Chapter 10 · Experience with Patellar Resurfacing and Non-Resurfacing – H.U. Cameron 65 10
10 Experience with Patellar Resurfacing and Non-Resurfacing
H. U. Cameron
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Summary
The role of patellar replacement in total knee arthroplas- ty is controversial. With a modern patella-friendly femoral component design, patellar resurfacing is fre- quently not necessary. In the revision situation, the most difficult and unresolved question is what to do with an eroded avascular patella following patellar component loosening. This is never an issue if the patella was not resurfaced at the index operation.
The Role of the Trochlear Groove
Femoral component designs in total knee arthroplasty have evolved significantly in the past 10 years. Prior to that,most femoral component trochlear grooves were rel- atively shallow and patella-unfriendly. Results of knee re- placements introduced more than 10 years ago may not be comparable to outcomes with currently available im- plant designs. Virtually all total knee arthroplasties used with greater than 10-year follow-up required patellar re- placement to reduce anterior knee pain and to help stair- climbing ability. What is remarkable, given these patella- unfriendly designs, is that when bilateral cases have been studied, i.e., a replacement in one side versus none in the other, several studies, however flawed, reported no differ- ence in outcome [1]. To some extent this may reflect only the sensitivity of the instrument used,i.e.,the Hospital for Special Surgery (HSS) score,and indicates a need to focus more on the outcome measures specific to the patello- femoral joint.
Twelve years ago, in a cohort study, I evaluated the ef- fect of patellar resurfacing and non-resurfacing [2]. The knee system studied was the Tricon (Smith and Nephew, Memphis, Tenn.), which did not have a particularly patel- la-friendly trochlea. All patellar studies were carried out at 3 years following the index operation, when the knee had reached a steady state and before wear became an issue. There were 68 resurfaced and 43 unresurfaced patellas. The questions asked of these patients were: Was there any anterior knee pain, and was stair-climbing ability adequate? The incidence of anterior knee pain in
the replaced knees was 7.6% and in the unreplaced knees 17.6%; 61% of the patients with the replaced patella were able to use the operated limb as the lead leg on stairs with- out the use of a rail, as opposed to 37% of the unreplaced.
The HSS scores, however, were identical.
Given the relatively high incidence of anterior knee pain even in the patients with resurfaced patellas, I ques- tioned the etiology of their symptoms.Anterior knee pain does not necessarily correlate with patellar pathology.
Mild anterior knee pain is common in arthritic patients, but severe isolated anterior knee pain associated with patellofemoral arthrosis is surprisingly rare. In 25 years I have performed isolated patellofemoral replacement in less than 50 cases.
Patellar Pain – Postreplacement
If part of the unresurfaced patella makes contact with the metal of the femoral component, this is potentially a source of pain. I evaluated the effect of peripheral patel- lar bone contact with the femoral component by having a
“wing” patella made [3]. The polyethylene wings com- pletely covered the patellar surface and any excess poly- ethylene was removed during surgery.At 3-year follow-up there were 290 inlay Tricon M patellar components and 171 wing components.The incidence of anterior knee pain was 7% for the inlay and 7.1% for the wings,indicating that contact per se between the femoral component and the unresurfaced area of the patella was not the problem.The question of patellar tilt was also examined. There was tilt of less than 20° in 25% of the inset patella and 10% of the winged patella. Therefore, patellar tilt did not appear to correlate with pain.
My impression has been that maltracking is fre- quently a source of anterior knee pain following revision total knee arthroplasty, but it is difficult to substantiate this clinical impression.
At 10 years after total knee arthroplasty with a metal- backed patella, wear was present in 75% of cases and was the most common cause of knee revision [4].
66 II . Past Failures
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Current Experience
In the past, most surgeons felt that patellar replacement was an advantage; what of the present? The Profix knee (Smith and Nephew, Memphis, Tenn.) has a patella- friendly groove. When this became available I cautiously stopped resurfacing the patella. Initially, I replaced the patella in patients who complained preoperatively of an- terior knee pain, which is surprisingly uncommon even when bone is exposed and significantly eroded.
A recent review of the records of more than 700 cases showed an incidence of anterior pain of only 3%, a vast re- duction from the previous generation of knee-replacement designs. Only three patients felt that their anterior knee symptoms were of sufficient magnitude to justify patellar resurfacing. Of these, two experienced no immediate im- provement after patellar resurfacing but 3 years later have no pain. One did experience immediate pain relief, but 4 years later the pain has recurred. These results have en- couraged me to completely abandon patellar resurfacing.
I had felt that extending the trochlear groove would support the patella,giving full metal contact through 105°
of knee flexion,and would reduce patellar pain.A cruciate- substituting knee requires a box and therefore a relative- ly short trochlea.After reviewing the results of the Profix cruciate-retaining versus cruciate-substituting knees, however, I found no difference in anterior knee pain. The reason that I chose not to resurface any of the posterior cruciate-substituting knees was my concern that the patellar implant would catch in the box or that the patel- lar surgery would encourage overgrowth of surrounding tissues to produce the patellar clunk phenomenon. Find- ings from one knee design, however, cannot be reliably extrapolated to a different knee system. Popovic and Lemair [5] found a 50% incidence of anterior knee pain when the posterior-substituting rotoglide knee was used as opposed to a much lower incidence with the cruciate- retaining version. They hypothesised that the sharp edge of the box was the source of the problem,so it would seem that box geometry can contribute to patellar pain.
Revision Total Knee Arthroplasty
Patellar maltracking is a common problem in revision total knee arthroplasty, particularly since earlier instru- mentation seldom allowed control of external rotation of the femoral component.Until recently,the advantage of 3°
of external rotation of the femoral component, which leads to lateralization of the trochlear groove and much improved patellar tracking, was not recognized. Even today, posterior referencing instruments oriented along the posterior condylar line will routinely internally rotate the femoral component in the valgus knee, which com- monly has lateral femoral condylar dysplasia.
The diagnosis of an internally rotated femoral com- ponent can be made by carefully controlled skyline radi- ographs. If the X-ray is taken with the knee in too much flexion, it may be unhelpful, and some authors have ad- vocated CT scanning [6]. Intra-operative derotation of the femoral component cannot be accomplished by sim- ply trying to manually externally rotate the femoral com- ponent,since it will usually return to its original position.
Resecting the anterolateral femoral condyle and aug- menting the posterior lateral femoral condyle also allows only limited correction, because notching of the femur will occur.My preferred technique is to resect some of the posterior medial femoral condyle and insert a screw into the anterior medial femoral condyle, leaving the head protruding. The screw can be turned in and out, forcing the femoral component into external rotation and thus providing the degree of correction necessary to ensure good patellar tracking. The screw is simply buried in cement during the cementation process.
The Unreplaced Patella
If the patella has been tracking correctly prior to revision surgery, no further treatment is necessary. If it has been maltracking or is laterally subluxed, the articular surface may be grooved. If the groove is small it can be ignored.
However, if the groove is deep, further surgery is neces- sary. If the groove is far lateral, the lateral edge of the patella may be smoothed to produce a convex surface. If it is far medial,as it can be in extreme cases,shaving alone may produce a convex surface. If convexity of the patellar component cannot be restored, either a medial edged re- section or a patellar replacement with a large implant may be required.
Replaced Patella – not Loose
Treatment of the patellar replacement during revision to- tal knee arthroplasty is dependent upon the degree of polyethylene wear. If the wear is not gross and the patel- la component is not metal-backed, it can be retained. The geometry may not completely match the trochlear geom- etry of the revision femoral component; however,the typ- ical presence of a patellar meniscus around the periphery of the replaced patellar component tends in general to compensate for these discrepancies. The patellar menis- cus is aneural and should not be excised if the original patellar component is to be retained.
If there is severe polyethylene wear, particularly if the patellar component is metal-backed, revision should be performed. If the patient is extremely elderly, patellar revision for wear may not be necessary. However, even elderly patients can have a long life expectancy. The pa-
Chapter 10 · Experience with Patellar Resurfacing and Non-Resurfacing – H.U. Cameron 67 10
tient’s age and activity should be considered,as well as the amount of patellar component wear, when the decision is made to retain or revise the component.
In removing a well-fixed patellar component, use of too much force must be avoided since the patella can be fractured or the patellar tendon avulsed.The patella must be stabilized with sharp towel clips proximally and dis- tally to prevent excessive traction on the patellar tendon.
If necessary, the implant-cement or implant-bone inter- face can be loosened with a very small high-speed burr.
The membrane is then removed. Unless very little of the patella was resected at the original operation, no further reaming should be done. The implant bed is simply roughened up with a high-speed burr and small holes are drilled transversely or obliquely rather than anteroposte- riorly; anteroposterior drilling tends to inadvertently penetrate the anterior surface of the patella, thereby sig- nificantly weakening it. A new patellar component, gen- erally biconvex is then cemented in place. In cementing a revision patellar component it is generally better to apply pressure to the implant with one's thumb during the ce- ment-curing process, because if the bone bed is asym- metric, clamps may tend to tilt the patellar component against the remaining bone.
If patellar fracture occurs, internal fixation is neces- sary, provided bone stock is adequate. Due to the reduced area of bone contact, it is unlikely that simple cerclage wiring will produce adequate stability to ensure union.
Additional compression screws should be considered. If a new patellar component is cemented in place, ingress of some of the cement into the fracture gap is almost in- evitable, with the increased likelihood of a non-union. It would seem preferable, therefore, not to insert a new patellar component,recognizing that patellar pain is like- ly at least for the first year. Should the pain persist after sound union, delayed patellar resurfacing can be per- formed.
Loose Patellar Component
If the patellar component is loose it should be removed.
If adequate bone stock remains, a new patellar compo- nent can be cemented in place after thorough débride- ment and removal of all osteolytic cysts and membrane.
Frequently, however, the remaining bone is not adequate to support a new prosthesis. The eroded, hollowed-out, thin avascular patella can be very difficult to treat [7]. If a new patellar component is cemented in place under such circumstances, early loosening, at least radiologically, is likely to occur (⊡ Fig. 10-1).
In an effort to improve cement fixation, I have used multiple screws inserted transversely across the patella, like rebars. Whether or not this will add to the longevity is not clear.Alternatively,cementless revision with porous
tantalum can be useful. However, cementless tantalum patellar revision has been reported to be associated with a 40% incidence of anterior knee pain. Cementless tanta- lum patellar revision may be appropriate for cases in which reaming is not possible because of poor patellar bone stock.
Hanssen [8] reported on bone-grafting the defect with morselized allograft and covering it with a mem- brane to promote bone regeneration. However, bone grafting may not be successful if the bone bed is avascu- lar. If the patella cannot be revised, anterior knee pain should be anticipated at least for 1 or 2 years. The hol- lowed-out patella often does not fit in the trochlear groove, and patellar instability may result. If so, then the lateral one third of the patella should be removed to pro- duce a reasonable fit in the trochlear groove. However, this procedure may also cause patellar avascular necrosis, due to disruption of the intraosseous blood supply.
Immediate patellectomy is not usually a viable option because immobilization in extension, which would be re- quired for several weeks, would likely result in reduction of range of motion.It may be preferable,therefore,to sim- ply resect the lateral one third of the patella. If avascular necrosis does not occur, the initial severe patellofemoral pain may decrease after 2–3 years. If avascular necrosis occurs, it is occasionally completely asymptomatic. More typically, however, the patella slowly fragments. Since the process is slow, disruption of the extensor mechanism with a quadriceps lag usually does not occur.
Revision Results
For the purpose of this book chapter, I have reviewed my results of revision total knee arthroplasty, concentrating on the patella. The knee designs evaluated included the Tricon II, TCIII, a cruciate-retaining Profix, and a cru- ciate-substituting Profix. Follow-up of these cases is be- tween 2 and 15 years.
⊡ Fig. 10-1.During revision total knee arthroplasty, a new patellar com- ponent was cemented in place. The radiolucent line between the cement and bone has been present since revision. While this patient’s patellar component has not required additional surgery, it is at least radiological- ly loose
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68 II . Past Failures
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There were 127 Tricon II knees, 12 Profix CR, 38 Profix CS, and 64 TC III-type knees. Of the Tricon II knees, 6.3%
have required revision and of the TC IIIs,3%.The fact that the Tricon has the longest follow-up may have influenced this. Patellofemoral pain (any anterior knee pain at all) was present in 25.6% of Tricon II, 0% of Profix CR, 10.5%
of Profix CS, and 20.3% of the TC III knees (⊡ Tables 10- 1–3).
It is apparent from these results that there has been a significant reduction in patellofemoral pain following re- vision surgery using a patella-friendly trochlea and ex- ternal rotation of the femoral component. The incidence of avascular necrosis has also been reduced significantly.
While the incidence of patellofemoral pain has also been reduced significantly, the cases in which a patel- loplasty of the patella with or without a lateral edge re- section is required remain a very significant problem, for which there is no satisfactory solution.This problem does not arise if the patella was not replaced at the time of the primary procedure. Surgeons carrying out knee replace- ment, therefore, should understand the femoral compo- nent trochlear geometry of the implant that they are using, and should consider not resurfacing the patella if the femoral component is patella-friendly.
References
1. Barrack RL (2003) All patella should be resurfaced during primary total knee arthroplasty – in opposition. J Arthroplasty 18 [Suppl 1]:35–38 2. Cameron HU: 1991: Comparison between patella resurfacing with an
inset plastic button in patellaplasty. Can J Surg 34:49–53
3. Cameron HU (1992) Patella resurfacing in total knee replacement. J Western Pacific Orthop Assoc 29:57–61
4. Cameron HU (1994) Tibial component wear in total knee replacement.
Clin Orthop 309:29-32
5. Popovic N, Lemair E (2003) Anterior knee pain with a posterior stabilized mobile bearing knee prosthesis; the effect of femoral component design.
J Arthroplasty 18:396–401
6. Berger RA, Crossetts LS, Jacobs JJ, et al (1998) Malrotation causing patel- lo-femoral complications after total knee arthroplasty. Clin Orthop 356:144
7. Neilson CL, Lonne JH, Lakji A, et al (2003) Use of trabecular metal patella for marked patellar bone loss during revision total knee arthroplasty.
J Arthroplasty 18:37–41
8. Hanssen AD (2001) Bone grafting for severe patellar bone loss during revision total knee arthroplasty. J Bone Joint Surg [Am] 83:171–176
⊡ Table 10-1. Overall patellofemoral results of various knee replacement designs
Implant Tricon Profix Profix TC III design (in %) (CR, in %) (CS, in %) (%)
Re-revised 6.3 0 0 3.0
Fair and poor 20.5 33.3 26.3 60.8
Lateral release 9.5 0 13.6 20.1
Derotated 0 16.7 15.6 5.8
Patellofemoral 25.6 0 10.5 20.3
ache
Patellar AVN 14.6 0 5.3 4.5
⊡ Table 10-2.Patellofemoral pain
Implant Tricon Profix Profix TC III design (in %) (CR, in %) (CS, in %) (%)
No replacement 11.0 0 9.1 15.8
Original patella 31.1 0 0 9.1
New cemented 16.9 0 0 7.1
New press fit 36.7 Not Not Not
performed performed performed
Patelloplasty 57.4 0 40.0 100
Patelloplasty 81.6 0 0 20
and lateral edge resection
⊡ Table 10-3.Fair and poor results
Implant Tricon Profix Profix TC III design (in %) (CR, in %) (CS, in %) (%)
No replacement 22.2 2.5 45.5 42.1
Original patella 12.5 0 0 54.5
New cemented 25.5 25.0 16.6 78.6
New press fit 0 Not Not Not
performed performed performed Patelloplasty 57.0
} }68 }25 }37.5 }26.7
Patelloplasty 72.7 and lateral
edge resect
