Management of Complications in Carpal Fractures (Malunion, Nonunion)

8 Management of Complications in Carpal Fractures (Malunion, Nonunion)

Lampert M.D. Hohenstein A, and Max Haerle

Abstract

Fractures of the carpal bones differ substantially in incidence. Apart from the scaphoid, they can frequently be treated conservatively with good results. Relevant concomitant soft tissue injuries are rare. Although scaphoid fracture is the most common fracture of the carpal bones, its treatment is still burdened with various unresolved difficulties and risks in the course of treatment. An overview of the most common complications is given in this chapter, with specific emphasis on scaphoid nonunion. Different treatment options are discussed, along with their indications and limitations, and a treatment algorithm is suggested.

Keywords: carpal fracture, scaphoid fracture, malunion, nonunion, humpback deformity, bone graft, osteosynthesis

8.1 Introduction

Fracture of the carpal bones can occur as a principle in any carpal bone. The frequency with which they occur is illustrated in Fig. 8‑1. Besides the scaphoid, the triquetrum is most affected, but rarely presents a source of complication. Most times in carpal bones, conservative treatment is sufficient and complications are rare. This is true for most fractures besides the scaphoid, unless they occur in a feature of massive trauma of the wrist, which is difficult to be analyzed in a statically reproducible way. Uncommon fractures of the wrist, which may be a recurrent source of complications, are the fractures of the hook of the hamate and the pisiform fractures.

Fig. 8.1 Relative incidence of carpal bone fractures.

In the treatment of scaphoid fractures, many pitfalls lurk along the path during the whole course from the initial injury to the—at best—restitutio ad integrum. In particular, a delayed or absent bony union occurs in approximately 10% of all fractures.¹ Risk factors for scaphoid nonunion are: location of fracture (proximal third), fracture displacement, carpal instability, time to treatment, heavy labor, and smoking.²^,³ The long-term consequence of an untreated scaphoid nonunion could be severe osteoarthritis and pain in the vast majority of cases (75–100%) after 10 years,⁴^,⁵ which occurs in the typical pattern of a scaphoid nonunion advanced collapse (SNAC-Wrist).⁵

A number of frequent main problems in the treatment of scaphoid fractures can be identified⁶:

●The patient trivializes the injury and does not turn to a doctor.

●The doctor does not initiate adequate imaging diagnostics.

●The fracture is not detected in imaging diagnostics.

●The grade of dislocation or instability of a detected fracture is not adequately assessed.

●Despite a correct diagnosis, no adequate therapy is initiated.

●Despite an adequate indication, therapy is not carried out correctly.

●Despite state-of-the-art diagnostics and therapy, the fracture does not heal due to anatomical peculiarities of the scaphoid or secondary factors.

8.2 Uncommon Carpal Fractures

Hook of hamate and pisiform fractures are by far less frequent than fractures of the scaphoid. Fractures of the hamate and pisiform occur as isolated injuries, in many cases on direct impact of a club or bat in athletes or tool handles or grips in workers. Both fracture types have in common a considerable risk of being missed on clinical examination and standard plain radiographs with the consequence of the development of complications. Most common are painful nonunions, as well as irritation or injury to the deep or superficial branch of the ulnar nerve from either direct impact or pressure from hematoma or edema. Furthermore, hook of hamate fractures can lead to flexor digitorum profundus (FDP) tendinopathy or even rupture. Both fracture types usually present with tenderness over the hypothenar eminence. On clinical suspicion, a radiograph with carpal tunnel or special pisiform projection should be acquired; in case of doubt, a computed tomography reliably visualizes the fracture.

In the absence of dislocation, these fractures are commonly treated conservatively; in cases of dislocated fractures, minimally invasive placement of cannulated screws can be considered. In cases of nonunion after unsuccessful conservative treatment or for undiagnosed as well as comminuted fractures, excision of the respective bone commonly leads to good results without relevant functional impairments.7^,⁸

8.3 Scaphoid Fractures

8.3.1 (Patho-)Physiology of Fracture Healing in the Scaphoid

Approximately 80% of the scaphoid is covered with cartilage; therefore, secondary (i.e., periosteal) bone healing with formation of callus does not take place in a significant manner. Being the major mechanical link between the proximal and the distal row of carpal bones, the scaphoid is exposed to severe shearing and bending forces especially on its distal part, thus creating repeated interfragmentary motion in case of a fracture, with a tendency to collapse into a dorsally angulated “humpback deformity.”

The major blood supply to the scaphoid is from the radial artery, whose branches enter the nonarticular portion of the scaphoid at the dorsal ridge at the level of the waist or distal part and supply the proximal 70 to 80% of the bone. The volar scaphoid branches from the radial artery and its superficial palmar branch supply the distal 20 to 30% of the scaphoid. Both the volar and the dorsal branches reach the scaphoid on more distal level; therefore, the vascularity of the proximal pole predominantly depends on retrograde intraosseous blood flow, which poses a high risk for avascular necrosis.⁹

Taking this into account, it becomes evident that the factors’ stability and blood supply are alternately dependent on each other. Neither will a sufficient neovascularization be likely to cross an unstable fracture site, nor will poorly vascularized bone fragments be likely to unite. Although both factors are crucial for successful fracture treatment, in the clinical setting, direct bone contact and rigid stability are absolute conditions but there is no evidence for the principle “the more—the better” concerning the compression forces of different devices.¹⁰^,¹¹ Too much compressive strain might rather impair intraosseous blood flow and increase the risk for hardware complications.

8.3.2 Complications in Fracture Healing

Unavoidable Complications

Due to its particular geometry, the local biomechanical strain, and its tenuous vascular pattern, fractures of the scaphoid are prone to complications during any kind of therapy. Even in state-of-the-art operative treatment with correct placement of implant, nonunion may occur in up to 10% of scaphoids.¹ Conservative treatment of nondisplaced scaphoid fractures is accompanied with similar nonunion rates as the operative therapy, but the latter have a faster return to work and less time spent in a cast, traded in for the risks of the operative procedure.¹² Considering the location, proximal pole fractures are more likely to develop complications.³ Primary fracture dislocation >1 mm is another major risk factor for complications.

Sources of Complications

Failed Primary Nonsurgical Treatment

Although there is a trend toward a more aggressive indication for an operative therapy using minimally invasive screw fixation of undisplaced scaphoid fractures classified A1/A2 according to Herbert/Krimmer, operative therapy is still not proven to yield superior long-term results in comparison to conservative treatment. Nevertheless, it enables an earlier return to activity (work/sport) in the predominantly young and active population suffering from scaphoid fractures.¹² If immobilization is started duly, conservative therapy provides an equivalent end result.¹³ Immobilization is carried out in a short arm cast in slight wrist extension, usually with inclusion of the first carpometacarpal joint, although there is no evidence, that this is necessary. Immobilization of the elbow, however, is generally considered obsolete, since it does neither provide superior immobilization nor higher union rates, but is associated with the risk of permanent restrictions of elbow motion. Fractures of the tuberculum (A1) usually heal within 4 weeks, fractures of the waist (A2) within 6 to 8 weeks. Nevertheless, even with correct indication and execution of the conservative therapy, nonunions still occur in 5 to 12% of cases.¹

Malreduction of Fractures

A condition sine qua non for success of the operative treatment of a scaphoid fracture is an anatomical reposition. It is generally accepted that computed tomography is the modality of choice for staging of scaphoid fractures and thus for initiation of an adequate therapy.¹⁴ During the operation, however, the usual imaging modality is fluoroscopy, which has improved the results substantially; nevertheless, it suffers from the limited information content of any two-dimensional imaging technique and a relatively poor spatial resolution. Failure to recognize and address displacement or associated carpal lesions can be a predisposition for pseudarthrosis, axial (e.g., “humpback”), or rotational deviations.

Malpositioning of Implants

Proper intraosseous placement of the screw is crucial for successful treatment of scaphoid fractures. For maximal biomechanical stability, and thus increase in the likelihood of bone union, screws should be placed in the central axis of the scaphoid in scaphoid waist fractures. In cases of small proximal pole fragments or oblique fractures, screw placement perpendicular to the fracture line may be necessary and also provides sufficient stability. The dorsal approach is more prone to technical errors and associated with the risk of impairing blood supply to the scaphoid⁹ and affecting the cartilage as well as the scapholunate ligament. Choosing the maximal possible screw length does not seem to provide superior stability. Due to its curvature in two planes, screw placement is technically demanding and misplacements still occur even in experienced hands despite the routine use of fluoroscopic control (Fig. 8‑2). To overcome this problem, intraoperative 3D-imaging and even robot-assisted screw placement have been suggested in pilot studies.

Fig. 8.2 (a, b) Malpositioning of headless screw.

Failure of Bone Healing

As stated above, osteosynthesis in the scaphoid has to create equilibrium between the competing demands of providing rigid stability to the fracture without compromising the precarious intraosseous blood supply. Therefore, both mechanically insufficient and overaggressive placements of implants are inappropriate. Yet, exact definition of complication rates according to single implants is difficult to impossible.

8.3.3 Surgical Interventions for Complication in the Healing Process

Malunion

The first goal of the treatment in scaphoid fractures is to achieve bone union. However, it has been shown that malunions of the scaphoid, namely the so-called “humpback deformity,” result in pain and restriction in the range of motion and are prone to the development of posttraumatic osteoarthritis. The option of a correction osteotomy should therefore be taken into consideration in cases of malunion. Nevertheless, correction osteotomy is a complex invasive procedure, and its results are not necessarily superior to conservative therapy; therefore, the benefits and risks have to be discussed thoroughly with the patient. In asymptomatic cases, restraint is called in most instances. Technically, in cases of torsion or a lateral offset, osteotomy is performed in the former fracture site, followed by open reposition under fluoroscopic control and (re-)osteosynthesis, usually using a volar approach. In the most common deformity, the “humpback,” the Linscheid maneuver is often helpful for reposition and correction of the dorsal intercalated segment instability (DISI) deformity, which will then result in a wedge-shaped palmar defect due to the initial bone resorption. In these cases, a bone graft in size and shape of the defect is compulsory, with the usual harvesting site being the iliac crest. Osteosynthesis is performed with cannulated screws, plates, or K-wires in most instances. Options for salvage procedures are dorsal cheilectomy, radial styloidectomy, or other methods, which can also be applied in cases of SNAC-wrist, such as four-corner fusion, proximal-row carpectomy, or d-enervation of the wrist.15

Nonunion

A much more frequent complication is the formation of a nonunion subsequent to a scaphoid fracture. By definition, a delayed union is considered a pseudarthrosis after 6 months. In the scaphoid, however, the above-mentioned biomechanical and vascular peculiarities often cause an irreversible nonunion as recently as 8 weeks after trauma (Fig. 8‑3). The underlying principle of the multitude of reconstructive options is the transformation of the pseudoarthrotic zone into an “acute-injury” setting, which is then attended with appropriate immobilization and solid blood supply. Depending on the time elapsed since the primary injury, its location, and the extent of the nonunion interface as well as eventual deformities, different operative approaches will apply. Slade and Dodds¹⁶ introduced a classification scheme as a guide for decision-making in treatment (Table 8‑1).