1 Introduction

Intertrochanteric fractures (ITF) count for about half of all hip fractures and are related to osteopenia and advancing age. Many surgical options are available for the treatment of these fractures ranging from Dynamic hip screw fixation (DHS), long and short intramedullary nailing, proximal femoral locking plate and hip arthroplasty.¹

The ITF with long comminuted posteromedial cortex, subtrochanteric extension, reverse obliquity and incompetent lateral wall are the unstable and are usually associated with poor surgical outcomes.²

Historically, Posteromedial comminution has been considered the most important factor for the surgical management of ITF.^3,4 Recently, attention and significance has been attributed to lateral femoral wall thickness as well.^5–7 Anatomically, lateral femoral wall is characterised as the lateral femoral cortex distal to the vastus ridge and it acts as the lateral buttress from a biomechanical perspective.

DHS is considered gold standard surgery for surgical fixation of stable ITF. It is to be avoided in unstable fracture patterns and in patients with pre-operative lateral femoral wall fracture (LWF).^8,9 Post-operative LWF has been reported to occur in about 21% of ITF with subsequent approximately 22% of these patients requires re-surgery.^10,11 Studies have shown that cortical thickness of bone is directly proportional to the resistance offered by bone to the deforming forces.¹² Though cortical wall thickness is a critical factor in LWF, low BMD could be an important contributing factor to this complication.

In this study we aimed to find out the association of lateral femoral wall thickness and bone mineral density in patients sustaining LWF during DHS surgery. We hypothesised that patient with thin lateral femoral wall and osteopenia or osteoporosis could have increased incidence of postoperative LWFs.

2 Patients and methods

This prospective study was conducted after obtaining Institutional Review Board (IRB) and ethical approval at a tertiary trauma care centre. All patients with hip fractures diagnosed on plain radiography as ITF were included. The Inclusion criteria was ITF less than 3 weeks old treated with sliding screw in patients with age more than 18 years and Body Mass Index (BMI) less than 30.

Patients with pathological or open ITF, preoperative LWF and impaired neurological status were excluded from the study. The study comprised a total of 70 patients with ITF. All patients were managed as per ATLS protocol before surgical interventions.

Preoperative radiograph included an antero-posterior (AP) radiograph of pelvis with both hips, affected hip with femur full length AP (20° internal rotation) in traction and cross table lateral view. The lateral femoral wall thickness was measured on Picture Archiving and Communication System (PACS) software, by measuring a distance (in mm) from a reference point approximately 3 cm distal to the innominate tubercle of the greater trochanter, at an angle of 135° upward to the fracture line on anteroposterior radiograph pre-operatively (Fig. 1). One of the authors (AV) has measured the pre and post radiograph findings at different time intervals and same was confirmed by the two senior authors VKJ and RKA.

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Fig. 1 Radiograph of left hip joint showing measurement of lateral femoral wall thickness in inter-trochanteric fracture.

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Dual energy x-ray absorptiometry (DEXA) of contralateral hip and lumbosacral spine was performed preoperatively to measure bone mineral density.

Under regional anaesthetic and fluoroscopic supervision, all patients had DHS fixation. Lateral femoral wall thickness was assessed during surgery. Intra operatively the lateral wall thickness was measured by using the depth gauze. From a reference point 3 cm distal to the innominate tubercle of the greater trochanter, the depth gauze was passed through reamer hole at an angle of 135° till the fracture line as seen under fluoroscopic image and the distance was measured in millimetres (mm).

Postoperatively at second day, AP view of pelvis with both hips and AP & lateral radiograph of affected hip with thigh were taken and evaluated for implant positioning, LWF and tip-apex distance (TAD). The tip-apex distance (TAD) in millimetres is the total of the distances between the lag screw tip and the apex of the femoral head in both the AP and lateral radiographic views. TAD was determined using the method devised by Baumgaetner et al.¹³ A post-operative radiograph of the LWF is shown in Fig. 2.

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Fig. 2 Postoperative radiograph hip joint showing lateral wall fracture.

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Routine follow-up was conducted at 1, 2, 3, 6 and 12 months. At follow-up radiological assessment was also done to find out any postoperative LWF, progression of ITF union and implant failure.

Data collection: Data was collected from in-hospital records, PACS, discharge summaries and follow-up assessments. The primary outcome of the study was to predict the thickness of lateral femoral wall which can cause LWF after DHS and its correlation with BMD.

3 Results

3.2

3.2 Lateral femoral wall fracture (LWF)

11 patients had LWF. Fig. 2 shows radiograph of the patient showing LWF. The mean lateral femoral wall thickness was 19.545 mm in these patients who had postoperative LWF as compared to mean lateral femoral wall thickness of 29.285 mm in the other 54 patients. (P < 0.001, student's t test-unpaired). Data of lateral femoral wall thickness in different fracture classification groups and its relationship with LWF is shown in Table 2.

Table 2 Data of lateral femoral wall (LFW) thickness in different fracture classification groups and its relationship with LFW fracture.

S No.	AO Fracture classification	Patients (n)	Mean LFW thickness (mm)	p-value
1.	AO 31-A1.1 to AO 31-A1.3	12	25.917	<.001
	With LFW fracture	1	19.400
	Without LFW fracture	11	26.509
2.	AO 31-A2.1 to AO 31-A2.3	53	28.026	<.001
	With LFW fracture	10	19.560
	Without LFW fracture	43	29.995

Mean lateral femoral wall thickness as measured during surgery was 16 mm in 11 patients who had postoperative LWF as compared to mean lateral femoral wall thickness of 28 mm in other 54 patients. (P < 0.001, Mann-Whitney U test) There was no statistically significant association between lateral femoral wall fracture and fracture classification. (p = 0.062, Chi square test).

According to receiver operating characteristics (ROC) curve, the threshold of lateral femoral wall thickness that can forecast LWF was less than 25 mm with 81.5% sensitivity (95%. CI 68.6%-90.7), 90.9% specificity (95%. CI 58.7%–99.8%). The area under the curve was 0.9149832, which was statistically significant (p < 0.001) (Fig. 3).

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Fig. 3 Receiver operating characteristics (ROC) curve showing sensitivity and specificity.

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The mean time to union for LWF was 100 days (range 80–120 days) and in patients without LWF it was 100 days (range 86–130 days). The difference in union time between these two groups was not statistically significant (p = 0.231, Mann-Whitney U test).

4 Discussion

The thickness of lateral femoral wall is an important predictor for the occurrence of post-operative LWF. This study shows 25 mm of lateral femoral wall as a cut off value for post-operative LWF in patients with ITF undergoing DHS fixation. Hsu CE et al. reported threshold lateral femoral wall thickness to be 20.5 mm.¹⁰ Recently; in a prospective study by Pradeep et al. LFW was found in about 20% cases during DHS fixation. The threshold for lateral wall thickness that can predict LFW is 21 mm, according to the authors, with 95% sensitivity and 88.2% specificity. In our study, the cut off point for lateral femoral wall thickness is 25 mm which higher than the 20.5 mm of the study by Hsu CE et al. and 21 mm of the study by Pradeep AR et al. Study by Hsu CE et al. was conducted in Taiwan and by Pradeep AR et al. in South India.^10,14 We believe that short stature and racial differences may be the reason for this difference in the threshold of lateral femoral wall thickness. More studies from various geographic regions may give more accurate information in this regard.

The first report of post-operative LWF in 24 patients was reported by Gotfried.⁹ The reported incidence of LWF is approximately 20%.^10,11 This study also documented similar results with LWF incidence of approximately 17%.

ITF generally do not show medialization as the intact superior-lateral part of the distal fragment which rests against the proximal fragment prevents the pull of adductor muscles. However, in case of LWF, the distal fragment cannot oppose the pull of adductor muscles. Henceforth, femoral medialization is a common finding associated with LWF and is responsible for postoperative fracture collapse & DHS fixation failure.^5,15,16

Majority of patients (8/11 patients) in this study, having post-operative LWF had unstable ITF (AO31-A2.2 and 2.3) compared to 3 patients having stable ITF (AO31-A1.1 to 2.1). As we move from AO 31-A1.1 to AO 31-A2.3, there is progressive reduction in the thickness of lateral femoral wall and incidence of LWF increases. Similar finding has been observed by other studies.^11,15 As a result, even in stable ITF, extra caution should be exercised to avoid further lateral wall damage during DHS fixation. (AO31-A1.1 to 2.1).

Because there can be intra and inter observer biases when diagnosing A2.1 and A2.2 fracture patterns, it's a good idea to keep in mind that patients with A2.1 and A2.2 fractures with lateral femoral wall thickness less than 25 mm are at a higher risk of LWF.¹⁷

Despite LWF there was no problem in union if the fracture was in stable group as per classification (3 patients). The high union rate in stable fracture may be attributed to the fact that posteromedial bone of the femur prevents micromotion of proximal fragment, which is not the case in unstable fractures due to comminution.¹⁰ With LWF (in unstable group) union was also achieved but time taken was longer and was statistically significant.

In the current study we have also tried to accesses the role of bone mineral density (BMD) with the incidence of LWF during DHS surgery for ITF. We found the osteopenia in both groups. The T-score of contralateral hip was −2.255 in LWF patients; while it was −2.428 in patient without LWF. This difference in mean was not significant between both groups. Pradeep et al.¹⁴ evaluated cortical thickness index (CTI) to evaluate osteoporosis in LWF and without it in an attempt to demonstrate the link between osteoporosis and LWF. Authors found a mean value of CTI was comparable in both the groups. This suggests that osteoporosis has no role on LWFs during DHS fixation. In contrast to this study by Joshi et al. suggests by measuring Singh's index an association between osteoporosis and the incidence of LWF. However, this association was more with an unstable intertrochanteric fracture.¹⁸

5 Conclusion

Lateral femoral wall thickness is a reliable and easily reproducible parameter to predict postoperative LWF. Though a causal relationship between BMD and post-operative LWF could not be stablished by this study. Perhaps a larger multi-centre study with a larger cohort needs to be conducted to establish such a relationship as well as to look for influence of osteoporosis on LWF. DHS fixation should be avoided in ITF patients with Lateral femoral wall thickness <25 mm and other implant choices should be explored for management of these patients.