Intra-articular Fractures at the Base of the First Metacarpal

21 Intra-articular Fractures at the Base of the First Metacarpal

Yuka Igeta, Sybille Facca, Philippe A. Liverneaux

Abstract

Intra-articular fractures at the base of the first metacarpal are frequent and their consequences can affect the opposition of the thumb. They usually occur after trauma in compression along the axis of the thumb in flexion. Restoring the anatomy and biomechanics of the trapeziometacarpal joint is essential when treating these injuries, hence why surgical treatment is usually indicated. We distinguish small-fragment and large-fragment Bennett’s fractures, articular three-fragment Rolando’s and comminutive fractures of the base of the first metacarpal. All carry the risk of narrowing of the first web. Recent studies have described poor results with conservative treatment. Surgical techniques are varied: percutaneous surgery, open surgery, and arthroscopic surgery. The techniques of osteosynthesis are various: locking plates, and direct or indirect screw fixation or pinning. The prognosis depends on the quality of the restoration of the mobility of the trapeziometacarpal joint.

Keywords: first metacarpal, fracture, Bennett, Rolando

21.1 Trauma Mechanism

Intra-articular fractures at the base of the first metacarpal generally occur after trauma by compression along the axis of the thumb in flexion. It is estimated to occur in 4% of hand fractures.1

21.2 Classification

Intra-articular fractures can be divided into Bennett’s fractures, Rolando’s fractures, and comminuted fractures 2,3 ( Fig. 21.1).

Described by Edward H. Bennett in 1882,⁴ fracture dislocation of the base of the thumb metacarpal is remarkable for its frequency and the extensive literature on its description and treatment.⁵ They are similar to the pure trapeziometacarpal dislocations. They differ by the presence of a distinct separate fracture of a variable size. The smallest fragment comprises the anteromedial corner of the base of the thumb metacarpal, and stays in place ( Fig. 21.1), attached to the trapezium, because of the attachment of the oblique posteromedial ligament. The largest fragment of the bulk of the thumb metacarpal undergoes a double movement, first a dorsoradial trapeziometacarpal subluxation, under the effect of abductor pollicis longus and then adduction, narrowing the first web, under the effect of the medial thenar muscles. Depending on the size of the small anteromedial fragment, there are two types of Bennett’s fractures according to Gedda: the ones with a large-fracture fragment (type I), and the others with a small-fracture fragment (type II).⁶

Rolando’s fractures differ from Bennett’s fractures by direction, number, and displacement of the fracture lines ( Fig. 21.1). An extra-articular fracture line, generally transverse, separates diaphysis and epiphysis. A second vertical intra-articular fracture line splits the epiphysis into two fragments. A central joint depression is often present. Each of these fragments undergoes a specific displacement. The large distal diaphyseal fragment is pulled in adduction, thus closing the first web under the effect of medial thenar muscles. The lateral epiphyseal fragment is drawn upward and outward, under the effect of the long abductor of the thumb. The medial epiphyseal fragment remains in place, attached to the trapezium, because of the oblique posteromedial ligament.

Fig. 21.1 (a–c) Classification of the fractures of the base of the first metacarpal. Above fracture lines: Bennett (B), Rolando (R), comminuted (C). The little red line represents the oblique posteromedial ligament. Below displacements under the effect of the abductor pollicis longus (black arrow), and internal thenar muscles (green arrow).

Comminuted fractures can be regarded as Rolando’s fractures, of which they represent the worse stage ( Fig. 21.1).

21.3 Clinical Signs and Tests

The actions of the adductor pollicis and abductor pollicis longus tend to tilt the distal fragment causing adduction (varus) and shortening (dorsal subdislocation) of the first web.3,7

21.4 Investigatory Examinations

The diagnosis is confirmed by standard posteroanterior (PA) or lateral radiographs. Further information can be obtained with computed tomography (CT) scans, 3D reconstructions, or by a series of six radiographic projections 8 ( Fig. 21.2).

21.5 Possible Concurrent Lesions of Bone and Soft Tissue

None.

21.6 Evidence

Treatment remains controversial. Although historical reports have noted satisfactory results with conservative treatments until the 1980s,9 recent studies have described poor results with closed reduction and casting alone for fractures of the base of the thumb metacarpal.^10–12 Most acute injuries of intra-articular fractures at the base of the first metacarpal are unstable and have similar risks of major complications if treated nonoperatively particularly narrowing of the first web.^13,14 Many osteosynthesis techniques have been described, including percutaneous pinning,¹⁵ open screw fixation,¹⁶ locking plates,^17,18 or arthroscopic techniques.¹⁹

Surgical indications depend on the size of the anteromedial fragment. For most authors, Bennett’s fractures with large fragment and Rolando’s fractures are usually treated by open reduction and internal fixation.²⁰ A step-off of greater than 1 mm increases the risk of post-traumatic arthrosis.¹⁰ Leclere et al¹⁶ reported their long-term results of treating 21 Bennett’s fractures with large fragment by open screw osteosyntheses. After 4 years, the overall strength of the hand was 89% of that of the contralateral side, but one patient had a secondary subluxation 9 weeks after surgery. Lutz et al²¹ reported results at a mean of 7 years comparing open screw fixation to percutaneous transarticular pinning in 32 Bennett’s fractures with large fragments. Although the percutaneous pinning group had a significantly higher incidence of adducted thumb deformities, the type of treatment did not influence the final clinical outcome nor the prevalence of posttraumatic radiological arthrosis. Postoperatively, a removable commissural splint is usually necessary for about 4 weeks, allowing early mobilization if the strength of the fixation permits it. We have developed a technique of percutaneous screw fixation under arthroscopy.¹⁹

If, the anteromedial fragment is too small to be fixed directly, reduction by external manipulation and percutaneous pinning is recommended by most authors.²⁰ Authors who recommend percutaneous pinning suggest various sites for the wires either through the trapezometacarpal joint^22,23 or extra-articular through the intermetacarpal spacing.²⁴ Intra-articular pins can cause further damage to the articular surface. Some authors have reported their results at a mean of 18 months after transarticular percutaneous pinning. Although the average strength was 80% of that of the contralateral side and the opposition of the thumb was complete in all patients, 16 of 21 patients presented at last follow with a thinning of the trapeziometacarpal joint indicating posttraumatic arthrosis.²⁵ The Iselin technique can also lead to complications. For example, if the distal pin protrudes from the dorsum of the second intermetacarpal space, it can cause irritation of the extensor apparatus of the index finger. In a series of 25 patients operated for fractures of the base of the first metacarpal with a mean follow-up of 24 months, there were three infections along the pin tracks and one notable cosmetic abnormality.¹⁵

21.7 Authors’ Favored Treatment Option

After manual closed reduction (axial traction on the thumb and pressure on the first metacarpal base), two 18-mm K-wires are used to maintain maximal first web opening ( Fig. 21.3, Fig. 21.4). The proximal K-wire is placed so that it runs obliquely distally and medially, crossing the two cortices of the base of the first metacarpal and only the first cortex of the second metacarpal, sparing the second cortex as described by Iselin in his original technique²⁴ ( Fig. 21.2). For Bennett’s fractures, the proximal pin is distal to the fracture fragment. The distal K-wire, unlike in the original technique, is made to cross obliquely proximally and medially, first the two cortices of the head of the first metacarpal then the first cortex of the second metacarpal without breaching the second. Good position of the two pins is checked by fluoroscopy. Unlike the original technique, both pins are externalized 1 to 2 cm beyond the skin, bent at 90 degrees, and fixed together externally by a connector (HK2, Arex, Palaiseau, France), resembling an external fixator. The pins are then spread apart or brought closer together according to the required opening of the first web. The connector is then locked by pressure using specialized pliers (Manotte, Arex, Palaiseau, France). After locking, the two pins are cut at the connector level to prevent crowding of the system.

Fig. 21.2 Radiological projections of the trapezometacarpal according to Kapandji. The arrow represents the direction of ionizing radiation. (a) Three radiographs from the front (A = static, B = dynamic flexion, C = dynamic extension). (b) Three radiographs from the profile (D = static, E = dynamic retroposition, F = dynamic anteposition).

A simple dressing is placed at pin exit and immediate mobilization is encouraged without force. The patient was reviewed in 1 week, then at 2- week intervals with radiographical evaluation for secondary displacement. K-wires were removed in clinic 6 weeks postoperatively and force grip was allowed at 8 weeks.