The younger the patient, the more care is taken when implanting the prosthesis so as to implant the one to preserve bone mass in the future.

Implantation of artificial hip joint (arthroplasty) is one of the greatest achievements in modern medicine, with predictable and repeatable results. In the last few years, new surgical techniques and new implants have resulted in new insights.

Origins in the 20th century

The modern hip replacement implantation began in the 1970s, when John Charnley used bone cement and polyethylene. In order to decrease friction between the prosthesis components, Charnley placed a small prosthesis head, witha 22-mm-diameter, which, unfortunately, facilitated dislocation of the prosthesis. To prevent this, a larger head with 28-mm-diameter was made, and it increased stability but also the wear of a polyethylene joint insert (acetabulum). As the prosthesis became looser due to small polyethylene particles, new materials were developed. Hence, the highly cross-linked polyethylene and ceramic insert were introduced instead of the highly molecular polyethylene. At the same time, ceramic prosthesis heads, in combination with polyethylene or ceramic insert, and metal heads in combination with metal insert were implemented.

Cement versus cementless prosthesis

Elderly, less active people with poor bone quality, at risk of fracture during installation of the prosthesis body and impossibility of primary fixation, are implanted cement prosthesis. The prosthesis is fixed with bone cement, and there is no direct contact between the bone and the prosthesis. The cement, which fills the space between the bone and the prosthesis, loses its properties in the long run and the prosthesis becomes loose, which requires revision.

The cementless prosthesis is intended for younger persons and persons with a good bone mass. A solid primary fixation and rough structure of the prosthesis surface allows the creation of bone tissue around the prosthesis, which provides a permanent fixation. The durability of both types of prosthesis is equal.

A) Artroza desnog kuka.      B) Potpuna bescementa proteza kuka. (standardni trup, metalna glava 32 i polietilenski umetak)
A) A right hip arthrosis B) Cementless total hip prosthesis. (standard body, metal head 32 and polyethylene insert)

In clinical practice, the use of cementless prostheses is predominant, but in Croatia those prostheses are generally applied for all patients younger than 60 years. However, there are also hospitals which implant only this type of prosthesis. Some of the reasons are: easier and faster surgical implantation, usually minor revisions of the loosened cementless prosthesis and better final result for patients, especially for younger people. In addition, the industry offers new and better materials and models of cementless prostheses better adjusted to bone anatomy and biology.

Bearing surfaces in joint replacement

Durability of the prosthesis depends on the type of bearing surfaces – prosthesis head and cup implant which is fixed in the pelvis at the exact same place as the previous joint cup. A standard bearing surface is a metal prosthesis head made of cobalt and chromium alloy and a highly molecular polyethylene insert. Polyethylene wear releases particles that cause so called particle disease, leading to bone disintegration and loosening. In order to reduce polyethylene wear, the highly cross-linked polyethylene is introduced, providing better quality and better resistance to abrasion.

Implementation of ceramics as a bearing surface enables avoiding of the implant wear, since ceramics is an inert material. Its adverse features are fragility, cracking and creaking during motion after hip surgery, which occurs in a small number of patients.

The most resistant to abrasion is metal, thus a combination of a metal head and a metal implant provides the most resilient option. Adverse features of metal bearing surface is the release of metal ions which end up in blood and urine, although there is no evidence that they cause disorders, including carcinogenicity. In addition, some people may be sensitive to metal, so it is not recommended to implant them with metal prosthesis components.

Metal-polietelen
Metal-polyethylene
Metal-metal
Metal-metal
Keramika-keramika
Ceramics-ceramics
Keramika-plastika
Ceramics-plastics

Prosthesis head

A standard prosthesis head size (outer diameter) is 28 and 32 mm. In recent years the use of larger heads, the ones of 36 mm in diameter, has increased, but also large metal heads, but that depends on the size of the pelvic acetabulum, diameter of which is usually larger than 50 mm. A larger head increases stability of the prosthesis, reduces the possibility of dislocation, but also increases the friction.

Prosthesis body

Once the mechanical prosthesis body is loosened, it must be replaced. In order to bypass the damaged part of the femur (the canal), the prosthesis with a longer body is implanted. Implantation of revision prosthesis usually requires a direct access to the bone due to removal of the prosthesis and cement. Results of revision prosthesis surgeries are poorer than the ones of the primary surgery. In order to preserve the bone mass, especially in younger patients, the so called short prostheses have appeared in recent years. Unlike conventional prostheses, the body is shorter, which saves the bone. Additionally, if necessary, it allows subsequent implantation of the standard prosthesis and the patient does not lose the hip function. Any kind of bearing surface can be inserted on a short prosthesis body.

A) Artroza desnog kuka   B) Kratki trup proteze, keramička glava 36 mm i keramički umetak acetabuluma
A) A right hip arthrosis B) Short prosthesis body, ceramic 36 mm head and ceramic acetabular implant

Surgical approach

There are several existing approaches to hip surgery, but the most commonly used ones are rear and side approach. In case of a rear access there is no damage to hip abductor muscle (M. gluteus medius and minimus), while in case of the lateral approach the muscles are separated and sutured after implantation of the prosthesis. In case of a rear access dislocations of the prosthesis are more frequent. Using a minimally invasive approach means there is no separation of muscle and the incision is shorter. Its benefits are faster rehabilitation and preservation of the hip muscles, while its disadvantages are technically challenging surgeries and possible errors in prosthesis placement.      

When an artificial hip should be implanted

Razlozi za ugradnju proteze kuka najčešće su bol i ograničenje funkcije kuka. Među najčešćima su artroza kuka, reumatske bolesti, avaskularna nekroza, prijelom kuka i posttraumatska artroza (kao posljedica prijeloma).

Thromboembolism

The most common complication is a deep leg vein thrombosis, and a much less frequent complication is a pulmonary embolism. To reduce the possibility of embolism, athromboprophylaxis, including anticoagulants (drugs preventing blood clots) is regularly applied and elastic stockings should be worn after the surgery.

Infection

A deep infection after the hip replacement occurs in about 0.5 percent of cases. A local infection on the wound surface is more common in the first few weeks after the surgery, but an infection of the prosthesis can occur even years after implantation. In case of an infection treatment failure, the prosthesis must be removed. Once the inflammation is cured, a new prosthesis can be implanted, but only six months after removal of the first one.

Dislocation

Relativno je česta komplikacija i susreće se u oko četiri posto slučajeva. Razlozi su loše postavljena proteza i slabost mišica kuka. Za cijeljenje mekih česti kuka potrebno je oko dva mjeseca, a to je vrijeme u kojem je kuk najosjetljiviji za nastanak iščašenja. Mogučnost iščašenja bitno se smanjuje upotrebom večeg dijametra glave proteze i manjim oštečenjem mišića kuka. Prvih nekoliko mjeseci bolesnik mora izbjegavati određene položaje noge.

Loosening

The lifetime of the hip prosthesis is limited and usually amounts to 15-20 years. The prosthesis eventually becomes loose, which is a consequence of bone absorption due to impact of fine particles, occurring due to polyethylene wear (plastic cup insert) and the resulting fracture. In order to reduce bone absorption and prolong the prosthesis lifetime, ceramics (ceramic head and ceramic cup), metal (metal head and metal cup) and cross-linked polyethylene, which produce much fewer fine particles, were introduced as bearing surfaces.

Nerve damage

After the surgery a patient may experience a damage to the sciatic nerve (in about one percent of patients), and an inability to lift the foot. Damage to the femoral nerve occurs even more rarely. Nerve damage usually occurs because of a hip dislocation during surgery in patients with hip contracture, due to stretching and the pressure on the nerve with an instrument during the surgery. In most cases the nerve eventually recovers, usually six months after the surgery.

 

Leg length

After the implantation of a hip prosthesis, a leg length may be longer or shorter. Patients usually complain about a leg extension, but sometimes the leg must be extended due to stability of prosthesis and the anatomy of the hip. If there is a hip contracture before the surgery, the patient has a shorter leg feeling. After the surgery and resolution of contracture, once the mobility and hip functions are restored, the patient feels as if his/her leg was longer. If the legs are of an equal length in reality, i.e. if the anatomical leg length is equal, the problem will be solved in two to three months. If one leg is longer in reality, this problem will remain after the surgery, which can be resolved by a shoe or heel insert.

Death

Mortality after the hip prosthesis implantation is extremely rare and, according to the medical literature, occurs in 0.3 percent of cases. It most commonly occurs in elderly people who suffer from other concurrent diseases.

Individual adjustment

Today, a modern man does not want to suffer the pain and experience limitations in daily activities. A replacement of the hip joint, which enables a painless and functional joint, is one of the greatest achievements of modern medicine, with few rare complications. A type of hip prosthesis to be implanted is individually customized to each patient, depending on age, cause of damage, status of the hip (anatomic relationships, deformation, bone mass) and activities the patient would like to engage in after the surgery. As a rule, if the person is younger the tendency is to implant a hip prosthesis that will preserve bone mass for a possible revision surgery in the future. Taking all this into consideration, the physician selects the best possible solution in each case.

prof. dr. sc. Nikola Čičak, dr. med., spec. ortoped, AKROMION – Special hospital for orthopedics and traumatology, Krapinske Toplice
Original article published in the Vaše Zdravlje magazine, No.77, year XIII. Front page and article as attachment:

Front page
Original article

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