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Lower Extremity Angular Malunion: Evaluation and Surgical Correction Robert A. Probe, MD Abstract After diaphyseal fracture healing, the morphology of an involved bone is rarely left unaffected, and some alteration in length, rotation, angulation, and translation is expected.With mod- ern fracture care, such deviations from the original shape are generally small in magnitude and well tolerated by patients. However, on rare occasions, the change in bone morphology is suf- ficient to causeconcern. Functional im- pairment, cosmetic deformity, and the long-term effect of malalignment on joint integrity and stability are the most important problems. These concerns are particularly germane in the lower extremity, in which the altered distri- bution of weight-bearingstresses leads to abnormalforce concentrationsacross joints. 1 Furthermore, tilting of the knee and ankle joint surfaces can lead to detrimental shear stress within articular cartilage, as well as to changes in joint contactarea. 2,3 When these conditions require management, an osteotomy must be designed to restore normal alignment, length, and horizontal joint line orientation. It is critical for the treating physician to fully assess and characterize these angular malunions. The physician also should understand the implications for the joint, the indications for an osteotomy, and preoperative osteotomy planning. Normal Biomechanics of the Lower Extremity To understand the pathomechanics of malunion, thesurgeon firstmust have a thorough knowledge of normal lower extremity mechanics. Although differing methodologies of measurement and ethnic variation cause some discrepancies in reported values, a few generalizations are appropriate. 4-7 The mechanical axis of the lower extremity passes from the femoral head through the calcaneal tuberosity. Because of the variable position- ing of the tuberosity and the difficul- ty in radiographic evaluation, this is most commonly approximated by using the center of the femoral head and center of the ankle as the outermost points of a line defining the mechanical axis. Using these two points as references, the average mechanical axis crosses the knee 10 mm medial to its frontal plane center (Fig. 1, A). Radiographically, this is approximated by the position of the medial tibial spine. In the sagittal plane, the mechanical axis from the center of the femoral head to the center of the ankle lies just anterior to the center of rotation of the knee joint (Fig. 1, B). Functionally, this anterior position of the mechanical axis is desirable because it allows for passive locking of the knee in full extension. The mechanical axis of the tibia directly coincides with the anatomic axis; however, because of the medial Dr. Probe is Chairman, Department of Ortho- paedics, Scott & White Memorial Hospital,Scott, Sherwood and Brindley Foundation, and Associ- ate Professor, The Texas A&M University Sys- tem Health Science Center, College of Medicine, Temple, TX. Neither Dr. Probe nor the department with which he is affiliated has received anything of value from or owns stock in a commercial company or insti- tution related directly or indirectly to the subject of this article. Reprint requests: Dr. Probe, 2401 S 31st Street, Temple, TX 76508. Copyright 2003 by the American Academy of Orthopaedic Surgeons. The lower extremity has a mechanical axis with joint orientation that allows joint longevity and efficiency in bipedal gait. When normal alignment is lost because of trauma or other conditions, deviations from this anatomic norm may be deleterious to long-term joint function. In fractures that have healed with angular malunion, all facets of the deformity must be carefully considered, including alteration in length, rotation, alignment, and translation. Once all elements are fully defined, the effects of the malunion on mechanical axis and joint orientation can be understood. Tech- niques for surgical correction include wedge, dome, and oblique osteotomies and distraction osteogenesis. Each method possesses characteristics appropriate for certain clinical situations. Judicious patient selection and thoughtful preoperative planning may allow restoration of normal mechanics. J Am Acad Orthop Surg 2003;11:302-311 302 Journal of the American Academy of Orthopaedic Surgeons position of the femoral head relative to the shaft, there is a difference between the mechanical and anatomic axes of the femur. The femoral mechanical axis is the line from the center of the femoral head to the center of the knee; the anatomic axis is the line from the piriformis fossa to the center of the knee. In an individual of average size, the anatomic axis is in 6°of valgus compared with themechanical axis. This angle may be increased in shorter femurs and decreased in longer femurs, making comparison with the contralateral side beneficial. Joint Orientation The frontal plane orientation of the joints also should be defined. The neck-shaft angle commonly has been used for the hip and proximal femur; however, this value is dependent on landmarks that change radiographically with different degrees of hip rotation. An alternative method, described by Chao et al, 4 is the proximal femoral orientation angle. This angle is formed by the divergence of a line from the tip of the greater trochanter to the center of the femoral head and the femoral mechanical axis. Although individual variation may be present, 90° (parallel to the floor) is a reasonable estimate in the absence of compara- tive contralateral films (Fig. 2). In stance, the knee joint line is oriented in 3° of valgus relative to the mechanical axis. As a result, the distal femoral articular surface is in slight valgus relative to the femoral mechanical axis, and the proximal tibial articular surface is in slight varus relative to its mechanical axis. This knee valgus is valuable because, during gait, the limb assumes a 3° varus position as the foot is planted beneath the body’s center of gravity. The medial inclination of the limb makes the knee axis parallel to the floor during weight bearing. The orientation of the ankle joint is usually perpendicular to the mechanical axis. 4 Individual patients may dem- onstrate deviation from these popu- lation averages and, when available, the joint inclination of a normal op- posite side provides valuable com- parative information. Patient Evaluation Deformity Assessment Accurate malunion surgery begins with precise definition of the deformity. Implications of a corrective osteotomy cannot be known unless the malunion is precisely characterized three-dimensionally. Leg-length discrepancy can be estimated with cal- ibrated blocks leveling the anterior superior iliac spines to palpation. The relative contribution of the tibia to the length discrepancy can be estimated with the patient prone and the knees flexed 90°. In this position, the discrepancy in sole height usually can be attributed to the tibia, with the re- mainder of the discrepancy account- ed for by the femur. Increased precision can be obtained with leg-length radiographs on a ruler or with com- puted tomography. 8 Overall limb rotational differences can be estimated by comparing maximal internal and external rotation of the lower limbs. The tibial component can be ascer- Figure 1 A, The frontal plane mechanical axis (dashed line) of the lower extremity extends from the center of the femoral head, across the medial tibial spine, to the center of the ankle. B, The sagittal plane mechanical axis (dashed line) extends from the center of the femoral head, anterior to the center of rotation of the knee, to the center of the ankle. Figure 2 Frontal plane orientation of the lower extremity joints. The center of the femoral head to the tip of the trochanter line should be parallel to the floor. The knee is in 3° of valgus, and the ankle typically is oriented parallel to the floor. Robert A. Probe, MD Vol 11, No 5, September/October 2003 303 tained by having the patient sit with the knees flexed 90° and the ankles at neutral. In this position, the difference in the projection of the foot will describe the rotational difference within thetibias. Obtaining a comput- ed tomographyscan through the femoral neck, supracondylar femur, and distal tibia and comparing the rotational position of the two extremities gives a very accurate measurement of rotational deformity. 9 Angular deformity is usually estimated by superimposing intersect- ing linescentered inthe medullary canal of the proximal and distal fragments on both anteroposterior (AP) and lateral radiographs. How- ever, this technique is subject to error if a short metaphyseal segment is present because it can be difficult to accurately determine the axis. Phys- iologic bowing of the femur or the tibia also can make drawing accurate lines along the medullary canal difficult. Milner 10 reviewed a series of malunited tibial fractures and found an error range of 11.7° (from −6.2° to 5.5°) in the coronal plane when rely- ing on the medullary canal as an axis reference. Increased accuracy may be achieved by using a reversed radiograph of the contralateral side as a template. Themechanical axis maybe drawn on the uninjured side, followed by superimposition of the side with the deformity on which the proximal and distal mechanical axes have been drawn. Divergence of the proximal and distal mechanical axes indicates true angular deformity. The point of intersection of the proximal and distal axes has been called the center of rotation of angulation. 11 In cases of pure angulation, this intersection occurs at the apex of the deformity. In cases of angulation with translation, the center ofrotation of angulationis moved away from the site of maximal angular deformity, at a distance proportional to the amount of translation (Fig. 3). One advantage of this method of biplanar radiographic assessment is its simplicity: sagittal and frontal plane deformity can be estimated with any set of standard radiographs. A second advantage is that the effects of the malunion on both the frontal and sagittal plane mechanical axes can be estimated. The principal disadvantage is that this method rarely defines the true magnitude and orientation of the angular deformity. 12 If angulation is seen on both AP and lateral radiographs, the true magnitude of angulation will be greater than that seen on either view, and the plane of deformity usually is some- where in between. With the deformity measured onAP and lateral radiographs, trigonometric calculations can help define the true plane and position of the deformity, according to the following formula: 12 Orientation angle from frontal plane = arc tan tan (lateral) tan (anteroposterior) True magnitude = arc tan √tan 2 (lateral) + tan 2 (anteroposterior) Alternatively, the plane and magnitude of the deformity may be defined on fluoroscopic examination. All extremities with angular deformity may be rotated into a plane in which no angular deformity is seen on fluoroscopy. Orthogonal to this plane is the plane of maximal angular deformity. Quantitative assessment ofthe deformity can be obtained from the radiographs in this projection. Once the magnitude of the deformity is defined, its effects on joint mechanics must be assessed. This is a function of the magnitude and direction of the angular deformity as well as its location within the leg. For ex- ample, a 20° valgus deformity in the subtrochanteric region of the femur will result mainly in leg lengthening, but a 20° valgus deformity of the supracondylar region will result in shortening and substantial lateral translation of the mechanical axis. Computer-modeled effects on length, mechanical axis, and joint orientation of various 20° malunions are listed in Table 1.The variability inme- chanical consequences of these malunions underscores the necessity of considering both the magnitude and location of the malunion. In gen- eral, as the deformity approaches the knee, the mechanical axis is translat- ed mediallyfor a varus deformityand laterally for a valgus deformity. An- gular malunionsaround theknee also have the greatest effect on leg length. As the deformity approaches the hip or ankle, effects on the mechanical axis are diminished; however, the adjacent joint becomes increasingly malaligned. Figure 3 In cases of combined translation and angulation, the center of rotation of angulation (dark dot) may be defined such that rotation centered on this point will correct both deformities. This point is defined by the intersection of the mechanical axes of the proximal and distal segments (dashed lines). Lower Extremity Angular Malunion: Evaluation and Surgical Correction 304 Journal of the American Academy of Orthopaedic Surgeons Mathematical formulas and nomograms have been developed to assist in the understanding of the mechanical effects of particular malunions. 13,14 Puno et al 13 described trigonometric methods of calculating these effects; however, because many physicians are not familiar with this methodology, it is more common for the mechanical axis and joint orientation to be measured radiographically. These measurements should be taken on a full-length radiograph from a 51-in cassette, covering the hip to the ankle. The beam should be centered on the knee, with the patella pointing directly forward and the x-ray tube 10 feet away. The line from the femoral head to the center of the ankle defines the mechanical axis. Aperpendicular line from the mechanical axis to the medial tibial spinedefines the moment arm of axis deviation. Malalignment of the knee may be estimated from this long leg radiograph; however, dedi- cated AP views of the hip and ankle are preferred for measurement of their respective orientation because of the parallax error on long leg radiographs. Limb axis translation also has an effect on mechanical axis shift as well as joint orientation. Angulation and translation have been shown to be in- dependent of each other, with the direction and magnitude of the two deformities unrelated. 12 The composite effects of these two variables are best discerned by review of long leg, weight-bearing radiographs. Symptom Assessment Other important considerations in patient evaluation include the status of local muscle strength, ligamentous stability, cartilage integrity, and range of motion of the joints of the affected extremity. Mild medial mechanical axis displacement (varus) may be poorly tolerated with incompetent lateral ligaments of the knee. 15 Sim- ilarly, if the medial chondral surface of the knee has been damaged, medial axis deviation is likely to exac- erbate arthritic symptoms. Ankle malalignment may be well tolerated in the setting of a supple subtalar joint, but a foot with a stiff subtalar joint will be intolerant to minor degrees of ankle malalignment. 3 Final- ly, a well-developed quadriceps muscle may compensate for posterior displacement ofthe sagittal planeme- chanical axis; however, a patient with a weak muscle likely would experience symptomatic buckling of the knee. Symptoms attributable to malunion may be apparent immediately after fracture healing or may mani- fest over alonger period of time. Short- term consequences are infrequent and usually arise when a malunion is severe enough to exceed the compen- satory limits of adjacent joints. For ex- ample, a procurvatum deformity of the distal femur, which places the sagittal plane mechanical axis posterior to the knee and thus prevents locking of theknee during the stance phase of gait, could be expected to be symptomatic immediately. Likewise, a patient with a varus distal tibial malunion that exceeds the compen- satory valgus effect that can be obtained through the subtalar joint would experience disruption of gait mechanics and noticeable symptoms. Chronic Effects of Malunions Delayed-onset symptoms caused by altered mechanical forceson the joints are more common than immediate symptoms. Although a direct causal relationship between joint deteriora- tion and altered mechanical loads re- sulting from malunion has not been established, an increasing number of animal, cadaveric, and clinical stud- ies support this hypothesis. In a rab- bit model in which 30° angular malunions were created in the proximal tibia, Wu et al 16 observed histo- logic changes in both cartilage and bone on the overloaded condyle over a 34-week period. The cartilage demonstrated irregularity and loss of the superficial horizontal layer, as well as clefts extending into the transition zone. The subchondral bone showed increased thickness and decreased porosity. The location of chondral changes showed direct correlation with changes in the subchondral plate, suggesting that increased subchondral plate stiffness may play a causative role in the overlying cartilage changes. Simulated malunions of varying degrees and directions in human ca- Table 1 Mechanical Implications of Various 20° Frontal Plane Malunions* Malunion Length Change Mechanical Axis Change Knee Orientation Ankle Orientation 20° subtrochanteric valgus +11mm 14mm lateral 2° valgus 2° valgus 20° subtrochanteric varus −18 mm 11 mm medial 2° varus 2° varus 20° supracondylar varus −11 mm 64 mm medial 10° varus 10° varus 20° proximal tibia varus −9mm 57mm medial 8° valgus 12° varus 20° distal tibia varus −4mm 12mm medial 1° valgus 19° varus * Malunion consequences derived with computer modeling software (LightwaveMod- eler; Newtek, San Antonio, TX). Leg length changes reflect the absolute distance from the top of the femoral head to the ankle and not actual bone segment lengthening. Robert A. Probe, MD Vol 11, No 5, September/October 2003 305 davers have been used to demon- strate changes in contact pressures within the joint. 1-3 McKellop et al 1 used pressure-sensitive film to dem- onstrate doubling of contact pressure across the knee with simulated 20° malunions in both varus and valgus directions. Tarr et al 2 demonstrated that simulated malunions in the distal third of the tibia could alter the shape and diminish the size of tibiotalar contact. In subsequent experimental work, Ting et al 3 demonstrated that simulated subtalar stiffness potentiated these mechanical alterations. The conclusions of these stud- ies are that simulated malunions ap- pear to alter contact pressure within adjacent joints and that these changes are maximized as the deformity is placed closer to the joint. The finding that may be extrapo- lated from these animal and cadaveric data is that the presence of an altered mechanical environment within the joint places the joint at increased risk for degenerative arthropathy. Puno et al 17 reviewed 27 patients with 28 tibial shaft fractures a mean of 8.2 years after injury. They measured articular malalignment rather than just the degree of malunion. This distinc- tion is important because it takes into consideration both the magnitude and location of the malalignment. Regres- sion analysis showed that the greater the ankle malalignment, the poor- er the ankle function scores. The knee did not show similar results; however, mean malalignment in the knee was only 1.3° compared with 6.6° in the ankle. Kyro et al 18 compared the function of 17 patients with tibial malunion to that of47 patients without malunion and found significantly(P <0.05) more subjective complaints and functional limitations in patients with angulation >5°. In another series of 14 patients with malaligned tibial or femoral fractures followed up at a mean of 31.7 years, there was progressive knee deformity thought to be directly related to a combination of the calculated increased angular force on the tibial plateau and time from original injury. 19 This seems to document the detrimental effects of altered mechanical axis on long-term joint function. van der Schoot et al 20 reviewed 88 patients at a mean follow-up of 15 years after tibial fracture. They found a statistically significant (P < 0.001) relationship between tibial malalignment and degenerative changes in the knee and ankle. Not all of the literature supports this thesis of long-term detrimental effect. Merchant and Dietz 21 reviewed 37 patients after tibial shaft fracture at a mean follow-up of 29 years. In patients with >5° varus, radiographic arthrosis was noted in the ankles; however, there was no correlation with the degree of malunion and knee or ankle function scores. Milner et al 22 reviewed 164 patients at a minimum of 30 years after treatment of tibial shaft fracture. They found increased subtalar stiffness associated with angular malunion but no statistically significant association of malunion with ankle or knee arthritis. This study is valuable because it confirms that mi- nor degrees of malunion are tolerated at the knee and ankle; however, ex- panding these conclusions to more severe deformities is not warranted because only 4% of patients had healed with coronal plane malunion ≥10°. Be- cause of these conflicting reports, as- cribing long-term functional deficit to malunion remains controversial, es- pecially because the effect of the original extremity trauma on the joint surface cannot be accurately determined. 23 Surgical Indications Common indications for malunion correction include ligamentous instability on the convex side of the deformity, 15 leg-length discrepancy >2 cm, inability to place the foot in a plan- tigrade position, and unicondylar arthritis of theknee. However, the symptoms caused by these mechanical alterations frequently can be improved nonsurgically. Load-transferring brac- es, shoe orthoses, shoe lifts, and an- algesics all may have potential benefit and should be tried before surgical intervention. If these prove to be in- effective in relieving symptoms, osteotomy may be considered. The origin of pain in patients with angular malunion may be multifac- torial and is often unclear. Potential etiologies include overloaded ligamentous structures, local muscle and tendon irritation, and tensile strain of bone. Theoretically, all of these sourc- es of pain could be improved by corrective osteotomy. Uncertainty about the long-term outcome of malunion often has made decision-making problematic, espe- cially for patients with asymptomat- ic angular malunion. The mainstay of treatment in this group is patient ed- ucation about future risk of degenerative arthritis. At minimum, patients should be made aware that osteotomy is a treatment option should symptoms develop. There are no de- finitive criteria to determine wheth- er osteotomy is indicated; however, in active individuals, commonly used guidelines are varus malalignment of the knee or ankle >10°, valgus malalignment of the knee or ankle >15°, or a 20-mm medial shift in the mechanical axis. A patient considering osteotomy for cosmeticreasons musthave aclear understanding of the risk and magnitude ofthe contemplated procedure and have realistic expectations re- garding outcome. Joint fibrosis, muscle weakness, and articular changes all may contribute to posttraumatic limb dysfunction and are not generally improved with malunion correction. Surgical Planning Correction of angular deformity re- quires decisions to be made about the location and type of osteotomy and the method of osteotomy stabiliza- Lower Extremity Angular Malunion: Evaluation and Surgical Correction 306 Journal of the American Academy of Orthopaedic Surgeons tion. Selection of an osteotomy site is a balance between the geometrically ideal position and biologic factors. Ideally, the angular correction should be centered coincident with the center of rotation of angulation, although other considerations, such as the quality ofthe soft-tissue envelope,the healing potential of the osteotomized bone, and the ability to provide rigid internal fixation, may justify movement of the osteotomy site from the center ofrotation ofangulation. How- ever, if the osteotomy site is moved from the center of rotation of angulation, the intercalary segment remains angulated, which will create a secondary translation deformity. Of- ten these secondary deformities are clinically insignificant; however, their presence should be anticipated and their consequences considered. If the preoperative plan suggests notable deformity, accommodating translation maybe planned for the distalseg- ment. Each type of osteotomy—closing wedge, openingwedge, neutral wedge, dome, and oblique osteotomy and distraction osteogenesis—has inherent characteristics that should be considered in surgical decision-making.Clos- ing wedgeosteotomy,in which thecen- ter of rotation is on the concave side of the deformity, is the most common method of angular correction. The advantages of this technique include the ability to apply it directly at the center of rotation of angulation, the resultant contact of viable bone, and the precision the osteotomy affords. There are several drawbacks to the closing wedge osteotomy: extensive surgical exposure is required; ligaments and tendons that cross the osteotomy are functionally lengthened; and the bone segment is shortenedwith the removal of the triangular wedge of bone. The length lost in the osteotomized bone segment is equal to half the height of the triangle’s base. More complex are the changes in leg length that result from correction of the angular deformity. These changes are dependent on the direction, location, and magnitude of the deformity. Despite the removal of bone, a net increase in leg length often results from the correction. No- mograms have been developed to assist in the estimation of overall leg length change from corrective osteotomy. 14 Some qualitative conclusions can be drawn from these nomograms: (1) correction of varus deformity al- ways results in leg lengthening, (2) the amount of lengtheningfrom varus correction is greatest adjacent to the hip and diminishes as the osteotomy approaches the ankle, (3) correction of valgus deformity in the proximal third of the femur leads to limb shortening, and (4) length gains from correction of distal valgus deformities are greatest at the knee and diminish to- ward the ankle. The advantages of opening wedge osteotomy are regained length and the ability to do the osteotomy per- cutaneously or with an intramedul- lary saw. The amount of lengthening is equal to half the height of the dis- tracted triangular base. The amount of linear bone lengthening will be ad- ditive to any length derived from limb straightening. The primary disadvantages of this technique include the potential for introduction of un- wanted length and creation of a triangular bone defect. In adults, triangular bone defect often must be filled with graft, which incurs the morbid- ity associated with graft harvest and a risk of osteotomy nonunion. Neutral wedge osteotomy (Fig. 4) combines closing and opening wedge osteotomies.Aclosing wedge osteotomy is done on the convex side of the deformity, with the apex of the resected triangle in the middle of the osteotomy site. Opposing the surfaces of the closing wedge creates an opening wedge on the contralateral side. Figure 4 Neutral wedge osteotomy combines the features of closing (A) and opening (B) wedge osteotomies. The resected wedge may be used on the contralateral side as an osteo- genic graft. Robert A. Probe, MD Vol 11, No 5, September/October 2003 307 If theosteotomy apex is moved slight- ly to the concave side of the middle of the deformity, the resected triangle of bone may be used as graft for the resultant opening wedge defect. The rationale for movement of the apex in a concave direction is to ac- commodate for the bone lost in the resected triangle from the passage of a saw blade. In this combined osteotomy, the point of rotation is the apex of the closing wedge osteotomy, and bone segment length should remain unchanged. Dome osteotomy uses a bony cut followed by correctional rotation across this arced surface (Fig. 5). The arc of the osteotomy can be considered to be a portion of a circle, with the center of the circle defining the point ofrotation ofthe osteotomy. The orientation of the concavity of the dome is critical because its direction defines the point of rotation. Ideally, this point of rotation will coincide with the center of rotation of angulation so that limb translation is not introduced. Although the bone will be restored tonormal alignment overall, residual angular deformity within the segment of bone between the point of rotation and the osteotomy will remain. This residual malaligned segment creates translation at the osteotomy site. Creating a dome with as short a radius as practicable will minimize the translational effects of this segment. Dome osteotomy is tra- ditionally done in the metaphyseal portion of long bones. This allows the osteotomy to be made through can- cellous bone, with its inherent superior healingcapabilities. The dome osteotomy is advantageous because adjustments can be made in angular correction, no bone resection is required, and the contacting metaphyseal bone usually heals rapidly. The primary disadvantages of the dome osteotomy are that it is generally re- stricted to metaphyseal sections of bone, angular correction is tied to translation across the osteotomy site, and there is no capacity to correct for rotation. Combined deformities of angulation and rotation may be managed by creating an osteotomy oblique to the long axis of the bone. If a tibia is split along the coronal plane, rotation of the anterior and posterior halves will result in only an angular change of these two parts. If a horizontal osteotomy is made in the middiaphysis, rotation of proximal and distal segments results in only rotational change. Between these two extremes are osteotomies that, when rotated, result in both rotational and angular correction. This principle may be used to create the single-cut osteotomy for correction of angulation and rotation. 24,25 The orientation of this osteotomy has been defined by mathematical formulas; 24,25 the most straightforward determination of orientation is defined by the following formula: 24 Angle from long axis in no-angulation view = arc tan axial rotation angular deformity Intraoperatively, the no-angulation view of the bone is found with fluoroscopy. The cut is created with the width of the blade turned parallel to this plane, deviating away from the long axis of the bone by the defined angle (Fig. 6). In malunions in which the angular deformity predominates, this cut becomes steep and difficult to execute. Advantages of this osteotomy include a large surface area for healing and the ability to perform in- terfragmentary fixation and add length by sliding along the osteotomy surface after rotation. Angular correction also can be achieved with distraction osteogenesis, 26 using hinges incorporated into an external fixation frame. The hinges are placed on the convex side of the deformity with the axis serving as the point of rotational correction, thus creating a trapezoidal opening wedge, which has the potential of adding length. An additional benefit is that, after angular correction, the surgeon has the ability to resolve any residual length discrepancy with fur- ther distraction. Placement of the hinges proximal or distal to the apex of angulation may additionally allow for simultaneous translational correction (Fig. 7). Recently developed software advancements have expanded the capabilities of distraction osteogenesis by allowing for the simultaneous correction of length, angulation, translation, and rotation with a single frame. 27 Despite these frame advances, distraction osteogenesis continues to require prolonged peri- ods of external fixation with its atten- dant complications, including pin- tract infections, joint contracture, and delayed regenerate formation. Be- cause of these potential difficulties, this technique is generally reserved for patients with complex multipla- Figure 5 A and B, Dome osteotomies are created as an arc with the point of rotation (dot) centered at the center of rotation of angulation. Angular correction is correlated to translation. The larger the radius, the more translation produced by a given angular correction. Lower Extremity Angular Malunion: Evaluation and Surgical Correction 308 Journal of the American Academy of Orthopaedic Surgeons nar deformity, length discrepancy, or compromised soft tissue. The final component of surgical planning is to determine the method of osteotomy stabilization. Cast im- mobilization has the potential advantage ofallowing postoperative adjustments, although the less rigid control of osteotomy alignment is a draw- back. External fixation also allows postoperative adjustment and provides increased rigidity relative to casting. However, pin-tract complications and the prolonged period of use necessary for diaphyseal osteotomy detract from its utility. Locked in- tramedullary devices can be used to stabilize an osteotomy; if the medullary canal remains, insertion of a rod may help restore alignment. 28 The disadvantage is that a second surgical site is required for insertion. Plate fixation hasbeen used mostcommon- ly in osteotomy stabilization. Because open exposure is generally required for osteotomy, plate application may be done through that incision. The plate also may serve as an adjunctive tool for realignment. If placed on the convex side, the plate may be fixed to one end of the bone and a compres- sion device attached to pull the bone back into alignment. 29 Another advantage of plate fixation over in- tramedullary rods is the ability to stabilize short metaphyseal segments. Results Because of the relative infrequency of corrective osteotomy for malunion, there is a dearthof clinical seriesdem- onstrating patient outcomes. Graehl et al 30 reported on supramalleolar dome and wedge osteotomies done in eight patients with tibial malunion. Although complications were frequent, the seven patients who main- tained correction reported symptomatic improvement. Sanders et al 31 performed oblique single-cut osteotomies in 15 patients with tibial deformity. Mean deformity was 14° in the coronal plane and 13° in the sagittal plane, with mean shortening of 2.2 cm. In the 12 patients with adequate follow-up, osteotomy healed in 10 at a meanof 4.5 months.All10 were able to return to preinjury employment and were pleased with the surgical result.Average postoperative deformity correction was to within 1° in the coronal plane and 2° in the sagittal plane, with an average lengthening of 1.3 cm. Two failures were noted: one wound dehiscence and one frac- tured plate.Based on their experienc- es, the authors recommended this technique for correction of angular tibial deformity. They were somewhat disappointed with their results in re- gaining limb length and recommended that distraction techniques be considered if length discrepancy exceeds 2.5 cm. No mention was made of preoperative rotational deformity or the rotational changes necessarily in- curred with this technique. 32 Sangeorzan et al 33 reported on four patients with combined rotational and angular deformity of the tibia. With mathematical planning, all four patients obtained correction of angulation and rotation with a single-cut osteotomy. One patient had postoperative infection, which resolvedwith débridement and delayed primary closure. In their series of 23 pediat- ric and adult patients treated for lower extremity deformity, Tetsworth and Paley 23 demonstrated the effec- tiveness of Ilizarov methodology in correcting deformity. The average mechanical axis deviation was re- duced from 48 to 8.6 mm; the obliq- uity of the knee joint improved from 16° to 3°. However, complications Figure 6 A, Simultaneous correction of both angulation and translation is possible with single-cut osteotomies. B, The saw blade is oriented parallel to the plane of maximum angular deformity at an angle of inclination (short dashed line) derived from a mathematical formula. Long dashed line = long axis of the bone. Robert A. Probe, MD Vol 11, No 5, September/October 2003 309 were frequent, with universal occur- rence of pin-tract infection and a 36% incidence of major complications. Av- erage frame time was 158 days, and marked improvement occurred in the latter half of the study. This suggests that, as with many of these complex techniques, experience contributes to successful results. Summary Normal lower extremity alignment is ideal for a mechanically efficient bipedal gait. When components of the lower extremity are traumatically altered, function may be affected. A thorough understanding of thesignif- icance of the altered mechanics and a preoperative plan that allows com- plete rectification of this multifacet- ed, complex problem is necessary before attempting surgical management of lower extremity malunion. The complexity of osteotomy and distraction osteogenesis, and the compro- mise in local tissues imparted by pre- vious trauma, make these procedures susceptible to complication. It is im- perative for the surgeon and patient to consider fully the risks and ben- efits during the decision-making pro- cess. References 1. McKellop HA, Sigholm G, Redfern FC, Doyle B, Sarmiento A, Luck JV Sr: The effect of simulated fracture-angulations of the tibia on cartilage pressures in the knee joint. J Bone Joint Surg Am 1991;73: 1382-1391. 2. Tarr RR, Resnick CT, Wagner KS, Sarmiento A: Changes in tibiotalar joint contact areas following experimentally induced tibial angular deformities. Clin Orthop 1985;199:72-80. 3. 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