A Retrospective Analysis of Lower Limb Deformity Correction using Three-dimensional Computed Tomography Scan

Abstract

Introduction:

Standard deformity correction is based on full-length true anteroposterior (AP) and lateral radiographs. However, a three-dimensional computed tomography (3D-CT) scan may provide a more intricate and detailed understanding of the deformities, to plan for the accurate correction. We present a retrospective evaluation of the deformities in three-dimensional projection with 3D-CT scans and its application on the correction of malalignment of the lower limbs.

Materials and Methods:

Planning of 107 cases of deformities in the lower limb was done using a 3D-CT scan over a 5-year period from September 2017. Evaluation was done by measuring angles and lines from true AP and lateral image sections of 3D-CT scans instead of standing full length lower limb radiographs (Orthoscanogram). Osteotomies were stabilized with Ilizarov fixation, followed by correction with Hexapod system (ORTHO-SUV, Pitkar, India).

Results:

The use of 3D-CT scan AP and lateral images provided accurate planning for deformity correction. Deformities can be understood in all three planes including rotational malalignment in a single scan.

Conclusion:

The precise information of the deformity in sagittal, frontal, and rotational planes is obtained by doing a 3D-CT scan, which allows for further precise planning and correction of lower limb deformities.

INTRODUCTION

Accurate assessment and correction of lower limb deformities are essential for both adults and children. It helps prevent impaired biomechanics, which can lead to irreversible early degenerative damage in the surrounding joints. By addressing these deformities, we can protect joint health and ensure better overall mobility and function. An accurate and precise understanding of the orientation of the skeleton involved is essential for reproducing the correction via osteotomies. Full-length standing anteroposterior (AP) and lateral radiographs are used to plan deformity correction till now.[1,2] Complex deformities in lower limbs are frequently found in multiple planes. Obtaining a true AP and lateral full-length radiograph for all the joints simultaneously in complex deformities of the lower limb, especially with rotational component, is very difficult. This is where the standard AP and lateral radiographs fail to depict the multiplanar deformities accurately. Obtaining accurate AP and lateral radiographs of a deformed limb poses significant challenges, particularly when these procedures are performed infrequently by radiographers in a clinical setting. Despite meticulous efforts, the probability of capturing an oblique view is considerably higher. Consequently, this complicates the ability to obtain precise measurements necessary for optimal deformity correction. Relying solely on radiographic images may result in inaccuracies, which can contribute to suboptimal correction of the deformity and ultimately lead to poor functional outcomes. Three-dimensional computed tomography (3D-CT) scan can provide additional information on the deformities, including their orientation.[3] 3D-CT scan provides an accurate description of deformity in all planes.[,4,5,6] We present a novel solution to this problem with the use of 3D-CT scan images instead of radiographs for lower limb deformity planning and correction.

MATERIALS AND METHODS

Over a 5-year period, starting in September 2017, 107 patients at the Polio and Deformity Correction Centre in Bhola Hospital, Kurukshetra, Haryana, India, were evaluated for lower limb deformity correction and underwent 3D-CT scanning as a prerequisite for preoperative planning. All patients aged 10 years to 50 years undergoing deformity correction in the lower limbs were included in the present retrospective study. Hospital records were uprooted from hospital information management computer system. Patients aged <10 years, more than 50 years, patients with comorbidities, and patients with systemic illnesses affecting bone healing were excluded from the study. The study was approved by the institutional review board. All patients provided informed consent for inclusion into the study. Many patients presented with full-length radiographs, which often failed to provide a true AP view [Figure 1]. To mitigate the risk of erroneous angle calculations essential for deformity correction, a preliminary assessment was conducted using lower limb scanograms with the patella centered, as illustrated in Figure 2. This approach aimed to ensure accurate angle measurements, which are crucial for effective deformity correction. Digital Imaging and Communications in Medicine (DICOM) images were acquired from the scanning console, facilitating a reproducible platform for the digital extrapolation of lines and precise angle measurements. The 3D-CT scan was done for all patients undergoing surgical correction of deformities. To obtain a straight limb and accurate 3D-CT images in cases with flexion deformities, the following improvised technique was employed: both feet were tied together at the ankles in complete dorsiflexion and the limb was placed at an angle over a firm Styrofoam block [Figure 3]. This ensured that the knees remained in full extension, which was a prerequisite for obtaining 3D-CT scans to assess sagittal plane deformities. A stable weight was placed on the front of the thigh, and both the feet were raised on a platform to maintain this position during CT scan [Figure 4]. This allowed for proper AP and lateral views of the limb in both coronal and sagittal planes during the 3D-CT scan. Three templates were made in all cases, i.e., true AP in the frontal plane with patella forward, true sagittal plane from the medial side, and true sagittal plane from the lateral side as illustrated in Figure 5. Now, all the angles and deformity calculations, which are routinely done as advocated by Paley et al., are done on these templates described [Figure 6].[1] The levels of the deformities are marked and measured. In another transverse plane, rotational issues were also added when correcting the deformities. The level of osteotomies was demarcated on the 3D-CT scan. The length and thickness of the Schanz pins and their placement were decided after taking a rough estimate of the kind of measurements for the rings, their size, number, position, and placement. The direction of insertions of Schanz pins was also evaluated to avoid injury to neurovascular structures. Accurate calculations of angles were made with the full-length 3D-CT images by rotating the limb in 5° increments in the following positions: (i) patella forward, (ii) hip forward, and (iii) ankle forward. This method enabled precise quantification of rotational deformities in the femur and tibia relative to each other.

Figure 1.

Full-length radiograph in the frontal plane showed a left lower limb deformity, but patella is not centered

Figure 2.

Full-length radiograph of the lower limb with patella in center and limb length discrepancy compensated by wooden block under the short limb

Figure 3.

Improvised technique to obtain straight limb in flexion deformity of the knee; both the feet tied together at the ankles in complete dorsiflexion and the limb was placed at the angle over a firm Styrofoam block

Figure 4.

Patella marked in the center, while both the feet are tied together to keep dorsiflexion with a stable weight on the front of thigh to take computed tomography scan of the limb

Figure 5.

Three-dimensional computed tomography full-length scan of the lower limb in the front plane patella in the center, true anteroposterior view, and lower limb in the sagittal plane with both condyles overlapping showing a sagittal plane view, true lateral view

Figure 6.

Accurate and precise assessment of the deformities in both anteroposterior and lateral projections of the computed tomography scan

These techniques facilitated the acquisition of high-quality 3D-CT scan images and allowed for more accurate and precise measurements of lower limb deformities, which is essential for effective preoperative planning and surgical correction.

Patients were subjected to all applicable preoperative examinations for preanesthesia checklist. Patients were operated in supine position under regional or general anesthesia under image intensifier control.

Postoperative management

Pin tracts were sealed with povidone iodine-soaked gauge pieces dressed at regular intervals. The patients were demonstrated pin site care and dressing every alternate day. Deformity correction was done under supervision during hospitalization period using Hexapod correction system. Range of motion exercises and muscle strengthening exercises of all joints in lower limb were advised as per pain tolerated.

RESULTS

Between 2017 and 2022, a total of 107 patients underwent deformity correction at our institution. Among these, 62 were male and 45 were female, with a mean age of 31.7 years (ranging from 10 to 50 years). Of these patients, 89 were treated for postpolio residual sequelae, which included one case of hyperextension deformity and the remainder presenting with fixed flexion deformities (FFDs) at the knee. In addition, one polio patient presented with an extra-articular fracture of the proximal third of the tibia, which was stabilized alongside an intertrochanteric osteotomy performed during the same surgical session. Ten polio patients required concurrent procedures at the foot and ankle, which included Tendo-Achilles lengthening, posteromedial soft tissue release, triple arthrodesis, or pantalar fusion. The majority of patients underwent supracondylar osteotomy, intertrochanteric osteotomy, and, when necessary, high tibial and fibular osteotomies, as summarized in Table 1. Three patients had surgeries for knee osteoarthritis, with two undergoing high tibial osteotomies and one receiving a supracondylar osteotomy; one of these patients also had simultaneous genu valgum correction. Three patients received corrections for congenital talipes equino varus (CTEV), including one with bilateral involvement. Seven patients with cerebral palsy underwent bilateral corrections, three of whom had hemiplegia. Five patients were treated for deformities around the knee joint, including one patient with a deformity due to postseptic arthritis sequelae resulting in a limb shortening of 6 cm, and another with a deformity secondary to posttraumatic nonunion. Two patients were treated for genu valgum and one for bilateral genu varum. All patients had application of Ilizarov ring fixator along with Hexapod frame for bony deformity correction. All patients were mobilized on the 1^st postoperative day, with gradual weight-bearing introduced as tolerated. Out of the 107 patients, 91 underwent gradual correction using the Hexapod frame (Ortho-SUV, Pitkar, India); rest of 16 patients had acute correction. After achieving the desired correction, patients were transitioned from the Hexapod to a set of straight connecting rods with hinges. Patients were monitored using SUV software for daily adjustments to the frame. All patients had full correction of bony deformities. Serial radiographs were taken to assess bony union. The average duration of hospitalization for all patients was 4.6 months (range, 3–6 months). The Ilizarov frame was removed only after full bony consolidation at the osteotomy sites was confirmed, allowing for discharge. The cases were categorized as follows: polio (n = 89), cerebral palsy (n = 7), osteoarthritis (n = 2), CTEV (n = 3), and miscellaneous deformities (n = 6). Representative figures illustrating the planning and correction of lower limb deformities are presented in Figures 7 and 8, respectively. Superficial pin tract infection occurred in 19 patients, which was managed with pin site care and oral antibiotics. No patient had deep pin tract infection or infection at corticotomy site or refracture after fixator removal. No patient had postoperative loss of range of motion more than 15° in knee, hip, or ankle of the affected limb. All patients were active without any significant pain. No patient had iatrogenic neurovascular injury or reflex sympathetic dystrophy.

Table 1.

Details of operative procedures done in patients with lower limb malalignment

Corrective operative procedure of deformed bones	Number of patients
Supracondylar osteotomy	24
Supracondylar osteotomy + intertrochanteric osteotomy	35
Supracondylar osteotomy + supramalleolar osteotomy	2
Supracondylar osteotomy + intertrochanteric osteotomy + high tibial osteotomy	8
Intertrochanteric osteotomy + high tibial osteotomy	11
Supracondylar osteotomy + intertrochanteric osteotomy + supramalleolar osteotomy	6
Intertrochanteric osteotomy	7
High tibial osteotomy	3
Intertrochanteric osteotomy + high tibial osteotomy + supramalleolar osteotomy	1
Supramalleolar osteotomy	2
Supracondylar osteotomy + high tibial osteotomy + supramalleolar osteotomy	2
High tibial osteotomy + supramalleolar osteotomy	1
Supracondylar osteotomy + high tibial osteotomy	3
Supracondylar osteotomy + supramalleolar osteotomy	2

Figure 7.

A 13-year-old female with bilateral genu varum, operated by means of high tibial osteotomy and fibular osteotomy

Figure 8.

A 24-year-old female with congenital deformity of the right lower limb and genu varum deformity of the right knee joint and distal tibia in varus operated by means of high tibial osteotomy and supramalleolar osteotomy

DISCUSSION

3D-CT scanning of skeletal deformities provides a comprehensive perspective for deformity assessment and correction strategies. The primary advantage of 3D-CT is its ability to evaluate deformities across all anatomical planes in a single investigation, significantly enhancing the precision of preoperative planning compared to standard radiographs.[3,4] This advanced imaging modality allows for angle calculations with an accuracy of up to 0.001° using DICOM software on a volume rendering platform. Furthermore, digital images can be easily shared among team members to facilitate the evaluation and improve interobserver reliability.[5,6] In contrast, the equipment necessary for obtaining standing full-length weight-bearing X-ray scanograms is not widely available among hospitals and is limited to a few specialized centers with trained radio technicians. Conversely, 3D-CT is now more readily accessible in many urban areas.

3D-CT scan is particularly beneficial for identifying deformities with center of rotation of angulation located near the epiphyses, allowing for meticulous treatment planning.[,8,9] The high-resolution images produced by 3D-CT scan offer extensive magnification and a user-friendly interface, thereby enhancing measurement accuracy. The overall magnitude of the deformity can be assessed from a comprehensive view, visualizing the entire limb in a single frame. In cases of complex deformities characterized by multiple malorientation, malalignment, and malrotation syndromes, 3D-CT scanning is invaluable for mapping the relationship between the apex of the deformity and surrounding neuromuscular structures, thereby minimizing the risk of intraoperative injury to these critical components.[3,7,9,10]

Proximal femoral deformities are often obscured when attempting to obtain full-length lateral radiographs due to overlapping soft tissue shadows. 3D-CT scan effectively delineated the bone outlines, enabling accurate identification of abnormalities and necessary corrections.[9,10] Specifically, a precise line drawn from the head of the femur to the midpoint of the ankle is essential for accurately determining FFDs at the knee, underscoring the importance of a complete lateral view of the femoral head in deformity assessment.[11] In addition, 3D-CT scans facilitate the assessment of healthy muscle mass in comparison to affected poliotic muscles, providing an indirect measure of muscle power in each segment.[12] This information is crucial for planning potential muscle or tendon transfer procedures in conjunction with deformity correction. When placing Schanz pins and Ilizarov wires, consideration of the trajectory of vessels and nerves is essential for ensuring their protection against iatrogenic injury. Knowledge of the proximity of the osteotomy site to these structures allows for precise surgical planning and execution.

Radiation exposure from extremity radiographs is approximately 0.1 mSv per view. To fully ascertain the bony morphology of a deformed lower limb, a minimum of five views (including pelvis AP, full femur AP and lateral, full leg AP and lateral) would result in a total radiation exposure of around 1 mSv for both limbs.[13,14] In comparison, a full-body CT scan also delivers approximately 1 mSv of radiation.[14] Thus, scanning only the lower limbs results in a radiation dose of 0.5 mSv per side, which is comparable to the cumulative exposure from multiple radiographs.

The authors suggest the following advantages of use of 3D-CT scan images over full-length AP and lateral radiographs for planning of bony deformity correction:

1. Obtaining accurate full-length scanograms, especially in the sagittal plane, is challenging with radiography. 3D-CT scan allows precise delineation of the proximal femur and easy calculation of femoral anteversion/retroversion

2. Radiographs often fail to show complete overlap of the femoral condyles, essential for assessing the true lateral view. This can lead to errors in measuring sagittal plane deformities, which is compounded in complex deformities. 3D-CT avoids these technical limitations

3. 3D-CT enables accurate assessment of rotational deformities and the relationship between maloriented joints above and below diaphyseal deformities in multiple planes

4. 3D-CT scanning is not affected by patient positioning

5. Specific tissues like bone, muscle, tendon, and skin can be selectively highlighted in the 3D reconstructions

6. The shape and deformities of bones and joints are easily evaluated with 3D-CT

7. DICOM images from 3D-CT can be used to create 3D models of deformed joints, allowing surgeons to comprehensively assess complex deformities for planning correction

8. In polio limbs, the posterior proximal tibial angle differs between the medial and lateral views on 3D-CT in the sagittal plane. This aids in assessing and planning correction of the knee flexion deformities.

We have progressed from a time, in the initial part of the 20^th century when plaster castings and manipulations were done. Then, more precision has come with the help of Ilizarov combined with computer-assisted Hexapod fixators.[15] In the last 20 years, the advancement in biomedical engineering has introduced the Hexapod fixator systems.[16] This has ensured that deformity correction can be done in the most user-friendly manner.

CONCLUSION

Use of 3D-CT scan images as AP and lateral views instead of radiographs helps in accurate planning and 3-dimensional (sagittal, frontal, and coronal planes) correction of lower limb deformities.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.