Clinical Study of the Pronator Quadratus Muscle
Pronator quadratus (PQ) muscle is a quadrilateral muscle with attachments at the distal volar aspect of the ulna and radius. Cadaver studies have confirmed the importance of the PQ muscle in the function of the forearm. Stuart reported that the superficial head of the PQ muscle is the prime mover in forearm pronation and the deep head is a dynamic stabilizer of the distal radioulnar joint in a study of healthy volunteers. In this study, we did not try to identify these two portions. McConkey et al.. showed that paralysis of the PQ muscle with lidocaine resulted in a significant decrease in pronation torque. The PQ muscle also has been shown to be essential to the blood supply of the distal radius, which is thought to be important in fracture healing. Rath et al.. reported that the anterior interosseous artery supplies blood to the PQ muscle, and Lee et al.. demonstrated that, in addition to the PQ, this artery also supplies blood to the distal radial periosteum. Incision of the PQ inevitably damages the blood supply. Tobe et al.. suggested that the MIPO technique prevents soft tissue damage and adhesions around the PQ muscle and provides good functional results immediately after surgery. Sen and Harvey described a "pronator-sparing" technique and cited several advantages: decreased stiffness, lower risk of postoperative tendon rupture because the PQ muscle serves as a protective layer between the plate and the flexor tendons, additional stability of the distal radioulnar joint, and preservation of the volar blood supply to the distal radius and the capsule of distal radioulnar joint. Unlike MIPO techniques, we preserve the PQ muscle with the concept of minimal invasive surgery during conventional approach.
In a cadaver study by Takada et al., the anatomic pictures of the pronator quadratus muscle were demonstrated. The average width from the proximal edge to the distal edge of the PQ muscle was 35.4 mm (range, 31–39 mm). Our clinical study showed this live tissue value was 37.2 mm (range, 30–41 mm). The distance from the distal edge of the PQ muscle to the lunate fossa of the distal radius was 16.2 mm (range, 12–19 mm), and the average distance from the distal edge of the PQ muscle to the scaphoid fossa of the distal radius was 17.6 mm (range, 11–21 mm). The average distance from the fracture site s to the lunate fossa of the distal radius was 12.2 mm (range, 7.3–17 mm), and the fracture site to the scaphoid fossa of the distal radius was 13.2 mm (range, 9.4–18.8 mm).
All but nine of the factures located distal to the distal edge of the PQ muscle but all were around it. In this study, 3.5 mm 3/3 T-plate (AO, Switzerland) instead of locking plate was used. The distance between the distal end of the T-plate to the center of screw hole of longitudinal limb is 15 mm, 26 mm, 43 mm for the distal, middle, and proximal hole respectively. The distance between the distal end of T-plate and the hole of the transverse limb of T-plate is 5 mm, so the plate surely could be placed over the distal fracture fragment well. Usually traction of PQ muscle could provide enough space to introduce distal two screws of the longitudinal limb of T-plate. Takada et al. emphasized that the length of the plate should be more than 52 mm to prevent damage to the PQ muscle. The proximal screw of the plate (3 holes for longitudinal limb) is usually under the PQ muscle. Inserted through PQ with blunt dissection in our study could lead less damage to the muscle. Another advantage of the sparing of PQ muscle is saving the operation time to repair as well. To simplify the measurement, AO 23-A2 fracture type was chosen in this study. This PQ muscle sparing surgery is feasible and could be provided to other type of fracture.
Discussion
Pronator quadratus (PQ) muscle is a quadrilateral muscle with attachments at the distal volar aspect of the ulna and radius. Cadaver studies have confirmed the importance of the PQ muscle in the function of the forearm. Stuart reported that the superficial head of the PQ muscle is the prime mover in forearm pronation and the deep head is a dynamic stabilizer of the distal radioulnar joint in a study of healthy volunteers. In this study, we did not try to identify these two portions. McConkey et al.. showed that paralysis of the PQ muscle with lidocaine resulted in a significant decrease in pronation torque. The PQ muscle also has been shown to be essential to the blood supply of the distal radius, which is thought to be important in fracture healing. Rath et al.. reported that the anterior interosseous artery supplies blood to the PQ muscle, and Lee et al.. demonstrated that, in addition to the PQ, this artery also supplies blood to the distal radial periosteum. Incision of the PQ inevitably damages the blood supply. Tobe et al.. suggested that the MIPO technique prevents soft tissue damage and adhesions around the PQ muscle and provides good functional results immediately after surgery. Sen and Harvey described a "pronator-sparing" technique and cited several advantages: decreased stiffness, lower risk of postoperative tendon rupture because the PQ muscle serves as a protective layer between the plate and the flexor tendons, additional stability of the distal radioulnar joint, and preservation of the volar blood supply to the distal radius and the capsule of distal radioulnar joint. Unlike MIPO techniques, we preserve the PQ muscle with the concept of minimal invasive surgery during conventional approach.
In a cadaver study by Takada et al., the anatomic pictures of the pronator quadratus muscle were demonstrated. The average width from the proximal edge to the distal edge of the PQ muscle was 35.4 mm (range, 31–39 mm). Our clinical study showed this live tissue value was 37.2 mm (range, 30–41 mm). The distance from the distal edge of the PQ muscle to the lunate fossa of the distal radius was 16.2 mm (range, 12–19 mm), and the average distance from the distal edge of the PQ muscle to the scaphoid fossa of the distal radius was 17.6 mm (range, 11–21 mm). The average distance from the fracture site s to the lunate fossa of the distal radius was 12.2 mm (range, 7.3–17 mm), and the fracture site to the scaphoid fossa of the distal radius was 13.2 mm (range, 9.4–18.8 mm).
All but nine of the factures located distal to the distal edge of the PQ muscle but all were around it. In this study, 3.5 mm 3/3 T-plate (AO, Switzerland) instead of locking plate was used. The distance between the distal end of the T-plate to the center of screw hole of longitudinal limb is 15 mm, 26 mm, 43 mm for the distal, middle, and proximal hole respectively. The distance between the distal end of T-plate and the hole of the transverse limb of T-plate is 5 mm, so the plate surely could be placed over the distal fracture fragment well. Usually traction of PQ muscle could provide enough space to introduce distal two screws of the longitudinal limb of T-plate. Takada et al. emphasized that the length of the plate should be more than 52 mm to prevent damage to the PQ muscle. The proximal screw of the plate (3 holes for longitudinal limb) is usually under the PQ muscle. Inserted through PQ with blunt dissection in our study could lead less damage to the muscle. Another advantage of the sparing of PQ muscle is saving the operation time to repair as well. To simplify the measurement, AO 23-A2 fracture type was chosen in this study. This PQ muscle sparing surgery is feasible and could be provided to other type of fracture.