Principles of Deformity Correction and Corrective Osteotomies.

Deformity correction is the systematic restoration of abnormal skeletal alignment while preserving limb function, joint orientation, length, rotation and soft-tissue balance. Successful correction requires considerably more than simply straightening a visibly angulated bone.

A deformity may exist in the coronal, sagittal or axial plane, may involve translation or shortening, and may occur at one or multiple levels. The fundamental principles of deformity correction therefore involve defining the deformity accurately, locating its apex, determining the desired correction and selecting an osteotomy that produces the correction without creating a new deformity.

The central concept in deformity correction is the CORA – Centre of Rotation of Angulation.

Not every radiographic deformity requires surgery. The clinical importance of a deformity depends on its magnitude, location, associated symptoms, effect on adjacent joints and potential for progression.

• Abnormal mechanical loading of adjacent joints.
• Pain during weight bearing or activity.
• Progressive joint degeneration.
• Altered gait or limb function.
• Joint instability.
• Restriction of movement.
• Leg-length discrepancy.
• Rotational malalignment.
• Cosmetic deformity.
• Difficulty with future arthroplasty or reconstructive surgery.

Treatment should therefore be directed toward the functional consequences of the deformity rather than the radiograph alone.

Complex deformities frequently contain several of these components simultaneously.

Coronal Plane

Coronal plane deformities are evaluated on AP radiographs and generally produce varus or valgus alignment abnormalities.

Sagittal Plane

Sagittal deformities are evaluated on lateral radiographs and may produce procurvatum or recurvatum.

Axial Plane

Axial deformities produce internal or external rotational malalignment. They may be difficult to quantify using conventional radiographs and are often evaluated clinically or with CT when precise measurement is required.

• Varus: distal segment is directed toward the midline.
• Valgus: distal segment is directed away from the midline.
• Procurvatum: apex of deformity is directed anteriorly.
• Recurvatum: apex of deformity is directed posteriorly.

Deformities should preferably be described systematically by the direction of angulation, magnitude, level and associated translation, rotation or shortening.

Deformity analysis begins with the patient rather than the radiograph. Clinical examination is essential because rotational deformity, soft-tissue contracture and functional compensation may not be adequately demonstrated on standard radiographs.

• Observe standing alignment.
• Assess gait.
• Determine whether the deformity is unilateral or bilateral.
• Assess hip, knee and ankle range of motion.
• Look for joint contractures.
• Assess rotational profile.
• Measure true and apparent limb length.
• Evaluate ligamentous stability.
• Assess neurovascular status.
• Look for scars, previous incisions and soft-tissue compromise.

Lower-limb deformity analysis commonly requires a properly positioned, weight-bearing full-length AP radiograph that includes the hip, knee and ankle.

Additional imaging may include:

• Lateral long-leg radiograph.
• Dedicated joint radiographs.
• CT rotational profile.
• CT for complex multiplanar deformity.
• Three-dimensional reconstruction for selected cases.

Poor positioning can create an apparent angular deformity. Rotation during radiography can significantly alter measured alignment.

Mechanical Axis

The mechanical axis represents the functional load-bearing axis of a bone or limb.

For the femur, the mechanical axis extends approximately from the centre of the femoral head to the centre of the knee.

For the tibia, the mechanical axis extends approximately from the centre of the knee to the centre of the ankle.

Anatomical Axis

The anatomical axis follows the longitudinal axis of the diaphysis.

The femoral anatomical and mechanical axes are different because of the offset of the femoral head from the shaft. In the tibia, the anatomical and mechanical axes are much more closely aligned.

Mechanical axis deviation describes displacement of the weight-bearing axis of the lower limb relative to the knee.

• A medially shifted mechanical axis is generally associated with varus alignment.
• A laterally shifted mechanical axis is generally associated with valgus alignment.

The magnitude and clinical importance of mechanical axis deviation must be interpreted together with joint orientation, symptoms and the location of the deformity.

Joint orientation lines describe the inclination of an articular surface relative to the mechanical or anatomical axis of the adjacent bone.

Frequently used lower-limb measurements include:

Joint orientation angles help determine whether a deformity arises from the femur, tibia or both and whether it is primarily metaphyseal or diaphyseal.

The Centre of Rotation of Angulation (CORA) is the point at which the proximal and distal reference axes of an angular deformity intersect.

The CORA identifies the approximate apex and level of the angular deformity and is one of the fundamental concepts in osteotomy planning.

When the osteotomy and correction are performed at the CORA, pure angular correction can occur without producing secondary translation.

1. Identify the proximal segment of the deformity.
2. Draw its appropriate anatomical or mechanical axis.
3. Identify the distal segment.
4. Draw its corresponding axis.
5. Extend both lines until they intersect.
6. The intersection represents the CORA for a simple uniapical angular deformity.

The angle between these axes represents the magnitude of angular correction required in that plane.

These principles explain why an osteotomy performed away from the true apex of deformity may require deliberate translation to restore both proximal and distal axes.

The axis around which an angular correction occurs is referred to as the Axis of Correction of Angulation (ACA).

In a simple two-dimensional correction, rotation of one bone segment around the correction axis changes the angular relationship between the proximal and distal segments.

The position and orientation of the correction axis become particularly important in multiplanar deformity correction.

Uniapical Deformity

A uniapical deformity has a single principal apex. The proximal and distal axes intersect at a single CORA.

Multiapical Deformity

A multiapical deformity contains deformity at more than one level. Attempting to correct the entire deformity with a single osteotomy may create substantial translation or an abnormal bone shape.

Such deformities may require multiple osteotomies or more complex three-dimensional planning.

An osteotomy is a controlled surgical division of bone performed to alter alignment, length, rotation or joint orientation.

The osteotomy is only one component of deformity correction. Successful reconstruction requires appropriate planning, correction, fixation and management of the surrounding soft tissues.

In a closing-wedge osteotomy, a wedge of bone is removed and the remaining surfaces are brought together to achieve angular correction.

Advantages

• Large area of direct bone contact.
• Usually inherently stable after closure.
• Predictable angular correction.
• Often does not require structural grafting.

Disadvantages

• Shortens the bone.
• Requires accurate wedge resection.
• Correction is less easily adjusted after the wedge has been removed.
• May produce unwanted translation depending on osteotomy location.

In an opening-wedge osteotomy, the bone is partially or completely divided and the osteotomy is gradually opened until the desired correction is obtained.

Advantages

• Fine intraoperative adjustment of correction.
• Avoids removal of a bone wedge.
• Can preserve or increase length.

Disadvantages

• Creates an osseous gap.
• May require bone graft or bone substitute depending on gap and location.
• May place soft tissues under tension.
• Loss of correction can occur if fixation is inadequate.

Many opening- and closing-wedge osteotomies preserve a cortical hinge on the side opposite the osteotomy opening or closing.

An intact hinge:

• Provides additional stability.
• Helps control the correction.
• Maintains some biological continuity.
• Reduces uncontrolled translation.

Hinge fracture is an important complication of wedge osteotomy and may reduce construct stability.

A dome osteotomy uses a curved bone cut. The distal segment rotates along the curved osteotomy surface to achieve correction.

Advantages

• Large bone contact area.
• Minimal shortening or lengthening.
• Angular correction can occur without removing a large wedge.
• Useful for selected metaphyseal deformities.

Limitations

• More technically demanding.
• Requires accurate planning.
• Fixation may be technically more complex.

An oblique osteotomy creates a long inclined bone surface. Rotation or sliding along the osteotomy can produce angular, rotational and sometimes length correction.

The large surface area may favour union, but the geometry of correction must be carefully planned because translation and length changes may accompany rotation.

A transverse osteotomy is particularly useful when the principal correction required is rotation or translation.

Because a transverse osteotomy has limited inherent rotational stability, stable fixation is essential.

Derotational osteotomy is performed when abnormal femoral or tibial torsion produces clinically significant rotational malalignment.

The bone is divided and one segment is rotated relative to the other by a predetermined amount. Rotational correction should be planned using reliable clinical and, where necessary, CT-based measurements.

Intraoperative reference markers or pins can be placed before osteotomy to quantify the amount of rotation achieved.

Translation is not necessarily an error. When an osteotomy is performed away from the CORA, intentional translation may be required to restore the proximal and distal mechanical axes.

Angulation at a level different from the CORA requires translation if the original axes are to be restored correctly.

Limb-length discrepancy should therefore be considered before selecting an osteotomy. A closing wedge may be undesirable in an already shortened limb.

Acute Correction

Acute correction is performed during a single operation and the corrected bone is immediately stabilised using internal or external fixation.

Advantages:

• Immediate restoration of alignment.
• Shorter correction period.
• Can be combined with plate or intramedullary fixation.

Limitations:

• Soft tissues must tolerate the immediate correction.
• Large corrections may threaten neurovascular structures.
• Complex multiplanar correction may be technically difficult.

Gradual Correction

Gradual correction uses an external fixation system to progressively alter alignment over time. This allows bone and surrounding soft tissues to adapt to the correction.

Circular and hexapod external fixation systems can be used for gradual correction of complex deformities.

These systems may simultaneously address:

• Angulation.
• Translation.
• Rotation.
• Shortening.

Gradual correction is particularly valuable when the deformity is severe, multiplanar or associated with major limb-length discrepancy.

Distraction osteogenesis is the formation of new bone between gradually separated viable bone surfaces following a controlled corticotomy or osteotomy.

The classical process contains several phases:

1. Osteotomy/corticotomy: controlled division of bone.
2. Latency phase: initial biological response before distraction begins.
3. Distraction phase: gradual separation stimulates regenerate formation.
4. Consolidation phase: regenerate progressively mineralises and matures.
5. Remodelling phase: new bone adapts to mechanical loading.

The Ilizarov method demonstrated that controlled gradual mechanical distraction can stimulate the formation of new bone and adaptive changes in surrounding soft tissues.

Important concepts include:

• Stable fixation.
• Low-energy bone division with preservation of biology.
• Appropriate latency.
• Gradual controlled distraction.
• Functional loading where appropriate.
• Preservation of blood supply.

A commonly taught starting distraction rate for limb lengthening is approximately 1 mm per day divided into several increments, but the rate and rhythm must be adjusted according to patient age, bone, regenerate quality and clinical circumstances.

Angular deformity and limb-length discrepancy should be analysed independently even when they coexist.

A patient may require:

• Angular correction alone.
• Lengthening alone.
• Angular correction combined with lengthening.
• Correction of angulation, translation and rotation simultaneously.

The correction strategy should address every clinically important component without introducing an unnecessary secondary deformity.

High tibial osteotomy demonstrates how deformity correction can redistribute load across a joint. In appropriately selected patients with symptomatic medial compartment knee overload associated with varus alignment, correction can shift the mechanical axis laterally and reduce medial compartment loading.

Techniques include:

• Medial opening-wedge high tibial osteotomy.
• Lateral closing-wedge high tibial osteotomy.

Correction should be based on the location of deformity and desired postoperative mechanical alignment rather than performing an osteotomy simply because varus is present.

Distal femoral osteotomy is commonly used when a clinically significant coronal deformity originates primarily from the distal femur.

A classic application is correction of valgus malalignment associated with lateral compartment overload in an appropriately selected patient.

Performing a tibial osteotomy for a deformity that actually originates from the femur may produce an abnormal joint-line orientation despite apparent correction of the overall mechanical axis.

Correct the deformity at the bone and level from which it originates whenever reasonably possible.

Restoration of the overall mechanical axis does not automatically mean that the deformity has been corrected appropriately.

An osteotomy performed at the wrong level may restore the hip-knee-ankle relationship while creating excessive obliquity of the knee or ankle joint line.

Deformity planning should therefore consider both:

• Overall limb mechanical alignment.
• Individual joint orientation angles.

When a deformity arises from both the femur and tibia, correcting the entire mechanical axis at only one bone may produce excessive joint-line obliquity.

In selected severe or complex deformities, a double-level osteotomy allows the correction to be distributed between the femur and tibia while maintaining more physiological joint orientation.

Fixation must maintain the planned correction until sufficient biological healing has occurred. Choice of fixation depends on the osteotomy, bone involved, patient factors and whether correction is acute or gradual.

• Conventional plates.
• Locking plates.
• Intramedullary nails.
• K-wires in selected paediatric osteotomies.
• Monolateral external fixation.
• Circular external fixation.
• Hexapod frames.

The fixation strategy should provide adequate mechanical stability while respecting the biology of the osteotomy.

Osteotomy healing follows the same broad biological principles as fracture healing. Preservation of periosteal and endosteal blood supply improves the environment for union.

Important principles include:

• Atraumatic soft-tissue handling.
• Avoidance of unnecessary periosteal stripping.
• Low-energy osteotomy technique where appropriate.
• Stable fixation.
• Preservation of a viable cortical hinge when intended.
• Appropriate grafting when a substantial defect requires biological support.

Acute correction changes not only bone alignment but also the length and course of nerves, vessels, muscles and fascia.

Excessive acute correction may cause:

• Nerve stretch injury.
• Vascular compromise.
• Compartment syndrome.
• Soft-tissue contracture or excessive tension.

Severe corrections may therefore be safer when performed gradually.

• Under-correction.
• Overcorrection.
• Loss of correction.
• Unintended translation.
• Unintended rotational deformity.
• Joint-line obliquity.
• Delayed union.
• Nonunion.
• Hinge fracture.
• Implant failure.
• Infection.
• Neurovascular injury.
• Compartment syndrome.
• Joint stiffness.
• Hardware irritation.
• Recurrent deformity.

1. Define the clinical problem. Determine why the deformity requires correction.
2. Obtain appropriate imaging. Use properly positioned full-length and orthogonal radiographs.
3. Draw the mechanical and anatomical axes.
4. Assess joint orientation. Determine which bone and which segment is abnormal.
5. Identify the CORA.
6. Determine the magnitude and direction of correction.
7. Assess rotation and limb length separately.
8. Choose the osteotomy level. Ideally correct near the origin/apex of the deformity when feasible.
9. Select the osteotomy type. Opening wedge, closing wedge, dome, transverse, oblique or another planned geometry.
10. Predict translation and length change.
11. Choose acute or gradual correction.
12. Plan fixation and postoperative rehabilitation.

• CORA = Centre of Rotation of Angulation.
• The CORA is located at the intersection of the proximal and distal reference axes in a simple uniapical angular deformity.
• An osteotomy performed at the CORA can correct angulation without requiring secondary translation.
• If the osteotomy is performed away from the CORA, translation may be required in addition to angulation.
• Deformity must be analysed in the coronal, sagittal and axial planes.
• Varus and valgus are principally coronal plane descriptions.
• Procurvatum and recurvatum describe sagittal plane deformity.
• Rotational deformity may require clinical assessment and CT for accurate quantification.
• Closing-wedge osteotomy generally causes shortening.
• Opening-wedge osteotomy creates a gap and can preserve or increase length.
• Dome osteotomy allows angular correction with relatively little alteration in length.
• Preserving the cortical hinge improves stability in many wedge osteotomies.
• Mechanical axis correction alone is insufficient if abnormal joint-line orientation is created.
• Deformity should be corrected at the bone and level from which it originates whenever feasible.
• Multiapical deformity may require more than one osteotomy.
• Gradual correction is useful for severe multiplanar deformity and deformity associated with substantial shortening.
• Distraction osteogenesis permits simultaneous correction of deformity and limb length.
• The goal is not simply a straight X-ray – it is restoration of functional mechanical alignment, joint orientation, rotation and length.

1. Start with the patient: identify symptoms, functional impairment, gait, rotation, limb length and joint motion.
2. Define the deformity: angulation, translation, rotation and shortening.
3. Identify its plane: coronal, sagittal, axial or multiplanar.
4. Determine its origin: femur, tibia or both; metaphyseal, diaphyseal or multiapical.
5. Identify the CORA: locate the true apex of angular deformity.
6. Plan the correction: calculate the magnitude and direction of correction and determine whether translation is required.
7. Select the osteotomy: opening wedge, closing wedge, dome, oblique, transverse or multiplanar.
8. Consider length and rotation: a straight limb may still be functionally abnormal if these components remain uncorrected.
9. Preserve biology: minimise soft-tissue stripping and protect the vascularity of the osteotomy.
10. Protect the correction: choose fixation capable of maintaining alignment until union.
11. Evaluate the final limb as a whole: mechanical axis, joint orientation, rotation, length and clinical function must all be considered.

Deformity correction is not simply the correction of an angle. The objective is restoration of the mechanical axis, joint orientation, rotation and limb length while preserving bone biology and soft-tissue function.