RECONSTRUCTION 2023, Jan, 16 | 12:00 am

Primary THA— The Kinectiv® Stem

Introduction

 

A primary goal of successful total hip arthroplasty (THA) is to re-establish correct hip biomechanics. This means optimal leg length, offset, center of rotation, tension and avoidance of impingement. Modularity is a common and fully accepted technique to achieve this in revision stems but has not until recently come into focus for use in primary surgery. Although there are definite advantages with modularity and the technique has evolved significantly it is still not commonly used, possibly largely because stems work very well already and adding modularity may seem unnecessary. Also, new technology always carries a certain risk and since we have seen case reports reporting neck fractures it is probably quite reasonable to wait for longer term follow-up in trials.1-6 There are however good reasons to look at modular necks and some very obvious advantages for the surgeon who wants to take balancing and optimization of mechanics to a new level.7

 

Advantages

 

  • Facilitates joint balancing and positioning of head center

  • Independent correction of offset, tension and leg length

  • Avoiding impingement

  • Achieving correct combined anteversion angle

  • Improving ROM

  • Facilitates stem insertion and reduces fracture risk

  • Facilitates cup revision and liner exchange.

     

    Disadvantages

     

  • Less proven technology

  • Corrosion

  • Neck fractures

  • Neck stem dissociation

  • Increased cost.

 

Contraindications

 

There are no definite contraindications but a few unfavorable situations exist for the use of modularity. Heavy male patients in combination with a long neck, high offset or poor

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Total Hip Arthroplasty

 

Figure 23.1: A fractured neck of a METHA stem8

Figure 23.2: A modular stem/body implant

 

anteversion might overstress the neck stem junction leading to fatigue fracture.1-4 Fractures have been reported for the METHA (Aesculap)8 (Fig. 23.1) and Profemur (Wright) necks under such circumstances and also for other stems.

A very loose hip might risk disengagement of the neck stem junction, especially if the cup is constrained.9,10 Dislocation at the stem-neck junction might possibly also happen when repositioning a dislocation but this risk must be regarded as minor and is less than that for a neck-head disassociation. The Zimmer Kinectiv® necks show better stability for the stem-neck junction than for the neck-head junction.11

 

Modularity   in   Total   Hip   Arthroplasty   (THA)          

 

 

Revision type stems with modularity have long been used for primary surgery in special circumstances. S-ROMs, for example, often used for replacement of severely anteverted necks in DDH. There are also stems with modularity between distal and proximal stem meant to achieve better fit and fill and one variation of this was the Magron stem (now withdrawn)12 (Fig. 23.2). These interesting and overinventive modular stems show high

 

Figure 23.3: The ESKA stem which is a round in round taper like a normal head/neck

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Modular Necks for Primary THA—The Kinectiv® Stem

 

Figure 23.4: The APEX modular necks incorporating the lat-prox body

Figure 23.5: The ANCA FIT stem

 

revision rates in the Australian registry.13 It is not my intention to discuss their pros and cons here and I will instead limit this chapter to what I believe makes more sense, modular necks.

There have been a few historical trials with modular necks since the 40s but the modern form of an oval in oval Morse taper was developed during the late 80s by Cremascoli Orth (Milan, Italy). After in vitro testing it was initially used by a few surgeons including Aldo Toni. He later reported on 1734 ANCA FIT modular stems with the Cremascoli modular necks which were followed for 8 years without any failures.14,15

The risks with modular heads were widely debated in the 80s but today they are totally accepted and work well although the Titanium-CoCr coupling should corrode more than one between components of the same material.5

Stem-neck modularity has been more controversial because of increased neck fracture risk.1-5 This seems to be fairly implant specific and some brands of modular necks have done better than others, making their way into mainstream orthopedics. Aesculap with METHA stem has used modularity but in a big study of 5000 stems the neck fracture rate was 1.4 percent and a few changes had to be made to the construction.8 Another type of neck modularity is the ESKA system where the neck stem junction is round in round, like that of the neck and head (Fig. 23.3). This has also been used for 10 plus years by now. Another variety again is the Apex where the most proximal part of the stem including the neck is modular (Fig. 23.4). This is also a well proven and seemingly safe technique, possibly less prone to corrosion induced fractures since the proximal lateral neck is not subject to major corrosion. On the other hand it is more aggressive on the trochanter, however Keggi reported excellent results and no fractures after 600+ stems used since 2004 (JISRF 2008).

Today more than 200,000 Cremascoli type necks have been used mainly for the Profemur but also for ANCA FIT (Fig. 23.5). With increasing use a couple of neck fractures have recently been reported in the literature for Profemur.1-4 Long-term studies are still few in number but Sakai recently published a randomized 14.5 year follow-up of 74 Cremascoli stems16 finding no failures, generally better radiological results than his nonmodular stems and speculated it was due to less impingement problems. Blakey published a 5 year study on 352 ANCA FIT stems also without any problems.17 From a Wrigtht Medical symposium in Rome on modular hips we find many studies following altogether 8200 implants with just 1 fracture (of an older type).14

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The Cremascoli type of neck used for the ANCA FIT and the Profemur stems can be regarded as the gold standard today. The same type of oval in oval Morse taper modularity is now used by Zimmer for the new Kinectiv® stem following quite extensive lab testing and trials of their modular neck technology.11

 

Total Hip Arthroplasty

 

REASONS FOR USING MODULAR NECKS

Doing a THA today I think we aim a bit higher than yesterday and try harder to optimize joint mechanics. This means planning the surgery by templating and deciding where to put the hip center to obtain correct leg length.18 It is also important to correctly position the rotational center in AP and offset to balance the joint and soft tissues well to avoid unnecessary pain, weakness and dislocations. This is of course easier to do, if offset can be corrected independently to leg length and vice versa.

The desired anteversion is often hard to get with a straight stem.19 An anteverted stem results in better rotational stability20 and is also great help in obtaining the correct combined anteversion angle of around 35 degrees. Also if the cup is not perfectly positioned a modular neck can better compensate for it and impingement can more easily be avoided.21

Except for the obvious advantages for optimizing hip mechanics there are other reasons for modularity as less fracture risks. Uncemented stems are a bit unpredictable and sometimes sit a bit proud to the intended position. This is sometimes solved with a few hammer blows and sometimes a fracture occurs. In other cases the stem goes too far down femur and it is tempting to stop tapping it in, resulting in postoperative subsidence, etc. There is no need for these problems with modularity, we can compensate for a suboptimal position using components. By using only one size heads the neck shape can be optimally matched to it in order to improve ROM.11 Finally a cup or liner revision is made significantly easier, if the neck can be detached for better access.

 

REASONS TO BE CAUTIOUS

We have great results with stems already and cemented stems are less improved by modularity. If a high offset option is available almost any position of the rotational center and leg length can be achieved simply by rotating or inserting the stem deeper or higher in the cement and using different neck lengths.

Corrosion is a problem in all metal joint replacements mainly due to the sheer surface of the implant but also every interface junction will produce some metal debris.21,22 Fretting and increased release of metal does not however, seem to be much of an issue in general terms. The addition of a modular neck might increase corrosion related metal debris by a few percent only.11,22-24

The main problem and risk with the modular stems is neck fractures. Lately a couple of case reports have been published about fractured Profemur stems;1-4 however, the handful of reports have to be seen in the light of the >200,000 implanted. Fracture incidence for some other implants has been higher however, and the exact type of modularity and quality of manufacturing is certainly of major importance.8,11,23 The main reason for the problem seems to be local micromovement induced corrosion, fretting and finally fatigue fracture at the lateral part of the neck-stem junction.5,8,22-25 Risk factors seem to be heavy males and long varus necks with high offset. It seems wise to avoid using such systems in these.

Finally the remote possibility of a neck-stem disassociation has to be included in the risks as well.9,10,26 The increased cost (same as a head) and value for money is probably more of an issue.

 

TESTS AND STUDIES

Fretting and increased release of metal does not seem much of an issue in terms of increased metal load in the body22-24 and the problem is more the local effect on neck toughness. In a

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Modular Necks for Primary THA—The Kinectiv® Stem

 

lab study of tapered necks as well as retrieved ones after 5 years in vivo the junctions were found to be stable and resistant to relevant wear mechanisms.26-28 This group felt the advantages would outweigh the risks. Quite the opposite opinion was however, received from Grupp et al who studied 68 failed necks from retrievals.8 They found corrosion as a reason for fatigue fracture of the modular necks and advocated the use of CoCr instead of titanium. They warned against usage in heavy males and to avoid contamination of the taper on insertion to reduce corrosion. Other in vivo retrieval studies as well as lab studies support the findings of corrosion of the junction. The mechanism seems to be crevice corrosion enhanced by micromovements of the tapered neck leading to loss of the oxidized layer along with fretting of the metal and with time weakening of the neck, making it susceptible to fatigue fractures.25,29 If this is a considerable risk for all types of modularity and whether it is greater for CoCr or titanium is still debated. Clearly it seems some constructions are safer in this regard than others.16,29 The reasons for these differences are certainly multifactorial and the material, length and shape of the engaged taper play different roles.11,22 It is possible that too firm a hammering to seat the neck could damage the tapered fit and increase corrosion,26 and also other factors such as debris in the taper junction and poor anteversion might increase the risk of micromotions, corrosion and fracture.

 

THE KINECTIV® STEM

Zimmer has done extensive research into the modular neck technology and published a white paper on results, etc.11 This has resulted in a modular hip stem system called Kinectiv®. The body of the stem like many others looks like the successful and well proven Taperlock and Accolade (Figs 23.6A and B). It is made of titanium alloy and proximally coated. It is wedge shaped and thin in AP with a cut off at the lateral shoulder to facilitate MIS. The modular neck is made out of the same titanium alloy and has a long taper to fit into the stem with good stability (Fig. 23.7A). Such a long tapered neck fitting is probably very important to lessen micromovements and stress on the neck (Fig. 23.7B).

 

 

A size zero head is always used since the necks are perfectly shaped to fit such a head and thereby increase the head neck ratio, improving range of motion. It comes with 32 different necks but most act doubly if turned 180 degrees so in total these can construct 60 different neck options (Fig. 23.8). The range of both offset and length is 16 mm in 5 steps

 

Figures 23.6A and B: The Kinectiv® stem by Zimmer

(A) Stem; (B) Radiograph of implanted stem

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Figure 23.7A: Kinectiv® modular necks shaped for optimal fit with a zero head

Figure 23.7B: Stability of stem neck functions with different metals used

 

 

 

Figure 23.8: Modular trial necks. Another two trays with anteverted and retroverted necks can be opened if needed

 

from smallest to biggest. (Fig. 23.9) Version can be changed independently by moving the head center 4 mm anterior or posterior (Fig. 23.10).

To address fatigue, fretting and corrosion both neck and stem are made of the same titanium alloy, which was found to perform better than CoCr in junction stability and corrosion.11 As shown by Grupp et al it is also important to well clean the taper junction to minimize micromovement and thereby corrosion8 (Fig. 23.11). Further on a corrosion fatigue

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Total Hip Arthroplasty

 

 

 

 

 

Figure 23.9: Offset and leg length options available, independant of each other

 

 

 

 

Figure 23.10: Optional anteverted or retroverted head center

 

 

 

Figure 23.11: Stability and micromotion of different neck-stem options with and without contamination8

 

Modular Necks for Primary THA—The Kinectiv® Stem

 

loss test showed about equal metal mass loss for the stem-neck junction and the neck-head junction (Fig. 23.12). This was far less than for a standard neck with a long skirted head or a CoCr head on a CoCr neck.11 Corrosion occurs but is negligible in comparison to the corrosion of the whole stem.22 It is the local crevice corrosion in the junction leading to fatigue which is the main issue.

This is an implant launched by a major orthopedic company and rigorously tested using state of the art technology.11 It is based on a well known stem in combination with the gold standard modular neck type. Still however, we have very little factual evidence and few reports on its in vivo performance. I have used it for 3 years now without any mechanical failures.

 

WHY USE MODULARITY

There are several good reasons to use a modular neck for uncemented stems.

The first reason is to make the surgery easier and that is of great importance, not just for the less experienced. Most early failures of hip replacements as dislocations, leg length

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Total Hip Arthroplasty

 

Figure 23.12: Corrosion of head-neck and neck-stem interfaces (By Zimmer)

 

discrepancies, fractures or stem subsidence are due to surgical errors and a modular stem can minimize such errors. The stem is simply inserted with gentle hammering until it stops, there is no need to persuade it further and risk fractures. Nor do you need to stop before it is stable fixed although it may go in further than expected. Once the stem is in place and solidly fixed we can build from there. Leg length is first measured and perfected then joint tension and finally anteversion are addressed. To do it stepwise like that makes it less complicated.

It is rewarding trying a few options and often you find a better solution than what was first intended. We can measure and try forever but it is always the tension and dislocation risk that finally decides what to use and it is often better to lengthen a bit instead of overly increasing offset and risk trochanter pain, etc. Impingement of neck and cup is a major reason for dislocations, implant loosening and high wear, also of crosslinked poly. The possibility of checking for contact between implants and if needed changing neck angle or offset to avoid it is a much better option than repositioning the cup.

A retroverted stem can be useful for correcting a high anteversion as in DDH.

Lastly modular heads facilitate cup revision and liner exchange should it be needed. The Kinectiv® stem itself is only proximally coated and thin in AP. This allows a flexible osteotome to loosen it from bone and the stem can hopefully be revised without an extended osteotomy.

 

TECHNIQUE

As we all know but probably do a bit half-heartedly, surgery begins with proper preoperative planning. With digital X-rays it can be hard to trust stem size but templating for size can help avoid undersizing the stem (Fig. 23.13). I always measure the intended rotational center in relation to Greater Trochanter on preoperative X-rays and also the distance from head neck junction to the intended cut. The lesser trochanter is not a good guide in mini invasive surgery or anterior approaches.

Another method is to measure the length of the removed head from it is rotational center to the saw cut and then do the same when trying the modular necks. Since the Kinectiv® stem is collarless it is not terribly crucial where the neck is cut but templating definitely helps in getting it right.

Preparing for the stem starts with a box chisel to remove the remainder of lateral cortex and to allow stem and broaches to go straight in (Fig. 23.14). If the piriformis is spared the posterior part of the wide attachment can be detached from bone to avoid damaging it. The box chisel should not remove a big chunk of cancellous bone, this is spared to be impacted by the broaches. I start with the smallest broach to create a hole into the canal (Fig. 23.15). Then I use the small rasp to remove bone from lateral to avoid varus (Fig. 23.16). You want a good cortical contact laterally and medially but a lot of impacted cancellous bone and good bone stem contact anterior and posterior. No reason to use every broach in the box, go

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Modular Necks for Primary THA—The Kinectiv® Stem

 

Figure 23.13: Templating of a hip using a Kinectiv® template. Measured distance of center of rotation below GT and position of the cut from head-neck junction

 

 

 

 

 

Figure 23.14: Box chisel to remove bone from lateral neck

 

Figure 23.15: Broach going in to open up and impact cancellous bone

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Total Hip Arthroplasty

 

Figure 23.16: Rasping and removing bone laterally to avoid varus and get a bigger stem in with cortical contact

 

Figure 23.17: Broach in situ with preserved bone posterior and anterior

 

straight up to one below the intended size. This will save bone from being removed by the broaches and achieve better stem bone contact (Fig. 23.17). The patient’s neck anteversion has to be accepted as it is. You cannot change it a whole lot when using a flared wedged stem unless you undersize it and the result of trying is likely to be a calcar fracture. When the broach is rotationally stable and cortical contact is felt and heard the size is correct. Insert stem and count on it to sit a few mm proud of the position you had for the broach.

Trial necks for the broach are available but I rarely use them knowing a minor positioning anomaly can be compensated for using the different necks (Fig. 23.18). They are however, safer and helpful at first until you know your prosthesis better. It is now time to hammer the stem in with gentle blows until it stops, no more. Accept the position you get, if not optimum you can compensate for it. Most often it will sit a few mm proud of the position you had with the broach (Fig. 23.19).

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Modular Necks for Primary THA—The Kinectiv® Stem

 

Figure 23.18: Trial necks for broaches to use if preferred

 

Figure 23.19: Stem is tapped in

 

Start up trying the neck size you think is correct (Fig. 23.20). Measure and decide about leg length first. Measure the knee position compared to before dislocation. Measure head center in relation to GT and compare to your templating. Then do a longitudinal chuck test and check tension, is it sloppy or tight? Is the extension OK? When it is OK try to decide about offset, try lateral chuck, compare offset to template and check, if the capsule is long enough to resuture (indicating a reasonable offset). Now check impingement, stability and combined anteversion angle and decide if an angled neck is warranted (Fig. 23.21). A few solutions, can be tried and it is always rewarding and sometimes improvements can be made. Finally attach neck and head after cleaning and drying the junction secure it all with a gentle taps (Figs 23.22 and 23.23). Wash, suture capsule, etc. (Fig. 23.24).

 

Discussion                        

Modular necks are certainly very helpful for achieving good THA result. It is also an easy and very quick way to implant a stem and get good results. Modularity facilitates balancing and

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Total Hip Arthroplasty

 

Figure 23.20: Trial neck attached to the real stem

 

 

 

Figure 23.21: The combined anteversion test done by making the neck go straight in to cup and then measuring angle of Tibia relative to the floor

 

Figure 23.22: Dry and clean the stem/neck taper well to minimize micromovement, etc.

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Modular Necks for Primary THA—The Kinectiv® Stem

 

Figure 23.23: The neck and ceramic head is secured and repositioned

 

Figure 23.24: Capsule/rotators suture to bone

 

optimization of joint mechanics as well as leg length and stability. This is of course especially beneficial for the beginner but I think many THAs could be better balanced by using one of the 60 options available.

The benefits with modularity have to be balanced against the downsides. A slightly larger inventory as well as a tray of neck trials are issues but cost is probably more important. The combination of heavy patients and high offset seems to pose fracture risk and is better avoided. The major problem is the fact that the technology is fairly new and not well followed up overlong timeframes. Neck fractures due to corrosion and fatigue are the main concerns here. There are different manufacturers and different ways to do these modular necks and they will probably have different results. The Kinectiv® stem and necks are well tested in the lab but still only over very short time in vivo. Only time and better studies will finally tell how much of a risk it includes to use modularity, and whether patients do better or not. For now I think it is a quick and helpful technology for both the novice and the dedicated surgeon, with benefits outweighing the downsides.

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POSTOPERATIVE REHABILITATION

I believe in pre-emptive analgesia and reducing inflammation to lessen pain and facilitate rehabilitation. Reducing blood loss is also important to make patients feel better and exercise more and of course to avoid transfusions which we know is detrimental in many ways.

The normal routines include a meeting with a physio the week before operation and start doing their exercises as well as practice with crutches. This is simple and very effective way to reduce length of stay.

Patients arrive at hospital 3 hours before operation and shower with chlorhexidine soap. They get 1 gm of tranexamic acid every 6 hours to reduce bleeding as well as premed with diazepam.

During surgery, spinal anesthesia with some propofol to sleep. Mini invasive surgery to minimize trauma. PCA for pain and antiemetics as zofran if needed. I inject into the tissues 150 ml of 0.2% naropin, mixed with toradol, adrenalin and SoluMedrol. I take my time stopping bleeders and use no drain to save blood.

First morning all lines are taken and patients are mobilized with full weight bearing.

Paracetamol in full dose and celebrex 200 mg for all. Slow release oxycontin if required.

Patients have no restriction on movements, are allowed to sit in normal chairs, sleep on the side and walk unaided when they feel for it. They get information about dislocations and how it happens. Most go home day 3 or 4 to continue their exercises and see me again at 6 weeks. I do an X-ray the postoperative day and at follow up at 1 year only.

 

Total Hip Arthroplasty

 

Illustrative                      Case                     

An X-ray showing both hips worn out with OA (Fig. 23.25A). Sequential bilateral total hip arthroplasty using the Kinectiv® stem was done, first the right hip (Fig. 23.25B) followed one year later by the left (Fig. 23.25C). The patient is doing well clinically and radiologically, at the end of 2 years (Right) and 1 year (Left) (Fig. 23.25D).

 

 

 

Figure 23.25A: Bilateral osteoarthritis hips

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Figure 23.25B: Right THA using Kinectiv® stem at 2 years postoperative

Figure 23.25C: Left THA using Kinectiv® stem at 1 year

 

 

 

 

Modular Necks for Primary THA—The Kinectiv® Stem

 

Figure 23.25D: X-ray pelvis with both hips at 2 years follow-up. Patient is doing well clinically

 

References                       

  1. Atwood SA, Patten EW, Bozic KJ, Pruitt LA, Ries MD. Corrosion-induced fracture of a double-modular hip prosthesis: a case report. J Bone Joint Surg Am 2010;92(6):1522-5.

  2. Skendzel JG, Blaha JD, Urquhart AG. Total hip arthroplasty modular neck failure. J Arthroplasty 2011 Feb;26(2):338.e1-4. Epub 2010 Apr 9.

  3. Wilson DA, Dunbar MJ, Amirault JD, Farhat Z. Early failure of a modular femoral neck total hip arthroplasty component: a case report. J Bone Joint Surg Am 2010;92(6):1514-7.

  4. Wright G, Sporer S, Urban R, Jacobs J. Fracture of a modular femoral neck after total hip arthroplasty: a case report. J Bone Joint Surg Am 2010;92(6):1518-21.

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  5. Collier JP, Mayor MB, Williams IR, Surprenant VA, Surprenant HP, Currier BH. The tradeoffs associated with modular hip prostheses. Clin Orthop Relat Res 1995;(311):91-101.

  6. Dunbar M J, The proximal modular neck in THA: A Bridge Too Far: Affirms Orthopedics 2010;33(9):640.

    Total Hip Arthroplasty

     

  7. Duwelius PJ, Hartzband MA, Burkhart R, Carnahan C, Blair S, Wu Y, Grunkemeier GL. Clinical results of a modular neck hip system: hitting the “bull’s-eye” more accurately. Am J Orthop (Belle Mead NJ) 2010;39(10 Suppl):2-6.

  8. Grupp M, Weik T, Bloemer W, Knaebel HP. Modular titanium alloy neck adapter failures. BMC Musculoskeletal Disorders 2010;11:3.

  9. Pellicci PM, Haas SB. Disassembly of a modular femoral component during closed reduction of the dislocated femoral component. A case report. J Bone Joint Surg Am 1990;72(4):619-20.

  10. Sporer SM, DellaValle C, Jacobs J, et al. A case of disassociation of a modular femoral neck trunnion after total hip arthroplasty. J Arthroplasty 2006;21:918.

  11. Hertzler JS, Johnson TS, Meulink SL. Performance and evaluation of Kinectiv Technology. Zimmer white paper 2008.

  12. Kop AM, Swarts E. Corrosion of a hip stem with a modular neck taper junction: a retrieval study of 16 cases. 2009 Oct;24(7):1019-23. Epub 2008 Oct 5.

  13. www.dmac.adelaide.edu.au/aoanjrr

  14. Toni A, et al. Rome symposium on profemur modular necks. 1-2 June 2007. Published by Wright Medical.

  15. Toni A, Sudanese A, Paderni S, Guerra E, Bianchi G, Antonietti B, Giunti A.Cementless hip arthroplasty with a modular neck. Chir Organi Mov 2001;86(2):73-85.

  16. Sakai T, Ohzono K, Nishii T, Miki H, Takao M, Sugano N. A modular femoral neck and head system works well in cementless total hip replacement for patients with developmental dysplasia of the hip. J Bone Joint Surg Br. 2010;92(6):770-6.

  17. Blakey CM, Eswaramoorthy VK, Hamilton LC, Biant LC, Field RE. Mid-term results of the modular ANCA-Fit femoral component in total hip replacement. J Bone Joint Surg Br 2009;91(12): 1561-5.

  18. Dorr LD, Wan Z, Malik A, Zhu J, Dastane M, Deshmane P. A comparison of surgeon estimation and computed tomographic measurement of femoral component anteversion in cementless total hip arthroplasty. J Bone Joint Surg Am 2009;91(11):2598-604.

  19. Omlor GW, Ullrich H, Krahmer K, Jung A, Aldinger G, Aldinger P. A stature-specific concept for uncemented, primary total hip arthroplasty. Acta Orthop 2010;81(1):126-33.

  20. Gill HS, Alfaro-Adrián J, Alfaro-Adrián C, McLardy-Smith P, Murray DW. The effect of anteversion on femoral component stability assessed by radiostereometric analysis. J Arthroplasty 2002;17(8):997-1005.

  21. Malik A, Maheshwari A, Dorr LD. Impingement with total hip replacement. J Bone Joint Surg Am 2007;89(8):1832-42. Review.

  22. Viceconti M, Baleani M, Squarzoni S, Toni A. Fretting wear in a modular neck hip prosthesis. J Biomed Mater Res 1997;35(2):207-16.

  23. Viceconti M, Ruggeri O, Toni A, Giunti A. Design-related fretting wear in modular neck hip prosthesis. J Biomed Mater Res 1996;30(2):181-6.

  24. Baleani M, Viceconti M, Walchholz K, Toni A. Metallic wear debris in dual modular hip arthroplasty. Chir Organi Mov 1997;82(3):231-8.

  25. Rodrigues DC, Urban RM, Jacobs JJ, Gilbert JL. In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants. J Biomed Mater Res B Appl Biomater 2009;88(1):206-19.

  26. Pallini F, Cristofolini L, Traina F, Toni A. Modular hip stems: determination of disassembly force of a neck-stem coupling. Artif Organs 2007;31(2):166-70.

  27. Schramm M, Wirtz DC, Holzwarth U, Pitto RP. The Morse taper junction in modular revision hip replacement—a biomechanical and retrieval analysis. Biomed Tech (Berl) 2000;45(4):105-9.

  28. Nganbe M, Khan U, Louati H, Speirs A, Beaulé PE. In vitro assessment of strength, fatigue durability, and disassembly of Ti6Al4V and CoCrMo necks in modular total hip replacements. J Biomed Mater Res B Appl Biomater 2011 Feb 2. doi: 10.1002/jbm.b.31794. [Epub ahead of print]

  29. Goldberg JR, Gilbert JL. In vitro corrosion testing of modular hip tapers. J Biomed Mater Res B Appl Biomater 2003;64(2):78-93.