Orthopedics

Feature Article 

Failure Patterns of Femoral Neck Fracture Fixation in Young Patients

David J. Stockton, MD; Karan Dua, MD; Peter J. O'Brien, MD, FRCSC; Andrew N. Pollak, MD; C. Max Hoshino, MD; Gerard P. Slobogean, MD, MPH, FRCSC

Abstract

The primary purpose of this study was to describe the failure patterns of femoral neck fracture fixation in young patients. The secondary purpose was to determine if pattern of failure varies by type of implant. Adult patients (age range, 18–55 years) who experienced a “fixation failure” following internal fixation of a femoral neck fracture were identified from 5 level 1 trauma centers. Failure was defined by screw cutout, implant breakage, varus collapse (<120° neck-shaft angle), or severe fracture shortening (≥1 cm). When multiple complications were identified, mechanical failures were preferentially noted for the analysis. Failure patterns were compared between patients who received multiple cancellous screws and patients who received a sliding hip screw plus a derotation screw. Severe fracture shortening was the most common complication identified (61%). No differences in the incidence of severe shortening (P=.750) or implant breakage (P=1.000) were detected between the fixation groups. However, among the failures with a sliding hip screw plus a derotation screw construct, a greater portion were related to screw cutout (38% for a sliding hip screw plus a derotation screw vs 7% for screws, P=.019). Failures with multiple screws were associated with varus collapse (25% for screws vs 0% for a sliding hip screw plus a derotation screw, P=.037). Severe shortening was the most common fixation failure. Sliding hip screw plus derotation screw implants were associated with screw cutout. Multiple cancellous screw implants failed by varus collapse. Selecting a surgical implant based on its likely failure pattern may allow surgeons to minimize the severity of failure or the need for secondary conversion to hip arthroplasty. [Orthopedics. 2019; 42(4):e376–e380.]

Abstract

The primary purpose of this study was to describe the failure patterns of femoral neck fracture fixation in young patients. The secondary purpose was to determine if pattern of failure varies by type of implant. Adult patients (age range, 18–55 years) who experienced a “fixation failure” following internal fixation of a femoral neck fracture were identified from 5 level 1 trauma centers. Failure was defined by screw cutout, implant breakage, varus collapse (<120° neck-shaft angle), or severe fracture shortening (≥1 cm). When multiple complications were identified, mechanical failures were preferentially noted for the analysis. Failure patterns were compared between patients who received multiple cancellous screws and patients who received a sliding hip screw plus a derotation screw. Severe fracture shortening was the most common complication identified (61%). No differences in the incidence of severe shortening (P=.750) or implant breakage (P=1.000) were detected between the fixation groups. However, among the failures with a sliding hip screw plus a derotation screw construct, a greater portion were related to screw cutout (38% for a sliding hip screw plus a derotation screw vs 7% for screws, P=.019). Failures with multiple screws were associated with varus collapse (25% for screws vs 0% for a sliding hip screw plus a derotation screw, P=.037). Severe shortening was the most common fixation failure. Sliding hip screw plus derotation screw implants were associated with screw cutout. Multiple cancellous screw implants failed by varus collapse. Selecting a surgical implant based on its likely failure pattern may allow surgeons to minimize the severity of failure or the need for secondary conversion to hip arthroplasty. [Orthopedics. 2019; 42(4):e376–e380.]

Complications following internal fixation of femoral neck fractures in non–geriatric patients are an important consideration in their management. A recent meta-analysis cited incidences of 18.0% for reoperation, 14.3% for avascular necrosis, and 9.3% for nonunion.1 Although fracture displacement and inadequate reduction have well-established associations with higher rates of complications,2 recent studies have suggested that implant choice may affect healing outcomes; the optimal fixation device remains controversial.3 In the absence of a clearly superior implant, having a clear understanding of the failure profile for each treatment option becomes even more important.

The most common implants involve multiple parallel cancellous screws (placed in a triangle or an inverted triangle fashion) or a sliding hip screw plus a derotation screw (SHS).3 These constructs theoretically promote healing by allowing the proximal fragment to slide distally and achieve compression across the fracture site. Although both of these devices allow for compression across the fracture site, too much fracture shortening results in worse functional outcomes in elderly patients4 and in adult patients younger than 60 years.5 In addition, each implant has its own unique properties. Cancellous screws are less invasive and preserve more bone stock, but they have no biomechanical resistance to varus forces. The sliding hip screw is a fixed angle device and is more rigid biomechanically, but it has not been proven that this rigidity improves fracture healing.

For non–geriatric patients with femoral neck fractures, it is currently unknown what the frequency and distribution of mechanical failure is between the 2 most popular implants and whether a particular type of failure is more commonly associated with the surgical implant selected. The primary purpose of this study was to describe the failure patterns of femoral neck fracture fixation in young patients. The secondary purpose was to determine if pattern of failure is determined by type of implant.

Materials and Methods

Patient Enrollment

The authors retrospectively identified fixation failures from prospectively maintained databases at 5 level 1 trauma centers, with 1 located in Vancouver, British Columbia, Canada; 1 located in Baltimore, Maryland; and 3 located in hospitals in mainland China. Institutional review board approval was obtained at the coordinating institution, with ethics committee concurrence at all 5 participating sites. Patients were included if they (1) presented between January 2003 and May 2013; (2) were 18 to 55 years old and had a closed femoral neck fracture; (3) were treated with closed or open reduction and fixed with either multiple cancellous screws or SHS; (4) experienced fixation failure; (5) had appropriate radiographs obtained at the time of injury, during surgery, and at follow-up; and (6) had at least 6 months of follow-up. Patients were excluded if they (1) were treated with arthroplasty, cephalomedullary nail, or other ipsilateral femoral shaft fixation; (2) had a pathologic or fragility fracture; or (3) had a concomitant closed head injury (Glasgow Coma Scale score <14), a spinal cord injury, or a preexisting psychiatric illness that impaired their ability to complete follow-up.

Fracture Management

All treatment decisions, including the reduction and fixation methods, were made by the attending surgeon. Postoperatively, patients were kept non–weight bearing for at least 6 weeks, with many surgeons electing to restrict weight bearing for 2 to 3 months.

Outcome Measurements

Fixation failure was defined by screw cutout, implant breakage, varus collapse (<120° neck-shaft angle), or severe fracture shortening (≥1 cm). These modes of failure were deemed likely to be implant related and therefore potentially modifiable. The authors included severe shortening because it represents failure of the fixation to maintain a length-stable reduction. The method used to determine fracture shortening has been previously described and shown to have excellent inter-rater reliability.6 Briefly, femoral neck shortening is quantified by measuring the screw with the largest amount of lateral protuberance compared with its initial fixation position and adjusted for magnification using the known screw diameter. Nonunion and avascular necrosis events were not included in the outcome analysis because they were not deemed direct fixation failures1,7,8; instead, the authors captured the mechanical consequence of these outcomes by measuring the resultant varus collapse or screw cutout.

In addition to primary outcomes, baseline fracture characteristics were identified and controlled for in the authors' analysis. All injury radiographs were reviewed to determine the fracture classification (Garden,9 Pauwels,10 and OTA11), level of fracture, and fracture displacement. Pauwels type 3 fractures (fracture line ≥50° to the horizontal) were considered vertical, and Garden type 3 and 4 fractures were considered displaced. Intraoperative and early postoperative radiographs were used to assess quality of reduction using the criteria outlined by Upadhyay et al.12 In this system, varus angulation of the principal compressive trabeculae of less than 160° on the anteroposterior view and posterior angulation of the femoral neck (ie, apex-anterior angulation) of greater than 5° on the lateral view are considered to indicate an unsatisfactory reduction. Grade I reductions are satisfactory on both the anteroposterior and the lateral, grade II have an unsatisfactory reduction on either the anteroposterior or the lateral, and grade III are unsatisfactory on both the anteroposterior and the lateral views.

Statistical Analyses

This retrospective cohort study adhered to the STROBE guidelines ( www.strobe-statement.org) for reporting observational studies. All analyses were performed with JMP 9 statistical software (SAS Institute Inc, Cary, North Carolina). Descriptive statistics were used to characterize all variables of interest. Mean and standard deviation or median and interquartile range were used depending on the distribution of continuous variables. Count and proportion were used to describe nominal data. Relationships between groups regarding the primary outcome variables were investigated using the chi-square test and Fisher's exact test. When multiple complications were identified, mechanical failures were preferentially noted for the analysis. Significance was set at P<.05 for all final analyses.

Results

Two hundred fifteen patients 18 to 55 years old with a femoral neck fracture were screened for fixation failure events. Forty-four failures were identified, with a failure rate of 19% for SHS and a failure rate of 24% for cancellous screw constructs. There were 16 SHS failures and 28 cancellous screw failures. Patient demographics and fracture characteristics are summarized in Table 1.

Patient and Fracture Characteristics

Table 1:

Patient and Fracture Characteristics

Screw cutout (18%), varus collapse (34%), and implant breakage (5%) represented the most severe mechanical fixation failures; however, these failures rarely occurred in isolation (Figure 1). For example, of the 8 patients who experienced screw cutout, 5 of them also failed in varus and 6 had severe shortening. Similarly, 15 patients experienced varus collapse; only 3 of these patients did not have coexisting shortening (1 had cutout and 2 had implant breakage). Although 61% of the cases of failure involved isolated severe fracture shortening, the overall prevalence of severe shortening in the failure cohort was 91%.

Representation of simultaneous mechanical failure patterns occurring in young patients with femoral neck fractures.

Figure 1:

Representation of simultaneous mechanical failure patterns occurring in young patients with femoral neck fractures.

Although no differences in the incidence of severe shortening (P=.750) or implant breakage (P=1.000) were detected between the 2 fixation groups, a significant difference in the distribution of failure patterns was detected (P=.024). A sliding hip screw plus a derotation screw was associated with screw cutout (38% vs 7% for cancellous screws, P=.019), whereas cancellous screws were associated with varus collapse (25% vs 0% for SHS, P=.037).

Discussion

In this cohort of 44 patients with femoral neck fracture fixation failures, the authors found that screw cutout, varus collapse, and implant breakage routinely occurred in conjunction with severe fracture shortening; however, severe shortening was the most common isolated mode of fixation failure. In addition, the authors found that mechanical failures of cutout and varus collapse were strongly associated with the implant construct selected.

Severe femoral neck shortening has emerged as an important complication in non–geriatric patients with femoral neck fractures, having a prevalence of 13% to 32%.5,6 This phenomenon has long been an important consideration in the hip arthroplasty literature owing to the effect on the abductor moment arm of the hip.13,14 The current findings show that a large portion of fixation failures occur through shortening along the femoral neck axis. This complication alone results in a poorer functional outcome for those patients,5 and whether this is due to a shortened abductor moment arm or symptomatic protruding hardware remains to be elucidated.15

This study adds valuable information to the debate over the optimal fixation method for non–geriatric patients with femoral neck fractures. Recently, Hoshino and O'Toole16 compared the incidence of nonunion and avascular necrosis after fixation of displaced femoral neck fractures in patients 16 to 60 years old treated with SHS or with multiple cancellous screws in a Pauwels screw configuration. This configuration consists of multiple cancellous screws placed parallel to the femoral neck and 1 lag screw directed transverse to the fracture line, from the greater trochanter into the inferior neck. Fewer complications were observed in the SHS group (21%) vs the screws group (60%), and avascular necrosis was less frequent in the SHS group (2%) vs the screws group (33%). They recommended against the use of cancellous screws in a Pauwels screw configuration and theorized that that particular configuration does not allow for compression following the index surgery, which is perhaps a key component for revascularization and bone healing.

A sliding hip screw plus a derotation screw and multiple cancellous screw constructs each have advantages and disadvantages. Cancellous screws are easier and less invasive to insert, maintain more bone stock, and possibly have improved rotational strength and preservation of femoral head vascularity.16–19 A recent survey found that for patients younger than 60 years with femoral neck fractures treated with internal fixation, 90% of surgeons prefer this type of fixation for nondisplaced fractures and 68% of surgeons prefer this type of fixation for displaced fractures.20 Proponents of fixed angle devices cite the greater biomechanical strength, particularly in more vertical fractures and basicervical fractures. These devices also have a greater ability to resist varus angulation and inferior displacement of the head.16,21–24 The current study showed that this greater ability to resist varus angulation is associated with a greater risk of cutout through the femoral head. Conversely, the inability of multiple cancellous screws to resist varus deformation is associated with a propensity to fail via that mechanism.

In the absence of a clearly superior implant, the surgeon and the patient may wish to consider which type of complication they would rather deal with when faced with a non–geriatric femoral neck fracture. If SHS is chosen and cutout occurs, there is little recourse other than total hip arthroplasty for younger, active patients. If cancellous screws fail either with shortening or with varus, options that retain the femoral head may be feasible, including vascularized fibula bone graft and valgus-producing intertrochanteric osteotomy. These key data may be useful during surgical decision-making and implant selection.

This study had several limitations. Although a comparison of the rate of failure for each implant would yield useful information, the authors refrained from doing so because of potential nonrandom treatment allocation due to selection bias. In addition, the authors' method of measuring shortening does not account for intraoperative shortening and therefore may not represent the full extent of anatomic femoral neck shortening. Shortening was measured using the most protuberant screw by comparing follow-up radiographs with radiographs after reduction. This technique has demonstrated excellent reliability and has the benefit of being simple and reproducible. The authors believed that this approach was most appropriate because their research question focused on whether the implant failed mechanically after fixation and not on any intraoperative shortening that was induced by the surgeon during reduction.

Despite these limitations, this study had several strengths. To the authors' knowledge, this represents the largest series of young patients with femoral neck fracture complications. The authors have reported specific details of the fixation failure patterns. The results were further strengthened by the inclusion of 5 centers across 3 countries, which increases their generalizability. Finally, these findings highlight important considerations in the ongoing debate surrounding the optimal implant to treat these difficult fractures.

There are numerous interesting frontiers in the care of femoral neck fractures in young patients. New or modified methods of fixation, perhaps with length-stable constructs or with buttressing of vertical fractures, warrant further study.25,26 In addition, biomechanical studies have also suggested that the ideal implant may vary based on the characteristics of the femoral neck fracture. This deserves further clinical evaluation27 and was recently explored in hip fractures in the elderly.28

Conclusion

These results can help surgeons and patients understand the likely outcome should fixation of a non–geriatric femoral neck fracture fail. Severe shortening is the most common fixation failure, and neither implant prevents this complication. Sliding hip screw plus derotation screw constructs are associated with screw cutout, whereas multiple cancellous screws fail in varus. Selecting a surgical implant based on its likely failure pattern is an additional factor that surgeons may wish to consider when trying to optimize the care of young patients with femoral neck fracture.

References

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Patient and Fracture Characteristics

CharacteristicAll PatientsPatients With SHSPatients With Cancellous Screws
Age, mean±SD, y42.0±9.941.2±11.142.4±9.4
Male84%88%82%
Fracture severity
  Displaced95%96%94%
  Vertical52%44%57%
Fracture OTA class
  31.B14%0%7%
  31.B266%75%61%
  31.B330%25%32%
Reduction quality
  Grade I33%18%60%
  Grade II67%82%40%
  Grade III0%0%0%
Authors

The authors are from the Department of Orthopaedics (DJS, PJO) and the Clinician Investigator Program (DJS), University of British Columbia, Vancouver, British Columbia; the Department of Orthopaedics (KD, ANP, GPS), R Adams Cowley Shock Trauma Center, University of Maryland School of Medicine, Baltimore, Maryland; and the Department of Orthopaedic Surgery (CMH), Harbor-UCLA Medical Centre, Torrance, California.

Drs Stockton and Dua have no relevant financial relationships to disclose. Dr O'Brien has received research support from DePuy, Synthes, and Zimmer and is on the speaker's bureau of Synthes, Zimmer, and Stryker. Dr Pollak receives royalties from Globus Medical, Smith & Nephew, and Zimmer. Dr Hoshino is a paid consultant for Smith & Nephew and Stryker and has received research support from Conventus. Dr Slobogean is a paid consultant for Smith & Nephew and Zimmer Biomet.

Correspondence should be addressed to: Gerard P. Slobogean, MD, MPH, FRCSC, Department of Orthopaedics, R. Adams Cowley Shock Trauma Center, University of Maryland School of Medicine, 6th Fl, Ste 300, 110 S Paca St, Baltimore, MD 21201 ( gslobogean@som.umaryland.edu).

Received: May 15, 2018
Accepted: October 03, 2018
Posted Online: March 27, 2019

10.3928/01477447-20190321-03

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