Endoprosthesis

from Wikipedia, the free encyclopedia
X-ray of a cementless hip replacement

The endoprosthesis (from Greek: endo "inside"), also known as joint replacement , is an implant that remains permanently in the body and replaces a damaged joint in whole or in part.

Applications

The best known are probably the artificial hip joints. Today endoprostheses are also available for other joints ( knee joint , shoulder joint , more rarely an ankle joint endoprosthesis as well as elbow and finger joint prostheses), whereby arthritic joint changes are a frequent indication. In veterinary medicine (dogs / cats) has now held the artificial hip joint feeder.

Essentially, all foreign spare parts that are completely inserted into the body are endoprostheses, also called implants. This also includes heart valve replacements , vascular replacements or breast implants . In addition, there are special implants that are not only hidden in the body, but emerge, and can therefore also be referred to as endo-exo-prostheses, such as dental implants , cochlear implants or endo-exo-prostheses after amputation e.g. B. the thigh or the upper arm. However, the present article deals exclusively with the joint endoprostheses used in orthopedics and trauma surgery.

Worldwide sales for endoprostheses amounted in 2012 to 43.1 billion US dollars , an increase of 1.2% meant. The market share for knee endoprostheses was 49% and for hip endoprostheses 42%, while the other joints only made up 9%. Almost 200 companies worldwide sell endoprostheses, with the top ten companies sharing 94% of the market among themselves.

Anchoring the prosthesis in the bone

Basically, the permanent hold of a prosthesis is created by the newly formed bone substance that tightly encloses the prosthesis. This bony integration requires the prosthesis to be precisely fitted into the bone bed. By bone cement the fit can be methodically simplified. One differentiates accordingly

  • cemented prostheses
  • cementless prostheses
  • Hybrid prostheses in which, for example, the acetabular prosthesis is cemented and the stem is cementless

Materials / material pairings

Classic pairing: stainless steel and ultra-high molecular weight polyethylene UHMW-PE

The prosthesis shaft of a hip prosthesis usually consists of

  • Titanium alloys (TiAl6V4, TiAl6Nb7 - forged alloy ) (cementless)
  • CoCrMo forged alloys (cemented)
  • (not anymore today) CoNiCrMo forged alloys
  • (isolated) fiber-reinforced plastics

The femoral and tibial components of a knee implant are usually made of

  • CoCrMo casting alloys
  • Titanium alloys (castings or milled forgings)

Typical sliding pairings in the articulation area in total endoprostheses (TEPs) (i.e. replacement of the joint head and joint socket) are

The articulation range of polyethene is exclusively so-called UHMWPE, ultra high molecular weight polyethylene , which has very good tribological properties due to its high crystallinity and long molecular chains in combination with the metals and ceramics used .

To reduce the inevitable abrasion, which can reduce the durability of a joint endoprosthesis, more and more cross-linked polyethylene structures have been used since the early 2000s. This so-called XUHMWPE (cross-linked UHMWPE) is produced by irradiation ( beta or gamma radiation ) of UHMWPE. As a more recent development, since around 2010 more and more manufacturers have also been offering endoprostheses in which the (X) UHMWPE contains up to one percent by weight of antioxidants, v. a. Contains vitamin E. This promises better material properties and, above all, better resistance to oxidation. While this has already been shown in hip simulators and the protective mechanism of antioxidants is well understood, scientific evidence for the better durability of such polyethylenes in practice is still pending.

Due to the very poor tribological properties of titanium, it is not used as a material for articulating prosthesis parts. Only modified titanium surfaces, which use titanium nitride for hardening, are occasionally used for articulation surfaces.

In principle, more and more nickel-free endoprostheses are used, since the relatively common nickel allergies can lead to post-operative complications.

The trend in hip endoprosthetics is also moving more and more towards cement-free anchoring, even for patients of old age, provided that their bone substance still allows the cement-free version.

General Risks

With all elective prosthesis implants, which are planned and not necessary as a result of an accident, concomitant illnesses, medication and the physical and mental state of the patient have a significant influence on the result. Wound healing disorders , infections and loosening are at least twice as common in smokers , which is why it is advisable to refrain from smoking in the six weeks before and after the planned operation.

The surgical results in the clinics that carry out these interventions very often tend to be better than in clinics with a small number of these interventions. This is particularly clear with unicondylar knee replacement .

hip

The pioneers of hip arthroplasty in Germany in the 1960s were Hans-Wilhelm Buchholz and Hans-Hermann ("Peter") Lubinus. If both the joint head and the joint socket are replaced, it is a total endoprosthesis (TEP) of the hip (total hip endoprosthesis, HTEP). If only the femoral head is replaced, it is called a hemi-endoprosthesis (HEP).

Current developments

According to evaluations of the German endoprosthesis register, there is a trend towards cement-free hip stems, which, according to the 2019 annual report, are used in two thirds of all cases, and of which less than 15% are short-stem prostheses. When it comes to pans, there is a strong tendency towards "pressfit" pans, which are currently dominating. While in 2000 every second pan was a screw-on pan, today this is only every eighteenth. With a share of 84%, sliding pairings made from cups with highly cross-linked polyethylene and ceramic heads are standard, while metal-metal pairings are no longer used.

Resurfacing

In this more recent development, the head of the femur and the femoral neck are only partially removed, the femoral shaft is not drilled open, but only the surface of the joint head is removed and replaced with a metal cap. These prostheses, also known as “McMinn” or “hip cap prostheses” ( resurfacing ), are more likely to be indicated for younger patients because they offer more options for a later revision. The low bone loss, the low risk of dislocation and the preservation of the physiological joint mechanics are considered to be the greatest advantages of resurfacing. However, the bone protection is put into perspective by a larger cup milling, the metal wear in the large metal-metal-hard pairing represents a problem that has not yet been resolved, and the long-term fate of the remaining femoral head under the cemented cap has not yet been clarified. In October 2010, DePuy recalled the ASR XL acetabular cup and hip resurfacing system. In March 2012, The Lancet published a study according to which the revision rate of large metal-on-metal prostheses (52 mm heads) after five years was 5.1% (in 60-year-old men) more than twice as high is like other prostheses with 2% (40 mm heads, 60 year old men). It recommends not to use metal-on-metal prostheses. In 2013, Depuy Synthes had to take another hip prosthesis off the market as there were frequent premature revisions. The Adept 12/14 Modular Head component for a total hip replacement is being recalled.

A hip prosthesis that combines ceramic (joint ball) and metal (hip socket) was approved for the first time in the USA in June 2011 . In the previous two-year clinical study , 194 new ceramic-on-metal prostheses were compared with 196 patients with conventional metal-on-metal prostheses at eleven clinics in the USA and Canada. The number of revision operations required was low (two and three in both groups); there were “no increased intra- or postoperative complications”. The US regulatory authority FDA then granted the US manufacturer DePuy Orthopedics Inc. from Warsaw (Indiana) state approval for its product. A post-marketing study was also carried out, in which the metal-ion concentration in the blood should also be checked.

Since surface replacement prostheses have been more problematic over the years than initially assumed, they are increasingly controversial. A Canadian follow-up of 2,450 patients after a mean 3.4 years showed a five-year survival rate of 96.4% in men and 93.6% in women. In the multivariate analysis, female sex ( hazard ratio HR = 2.4), smaller femoral heads under 48 mm, some special prosthesis models and a history of childhood hip disorders (HR = 2.4) were independent risk factors for premature loosening, so the commentator said as well As the authors of the study recommended, resurfacing the hip should only be used in exceptional indications in women and only used in men with a prosthesis head diameter of 50 mm or more

Short stem prosthesis

Metaphyseally anchored short stems

The so-called short-stem prostheses are somewhat in competition with resurfacing in younger patients, also with the need to protect the bones. After several years of experience, the short stems have delivered good durability results in some cases. Some have not proven their worth and have been withdrawn from the market. They are also more expensive than the cemented endoprostheses.

Operative treatment

The operation can be performed under general anesthesia or with spinal anesthesia . First, the worn joint surfaces and the previous joint head on the thigh are removed and the remaining bone is prepared for the implant. The two joint components are then implanted and anchored using the alternatives described above. An abduction of 40 ± 10 ° and an anteversion of 15 ± 10 ° should be aimed for for the acetabulum . Outside of this “safe zone” (according to Lewinnek 1978) the risk of prosthesis dislocation increases fourfold, and there is also an increased risk of premature wear the prosthesis components and for an impingement of the prosthesis. Then a trial head is placed on the shaft and the hip is adjusted to check leg length, secure hold and axial stability. A trial femoral head with a longer or shorter neck, with more or less offset, can possibly be tried out until a secure and stable hold is found. Finally, the new femoral head is put on, the hip joint repositioned and finally the wound is closed. One to two hours can be expected for the entire operation to the wound closure. The patient then comes to a wake-up unit for monitoring. After another two to four hours, you will be transferred back to the normal or monitoring station. The hip joint was temporarily implanted by a robot ( ROBODOC ), but the system was discontinued due to increased risks.

Minimally invasive hip replacement

Minimally invasive implanted endoprosthesis
Surgical scar after installing an endoprosthesis in the right hip

Modern minimally invasive surgical techniques now allow a type of implantation that is gentle on the tissue. These are minimally or less invasive approaches to the hip joint. However, the definition of the minimally invasive approach is currently being discussed controversially. What is certain, however, is that this predicate “minimally invasive” in connection with the lowest possible soft tissue irritation can not only be claimed by a single method, but that several procedures can be considered minimally invasive. One advantage is the faster rehabilitation of the patient than with conventional techniques due to the gentler soft tissue treatment. However, this only affects the first few days after the operation. In the further course there is no difference between the individual techniques in terms of mobility or loading capacity of the hip joint. The minimally invasive technique cannot be used for every hip joint disease and has its limits.

In the case of advanced osteoarthritis of both hip joints, both of these can be endoprosthetically replaced in specialized centers within one anesthesia if there are no internal or anesthesiological problems. The advantage is the shorter follow-up treatment time and the fact that only one hospital stay is necessary. However, the blood transfusion rate is higher.

Care after the operation

In the first few days after the operation, wound pain is relieved with medication . The physiotherapy exercise therapy the operated leg begins. The postoperative procedure differs significantly between cemented and cementless prostheses. While the great advantage of cemented prostheses is that mobilization begins on the first day after the operation and the patient can take the first steps under (pain-limited) full load, with cement-free prostheses there is no load at all or only in the first postoperative week partial loading of the prosthesis so that the rather slow bony integration is not disturbed.

In the first few weeks, medical walkers and forearm crutches are used to improve gait security and not to overload the hip joint that has been operated on. In-patient treatment in most clinics takes about eight to ten days after an uncomplicated procedure. During this time, follow-up treatment will be determined. In these rehabilitation clinics , mobility should be further improved and the muscles that stabilize the hip joint should be specifically trained.

In specialized clinics, long-term results of over 15 years can be achieved with standard implants. In more than 90% of cases, they allow a good functional result (walking, standing) with extensive freedom from pain.

Regular follow-up checks in the outpatient clinic or at the orthopedic surgeon's with clinical and radiological examination should accompany these results in the long term.

Risks of the intervention

Periprosthetic refracture of the femoral shaft (rectangular shaft, Dall Miles plate)

The implantation of an artificial hip joint is associated with the general risks of a moderate surgical procedure. These include the formation of blood clots in the legs ( thrombosis ) during or after the operation, impaired wound healing, infections (see also osteomyelitis ), postoperative bruising ( hematoma ), secondary bleeding and the possibility of damage to nerves and blood vessels . Occasionally, blood loss may occur during the operation, which requires a blood transfusion (autologous or foreign blood). An implant allergy to components of the endoprosthesis can make it necessary to replace the artificial joint (revision surgery), similar to an infection.

The risk of thrombosis can be reduced by starting prophylaxis after the operation. As a rule, this prophylaxis is carried out over four to six weeks. In randomized clinical studies , the risk of thrombosis without prophylaxis was 1.4–6.0% in the first three months. A nationwide cohort study from Denmark showed a thrombosis risk of 0.79% in the first three months and 0.29% in months 4 to 12 after a hip prosthesis operation despite prophylaxis, which is a relative to a non-operated comparison group adjusted relative risk of 15.84 for the first three months and of 2.41 for the following nine months. Age, gender and comorbidities had no significant influence on this.

A specific risk for the procedure is a rarely occurring rupture of bone tissue on the thigh, which then requires additional stabilization with wiring or screws. In around 3% of patients, a so-called endoprosthesis loosening occurs over the course of ten years , which is associated with pain and possibly inflammatory changes and may require revision surgery with a change of the endoprosthesis. In the case of intact soft tissue , the replacement of the prosthesis takes place as a “one-stage” (i.e. one- stage ) and for non-intact and abscess formation as a “two-stage replacement” ( two -stage ), each with a different perioperative procedure.

In some patients, heterotopic ossifications appear in the first few months after surgery . Without suitable countermeasures, they can destroy the mobility gained by the operation. Preventive X-ray irradiation of the surrounding tissue immediately before the operation (usually with 7  Gy using a linear accelerator ) reduces the formation of new bones in known risk patients. Also for the prophylaxis of heterotopic ossifications, an anti-inflammatory drug (usually indomethacin ) is very often given postoperatively .

A US analysis of the risk of deep wound or prosthesis infections (0.5% in the study) after primary use of a hip endoprosthesis in over 30,000 operations revealed in a multivariate analysis as risk factors :

  • Simultaneous bilateral prosthesis surgery (hazard ratio HR = 4.80, confidence interval CI = 2.09–11.1)
  • Reduced health with an ASA score of at least 3 (HR = 2.20, CI = 1.55–3.11)
  • Overweight with a body mass index BMI> 30 (HR compared to normal weight = 2.37, CI 1.55-3.61)
  • Female patients (HR = 1.43, CI = 1.01–2.04)

In contrast, there was no increased risk in diabetes (which was only a risk factor in the univariate analysis, but in which the BMI was a confounder ). Age, the underlying diagnosis, ethnicity , surgical approach and fixation method played no role, nor did the frequency of surgery by the surgeon or the hospital. Also, special clean room technologies ( laminar airflow and body exhaust suites ), previous administration of antibiotics or the type of anesthesia procedure were not associated with a changed risk of infection. Research is being carried out on antibacterial coatings for implants and instruments.

Persistent pain after the procedure

The International Association for Pain Research defines persistent pain after surgery as lasting at least three months.

According to an independent study, half a year after the operation, 58% of the patients surveyed said that they had had pain on the operated hip in the 4 weeks prior to the survey. Moderate to severe pain affects 17% of the operated patients.

shoulder

The first shoulder prosthesis was presented as a monoblock prosthesis by CS Neer as early as the 1950s, initially for the treatment of complex humerus head fractures, but later also for shoulder joint wear. In the second generation, prostheses were developed in which calottes and shafts of different sizes could be combined with one another. Thanks to the third generation of modular prostheses, the offset between the diaphysis and metaphysis, the inclination and retroclination of the humeral head could also be set variably, thus enabling the prosthesis to be positioned according to the individual anatomy. Current fourth-generation prostheses differ only slightly from this, especially in terms of their anchoring to the glenoid and the humerus shaft, as well as the options for a prosthesis revision.

In addition to the total endoprosthesis with replacement of the shoulder socket (the glenoid), more hemiendoprostheses will continue to be used in Germany in 2011 where the glenoid is not replaced. In addition to the conventional stem prosthesis, there are also prosthesis types with a short stem, stemless prostheses and the cap-like humeral joint surface replacement for the humerus component. Modular long-stem prostheses are also a frequent indication, particularly in traumatology.

Inverse prostheses (delta), in which the glenoid component is spherical and articulates with a concave humerus socket, are used particularly in the case of defective rotator cuffs, but also increasingly after humerus head fractures and in the event of a revision of a loosened shoulder prosthesis.

knee

A differentiation is made in knee TEP:

  • Uncoupled (uni- and bicondylar) endoprostheses. In the unicondylar, only the inner or (less often) the outer condyle (= joint role ) is used. of the thigh bone and the opposite half of the joint surface of the head of the tibia (two implants). The bicondylar endoprosthesis replaces both condyles and the entire articular surface of the tibial head. A polyethylene inlay is interposed. The bicondylar TEP can (should) be supplemented by a plastic replacement of the retropatellar articular surface. Both collateral ligaments must be intact for the use of an uncoupled knee prosthesis. Posterior stabilized inlays are used when the posterior cruciate ligament is resected.
  • Coupled prostheses are axis-guided hinge joints. They are used when the ligament stability of the joint is insufficient. This is especially the case with pronounced knock knees or bow legs. The axis-guided knee prosthesis is also suitable for replacing the prosthesis where ligament destruction and / or bone loss is to be expected.

Upper ankle

Load on endoprostheses

Prosthetic sockets for telemetric load measurement

Little was known about the actual mechanical loads on endoprostheses. Exact knowledge of the size and direction of the forces and moments acting is a prerequisite for improving the implants and their anchoring in the bone. A research team from the Julius Wolff Institute of the Charité - Universitätsmedizin Berlin has been developing endoprostheses with integrated measurement electronics for many years, with which the joint load in the patient is measured and wirelessly transmitted to a computer. The loads, which can be several times the body weight, are measured for the various everyday activities, stored in a database and made available to interested parties on the Internet. In addition to hip, shoulder and knee prostheses, spinal implants were also instrumented for in vivo measurements.

Load measurement with the knee endoprosthesis in place

register

A corresponding register can be set up to record long-term experience with the prosthesis and the success rate of operations. For obvious problems with prostheses 1979, the first was in Sweden and Finland arthroplasty created, Norway followed this example in 1987. The creation of such a register can lead to a reduction in the number of subsequent operations and to the discovery of problematic prosthesis models. By October 2011, 19 countries had already introduced such a register. In Germany, the Endoprosthesis Register Germany (EPRD) has been tested as the central registration register since October 2011.

literature

  • Rüdiger Döhler : Do we need new hip prostheses? In: Surgical General . No. 7, 2006, pp. 471-475.
  • Ulrich Hinkelmann, Michael Fleischhauer (ed.): The endoprosthesis. The artificial hip and knee joint explained step by step. 2nd Edition. Elsevier, Urban & Fischer, Munich / Jena 2007, ISBN 978-3-437-47191-9 . (3rd edition: The new hip and knee joint, the endoprosthesis explained step by step. 2013, ISBN 978-3-437-47192-6 )

Web links

Individual evidence

  1. ↑ Orthoworld: The Orthopedic Industry Annual Report, For Year Ending December 31, 2012. Quoted from "move - Belgium", information from Mathys Orthopedics Belux NV-SA, Leuven / Belgium, November 2013.
  2. ↑ Vera Zylka-Menhorn: Endoprothetik: Active role of the patient asked Deutsches Ärzteblatt 2020, Volume 117, Issue 9 of February 28, 2020, Page A-438 / B-382 / C-369, Link
  3. ↑ Endoprosthesis Register Germany (EPRD): Annual Report 2019, [1]
  4. ↑ Vera Zylka-Menhorn: Endoprothetik: Active role of the patient asked Deutsches Ärzteblatt 2020, Volume 117, Issue 9 of February 28, 2020, Page A-438 / B-382 / C-369, Link
  5. ↑ On the recall of the system by the manufacturer ( Memento from February 14, 2013 in the Internet Archive )
  6. ↑ Recall DePuy ASR ™ Hip Replacement System and ASR ™ XL Acetabular System, DePuy. ( Memento from December 14, 2013 in the Internet Archive )
  7. ↑ Alison J Smith, Paul Dieppe, Kelly Vernon, Martyn Porter, Ashley W Blom: Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales. In: The Lancet . Vol. 379, Issue 9822, March 31, 2012, pp. 1199-1204. (abstract)
  8. ↑ Depuy: Return of Adept hip prostheses - Monday, February 18, 2013 - aerzteblatt.de Recall for modular femoral heads of the ADEPT product family, DePuy International Ltd.
  9. ↑ Deutsches Ärzteblatt from June 16, 2011: USA: First ceramic-metal hip prosthesis
  10. ^ Canadian Arthroplasty Society: The Canadian Arthroplasty Society's experience with hip resurfacing arthroplasty. In: The Journal of Bone and Joint Surgery [Br]. 95-B, 2013, pp. 1045-1051; doi: 10.1302 / 0301-620X.95B8.31811 .
  11. ^ FS Haddad: Metal-on-metal. More questions than answers. In: Journal of Bone and Joint Surgery [Br]. 95-B, 2013, pp. 1009-1010; doi: 10.1302 / 0301-620X.95B8.32673 .
  12. ↑ AB Pedersen, SP Johnson, HT Sørensen: Increased one-year risk of symptomatic vebous thromboembolism followinf total hip replacement. In: Journal of Bone and Joint Surgery. Volume 94-Br, Issue 12, December 2012, pp. 1598-1603.
  13. ^ Marianne Abele-Horn: Antimicrobial Therapy. Decision support for the treatment and prophylaxis of infectious diseases. With the collaboration of Werner Heinz, Hartwig Klinker, Johann Schurz and August Stich, 2nd, revised and expanded edition. Peter Wiehl, Marburg 2009, ISBN 978-3-927219-14-4 , p. 177 ( procedure for changing prostheses ).
  14. ↑ Preoperative radiation for the prevention of heterotopic ossification after hip replacement. often cited dissertation on this topic.
  15. ↑ RS Namba, MCS Inacio, EW Paxton: Risk factors associated with surgical site infection in 30 491 primary total hip replacements. In: Journal of Bone and Joint Surgery. British Edition, Volume 94-B, 2012, pp. 1330-1338.
  16. ↑ V. Wylde, S. Hewlett, ID Learmonth, P. Dieppe: Persistent pain after joint replacement: prevalence, sensory qualities, and postoperative determinants. In: Pain. 2011.
  17. ↑ IASP. Classification of chronic pain. Pain 1986; S1-226.
  18. ^ Clinical relevance of persistent postoperative pain after total hip replacement - a prospective observational cohort study. In: J Pain Res. 10, 2017, pp. 2183-2193.
  19. ↑ CS Neer, THJ Brown, HL McLaughlin: Fracture of the neck of the humerus with dislocation of the head fragment. In: The American Journal of Surgery . 85, 1953, pp. 252-258.
  20. ↑ Markus Loew: Shoulder endoprosthetics - principles and indications. In: Orthopedics and trauma surgery. up2date 2011, pp. 503-518.
  21. ↑ Endoprostheses with integrated measuring electronics ( Memento of the original from July 23, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Julius Wolff Institute of the Charité @1@ 2Template: Webachiv / IABot / jwi.charite.de
  22. ↑ Harro Albrecht: Dangerous spare parts. In: The time . October 27, 2011, No. 44, p. 51 ( online version )