Volar Locking Plate Fixation of Distal Radius Fracture with a Flexor Carpi Radialis Brevis and a Hypoplastic Pronator Quadratus

Learning Point of the Article:

A flexor carpi radialis brevis (FCRB) appears in several percent of patients with distal radius fracture treated surgically. The patient with an FCRB may have a hypoplastic pronator quadratus (PQ). It makes the covering of the volar locking plate by the PQ difficult.


Case Report | Volume 9 | Issue 3 | JOCR May-June 2019 | Page 11-14 | Takafumi Hosokawa, Morimichi Suto, Tsuyoshi Tajika, Hirotaka Chikuda. DOI: 10.13107/jocr.2250-0685.1396


Authors: Takafumi Hosokawa[1], Morimichi Suto[1], Tsuyoshi Tajika[2], Hirotaka Chikuda[2]

[1]Department of Orthopaedics Surgery, Tone Chuo Hospital, Numasu-machi, Numata, Gunma, 378-0012, Japan,
[2]Department of Orthopaedics Surgery, Gunma University Graduate School of Medicine, Showa-machi, Maebashi, Gunma, 371-8511, Japan.

Address of Correspondence:
Dr. Takafumi Hosokawa,
Department of Orthopaedics Surgery, Tone Chuo Hospital, 910-1, Numasu-machi, Numata, Gunma, 378-0012, Japan.
E-mail: thosokawa310@gmail.com


Abstract

Introduction: Recently, distal radius fracture (DRF) has been treated with internal fixation using volar locking plates and several reports describing patients with a flexor carpi radialis brevis (FCRB) appeared. However, no studies have so far investigated the location of the FCRB relative to the volar locking plate.
Case Report: We herein report three cases of DRF with an FCRB. Two patients had a bilateral FCRB, and an FCRB was detected in 5 of 174 limbs (2.9%). In all cases, the FCRB had a muscle belly and was retracted to the radial side and volar plate fixation was performed without difficulty. The pronator quadratus (PQ) under the FCRB was thin. In one case, the PQ was hypoplastic and restoration was impossible. The distance from the plate to the FCRB and that from the plate to the flexor pollicis longus (FPL) tendon were examined postoperatively using ultrasound. In the case in which the PQ could not be restored, the FPL tendon was located close to the plate and the FCRB was in contact with the plate.
Conclusion: As volar locking plate fixation of a DRF with an FCRB and a hypoplastic PQ may cause the restoration of the PQ impossible, the operation should be performed more carefully and follow-up is necessary to avoid post-operative FPL tendon injury and FCRB tendinopathy due to friction with the plate.
Keywords: Flexor carpi radialis brevis, distal radius fracture, ultrasound, hypoplastic pronator quadratus.


Introduction
Recently, distal radius fracture (DRF) has been treated with internal fixation using a volar locking plate. The opportunities to expand the volar side of the forearm are increasing, and several reports about flexor carpi radialis brevis (FCRB) have appeared. These reports often describe the pronator quadratus (PQ) as hypoplastic[1, 2, 3]. However, there are few reports on the covering condition of the plate, and there have been no reports on ultrasound examination after volar locking plate fixation of DRF in patients with an FCRB. We herein report three cases of DRF in patients with an FCRB; operation views and ultrasound findings.

Case Report
Between 2011 and 2017, 168 patients (171 limbs) with DRF were surgically treated. Three of these patients were found to have an FCRB. They had no previous problems with their affected wrist. The operation was performed with a trans-flexor carpi radialis (FCR) approach. The fracture was reduced, and volar plate fixation was performed. We investigated the following points: (1)The operation views and(2) the post-operative ultrasound examination of the distal radius, the shortest distance from the plate to the dorsal border of the FCRB, and the shortest distance from the plate to the dorsal border of the flexor pollicis longus (FPL) tendon. In the ultrasound examination, we used an L4-12r-RS6 system (GE Healthcare, Japan); the examination was performed with the patient in supine position, with their forearm supinated, and their wrist and fingers in a neutral position.

Results
The results of the examinations are shown in Table 1. In all cases, the operation was performed with a trans-FCR approach (Fig.1). The FCR sheath was released and the FCR tendon was retracted to the ulnar side and the gliding floor was cut open. This would usually reveal the FPL and PQ. However, in these cases, an anomalous muscle belly appeared which was thought to be an FCRB. The FCRB had a tendon portion and a muscle belly, running radiodorsal from the FCR, radial from the FPL, and volar from the PQ. The PQ was thin under the FCRB, and in Case 3, the PQ was hypoplastic. The FCRB was retracted to the radial side and the PQ was cut at the center of the radius. Volar plate fixation was performed as planned without difficulty. In Cases 1 and 2, the PQ and the intermediate fibrous zone (IFZ) were restored and the floor of the FPL was reconstructed. However, in Case 3, the PQ was hypoplastic and restoration was impossible. At 3months after operation, the FPL tendon was close to the plate (0.05 mm) and the FCRB was observed to be in contact with the plate on ultrasound (Fig.2). In Cases 1 and 3, an FCRB was also observed on the unaffected side on ultrasound. As the FPL was likely to rupture in Case 3, removal of the plate was performed at 9months after operation although there was no pain or no crepitation. The floor of the FPL tendon had been covered by membranous tissue, and the FPL tendon was not injured. The plate was removed easily. The FCRB looked intact, but the part of the FCRB in contact with the plate looked degenerative and excised to examine histologically. Histologic examination showed tendon and striated muscle with degeneration (fibrosis) and atrophic change.

Discussion
In this report, FCRB was observed in 2.9% of 174 limbs (5/174 limbs, 3/168 patients); this prevalence was similar to the previous reports (Table 2)[3, 4, 5, 6, 7, 8, 9, 10]. Cases 1 and 3 had bilateral FCRBs, while Case 2 had a unilateral FCRB. In the first cadaveric study of the FCRB, which was reported by Fano, in 1851, the FCRB was described as a “radiocarpien”since then, there have been other reports based on cadaver studies [4, 5, 6]. The first reports on the FCRB in vivo appeared after 2000, while the first reports related to surgery for DRF in patients with an FCRB were published after 2010 [1, 3, 7, 8, 9, 11, 12]. The reported prevalence was 0.9–8.7% and cases were unilateral or bilateral. In our three cases, the FCRB had a muscle belly. Traction of the FCRB caused no wrist motion and it may be useless to wrist flexion, as was noted by Ho and Yeo [8]. The PQ under the FCRB was thin, and in Case 3, it was hypoplastic. In the previous reports, an FCRB has muscle bellytype and tendon type, and a hypoplastic PQ with an FCRB has been reported, similarly to our Case 3 [1, 2, 3]. We examined the location of FCRB, FPL tendon, and plate after operation. In Case 3, the PQ could not be restored, the FPL tendon was close to the plate (0.05 mm) and the FCRB was in contact with the plate. To avoid flexor tendons injury, Orbay and Touhami advocated the restoration of the PQ and the IFZ [13]. However, there are few reports on the coverage of the volar locking plate by the PQ in a patient with an FCRB. Nagata et al. reported five cases in which the PQ could be restored after volar locking plate fixation [3]. In Cases 1 and 2, because the PQ– although thin –was repaired, friction between the FPL tendon or the FCRB and the plate would likely have been mild. However, in Case 3, the plate could not be covered by the hypoplastic PQ. Thus, the distance from the plate to the FPL tendon was very short (0.05 mm), and the FCRB was in contact with the plate. FPL tendon rupture might occur in the future. Thus, we removed the plate. On the other hand, the muscle belly-type FCRB was full of muscle belly and there was little gliding at the wrist; thus, the probability of a tear due to friction may be lower in comparison to the FPL. Smith and Kakar reported the ultrasound findings in a case in which a patient experienced an FCR tear and FCRB tendinopathy after lifting a heavy file at work [12]. Kordahi et al. reported the case of a patient with radial side wrist pain with a partial FCRB tear [14]. Nagata et al. histologically confirmed FCRB tenosynovitis, based on the examination of tissue specimens that were excised when they removed the plate of a patient with the left wrist pain when actively flexing [3]. However, these reported tendinopathies occurred in patients with a tendon-type FCRB. In cases involving a muscle belly-type FCRB, like our cases, the FCRB might occupy the palmar space of the radius and the PQ might be hypoplastic, as Dodds and Nagata et al. described [2, 3]; then, the restoration of the PQ might be impossible. In such cases, restoration of the PQ is more important to prevent friction between the FPL tendon and the plate. Suturing the hypoplastic PQ and the FCRB to avoid FPL tendon rupture may be valid; however, we did not employ this approach.

Conclusion
DRF patients with a muscle belly-type FCRB and a hypoplastic PQ should be carefully followed after internal fixation with a volar locking plate because the covering of the plate by the PQ might be impossible.

Clinical Message
The patient with an FCRB may have a hypoplastic PQ. When DRF with an FCRB was treated using volar locking plate, the covering of the plate by the PQ might be impossible. Covering the plate is important but difficult, follow-up is necessary to avoid the FPL rupture.

References
1. Kang L, Carter T, Wolfe SW. The flexor carpi radialis brevis muscle: An anomalous flexor of the wrist and hand. A case report. J Hand Surg Am 2006;31:1511-3.
2. Dodds SD. A flexor carpi radialis brevis muscle with an anomalous origin on the distal radius. J Hand Surg Am 2006;31:1507-10.
3. Nagata J, Kojima Y, Satomura K, Ishiko T, Ajiki T. Anatomic variations of flexor carpi radialis brevis: A report of five cases. J Hand Surg Asian Pac Vol 2016;21:113-5.
4. Carlton A. Flexor carpi radialis brevis vel profundus. J Anat 1935;69:292-31.
5. Nakahashi T, Izumi R. Anomalous interconnection between flexor and extensor carpi radialis brevis tendons. Anat Rec 1987;218:94-7.
6. Yoshida Y, Yasutaka S, Seki Y. Studies on the flexor carpi radialis profundus and palmarisprofundus muscles in man. Acta Anat Nippon 1983;58:59-67.
7. Mantovani G, Lino W, Fukushima WY, Cho AB, Aita MA. Anomalous presentation on flexor carpi radialis brevis: A report of six cases. J Hand Surg Eur Vol 2010;35:234-5.
8. Ho SY, Yeo CJ. The flexor carpi radialis brevis muscle an anomaly in forearm musculature: A review article. Hand Surg 2011;16:245-9.
9. Lee YM, Song SW, Sur YJ, Ahn CY. Flexor carpi radialis brevis: An unusual muscle of the wrist. Clin Orthop Surg 2014;6:361-4.
10. Mimura T, Uchiyama S, Hayashi M, Uemura K, Moriya H, Kato H. Flexor carpi radialis brevis muscle: A case report and its prevalence in patients with carpal tunnel syndrome. J Orthop Sci 2017;22:1026-30.
11. Chong SJ, Al-Ani S, Pinto C, Peat B. Bilateral flexor carpi radialis brevis and unilateral flexor carpi ulnaris brevis muscle: Case report. J Hand Surg Am 2009;34:1868-71.
12. Smith J, Kakar S. Combined flexor carpi radialis tear and flexor carpi radialis brevis tendinopathy identified by ultrasound: A case report. PM R 2014;6:956-9.
13. Orbay JL, Touhami A. Current concepts in volar fixed-angle fixation of unstable distal radius fractures. Clin Orthop Relat Res 2006;445:58-67.
14. Kordahi AM, Sarrel KL, Shah SB, Chang EY. Flexor carpi radialis brevis: Case report of a symptomatic tear. Skeletal Radiol 2018;47:1705-8.


Dr. Takafumi Hosokawa   Dr. Morimichi Suto  Dr. Tsuyoshi Tajika Dr. Hirotaka Chikuda 

How to Cite This Article: Hosokawa T, Suto M, Tajika T, Chikuda H. Volar Locking Plate Fixation of Distal Radius Fracture with a Flexor Carpi Radialis Brevis and a Hypoplastic Pronator Quadratus. Journal of Orthopaedic Case Reports 2019 May-June; 9(3): 11-14.

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