Review Question - QID 219571

Flexor tendon injuries are a potential complication after volar plate fixation of distal radius fractures. Plate positioning distal to the watershed line and volar to the most volar aspect of the rim (as demonstrated in Figure A) increases the risk of flexor tendon injury.

The patient presented to the clinic nine months postoperatively after distal radius fracture fixation with symptoms and an examination concerning for flexor pollicis longus (FPL) tendon rupture. Flexor tendon injury is a recognized complication after volar plate fixation. The risk is increased with plate positioning distal to the watershed line (located at the distal extent of the pronator fossa laterally, representing the most volar aspect of the volar radial surface) and volar to a critical line drawn from the most volar aspect of the rim, extending proximally parallel to the volar cortex.

Soong et al. reported a parallel series of patients with distal radius fractures treated with one of two volar plate designs. They radiographically assessed plate position relative to a line drawn tangential to the volar-most aspect of the volar rim, parallel to the volar cortex of the radial shaft. Plate position was graded on a scale of zero to two (0 = plate does not extend volar to this line, 1 = plate is volar to this line, but proximal to the volar rim, and 2 = plate is directly on or distal to the volar rim). They found that in the first group of patients, Grade 2 plate prominence was present in 46 (63%) patients, and there were three cases of flexor tendon rupture, two of which were in patients with Grade 2 plate prominence. In the second group, there were no cases of Grade 2 plate prominence and no postoperative flexor tendon ruptures. The authors concluded that plate prominence at the Watershed line may have contributed to the increased risk of flexor tendon injury observed in the first group of patients.

Wurtzel et al. utilized the above-mentioned grading system to assess the effects of volar tilt, wrist extension, and plate position on contact between the FPL tendon and volar plates in six cadaveric models. They found that plates placed distal to the watershed line (Soong Grade 2) had the most contact throughout wrist range of motion and concluded that volar tilt, wrist extension, and plate position were independent risk factors to determine contact between the volar plate and FPL tendon, with a higher Soong Grade plate position resulting in greater contact.

Zhang et al. reviewed the utility of pronator quadratus repair to provide a biological barrier between distal radius volar locking plates and the flexor tendons to minimize irritation. They discussed the results of sonographic studies that showed increased distances between the plate and tendon with pronator quadratus repair. However, there is no clear association between pronator quadratus repair and the prevention of tendon irritation or rupture. Most notably, the authors included the results of a prospective study in which 33 patients were treated with volar plating and pronator quadratus repair. 30% of patients with Soong Grade 1 plate prominence and 100% of patients with Soong Grade 2 prominence developed FPL attrition. They ultimately concluded that there is no clear evidence to support the efficacy of pronator quadratus repair in preventing flexor tendon injury, particularly when there is higher Soong Grade plate prominence.

Figure A demonstrates a volar distal radius plate placed distal to the volar rim and watershed line.
Figure B demonstrates a volar distal radius plate placed proximal to the volar rim and watershed line.
Figure C demonstrates dual dorsal plating of the distal radius.
Figure D demonstrates percutaneous pinning of a distal radius fracture.
Figure E demonstrates external fixation of a distal radius fracture.

Illustration A shows the radiograph seen in Figure A with Soong’s line added, demonstrating Grade 2 plate prominence.
Illustration B shows the radiograph seen in Figure B with Soong’s line added, demonstrating Grade 0 plate prominence.

Incorrect Answers:
Answer 2: A volar plate placed proximal to the volar rim is less likely to contribute to a postoperative FPL tendon rupture than a plate placed distal to the volar rim.
Answer 3: Dorsal plating is more often associated with extensor tendon irritation or rupture.
Answer 4: Superficial branch of the radial nerve injury and pin tract infections are more common complications after percutaneous pinning.
Answer 5: Neurologic injury, stiffness, malunion, nonunion, and pin site complications are more common after external fixation.