Does femoral offset recover and affect the functional outcome of patients with displaced femoral neck fracture following hemiarthroplasty?
Introduction
The aging society has posed a grave problem related to hip fractures worldwide [1], [2], [3]. Although the hip fracture incidence in some western countries is decreasing [1], [2], [3], the social and economic burden associated with hip fracture have impacted many Asian countries such as Korea, Japan, and China [4], [5], [6]. Hip fracture is a clinical nuisance to clinicians due to high morbidity and mortality [7]. Unlike trochanteric fractures, displaced femoral neck fractures are treated with arthroplasty [8]. Favorable reports on the outcome after total hip arthroplasty in elderly patients have been presented recently [8], [9], [10]. However, bipolar hemiarthroplasty remains the first treatment of choice for this condition [8].
Unlike modular stem, conventional femoral stems do not provide options for variable offset [11]. Therefore, restoring preoperative vertical and horizontal offset is not always possible [12]. Change of horizontal femoral offset (FO) after bipolar hemiarthroplasty for treating displaced femoral neck fracture has not been paid much attention so far despite its clinical significance compared to total hip arthroplasty [13], [14]. Moreover, past studies have reported inconsistent results regarding the importance of offset change [13], [14]. It has been reported that FO can affect the abductor lever arm, muscle strength, joint reaction force, and joint stability in studies conducted in total hip arthroplasty patients [12], [15], [16], [17]. Likewise, postoperative clinical outcome, activity of daily living, and quality of life after bipolar hemiarthroplasty can be influenced by change of horizontal offset [14]. Moreover, after the surgery, these patients would probably survive longer than before due to lengthened life expectancy. Thus, factors affecting quality of life of these patients would be of paramount interest.
One plausible explanation of the paucity regarding this subject might be the difficulties in evaluating horizontal offset. Vertical offset or leg length discrepancy is easy to evaluate postoperatively in plain radiographs because it is hardly affected by the rotation of affected limb. However, measurement of horizontal offset can be greatly influenced by the rotation of the lower extremity and the anteversion of the femoral stem [17]. Previous studies have acknowledged this limitation [18], [19] while some were confined to such error [20], [21]. Accurate measurement of FO change would be mandatory for proper interpretation of its effect on the postoperative functional outcome.
We hypothesized that FO after bipolar hemiarthroplasty in elderly subjects with displaced femoral neck fracture might differ from the preoperative value and that the amount of change could affect the functional outcome if measured free of radiographical error. Therefore, the objectives of this study were: (1) to investigate the accurate change of femoral offset after hemiarthroplasty in elderly patients with displaced femoral neck fracture, and (2) to clarify whether there was an association between FO change and postoperative functional outcome.
Section snippets
Methods
The study protocol was approved by the Institutional Review Board of our institution. This retrospective observational study was conducted in a single university hospital located in a city with one million inhabitants of East Asians. The hospital has a level 1 trauma center specialized for acute traumas.
One hundred hips in 100 consecutive patients (75 women and 25 men) with displaced femoral neck fracture who underwent bipolar hemiarthroplasty in a single institution were enrolled in the
Results
Patient demographics are reported in Table 1 and five patients passed out during follow-up 1-year. There was no dislocation. The mean preoperative offset measured in the preoperative CT scan of the contralateral hip was 37.4 ± 2.5 mm (range, 30.0–40.5). The offset was increased by 12.7 ± 9.6% (range, −5.4 to 46.7%) after the surgery. Only 25.0% of postoperative offset after hemiarthroplasty changed within ±5% of the preoperative offset. A total of 45.0% of postoperative offset changed within ±10% of
Discussion
In this observational study, we determined whether FO before and after bipolar hemiarthroplasty differed in elderly subjects with displaced femoral neck fracture and whether the amount of change would possibly worsen the functional outcome in such patients. FO increase of more than 20% of preoperative offset resulted in worse functional outcome scores such as MBI and HHS. Although tremendous literature has focused on FO change in the total hip arthroplasty patients [15], [16], [17], [20], [21],
Conclusion
In summary, the current study showed that FO was not correctly restored in 23% of patients receiving bipolar hemiarthroplasty for displaced hip fracture after correction of the rotational error in plain radiographs. Restored FO positively affected MBI, but not HHS. This suggests that restoring FO has clinical relevance in the functional outcome. Therefore, surgeons are recommended to pay attention to restoring the original FO, even in bipolar hemiarthroplasty setting. Further study is needed to
Conflict of interest
None.
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Associations between implant alignment or position and patient-reported outcomes after total hip arthroplasty
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