Radioulnar synostosis, the bony or fibrous bridging of the radius and ulna, presents a complex challenge in orthopedic surgery. This congenital or acquired condition eliminates the normal rotation of the forearm, leading to significant functional impairment and often a visibly abnormal forearm contour. Management requires a nuanced approach, balancing the potential for improved motion against the risks of instability and neurovascular compromise. The primary goal of treatment is to restore a functional arc of pronation and supination, alleviate pain, and prevent progressive deformity, particularly in the setting of progressive synostosis or post-traumatic bridges.
Indications for Surgical Intervention
Not every case of radioulnar synostosis demands surgical correction. The decision to proceed to operation is primarily driven by symptomatology and functional limitation. Indications generally include progressive restriction of forearm rotation that impedes activities of daily living, such as difficulty turning a doorknob, using a keyboard, or performing overhead tasks. Pain, whether originating from the synostosis itself or from secondary overuse of adjacent joints, is another strong indicator. Cosmetic concerns, particularly in progressive cases where the forearm appears markedly bowed or rotated, also warrant consideration for intervention, especially in younger patients where psychological and social development may be impacted.
Preoperative Assessment and Planning
Comprehensive preoperative evaluation is critical to surgical success and hinges on a meticulous assessment of the contracture. The surgeon must quantify the arc of motion, documenting the degrees of pronation and supination lost, and identify the level and characteristics of the synostosis. Imaging is paramount, with high-resolution CT scans providing a three-dimensional roadmap of the bony bridge, its location (proximal, middle, or distal third), and its relationship to the radiocapitellar joint. Dynamic fluoroscopy can help assess the integrity of the remaining joints. Planning must also anticipate the type of osteotomy—shortening, lengthening, or rotation—and the necessary soft tissue releases, with the ultimate aim of achieving a stable, well-aligned limb with a functional arc of motion.
Surgical Techniques and Osteotomy Strategies
Approach and Exposure
Surgical exposure typically follows a posterolateral incision, which provides optimal visualization of the synostosis while minimizing injury to the posterior interosseous nerve (PIN). The interval between the extensor carpi ulnaris and the flexor carpi ulnaris is developed, and the synostotic segment is carefully identified. Meticulous protection of the PIN is paramount, as its traction or retraction during bone work can lead to transient or permanent wrist and finger drop.
Osteotomy and Correction
The core of the procedure involves the osteotomy of the synostotic bridge. The technique is highly individualized. A shortening osteotomy is often preferred, especially in unilateral cases, as it avoids the biomechanical complexities of bone grafting and the risk of nonunion associated with lengthening. The bone is cut in a controlled manner, often with a rotational component to correct the deformity and maximize the arc of supination and pronation. In select cases, particularly in bilateral or progressive synostosis in growing children, a lengthening procedure using an external fixator or internal instrumentation may be necessary to equalize limb length, though this carries a higher risk of complications like pin tract infection and nonunion.
Soft Tissue Management and Stabilization
Simply cutting the bone is insufficient; the biological and mechanical environment must be optimized for healing. The interosseous membrane, if present and viable, is preserved as a biological spacer to prevent re-synostosis. In cases of significant shortening or when the bridge is extensive, an autogenous bone graft, often harvested from the iliac crest, may be placed to fill the defect and provide structural support. Crucially, the forearm is stabilized, typically with a single, well-positioned intramedullary rod spanning the radius and sometimes the ulna. This rigid internal fixation provides immediate stability, allows for early mobilization, and is a cornerstone of modern protocols, reducing the reliance on cumbersome external fixation.
