Morphometry of the anterior interosseous nerve: a cadaveric study (original) (raw)
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Open Journal of Orthopedics, 2012
Background: The etiology and treatment of spontaneous paralysis variants of anterior interosseous nerve (AIN) syndrome remains controversial. Variation and multiple sites of potential compression complicate the successful performance of neurolysis. This anatomic study of the AIN and sites of potential compression in the proximal forearm facilitates critical steps involved in neurolytic procedures and management. Methods: Upper extremities of twelve cadavers were examined to evaluate potential sites of AIN compression in the proximal forearm. Potential sites of musculoaponeurotic compression were evaluated, including: lacertus fibrosus; inferior fibrous arch of the humeral head of the pronator teres (PT) muscle; inferior fibrous arch of the ulnar head of the PT muscle; fibrous arch in the flexor digitorum superficialis (FDS) muscle; Gantzer's muscle; and vascular structures near the AIN and median nerve. Results: The AIN arose at a mean distance of 54.5 mm distal to the elbow from the posterior (n = 9) or ulnar side (n = 3) of the median nerve. Relative positions of AIN branches were variable. A fibrous arch was found between the lacertus fibrosus and the PT in two cases. Nine cadavers had two fibrous arches in the PT and FDS, and three cadavers had one arch. An accessory head in the FDS was found to be a risk of AIN compression. Gantzer's muscle was present in six cases, crossing the AIN superficially. Two potentially compressive vascular arches were identified. Conclusions: Our observations confirm that multiple musculoaponeurotic and/or vascular structures can contribute to AIN compression in the proximal forearm. Understanding the complex anatomic relationships of this nerve is crucial to improving outcomes of neurolysis in cases of non-regressive AIN paralysis.
Anterior Interosseous Nerve: Variations in Distribution and Possible Structures Causing Entrapment
Aim: To study the origin, course, branches and relations of AnteriorInterosseous Nerve (AIN) Objectives: 1. To study the variations in origin and branching pattern of AIN 2. To find out the anatomical structures that can compress the nerve during its course in the forearm resulting in entrapment syndrome. 3. To look for anastomosis between median nerve or AIN with ulnar nerve in the forearm. Materials and Methods: Twenty four upper limbs of embalmed cadavers were dissected in the Department of Anatomy, Government Medical College, Kozhikode. Results: 1. Site of origin of AIN : 4-9 cm distal to intercondylar line 2. AIN supplied medial head of FDP also in4.17% cases 3. Following anatomical structures were found to be crossing the AIN a) Deep head of pronator teres(25 %) b) Accessory head of Flexor PollicisLongus (29.17 %) c) Accessory heads of Flexor DigitorumSuperficialis (4.17 %) d) Accessory head of Flexor DigitorumProfundus(4.17%) e) Muscular branch of ulnar artery (4.17 %) 4. In one case, there was Martin-Gruber anastomosis (4.17%) Conclusions: 1. There is wide variation in the site of origin of AIN. In the two limbs of same person, there were variations. 2. There were structures crossing the nerve , likely to cause its compression. 3. The existence of anastomoses between median and ulnar nerve lessen the effects of cut injuries of nerves, than the anticipated effects. 4. The above anatomical findings will be useful for clinicians dealing with reduction of fracture of bones of forearm, fasciotomies, nerve entrapment and nerve injuries.
Quantitation of and superficial surgical landmarks for the anterior interosseous nerve
Journal of Neurosurgery, 2006
HERE is a paucity of information in the neurosurgical literature regarding the surgical anatomy of the AIN. In the proximal forearm, the AIN, having approximately 1700 axons, 25,26 arises from the median nerve and travels distally between the FDS and FDP muscles. Although it initially parallels the median nerve and is its largest motor branch in the forearm, the AIN quickly passes dorsally or dorsomedially 17 in the interval between the FPL muscle laterally and the FDP muscle medially, providing branches to each of these muscles (approximately the radial half of the FDP muscle). Diminished in size, the AIN reaches the anterior part of the interosseous membrane and travels distally with the anterior interosseous artery (Figs. 1 and 2), extending deep to the PQ muscle where after innervating this muscle, it sends filaments to the ligaments and articulations of the intercarpal, radiocarpal, and distal radioulnar joints. Although the AIN is deeply situated, its injury causes paralysis of the entire FPL and PQ muscles and a variable amount of the radial portion of the FDP muscle, especially the part serving the second digit. Characteristically, paresis or an inability to flex the terminal phalanx of the first and second digits occurs when pronation of the forearm is impaired, especially while the forearm is flexed. Although chronic wrist pain has been attributed to AIN injury, sensory defect has not. 4,5,7 Patients may also feel a dull pain in the proximal one third of the forearm, which is aggravated by radial pressure at the level of the tendinous arch of the FDS muscle. 18 Materials and Methods The AIN in 20 formalin-fixed upper extremities from 10 adult cadavers (mean age 73 years at the time of death, range 62-84 years) was dissected, and measurements were obtained between this nerve and surrounding superficial osseous landmarks. Four male and six female cadavers were used in this study. All measurements were ob
Clinical Anatomy, 2004
A detailed description of the accessory head of flexor pollicis longus muscle (AHFPL) in the Thai population has not been reported. Because it is one of the causes of anterior interosseous nerve syndrome (AINS), a study was carried out on 120 Thai cadavers (70 embalmed, 50 fresh; 78 male, 42 female) to elucidate the prevalence of AHFPL, its morphology and relationship with the anterior interosseous nerve (AIN). The prevalence of AHFPL was 62.1% (149/240) with 74.5% (111/149) of its origin on medial epicondyle, 23.5% (35/149) on coronoid process and 2% (3/149) on flexor digitorum superficialis muscle. One hundred percent of its insertion was on the ulnar border of flexor pollicis longus tendon, and it was 98% (146/149) fusiform-shaped and 2% (3/149) slender shaped, with a diameter between 0.8-16.0 mm (average 6.7 mm), averaging 6.5 mm on the right and 4.2 mm on the left. The right was significantly statistically larger than the left (P Ͻ 0.05). The average distance from the mid-point of the distal wrist crease to the insertion point of AHFPL was 12.8 cm. Four patterns of relationship with AIN were noted including: 1) I AIN passed anterior to AHFPL, 13.4% (20/149); 2) AIN passed lateral to AHFPL, 65.8% (98/149); 3) AIN passed posterior to AHFPL, 8.1% (12/149); and 4) AIN passed both lateral and posterior to AHFPL, 12.8% (19/149). We believe that the latter two patterns (3 and 4) with AIN passing posteriorly would be more likely to be associated with AINS due to anatomic considerations. Clin.
AAEM case report #25: Anterior interosseous nerve syndrome
Muscle & Nerve, 1992
A case study is reported regarding a 57-year-old woman, chose chief complaint was weakness in her thumb that she had noted while gardening. The patient described difficulty pulling weeks out because of an inability to get a firm grip when using the thumb. Physical examination showed weakness of the flexor pollicis longus and flexor digitorum profundus to the index finger. There was no other weakness and no clinical sensory deficit. Electrodiagnostic studies revealed normal median motor and sensory nerve conduction studies with needle examination abnormalities noted only in the flexor pollicis longus, flexor digitorum profundus, and pronator quadratus. The literature on anterior interosseous nerve syndrome (AINS) is reviewed. It is important to differentiate those with idiopathic AINS as part of a neuralgic amyotrophy picture from those with an anatomic cause such as a fibrous band or anomalous muscle. Electrodiagnostic examination can be useful to help make this distinction.
Journal of Hand Surgery, 2005
This anatomical study of 40 upper limbs from cadavers investigated the branching pattern of the anterior interosseous nerve in its distal part using the operating microscope. An articular branch to the wrist joint and/or the distal radioulnar joint was only found in seven of the 40 specimens and was always a small terminal continuation of the anterior interosseous nerve after the nerve had passed through the pronator quadratus and innervated it. Therefore, we do not recommend division of the anterior interosseous nerve from the dorsal approach through the interosseous membrane before it gives off its muscular branches to the pronator quadratus. This risks damage of the innervation of this muscle of importance for initiation of hand pronation.
Anterior interosseous nerve syndrome: literature review and report of 11 cases
European Journal of Plastic Surgery, 1998
The anterior interosseous nerve syndrome (AINS) is characterized by weakness of the flexor pollicis longus and the flexor digitorum profundus of the index finger. The orthopedic literature suggests that this syndrome is caused by mechanical compression of the nerve (an entrapment neuropathy) and that decompression should take place after an observational period of 6 to 12 weeks. The neurological literature suggests that AINS is a form of neuralgic amyotrophy and that it is safe to treat patients with AINS nonoperatively to obtain good results. With this controversy in mind, a retrospective follow-up study of 11 patients with this syndrome was conducted. Eight patients were operated on and three patients were treated conservatively. The question whether a patient should be operated on or not, cannot easily be answered. It is recommended that spontaneous recovery should be awaited in patients having other neurological symptoms in combination with AINS. In patients with symptoms caused by AINS only, the observation period should be 8 to 12 months.
Anterior interosseous nerve syndrome presenting with pronator teres weakness: A case report
Muscle & Nerve, 1997
Anterior interosseous nerve syndrome (AINS) has been well described. A key muscle to examine clinically and on electromyography is the pronator teres, as this can differentiate between forearm and more proximal entrapment sites. We present a case of AINS with marked weakness and denervation of pronator teres. At operation the anterior interosseous nerve gave rise to the nerve to pronator teres and was entrapped by a fibrous band from the deep head of pronator teres.
Folia Morphol. Vol. 67, No. 1, pp. 63–71
Entrapment neuropathy in the forearm is not uncommon. Surgical interference for nerve decompression should be preceded by accurate diagnosis of the exact cause and site of the nerve entrapment. The aim of the present study was to investigate the prevalence of accessory heads of the flexor pollicis longus and flexor digitorum profundus muscles (FPLah) and (FDPah) in Egyptians and their topographical relationship with both the median nerve and its anterior interosseous branch. A total of 42 upper limbs of embalmed cadavers, 36 from males and 6 from females, were examined to elucidate the prevalence of both the FPLah and the FDPah muscles, their origin, insertion, nerve supply and morphology. The distribution of these two muscles in the right and left male and female upper limbs and their relationship to the anterior interosseous and median nerves were recorded. The total lengths of both accessory muscles and the lengths of their fleshy bellies and tendons were also measured. The FPLah was found to be present more frequently (61.9%) than it was absent, whereas the FDPah was observed in only 14.24% of the specimens examined. The combination of the accessory muscles in the same forearm was noticed in 9.52% of cases. As regards side, the FPLah appeared in 77.7% of the right forearms and in 50% of the left, while the FDPah was found in only 25% of the left forearms. The accessory muscles showed no single morphology, as the FPLah appeared fusiform in 53.8%, slender in 30.8% and voluminous fusiform in 15.4%, while the FDPah was slender in 66.6% and triangular in 33.3% of specimens. The FPLah arose mainly from the under surface of flexor digitorum superficialis, while the FDPah took its origin from the under surface of flexor digitorum superficialis or from the medial epicondyle. The insertion of the FPLah was mainly into the upper third of the FPL tendon, while the FDPah tendon joined the tendons of the flexor digitorum profundus muscle to the index or middle and ring fingers. The FPLah was found between the median nerve anteriorly and the anterior interosseous nerve posteriorly. Both FPLah and FDPah took their nerve supply mainly from the anterior interosseous nerve and, less64 Folia Morphol., 2008, Vol. 67, No. 1 INTRODUCTION Today’s human possesses a distinct and well-developed flexor pollicis longus muscle (FPL), an extrinsic thumb flexor which is “either rudimentary or absent” in great apes. The FPL is concerned with precise grasping and functioned initially to stabilise the terminal pollical phalanx against loads applied to the thumb’s apical pad during forceful movements. FPL activity increases most when resistance is increased to the thumb pad. In contrast, relatively low levels of FPL activity are observed during fine manipulations [6]. The FPL muscle arises chiefly from the anterior surface of the radius (below the anterior oblique line and above the insertion of the pronator quadratus) and an adjoining strip of interosseous membrane. The oblique cord represents phylogenetically degenerate fibres of the upper part of the muscle. The fibres of this unipennate muscle descend obliquely to insert onto a tendon which forms high on the ulnar border of the muscle [17]. The flexor digitorum profundus (FDP) muscle arises from about the upper three-quarters of the anterior and medial surfaces of the ulna, the medial side of the coronoid process and proximal three-quarters of the posterior border of the ulna, in addition to the interosseous membrane. The part acting on the index finger is usually distinct, but other tendons are interconnected as far as the palm [24]. During the fourth week of development somatic mesoderm invades the limb buds and forms ventral and dorsal condensations. The ventral condensation gives rise to the flexors and pronators of the upper limb [12]. Complex muscle patterns are formed by successive splitting of the muscle masses and subsequent growth and differentiation [9, 26]. In 1813, Gantzer described two accessory muscles in the human forearm which bear his name. The more frequent muscle was found to arise from the coronoid process of the ulna coursing distally to attach to the FPL. The less frequently observed muscle was found to arise from the coronoid process and course to join the FDP [25]. Compression neuropathies of the median nerve in the proximal forearm are unusual lesions. Many patients have vague symptoms for many months or even years prior to confirmation of a diagnosis of either pronator syndrome or anterior interosseous nerve syndrome of the forearm [5]. The most common cause of anterior interosseous nerve syndrome is entrapment of the nerve near its origin from the median nerve by a variety of structures [19]. Seven different anatomical structures may compress the median nerve and anterior interosseous nerve. One of these structures is the accessory head of flexor pollicis longus muscle (FPLah) [2, 11] Patients with anterior interosseous nerve syndrome often present initially with acute pain in the proximal forearm, which lasts several hours to days. The pain subsides, to be followed by paresis or total paralysis of the pronator quadratus, FPL and the radial half of the FDP, either individually or together. The partial anterior interosseous nerve lesion is frequently misdiagnosed as tendon rupture. Patients with a complete lesion will have a characteristic pinch deformity [13, 20]. While rare in comparison to carpal tunnel syndrome, anterior interosseous nerve syndrome is suspected if a patient with carpal tunnel syndrome fails to respond to conservative or surgical intervention [21]. Because it is one of the causes of anterior interosseous nerve syndrome, the morphology and relations of the FPLah are of great interest from the clinical point of view. The presence of accessory heads of the deep muscles of the forearm has to be borne in mind in cases of nerve compressions in the forearm frequently, from the median nerve. The mean values of the total lengths of FPLah and FDPah were 74.66 mm and 208.33 mm, respectively. Cadaveric dissection in this study confirmed the prevalence of the FPLah and FDPah in Egyptians and demonstrated the relationship of the FPLah to the median nerve and its anterior interosseous branch. These findings may provide the surgeon with information for the differential diagnosis of the causes and sites of anterior interosseous nerve syndrome and entrapment neuropathy of the median nerve in the forearm (Folia Morphol 2008; 67: 63–71)