The palmaris longus muscle and its relations with the antebrachial fascia and the palmar aponeurosis

Imaging of Anatomical Variants Around the Wrist and Hand

Wrist and hand anatomy may present several clinically relevant variants that involve bones, muscles, tendons, and nerves. Thorough knowledge of these abnormalities and their appearance in imaging studies is useful for proper management. In particular, it is necessary to differentiate the incidental findings that do not represent a trigger for a specific syndrome from those anomalies causing symptoms and functional impairment. This review reports the most common anatomical variants encountered in clinical practice and briefly discusses their embryogenesis, related clinical syndrome if present, and their appearance using different imaging techniques. The information each diagnostic study (ultrasonography, radiographs, computed tomography, and magnetic resonance imaging) may provide is described for each condition.

Ultrasound Imaging of Brachial and Antebrachial Fasciae

Knowledge about fasciae has become increasingly relevant in connection to regional anesthesiology, given the growing interest in fascial plane, interfascial, and nerve blocks. Ultrasound (US) imaging, thanks to high definition, provides the possibility to visualize and measure their thickness. The purpose of this study was to measure and compare, by US imaging, the thickness of deep/muscular fasciae in different points of the arm and forearm. An observational study has been performed using US imaging to measure brachial and antebrachial fasciae thickness at anterior and posterior regions, respectively, of the arm and forearm at different levels with a new protocol in a sample of 25 healthy volunteers. Results of fascial thickness revealed statistically significant differences (p < 0.0001) in the brachial fascia between the anterior and the posterior regions; in terms of the antebrachial fascia, no statistically significant difference was present (p > 0.05) between the regions/levels. Moreover, regarding the posterior region/levels, the brachial fascia had a greater thickness (mean 0.81 ± 0.20 mm) than the antebrachial fascia (mean 0.71 ± 0.20 mm); regarding the anterior region/levels, the antebrachial fascia was thicker (mean 0.70 ± 0.2 mm) than the brachial fascia (mean 0.61 ± 0.11 mm). In addition, the intra-rater reliability reported good reliability (ICC_2,k: 0.88). US imaging helps to improve grading of fascial dysfunction or disease by revealing subclinical lesions, clinically invisible fascial changes, and one of the US parameters to reliably evaluate is the thickness in the different regions and levels.

Morphometric analysis and surgical adequacy of palmaris longus as a tendon graft. A systematic review of cadaveric studies

INTRODUCTION

The tendon of the palmaris longus is commonly used as a tendon graft in many reconstructive surgeries. Easy to access and at proximity to the hand, the palmaris longus tendon is considered as the optimal tendon source for hand reconstructive surgery. However, and besides its inconsistency, the size of the palmaris longus tendon is reported to show variability. The aim of this study is to look for the surgical adequacy of the palmaris longus tendon by conducting a quantitative synthesis on its length and width in human populations and its correlation with the forearm length.

METHODS

Twenty-four studies met the inclusion criteria including 1761 cadaveric limbs.

RESULTS

The results were as following: (a) the mean palmaris longus tendon length was of 13.9 ± 2.6 cm, (b) the mean ratio palmaris longus tendon length/forearm length was of 0.545 ± 0.06, (c) the weighted correlation value was of 0.686, and (d) the mean palmaris longus tendon width was of 4.0 ± 1.7 mm. Only five studies reported a palmaris longus tendon length of more than 15 cm. The palmaris longus tendon length was shown to vary between ancestries; the Japanese had the shortest while Malaysian the longest palmaris longus tendons. All studies but one reported a palmaris longus tendon mean width of more than 3 mm where the minimal mean palmaris longus tendon width was of 2.5 mm.

CONCLUSION

While the requested length depends on the recipient site and/or type of reconstructive surgery, the palmaris longus tendon often met the required diameter for grafting. Our review demonstrated that while palmaris longus length varies between ancestries, its width is often adequate for grafting. In addition, the forearm length could be a good predictor of palmaris longus tendon length; such correlation could assist surgeons when planning to use palmaris longus tendon as a graft source.

Anomalous Muscles of the Wrist Encountered During Endoscopic Carpal Tunnel Surgery

OBJECTIVE

Anomalous muscles of the wrist are infrequently encountered during carpal tunnel surgery. Anatomic variants of the palmaris longus (PL), flexor digitorum superficialis, lumbricalis and abductor digiti minimi (ADM) have been reported but are usually clinically insignificant. Anomalies of the wrist muscles, encountered during endoscopic carpal tunnel surgery have rarely been described. I conducted this study to evaluate muscular anomalies of the volar aspect of the wrist, encountered during endoscopic carpal tunnel surgery.

METHODS

I studied a consecutive series of 1235 hands in 809 patients with carpal tunnel syndrome who underwent single-portal endoscopic carpal tunnel release (ECTR) from 2002 to 2014. Nine hundred seventy-three hands in 644 patients who had minimal 6-month postoperative follow-up were included in the study. The postoperative surgical outcome was assessed at least 6 months after surgery.

RESULTS

In eight patients, anomalous muscles were found under the antebrachial fascia at the proximal wrist crease and superficial to the ulnar bursa, passing superficial to the transverse carpal ligament . Those anomalous muscles were presumed to be variants of the PL or accessory ADM muscle, necessitating splitting and retraction to enter the carpal tunnel during the ECTR procedure. Other muscle anomalies were not seen within the carpal tunnel on the endoscopic view. The surgical outcome for all eight wrists was successful at the 6-month postoperative follow-up.

CONCLUSION

Carpal tunnel surgeons, especially those using an endoscope should be familiar with unusual findings of anomalous muscles of the wrist because early recognition of those muscles can contribute to avoiding unnecessary surgical exploration and unsuccessful surgical outcomes.

Decreased amplitude of surface electromyo- graphic recordings of muscle activation along the posterior myofascial kinematic chain in subjects with chronic nonspecific low back pain compared to healthy subjects

BACKGROUND

The concept of myofascial continuity suggests that muscles activate along kinematic chains with common fascial coverings. Yet, the literature lacks evidence in regards to the function of anatomical chains in populations suffering from low back pain (LBP).

OBJECTIVE

To examine muscle activations along the superficial back line in LBP patients compared to healthy controls.

METHODS

The sample study included 20 males with chronic LBP (mean age 28.7 (± 3.05) years, mean BMI 24.91 (± 2.76)) and 17 healthy controls (mean age 31.06 (± 7.76) years, mean BMI 23.46 (± 3.43)). Muscle activation (gastrocnemius, hamstrings, erector spine, and upper trapezius) along the superficial back line was measured using surface EMG. All subjects underwent five test conditions: Conditions 1-3 involved passive movement, active movement and active movement against maximum isometric resistance of the right gastrocnemius muscle. Conditions 4 and 5 involved neck extension without and with isometric resistance from the prone position. The main outcome was relative muscle activation amplitude between research and control subjects.

RESULTS

Muscle activation along the posterior anatomical chain was observed during distal movement (plantar flexion or neck extension). LBP patients showed significant lower muscle activation in the erector spine of lower back region compared with the control group during active plantar flexion and active neck extension (p< 0.05). Lower muscle activation in other regions (gastrocnemius, hamstrings, erector spine level T6) was observed in the research group (although not significant).

CONCLUSION

LBP may cause or result in a lower muscle activation of the posterior kinematic myofascial chain muscles.

A rare variation of intrinsic and extrinsic hand muscles represented by a bi-ventered first lumbrical extending into the carpal tunnel combined with bilateral fifth superficial flexor digitorum tendon regression

A rare unilateral variation of the first left lumbrical muscle was discovered in a female Caucasian cadaver dissected during a first year anatomy course at the Paracelsus Medical University - Nuremberg, Germany. The muscle possessed two venters with the first originating near the medial epicondyle of the humerus together with the intramuscular tendon of the superficial flexor digitorum tendon, and the second presenting as a regular first lumbrical muscle with radial palmar origin from first tendon of the deep flexor digitorum muscle. Both muscle bellies were connected by a 1.42mm thick tendon that passed beneath the median nerve and ran through the carpal tunnel. The second belly was enlarged and entered the distal part of the carpal tunnel. Interestingly, the donor revealed further rare variations such as a bilateral regression of the fifth superficial flexor tendons to an obviously non functional connective tissue strand, lack of both palmaris longus muscles, a discoid lateral meniscus in the left knee, and reduction of the plantaris muscle to a fascia-like structure on the right leg. Lumbrical muscle variations extending into the carpal tunnel, especially those associated with auxiliary tendons, have significant clinical relevance due to their association with carpal tunnel syndrome.

Anatomical variations of the palmaris longus muscle including its relation to the median nerve - a proposal for a new classification

BACKGROUND

The palmaris longus (PL) muscle is characterised by high morphological diversity, and its tendon crosses the median nerve (MN) at different levels. Due to the fact that the palmaris longus tendon is routinely harvested for reconstruction of other tendons, knowledge of its morphological variations is clinically important. Therefore, the purpose of the study was to suggest a new morphological classification of the PL muscle and characterise the relationship of its tendon to the median nerve.

METHODS

Standard dissection was performed on 80 randomised and isolated upper limbs (40 left and 40 right) fixed in a 10% formalin solution. Measurements of muscle belly and tendon were obtained. The course and location of tendon insertion, as well as its relationship to the median nerve, were noted.

RESULTS

The palmaris longus muscle was present in 92.5% of specimens. Three types of palmaris longus muscle were identified based on the morphology of its insertion (types I-III) and these were further subdivided into three subgroups (A-C) according to the ratio of the length of the muscle belly and its tendon. The most frequent was type I (78.8%), where the tendon attached to the palmar aponeurosis, and subtype B, where the tendon-to-belly ratio was 1-1.5 (41.1%). The mean distance from the interstyloid line to the crossing between the median nerve and the palmaris longus tendon was 31.6 mm. In addition, two types of palmaris longus were described.

CONCLUSION

The presented classification of palmaris longus muscle types allows a better characterization of its diversity and may be useful in planning tendon grafting.

Structural and functional anatomy of the palmaris brevis: grasping for answers

The palmaris brevis (PB) is a small cutaneous hand muscle that has been described as the most mysterious muscle from a functional and developmental perspective [Kaplan () Kaplan's Functional and Surgical Anatomy of the Hand]. Functionally, the PB is considered to deepen the hollow of the palm and to protect the neurovasculature of the ulnar canal. Although the function of the PB has been inferred from cadaveric observations, the electromyographic (EMG) activity of this muscle has not been explored systematically during specific movements of the hand. The purpose of this study was to record PB intramuscular EMG activity during dynamic grasping tasks, and to quantify the change in PB muscle length (M_L ) and thickness (M_T ) incurred during maximal contraction using ultrasound imaging. Intramuscular EMG was recorded from the PB in the dominant hands of 12 healthy participants (11 males, one female; age: 27 ± 4 years) during maximal abduction, flexion and opposition of the 5th digit, and two grasping tasks. Abduction of the 5th digit yielded the greatest EMG activity in most individuals (seven out of 11), and produced significantly less PB EMG activity when compared with grasping a cylindrical-shaped object (P = 0.003) but not a spherical-shaped object (P = 0.130). During maximal abduction of the 5th digit, PB M_L decreased in both the left (28 ± 11%; P = 0.002) and right (32 ± 5%; P = 0.002) hands. Similarly, a concomitant increase in PB M_T was observed in the left (68 ± 30%; P = 0.002) and right (85 ± 44%; P = 0.002) hands during the same contraction. These EMG results indicate that the PB is voluntarily activated during prehensile and non-prehensile movements of the hand with significant changes in muscle architecture. The study supports the preservation of the PB in surgical procedures based on its proposed protective role as a muscular barrier to the neurovasculature within the ulnar canal.

A Cadaveric Study for the Improvement of Thread Carpal Tunnel Release

PURPOSE

The thread carpal tunnel release (TCTR) technique has been improved and offers more precise control in dissecting thread placement. The purpose of this cadaveric study was to test the procedure operationally and verify the modified TCTR anatomically.

METHODS

Eleven unembalmed cadaver wrists underwent the transverse carpal ligament (TCL) release by using the modified TCTR technique. An experienced observer dissected each specimen and assessed for completeness of release under direct visual assessment. Injury to the superficial palmar aponeurosis (SupPA), the Berrettini and common digital nerve branches were also recorded as a secondary outcome.

RESULTS

Eleven out of 11 wrists (100%) underwent the modified TCTR with complete release of the TCL. All 11 wrists were released without damage to any vital neurovascular structure including the Berrettini branch and the common digital nerves. The SupPA remained intact in all 5 wrists performed with the preservation steps.

CONCLUSIONS

The modified TCTR technique demonstrated complete division of the TCL while protecting the SupPA as well as the Berrettini and common digital nerve branches.

CLINICAL RELEVANCE

The modified TCTR has the potential to offer a clinically safe and effective minimally invasive procedure for complete carpal tunnel release.

Use of the tendon of the palmaris longus muscle in surgical procedures: study on cadavers

Objective

Demonstrate that the tendon of palmar long can be estimated in relation to its length and width before using it as a graft in surgical procedure.

Methods

There were examined 60 forearms of 30 corpses of black ethnicity; measure the length and width of the tendon of the palmaris longus muscle and compared the length of the forearm.

Results

There are notes their absence unilateral right in two female corpses. The medium length and width were more or less respectively 11.9, 15.2 mm and 4.1 + 1.5 mm. The total average forearm length of 275.4 was more or less 17.9 mm.

Conclusion

There is a significant relationship between the length of the tendon and the length of the forearm; so we can evaluate the size of the tendon of the palmaris longus muscle when it is necessary to use it for grafts. Levels of Evidence IV, Case series.

Clinical prevalence of palmaris longus agenesis: a systematic review and meta-analysis

We report a systematic review and a proportion meta-analysis of prevalence studies evaluating the prevalence of palmaris longus agenesis (PLA) in the literature. The overall PLA rate was defined to be the primary outcome. Secondary outcomes were rates of PLA in relation to ethnicity, laterality, side, gender, age, and hand dominance. We identified 26 articles which met the inclusion criteria. Meta-analyses showed an overall PLA pooled rate of 20.25%, higher than the commonly reported overall rate of 15%. Our results also showed significantly lower pooled rates in Africans (11.3%) and East Asians (4.5%) when compared to Arab Middle Eastern population (41.7%). A subgroup analysis of the African group showed a pooled rate of 2.71%, the lowest, in the East and South East African population. The pooled rate was 26.3% among Caucasians, 26.16% among South and Southeast Asians and 34.13% among Turkish. In discordance with the literature, PLA was statistically more predominant on the right side. No significant differences in PLA rates were found for laterality, gender, the combination of gender and side or the combination of gender and laterality. The lowest rate of PLA found in East and South East African populations might be indicative of the subsequent phylogenetic degeneration of the palmaris longus muscle in modern humans after the "Out of Africa" migration.

Degenerative trends of the palmaris longus muscle in a South African population

The literature reports that the palmaris longus muscle (PL) is only found in mammals in which the forelimbs are weight-bearing extremities. It is suggested that the function of this muscle has been taken over by the other flexors in the forearm. Terms used in the literature to describe the diminishing of this muscle include retrogressive or phylogenetic degenerative trends. The aims of this study were to determine the prevalence of PL in a South African population and whether a phylogenetic degenerative trend for the PL exists. To determine the prevalence of the PL, five groups, representing different age intervals (Years 0-20, 21-40, 41-60, 61-80, and 81-99) were used. A sample of 706 participants of various ages was randomly selected. Statistical analysis included comparisons of the prevalence of the muscle between males and females and left and right sides, using a student t-test. A Chi-squared test was used to determine a possible phylogenetic degenerative trend of PL within the five groups. The sample yielded a bilateral absence of the PL in 11.9% of the cases. The muscle was unilaterally absent on the left side in 7.65% and 6.94% on the right side. The Chi-squared tests revealed a P-value of 0.27 for the left arm and 0.39 for the right arm. No obvious trend could be established for the phylogenetic degeneration of the PL in this study. It would appear that the PL muscle should not be considered as a phylogenetically degenerating muscle in a South African population.

Morphological study of the proximal boundary of the flexor retinaculum and of its constituent parts

The proximal boundary of the flexor retinaculum is not readily demarcated, and previous reports of three distinct regions of the flexor retinaculum were not consistent with the authors' experience. This study was undertaken to clarify the proximal boundary and the constituent parts of the flexor retinaculum. A total of 56 cadaveric wrists were used in the study. The proximal boundary of the flexor retinaculum was identified by a change in thickness and colour of the longitudinally sectioned surface of the continuous membranous sheet of the flexor retinaculum and antebrachial fascia. Steel wires were placed on the proximal and distal boundaries, and anteroposterior radiographic images were taken. MRI was carried out before dissection or serial section. The locations of the proximal and distal boundaries of the flexor retinaculum varied. The flexor retinaculum was comprised of two parts, which were distinguishable by thickness and transparency. These two parts were also identified on MR images and by light microscopy.

Prevalence of the palmaris longus through clinical evaluation

PURPOSE

Most standard textbooks of hand surgery report on the rate of palmaris longus muscle absence of 15%. The aim of the study was to determine the absence of palmaris longus and to correlate it with age, sex and body side.

METHODS

The study included 800 subjects (400 male and 400 female). They were initially asked to do the standard test for the assessment of the palmaris longus tendon. If the tendon was not visualized or palpable, four additional tests were done to confirm its absence.

RESULTS

Unilateral absence of the palmaris longus was recorded in 173 (21.6%) and bilateral in 127 (15.9%) study subjects. According to body side, right-sided absence of palmaris longus was found in 69 (8.6%) and left-sided in 104 (13%) subjects, yielding a statistically significant difference. Bilateral absence was slightly more common in men. The prevalence of palmaris longus absence on the right and left side was similar in men, whereas in women it was significantly more common on the left side. Differences between the three age groups (young, middle-aged and old) were not significant; however, the middle-aged and young groups showed a lower rate of palmaris longus presence as compared to old-age group.

CONCLUSIONS

It has been suggested that this tendon is rapidly disappearing in humans. The results of our study show a relatively high incidence of tendon absence and pointed to more pronounced loss of the muscle on the left side.