Extensor tendon lacerations most commonly occur in men (83%), in the dominant hand (60%), in the thumb and secondly the index finger (Patillo and Rayan 2012). Tendon injuries were found to be caused by a variety of mechanisms in a study done in 2014 that include a knife, saw, crush injury, degloving injury, and bite injury (De Jong 2014). The patient can present in different manners depending on what zone is affected. Zone I can cause a mallet finger deformity where the tip of the finger distal to the DIP cannot extend. Zone II injuries can affect the central slip.
These injuries should be tested with an elson test to check if the central slip is intact. This test is done by flexing the PIP over the edge of a table and checking if the DIP is rigid or soft and if the tip of the finger can extend. Zone V injuries, commonly human bites, can cause a sagittal band injury leading to extensor tendon subluxation (Amirtharajah et. al 2015). Evaluation of a laceration must be extensive. The mechanism of the injury must be understood for contamination and the possibility of a full laceration of the tendon. Each digit and hand bilaterally must be examined.
If the finger with a laceration is rested in flexion, the tendon may be completely severed. If the joint distal to the laceration cannot fully extend, the tendon may be partially lacerated. In order to test thoroughly for complete and partial lacerations, the finger should be tested in flexion and extension and then in extension with resistance. Different tendons are responsible for the extension of different digits. Extensor policis longus and brevis extend the thumb, extensor digitorum extends digits two through five, and extensor digiti minmi extends the fifth digit (Griffin et al. 012).
Generally, if the tendon is more than 50% lacerated and cannot resist extension, then the tendon should be fixed surgically. However, if the tendon can resist extension and is either 50% lacerated it can be splint in extension and surgically fixed at a later time or treated with a splint and undergo therapy. However, injury to a specific zone and certain circumstances can change the criteria for treatment (Milner 2011). Soft tissue and bony involvement should always be evaluated bilaterally at the area and above and below.
Range of motion should be investigated for all of these areas. A good neurovascular exam should take place to test the sensory and motion of the radial, median, ulnar, and digital nerves as well as checking capillary refill (Griffin et al. 2012). For prophylaxis, the use of a Tdap shot and antibiotics should be taken under consideration based on the individual. A Tdap shot should be given if the patient is an adult and has not had one or less than three tetanus toxoid vaccines or if they have had three or more doses, but it has been over 10 years.
Otherwise it is unnecessary to give the patient a Tdap shot if the patient has had three or more doses and it has been less than 10 years (CDC 2015). As for antibiotic prophylaxis, a study done in 2012 found that a two day course of Cephalexin 500mg po qid was as effective as a five day course in a simple contaminated wound or laceration (Ghafouri 2012). For zone II injuries seen in this case, immobilization is adequate for 2-4 weeks if the tendon is 50% lacerated and there is no lag in extension actively or if there is difficulty with resistance in extension.
However, if it is more than 50% lacerated and the finger cannot maintain extension with resistance, the tendon can be repaired by a few different techniques. Treatment can include using a figure-of-eight suture, a tendon graft using palmaris longus, or a local tendon flap where the central tendon is turned over as a bridge to connect the two areas (Amirtharajah et al. 2015). Many of the other zones have specific repair techniques. Zone I can be repaired with full thickness sutures which continue through the tendon and the periosteum.
If it is unstable, the tip of the finger can be pinned in extension for 6-8 weeks (Milner 2011). Zone III injuries may damage the central slip at the area of the PIP. If the lateral bands are still intact, they can be sutured to make a central slip. If they are not, then the FDS can be sutured to reconstruct the central slip (Milner 2011). Zone IV injuries usually require tendon repair through suturing. The different types of suturing techniques include a mattress, figure-of-eight, modified Bunnell, modified Kessler, and modified Becker.
A study done by Newport showed that the Bunnell and Kessler techniques had no gapping and the Bunnell was the strongest compared to the others (Newport 2005). For combined extensor injuries, a staged silicone implant is an option. A silicone rod can be placed in the pretendinous fascia and 3-4 months later exchanged for a palmaris longus tendon graft (Adams 2007). Zone V is usually a human bite injury or “fight bite” and needs to be treated with antibiotics. The recommendation is Augmentin 875/125mg po bid. The degree of laceration of the tendon is usually small and does not need to be repaired.
Zone VI lacerations are very difficult to diagnose the degree of laceration of the tendon because they can retract over the metacarpals. The best suture repair for these types of injuries is a running-interlocking horizontal mattress. Zone VII lacerations must be repaired due to the relationship with the retinaculum and zone VIII lacerations should be repaired at the musculotendinous junction (Milner 2011). Complications that can occur from repair include adhesion formations, tendon rupture, and deformities.
Adhesion formations occurs commonly from zone IV and VII lacerations. It can be prevented by protected range of motion and dynamic splinting. The loss of flexion can be treated by extensor tenolysis. Tendon rupture occurs at an incidence of 5% usually after poor suturing technique or material. It should be repaired early or the tendon can be reconstructed if ruptured late. Other deformities include a swan neck or a boutonniere. A swan neck deformity can occur through prolonged DIP flexion by subluxation of the lateral bands dorsally.
A boutonniere deformity occurs through DIP extension by subluxation of the lateral bands volarly (Milner 2011). Comments: For this case, the unique circumstances influenced and individualized treatment. Options were discussed among physicians since the patient had remained at work for an unknown amount of hours and then went to an urgent care facility where the laceration was sutured closed. There is little research on the infection rate of re-opening wounds in relation to exploration of tendon injuries.
However, it is known that the “golden period” for treatment of an acute wound is 6 hours based on studies of bacterial colonization. An acute wound should be cleaned and repaired before this time (Waseem 2012). It is unclear if the patient made it to the urgent care within a 6 hour period of time, but the bacterial contamination was most likely less at this point in time than at the time of his presentation in the emergency department. The decision to either re-open the wound to explore the tendon or keep the wound closed was made through clinical reasoning.
Residents and attendings decided that the outcome of his strength and testing of his finger was fairly functional and with re-opening the wound the possibility of introducing or re-introducing an infection could be more harmful to the patient. It was also discussed that even if they re-opened the wound, the tendon may not even need to be repaired. With little research in this area, clinical judgement along with the explanation of the circumstances with the patient were key in deciding the best plan of treatment in this situation.