Chỉnh hình xương đùi ppsx

Vol 7, No 6, November/December 1999 349 The outcome of primary cemented total hip arthroplasty is dependent on good operative technique. Me- ticulous surgical craftsmanship, not just the presence or absence of cement or the use of a specific implant, plays an important role in prosthetic longevity. Most research to date on cemented arthroplasty has focused on means of optimizing the bone-cement interface, the cement mantle thickness, the biomechanical properties of the cement, and the implant design. 1-3 These advances have certainly improved the success of this procedure, so that we can now expect failure rates of only 10% to 15% at 15 to 20 years. 4 Unfortunately, research has neglected preparation of the bone in the construct, except in demon- strating that pressurized cement penetration into a debris-free surface is necessary for a durable interface. Controversy has recently emerged regarding the optimal method of bone preparation for a cemented femoral stemÑspecifically, whether there is a need for both reaming and broaching The intro- duction of these two techniques was meant to improve long-term performance. However, the effica- cy and necessity of reaming and/or broaching in cemented hip replacement has never been scientifically established. Most surgeons who perform hip arthroplasty today use some combination of reaming and broaching to prepare the femoral canal for cementation, depending on the implant system used and the experience of the surgeon. It is difficult, however, to establish how and why this technique developed. The literature is replete with often mis- leading and unfounded recommendations regarding both the benefit Dr. DiGiovanni is Assistant Professor of Orthopaedic Surgery, Brown University School of Medicine, Providence, RI. Dr. Garvin is Professor of Orthopaedic Surgery, University of Nebraska Medical School, Omaha. Dr. Pellicci is Associate Professor and Vice Chief, Hip and Knee Service, The Hospital for Special Surgery, New York, NY. Reprint requests: Dr. DiGiovanni, University Orthopaedics, 2 Dudley Street, Providence, RI 02901. One or more of the authors or the departments with which they are affiliated have received something of value from a commercial or other party related directly or indirectly to the subject of this article. Copyright 1999 by the American Academy of Orthopaedic Surgeons. Abstract Surgical techniques continue to be refined to improve the results of primary cemented total hip arthroplasty. Although there has been much research in the areas of cementation and implant design, little work has specifically addressed how bone preparation can be optimized on the femoral side. On the basis of available scientific data, it appears that the broach-only system has several potential advantages over the traditional ream-and-broach technique. Broaching is usually faster, leaves behind more bone stock, and may improve both microinterlock and macrointerlock. Additionally, the excess bone resulting from broaching without reaming does not seem to compromise fixation at the bone-cement interface. Such differences may become even more important as the indications for cemented hip arthroplasty broaden to include increasingly younger and more active patients, because revision in these individuals is likely. In most cases, reaming is probably counterproductive, although it may be advantageous when used to open the femoral canal, to prevent varus stem orien- tation, and to manage sclerosis or deformity of bone due to a preexisting hip dis- order or the presence of internal fixation devices. Regardless of which method is chosen, good bone surface cleansing and cement penetration remain paramount. More studies comparing reamed and nonreamed preparation are necessary to resolve this controversial issue definitively. J Am Acad Orthop Surg 1999;7:349-357 Femoral Preparation in Cemented Total Hip Arthroplasty: Reaming or Broaching? Christopher W. DiGiovanni, MD, Kevin L. Garvin, MD, and Paul M. Pellicci, MD Perspectives on Modern Orthopaedics and the outcome of these different forms of canal instrumentation. Review of the hip registry at the Hospital for Special Surgery, where over 1,600 total hip replacements are performed each year, identified more than 10 different manufactur- ers of cemented femoral implant designs. The instructional manuals accompanying these implants were scrutinized, but no agreement was found among manufacturer recommendations. Although the stems were considered modern prostheses with little design distinction, recommendations for bone preparation ran the spectrum from broaching only to reaming and broaching to various modifications of each. In no case was any scientific reference provided to justify a given technique. It became clear that the guidelines of the orthopaedic man- ufacturing industry are based on practice and experience rather than scientific principles. This dearth of scientific information has fueled the debate regarding the most appropriate form of canal preparation in cemented hip replacement. How- ever, a review of the available basic science and clinical data that com- pare reaming and broaching with broaching alone can provide an accurate representation of the advantages and disadvantages of each method of bone preparation in cemented arthroplasty. Role of Instrumentation Some form of femoral canal preparation is required before the intro- duction of cement and a femoral component when performing a total hip arthroplasty. Various rationales have been proposed for each type of canal preparation, many of which can be challenged on closer inspec- tion. However, the outcome of cemented hip replacement has been unequivocally proved to be dependent on certain details in technique. The best reason to instrument (i.e., ream or broach) the femoral canal is to obtain an optimal interface. Many studies have demonstrated how important the stability of the bone-cement and prosthesis- cement interfaces is to long-term performance. 1 In fact, the concept of cement osseointegration was considered as early as the 1970s by Charnley, among others. Pioneer- ing research by Harris and others 5,6 documented enhancement of interface durability and clinical outcome by the use of successive generations of cement technique (although this is not true of all third-generation cement designs). Another good reason to prepare the bone in the proximal femur is to maintain a cement mantle thickness of at least 2 mm, devoid of defects. Many finite element and strain- gauge analyses, as well as autopsy studies, have shown that this mini- mizes cement stress, strain, and the incidence of fracture, thus decreasing the occurrence of mechanical failure. 2 A third proven requirement for successful arthroplasty is a centered component in proper version. Ap- propriate version avoids impinge- ment and decreases dislocation, and centering obviates thin lateral mantle defects, which some researchers feel can deteriorate under stress or can create pathways for particulate debris. 7 While these goals legitimize preparation of the proximal femoral canal for total hip arthroplasty, some of the arguments specifically advocating reaming and broaching in the literature have questionable validity. For example, having one reaming or broaching system for both cemented and uncemented devices just to minimize decision making for the surgeon and to make inventory convenient for manu- facturers is a poor reason to ream and broach every cemented femur. Additionally, the most common yet least referenced remark found in the literature to support reaming and broaching is the need to remove all loose, weak, cancellous bone. 8-10 This is based on an unproven belief that maintenance of anything other than paraendosteal cancellous bone tends to weaken or otherwise render mechanically inadequate the bone-cement interface. It probably accounts in large part for the controversy surrounding bone preparation. Historically, the concept of cancellous bone removal in cemented hip replacement dates back to CharnleyÕs experience. 11 He felt that cancellous bone had little osteogenic potential irrespective of its blood supply. Charnley encouraged curettage of all medullary cancellous bone, particularly anteromedially and posteriorly, believing it to be incapable of any significant load- bearing capacity. Although it is difficult to argue with CharnleyÕs results, it is now known that native cancellous bone has tremendous osteoconductive, osteogenic, and osteoinductive potential. Since that time, many authors have stated that they agree with Charnley, although the data they present may not totally support their conclusions. For example, the authors of a radiographic outcome study followed more than 800 hips for 21 years and correlated multiple variables, such as stem ori- entation, canal fill, cement mantle thickness, and cancellous bone thickness, with survival. 9 The best results (in terms of loosening or progressive radiolucent lines) were noted when there was less than 2 mm of proximal-medial cancellous bone visualized on postoperative radiographs. The authors stated that progressively worse results could be expected as more cancellous bone was left behind. How- ever, many of the hips used in for- mulating these extrapolated and unproven outcomes were omitted Femoral Preparation in Cemented Total Hip Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 350 from comparison due to inadequate length of follow-up or missing information on the status of the cancellous bone. Furthermore, the P values (<0.05) for these bone variables were not only barely significant statistically but were also subject to other, unaccounted for confounding variables, such as radiographic obliquity. Another example is a clinical study in which 30 femoral stem specimens were analyzed after revision for mechanical failure. 8 The authors noted evidence of both cement fracture and bone micro- fracture and concluded that initial fixation was contingent on an adequate interface, which necessitated Òremoval of poor cancellous bone that would tend to weaken the interface.Ó Although the authors suggested many scientifically validated means to obtain an adequate interface, that comment represents their only unreferenced and unsupported example. Such statements represent the opinion of the authors rather than scientific conclusions based on appropriate experimental evidence. Some form of proximal femoral instrumentation is thus reasonable and necessary to ensure that certain scientifically substantiated goals for achieving successful hip replacement are met. The question then becomes whether both reaming and broaching should be performed to accomplish these goals and, if so, how much of each. Another question is whether reaming brings us one step closer to a revision surface by decreasing macrointerlock and microinterlock or one step farther from revision by eliminating unstable or incompetent cancellous bone. These issues remain unresolved. Functions of Reaming and Broaching Various functions of reaming are considered standard in hip replacement surgery. A canal finder is commonly introduced to identify the intramedullary portion of the femur. It is also used to remove bone from the greater trochanteric area (laterally) to prevent varus positioning of the component. Reaming may be necessary to open a pathologically small canal (as in developmental hip dysplasia) so as to allow fitting of a desired implant. (It should be borne in mind, however, that the emphasis should be on fitting the implant to the femur and not vice versa.) It can also help remove impeding scle- rotic areas in the event of preexisting hardware. These techniques remain relatively unchallenged in the orthopaedic literature. They do not un- necessarily compromise endosteal bone stock, and they may facilitate the achievement of goals often unobtainable by other means, such as broaching. Debate revolves around the more traditionally described purpose of reaming: to further remove incompetent bone and provide the distal canal dimensions necessary for component implantation. Curettage of cancellous bone is often performed concomi- tantly to accomplish these tasks. This combination is subject to even greater criticism when considering routine total hip replacement with the use of standard-length stems. Broaching has three functions: opening the canal for an adequate cement mantle, ensuring proper alignment, and facilitating intraop- erative limb-length measurement or trial reduction. There is general agreement on the need for a broach to accomplish these objectives. Systems dependent solely on judi- cious broaching usually provide adequate distal canal dimensions for their implants, obviating the need to remove any additional cancellous bone by adjuvant reaming. One criticism of broaching is the undeniable mismatch that exists between the anatomy of the human femur and the design and size limi- tations of any implant system. As several authors have pointed out, surgeons often attempt to stan- dardize their patients by using identical broach sizes in patients with vastly different canal geome- tries, which leads to markedly different amounts of bone removal. 2,10 This variability potentially con- founds investigation of broach- only techniques. Reaming Versus Broaching: Clinical Outcome Regardless of this debate, it is clear that good clinical data exist demon- strating effective long-term results with the use of both reaming and broaching as well as broaching- only systems. The experience at the Hospital for Special Surgery, where until recently many surgeons have been both reaming and broaching for more than 10 years, is an example of clinical success with this technique. Some surgeons at that institution continue to ream and broach because they were trained with that technique and have had good clinical results with it. Others have changed to broach-only systems in an effort to preserve bone stock and improve interdigitation. 12 Various groups continue to support the ream (or curettement) and broach concept on an outcomes basis. 13 Many researchers who favor reaming and broaching cite findings of femoral stem fractures in a retro- spective study of predominantly T-28 stems implanted with broaching alone. 14 The authors of that study concluded that inadequate proximal cancellous bone removal was responsible for the early proximal loosening and cantilever bend- ing that caused stem fracture despite good distal fixation. Although this is one possible theory, numerous Christopher W. DiGiovanni, MD, et al Vol 7, No 6, November/December 1999 351 other factors likely played a role. For example, the end result in many of these hips was trochanteric non- union or gross limb-length discrep- ancy. In addition, 53% had cement voids, and 43% demonstrated calcar resorption. Most significantly, 69% of the stems had also been placed in varus, although this latter difficulty could have been related to the use of a broach-only system. Additionally, almost half of the patients had some degree of polyethylene wear, and it is plausible that the proximal loosening found in this study was predominantly due to debris-generated osteolysis, which is known to occur in a gravity-dependent manner. Finally, there was no adequate control group, and the implant used in most patients has had a poor track record. In fact, multiple previous studies of stem fracture and mechanical failure have suggested that the predominant mode of failure was improper insertion of cement and often some combination of metal defects, malpositioning, and/or patient weight in excess of about 80 kg. 15 Numerous other reports have nonetheless demonstrated superior clinical results with ream-and-broach designs with relatively long-term follow-up. For example, Weber, 16 noted a 92% rate of good or excellent outcome at 7- to 11-year follow-up. The results obtained with a number of broach-only systems have also been reported in the literature. For example, Kavanagh et al 17 reported excellent 20-year follow-up results with a broach-only system at the Mayo Clinic. The probability of survivorship of the 333 Charnley- Thackray devices used in that study was 84%. The rates of loosening, revision, and failure were linear over this time period, and analysis of the modes of femoral failure or loosening at 15 years revealed that most instances resulted from cement fatigue failure rather than bone-cement interface failure. One would have expected high rates of proximal loosening, stem fracture, and, most important, failure at the bone-cement interface if excess cancellous bone left proximally was responsible for early failure. Good results at long-term follow-up have also been reported in a number of other studies in which broach-only systems were used. 18 From the perspective of functional outcome, therefore, it appears that either means of preparing the cemented femur offers acceptable alternatives with good clinical results. Resolution of this issue may, at least on these grounds, be irrelevant; however, there are other important factors to consider. Reaming Versus Broaching: The Data The controversy surrounding reaming and broaching results in part because there are adherents for each of two diammetrically opposed concepts: (1) the need to maintain all possible bone and (2) the need to eliminate any excess bone. The literature is confusing on this issue. The authors of one cadaveric study of trabecular bone concluded that a twofold increase in shear strength could be found within 3 mm of the trabecular endosteal attachment. 19 However, they mere- ly state what is intuitive: namely, that bone gets stronger closer to its attachment site. Neither that study nor CharnleyÕs preceding work addresses the issue of whether bone may be sufficient for structural support at greater distances from the endosteum, especially when surrounded by a cement matrix. Beckenbaugh and Ilstrup 20 concluded in their 4- to 7-year follow- up of 253 Charnley procedures that failure to remove the cancellous bone or to pack cement in the proximal medial or lateral femoral canal correlated with a two- to threefold increase in loosening. After considering this in combination with all the other potentially causative variables, such as canal size, stem position, and cement technique, however, they conceded that statis- tical differences were difficult to delineate. Many still support removing weak cancellous bone because they believe it is incapable of supporting a cemented implant. However, recent data on the impaction grafting technique, which could be considered an extreme form of leaving unstable (i.e., dead or allograft) bone behind, suggest otherwise. 21,22 Not only have most of these implants continued to perform fairly well at intermediate-term follow- up in those studies, but the stems that have gone on to subside usually have done so at the prosthesis- cement interface rather than at the bone-cement interface. Despite the influence of construct design, the bone-cement interface is still where one would expect failure if a complex becomes incapable of mechanical support. One can certainly counter that as- sumption by drawing a distinction between the innate structure of any remaining weak, mechanically insufficient autogenous bone and a densely packed shell of allograft bone added to the femur. Such a comparison is appropriate because it is technically difficult and time consuming (hence, often questionable) to achieve the compression necessary for mechanically sound impaction grafting, particularly when the femoral envelope is poor or lengthy. Furthermore, once a construct is surrounded by cement, its initial differential mechanical stability may be of absolutely no importance. Noble 10 has advocated Òcon- trolledÓ reaming, while acknowl- edging (1) that there is little cancellous framework below the lesser Femoral Preparation in Cemented Total Hip Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 352 trochanter to begin with; (2) that the indigenous bone is capable of significant bond strength, even in the elderly; and (3) that the diaphy- seal region is an additional safe- guard against torsional failure in the event of more proximal loosening. It might be reasonable to ask then: if all this is so, why ream at all? Maloney 23 has recommended against any reaming for cemented hip arthroplasty. While having the strongest available (i.e., paraendosteal) porous bone exposed to cement is plausible in theory, in reality bone strength derives from both quality and quantity. Since most current hip replacements are performed in older individuals, this quality is not often present; therefore, why affect quantity as well? Furthermore, some authors believe that even more important than microinterlock is the bulk shape of the bone cavity, or Òconstraint for fixation.Ó 3,24 This geometry is obviously inversely proportional to the amount of instrumentation (i.e., reaming) used. A number of recent basic scientific studies have favored broach- only systems. They suggest that native cancellous bone is capable of considerable bond strength and structural support, even in elderly individuals with osteoporotic bone. Two papers at the 1993 Annual Meeting of the American Academy of Orthopaedic Surgeons compared outcomes of canal preparation with the use of various forms of reaming and/or broaching. Newman et al 25 evaluated fully toothed broaching versus size-matched distal reaming followed by proximal broaching. Identical femoral implants were then cemented into five matched pairs of fresh cadaveric femora. Modern cement technique was uti- lized, and all specimens were allowed to cure for 24 hours, were sectioned into 1-cm-thick slices, and were then subjected to mechanical testing for evaluation of the bone- cement interface. The reamed specimens demonstrated a 22% (P<0.017) lower peak load to failure and 39% (P<0.041) less work to failure compared with the broached specimens. Balu et al 26 compared the outcome with flexible reaming, rigid conical reaming, and no reaming (control) in a similarly designed investigation. After preparation of 14 matched femora, cement was injected and allowed to cure for 48 hours. The specimens were then sectioned in 1-cm-thick slices, and the constructs were independently loaded cyclically in fully reversed tension and compression at a fre- quency of 0.5 Hz until failure in shear. Compared with nonreamed specimens, an average 23.3% ± 3.2% loss of the rough endosteal surface occurred after only a 1-mm increase in canal diameter with flexible reaming and a 7.0% to 14.6% loss with rigid reaming, the latter being dependent on insertion technique. The authors also noted lower shear strength at the bone-cement interface with flexible reaming (49% [P<0.001]) and with rigid reaming (70% [P<0.0001]) compared with control values (2.93 ± 0.95 MPa). Furthermore, the decrease in the shear stress required for 100 µm of displacement in these specimens was 43% after rigid reaming and 54% after flexible reaming. Nonreamed specimens had bone-cement interface strengths adequate for supporting cemented prostheses even in weak cancellous bone. The authors of both studies concluded that reaming lowers the quality of bone-cement interface fixation strength compared with broaching, and recommended against reaming in preparing for cemented femoral replacement. Although it is difficult to directly apply these in vitro data to clinical situations, the remodeling seen after impaction grafting suggests that time should not be a factor as long as the bone within the cement composite carries some of the load. 21 This concept is sup- ported by Dohmae et al, 27 who experimentally quantified progressive loss of shear strength at the bone-cement interface between primary arthroplasty and subse- quent revisions in human femora. After the first revision, this value decreased dramatically to 20.6% and fell further to 6.8% after the second revision. A recent laboratory investigation evaluated canal preparation in cadaveric femora through the use of a special wet-grinding process with diamond cutters. 28 Its effect on the residual osseous architecture was compared with that of a traditional rasping technique. This atraumatic diamond instrumentation was found to preserve the native cancellous architecture and its surrounding vasculature. Rasp- ing morsellized and eliminated the cancellous bone required for cement interdigitation. Although cancellous bone itself cannot be considered an adequate load bearer, a construct stiffened by means of in- clusion of cement was found to be highly capable of successful load bearing. A number of studies have con- firmed that success of cemented hip arthroplasty directly correlates with preservation of the osseous framework and is dependent on uniform cement interdigitation to avoid stress shielding (Fig. 1). 29 In an ani- mal study, Breusch and Draenert 28 also disproved the notion that bone trabeculae embedded in polymethylmethacrylate are destined for atro- phy and fibrous substitution. They demonstrated histologically that polymethylmethacrylate cannot generate heat in smaller (<1 mm 2 ) cancellous honeycombs; the trabeculae subsequently shrink, leaving an area capable of rapid revasculari- zation and remodeling. Christopher W. DiGiovanni, MD, et al Vol 7, No 6, November/December 1999 353 Other studies also suggest that aggressive reaming may lead to failure of cement fixation. For example, two recent macroscopic anatomic evaluations of the endosteal surface of the proximal femur have indicated that bone geometry is indeed important in bone-cement interface failure. 5,30 In both studies, specimens were brushed, lavaged, cemented, and then sectioned axi- ally and loaded. In the study by Bean et al, 30 each specimen was later recut coronally and sagittally prior to mechanical testing to allow regional evaluation of the bone-cement interface on the anterior, posterior, medial, and lateral surfaces without the confounding variable of endosteal irregularity. Their results indicated that the interfacial shear strength was highest medially (by 30%) and lowest laterally; the values in the anteroposterior regions were intermediate. The differences were statistically significant. In the study by Bugbee et al, 5 a closed system was used. Interfacial shear strength did not increase from proximal to distal, presumably because cement penetration and interdigitation were more uniform due to prevention of proximal leakage. The results of these two studies point out the variability in bone- cement interface strength of the proximal femur and the importance of maintaining trabecular patterns. This is especially necessary when such geometry is perpendicular to the shear plane, hence providing maximal resistance to stress. They also indicate how vital proximal medial metaphyseal bone is. Iron- ically, this is where many surgeons choose to curette and remove most of the loose cancellous bone. This habit is likely engendered by the belief that ÒremovableÓ bone should be removed and is perpetuated by the fact that this is the region with the greatest visibility and accessi- bility. Bone-Cement Osseointegration Adequate cement osseointegration usually requires 8 to 12 weeks to mature after the index arthroplasty. Some researchers support reaming to remove the dead, interposed bone debris, which they believe obstructs cement osseointegration. While this may be true, to our knowledge no one has been able to demonstrate that ingrowth of surrounding bone becomes easier and improves outcome under these circumstances. Additionally, this concept does not address the fact that, even if only stable, intact bone is left behind, there will still be a 2- to 3- mm area of osteonecrosis due to adjacent monomer and heat pro- duction during cement curing. 31 Considering that only about 5 mm of cancellous bone remains after initial canal preparation, any modification in preparation that further eliminates this bone before cementing makes even less sense. Al- though there is some evidence to suggest that successful osseointegration occurs only in a sufficiently stable mechanical environment, impaction grafting results seem to contradict this evidence. A few studies have shown that, despite a much greater interface of both dead and foreign bone interposed between cement and host bone, impaction grafting still appears to demonstrate impressive remodeling and at least partial incorpora- tion of the morsellized allograft on histologic sectioning. 21 Cement osseointegration is evidently unim- paired in this setting, and it is therefore difficult to expect otherwise in the less disturbed biologic milieu of primary joint replacement, although this comparison Femoral Preparation in Cemented Total Hip Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 354 Fig. 1 Anteroposterior (A) and lateral (B) radiographs of the hip of a 68-year-old man who underwent total hip replacement for osteoarthritis. A broach-only hip system was used. Note the uniform cement mantle around the stem and the thickness of the cancellous bone that remains after appropriate broaching. A B may be flawed because of the inherent differences in these techniques. Charnley and others have also found that bone can be in inti- mate mechanical contact with cement for prolonged periods of time without the development of an interposed soft-tissue mem- brane. 32 Mechanical Failure An important factor when considering how much bone should be left in the femoral canal is delineat- ing whether cement or bone fails first. The best biomechanical con- clusion that can be drawn from a number of articles on this compli- cated subject is that the weaker part essentially fails first. 8,33 With large cement intrusions in porous bone, the bone can be expected to fracture first. If small intrusions exist in relatively dense bone, the cement can be expected to be the initial site of failure. The actual in vivo situation probably lies some- where between these extremes and is dependent on multiple patient and surgeon variables. Hence, if larger quantities of remnant loose cancellous bone are left behind, the possibility of increased micromotion arises. Kaufer et al 34 have ascribed micromotion at the bone-cement interface to trabecular resorption and consequent diminution of mantle support. They believe this mechanical disruption succeeds the necrotic stage of implantation, and that stability at this point relies on centrifugal interface anchorage until the newly remodeled local support structure forms. Whatever the mechanism, there is likely to be some relative increase in micromotion if more weak, ÒunstableÓ bone remains. Although mechanical failure at the bone-cement interface has been shown to be unequivocally related to both poor bone preparation 16,19,30 and cement pressurization, 5,33 it has not necessarily been shown to be secondary to initial poor bone quality. Ling 35 has stated that Òdue to differences in elastic moduli in cemented [total hip arthroplasty], one cannot be concerned with prevention of all movement (impossi- ble), but only with unacceptable movement.Ó He quotes Swanson in defining the acceptable situation as Òcyclic displacement of the implant relative to bone . . . if its amplitude does not increase progressively with each successive application of load, and it does not give rise to pain or bony destruc- tion.Ó Given the data from these previous studies and the outcomes of impaction grafting, it is unlikely that the possibly small increase in micromotion would have any significant clinical effect. Such data clearly contradict NobleÕs theory that Òall weak trabeculae must be removed [from the metaphysis] to leave a structure capable of supporting the cemented prosthesis.Ó 10 A study comparing micromotion and migration in specimens from primary cemented, cementless, and impaction-grafted specimens in human cadaveric femora revealed little difference between the cemented and impaction-grafted specimens after cyclic load testing. 36 The largest changes (often by an order of magnitude) occurred in rotation and translation in the non- cemented specimens. The results were statistically valid in almost all cases. Even with aggressive load- ing, the greatest micromotion found in the allograft cemented recon- structions barely exceeded what is considered desirable for bone for- mation (0 to 28 µm) by 4 µm. Heiple et al 24 found a strong cor- relation between inherent cancellous bone shear strength and bone- cement interface strength (P<0.001). This would indicate that weakened bone left behind could render the bone-cement interface less durable. Interestingly, in a recent presen- tation, Chareancholvanich et al 37 challenged how femoral canals should be prepared for total hip arthroplasty. They tested the stability of primary cementless femoral implants by using the compaction of existing cancellous bone rather than removal via toothed broaching and/or reaming as a method of preparation. The mechanical stability of the femoral implants in this setting was impressive, suggesting that perhaps we should not be removing any bone at all in the course of canal preparation, but rather only pushing it aside. Al- though the concept is intriguing, their data await corroboration. Treatment of Retained Bone Properly preparing the bone left behind after reaming or broaching is of paramount importance to the longevity of cemented prostheses. A number of studies have shown that cleansing the surface of the bone to remove surface debris, mar- row, fat, and blood via brushing and lavage is necessary for good penetration and a stable interface. 38 Research also suggests that the strength of the bone-cement interface is increased by increasing intru- sion of the cement through adequate canal plugging and pressurization. Krause et al 33 compared shear and tensile strengths of finger-packed and pressurized cement specimens in prepared cadaveric tibiae that were uncleaned, brushed, bloodied (but not dried), lavaged, or high- lavaged. They noted the greatest improvement in strength in the uncleaned specimens that were pressurized. This not only under- scores the importance of pressurization, but may also support the need for minimal bone disruption. Christopher W. DiGiovanni, MD, et al Vol 7, No 6, November/December 1999 355 Summary There is as yet no definite answer as to whether we should be both reaming and broaching or broaching alone in cemented hip arthroplasty. From a clinical perspective, results with both broach-only and combined systems have been acceptable on the basis of historical standards. That there are myriad established ways of doing things might suggest that they all work well. However, it might also indicate that none of them works well, that conflicts of interest influence decisions, or that the subject has not been sufficiently studied. Despite prevailing usage, the case for reaming and broaching lacks sound data and comparative trials in its support. Femoral canal reaming not only removes additional stable cancellous bone (microinterlock), which probably brings us closer to a revision surface, but also removes the weak cancellous bone often indicative of osteoporosis, a setting more needy of conservative than aggressive bone handling. It has been alternatively suggested that aggressive reaming and curettement might actually keep us further from revision, although the scientific data we have reviewed do not seem to support this theory. Reaming can also lessen the a- mount of three-dimensional constraint (macrointerlock) obtainable within a native femur. However, we still cannot prove whether limited reaming is beneficial, indiffer- ent, or problematic under any of these circumstances. Therefore, in accordance with the concept of bone-stock preservation, it seems logical to minimize any instrumentation of the femoral canal, as long as the goals of cemented total hip arthroplasty are maintained. Re- gardless of method, good evidence suggests that both bone-surface cleansing and cement penetration remain paramount in producing good long-term outcomes. Today, the concept of bone preparation must be added to the arsenal of third-generation techniques, which historically have for- mally addressed only implant design and cementation in cemented total hip arthroplasty. While exces- sive reaming is clearly unnecessary in straightforward total hip arthroplasty, the usefulness of reaming or curettement should not be underes- timated. These techniques should probably be limited to finding the canal, ensuring a sufficiently neutral alignment and an adequate lateral mantle, and opening an abnormally small or deformed femoral canal for implantation. Such steps are critical and cannot be achieved without these instruments. Fully toothed broaching alone is indicated in most primary cases, and should theoreti- cally decrease surgical time, preserve bone stock, and improve microinterlock and macrointerlock of cement, seemingly without adverse- ly affecting the durability of the bone-cement interface. Although the potentially small differences between these techniques are not evident through comparison in any of the currently available long-term clinical studies of primary hip replacement, the impact of such changes may evolve when the outcome with the next generation of implants is evaluated in the same patients. This should be of particular concern in light of the recent trend toward hip replacement in increasingly younger, more active individuals, as indications for surgery broaden. It is possible that after more inten- sive study of surgical technique, no difference due to modification of bone preparation will be identified. Nonetheless, specific comparative and basic science studies are impera- tive to answer this and other ques- tions: Should we remove nonintact (as opposed to intact but weak, po- rotic, or unstable) autogenous bone? Should we not remove any bone, but instead compact it with a smooth broach to make room for an implant (assuming we can still meet the goals of cemented femoral replacement and avoid femoral fracture)? Despite the limited data and the remaining uncertainties, it seems that a recom- mendation of only toothed broaching during cemented hip replacement makes the most sense in most clinical situations. Femoral Preparation in Cemented Total Hip Arthroplasty Journal of the American Academy of Orthopaedic Surgeons 356 References 1.Linder L, Hansson HA: Ultrastruc- tural aspects of the interface between bone and cement in man: Report of three cases. J Bone Joint Surg Br1983; 65:646-649. 2.Huddleston HD: Femoral lysis after cemented hip arthroplasty. 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