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Can We Predict Fracture When Using a Short Cementless Femoral Stem in the Anterior Approach?

Published:March 18, 2022DOI:https://doi.org/10.1016/j.arth.2022.03.054

      Abstract

      Background

      Short cementless femoral stems may allow for easier insertion with less dissection. The use of short stems with the anterior approach (AA) may be associated with a considerable perioperative fracture risk. Our aim was to evaluate whether patient-specific femoral and pelvic morphology and surgical technique, influence the perioperative fracture risk. Furthermore, we sought to describe important anatomical thresholds alerting surgeons.

      Methods

      A single-center, multi-surgeon retrospective, case-control matched study was performed. Thirty nine periprosthetic fractures (3.4%) in 1,145 primary AA THAs using short cementless stems were identified. These were matched with 78 THA nonfracture controls for factors known to increase the fracture risk. A radiographic analysis using validated software measured femoral (canal flare index [CFI], morphological cortical index [MCI], and calcar-calcar ratio [CCR]) and pelvic (Ilium-ischial ratio [IIR], ilium overhang, and anterior superior iliac spine [ASIS] to greater trochanter distance) morphologies and surgical techniques (% canal fill). A multivariate and Receiver-Operator Curve (ROC) analysis was used to identify fracture predictors.

      Results

      CFI (3.7 ± 0.6 vs 2.9 ± 0.4, P < .001) and CCR (0.5 ± 0.1 vs 0.4 ± 0.1, P = .006) differed. The mean IIR was higher in fracture cases (3.3 ± 0.6 vs 3.0 ± 0.5, P < .001). Percent canal fill was reduced in fracture cases (82.8 ± 7.6 vs 86.7 ± 6.8, P = .007). Multivariate and ROC analyses revealed a threshold CFI of 3.17 which was predictive of fracture (sensitivity: 84.6%/specificity: 75.6%). The fracture risk was 29 times higher when patients had CFI >3.17 and II ratio >3 (OR: 29.2 95% CI: 9.5-89.9, P < .001).

      Conclusion

      Patient-specific anatomical parameters are important predictors of a fracture-risk. A careful radiographic analysis would help identify those at a risk of early fracture using short stems, and alternative stem options should be considered.

      Keywords

      In recent years, developments in total hip arthroplasty (THA) have focused on enhancing patient outcomes and implant survival, while reducing surgical complications. Cementless fixation of the femoral component remains a popular choice, with joint registry data showing an ever increasing trend toward the use of such implants in THA [
      AOANJRR
      Hip, knee & shoulder arthroplasty: 2020 annual report.
      ,
      National Joint Registry for England, Wales and Northern Ireland
      National Joint Registry 17th annual report.
      ]. Less-invasive surgical approaches to the hip through intramuscular and internervous planes, such as the anterior approach (AA), have simultaneously grown in popularity over the past decade by allowing the surgeon to perform THAs while reducing the damage to soft tissues, allowing for quicker recovery and less pain [
      • Rodriguez J.A.
      • Deshmukh A.J.
      • Rathod P.A.
      • Greiz M.L.
      • Deshmane P.P.
      • Hepinstall M.S.
      • et al.
      Does the direct anterior approach in THA offer faster rehabilitation and comparable safety to the posterior approach?.
      ,
      • Meneghini R.M.
      • Pagnano M.W.
      • Trousdale R.T.
      • Hozack W.J.
      Muscle damage during MIS total hip arthroplasty: Smith-Petersen versus posterior approach.
      ,
      • Taunton M.J.
      • Trousdale R.T.
      • Sierra R.J.
      • Kaufman K.
      • Pagnano M.W.
      John Charnley Award: randomized clinical trial of direct anterior and miniposterior approach THA: which provides better functional recovery?.
      ].
      One of the perceived challenges with the AA is the safe delivery of the femur into the surgical wound. Inadequate exposure of the femoral canal may result in difficulty with femoral preparation and nonoptimal sizing or malposition of the definitive component, which may contribute to the increased risk of early periprosthetic fracture noted [
      • Berend K.R.
      • Mirza A.J.
      • Morris M.J.
      • Lombardi A.V.
      Risk of periprosthetic fractures with direct anterior primary total hip arthroplasty.
      ]. To combat this challenge, shorter cementless femoral stems have been designed to allow for broach-only femoral preparation and easier introduction at a steeper angle into the femoral canal [
      • Dietrich M.
      • Kabelitz M.
      • Dora C.
      • Zingg P.O.
      Perioperative fractures in cementless total hip arthroplasty using the direct anterior minimally invasive approach: reduced risk with short stems.
      ,
      • Molli R.G.
      • Lombardi A.V.
      • Berend K.R.
      • Adams J.B.
      • Sneller M.A.
      A short tapered stem reduces intraoperative complications in primary total hip arthroplasty.
      ]. Short cementless stems may be an attractive option as theoretically they preserve the bone stock while allowing a more physiological transmission of load to the proximal femur and avoiding complications typically associated with cementless designs such as thigh pain [
      • Chen H.H.
      • Morrey B.F.
      • An K.N.
      • Luo Z.P.
      Bone remodeling characteristics of a short-stemmed total hip replacement.
      ,
      • Arno S.
      • Fetto J.
      • Nguyen N.Q.
      • Kinariwala N.
      • Takemoto R.
      • Oh C.
      • et al.
      Evaluation of femoral strains with cementless proximal-fill femoral implants of varied stem length.
      ].
      Despite these promising design features, short cementless stems may not be the most appropriate implant in patients predisposed to periprosthetic fracture. Female gender and age more than 65 years have been shown to carry an increased risk of intraoperative fracture, which usually occurs during the broaching process for an uncemented femoral component [
      • Abdel M.P.
      • Watts C.D.
      • Houdek M.T.
      • Lewallen D.G.
      • Berry D.J.
      Epidemiology of periprosthetic fracture of the femur in 32 644 primary total hip arthroplasties: a 40-year experience.
      ]. This is probably secondary to a poorer quality bone in this group of patients. An increasing Dorr ratio is associated with an increased risk of fracture [
      • Herndon C.L.
      • Nowell J.A.
      • Sarpong N.O.
      • Cooper H.J.
      • Shah R.P.
      • Geller J.A.
      Risk factors for periprosthetic femur fracture and influence of femoral fixation using the mini-anterolateral approach in primary total hip arthroplasty.
      ]. Whether stem length and prosthesis design have any impact on femoral complications remains unclear. Single-wedge and double-wedge cementless implants may have higher rates of periprosthetic fracture postoperatively compared with other design philosophies [
      • Carli A.V.
      • Negus J.J.
      • Haddad F.S.
      Periprosthetic femoral fractures and trying to avoid them: what is the contribution of femoral component design to the increased risk of periprosthetic femoral fracture?.
      ]. Tamaki et al reported an increased incidence of fractures using short cementless stems inserted through the anterior approach [
      • Tamaki T.
      • Jonishi K.
      • Miura Y.
      • Oinuma K.
      • Shiratsuchi H.
      Cementless tapered-wedge stem length affects the risk of periprosthetic femoral fractures in direct anterior total hip arthroplasty.
      ]. Conversely, Uçan et al reported similar radiographic and functional outcomes between short and standard length of cementless femoral stems at short-term follow-up [
      • Uçan V.
      • Ezici V.
      • Aliyev O.
      • Uzer G.
      • Tuncay İ.
      • Yıldız F.
      Comparison of tapered-wedge short and standard-length femoral stems in single-stage bilateral direct anterior total hip arthroplasty.
      ].
      The aim of this study was firstly to describe patient-specific pelvic and femoral morphology and surgical technique parameters associated with a perioperative fracture risk using a short cementless stem inserted through the anterior approach. Second, we sought to define radiographic thresholds that might be predictive of a fracture risk.

      Materials and Methods

      Study Design

      A retrospective, multi-surgeon, comparative, institutional review board–approved cohort study of 1,145 consecutive primary THAs performed at a single large academic center between 2014 and 2018 was conducted.

      Cohort

      All cases of intraoperative or early periprosthetic fracture around the femoral component were identified from a prospectively maintained arthroplasty database at our institution. An early periprosthetic fracture was defined as a fracture occurring within 6 weeks of surgery. Thirty nine fracture cases (3.4%) were identified and formed the cases. Cases were matched on a two-to-one ratio with 78 nonfracture cases (controls) for several variables including risk factors for periprosthetic fracture, age, gender, Dorr classification, body mass index (BMI), side, femoral component offset, and indication for surgery. For the whole cohort, the mean age and BMI was 66.9 ± 11.8 years and 27.3 ± 5.7 kg/m2, respectively and 57.3% (n = 67) were female. Patient characteristics are presented in Table 1.
      Table 1Patient Characteristics.
      DemographicsFracture (n = 39)Non-fracture (n = 78)P Value
      Age (y)67.7 ± 11.866.5 ± 11.9.593
      Mann-Whitney U-test.
      BMI (kg/m2)27.7 ± 6.427.0 ± 5.4.648
      Mann-Whitney U-test.
      Gender (%).895
      Chi-squared test.
       Male17 (43.6)33 (42.3)
       Female22 (56.4)45 (57.7)
      Laterality (%).485
      Chi-squared test.
       Right28 (71.8)51 (65.4)
       Left11 (28.2)27 (34.6)
      Dorr Classification (%).712
      Fisher’s Exact test.
       A24 (61.5)49 (62.8)
       B14 (35.9)24 (30.8)
       C1 (2.6)5 (6.4)
      Indication for surgery (%).684
      Chi-squared test.
       Osteoarthritis35 (89.7)70 (89.7)
       Acute hip fracture1 (2.6)3 (3.8)
       Post-traumatic arthritis1 (2.6)3 (3.8)
       Childhood deformity2 (5.1)0 (0.0)
       Osteonecrosis0 (0.0)1 (1.3)
       Inflammatory0 (0.0)1 (1.3)
      Femoral component offset (%).693
      Fisher’s Exact test.
       Standard offset32 (82.1)60 (76.9)
       High offset7 (17.9)15 (19.2)
       XR 1230 (0)3 (3.8)
      a Mann-Whitney U-test.
      b Chi-squared test.
      c Fisher’s Exact test.

      Surgical Procedure

      All THAs were performed through the anterior approach on either a standard operating table or an orthopedic positioning table (Hana Orthopedic Surgery Table, Mizuho OSI, Union City, CA). Four fellowship-trained orthopedic surgeons beyond their learning curves for the anterior approach performed all THAs. A cementless acetabular component (G7 Acetabular Shell; Zimmer Biomet, Warsaw, IN) with a highly cross-linked polyethylene liner and a short cementless femoral component (Taperloc Complete Microplasty stem; Zimmer Biomet, Warsaw, IN) were implanted in all cases. The Taperloc Complete Microplasty stem (Zimmer Biomet Orthopedics, Warsaw, IN) is a titanium alloy stem of a flat tapered wedge geometry design. The stem is proximally coated with a titanium alloy porous plasma spray coating to permit metaphyseal fixation and is 35-mm shorter than the Taperloc Complete Primary Femoral stem (Zimmer Biomet Orthopedics, Warsaw, IN). It can be classified as a type 1 cementless stem according to Khanuja et al [
      • Khanuja H.S.
      • Vakil J.J.
      • Goddard M.S.
      • Mont M.A.
      Cementless femoral fixation in total hip arthroplasty.
      ].

      Radiographic Measurements

      A radiographic assessment of morphological parameters of interest was performed on supine anteroposterior (AP) radiographs of the hips performed immediately preoperatively using a previously validated digital software (Surgimap software version 2.3.2.1; Nemaris Inc). All AP radiographs were standardized with both feet internally rotated 10°-15° and a film focus distance of 1.15 m. Radiographs were centered, with the symphysis pubis projected directly below the coccyx and both obturator foramina were symmetrical in appearance. A magnification error was corrected by reference to the templating ball of known size placed at the level of the hip, between the legs, and within the field of view.
      A radiographic analysis of the proximal femoral and pelvic geometry was performed to assess for radiographic risk factors associated with a risk of fracture. Proximal femoral geometry was analyzed using previously described radiographic parameters including canal-flare index (CFI) [
      • Noble P.C.
      • Alexander J.W.
      • Lindahl L.J.
      • Yew D.T.
      • Granberry W.M.
      • Tullos H.S.
      The anatomic basis of femoral component design.
      ], canal-calcar ratio (CCR) [
      • Dorr L.D.
      Total hip replacement using APR system.
      ], canal-bone ratio (CBR) [
      • Yeung Y.
      • Chiu K.Y.
      • Yau W.P.
      • Tang W.M.
      • Cheung W.Y.
      • Ng T.P.
      Assessment of the proximal femoral morphology using plain radiograph-can it predict the bone quality?.
      ], and the morphological cortical index (MCI) [
      • Spotorno L.
      • Romagnoli S.
      Indications for the CLS stem.
      ]. Pelvic geometry was analyzed using the ilium-ischial ratio (IIR) [
      • Swann R.P.
      • Pelt C.E.
      Indications for the direct anterior approach.
      ], ilium overhang, and distance from anterior superior iliac spine to the tip of the greater trochanter (AGT). Each of these measurements can be calculated on the AP radiograph (Fig. 1, Fig. 2). CFI is the ratio between metaphyseal width measured 2 cm proximal to the lesser trochanter (LT) and the endosteal diameter 10 cm distal to the LT. This differs from Dorr classification of the proximal femur which describes morphology in both the AP and lateral projections, using the cortical index to categorize into these subtypes [
      • Dorr L.D.
      • Faugere M.C.
      • Mackel A.M.
      • Gruen T.A.
      • Bognar B.
      • Malluche H.H.
      Structural and cellular assessment of bone quality of proximal femur.
      ]. CCR is the ratio of the endosteal diameter 10 cm below the LT to the endosteal diameter at the level of the LT, whereas the CBR is the ratio of the endosteal diameter to the external diameter at a level 10 cm below the LT. The MCI is described as the ratio of the external diameter at the level of the LT to the endosteal diameter at a point 7 cm below the LT.
      Figure thumbnail gr1
      Fig. 1Pelvic morphological parameters on antero-posterior pelvic radiograph, Ilium-ischial ratio (IIR) = A/B; ASIS to greater trochanter distance (AGT).
      Figure thumbnail gr2
      Fig. 2Schematic of measurements of proximal femoral morphology. Canal-flare index (CFI) = A/E; Canal-calcar ratio (CCR) = E/C; Canal-bone ratio (CBR) = E/F; Morphological cortical index (MCI) = B/D.

      Intraobserver and Interobserver Reliability

      Two observers (orthopedic fellow and orthopedic resident) blinded to outcome, ie, fracture case or control case, performed all measurements. Intraclass correlation was measured using the criteria defined by Landis and Koch [
      • Landis J.R.
      • Koch G.G.
      The measurement of observer agreement for categorical data.
      ]. Scores between 0.61 and 0.8 describe substantial agreements and those greater than 0.81 are considered almost perfect agreements. Excellent interobserver coefficients (ICC) were identified (ICC 0.751-0.970). One observer repeated measurements on 20% of all cases randomly selected and excellent ICC were identified (0.720-0.990).

      Statistical Analysis

      Descriptive statistics are presented as means and standard deviations. Categorical variables are presented as absolute numbers and percentages. Nonparametric tests were used for the data analysis. The Mann–Whitney U test was used to compare continuous data between groups. Cross-tabulated data were compared using the chi-squared test, or Fisher’s Exact test where any expected cell count was <5, and odds ratios (with 95% confidence intervals [CI]) were calculated. Correlations were tested using Spearman’s Rho. Morphological factors that were independent predictors of fractures were determined using a univariate and multivariate analysis. Variables that were correlated with one another were removed from the multivariate analysis. The Receiver-operating characteristic curve (ROC) analysis was performed on factors identified through a univariate and multivariate analysis to be of statistical significance [
      • Zweig M.H.
      • Campbell G.
      Receiver-operating characteristic (ROC) plots: a fundamental evaluation tool in clinical medicine.
      ]. The area under a ROC curve (AUC) ranges from 0.5, indicating a test with no accuracy in distinguishing a fracture risk, to 1.0 where the test perfectly predicts fracture. AUC of >0.7 identifies a test with acceptable discriminatory power [
      • Pepe M.
      The statistical evaluation of medical tests for classification and prediction.
      ]. All statistical analyses were performed using SPSS statistical software (version 28.0, SPSS Inc, Armonk, NY). Statistical significance was set at P < .05.

      Results

      Of the 39 fractures, 17 fractures (43.6%) occurred intraoperatively, whereas 22 occurred postoperatively (56.4%) (Table 2). Twenty cases (51.3%) were treated nonoperatively, whereas 9 cases (23.1%) were treated with open reduction internal fixation and 10 cases (25.6%) required revision of the femoral component. Differences between outcome groups and Vancouver fracture patterns in terms of pelvic and femoral morphology are presented in Table 3, Table 4. Significant differences were noted between case and control groups for several parameters, of which the most strongly significant were CFI (3.69 ± 0.60 vs 2.93 ± 0.44, P < .001, Mann–Whitney U test) and IIR (3.32 ± 0.55 vs 2.98 ± 0.48, P = .001). For most parameters, there were no differences between fracture types.
      Table 2Fracture Subtypes.
      Fracture locationIntraoperativePostoperativeTotal (%)
      Greater trochanter (GT)11213 (33.3)
      Vancouver B131013 (33.3)
      Vancouver B2088 (20.5)
      Vancouver B3022 (5.1)
      LT101 (2.6)
      Calcar202 (5.1)
      Total172239 (100)
      Table 3Pelvic and Femoral Morphological Parameters by Outcome.
      VariableFracture (n = 39)Nonfracture (n = 78)P Value
      Mann-Whitney U test.
      Pelvic parameters
       Ilium-ischial ratio (IIR)3.32 ± 0.552.98 ± 0.48.001
       ASIS to acetabulum distance (AA) (mm)72.8 ± 19.685.2 ± 12.3.002
       ASIS to greater trochanter distance (AGT) (mm)85.8 ± 21.998.9 ± 14.4.002
       Ilium overhang (yes/no) (%)24/15 (61.5)32/46 (41.0).036
      Chi-squared test.
      Femoral parameters
       Δfemoral offset (mm)−0.04 ± 6.044.30 ± 7.10.002
       Canal Flare Index (CFI)3.69 ± 0.602.93 ± 0.44<.001
       Canal-calcar ratio (CCR)0.45 ± 0.060.42 ± 0.06.006
       Canal-bone ratio (CBR)0.42 ± 0.070.47 ± 0.09.006
       Morphological cortical index (MCI)2.73 ± 0.352.70 ± 0.39.674
      Surgical Technique
       Canal fill at 1 cm (%)82.4 ± 16.085.4 ± 6.3.575
       Canal fill at 3 cm (%)82.8 ± 7.686.7 ± 6.8.007
      Bold indicates P values <.05.
      a Mann-Whitney U test.
      b Chi-squared test.
      Table 4Pelvic and Femoral Morphological Parameters by Vancouver Type (A or B).
      VariableFracture (n = 39)Vancouver a (n = 16)Vancouver B (n = 23)P Value
      Mann-Whitney U test.
      Pelvic parameters
       Ilium-ischial ratio (IIR)3.32 ± 0.553.19 ± 0.553.40 ± 0.53.297
       ASIS to acetabulum distance (AA) (mm)72.8 ± 19.672.53 ± 17.7773.01 ± 21.01.754
       ASIS to greater trochanter distance (AGT) (mm)85.8 ± 21.985.19 ± 18.8686.27 ± 24.12.777
       Ilium overhang (yes/no) (%)24/15 (61.5)10/6 (62.5)14/9 (60.9).918
      Chi-squared test.
      Femoral parameters
       Δfemoral offset (mm)−0.04 ± 6.040.60 ± 4.61−0.48 ± 6.92.865
       Canal Flare Index (CFI)3.69 ± 0.603.52 ± 0.413.78 ± 0.71.225
       Canal-calcar ratio (CCR)0.45 ± 0.060.47 ± 0.050.44 ± 0.07.198
       Canal-bone ratio (CBR)0.42 ± 0.070.45 ± 0.060.41 ± 0.08.012
       Morphological cortical index (MCI)2.73 ± 0.352.60 ± 0.252.84 ± 0.38.007
      Surgical Technique
       Canal fill at 1 cm (%)82.4 ± 16.083.39 ± 20.5786.88 ± 12.02.367
       Canal fill at 3 cm (%)82.8 ± 7.684.95 ± 7.0581.30 ± 7.73.160
      Bold indicates P values <.05.
      a Mann-Whitney U test.
      b Chi-squared test.

      Univariate and Multivariate Analysis

      Univariate and multivariate analyses are presented in Table 5, Table 6. Variables identified on a univariate analysis to be risk factors for fracture were selected for the multivariate model. As several variables were closely correlated with one another, the multivariate model analyzed those variables with the strongest statistical significance. CFI was weakly correlated with CCR (ρ = −0.186, P = .046). CCR and CBR were moderately correlated (ρ = 0.536, P < .001). A multivariate analysis revealed CFI (P < .001), IIR (P = .011), and canal fill at 3 cm (P = .012) to be the strongest predictors of fracture (R2 = 0.634).
      Table 5Univariate Analysis for Fracture Risk.
      VariableFractureOR (95% [CI])P Value
      YesNo
      Mean Age (y)67.7 ± 11.866.5 ± 11.9Not applicable.593
      Mann-Whitney U test.
      BMI (kg/m2)27.7 ± 6.427.0 ± 5.4Not applicable.648
      Mann-Whitney U test.
      Gender (%)1.054 (0.485-2.290).895
      Chi-squared test.
       Male17 (43.6)33 (42.3)
       Female22 (56.4)45 (57.7)
      Side1.348 (0.582-3.119).485
      Chi-squared test.
       Right28 (71.8)51 (65.4)
       Left11 (28.2)27 (34.6)
      Dorr ClassificationNot applicable.712
      Fisher’s Exact test.
       A24 (61.5)49 (62.8)
       B14 (35.9)24 (30.8)
       C1 (2.6)5 (6.4)
      IIR3.32 ± 0.552.98 ± 0.48Not applicable.001
      Mann-Whitney U test.
      AA72.8 ± 19.685.2 ± 12.3Not applicable.002
      Mann-Whitney U test.
      AGT85.8 ± 21.998.9 ± 14.4Not applicable.002
      Mann-Whitney U test.
      Ilium Overhang (yes) (%)24/39 (61.5)32/78 (41.0)2.300 (1.047-5.054).036
      Chi-squared test.
      Δfemoral offset (mm)−0.04 ± 6.044.30 ± 7.10Not applicable.002
      Mann-Whitney U test.
      Canal Flare Index (CFI)3.69 ± 0.602.93 ± 0.44Not applicable<.001
      Mann-Whitney U test.
      Canal-calcar ratio (CCR)0.45 ± 0.060.42 ± 0.06Not applicable.006
      Mann-Whitney U test.
      Canal-bone ratio (CBR)0.42 ± 0.070.47 ± 0.09Not applicable.006
      Mann-Whitney U test.
      Morphological cortical index (MCI)2.73 ± 0.352.70 ± 0.39Not applicable.674
      Mann-Whitney U test.
      Canal fill at 1 cm (%)82.4 ± 16.085.4 ± 6.3Not applicable.575
      Mann-Whitney U test.
      Canal fill at 3 cm (%)82.8 ± 7.686.7 ± 6.8Not applicable.007
      Mann-Whitney U test.
      Bold indicates P values <.05.
      a Mann-Whitney U test.
      b Chi-squared test.
      c Fisher’s Exact test.
      Table 6Multivariate Analysis.
      Nagelkerke R2 = 0.634
      VariableBeta ß95% Confidence IntervalP Value
      LowerUpper
      II ratio5.3581.46919.545.011
      AGT length0.9900.9551.027.593
      CFI23.5955.560100.126<.001
      Canal fill at 3 cm0.8870.8080.975.012
      Ilium overhang0.6100.1692.206.451
      Δ femoral offset0.9550.8641.056.371
      Bold indicates P values <.05.

      Receiver-Operator Curve Analysis

      A ROC curve was constructed to identify threshold values of fracture (Fig. 3). The area under the ROC curve for CFI as an independent predictor was 0.843 (95% CI: 0.765-0.922). A threshold CFI value of 3.17 would predict fracture with a sensitivity of 84.6% and specificity of 75.6% (P < .001), positive likelihood ratio of 3.467, and negative likelihood ratio of 0.204. For a CFI >3.17, the odds of fracture was 16.403 (OR: 16.403, 95% CI: 6.165-43.647, P < .001). When the threshold value of CFI >3.17 was combined with IIR >3, the odds of fracture was 29.2 times higher (OR: 29.200, 95% CI: 9.486-89.884, P < .001) (Fig. 4). An illustrative case is presented in Figure 5.
      Figure thumbnail gr3
      Fig. 3Receiver-operator characteristic curve (ROC) for CFI. Area under the ROC curve = 0.843 (95% confidence interval 0.765-0.922, P < .001).
      Figure thumbnail gr4
      Fig. 4Scatterplot of IIR and CFI for cases studied and fracture risk.
      Figure thumbnail gr5
      Fig. 5Illustrative case of patient with adverse radiographic parameters. A 66-year-old female patient with preoperative adverse radiographic parameters. IIR = 3.79, CFI = 3.42 (A). Postoperative radiograph demonstrating periprosthetic fracture around femoral component (B).

      Discussion

      At our institution, the AA has become the preferred surgical approach to primary THA and has been almost exclusively employed over the past decade. As a result, we were able to identify a large nonselective cohort of consecutive patients who have undergone THA with an AA using a commonly used short stem with an excellent track record (ODEP 10A). The overall incidence of periprosthetic fracture was 3.4% (39/1,145), requiring reoperation in 1.7% (19/1,145) and revision in 0.9% (10/1,145). Intraoperative fracture in AA THA may occur in up to 2.3% of cases [
      • Lee G.C.
      • Marconi D.
      Complications following direct anterior hip procedures: costs to both patients and surgeons.
      ]. The observed slightly higher fracture rate in our cohort may be explained by the inclusion of both intraoperative and early postoperative fractures. Furthermore, we included trochanteric and intraoperative calcar fractures (n = 16), of which most were treated nonoperatively. Our overall femoral revision rate of 0.9% is consistent with previous reports, including those from other institutions using the same stem design [
      • Berend K.R.
      • Mirza A.J.
      • Morris M.J.
      • Lombardi A.V.
      Risk of periprosthetic fractures with direct anterior primary total hip arthroplasty.
      ,
      • Greco N.J.
      • Lombardi A.V.
      • Morris M.J.
      • Hobbs G.R.
      • Berend K.R.
      Direct anterior approach and perioperative fracture with a single-taper wedge femoral component.
      ,
      • De Geest T.
      • Fennema P.
      • Lenaerts G.
      • De Loore G.
      Adverse effects associated with the direct anterior approach for total hip arthroplasty: a Bayesian meta-analysis.
      ].
      When fractures were compared with a matched cohort of nonfracture cases, two important radiographic thresholds were identified highlighting that certain hip morphology is associated with a significant fracture risk using the AA; CFI greater than 3.17 and IIR >3. Each of these two factors was a predictor of being at a fracture risk; however, the combination of both was associated with a very high risk and we would thus recommend caution if such morphology is present on preoperative evaluations if a short stem is planned to be used. A femoral component was associated with the fracture risk and we would thus recommend for heightened vigilance at the time of surgery to ensure appropriate size.
      Femoral exposure during AA THA is perceived as the more technically demanding aspect of the procedure, with implants being introduced at a steeper angle into the femoral canal [
      • Krismer M.
      • Nogle M.
      • Rachbauer F.
      Direct, anterior, single-incision approach.
      ,
      • Rodriguez J.A.
      • Kamara E.
      • Cooper H.J.
      Applied anatomy of the direct anterior approach for femoral mobilization.
      ]. Cementless femoral stems of a shorter design offer an attractive option to counter this problem while permitting soft tissue protection. Short-term and mid-term outcomes suggest these implants are safe with acceptable rates of revision [
      • van Oldenrijk J.
      • Molleman J.
      • Klaver M.
      • Poolman R.W.
      • Haverkamp D.
      Revision rate after short-stem total hip arthroplasty: a systematic review of 49 studies.
      ]. However, longer-term outcomes on the use of this stem design in THA are lacking. Dietrich et al suggest short stem designs may be protective for periprosthetic fracture in the AA compared with straight cementless stems (1.6% vs 6.8%) [
      • Dietrich M.
      • Kabelitz M.
      • Dora C.
      • Zingg P.O.
      Perioperative fractures in cementless total hip arthroplasty using the direct anterior minimally invasive approach: reduced risk with short stems.
      ], whereas Molli et al theorized that intraoperative periprosthetic fracture may be less with a short stem due to reduced load during broaching [
      • Molli R.G.
      • Lombardi A.V.
      • Berend K.R.
      • Adams J.B.
      • Sneller M.A.
      A short tapered stem reduces intraoperative complications in primary total hip arthroplasty.
      ]. Careful preoperative radiographic evaluation appears essential in the selection of an appropriate implant to avoid complications, particularly in the anterior approach. Several radiographic parameters have been described to evaluate pelvic and femoral morphology [
      • Noble P.C.
      • Alexander J.W.
      • Lindahl L.J.
      • Yew D.T.
      • Granberry W.M.
      • Tullos H.S.
      The anatomic basis of femoral component design.
      ,
      • Dorr L.D.
      Total hip replacement using APR system.
      ,
      • Yeung Y.
      • Chiu K.Y.
      • Yau W.P.
      • Tang W.M.
      • Cheung W.Y.
      • Ng T.P.
      Assessment of the proximal femoral morphology using plain radiograph-can it predict the bone quality?.
      ,
      • Spotorno L.
      • Romagnoli S.
      Indications for the CLS stem.
      ,
      • Swann R.P.
      • Pelt C.E.
      Indications for the direct anterior approach.
      ].
      In the present study, we found differences in several femoral and pelvic morphological parameters between groups. Fracture cases had a higher IIR and were more likely to have IIR >3 (80% vs 40%). A broader, more prominent, ilium may make exposure more difficult. This could obscure broaches from entering the femoral canal for preparation in a straight line, even when using offset broaches. Similarly, a higher CFI was detected in the fracture cases. A higher CFI suggests a broader metaphyseal region relative to the femoral canal, ie, a metaphyseal-diaphyseal “mismatch”. This theoretically results in engagement of a short stem early in the femoral canal, resulting in an implant undersized relative to the metaphysis. In addition, an overhanging prominent ilium may generate an unintended rotation during the rasping process and a suboptimal metaphyseal preparation. While some axial stability might be achieved by virtue of the tight canal, micromotion in the metaphysis may result in the failure of osseointegration [
      • Homma Y.
      • Kawakita S.
      • Baba T.
      • Watari T.
      • Kaneko K.
      Diagnosis of and early revision surgery for biological fixation failure due to proximal-distal mismatch of proximally coated tapered cementless stem.
      ,
      • White C.A.
      • Carsen S.
      • Rasuli K.
      • Feibel R.J.
      • Kim P.R.
      • Beaulé P.E.
      High incidence of migration with poor initial fixation of the Accolade stem.
      ]. A flat metaphyseal wedge stem design, such as the one used in the present study, is likely poorly tolerant of this lack of osseous support in the anteroposterior plane. Thus, patients with these adverse radiographic characteristics (Fig. 4) may be unsuitable for a short cementless stem inserted through the anterior approach.
      Surgical technique appears to play a role too. We observed a higher canal fill % at 3 cm from the LT in control cases. This would suggest that in fracture cases the component may have potentially been suboptimally sized relative to native anatomy. In this setting, a short stem that preferentially loads proximally may not tolerate the mismatch between implant and canal size, resulting in poor osseointegration. Our observations regarding CFI and canal fill are further supported by the findings of Ishii et al, who found poor osseointegration of a proximally coated stem was associated with a higher CFI and lower canal fill at 2 cm [
      • Ishii S.
      • Homma Y.
      • Baba T.
      • Ozaki Y.
      • Matsumoto M.
      • Kaneko K.
      Does the canal fill ratio and femoral morphology of Asian females influence early radiographic outcomes of total hip arthroplasty with an uncemented proximally coated, tapered-wedge stem?.
      ]. We suspect morphology and surgical technique are both likely contributory to a fracture risk. Recognizing this metaphyseal-diaphyseal mismatch on preoperative templating would potentially avoid this complication by selecting an alternative implant or fixation philosophy that might better control for rotation in the metaphysis or load beyond the metaphysis.
      Interestingly, our findings in relation to CFI and canal fill differ from those reported by Griffiths et al [
      • Griffiths S.Z.
      • Post Z.D.
      • Buxbaum E.J.
      • Paziuk T.M.
      • Orozco F.R.
      • Ong A.C.
      • et al.
      Predictors of perioperative Vancouver B periprosthetic femoral fractures associated with the direct anterior approach to total hip arthroplasty.
      ]. In their study, a lower CFI (2.75 vs 3.20) with higher canal fill was found to be predictive of early fracture following AA THA. However, there are several differences in methodology that may account for the observed differences in findings between studies. The Griffith study exclusively examined Vancouver type B fractures, whereas the present study evaluated all periprosthetic fractures, occurring both intraoperatively and postoperatively. Even so, we found no differences between fracture types for CFI (P = .225) and canal fill (P = .160). In addition, most of the fracture cases included in the study by Griffith et al were of Dorr type B anatomy (65.3%), whereas most of the fracture cases in the present study were of Dorr type A anatomy (61.5%).
      There are limitations to this study. First, the study design was limited by the retrospective nature of this case-control study, which may introduce selection bias. However, our groups were well matched for factors known to be associated with a fracture risk. Second, all measurements were taken on plain film radiography. It is possible that some subtle fractures may not have been detected on the AP radiograph alone. Computed tomography (CT) imaging might provide a more detailed three-dimensional assessment of proximal femoral anatomy and the position of the femoral component in the proximal femur. However, CT evaluation does generally form a part of the routine postoperative evaluation of THAs and would increase radiation exposure to patients. In addition, we used previously described techniques to assess component position on plain film radiography. Finally, only one type of femoral component was assessed in the present study. No comment can therefore be made as to whether the findings of this study are specific to the implant studied or can be applied more generally. Further study is required to investigate whether our observations may translate to other femoral component designs.

      Conclusion

      A preoperative radiographic assessment of femoral and pelvic morphology may be predictive of fracture following AA THA using a short cementless stem. The strongest predictors for fracture are CFI and IIR. In combination, hips with adverse CFI and IIR above threshold values may be at a higher risk of early periprosthetic fracture when using short cementless stems. Surgeons should consider an alternative implant design or fixation philosophy or an alternative approach to mitigate for this potential risk. Further investigation is needed to determine whether these observations differ by an implant design.

      Acknowledgment

      The authors wish to acknowledge the work of our colleague and friend Dr Michael J. Cochran who sadly passed before he could see his contributions to this study come to full fruition.

      Appendix A. Supplementary Data

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