Radioulnar Synostosis

Etiology

The etiology of congenital radioulnar synotosis is unknown. Congenital radioulnar synostosis may be seen in Tetrasomy X or any number of genetic syndromes, including Poland, Cornelia de Lange, Holt-Oram, Crouzon, and Apert syndromes. Radioulnar synotosis may result from SMAD6-deficiency; SMAD6 encodes an intracellular inhibitor of the bone morphogenetic protein (BMP) signaling pathway.[1][2][3] The growing limb bud typically undergoes longitudinal segmentation at approximately 7 weeks of gestation; if this process fails to occur or does so abnormally, a congenital radioulnar synostosis may develop.[4] An autosomal dominant inheritance pattern of radioulnar synostosis has been hypothesized, but no clear cause or definitive inheritance pattern has been proven.[5] 

The posttraumatic variant of radioulnar synostosis may result from any radius, ulna, or olecranon fracture.[6][7][8] There have been case reports of patients who underwent surgical repair of an olecranon fracture or a distal biceps tendon rupture that subsequently developed an osseous synostosis of the proximal radius and ulna.[8][9][10] Fractures involving both the radius and ulna with increased comminution at or near the same level can also increase the risk of developing a radioulnar synostosis.[11] In addition to the characteristics and location of the fracture, the severity of the surrounding soft tissue injury also increases the risk of synostosis development.[12] Disruption of the interosseous membrane during surgical fixation of forearm fractures also increases the risk of synostosis development.[13] A forearm fracture with a concomitant head injury is also a substantial risk factor for reasons that are not well understood.[14] 

Epidemiology

Congenital or syndromic radioulnar synostosis is exceedingly rare; less than 700 cases are reported in the literature.[3] Patients with congenital or syndromic radioulnar synostosis often present as young children with significant functional deficits or difficulties with activities of daily living. However, the diagnosis can be missed or delayed in unilateral cases where motion at the shoulder or wrist can compensate for the rotational deficit caused by the synostosis. Bilateral synostoses may present with asymmetric symptoms and functional deficits.[3] Historically, congenital radioulnar synostosis was thought to be more prevalent in males; the current data does not support a gender predilection.

Posttraumatic radioulnar synostosis is reported in 1.2% to 6.2% of patients sustaining combined radial and ulnar fractures; this incidence is likely underestimated due to incomplete follow-up or asymptomatic synostoses.[15] Posttraumatic radioulnar synostoses are less likely to be asymptomatic than congenital variants; adults are less able to produce compensatory motions than children.[3] 

There is an increased incidence of posttraumatic radioulnar synostosis when the original injury occurs in conjunction with a neurologic or traumatic head injury.[7] Garland et al reported the complications of operative management of combined radial and ulnar fractures in 3 patients with an associated spinal cord injury; all 3 developed posttraumatic radioulnar synostosis.[15] 

History and Physical

While radioulnar synostosis may present at any age, children with congenital radioulnar synostosis present around age 6 years, when tasks or activities of daily living requiring forearm rotation are limited due to an inability to achieve full pronation or supination. Affected children may have difficulty turning door knobs or throwing a ball. However, the anatomical level of the fusion determines which activities are most negatively affected. For example, children with a fixed pronation deformity may have difficulty with tasks requiring supination, such as washing their face, brushing their teeth, eating, or catching a ball. In contrast, children with a fixed supination deformity will have difficulty with tasks requiring pronation, such as typing, writing, or other tabletop activities requiring the palms to face downward. Patients may also demonstrate a block to elbow flexion or extension if the synostosis extends proximally or involves abnormal positioning of the radial head. 

The diagnosis of radioulnar synostosis may be delayed until adolescence if the patient can appropriately compensate for the impaired forearm rotation with shoulder, elbow, or wrist range of motion. For this same reason, the diagnosis may also be missed entirely. There have been reports of adults presenting with a new range of motion deficit with no known previous trauma who were subsequently diagnosed with congenital or idiopathic radioulnar synostosis.[4] However, the initial presentation of congenital radioulnar synostosis in adulthood is exceedingly rare.

Patients with posttraumatic radioulnar synostosis may present in the acute postoperative period or several years later, depending on the extent of their functional deficits. The synostosis development is often noted on routine postoperative imaging obtained to evaluate fracture healing. The extent of the functional limitations secondary to the synostosis may be difficult to ascertain until the fractures have healed and postoperative pain has resolved; both can cause patients to splint their range of motion unknowingly.

If patients with radioulnar synostosis present outside of the acute postoperative period, they may describe sustaining an injury to the elbow, forearm, or wrist requiring surgical intervention. Radial and ulnar fractures treated nonoperatively may develop a progressive loss of range of motion. These patients report painless, limited pronation and supination, causing difficulty with activities of daily living or work-related tasks.

The physical examination of patients with radioulnar synostosis will reveal a decreased or blocked range of motion with active and passive range-of-motion testing. A complete osseous fusion typically presents with a painless block of motion at the forearm, while partial or incomplete osseous fusion may allow for some motion, which may be painful. These findings are seen in congenital and posttraumatic radioulnar synostoses.

Evaluation

After obtaining a comprehensive medical history and performing a thorough physical examination, radiographic images of the elbow, forearm, and wrist should be obtained. (see Image. Radioulnar Synostosis.) Monitoring the progression of posttraumatic radioulnar synostosis is achieved via serial plain radiography; this will help determine the timing of surgical intervention. There is no evidence supporting the utility of laboratory evaluation in diagnosing radioulnar synostosis, and laboratory findings do not serve as prognostic or risk-recurrence indicators.

Several classification systems based on radiographic features have been described for congenital and posttraumatic radioulnar synostosis.

The initial classification system for congenital radioulnar synostosis was the Wilkie classification system; Cleary and Omer have modified this system into the Cleary classification system, which is currently the most widely used system. The Wilkie classification system described 2 types of congenital synostoses. A synostosis at the proximal aspect of the radius and ulna where the radius is longer and larger than the ulna was termed a Type 1 fusion, and a congenital anterior or posterior dislocation of the radial head with a fusion between the radius and ulna just distal to the epiphysis was termed a Type 2 fusion.[3] 

The Cleary classification system further delineates the relationship between the congenital synostosis and the anatomy of the radial head.[5][3] A Type 1 congenital synostosis in the Cleary system is defined as a fibrous synostosis with a reduced radial head; plain radiography of a Type 1 synostosis may reveal no atypical findings. A Type 2 congenital radioulnar synostosis is ossified with a reduced radial head. A Type 3 congenital synostosis is ossified with a posteriorly dislocated and hypoplastic radial head. A Type 4 congenital synostosis is ossified, and the radial head is anteriorly dislocated and may appear “mushroom-shaped.”[5][3]

Posttraumatic radioulnar synostoses are typically classified using the Hastings-Graham classification system; this system is a detailed modification of the Vince classification system initially described in 1987.[16][7] The Hastings-Graham system describes 6 types of radioulnar synostoses based on the anatomical area in which the synostosis occurs. Areas 1, 2, and 3 involve the proximal radius and ulna, Area 4 involves the radial and ulnar shafts, and Types 5 and 6 involve the distal radius and ulna. More specifically, a synostosis in Area 1 involves the ulnohumeral joint, Area 2 involves the proximal radioulnar joint, and Area 3 involves the bicipital tuberosity. A synostosis in Area 5 involves the pronator quadratus insertion, and Area 6 specifically involves the distal radioulnar joint.[17][7]

Imaging modalities other than plain radiography, such as computed tomography (CT) or bone scans, may further delineate the type of radioulnar synostosis and facilitate treatment planning. CT is often used for preoperative planning to define the parameters and location of the synostosis. Bone scans can characterize the maturity of a posttraumatic radioulnar synostosis to optimize the timing of surgical intervention and limit the risk of recurrence. 

Treatment / Management

The management of a radioulnar synostosis may be operative or nonoperative. The nature of the synostosis, its location, the functional deficits experienced by the patient, the positioning of the forearm, and the potential bilaterality of congenital synostoses must all be considered when developing a treatment plan. Congenital radioulnar synostosis is frequently treated conservatively; posttraumatic radioulnar synostosis is more likely to require surgical intervention.[18][7][19][20](B2)

Nonoperative Management of a Radioulnar Synostosis

The nonoperative management of a radioulnar synostosis is recommended if the normal range of motion is preserved or the functional deficits experienced by the patient are limited or minimal. Nonoperative management comprises extensive physical therapy; physical therapy will improve function to varying degrees. Combined therapy with a dedicated hand therapist and an occupational therapist will yield the best results. A fixed pronation deformity is not as well tolerated as fixed supination; tolerance is dictated by the needs or demands of the individual patient.[3] 

Operative Management of a Radioulnar Synostosis

The surgical management of a congenital radioulnar synostosis can either attempt to reposition the arm in a more functional position or mobilize the forearm to allow for an increased range of motion.[3] Typically, “mobilization” procedures comprise resection and interposition grafting, while “repositioning” procedures may include derotational osteotomies.[3][21][22][23] Multiple surgical techniques have been described; functional results vary, and no single technique has proven superior. Some studies have demonstrated success with mobilization procedures employing the resection of the bony synostosis followed by placement of any number of interposition grafts, including fascia lata autograft or allograft, forearm fascia and bone wax, vascularized adipofascial flap, free fat flap, silicon grafts, or anconeus rotational flaps.[8][3][4] (A1)

Derotational procedures comprise osteotomies of the radius and ulna at differing levels. Some derotational procedures are accompanied by internal fixation, and others feature postoperative immobilization with a cast until the osteotomy sites have healed. The modified Kanaya procedure employs a radial shaft osteotomy slightly more distal than the osteotomy originally described near the radial tuberosity. This modification did provide an improved postoperative rotational arc.[24] Most reported bilateral derotational osteotomies involve repositioning each arm at different positions: the nondominant arm in about 0 to 20 degrees of supination and the dominant arm in approximately 30 degrees of pronation.[25][3] One case study paired an isolated radius osteotomy with a pronator teres repair; postoperative functional outcomes were significantly improved.[26] The Ilizarov derotational method has demonstrated good functional results; this method allows for a gradual correction that can be personalized and adjusted to the patient’s movements and provides optimal rotation for activities of daily living.[27][3] Radial head excision has also been described and allowed for significant improvement in elbow flexion in patients with Cleary Type 4 synostosis.[3][28] (B3)

The timing of any surgical intervention is critical in reducing the risk of recurrence, as the synostosis should be allowed to mature before resection.[7][20] The Hasting and Graham classification recommended procedural interventions for each type of radioulnar synostosis; Area 1 synostoses may be treated with elbow arthroplasty, Area 2 synostoses with radial head resection, Areas 3 and 4 synostoses with resection and interposition grafting, Area 5 synostoses with the Suavé-Kapandji procedure, and Area 6 synostoses with a Darrach distal ulnar resection.[17][7] Many procedures that treat posttraumatic synostoses with interposition grafts utilize the same materials used in procedures to treat the congenital variant.[18][7][19][20](B2)

The use of adjuvant therapies to reduce the risk of recurrence of synostosis following surgical management has been reported but is not widely studied. Several case reports report employing a “triple therapy” comprising preoperative radiotherapy on the day of surgery, a surgical procedure, and postoperative indomethacin for 2 weeks with low recurrence rates.[18][19][20](B2)

In all cases of operative management, postoperative physical and occupational therapy with a dedicated hand therapist is imperative to reaching the best functional outcome. 

Differential Diagnosis

The differential diagnosis of radioulnar synostosis includes contracture of the soft tissues, fracture malunion, or a neurologic deficit.

Prognosis

The residual functional deficit determines the prognosis for congenital and posttraumatic radioulnar synostosis. Congenital radioulnar synostosis can be treated conservatively with intensive hand therapy with good functional results. Surgical intervention, whether the goal is repositioning or mobilization, has variable and unpredictable results.[3] The prognosis following the surgical management of posttraumatic radioulnar synostosis is excellent, but the risk for recurrence remains high if the proper surgical technique is not employed.[19][20]

Complications

The surgical management of radioulnar synostosis is usually well-tolerated. Risks associated with surgical intervention include the standard surgical risks of pain, bleeding, infection, and complications of anesthesia, and also:

• Recurrence of synostosis or malrotation
• Neurologic injury
• Compartment syndrome secondary to osteotomy
• Fracture
• Nonunion or malunion
• Soft tissue contracture or stiffness.