Significance of hip rotation on measurement of 'Tip Apex Distance' during fixation of extracapsular proximal femoral fractures

Conventional fluoroscopic views are inadequate to predict the Tip Apex Distance and articular clearance of sliding screw devices: A computed tomography-based analysis

INTRODUCTION

Tip-apex-distance (TAD) has been widely advocated as the index to predict the risk of screw cut out in hip fractures treated with sliding hip screw devices. The fluoroscopic extents of the femoral head can change with the slightest change in the limb position which includes internal and external rotations, adduction and abduction. These changes can affect the visible TAD and articular-clearance of the screw-tip. The purpose of this Computed-tomography(CT) based analysis is to analyze the variations of the radiographically visible articular-clearance and TAD measurements with limb positioning and to determine the appropriate fluoroscopic projections for different screw-positions within the femoral head.

MATERIAL AND METHODS

We retrospectively analysed CT studies of twenty healthy proximal femora. Spatial markers simulating screw tips were placed in the different combinations of anteroposterior(AP) and cephalocaudal(CC) positions. Software-based AP and lateral radiographs were developed for each screw position. Additional AP radiographs with femur in internal and external rotation, and lateral radiographs with the femur in adduction and abduction were developed. The variation of TAD and articular-clearance of the screw was measured among these radiographs for individual screw tip positions.

RESULTS

Screw tip placed centrally in AP and CC planes position didn't show any significant variation in TAD and articular-clearance with modified AP and lateral radiographs. Significant differences were observed in TAD and articular-clearance values for other screw tip positions. Anteriorly placed screw tips had higher TAD and articular-clearance values with external rotation and similar changes were observed with posteriorly placed tips in internal rotation. Inferiorly placed tips had higher articular-clearance and TAD with limb abduction and similar changes were observed for superiorly placed tips with limb adduction.

CONCLUSIONS

For the sliding screws placed in non-central locations, the clearance of the screw tip from the articular margins can not be appropriately estimated with conventional AP and lateral views. Additional views with the limb in internal rotation and external rotation in AP view, and adduction-abduction in lateral view are required to safely place the sliding screw in the femoral head. The limb should be brought to a neutral alignment for the accurate estimation of TAD.

Modified radiographic views to prevent the anterosuperior and posterosuperior bony violation during screw fixation of femoral neck fractures

INTRODUCTION

The standard anteroposterior and lateral fluoroscopic projections used during femoral neck fracture fixation provide a two-dimensional representation of the cephalocaudal and anteroposterior extents of the femoral neck. The radiographic representation differs from the actual extent of the femoral neck. The anterosuperior (AS) and posterosuperior (PS) surfaces of the femoral neck are at risk of bony breach by the fixation screws and that may get easily missed with standard fluoroscopic views. The current study aims at investigating the special fluoroscopy views, based on the orientation of the AS and PS surface of the femoral neck, that can help in the safe placement of screws near these surfaces without bony breach.

METHOD

A computed tomography-based analysis of fifty intact proximal femora was performed. The longitudinal axis of the proximal femoral shaft and the center of the femoral head were aligned along a common horizontal plane. The cephalocaudally constricted zone of the femoral neck was identified along its axis. The surface inclinations of the AS surface and the PS surface at the constricted zone of the femoral neck were measured in relation to the horizontal plane. The mean, standard deviation, overall range, interquartile ranges and gender-based variation of each of the two surface inclinations were measured.

RESULTS

The mean surface inclinations of the AS surface and the PS surface with reference to the horizontal plane were 55° ± 7.76° and 123.32° ± 7.88°, respectively. There were no significant side to side and male to female differences.

CONCLUSIONS

The modified radiographic views based on the surface inclinations of the AS and the PS surfaces can help in the localization of the critical zones of these surfaces which are at risk of bony breach with screw placement close to the surface. A prior fluoroscopic evaluation of these surfaces before guidewire placement can help in preventing the surface violation.

Developing an objective assessment of surgical performance from operating room video and surgical imagery

An unbiased, repeatable process for assessing operating room performance is an important step toward quantifying the relationship between surgical training and performance. Hip fracture surgeries offer a promising first target in orthopedic trauma because they are common and they offer quantitative performance metrics that can be assessed from video recordings and intraoperative fluoroscopic images. Hip fracture repair surgeries were recorded using a head-mounted point-of-view camera. Intraoperative fluoroscopic images were also saved. The following performance metrics were analyzed: duration of wire navigation, number of fluoroscopic images collected, degree of intervention by the surgeon's supervisor, and the tip-apex distance (TAD). Two orthopedic traumatologists graded surgical performance in each video independently using an Objective Structured Assessment of Technical Skill (OSATS). Wire navigation duration correlated with weeks into residency and prior cases logged. TAD correlated with cases logged. There was no significant correlation between the OSATS total score and experience metrics. Total OSATS score correlated with duration and number of fluoroscopic images. Our results indicate that two metrics of hip fracture wire navigation performance, duration and TAD, significantly differentiate surgical experience. The methods presented have the potential to provide truly objective assessment of resident technical performance in the OR.

The Scaphoid Safe Zone: A Radiographic Simulation Study to Prevent Cortical Perforation Arising from Different Views

PURPOSE

The purpose of this study was to simulate and calculate the probability of iatrogenic perforation of the scaphoid cortical bone when internal fixation appeared to be safe on radiographs. The results will assist surgeons in determining proper screw placement.

METHODS

Thirty scaphoids were reconstructed using computed tomography data and image-processing software. Different central axes were determined by the software to simulate the surgical views. The safe zone (SZ) and risk zone (RZ) were identified on the axial projection radiographs by comparing the scaphoid bone stenosis measured by the fluoroscopic radiographs with a three-dimensional reconstruction of the scaphoid stenosis. Each original axial projection radiograph was zoomed and compiled to match a calculated average image. The RZ, SZ, and probability of perforations in various quadrants were calculated.

RESULTS

Using a volar view (approach), the mean risks of cortical perforation were 25% with screws and 36% with k-wires. Using a dorsal view (approach), the mean risks of cortical perforation were 18% with screws and 30% with k-wires. A high risk of perforation was detected at the ulnar-dorsal zone.

CONCLUSION

Surgeons should be wary of screws that appear to lie close to the scaphoid cortex on both anteroposterior (AP) and lateral radiographs, particularly in the ulnar-dorsal and radial-dorsal quadrants, because such screws are likely to perforate the cortex. The position of the internal fixator should be assessed using a diagram outlining the various SZs. Therapeutic, Level III.

Assessing Wire Navigation Performance in the Operating Room

OBJECTIVE

There are no widely accepted, objective, and reliable tools for measuring surgical skill in the operating room (OR). Ubiquitous video and imaging technology provide opportunities to develop metrics that meet this need. Hip fracture surgery is a promising area in which to develop these measures because hip fractures are common, the surgery is used as a milestone for residents, and it demands technical skill. The study objective is to develop meaningful, objective measures of wire navigation performance in the OR.

DESIGN

Resident surgeons wore a head-mounted video camera while performing surgical open reduction and internal fixation using a dynamic hip screw. Data collected from video included: duration of wire navigation, number of fluoroscopic images, and the degree of intervention by the surgeon׳s supervisor. To determine reliability of these measurements, 4 independent raters performed them for 2 cases. Raters independently measured the tip-apex distance (TAD), which reflects the accuracy of the surgical placement of the wire, on all the 7 cases.

SETTING

University of Iowa Hospitals and Clinics in Iowa City, IA-a public tertiary academic center.

PARTICIPANTS

In total 7 surgeries were performed by 7 different orthopedic residents. All 10 raters were biomedical engineering graduate students.

RESULTS

The standard deviations for anteroposterior, lateral, and combined TAD measurements of the 10 raters were 2.7, 1.9, and 3.7mm, respectively, and interrater reliability produced a Cronbach α of 0.97. The interrater reliability analysis for all 9 video-based measures produced a Cronbach α of 0.99.

CONCLUSIONS

Several video-based metrics were consistent across the 4 video reviewers and are likely to be useful for performance assessment. The TAD measurement was less reliable than previous reports have suggested, but remains a valuable metric of performance. Nonexperts can reliably measure these values and they offer an objective assessment of OR performance.

Torsional malalignment, how much significant in the trochanteric fractures?

OBJECTIVES

The rotational alignment is definitely important in the long bones such as tibias and femurs. We also predict the importance of rotational alignment in the trochanteric fractures. So we measured torsional malalignment in trochanteric fracture and anlaysed their risk factors and their clinical significance.

METHODS

A total of 109 inpatients who had undergone internal fixation following trochanteric fracture and a postoperative pelvic CT scan between 2008 and 2013, with at least one year follow-up, were selected. Factors that affect torsional malalignment, such as age, gender, fracture stability, injured area, operative time, time of surgery after admission, and ASA status, were investigated. Factors that affect the patients' clinical results in malrotation, including ambulation time after surgery, postoperative complication rates, pain assessment of VAS one year postoperatively and Koval score, were also investigated.

RESULTS

Of the 109 subjects, torsional malalignment was observed in 28 (25.7%) subjects with a mean torsional malalignment angle of 20.7° (range: -31.2° to 27.1°). Torsional malalignment risk factors were fracture stability (p=0.021) and operative time (p=0.043). In terms of the time to ambulation after surgery, the postoperative complication rates, and the VAS and Koval scores at one year postoperatively, no statistically significant difference was observed between the torsional malalignment patients and the non-deformity patients.

CONCLUSIONS

In this study, 25.7% of the patients who had undergone internal fixation following trochanteric fracture experienced torsional malalignment. Major factors of the torsional malalignment were an unstable fracture and the consequent delay in the operative time. But the torsional malalignment was deemed to have no effect on clinical results.

Accuracy of the surgeon's eye: use of the tip-apex distance in clinical practice

Tip-apex distance is a well described method for assessment of screw placement in dynamic hip screw fixation of proximal femoral fracture. A distance of <25mm is associated with a significantly lower rate of cut out of the fixation device. Measurement is frequently performed retrospectively, although there has been no demonstration as to what accuracy the surgeon has of estimating tip-apex distance from image intensifier images, whilst scrubbed in theatre. Thirty-one clinicians working within orthopaedic departments were tested in their ability to identify adequacy of tip-apex distance on a series of image intensifier images. Level of seniority, awareness of the concept of tip-apex distance and use of the concept in clinical practice were each assessed. The accuracy in identifying the correct TAD was 82.5% in consultants, 83.8% in registrars and 71.1% in Senior house officers (SHO). The method was used in clinical practice by 50% of consultants, 89% of registrars and none of the SHOs.

The femoral neck safe zone: a radiographic simulation study to prevent cortical perforation with multiple screw insertion

OBJECTIVES

To calculate the probability of iatrogenic perforation when screws seem to be safe on radiographs. A risk zone (RZ) gradient is mapped to help surgeons determine the suitable screw positions.

METHODS

Using computed tomography data and image-processing software, 24 proximal femurs were reconstructed. The anteroposterior, lateral, and axial views were then simulated, and the safe zone and RZ were identified and calculated on the axial graphs. Each original axial graph was zoomed and compiled to match a calculated average image, and a gradient figure of the RZs was visualized.

RESULTS

All 24 femoral necks had cortical perforation RZs. The average risk percentage was 23.7%. The individual risk per quadrant was as follows: anterosuperior 2.5%, posteroinferior 3.8%, posterosuperior 6.7%, and anteroinferior 10.7%. Four safe and cortex-touching zones and a safe region were identified in femoral neck for 6.5-mm screws.

CONCLUSIONS

Surgeons should be wary of screws that appear close to the cortex on both radiographs, especially in the posterosuperior and anteroinferior quadrants, because such screws probably perforate the cortex. To minimize iatrogenic perforation, screw position should be assessed using a gradient figure of the RZs.

Multiple radiographic projections in detecting intra-articular screw penetration during fixation of femoral neck fractures

The authors performed a cadaveric study to evaluate the efficacy of multiple fluoroscopic projections in detecting intra-articular penetration of the screws during femoral neck fracture fixation and also to determine the most suitable radiographic projection. Models of intra-articular penetration in 8 normal proximal femur specimens were created by placing the pins in different quadrants of the femoral head and extending 1 mm beyond the femoral head surface. The tip-to-surface distance was measured on anteroposterior (AP) and lateral views, with the femur positioned at varying degrees of rotation, flexion, adduction, and abduction. After correcting for differences in magnification, associations between the tip-to-surface distance and femur position were noted. In certain femur positions and K-wire placements, conventional AP and lateral views did not show that the wire extended beyond the surface of the femoral head. The tip-to-surface distance on an AP radiograph with the femur in the neutral position was not comparable to that on the lateral view with the femur positioned at 20° of adduction (P=.821). However, the tip-to-surface distance on an AP radiograph with the femur in the neutral position varied significantly (P<.001) from all other tip-to-surface distances on either the AP or lateral projection. A linear association was found between the tip-to-surface distance and femur rotation angles on AP views and between femur adduction and abduction angles on lateral views. In conclusion, fluoroscopy in varied projections at different angles can detect unrecognized intra-articular screw penetration during internal fixation of femoral neck fracture. Additional special projection methods are suggested to identify and prevent intra-articular screw penetration.

Radiographic quantification of dynamic hip screw migration

PURPOSE

This study aimed to propose a technique to quantify dynamic hip screw (DHS®) migration on serial anteroposterior (AP) radiographs by accounting for femoral rotation and flexion.

METHODS

Femoral rotation and flexion were estimated using radiographic projections of the DHS® plate thickness and length, respectively. The method accuracy was evaluated using a synthetic femur fixed with a DHS® and positioned at pre-defined rotation and flexion settings. Standardised measurements of DHS® migration were trigonometrically adjusted for femoral rotation and flexion, and compared with unadjusted estimates in 34 patients.

RESULTS

The mean difference between the estimated and true femoral rotation and flexion values was 1.3° (95% CI 0.9-1.7°) and -3.0° (95% CI - 4.2° to -1.9°), respectively. Adjusted measurements of DHS® migration were significantly larger than unadjusted measurements (p = 0.045).

CONCLUSION

The presented method allows quantification of DHS® migration with adequate bias correction due to femoral rotation and flexion.

What is the relevance of the tip-apex distance as a predictor of lag screw cut-out?

Using a simple mathematical formulation, the relationship between the position of the lag screw tip (relevant to both intramedullary and extramedullary devices) and the concept of tip-apex distance (TAD) was derived. TAD is widely used in operating theaters as a surgical guideline in relation to the fixation of trochanteric fractures, and in clinical studies as a predictor of lag screw cut-out. In order to visualize better this concept, the locus of points having the same TAD was plotted and the dependence of TAD on the location of the lag screw tip was also reported. It was shown that TAD should be adjusted for the size of the femoral head (a variable which varies a lot according to the sex of the patient) while no correlation was found between TAD and bone morphometry indices obtained from micro-CT data (BV/TV and Tb.Th). Therefore, these results seem to suggest that TAD lacks mechanical justification and that predictors which are based on mechanical properties, such as bone density, should be investigated further.

The new technique of precise insertion of lag screw in an operative treatment of trochanteric femoral fractures with a short intramedullary nail

In order to reduce the incidence of cut-out, which is one of the serious postoperative complications of trochanteric femoral fractures, we paid special attention to the placement of lag screw in the femoral head. As a result, we devised a new technique that allows insertion of the lag screw at the first attempt into the optimal position on both planes, inferior half on the antero-posterior view and exactly central on the lateral view, without the need for any special devices other than the basic original set, using a trochanteric nail. For this technique, we have evaluated the proximal femoral profile under image intensifier, on the true lateral view projected parallel to the axis of the femoral neck and not on the conventional lateral view (Lauenstein view) with the projection parallel to the axis of the femoral shaft in a coronal plane. With the X-ray beam lying in the same plane with the targeting device including the nail and the guide sleeve, the guide pin is intended to pass through the guide sleeve and the middle of shadow of the proximal end of the targeting device, so that it can be inserted in the optimal position without fail, aligned with the middle axis of the femoral head. The deviation angle between the axes of the lag screw and the femoral head was measured on every postoperative lateral radiograph. The mean deviation angle of 1.6 degrees in the 39 fractures after the introduction of the new insertion technique was compared with 4.8 degrees in the 44 fractures before the introduction, which showed a significant difference between these groups (p<0.0001, Welch's t-test). When the lag screw can be placed exactly in the centre of the femoral head on the true lateral view, it can be set forward as closest to articular surfaces as possible on the postero-anterior view without a risk of penetration, so that the tip-apex distance could be easily achieved under 20mm, which leads to a reduction of postoperative cut-outs. This technique can be applied in other similar trochanteric nails, which gives them an advantage over the sliding hip screws.

The importance of surgical education in the accuracy of implant placement during hip fracture fixation

Background

Studies have found that tip apex distance (TAD) is the strongest independent predictor of lag screw cut-out following hip fracture fixation. The objective of this study was to understand the importance of introducing the concept of TAD to surgeons. The null hypothesis was that there were no differences between fractures fixed before awareness of TAD compared with fractures fixed after awareness of TAD.

Materials and Methods

This study involved assessing 75 consecutive radiographs retrospectively (before introduction of “tip apex distance” to surgeons) and 83 consecutive radiographs prospectively (after introduction of “tip apex distance” to surgeons). Radiographs were measured using a radiograph digitizer and software.

Results

Average TAD in radiographs measured retrospectively was 22.6 mm compared with 9.7 mm in radiographs analysed prospectively (P ≤ 0.001). The power of this study was 97%.

Conclusion

This study demonstrates that introducing the concept of “TAD” to surgeons, will improve the accuracy of lag screw placement during fixation of an extracapsular fracture. The improvements in lag screw placement will undoubted reduce cut-out of the implant post-surgery.

What's new in the management of proximal femoral fractures?

The incidence of proximal femoral fractures has increased significantly in recent years, and is expected to continue to rise with increasing life expectancy. However, the optimal method of treatment of these fractures is still debated. This article summarises current evidence concerning the most controversial issues in the treatment of intracapsular and extracapsular proximal femoral fractures. Despite initial enthusiasm, many new treatment options have been proved inferior to older, traditional methods, and physicians should be cautious when it comes to managing these fractures. It seems that meticulous surgical technique and implant selection according to fracture pattern and the characteristics of the individual patient offer the best route to optimal final outcome.

Measuring tip-apex distance using a picture archiving and communication system (PACS)

BACKGROUND

The sliding hip screw is currently the most frequently used prosthesis used to fix trochanteric fractures of the hip. The 'tip-apex distance' (TAD) has been found to be predictive of hardware failure, with a larger TAD being associated with an increasing risk of 'cut-out'. Previous studies have either used 'hard-copy' radiographs and geometrical aids or a mixture of scanned hard-copy images and extra software to measure TAD. The current study describes a new method of tip-apex distance estimation using an entirely digital picture archiving and communication system (PACS).

MATERIALS AND METHODS

Ten radiographs were measured for TAD by four surgeons of differing experience using the described measurement protocol, at two different time points (4 weeks apart). The results were then subjected to two-tailed t-tests to determine if they differed significantly.

RESULTS

No tests attained significance (i.e. no statistical difference existed between the observers' measurements and no difference existed over time from a single observer's results).

CONCLUSION

This study shows that TAD can be easily, accurately and, importantly, reproducibly measured using an entirely digitally based image capture and archiving system. The ease with which the measurements and calculations can be made will facilitate orthopaedic practitioners and trauma units in their auditing activities, and allows for quick TAD estimation in the 'X-ray meeting' environment.