Centralization of the femoral component in cemented hip arthroplasty using guided stem insertion

Transcription

1 Arch Orthop Trauma Surg (1998) 117 : Springer-Verlag 1998 ORIGINAL ARTICLE G. Köster H.-G. Willert T. Ernstberger H.-P. Köhler Centralization of the femoral component in cemented hip arthroplasty using guided stem insertion Received: 8 August 1997 Abstract In order to improve the positioning of the stem within the femur, to centralize it within the cement and to achieve a complete and homogeneous cement mantle, a new hip endoprosthesis with guided stem insertion was developed. The femoral component has a longitudinal channel that takes up a guidewire which directs it during insertion into the centre. The guidewire is attached to the cement stopper which is positioned in the marrow cavity before applying the bone cement. The first 100 endoprostheses of this type with an observation period of at least 6 years were assessed radiologically and clinically. The clinical evaluation according to the hip scores of Merle d Aubigne and Harris revealed a marked improvement between preoperative and postoperative values for all criteria. On radiological assessment 94% of the stems had a neutral position within the femur; 98% of the stems were found to be ideally centred within the cement distally, 80% distally and proximally; 74% of the cement cuffs had a complete and homogeneous cement layer between 2 and 5 mm medially and laterally, while 25% had partially a dimension of more than 5 mm, predominantly proximally. In only 3 cases was one part of the cement mantle found to be less than 2 mm. The radiological follow-up was also documented according to the delineated zones of Gruen. It revealed zonal radiolucent lines in 15 cases, combined in 11 cases with reactive lines, never extending up to 4 zones out of 14. Five prostheses had subsided moderately between 2 and 3 mm, and only one 8 mm. None of these radiological signs was associated with clinical symptoms. There were five cement fractures. Two stems were symptomatic, radiologically loose and revised. Beside these two cases of aseptic loosening there was one septic case, so that in total 97% of the implants are still functioning well. G. Köster ( ) H.-G. Willert T. Ernstberger H.-P. Köhler Department of Orthopaedic Surgery, University of Göttingen, Robert-Koch-Strasse 40, D Göttingen, Germany Introduction Excentric positioning of implants, direct contact between implant and bone as well as irregularities and defects in the cement cuff promote fragmentation and deterioration of the bone-cement interface [1, 4, 9, 10, 12, 24]. Deterioration of the cement and subsequent osteolysis form one of the factors which cause loosening and failure of cemented hip endoprostheses [27 31]. In particular, a thin cement mantle medially, a cement defect at the tip of the femoral component and a varus or excessive valgus position lead to increased failure rates [3, 7, 11, 19 21]. In an attempt to improve and facilitate the centring of the stem within cement and femur in combination with a complete and homogeneous cement mantle, we began in 1988 to use a new endoprosthetic system with guided stem insertion. The clinical and radiological results of the first 100 consecutively implanted devices of this new type after 6 years are presented here. Patients and methods Implants The stem is made of the forged-steel alloy Protasul-S-30. It is collarless, straight, rectangular in cross-section and tapered. A central longitudinal channel takes up a guidewire which centres the stem distally during insertion into the cement. Proximally, the position can be monitored visually. The guidewire itself is attached to the cement stopper, which is placed in the marrow cavity before cement application (Fig. 1). The stem s rectangular cross-section stabilizes the prosthesis and the cement against rotational forces, while its rounded edges prevent unfavourable stress developing in the cement. The dimensions of the broaches preparing the implant bed are somewhat larger than those of the stem; the difference corresponds to the thickness of the required cement mantle. As the cement is inserted, the marrow cavity is closed proximally by a seal in order to pressurize the bone cement dough. The stem was implanted in combination with a socket that consists of ultra-high molecular weight (UHMW) polyethylene RCH 1000 (Chirulen) which is surrounded by a mesh of forged steel alloy (Protasul-S-30) wire. To achieve an optimal cement

2 426 Fig. 1 The stem is inserted centrally using a removable guidewire which is attached to the cement stopper The primary radiological evaluation, directly after the operation, assessed the position of the implant within the femur in anteroposterior and lateral views, the centralisation of the device within the cement, the thickness of the cement mantle at four delineated levels (Fig. 2) and its quality concerning homogeneity. The radiological follow-up registered changes of the implant s position like subsidence, varus or valgus tilting, changes of the cement mantle like fractures or debonding, and changes of the implant bed such as the formation of radiolucent or sclerotic lines, osteolyses, cortical thickening and pedestal formation. Radiological follow-up assessment in each case was performed according to the zones as defined by Gruen et al. [8]. Implants were classified as loose when they showed a complete radiolucent line, osteolyses, subsidence of more than 1 cm or a symptomatic cement fracture. Results Clinical results Fig. 2 The four relevant levels (proximal medial and lateral, distal medial and lateral) arround the stem for measuring the cement mantle thickness (arrows) and the seven zones for radiological evaluation in the anteroposterior view The clinical results of the implanted hips showed after 6 years a marked improvement from pre-operative to postoperative values. The Merle d Aubigné rating scale revealed this improvement in all three criteria. It increased from 2.2 to 5.4 for pain, from 2.6 to 5.1 for walking ability and from 3.4 to 5.2 for joint mobility. The Harris hip score rose from 28.7 to Subjectively, 52% of the patients were very satisfied, 44% satisfied and 4% dissatisfied with the results of surgery. The patients who were displeased experienced complications, which will be mentioned later. Radiological results filling for all sizes, the required amount of cement is 60 g for the femur and 40 g for the acetabulum, which should be used in every procedure. Patients Between August 1988 and April 1990, 120 total hip endoprostheses of this new design were implanted in 114 patients. The average age of the patients at the time of operation was 75.3 years, ranging between 70 and 90 years. The indications for the joint replacement were primary and secondary osteoarthritis (106 hips), rheumatoid arthritis (7 hips), femoral neck fracture (4 hips) and avascular necrosis (3 hips). Twelve patients died during the follow-up period because of an unassociated disease with a well functioning prosthesis. Six patients were lost to follow-up or could not be documented completely. Thus, 96 patients with 100 endoprostheses were evaluated with an average observation period of 6.3 years, ranging between 6 and 7 years. Methods The clinical evaluation comprised an assessment according to the hip scores of Harris and Merle d Aubigné in addition to a subjective evaluation by the patient. The primary radiological assessment of the femoral stem showed in 94% a neutral position within the femur. A slight varus position was found in 3 cases, a valgus position in 3, never extending more than 10 deg. Concerning the position from the lateral view, 69% had a neutral position while in 28% the tip of the stem was aiming slightly to the dorsal cortex and in 3% to the ventral one. In 98% an ideally centric position within the cement distally was achieved, whereas 80% were centered distally and proximally. Only two stems were distally not centred because of a dislocated cement stopper. The cement mantle of the stem was measured at the same level in the four zones, proximal lateral and medial and distal lateral and medial. Overall, the mean thickness was 4.8 mm, ranging between 0 and 15 mm. On average, in 74% of the stems the cement layer had a thickness between 2 and 5 mm at all four levels. Only at level I was it smaller than 2 mm in two cases and at level Table 1 Distribution of cement mantle thickness at the four levels of the femoral stem < 2 mm 2 5 mm > 5 mm I 2% 63% 35% II 79% 21% III 1% 88% 11% IV 67% 33%

3 427 Fig. 3a c Preoperative X-ray (a) and radiographic check after implantation of the CF prosthesis in a 71-year-old woman immediately postoperatively (b) and 5 years later (c) a a b b c c III in one case (Table 1). Concerning homogeneity, there were only 12 cement mantles which showed air inclusions. In one case a primary debonding between implant and cement layer was visible, obviously caused by intraoperative movement of the stem before hardening of the cement. The radiological follow-up revealed only a few changes of the implant bed, implant position and cement mantle (Figs. 3 and 4). Radiolucent lines always appeared zonal, Fig. 4a c Radiographic course of a 72-year-old woman undergoing implantation of a CF prosthesis after bilateral femoral neck fracture because of severe osteoporosis. X-rays preoperative (a), postoperative (b) and after 7 years (c) were never complete and did not exceed 2 mm. They occurred in 15 components and were combined with sclerotic lines in 11. This phenomenon was generally localised to 2

4 428 zones and never extended up to 4 zones. Predominantly it was found in zones I, III and V. Additionally, 6 prostheses showed pedestal formations and 6 subsided moderately (between 2 and 3 mm), with one exception where the subsidence measured 8 mm. All pedestal formations were combined with subsidence. There was no varus or valgus tilting. Five cement fractures occurred. Three of them were asymptomatic. Two showed osteolyses, were classified as loose and revised after 4 and 5 years, respectively. The findings at revision disclosed that early loosening in these cases was caused by a false cementing technique: one case showed primary debonding between cement and implant, the second had a greater cement defect caused by the application of insufficient pressure. There were no relevant changes at the site of the cup which might have been able to influence the result of the stem. In particular, there was no significant wear and no aseptic loosening. Regarding heterotopic ossifications, 86% of the joints showed none or only small islands. Thirteen percent was classified as stage Brooker II without any clinical relevance concerning pain or range of motion. Only one hip with Brooker III had a mild limitation of motion. There was no Brooker IV. Complications included one trochanter tear-off, one intraoperative femoral fracture requiring cerclage, one transient femoral nerve lesion, one joint dislocation, one septic loosening and three deep vein thromboses with one pulmonary embolism. Discussion Since the introduction of polymethylmethacrylate for fixing components in hip arthroplasty 35 years ago by John Charnley [5], many modifications have been suggested to improve the long-term function of the endoprostheses. Not only different designs but also varying cementing techniques have been tried in clinical application. While different shapes, biomaterials and surface designs of cemented prostheses are all being wed, it is now generally accepted that the quality of the cementing technique is one of the most important factors for durability [2, 9, 13, 16, 20, 21]. Especially in elderly patients where a revision is less likely to be expected and primary stability is necessary for immediate weight-bearing, a cemented endoprosthesis seems to be preferable. However, the persisting risk of loosening because of cement deterioration and subsequent osteolysis should be minimized. It is also widely accepted now that a neutral position of the implant in the femur and a central position within the cement as well as a homogeneous cement mantle are important factors in preventing early failure [4, 9, 12, 21]. Most often, the area of osteolysis corresponds to either a focal defect in the cement mantle, a cement fracture or an area of very thin cement [10, 14]. Therefore, the aim in developing a new cemented endoprosthesis system was an improvement in positioning the components within the implant bed and an improvement in the quality of the cement mantle. The radiological evaluation of this system revealed in the majority of cases an ideal centring of the components and a good quality of the cement mantle on the femoral side. The percentage of neutral positioning is comparatively high [21]. Some femoral components showed for a few levels that the cement layer was thinner than 2 mm. However, in the majority of the implants, the cement mantle measured between 2 and 5 mm, which seems to be important for a good outcome [7]. Especially at the medial diaphysis where a thin cement mantle is said to be harmful [24], it never measured less than 2 mm. The radiological follow-up revealed a comparatively low number of radiolucent lines arround the stem at the bone-cement interface. They were never continuous. Such lines are well described with a higher incidence in other cemented prostheses [8, 22, 25], even when using modern cementing techniques [21]. Although it is not yet clear what causes these lines [6, 21], they have been observed in later follow-ups. The sclerotic lines were usually combined with radiolucent lines. The few pedestal formations in some femoral components were combined with subsidence of the stem. The formation of radiolucent or sclerotic lines, pedestals and subsidence were not related to clinical symptoms and are known as signs without clinical relevance when looking at long-term results. Only two cement fractures were symptomatic and combined with osteolyses: one seen in a stem which must have been moved during cement polymerisation because of a gap visible between the implant and cement mantle on the postoperative X-ray and the other appearing in a cement mantle with a defect. The other three cement fractures were asymptomatic and not combined with other radiological signs of loosening. Cement fractures are known in other prostheses [22, 26], and the incidence of local osteolyses seems to be higher in these areas [10]. But as described by Weber and Charnley [26], they usually remain asymptomatic and have a good prognosis. The fractures in two patients who became symptomatic and endangered could have been avoided by a proper cementing technique. The heterotopic ossifications showed no marked difference in quantity and extension to other endoprostheses [21 23, 25]. The rate of complications has to be assessed with regard to the age profile. Especially in thrombembolic complications the average age of 75.3 years is relevant [17, 18]. The results reveal that the required effects of centralising the femoral component and obtaining a homogeneous cement mantle were achieved. The 6-year results support further clinical application. References 1. Anthony PP, Gie GA, Howie CR, Ling RSM (1990) Localized endosteal bone lysis in relation to the femoral component of cemented total hip arthroplasties. J Bone Joint Surg [Br] 72:

5 Barrack RL, Mulroy RD Jr, Harris WH (1992) Improved cement techniques and femoral component looening in young patients with hip arthroplasty. A 12-year radiographic review. J Bone Joint Surg [Br] 74: Beckenbaugh RD, Ilstrup DM (1978) Total hip arthroplasty. A review of three hundred and thirty-three cases with long follow-up. J Bone Joint Surg [Am] 60: Carlsson AS, Gentz CF, Linder L (1983) Localized bone resorption in the femur in mechanical failure of cemented total hip arthroplasties. Acta Orthop Scand 54: Charnley J (1961) Arthroplasty of the hip. A new operation. Lancet 1: DeLee JG, Charnley J (1976) Radiological demarcation of cemented sockets in total hip replacement. Clin Orthop 121: Ebramzadeh E, Sarmiento A, McKellop HA, Llinas A, Gogan W (1994) The cement mantle in total hip arthroplasty. J Bone Joint Surg [Am] 76: Gruen TA, McNeice GM, Amstutz HC (1979) Modes of failure of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop 141: Harris WH, Davies JP (1988) Modern use of modern cement for total hip replacement. Orthop Clin North Am 19: Huddlestone HD (1988) Femoral lysis after cemented hip arthroplasty. J Arthroplasty 3: Kristiansen B, Jensen JS (1985) Biomechanical factors in loosening of the Stanmore hip. Acta Orthop Scand 56: Lee ALC (1991) Can cementing technique affect long-term results of total hip replacement. Orthop Rel Sci 2: Ling RSM (1991) Cementing technique in the femur. Tech Orthop 6: Maloney WJ, Jasty M, Burke DW, O Connor DO, Zalenski EB, Bragdon C, Harris WH (1989) Biomechanical and histologic investigation of cemented total hip arthropalsties. A study of autopsy-retrieved femora after in vivo cycling. Clin Orthop 249: Maloney WJ, Jasty M, Rosenberg A, Harris WH (1990) Bone lysis in well fixed cemented femoral components. J Bone Joint Surg [Br] 72: Mulroy RD Jr, Harris WH (1990) The effect of improved cementing techniques on component loosening in total hip replacement. An 11-year radiographic review. J Bone Joint Surg [Br] 72: Müller KH (1981) Lokale Komplikationen nach totalem Hüftgelenkersatz. Unfallheilkunde 84: Müller KH (1984) Ergebnisse und Perspektiven des künstlichen Hüftgelenkersatzes in der Traumatologie. Unfallheilkunde 87: Poss R, Brick GW, Wright RJ, Roberts DW, Sledge DW (1988) The effects of modern cementing techniques on the longevity of total hip arthroplasty. Orthop Clin North Am 19: Roberts DW, Poss R, Kelly K (1986) Radiographic comparison of cementing techniques in total hip arthroplasty. J Arthroplasty 1: Rusotti GM, Coventry MB, Stauffer RB (1988) Cemented total hip arthroplasty with contemporary techniques. A five-year minimum follow-up study. Clin Orthop 235: Salvati EA, Wilson PD Jr, Jolley MN, Vakili F, Aglietti P, Brown GC (1981) A ten year follow-up of our first one hundred consecutive Charnley total hip replacements. J Bone Joint Surg [Am] 63: Schulte KR, Callaghan JJ, Kelley SS, Johnston RC (1993) The outcome of Charnley total hip arthroplasty with cement after a minimum twenty-year follow-up. The results of one surgeon. J Bone Joint Surg [Am] 75: Star MJ, Colwell CW Jr, Kelman GJ, Ballock RT, Walker RH (1994) Suboptimal (thin) distal cement mantle thickness as a contributory factor in total hip arthroplasty femoral component failure. A retrospective radiographic analysis favoring distal stem centralization. J Arthroplasty 9: Sutherland CJ, Wilde AH, Borden LS, Marks KE (1982) A ten year follow-up of one hundred consecutive Müller curved-stem total hip replacement arthroplasties. J Bone Joint Surg [Am] 64: Weber FA, Charnley J (1975) A radiological study of fractures of acrylic cement in relation to the stem of a femoral head prosthesis. J Bone Joint Surg 57: Willert HG (1987) Die Zerrüttung des Zementköchers. In: Willert HG, Buchhorn G (eds) Knochenzement. Werkstoff, klinische Erfahrungen, Weiterentwicklungen. Aktuelle Probleme in Chirurgie und Orthopädie. Verlag Hans Huber, Bern, pp Willert HG, Puls P (1972) Die Reaktion des Knochens auf Knochenzement bei der Allo-Arthroplastik der Hüfte. Arch Orthop Unfall Chir 72: Willert HG, Ludwig J, Semlitsch M (1974) Reactions of bone to methacrylate after hip arthroplasty: a long-term gross, light microscopic, and scanning electron microscopic study. J Bone Joint Surg [Am] 56: Willert HG, Buchhorn G, Hess T (1989) Die Bedeutung von Abrieb und Materialermüdung bei der Prothesenlockerung an der Hüfte. Orthopäde 18: Willert HG, Bertram H, Buchhorn G (1990) Osteolysis in alloarthroplasty of the hip the role of bone cement fragmentation. Clin Orthop 258: