Long-Term Success of a Well-Cemented Flanged Ogee Cup

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Acetabular Components:

Long-Term Success of a Well-Cemented Flanged Ogee Cup

John Older

Summary

This chapter is entirely devoted to the flanged Ogee cup.

Initially, it presents evaluation of a cohort of 268 Ogee cups inserted by a single surgeon in a continuous series of primary Charnley low-friction arthroplasties. Clinically at 20 years, the revision rate for aseptic loosening of the Ogee cup was 2% a probability of 96.8% survival. Radio- logical evaluation at 13 years showed 89% of cups to have perfect bonding at the bone cement interface. The X-rays at 20 years are still being evaluated, but data suggests the excellent radiological bonding is being preserved.

Explanation of the design emphasises that the flange of the Ogee cup has two main functions. It assists pressurisation of the cement and stabilises the cup against the bony rim of the acetabulum. From the clinical and radiological evidence available, the use of the flanged Ogee cup is assisting sound bonding between cup and host bone in the acetabulum.

Introduction

The Ogee cup is a flanged cup developed by Charnley between 1979–1982. It was named Ogee because the double curvature of the plan of the face of the flange passing from concave to convex, resembles in cross section the type of curve best illustrated in the Ogee Arch of Gothic architecture (Oxford English Dictionary: »Ogee: Sinuous line of two opposite curves as in letter S«).

Material and Methods

At King Edward VII Hospital, Midhurst, West Sussex, Charnley personally used the first developmental Ogee

cup on the 29 November 1979. There followed a period of experimentation before the Ogee cup went into produc- tion. The surgeon author used an Ogee cup for the first time on 29 June 1982. This is a review of a continuous series of primary Charnley low fricton arthroplasties (LFA) using the Ogee cup, inserted by one surgeon, between June 1982 and December 1984.

There were 232 patients, 36 had bilateral LFAs, 28 simultaneous and 8 interval, giving 268 Ogee cups for review. The vast majority of patients (97.6%) had the LFA for primary osteoarthrosis. The age at operation ranged from 30 to 88, with a mean of 67 years (SD± 9.4). Females dominated with a ratio 3:1.

Operative Technique

Each operation took place in a Charnley Howarth Ultra- clean air enclosure with a body exhaust system. The procedure was a classical Charnley low friction arthroplasty, lateral approach with trochanteric osteotomy. The acetabulum was deepened transversely using a medial pilot hole which was covered with wire mesh as a cement restrictor.

Ebonated bone was left intact in the roof of the acetabulum. Three anchor holes 12.5 mm in diameter were made in pubic, ilial and ischial directions. In addition, a mul- tiplicity of 6-mm holes were distributed randomly over the acetabulum especially in the areas of dense, ebonated bone in the superior roof. The operative technique also involved assiduous irrigation with a syringe and sucker. A power-driven rotary nylon brush was used to help remove fibrous tissue and clean out soft marrow tissue from cancellous spaces, to leave the cancellous bone with a coarse texture to accept the cement ( chapter 2.2).

CMW 1 polymethylmethacrylate cement rendered radio-opaque with 10% barium sulphate with no antibi-

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otics was used in 97% of cups. The remaining cups were fixed with Palacos R cement.

The cups used in this series were machined from compression moulded sheets of Chirulen ultra high molecular weight polyethylene manufactured by Hoechst in Ger- many. The flanges were moulded from silane crosslinked medium density polyethylene. The finished cups were sterilised by gamma irradiation in an air environment using a dose range of 25–40 kGy.

Review

Two reviews have taken place. The initial review was at 12–14 years; data at 20–22 years is at present being ana- lysed. At 20 years, 151 patients had died all from causes unrelated to the implant, 5 (2%) of patients were lost to follow-up. There were therefore 76 patients alive, available for study.

Clinical Results

Excluding 9 revision patients, there were 130 patients alive with their Ogee cups at 12 years. One hundred and fifteen patients (89%) judged the procedure to be near perfect.

Eleven patients (8%) were less pleased, but still considered the arthroplasty satisfactory. Only four patients (3%) thought the result less satisfactory than they had hoped.

These figures had not changed at 20 years.

Prior to surgery, regarding subgroups 3 on the d’Aubigne-Postel scale [2,] patients were graded A – 90%, B – 8% and C – 2% the majority of hips were grade 3. This indicated severe pain when attempting to walk and very limited activity. At the first evaluation the majority of patients had improved to grade 6, a universal relief of pain over an average of 13 years, which did not vary between subgroups A, B and C. Assessment of the whole group showed their grading moved from an average pre-operative level of 333 to 665 and were maintained at this level. The only change at the 20 year evaluation was that 20% of the patients had become frail and subgroup C with a functional grade of 3 or 4. However, these hips remained pain free with a good range of movement. The Ogee cup was good and functional in 96% of patients until death or review.

Radiological Evaluation

At review, all patients had antero-posterior X-rays at two penetrations and oblique lateral views of the acetabulum.

At the first review, there were radiographs of 137 Ogee cups available for assessment. The X-rays were reviewed independent of the surgeon. Using the modified DeLee- Charnley method [3], grade I is considered perfect ac-

ceptance of cement with no demarcation of radio opaque cement from the bone of the acetabulum. This occurred in 89%. Slight or moderate demarcation affecting the up- per quadrant only (grade II) occurred in 6%. Severe demarcation (grade III) involving the whole circumference of the cup was seen in 5 (4%). There was only one cup with radiological evidence of migration.

At 20 years there are 55 radiographs available of patients with their original Ogee cup. At going to press, analysis of their radiographs is still in progress. The initial data suggests grade I, no demarcation is present in 78%.

Radiological evaluation continues and the results await further publication.

True Failure Requiring Revision Surgery

There have been 15 revisions. One patient had a fall and fractured the shaft of the femur around the stem of the femoral component. This was revised and replaced. The Ogee cup functioned well both clinically and radiologically for 18 years. A second patient had a periprosthetic femoral fracture at 17 years. Both components were replaced, the cup for wear with no sign of aseptic loosening.

Two cups have been revised for infection. One patient with psoriasis had a bilateral simultaneous LFA. Within months one hip became infected. It was revised as a one stage procedure. Both the original and revised Ogee cups continued to give good service for 17 years.

The other patient, 14 years after the original LFA, developed septicaemia from an abdominal abscess sec- ondary to Crohn’s disease. This led to an abscess in the thigh around the LFA. A Girdlesone excision arthroplasty was performed and later revised to a LFA using impacted morsellised allograft bone to reconstruct the acetabulum and proximal femur.

True aseptic loosening requiring revision surgery has occurred in 11 patients. Six of these patients had femoral component problems; four had both components replaced, but only the Ogee cup for wear, with no sign of aseptic loosening. The other two had the femoral stem only replaced, both Ogee cups are good.

Five patients had revision of the Ogee cup for aseptic loosening. Two patients had only the cup replaced, the other 3 had both implants changed. Of these 5 patients, 3 were revised at 12 years and the remaining 2 at 20 years.

This represents 1% revision of the Ogee cup at 16 years and 2% at 22 years for aseptic loosening.

Survivorship Analysis and Summary

This is a study to assess the outcome of the Ogee cup in the primary Charnley LFA. It gives a unique insight into the outcome, both clinical and radiological at 20–22 years

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excellent or good hips. This includes those patients too frail to travel to hospital for X-ray. The follow-up has been 98% and the Ogee Cup was good and functional in 96% of patients until death or review.

The Kaplan-Meier survivorship estimates, taking failure as revision of any component for any cause, shows a 93% probability of survival at 13 years. The 15 hips that required revision surgery for any cause, represent 5.6%

of 268 LFA’s at 20–22 years. A probability of survivorship of 88% at 20 years. However, the revision rate for aseptic loosening was 5/268, representing 2% at 22 years, i.e.

a 96.8% probability at 20 years. We cannot extrapolate beyond 20 years, as there are not enough cases to balance the revisions.

Review of the Literature

Garellick and colleagues [5, 6] evaluated clinically and radiologically a randomised, prospective study comparing the Charnley prosthesis using the all polyethylene flanged Ogee cup with a Spectron metal back cup. The aim of this study was to evaluate the influence of prosthetic design on early and long term clinical and radiographic outcomes.

After 7–11 years the Ogee cup performed remarkably well with no revision, a 100% survivorship at 11 years.

Four Spectron Cups were revised, survivorship of 97.4%.

In contrast, no Spectron femoral stem required revision, but five Charnley femoral prostheses were revised. Radio- logical evaluation revealed 23 Spectron cups to be loose, but only 4 Ogee cups were radiographically loose; these patients were satisfied and without pain. This is the only paper so far published giving long-term data on the Ogee cup. The disparity both clinically and radiographically il- lustrates that the design differences in these two implants had a significant influence on revision rates. As well as the flanged cup another contributing factor to the difference in cup revisions might be that the larger circumference femoral heads (Spectron 32 mm) have been shown to cre- ate greater frictional torque [4] and hence higher stresses on the bone-cement interface [5, 6].

Other reports on the flanged cup have been scanty.

Wroblewski [12] claimed revision for socket loosening has been reduced to 3% by the introduction of the Ogee flanged socket. Hodgkinson [7] reported a radiological review at 9–11 years comparing unflanged with flanged cups in Charnley cemented arthroplasties. The incidence of radiological demarcation at the cement-bone interface was significantly reduced in early radiographs after the use of a flanged socket and the advantage maintained in the long term results.

The same year, 1993, that Wroblewski and Hodgkin- son published, Kobayashi [8], in a 5–18 year review of 267

or ebornated bone in the acetabular roof, multiple 6 mm anchor holes and two steps of evolution in socket design, the flanged and later Ogee socket, benefited radiological socket survival. Valle [11] has presented the most up to date review, 123 consecutive primary hip arthroplasties by a single surgeon using cemented all polyethylene flanged cups. These were the first generation flanged cups before the Ogee cup. At a minimum of 20 years, 40 hips in 33 patients were alive and available for study. Two cups (5%) had been revised for aseptic loosening at 13.5 and 21.3 years post operation. Four additional cups had definite evidence of radiographic loosening. They concluded that the use of a cemented all polyethylene flanged acetabular component was associated with a low rate of repeat surgery.

All the surgical procedures in the cohorts reviewed by Kobayashi and Valle [8, 11] were performed by a single surgeon, Terayama and Lazansky, trained by the origina- tor of the LFA and Ogee cup, Charnley. This also applies to the author of this chapter. The surgical technique may have played a factor in the results observed.

Theory

The design of the cup has evolved in a series of stages since high density polyethylene was first used for cups in November 1962. Initially it was rimless. The conventional design of cup, which is basically a simple hemisphere, has three disadvantages. It pressurises and injects cement only when pressed into the acetabulum in a direction perpen- dicular to its face, at 45° to the long axis of the body. If pressed into the cement transversely, to keep the centre of the cup at a normal low level, a crescent of cement must appear between it and the superior lip of the acetabulum.

It will continue to ‘wobble’ while the cement is soft. This instability in the soft cement imposes a great strain on the surgeon attempting to hold it stationery while the cement is setting.

The pressure injection flanged cup was introduced in 1976 to overcome these disadvantages. This was the first design of cup to have a semi-flexible flange, which could be trimmed with scissors to fit the mouth of the reamed acetabulum. It restricts the escape of cement and enhances compression of the soft cement, especially around the rim of the acetabulum during the last few millimetres of pressing into position. It gives the cup a positive location in the acetabulum, produces mechanical stability so that the cement can polymerise without the cup ‘wobbling’.

A criticism of this first pattern of trimmable pressure injection flange was its failure to use a narrow strip of bone surface available in the most lateral part of the pos-

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terior wall of the acetabulum. Consider the anatomy of the socket seen as a transverse section of the acetabulum viewed vertically in a standing patient. The anterior wall of the normal acetabulum is shorter than the posterior wall. This shortness is frequently very marked. Neutral anteversion leaves a gap anteriorly and unused bone surface of the acetabulum posteriorly.

The Ogee socket makes use of the maximum area of bone surface on the posterior wall of the acetabulum, at the same time avoiding anteversion of the central part of the face. While the anterior part of the Ogee cup flange remains medially directed as in the previous patterns, the posterior part of the flange is directed somewhat later- ally. Trimming the rim of the flange is critical and must take account of the design of the flanged cup and the anatomy of the acetabulum. If the flange is not trimmed enough, it will ‘rim out’ – the rim may come against bone and prevent further pressurisation. If trimmed too much, the cup may ‘bottom out’ and prevent further pressurisation.

Shelley [10] evaluated the Ogee flange socket experi- mentally to determine its efficacy in pressurisation of the acetabular cement and compare it with unflanged cup.

The Ogee socket gave a consistently high injection pressure which could be maintained throughout the process of polymerisation. The importance of maintaining a continuous pressure on the cement throughout polymerisation was emphasised.

Parsch and colleagues [9] have evaluated the effects of an acetabular flange on cement pressurisation and cement penetration in 12 cadavers. The flanged cups produced greater intra acetabular peak pressures than the unflanged cups, but did not increase the average intra acetabular pressure. The cement penetration did not differ significantly between the two groups. They interpreted their findings as not supporting the use of flanged cups as the sole means of cement pressurisation in the acetabulum.

The use of the word ‘sole’ is very significant. The definition of ‘sole’ is ‘one and only, exclusive, unique’. The use of the flanged Ogee Cup is not solely to increase pressurisation.

A major concept of the flange is meticulous trimming of the rim to obtain accurate contact with the irregular rim of the acetabulum. This stabilises the cup and prevents bottoming out. Maintaining pressure on the cup until the cement has polymerised is essential to cause intrusion of viscoelastic cement into small cancellous bone.

Conclusions

The long term radiological study of the behaviour of bone in contact with cement, is a more important criteria of long-term success, than patient satisfaction. The behaviour of cement and bone in the femur has been gratifying.

However, in prospective studies of the cement – bone

interface, Charnley in 1979 [1] observed radiological demarcation of cement in the acetabulum in roughly 60%

of hips after an average period of 14 years. In 25% there was, with passage of time, progressive, severe demarcation and migration of cups. These were disturbing facts. The corollary that 40% of hips showed no demarcation, even after an average of 14 years was important, because if demarcation was caused by a basic problem such as too great a discrepancy between the elastic moduli of cement and bone, then 100% of cups ought to demarcate. That 40%

of cups appeared to have a perfect bone-cement interface could be explained by some factor of better technique in these perfect cases.

Nevertheless, Charnley [1] suggested we could not consider ourselves in control of the situation until a technique of using cement in the acetabulum significantly reduced the incidence of demarcation, to make it as rare as in the femur. Have the changes in the cup and technique over 20 years ago improved the long term results?

In this series, the radiological appearances of the cement – bone interface in the acetabulum demonstrated that 89% of cups at 13 years were perfectly accepted. At going to press, the definitive radiological analysis at 22 years is still in progress and will await further publication. It appears, however, that sound radiological bonding at the cement bone interface in the acetabulum is being maintained. This is surely cause for optimism and sup- ports the idea that there is no fundamental defect in the principal of using cement in the acetabulum. Radiological loosening in other series may therefore be a reflection of unsophisticated cement technique, poor acetabular components and adjacent bone, rather than the fault of cement.

The clinical and especially radiological long term results of the Ogee cup are excellent. It must answer Charnley’s original request in 1979 to control the situation in the acetabulum by significantly reducing the incidence of demarcation at the interface. Why are the results so good? I suggest that the clinical use of the flanged Ogee cup endorses the experimental results of Shelly and Charnley’s original conception of the flanged cup.

The flange firstly provides injection pressure on cement during insertion, giving better bone-cement bonding.

Secondly, positive location in the acetabulum giving stability whilst cement is setting. There is a third hypothesis, which may be impossible to prove. The rim, if correctly trimmed to sit precisely on the bone of the acetabulum, acts as a seal – the cement is confined and particles of cement cannot escape.

There is a fourth factor for success. It is now universal- ly recognised that surgical technique is a fundamental factor in the longevity of all hip prostheses. The preparation of the bony bed of the acetabulum, correct trimming of the flange, together with accurate insertion of the cement and cup, are all essential to long term success.

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▬

a revision rate for aseptic loosening of 2% and a probability of survivorship of 96.8%.

▬ Radiological review of Ogee Cup at 13 years showed that 89% of cups had perfect radiological bonding at bone cement interface.

▬ X-rays at 20 years are being evaluated. Data suggests excellent radiological bonding is being preserved.

▬ The flange of the Ogee cup restricts escape of cement, enhances pressurisation of cement, gives the cup a positive location in the acetabulum and maintains mechanical stability against the bone of the acetabulum.

References

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demarcation of the acetabular bone cement interface. J Arthro- plasty 5 (Suppl) 1990; 1

5. Garellick G, Malchau H, Herberts P. The Charnley versus the Spec- tron hip prosthesis. Clinical evaluation. J Arthroplasty 1999; 4:407–

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6. GarellickG, Malchau H, Regner H, Herberts P. The Charnley versus the Spectron hip prosthesis. Radiographic evaluation. J Arthro- plasty 1999; 4: 414–425

7. Hodgkinson JP, Maskell AP, Paul A, Wroblewski BM. Flanged acetabular components in cemented Charnley hip arthroplasty. J Bone Joint Surg 1993; 75B: 464–467

8. Kobayashi S, Terayama K. Factors influencing survival of the socket after primary low friction arthroplasty of the hip. Arch Orthop Trauma Surg 1993: 112; 56–60

9. Parsch D, Diehm C, Schneider S, New A, Breusch SJ. Acetabular cementing technique in THA – flanged versus unflanged cups, cadaver experiments. Acta Orthop Scand 2004; 75(3): 269–275 10. Shelley P, Wroblewski BM. Socket Design and Current Pressurisa-

tion in the Charnley Low Friction Arthroplasty. J Bone Joint Surg 1988; 79B: 358–363

11. Valle CJD, Kaplan K, Jazrawi A, Ahmed S, Jaffe WL. Primary Total Hip Arthroplasty with a Flanged Cemented All-Polyethylene Ace- tabular Component. J Arthroplasty 2004: 19: 23–26

12. Wroblewski B M, Siney PD. Charnley low-friction arthroplasty of the hip. Long term results. Clin Orthop 1993: 292; 191–201