310 THE JOURNAL OF BONE AND JOINT SURGERY

The Avon patellofemoral arthroplastyFIVE-YEAR SURVIVORSHIP AND FUNCTIONAL RESULTS

C. E. Ackroyd, J. H. Newman, R. Evans, J. D. J. Eldridge, C. C. Joslin

From Southmead Hospital, Bristol, England

� C. E. Ackroyd, MA, FRCS, Consultant Orthopaedic Surgeon� J. H. Newman, MA, FRCS, Consultant Orthopaedic Surgeon� R. Evans, RGN, Research Nurse� J. D. J. Eldridge, BSc, FRCS(Orth), Consultant Orthopaedic Surgeon� C. C. Joslin, MBChB, FRCS(Orth), Specialist RegistrarBristol Knee Group, Winford UnitAvon Orthopaedic Centre, Southmead Hospital, Westbury-on-Trym, Bristol BS10 5NB, UK.

Correspondence should be sent to Mr C. E. Ackroyd at 2 Clifton Park, Clifton, Bristol BS8 3BS, UK; e-mail: Kathiereynolds@2CP.co.uk

©2007 British Editorial Society of Bone and Joint Surgerydoi:10.1302/0301-620X.89B3. 18062 $2.00

J Bone Joint Surg [Br] 2007;89-B:310-15.Received 2 May 2006;Accepted after revision 17 November 2006

We report the mid-term results of a new patellofemoral arthroplasty for established

isolated patellofemoral arthritis. We have reviewed the experience of 109 consecutive

patellofemoral resurfacing arthroplasties in 85 patients who were followed up for at least

five years.

The five-year survival rate, with revision as the endpoint, was 95.8% (95% confidence

interval 91.8% to 99.8%). There were no cases of loosening of the prosthesis. At five years

the median Bristol pain score improved from 15 of 40 points (interquartile range 5 to 20)

pre-operatively, to 35 (interquartile range 20 to 40), the median Melbourne score from 10 of

30 points (interquartile range 6 to 15) to 25 (interquartile range 20 to 29), and the median

Oxford score from 18 of 48 points (interquartile range 13 to 24) to 39 (interquartile range 24

to 45). Successful results, judged on a Bristol pain score of at least 20 at five years, occurred

in 80% (66) of knees. The main complication was radiological progression of arthritis, which

occurred in 25 patients (28%) and emphasises the importance of the careful selection of

patients. These results give increased confidence in the use of patellofemoral arthroplasty.

Isolated patellofemoral arthritis is a well-recognised variant of the osteoarthriticknee.1 McAlindon et al2 drew attention tothe frequency of this condition in 1992 andrecently, Davies et al3 found that 9.2% of209 patients attending an orthopaedic out-patient clinic for painful arthritis of the kneehad radiological evidence of isolatedpatellofemoral osteoarthritis. We areincreasingly recognising trochlear dysplasiaas a cause of patellofemoral disease inyounger patients.

Surgical treatment by arthroscopic chond-rectomy, chondral grafting and a variety ofprocedures to correct malalignment has hada varying degree of success in the manage-ment of this condition.4,5 Fulkerson4

described excellent short-term results fromanteriorisation of the tibial tubercle, butthere was a tendency for symptoms and func-tion to deteriorate with time, with the resultsat ten years often showing progression of thearthritic process.5

Patellofemoral arthroplasty has beenavailable for approximately 50 years. Theearliest designs of implant were crudeattempts to resurface either the patella or thetrochlea.6 It was not until the 1970s thatseveral designs gave reasonable short-termresults.7-9 Residual malalignment of the

patella and wear of polyethylene were recur-ring problems, which were found in up to30% of cases.10-13 Progression of arthriticdisease in either the medial or lateral com-partments was also regularly encountered bymany authors.8,10-15 In 2001, Tauro et al13

described such progression in 8% of patientsat eight years and in 2003 Kooijman et al14

reported progression in 23% of patients at15 years. Cartier et al15 noted good resultsfor the Richards model II and III prosthesis(Smith and Nephew, Memphis, Tennessee),but by 11 years the survivorship haddecreased to 75% because of progression oftibiofemoral arthritis. These longer termstudies have shown excellent and long-lasting functional results in more than 50%of patients.13-15 Kooijman et al14 recordedgood or excellent functional results in 86%of residual cases at 15 years. Nevertheless,the results do not match those obtained fortotal knee replacement (TKR), and thereforea new arthroplasty was developed based on abetter understanding of patellofemoral kine-matics and design. The early results haveshown a low rate of complications and goodfunction.16 We now wish to record the mid-term results of the first three-yearprospective series of patients treated withthis implant.

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Patients and Methods

Prosthesis and technique. The Avon design (Stryker How-medica Osteonics, Allendale, New Jersey) was developedfrom the Kinemax Plus patellofemoral articulation (StrykerHowmedica Osteonics) introduced in the late 1980s,17

which had a rate of patellofemoral complications of0.3%.18,19 The femoral component has a broad symmetri-cal trochlear flange, which allows relatively unconstrainedmovement of the patella in extension and attempts toreproduce the normal trochlear anatomy, relying ondynamic muscle balancing rather than a deep constrainedgroove to maintain patellar stability. The trochlear groovenarrows around the arc of flexion so that the patellaengages in the groove and becomes more stable as the kneeflexes. The patellar component is manufactured from ultra-high-molecular-weight polyethylene with a medially offsetdome of 3 mm to facilitate patellar tracking (Fig. 1). Thetechnique of implantation has been published previously16

and is described in detail on the manufacturer’s website.20

An important part is the soft-tissue balancing which isessential to correct any lateral retinacular contracture. Thisinvolves release of the lateral patellofemoral synovial foldsand a peripatellar release of the retinaculum from thelateral edge of the patella with preservation of the soft-tissue retinacular envelope. In the first year of implantation

only a medium-sized component was available, but in thesecond and third years this was increased to three sizes.More recently, an extra-small size of component has beenintroduced. The post-operative management has changedover the years and there is now an accelerated regime. Thewound is infiltrated with bupivacaine 0.5% with adrena-line 1/200 000, and suction drains are not required. The legis elevated on two pillows at 30˚ with active rehabilitationcommencing on the first post-operative day. Intermittent icetherapy and anti-inflammatory medications are used toreduce discomfort.Selection criteria. The patients were selected carefully toensure that there was no co-existent tibiofemoral arthritis.The tibiofemoral joint was assessed by both anteroposte-rior and lateral weight-bearing radiographs, and a standingtunnel view at 30˚ of flexion is now our preferred choice.The patellofemoral joint was appraised by a tangential viewat 30˚ of knee flexion. Initially, treatment was only under-taken in patients with advanced patellofemoral arthritis. Asconfidence in the procedure grew, we extended the indica-tions to include younger patients with earlier disease andtrochlear dysplasia, and those with arthritic changes inwhom a previous re-alignment procedure had failed.The study. A prospective clinical study commenced inSeptember 1996, since when 424 patellofemoral arthro-plasties have been performed in 322 patients.

Although most of the operations were performed bythe senior authors (CEA, JHN), more than 20 consultantsurgeons and trainees contributed cases to the study. Theprospective nature of the study results in the number ofpatients available at each review interval changing con-stantly. We therefore decided to report the first three-year cohort of patients that had been followed for overfive years. Between September 1996 and November

Fig. 1

Photograph of the Avon patellofemoral prosthesis showing the upperand lower side of the trochlea and the offset dome patella.

Table I. Pre-operative diagnoses in the 109 knees

Diagnosis Number of knees (%)

Lateral facet osteoarthritis 70 (64)Symmetrical osteoarthritis 33 (30)Medial facet osteoarthritis 3 (3)Dislocation and osteoarthritis 2 (2)Post-traumatic osteoarthritis 1 (1)

Total 109 (100)

Table II. Pre-operative radiological changes at the patellofemoraljoint in 109 knees

Radiological changes Number of knees (%)

Lateral subluxation 76 (70)Lateral tilt 9 (8)Medial subluxation 2 (2)Patellar joint narrowing 5 (5)Gross cartilage loss

Lateral facet 47 (43)Medial facet 10 (9)Both facets 30 (28)

Table III. Previous surgery in the 109 knees

Previous surgery Number of knees

Arthroscopy 15Lateral release 2Chondrectomy 3Patellar realignment 2Fixation of fracture 1Nil 86

312 C. E. ACKROYD, J. H. NEWMAN, R. EVANS, J. D. J. ELDRIDGE, C. C. JOSLIN

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1999, 109 consecutive patellofemoral arthroplastieswere performed in 85 patients, 10 men and 75 women,with a mean age of 68 years (46 to 86). The pre-operativediagnosis and radiological findings are shown in Tables Iand II and indicate that nearly 70% of cases had involve-ment of the lateral facet of the patella. Previous surgicalprocedures had been performed on 23 knees (TableIII).The clinical details and diagnoses were recorded pre-operatively, and an ongoing prospective review wasundertaken at eight months, two years, five years andeight years.

Functional scoring was performed using the Bristolpain and knee,21 the Melbourne patellar22 and theOxford knee scores.23 We used the Oxford score with aminimum of 0 for the worst outcome and a maximum of48 for the best outcome. A full radiological series of theknee was taken pre-operatively, post-operatively and ateach review. The clinical reviews were carried out by theresearch physiotherapist and nurse, consultant surgeons,knee fellows, and by postal questionnaire in 11 patientswho were unable to attend the clinic. The results wereentered into the knee database which was administeredby a dedicated research secretary. Life-tables and Kaplan-Meier curves were constructed.

Results

Patients were followed for a mean of 5.2 years (5 to 8). Tenpatients (12 knees) died during this period, but none ofthese had had revision. Five patients (seven knees) were lostto follow-up leaving 90 knees (70 patients) in the study.Seven patients (seven knees) were too ill to attend forformal evaluation; thus 83 knees (63 patients) were avail-able for assessment.

The functional outcome scores showed considerableimprovement for pain, patellar function and knee function.The median Bristol pain score improved from 15 of 40(interquartile range (IQR) 5 to 20) points pre-operativelyto 35 (IQR 20 to 40) at five years (Fig. 2), the median Mel-bourne patellar score from 10 of 30 points (IQR 6 to 15) to25 (IQR 20 to 29) and the median Oxford knee score from18 of 48 points (IQR 13 to 24) to 39 (IQR 24 to 45) (Fig.3). The median range of movement pre-operatively was113˚ (54˚ to 120˚) and at five years was 115˚ (60˚ to 130˚).Figures 4 and 5 illustrate the results in one patient at a fol-low-up of eight years.

The condition of the articular cartilage and menisci ofthe knee was recorded at the time of the operation. Themedial meniscus was normal in all patients as was theanterior cruciate ligament in all but one. Three lateralmenisci were abnormal (frayed or split). There were minorchondral lesions in the tibial plateaux in seven knees. In 48knees (44%) some chondral abnormalities of Outerbridgegrade I or grade II24 were noted on the femoral condyles.Isolated femoral chondral lesions of less than 1 cm in diam-eter, were accepted and treated by localised chondrectomy.

Establishing a measurement of success of any prosthesisis imprecise. If the results are judged using a Bristol score of≥ 20 points, then 80% (66) of joints had a successful resultat five years. If an Oxford knee score of ≥ 25 points is used,then 78% (65) of patients were judged to be satisfactory atfive years.

There were six early complications (6.5%) including twocases of delayed wound healing, two of post-operativehaemarthrosis requiring evacuation by arthroscopy, onemanipulation under anaesthesia for stiffness and one caseof synovial inflammation. All the early complicationsresolved satisfactorily (Table IV). One patient had patellar

Pre-operative 2 yrs 5 yrs

15

35

35

10

20

30

40

x

x

x x

Sco

re

Fig. 2

Median Bristol pain scores pre-operatively and at two and five yearspost-operatively with interquartile range and outliers.

Pre-operative 2 yrs 5 yrs

10

20

30

40

48

18

37

39

x

Sco

re

Fig. 3

Median Oxford Knee scores pre-operatively and at two and five yearspost-operatively with interquartile range and outlier.

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instability, and a distal soft-tissue realignment procedurewas performed, with a fair result (pain score > 20). Noknees were revised for problems associated with thepatellofemoral arthroplasty itself and there have been nocases of deep infection, wear, loosening or fracture. In 25patients, (28%) radiological progression of osteoarthriticdisease of either the medial or lateral compartments of thetibiofemoral joint was noted. Revision was required in fourknees (4.2%) within the first five years because of such pro-gression, giving a survivorship of 95.8% (95% confidenceinterval (CI) 91.8% to 99.8%) with 90 knees at risk at five

years (Fig. 6, Table V). There were 11 further revisions afterfive years. If all patients lost to follow-up were treated asfailures, the worst case outcome is 90.3% (95% CI 84.6%to 96%).

If the thresholds for moderate and severe pain (a painscore < 20) were included as outcome criteria in addition torevision for progression of the disease, the five-yearsurvivorship was 88% (95% CI 80.9% to 94.1%).

Discussion

The Avon patellofemoral arthroplasty gave satisfactoryresults at five years with no evidence of functional deterio-ration as judged by the outcome criteria. The developmentof smaller incisions and acclerated rehabilitation are likelyto improve the recovery with a reduction in the rate of earlycomplications. Problems of maltracking, and wear of thepatellar component noted in previous designs werereduced.10,13 In spite of the fact that 70% of cases had pre-operative lateral malalignment with subluxation, post-operative patellar instability which required additionaltreatment was recorded in only one knee. This is a muchlower figure than in our previous series using the Lubinusimplant (Waldemar Link, Hamburg, Germany.)13

Fig. 4a Fig. 4b

Pre-operative standing a) anteroposterior, b) lateral and c) tangentialradiographs in a 60-year-old woman with severe patellofemoraldegeneration, pain (15/40) and reduced function (Oxford score 34/48).

Fig. 4c

Table IV. Early and late post-operative complications

Complications Number of knees

EarlyDelayed wound healing 2Post-operative haemarthrosis 2Manipulation under anaesthesia 1Synovitis 1

LatePatellar instability 1Progression of radiological disease 25Revision for progression at five years 4

Standing a) anteroposterior, b) lateral and c) tangential radiographs ofthe same patient at a follow-up of eight years, when there was no painand full function (pain score 40/40, Oxford score 37/48).

Fig. 5a Fig. 5b

Fig. 5c

314 C. E. ACKROYD, J. H. NEWMAN, R. EVANS, J. D. J. ELDRIDGE, C. C. JOSLIN

THE JOURNAL OF BONE AND JOINT SURGERY

Improved patellar tracking was the result of several factors.The broad shallow proximal trochlea of the prosthesisaccommodated the various positions of the patella in fullextension. The ability to engage the patella with increasingstability in flexion, and the placing of the trochlea so that itis introduced in slight external rotation and lateral trans-lation on the femur, is an important feature which accom-modates the lateral malalignment that exists in many ofthese patients.

The broad shallow trochlear means that careful balanc-ing of the soft tissues is essential, and this avoids theproblems with trochlear designs which have a deep groovethat allow larger articular surface contact. These designsrequire accurate placement of the prosthetic trochleargroove depending on the position of the patella in theparticular patient, and will allow no accommodation of thedynamic characteristics of tracking in the conscious activepatient.14,15

The development of more refined soft-tissue releases pre-served the integrity of the knee capsule while lengtheningthe tight retinacular structures that contributed to lateralmalalignment. In our opinion, the subperiosteal peripatel-lar release of the lateral retinacular contracture at thelateral border of the patella was particularly important.This avoided the need for a destructive mid-lateral releasein most cases.

There appeared to be no need to restrict function afterthe arthroplasty and the outcome scores showed successful

restoration of function which was maintained at least tofive years. Comparison with other series of patellofemoralarthroplasties and with TKR was difficult because of theuse of different scoring systems, and the fact that the widelyused American Knee Society score25 is insensitive to patello-femoral function, open to bias and has poor repeatability.21

We used a separate pain score which seemed to show satis-factory results. We have also used the Oxford Knee scorewhich is well validated and shows results at five and eightyears which were similar to those of unicompartmentalreplacement.26

Our first 109 cases were for well-established and oftenquite advanced patellofemoral osteoarthritis which hadbeen present for many years. There were a few cases withpersistent or recurrent pain, the main cause of which isarthritic disease progression in the tibiofemoral joint.Previous series have recorded this complication occurringin up to 10% of patients.13-15 Tauro et al13 in 2001recorded an 8% progression rate in patients undergoing theLubinus prosthesis at eight years, while Kooijman et al14

recorded 23% progression with the Richards Model IIprosthesis at 15 years. The present series recorded radio-logical disease progression in 25 patients (29%). Althoughthere have been only four revisions for this cause at fiveyears, and the survivorship curve for disease progression(Fig. 6) shows only a slow deterioration, there were 11more revisions by eight years.

A detailed radiological study of our cases with pro-gression of disease by Nicol et al27 showed that progres-sion in the tibiofemoral joint was more common thanexpected in contrast to the findings after unicompartmentalarthroplasty. The changes documented in the articularcartilage at operation showed that over 40% of the fem-oral condyles had some surface damage, which mayaccount for the high rate of arthritic progression. In ret-rospect, our original indications for patellofemoralarthroplasty were too general. Further investigation isrequired to identify factors which predispose to progres-sion of the disease. Pre-operative bone scanning or MRImay define those patients with isolated patellofemoraldegeneration.

It has become apparent that many younger patients withsignificant patellofemoral arthritis have some trochlear dys-plasia. Therefore, our indications have expanded to includeyounger patients with earlier disease and also as a salvageprocedure in patients who have failed to benefit from othersurgical procedures. Patients with persistent dislocation,

Table V. Life-table of survivorship at five years for revision for any cause

YearNumber entering year

Numberwithdrawn

Number at risk

Number of events

Proportion terminating

Proportion surviving

Cumulative survival (%) 95% Confidence Interval

0 to 1 109 9 104.5 0 0.000 1.000 100 100 to 1001 to 2 100 0 100.0 2 0.020 0.980 98 95.3 to 100.72 to 3 98 8 94.0 0 0.000 1.000 98 95.3 to 100.73 to 4 90 0 90.0 0 0.000 1.000 98 95.3 to 100.74 to 5 90 0 90.0 2 0.022 0.978 95.8 91.8 to 99.8

30

60

90

1 3 4 5

Survival

95% confidenceintervals

4050

01020

20

Cu

mu

lati

ve s

urv

ival

(%

)

Time (yrs)

70

80

100 99.8%95.8%91.8%

Fig. 6

Five-year Kaplan-Meier survival curve with revision as the end-point.All revisions were due to progression of arthritic disease.

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early arthritic damage with malalignment and post patellec-tomy syndrome have also been treated successfully.28

Some authors have suggested that patellofemoral arthri-tis should be treated by TKR. The series of Mont et al29 andLaskin and van Steijn30 have shown satisfactory results,and present persuasive arguments for this approach. How-ever, they compare their outcomes with those of older pub-lished series with different functional scoring systems,which does not give an adequate comparison. Compart-mental arthroplasty has many advantages, especially inyounger patients who have failed to respond to more con-servative surgery, since limited bone resection is under-taken. If necessary, revision surgery to a TKR isstraightforward.

The results of our series give increased confidence in iso-lated patellofemoral arthroplasty. We are continuing toreview this series and intend to report longer term results inthe future. The precise indications for the procedure need tobe refined, but our experience suggests that it can probablybe extended to younger patients with trochlear dysplasiaand considerable lateral malalignment with arthriticdamage. However, a larger series with longer follow-up ofyounger patients is required before this can be generallyrecommended. Progression of arthritic disease in thetibiofemoral joint remains a potential hazard. Carefulselection of patients is required to avoid this complication,particularly since patients over 70 years of age are likely tohave a satisfactory long-term result with TKR. We would like to thank colleagues for referring patients for treatment to theBristol Knee Group. We would like to thank Ms Susan Miller, the Knee ResearchSecretary, who has made a major contribution to the study in managing thedatabase and co-ordinating patient follow-up.

The author or one or more of the authors have received or will receive bene-fits for personal or professional use from a commercial party related directly orindirectly to the subject of this article. In addition, benefits have been or will bedirected to a research fund, foundation, educational institution, or other non-profit organisation with which one or more of the authors are associated.

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