INTRAMEDULLARY CANCELLOUS BONE BLOCK TO IMPROVE FEMORAL STEM FIXATION IN CHARNLEY LOW-FRICFION ARTHROPLASTY B. M. WROBLEWSKI, ADRIAN VAN DER RIJT

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1 INTRAMEDULLARY CANCELLOUS BONE BLOCK TO IMPROVE FEMORAL STEM FIXATION IN CHARNLEY LOW-FRICFION ARTHROPLASTY B. M. WROBLEWSKI, ADRIAN VAN DER RIJT From the Centrefor Hip Surgery, Wrightington, Wigan In order to improve the fixation of the stem in primary Charnley low-friction arthroplasty, the medullary canal was routinely closed off with a cancellous bone block. A prospective study of 611 consecutive arthroplasties was carried out between 1 and 5 years (average 2 years 9 months) after operation. There were two cases of radiological loosening of the stem, both of which could have been avoided. Five other patients showed demarcation of the bone-cementjunction at the calcar; two of these are considered to be at risk of loosening. There was no evidence of radiological loosening of the stem in 604 cases and the method is recommended for routine use in primary total hip arthroplasty. The concept of closing off the medullary canal before the insertion of the cement and the stem in total hip arthroplasty is attractive, if only because it restricts the flow of cement distally. Unless this is done it is the viscosity of the cement and the air trapped within the medullary canal which determine the quality of the cement injection. To rely solely on this for the cement-tobone bond means that its quality is unpredictable ; in addition it may possibly lead to embolisation of the medullary contents (Adams et a! ; Breed 1974; Herndon, Bechtol and Crickenberger 1974; Kallos et a!. 1974; Harris et a!. 1975). To vent the medullary canal would be to reduce the pressure of the cement injection and risk loosening. Oh et a!. (1978) described a method ofclosing off the medullary canal with the acrylic cement, and have also measured the pressures generated at various levels. The use of a plastic plug (Mallory 1981) and cancellous bone (Knight 1982) have also been described. In a previous study (Wroblewski 1982) it was pointed out that in 77.2% of cases of fractured stems there was radiological failure of the stem fixation within 12 months of operation. The same pattern was obvious in cases of revision for loosening of the stem (Wroblewski 1984, in preparation). Any improvement in the surgical technique to prevent such complications must be considered beneficial since the incidence of loosening of the stem in some series is high (Sutherland et a! ; Stauffer 1982). The purpose of this paper is to present the operative technique and the results of using an intramedullary cancellous bone block in the Charnley low-friction arthroplasty. The particular design employed was favoured for its ease and reliability in use. High-density polyethylene was avoided to prevent any possible adverse tissue reaction (Charnley 1963 ; Mendes et a!. 1972; Ewald et a! ; Wroblewski 1979). C C B. M. Wroblewski, FRCS, Consultant Orthopaedic Surgeon Centre for Hip Surgery, Wrightington Hospital, Wigan WN6 9EP, England. A. J. van der Rijt, FRCS, Orthopaedic Surgeon 84 Hampden Avenue, Wagga Wagga, 2650 New South Wales, Australia. Requests for reprints should be sent to Mr B. M. Wroblewski British Editorial Society of Bone and Joint Surgery 030l-620X/84/51 19 $2.00 L_._... _ Fig. Instruments designed for the intramedullary bone block technique : the trephine, the set of tampers and the vent. I VOL. 66-B, No. 5, NOVEMBER

2 640 B. M. WROBLEWSKI, A. VAN DER RIJT TECHNIQUE Instruments. The set consists offive instruments (Fig. 1). The trephine is designed to remove a 15 mm diameter block of bone, usually from the trochanteric bed close to the sectioned neck of the femur. The instrument also has a piston mechanism for ejecting the bone block. There is a set ofthree tampers measuring respectively 8, 10 and 14 mm in diameter. These are used first to assess the size of the medullary canal after its preparation and then to impact the bone block at the predetermined position. They are used sequentially from the largest to the smallest, both for assessment of size and for impaction. The offset on the tampers was specifically designed to meet the needs of surgeons who do not osteotomise the trochanter. The grooves are machined to avoid any pistoning effect during assessment or when impacting the bone block. The stop bar is arbitrarily set to leave a gap of about 2 cm beyond the tip of the standard Charnley stem. The vent allows proximal venting of the medullary canal when the two thumb method is used for injection of the cement. The ring allows for its easy withdrawal and the obturator ensures patency. Procedure. The lateral approach is used with elevation of the greater trochanter. The diagrams (Fig. 2) show the technique being used on the right femur which, during the operation, lies transversely over the left femur. The tibia is vertical and the open neck of the femur is facing the surgeon. (a) The neck of the femur is opened with the Charnley tapered reamer. (b) The bone block is taken from the trochanteric bed V a b C d p f g h Fig. 2 The procedure-see text for description of the nine stages. THE JOURNAL OF BONE AND JOINT SURGERY

3 INTRAMEDULLARY BONE BLOCK TO IMPROVE STEM FIXATION IN CHARNLEY ARTHROPLASTY 641 close to the neck of the femur, with care to avoid levering which could damage the neck. (Note the grip on the trephine.) (c) The medullary cdnal is prepared in the routine fashion. Trial reduction is performed at this stage and the definitive stem selected. (d) The size of the medullary canal is assessed using the tampers, starting with the largest. (e) The bone block is ejected from the trephine down the medullary canal. (f) The block is impacted to the required depth using the tampers in the order predetermined in stage (d). (g) Any fragments broken offthe bone block are removed with a curette. Wires for reattaching the trochanter are inserted and the fit of the definitive prosthesis tested. (h) The medullary canal is vented and the cement injected using the two-thumb method. Before its withdrawal, the vent is occluded to prevent back suction of its contents. (i) The prosthesis is inserted into its final position ; the injection pressure is increased by occluding the proximal exit from the femur as the stem is inserted. Since the pressure of cement injection is increased and also the resistance to the insertion of the stem, certain points must be emphasised. The bone block is invariably oversize (except in a very large medullary canal) and any part of it shed at impaction must be removed to ensure unimpeded fit ofthe stem. The cement must be used earlier than hitherto. The wire drill-holes should be inspected and any extruded cement removed; this is best done once the cement has set. The bone block is routinely taken from the area shown (Fig. 2b) because this is the best-quality cancellous bone and is normally wasted during the preparation of the medullary canal. Bone can, however, be taken from the femoral head or neck, or from elsewhere, and then impacted within the trephine with the largest tamper. These sites, however, may not provide a consistently good bone block and bone from the femoral head may be too hard for the purpose. No irrigation or brushing of the medullary canal has been used in this series. With time the bone block will almost certainly become incorporated, closing off the medullary canal. This has been confirmed in cases explored because of deep sepsis. The intramedullary bone block has not been used for revision operations : good quality cancellous bone is seldom available in sufficient quantity, and in revision for sepsis there is always the fear of producing a sequestrum. MATERIALS AND METHODS The notes and radiographs of 554 consecutive patients operated upon between September 1977 and June 1980 were reviewed. Six patients were excluded because of infection proved at revision, and 22 patients because their follow-up was less than 12 months ; nine of these 22 died within this period and 13 failed to attend. The remaining 526 patients with 61 1 Charnley low-friction arthroplasties are the subject of this study. In 30 patients bilateral arthroplasties had been performed simultaneously and in 55 patients the operations were staged. Routine standardisation of one-plane radiographs (Charnley 1979) allowed comparison for evidence of loosening. The following radiological criteria were used as evidence of loosening of the stem or the stem-cement complex. 1. Fracture of the cement at any level. 2. Separation of the lateral convex surface of the stem from the cement. 3. Endosteal cavitation ofthe femur at any level. 4. Change of the position of the stem or of the stemcement complex. 5. Demarcation at the bone-cement interface. The depth of medial cement between the cut surface of the femoral neck and the prosthesis, the extent of cement beyond the tip ofthe prosthesis, and the diameters of the femoral shaft and of the medullary canal were measured directly on the radiographs. The ratio of the medullary canal diameter to the shaft diameter was noted and the type and orientation of the prosthesis were recorded. RESULTS There were 349 women and 177 men. The average age at operation was 61 years, with a range of 20 to 87 years. The average weight was 147 lb (67 kg), with a range from 70 to 224 lb (32 to 102 kg). The average postoperative follow-up was 2 years 9 months, with a range of 1 year to 5 years 6 months. In 107 patients the follow-up was four years or more. The disorders which led to hip replacement are shown in Table I. The type of stem used and its orientation within the medullary canal is shown in Table II. The average thickness of the cement at the calcar was 1 1 mm (range 3 to 25 mm) and at the tip of the stem was 16 mm (range 0 to 50 mm). The ratio of medullary canal diameter to the femoral shaft diameter was 0.5 (range 0.3 to 0.8). In 604 hips (98.9%) there was no evidence of loosening asjudged by the criteria described above. Two hips (0.3%) had definite radiological evidence of loosening. A 34-year-old woman with osteoarthritis secondary to congenital dysplasia had, at 16 months, 4 mm separation at the bone-cement interface ; this progressed until, at 4 years 7 months the stem-cement complex had tilted into varus. In the second patient, a 47-year-old man with osteoarthritis secondary to a spastic dislocation, there was separation at the lateral aspect of the tip of the cement ; this was first noted at 2 years 1 1 months and measured 1.5 mm but did not progress over the next 24 years. VOL. 66-B, No. 5. NOVEMBER 1984

4 642 B. M. WROBLEWSKI, A. VAN DER RIJT Table I. Aetiology of the hip condition Primary osteoarthritis 448 Secondary osteoarthritis Congenital dysplasia 50 Perthes disease 8 Slipped femoral epiphysis 8 Idiopathic avascular necrosis 6 Fractured femoral neck 5 Traumatic dislocation 4 Old septic dislocation 2 Old tuberculous lesion 1 Spastic dislocation 1 Rheumatoid arthritis 64 Ankylosing spondylitis 8 Psoriatic arthritis 3 Paget s disease 3 convex shoulder of the prosthesis and the greater trochanter. All 65 patients had had a trochanteric osteotomy and this line occurred outside the cement mantle. No instance of separation of the prosthesis from the lateral surface of the cement was seen in association with this line. The average width of the line was 1 mm with a range of 0.5 to 2.0 mm. It had appeared by three months in 14 cases and by 12 months in 45. It became apparent on later radiographs in six cases at an average time of 34 months, with a range of 25 to 39 months. This line did not increase in width over the period of review. Controls. In 74 patients the contralateral hip had been operated upon without the use of an intramedullary bone block. Their average age at review was 66 years, with a range of 42 to 81 years. Their average weight was 144 lb (60 kg), with a range of 91 to 193 lb (42 to 88 kg). The average follow-up was six years with a range of 1 to 18 years. Radiological evidence of the failure of the stem fixation (using the criteria defined above) was present in 23 cases (31%); two failed by six months (in one the stem fractured at about the twelfth year), 19 failed by one year, and two by two years. Table II. Type of stem used and its orientation in the medullary canal Flanged stem Extra heavy 393 Heavy 123 Non-flanged stem Straight thick 56 Three-quarters neck 29 For congenital dislocation 10 Orientation Neutral 425 Valgus 180 Varus 6 In five hips (four patients) a radiolucent line appeared between the medial femoral neck and the cement, but this line never exceeded 2 mm in width. In three of these hips (two patients) the line was present by six months and did not progress over the 5 years 6 months and 4 years 3 months before these patients were reviewed. In the other two hips the lucent line appeared at 1 year 2 months and 3 years 6 months ; it slowly progressed in length over the 4 years 1 1 months and 4 years 8 months of review. The remainder of the bone-cement interface was unchanged in these patients. In 65 hips a lucent line appeared between the lateral DISCUSSION The improved radiological results of this review support the concept that the majority of cases of loosening of the femoral component are probably secondary to failure of mechanical fixation. The efficacy of an intramedullary bone block in occluding the femoral canal and enhancing cement injection is suggested by the results presented. Under conditions ofsecure fixation the bone-cement interface appears to be radiologically inert without evidence of progressive change. Demarcation of the bone-cement interface, lucent lines and endosteal cavitation do not appear to be the inevitable consequence of the use of acrylic cement. (The changes seen in the cortex of the medial femoral neck will be the subject of a further report.) A radiolucent line noted between the greater trochanter and the convex lateral surface ofthe prosthesis in 65 (10.6%) ofthe cases was apparent because ofa thin line of sclerosis on the cut cancellous surface of the trochanter; it was outside the cement mantle. Loudon and Charnley (1980) noted this same appearance in association with the dorsal flange (Cobra) prosthesis. They did not record measurable subsidence in association with it, nor was this found in the present study. It is possible that the sclerotic line occurs because of relative movement between the greater trochanter and the prosthesis, creating the appearance of a lucent line similar to that occasionally seen around a K#{252}ntscher nail or an uncemented intramedullary stem. It has been shown experimentally that the Charnley prosthesis slips within the cement mantle once subjected to load (McLeish 1977). Small amounts of slip would be THE JOURNAL OF BONE AND JOINT SURGERY

5 INTRAMEDULLARY BONE BLOCK TO IMPROVE STEM FIXATION IN CHARNLEY ARTHROPLASTY 643 difficult to detect because the appearance would be extremely sensitive to change in orientation. It has been demonstrated previously that radiological failure predates symptomatic failure by several years. In a retrospective analysis of patients with fractured femoral prostheses, Wroblewski (1982) found evidence of radiological failure by 12 months in 77.2% of patients. Weber and Charnley (1975) found that a fractured tip of cement was usually evident by six months after operation if it occurred at all. Stauffer (1982) and Sutherland et a!. (1982) found that the radiological failure rate of femoral components was non-linear, the majority of failures occurring in the first five years, although they did not specify how early these failures were evident. In the patients in this report operated upon without a bone block, signs of radiological failure occurred by 12 months in 21 of 23 patients. This further supports the observation that in the majority of cases the evidence of radiological failure of stem fixation can be seen within one year of operation. Once radiological failure has occurred it is probably the body weight and the activity level of the patient which determines if and when symptomatic failure will occur. It would be of interest to establish what, if any, changes of the femoral stem fixation can be observed in the patients with the longest follow-up available. Definite radiological evidence ofboosening occurred in two patients in this series. In one patient with spasticity this consisted of a lucent line at the tip and lateral wall of the bone-cement interface. This patient s activity level was restricted by his disease and by a dislocated contralateral hip. The changes may have been progressive if his level of activity had been greater. Gross loosening occurred in one patient with a dysplastic femur secondary to congenital dislocation. It had been necessary to ream the medullary canal down to cortical bone to accommodate the stem. Such a surface is unsuitable to key acrylic cement. The authors are in disagreement with the suggestion made by Knight (1982) that the medullary canal should be reamed to cortical bone. The amount of cement distal to the prosthesis did not appear to influence the result and it may be possible todispense altogether with cement distalto the prosthesis. We could find no evidence of an increased risk of femoral shaft fracture because of the sudden transition from a stiffened proximal femur to a normally flexible distal femur. The type of prosthesis did not appear to influence the results. Its orientation may have had some influence upon changes in the medial femoral neck but did not appear to influence the overall result. The diameter of the medullary canal or its ratio to that of the femoral shaft did not influence the results. Sutherland et a!. (1982) found a statistically significant increase in failure rate when a Muller stem occupied less than 50% ofthe medullary canal, but did not specify what proportion of the medullary canal was occupied by cement. It is more likely that the amount and quality of cement injection influenced the result, rather than the size of the prosthetic stem. In our series wide medullary canals were cleared to give firm cancellous bone. In all the patients studied, including those with loosening due to infection, there was no instance of fracture of the cement mantle seen on the radiographs. In the six cases of deep sepsis which were excluded from the study and in the one case of progressive loosening, the failure occurred at the bone-cement junction, the stem and the cement changing their orientation as a unit. This contrasts sharply with the description by Stauffer (1982) who reported that his most common type of loosening resulted from failure of the prosthesis-cement interface due to splitting of the cement mantle. It is possible, therefore, that the cement fracture was secondary to, rather than the cause of, loosening ; well-supported cement is unlikely to fracture. In the five hips (four patients) where the radiolucent line appeared between the medial femoral neck and the cement, a longer follow-up is awaited. In three of these hips the line has not so far progressed during the followup ; in the other two it is slowly progressing and this may indicate loss of the medial support of the stem, so that there is a risk of a stem fracture occurring in the future. A change in the technique of the medullary canal preparation may avoid this. The results in this series were compared with those of Harris, McCarthy and O Neill (1982) where acrylic cement was used to occlude the medullary canal and the cavity was filled in a retrograde manner using a cement gun. Their radiological loosening rate using anteroposterior and lateral radiography was 5.3% (9 out of 171 cases). In our series there have been no complications which could have been attributed to the method and we therefore recommend its routine use in primary total hip arthroplasty. REFERENCES Adams JH, Graham DI, Mills E, Sprunt 1G. Fat embolism and cerebral infarction after use of methylmethacrylate cement. Br Med J 1972 ; iii: Breed AL. Experimental production of vascular hypotension, and bone marrow and fat embolism with methylmethacrylate cement : traumatic hypertension of bone. C/in Orthop 1974; 102: Charnley J. Tissue reaction to polytetrafluorethylene. Lancet 1963 ;il: ai*rnley J. Lowfriction arthroplasty oft/se hip: theory andpractice. Berlin, Heidelberg, New York : Springer, 1979 : 134. VOL. 66-B, No. 5, NOVEMBER 1984

6 644 B. M. WROBLEWSKI, A. VAN DER RIJT Ewald FC, Sledge CB, Corson JM, Rose RM, Radin EL. Giant cell synovitis associated with failed polyethylene patellar replacements. C/in Orthop 1976; 115: Harris NH, Miller AJ, Bounie R, Wilson 5, Kind P. Experimental investigation of fat embolism after the use of acrylic cement in orthopaedic surgery. J Bone Joint Surg [Br] 1975 :57-8: Harris WH, McCarthy JC, O Neill DA. Femoral component loosening using contemporary techniques of femoral cement fixation. J Bone Joint Surg[AmJ l982;64-a: Herndon JH, Bechtol CO, Cnckenberger DP. Fat embolism during total hip replacement : a prospective study. J Bone Joint Surg [Am] 1974; 56-A: Kallos 1, Enis JE, Gollan F, Davis JH. Intramedullary pressure and pulmonary embolism of femoral medullary contents in dogs during insertion of bone cement and a prosthesis. J Bone Joint Surg [Am] l974;56-a : Knight WE. Femoral plugging using cancellous bone. C/in On/sop 1982; 163: London JR, Charnley J. Subsidence of the femoral prosthesis in total hip replacement in relation to the design of the stem. J Bone Joint Surg [Br] 1980 ; 62-B : McLeish RD. Some aspects offorces in the human lower limb. PhD Thesis, Victoria University of Manchester, 1977 : 93. Mallory TH. A plastic intermedullary plug for total hip arthroplasty. C/in Orthop 1981 ; 155: Mendes DG, Walker PS, Figarola F, Bullough PG. Total surface hip replacement in the dog : a clinical and pathological study. J Bone Joint Surg [Am] l972;54-a: I Oh I, Carlson CE, Tomford WW, Harris WH. Improved fixation of the femoral component after total hip replacement using a methacrylate intramedullary plug. J Bone Joint Surg [Am] 1978 ;60-A : Stauffer RN. Ten-year follow-up study of total hip replacement : with particular reference to roentgenographic loosening of components. J Bone Joint Surg [Am] l982;64-a: Sutherland CJ, Wilde AH, Borden IS, Marks KE. A ten-year follow-up of one hundred consecutive Muller curved-stem total hip-replacement arthroplasties. J Bone Joint Surg [Am] 1982 ;64-A : Weber FA, harnley J. A radiological study of fractures of acrylic cement in relation to the stem of a femoral head prosthesis. J Bone Joint Surg [Br] 1975;57-B:297-30l. Wroblewski BM. Wear of high-density polyethylene on bone and cartilage. J Bone Joint Surg [Br] 1979:61-B : Wroblewski BM. Fractured stem in total hip replacement : a clinical review of 120 cases. Acta Orthop Scand 1982 ; 53 : THE JOURNAL OF BONE AND JOINT SURGERY