Date Published: September 14, 2011
Publisher: SAGE-Hindawi Access to Research
Author(s): Charla R. Fischer, Peter Tang.
Extensor tendon injuries are widely believed to be straightforward problems that are relatively simple to manage. However, these injuries can be complex and demand a thorough understanding of anatomy to achieve the best functional outcomes. When lacerations occur in the forearm as in Zones VIII and IX injury, the repair of the extensor tendon and muscle, and posterior interosseous nerve (PIN) is often challenging. A review of the literature shows little guidance and attention for these injuries. We present four patients with injuries to Zones VIII and IX as well as a review of surgical technique, postoperative rehabilitation, and pearls that may be of benefit to those managing these injuries.
There is a prevailing assumption that extensor tendon injuries are not difficult to manage because they all have good outcomes [1, 2]. This may be due to the fact that extension in the hand is not essential to normal function and small losses in extension are easily compensated due to redundancy built into the extensor tendon system . Additionally, it may be due to the superficial location of these tendons making them more accessible than flexor tendons [3, 4]. This assumption may also explain the paucity in the literature on the long-term outcomes following extensor tendon repair , and on how to manage extensor tendon injuries especially in Zones VIII and IX (as classified by Verdan) . We have recently treated four of these injuries: three due to assault with a machete and one due to a fall on broken glass. The machete injury is similar to the “nightstick” fracture injury as it is natural reflex is to protect one’s face/head with one’s forearm during an attack. The purpose of this study is to highlight that extensor tendon injuries in Zones VIII and IX are challenging due to the proximity of the musculotendinous junction, and injury to the posterior interosseous nerve (PIN). We provide a surgical technique for treating these patients.
This is a retrospective chart review of four patients who presented to our institution between July 6, 2008 and June 9, 2009 with injuries to Zones VIII and XI. Zone VIII is defined as proximal to the extensor retinaculum synovial sheaths of the extensor tendons at the wrist and includes the distal one fourth of the forearm. Zone XI is defined as the proximal three fourths of the forearm . Three patients were assaulted with a machete and one fell on broken glass. These patients all underwent primary operative repair by the senior surgeon (PT). Three patients had posterior interosseous nerve lacerations in addition to multiple extensor tendon lacerations. After our institutional review board approved this study, these patients gave informed consent to participate in the study. All four cases are illustrated below. Patient results were evaluated according to Dargan’s  method: excellent, no flexion or extension lag; good, no flexion lag, extension lag of 15 degrees or less; fair, pulp to palm distance of 2 cm or less, extension lag 15 to 45 degrees; and poor, pulp to palm distance more than 2 cm, extension lag more than 45 degrees. We did not perform statistical analysis. Furthermore, a cadaveric dissection was done to illustrate anatomy.
Extensor tendon injuries are assumed to be simple to manage because they all have good outcomes [1, 2], and often the least experienced surgeon handles these injuries in less than ideal settings . This may explain the paucity in literature about Zone VIII and IX extensor tendon injuries which we would contend is a significant injury and is the focus of this paper. In terms of the anatomy, the dorsal forearm has a superficial and deep layer of muscles. Listing the muscles from radial to ulnar, the superficial layer consists of the ECRL, ECRB, EDC, EDM, and ECU. Again from radial to ulnar, the deep layer consists of the APL, EPB, EPL, and EIP. The PIN enters the dorsal forearm compartment by splitting the two heads of the supinator and emerging from under the Arcade of Frohse. It then travels between the superficial and deep muscle layers giving innervation to these muscles.