Malreduction in femoral shaft fractures

Learning objectives

1. Understand the incidence and causes of malreduction of femoral shaft fractures
2. Know techniques to detect and assess malreduction in these fractures
3. Be aware of different intraoperative methods to avoid femoral malreduction
4. Be aware of influential literature on this topic

High energy trauma

As every trauma surgeon knows, femoral fractures usually result from motor-vehicle accidents or other kinds of high-energy trauma. The amount of energy involved is often so great that it results in comminution. As we also know, the gold standard for treatment of these fractures is intramedullary (IM) nailing, which is associated with union rates close to 98%.

However, one common and well-known complication is malalignment. This commonly involves malrotation, leg-length discrepancy (LLD) or both. Rotational malreduction is normally considered anything more than 15˚ (Sullivan, 2021). Using this threshold, malrotation occurs in over 27% of femur fracture reductions. If subtrochanteric fractures are included, the incidence jumps to nearly 40%; and if the threshold is lowered to 10˚ almost 50% of patients are affected. For LLD, if the difference between leg lengths is more than 1.5cm, it is considered problematic.

With this type of fracture, then, malalignment is not uncommon. However, its functional implications are not well-documented. One reason for this gap in knowledge is that patients can compensate for many deformities. Still, even relatively small adjustments come at a cost. Over a period of years, LLDs or rotational maladjustments commonly lead to osteoarthritis.

One solution involves educational programs such as this one. AO Trauma’s hands-on courses and webinars inform orthopaedic surgeons around the world regarding tools and techniques to improve their fixation.

The need for comparable outcome measures

However, while such programs disseminate validated findings very well, a deeper problem limits the development of usable findings. Regarding femoral fractures, for example, when research teams use unique or unusual outcome measures, they make it very difficult to compare their results with those of other research teams. This can make it very difficult to decide what types or amounts of malrotation or malreduction are problematic to patients.

What we can say is that any malrotation will lead to malalignment in the mechanical axis, especially in the sagittal and coronal planes. This means the patient will have problems with running, and of course with many sports, but also with daily activities such as going up or down stairs. Another result is increased patellofemoral contact stress. Because almost no remodelling takes place on the axial plane, such problems improve very little over time. Where possible, then, the solution is to match both rotation and length to those of the uninjured limb.

CT imaging: gold standard for preoperative measurement of anteversion

The CT scan is the gold standard for anteversion measurement. In many instances, if the patient has undergone a whole body (pan) CT, it will be possible to measure the anteversion of the femoral neck preoperatively. When femoral fracture patients are received in centres where pan CTs are done, we can also ask for proximal views including both femurs. Especially if only one of the femurs is affected, this will allow an idea of the degree of anteversion.

Intraoperative views

Intraoperatively, it is very important to obtain proper fluoroscopic views. To begin with, when positioning the patient, we must ensure that the pelvis is square and level, i.e., not tilted, on the fracture table. If there is tilting, it will be necessary to adjust the anteroproximal (AP) view by adding or subtracting several degrees. With the pelvis squared on the fracture table, it is possible to obtain a true AP view of it. With that done, the next step is to look at the lesser trochanter. That will allow a very good idea of the amount of rotation in the proximal femur.

Guggenheim’s technique: using computer-generated models to check effects of changes in rotation angles (front and lateral views)

Guggenheim et al. used computer-generated images of the femur in the normal position. Starting from the centre of the femoral head, they drew the line of the mechanical axis, going through the centre of the knee, down to the centre of the ankle. At the same time, they drew the knee axis. They did the same thing using a lateral view, with the line going through the centre of the head, slightly anterior to the centre of the knee, and then through the centre of the ankle.

They then modelled a fracture with an externally-rotated distal femur to see how rotational differences would affect the mechanical axis. The results were very clear: the mechanical axis immediately moved posteriorly and laterally from its normal position in the joint. The same malrotation led to abnormal patellar tracking, causing abnormal forces on the patella and the knee, which would possibly lead to osteo-arthritis. This supports Sutherland et al.’s conclusion that, regardless of how well the patient may tolerate malrotation, any change in either direction alters the mechanical axis and places weight and other forces where they should not be.

Risk factors contributing to malalignment after IM nailing

Numerous factors can influence femoral alignment. These include

• the location of the fracture, especially if it involves the subtrochanteric area
• the use of external reduction, which leads to abnormal muscle forces on the proximal femur
• failure to ensure proper rotation before fixation, which leads to abnormal forces on the femur
• fracture type: transverse fractures are especially difficult to align
• free drilling of the distal locking screw
• unsuitable views during distal locking
• non-availability/non-use of image-guided distal locking.

How to assess malreduced femur fractures: CT is best

The next question is, how do we prevent malreduced femur fractures. Starting preoperatively, clinical assessment is used. However, this is not very accurate. It is often not possible to obtain the exact angles or accurately estimate the anteversion, especially on the normal side. In many cases, then, radiological imaging is essential for a proper assessment. As noted, the CT scan, if done pre-operatively, can be a very important tool in assessing the amount of anteversion in the proximal femur. Obtaining a plain radiograph of the other femur can be very helpful as well, particularly to match the lengths. It may also give an idea of the amount of anteversion in the proximal femur, as described below.

Intraoperative imaging to correct rotation, length

Intraoperatively, fluoroscopy is the tool used most. If 3d fluoroscopy or intraoperative CT scanning are available, these are also excellent tools that have been proven to give an accurate measurement of the amount of femoral anteversion, but a standard fluoroscope is enough. If you can use it to superimpose images on one another, so much the better. The beauty of 3d fluoroscopy or the intraoperative CT scans is that if any maladjustment is detected, it can be corrected immediately intraoperatively. If intraoperative imaging is not available, postoperative CT scans are also useful to assess proximal femoral rotation and femoral length.

CT scanogram (scout view) of anteversion

The CT scanogram (scout view) is the gold standard for measuring anteversion. It depends on taking cuts through the proximal femur to assess the amount of anteversion in the femoral head and the neck, then taking another cut through the distal femur to assess the angles in the distal femoral condyles. Comparing the two, it is possible to detect any malrotation in the femur.

There are two methods used. The first is to take measurements for the two femurs and determine the difference between the angles. With the second, the image of the proximal femur is superimposed onto that of the distal femur. The angle between the two indicates the amount of correction necessary.

Using the scout view to assess leg length discrepancy (LLD)

Leg length discrepancy can also be measured very accurately using the C-arm scout view. This is a very straightforward way to measure the length. Below is an example of the first method: a cut is scanned through the head and the neck and a line drawn through them to compare their angle to the horizontal plane.

In this situation, the difference between the head/neck cut and the horizontal plane was 25 degrees. Taking the angle from the neck/head and transferring it to the distal image would make it possible to draw another line along the posterior border of the distal femoral condyle and measure the angle between the two. And you could do the same on the other side. As you can see on the image below, the angle on the first side was 45˚; and on the second, it was 44˚. In the slide, the upper line represents the anteversion of the femoral neck; and the lower is the line representing the poster border of the femoral condyles.

The other way is to superimpose one image on the other. Of course, this is only possible if the CT machine has the capability of doing this. As the slide shows, measuring the angles after super-imposing them gives exactly the same values as the first method. Considering that both of these methods are very accurate, if you have the ability to superimpose one image on the other, this is much quicker and easier method of measuring the amount of rotation in the distal femur.

Using the scout view to measure leg length discrepancy (XY of two whole legs)

The scout view of the CT scan (topogram) can easily be used to measure femoral length. This shows a patient with bilateral femoral fractures. On the patient’s right leg, regaining the length was fairly simple. However, the other side had severe comminution and bone loss. Postoperatively, there was a clear discrepancy in length of roughly 2 cm. This is very easily measured with the scout view of the CT scan. The more difficult problem is how to detect and assess rotation in the femur.
Angular deformity is much less of a problem with nailing than with plating

Measuring the angles will also tell you whether there is angular deformity. This is much less of a problem with nailing of the femur than with plating. Malrotation and ligament discrepancy are more common with intramedullary nailing—although the newer nails can be used to help correct the rotation (more on this below). The following paragraphs outline intraoperative techniques to minimize these problems.

Fluoroscopic views: using the uninjured side as a reference model

Many of us only have access to regular fluoroscopy. If one side is uninjured, it is critical to use that side as a reference. So, if suitable preoperative images are not available, it is very important to correct them intraoperatively.

To assess the amount of anteversion, start with the distal femur. (24:12) For that view, ensure that the two condyles are superimposed on each other. This gives a very good lateral view. The C-Arm should start in the 90˚ position. To assess the proximal femur, look at the lesser trochanter to see how prominent it is. That should allow estimation of how much anteversion will be necessary. The difficulty here is not usually in imaging the distal femur, but in obtaining proper anteroposterior (AP) and lateral views of the proximal end.

AO Trauma: Optimizing intraoperative imaging during proximal femoral fracture fixation

This document was developed by the AO Trauma team specifically to help obtain proper views of the proximal femur—both AP and lateral views.

(25:22) A smooth line crossing over the culsa and lining up with the head

For an AP view of the proximal femur, there has to be a smooth line over the medial side and over the culsa, lining up very nicely with the head. You should be able to see the greater trochanter clearly and the lesser trochanter on the medial side. There should be no varus or valgus deformities in the proximal femur. To capture this image, the C-arm should be centred over the proximal femur.

(26:19) Capturing a lateral image lining up the head, neck and shaft of the femur

The lateral view is the tricky one. In these situations, once the patient is placed on the table, the C arm often needs several adjustments. Starting at 90 degrees, it can be moved gradually up, as necessary, to 85, 80, 70, 75 degrees, until the image shows the head, neck and shaft of the femur all in one line. The angle necessary varies with the amount of anteversion in the femur. With more anteversion, this angle is going to move more towards 75 or 70˚; with less, it will be around 80 or 85˚. It is critical to have a proper lateral view of the proximal femur with the head, neck and shaft all in a line. And a line drawn along the posterior aspect of the head, neck and the shaft should be smooth.

(27:22) Rotating the femur to test alignment

Now, another way to look at this is to look at the relation between the greater trochanter and the femoral head. In a study on whole fresh frozen cadavers, Kenaway et al., imaged the proximal femur in different types of rotation—in neutral internal and external rotation.

Testing for contact between the head and the greater trochanter as a sign of external rotation deformity

After obtaining the desired view of the proximal femur, they checked the relation between the posterior border of the greater trochanter and the head of the femur. The sign of an external rotation deformity is the head knocking against the posterior border of the greater trochanter. An image showing this indicates that the proximal femur is externally rotated (Mohamed Kenaway et al., 2011).

(28:26) Proper AP and lateral views of the proximal femur are essential before nailing

Before starting nailing, this technique’s developers strongly emphasize the importance of obtaining AP and lateral views of the proximal femur showing that any rotational deformity has been corrected.

Another study focussed on minimizing ligament discrepancy after IM nailing. This was a prospective case series looking at 98 patients with combined femur fractures managed with IM nailing. All had postoperative CT scanograms. Using a 1.5cm discrepancy as a cutoff, they found that 21% had unacceptable ligament discrepancies. There was no difference regarding how the nailing was done, i.e., whether it was antegrade versus retrograde. There was no difference in age, sex, location or the surgeons’ experience.

Checking leg length vs uninjured side is most accurate

The indicated way to look for the leg length is very low-tech: before starting, we measure the image of the uninjured side with a ruler. Measurements taken this way are more reliable than a preoperative scan.

(29:49) Preoperative images can be uncalibrated, misleading

A ruler and an intraoperative scan are recommended because if the pre-operative x-ray technician did not calibrate the x-rays correctly, measurements from those images will not be reliable. So it is good practice to make the necessary measurements intraoperatively, and to use the same ruler to measure both the injured and the uninjured side.

(30:40) Working with 2nd generation or later anteversion IM nails: proximal locking choices

One common way to prevent malrotation of the proximal femur is through the use of newer designs of intramedullary nails. Second-generation IM nails have a built-in anteversion. Because the nail’s anteversion helps obtain the proper rotation, it may be preferable to use proximal locking into the neck and head instead of other possible positions. As this was first described by Chris Espinoza, it is known as the Espinoza technique.

(31:44) The Espinoza technique

When lining up the IM nailing jig with the proximal femur, an accurate entry point is essential

Basically, the Espinoza technique depends on knowing the anteversion of the proximal femur. As many second- and third-generation nails are designed to adjust anteversion, the jig can be used as a guide to restore proper rotation in the femur. After obtaining correct lateral views but before starting proximal locking, it is necessary to ensure that the jig for the proximal femur is lined up exactly over the centre of the head and the neck. For that to be possible, the entry point into the femur has to be exactly through the middle of the greater trochanter: it cannot have shifted laterally or medially, it cannot be anterior or posterior. The entry point has to be as accurate as possible.

(32:39) Checking the lateral view of the proximal femur

Once the nail has passed into the femur and the locking jig is attached, double-check first that you have the correct lateral view of the proximal femur, and second that the jig is lined up with the femur, centred on the neck and the head. Then, before putting the screws in, check that they are directed into the middle of the neck and the head. The next step would be to obtain a lateral view of the distal femur: you need to see a complete, perfect circle in the distal locking holes of the nail. At this point, it does not matter how the distal femur looks—whether or not the condyles are aligned.

(33:39) After proximal locking, aligning and stabilizing distal femur

Once the proximal locking is complete, a perfectly circular lateral view of the distal nail hole is necessary. With the proximal femur stabilized, the distal femur can be rotated either internally or externally until the two condyles are superimposed on each other. Once they are aligned, the distal nails can be locked.

(34:55) Raoul’s comparison of the Espinoza method to the previous/conventional technique

Raoul (2002) compared the Espinoza method to the conventional technique, which used the patella and lesser trochanter to determine rotation/anteversion. Especially using first-generation femoral nails, which have no anteversion function, the older system depended on accurate fluoroscopic views. To judge the amount of rotation, the patella would have to be centred over the distal femur and the lesser trochanter neither prominent nor hidden—which would indicate respectively either external or internal malrotation—and the fractured femur stabilized in the neutral position.

Espinoza method found superior

Postoperatively, Raoul took a CT scanogram of each patient to measure the amount of anteversion and check for ligament discrepancy. In the traditional group, malrotation of more than 15 degrees was found in eight of the 27 patients (ca.30%). With the Espinoza technique, more than 15 degrees of malrotation was only found in one case. So the conclusion is that, in patients with normal anteversion and comminuted fractures, during locked IM nailing, the inherent anteversion produced by second-generation nails can safely be used to minimize malrotation of the femur, and is superior to the traditional fluoroscopic technique.

Conclusion

Malrotation is a well-known complication in femoral fractures. Treating it with IM nailing and understanding the anatomy of the proximal femur in relation to the distal femur is very important. Preoperative assessment of the other femur—if it is un- or less-injured—is important for preoperative planning. Correct intraoperative fluoroscopic views or postoperative CT scans of the femur are the most reliable ways to assess and correct anteversion and leg-length discrepancy.