Hip Replacement caractéristics

1. Hip Replacement – Criterias of their implantation:

A surgery can be described as "minimaly invasive" with less heavy operation and post-operative care, it must apply some criterias and this, as much as possible, combined with themselves :

1.a. The operation time : shorter it is, less operational and post-operative morbidity are important ; besides, the operation time is often equivalent the anesthesia time; so, it is necessary to privilege less heavy procedures making it possible to reduce the operation time.
It is necessary to consider the following parameter "installation of the patient" : we will see low in the way used to implant the prosthesis (antero-lateral way), the patient is installed naturally on the back, allowing a better respiratory ventilation during the operation, on the contrary to the other approaches which impose the installation of the body on a lateral side such as the posterior approach.

1.b. The approach procedure: : : is defined by the anatomical advance to reach the operative field; it will be necessary to privilege a way less dilapidating which will use the shortest advance, circumventing significant zones such as vascular axes and which will preserve the bone and muscular capital.
Ideally, it is the antero-lateral approach (Hardinje) which offers these advantages:
Indeed, the access is easier : after incision of the fascia lata (directly under the skin), we access in front of the gluteus muscle (which it is imperative to preserve the stability of the hip), reach directly the anterior side of the articular capsule.
This way is anatomically more advantageous than the postero-lateral approach which is more often used in France opposite to the USA, because this approach imposes a section of the pelvi-trochanterians muscles which constitute a genuine posterior stay of which the section can involve a posterior instability.
All these surgical approaches depend on the habits of the surgeon so we can't say one is better than the other but in my experience I believe that the lateral approach offers more advantages.

Another parameter is to be evocated: "the size of the skin incision" which does not constitute, truly, a criteria of "minimaly invasive" surgery; indeed, a very restricted incision can impose a more complicated procedure using a heavy and complex instrumentation and so increase the operation time. We can't say that a "minimally invasive" surgery is limited only on the smallest skin incision.

1.c. Characteristics of the implants used:

There are several marks and models of prosthesis currently on the market and it is not always obvious, for the patient, to make a choice.

We can make the difference between the cemented prostheses and cementless prostheses.

1.c.1 the cemented stem prostheses:

To be implanted, these prostheses require the use of a cement known as biological. It is composed by a powder which, when it is mixed with a solvent, undergoes a chemical reaction of polymerization to the air allowing the immediate fixing of the implants (femoral and acetabulum). These prostheses must be less and less used because, at first, the preceding chemical reaction can generate vascular disorders (decrease of the blood pressure) at the time of the implantation; and also, these prostheses can become complicated, in their evolution, of loosening and need a revision surgery.

The loosening of the prosthesis:

It is about the degradation of cement which links the prosthesis with the bone.
Then, it forms spaces and cavities around the prosthesis making it unstable and mobile.
The bone which surrounds the prosthesis undergoes a degeneration (lysis).
Clinically, that results in permanent pains during the walk.

The revision of the hip prosthesis:

It is about the operation which it is necessary to carry out when loosening appears.
This operation is considered more complex because it concerns the older patients, the operation comprises several operative stepsthe getting out of the old prosthesis and the whole of cement (delicate procedure because cement, if it is certainly disunated from the prosthesis, is sometimes very adherent with the bone which is very weakened); then a new prosthesis is posed with sometimes the need of carrying out procedures of reconstruction using bone graft to put in the bottom of the acetabulum or for using longer femoral stems to include a weakened zone of the femur.

This is the reason why the cementless prostheses should be undoubtly preferred to them.

1.c.2 Cementless stem prostheses:

So, in order these prostheses have a great lifetime so much immediatly (at the moment of their implantation) than in the long term, it is necessary to use other processes than the cement. 2 considerations should be evocated thus:

• 1.c.2.1. The coating of the protheses:

  Instead of being on polished surface, these prostheses have a coating made up of a matter close to the calcic components of the bone : the hydroxy-apathite. To improve anchoring of the prosthesis in the surrounding bone, this surface is materialized by a porous netting (porous coating). So this coating, to some extent natural, will be habited again by the bone which surrounds the prosthesis and will thus avoid any risk of rejection.

• 1.c.2.2. mode of fixing of the protheses:

  The fixing of these prostheses is done into 2 phases:
  *the primary or immediate fixing (during the installation) of the acetabulum component is ensured by grooves or peripheral barbs which will be inserted in the bone at the time of the impaction of the acetabulum and will thus allow its perfect stability; the bottom of acetabulum is reconstructed beforehand by using spheric rimmers of increasing diameter to withdraw all the worn cartilage.
  The primary fixing of the femoral stem: the femur is prepared to receive the femoral stem by using rimmers which have the same form than the femoral stem, of increasing size until obtaining a perfect stability of this rimmer; the size of the femoral stem corresponds to the size of the rimmer; it is fixed by impaction.
  
  *secondary fixing: takes over towards the 45 day by the new bone growth inside the coating of the implants previously described.

2. Criteria of the post-operative period

The objective is is to find immediately the articular functionality after the operation, , under cover of an effective treatment against the pain (a specific post-operative procedure is applied); in fact, for the lower limb:: the resumption of walk with a full support (or relieved with 2 crutches) early after the operation is one of the essential objectives; indeed, that allows :

• bone growth around the implants;
• reinforcement of the bone capital;
• the maintenance of the muscular trophicity (indeed, walking without full support and don't doing physical exercices make the muscles weakened);
• reduction in the hospitalization time;
• the return at home avoiding to go to Rehabilitation Center, in a lot of cases (except in situations of environmental insulation).

In summary:

TENDENCY TOWARDS A LESS INVASIVE SURGERY
1. Criteria of the operation itself	1.a. The operation duration		the shorter and more adapted anaesthesia (loco- regional = péridural)
			Patient lying on the back
	1.b. Surgical approaches		The antero-external appoach (Hardinje) is more advantageous
	1.c. The caractéristics of the implants used		1.c.1. The cemented stem prothesis ("1st generation")	Possible complications: Loosening needing revision of the prosthesis
			1.c.2. 2 The cementless stem prosthesis ("2d generation")	1.c.2.1. Prosthesis coating
				1.c.2.2. Way of prosthesis fixation	*primary fixation
					*secondary fixation
			1.c.3. hip resurfacing ("3d generation")	Remove only the damaged cartilage (conservative surgery)
2. Post-operative criterias		The recovery of the normal walk with complete support early Makes the capital bone stronger Maintains the muscular trophycity The reduction of the hospitalization time The coming back directly at home in the main cases
The most advantages association		Anterior approach Local anesthesia ("peridural") Hip resurfacing in the indicated cases