reflection spiked acetabular component
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REFLECTIONSpiked Acetabular Components
Nota Bene: This technique description herein is made available to the healthcare professional to illustrate the authorssuggested treatment for the uncomplicated procedure. In the final analysis, the preferred treatment is that whichaddresses the needs of the patient.
Reflecting the commitment to low wearDesigned with fixation and surgical efficiency in mind, the REFLECTION AcetabularCup system minimizes wear and maximizes the integrity of the modular connection.REFLECTION Acetabular Components offer a variety of choices, allowing the surgeonversatility for indication and preference.
The MICROSTABLE Liner Locking Mechanism and the polished inner surface reflectSmith & Nephews continued leadership in advanced technology.
Technique described byCecil H. Rorabeck, MD, FRCS(C)University of Western Ontario Canada
REFLECTION Acetabular ComponentsDesign features
Liner/shell stabilityAs shown in many independent studies, theMICROSTABLE Liner Locking Mechanism has thelowest level of liner/shell motion of the shellstested.1-4 Internal Smith & Nephew testing furtherdemonstrates the superiority of the lockingmechanism over competitive designs andSmith & Nephews commitment to minimizewear due to micromotion.5
PolishingMotion between the liner and shell has beenproven to cause wear on the back side of theliner. The rougher the counterface, the morethe wear. These facts support the need fora refined finish on the inside of the shell.The polished inner surface of REFLECTIONAcetabular Components is a feature thathas very low roughness that is withinthe standard required of femoral heads.6
Range of motionSmith & Nephew understands the issue ofimpingement, and that range of motion (ROM)is not just dependent on neck design. As aresult, REFLECTION liners are designed toallow maximum ROM when combined withSmith & Nephew stems and have beenshown to improve ROM over competitiveofferings.7 The overhang, while giving 20of additional support, maintains a low profileto minimize impingement.
Porous coatingAll REFLECTION shells feature RoughCoatporous coating. RoughCoat provides ascratch-fit and enhances initial friction andstability. The 2-3 bead layering has a 20-40%average porosity and 170 microns average poresize. This pore size has been shown topromote bone in-growth.8 The sintered beadsprovide a three-dimensional interlock withbone that plasma spray cannot offer.9
Hole coverHaving an apex hole in the shell allows easyassessment of cup seating.10 The watertight apexhole cover has a unique design that seals theshell, which prevents debris transfer as well asminimizes polyethylene creep.11
Poly thicknessWith a 5mm thick liner for the 46mm OD cupand 7mm for the 50mm cup (for a 28mmfemoral head), REFLECTION AcetabularComponents meet the challenge of polythickness.12,13 Unlike many acetabular cupdesigns, our poly thickness is not compromisedby the locking mechanism. If additionalthickness is desired, the lateralized liners canbe used, allowing 4mm more thickness at theapex and approximately 2mm additionalthickness in the load-bearing area.
Acetabular cup size
Femoralhead size 42 44 46-48 50-52 54-56 58-60 62-64 66-68 70-76
22mm 6 7 8 10 12 13 15 17 19
26mm NA 5 6 8 10 11 13 15 17
28mm NA NA 5 7 9 10 12 14 16
32mm NA NA NA 5 7 8 10 12 14
36mm NA NA NA NA 5 6 8 10 12
REFLECTION Spiked Acetabular ComponentsDesign features
SpikesThe use of spikes in cup fixation remains apopular option. Traditionally, these cups weredesigned with porous coating on the spikes,which made revisions difficult. The spikes of theREFLECTION Spiked Acetabular Component aresmooth, which allow rigid stability at the time ofinsertion but also makes them easier to separatefrom the bone if a revision is ever necessary. Inaddition, because the spikes allow initial stabilitywithout screws, the lack of screw holesminimizes the chance for polyethylene debrismigration. To aid insertion of the cups, the spikelocations are indicated on the face of the shell.
1. Preoperative planning 2. Acetabular exposure
3. Acetabular reaming 4. Acetabular trialing
5. Acetabular shell insertion 6. Acetabular liner insertion
REFLECTION Spiked Acetabular Components
REFLECTION Spiked Acetabular ComponentsPreoperative planning
Preoperative X-Rays should include an AP of thepelvis centered over the hips and a lateral of theaffected hip.
Templating can be done on the affected side, butit is important that the contralateral hip also betemplated to verify the size.
To ensure a congruent fit, the acetabularcomponent should sit against the subchondralbone and the medial aspect of the acetabulum,as indicated by the teardrop.
The center of rotation also should be marked forsubsequent reference.
Instrument tip:The templates have holes that allow youto mark the center of the standard lineror the +4mm lateralized liner.
Shown with standard and +4mmlateralized liner head centers.
REFLECTION Spiked Acetabular Components
Complete exposure of the acetabulum isrequired, regardless of the type of approach.
First, resect the acetabular labrum and place ablunt retractor anteriorly.
After identifying the transverse acetabular ligament,divide it inferiorly and place a blunt retractor aroundthe inferior margin of the acetabulum.
Depending on the exposure, a third retractorcan be placed posteriorly following the excisionof the labrum.
Remove all soft tissue and osteophytes in orderto define the medial wall.
The acetabulum must be medialized to restorethe normal center of hip rotation.
Surgical tips:To minimize the need of assistance,each of the acetabular retractors canbe tied directly to a Charnley retractor.
Dividing the transverse acetabularligament will allow reaming to begininferiorly, preventing the tendency ofthe reamer to migrate superiorly.
A medial osteophyte is often presentin the fovea, which is usually visibleon the preoperative radiographs.
REFLECTION Spiked Acetabular ComponentsAcetabular reaming
Select an acetabular reamer that is considerablysmaller than the templated size of the cup.Generally, a 46mm reamer is suitable.
Position the initial reamer in a vertical direction(1) to ensure the reamer is taken down to themedial wall.
Direct the second reamer and all subsequentreamers in approximately 45 of abduction and20 of anteversion for final position of theacetabular component (2).
Preserve subchondral bone to provide goodsupport for the prosthesis.
Frequently palpate the posterior and anteriorwalls of the acetabulum during the reamingprocess as these walls will determine the largestacetabular size that can be accommodated.
When using the REFLECTION Spiked Cup, theacetabulum should be under-reamed by 1mm.Since the cups are available in even sizes, thelast reamer used should be an odd-sized reamer.
Surgical tips:Each successive reamer must be fullyseated within the acetabulum. Failure todo so will result in lateralization of thetrial and exposure of the porous coating.If lateralization or exposure occurs, goback to a smaller reamer and beginagain, checking each size to ensure thatthe reamers are fully seated.
Increasing the reamer size by 2mm isrecommended, although in smallerpatients 1mm increments maybe preferred.
Mark the medial wall with anelectrocautery prior to using the lastreamer. If the last reamer does notremove the mark, repeat reaming,dropping back a size if necessary.
Instrument tip:The REFLECTION reamer has an openback, which helps visualize reamingand allows easy access to bone chips.This style of reamer is hemisphericaland when fully seated it should becovered by the rim of the acetabulum.
Gently rock reamer handle back andforth approximately 5 for last sizeused ONLY to ensure rim is accuratefor the desired press fit.
After the preparation of the acetabulum,the trial shell should be inserted to verify sizeand position of the cup.
If trial reduction using a trial insert is desiredat this time, then the preparation of the femurshould occur up until the trial reductionstage. The hip should be reduced and leglength, offset, and component position shouldbe assessed.
Because of the spikes, orientation of the shell isdifficult to change once it is impacted into thebone. For this reason, it is necessary for thesurgeon to note the appropriate orientation ofthe acetabular trial to position the cup correctly.
Surgical tips:Unlike standard shells whereorientation can be changed after it isimpacted in the bone, spiked shellscannot be changed. Therefore, it issuggested that the surgeon optimizethe orientation of the trial and markthe bone for identical correctalignment of the shell.
The bone at the edge of the trial shellcan be marked with an electrocauteryto help in final component positioning.
In a relatively normal acetabulum, thefinal component can be positionedand head coverage adjusted usingoverhang liners.
Instrument tip:The trial shells are the exact sizespecified and slightly less thanhemispherical. They can be used toassess the accuracy of reaming or canbe press-fit into the acetabulum if usinga larger size than the final reamer.
REFLECTION Spiked Acetabular ComponentsAcetabular shell insertion
Select the appropriate acetabular implant, attachthe shell to the cup positioner/impactor andinsert it into the acetabulum.
Rotate the X-bar