19 Avulsion Fractures of the Flexor and Extensor Tendons Abstract Except for the mallet fractures, avulsion fractures of the tendons are rare injuries. Unlike flexor digitorum profundus (FDP) avulsion injuries where most surgeons agree on the need for intervention, the indications and nature of intervention in mallet fractures can generate lively discussion. Much academic energy has gone into defining the role of fracture size to joint subluxation, but this chapter will remind us that these two issues are related not causal. Even the surgeon who believes strongly that most of these can be treated nonoperatively will eventually encounter a case where the volar subluxation needs to be addressed to correct the normal joint kinematics of rolling and not hingeing. Keywords: mallet injury, mallet fracture, jersey finger, flexor digitorum profundus avulsion The typical mallet injury with a small fragment or no fragment is caused by forced flexion of the fingertip against resisted extension. This can be in domestic accidents or on the sport field. Axial load in extension causes a larger fragment dorsally and the likelihood of volar subluxation of the joint. This will be described later. There is much confusion related to the concept of a fracture of the dorsal aspect of the terminal phalanx. The literature continues to wrestle with the issues of the size of the fragment, the displacement, and whether there is volar subluxation of the joint. Doyle’s classification of mallet finger injuries ( Recent literature has tried to identify a specific percentage of joint surface involvement that will be a predictable cause of volar subluxation2,3 and this figure seems to hover around the 43 to 52% mark. Kim and Kim3 also suggest that a delay to extension splinting and therefor ongoing unresisted FDP activity is a major cause of volar subluxation. Table 19.1 Doyle’s classification of mallet finger injuries
19.1 Extensor Avulsion Fractures
19.1.1 Mallet Fractures
Trauma Mechanism
Classification
Table 19.1) separates the 4B from 4C on the size of the fragment as it relates to the articular surface, but does not mention the volar subluxation of the joint.1
Type | Description |
1 | Closed injury with or without small avulsion fracture |
2 | Open injury (laceration) |
3 | Open injury (deep abrasion involving skin and tendon substance) |
4 | Mallet fracture |
| A: Distal phalanx physeal injury (pediatric) |
| B: Fracture fragment involving 20–50% of articular surface |
| C: Fracture fragment involving > 50% of articular surface |
An unfortunately forgotten paper going back to 1983 gives us the answer to this issue.4 A forced flexion against resisted extension force, the classic mallet mechanism, such as catching a ball, will result in a true avulsion fracture that by definition will be small and not result in volar subluxation.
If the force strikes the finger as an axial load in slight extension, the fracture produced is by shear, not avulsion, and will be a large fragment by definition. Langer and Engber called this the hyperextension mallet. This volar shear moment is what causes the volar subluxation. The mechanism of injury dictates the size of the fragment and whether there is volar subluxation or not. These two are associated not causal. The truth is that most patients cannot recall exactly what position the finger was in at the time of force and what direction the force was applied. To reiterate, the size of the fragment is not the cause of whether there is volar subluxation or not (
Fig. 19.1 and 
Table 19.2).
Indications for surgery have also been much debated over time. Fractures involving more than 30% were considered indications for intervention. Marked displacement of the dorsal fracture, and therefore the potential for delayed or nonunion, is considered by some as an indication for surgery, but this remains a very subjective decision. What is agreed by most surgeons is that this joint does have an incredible ability to remodel over time and that long-term arthrosis is rarely a problem unless there has been volar subluxation. While not universally accepted, many hand surgeons would consider volar subluxation an indication for intervention.
Clinical Signs, Tests, and Investigations
The typical posture of a mallet finger is an extensor lag at the distal interphalangeal joint (DIPJ). It usually takes a few months to develop a fixed flexion deformity.
Table 19.2 Our proposed classification and treatment options
Type | Description | Treatment |
1 | Closed injury | Extension splint |
2 | Open injury (laceration) | Repair and K-wire |
3 | Open injury (deep abrasion involving skin and tendon substance) | Soft tissue reconstruction and K-wire |
4 | Mallet fracture |
|
| A: Distal phalanx physeal injury (pediatric) | Might need surgery if nail bed incarcerated In physis (Seymour’s lesion) |
| B: Typical flexion mallet with fracture and no joint subluxation | Mallet splint unless markedly displaced and risk of nonunion |
| C: Extension type mallet with large fracture and joint subluxation | Needs surgery |
Any bruising or dorsal tenderness is suspicious of a fracture and an X-ray should be taken. It is important to request a true lateral centered on the DIPJ and the condyles of the head of the middle phalanx should be superimposed and seen as one.
Evidence
A 2004 Cochrane Database review by Handoll and Vaghela5 suggested there was insufficient evidence to determine when surgery is indicated. Most authors agree that splinting is indicated for all nonbony mallets as well as fracture mallets without joint subluxation. There is no trial looking at only volar subluxed mallet fractures randomized into splintage versus surgery.
Treatment Options
How to correct the volar subluxation and reattach the bone fragment is also a matter of much debate. There have been numerous intervention techniques offered. Widely used is the extension blocking K-wire concept. This involves flexing the joint and passing a K-wire proximal to the dorsal fragment to block its dorsal and proximal movement. The joint is then extended to reduce the fracture and a second retrograde wire is passed to immobilize the DIPJ (
Fig. 19.2).6
Fig. 19.2 (a-c) Ishiguro technique.
There are two issues with this technique. The first is that the dorsal wire passes through an exceptionally thin soft tissue envelope and is essentially intra-articular. Any wire sepsis has a real risk of a destructive septic arthritis of the DIPJ. The second issue is that because this is a hyperextension injury, any extension of the joint at the end of the procedure is likely to exacerbate the volar subluxation, which is the indication for surgery in the first place. The surgeon has to take great care not just to extend the terminal phalanx but to translate dorsally as well before placing the retrograde wire.
If the fragment is large enough, then direct open reduction internal fixation (ORIF) can be used, but beware of fracturing the already tiny fragment. Usually, 1- or 1.3-mm screws are used. Tension band suturing or wire has been used by Jupiter and Damron.7,8
Pullout sutures tied over a button and gauze on the volar aspect of the pulp, all inside techniques,9,10 and even external fixation has been attempted. All techniques risk wound breakdown, nail deformity, arthrosis, and stiffness.
Author’s Preferred Technique
Indications
• Any fracture with volar joint subluxation.
• Significantly displaced dorsal fragment that does not reduce on extension splinting (irrespective of size). The author acknowledges that deciding on which fracture gaps are at increased risk of delayed or nonunion is a very subjective decision.
Surgical Strategy
• If the size of the fragment is deemed large enough to accept a 1-mm screw without risking fragmentation, then this is preferred (rare).
• For most mallet fractures, we do a transosseous suture technique.
Surgical Technique
The surgical procedure is performed either under general anesthetic or regional anesthetic (Bier’s block).
The patient lies supine with the arm placed outstretched on a hand operating table. A bloodless field is created with the use of a tourniquet. A dorsal Y-shaped (Mercedes Benz) incision is utilized (
Fig. 19.3). Full-thickness skin flaps are elevated with careful protection of the germinal matrix.
At this stage, care needs to be taken to elevate the fracture from distal to proximal. Obviously, it would be a catastrophic surgical error to attempt to create a dissection plane between the fracture and the extensor tendon. The fracture is carefully elevated from the fracture bed and reflected proximally. The fractured terminal phalanx can be seen sitting in a volar subluxed position. Careful curettage of the fracture bed should remove most of the hematoma and/or early soft callus. Usually, the terminal phalanx can be reduced from the volar subluxed position, but in the case of a substantial delay, it might be necessary to perform a limited release of the collateral ligaments.
At this stage, the very small fragment is held with an Adson forceps. A 23-gauge needle is then chosen as a drilling device. The hub needs to be removed and the needle placed into a wire driver. Two holes are drilled parallel starting from the raw fracture surface of the fragment and exiting on the dorsal base at the insertion of the extensor tendon (
Fig. 19.4).
