot to assist me during the procedure. I always recommend the most suitable therapeutic option, even if it is not the one the patient would prefer”, explains Dr. Massaro.

The first phase of the operation is that of bone preparation: the residual cartilage of the damaged compartment is processed millimetrically and then replaces it and the bone with metal coatings that recreate the surface of the joint.

Very high-density polyethylene insert is placed between the two metal components to create an impeccable surface: smooth and sliding. In this phase, the surgeon evaluates the thickness of the insert in order to adapt it to the original cartilage volume.

Post operation

The patient wakes up in the recovery room, where he / she is gradually removed from anesthesia and a control x-ray is taken, after he / she is transferred to the ward.

After a partial knee replacement patients experience less pain in the postoperative period, compared with a total knee replacement. Less pain and less swelling often lead to faster recovery and optimal results: patients usually return home within 1-3 days after the surgery.

Symptoms associated with pain can be controlled with the help of drugs prescribed by the doctor. Pain management is important for improving psychological state of the patient, as it contributes to his/her involvement in rehabilitation.

It is necessary to perform rehabilitation exercises recommended by a physiotherapist to restore all functions and maximum joint strength as soon as possible.

The orthopedic surgeon may suggest to use a cane or crutches for the first few days after the surgery. However, patient can load the weight on the knee straightaway without any fear.

After the surgery, the patient will be scheduled periodic visits to assess the recovery process of the operated joint.

The outcomes and recovery period are very subjective, usually patients return to normal activities within 6 weeks after single knee surgery.

Possible complications

Like all interventions, this type of surgery has several possible complications, albeit with a low probability. The orthopedic surgeon should inform the patient about possible risks, as well as illustrate specific measures that will be taken to avoid it.

A blood clot formation in the veins of the legs is possible, for which blood thinners, such as low molecular weight heparin, are administered.

As with any surgical intervention there is a possibility of wound infection, which is usually avoided by antibiotics.

It is also necessary to consider risks associated with anesthesia, although, as we have already mentioned, attempts are made to minimize the use of opiates.

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