Knee replacement

A knee prosthesis, or knee prosthesis is a knee prosthesis implanted prosthesis ( stent ) to replace the functions of the knee joint and / or its supporting apparatus according to a loss of function. The knee prosthesis is mainly used for severe degenerative diseases of the joints ( knee osteoarthritis ) and after injuries of the knee as a surgical treatment to restore a pain-free range of motion and possibly also the knee joint stability ( at Bandinstabilitätten ). Depending on the severity of the injury partial or total knee prostheses are used. The prosthetic knee after prosthetic hip joint endoprosthesis with the second most common in Germany about 175,000 operations a year ( first implantations 2009).

Possible indications and contraindications

The use of a knee prosthesis may be necessary:

• Degenerative osteoarthritis ( damage to the articular cartilage )
• Rheumatoid arthritis ( inflammation of the joint with cartilage damage)
• Posttraumatic arthritis (arthritis after accident )
• Symptomatic knee instability ( injury to the ligaments )
• Knee bracing (reconstruction of motion of the joint )
• Deformities of the knee joint
• Reconstruction of a knee joint function after resection during tumor surgery

Depending on the disease and its severity, the doctor from the different types of implants have to select the best possible solution and treatment for the patient. The correct indication is at the sole responsibility of the treating physician. These patients should also be included in the decision-making process so that doctors and patients talk about the ideas and needs of patients and the processes and expected operating results. Thus, these factors may be considered when determining indications.

A prosthetic knee should not be used when a reconstructive intervention (eg osteotomy ) for the treatment of joint suffering is possible acute or chronic infections are present in the hinge or in the proximity or systemic infections. Contraindications are also disturbances in the bone itself, such as metabolic disorders, osteoporosis or osteomalacia, damage to the bone structure, preventing the stable anchoring of the implant or bone tumors in the field of implant fixation. In bony malformations or extreme Achsfehlstellungen the knee prosthesis is also hardly used. A possible or proven metal allergy or intolerance also is a contraindication represents an expected overload of the implant, for example, obesity (overweight) is considered a risk constellation; as medication, drug or alcohol addiction.

Classification of knee prostheses

Knee prostheses are divided according to their degree of coupling a. That is the more functionality the natural ligaments in the knee joint is damaged and must be signed by the knee prosthesis, the higher the degree of coupling. The knee joint is a so-called rolling-sliding joint. During the normal gait of the lower leg rotates around the femur and slides forward. The kinematics of the knee is very complicated.

During the movement of the flexion in the extension ( the diffracted in the stretched knee) of the legs rotates around the thighs to the front. In this case, the foot and thus the lower leg rotates around the medial (inner) condyle to the outside. During the movement of the extension in the flexion of the lower leg rotates rearwardly about the thigh. Thereby, the foot rotates inwardly, and the lower legs to slide forward. This complex kinematics is due to the shape of the articular surfaces, the menisci, and especially by the arrangement of ligaments and muscles.

The so-called Uniknie ( unicondylar ( syn. monocondylar ) sliding prosthesis ) is to apply when all the bands of the knee joint are fully functional and only one of the two condyles present damage to the articular cartilage. While the component femoral uniform consists of a metal alloy, there tibial three different basic types: pure polyethylene component (so-called all- poly, for example, Genesis, Journey, Mod I, St. George, UC plus ) firmly fixed PE component having a metal base (so-called. metal- backed, for example, Genesis, Journey, Mod II, UC Plus) or analog versions with mobile PE component (eg Oxford, LCS uni ). A bicondylar primary prosthesis can be used if at least two of the three hinge portions (inner or outer compartment and patella with plain bearing ) and possibly also the anterior cruciate ligament are damaged, but the other bands are sufficiently functional. It will be replaced in both the femur and the tibia, the articular surfaces. The menisci are removed. There are also single implant systems that can be used even with an intact anterior cruciate ligament.

If no, the rear, the anterior cruciate ligament are not yet received, a so-called posterior stabilized prosthesis ( PS knee) is used. Here, the knee prosthesis assumes already the functions of the cruciate ligaments and forces the tibia with increasing flexion to the front or the femur backwards. For the Drehgleitmechanismus There are basically three methods that each have a different design of the tibial component, while femoral and patellar component remain the same:

• The tibial component consists entirely of polyethylene, and this is set directly by means of bone cement to the prepared shin bone (all- polyethylene).
• A polyethylene component is fixed firmly placed on a metal component, which in turn is anchored in the tibia, either with or without cement (modular metal backed or fixed bearing ).
• A polyethylene component is mounted on a metal component that it can move in a given frame against the metal component, a sliding mechanism in knee flexion is predominantly ( rotating platform, or mobile bearing ). The metal component in turn is cemented or uncemented fixed in the prepared tibia.

A prospective randomized study has these three components of a manufacturer with always the same femoral and Patellakomponenten compared, the operators were very experienced and familiar alike with all three tibial components, and could in each case 75-76 patients per group after two and five years, no significant still demonstrate clinical differences, what agility, strength, function, and satisfaction related. With a total of only four revisions, this study allows no conclusions about the long-term stability.

Both the ligaments and the collateral ligaments damaged, the joint capsule and muscle apparatus intact, but yet well, a so-called rotation achsgeführte prosthesis ( Rotating hinge ) may be used. Here, the implant takes the stabilization of the joint of both the front and rear and left and right. But it allows a rotation of the tibia to the femur, that is the foot can be rotated to the outside.

As a last resort applies the achsgeführte knee. Are the capsule and the muscular apparatus damaged, which is often associated with large bone defects appears, change the rotation of the tibia against the femur, ie the rotation of the foot restricted, and the knee joint are stabilized so on. This can now be moved only the tibia against the femur to the front and rear.

Individual knee joint prostheses

Especially in younger patients occasionally come individually for the patient and the geometry of prostheses fabricated for use. In this case, the necessary measures must be determined by computed tomography. On the basis of the CT data is a virtual 3D model of the patient's knee is created on the computer, resulting in a template is generated, a so-called negative mold, by means of which the implant is made ​​. Also the necessary surgical tools is individually tailored to the anatomy of the patient and the generated 3-D printing process. The surgical tool is used to carry out the precise bone cuts and the positioning of the replacement joint. Correct positioning and orientation is to lead to the lowest possible consumption of bone and a long service life of the prosthesis. This method can be used for both partial dentures as well as a total knee arthroplasty. In addition to higher costs for the individual preparation of the prosthesis resulting from this process, a higher radiation exposure from computed tomography and a longer operating time. That the durability of the prosthesis can be extended, it is not been established in long-term course.

Historical

The first implantation of hinge joints in 1890 by the Berlin surgeon Themistocles Gluck: In three patients with joint destruction in the context of tuberculosis a simple hinge made ​​of ivory has been implanted, the fixation was performed with nickel-plated screws and rosin, of resin. The attempts failed due to infection. Another attempt was made by Judet in 1947 with an acrylic resin denture. The first Scharnierendoprothese that was successfully implanted in greater numbers, was the model of Walldius from 1951, which was further modified several times in the sequence. Other famous early forms of Scharnierendoprothese were the models of Shiers from 1953, Engelbrecht from 1970, Groupe Guepar from 1970, Sheehan 1971, Blauth 1972 and Gschwend Veil Bähler (GSB ) from 1972.

An isolated replacement of the femoral condyles was made in individual cases by the development of Campbell in 1940, Smith -Petersen from 1942 and Rocher from 1952. Larger numbers of cases are known for models of Aufranc Jones Kermond from 1953 as well as platform Pepler from 1955.

The isolated tibial replacement was performed in the first models of Marquard in 1951, McKeever 1952 and McIntosh from 1956.

The first Gleitflächenersatzprothesen, ie the replacement of the femoral and tibial sliding medially and / or laterally without mechanical coupling came from Gunston 1968 ( femoral steel, tibial polyethylene) and Engelbrecht (Model St. George) from 1969 ( femoral cobalt chromium molybdenum steel, tibial polyethylene), Freeman / Swanson from 1970 and marble from 1975.

Materials of Construction

The material most commonly used is the cobalt-chromium - iron alloy according to ISO 5832-4 CoCr29Mo for the femoral and tibial components of the implant. For Augmentationskeile plates and a cobalt -chromium alloy is used according to ISO 5832-12 frequently. There are also titanium alloys or surface coatings of zirconium nitride, titanium nitride or Titanniobnitrid used, which are mainly used for patients with metal allergy such as nickel allergy. Titanium alloys with the titanium to the articulating surfaces, due to the low abrasion resistance, a special surface hardening is treated with nitrogen ions. The surface coatings are applied by vapor deposition in the PVD process. The inlays ( Meniskenersatz ) are usually manufactured from UHMWPE ( ultra high molecular weight polyethylene ) according to ISO 5834-2.

Anchoring of the implant

Implants are often anchored to the bone with bone cement. Optionally, an anchorage without PMMA ( bone cement ) can be selected. Here, the implant components are usually provided with a coating which has a particularly porous and thus large surface area, which favor a An-/Einwachsen of the bone, thus ensuring a safe anchorage. Has grown up of the bones in this layer, the implant holds by the so-called press fit. That is, the implant ( the bone ) will be prepared so that the prosthesis is clamped in the bone.

Loading of the implant

In order to stabilize the body, acting in the knee joint significant muscle forces, in addition to body weight to compress the joint and charge it. These forces can be approximately calculated using mathematical models or measured directly by measuring instrumented prostheses. For example, researchers at the Julius Wolff Institute Berlin's Charité Hospital have developed an instrumented knee prosthesis for load measurement and used in several patients. The measured data are transmitted wirelessly to a computer. The results show that already applied to the joint during walking, a resultant force of about 2.5 times the body weight. When descending stairs, the resultant force increases even up to 3.5 times the body weight.

Results

In a recent study of the Swedish arthroplasty of 2012 totaled for primary implantation of the entire knee joint ( total hip replacement with and without patellar ) Ten -year survival rates of approximately 95% and for unicondylar sledge prostheses of approximately 85 % - 90 %. This means that, statistically after ten years of about 5 %, or 10-15% of the knee joints were removed and replaced, does not, however, all other endoprostheses. From this it can be deduced but neither the individual nor the individual's risk changing clinical and subjective individual result. Target size alone was the performed expansion or change. Reasons for a change of unicondylar sledge prosthesis can eg Be the osteoarthritis of the previously unserved compartments with an intact prosthesis itself, conversely, a not impersonated endoprosthesis in principle to the change operation queue, which was not carried out for other reasons.

Swell

• Ch Lüring, H. Bäthis, M. et al. , Navigated knee arthroplasty: A location determination under evidence-based criteria. Dtsch Arztebl 2005; 102 ( 34-35 ) (pdf )
• J. Jerosch, S. Fuchs, J. Heisel: knee arthroplasty - a location determination. Dtsch Arztebl 1997; 94 (8 ) (pdf )
• Plamer, SH; Cross MJ: Total Knee Arthroplasty. ( eMedicine, English review article )
• Federau, H.: The development of total knee arthroplasty. Dissertation Faculty of Medicine Munich 1979
• Green, S.: Short - and medium-term results of alloarthroplastischen supply of the knee joint with uni- and bicondylar sledge prostheses. Dissertation Faculty of Medicine, University of Cologne 1992