|Year : 2022 | Volume
| Issue : 1 | Page : 46-49
The dimensions of pronator quadratus and its neurovascular structures – A cadaveric study with its clinical implications in distal forearm surgeries
Sudha Ramalingam, Deepa Somanath
Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Puducherry, India
|Date of Submission||07-Jul-2021|
|Date of Acceptance||25-Dec-2021|
|Date of Web Publication||15-Jun-2022|
Dr. Deepa Somanath
Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Puducherry - 605 107
Source of Support: None, Conflict of Interest: None
Introduction: The pronator quadratus is one of the deep muscles of the front of the forearm. The neurovascular supply of the muscle is derived from the anterior interosseous nerve and vessels. This muscle is approached in various surgical procedures involving the distal radius. Its nerve can be utilised as a graft in case of peripheral nerve lesions and the anterior interosseous artery perforator flap is used for wrist and hand surgeries. Hence, the anatomy of the muscle and its neurovascular pedicle is needed in orthopedic surgeries. Materials and Methods: In this study, 84 upper limbs from 24 male and 18 female cadavers, age ranging from 55 to 78 years, were dissected to study the pronator quadratus muscle and its neurovascular supply in the Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Pondicherry. Various levels of measurements regarding the length and width of the muscle were considered. The number of branches of its neurovascular structures and their levels of entry into the muscle from various landmarks was measured. The Student t-test was applied to identify the P-value regarding the difference between the subjects. Results: No significant differences were observed regarding the measurements of the muscle and its neurovascular structures between male and female cadavers. Conclusion: This study can be useful for the surgeries involving the lower part of front of forearm. Since no significant difference was found between the genders regarding the variables, the morphometry of the muscle and its supply can be generalised for both sexes.
Keywords: Anterior interosseous artery, anterior interosseous nerve, deep flexors of forearm, distal radius fracture, volar plating
|How to cite this article:|
Ramalingam S, Somanath D. The dimensions of pronator quadratus and its neurovascular structures – A cadaveric study with its clinical implications in distal forearm surgeries. J Orthop Traumatol Rehabil 2022;14:46-9
|How to cite this URL:|
Ramalingam S, Somanath D. The dimensions of pronator quadratus and its neurovascular structures – A cadaveric study with its clinical implications in distal forearm surgeries. J Orthop Traumatol Rehabil [serial online] 2022 [cited 2022 Dec 9];14:46-9. Available from: https://www.jotr.in/text.asp?2022/14/1/46/347371
| Introduction|| |
The pronator quadratus (PQ) is the deeply seated muscle of the front of distal forearm. It is rectangular, parallel to the axis of forearm connecting distal parts of ulna and radius. It consists of superficial and deep heads. The superficial head helps in pronation of forearm with the elbow flexed while the deep head stabilizes the distal radio-ulnar joint. The PQ is supplied by the distal part of anterior interosseous nerve (AIN), which is a branch of the median nerve. The source of vascularity for PQ is the anterior interosseous artery (AIA) from the ulnar artery.
The most common fracture that involves the forearm is the fracture of distal radius. The surgical treatment for the above condition includes internal fixation such as volar plating, osteosynthesis, dorsal plating, radial plating, intramedullary nailing, and fragment-specific fixation. In case of nonunion of scaphoid fracture, a graft from the distal radius is used. Currently, an osteomuscular graft is preferred from the distal radius along with a part of PQ muscle and its blood vessel. Lower radius shortening is done by osteotomy technique to treat the necrotic lunate bone in Kienbock's disease. Cortical and periosteal-metaphyseal branches of AIA are the major sources for the vascularity of the distal radius. These branches arise from AIA deep to the proximal part of PQ, and during the surgical reduction of the distal radius, these vessels are to be taken care of to avoid nonunion. The distal forearm is devoid of superficial expandable muscles; hence, it loses its myocutaneous flap potential. The source of the flap in such a condition would be from the groin to cover the lower part of forearm. The PQ can be the local muscle flap to provide a bed for the skin grafting over the exposed flexor tendons on the ventral aspect of the distal forearm.
Nerve transfer surgery in case of peripheral nerve lesion achieves re-innervation of the affected muscle to produce functional recovery. It is not necessary to harvest a nerve graft from another place since a local nerve is available for functional nerve reconnection. The terminal part of AIN is utilized to re-innervate the motor branch of the ulnar nerve in distal ulnar nerve palsy. Thus, detailed knowledge of PQ and its neurovascularity is essential in the treatment of injuries of the distal forearm, wrist, and proximal part of palm.
| Materials and Methods|| |
In the present study, 84 upper limbs from 24 male and 18 female cadavers, age ranging from 55 to 78 years, were dissected to study the PQ muscle and its neurovascular supply in the Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Pondicherry. A longitudinal incision was made in the middle of the front of forearm, commencing 8 cm distal to the elbow extending up to the wrist joint line. An upper horizontal incision was given across the forearm 8 cm distal to the elbow. A lower horizontal incision was given across the wrist joint line, and the PQ was exposed after reflecting deep flexor tendons.
The measurements evaluated in this study regarding the muscle were radial and ulnar length, proximal and distal width, distance from elbow to proximal and distal borders of PQ, and distance from wrist joint line to proximal and distal borders of PQ. Regarding the AIN, the number of branches, the point of entry of the nerve from the wrist, point of entry of the nerve from the elbow, distance from the lateral side of radius to the entry point of nerve, and distance from the medial side of ulna to the entry point of nerve were studied. Pertaining to the AIA, the number of branches, origin of the proximal branch from the wrist, origin of proximal branch from elbow, and side of emergence of the branches were considered.
The data were analyzed using Student's t-test. The values were represented in mean and standard deviation and the P value was considered if the difference between the subjects is <0.05.
| Results|| |
[Table 1] shows the values of the mean and standard deviation of morphometry of PQ muscle. There was no statistically significant difference between males and females (P > 0.05).
[Table 2] shows the values of the mean and standard deviation of the branching pattern of the AIN. No statistically significant difference was observed between the genders (P > 0.05).
[Table 3] shows the values of the mean and standard deviation of the branching pattern of the AIA. The male and female groups did not show a statistically significant difference (P > 0.05).
| Discussion|| |
The anatomical knowledge of the PQ muscle is required for electromyographic studies in case of AIN injury, volar plating in fractures of the distal radius and muscle flaps. In the present study, the proximal width of the PQ was 4.23 ± 0.86 cm and 4.06 ± 0.9 cm; distal width was 4.00 ± 0.80 cm and 3.81 ± 0.84 cm; distance from elbow to proximal border was 19.24 ± 2.63 cm and 19.70 ± 2.76 cm; and distance from wrist to proximal border was 2.35 ± 1.40 cm and 2.13 ± 1.24 cm in males and females, respectively [Table 1]. Ilyas reported that the distal extent of the PQ muscle has to be identified during implantation of the volar plate in distal radial fracture. The water-shed line is defined as the junction between the volar radiocarpal ligaments and the distal margin of PQ muscle. Hence, the implantation of a plate below this limit would irritate the flexor tendons of the forearm. In the present study, the mean value of the length of radial attachment was 5.49 ± 1.20 cm and 5.36 ± 1.16 cm; the length of ulnar attachment was 5.67 ± 1.30 cm and 5.44 ± 1.30 cm in males and females, respectively. The distance from wrist to the distal border was 2.84 ± 0.62 cm and 3.73 ± 0.87 cm, distance from elbow to the distal border was 24.22 ± 1.72 cm and 24.42 ± 1.57 cm in males and females, respectively [Table 1], but Hinds et al. documented 4.6 cm length and 3.8 cm width for PQ in 25 cadaveric studies. Carlson et al. reported the mean width of PQ as 3.6 ± 0.3 cm and the mean length of 4.5 ± 0.4 cm. In Henry and trans-FCR approach, the PQ muscle is dissected along its lateral attachment on the distal radius and elevated medially. Such dissection must be restricted to the radial side of the muscle to facilitate the repair of PQ upon closure.
Takada and Otsuka documented that the length of the plate must be >5.2 cm to avoid PQ muscle damage. The proximal screw of the vertical limb of the T plate is inserted through the muscle and traction of the muscle is required to introduce distal two screws of the plate. The neurovascular supply of the muscle is to be taken care of in such procedures. Dellon and Mackinnon explored that the PQ muscle flap can be used to cover the distal forearm instead of the groin flap. For this purpose, the muscle can be approached through a longitudinal incision 12 cm proximal to the wrist crease between tendons of flexor pollicis longus and flexor digitorum profundus. The dorsal branch and perforating branches of AIA must be ligated, and the branch of AIN should be cut to release the muscle which provides a bed for skin grafting.
The distal part of AIN can be used to re-innervate the injured lower part of the ulnar nerve. The ulnar nerve is traced for its distal motor branch from the hand to lower forearm. The distal part of the AIN is released from the PQ muscle and directed posterior to the flexor digitorum profundus to access the motor branch of the ulnar nerve to avoid clawing of medial two fingers of the hand. Barbour et al. reported that the distal AIN can be connected to motor fascicles of the ulnar nerve in the distal forearm in an end-to-side manner for functional motor recovery of the ulnar digits.
Lee et al. described the needle insertion point of PQ muscle in needle myography could be 2–3 cm proximal to the styloid process adjacent to the anterior surface of ulna in the supinated forearm, otherwise, in a space between extensor tendons on the posterior aspect of the lower part of forearm. The deeper location of the PQ muscle often poses difficulty in inserting a needle at the motor entry point of AIN during needle electromyography and in the administration of neurolytic agents to reduce the spasm of the muscle. In this study, the mean value of the distance from the wrist to nerve entry point is 5.50 ± 0.65 and 5.70 ± 0.69 cm in males and females, respectively [Table 2]. Similarly, Alves et al. inferred that the distance between the wrist articular line and penetration of proximal branch of AIN into the muscle on the right and left sides were 5.4 cm and 5.6 cm, respectively. Safwat and Abdel-Meguid demonstrated the PQ muscle is supplied by AIN via its branches along the entire length of the muscle which is also featured in the present study. Hence, the distances from the landmarks to the proximal branch of AIN's nerve entry point were considered as the motor endpoint. Bertelli et al. reported that the number of myelinated nerve fibers in the distal part of AIN is about 65% of fibers from the posterior interosseous nerve. In addition, the transfer of distal AIN to the posterior interosseous nerve in restoring the full range of thumb motion was successful in five patients.
AIA is the potential source for fasciocutaneous, osteocutaneous, neurovascular, and muscular flaps. The PQ muscle is usually utilized in healing the nonunion of scaphoid fracture as osteomuscular graft along with anteromedial cortex of distal radius along with the anterior carpal branch of AIA. To raise the graft, the PQ muscle must be released from the radial attachment toward the ulnar side to save the pedicle., An AIA perforator flap is the best choice for dealing with wrist and hand surgeries. In general, AIA gives two perforating branches, namely superior and inferior. The inferior branch of AIA pierces the interosseous membrane and goes dorsally to anastomose with the dorsal arterial network of the wrist which maintains the retrograde blood flow. Usually, based on the superior branch of AIA, the island flap is elevated. The branches of AIA arise within the PQ muscle and run to the distal radius as metaphyseal and epiphyseal arteries and form a vascular network within the bone. These vessels are responsible for the healing of distal radial fractures. In this study, the number of branches piercing the PQ muscle is 2.84 ± 0.62 and 3.73 ± 0.87 in the case of males and females, respectively [Table 3]. Thus, these vessels have to be taken care of during surgical closure of distal radial fracture. In this study, the limitations were the nonavailability of adequate number of cadaveric limbs, nonconsideration of the direction of muscle fibers, and anatomical variations of the PQ and nerve and blood vessels.
| Conclusion|| |
This article reveals various measurements of PQ and its neurovascular pedicle. The results may facilitate the surgeons to locate the structures precisely during surgeries that involve muscular graft, nervous graft, and osteomuscular graft along with its blood vessel. This detailed anatomy may also be helpful in the surgical reduction of distal radius fractures to avoid injury to the studied variables. Since no significant difference was found between the genders regarding the variables, the morphometry of the muscle and its supply can be generalized for both sexes in case of surgery involving the distal forearm.
The authors thank the management and the Department of Anatomy of Sri Manakula Vinayagar Medical College and Hospital, Pondicherry, for their valuable support.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]