72 Scaphoid Nonunion
72.1 Patient History Leading to the Specific Problem
A 17-year-old adolescent boy presents with complaints of wrist pain and limited wrist function. He has had mild wrist pain ever since he fell on his outstretched hand 3 months ago while playing football, for which he did not seek medical care. The pain was aggravated after falling on the same wrist, while flexed, a month ago. The pain is generalized and increases with wrist movement, especially extension.
72.2 Anatomic Description of the Patient’s Current Status
On examination, the patient was nontender around the wrist, but he had a limited range of motion especially in extension with a maximum of 10 degrees. Plain radiographs revealed a scaphoid waist fracture with displacement and bone resorption around the fracture site, and a sclerotic proximal pole in the anteroposterior (AP) view (▶Fig. 72.1a). In the lateral view, the scaphoid showed a humpback deformity and the lunate was in a mildly extended position, a condition known as dorsal intercalated segment instability (DISI) deformity (▶Fig. 72.1b). CT of the wrist demonstrated an ununited scaphoid waist fracture with marked resorption and cystic changes at the fracture site and a humpback deformity (▶Fig. 72.1c–e). There were no signs of wrist or carpal arthritis. MRI demonstrated changes suggesting early avascular necrosis (AVN) of the proximal pole of the scaphoid (▶Fig. 72.1f).
72.2.1 Anatomic Etiology of Complication
Blood supply to the scaphoid is critical and is predominantly retrograde. Seventy to 80% of the blood supply to the scaphoid including the proximal pole is from branches of the radial artery entering distally through the dorsal ridge (▶Fig. 72.2). A fracture may disrupt this pattern of blood supply and eventually lead to AVN of the proximal pole and could contribute to the development of fracture nonunion. Other factors that have been related to the development of a scaphoid nonunion are fracture displacement more than 1 mm, delay in treatment more than 4 weeks, and tobacco use.
72.3 Recommended Solution to the Problem
Early diagnosis and treatment of a scaphoid fractures is the primary means of preventing the development of a scaphoid nonunion. Many scaphoid fractures can be minimally symptomatic, as in our patient’s case. Minimal discomfort may delay the diagnosis of an acute fracture. Additionally, many scaphoid fractures may not be seen on the initial AP and lateral radiograph, leading to an inappropriate diagnosis of a wrist sprain. While the diagnosis of acute scaphoid fractures is beyond the scope of this chapter, it should be emphasized that acute radial-sided wrist pain, and specifically snuff box tenderness following trauma, warrants close monitoring to rule out the presence of an occult scaphoid fracture.
Primary treatment of scaphoid fractures includes casting and open reduction and internal fixation. Open reduction and fixation is usually reserved for cases where the fracture is displaced or involves the proximal pole. Casting is most appropriate for nondisplaced fractures. Various options exist to manage a scaphoid fracture that proceeds to nonunion including fixation and bone grafting techniques; however, if the nonunion is associated with AVN, collapse, and carpal instability (as evident by a humpback deformity or DISI), it is more difficult to treat. In the case of our patient, structural support is needed to restore scaphoid height and correct midcarpal instability, and a bone graft with a vascular supply is needed to overcome the difficult healing environment associated with AVN. Without adequate treatment, the scaphoid will fail to unite and carpal collapse will progress, leading to a predictable pattern of arthritis know as scaphoid nonunion advanced collapse (SNAC) arthritis.
Vascularized bone grafts are a good treatment choice for scaphoid nonunions where the proximal pole’s vascularity is compromised and have a well-established track record within the literature. Vascularized bone grafts allow for primary and accelerated bone healing. Vascularized grafts can be pedicled grafts harvested locally from nearby bones such as the distal radius, the first metacarpal, or free flaps that require microsurgical anastomosis at the recipient site. The free vascularized medial femoral condyle (MFC) graft has been shown to be effective in providing structural support in the setting of carpal instability and is capable of restoring scaphoid geometry and carpal alignment. It is associated with minimal donor site morbidity and possesses bone density that is similar to that of the scaphoid. The MFC has shown reliable results of achieving scaphoid union and has a shorter average healing time than other forms of bone grafting.
72.3.1 Recommended Solution to the Problem
• The MRI and CT suggest evidence of nonunion with probably AVN of the proximal pole. In addition, there is scaphoid collapse and midcarpal instability. All these risk factors support the use of a free vascularized bone graft. Our preference is to use the MFC graft due to its ease of harvest, minimal donor site morbidity, and length of vascular pedicle.
• To restore scaphoid anatomy, a vascularized volar wedge graft is required to correct the humpback deformity.
Fig. 72.1 (a) Anteroposterior view of the wrist showing a scaphoid nonunion, with cyst formation and bony resorption. (b) Lateral radiograph of the wrist showing a humpback deformity and loss of intrascaphoid angle. (c) CT image of the wrist showing cystic osteolysis at the fracture site and increased density of the proximal pole. This can be suggestive of avascular necrosis. (d) Lateral image from CT showing dorsal osteophyte on distal portion of scaphoid with collapse of scaphoid. (e) Lateral image from CT showing lunate in extended posture, suggesting dorsal intercalated segment instability. (f) MRI of the wrist. MRI shows clear line of demarcation between proximal and distal poles. This finding may be suggestive of avascular necrosis of the proximal pole.