Tendon and Neurovascular Bundle Displacement in the Palm With Hand Flexion and Extension: An MRI and Gross Anatomy Correlative Study

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1 JOURNAL OF MAGNETIC RESONANCE IMAGING 23: (2006) Clinical Note Tendon and Neurovascular Bundle Displacement in the Palm With Hand Flexion and Extension: An MRI and Gross Anatomy Correlative Study Holly C. Canuto, PhD, 1 Miguel L.R. Oliveira, MRCS, 2 Kenneth W. Fishbein, PhD, 1 and Richard G. Spencer, MD, PhD 1 * This study evaluated the correlative use of MRI methods and gross anatomy to monitor tendon displacement in the central region of the palm at rest and during flexion and extension of the metacarpophalangeal and interphalangeal joints with respect to the corresponding neurovascular bundles (NVBs). In all of the samples the neutral and extended positions showed the NVB to be palmar with respect to the flexor tendons, while during flexion tendon displacement caused the NVB to be dorsal to both the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons. T1-weighted MR images correlated with gross anatomical slides demonstrated that significant changes occur in the relative positions of the flexor tendons and associated NVBs of the palm upon flexion and extension. Key Words: MR imaging; palm; tendon; neurovascular bundle (NVBs); cadavers J. Magn. Reson. Imaging 2006;23: Published 2006 Wiley-Liss, Inc. MOST FUNCTIONAL ANATOMIC STUDIES of tendon and nerve displacement in the hand (1 3) have focused on biomechanical stresses and dynamic alterations in wrist anatomy. One of the main focuses of these studies is carpal tunnel syndrome (2). In this regard, noninvasive magnetic resonance imaging (MRI) methods have been used to illustrate palmar anatomy with the hand in the neutral (resting) position (4). Dynamic anatomic changes that occur in the palm, in particular, in terms of the positioning of the palmar tendons and neurovascular bundles (NVBs; palmar digital artery and nerve) as a function of flexion and extension of the hand have not been fully investigated by an MRI and gross anatomy correlative study. 1 Nuclear Magnetic Resonance Unit, National Institute on Aging, National Institutes of Health, Baltimore, Maryland, USA. 2 Orthopaedic Biomechanics Laboratory, Johns Hopkins Bayview Medical Center, Baltimore, Maryland, USA. *Address reprint requests to: R.G.S., Nuclear Magnetic Resonance Unit, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD spencerri@grc.nia.nih.gov Received August 23, 2005; Accepted January 26, DOI /jmri Published online 28 March 2006 in Wiley InterScience ( wiley.com). Aside from the basic interest attached to defining this functional anatomy, such studies may contribute to our understanding of lacerations that occur in the central region of the palm, known as zone III (5), the area of the lumbrical origin between the distal margin of the transverse carpal ligament and the beginning of the critical area of pulleys or first annulus. Lacerations that occur just proximal to the head of the metacarpals are among the most commonly encountered injuries to the hand. The structures that are most readily damaged in such injuries are those that are the most superficial. Accordingly, in this study we used MRI to evaluate tendon displacement in zone III of the palm (Fig. 1) with respect to the corresponding NVBs at rest and during flexion and extension. MATERIALS AND METHODS Cadavers Experiments were performed on 10 non-embalmed cadaveric right arms (from five males and five females; mean age at death 65 years) that were disarticulated at the humerus. A custom-made device (Fig. 2) was used to ensure reproducible positioning and standardized grip force. The donors were free of known musculoskeletal pathologies. Images were acquired for all samples with the hand in the resting position. Four hands were then imaged in flexion and extension. Differences observed during flexion were later confirmed by analysis of four additional specimens in flexion. For all images the arm was secured by a bone screw inserted through the wrist that allowed movement of the distal and proximal interphalangeal and metacarpophalangeal joints. During flexion and extension of the palm, involving the metacarpophalangeal and interphalangeal joints, a 10-cm longitudinal incision was made over the ventral aspect of the forearm 1 cm proximal to the bone screw to expose the flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons. A smaller 2-cm incision was also made on the dorsal aspect of the forearm to allow dissection of the extensor tendons. FDS and FDP tendons to the second, third, fourth, and fifth digits were identified and individually sutured along the length of the tendon, approximately 5 cm. The thumb Published 2006 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America. 742

MRI/Tendon NVB Displacement 743 Figure 1. Flexor and extensor tendon palmar zones (5). [Color figure can be viewed in the online issue, which is available at www. interscience.wiley.com.

2, white arrow) and attached to each suture. Flexion of the hand was achieved while maintaining the wrist at 30 of dorsiflexion by applying traction to the wrist extensors.

2 MRI/Tendon NVB Displacement 743 Figure 1. Flexor and extensor tendon palmar zones (5). [Color figure can be viewed in the online issue, which is available at www. interscience.wiley.com.] was not involved in this study. Tension was applied independently to each tendon by careful adjustment of thumb screws that were positioned on supports at the base of the apparatus (Fig. 2, white arrow) and attached to each suture. Flexion of the hand was achieved while maintaining the wrist at 30 of dorsiflexion by applying traction to the wrist extensors. For hand extension, a neutral position of the wrist was maintained while tension was applied to the finger extensor tendons. Results with the hand in flexion and extension were compared with results obtained with the hand in the neutral position. A custom-built dynamometer was used to implement a standardized overall grip force of 6 pounds, distributed as a measured load to each finger in the following percentages: index 32%, middle 33%, ring 24%, and little 12% (6). After initial imaging, liquid latex was injected into the palmar digital arteries via two catheters that were placed in the radial and ulnar arteries, respectively, resulting in a clearly defined visualization of the NVBs by dilation of the previously collapsed palmar arteries. MRI was repeated while the exact slice geom- Figure 2. a: Purpose-built device to allow reproducible positioning of the cadaver hand 1 indicates the position of the tension adjustment screws. b: Enlarged figure of the region indicated by X showing the dissection of the flexor and extensor tendons on the dorsal and ventral aspects of the arm, respectively. White arrow indicates threading of the suture into tension adjustment screws. [Color figure can be viewed in the online issue, which is available

relative to a line connecting the centers of the FDS and FDP tendons (black arrows). The FDS (numeral 1) and FDP (numeral 2) are circled in green.

3 744 Canuto et al. Figure 3. Gross anatomical slice of a cadaver hand in extension, illustrating the relative position of each NVB in relation to the associated flexor tendons assessed using a relative scale based on the depth relative to a line connecting the centers of the FDS and FDP tendons (black arrows). The FDS (numeral 1) and FDP (numeral 2) are circled in green. Red liquid latex was utilized to fill the vascular system, where the digital artery and digital nerve bundles (NVBs) are shown in red. Examples of a dorsal metacarpal vein and dorsal metacarpal artery are shown in a and b, respectively. [Color figure can be viewed in the online issue, which is available at etry used prior to the addition of latex was retained. After imaging, the specimens were frozen, and gross anatomical slices were then cut to correspond to the transverse MRI planes. MRI MR images were obtained using a 1.9 Tesla, 31-cm Bruker BioSpec MRI scanner (Bruker Medizintechnik GmbH, Ettlingen, Germany) with a shielded gradient set (inside diameter 20 cm; available gradient strength 100 mt m 1 ), and a birdcage resonator (inside diameter 15 cm). Imaging was performed at room temperature using a two-dimensional spin-echo sequence with TR/TE 500/23, FOV cm and a matrix providing an in-plane resolution of 292 in both the read and phase-encode directions. Twelve transverse slices of 1.1-mm thickness were obtained with 2.5-mm center-to-center slice spacing. Data planes were carefully selected to be consistent between samples. Sixteen signal averages were used. Data Processing and Flexor Tendon Depth Analysis Transverse MR sections through the palm 4 mm below the fifth metacarpal head were compared among all samples. Compared to the radial aspect, in most cases the ulnar side of the palm showed more pronounced vascular features, which allowed for clear identification of NVBs and their related flexor tendons. The second digit was omitted. The relative position of each NVB in relation to the associated flexor tendons was assessed using a relative scale based on the depth relative to a line (Fig. 3, black arrows) connecting the centers of the FDS (Fig. 3, numeral 1) and FDP tendons (Fig. 3, numeral 2). RESULTS MR images of 10 cadaver hands were recorded in three positions of hand function: neutral, flexion, and extension (Fig. 4a c, respectively). The T1-weighted images allowed the vascular and flexor tendon structures to be clearly defined in all functional positions. The location of the neurovascular structures was determined by comparison of MR images acquired before and after the injection of liquid latex, with further confirmation achieved by analysis of gross anatomical slices. The correlation between the anatomy shown in the MRI images and the gross anatomical slices was excellent (Fig. 5). In the neutral position the NVBs were ventral to the FDS tendons (Fig. 6a). A comparison of the MR images and gross anatomical slices clearly showed tendon displacement upon flexion of the metacarpal and interphalangeal joints (Fig. 6b) as compared to the hand in the Figure 4. T1-weighted MRI images of the hand in (a) the neutral position, (b) flexion, and (c) extension. The second digit FDS/FDP and the fifth metacarpal are indicated for anatomical reference in a and b, and the third digit FDS/FDP is illustrated in c. Red circles indicate the location of the NVBs. [Color figure can be viewed in the online issue, which is available

MRI/Tendon NVB Displacement 745 Figure 5. (a) Gross anatomical slice and (b) T1-weighted MR image of a hand in the extended position, palmar side facing up.

[Color figure can be viewed in the online issue, which is available neutral position. FDS and FDP tendon displacements were observed in all 10 samples.

4 MRI/Tendon NVB Displacement 745 Figure 5. (a) Gross anatomical slice and (b) T1-weighted MR image of a hand in the extended position, palmar side facing up. The 1) FDS/FDP of the third digit, 2) NVB for the third digit, and 3) third metacarpal are shown for anatomical reference. [Color figure can be viewed in the online issue, which is available neutral position. FDS and FDP tendon displacements were observed in all 10 samples. All neutral and extended positions showed the NVB to be palmar with respect to the flexor tendons, while during flexion tendon displacement caused the NVB to be dorsal to these tendons. DISCUSSION The positioning of vascular structures in the palm with respect to musculoskeletal structures such as bone and tendon appears to depend strongly on the functional position of the hand. Tendon and median nerve translation within the carpal tunnel with finger flexion and extension has been observed in vivo using MRI (2,7). A similar MRI study monitored depth changes in NVB positioning in the forefoot during weight-bearing exercises (8). In this study we have demonstrated that significant changes occur in the relative positions of the flexor tendons and associated NVBs of the hand upon flexion and extension. Tendon motion is constrained primarily by the palmar fascia and overlying skin, permitting substantial variation in position corresponding to hand position. In all cases the tendons shifted to a more superficial position upon flexion and were deepest with the hand in the neutral and extended positions. Such displacement with respect to the skin surface may have significant implications for the nature of injury to the tendons and to their associated NVBs as a function of hand position. Figure 6. Correlation of T1-weighted axial MRI slices (below) and equivalent gross anatomy (above) showing FDS and FDP tendon displacement (green circles) with respect to NVBs (yellow arrows) in (a) the neutral position and (b) flexion. [Color figure can be viewed in the online issue, which is available at www. interscience.wiley.com.]

5 746 Canuto et al. In conclusion, although the results of this study are not directly applicable to a specific clinical problem, they are likely to apply to in vivo situations and provide a potential explanation for the clinical observation of a greater propensity toward flexor tendon injury in lacerations sustained during hand flexion, including gripping, as compared to injuries sustained with the hand in the neutral position. ACKNOWLEDGMENTS We thank Miguel Oliveira, MD, and Stephen Belkoff, PhD, at the Orthopaedic Biomechanics Laboratory, Johns Hopkins Bayview Medical Center, Baltimore, MD, USA. REFERENCES 1. Hormann M, Traxler H, Ba-Ssalamah A, et al. Correlative highresolution MR-anatomic study of sciatic, ulnar, and proper palmar digital nerve. Magn Reson Imaging 2003;21: Keir PJ, Wells RP. Changes in geometry of the finger flexor tendons in the carpal tunnel with wrist posture and tendon load: an MRI study on normal wrists. Clin Biomech (Bristol, Avon) 1999;14: Yu J, Habib P. Normal MR imaging anatomy of the wrist and hand. Magn Reson Imaging Clin N Am 2004;12: Weiss KL, Beltran J, Shamam OM, Stilla RF, Levey M. High-field MR surface-coil imaging of the hand and wrist. Part I. Normal anatomy. Radiology 1986;160: Verdan C. Practical considerations for primary and secondary repair in flexor tendon injuries. Surg Clin North Am 1964;44: Li ZM. The influence of wrist position on individual finger forces during forceful grip. J Hand Surg (Am) 2002;27: Ugbolue U, Nguyen T, Guo X, Wang Y, Li Z. Morphometric changes of the carpal tunnel contents during pinching. In: Proceedings of the 11th Annual Meeting of ISMRM, Toronto, Canada, Weishaupt D, Treiber K, Jacob HA, et al. MR imaging of the forefoot under weight-bearing conditions: position-related changes of the neurovascular bundles and the metatarsal heads in asymptomatic volunteers. J Magn Reson Imaging 2002;16:75 84.

Muscles of the hand Prof. Abdulameer Al-Nuaimi

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