Kajeandra Ravichandiran

Three‐dimensional study of the musculotendinous architecture of lumbar multifidus and its functional implications

Lumbar multifidus (LMT) is a key muscle, which provides stability to the lumbar spine, and has been shown to have altered neuromuscular recruitment following acute episodes of low back pain. Architectural parameters are important determinants of function, but have not been well documented for LMT. Therefore, the purpose of this study is to model and quantify the architecture of LMT throughout its volume. Nine male and one female formalin‐embalmed cadaveric specimens (average age 80 ± 11 years) without any evidence of spinal deformity/pathology were used. The musculotendinous components of LMT were serially dissected and digitized. Next, the data were imported into MAYA™ to create a three‐dimensional model of each segment of LMT from which architectural parameters including fiber bundle length (FBL), fiber bundle angle (FBA), and tendon length were quantified. Water displacement was used to determine volume. The data were analyzed using paired t‐tests and ANOVA followed by Tukeys post‐hoc test (P ≤ 0.05). LMT (L1–L4) has three architecturally distinct regions: superficial, intermediate, and deep. Intermediate LMT was absent in all specimens at L5. Mean FBL decreased significantly (P ≤ 0.05) from superficial (5.8 ± 1.6 cm) to deep (2.9 ± 1.1 cm) as did volume (superficial, 5.6 ± 2.3 ml; deep, 0.7 ± 0.3 ml) measured at each region. By contrast, mean FBA increased from superficial to deep. The current study lends further evidence to support the role of different regions within LMT to serve distinct functions particularly to produce movement and/or control stability. Clin. Anat. 21:539–546, 2008.

Three-dimensional study of pectoralis major muscle and tendon architecture.

A thorough understanding of the normal structural anatomy of the pectoralis major (PM) is of paramount importance in the planning of PM tendon transfers or repairs following traumatic PM tears. However, there is little consensus regarding the complex musculotendinous architecture of the PM in the anatomic or surgical literature. The purpose of this study is to model and quantify the three‐dimensional architecture of the pectoralis muscle and tendon. Eleven formalin embalmed cadaveric specimens were examined: five (2M/3F) were serially dissected, digitized, and modeled in 3D using Autodesk® Maya®; six (4M/2F) were dissected and photographed. The PM tendon consisted of longer anterior and shorter posterior layers that were continuous inferiorly. The muscle belly consisted of an architecturally uniform clavicular head (CH) and a segmented sternal head (SH) with 6–7 segments. The most inferior SH segment in all specimens was found to fold anteriorly forming a trough that cradled the inferior aspect of the adjacent superior segment. No twisting of either the PM muscle or tendon was noted. Within the CH, the fiber bundle lengths (FBL) were found to increase from superior to inferior, whereas the mean FBLs of SH were greatest in segments 3–5 found centrally. The mean lateral pennation angle was greater in the CH (29.4 ± 6.9°) than in the SH (20.6 ± 2.7°). The application of these findings could form the basis of future studies to optimize surgical planning and functional recovery of repair/reconstruction procedures. Clin. Anat. 22:500–508, 2009.

Subacromial morphometric assessment of the clavicle hook plate

BACKGROUND Clavicle hook plates are an effective plate fixation alternative for distal clavicle fractures and severe acromioclavicular joint dislocations. However, post-operative complications associated with the subacromial portion of the hook include acromial osteolysis and subacromial impingement. We examine and quantify the three-dimensional position of the subacromial portion of the hook plate relative to surrounding acromial and subacromial structures in a series of cadaveric shoulders to determine if hook positioning predisposes the shoulder to these noted post-operative complications. MATERIALS AND METHODS Fifteen cadaveric shoulders (seven males, eight females) were implanted with 15- or 18-mm hook plates. Dimensions of the acromion and hook plate were digitised and reconstructed into a three-dimensional model to measure acromion dimensions and distances of the subacromial hook relative to surrounding acromial and subacromial structures. RESULTS Inter-specimen dimensions of the acromion were highly variable. Mean acromion width and thickness were greater in males than in females (p=0.01). The posterior orientation of the subacromial hook varied widely (mean posterior implantation angle=32.5+/-20 degrees, range 0-67 degrees). The hook pierced the subacromial bursa in 13/15 specimens, made contact with the belly of the supraspinatus muscle in 9/15 specimens, and had focal contact at the hook tip with the undersurface of the acromion in 9/15 specimens. CONCLUSIONS The wide range of acromial dimensions leads to a high degree of variability in the positioning of the subacromial hook. The observed frequency of hook contact with surrounding subacromial structures in a static shoulder confirms that the position of the hook portion of the implant can predispose anatomic structures to the post-operative complications of subacromial impingement and bony erosion.

Investigation of the static and dynamic musculotendinous architecture of supraspinatus

To date, the architecture of supraspinatus (SP) and its relation to joint position has not been investigated. The purpose of this study was to quantify the dynamic architecture of the distinct regions of SP using ultrasound (US). Seventeen subjects (8 M/9 F), mean age 36.4 ± 12.7 years, without tendon pathology were recruited. The SP was scanned in relaxed and contracted states. For the contracted state, SP was scanned with the shoulder actively abducted to 60° and the glenohumeral joint in neutral rotation; 80° external rotation; 80° internal rotation. Fiber bundle length (FBL) and pennation angle (PA) of distinct regions, and muscle thickness were computed. Measurements of the posterior region were limited because of acromion shadowing. Parameters between regions and changes between relaxed and contracted states were analyzed using paired t‐tests and repeated measures ANOVA (P < 0.05). On contraction in the anterior region, mean percentage of FBL shortening ranged between 9% and 21%. However, in the posterior region, shortening of approximately 2% only occurred in two of the three positions; lengthening of approximately 2.5% occurred in internal rotation. For the anterior region, the mean PA increased the least in the externally rotated position, and the mean PA of the middle part was smaller than the deep part for all states. Findings suggest changes in the architecture are not uniform throughout the muscle and joint position may play an important role in force production. The US protocol may serve as an outcome measure of adaptive changes of muscle function following surgery, training, and rehabilitation. Clin. Anat. 23:48–55, 2010.

Cadaveric study of sacroiliac joint innervation: implications for diagnostic blocks and radiofrequency ablation.

Background and Objectives Optimization of clinical outcomes of lateral branch radiofrequency ablation or blocks for sacroiliac joint (SIJ) pain requires precise nerve localization; however, there is a lack of comprehensive morphological studies. The objectives of this cadaveric study were to document SIJ innervation relative to bony landmarks in 3 dimensions and to identify reference points visible under ultrasound and fluoroscopy for optimal needle placement. Methods In 25 cadaveric hemipelves, L5-S4 lateral branches were exposed, digitized, and modeled in 3 dimensions. The models were used to compare innervation patterns between specimens and to quantify the distances of the nerves innervating the SIJ relative to the transverse sacral tubercles (TSTs) and posterior sacral foramina. Quadrants of origin of the nerves were recorded. Results The SIJ was innervated by the posterior sacral network: S1-S2 contributed in all specimens, S3 in 88%, L5 in 8%, and S4 in 4%. Most frequently, the lateral branch(es) emerged from the inferolateral S1, superolateral and inferolateral S2, and superolateral S3 quadrants. All TSTs were easily identifiable elevations that were used to landmark the nerves innervating the SIJ. The majority of branches of the posterior sacral network crossed the lateral sacral crest between TST1-3, with the greatest concentration between TST2-3. Only 3 specimens had a branch superior or inferior to these landmarks. Conclusions Based on the innervation pattern and using bony landmarks identifiable under ultrasound and fluoroscopy, 2 radiofrequency ablation techniques were proposed. Further research is required to determine the accuracy and reliability of needle placement and to evaluate clinical outcomes.

Determining physiological cross-sectional area of extensor carpi radialis longus and brevis as a whole and by regions using 3D computer muscle models created from digitized fiber bundle data

Architectural parameters and physiological cross-sectional area (PCSA) are important determinants of muscle function. Extensor carpi radialis longus (ECRL) and brevis (ECRB) are used in muscle transfers; however, their regional architectural differences have not been investigated. The aim of this study is to develop computational algorithms to quantify and compare architectural parameters (fiber bundle length, pennation angle, and volume) and PCSA of ECRL and ECRB. Fiber bundles distributed throughout the volume of ECRL (75+/-20) and ECRB (110+/-30) were digitized in eight formalin embalmed cadaveric specimens. The digitized data was reconstructed in Autodesk Maya with computational algorithms implemented in Python. The mean PCSA and fiber bundle length were significantly different between ECRL and ECRB (p < or = 0.05). Superficial ECRL had significantly longer fiber bundle length than the deep region, whereas the PCSA of superficial ECRB was significantly larger than the deep region. The regional quantification of architectural parameters and PCSA provides a framework for the exploration of partial tendon transfers of ECRL and ECRB.

Robust estimation of physiological cross-sectional area and geometric reconstruction for human skeletal muscle

Understanding muscle architecture is crucial to determining the mechanical function of muscle during body movements, because architectural parameters directly correspond to muscle performance. Accurate parameters are thus essential for reliable simulation. Human cadaveric muscle specimen data provides the anatomical detail needed for in-depth understanding of muscle and accurate parameter estimation. However, as muscle generally has non-uniform architecture, parameter estimation, specifically, physiological cross-sectional area (PCSA), is rarely straightforward. To deal effectively with this non-uniformity, we propose a geometric approach in which a polygon is sought to best approximate the cross-sectional area of each fascicle by accounting for its three-dimensional trajectory and arrangement in the muscle. Those polygons are then aggregated to determine PCSA and volume of muscle. Experiments are run using both synthetic data and muscle specimen data. From comparison of PCSA using synthetic data, we conclude that the proposed method enhances the robustness of PCSA estimation against variation in muscle architecture. Furthermore, we suggest reconstruction methods to extract 3D muscle geometry directly from fascicle data and estimated parameters using the level set method.

Lateral pterygoid muscle: A three‐dimensional analysis of neuromuscular partitioning

The lateral pterygoid (LP) has been implicated in temporomandibular joint (TMJ) pathology. Few studies have examined muscle architecture of the superior (SLP) and inferior (ILP) heads of LP; moreover, the pattern of intramuscular innervation is poorly defined. The purpose of this study was to determine patterns of intramuscular innervation of LP using 3D modeling. The superior and lateral aspects of LP were exposed in 10 embalmed cadaveric specimens. Nerves entering the muscle, all branches of the mandibular nerve (V3), were followed intramuscularly in short segments and sequentially digitized. Muscle volume, surrounding bone, and the TMJ disc were also digitized. The data were reconstructed into 3D models (Maya®) that were used to determine patterns of intramuscular innervation. It was found that the SLP had independent sources of innervation to each of the quadrants in its superior part (masseteric/posterior deep temporal/middle deep temporal/buccal) and one primary source of innervation (buccal) to the quadrants of the inferior part. This difference in innervation is significant as the superior part attaches to the TMJ disc‐capsule complex, whereas the inferior part attaches to the mandibular condylar neck. Differing sites of attachment and sources of innervation for each part suggests that movement of the TMJ disc‐capsule complex, independent of the condyle, may be possible. The buccal nerve supplied both the medial and lateral quadrants of the ILP, with the medial quadrants receiving additional innervation from V3 muscular branches. Results of this study could be used to direct EMG/ultrasound studies of LP function as related to TMJ disorders. Clin. Anat. 25:576–583, 2012.

Neuromuscular partitioning in the extensor carpi radialis longus and brevis based on intramuscular nerve distribution patterns: A three-dimensional modeling study.

Differential activation of specific regions within a skeletal muscle has been linked to the presence of neuromuscular compartments. However, few studies have investigated the extra‐ or intramuscular innervation throughout the muscle volume of extensor carpi radialis longus (ECRL) and brevis (ECRB). The aim of this study was to determine the presence of neuromuscular partitions in ECRL and ECRB based on the extra‐ and intramuscular innervation using three‐dimensional modeling. The extra‐ and intramuscular nerve distribution was digitized and reconstructed in 3D in all the muscle volumes using Autodesk Maya in seven formalin embalmed cadaveric specimens (mean age, 75.7 ± 15.2 years). The intramuscular nerve distribution was modeled in all the muscle volumes. ECRL was found to have two neuromuscular compartments, superficial and deep. One branch from the radial nerve proper was found to innervate ECRL. This branch was divided into anterior and posterior branches to the superficial and deep compartments, respectively. Five innervation patterns were identified in ECRB with partitioning of the muscle belly into two, three, or four compartments, in a proximal to distal direction depending on the number of nerve branches entering the muscle belly. The ECRL and ECRB both demonstrated neuromuscular compartmentalization based on intramuscular innervation. According to the partitioning hypothesis, a muscle may be differentially activated depending on the required function of the muscle, thus allowing multifunctional muscles to contribute to a variety of movements. Therefore, the increased number of neuromuscular partitions in ECRB when compared with ECRL could be due to the need for more differential recruitment in the ECRB depending on force requirements. Clin. Anat. 25:366–372, 2012.

Musculotendinous Architecture of Pathological Supraspinatus: A Pilot In Vivo Ultrasonography Study

Architectural changes associated with tendon tears of the supraspinatus muscle (SP) have not been thoroughly investigated in vivo with the muscle in relaxed and contracted states. The purpose of this study was to quantify the geometric properties within the distinct regions of SP in subjects with full‐thickness tendon tears using an ultrasound protocol previously developed in our laboratory, and to compare findings with age/gender matched normal controls. Twelve SP from eight participants (6 male/2 female), mean age 57 ± 6.0 years, were investigated. Muscle geometric properties of the anterior region (middle and deep parts) and posterior region (deep part) were measured using image analysis software. Along with whole muscle thickness, fiber bundle length (FBL) and pennation angle (PA) were computed for architecturally distinct regions and/or parts. Pathologic SP was categorized according to the extent of the tear in the tendon (with or without retraction). In the anterior region, mean FBL of the pathologic SP was similar with normal controls; however, mean PA was significantly smaller in pathologic SP with retraction compared with normal controls, in the contracted state (P < 0.05). Mean FBL in the posterior region in both relaxed and contracted states was significantly shorter in the pathologic SP with retraction compared with normal controls (P < 0.05). Findings suggest FBL changes associated with tendon pathology vary between the distinct regions, and PA changes are related to whether there is retraction of the tendon. The ultrasound protocol may provide important information on architectural changes that may assist in decision making and surgical planning. Clin. Anat., 2013.