Change in Femoral Offset after Closed Reduction and Dynamic Hip Screw Osteosynthesis Via Lateral Approach in Patients with Medial Femoral Neck Fracture: A Retrospective Analysis

Abstract

Objective

Closed reduction and dynamic hip screw (DHS) osteosynthesis are preferred as joint‐preserving therapy in case of medial femoral neck fractures (MFNFs). A change in the femoral offset (CFO) can cause gait abnormality, impingement, or greater trochanteric pain syndrome. It is unknown whether the femoral offset (FO) can be postoperatively fully restored. The aim of the study was to investigate the extent of a possible CFO in hip joints after DHS osteosynthesis in the case of an MFNF.

Methods

In this retrospective study, 104 patients (mean age: 71.02 years, men: n = 50, women: n = 54) with MFNF who underwent closed reduction and DHS osteosynthesis were analyzed by postoperative x‐rays to assess CFO between the operated (OS) and nonoperated joint side (NOS). The studies covered the time period 2010–2020. A statistical comparison was performed between the mean values of FO between OS and NOS, taking into account patient age, gender, and fracture severity.

Results

All operated hip joints showed a CFO. In 76.0% (79 of 104), the FO decreased (FOD), and in 24.0% (25 of 104), the FO increased (FOI). A critical CFO (>15% CFO) was detected in 52.9% (55 of 104). In hip joints with postoperative FOD, the mean FO between NOS (49.15 mm [±6.56]) and OS (39.32 mm [±7.87]) and in hip joints with postoperative FOI the mean FO between NOS (41.59 [±8.21]) and OS (47.27 [±6.68]) differed significantly (p < 0.001). Preoperative FO (r _S: −0.41; p > 0.001) and caput–collum–diaphyseal angle (CCD; r _S: 0.34; p > 0.001) correlated with postoperative CFO. FOD was found in hip joints with a preoperative FO >44 mm and CCD <134° vice versa FOI in hip joints with a preoperative FO <44 mm and CCD >134°.

Conclusion

Closed reduction and DHS osteosynthesis in patients with MFNF result in a clustered significant CFO. The individual FO should be taken into account pre‐ and intraoperatively to avoid a postoperative extensive CFO.

One hundred and four patients with medial femoral neck fractures were retrospectively analyzed with regard to postoperative changes of the femoral offset (FO). Seventy‐five percent of the collective showed a decrease of FO and 25% an increase. Fifty‐three percent showed a critical change in FO (>15% referenced to the FO of the contralateral hip). Therefore, exact pre‐operative planning, considering the contralateral healthy hip joint, is mandatory to restore the individual FO of the femoral neck in the best possible manner.

Introduction

Medial femoral neck fractures (MFNFs) are among the most common fractures near the hip joint.^{1, 2} The MFNF is primarily a fracture of the elderly, although high‐impact trauma accidents can also commonly lead to MFNF in younger patients. ³ In general, the number of hip fractures is increasing, and worldwide it has been estimated that the number of hip fractures will rise to 2.6 million by 2025 and to 6.25 million in 2050.^{4, 5, 6} Optimal surgical treatment is essential in order to be able to handle the expected higher supply volume in the future.

MFNF includes all fractures in group 31‐B1 and 31‐B2 according to AO‐classification system. Fractures classified as 31‐B3 are lateral femoral neck fractures. ⁷ To differentiate between medial and lateral femoral neck fractures, the proximal fracture entry into the femoral neck is assessed. If this is medial to the base of the femoral neck at the greater trochanter, the fracture is classified as a MFNF.^{8, 9} Closed reduction and osteosynthesis with a dynamic hip screw (DHS) is recommended as joint preserving operative therapy of MFNF.^{10, 11} Compared with cannulated screw osteosynthesis, DHS tends to have lower revision rates and appears to achieve slightly better postoperative results in the case of displaced fractures. ¹² The lateral approach has proven to be established due to the protection of the vasto‐gluteal muscles.^{9, 12, 13} The goal of the surgical treatment is the anatomical restoration of the femoral neck and sufficient stabilization of the fracture by osteosynthesis. Anatomical restoration of the femoral neck includes reconstruction of the femoral offset (FO).^{14, 15, 16} The FO is defined as the distance from the center of rotation of the femoral head to a line bisecting the shaft axis of the femur. ¹⁷ The restoration of FO is important for a good postoperative function of the hip joint with sufficient motion of the hip joint and physiological function of the hip‐encircling muscles.^{18, 19}

Change in the femoral offset (CFO) refers to either an increase or a decrease in the FO. A femoral offset decrease (FOD) changes the leverage ratios between the pelvis and the greater trochanter,^{12, 14} which can be accompanied by a loss of joint stability^{20, 21, 22} due to a reduction in the leverage of the hip abductors.^{18, 23, 24} Clinically, the problem is revealed by the “Trendelenburg sign.”^{25, 26, 27} Furthermore, a loss of FO has a negative effect on the mobility of the hip joint.^{28, 29} In extreme cases, intra‐ or extra‐articular impingement can occur.^{30, 31} An FOD of more than 15% is considered critical.^{32, 33} On the other hand, a femoral offset increase (FOI) can cause a greater trochanteric pain syndrome. As with critical FOD, the cutoff value for a critical FOI is defined as an increase in FO as more than 15% compared with the individual anatomical FO.^{32, 33, 34, 35}

Moreover, the FO is influenced by the centrum–collum–diaphyseal angle (CCD). A higher varus configuration of the femoral neck results in an increase of FO, while a more pronounced valgus configuration requires a decrease of FO. ³⁶ DHS osteosynthesis has already been linked to changes in the femoral offset (CFO).^{9, 12, 15}

To our knowledge, there are no studies in which the FO was examined postoperatively with regard to a change after joint‐preserving therapy with closed reduction and stabilization using DHS osteosynthesis in patients with MFNF. Therefore, the aim of the study was to analyze the extent of a possible CFO in patients with MFNF after closed reduction and DHS osteosynthesis based on a retrospective analysis of radiograph images. Furthermore, whether age, gender, or fracture severity has an influence on a possible postoperative CFO and whether the postoperative CFO is associated with osteosynthesis failure (OF) were analyzed.

Methods

Patients, Inclusion, and Exclusion Criteria

Between 2010 and 2020, 128 patients underwent osteosynthesis with a DHS and an additional anti‐rotation screw after MFNF in the clinic of the study was conducted. The operations were performed by six different senior surgeons. After applying inclusion and exclusion criteria, 104 patients were included in the final analysis. The study was approved by the local ethics committee (IRB number 34/7/20) and performed in accordance with the principles expressed in the Declaration of Helsinki. All x‐rays were assessed by a senior radiologist, MPM, and TH. Without exception, the evaluated x‐ray images were taken as part of routine pre‐ and postoperative diagnostics.

Inclusion criteria were as follows:

1. All patients older than 18 years who underwent closed reduction and DHS osteosynthesis after MFNF were included in further analysis.

Exclusion criteria were as follows:

1. Patients with former osteosynthesis treatment or hip joint replacement on the contralateral joint were excluded.

2. Patients who underwent open reduction were also excluded.

3. Incomplete postoperative radiographic diagnostics and extremely derotated images were excluded.

4. Likewise, patients with tumor and congenital or developmental structural changes of the hip joint were excluded.

Figure 1 shows a flowchart of the inclusion and exclusion procedure of the initial study collective.

FIGURE 1.

Flowchart of inclusion and exclusion process of the initial collective: 128 patients who underwent dynamic hip screw osteosynthesis in case of medial femoral neck fractures were examined. Patients with former osteosynthesis or arthroplasty of ipsi‐ or contralateral hip (n = 12), incomplete or extremely rotated postoperative x‐rays (n = 9), as well as patients who underwent an open reduction (n = 3) were excluded. In consequence, 104 patients were included in the final analysis.

X‐Ray Imaging, Parameters, and Methods of Measurement

For each patient, pre‐ and postoperative pelvic overview and axial view (of fractured side) scans were evaluated. All radiological images were taken with the patient in a prone position. In accordance with the positioning protocol, the patients were placed horizontally with the pelvis on the radiography table. Postoperative radiograph imaging was taken regularly on the second postoperative day. All measurements were taken via the PACS system (Picture Archiving and Communication System). Software from GE Healthcare called Centricity™ Universal Viewer was used (RA1000, edition 2019, Buckinghamshire, Great Britain). Every fracture was classified according to Garden ³⁷ and Pauwels. ³⁸ FO and CCD were measured on the operated and contralateral healthy proximal femur side according to established methods (Figure 2).^{15, 39} To determine the FO, the distance from the femoral head center of rotation to the femoral shaft axis was measured. The angle between the femoral axis and the femoral neck axis was measured to determine the CCD (Figure 2). Patient age, gender, operated side, and OF in the first postoperative year were assessed. Patients with an OF were classified as the failure group (FG). Patients without OF were classified as the nonfailure group (NFG). Hip head necrosis, a cutting out of the DHS, or inacceptable fracture dislocation was defined as OF.

FIGURE 2.

Exemplary depiction of the measurements of the femoral offset (FO, A) and caput–collum–diaphyseal angle (CCD, B): The measurements of FO and CCD were done in coronal view of the hip joint. To determine the FO, the horizontal distance between the center of rotation (red point) of the femoral head (red circle) and femoral diaphysis axis was measured (A). For determination of the CCD, the angle between the femoral diaphysis and the femoral collum axis was measured (B).

Statistics

For statistical comparison of FO and CCD in the nonoperated joint (NOS) and operated joint side (OS), a one‐sample t‐test was used. In both groups, postoperative changes in FO were classified as either a decrease of the femoral offset (FOD) or an increase of the femoral offset (FOI). Likewise, the postoperative caput–collum–diaphyseal angle was analyzed. Changes in the caput–collum–diaphyseal angle were classified in decrease of CCD (CCDD) and increase of CCD (CCDI). To analyze potential differences in fracture morphology according to Garden and Pauwels between NFG and FG, ordinal logistic regressions were used. To detect possible differences in changes in FO between groups, a two‐sample t‐test was applied. For correlation analysis of the postoperative FO change with preoperative FO, CCD and postoperative CCD change, as well as patient age and fracture morphology, the Spearman correlation test was used. Moreover, a multivariate correlation analysis for testing two‐way interactions was performed. To capture potential connections between critical CFO and fracture, severe chi‐square test was used. For analysis of difference in CFO in different fracture grades, the Kruskal–Wallis test was applied. A two‐sample t‐test was used for the comparison of gender. Overall, mean ± standard deviation is stated. The intraclass correlation coefficient (ICC) for intra‐ and inter‐observer reliability was determined in order to record the quality of the measurements. Statistical analysis was performed with GraphPad Prism 9.00 (GraphPad Software, San Diego, USA) R 4.0.5 (The R Foundation for Statistical Computing, Vienna, Austria) and Microsoft Excel (Microsoft Office 2016, Redmond, USA). Significant differences are marked with asterisks (***p < 0.001, **p < 0.01, *p < 0.05).

Intra‐Observer and Inter‐Observer Reliability

ICC for intra‐observer reliability ranged from 0.95 to 0.99 and inter‐observer reliability ranged from 0.94 to 0.97, indicating excellent reliability, taking into account the initial measurements, the control measurements by the same examiner, as well as the measurements by a second examiner.

Results

Characteristics of the Study Population

In this study, 50 males (48.1%) and 54 females (51.9%) were analyzed. The mean age of the study population was 71.02 years (±14.34 years).

Postoperative Changes of the Femoral Offset and CCD Angle

In all patients (104 of 104), a CFO could be detected. In 76.0% (79 of 104), an FOD, and in 24.0% (25 of 104), an FOI could be found. Critical changes in the postoperative FO (>15% FOD or FOI) were found in 52.9% (55 of 104) of all patients. Forty‐seven patients showed a critical FOD and 8 patients showed a critical FOI (Figure 3). Figure 4A,B represents an example for a critical FOD and Figure 5A,B represents a critical FOI.

FIGURE 3.

Extent of postoperative change in femoral offset (CFO) grouped in patients with postoperative decrease of FO (FOD, A) and postoperative increase of FO (FOI, B): 79 patients showed a postoperative FOD compared with the contralateral hip joint. Eighteen of these 79 had an FOD of 0%–10%, 14 had an FOD of 10%–15%, and 47 had an FOD of more than 15% (A). In 25 cases, a postoperative FOI was detected. Fourteen of these 25 patients had an FOI of 0%–10%, 3 had an FOI of 10%–15%, and in 8 patients, an FOI of more than 15% was found (B).

FIGURE 4.

Examples of critical postoperative FOD: (A) shows a preoperative pelvic overview image, which detected a femoral neck fracture (AO 31B2.1) on the left side. The postoperative X‐ray image is shown below. The fracture was treated with dynamic hip screw osteosynthesis. A critical FOD (−20.3%) is shown. The FO on the operated side (OS) totals 40.8 mm. The non‐fractured contralateral side (NOS) has an FO of 51.2 mm. (B) shows a preoperative pelvic overview image, which detected a femoral neck fracture (AO 31B2.1) on the left side. The postoperative X‐ray image is shown below. The fracture was treated with dynamic hip screw osteosynthesis. A critical FOD (−16.7%) is shown.

FIGURE 5.

Examples of a critical postoperative FOI: (A) shows a preoperative pelvic overview image, which detected a femoral neck fracture (AO 31B2.3) on the right side. The postoperative X‐ray image is shown below. The fracture was treated with dynamic hip screw osteosynthesis. A critical FOI (+38.2%) is shown. The FO on the operated side (OS) totals 46.7 mm. The nonfractured contralateral side (NOS) has an FO of 33.8 mm.(B) shows a preoperative pelvic overview image, which detected a femoral neck fracture (AO 31B2.2) on the right side. The postoperative X‐ray image is shown below. The fracture was treated with dynamic hip screw osteosynthesis. A critical FOI (+26.5%) is shown. The FO on the operated side (OS) amounts 52.1 mm. The non‐fractured contralateral side (NOS) has an FO of 41.2 mm.

In patients with a postoperative FOD, a significant difference between the mean FO of the NOS (49.15 mm [±6.56]) and the mean FO of the OS (39.32 mm [±7.87]) could be found (p < 0.001). In patients with a postoperative FOI, the mean FO between NOS (41.59 [±8.21]) and OS (47.27 [±6.68]) differed significantly (p < 0.001).

In 67.3% (70 of 104) of cases, an increased CCD (CCDI) and in 32.7% (34 of 2014) a decreased CCD angle (CCDD) could be detected.

In patients with a postoperative FOD, the mean CCD (131.06° [±5.74]) of the NOS was significantly smaller than the mean CCD (135.78° [±6.08]) of the OS (p < 0.001). In patients with a postoperative FOI, the mean CCD (136.40° [±6.37]) of the NOS was significantly higher than the mean CCD (132.21° [±3.79]) of the OS (p < 0.001). The results are summarized in Table 1.

TABLE 1.

Postoperative change in the femoral offset (FO) and CCD in the group of patients with a postoperative femoral offset decrease (FOD) and increase (FOI) according to the nonoperated joint side (NOS) and operated joint side (OS).

Group of patients	Parameters	NOS (n = 104)	OS (n = 104)	Postoperative change	p‐value
FOD (n = 79)	FO in mm	49.15 (±6.56)	39.32 (±7.87)	±11.90 (19.99%)	<0.001 (***) a
FOD (n = 79)	CCD in °	131.06 (±5.74)	135.78 (±6.08)	±5.13 (3.72)	<0.001 (***) a
FOI (n = 25)	FO in mm	41.59 (±8.21)	47.27 (±6.68)	±19.04 (16.04%)	<0.001 (***) a
FOI (n = 25)	CCD in °	136.40 (±6.37)	132.21 (±3.79)	±4.11 (2.92%)	0.002 (**) a

^a Paired parametric t‐test.

^*** p < 0.001.

^** p < 0.01.

Correlation between Postoperative Changes of Femoral Offset and CCD Angle

There was a significant inverse correlation between the postoperative CFO of the operated joint side and the FO of the healthy contralateral NOS (r _S: −0.41; p > 0.001). In addition, the postoperative CFO of the operated joint side correlated significantly with the CCD of the healthy contralateral NOS (r _S: 0.34; p > 0.001). A significant inverse correlation could be detected between the postoperative CFO and the postoperative change in CCD angle (r _S: −0.66; p > 0.001) of the operated joint side (Figure 6A–C). According to these data, a postoperative FOD was found in hip joints with a preoperative FO >44 mm and CCD <134°, while a postoperative FOI was observed in hip joints with a preoperative FO <44 mm and CCD >134°.

FIGURE 6.

Correlation analysis between postoperative femoral offset (FO) change and FO of the nonoperated side (NOS), CCD angle of the nonoperated side (NOS), and postoperative CCD change: The analysis was based on the Spearman correlation test. A significant inverse correlation (r _S = −0.41; p < 0.001) between the postoperative femoral offset change in the operated joint side and the FO NOS was detected (A). There was a significant correlation (r _S = 0.34; p < 0.001) between the postoperative femoral offset change in the operated joint side and the CCD NOS (B). A significant inverse correlation (r _S = −0.66; p < 0.001) between the postoperative femoral offset change in the operated joint side and the postoperative CCD change in the operated joint side was found (C).

Correlation between Postoperative Changes in Femoral Offset and CCD, Age, and Multivariate Correlation Analysis

Correlation analysis revealed no significant associations between postoperative changes in FO (p = 0.433) and CCD (p = 0.332) in relation to patient age. A multivariate correlation analysis between CFO and postoperative change in CCD, FO of NOS, CCD of NOS, patient age, Garden score, and Pauwels score showed no significant differences when testing for two‐way interactions.

Association between Gender and Postoperative Change in the Femoral Offset

Female patients (73.89 years [±13.09]) were significantly older than male patients (67.98 years [±14.99]). The analysis showed a p‐value of 0.037. There was no significant difference for neither mean FOD (males: −10.56 mm [±6.12]; females: −9.41 mm [±5.64]; p = 0.400) nor mean FOI (males: +4.44 mm [±3.18]; females: +7.03 mm [±6.45]; p = 0.247) between male and female patients. In addition, CCDD (males: −5.56 mm [±3.59]; females: −6.28 mm [±5.97]; p = 0.695) and CCDI (males: +5.88 mm [±4.30]; females: +7.33 mm [±4.59]; p = 0.184) did not differ significantly between the groups. All results are presented in Table 2.

TABLE 2.

Interrelation between gender and postoperative change in the femoral offset.

Parameters		Men (n = 50)	Women (n = 54)	p‐value
Age	[years]	67.98 (±14.99)	73.89 (±13.09)	0.037 (*) a
FOD	[mm]	−10.56 (±6.12) 36/50 (72.0%)	−9.41 (±5.64) 42/54 (77.8%)	0.400 a
FOI	[mm]	+4.44 (±3.18) 14/50 (28.0%)	+7.03 (±6.45) 12/54 (22.2%)	0.247 a
CCDD	[°]	−5.56 (±3.59) 19/50 (38.0%)	−6.28 (±5.97) 15/54 (27.8%)	0.695 a
CCDI	[°]	+5.88 (±4.30) 31/50 (62.0%)	+7.33 (±4.59) 39/54 (72.2%)	0.184 a

^a Two sample t‐test.

^* p < 0.05.

Association between Fracture Severity and Postoperative Change in the Femoral Offset

The comparison of postoperative CFO in dependency of fracture severity showed no significant difference (p = 0.516 in accordance with Pauwels classification fracture severity; p = 0.212 in accordance with Garden classification fracture severity) (Figure 7). No significant differences were found in contingency analysis of noncritical (<15°) and critical (>15%) postoperative CFO depending on fracture severity (Figure 8). According to Garden classification, p‐value was 0.803 (8a), and according to Pauwels classification, p‐value was 0.264 (8b).

FIGURE 7.

Comparison of postoperative change in femoral offset depending on fracture severity: Analysis based on Kruskal–Wallis test. There were no significant differences in the postoperative change in femoral offset between the different severity groups according to Garden (p = 0.516; A) and Pauwels (p = 0.212; B) classification.

FIGURE 8.

Contingency analysis of noncritical (<15°) and critical (>15%) postoperative change in femoral offset depending on fracture severity: Chi‐square test was used for analysis. There were no significant differences between noncritical and critical postoperative change in femoral offset in dependency of fracture grade according to Garden (p = 0.803; A) and Pauwels (p = 0.264; B) classification.

Association between CFO and Osteosynthesis Failure

In 15.4% of patients (16 of 104), an early OF could be detected in the first postoperative year (mean: 5.2 months [±6.50]). There was no OF in 84.6% (88 of 104) of cases. No significant differences were found between the NFG and the FG regarding Garden and Pauwels classification (Table 3).

TABLE 3.

Distribution of the analyzed fractures according to the different grades of fracture classification after Garden and Pauwels.

Classification		Total (n = 104)	NFG (n = 88)	FG (n = 16)	p‐value
Garden score					0.901*
Garden 1	[∅]	8/104 (7.7%)	8/88 (9.1%)	0/16 (0.0%)
Garden 2	[∅]	7/104 (6.7%)	7/88 (8.0%)	0/16 (0.0%)
Garden 3	[∅]	41/104 (39.4%)	34/88 (38.6%)	7/16 (43.8%)
Garden 4	[∅]	48/104 (46.2%)	39/88 (44.3%)	9/16 (56.3%)
Pauwels score					0.660*
Pauwels 1	[∅]	12/104 (11.5%)	9/88 (10.2%)	3/16 (18.8%)
Pauwels 2	[∅]	78/104 (75.0%)	69/88 (78.4%)	9/16 (56.3%)
Pauwels 3	[∅]	14/104 (13.5%)	10/88 (11.4%)	4/16 (25.0%)

Note: Explanation: Table 3 shows patient distribution according to the grade of fracture severity for each Garden and Pauwels classification of the final included patients and saparate of patients without recorded osteosynthesis failure (NFG), as well as with osteosynthesis failure (FG).

^*Ordinal logistic regression.

There was no significant difference between the mean FOD in NFG (−9.77 mm [±5.99]) and FG (−10.14 mm [±5.75]) (p = 0.844) or mean FOI (NFG: +6.04 mm [±5.41]; FG: +3.80 mm [±3.24]) (p = 0.355). Likewise, no significant difference was found for CFO between NFG (−1.87 mm [±5.70]) and FG (−3.17 mm [±4.50]) (p = 0.783). These results are summed up in Table 4.

TABLE 4.

Analysis for failure of osteosynthesis regarding CFO between the nonfailure group (NFG) and the failure group (FG).

Parameters		NFG (n = 88)	FG (n = 16)	p‐value
FOD (n = 79)	[mm] [%]	−9.77 (±5.99) −20.13 (±12.27)	−10.14 (±5.75) −19.21 (±9.50)	0.844 a
FOI (n = 25)	[mm] [%]	+6.04 (±5.41) +17.21 (+20.18)	+3.80 (±3.24) +9.91 (±9.11)	0.355 a
CFO (n = 104)	[mm] [%]	−1.87 (±5.70) −3.93 (±16.23)	−3.17 (±4.50) −4.65 (±9.31)	0.783 a

^a Two‐sample t‐test.

Discussion

In the present study, the postoperative radiographs of 104 patients with an MFNF were retrospectively analyzed after closed reduction and osteosynthesis with a DHS. In 52.9% (55 of 104) of all analyzed hip joints, a critical change in the FO was detected. The findings of the presented study suggest that the preoperative FO and the preoperative CCD have an influence on the postoperative changes of the FO.

The Importance of the Femoral Offset and Effects of DHS Osteosynthesis

The FO is an important morphological parameter as it has an impact on the biomechanical forces acting on the hip joint.^{39, 40} It has already be shown that changes in the FO can result in pronounced clinical symptoms.^{29, 30} These clinical findings indicate the importance of restoring the individual anatomical FO as best as possible in hip joint surgeries. After analyzing x‐ray images, it was shown that in 100% of cases, closed reduction and stabilization with DHS osteosynthesis of MFNF lead to a postoperative change in the FO compared with the contralateral healthy hip joint (75% FOD and 25% FOI) independent of age, gender, or fracture severity. The higher number of cases with FOD can in part be explained by the osteosynthesis principle of the DHS: Telescoping of the DHS is intended to allow the head and neck fragment to slide against the femoral shaft and thus permit continuous contact between the fracture surfaces. The more pronounced the telescoping, the greater the FOD can become. ¹⁴ In addition, earlier studies have shown that a valgus reposition shows a higher postoperative stability, so surgeons tend to strive for a valgus reposition angle intraoperatively.^{41, 42, 43, 44, 45} Valgus reposition means a higher CCD angle. We could show that changes in the CCD angle correlate with CFO, which is in accordance with the study of Lechler et al., which described a more pronounced varus femoral neck configuration results in an increased FO and a more pronounced valgus configuration in a decreased FO. ³⁶ This confirms acceptance that the reduction of the fracture has an influence on the postoperative CFO. An extensive reduction in valgus will more likely show a postoperative FOD, while an extensive reduction in varus will more likely show a postoperative FOI.

Main Findings of the Study and Clinical Consequence

However, it could be shown that the individual anatomical FO and the CCD also influence the postoperative FO change. Based on our results, hip joints with a preoperative femoral offset >44 mm and a CCD angle <134° seem to have a higher risk for decrease of the postoperative FO after treating an MFNF with DHS osteosynthesis. In contrast, hip joints with a preoperative femoral offset <44 mm and a CCD >134° tend to have an increase in the postoperative FO (Figure 6). According to these radiological based study results, it can be concluded that to avoid excessive postoperative CFO, the individual FO and CCD should already be determined in the preoperative planning and taken into account intraoperatively in order to restore the individual anatomy of the femoral neck as best as possible. Particularly, in the case of displaced MFNFs, the morphology of the proximal femur cannot adequately be analyzed preoperatively by only looking at the fractured side of the joint. For this reason, x‐ray with a pelvic overview, which includes the contralateral healthy hip joint, should always be performed preoperatively. In the absence of previous images, only the healthy contralateral side serves as a reference for the hip joint morphology for the surgeon. This principle is likewise established for planning endoprosthetic joint replacement.^{16, 40, 41}

Detection of Critical Postoperative Changes of the Femoral Offset

CFO of more than 15% compared with the individual anatomical FO is defined as a critical CFO.^{32, 33, 34} According to this definition, we detected a high number of cases of 52.9% (55 of 104) of all analyzed hip joints with a critical CFO in the presented study, either by a critical FOD (47 of 79) or a critical FOI (8 of 25). Sariali et al. showed that an FOD over 15% seems to be critical, because of a general reduction in range of motion and a lower swing speed while walking. ²⁴ Furthermore, joint and gait instability or an impingement may arise. The authors examined 28 patients who underwent total hip arthroplasty (THA) in case of unilateral primary osteoarthritis. Their analysis is based on pre‐ and postoperative CT imaging as well as dynamic analysis of motion for the operated and nonoperated side. Sariali et al. ³² and Pianka et al. ³⁴ described that an FOI of more than 15% referenced on the contralateral healthy hip side seems likewise critical and often results in a greater trochanteric pain syndrome. These studies are based on gait analysis and finite element models after endoprosthetic joint replacement. To the authors’ knowledge, there are no studies that showed such a high percentage of critical changes in the femoral offset after closed reduction via DHS osteosynthesis in cases of MFNF. Due to the retrospective study design, no statement can be made as to whether this critical CFO, in the case of femoral head preservation therapy, is associated with similar clinical symptoms that are described after endoprosthetic joint replacement of the hip joint. However, the present study provides an impetus to further explore this issue. Future studies should investigate patients after hip head‐preserving osteosynthesis therapy in a prospective model via gait analysis.

Surprisingly, there was no association between age or fracture severity and CFO. We would have expected a greater risk of compression of the fracture and a change in the CFO as a result of both the age due to poorer bone quality and the severity of the fracture. However, we could not find such an association in the statistical analysis of our data. Further studies should examine this association again in order to get greater clarity here. Moreover, we could not find an association between CFO and OF in the first postoperative year. Here, we would have thought that we would find a correlation showing that hips with a postoperatively decreased CCD angle and thus an increase in FO would show a greater risk of OF.

Limitations

A limitation of the study is that there was no x‐ray imaging before the fracture‐causing accident. Therefore, the actual side‐related morphological changes after surgical treatment cannot be recorded directly on the affected joint side. Corresponding to surgical treatment with an endoprosthesis of femoral neck fracture, the contralateral healthy hip joint side was used as reference. Due to the retrospective nature of the present study, no statements can be made regarding the actual clinical outcome of the patients. It should also be noted that no computer tomography was performed preoperatively. This is superior to the conventional X‐ray in depicting the fracture morphology. Regardless of these limitations, this study provided important and completely new insights for understanding the FO in the treatment of patients with MFNF. The probability of two identical measurement results of the pre‐ and postoperative FO is to be considered rather low. In view of these circumstances, small differences between the two measurements should not be described as “change in FO.”

Conclusion

In the present study, 104 patients with an MFNF were analyzed after closed reduction and osteosynthesis with a DHS. The analysis showed that operative treatment with a DHS leads to a significant change in the postoperative radiological FO. In 52.9% (55 of 104) of all analyzed hip joints, a critical change in the FO was detected. It seems that the individual anatomical FO and the CCD have an influence on the postoperative FO change. Therefore, exact preoperative planning, considering the contralateral healthy hip joint, is mandatory to restore the individual FO of the femoral neck in the best possible manner. In order to be able to make statements about the actual clinical functional outcome of patients with critical changes of the FO, prospective studies should be conducted in the future. Age, gender, and fracture severity had no influence on the FO or the CCD. The change in postoperative FO had no influence on OF.

Ethics Statement

The study was approved by the ethics committee of the University of Göttingen (IRB number 34/7/20) and performed in accordance with the principles expressed in the Declaration of Helsinki.

Conflict of Interest Statement

The authors declare that they have no competing interests.

Funding Information

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Author Contributions

MPM and TH designed the study. MPM performed all experimental procedures. Data analysis was carried out by MPM, TH, and RG. MPM and TH wrote the manuscript. MPM, MTS, DS, RG, PJR, KJ, WL, and TH critically revised it for important intellectual content. All authors have approved the final version of the article, including the authorship list.

Consent for Publication

The data collection was carried out purely retrospectively on the basis of the electronic files of the patients from the Clinic for Trauma Surgery, Orthopedics and Plastic Surgery and the Institute for Diagnostic and Interventional Radiology at the University Medical Center Goettingen (UMG), so there was no voluntariness. The project‐specific “informed consent” is not required, as obtaining consent is considered disproportionate. The need for informed consent was waived by the ethics committee of the University of Göttingen due to the retrospective nature of the study.

Data Availability Statement

The datasets used and analyzed during the current study are available from the corresponding author, anonymized upon reasonable request.