Orthopedics

Feature Article 

The Role of Stem Modularity in the Failure of Internal Fixation in Geriatric Patients With Distally Fixed Hemiarthroplasty

Osman Çiloglu, MD; Evren Karaali, MD

Abstract

The aim of this study was to compare the radiological and clinical outcomes of the same make of modular and monoblock tapered fluted stems in patients with failure of internal fixation following osteoporotic intertrochanteric fracture. This retrospective, comparative study included patients older than 65 years who underwent hemiarthroplasty with a modular or monoblock distally fixed fluted stem and had failed treatment with proximal femoral nailing between 2012 and 2017, with at least a 2-year follow-up period. Radiographic and clinical evaluations of the groups were compared. The modular group comprised 22 males and 18 females with a mean age of 85.05±7.1 years, and the monoblock group comprised 27 males and 17 females with a mean age of 83.27±7.0 years. No significant difference was observed between the groups regarding the preoperative and final-visit Harris Hip Score and Parker and Palmer Mobility Score values (P>.05 for both). More patients showed osseous restoration in the monoblock group, but not to a significant level. The groups were similar regarding mortality rates. Stem length was greater in the modular group, but the proximal femoral part and stem size were similar in the groups (P<.05 for all). Canal filling at levels A, B, and C was negatively correlated (weak) with the proximal femoral bone restoration (P<.001 for all). Canal filling at level B was negatively correlated (weak) with the stress shielding of the femur (P<.05 for all). When comparing the modularity of the stem by minimizing the variations of both prostheses, such as brand and geometric design, there was no significant difference in either clinical or radiological evaluations. [Orthopedics. 2021;44(1):e119–e124.]

Abstract

The aim of this study was to compare the radiological and clinical outcomes of the same make of modular and monoblock tapered fluted stems in patients with failure of internal fixation following osteoporotic intertrochanteric fracture. This retrospective, comparative study included patients older than 65 years who underwent hemiarthroplasty with a modular or monoblock distally fixed fluted stem and had failed treatment with proximal femoral nailing between 2012 and 2017, with at least a 2-year follow-up period. Radiographic and clinical evaluations of the groups were compared. The modular group comprised 22 males and 18 females with a mean age of 85.05±7.1 years, and the monoblock group comprised 27 males and 17 females with a mean age of 83.27±7.0 years. No significant difference was observed between the groups regarding the preoperative and final-visit Harris Hip Score and Parker and Palmer Mobility Score values (P>.05 for both). More patients showed osseous restoration in the monoblock group, but not to a significant level. The groups were similar regarding mortality rates. Stem length was greater in the modular group, but the proximal femoral part and stem size were similar in the groups (P<.05 for all). Canal filling at levels A, B, and C was negatively correlated (weak) with the proximal femoral bone restoration (P<.001 for all). Canal filling at level B was negatively correlated (weak) with the stress shielding of the femur (P<.05 for all). When comparing the modularity of the stem by minimizing the variations of both prostheses, such as brand and geometric design, there was no significant difference in either clinical or radiological evaluations. [Orthopedics. 2021;44(1):e119–e124.]

Internal fixation with an open or closed reduction technique is an option in the treatment of intertrochanteric fractures of the femur in geriatric osteoporotic patients, yet fixation failure can be seen in 3% to 13% of these patients.1–3 Failure of fixation in geriatric patients can lead to serious complications such as prolonged immobilization.4,5 Arthroplasty surgery is recommended in cases of fixation failure because it allows early mobilization. In this context, the use of tapered fluted stems in arthroplasty surgeries has increased in recent years because it is thought that they achieve more axial and rotational stability compared with porous-coated cylindrical stems.6–11

Femoral bone regeneration is of paramount importance in revision surgeries in terms of maintaining the proximal femoral bone stock. Femoral bone restoration has been reported at rates of 17% to 56% and 47% to 88% in modular and monoblock tapered fluted stems, respectively.11 Moreover, modular and monoblock stems have shown successful clinical outcomes in the mid-term and long-term follow-up periods. However, stress shielding and proximal femoral bone restoration values are important in the selection of the stem by the surgeon.

There has been only 1 study published comparing modular and monoblock stems in terms of stress shielding and femoral bone restoration. However, the stems used in that study had different geometric and biomechanical characteristics, such as stem spine length, and were of different brands.11 The make and geometric/biomechanical characteristics can be considered to have affected the outcomes.12 Therefore, the objective of this study was to compare the radiological and clinical outcomes of the same make of modular and monoblock tapered fluted stems in patients with failure of internal fixation following osteoporotic intertrochanteric fracture.

Materials and Methods

Study Design and Participants

This retrospective, comparative study included patients older than 65 years who underwent hemiarthroplasty with a modular or monoblock distally fixed fluted stem and had failed treatment with proximal femoral nailing between 2012 and 2017, with at least a 2-year follow-up period. Patients with acetabular erosion, being younger than 65 years, with a fracture due to nonosteoporotic causes (eg, malignancy, trauma), or with a follow-up period of less than 2 years were excluded from the study. This study received ethics committee approval, and informed consent was obtained from all patients.

Surgery

All surgical procedures were performed with a posterolateral surgical approach by the same surgical team with the patient in the lateral position, as described by Moore.13 A fluted tapered stem was used in the monoblock group (Monoblock Prosthesis; Tipmed Medical Devices) and in the modular group (Tipmed S2 Modular Prosthesis) (Figure 1). The patients were mobilized on the day after surgery using crutches, and weight bearing was permitted as tolerated.

Monoblock and modular tapered fluted titanium stems.

Figure 1:

Monoblock and modular tapered fluted titanium stems.

Clinical and Radiographic Evaluation

All patients were evaluated at 1, 3, 6, and 12 months postoperatively and annually thereafter. Radiographic and clinical evaluations were performed at each follow-up examination.

Proximal bone restoration in residual osteolytic areas was classified as osseous restoration, constant defects, or increasing defects.14

Evaluations were also made of stem stability, femoral stress shielding, any radiolucent lines and focal osteolysis around the femoral stem, stem diameter, and 3 levels of medullary canal filling (the ratio of stem width to femoral canal width; level A at the proximal third of the stem, level B at the midpoint of the stem, and level C at the distal third of the stem).15–18 Subsidence of the femoral component was evaluated according to the change in the distance of the implant from the superolateral edge at the shoulder of the prosthesis to the tip of the greater trochanter on the anteroposterior radiograph.19

Limb-length discrepancy was measured as the distance between the interteardrop line and the lower margin of the lesser trochanter. A difference of greater than 2 cm between the 2 limb lengths was defined as failure.20 The presence of heterotopic ossification presence was noted.21 The stem was classified as varus or valgus if there was 5° or more between the stem axis and the anatomical axis of the femur.

Statistical Analysis

SPSS software (IBM Corp) was used to analyze the data. Descriptive data were given as mean, standard deviation, median, number, or percentage. Between-group comparisons of the numerical data were made using the Student's t test or Mann–Whitney U test according to the conformity of the data to normal distribution. Categorical data were compared using the chi-square test. Pearson correlation analyses were performed for the correlation analyses. P<.05 was accepted as statistically significant.

Results

A total of 84 patients were evaluated. The modular group comprised 22 males and 18 females with a mean age of 85.05±7.1 years (range, 73–90 years), and the monoblock group comprised 27 males and 17 females with a mean age 83.27±7.0 years (range, 70–97 years). Clinical and demographic features are summarized in Table 1. No significant difference was observed between the groups in terms of age, sex, body mass index, and Singh index values (P>.05 for all). No significant difference was observed between the groups in terms of preoperative and final-visit Harris Hip Score (HHS) and Parker and Palmer Mobility Score values (P>.05 for both). More patients showed osseous restoration in the monoblock group, but not at a significant level. The mortality rates were similar in both groups. Focal osteolysis was found in 17.5% and 2.3% of the patients in the modular group and monoblock group, respectively (P=.025). Early postoperative and final control radiographs showing osteolysis are presented in Figure 2.

Clinical and Demographic FeaturesClinical and Demographic Features

Table 1:

Clinical and Demographic Features

Early postoperative (A) and final control (B) anteroposterior radiographs of hemiarthroplasty with a modular tapered fluted titanium stem. The arrows indicate stress shielding and focal osteolysis at the stem junction. Early postoperative (C) and final control (D) anteroposterior radiographs of hemiarthroplasty with monoblock tapered fluted titanium stem.

Figure 2:

Early postoperative (A) and final control (B) anteroposterior radiographs of hemiarthroplasty with a modular tapered fluted titanium stem. The arrows indicate stress shielding and focal osteolysis at the stem junction. Early postoperative (C) and final control (D) anteroposterior radiographs of hemiarthroplasty with monoblock tapered fluted titanium stem.

The comparisons of stem diameter, length, and medullary canal filling at levels A, B, and C are summarized in Table 2. The diameter at level A was significantly higher in the monoblock group. Canal filling at levels A and C was significantly higher in the monoblock group. Stem length was greater in the modular group, and the proximal femoral part and stem size were similar in both groups (P<.05 for all).

Comparison of Stem Diameter, Length, and Medullary Canal Filling

Table 2:

Comparison of Stem Diameter, Length, and Medullary Canal Filling

Correlation analyses are presented in Table 3. Canal filling at levels A, B, and C was negatively correlated with proximal femoral bone restoration (P<.001 for all). Canal filling at level B was negatively correlated with stress shielding of the femur (P<.05 for all).

Correlation Analyses

Table 3:

Correlation Analyses

Discussion

The aim of this study was to compare the clinical and radiological outcomes of modular and monoblock fluted tapered femoral stems (from the same brand with the same geometric properties). The groups showed similar results both radiologically and clinically.

There are many studies in the literature showing the advantages of fluted tapered stems in revision hip surgeries. Hnat et al8 found that the fluted tapered stem had a lower stress-shielding rate compared with cobalt chrome-plated prosthetics due to the lower elastic modulus. In a study that compared fluted tapered titanium stems and cylindrical chromium cobalt stems, the results showed less thigh pain and lower fracture rates in the group applied with fluted tapered stem.9,10

There are only a few studies that have compared the modular and monoblock systems of distally fixed tapered fluted stems, and in those studies, comparisons were made of 2 stems of different brands and geometric characteristics.11,22 In addition, when evaluating the effect of stem length and filling rate, there was no intragroup evaluation in the aforementioned studies. The main strength of the current study was that monoblock and modular stems of the same brand and with similar geometric properties were used in a similar protocol.

In this study, the effect of stem stiffness was compared (ie, modular or monoblock) on osseous restoration and femur stress shielding, and the results showed no statistically significant difference. Huang et al11 stated that their results showed a significant difference in favor of the monoblock group. However, in that study, the prosthetic designs were different. The distal part of the modular system was shorter and curved in that study, which allowed the surgeon to impact a thicker distal section. It was emphasized that the thicker distal section was stiffer, which would cause an overall reduction in strain on the femur but reduce the effectiveness of proximal stem-bone contact and strain transfer.

Rodriguez et al16 also reported diaphyseal stress shielding with modular stems in 29.7% of the patients, and Amanatullah et al23 stated this rate to be 23%. Although stress shielding was not seen to have any effect on postoperative HHS, severe femoral stress shielding may increase the risk of periprosthetic fractures. In the current study, no difference was determined between the groups in terms of bone regeneration and stress shielding. This was attributed to there being no design difference between the stem spine and distal stabilization so that the surgeon can offer a similar variety in terms of distal fixation in each stem.

One of the main drawbacks of the modular prosthesis is the risk of fracture at the junction.24,25 Modular junction fracture is more common in older prosthetic designs.26 In the current study, no stem breakage occurred in any modular group, which was attributed to the use of new-generation prosthetics and the high rate of filling. At the same time, because it was not necessary to use the standard short distal stem as in the old prosthetic designs in the modular group, it was determined that a longer stem could be used as the necessary factor to reduce strain transfer, thereby providing stable fixation.

The rates of dislocation in the literature have been reported to be similar in modular (2% to 12%) and nonmodular (5% to 13%) stems.9,10,16,26–28 In the current study, the rates of dislocation were similar in both groups. Modular prostheses is advantageous over monoblock stems in cases of development of dislocation. As with the modular stem, it is possible to change the length and anteversion of the proximal body with less invasive surgery and shorter surgery time without touching the entire stem.29–31

In another study of modular femoral stems, including ZMR (Zimmer) and Mallory-Head (Biomet), severe fretting-crevice corrosion was observed at the taper junction. This was seen to be due to crevices in the geometry of the implants, where fluids could enter and initiate fretting at the taper junction with release of particles due to wear and focal osteolysis.32 Similarly, in the current study, focal osteolysis was found in 17.5% and 2.3% of the patients in the modular group and monoblock group, respectively. This fact is significant because osteolytic areas can lead to periprosthetic fracture or loss of structural support for the prosthetic components.33

Femoral stem length was found to be unrelated to femoral bone regeneration and stress shielding and negatively correlated with the filling rate. It was thought that this might have weakened the circulation of the bone as the filling rate increased. Therefore, using a longer stem rather than forcing the filling rate to achieve stem stability may be more advantageous in terms of femoral bone regeneration and stress shielding.

Of the patients in the current study, 3 in the modular group and 6 in the monoblock group developed dislocation. In the treatment of dislocated patients, it was observed to be easier to operate on the modular system with the ability to make modifications to the proximal part in case of possible revision. Because the complication rate in revision surgery is higher in geriatric and osteoporotic patients than in primary cases, the advantages of the modular stem should not be ignored, and the possibility of complications developing should be kept in mind.

There are some important drawbacks to the current study. The retrospective design is the main limitation. Also, the follow-up period could be longer.

Conclusion

When comparing the modularity of the stems, by minimizing the variations of both prostheses, such as brand and geometric design, there was no significant difference in both clinical and radiological evaluations. Thus, it can be concluded that the design of the prosthesis rather than its modularity affects the outcomes and complications.

References

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  13. Moore AT. The self-locking metal hip prosthesis. J Bone Joint Surg Am. 1957;39:811–827. PMID:13438939
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  16. Rodriguez JA, Deshmukh AJ, Klauser WU, Rasquinha VJ, Lubinus P, Ranawat CS. Patterns of osseointegration and remodeling in femoral revision with bone loss using modular, tapered, fluted, titanium stems. J Arthroplasty. 2011;26(8):1409–1417.e1. doi:10.1016/j.arth.2011.06.021 [CrossRef] PMID:21855273
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  19. Meijerink HJ, Gardeniers JW, Buma P, Lemmens JA, Schreurs BW. Hydroxyapatite does not improve the outcome of a bipolar hemiarthroplasty. Clin Orthop Relat Res. 2004;421:143–150. doi:10.1097/01.blo.0000126307.64581.c6 [CrossRef] PMID:15123939
  20. Woolson ST, Hartford JM, Sawyer A. Results of a method of leg-length equalization for patients undergoing primary total hip replacement. J Arthroplasty. 1999;14(2):159–164. doi:10.1016/S0883-5403(99)90119-5 [CrossRef] PMID:10065720
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  22. Huang Y, Zhou Y, Shao H, Gu J, Tang H, Tang Q. What is the difference between modular and nonmodular tapered fluted titanium stems in revision total hip arthroplasty. J Arthroplasty. 2017;32(10):3108–3113. doi:10.1016/j.arth.2017.05.021 [CrossRef] PMID:28602532
  23. Amanatullah DF, Howard JL, Siman H, Trousdale RT, Mabry TM, Berry DJ. Revision total hip arthroplasty in patients with extensive proximal femoral bone loss using a fluted tapered modular femoral component. Bone Joint J. 2015;97-B(3):312–317. doi:10.1302/0301-620X.97B3.34684 [CrossRef] PMID:25737513
  24. Efe T, Schmitt J. Analyses of prosthesis stem failures in noncemented modular hip revision prostheses. J Arthroplasty. 2011;26(4):665. doi:10.1016/j.arth.2010.05.020 [CrossRef] PMID:20634038
  25. Lakstein D, Eliaz N, Levi O, et al. Fracture of cementless femoral stems at the mid-stem junction in modular revision hip arthroplasty systems. J Bone Joint Surg Am. 2011;93(1):57–65. doi:10.2106/JBJS.I.01589 [CrossRef] PMID:21209269
  26. Brown NM, Tetreault M, Cipriano CA, Della Valle CJ, Paprosky W, Sporer S. Modular tapered implants for severe femoral bone loss in THA: reliable osseointegration but frequent complications. Clin Orthop Relat Res. 2015;473(2):555–560. doi:10.1007/s11999-014-3811-7 [CrossRef] PMID:25053289
  27. Abdel MP, Cottino U, Larson DR, Hanssen AD, Lewallen DG, Berry DJ. Modular fluted tapered stems in aseptic revision total hip arthroplasty. J Bone Joint Surg Am. 2017;99(10):873–881. doi:10.2106/JBJS.16.00423 [CrossRef] PMID:28509828
  28. Huddleston JI III, Tetreault MW, Yu M, et al. Is there a benefit to modularity in ‘simpler’ femoral revisions?Clin Orthop Relat Res. 2016;474(2):415–420. doi:10.1007/s11999-015-4474-8 [CrossRef] PMID:26245164
  29. Cross MB, Paprosky WG. Managing femoral bone loss in revision total hip replacement: fluted tapered modular stems. Bone Joint J. 2013;95-B(11)(suppl A):95–97. doi:10.1302/0301-620X.95B11.32763 [CrossRef] PMID:24187363
  30. Sheth NP, Nelson CL, Paprosky WG. Femoral bone loss in revision total hip arthroplasty: evaluation and management. J Am Acad Orthop Surg. 2013;21(10):601–612. doi:10.5435/JAAOS-21-10-601 [CrossRef] PMID:24084434
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  32. Rodrigues DC, Urban RM, Jacobs JJ, Gilbert JL. In vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip-implants. J Biomed Mater Res B Appl Biomater. 2009;88(1):206–219. doi:10.1002/jbm.b.31171 [CrossRef] PMID:18683224
  33. Ries MD, Link TM. Monitoring and risk of progression of osteolysis after total hip arthroplasty. J Bone Joint Surg Am. 2012;94(22):2097–2105. PMID:23310970

Clinical and Demographic Features

VariableModular group (n=40)Monoblock group (n=44)P
Age, mean±SD, y85.05±7.183.27±7.0.131
Sex, No.
  Male22 (55.0%)27 (61.4%).293
  Female18 (45.0%)17 (38.6%)
Body mass index, mean±SD, kg/m229.10±3.030.02±3.0.436
Singh index, No.
  117 (42.5%)14 (31.8%).507
  216 (40.0%)23 (52.3%)
  37 (17.5%)7 (15.9%)
Follow-up, mean±SD, mo32.15±4.733.59±4.5.325
Weight-bearing time, mean±SD, d14.22±5.814.20±5.8.981
Harris Hip Score, mean±SD
  Preoperative45.02±23.548.68±23.3.350
  Postoperative78.23±9.080.29±8.3.156
Parker and Palmer Mobility Score, mean±SD
  Preoperative4.66±1.04.47±0.9.246
  Postoperative6.25±1.16.32±1.0.698
Complication, No.
  Dislocation3 (7.5%)6 (13.6%).832
  Infection2 (5.0%)4 (9.1%).434
  Fracture1 (2.5%)2 (4.5%).967
  Reoperation2 (5.0%)4 (9.1%).799
  Subsidence4 (10.0%)4 (9.1%).940
  Discrepancy2 (5.0%)1 (2.3%).959
  Heterotopic ossification7 (17.5%)9 (20.5%).998
  Osteolysis7 (17.5%)1 (2.3%).025
Femoral stress shielding, No.
  022 (55.0%)30 (68.2%).297
  19 (22.5%)10 (22.7%)
  24 (10.0%)1 (2.3%)
  33 (7.5%)3 (6.8%)
  42 (5.0%)0 (0%)
Proximal femoral bone restoration, No.
  Increasing defects4 (10.0%)1 (2.3%).180
  Constant defects26 (65.0%)26 (59.1%)
  Osseous restoration10 (25.0%)17 (38.6%)
Mortality, No.
  During hospital stay2 (5.0%)2 (4.6%).998
  <6 weeks4 (10.0%)4 (9.1%)
  6–24 weeks7 (17.5%)8 (18.2%)

Comparison of Stem Diameter, Length, and Medullary Canal Filling

VariableMean±SDP

Modular group (n=40)Monoblock group (n=44)
Diameter at level, mm
  A16.86±1.017.40±0.8.005
  B15.87±1.016.29±0.8.086
  C12.56±0.612.56±0.6.908
Canal filling at level
  A0.87±0.10.81±0.1.013
  B0.89±0.10.87±0.1.199
  C0.87±0.10.81±0.1.020
Proximal femoral part, mm53.25±9.250.22±7.9.109
Stem size, mm16.40±0.816.04±1.0.086
Stem length, mm169.5±23.5160.0±0.0.015

Correlation Analyses

VariableProximal femoral bone restorationDegree of stress shielding of the femur


rPrP
Age0.059.4800.071.393
Body mass index−0.047.170−0.231a.034
Preoperative Harris Hip Score−0.075.3680.088.293
Preoperative Parker and Palmer Mobility Score−0.043.6080.194.078
Diameter at level
  A−0.024.775−0.118.287
  B−0.009.913−0.194.076
  C−0.128.126−0.095.392
Canal filling at level
  A−0.387b<.001−0.191.082
  B−0.391b<.001−0.218a.046
  C−0.390b<.001−0.201.066
Stem length0.178.1060.091.412
Proximal femoral part0.215a.0490.092.404
Stem size0.107.333−0.194.076
Singh index−0.086.302−0.014.897
Authors

The authors are from the Department of Orthopaedics and Traumatology, University of Health Sciences, Adana Health Practice and Research Center, Adana, Turkey.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Osman Çiloglu, MD, Department of Orthopaedics and Traumatology, University of Health Sciences, Adana Health Practice and Research Center, Mithat Ozhan Bulvarı Kısla Mah No:1, Yuregir/Adana, Turkey ( osmanciloglu@gmail.com).

Received: October 27, 2019
Accepted: January 20, 2020
Posted Online: October 22, 2020

10.3928/01477447-20201007-02

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