THE MODERN TECHNOLOGIES OF TREATMENT OF SEVERE BONE DEFECTS IN THE ACETABULUM REGION: WHICH PROBLEMS ARE SOLVED WITH INDIVIDUAL

THE MODERN TECHNOLOGIES OF TREATMENT OF SEVERE BONE DEFECTS IN THE ACETABULUM REGION: WHICH PROBLEMS ARE SOLVED WITH INDIVIDUAL IMPLANTS?

Kovalenko A.N., Shubnyakov I.I., Bilyk S.S., Tikhilov R.M.

Russian Scientific Research Institute of Traumatology and Orthopedics named after R.R. Vreden,
North-Western State Medical University named after I.I. Mechnikov, Saint Petersburg, Russia

The presence of bone defects in the region of the acetabulum is a serious issue in revision replacement of the hip joint. The treatment techniques show the significant variance and depend on the size of bone defects, the quality of a remaining bone, presence of intact columns of the acetabulum or disordered integrity of the pelvic ring that determine the possibility for appropriate fixation and the sufficient square of contacting with a vital bone [20, 22, 41]. During revision hip joint replacement, the complicacy of treatment of extensive acetabular defects is confirmed by the presence of multiple variants of reconstruction with no advantages.
According to the data of the national registry of joint replacement in the Great Britain, most revision cases are performed because of aseptic loosening (51 %), pain syndrome (22 %), dislocations (15.6 %). 8,923 revision procedures of hip joint replacement were conducted among 89,288 primary surgical operations. The acetabular component was replaced in 69 % of all revision procedures: independently in 27 % and in combination with the femoral component in 42 % [7]. According to the data from the joint replacement registry of Russian Scientific Research Institute of Traumatology and Orthopedics named after R.R. Vreden, the acetabular component was replaced in approximately 60 % of revision procedures [6]. The persistent trend to increasing amount of operations is observed both for primary and revision joint replacement. The ratio between revision and primary operations can vary from 1:10 to 1:5 [6, 27, 28].
The incidence of defects of type 3B (W.G. Paprosky) or disordered integrity of the pelvic ring is 1-5 % after revision hip joint replacement [11, 12]. The aim of revision of the acetabular component is achievement of stable fixation, restoration of the anatomical center of rotation of the hip joint and providing the correct position of the fixed component [13].
However the field of potential contacting with standard cementless acetabular components is often decreased by severe defects, which are often caused by osteolysis and stress shielding. The individual acetabular implants have been offered as a new perspective option for severe acetabular defects or for highly compromised (in the context of biology) bone bed, for example, after bone radiation exposure [16].
This review describes the requirement, indications, the features of presurgical planning, designing, production, results, economic efficiency and advantages and disadvantages of individual acetabular constructs produced with 3D printing technique.

The modern trends relating the offers and requirements for individual acetabular implants

The extensive loss of bone tissue and massive acetabular defects present the significant problem of revision operations for the hip joint and they are the most difficult cases in prosthetic surgery [18, 23]. According to some authors, the proportion of massive defects of the acetabulum can be 8.5 % (without consideration of integrity of the pelvic ring) among revision operations for the hip joint [32] and 27 % for revision surgery of the acetabulum [19]. The rate of single acetabular injuries is significantly lower. In the studies by Berry D.J. it was 0.9 % in the sample with 3,505 acetabular revisions [12].
According to the Danish National Registry of Endoprosthetics, the rates of defects of types 2 and 3 (Paprosky classification) and disorders of pelvic ring integrity increases with absolute and relative numbers of costs for revision of total hip joint replacement. In the Norwegian registry the number of such acetabular defects is stable for defects Paprosky 3A and Paprosky 3B per year for the last 5 years [43]. Possibly, the requirement for such implants will be increasing with population aging and trends to total hip joint replacement.
According to the data of the producers, during the last 9 years one has been observing the increase in using such 3D printed implants. For example, OSSIS company produced 26 implants in 2014 and only 65 since 2007 [43].

The indications and the contraindications for individual implants in revision surgery of the hip joint

The indications for using the individual constructs in revision hip joint replacement include previous unsuccessful revisions with anti-protrusion constructs or porous augments; big bounded defects with possible disordered integrity of the pelvic ring; evident disordered integrity of the pelvic ring and difficult cases of recurrent joint replacement, when other variants are intricate because of bone tissue deficiency [11]. The use of the individual three-flanged acetabular component is especially important for disordered integrity of the pelvic ring, because it provides precise and stable reconstruction of acetabulum anatomy, bone plastics of defects and restoration of hip joint biomechanics and provides the adequate contact with a healthy bone [43].
The alternative reconstructive techniques require both adaptation of constructs and/or allografts to the borders of a defect and adaptation of bone bed to installed constructs [35]. Bone adaptation is minimal in case of using the individual components. Therefore, the use of the individual constructs is especially actual in patients with extremely intense loss of bone mass, where adaptation and fixation of allografts and augments is not possible (Fig. 1).

Figure 1. Reconstruction of the defect in the region of the acetabulum demonstrates absence of the posterior column:
a) left-side view
figure 1а
b) posterior view
figure 1b 

The contraindications include the active infectious process and patients with contraindications to surgery according to their health condition.

Presurgical estimation and planning

The principal difference between other types of reconstruction and the use of the individual constructs consists in difficulties for reconstruction of the acetabular component and possible disorder of the pelvic ring identified at the presurgical stage. It is necessary for designing and production of the component. Estimation is often conducted with use of the classification by Paprosky W.G. and also CT images of patients with defects of type 3 are considered [21, 31]. The producers of the individual implants usually recommend a specific CT protocol for such cases. A surgeon makes a final decision about possible use of the individual component, when a virtual or sometimes printed model of a half of the pelvis is ready. This is a multifactorial decision that includes the essence of a patient’s problem, individual experience of a surgeon and preference in treating extensive acetabular defects, which are difficult to treat with standard hemispheric components with porous covering. A surgeon should consider that time from making a decision to possible implanting can take from 2 to 8 weeks. Therefore, patients should be preliminarily examined in outpatient conditions.

Designing

Preparation and development of the individual three-flanged components is initiated with thin-slice CT images with 0.5-1 mm pace. The images are sent to the 3D modelling laboratory, where a three-dimensional model of the pelvis is created in full scale (Fig. 2). Such model demonstrates the higher accuracy than 2D X-ray image in estimation of a defect in the acetabular region and for surgical planning [5].

Figure 2. The scheme of obtaining three-dimensional reconstruction of the pelvis
figure 2


A surgeon can estimate a virtual model of an acetabular defect or its plastic copy. If after reviewing the defect cannot be replaced with the common techniques, then an individual construct is developed. Such implant has the acetabular, sciatic and pubic flanges. So, it is called a three-flanged implant.
Before production of the implant, a surgeon should note the regions of an overhanging bone on the pelvic model which can be removed for simplifying the placement of the flanges of the construct. It is especially important for a bone, which outstands from the surface of the iliac, ischial or pubic bones and impedes the congruent joining of the flange surfaces (Fig. 3).

Figure 3. Planning the individual acetabular implant for the patient I. with disordered integrity of the pelvic ring to the right:
a) positions of the individual implant

figure 3a 

b) the arrows indicate the regions of conflict in the bone and the implant, and the bone regions to be removed

figure 3b 

Moreover, a surgeon should mark the preferential direction and places of position for the fixing screws [1]. The sciatic flange usually has 3-6 holes for fixation with screws, whereas the iliac flange should have 2 ranks with 2-4 screw holes. The smallest pubic flange can be without holes. Interaction of specialists during the process of development and production of the implant can give clearer picture of future events and the implant correspondence to the patient’s anatomy.
A surgeon can estimate the positioning and compliance between the implant and the defect with use of the produced prototype of the implant with the model of a half of the pelvis with the defect. The center of rotation, anteversion and inclination of the implant are established with consideration of the anatomic landmarks including the obturator foramen, the iliac wing and the pubic bone [37]. However according to our opinion, the ideal variant for reconstruction of positioning the rotation center and spatial orientation is their mirror reflexion from the opposite healthy side [4]. Even in cases with pathologic change in the contralateral hip joint, full three-dimensional visualization of the pelvis allows minimizing the error in orientation and position of the acetabular component. Since the three-dimensional model of the pelvis is constructed with DICOM images including the data of spatial orientation of the pelvis and its position towards the horizontal, vertical and sagittal planes (Fig. 4), then it is not difficult to set the angle of horizontal inclination and anteversion of the acetabular hemisphere with high accuracy to the extent of a millimeter.

Figure 4. a) designing of the rotation center, position and orientation of the acetabular component of the implant

figure 4a

b) designing of the flange component with specified position and orientation of the rotation center

figure 4b 

Production technology

After the final confirmation of the constructive decision about the implant, its final metal variant is produced. There are several variants of production of the individual construct. The first variant is production of the final titanium alloy implant by means of counterproof technique from the clay prototype. The porous or hydroxyapatite covering is applied along the medial surface for achieving the osteointegration [44].
The other variant is 3D printing with titanium powder. The construct is produced by means of layer-by-layer electronic in-beam melting or laser agglomeration of titanium powder. This technique is known as additive production [3]. For decreasing the final rigidity, potential stress-shielding of the final product can be calculated according to its geometry [42]. The implant can be adapted to different surfaces depending on specific mechanical and biological problems. For example, the porous surface can be built for provision of bone biointegration, whereas silver coating can decrease the risk of infectious complications [8]. Surface polishing can decrease the possible irritation of soft tissues. Solid parts of the flanges are formed for provision of reliable fixation of the constructs with use of screws. At the same time, they are the unified whole with the printed acetabular cavity. As result, the accuracy of the implant positioning to the remaining bone bed minimizes the requirement for greater resection of the bone, because it happens during placement of the ready typical constructions. The designed holes of the construct with locked screws and direction along bone tissue can provide higher efficiency of the use and better fixation to the available bone [9]. Moreover, during CT with vascular opacification it is possible to design the direction of screws with provision of maximal fixation and, at the same time, with exclusion of the risk of injuries to the magistral vessels [34] (Fig. 5).

Figure 5. Planning the position of the acetabular component and screws during revision endoprosthetics. The arrow shows the coincidence between screw direction and location of subiliac artery.

figure 5
 

Surgical technique

The common technique for revision hip joint replacement is used, when special attention is given to extensive exposure of the ischial, iliac and pubic bones to provide the adequate visibility of a defect and surfaces used for fixation. The individual construct is placed after removal of the previous implant and elimination of scars in the bone bed. The individual solution simplifies the implantation of the new implant and, as result, decreases the duration of surgery because absence of requirement for modelling the construct in compliance with the defect of spatial orientation of the acetabular socket, difficulty of fixation, associated with identification of a bone with sufficient density and appropriate length of screws. It is a potential advantage in older patients with multiple concurrent pathologic states. Visualization of the ischial bone can cause some difficulties, with requirement for trochanteric osteotomy in some cases. Bone exposure for placement of the ischial flange is safely performed with subperiosteal detachment of soft tissues on the posterior surface of the ischial bone. At this stage it is necessary to take care for preventing of the ischial nerve damage. Blenderized bone crumb can be placed under the construction with the aim of bone plastics.
The high speed drill is used for removal of the excess of the bone marked in the 3D model of the defect. The fixation of the pubic flange requires the detachment of the periosteum and is produced with preventing the possibility of damages of the vascular and neural structures. Fixation is initiated from the ischial flange. 9-15 screws are required for appropriate fixation of the implant.
After fixing the whole construction, the test insert is installed and experiental reduction of the hip is performed. The models of the insert can differ in various producers and it is important to understand the possibility for fixing the cementless insert in the individual construct before the surgery. Another variant is fixation of the polyethylene component to the three-flange construct with use of cement. The lateralized, eccentric and connected variants can be used for achievement of necessary length, tension of soft tissues and stability.
Then the cement cup or the cementless insert are installed, in dependence on the fixation type for the individual construct. The postsurgical period is individual like for other revision operations, but, as a rule, partial load is recommended for 3 months.
Holt G.E. and Dennis D.A. reported their results of 26 three-flanged constructs 4.5 months after the surgery, including 3 cases of disordered integrity of the pelvic ring (AAOS type 4) [24]. Two of three hip joints with disordered integrity of the pelvic bone demonstrated the loosening of the ischial screws with failed fixation of the ischial flange. Fractures of the screws were not identified. Although these three cases cab be considered as radiological inadequacy, 2 of 3 patients refused from additional surgery. Bad fixation of the ischial flange is sometimes not associated with failed fixation. In the study by Berasi C.C., a patient with similar worsening fixation of the ischial flange demonstrated the stable implant during 11 years [11]. Therefore, regarding the implant installment, the special attention is given to the problem of the ischial flange fixation. As result of extensive osteolysis, the quality of the ischial bone can be low. First of all, for prevention of loosening, the screws should be twisted into the ischial bone; it allows pulling the component downwards and providing the contact between the flange and the bone tissue. Other variant for improving fixation of the screws is cement augmentation for the ischial bone defect before introduction of the screws. Although most publications with middle- or long term outcomes of the individual acetabular implants are dedicated to the constructs without the possibility for using the locked screws, their use is one of the options for decreasing the risk of failed fixation [14, 17, 24, 26, 37].

Economic effectiveness

There are few publications concerning the economic effectiveness of the individual implants. However the potential advantages include the decreasing time of the surgery and indirect decrease in the rate of complications. According to DeBoer D.K., the sum costs for computer tomography, modelling and production of the implant can be higher than the costs for the surgery. The price of the three-flanged cup was about $8,500 in 2006. Such high price can be justified with improvement in the clinical outcomes [17].
According to the data from Taunton M.J., the costs for the individual construct was $12,500 including the costs for the cup, the screws, the polyethylene insert and the production process. The comparable construction including the tantalic cup, the screws, the anti-protrusion cage and the polyethylene insert was $11,250. For the construct including the tantalic cup, the screws, the anti-protrusion cage, the polyethylene cage and additional two porous metal augments, the costs were $14,500 [37].
Despite of significant variations of the price in different regions, according to Wyatt M.C., the comparative prices in the financial network of the National Healthcare System of Great Britain are £13,000 for the individual implants MOBELIFE, £11,000 for OSSIS and £7,000 for TMTCup-Cage with the augments for similar cases. It is evident that the initial price of the individual implants can be significantly higher as the alternative variant made of trabecular metal [43].
Therefore, the direct price of the individual acetabular constructs varies in comparison with the similar alternative solutions from similar prices to 36-46 % higher. But such comparison does not consider the influence of the technique on the basic outcome and the degree of improvement in the quality of life. It is not right time for making conclusions about the economic efficiency of the technique without consideration of results of the cost efficiency analysis, which is absent in the publications at the present time.

The evidential basis of individual acetabular implants

Defects of degree 3 according to Paprosky

During the comparison of the results of administration of the individual acetabular constructs, the rate of revision in the study by Berasi C.C. (8 %) was similar like in the studies by Wind M.A. et al. and Holt G.E. and Dennis D.A. (12 %) in the patients with 3B type acetabular defect according to Paprosky [11, 24, 40]. Joshi A.B. et al. reported about 7 % rate of revision in their similar study of the patients with the acetabular defect of type 3 according to the classification from American Academy of Orthopedic Surgeons (AAOS) [26], although two other studies showed no unfavorable outcomes of the three-flanged component in the patients with III/IV AAOS type acetabular defect [14, 15].
The study by Berasi C.C. showed the lower rate of recurrent revision for all causes (17 %) [11] than in the studies by DeBoer D.K. (30 %) and Taunton M.J. et al (35 %) [17, 37], where the patients with disordered integrity of the pelvic ring received the surgery. The relatively short period of the long term follow-up in the study by Berasi C.C. (57 months on average) could influence on the lower rate of complications in comparison with the above-mentioned studies (123 months and 76 months correspondingly) [11]. The individual three-flanged components were reviewed as the modern treatment technique for acetabular bone defects in the study by Nieminen J. et al. who estimated several techniques for treating complex acetabular defects [30]. However they reported that a successful outcome requires complete osteointegration. Barlow B.T. et al. indicated 13.5 % rate of revision after implantation of the individual constructs. The mean time after previous surgery was 4 years and 3 months. They considered the correct center of rotation as the factor of a good outcome. More than 2 cm lateralization was associated with bad outcomes [10].

Disordered integrity of the pelvic ring

DeBoer D.K. et al. investigated the sufficiently big group of the patients with disordered integrity of the pelvic ring. All patients received the same type of the construct – the individual three-flanged cup [17]. The group of the patients was similar with the group in the study by Berry D.J. et al. [12] and Stiehl J.B. et al. [36], with higher number of the women with the bone defect of IVb type according to AAOS. The rate of complications was similar with the above-mentioned studies. Dislocations were the main complications, but it is not surprising for patients with previous multiple revisions of the hip joint.
The predisposition to dislocations can influence on the treatment protocol. In case of weak tone of the abductor muscles before the surgery, it is currently recommended to install the connected insert or the frictional couple with double mobility [38]. The appropriate design of the cups with specific attention to anteversion and inclination of the component is highly important from the perspective of minimizing risk of dislocation [29]. In their previous publication DeBoer D.K. et al. reported the results of reconstruction of the acetabular component with using the three-flanged components for big acetabular defects with or without disordered integrity of the pelvic bone (defects of AAOSIII/IV type) [14]. After 4.4 years no cases of mechanical or clinical failure were identified.
Joshi A.B. et al. reported the series of reconstructions with three-flanged implants for the defects AAOS type III [26]. After 4.8 years one Girdlestone’s surgery was conducted for infection. Another patient received the recurrent revision with new three-flanged implant because of the dislocation. All other constructs were stable and without fractures of the screws, migration or heterotopic ossification more than 2nd degree.
Holt G.E. and Dennis D.A. reported the results 4.5 years after 26 three-flanged reconstructions including 3 cases with disordered integrity of the pelvic ring AAOS type IV [24]. Two of three hip joints with disordered integrity of the pelvic ring were complicated by loosening ischial screws with lost fixation of the ischial flange.
The increase between the average presurgical and postsurgical Harris score was 23 points in the series by Berasi C.C. that is similar with the average score reported by Wind M.A. et al., but lower than in the studies by Christie M.J., DeBoer D.K. and Holt G.E. [11, 14, 24, 40].

The comparative studies of other techniques for treating severe defects

According to the recently published metaanalysis of treatment of severe acetabular defects, the mean rate of revision was 15.9 % (3.8-30.3) for the individual constructs [25].
The metaanalysis included 5 studies of level IV evidence with 193 patients (197 hip joints) [14, 17, 24, 26, 37]. All reports contained the information about the mean age (65.8 years) and duration of the follow-up (the mean period 4.5-10 years). None of these studies reported the adequate results of specific indications for revision surgery, but all studies mentioned that the indications for ITVC were bone defects of types 3-4 of the acetabulum according to the classification AAOS.
Besides one study without estimation of the clinical results of the hip joint scores [37], all studies reported the mean postsurgical improvement according to Harris and PMA. While the mean improvement in Harris score was 42.3 points (38-48.8), PMA scores were used only in one study with improvement of 3 points.
Therefore, the mean level of revision was 7.8 % and the rate of complications was 22 % for the period of 5 years [14, 24, 26]. However these values increased to 30 % and 35 % correspondingly in the studies with duration of more than 10 years [17, 37].
The most common complications without requirement for revision were dislocations with the rate from 4 % to 30 % according to the compared publications [14, 17, 24, 26, 37, 40]. Although Berasi C.C. did not identify this complication, in this study one three-flanged component (revision after deep infection) was reinstalled and was further exposed to two revisions of the insert and the hip component for treatment of the displaced endoprosthesis. As a rule, at the moment of the use of the individual implants, the patients are exposed to more than one revision surgery, and the muscular disbalance is often accompanied by deficiency of bone tissue in the region of attaching the gluteal muscles [39]. Therefore, despite of the possibility for highly-accuracy positioning for the individual acetabular component, the problem of dislocations is still actual. For these cases the optimal variants are the heads with double mobility [38], and the connected inserts without biointegration of the acetabular component increases the risk of displacement of the acetabular construct [45]. Another complication is neural injury, which is a minor complication with the rate from 4 to 8 % [24, 26, 37]. Several studies reported the absence of migration in the X-ray images during the long term follow-up, although some other studies showed the rate of migration of 11-14 % [27, 37, 40].
The metaanalysis of various treatment techniques for severe acetabular defects showed 24.5 % (18-35 %) of complications for the individual constructs. The local complications included dislocations (13.2 %), nerve paresis (5.6 %), infection (2.5 %), aseptic loosening (2.5 %) and seroma (1 %), but without systemic complications [25].

CONCLUSION AND PERSPECTIVES

The implementation of the porous metal acetabular components or the augments has significantly extended the possibilities for reconstruction of severe cases of acetabular destruction. However there are some cases of massive defects of the acetabulum which cannot be successfully fixed with the augments and cup-cage systems. In such situations it is appropriate to consider the structural allografts or the individual acetabular components. Implementation of the individual allografts is associated with high variability of the size and the shape of an acetabular defect [14]. The individual components are produced on the basis of CT images with 3D reconstruction and rapid prototyping. Such technique has become popular in the previous decade. The potential advantage of these components is precise positioning, fixation and the possibility for individual approach to each patient. According to the international literature, the results are contradictory.
The metaanalysis with comparison of alternative types of treatment showed that individual components demonstrated almost two times higher level of revision in comparison with the anti-protrusion constructs without or with bone plastics, big cups or constructs made of trabecular metal [25]. It is evident that the individual implants are not the panacea for severe acetabular defects, but there are several reasons for such results. Surgeons use the individual constructs in cases, when available variants for reconstruction are impossible. 3B defects can demonstrate high variations in sizes and geometry. These cases are most difficult, despite the same category of the classification. Secondly, the available long term results of the treatment are partially associated with the first generations of the individual implants with the limited possibility for biointegration as compared to the trabecular metal constructs or common acetabular components. Thirdly, the available publications do not show the homogeneity of treated defects. The adequate estimation requires more precise quantitative and qualitative classification of defects as compared to the present time. Possibly, it is worth to conduct the separate estimation for the disordered integrity of the pelvic ring and 3B defects. Moreover, considering the fact that almost all series include several tens of the patients and present the first surgical experience, one can suppose that the rate of the complications is associated with implementation of the new implants with different types of installation and with the fact that each case can demonstrate significant changes as compared to the previous one [2, 32].
Finally, one can say that the price of the individual constructs is sufficiently high, but similar with the price of the modern revision systems made of highly porous materials and used for the analogous severe defects. As far as the production techniques improves and the requirements for the individual implants increase, the availability will be increasing. The individual constructs are convenient and high tech implants with the individual form factor. They can be the last option, when the possibility of the well-known treatment techniques is depleted. The basic conditions for good results (like for other cementless implants) are the possibility for stable fixation, biointegration and restoration of favorable biomechanical parameters.
As result, the efficient estimation and use of the individual constructs require the development of more precise indications for using with consideration of discrete quantity of the square of possible contacting with the bone and with consideration of defect geometry, admissible displacement of rotation center, minimally sufficient contact square and the thickness of the implant walls, providing the stability of the construct, and estimation of possibilities for osteointegration of the construct and the reconstructive techniques for bone tissue in the defect field, providing the secondary biological stabilization and long term results.

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