In no area of orthopaedics is it more important for the clinician to accurately assess and plan the management of their patient’s treatment than in pediatric limb reconstruction. The inherent complexity of these patients with lower limb discrepancy and deformity combined with the effects of growth and development means that the treating surgeon has to consider a large number of variables before recommending a particular program of treatment.1
A systematic approach to assessment of the child with a complex lower limb deformity is essential to achieve the desired outcome with the lowest rate of complications.
Although a general history of a child’s problem is core in any evaluation, there are a number of particular areas of importance when assessing the patient with a complex lower limb deformity. In the growing child one needs to have a clear understanding of what the effects of growth have had over time on the deformity and to what extent the deformity is affecting activities of daily living. Clarification of the goals the child and family are seeking can be difficult but in doing so any unrealistic expectations can be identified and addressed from the outset.
Key elements of the medical history for patients undergoing limb reconstruction are:
- Current problem
- Previous treatment
- Clarification of diagnosis
- Parental concerns and expectations
- Psychosocial stability2
- Support networks—family, school, and community
- Family financial situation
The process of undertaking a clinical examination generally follows a standard pattern that minimizes the potential to miss important findings that could influence the type of treatment undertaken. Unfortunately, in pediatric practice, younger children may not be predisposed to the examiners wishes so it is important that the clinician is flexible in their approach and be prepared to use observation, often surreptitiously, as a means to gain the clinical information required. Often second or third consultations maybe required for a child to become comfortable enough to allow direct examination.
Observational Gait Analysis
In the more standardized approach, the clinical examination should start with an appropriately exposed patient undergoing observational gait analysis. The examination of gait requires considerable practice but is an essential part of the assessment as it reflects a summation of the lower limb function being translated into propulsion. The presence of a limp, a disturbance to the rhythm of walking, requires the observer to carefully analyze the individual components of the walking cycle to come to a conclusion as to the underlying cause of the observation (Fig. 1).
The patient should be examined from the front, back, and side, both in walking and in most cases running.3 It is best to start looking for abnormal truncal movements and then focus on the end organ that is the foot. What is the progression angle? Which part of the foot makes contact with the ground first? Are the 3 rockers present? Is there clearance through swing? (Fig. 2).
It is then much easier to look at the other individual components of gait within a kinematic framework and then come to a global conclusion about the gait pattern with the specific disturbance well understood.
Now with the patient standing in a balanced position the overall alignment in the coronal and sagittal plane can be appreciated. The interplay between the spine and pelvis and lower limbs is complex and may require a number of special tests to determine whether one or other is driving the perceived deformity. For example, if a patient is found to have a spinal curvature a forward bend test would reveal a rib hump if this is a true scoliosis but not if a list. A flexible list because of a limb-length discrepancy would correct if the patient sits.
If a patient has a limb-length discrepancy without joint contracture or instability, then it is best to assess alignment with an appropriately sized block under the short limb to level the pelvis and balance the spine before commenting on the observed posture.
The assessment of joint range of motion and stability is an essential part of the clinical examination especially so when it comes to determining limb-length discrepancy. Joint contractures may occur as part of the underlying disease process or be a reflection of long-standing compensation for deformity at another level.4 The most obvious example is exaggerated lumbar lordosis because of a fixed flexion contracture of the hip. The importance of identifying and recognizing contractures and compensations cannot be overemphasized as correction of deformity at one site could potentially lead to the induction of a problem at another. One such example would be a patient with a long-standing genu varum who compensates with subtalar valgus and forefoot pronation to keep the foot flat to the ground. Correction of the genu varum may lead to abnormal loading of the foot medially if those joints are stiff and unable to correct.
The presence of joint instability may be because of soft tissue or bony issues. The clinical examination aims to distinguish between these 2 problems but often in complex situations the examination needs to be supplemented with specific imaging or examination under anesthesia with or without arthrography.
Although it is generally easy to appreciate coronal and sagittal plane alignment, the axial plane can have major effects on lower limb function and is often underappreciated during the clinical examination. The Staheli et al5 rotational profile is an excellent approach to the clinical assessment of lower limb rotational alignment as consists of the following elements.
- Foot progression angle
- Arc of hip rotation in extension
- Thigh foot angle
- Foot shape
Joint laxity may lead to spurious measurements of rotation and often radiologic assessment is also required.
It is always important to save the assessment of the limb lengths to the end of the examination as prior knowledge of joint contracture or instability will direct the method by which limb-length discrepancy is determined.
Limb-length discrepancy can be categorized as true (segmental bony shortening), functional (joint contracture or instability), or combined. Functional limb-length discrepancy is also known as “apparent” discrepancy (Fig. 3).
True limb-length measurements can easily be made utilizing blocks of various sizes placed under the foot until the examiner is satisfied that the patient is standing level. Care must be taken in patients who have an asymmetric pelvis, say from hemihypertrophy or from previous surgery, as this can lead to spurious measurements. If there is a functional element to the discrepancy, then both limbs need to be placed in similar positions and measured with a tape from corresponding boney points. This assessment is difficult to perform and the mechanical axis radiograph may not provide the correct answer. It is in this situation that the computed tomographic (CT) scanogram or EOS examination can provide the correct answer as simultaneous orthogonal images are obtained that allow biplanar assessment of the skeleton (Fig. 4).
The mechanical axis radiograph is the workhorse investigation for deformity analysis. This radiograph attempts to accurately reproduce the skeletal structures that contribute to lower limb deformity. To obtain a true representation of the patient’s skeleton, the clinician needs to have a close working relationship with the radiographer to ensure the correct exposure and positioning of the patient is achieved.
In general, the patient is placed in a balanced position with the patellae pointing forward, knees in neutral extension and heels in the same position. If the patient has a limb-length discrepancy, an appropriate raise should be placed under the foot to level the sacrum. If the patella is subluxated, the epicondylar axis should be put parallel to the plane of the film and if there is a significant rotational malalignment, consider taking the image with both the patella forward and then feet forward to uncover the effect of the rotation on any underlying deformity6 (Fig. 5).
Patients with fixed coronal or sagittal plane deformities are challenging to image and hence segmental films at right angles to the underlying bone may be required.
Common Forms of Mechanical Axis Imaging
- Teleoroentgenogram—1 m film, tube to film distance 3 m, prone to exposure issues and parallax.
- Computer radiology—3 separate stitched images, better exposure, and reduced parallax.
- EOS—parallel beam biplane image capture, low radiation dose, no parallax, even exposure, difficult positioning, and potential for movement artifact.
The mechanical axis radiograph will not provide all of the information about the underlying deformity especially when dealing with joint pathology.6 Specific radiologic investigations may be required for each joint and may also include the use of stress views and arthrography.
Axial imaging is used to assess 3 dimensional anatomy and rotational alignment. Such imaging can be transformed into 3 dimensional models that can powerfully illuminate complex deformities and clarify surgical planning. Although CT scanning exposes the patient to higher radiation doses, if used appropriately it can be an important tool that allows the development of virtual and real models of the boney segment or joint that can be manipulated and operated upon as a prequel to the actual surgery.
Three dimensional instrumented gait analysis is a technically demanding process that requires a significant investment and highly trained staff. High quality video combined with kinematic and kinetic data can greatly help understand the cause of gait disturbance especially in the situations of neurological disturbance. When such gait analysis is not readily available, one should not underestimate how much information can be obtained by good biplanar video of a patients gait without a full-instrumented analysis.
How the end organ of the limb loads can be difficult to visualize and foot pressure studies provide some insight into both dynamic and static aspects of weight-bearing. Perspex standing platforms are simple devices that clearly show static pressure distribution and can help clarify the degree and type of correction required. Dynamic studies demonstrate the progression of weight-bearing during the stance phase of walking and help with an understanding of load transference.
As previously described axial imaging from both CT and magnetic resonance imaging can be manipulated to produce virtual 3 dimensional images of bones, joints, and specific soft tissue structures. In the simplest form, these images can be viewed from multiple perspectives to give clarity to the underlying deformity. It is now possible to use software to perform virtual deformity correction either to a known normal or utilizing a mirrored opposite normal limb. Implants can be trialed and different surgical techniques explored.
These images can be used to produce a range of printed models for handling, manipulation, and even sham surgery. None of these techniques should be used as an alternative to careful clinical examination and experience as there is a considerable difference as to what can be done virtually to what is possible both anatomically and physiologically.
ANALYSIS AND PLANNING
The information acquired from the history, examination, and investigations now needs to be analyzed and synthesized into a treatment algorithm that is specific for the patient.
The formal process of deformity analysis usually starts with the mechanical axis radiograph in most cases and supplemented with analysis of other imaging and investigations. Analysis of the mechanical axis radiograph7 may be done on the long film but most commonly the DICOM file of the image is transferred into one of the commercial analysis packages that use various degrees of semiautomation to assist the surgeon.
In essence the standard steps undertaken are8:
- Overall limb alignment—does the deformity affect the axis of the limb?
- Orientation tests—does the deformity affect the axis of the bone?—is there deformity in the joint?
- Identify deformity—where is the rotation axis of the deformity? (Fig. 6)
Depending on the circumstances, this analysis is performed in both the coronal and sagittal plane taking into account any rotational malalignment.
All other imaging also needs to be analyzed and the results of other investigations taken into consideration in arriving at a treatment plan. Virtual surgery can be performed in 2D or 3D, various techniques and implants tested and the result of the correction planned reviewed.
At this stage, there are a series of questions that surgeons need to ask themselves before committing to the proposed surgery.
- Do I understand the natural history of this condition?
- Can I positively change this natural history?
- Is my global deformity analysis correct?
- What are the alternative treatments?
- Do I have the required skills to do this procedure?
If the answer to any of these questions is equivocal then either further information is required, other options explored or referral made to a more experienced service.
Limb reconstruction techniques are evolving and becoming more accurate with less invasion of the patient. Such progress means that very careful evaluation and planning is even more important to avoid significant morbidity for this complex group of patients.9
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