A sunken knuckle is a noticeable depression where the normal prominence of a knuckle should be, typically visible when the hand is formed into a fist. This condition is generally the result of a previous injury, most often a fracture of one of the metacarpal bones. The aesthetic change is a primary concern, often accompanied by functional limitations in hand movement and grip strength. Addressing a sunken knuckle requires a precise understanding of the underlying skeletal issue and a targeted treatment approach to restore the hand’s contour and mechanical function.
Identifying the Underlying Cause
The hand’s structure consists of five metacarpal bones, which connect the wrist to the finger joints. A sunken knuckle arises when one of these bones fractures and heals in an improper alignment, a complication known as malunion. This malunion typically involves angulation and shortening of the bone.
When a metacarpal bone breaks, the fragments often collapse, causing the head of the bone to tilt toward the palm (apex dorsal angulation). This angulation shortens the bone, pulling the metacarpophalangeal joint backward and downward. The knuckle, the prominent head of the metacarpal, appears sunken because it no longer aligns with adjacent knuckles when the hand is flexed.
Diagnosis begins with a physical examination to assess finger alignment, looking for rotational deformity or scissoring when the patient makes a fist. Imaging studies then quantify the extent of the malunion. Standard X-rays provide detailed views of the angulation and shortening, while a Computed Tomography (CT) scan may be necessary in complex cases to evaluate rotation or joint surface involvement. These precise measurements dictate the appropriate path forward.
Non-Surgical Management Strategies
Non-surgical treatment rarely provides a cosmetic fix for a sunken knuckle resulting from a healed malunion. Since the bone has solidified in its shortened or angled position, external manipulation cannot lengthen or straighten the bone. Therefore, non-operative approaches focus entirely on maximizing the functional capacity of the hand despite the permanent skeletal deformity.
Physical and occupational therapy are the cornerstones of non-surgical management, aiming to address stiffness, improve range of motion, and increase grip strength. Specialized hand exercises target the movement of the metacarpophalangeal (MCP) joint and the flexor and extensor tendons. Dynamic splinting may also be employed to gently stretch contracted soft tissues and prevent further stiffness.
The decision to pursue non-surgical management is based on the severity of the functional limitation. Many malunions, especially in the ring and little fingers, are surprisingly well-tolerated functionally. Non-operative treatment is preferred when the functional impairment is minor and the patient accepts the permanent cosmetic change.
Surgical Reconstruction Options
Surgical intervention is the definitive method for correcting a sunken knuckle, as it physically realigns and restores the normal length of the metacarpal bone. The procedure is a corrective osteotomy, which involves precisely cutting the healed, deformed bone to re-establish proper alignment at the original fracture site.
The specific technique depends on the deformity. A closing wedge osteotomy corrects angulation, while an opening wedge osteotomy is necessary to regain lost bone length. For significant shortening, the opening wedge creates a gap filled with a bone graft, often taken from the patient (autograft), to restore metacarpal length and the knuckle’s correct height.
The corrected bone fragments are held rigidly in place using internal fixation, typically small metal plates and screws. Rigid fixation is paramount because it provides the stability required for the bone to heal and permits earlier movement of the adjacent joints, minimizing the risk of post-operative stiffness.
Recovery and Functional Restoration
The post-operative phase following a corrective metacarpal osteotomy focuses on bone healing and functional recovery. Immediately after surgery, the hand is typically immobilized in a splint or cast for two to six weeks, depending on the fixation method and bone graft used. During this time, careful attention is paid to controlling swelling and managing pain.
Once the internal fixation is stable, hand therapy begins. Physical and occupational therapists work to combat stiffness, which can quickly limit function after hand surgery. Therapy involves a progressive regimen of active and passive range-of-motion exercises to restore full finger and wrist movement.
The primary goals of rehabilitation are to regain the ability to form a composite fist and restore grip strength. Patients can expect to continue therapy for several months, with a gradual return to normal activities. In some cases, the internal hardware may be removed in a second, minor procedure if it causes irritation or limits tendon glide after the bone is completely healed.