A radiological study to define safe zones for drilling during plating of clavicle fractures

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1 UPPER LIMB A radiological study to define safe zones for drilling during plating of clavicle fractures A. Sinha, J. Edwin, B. Sreeharsha, V. Bhalaik, P. Brownson From Royal Liverpool and Broadgreen University Teaching Hospitals NHS Trust, Liverpool, United Kingdom This study investigated the anatomical relationship between the clavicle and its adjacent vascular structures, in order to define safe zones, in terms of distance and direction, for drilling of the clavicle during osteosynthesis using a plate and screws following a fracture. We used reconstructed three-dimensional CT arteriograms of the head, neck and shoulder region. The results have enabled us to divide the clavicle into three zones based on the proximity and relationship of the vascular structures adjacent to it. The results show that at the medial end of the clavicle the subclavian vessels are situated behind it, with the vein intimately related to it. In some scans the vein was opposed to the posterior cortex of the clavicle. At the middle one-third of the clavicle the artery and vein are a mean of mm (5.4 to 26.8) and mm (5 to 26.1) from the clavicle, respectively, and at a mean angle of 50 (12 to 80) and 70 (38 to 100), respectively, to the horizontal. At the lateral end of the clavicle the artery and vein are at mean distances of 63.4 mm (46.8 to 96.5) and mm (50 to 109), respectively. An appreciation of the information gathered from this study will help minimise the risk of inadvertent iatrogenic vascular injury during plating of the clavicle. A. Sinha, MBBS, MRCS(Ed), Specialist Registrar in Trauma and Orthopaedics J. Edwin, MRCS, DNB Orth, Dip. Orth, Specialist Registrar in Trauma and Orthopaedics Queen Elizabeth Hospital, Stadium Road, Woolwich, London SE18 4QH, UK. B. Sreeharsha, MBBS, FRCR, Specialist Registrar in Radiology V. Bhalaik, MBBS, MRCS, FRCS(Tr & Orth), Consultant Hand and Upper Limb Surgeon Wirral University Teaching Hospital NHS Foundation Trust, Upton, Wirral CH49 5PE, UK. P. Brownson, DM, FRCS(Ed), FRCS(Tr & Orth), Consultant Orthopaedic Shoulder Surgeon Royal Liverpool and Broadgreen University Teaching Hospitals NHS Trust, Prescot Street, Liverpool L7 8XP, UK. Correspondence should be sent to Mr A. Sinha; apurv16@gmail.com 2011 British Editorial Society of Bone and Joint Surgery doi: / x.93b $2.00 J Bone Joint Surg Br 2011;93-B: Received 20 December 2010; Accepted after revision 31 May 2011 Fractures of the clavicle typically occur in young, active individuals and account for between 2.6% and 4% of all fractures, with up to 80% occurring in the middle third. 1-3 Traditionally treatment has been non-operative 2,3 and there is a general consensus that undisplaced fractures should continue to be managed in this manner, as the majority heal without sequelae. 4 On the other hand, outcomes following non-operative management of displaced midclavicular fractures are less favourable, with several studies showing increased rates of nonunion and symptomatic malunion. 5-8 Displaced fractures of the clavicle that have been managed non-operatively have been reported to show nonunion rates of up to 15%, compared with 2% for internally fixed fractures. 8 Consequently, over the past decade there has been an increased tendency to operate on displaced fractures of the clavicle. The aim of this study was to establish safe zones for drilling screw-holes during osteosynthesis of the clavicle, by defining the proximity of the adjacent major blood vessels using reconstructed three-dimensional (3D) CT angiograms. The precision of CT angiography in accurately demonstrating even microvascular structures has already proved useful in studies requiring detailed anatomical visualisation of the vascular system. 9 We believe that this work represents the first study to use CT angiography to determine safe drilling trajectories and depths for the clavicular plating. Patients and Methods Institutional approval was acquired to obtain 26 normal CT arteriograms of the neck and shoulder region, which had been requested by vascular surgeons to evaluate the subclavian vessels for non-trauma reasons. In the selected scans the most common reason for referral was ischaemic symptoms in the upper limb in 23 patients, thrombus in the subclavian or brachial artery in two and intraoperative injury to the subclavian vessel in one. All scans were performed with the patient in the supine position with arm by the side of the patient in neutral rotation. Images were reconstructed in 3D and analysed by a senior radiologist (BS) using the Picture Archiving and Communication System (PACS) on radiologically diagnostic screens with minimum screen resolution of pixels. Three locations, representing the medial (A), middle (B) and lateral (C) zones of the clavicle, were defined (Fig. 1). Point A was located 1 cm lateral to the medial end of the clavicle, point B in the middle, and point C 1 cm medial to the lateral end. The parameters measured included the length of VOL. 93-B, No. 8, SEPTEMBER

2 12 48 A. SINHA, J. EDWIN, B. SREEHARSHA, V. BHALAIK, P. BROWNSON Fig. 1 Fig. 2 Photograph of a non-anatomical model showing the three points A, B and C on the clavicle representing the three zones: medial (Red), middle (Amber) and lateral (Green), respectively. Sagittal section at the medial one-third (point A) of the clavicle in a three-dimensional reconstructed CT arteriogram (SA, subclavian artery; SV, subclavian vein). Table I. The mean (range) distance in mm of the artery and vein from the clavicle, the thickness of the clavicle in the three zones, and the direction of the vessels Point A (medial one-third) Point B (middle one-third) Point C (lateral one-third) Parameter Mean (mm) (range) Direction from clavicle Thickness Distance of artery Distance of vein Thickness Distance of artery Distance of vein Thickness Distance of artery Distance of vein (13.32 to 34.16) (5.00 to 44.70) 4.77 (0.00 to 15.90) (11.47 to 28.35) (5.40 to 26.80) (5.00 to 26.10) (9.50 to 17.99) (46.80 to 96.50) (50.00 to ) Posterior the clavicle (as measured on 3D CT reconstruction images); its thickness at points A, B and C; the minimum distance of the artery and vein from points A, B and C; and the direction and location of the vessels with respect to the clavicle in each of the three zones. Measurements for minimum distances were taken from the cortex closest to the vessel to the tunica adventitia of the vessel concerned. The trajectories were measured at Point B. The angle between a line joining the centre of clavicle and the centre of the vessel in relation to the horizontal plane was noted in sagittal 3D CT reconstruction images. There were 11 men and 15 women in the study, with an average age of 51 years (20 to 85), and all were considered to be skeletally mature. The subclavian arteriograms were from the right shoulder in 11 and the left in 15. No difference in the bone-vessel relationship was noted between the sides. Statistical analysis. Data were analysed using Microsoft Excel (Microsoft, Redmond, Washington). Mean values, SD and range were calculated in each category. An unpaired two-tailed t-test was used to test statistical significance when comparing males with females. Posteroinferior (See Table III and Fig. 5 for angles) Inferior Results At the medial end of the clavicle (point A) the subclavian vessels lay posteriorly (Fig. 2). The mean distance of the subclavian vein from the clavicle was 4.77 mm (0.00 to 15.90), the mean distance of the subclavian artery was mm (5.00 to 44.70) and the mean thickness of the clavicle was mm (13.32 to 34.16) (Table I). There were no significant gender differences in the measurements taken at this point (unpaired t-tests, p? 0.45) (Fig 3; Table II). In the middle of the clavicle (point B) the vessels lay posteriorly and inferiorly (Fig. 4). The artery and vein were at a mean angle of 50 (12 to 80 ) and 70 (38 to 100 ) to the horizontal plane of the clavicle, respectively (Figs 4 and 5; Table III). Here, the mean distance of the artery and vein from the clavicle was mm (5.40 to 26.80) and mm (5.00 to 26.10), respectively. The mean thickness of the clavicle was mm (11.47 to 28.35) (Table I). Once again there were no significant gender differences in the measurements taken at this point (unpaired t-tests, p? 0.09) (Figs 3 and 6; Table II). At the lateral end of the clavicle (point C) the vessels lay inferiorly (Fig. 7). Here, the mean distance of the artery and THE JOURNAL OF BONE AND JOINT SURGERY

3 A RADIOLOGICAL STUDY TO DEFINE SAFE ZONES FOR DRILLING DURING PLATING OF CLAVICLE FRACTURES 1249 Distance (mm) 180 Male Thickness at A medial Female Thickness at B middle Fig. 3 Thickness at C lateral Length of clavicle L Histogram showing the mean length and thickness of the clavicle at points A, B and C between men and women. vein from the clavicle measured mm (46.8 to 96.5) and mm (50.0 to 109.4), respectively. The mean thickness of the clavicle was mm (9.50 to 17.90) (Table I). At this point there were significant gender differences in the distances measured between the vessels and the clavicle (artery, p = 0.02; vein, p = 0.03; unpaired twotailed t-tests) (Figs 3 and 6). The distances of the artery and vein from the clavicle were a mean of mm and mm greater in men than in women, respectively (Table II). The mean length of the clavicles measured on 3D CT reconstruction images was 147 mm (120 to 165); the male clavicle was longer than the female clavicle, with a mean length of mm (128 to 165) compared with mm (120 to 164) respectively, but this was not statistically significant (p = 0.49). There were no significant gender differences in the thickness of the clavicles with the mean thickness at points A, B and C being mm (13.32 to 34.16), mm (11.47 to 28.35) and mm (9.50 to 17.99), respectively (Table I). Discussion Three-dimensional CT angiography enables detailed and precise in vivo visualisation of the peri-clavicular blood vessels and is capable of reliably measuring microvascular structures with an internal diameter as small as 0.4 mm. 9 The risk of iatrogenic injury to adjacent vital structures such as the subclavian vessels during the use of a plate and screws during osteosynthesis of the clavicle is well known, particularly during drilling and tapping. Inappropriately directed or excessively long screws have also been implicated in the development of late complications such as thoracic outlet syndrome The major structures at risk of injury include the subclavian vein, the subclavian artery, the brachial plexus and the cervical pleura. The brachial plexus, although at risk of injury, is further away from clavicle than the vessels in relation to the medial two-thirds of the bone. A CT arteriogram demonstrates the brachial plexus less precisely and clearly than the vessels, and thus was not considered in this study. A wide variety of plates are currently available which may be applied either superiorly or anteriorly for the fixation of clavicular fractures. They pose a varying degree of risk with regard to inadvertent vascular injury during plating, depending on where the clavicle is drilled. The subclavian vessels follow an oblique course along the length of the clavicle, beginning posterosuperiorly to it at its medial end and eventually dipping down into the axilla inferior to it at the lateral end. Upon crossing the lateral border of the first rib the vessels continue onward as the axillary vessels (Fig. 1). 17 Based on the results of this study a simple colour-coded traffic light system was devised which subdivides the clavicle into three zones: Red (medial), Amber (middle) and Green (lateral) to reflect the potential risk for inadvertent vascular injury during screw placement in each zone according to the proximity of the blood vessels. In the Red (medial) zone the subclavian vessels are situated behind the clavicle. The vein is intimately related to the clavicle, whereas the artery is somewhat protected by the intervening scalenus anterior (Fig. 2). The mean distance of the vein from the clavicle was 4.77 mm and the artery mm; in some cases the subclavian vein was in immediate contact with the posterior cortex of the clavicle (Table I). An anteroposterior screw trajectory poses the greatest risk of injury to the subclavian vein in this zone (Figs 2 and 8), whereas a craniocaudal screw trajectory, as performed in superior plating, appears to be a safe option (Fig. 8). In the Amber (middle) zone the subclavian vessels pass laterally and begin their descent towards the axilla, taking up a position posteroinferior to the clavicle. The vessels eventually cross the lateral border of the first rib, continuing onward as the axillary vessels. 17 The vessels are now much closer together, with the mean distance of the vein and artery from the clavicle measuring mm and mm, respectively (Table I). Although the rate of descent of the vessels gradually increases as they course laterally, they continue to remain within a posteroinferior quadrant relative to the clavicle. The vein and artery are at a mean angle of 70 and 50, respectively, to the horizontal plane of the clavicle (Fig. 5, Table III). In the Amber zone a posteroinferior screw trajectory poses the greatest risk of injury (Fig. 9), with the subclavian vein being at highest risk. Anteroposterior screw placement, as performed in anterior or anterior-inferior plating, appears to be the safest option for this zone (Fig. 10). The subclavian vein remains in closest proximity to the clavicle in the Red and Amber zones and is the vital structure most likely to be inadvertently injured. At the lateral end of the clavicle (point C) it descends more acutely within the axilla, thereby placing the artery in closer proximity to the clavicle. The mean distance of the artery and vein to the clavicle at this point was mm and mm, respectively (Table I). There were also VOL. 93-B, No. 8, SEPTEMBER 2011

4 1250 A. SINHA, J. EDWIN, B. SREEHARSHA, V. BHALAIK, P. BROWNSON Table II. Comparison between the mean parameters in men and women. A negative difference means a higher value in women Parameter Males Females Difference p-value (unpaired t-test) Length of clavicle (mm) Lateral end of the clavicle Thickness (mm) Distance of artery (mm) Distance of vein (mm) Middle of the clavicle Thickness (mm) Distance of artery (mm) Distance of vein (mm) Medial end of the clavicle Thickness (mm) Distance of artery (mm) Distance of vein (mm) Fig. 4 Sagittal section at the middle (point B) of the clavicle in a threedimensional reconstructed CT arteriogram (SA, subclavian artery; SV, subclavian vein). Fig. 5 significant gender-based differences in measurements taken at this point, with the mean distances from clavicle to artery and vein being mm and mm greater, respectively, in men than in women (Table II, Fig. 6). As both the artery and vein are at a considerable distance from the clavicle at this point, this is referred to as the Green zone (Fig. 7). It is important to note that the distances measured are only accurate when the arm is placed in the neutral or anatomical position. Abduction of the shoulder or the use of reduction forceps are manoeuvres sometimes used during fracture reduction and can alter the anatomy considerably. It is therefore advised that caution be exercised while performing these manoeuvres and drilling or tapping the clavicle. Alternatively, the arm should be returned to its neutral position following fracture reduction prior to drilling. Illustration showing the subclavian artery (SA) and vein (SV) making an mean angle of 50 and 70 with the horizontal, respectively, in relation to the clavicle at point B (middle one-third). The images obtained for this study were taken in supine subjects, whereas most operations on the clavicle are performed with the patient in the beach chair position and sometimes with a sandbag under the scapula depending on surgeon preference. This may alter the anatomical relationships in this area, although we are not aware of any evidence to suggest that this would be significant. Most fractures are in the middle and lateral one-third of the clavicle. The conclusion from our study is that in these fractures anterior and anterior-inferior plating is safer than dorsal (Fig. 10). THE JOURNAL OF BONE AND JOINT SURGERY

5 A RADIOLOGICAL STUDY TO DEFINE SAFE ZONES FOR DRILLING DURING PLATING OF CLAVICLE FRACTURES 1251 Table III. The mean (range) angles of the artery and vein in relation to the clavicle at point B Mean (range) Angle of artery ( ) Angle of vein ( ) (12 to 80) (38 to 100) 90 Distance (mm) 80 Male Female Fig. 8 Vein from Artery from A A Point A medial Vein from Artery from Vein from Artery from B B C C Point C Point B lateral middle Photograph of a model showing the medial end (point A) of the clavicle and the subclavian vessels, with two drills showing anteroposterior and craniocaudal trajectories (SV, subclavian vein, SA, subclavian artery; BP, brachial plexus). Fig. 6 Histogram showing the mean distances of the subclavian artery and vein from the clavicle at points A, B and C between men and women. Fig. 9 Fig. 7 Photograph of a model showing a dangerous trajectory represented by a drill at point B (middle one-third). Inset image shows the mean angles of the subclavian artery (SA) and vein (SV) with the horizontal in relation to the clavicle. Sagittal section at the lateral end (point C) of the clavicle in a threedimensional reconstructed CT arteriogram (SA, subclavian artery; SV, subclavian vein). In fractures of the medial third, the subclavian vein is very close to the clavicle, and in some scans was even apposed to posterior cortex (Fig. 2, Table I). Therefore, in this zone extreme caution should be exercised in dissecting around, manipulating with forceps, drilling or tapping the clavicle. A craniocaudal direction for drills, taps and screws is less likely to damage the vein and therefore favours superior plating, although access is more difficult owing to the patient s head and neck getting in the way. Anterior plating, which VOL. 93-B, No. 8, SEPTEMBER 2011 appears technically easier, will clearly pose a significant risk of damage to the subclavian vein (Figs 2 and 8). If an anteroposterior trajectory cannot be avoided, direct visualisation of the vein or using a metallic restraint beyond the posterior cortex of the clavicle while drilling or tapping is recommended. Using reconstructed 3D CT arteriograms, we were able to define the in vivo anatomical relationship of the clavicle with its adjacent vessels. In the Red zone (medial one-third), anteroposterior screw trajectories are to be avoided because of the proximity of the subclavian vein; in the Amber zone (middle one-third) posteroinferior screw trajectories are to be avoided because of the proximity of both the vein and the

6 1252 A. SINHA, J. EDWIN, B. SREEHARSHA, V. BHALAIK, P. BROWNSON The authors are grateful to the Radiology Department and Consultant Radiologist Dr Hifz-ur-Rahman Aniq at Royal Liverpool and Broadgreen University Teaching Hospitals NHS Trust, and Mr P. Ralte, for their support and help with this research project. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Fig. 10 Illustration showing an anterior plate with safe trajectory and screw placement at the middle one-third of the clavicle (point B) with the mean distance of the subclavicular vein (SV; 12 mm) and artery (SA; 17 mm). artery; and in the Green zone caution should be taken when using craniocaudal trajectories. In the middle and lateral thirds of the clavicle, where the majority of fractures occur, anterior and anterior-inferior plating appears to be safer. An understanding and appreciation of the proximity and relationship of the vessels with respect to the clavicle will hopefully enable surgeons to further minimise the risk of vascular injury during plating of the clavicle. Listen live Listen to the abstract of this article at References 1. Nordqvist A, Petersson C. The incidence of fractures of the clavicle. Clin Orthop 1994;300: Crenshaw AH Jr. Fractures of the shoulder, arm and forearm. In: Canale ST, ed. Campbell's operative orthopaedics. Vol. 3. Tenth ed. St Louis: Mosby, 2003: Craig EV. Fractures of the clavicle. In: Rockwood CA Jr, Buchholz RW, Green DP, Heckman JD, eds. Rockwood and Green's fractures in adults. Vol. 1. Fourth ed. Philadelphia: Lippincott Williams and Wilkins, 1996: Khan LA, Bradnock TJ, Scott C, Robinson CM. Fractures of the clavicle. J Bone Joint Surg [Am] 2009;91-A: Robinson CM, Court-Brown CM, McQueen MM, Wakefield AE. Estimating the risk of nonunion following nonoperative treatment of a clavicular fracture. J Bone Joint Surg [Am] 2004;86-A: Hill JM, McGuire MH, Crosby LA. Closed treatment of displaced middle-third fractures of the clavicle gives poor results. J Bone Joint Surg [Br] 1997;79-B: McKee MD, Wild LM, Schemitsch EH. Midshaft malunions of the clavicle. J Bone Joint Surg [Am] 2003;85-A: Zlowodzki M, Zelle BA, Cole PA, Jeray K, McKee MD. Treatment of acute midshaft clavicle fractures: systematic review of 2144 fractures: on behalf of the Evidence-Based Orthopaedic Trauma Working Group. J Orthop Trauma 2005;19: Tregaskiss AP, Goodwin AN, Bright LD, Ziegler CH, Acland RD. Three-dimensional CT angiography: a new technique for imaging microvascular anatomy. Clin Anat 2007;20: Lyons FA, Rockwood CA Jr. Migration of pins used in operations on the shoulder. J Bone Joint Surg [Am] 1990;72-A: Norrell H Jr, Llewellyn RC. Migration of a threaded Steinmann pin from an acromioclavicular joint into the spinal canal: a case report. J Bone Joint Surg [Am] 1965;47-A: Rey-Baltar E, Errazu D. Unusual outcome of Steinman wire: case of fractured clavicle. Arch Surg 1964;89: Glauser F, Kremens V. Unusual sequela following pinning of medial clavicular fracture. Am J Roentgenol Radium Ther Nucl Med 1956;76: Johnson B, Thursby P. Subclavian artery injury caused by a screw in a clavicular compression plate. Cardiovasc Surg 1996;4: Casselman F, Vanslembroek K, Verougstraete L. An unusual cause of thoracic outlet syndrome. J Trauma 1997;43: Shackford SR, Connolly JF. Taming of the screw: a case report and literature review of limb-threatening complications after plate osteosynthesis of a clavicular nonunion. J Trauma 2003;55: Warwick R, Williams PL. The subclavian system of arteries. In: Gray's anatomy. 35th ed. Edinburgh: Longmans Green and Co., 1973:1551. THE JOURNAL OF BONE AND JOINT SURGERY