A systematic review of undisplaced femoral neck fracture treatments for patients over 65 years of age, with a focus on union rates and avascular necrosis

To the best of our knowledge, this is the first systematic review to focus on the optimal treatment for undisplaced FNFs. We investigated whether conservative treatment was optimal for the common problem of undisplaced FNFs in the elderly. We developed explicit inclusion and exclusion criteria, assessed the methodological quality of all studies, explored the reproducibility of all selection and assessment criteria, performed quantitative analysis, and explored possible reasons for observed differences among studies. We found data paradox and confirmed the correct data of the original paper [20]. The validity of our findings is strengthened by the fact that we strictly followed the suggestions of the Cochrane Handbook for Systematic Reviews of Interventions (version 5.0.2) and the PRISMA 2009 checklist.

One of our most important findings is that fractures that were surgically treated had higher union rates and comparable non-union rates to those treated conservatively. Obviously, fixation affords stability and stiffness, directly enhancing the strength of the femoral neck [41, 42]. Biomechanical studies have confirmed that fracture fixation and immobilization affect the pattern of skeletogenic stem cell differentiation into osteoblasts; mechanical fixation would obviously influence neovascularization [43]. Thus, fixation promotes bone union. In some studies [13‐15, 20], the union rates reached 90%. Fixation failure is a rare complication after surgery to treat undisplaced fractures. The fixation failure rate in our meta-analysis was only 3.3% (45/1366).

Conservative treatment is an option for undisplaced FNFs, the advantage being that surgery is avoided, but most studies revealed a significant risk of displacement during non-operative treatment. The risk varied from 14.1 to 55.7% [9‐12, 26‐28]. Verheyen et al. [28] explored the rate of secondary displacement in 105 patients. Forty-eight patients (46%) were at risk of such displacement; the patient group had a high mean age. Secondary displacement was more common in patients aged >70 years, in agreement with the data of Raaymakers [27], who reported secondary instability in 41% of patients >70 years of age. In healthy patients <70 years of age, the value was 7%. Secondary displacement is very rare after surgical treatment.

AVN is a well-recognized complication of FNFs, caused by alterations in the blood supply [7, 44]. AVN often develops 2–3 years after treatment. We found no significant difference between the two treatment groups in terms of AVN. However, AVN tended to be less common in surgical patients. Massive rupture of the retinacular vessels may occur when the femoral head is rotated during surgery; this may trigger AVN [45]. Thus, fixation potentially adversely affects the vascularity of the femoral head [46]. On the other hand, fixation prevents micromotion of the fracture site, facilitating vascularity. In Brodetti et al.’s cadaver experimental study [47], they inserted nails or screws into various sites to observe changes in blood supply; they found that such insertions were unlikely to contribute to further devascularization of the femoral head. Bentley et al. [15] followed up patients for >3 years and found that, although no AVN occurred in the first year, AVN did develop after 2 years in both groups. The incidence did not vary greatly between those who underwent conservative (14%) and surgical (18%) treatment. Hence, follow-up is very important to AVN detection.

Re-operation to deal with complications is a commonly reported outcome measure. After conservative treatment, re-operations were principally attributable to secondary displacement and latent AVN [11, 28]. Non-union, fixation failure, and AVN were the most common reasons for re-operation after surgical treatment [7]. The re-operation rate differed significantly (p < 0.01) between the two treatment options. Overall, the outcomes were better after surgery. It is true that patients are exposed to extra risks (including anesthesia and bleeding) during surgery. We found no evidence suggesting that complications associated with anesthesia and surgery outweighed the increased risk of fracture-healing complications characteristic of conservative treatment. On the contrary, surgical treatment significantly reduced the risk of fracture displacement and significantly increased the union rate. Patients undergoing re-operation generally underwent hemiarthroplasty or arthroplasty [7, 11]. Overall, surgical treatment must be recommended.

Many clinical reports on treatment outcomes have focused on surgical rather than functional outcome measures. The objective functional results of various treatments are rarely assessed. The Harris hip score (HHS) is the most common modality used to assess hip function. In one study [40] on patients aged >60 years, Yih et al. reported an HHS of 84.2 ± 5.2 for those treated via insertion of dynamic hip screws and 82.6 ± 5.1 for those undergoing osteosynthesis using cannulated screws. Some studies employed fairly crude outcome measures (pain and mobility level documented in a rudimentary manner). In a recent study of 224 patients who completed self-evaluation questionnaires >3 years after internal fixation, Rogmark et al. found that 40% reported average to severe pain when walking and 25% pain at rest. [25] Functional results are rarely assessed in those treated conservatively. In one comparative study [17], Cserhati et al. recorded the levels of pain and mobility. Of 39 patients, 5.6% (10/39) reported poorer mobility status after conservative treatment compared with 45.2% (28/62) of those who underwent surgery; 51.3% (20/39) of patients reported severe or moderate pain when weight-bearing after conservative treatment compared with 61.3% (38/62) of those who underwent surgical treatment. It thus seems that conservative treatment afforded better outcomes. In terms of mortality, this was higher (68%; 83/122) after conservative treatment than the 50.4% (63/125) after surgical treatment. Therefore, the overall outcome is better after surgical treatment.

In terms of surgery, primary hemiarthroplasty of an undisplaced FNF is a possible alternative treatment. Parker et al. [37] randomized 692 patients with undisplaced FNFs to hemiarthroplasty (346 patients) or internal fixation (346 patients). Fixation was associated with a significantly reduced operative time (43 vs. 67 min), less blood loss, and a lower 1-year mortality rate (19 vs. 26%). The additional benefits of fixation were less pain at 1 year, less reduction in mobility, and a reduced dependence on walking aids. Re-operations were required by 5.5% (19/346) of the hemiarthroplasty group and 14.5% (50/346) of the fixation group. Hui et al. [32] and Sikand et al. [38] also evaluated re-operation and mortality levels. Internal fixation was associated with lower mortality but a greater need for re-operation, compared with hemiarthroplasty. The increased risk of mortality associated with hemiarthroplasty indicates that hemiarthroplasty cannot be recommended to treat an undisplaced FNF.

A precise diagnosis is important prior to choosing a treatment option. Radiography has certain limitations when used to distinguish FNF types, which can result in misdiagnosis. A patient may in fact have a displaced FNF but be diagnosed with an undisplaced one [6, 10]. In addition, diagnoses using the Garden classification are very inconsistent. Zlowodzki et al. [48] surveyed the preferences of orthopedic surgeons in terms of FNF classification systems and asked whether they thought they could distinguish the four different Garden fracture types. Of all surgeons, 96% felt that they could distinguish between undisplaced (Garden I/II) and displaced (Garden III/IV) fractures. However, the Garden classification system exhibits great variability. Therefore, X-rays combined with a CT scan should be routinely used for diagnosis [6].

We reviewed the conservative treatments employed [9‐12, 15, 17, 26‐28]. Careful nursing and optimal physician management allowed gradual mobilization to commence with exercises in bed, followed by partial weight-bearing, with the aid of crutches, for ≥8 weeks after fracture. The outcomes were satisfactory [9, 15]. However, only a few patients adhered to their rehabilitative protocols in the long term. If a patient without a comorbid condition can guarantee good compliance, conservative treatment may also be recommended. In addition, patients with surgical risks must be treated conservatively.

Our work had certain limitations: (1) Most studies were retrospective in nature. Ignoring such studies would have underpowered our analyses and negatively affected the accuracy of our findings. A future strictly designed and adequately powered RCT is essential. (2) We pooled Garden I and Garden II FNFs; their prognoses did not differ greatly. A future study could compare treatment outcomes between patients with these two types of FNF. (3) We explored possible publication bias using Begg, Egger, and funnel plots. The included studies did not meet the standards required by these methods; it was thus difficult to evaluate publication bias.

Ideally, a randomized trial would reveal whether surgical or conservative treatment should be preferred for undisplaced FNFs. We suggest that future studies should prospectively compare the outcomes and complication rates of different internal fixation techniques and conservative methods.