Computer-assisted distal radius osteotomy

Computer-Assisted Distal Radius Osteotomy George S. Athwal, MD, FRSC, Randy E. Ellis, PhD, Carolyn F. Small, PhD, David R. Pichora, MD, FRSC, Kingston, Canada

Purpose: To establish the accuracy, precision, and clinical feasibility of a novel technique of computer-assisted distal radius osteotomy for the correction of symptomatic distal radius malunion. Methods: Six patients underwent a computer-assisted distal radius osteotomy and were followed-up for an average of 25 months. Objective radiographic measurements and functional outcomes, as measured by clinical examination including grip strength and range of motion, and Disability of the Arm, Shoulder and Hand (DASH) questionnaires, were used. Results: The mean radiographic parameters included an increase of radial inclination to 21° from 12° (normal, 23°). Dorsal and volar tilt (malunion) were corrected to 9° from ⫺30° and 21°, respectively (normal, 10°). Ulnar variance was corrected to 1.9 mm from 7.5 mm (normal, ⫹1.5 mm). Normal is defined as the average of the contralateral limb radiographs. The mean clinical outcome measures at an average of 25 months included a DASH global score of 14, a DASH individual item average score of 1.6, and an average affected side grip strength of 79% when compared with the unaffected side. Conclusions: The results of the computer-assisted technique were comparable with published results of traditional non– computer-assisted opening wedge osteotomy techniques. This technique allows a surgeon to accurately and precisely recognize and correct 3-dimensional deformities of the distal radius including axial malalignment (supination). The technique has the added benefit of reducing radiation exposure to the patient and surgical team because fluoroscopy is not used during the procedure. Additional benefits of the computer-assisted technique include the ability to perform multiple surgical simulations to optimize the alignment plan, and it serves as an excellent teaching tool for less-experienced surgeons. (J Hand Surg 2003;28A:951–958. Copyright © 2003 by the American Society for Surgery of the Hand.) Key words: Malunion, osteotomy, radius fracture, computer-assisted surgery.

Fractures of the distal radius constitute about one sixth of all fractures seen in the emergency room.1 From the Division of Orthopaedic Surgery, Department of Surgery, the School of Computing, and the Department of Mechanical Engineering, Queen’s University, Kingston, Canada. Received for publication February 15, 2002; accepted in revised form June 26, 2003. Supported in part by the Natural Sciences and Engineering Research Council of Canada, the Ontario Research and Development Challenge Fund, and the Institute for Robotics and Intelligent Systems. No benefits in any form have been received or will be received by a commercial party related directly or indirectly to the subject of this article. Reprint requests: D. R. Pichora, MD, FRCSC, Division of Orthopaedic Surgery, Kingston General Hospital, 76 Stuart St, Kingston, Ontario, Canada K7L 2V7. Copyright © 2003 by the American Society for Surgery of the Hand 0363-5023/03/28A06-0010$30.00/0 doi:10.1016/S0363-5023(03)00375-7

Current treatment methods for distal radius fractures lead to satisfactory results in the majority of patients. Malunion, however, is a recognized complication and usually can be prevented by appropriate treatment of the original fracture. McGrory and Amadio2 reported that the incidence of distal radius malunions in fractures treated by simple cast immobilization ranged from 12% to 70% and the pooled mean was 23%. The incidence after primary surgical treatment ranged from 0% to 33% (pooled mean, 10.6%). Unfortunately malunion may cause alterations in alignment, kinematics, and load transfer across the wrist. Patients may experience pain, arthrosis, reduced range of motion, reduced grip strength, carpal instability, cosmetic deformity, late neuropathy, or tendon rupture.2– 6 The Journal of Hand Surgery

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Figure 1. (A) Our computer-assisted 3-dimensional surgical planner uses the contralateral normal wrist as a template. The (B) malunited wrist undergoes a (C) virtual osteotomy and is aligned to the template. (D) The surgical planner then digitizes a plate onto the realigned radius and saves the coordinates and orientations of the screw holes for intraoperative referencing.

A malunited fracture of the distal radius usually involves a 3-dimensional deformity.3,7,8 The ability to appreciate adequately the complex deformity is difficult with plain radiographs and conventional computed tomography (CT). Reformatted 3-dimensional CT images have enhanced the conceptualization of multidirectional deformities, however, they often require additional interpretation by radiologists and they still only serve as visual templates for intraoperative referencing.7,9,10 Computer-assisted techniques have been developed to assist surgeons in the appreciation of complex multidirectional deformities and to achieve improved corrections. The BIZCAD system, the earliest technique, used 2 orthogonal radiographs to generate simple geometric models to assist in the planning of the osteotomy.11–13 This system provided limited planning and intraoperative guidance. Jupiter et al7 used computer-assisted design and computer-assisted manufacturing to generate 3-dimensional solid models of both the patient’s malunited radius and the normal contralateral radius. These models gave the surgeon hands-on appreciation of the deformity and allowed the determination of the size and shape of

the deformity. Although these models gave valuable qualitative feedback, there was no direct link between the models and the patient’s intraoperative anatomy. Also, because of the high manufacturing costs the investigators recommended that they only be used in complex malunions for which plain radiographs and CT imaging provide insufficient information for planning the corrective procedure. We have developed a CT-based computer-assisted surgical planner and an intraoperative guidance system for the 3-dimensional correction of distal radius malunions. Briefly, the computer-assisted system is a 2-step process. The first step is the preoperative plan, which incorporates a CT-based 3-dimensional reconstructed surface mesh of both forearms and a digitized model of a distal radius fixation plate. By using the preoperative planner a virtual osteotomy is conducted and the malunited distal radius fragment is realigned to best fit the surface geometry of the normal template. Next the digitized fixation plate is fit to the corrected radius (Fig. 1). This final plan then is reverse engineered so that the coordinates of the 2 proximal and 2 distal screw holes are mapped onto the original malunion model. These, along with the

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Figure 1. (Continued)

coordinates for the osteotomy plane, are saved and imported into the guidance software. The second step is the intraoperative guidance system, which links the preoperative plan and the intraoperative environment. Registration is the mating of the patient-specific preoperative plan to landmarks on the patient’s in vivo distal radius via the attachment of infraredemitting diodes (IRED) (Traxtal Technologies, Toronto, Canada) to the radius, which are monitored by an optical tracking device (OPTOTRAK 3020, Northern Digital Inc., Waterloo, Canada). An IRED target also is attached to the drill so that its location and orientation in space can be referenced to the preoperative plan and to precise locations on the patient’s exposed distal radius. While viewing virtual images of the radius with the planned locations of the screw holes and the surgical drill, the user-computer interface guides the surgical tools to the location of the planned osteotomy and to the locations and orientations of 4 screw holes in the fixation plate. Fluoroscopy is used only at the end of the procedure to verify the correction obtained. We have conducted a laboratory study comparing the computer-assisted technique with the traditional fluoroscopic-guided opening-wedge technique on plastic models simulating distal radius malunions.

Our conclusions showed that the computer-assisted method markedly improved most of the geometric variables, notably reducing the maximum error of correction and the SD of the correction error.14

Materials and Methods Between 1998 and 2000, 6 manually active patients were treated with a computer-assisted distal radius osteotomy at Kingston General Hospital. The procedures all were performed by the senior author (D.R.P.) with informed consent of the patients and approval of the Research Ethics Board. Indications were individualized for each patient; however, complaints of pain, stiffness, and cosmetic deformity were universal. Criteria for exclusion from this study included advanced osteoarthritis at the radiocarpal joint, manually inactive patients, severe osteoporosis, and reflex sympathetic dystrophy. There were 4 men and 2 women (Table 1); their ages ranged from 43 to 69 years (average age, 50 y). The initial fracture patterns were known in all patients and were classified according to the AO/ASIF system.15 Two cases involved the dominant hand and 4 cases involved the nondominant hand. Five cases resulted from a fall on an outstretched hand and the sixth was a high-energy injury from a fall from a roof (case 4) resulting in

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Table 1. Patient Data

Case

Age, Gender

Dominant Hand/ Injured

1 2 3 4

58, M 56, M 69, M 50, M

R/L R/L L/L R/both

5 6

69, F 43, F

R/R R/L

Mechanism of Injury

AO/ASIF Classification

Fall Fall Fall Fall from roof (4 m) Fall Fall

C2 A3 A3 C2 Gustilo I A3 A3

Initial Treatment Cast Cast Closed reduction and cast I&D, closed reduction, external fixation Closed reduction and cast Closed reduction and cast

Associated Injuries

Time to Union of the Osteotomy

None None None Calcaneus

10 10 9 12

wk wk wk wk

None None

12 wk 10 wk

I&D, irrigation and debridement. Demographic data for the six case subjects are presented.

bilateral distal radius fractures and a calcaneus fracture. The initial treatment in all except one was nonsurgical and consisted of 2 patients undergoing cast immobilization without reduction and 3 undergoing closed reduction and cast immobilization. Case 4 presented with a Gustilo type I open fracture that had been treated by irrigation, debridement, and external fixation. On presentation all fractures had solid bone union. There were 4 dorsal and 2 volar malunions averaging ⫺30° and 21° of volar tilt, respectively. The average time from injury to osteotomy was 9.3 months (range, 5–17 mo). At an average follow-up period of 25 months (range, 15–36 mo) the patients underwent clinical and radiographic evaluation. They were assessed for ranges of motion in 3 planes (flexion-extension, radioulnar deviation, and pronation-supination) with a goniometer. Grip strength was measured with the patient’s arm adducted and the elbow flexed at 90° (Jamar dynamometer, Therapeutic Equipment, Clifton, NJ). Three consecutive dynamometer measurements were taken on each hand, and the average readings for the affected hands and unaffected hands were compared. All patients completed the Disability of the Arm, Shoulder and Hand (DASH)16,17 questionnaire at the time of the most recent follow-up clinical assessment. It is a 30-item questionnaire that has shown reproducibility and validity; it has 21 physical function items, 6 symptom items, and 3 social/role function items. The DASH thus yields a global score ranging from 0 to 100, with higher scores representing greater disability. The patients also were asked if they were satisfied with the surgery and if they would undergo a similar procedure again if indicated. True posteroanterior and true lateral radiographs of the wrist were assessed in a blinded fashion by one independent observer. A true posteroanterior radio-

graph is done with the shoulder abducted to 90°, the elbow flexed at 90°, and the forearm in neutral rotation. A true lateral radiograph is obtained with the shoulder adducted, elbow flexed at 90°, and the forearm in neutral rotation. The preoperative and final radiographs were assessed for 3 parameters: volar tilt, radial inclination, and ulnar variance.3,4,10,19 –23

Surgical Technique This computer-assisted technique differs from the traditional method in several key ways. Five major steps are involved in the procedure.

Step I: Patient scanning. Both of the patient’s forearms were CT scanned in neutral rotation using a helical CT (General Electric, Milwaukee, WI). Images included the entire radius and ulna with reformatted scans of the periarticular segments. Step II: 3-D model generation. Voxel intensities were extracted from the CT scans to create 3-dimensional isosurface models of both forearms.14 Models of the uninvolved wrist were mirrored to serve as the template for correction.

Step III: Plan creation. The planning was done on custom software using a graphics workstation (SUN Microsystems, Sunnyvale, CA). Creation of the preoperative surgical plan involved 5 steps: (1) initial alignment: the 2 ulnas and proximal ends of the radii were aligned; this overlapping of normal and abnormal anatomy showed the deformity; (2) virtual osteotomy: a virtual osteotomy was created in the region of the original fracture; (3) aligning the distal radii: the distal fragment of the malunited radius was translated and rotated to align with the template radius; (4) positioning of the fixation plate: once the surgeon was satisfied with the corrected radius a digitized fixation plate model was positioned

Athwal et al / Computer-Assisted Distal Radius Osteotomy

as it would be at surgery; (5) saving the plan: the locations and orientations of 2 distal and 2 proximal drill holes for the plate were saved for use by the intraoperative guidance system.

Step IV: Intraoperative registration. Once in the operating room, a standard dorsal approach to the distal radius was used through the third-fourth extensor interval. The surgeon registered the in vivo distal radius to the isosurface model on the surgical planner via a computer algorithm whereby spotlights on distinctive landmarks on the model are contacted sequentially with a registration-tracking probe. An IRED dynamic referencing body mounted on the radius via a small external fixator (Synthes, Paoli, PA) and a similar IRED tracker mounted on the registration probe were tracked and linked to the guidance software via the optical tracking device (OPTOTRAK). A total of 10 to 15 surface points were collected to refine the registration estimate. A sequence of robust estimators was used to discard statistical outliers from the data in a mathematically disciplined manner.18

Step V: Image-guided surgery. The preoperative plan with its 3-dimensional bone and plate models were imported into a custom surgical guidance system running on a workstation (Unix; SUN Microsystems). The optical tracking device was used for tracking the surgical tools and patient movements. The sequence of the surgical procedure was: 1. Using a drill with a calibrated IRED target tracked by the optical tracking device, the 2 proximal and 2 distal pilot holes for the fixation plate were drilled with image guidance. The locations of the drill holes were dictated by the preoperatively planned final location of the plate. 2. The radius was cut at the predetermined location using image guidance. 3. The plate was affixed to the distal fragment creating a distal fragment/plate complex. 4. The distal fragment/plate complex was distracted progressively across the osteotomy site with a laminar spreader. The brachioradialis insertion was released universally to help overcome the soft-tissue contracture. 5. Once the proximal holes in the plate aligned with the pilot holes in the proximal radius, the correct alignment had been achieved and the distal fragment/plate complex was fixed in the correct position. 6. The bone defect was filled with iliac crest cancel-

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lous bone graft. The remaining screw holes in the plate were fixated with screws without image guidance. Perioperatively patients received prophylactic antibiotics for 24 hours and had a volar splint applied for a period of 4 to 6 weeks. Active finger motion was encouraged and early active wrist range of motion exercises were performed under the supervision of a Certified Hand Therapist.

Results Results were assessed 15 to 36 months (average, 25 mo) after osteotomy. The only surgical complication was an iatrogenic partial laceration of the extensor pollicis longus tendon that was incarcerated in the fracture callus in case 4, which primarily was repaired. The average time to final healing of the osteotomy was 11 weeks; there were no nonunions, delayed unions, or neurologic injuries. No superficial or deep wound infections were encountered. There were no tendon ruptures or problems with tendon function, however, 2 patients underwent hardware removal for irritation. All patients were pleased with the surgical outcome and would have the procedure again in a similar situation. All reported improved pain, function, and appearance. Of the 3 patients who were employed previous to their injury, one returned to their original job, another changed occupations but not specifically because of wrist dysfunction, and the third underwent mandatory age-related retirement. Two patients were retired previous to their injury and the last patient (case 4) was on long-term disability for a back injury before his fall from a roof causing a calcaneus and bilateral wrist fracture. The radiographic parameters improved dramatically (Table 2). Mean radial inclination improved from 12° before surgery to 21° after surgery (template 23°). The mean ulnar variance improved from 7.5 mm before surgery to 1.9 mm after surgery (contralateral mean, 1.5 mm). Mean volar tilt improved from ⫺30° for dorsal malunions and 20° for volar malunions before surgery to 9° after surgery (template, 10°). Case 4 was initially templated using the opposite wrist. However, since this wrist had also been fractured, we modified the templating to achieve the average radiographic indices of the template wrists of the other 5 cases—radial inclination: 23°, volar tilt: 10°, and ulnar variance: ⫹1.5 mm. As shown in Table 3 the average postoperative range of motion measured 87% (range, 77% to 97%) of the

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Table 2. Mean Radiographic Parameters

Radial inclination (°) Volar tilt (°) Ulnar variance (mm)

Distal Radius Malunion (Before Surgery)

Template (Contralateral Normal Wrist)

Post–Computer-Assisted Distal Radius Osteotomy

12 Dorsal ⫺30, volar ⫹21 ⫹7.5

23 10 ⫹1.5

21 9 ⫹1.9

The mean preoperative and postoperative values of the 3 radiographic parameters (radial inclination, volar tilt, and ulnar variance) are presented.

motion of the contralateral wrist. The average grip strength was 30 kg (range, 22– 45 kg) compared with 38 kg (range, 25–51 kg) in the contralateral hand. The global DASH scores averaged 14.0 (range, 3.3–53.3) and our average per item DASH score averaged 1.6 (range, 1.1–3.1). A DASH score of 0 represents no disability and higher DASH scores represent greater disability. When constructing the preoperative plans it was noted that all of the malunions with dorsal tilt also exhibited rotational malalignment about the long axis of the radius, which cannot be appreciated from the plain radiographs. An average of 15° of supination of the distal fragment was required to achieve anatomic correction (Fig. 2). There was no appreciable rotational deformity in the volar malunions.

Discussion Symptoms and functional impairments related to distal radius malunion have long been recognized.2– 6 Distal radius osteotomy is an effective treatment option for correction of deformity. Fernandez,4 Jupiter et al,7 and others11–13 all have stressed the importance of thorough preoperative planning and pre-

cise surgical technique to ensure successful outcomes. Plain radiographs provide adequate information on the degree of deformity in the coronal and sagittal planes, however, they fall short on complex 3-dimensional deformities.7,9 Jupiter et al7 attempted to address this by using computer-assisted design and computer-assisted manufacturing to construct solid models. These solid models assisted in the understanding of the deformities and aided in preoperative planning. We report the design and implementation of a preoperative planning system that works in concert with an intraoperative guidance system to assist a surgeon in correcting distal radius deformities. The unique ability to prepare a preoperative plan and to manipulate bone fragments in tracked 3-dimensional space using tracked surgical instruments allows the potential for a surgeon to achieve more consistently a technically superior osteotomy. This represents an advance in orthopedic technology. The clinical findings reported in this article are consistent with our laboratory in vitro simulations in which we identified improved accuracy of correction

Table 3. Final Wrist Function Range of Motion (Affected/Opposite)

Case 1 2 3 4 5 6 Average

Radial Ulnar Flexion Extension Deviation Deviation Pronation Supination (°/°) (°/°) (°/°) (°/°) %/% %/% 50/70 65/70 60/70 45/68 40/60 20/60 47/66

25/45 45/40 35/45 45/48 45/60 60/60 42/50

10/25 30/40 20/15 20/25 15/25 15/20 18/25

30/30 40/50 20/35 30/39 35/35 30/40 31/38

85/85 80/80 80/80 85/80 65/75 70/75 78/79

80/85 75/80 70/75 60/80 80/80 80/80 74/80

Total as % 77% 92% 91% 83% 82% 97% 87% 77% to 97%

Grip Strength (Affected/ Opposite)

DASH Global Score

DASH Average Score per Item

29/51 kg 57% 3.3 1.1 33/34 kg 97% 5.8 1.2 27/37 kg 73% 5.0 1.2 45/46 kg 98% 53.3 3.1 22/25 kg 88% 10.0 1.4 22/37 kg 59% 6.7 1.3 79% 14.0 1.6 57% to 98% 3.3–53.3 1.1–3.1

Range of motion is presented both individually for each of the 6 parameters measured and also as a global percentage value. Grip strength is given as a percentage of the value of the opposite side. Functional outcomes were assessed with the DASH questionnaire. A DASH score of 0 represents no disability and higher scores represent greater disability. The DASH is presented as a global score and as a mean score per item.

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Figure 2. An axial view of the model allows for assessment and correction of distal radius malrotation.

and improved precision of correction of malunions with computer assistance.14 Our preoperative surgical plans were achieved consistently. The radiographic correction obtained is comparable with that of other investigators, as is the grip strength and range of motion.4,5,8,10,21,22 Only a few studies have used the DASH questionnaire, and of these the DASH score is reported variably. We reported the DASH as both the global score and as the average score per item. Jones and Trumble (unpublished data) reported an average score per item of 1.7 after surgery in 20 patients treated with traditional 3-dimensional distal radius osteotomy at a minimum of 2 years of follow-up evaluation. Some investigators8,10 have reported that dorsal malunions are associated with supination of the distal fragment in addition to the classic findings of decreased radial inclination, loss of palmar tilt, and shortening. Our findings of axial malalignment are contrary to these reports, we found that in dorsally tilted malunions the distal fragment was pronated (average 15°). It is not clear whether this residual pronation is a result of the initial injury or the effects of reduction and cast treatment. Specific benefits of the computer-assisted system include reduced radiation exposure to the patient and

surgical personnel because intraoperative fluoroscopy is not required. Additional benefits include the ability to perform multiple simulations of the surgical procedure to optimize the alignment plan and to identify potential intraoperative problems. The surgical planner is an excellent teaching tool because it allows the appreciation of the multiplanar aspects of a deformity and the rotations and translations required for correction. The sophisticated nature of the planner allows the exact calculation of the geometry of the gap in the radius after distraction and in the future these data may be used with computer-assisted design/computer-assisted manufacturing technology to mill bone graft or bone substitute to precise dimensions. Further, the incorporation of guidance software and surgical tracking technology allows a surgeon to achieve the preoperative plan with a high degree of precision. This is a particular advantage for complex deformities for which the traditional surgical technique may be difficult to perform even by an experienced surgeon and which has a steep learning curve for the relatively inexperienced surgeon. This study has some limitations. One technical problem encountered was bending of the fixation plate in some cases owing to the excessive soft-tissue resistance to distraction of the osteotomy fragments,

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which could account for our slightly undercorrected ulnar variance. We have found that release of brachioradialis helps to reduce these soft-tissue forces. Potential risks of computer-assisted technique are that successful outcomes depend on the accuracy of the preoperative plan and poor planning may compromise surgical outcomes. Registration of the patient to the surgical planner and guidance system is critical; poor registration also may lead to poor outcomes. Computer-assisted planning and guidance have been shown to improve notably most of the geometric variables and most importantly to enhance precision in distal radius osteotomy. The capability to correct deformities with 6 degrees of freedom in a controlled and reproducible manner, and with reduced radiation exposure to patients and operating room staff, are notable benefits. This initial account of computer-assisted cases indicates that accurate and reliable anatomic results along with excellent clinical outcomes can be obtained. We believe that this pilot study indicates that computer-assisted distal radius osteotomy is feasible technically and that it provides a new treatment option for complex distal radius malunions. The authors thank Heather Lockett and Shawn Leclaire for assistance with model creation and data collection. The authors also acknowledge the contribution of Edward Vasarhelyi to the writing of the manuscript.

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