Injury to neurovascular structures with insertion of traction pins around the knee

Abstract

Objective

Identify risk to neurovascular structures around the knee with placement of skeletal traction pins.

Methods

Kirchner wires were inserted into cadaveric limbs followed by layer dissecting of each leg. Correlations between weight, height, BMI, and distance were determined after calculating the average distance with deviation between each anatomic structure and the Kirschner wire.

Conclusion

Insertion of traction pins around the knee did not result in injury to neurovascular structures. Both weight and BMI positively correlated with distance between implants and neurovascular structure. Data collected suggests similar trends for all other anatomic structures.

1. Introduction

Skeletal traction was once used as definitive treatment of long bone fractures, but today is most commonly applied as a temporary method of stabilizing fractures in a damage control setting.3, 11 Contemporary practice uses skeletal traction for temporary stabilization until definitive surgical fixation can be performed.1, 2, 3 Benefits of skeletal traction include maintenance of limb length, pain control, minimizing blood loss, and limiting further soft tissue injury. Clinical examples include: femur fractures, vertically unstable pelvic ring injuries, and acetabular fracture-dislocations.¹¹

Bedside insertion of larger Steimann pins or smaller Kirschner wires are connected to 15–20 pounds of weight and attached to an appropriate traction frame. Damage to neurovascular structures, local soft tissue infection, osteomyelitis, thermal injury, and physeal injury are all possible complications of skeletal traction.1, 4 Traction pin insertion techniques are well described and focus on minimizing injury to the surrounding soft tissue (1, 2, 3, 4, 5). Historically, distal femoral traction pins have been inserted from a medial to lateral while proximal tibial traction pins have been inserted from lateral to medial. One main concern with application of skeletal traction is iatrogenic damage to surrounding neurovascular structures. To our knowledge, an anatomic study that evaluates the risk to neurovascular structures with insertion of a traction pin into the distal femur through a medial entry or a proximal tibia traction pin placed through a lateral approach has not been previously done. The purpose of this study is to identify the relationship of neurovascular structures around the knee with placement of distal femoral and proximal tibial skeletal traction pins.

2. Methods

Fourteen lightly embalmed cadaveric limbs from seven specimens were used for the insertion of distal femur and proximal tibia Kirschner wires. Distal femoral traction pins were placed with the specimen in a supine position, the knee flexed and supported to 45°, and the patella facing directly anterior. The sharp end of a 1.6 mm (mm) smooth Kirschner wire was used to pierce the skin of the medial distal thigh, at the level of the proximal pole of the patella. The mid-sagittal plane of the femur was determined by palpating the anterior and posterior cortex of the femur with the wire. The wire was advanced parallel to the knee joint from medial to lateral and in bicortical fashion using a power driver (Synthes, Paoli, PA) until the wire fully exited the lateral skin. Without changing position of the leg, a bicortical 1.6 mm smooth Kirschner wire was inserted into the proximal tibia. The entry site utilized was 1 cm (cm) distal and 2 cm posterior to the tibial tubercle. The wire was introduced through the anterior compartment of the lateral tibia, placed down to bone, and the mid-sagittal plane of the tibia was determined by using the wire to palpate the anterior and posterior cortex of the tibial. The wire was then advanced using a power driver in bicortical fashion parallel to the knee joint from lateral to medial until it exited the medial skin. All wires were inserted by a single fellowship trained orthopedic trauma surgeon. Fluoroscopic imaging for wire insertion was not used so as to reproduce clinical practice. This process was repeated on each specimen.

Following insertion of traction pins, each leg underwent layered dissection by an anatomist (R.S.). Superficial and deep neurovascular structures of the distal femur including the great saphenous vein, saphenous nerve, femoral artery, and femoral vein were carefully identified. For the proximal tibia, the superficial peroneal nerve, deep peroneal nerve, anterior tibial artery, and anterior tibial vein were also identified. The distance between each anatomic structure and the Kirschner wire was measured with a digital caliper with a tolerance of 0.1 mm. The average distance with deviation between each anatomic structure and the Kirschner wire was calculated. Differences in distance between left and right extremities were compared using a student's t test (p < 0.05). Injury to any anatomic structure was documented as present or absent.

3. Results

Fourteen lower extremities in seven lightly embalmed cadavers (2 females and 5 males) were utilized and then dissected. The average age was 78 ± 13 with an average body mass index of 24.5 ± 9.5 (Table 2). No anatomic structures were injured during insertion of either distal femoral or proximal tibia Kirschner wires. Average distances between implant and anatomic structures are listed in Table 1. The average distance between Kirschner wires and neurovascular structures ranged from 17.25 mm, for the anterior tibial artery, to 45.5 mm, for the great saphenous vein. The average distance between the Kirschner wire and individual anatomic structures in the femur are listed in Table 1. The average distance between the Kirschner wire and the great saphenous vein was 45.5 mm, the saphenous nerve was 30.75 mm, the femoral artery 28.75 mm, and the femoral vein was 29.85 mm. In the proximal tibia, the average distance between the Kirschner wire and anatomic structures are listed in Table 1. The average distance between the Kirschner wire and the anterior tibial artery was 17.25 mm, anterior tibial vein was 17.75 mm, the deep peroneal nerve was 22.1 mm, and the superficial peroneal nerve 32.05 mm. All anatomic structures of the distal femur and proximal tibia were noted to rest posterior to the trajectory of the K-wire. Student's t test showed no difference between left and right extremities when comparing distance between implant and anatomic structure (Table 3). Correlations were evaluated to determine if distance between implants and anatomic structures varied with height, weight, or BMI (Table 4). Given the small sample size correlations were reported with p values <0.100. Both weight and BMI positively correlated with distance between implants and the great saphenous vein (p < 0.046). Similarly weight statistically correlated with distance to anterior tibia artery (p < 0.022) indicating that implants were further from anatomic structures in larger individuals. Data collected suggests similar trends for all other anatomic structures.

Table 2.

Patient demographics.

Specimen	Sex	Height	Weight	BMI
1	M	75″	205	25.6
2	F	62″	78	14.3
3	M	70″	280	40.2
4	F	67″	220	34.5
5	M	69″	125	18.5
6	M	69″	140	20.7
7	M	70″	125	17.9

Table 1.

Average distance between neurovascular structure and implant.

	Left avg. (mm)		Right avg. (mm)	Combined R&L (mm)
Left femur		Right femur
Great Saphenous Vein	50.9 ± 24.7 (28–90)	Great saphenous vein	40.1 ± 22.2 (11–80)	45.50
Saphenous nerve	31.6 ± 13.1 (16–51)	Saphenous nerve	29.9 ± 17.0 (8–50)	30.75
Femoral artery	27.6 ± 12.3 (15–45)	Femoral artery	29.9 ± 16.1 (8–50)	28.75
Femoral vein	28.3 ± 11.6 (16–45)	Femoral vein	31.4 ± 17.0 (12–55)	29.85
Left tibia		Right tibia
Super peroneal nerve	30.7 ± 7.7 (20–43)	Super peroneal nerve	33.4 ± 11.5 (21–55)	32.05
Deep peroneal nerve	23.9 ± 7.7 (12–33)	Deep peroneal nerve	20.3 ± 7.5 (7–32)	22.10
Anterior tibial artery	17.9 ± 4.5 (12–25)	Anterior tibial artery	16.6 ± 5.9 (10–26)	17.25
Anterior tibial vein	18.9 ± 4.6 (13–25)	Anterior tibial vein	16.6 ± 4.0 (11–21)	17.75

Table 3.

Comparison of left and right distances between anatomic structure and implant.

	Left	Right	Correlation
Paired t test
Great saphenous vein	50.9 ± 24.7	40.2 ± 22.3	t = 1.5	p = 0.177
Saphenous nerve	31.6 ± 13.1	29.9 ± 17.0	t = 0.5	p = 0.664
Femoral artery	27.6 ± 12.3	29.9 ± 16.1	t = 0.6	p = 0.593
Femoral vein	28.3 ± 11.6	31.4 ± 17.0	t = 0.8	p = 0.461
Super peroneal nerve	30.7 ± 7.7	33.4 ± 11.5	t = 0.8	p = 0.470
Deep peroneal nerve	23.9 ± 7.7	20.3 ± 7.5	t = 1.0	p = 0.356
Anterior tibial artery	17.9 ± 4.5	16.6 ± 5.9	t = 0.5	p = 0.662
Anterior tibial vein	18.9 ± 4.6	16.6 ± 4.0	t = 0.9	p = 0.417

Table 4.

Correlations between distance and body size.

Right femoral great saphenous vein and weight	r = 0.715	p = 0.071
Right femoral great saphenous vein and BMI	r = 0.764	p = 0.046
Left femoral great saphenous vein and weight	r = 0.722	p = 0.067
Left deep peroneal nerve and weight	r = 0.726	p = 0.065
Right anterior tibial artery and height	r = 0.674	p = 0.097
Left anterior tibial artery and weight	r = 0.828	p = 0.022
Left anterior tibial artery and BMI	r = 0.744	p = 0.055
Left anterior tibial vein and weight	r = 0.648	p = 0.082

4. Discussion

In the 14th century, Guy de Chauliae introduced continuous isotonic traction for the treatment of femur fractures.⁸ Since that time, the principle of isotonic traction has fundamentally remained the same.¹⁰ Over time though, the use of skeletal traction has become more common and is a procedure used frequently. Skeletal traction has transitioned from a common methodology of definitive treatment to a technique of temporary stabilization in the algorithm of lower extremity fractures (16). Prior anatomic studies have defined the surrounding neurovascular anatomy of the distal femur and proximal tibia. Traditional teaching has utilized this knowledge to place distal femoral and proximal tibial skeletal traction pins in specific directions and through zones that minimize damage to nearby neurovascular structures.2, 6, 7, 9

Our study shows that distal femoral and proximal tibial Kirschner wires are able to be inserted using traditional guidelines while maintaining an adequate safe distance from nearby neurovascular structures. Traditional teaching dictates femoral pin insertion from medial to lateral to minimize damage to the femoral artery and vein as they traverse Hunter's canal as well as proximal tibial pin insertion from lateral to medial to minimize damage to the superficial peroneal nerve. We found that when using a starting point at the superior pole of the patella and mid-sagittal plane of the femur, the femoral vessels are on average greater than 30 mm from the Kirschner wire and were not damaged in any cadaver. Similarly, when using the proximal tibial staring point described above, the superficial peroneal nerve is 32.05 mm away from the Kirschner wire and was not injured in any specimen. The two structures found to be at greatest risk for injury are the anterior tibial artery and vein. These two vessels have the narrowest average safe distance from the Kirschner wire of 17.25 mm and 17.75 mm, respectively. Assuming a normal branching pattern of the popliteal artery, the anterior tibial artery is the first branch just below the level of the knee. The anterior tibial artery travels posterior to the popliteus muscle and continues into the anterior compartment of the lower leg just inferior to the head of the fibula. It continues distally on the anterior surface of the interosseous membrane adjacent to the lateral aspect of the tibia.13, 14 Proper technique for Kirschner wire insertion at this level is imperative to minimize iatrogenic injury with placement of the proximal tibia traction pin. From this study, we confirmed that a lateral starting point 1 cm distal and 2 cm posterior to the tibial tubercle allows safe placement of traction pins.

Kwon and colleagues recently performed a similar anatomic study using a lateral entry point for the distal femoral traction pin. They proposed this technique as a safe alternative to the traditional medial insertion site in patients where it is difficult to gain access to the medial border. They noted that the femoral artery was relatively safe when placing distal femoral traction from lateral to medial. Their study also showed that the superior medial geniculate artery was the structure most susceptible to iatrogenic injury. Regardless of the entry point direction, utilizing a starting point at the level of the superior pole of the patella and not straying posterior on the medial side of the knee minimizes iatrogenic damage to the femoral vasculature.

Larger threaded or smooth Steimann pins have been and are still being utilized clinically. These larger pins are stronger and do not bend when traction is applied, however, their larger size make damage to nearby structures more likely. In this study, we utilized a smooth 1.6 mm Kirschner wire. The smaller size of the Kirschner wire also decreases damage to surrounding neurovascular structures. Tensioning the wire with a Kirschner bow strengthens the construct and does not allow for wire bending with the application of weight. One negative aspect of the Kirschner bow was recently demonstrated by Obremskey et al by the bow being highly ferromagnetic and therefore prohibiting MRIs.¹⁵

There are several limitations to this study. First, the small sample size used was definitely influenced by the variability seen in our cadavers. Having more specimens would have increased the power of our study, and may elucidate the non-statistically significant correlations observed in the present study. However with this in mind, this data may still be applicable to the general population. Secondly, there is a noticeable deviation when comparing the right side and left side of the same specimen. Reasons for this include slightly different locations of Kirschner wire insertion, variations in the amount of soft tissue manipulation that took place during the meticulous dissections, or perhaps this represents natural variations. These wires were placed in similar fashion as one would do clinically. The start site used is a generalized location and even small changes could affect the subsequent anatomic measurements. This difference is not statistically significant and such discrepancies are likely reproduced with clinically inserted Kirschner wires. Lastly, all possible structures were not studied or dissected out. For the distal femur, avoiding potential injury to the femoral artery is the main focus. Applying the findings Kwon et al showed,⁵ the geniculate system is also at risk with a medial start site. Although the clinical sequela of such an injury is unknown, it is certainly not as potentially catastrophic as that of damage to the femoral artery.

5. Conclusion

The need for temporary fracture stabilization using lower extremity skeletal traction in the perioperative setting as well as during the resuscitation period of unstable trauma patients remains. Insertion of skeletal traction is not benign and carries risk of damage to surrounding soft tissue structures. Using the currently accepted insertion technique for distal femoral and proximal tibial traction pin insertion, we were able to show that the insertion of a 1.6 mm Kirschner wire does not violate the neurovascular structures of the distal femur nor neurovascular structures proximal tibia. The anterior tibial artery and vein are the structures at greatest risk of iatrogenic injury, and these structures were consistently located posterior to the implant. While the sample size was too small to demonstrate consistent correlation between BMI and distance to anatomic structures, this data suggests that patients with lower BMI are at greater risk for injuring neurovascular structures during traction pin insertion. An accurate starting position and maintaining a proper trajectory minimizes this risk of damage to surrounding neurovascular structures while safely allowing the positive clinical effects of skeletal traction.

Author contributions

The author contributions for the paper being submitted titled “Injury to neurovascular structures with insertion of traction pins around the knee” are as follows:

1. Jason A. Lowe, M.D. – Literature search, design, interpretation, writing, figures.

2. Jamie Rister, M.D. – Literature search, study application, writing.

3. Jonathan Eastman, M.D. – Design, writing.

4. Jonathan Friend – Data collections, figures.

Conflicts of interest

All authors have none to declare.