Evaluation of Flexor Pollicis Longus Tendon Rupture after Treatment of Distal Radius Fracture with the Volar Plate

Abstract

Background  The aim of this study is to evaluate the frequency of flexor pollicis longus (FPL) tendon rupture and factors leading to this rupture during the follow-up of patients who underwent volar plate fixation because of distal radius fracture.

Patients and Methods  A total of 109 distal radius fractures of 102 patients treated with volar plate fixation and periodically followed up for at least 1 year between January 2013 and May 2018 were evaluated. Fractures were categorized according to the AO Foundation/Orthopaedic Trauma Association (AO/OTA) Fracture-Dislocation Classification and Soong's grading was used for classifying volar plate position. All patients operated were inquired retrospectively in terms of flexor tendon rupture.

Results  Gender distribution revealed 45 females and 57 males. Mean age was 47.9 (range: 17–88) years. Mean period of follow-up was 27 months. Distribution of fractures in accordance with the AO/OTA distal radius classification was 6, 8, 7, 12, 24, 33, 11, and 8 patients with types A2, A3, B1, B2, B3, C1, C2, and C3, respectively. When volar plate positions were analyzed with Soong's classification, it revealed that 79 (72.4%), 23 (21.1%), and 7 (6.5%) plates were grade 0, 1, and 2, respectively. In total, evaluating the three patients with FPL rupture, it revealed that the volar plate was positioned distally during fixation because the fracture line had advanced to the distal of the watershed line, the distal portion of the plate had lost complete connection with the bone, and at this portion, it was observed that the pronator quadratus muscle was not covering the plate entirely (Soong's classification grade 2). Patients did not have additional flexor tendon injury.

Conclusion  FPL tendon rupture is a rare but serious complication of volar plate fixation performed for distal radius fractures. We believe that appropriate choice of implant and careful surgical technique, along with the close follow-up of patients, with Soong's classification grade-2 volar positions would help in preventing this complication.

Level of Evidence  This is a Level 3a, differential diagnosis/symptom prevalence study.

Distal radius fractures are frequently encountered, and their surgical treatment has been increasing in recent years. ¹ Among the various techniques used in the surgical treatment of distal radius fractures, open reduction and internal fixation with the volar plate are among the most common treatment options ( Fig. 1 ). ²

Fig. 1.

Distal radius volar plate position. FPL, flexor pollicis longus.

Depending on differences in the definition of complications, the rates of early- and late-term complications in distal radius fractures range from 6 to 80%. ³ Following the treatment of distal radius fractures, the problems encountered may range from mild, such as issues relating to flexor tendons, irritation-related tendinitis, and tenosynovitis, to serious, such as adhesion formation and tendon rupture. However, complications related to the flexor tendon were found to be related to open reduction and internal fixation with the volar plate. ^{2 4} Flexor tendon rupture following volar plate fixation for distal radius fracture is rare but observed at a rate of 4.3% and reported as the most common late complication of the procedure. ^{5 6}

In this study, the aim is to evaluate the frequency of flexor pollicis longus (FPL) tendon rupture, the factors leading to this rupture, and cases with this complication encountered during the follow-up of patients who underwent open reduction and internal fixation with the volar plate because of distal radius fracture.

Patients and Methods

This study included distal radius fracture patients who underwent open reduction with the modified Henry approach and fixation with the radius distal volar plate (Acu-Loc distal radius precountered anatomic volar plate system, Acumed LLC, Hillsboro, OR,) and who were followed-up periodically for at least 1 year at our clinic from January 2013 to May 2018. The AO/OTA distal radius classification system was used for fractures. The position of the volar plates inserted was evaluated with Soong's grading. ⁷ Radial height, radial inclination, articular step-off, and volar tilt values were measured from the patients' preoperative and postoperative radiographs. Patients with associated tendon injury at the time of distal radius fracture, open fractures, known rheumatologic diseases, neurologic deficit at the upper extremity to be operated, with plegia, and cases treated with other methods were excluded. All patients were operated by the same surgical team. They were evaluated retrospectively in terms of FPL tendon rupture. The thumb mean active interphalangeal joint flexion degrees, visual analogue scale (VAS) scores, Quick Disabilities of the Arm, Shoulder, and Hand scores (quickDASH), and Kapandji thumb opposition scores of the patients who reoperated because of FPL tendon rupture were evaluated.

Results

Among 243 patients who underwent surgical treatment for distal radius fracture at our clinic from January 2013 to May 2018, a total of 109 distal radius fractures of 102 patients deemed appropriate in terms of the evaluation criteria were included in the study. The female to male ratio was 45 (44.1%) to 57 (55.9%). The mean age of the patients was 47.9 (minimum: 17, maximum: 88) years. The mean follow-up period was 27 (range: 12–72) months. According to the AO/OTA distal radius classification, the distribution of fractures was as follows: 6, 8, 7, 12, 24, 33, 11, and 8 fractures had A2, A3, B1, B2, B3, C1, C2, and C3 fracture types, respectively. All patients were operated with the modified Henry approach. The Acu-Loc distal radius precountered anatomic volar plate system (Acumed LLC, Hillsboro) was used in all cases. The positions of the volar plates were evaluated with postoperative X-rays in accordance with the Soong classification, and it revealed that 79 (72.4%), 23 (21.1%), and 7 (6.5%) plates were grades 0, 1, and 2, respectively. ⁷ In all patients, the pronator quadratus muscle was repaired and used to cover the plate, but in cases of plates inserted to the distal portion of the watershed line, the coverage was observed to be insufficient. Evaluation of the preoperative radiographs of all the patients showed that the mean radial height was 3.75 mm, mean radial inclination was 17 degrees, mean articular step-off was 2.5 mm, and mean volar tilt was 6.8 degrees dorsally. Evaluation of the postoperative radiographs of the same group showed that the mean radial height was 13.6 mm, the mean radial inclination was 24.5 degrees, the mean articular step-off was 0.5 mm, and the mean volar tilt was 7 degrees volarly. A significant improvement was observed between the preoperative and postoperative radiographs of the patients ( Table 1 ).

Table 1. Preoperative and postoperative X-ray parameters of patients.

	Preoperative				Postoperative
	Mean radial height (mm)	Mean radial inclination (degree)	Mean articular step-off (mm)	Mean volar tilt (degree)	Mean radial height (mm)	Mean radial inclination (degree)	Mean articular step-off (mm)	Mean volar tilt (degree)
All patients	3.75	17	2.5	−6.8	13.6	24.5	0.5	7
FPL tendon rupture patient	1.6	12	4	−9.3	11.6	23.3	1	4

Abbreviation: FPL, flexor pollicis longus.

During postoperative follow-up, in three patients who had loss of motion in the interphalangeal joint of their thumbs, FPL tendon rupture was identified. Additional flexor tendon injury was not encountered. The mean age of the above-mentioned three patients was 51.3 (range: 48–56) years, and two of them were males, whereas the third patient was female. According to the AO/OTA classification, two patients were type C1, and one patient was type C3. None of these patients had a known rheumatologic disease. None of them used steroid medication. The first case applied with sudden-onset loss of flexion at the interphalangeal joint of the thumb at month 8, following volar plate fixation, because of distal radius fracture ( Fig. 2 ). Surgical exploration revealed that the radius distal volar plate was placed at the distal of the watershed line, and the pronator quadratus muscle did not cover the plate completely. Furthermore, the plate was connected with the ruptured FPL tendon. This patient applied in a short time following FPL rupture, without any gap between tendon ends and with sufficient tendon excursion, so primary repair was performed. The second case applied at 11 months postoperative, with loss of thumb flexion in the preceding week ( Fig. 3 ). Surgical exploration revealed that the radius distal volar plate was at the distal part of the watershed line, and the coverage that the pronator quadratus muscle supplied to the plate was insufficient; additionally, a screw head at the distal portion of the plate had volar interference. Tendon excursion was good, and a gap was observed between the FPL tendon ends, so single-stage tendon grafting with the palmaris tendon graft was performed. The third case applied at 13 months postoperative, with loss of flexion at the thumb for the 2 preceding months ( Fig. 4 ). Surgical exploration showed that the radius distal volar plate was at the distal part of the watershed line, and the coverage that the pronator quadratus muscle supplied to the plate was insufficient. A wide gap was observed between the ruptured FPL tendon ends. The incision was lengthened for a better view of the ruptured tendon ends. The proximal part of the tendon was proximally retracted and had fibrosis, along with decreased tendon excursion, so the fourth flexor digitorum superficialis (FDS) tendon was transferred to the FPL.

Fig. 2.

First case, 8-month postoperative wrist X-ray, Soong's grade 2.

Fig. 3.

Second case, preoperative and 11-month postoperative wrist X-ray, Soong's grade 2 and protruded screw head.

Fig. 4.

Third case, preoperative and 13-month postoperative lateral wrist X-ray, Soong's grade 2.

Evaluation of the preoperative radiographs of the patients who had FPL tendon rupture showed that the mean radial height was 1.6 mm, mean radial inclination was 12 degrees, mean articular step-off was 4 mm, and mean volar tilt was 9.3 dorsally. Evaluation of the postoperative radiographs of the same group showed that the mean radial height was 11.6 mm, the mean radial inclination was 23.3 degrees, the mean articular step-off was 1 mm, and the mean volar tilt was 4 degrees volarly. A difference was observed between the radiographic measurements of the patients with and without FPL tendon rupture, but a statistical analysis was not possible because of the insufficient number of patients. The fracture pattern was thought to be the reason of this difference in radiographic measurements, which also complicated the placement of the plate.

The mean follow-up time of the patients after treatment for FPL tendon rupture was 20 months. At the 12th month evaluation of the patient who underwent primary repair after FPL tendon rupture, the thumb mean active interphalangeal joint flexion was 55 degrees, VAS score was 2, quickDASH score was 4.5, and Kapandji thumb opposition score was 9. At the 32nd month evaluation of the patient who underwent single-stage tendon grafting with palmaris longus tendon graft after FPL rupture, the thumb mean active interphalangeal joint flexion was 45 degrees, VAS score was 3, quickDASH score was 11.4, and Kapandji thumb opposition score was 7. At the 16th month evaluation of the patient who underwent FDS-4 tendon transfer after FPL tendon rupture, the thumb mean active interphalangeal joint flexion was 25 degrees, VAS score was 5, quickDASH score was 20.5, and Kapandji thumb opposition score was 5. As expected, primary repair gave the best results, whereas tendon transfer gave the worst ones. However, an evaluation with a larger patient group is obligatory because of the insufficient number of patients and the difference between the postoperative evaluation times of the patients in this study.

All patients stated that they had a painful prodromal period for approximately 2 weeks before the rupture and that the mean period between the plate fixation and FPL rupture was 10.6 (range: 8–13) months. In patients with FPL rupture, it was observed that the volar plate was placed distally because the fracture had advanced to the distal portion of the watershed line, the connection between the distal part of the plate and the bone was not complete, and the coverage that the pronator quadratus muscle supplied to the plate was not efficient. In all these three patients who were reoperated because of FPL rupture, the plates were removed because of the complete union seen during the surgery.

Discussion

In the surgical treatment of distal radius fractures, the choice of dorsal plates has been reported to be associated with various complications, such as extensor tendon injury or rupture, because of the challenge of producing an implant that could fit the irregular bone contour. ⁸ At the volar side of the radius, flexor tendons lie away from the radius until they reach the transverse protuberance at the most distal end of the bone because of the structural concave curvature. Volar fixation theoretically places the plate away from the tendons, whereas burying it under the pronator quadratus muscle avoids connection with the tendons.

The watershed line, which is between the distal side of the pronator muscle, the most protruding part of the bone at the volar side and the initiation point of radiocarpal ligaments, is the area where flexor tendons and the bone are closest to each other. ⁹ Volar plates extending the watershed line have been reported to cause flexor tendon ruptures, mostly FPL, because in time, they come into contact with the flexor tendons ( Fig. 5 ). ¹⁰ Soong et al classified volar plate positions by using postoperative lateral X-rays. ⁷ According to the classification proposed by Soong et al, 7 of the 109 fractures we fixated with the volar plate were grade 2. In all three patients with FPL rupture, the volar plate was placed at the distal side of the watershed line, and it was grade 2 in accordance with the Soong classification.

Fig. 5.

( A ) Correctly, proximal placement of the distal radius volar plate to the watershed line and coverage with the pronator quadratus muscle to prevent FPL irritation. ( B ) Incorrectly, distal placement of the distal radius volar plate to the watershed line and plate in contact with the FPL tendon. Tendinitis (marked with a star symbol) of FPL because of plate irritation. FPL, flexor pollicis longus.

Four patients, whose cases were classified as grade 2 according to the Soong classification and without rupture, were scheduled for a close follow-up and plate removal, in case flexor tendon irritation occurs.

Other factors reported in the pathogenesis of flexor tendon rupture following volar plate placement for the treatment of distal radius fractures include steroid use, screw heads getting out from the volar side, incorrect reduction, incorrect use of plate, compression during fracture follow-up, tendinopathy of any reason, and iatrogenic injury. ^{10 11 12} In one of the present patients with FPL tendon rupture, the screw head had volar interference. None of our patients with FPL tendon rupture used steroids.

Completely covering the distal side of the volar plate with the pronator quadratus muscle is believed to be of utmost importance in terms of preventing flexor tendon injury. ⁵ If the plate needs to be placed more distally, the patient should be followed-up closely in the postoperative term, and the plate should immediately be considered for removal at the first signs of flexor tendon irritation. ¹³ However, the problem of an irritated flexor tendon may not always be solved by repairing the pronator quadratus muscle because muscle quality may not always be optimal. ¹⁴ The routine procedure of the present authors in patients operated with distal radius fracture is to cover the plate with the pronator quadratus muscle. Among patients, reoperated because of FPL tendon rupture, the distal portion of the plate was found to be not covered with the pronator quadratus muscle, and we believe that in precountered anatomic volar plate placements advancing to the watershed line, completely covering the distal portion of the plate with the muscle, is challenging.

The preferred treatment method for FPL rupture following fixation of the distal radius with the volar plate remains undetermined, and the outcome of final surgery is not clearly defined. ¹⁵ When FPL rupture occurs as a result of long-term rubbing to the volar plate, there is mostly synovial hypertrophy, fibrotic tissue, retraction, and associated tendon defect, all of which hinder primary repair and may therefore require a tendon graft or transfer. ⁵ FPL reconstruction with the palmaris longus autograft is reported as a valuable treatment option in terms of the good functional recovery of the hand as long as the FPL tendon has at least 2 cm of excursion. ¹⁵

When tendon irritation is suspected during follow-up using conservative and surgical treatment methods, the use of ultrasound is effective in diagnosis and treatment. ¹⁶ In the present study, physical examination findings were of top priority during evaluation, and routine ultrasound was not performed. In patients with FPL tendon rupture, ultrasound may not be required because of the apparent physical examination findings, but it could be beneficial in patients suspected of tendinitis. In patients, whose follow-up X-rays reveal distal plates or plates elevated from the bone, FPL tendon rupture should immediately come to attention. ¹⁷ The present authors believe that routine ultrasound associating movement control with dynamic evaluation of the tendon would be helpful.

Conclusion

Despite advances in plate design, rupture of the FPL tendon is a serious complication of distal radius fractures fixated with the volar plate. Preventing this complication requires the appropriate choice of implant and a precise surgical technique. Patients should be warned about the potential complications and advised to report to the hospital immediately if crepitation or pain in the thumb or other fingers is encountered during follow-up. This complication requires awareness, and in symptomatic patients, removal of the plate should be planned to avoid complete rupture.