the procedure included augmentation with transcortical wiring of an onlay - type prosthesis in twelve knees ( nine patients ) after it had been determined that conventional resurfacing was inadequate .
this technique was indicated when the thickness of the remnant patella was less than 8 mm and the cortical rim was not intact .
there were 9 patients ( 12 knees ) with a mean age of 68 years ( range , 53 to 80 years ) at the time of surgery .
the patellae were revised because of infection ( five knees ) , loosening of the patellar component ( four knees ) and polyethylene wear in the presence of a metal - backed patella ( three knees ) .
an onlay - type , all polyethylene prostheses ( universal dome patella , scorpio , stryker , nj , usa ) which are compatible with the femoral component were used .
after arthrotomy using a medial parapatellar approach , the patella is everted laterally and fixed in this posture by grasping the quadriceps tendon or patella tendon with towel clips .
cement stuck to the undersurface of the prosthesis is meticulously removed with an oscillating saw and a high - speed burr after implant removal . the new , properly sized patellar prosthesis
is then placed on the undersurface , implant location is decided and the margin of the prosthesis and the contact points for each peg are marked .
bone bed preparation is performed with a burr according to marking lines and contact points .
on fitting the patellar prosthesis , a check is made to determine whether it matches the concave portion of the undersurface and confirm the peg sites .
three points are then drilled for the pegs and bone holes are placed for wire passage .
the next steps involve connecting the wires to the pegs and passing through drill holes .
a wire is connected to one peg by winding it around the narrow part of the neck under the peg head and fixing it to the peg .
the three wires on the pegs are passed from the undersurface of the patella to the outer surface through the bone holes .
before the prosthesis is brought into contact with the patella , the space between the bone bed and the polyethylene is filled with cement ( fig .
2 ) . after approximating the patellar prosthesis to remaining bone as closely as possible ,
the prosthesis is compressed with a compressor and the cement is given time to harden .
subsequently , sufficient tension is placed on the three wires on the outer surface with wire holders and the wires are twisted together immediately above the cortex . after checking that the wires are under sufficient tension , they are cut and their ends are pressed with an impactor to prevent irritation ( fig .
after arthrotomy using a medial parapatellar approach , the patella is everted laterally and fixed in this posture by grasping the quadriceps tendon or patella tendon with towel clips .
cement stuck to the undersurface of the prosthesis is meticulously removed with an oscillating saw and a high - speed burr after implant removal . the new , properly sized patellar prosthesis
is then placed on the undersurface , implant location is decided and the margin of the prosthesis and the contact points for each peg are marked .
bone bed preparation is performed with a burr according to marking lines and contact points .
on fitting the patellar prosthesis , a check is made to determine whether it matches the concave portion of the undersurface and confirm the peg sites .
three points are then drilled for the pegs and bone holes are placed for wire passage .
the next steps involve connecting the wires to the pegs and passing through drill holes .
a wire is connected to one peg by winding it around the narrow part of the neck under the peg head and fixing it to the peg .
the three wires on the pegs are passed from the undersurface of the patella to the outer surface through the bone holes .
before the prosthesis is brought into contact with the patella , the space between the bone bed and the polyethylene is filled with cement ( fig .
2 ) . after approximating the patellar prosthesis to remaining bone as closely as possible ,
the prosthesis is compressed with a compressor and the cement is given time to harden .
subsequently , sufficient tension is placed on the three wires on the outer surface with wire holders and the wires are twisted together immediately above the cortex . after checking that the wires are under sufficient tension , they are cut and their ends are pressed with an impactor to prevent irritation ( fig .
if the patellar component can be retained during revision tka , this may offer the best option in terms of morbidity .
however , if the prosthesis is malpositioned , damaged or mechanically loose , removal is probably the advisable option .
the onlay - type all polyethylene patellar prosthesis is an efficient tool when patellar bone stock is sufficient , being over 10 to 12 mm.5 ) but it is not easy to determine an optimal procedure if bone stock is poor . according to maheshwer et al.,2 )
patellar resurfacing using an all polyethylene biconvex patellar prosthesis is successful when the remnant patellar thickness is less than 10 mm and the peripheral rim is intact .
when the bone stock is too thin or the peripheral rim has been destroyed , it is highly likely to fail when a prosthesis is only cemented to bone .
a biconvex patellar prosthesis may also not be likely to be effective . in our series ,
the remnant patellar thickness averaged 5.6 mm ( range , 3.2 to 7 mm ) and variable amounts of the peripheral patellar rim were damaged . with regard to these cases , some authors advocated alternative options including a porous tantalum component , a bone grafting and soft tissue flap procedure or a gull - wing osteotomy .
nelson et al.4 ) evaluated short - term results following patellar resurfacing with a trabecular metal patella in the setting of marked patellar bone loss .
hanssen6 ) suggested a bone grafting and soft tissue flap procedure . at final follow - up of nine patients
, it was found that the mean patellar thickness increased from 8 to19.7 mm and their functional outcomes were improved .
klein et al.7 ) performed a gull - wing osteotomy in a nonresurfacable patella and reported that there was a significant improvement in the range of motion and knee society scores .
though several shortcomings were encountered during follow - up period , the above techniques showed reasonable outcomes.3,4,6,7 ) however , further follow - up is required to assess the longer term benefits of these methods .
the deficient patella was revised using this technique when the thickness of the remnant patella was less than 8 mm and the cortical rim was not intact .
moreover , it is easily reproducible and does not need a long learning curve , in our experience . because it protects the extensor mechanism and provides the same contact during patellofemoral articulation as primary tka , painless articulation is possible and
hereby , the range of motion is improved . however , there are a few concerns about the use of this procedure in thin patellae .
it may not be indicated if the osseous cortical shell is too thin for wiring , so the use of transcortical wires place the patella at risk to fracturing .
also , the problems related with prominent hardware also may occur as is oft en seen with internal fixation of patellar fractures . at a mean 10.3 months follow - up of our series , there was one patellar fracture arising during flexion exercise one week after surgery that was treated with partial patellectomy .
our described technique includes connecting wires to the three pegs of the patellar component , passing the wires from the undersurface of the patella to the outer surface through the bone holes and , after compression of a cemented prosthesis , twisting the wires under sufficient tension .
we believe that this technique provides a good alternative option in managing the deficient patella in revision total knee arthroplasty , although any prolonged benefits will require long - term follow - up .
 the management of patellae with a severe bony deficiency during revision total knee arthroplasty is a challenging problem . 
 however , using a technique of augmentation with transcortical wiring of an onlay - type prosthesis allowed the authors to revise a deficient patellae successfully . after making the decision to revise the existing patellar component , 
 the procedure was found to be technically straightforward . 
 furthermore , the procedure does not require sophisticated instruments , only an onlay - type prosthesis , cement and wires . 
 this technique entails fixing wires to the three pegs of the patellar component , passing the wires through drill holes in the anterior cortex and , after compression of a cemented prosthesis , augmenting the fixation by twisting the wires anteriorly . 
 we believe that stable fixation and painless articulation will be obtained with the described technique for deficient patellae . 