PRINCIPLES AND TECHNIQUES OF OSTEOTOMY
CHARLES D. NEWTON
- Definition and Indications
DEFINITION AND INDICATIONS
Osteotomy is an elective surgical procedure in which bone is cut in an attempt to correct an abnormality that has resulted from trauma or disease. Osteotomy allows for correction in six different planes: valgus/varus, flexion/ extension, internal/external rotation, lengthening/shortening, medial/lateral displacement, or dorsal/ventral displacement.(1)
Osteotomy is used for several specific indications: (1) variation in growth of paired bones; (2) eccentric epiphysiodesis; (3) diaphyseal angulation due to malunion fractures or growth anomalies; (4) torsional deformities; (5) limb length discrepancy; and (6) correction of disease whereby an osteotomy of normal bone may correct a disease condition.
VARIATION IN GROWTH OF PAIRED BONES
Trauma, disease, or genetic predisposition may lead to the premature closure of an epiphyseal plate in the radius and ulna or the tibia and fibula. If the unaffected bone continues to lengthen while the damaged bone lengthens at a slower rate, the normal bone will be forced to bow away from the shortened bone. Osteotomy is necessary to straighten the deformity and return the limb to a normal function and appearance.(3)
Trauma to a portion of a growth plate may result in a selective slowing or cessation of growth in only that part. Continued growth from the unaffected side results in a deformity at the epiphysis. Such an injury commonly occurs in trauma to the lateral side of the distal radial physis or trauma to the lateral side of the distal tibial physis. Such an injury may occur to any physeal plate. Osteotomy through the site of maximal deformity is necessary to return the bone to normal anatomical position and should result in improved function in the involved limb.
DIAPHYSEAL ANGULATION DUE TO MALUNION
Long-bone fractures that have healed without reduction or bones in which fixation was removed prematurely may heal in angular, rotational, or shortened positions that are nonfunctional. Such bones may be osteotomized, realigned, and allowed to unite in proper alignment. Improved limb function will invariably result.
Torsional abnormalities occur most often as the result of fracture malalignment or genetic disease. Miniature breed dogs with medial patellar luxation may demonstrate proximal tibial torsion as the primary deformity leading to patellar luxation. Osteotomy to derotate the entire proximal tibia or only the tibial tuberosity may be necessary to restore more normal function to the affected limb.
LIMB LENGTH DISCREPANCY
Trauma or disease to growing physes may result in gross shortening of a long bone or pair of long bones. While dogs and cats have the ability to adapt to some bone shortening, eventually the shortening may become so severe as to render the affected limb useless. In such instances osteotomy may be performed and the bone ends forceably distracted mechanically to restore sufficient bone length to allow limb use. Such a procedure can also be useful to force paired bones to lengthen at a similar rate.
CORRECTION OF DISEASE
Corrective osteotomy in the very young animal who is affected by hip dysplasia may result in the formation of a deep congruent acetabulum and allow the animal to continue to mature without the disease becoming more severe. In many instances the effects of the disease process have been effectively eliminated.
Osteotomy to correct disease can be successful only if performed early, before the secondary changes of the disease occur. Osteotomy of bony prominences is a common procedure used to facilitate surgical exposure of bones or joints. When employed for this purpose the same precautions must be adhered to as when using osteotomy to correct abnormality.
The basic principles of osteotomy and subsequent fixation of the osteotomy site are the same as for any internal fixation. Accurate alignment and reduction of the osteotomy gap must be accomplished; rigid fixation, using internal fixation or external fixation must be provided; soft tissues must be carefully protected from the saw or osteotome during osteotomy; postoperatively the animal should be encouraged toward early exercise to hasten the return of limb function.
In order to accomplish successful osteotomy, it is necessary to optimize the patient's condition prior to this elective procedure. Therefore, the animal should be healthy, possess no generalized disease that might make it a poor surgical candidate, and have no localized problems such as bacterial dermatitis over the surgical site, open wounds, or sepsis of the involved bone intended for osteotomy.
It is imperative to plan an osteotomy procedure so as to minimize any chance for error. Preoperative radiographs in at least two views should be taken of both the affected bone or bones and the normal unaffected contralateral limb. Radiographs must include the entire joint above and below the deformed bone. The surgeon must be aware that plain radiography will delineate deformity only in the cranial-caudal and medial-lateral dimensions; rotational deformity cannot be demonstrated unless image intensification is available, allowing for axial radiographs to be taken. In order to plan the degree of bone correction and the ideal location within the bone for correction, paper tracings of the radiographs are helpful. This will allow the surgeon to cut or trace the intended osteotomy in paper templates and hopefully make mistakes on the templates rather than on the deformed bone. The use of paper templates is common among experienced surgeons and not to be considered a remedial exercise for only the neophyte.
When performing osteotomy, the surgeon should attempt to perform the correction at the site of greatest deformity. This will allow for optimal cosmetic results as well as functional results. At times, when the deformity is so close to the bone end as not to allow for adequate internal fixation, the osteotomy site should be moved. A cosmetic end result is always desirable, but it does not take precedence over the other principles of internal fixation.
When performing the osteotomy with an osteotome, hand saw, or power saw, all surrounding tissues must be protected from saw trauma. This is done best by placing an encircling retractor around the bone, being especially careful to protect soft tissues on the unseen surface beneath the bone. When using power equipment, the bone surfaces and the saw blade should be lubricated with roomtemperature saline to prevent thermal burn to the bone ends or surrounding soft tissues.
When possible, depending on the type of osteotomy desired, an attempt should be made to have osteotomy surfaces fit together smoothly. This will minimize the stress placed on the fixation used to stabilize the bone ends. When surfaces cannot fit smoothly, defects should be packed with autogenous cancellous bone.
The end point of any osteotomy should be return of the cut bone pieces to a position of optimum function. This necessitates aligning the joint above and below the deformity and being certain they are parallel. In most instances this requires rotational correction as well as realignment in a medial-lateral plane or cranial-caudal plane. Hopefully, once this has been accomplished, the end result is also improved cosmetically; however, if it is not, the osteotomy should not be redone. A functional end result always takes precedence over cosmesis.
Following realignment, rigid internal or external fixation is used to ensure bone fragment stability. If internal fixation is used, the animal should be encouraged to use the limb early to maintain normal joint motion during the recovery phase of treatment.
The following techniques of osteotomy are used singly or in combination to correct bony deformity.
Transverse osteotomy is used for rotational deformity in which no angulatory correction is needed. The osteotomy is performed at the area of major rotation by cutting a transverse plane through the bone. The angle of derotation is accomplished by correction to the predetermined degree by use of guide wires or by scoring the bone (Fig. 40-1). Osteotomy reduction is accomplished with a tension band plate. When transverse osteotomy technique is employed, the fixation is very stable, since flat surfaces are being opposed and no limb length is lost.
Cuneiform osteotomy (wedge osteotomy) is used primarily to correct angular deformity, but may be used for angular and rotational problems if both exist simultaneously.
FIG. 40-1 Line drawings demonstrating transverse osteotomy.
OPENING WEDGE OSTEOTOMY
Opening wedge osteotomy is accomplished using a single transverse cut. The wedge is then opened on the concave surface. The resulting wedge must be packed with cancellous bone following rigid internal fixation (Fig. 40-2).
CLOSING WEDGE OSTEOTOMY
Closing wedge osteotomy is accomplished by removing a predetermined sized wedge of bone from the point of maximal deformity. The base of the wedge is at the convex surface of the deformity. After removing the wedge, the resulting gap is closed, and rigid internal fixation is applied (Fig. 40-3).
COMBINATION OPENING-CLOSING WEDGE OSTEOTOMY
Combination opening-closing wedge osteotomy is used in animals in whom angulation needs correction but limb length cannot suffer further loss. Using this technique, the predetermined wedge of correction is divided in half, removed from the convex surface, and reinserted from the concave surface. Thus the correction is complete and no bone shortening results (Fig. 40-4). Rigid internal fixation is necessary to maintain alignment and retain the wedge graft.
Oblique osteotomy can be used to correct multiparameter abnormalities. In its purest form, it allows two bones to be separate or lengthened and still allow for point contact (Fig. 40-5). In rotational and varus or valgus deformity, it can be used to provide total correction by placing the proximal obliquity into the medullary cavity of the distal fragment, thus providing a pivotal point for derotation and varus or valgus realignment (Fig. 40-6).
The method of osteotomy to be used will be determined by the type of correction needed, the abilities of the surgeon, and the equipment available.
FIG. 40-2 Line drawings demonstrating opening wedge osteotomy.
FIG. 40-3 Line drawings demonstrating closing wedge osteotomy
FIG. 40-4 Line drawings demonstrating combination openingclosing wedge osteotomy.
Osteotomy can be performed with minimal surgical exposure as has been described by Rudy.(2) Closed technique involves multiple bony perforation with a Steinmann pin. Following sufficient perforations through the same plane, in various directions, the bone can be completely divided by a sharp stress at the site of multiple perforation. The resulting osteotomy is rough and allows for correction of rotation, varus/valgus, or displacement. Owing to roughness of the osteotomy site, the realignment should be relatively stable internally and can be stabilized externally.
The advantages of such a technique are the following: minimal equipment is needed to perform the osteotomy, and surgical exposure is not necessary; therefore the risk of contamination of the osteotomy site may be less than in open osteotomy. The disadvantages of closed osteotomy are potential damage to surrounding soft tissues, lack of control and exactness in osteotomy, impossibility to perform any technique but transverse osteotomy, inability to fill defects if doing open wedge procedures, and inability to use internal fixation.
FIG. 40-5 Line drawings demonstrating oblique osteotomy used for bone lengthening.
FIG. 40-6 Line drawings demonstrating oblique osteotomy used for rotational correction as well as correction of varus or valgus.
Surgical exposure of the bone to be cut allows for complete visualization of the affected area, adequate soft tissue protection, and the ability to perform any type of osteotomy desired. If the first correction is inadequate, it can be corrected immediately.
Osteotomy is best performed using an oscillating or reciprocating saw. Both tools allow for rapid and exact osteotomy; however, they do require intraoperative lubrication to prevent thermal injury to bone or soft tissue.
Hand saws certainly cut bone adequately, but they require much more surgical exposure and severe soft tissue retraction in order to cut a diaphysis. Gigli wires can be used to perform transverse osteotomy; however, other osteotomy techniques are difficult. Gigli wires require minimal retracting or surgical exposure. Like all friction producing saws, hand saws and Gigli wire saws should be lubricated to prevent thermal injury.
Osteotomes are very useful for cutting small bony prominences but rarely are used to cut diaphyses. An osteotome is most useful to cut through cancerous bone and therefore is used primarily in osteotomy aimed at providing surgical exposure. Occasionally, osteotomes may be used to cut a diaphysis if the osteotomy pattern has first been outlined using penetrating Steinmann pin tracts.
The advantages of open osteotomy are the complete visualization of the surgical site, ability to use power equipment and cut any type of correction needed, allowance for visual reduction of correction, and cancerous grafting of open wedges, and ability of the surgeon to ensure rigid internal fixation if desired.
Disadvantages of open osteotomy are the potential risk of traumatizing soft tissues through overzealous retraction and the added concern for wound contamination.
Osteotomies can be stabilized using all conventional forms of internal or external fixation. It is preferable to choose a type of fixation that best protects the osteotomy site from forces that will tend to return the fragments to their original positions. The selection of fixatives will also reflect the equipment available to the surgeon.
Diaphyseal osteotomy can be stabilized using intramedullary pins, pin and wire combinations, plates and screws, the Kirschner-Ehmer apparatus, the Stader apparatus, or external fixatives that properly immobilize the joints above and below the osteotomy.
Metaphyseal osteotomy can be stabilized using all the abovementioned techniques but is also amenable to internal stapling or wiring techniques followed by proper external fixation.
Apophyseal osteotomy, as commonly used to gain surgical exposure, is usually stabilized using a tension band wire, multiple pins, multiple nails, or interfragmentary screw fixation. Since most such osteotomies have a major tendon or ligament that tends to distract the reduced fragment, a tension band wiring technique is preferable to allow for sooner return to full function without the added risk of fragment distraction or non union.
REFERENCES1. Newton DC, Nunamaker DM: Osteotomy. In Manual of Internal Fixation for Small Animals, pp 255-264. New York, Springer-Verlag, 1984
2. Rudy RL: Corrective osteotomy for angular deformities. Vet Clin North Am 1:549, 1971
3. Rudy RL: Correction of growth deformity of the radius and ulna. In Bojrab MJ: Current Techniques in Small Animal Surgery, pp 535-542. Philadelphia, Lea & Febiger, 1975