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Reduced Incidence of Intraoperative Femur Fracture With a Second-Generation Tapered Wedge Stem
The Journal of Arthroplasty xxx (2017) 1e5
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Reduced Incidence of Intraoperative Femur Fracture With a Second-Generation Tapered Wedge Stem Andrew N. Fleischman, MD *, Max M. Schubert, BS, Camilo Restrepo, MD, Antonia F. Chen, MD, MBA, Richard H. Rothman, MD, PhD Department of Orthopaedic Surgery, The Rothman Institute at Thomas Jefferson University, Philadelphia, Pennsylvania
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 March 2017 Received in revised form 26 April 2017 Accepted 8 June 2017 Available online xxx
Background: Intraoperative fractures during total hip arthroplasty (THA) are more common when using cementless stems. The purpose of this study was to investigate the impact of a new shorter secondgeneration cementless, tapered wedge stem with improved proximal femoral fit in reducing the incidence of intraoperative fracture. Methods: A retrospective study was conducted on primary THA cases performed at a single institution using a first-generation or second-generation cementless stem from 2006-2016. All intraoperative femur fractures were identified, as well as early 30-day postoperative periprosthetic femur fractures, which could represent nondisplaced intraoperative fractures that were initially missed. Risk for intraoperative femur fracture was analyzed using logistic regression, accounting for demographic covariates and surgeon. Results: Of 6473 primary THA performed with a cementless, tapered wedge stem during the study period, 3126 used a first-generation stem and 3347 used a second-generation stem. The incidence of intraoperative fracture was 1.79% for first-generation stems and 0.24% for second-generation stems, representing a 7.5-fold reduction of risk for fracture. After accounting for covariates, the odds of intraoperative fracture were 0.33 using the second-generation stem relative to the first-generation stem (P ¼ .01). However, there was no significant difference in the odds of early 30-day postoperative fractures using the second-generation stem (odds ratio 0.93, P ¼ .56). Conclusion: A new second-generation cementless stem resulted in a 7.5-fold decrease in the incidence of intraoperative femur fracture compared with the preceding stem. © 2017 Elsevier Inc. All rights reserved.
Keywords: intraoperative fractures arthroplasty hip cementless tapered wedge stem
Cementless, tapered wedge stems for total hip arthroplasty (THA) have grown in popularity, in large part, because of their relative ease and efficiency of implantation. However, intraoperative femur fractures are more common with cementless THA compared with cemented THA, occurring in 1%-4% of cases during broaching or final impaction, as surgeons attempt to obtain a tight press-fit [1e5]. In addition to cementless fixation, female gender, advanced age, and small stem size have all been found to be predisposing risk factors for intraoperative fractures [3,6].
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2017.06.018. * Reprint requests: Andrew N. Fleischman, MD, Department of Orthopaedic Surgery, The Rothman Institute, 125 S 9th St. Ste 1000, Philadelphia, PA 19107. http://dx.doi.org/10.1016/j.arth.2017.06.018 0883-5403/© 2017 Elsevier Inc. All rights reserved.
Although satisfactory outcomes may be achieved by treating intraoperative fractures with cerclage wiring, fractures not identified and treated intraoperatively can later become displaced and present as early postoperative periprosthetic fractures [7]. It has also been suggested that as many as 40% of fractures may be missed by surgeons intraoperatively [8]. Furthermore, intraoperative fracture may have detrimental long-term implications on THA outcomes [4,6,9,10]. Thus, minimizing the risk for intraoperative fracture should be considered a best surgical practice. Although first-generation cementless, tapered wedge stems demonstrated excellent midterm to long-term outcomes, they have also been associated with a higher rate of femur fracture [11e15]. However, shorter cementless stems with a reduced femoral geometry have been previously shown to decrease fracture risk [16,17]. Therefore, a specific second-generation tapered stem was designed to provide a medial curvature that was more size-specific based on 556 computed tomography scans taken from a diverse
2
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Table 1 Modifications for Second-Generation Tapered Stem [18e21].
Size-specific medial curvature conforming to native geometry Improved proximal femoral fit and fill Larger proximal relative to distal stem size to reduce distal only engagement Shorter stem design without loss of initial stability Distal lateral relief to reduce stem insertion length
group of patients (Table 1) [18]. The result was an implant that more closely approximated femoral geometry, with improved implant fit and initial stability [18,19]. With enhanced proximal fixation, the stem length of the second-generation stem was shortened without compromising stability, and a lateral relief was implemented distally to ease stem insertion and potentially reduce the likelihood of fracture [20,21]. With regard to second-generation tapered femoral stems, the impact of the aforementioned design changes on the risk for intraoperative femur fracture has not been previously investigated. Therefore, the purpose of this study was to compare the incidence of intraoperative femur fracture between first-generation and second-generation cementless, tapered wedge stems, including fractures identified and addressed intraoperatively and fractures occurring in the early 30-day postoperative period that could represent nondisplaced intraoperative fractures that were not immediately identified. Materials and Methods A retrospective study was conducted on primary THA cases performed at a single institution from 2006-2016. Patients were identified as those who received either a first-generation (Accolade TMZF, Stryker Orthopaedics, Mahwah, NJ) or second-generation (Accolade II, Stryker Orthopaedics, Mahwah, NJ) cementless, proximally coated, double tapered wedge femoral stem. The second-generation stem is shorter than the first-generation stem and was designed using a large computed tomography database and bone measurement system to potentially have a better femur fit. Improved fit compared with the same first-generation stem used in this study was demonstrated in a previous radiographic study [19]. First-generation stems were implanted from 2006-2011, and second-generation stems were implanted from 2011-2016. Patients undergoing THA for hip fracture or conversion THA with removal of previously implanted hardware were excluded. All THAs were performed by 1 of 7 fellowship-trained arthroplasty surgeons using either a direct lateral (modified Hardinge) [22], direct anterior (modified Smith-Peterson) [23], or anterolateral (WatsonJones) [24] approach from a supine position. The surgical approach was surgeon dependent. All cases were performed using cementless acetabular and femoral components, and the femur was prepared by reaming followed by step-wise broaching. Patients were permitted to weight bear as tolerated immediately after surgery. Both intraoperative femur fractures and early postoperative periprosthetic femur fractures occurring within the first 30 days postoperatively were identified. All cases requiring intraoperative cerclage (Dall-Miles Cable System, Stryker Orthopaedics, Mahwah, NJ) or immediate conversion from a short, tapered wedge femoral stem to a long revision stem based on operating room utilization reports were reviewed to identify intraoperative femur fractures. Neither intraoperative cerclage cables nor long revision stems would typically be used in uncomplicated primary THA at our institution. All patients requiring early reoperation, revision THA and/or open reduction and internal fixation, or coded as having a diagnosis of periprosthetic fracture or mechanical failure (ICD-9/10 codes: 996.40, 996.43, 996.44, 996.47, T84.498A, T84.019A,
T84.049A, T84.099A) within the first 30 days after primary THA were manually reviewed to identify early postoperative fractures. Statistical Analysis All bivariate analyses were performed using a Mann-Whitney U test for continuous variables and Fisher exact test for categorical variables. Risk for intraoperative femur fracture was analyzed using a logistic regression, accounting for demographic covariates (age, gender, body mass index [BMI], and Charlson comorbidity index) and surgeon. Regression analysis was not performed for early postoperative fractures because of the low number of such events. All analyses were performed using R Statistical Computing Environment version 3.3.2 (R Foundation, Vienna, Austria). Results Of 12,351 primary THAs performed during the study period, 6473 cases were identified that used a specific first-generation (n ¼ 3126) or second-generation (n ¼ 3347) femoral stem and met study inclusion criteria. Although patient demographics were similar between groups, there were statistically significant differences, as patients who received a second-generation stem were older and had lower BMIs (Table 2). There were also differences in perioperative characteristics. Patients with second-generation stems were more likely to undergo THA from a direct anterior approach and undergo simultaneous, bilateral THA compared with those receiving firstgeneration stems. In addition, both operative duration and length of hospitalization decreased for patients who received secondgeneration stems. The incidence of intraoperative femur fracture was 1.79% (95% confidence interval [CI] 1.36%-2.32%; 56 of 3126 cases) for firstgeneration stems and 0.24% (95% CI 0.10%-0.47%; 8 of 3347 cases) for second-generation stems (Fig. 1). After accounting for covariates, the adjusted incidence of intraoperative fracture was 1.64% (95% CI 1.02%-2.50%) for first-generation stems and 0.53% (95% CI 0.22%1.09%) for second-generation stems (Table 3). The odds of intraoperative femur fracture were considerably lower using the second-generation stem, both unadjusted (odds ratio [OR] 0.13; 95% CI 0.05-0.28; P < .0001) and after accounting for covariates (OR 0.33; 95% CI 0.13-0.71; P ¼ .01). In addition to the second-generation stem, male gender (OR 0.45; 95% CI 0.26-0.76) and younger age (OR 0.68; 95% CI 0.55-0.83) significantly reduced the risk for intraoperative fracture (Table 4). The risk of fracture by surgeon varied from an OR of 0.10-2.70 relative to the median fracture rate among surgeons (Fig. 2). The relative decrease in the incidence of intraoperative fracture using the second-generation stem compared with the firstgeneration stem was similar for both men (adjusted; 1.05% vs 0.34%,
Table 2 Comparison of Baseline Patient Demographics and Perioperative Characteristics. Variable
First Generation (n ¼ 3126)
Second Generation (n ¼ 3347)
P Value
Age, y Male gender, % BMI, kg/m2 CCI Simultaneous, bilateral, % Operative time, min DA approach, % LOS, d
62.6 (12.4) 47.6% 28.5 (5.6) 0.31 (0.79) 10.4% 69.6 (30.8) 21.6% 3.2 (2.3)
63.5 (10.6) 49.7% 28.0 (4.6) 0.31 (0.79) 17.6% 64.4 (34.5) 64.6% 1.4 (1.2)
.01a .08 .04a .65 <.0001a <.0001a <.0001a <.0001a
Continuous variables reported as mean (standard deviation). BMI, body mass index; CCI, Charlson comorbidity index; DA, direct anterior; LOS, length of hospital stay. a Statistically significant.
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3
Fig. 1. Incidence of periprosthetic femur fracture by stem generation.
respectively) and women (adjusted; 2.30% vs 0.76%, respectively) (Table 3). Nearly all intraoperative fractures (61 of 64 cases) were repaired with cerclage cabling, and the remaining 3 cases underwent conversion to a long femoral stem. The incidence of early postoperative periprosthetic femur fracture within the first 30-days postoperatively was 0.19% (95% CI 0.09%-0.42%; 6 of 3126 cases) for first-generation stems and 0.18% (95% CI 0.08%-0.39%; 6 of 3347 cases) for second-generation stems (Fig. 1). There was no significant difference in the odds of early postoperative fracture using the second-generation stem (OR 0.93; 95% CI 0.30-2.90; P ¼ .56). However, there was a significant reduction in the odds of combined intraoperative and early postoperative femur fractures using second-generation stems (OR 0.21; 95% CI 0.12-0.37). Only a single patient (1.56%) with an intraoperative femur fracture repaired by cerclage was found to have subsequently suffered an early postoperative periprosthetic femur fracture. Discussion Cementless, tapered wedge stems have become a mainstay of primary THA, demonstrating excellent midterm to long-term outcomes [11e14]. However, intraoperative femur fracture remains a well-known complication of cementless THA [1e5], and minimizing the risk of intraoperative femur fracture should be
considered a best surgical practice. Although one theoretical benefit of a new shorter second-generation tapered stem with an improved proximal femoral fit was a reduced incidence of intraoperative fracture, this hypothesis had not been previously investigated. Therefore, the purpose of this study was to compare the risk for intraoperative femur fracture and early 30-day postoperative periprosthetic femur fracture for a first-generation and second-generation cementless, tapered wedge stem. While the first-generation tapered femoral stem was successful, design changes for its successor sought to improve implant fit for a broader range of patients with varying femoral geometries [18]. Based on our study results, this new stem design greatly reduced the incidence of intraoperative femur fracture 7.5-fold from firstgeneration to second-generation stems. This reduction in risk for fracture most likely reflects an improvement of stem fit within the native geometry of the proximal femoral canal. The shortened stem length and distal lateral relief also makes it less likely that the distal end of the implant will prematurely engage the diaphysis before reaching a metaphyseal press-fit, allowing the femoral stem to sit above the medial calcar. When the diaphysis is engaged first, there may be a tendency for over-impaction to fully seat the stem, which may predispose patients to intraoperative fracture. Despite a clear improvement with regard to intraoperative fracture for the second-generation femoral stem, there did not appear to
Table 3 Incidence of Intraoperative Periprosthetic Femur Fracture (Unadjusted and Adjusted). First Generation
Overall Male Female
Second Generation
Unadjusted
Adjusted
Unadjusted
Adjusted
1.79% (1.36%-2.32%) 1.34% (0.82%-2.07%) 2.20% (1.54%-3.03%)
1.64% (1.02%-2.50%) 1.05% (0.57%-1.80%) 2.30% (1.38%-3.61%)
0.24% (0.10%-0.47%) 0.06% (0.00%-0.33%) 0.42% (0.17%-0.86%)
0.53% (0.22%-1.09%) 0.34% (0.13%-0.76%) 0.76% (0.31%-1.60%)
Incidence (95% confidence interval). Adjustment based on the following assumptions: age of 63 y, BMI of 28 kg/m2, CCI of 0, median fracture rate among surgeons. BMI, body mass index; CCI, Charlson comorbidity index.
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Table 4 Baseline Risk Factors for Intraoperative Periprosthetic Femur Fracture. Variable
Odds Ratio
95% Confidence Interval
P Value
Second-generation stem Male gender Age (per decade) BMI, kg/m2 (per point) CCI (per point)
0.33 0.45 0.68 1.01 0.85
0.13-0.71 0.26-0.76 0.55-0.83 0.97-1.05 0.52-1.21
.008a .004a <.0001a .54 .44
BMI, body mass index; CCI, Charlson comorbidity index. a Statistically significant.
be an analogous reduction in the incidence of early postoperative periprosthetic femur fracture after transitioning to the secondgeneration stem. The incidence of such fracture within the first 30 days postoperatively was 0.19% with first-generation stems and 0.18% with second-generation stems. Based on our hypothesis that a subset of early postoperative femur fractures may actually represent nondisplaced intraoperative fractures that were not identified and treated during the index surgery, we expected that the incidence of such fracture would also decrease using second-generation stems. However, early postoperative fractures, in reality, may more commonly be the result of elderly patients who have suffered falls. We also noted that cerclage wire fixation appeared to be an effective method to prevent fracture propagation, as only a single intraoperative fracture subsequently presented as an early postoperative periprosthetic fracture. We assumed that periprosthetic fractures occurring greater than 30 days postoperatively would be less likely a reflection of technical or implant-related factors than those occurring within 30 days after surgery. In addition to implant-related factors, multiple studies have evaluated demographic risk factors for intraoperative fracture. Most notably, the risk for intraoperative fracture has been shown to be higher for women and elderly patients [3,6]. However, the influence of BMI on fracture risk is less certain. Although there were statistically significant differences in baseline demographics
between patients receiving a first-generation or second-generation stem, these differences were quite small. Nevertheless, we chose to account for demographic covariates (age, gender, BMI, comorbidity) within the regression analysis. Reflecting prior literature, female gender and advanced age significantly increased the odds for intraoperative fracture in our study. However, the ensuing statistical adjustment of risk for intraoperative fracture between implant cohorts did little to modify our conclusions. Although this was the first study to compare these two generations of stems for intraoperative and early postoperative fracture, the major limitation of this study was the historical nature of our comparison, in which first-generation stems were implanted from 2006-2011 and second-generation stems were implanted thereafter. As a result, we observed several differences between cohorts that likely reflect changes in practice over the course of the study period. Length of hospitalization decreased over the past decade, and simultaneous, bilateral THA have become more common during that period in our institution. However, the methods and procedures of cementless femoral stem implantation have remained largely unchanged for both generations of tapered wedge stems. The most noteworthy change during the transition from the first-generation to the second-generation stem was the volume of THA performed by each individual surgeon using such a stem. As the fracture rate varied by surgeon, we chose to incorporate surgeon into the statistical model (Fig. 2). We also observed a shift in those variables that were highly surgeon-dependent, namely surgical approach and operative duration. Although the predominant surgical approach changed from the direct lateral approach with first-generation stems to the direct anterior with secondgeneration stems, each surgeon used only a single approach for nearly all THA cases. As such, few cases and no fractures occurred in cases performed during a surgeon's learning phase with a new surgical approach. Furthermore, because the direct anterior approach has been associated with a higher risk of intraoperative femur fracture, and there were actually fewer intraoperative fractures in the second-generation stem cohort, we do not expect
Fig. 2. Incidence of intraoperative femur fracture by surgeon and volume.
A.N. Fleischman et al. / The Journal of Arthroplasty xxx (2017) 1e5
that surgical approach was a major confounding factor [25]. In addition, we do not believe that the decrease in operative duration reflects a change in perioperative procedure, although it is possible that less time may be needed for femoral preparation with a shorter second-generation stem that more closely approximates native geometry. Another limitation is that our proposed method of identifying early postoperative fractures may have missed a small subset of intraoperative or early postoperative fractures. Intraoperative fractures that underwent cerclage wiring with an alternative to the Dall-Miles Cable System would not have been identified. However, Dall-Miles cables are the only cable system readily available at our institution and would be used for most intraoperative periprosthetic fractures. Furthermore, intraoperative fractures that were missed by the operating surgeon or for which there was no intervention may have also been omitted. However, we expect that many of such cases would have presented in the early postoperative period. Lastly, early postoperative fractures that were treated conservatively and not provided an appropriate diagnosis code or fractures treated at an outside institution may have also been missed. In addition, given the small number of patients who underwent conversion to a long femoral stem, further subgroup analysis comparing periprosthetic fractures repaired with cables or long revision stems was not feasible. Despite the above limitations, we found that a secondgeneration cementless stem resulted in a 7.5-fold decrease in the incidence of intraoperative femur fracture compared with the preceding stem. This study demonstrates the critical impact that even seemingly subtle changes in implant design can have on the beneficial outcomes of our patients. References [1] Sidler-Maier CC, Waddell JP. Incidence and predisposing factors of periprosthetic proximal femoral fractures: a literature review. Int Orthop 2015;39:1673e82. [2] Nowak M, Kusz D, Wojciechowski P, Wilk R. Risk factors for intraoperative periprosthetic femoral fractures during the total hip arthroplasty. Pol Orthop Traumatol 2012;77:59e64. [3] Zhao R, Cai H, Liu Y, Tian H, Zhang K, Liu Z. Risk factors for intraoperative proximal femoral fracture during primary cementless THA. Orthopedics 2017;40:e281e7. [4] Fitzgerald Jr RH, Brindley GW, Kavanagh BF. The uncemented total hip arthroplasty. Intraoperative femoral fractures. Clin Orthop Relat Res 1988:61e6. [5] Berry DJ. Epidemiology: hip and knee. Orthop Clin North Am 1999;30: 183e90. [6] Ponzio DY, Shahi A, Park AG, Purtill JJ. Intraoperative proximal femoral fracture in primary cementless total hip arthroplasty. J Arthroplasty 2015;30: 1418e22.
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[7] Berend KR, Lombardi Jr AV. Intraoperative femur fracture is associated with stem and instrument design in primary total hip arthroplasty. Clin Orthop Relat Res 2010;468:2377e81. [8] Williams DS, Petruccelli D, de Beer J. Intra-operative fractures of the greater trochanter and calcar during hip arthroplasty: an outcome study. Bone Joint J 2010;92-B(Suppl I):108. [9] Sharkey PF, Hozack WJ, Booth Jr RE, Rothman RH. Intraoperative femoral fractures in cementless total hip arthroplasty. Orthop Rev 1992;21:337e42. [10] Thillemann TM, Pedersen AB, Johnsen SP, Soballe K. Inferior outcome after intraoperative femoral fracture in total hip arthroplasty: outcome in 519 patients from the Danish Hip Arthroplasty Registry. Acta Orthop 2008;79: 327e34. [11] Casper DS, Kim GK, Restrepo C, Parvizi J, Rothman RH. Primary total hip arthroplasty with an uncemented femoral component five- to nine-year results. J Arthroplasty 2011;26:838e41. [12] Pierce TP, Jauregui JJ, Kapadia BH, Elmallah RK, Cherian JJ, Harwin SF, et al. Second-generation versus first-generation cementless tapered wedge femoral stems. Orthopedics 2015;38:550e4. [13] Kolisek FR, Chughtai M, Mistry JB, Elmallah RK, Jaggard C, Malkani AL, et al. Outcomes of second-generation tapered wedge femoral stem. Surg Technol Int 2016;28:275e9. [14] Issa K, Stroh AD, Mont MA, Bonutti PM. Effect of bone type on clinical and radiographic outcomes of a proximally-coated cementless stem in primary total hip arthroplasties. J Orthop Res 2014;32:1214e20. [15] Carli AV, Negus JJ, Haddad FS. Periprosthetic femoral fractures and trying to avoid them: what is the contribution of femoral component design to the increased risk of periprosthetic femoral fracture? Bone Joint J 2017;99-B(1 Suppl A):50e9. [16] Sueyoshi T, Berend M, Meding J, Malinzak R, Lackey W, Ritter M. Changes in femoral stem geometry reduce intraoperative femoral fracture rates in total hip replacement. Open J Orthop 2015;5:115e9. [17] Molli RG, Lombardi Jr AV, Berend KR, Adams JB, Sneller MA. A short tapered stem reduces intraoperative complications in primary total hip arthroplasty. Clin Orthop Relat Res 2012;470:450e61. [18] Wuestemann T, Bastian A, Parvizi J, Nessler J, Kolisek F, Nevelos J. A novel tapered hip stem design optimized for femoral fit in a wide array of bone types. Bone Joint J 2012;94-B(Suppl XXXVII). [19] Issa K, Pivec R, Wuestemann T, Tatevossian T, Nevelos J, Mont MA. Radiographic fit and fill analysis of a new second-generation proximally coated cementless stem compared to its predicate design. J Arthroplasty 2014;29: 192e8. [20] Collopy D, Wuestemann T, Race A, Nevelos J. Comparison of the immediate post-operative stability of a novel, shortened, tapered hip stem to a predicate design. Bone Joint J 2013;95-B(Suppl 15):43. [21] Lovell T, Hozack W, Kreuzer S, Merritt P, Nogler M, Puri L, et al. A1190. Influence of stem length on the insertion path in THR. Bone Joint J 2011;93B(Suppl IV):421. [22] Austin MS, Rothman RH. Acetabular orientation: anterolateral approach in the supine position. Clin Orthop Relat Res 2009;467:108e12. [23] Restrepo C, Parvizi J, Pour AE, Hozack WJ. Prospective randomized study of two surgical approaches for total hip arthroplasty. J Arthroplasty 2010;25: 671e9. [24] Carlson DC, Robinson Jr HJ. Surgical approaches for primary total hip arthroplasty. A prospective comparison of the Marcy modification of the Gibson and Watson-Jones approaches. Clin Orthop Relat Res 1987:161e6. [25] De Geest T, Vansintjan P, De Loore G. Direct anterior total hip arthroplasty: complications and early outcome in a series of 300 cases. Acta Orthop Belg 2013;79:166e73.
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Reduced Incidence of Intraoperative Femur Fracture With a Second-Generation Tapered Wedge Stem Andrew N. Fleischman, MD *, Max M. Schubert, BS, Camilo Restrepo, MD, Antonia F. Chen, MD, MBA, Richard H. Rothman, MD, PhD Department of Orthopaedic Surgery, The Rothman Institute at Thomas Jefferson University, Philadelphia, Pennsylvania
a r t i c l e i n f o
a b s t r a c t
Article history: Received 1 March 2017 Received in revised form 26 April 2017 Accepted 8 June 2017 Available online xxx
Background: Intraoperative fractures during total hip arthroplasty (THA) are more common when using cementless stems. The purpose of this study was to investigate the impact of a new shorter secondgeneration cementless, tapered wedge stem with improved proximal femoral fit in reducing the incidence of intraoperative fracture. Methods: A retrospective study was conducted on primary THA cases performed at a single institution using a first-generation or second-generation cementless stem from 2006-2016. All intraoperative femur fractures were identified, as well as early 30-day postoperative periprosthetic femur fractures, which could represent nondisplaced intraoperative fractures that were initially missed. Risk for intraoperative femur fracture was analyzed using logistic regression, accounting for demographic covariates and surgeon. Results: Of 6473 primary THA performed with a cementless, tapered wedge stem during the study period, 3126 used a first-generation stem and 3347 used a second-generation stem. The incidence of intraoperative fracture was 1.79% for first-generation stems and 0.24% for second-generation stems, representing a 7.5-fold reduction of risk for fracture. After accounting for covariates, the odds of intraoperative fracture were 0.33 using the second-generation stem relative to the first-generation stem (P ¼ .01). However, there was no significant difference in the odds of early 30-day postoperative fractures using the second-generation stem (odds ratio 0.93, P ¼ .56). Conclusion: A new second-generation cementless stem resulted in a 7.5-fold decrease in the incidence of intraoperative femur fracture compared with the preceding stem. © 2017 Elsevier Inc. All rights reserved.
Keywords: intraoperative fractures arthroplasty hip cementless tapered wedge stem
Cementless, tapered wedge stems for total hip arthroplasty (THA) have grown in popularity, in large part, because of their relative ease and efficiency of implantation. However, intraoperative femur fractures are more common with cementless THA compared with cemented THA, occurring in 1%-4% of cases during broaching or final impaction, as surgeons attempt to obtain a tight press-fit [1e5]. In addition to cementless fixation, female gender, advanced age, and small stem size have all been found to be predisposing risk factors for intraoperative fractures [3,6].
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2017.06.018. * Reprint requests: Andrew N. Fleischman, MD, Department of Orthopaedic Surgery, The Rothman Institute, 125 S 9th St. Ste 1000, Philadelphia, PA 19107. http://dx.doi.org/10.1016/j.arth.2017.06.018 0883-5403/© 2017 Elsevier Inc. All rights reserved.
Although satisfactory outcomes may be achieved by treating intraoperative fractures with cerclage wiring, fractures not identified and treated intraoperatively can later become displaced and present as early postoperative periprosthetic fractures [7]. It has also been suggested that as many as 40% of fractures may be missed by surgeons intraoperatively [8]. Furthermore, intraoperative fracture may have detrimental long-term implications on THA outcomes [4,6,9,10]. Thus, minimizing the risk for intraoperative fracture should be considered a best surgical practice. Although first-generation cementless, tapered wedge stems demonstrated excellent midterm to long-term outcomes, they have also been associated with a higher rate of femur fracture [11e15]. However, shorter cementless stems with a reduced femoral geometry have been previously shown to decrease fracture risk [16,17]. Therefore, a specific second-generation tapered stem was designed to provide a medial curvature that was more size-specific based on 556 computed tomography scans taken from a diverse
2
A.N. Fleischman et al. / The Journal of Arthroplasty xxx (2017) 1e5
Table 1 Modifications for Second-Generation Tapered Stem [18e21].
Size-specific medial curvature conforming to native geometry Improved proximal femoral fit and fill Larger proximal relative to distal stem size to reduce distal only engagement Shorter stem design without loss of initial stability Distal lateral relief to reduce stem insertion length
group of patients (Table 1) [18]. The result was an implant that more closely approximated femoral geometry, with improved implant fit and initial stability [18,19]. With enhanced proximal fixation, the stem length of the second-generation stem was shortened without compromising stability, and a lateral relief was implemented distally to ease stem insertion and potentially reduce the likelihood of fracture [20,21]. With regard to second-generation tapered femoral stems, the impact of the aforementioned design changes on the risk for intraoperative femur fracture has not been previously investigated. Therefore, the purpose of this study was to compare the incidence of intraoperative femur fracture between first-generation and second-generation cementless, tapered wedge stems, including fractures identified and addressed intraoperatively and fractures occurring in the early 30-day postoperative period that could represent nondisplaced intraoperative fractures that were not immediately identified. Materials and Methods A retrospective study was conducted on primary THA cases performed at a single institution from 2006-2016. Patients were identified as those who received either a first-generation (Accolade TMZF, Stryker Orthopaedics, Mahwah, NJ) or second-generation (Accolade II, Stryker Orthopaedics, Mahwah, NJ) cementless, proximally coated, double tapered wedge femoral stem. The second-generation stem is shorter than the first-generation stem and was designed using a large computed tomography database and bone measurement system to potentially have a better femur fit. Improved fit compared with the same first-generation stem used in this study was demonstrated in a previous radiographic study [19]. First-generation stems were implanted from 2006-2011, and second-generation stems were implanted from 2011-2016. Patients undergoing THA for hip fracture or conversion THA with removal of previously implanted hardware were excluded. All THAs were performed by 1 of 7 fellowship-trained arthroplasty surgeons using either a direct lateral (modified Hardinge) [22], direct anterior (modified Smith-Peterson) [23], or anterolateral (WatsonJones) [24] approach from a supine position. The surgical approach was surgeon dependent. All cases were performed using cementless acetabular and femoral components, and the femur was prepared by reaming followed by step-wise broaching. Patients were permitted to weight bear as tolerated immediately after surgery. Both intraoperative femur fractures and early postoperative periprosthetic femur fractures occurring within the first 30 days postoperatively were identified. All cases requiring intraoperative cerclage (Dall-Miles Cable System, Stryker Orthopaedics, Mahwah, NJ) or immediate conversion from a short, tapered wedge femoral stem to a long revision stem based on operating room utilization reports were reviewed to identify intraoperative femur fractures. Neither intraoperative cerclage cables nor long revision stems would typically be used in uncomplicated primary THA at our institution. All patients requiring early reoperation, revision THA and/or open reduction and internal fixation, or coded as having a diagnosis of periprosthetic fracture or mechanical failure (ICD-9/10 codes: 996.40, 996.43, 996.44, 996.47, T84.498A, T84.019A,
T84.049A, T84.099A) within the first 30 days after primary THA were manually reviewed to identify early postoperative fractures. Statistical Analysis All bivariate analyses were performed using a Mann-Whitney U test for continuous variables and Fisher exact test for categorical variables. Risk for intraoperative femur fracture was analyzed using a logistic regression, accounting for demographic covariates (age, gender, body mass index [BMI], and Charlson comorbidity index) and surgeon. Regression analysis was not performed for early postoperative fractures because of the low number of such events. All analyses were performed using R Statistical Computing Environment version 3.3.2 (R Foundation, Vienna, Austria). Results Of 12,351 primary THAs performed during the study period, 6473 cases were identified that used a specific first-generation (n ¼ 3126) or second-generation (n ¼ 3347) femoral stem and met study inclusion criteria. Although patient demographics were similar between groups, there were statistically significant differences, as patients who received a second-generation stem were older and had lower BMIs (Table 2). There were also differences in perioperative characteristics. Patients with second-generation stems were more likely to undergo THA from a direct anterior approach and undergo simultaneous, bilateral THA compared with those receiving firstgeneration stems. In addition, both operative duration and length of hospitalization decreased for patients who received secondgeneration stems. The incidence of intraoperative femur fracture was 1.79% (95% confidence interval [CI] 1.36%-2.32%; 56 of 3126 cases) for firstgeneration stems and 0.24% (95% CI 0.10%-0.47%; 8 of 3347 cases) for second-generation stems (Fig. 1). After accounting for covariates, the adjusted incidence of intraoperative fracture was 1.64% (95% CI 1.02%-2.50%) for first-generation stems and 0.53% (95% CI 0.22%1.09%) for second-generation stems (Table 3). The odds of intraoperative femur fracture were considerably lower using the second-generation stem, both unadjusted (odds ratio [OR] 0.13; 95% CI 0.05-0.28; P < .0001) and after accounting for covariates (OR 0.33; 95% CI 0.13-0.71; P ¼ .01). In addition to the second-generation stem, male gender (OR 0.45; 95% CI 0.26-0.76) and younger age (OR 0.68; 95% CI 0.55-0.83) significantly reduced the risk for intraoperative fracture (Table 4). The risk of fracture by surgeon varied from an OR of 0.10-2.70 relative to the median fracture rate among surgeons (Fig. 2). The relative decrease in the incidence of intraoperative fracture using the second-generation stem compared with the firstgeneration stem was similar for both men (adjusted; 1.05% vs 0.34%,
Table 2 Comparison of Baseline Patient Demographics and Perioperative Characteristics. Variable
First Generation (n ¼ 3126)
Second Generation (n ¼ 3347)
P Value
Age, y Male gender, % BMI, kg/m2 CCI Simultaneous, bilateral, % Operative time, min DA approach, % LOS, d
62.6 (12.4) 47.6% 28.5 (5.6) 0.31 (0.79) 10.4% 69.6 (30.8) 21.6% 3.2 (2.3)
63.5 (10.6) 49.7% 28.0 (4.6) 0.31 (0.79) 17.6% 64.4 (34.5) 64.6% 1.4 (1.2)
.01a .08 .04a .65 <.0001a <.0001a <.0001a <.0001a
Continuous variables reported as mean (standard deviation). BMI, body mass index; CCI, Charlson comorbidity index; DA, direct anterior; LOS, length of hospital stay. a Statistically significant.
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Fig. 1. Incidence of periprosthetic femur fracture by stem generation.
respectively) and women (adjusted; 2.30% vs 0.76%, respectively) (Table 3). Nearly all intraoperative fractures (61 of 64 cases) were repaired with cerclage cabling, and the remaining 3 cases underwent conversion to a long femoral stem. The incidence of early postoperative periprosthetic femur fracture within the first 30-days postoperatively was 0.19% (95% CI 0.09%-0.42%; 6 of 3126 cases) for first-generation stems and 0.18% (95% CI 0.08%-0.39%; 6 of 3347 cases) for second-generation stems (Fig. 1). There was no significant difference in the odds of early postoperative fracture using the second-generation stem (OR 0.93; 95% CI 0.30-2.90; P ¼ .56). However, there was a significant reduction in the odds of combined intraoperative and early postoperative femur fractures using second-generation stems (OR 0.21; 95% CI 0.12-0.37). Only a single patient (1.56%) with an intraoperative femur fracture repaired by cerclage was found to have subsequently suffered an early postoperative periprosthetic femur fracture. Discussion Cementless, tapered wedge stems have become a mainstay of primary THA, demonstrating excellent midterm to long-term outcomes [11e14]. However, intraoperative femur fracture remains a well-known complication of cementless THA [1e5], and minimizing the risk of intraoperative femur fracture should be
considered a best surgical practice. Although one theoretical benefit of a new shorter second-generation tapered stem with an improved proximal femoral fit was a reduced incidence of intraoperative fracture, this hypothesis had not been previously investigated. Therefore, the purpose of this study was to compare the risk for intraoperative femur fracture and early 30-day postoperative periprosthetic femur fracture for a first-generation and second-generation cementless, tapered wedge stem. While the first-generation tapered femoral stem was successful, design changes for its successor sought to improve implant fit for a broader range of patients with varying femoral geometries [18]. Based on our study results, this new stem design greatly reduced the incidence of intraoperative femur fracture 7.5-fold from firstgeneration to second-generation stems. This reduction in risk for fracture most likely reflects an improvement of stem fit within the native geometry of the proximal femoral canal. The shortened stem length and distal lateral relief also makes it less likely that the distal end of the implant will prematurely engage the diaphysis before reaching a metaphyseal press-fit, allowing the femoral stem to sit above the medial calcar. When the diaphysis is engaged first, there may be a tendency for over-impaction to fully seat the stem, which may predispose patients to intraoperative fracture. Despite a clear improvement with regard to intraoperative fracture for the second-generation femoral stem, there did not appear to
Table 3 Incidence of Intraoperative Periprosthetic Femur Fracture (Unadjusted and Adjusted). First Generation
Overall Male Female
Second Generation
Unadjusted
Adjusted
Unadjusted
Adjusted
1.79% (1.36%-2.32%) 1.34% (0.82%-2.07%) 2.20% (1.54%-3.03%)
1.64% (1.02%-2.50%) 1.05% (0.57%-1.80%) 2.30% (1.38%-3.61%)
0.24% (0.10%-0.47%) 0.06% (0.00%-0.33%) 0.42% (0.17%-0.86%)
0.53% (0.22%-1.09%) 0.34% (0.13%-0.76%) 0.76% (0.31%-1.60%)
Incidence (95% confidence interval). Adjustment based on the following assumptions: age of 63 y, BMI of 28 kg/m2, CCI of 0, median fracture rate among surgeons. BMI, body mass index; CCI, Charlson comorbidity index.
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Table 4 Baseline Risk Factors for Intraoperative Periprosthetic Femur Fracture. Variable
Odds Ratio
95% Confidence Interval
P Value
Second-generation stem Male gender Age (per decade) BMI, kg/m2 (per point) CCI (per point)
0.33 0.45 0.68 1.01 0.85
0.13-0.71 0.26-0.76 0.55-0.83 0.97-1.05 0.52-1.21
.008a .004a <.0001a .54 .44
BMI, body mass index; CCI, Charlson comorbidity index. a Statistically significant.
be an analogous reduction in the incidence of early postoperative periprosthetic femur fracture after transitioning to the secondgeneration stem. The incidence of such fracture within the first 30 days postoperatively was 0.19% with first-generation stems and 0.18% with second-generation stems. Based on our hypothesis that a subset of early postoperative femur fractures may actually represent nondisplaced intraoperative fractures that were not identified and treated during the index surgery, we expected that the incidence of such fracture would also decrease using second-generation stems. However, early postoperative fractures, in reality, may more commonly be the result of elderly patients who have suffered falls. We also noted that cerclage wire fixation appeared to be an effective method to prevent fracture propagation, as only a single intraoperative fracture subsequently presented as an early postoperative periprosthetic fracture. We assumed that periprosthetic fractures occurring greater than 30 days postoperatively would be less likely a reflection of technical or implant-related factors than those occurring within 30 days after surgery. In addition to implant-related factors, multiple studies have evaluated demographic risk factors for intraoperative fracture. Most notably, the risk for intraoperative fracture has been shown to be higher for women and elderly patients [3,6]. However, the influence of BMI on fracture risk is less certain. Although there were statistically significant differences in baseline demographics
between patients receiving a first-generation or second-generation stem, these differences were quite small. Nevertheless, we chose to account for demographic covariates (age, gender, BMI, comorbidity) within the regression analysis. Reflecting prior literature, female gender and advanced age significantly increased the odds for intraoperative fracture in our study. However, the ensuing statistical adjustment of risk for intraoperative fracture between implant cohorts did little to modify our conclusions. Although this was the first study to compare these two generations of stems for intraoperative and early postoperative fracture, the major limitation of this study was the historical nature of our comparison, in which first-generation stems were implanted from 2006-2011 and second-generation stems were implanted thereafter. As a result, we observed several differences between cohorts that likely reflect changes in practice over the course of the study period. Length of hospitalization decreased over the past decade, and simultaneous, bilateral THA have become more common during that period in our institution. However, the methods and procedures of cementless femoral stem implantation have remained largely unchanged for both generations of tapered wedge stems. The most noteworthy change during the transition from the first-generation to the second-generation stem was the volume of THA performed by each individual surgeon using such a stem. As the fracture rate varied by surgeon, we chose to incorporate surgeon into the statistical model (Fig. 2). We also observed a shift in those variables that were highly surgeon-dependent, namely surgical approach and operative duration. Although the predominant surgical approach changed from the direct lateral approach with first-generation stems to the direct anterior with secondgeneration stems, each surgeon used only a single approach for nearly all THA cases. As such, few cases and no fractures occurred in cases performed during a surgeon's learning phase with a new surgical approach. Furthermore, because the direct anterior approach has been associated with a higher risk of intraoperative femur fracture, and there were actually fewer intraoperative fractures in the second-generation stem cohort, we do not expect
Fig. 2. Incidence of intraoperative femur fracture by surgeon and volume.
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that surgical approach was a major confounding factor [25]. In addition, we do not believe that the decrease in operative duration reflects a change in perioperative procedure, although it is possible that less time may be needed for femoral preparation with a shorter second-generation stem that more closely approximates native geometry. Another limitation is that our proposed method of identifying early postoperative fractures may have missed a small subset of intraoperative or early postoperative fractures. Intraoperative fractures that underwent cerclage wiring with an alternative to the Dall-Miles Cable System would not have been identified. However, Dall-Miles cables are the only cable system readily available at our institution and would be used for most intraoperative periprosthetic fractures. Furthermore, intraoperative fractures that were missed by the operating surgeon or for which there was no intervention may have also been omitted. However, we expect that many of such cases would have presented in the early postoperative period. Lastly, early postoperative fractures that were treated conservatively and not provided an appropriate diagnosis code or fractures treated at an outside institution may have also been missed. In addition, given the small number of patients who underwent conversion to a long femoral stem, further subgroup analysis comparing periprosthetic fractures repaired with cables or long revision stems was not feasible. Despite the above limitations, we found that a secondgeneration cementless stem resulted in a 7.5-fold decrease in the incidence of intraoperative femur fracture compared with the preceding stem. This study demonstrates the critical impact that even seemingly subtle changes in implant design can have on the beneficial outcomes of our patients. References [1] Sidler-Maier CC, Waddell JP. Incidence and predisposing factors of periprosthetic proximal femoral fractures: a literature review. Int Orthop 2015;39:1673e82. [2] Nowak M, Kusz D, Wojciechowski P, Wilk R. Risk factors for intraoperative periprosthetic femoral fractures during the total hip arthroplasty. Pol Orthop Traumatol 2012;77:59e64. [3] Zhao R, Cai H, Liu Y, Tian H, Zhang K, Liu Z. Risk factors for intraoperative proximal femoral fracture during primary cementless THA. Orthopedics 2017;40:e281e7. [4] Fitzgerald Jr RH, Brindley GW, Kavanagh BF. The uncemented total hip arthroplasty. Intraoperative femoral fractures. Clin Orthop Relat Res 1988:61e6. [5] Berry DJ. Epidemiology: hip and knee. Orthop Clin North Am 1999;30: 183e90. [6] Ponzio DY, Shahi A, Park AG, Purtill JJ. Intraoperative proximal femoral fracture in primary cementless total hip arthroplasty. J Arthroplasty 2015;30: 1418e22.
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[7] Berend KR, Lombardi Jr AV. Intraoperative femur fracture is associated with stem and instrument design in primary total hip arthroplasty. Clin Orthop Relat Res 2010;468:2377e81. [8] Williams DS, Petruccelli D, de Beer J. Intra-operative fractures of the greater trochanter and calcar during hip arthroplasty: an outcome study. Bone Joint J 2010;92-B(Suppl I):108. [9] Sharkey PF, Hozack WJ, Booth Jr RE, Rothman RH. Intraoperative femoral fractures in cementless total hip arthroplasty. Orthop Rev 1992;21:337e42. [10] Thillemann TM, Pedersen AB, Johnsen SP, Soballe K. Inferior outcome after intraoperative femoral fracture in total hip arthroplasty: outcome in 519 patients from the Danish Hip Arthroplasty Registry. Acta Orthop 2008;79: 327e34. [11] Casper DS, Kim GK, Restrepo C, Parvizi J, Rothman RH. Primary total hip arthroplasty with an uncemented femoral component five- to nine-year results. J Arthroplasty 2011;26:838e41. [12] Pierce TP, Jauregui JJ, Kapadia BH, Elmallah RK, Cherian JJ, Harwin SF, et al. Second-generation versus first-generation cementless tapered wedge femoral stems. Orthopedics 2015;38:550e4. [13] Kolisek FR, Chughtai M, Mistry JB, Elmallah RK, Jaggard C, Malkani AL, et al. Outcomes of second-generation tapered wedge femoral stem. Surg Technol Int 2016;28:275e9. [14] Issa K, Stroh AD, Mont MA, Bonutti PM. Effect of bone type on clinical and radiographic outcomes of a proximally-coated cementless stem in primary total hip arthroplasties. J Orthop Res 2014;32:1214e20. [15] Carli AV, Negus JJ, Haddad FS. Periprosthetic femoral fractures and trying to avoid them: what is the contribution of femoral component design to the increased risk of periprosthetic femoral fracture? Bone Joint J 2017;99-B(1 Suppl A):50e9. [16] Sueyoshi T, Berend M, Meding J, Malinzak R, Lackey W, Ritter M. Changes in femoral stem geometry reduce intraoperative femoral fracture rates in total hip replacement. Open J Orthop 2015;5:115e9. [17] Molli RG, Lombardi Jr AV, Berend KR, Adams JB, Sneller MA. A short tapered stem reduces intraoperative complications in primary total hip arthroplasty. Clin Orthop Relat Res 2012;470:450e61. [18] Wuestemann T, Bastian A, Parvizi J, Nessler J, Kolisek F, Nevelos J. A novel tapered hip stem design optimized for femoral fit in a wide array of bone types. Bone Joint J 2012;94-B(Suppl XXXVII). [19] Issa K, Pivec R, Wuestemann T, Tatevossian T, Nevelos J, Mont MA. Radiographic fit and fill analysis of a new second-generation proximally coated cementless stem compared to its predicate design. J Arthroplasty 2014;29: 192e8. [20] Collopy D, Wuestemann T, Race A, Nevelos J. Comparison of the immediate post-operative stability of a novel, shortened, tapered hip stem to a predicate design. Bone Joint J 2013;95-B(Suppl 15):43. [21] Lovell T, Hozack W, Kreuzer S, Merritt P, Nogler M, Puri L, et al. A1190. Influence of stem length on the insertion path in THR. Bone Joint J 2011;93B(Suppl IV):421. [22] Austin MS, Rothman RH. Acetabular orientation: anterolateral approach in the supine position. Clin Orthop Relat Res 2009;467:108e12. [23] Restrepo C, Parvizi J, Pour AE, Hozack WJ. Prospective randomized study of two surgical approaches for total hip arthroplasty. J Arthroplasty 2010;25: 671e9. [24] Carlson DC, Robinson Jr HJ. Surgical approaches for primary total hip arthroplasty. A prospective comparison of the Marcy modification of the Gibson and Watson-Jones approaches. Clin Orthop Relat Res 1987:161e6. [25] De Geest T, Vansintjan P, De Loore G. Direct anterior total hip arthroplasty: complications and early outcome in a series of 300 cases. Acta Orthop Belg 2013;79:166e73.