Cubitus Varus and Gunstock Deformity
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Direct answer
Cubitus varus, the gunstock deformity, is a varus malalignment of the elbow in which the forearm angles inwards when the joint is straightened. It most often results from a malunited supracondylar humeral fracture in which the distal fragment was displaced medially and posteriorly. The Baumann angle, measured on an anteroposterior radiograph, is the standard tool for assessing it, and a French lateral closing wedge osteotomy is a common correction.
What you must remember
- Deformity: varus angulation at the elbow, which gives a gunstock appearance when the arm is straightened.
- Commonest cause: a malunited supracondylar fracture of the humerus, usually after inadequate reduction of medial displacement.
- Baumann angle: formed by the line along the lateral condylar physis and a line perpendicular to the humeral shaft; the normal range is roughly 9 to 26 degrees (mean about 15 to 20). In the older convention that uses the shaft axis itself, the normal is about 64 to 81 degrees and the angle is larger in varus.
- Comparison: the Baumann angle is always compared with the opposite elbow, since, with the perpendicular-to-shaft convention, a value smaller than the normal side indicates varus.
- Problems: a cosmetic deformity, with restricted motion, occasional lateral elbow instability and, rarely, pain.
- French osteotomy: a lateral closing wedge osteotomy of the distal humerus that removes the excess varus through a lateral approach.
- Timing: correction is planned once the deformity is established and the surgeon has assessed the remaining growth.
From a bent elbow to a planned osteotomy
A 9-year-old child has an elbow deformity six months after a supracondylar fracture treated by closed reduction, with a visible inward angle of the forearm and a normal radial pulse. The task is to measure the deformity, then decide whether it matters functionally and cosmetically.
- Assess the carrying angle clinically: compare both elbows with the arms extended and the palms forward, noting the amount of varus and any change with rotation.
- Measure the Baumann angle: on a true anteroposterior radiograph, draw the humeral shaft axis (and its perpendicular) and the lateral condylar physeal line, and compare the result with the opposite elbow.
- Check nerves and range of motion: test ulnar and radial nerve function and elbow movement, since the malunion may coexist with other problems.
- Decide on the indication: correction is considered for cosmetic concern, functional loss or instability, whereas a mild varus with full function may need no surgery.
- Plan the French osteotomy: a lateral closing wedge osteotomy removes the excess varus, and the fixation is chosen to hold the corrected alignment until union.
- Follow up the result: repeat radiographs check union and the Baumann angle, and clinical review confirms that elbow movement is preserved as the child grows.
Viva angles on the Baumann angle
Examiners test whether you can recognise a malunion, measure it and choose when to correct it.
- Trap: attributing the deformity to a congenital or growth disorder. Correct: a history of supracondylar fracture with medial displacement points to malunion, and the Baumann angle confirms the varus.
- Trap: operating on every varus elbow. Correct: a mild varus with full function is often accepted, so surgery is reserved for cosmetic concern, functional loss or instability.
- Trap: relying on the clinical carrying angle alone. Correct: the clinical angle changes with arm position and rotation, so the Baumann angle on a true anteroposterior view is the reliable measure.
Frequently asked questions
What causes cubitus varus after a childhood elbow injury?
Cubitus varus most often follows a supracondylar humeral fracture that healed with medial displacement or posterior tilt of the distal fragment. Inadequate reduction at the time of injury is the main reason the deformity develops, and it becomes visible during growth.
What is the Baumann angle used for in cubitus varus?
The Baumann angle measures the alignment of the distal humerus on an anteroposterior radiograph, using the humeral shaft and the lateral condylar physeal line. With the perpendicular-to-shaft convention (normal roughly 9 to 26 degrees), a value below that of the opposite elbow indicates varus; with the older shaft-axis convention (normal about 64 to 81 degrees) the value rises in varus, so state the convention used.
What is a French lateral closing wedge osteotomy?
A French lateral closing wedge osteotomy is a corrective operation on the distal humerus that removes a wedge of bone from the lateral side to close the varus angle. It is performed through a lateral approach and is held with fixation until the bone heals.
When is surgery indicated for cubitus varus?
Surgery is considered when cubitus varus causes cosmetic concern, loss of function or lateral elbow instability. A mild deformity with full movement and no symptoms is often managed without an operation, and the decision is taken after assessment of remaining growth.
How does cubitus varus differ from cubitus valgus?
Cubitus varus is an inward angulation of the forearm, most often from a malunited supracondylar fracture, while cubitus valgus is an outward angulation, often after lateral condyle injury. Tardy ulnar nerve palsy is the classic complication of valgus deformity.