Malalignment of the lower extremity is presumed to cause and/or accelerate degenerative arthritis. The limited data available on the long-term effects of lower extremity malalignment supports this conclusion. Strong evidence that deformities in children cause degenerative disease does not exist, although a review of the available literature suggests a relationship. A small body of literature relates to gait analysis as it relates to deformity correction, which may lead to future advances in the understanding of lower extremity deformity.
The knee is the most common joint to require arthroplasty.1 As a result the largest body of literature available to review with regard to deformity prevention and correction centers on the knee. Realignment procedures have been traditionally utilized in hopes of preventing or delaying arthroplasty, with varying success.2
A PubMed search was conducted using appropriate keywords and phrases: natural history pediatric deformity, lower extremity malalignment, knee arthritis deformity, fracture knee arthritis, genu varum arthritis, genu valgum arthritis. Various combinations of these search terms were also used. As the knee remains the most common joint to undergo arthroplasty, literature search was focused in this area. Identified articles were then reviewed, and any pertinent references obtained and also reviewed. In order to remain strictly relevant to pediatrics, articles reviewing deformities acquired in adulthood were not referenced. Biomechanical data and animal studies were included when data and experimental design was focused on potential long-term results of malalignment.
Clinical and Experimental Data With Regard to Long-term Consequences of Joint Malalignment
The role of coronal plane deformity and subsequent generation of pathologic forces through the knee joint has been examined by McKellop et al3 Simulated malalignment was created in 5 degree increments up to 20 degrees at multiple levels in the tibia. Varus and valgus deformities were analyzed. The level of deformity was critical in determining the amount and distribution of load measured in the joint. At 20 degrees, a distal third deformity increased stress up to 26% in direction of deformity on the concave side, and unloaded the convex compartment up to 32%. In contrast, proximal deformities generated an increase of 106% and decrease of 89% in the concave and convex compartments, respectively. The role of deformity level on the pathologic forces created is illustrated in the Figure 1.
The authors concluded that varus and valgus deformity were equally deleterious to joint loads.3 However, their model assumed the mechanical axis to pass directly through the center of the knee. This contrasts with multiple papers that found average slight varus alignment in normal subjects.4–6 This assumption could have led to slight bias toward an increased valgus load at “neutral” in this study when compared with in vivo settings.
Sagittal plane deformity has not been specifically studied in biomechanical models. However, one study did examine the effect of high tibial osteotomy with increasing posterior slope as a possible treatment for joint unloading. Pressure mapping in various degrees of increased tibial slope demonstrated decreased articular pressures in the posterior aspects of the knee after flexion osteotomy.7 The effect of deformity has not been evaluated. Recurvatum of the tibial slope is thought to add strain to the anterior cruciate ligament. Further study is needed to determine the effect of sagittal plane deformity on long-term joint health.
In Vivo Experimental Studies
Two animal studies support the conclusion that coronal plane deformity of the lower extremity leads to degenerative joint disease. Wu et al8 analyzed the effect of deformity on the knee joints of New Zealand White Rabbits. Varus, valgus, or neutral osteotomies were created in the right tibia of each rabbit. Histologic evidence of a degenerative process was evident in the synovium after 12 weeks in animals with deformity; no cartilage or meniscal damage was yet evident. By 34 weeks however, all specimens with deformity demonstrated degenerative changes in the cartilage, and osteophytes were present. Varus appeared to generate more severe changes than valgus.8
Another study analyzed the role of unicompartmental increased joint loading in the absence of deformity using a compressive device applied to rabbit knees.9 This allowed for control of both the magnitude and duration of increased load experienced by the joint surfaces. Gross pathologic changes were found in the medial compartments of all knees, with lesion severity increased by higher magnitude forces and longer duration of force. Interestingly, the duration of stress was more important than the absolute amount of stress in creating arthritic change.9 Implications of this finding on clinical practice are unclear.
Clinical Cross Sectional Data
The development of arthritis secondary to mechanical axis deviation (MAD) in human subjects is not well documented in the literature. Zayer10 reported on 86 patients with long-term follow-up of Blount Disease. No patient developed arthritis before the age of 30, regardless of amount of deformity. However, after age 30, 11 of 27 knees demonstrated arthritic changes. Increasing deformity was associated with worse prognosis, although this did not reach statistical significance.10
Two studies evaluated the long-term outcome of malunited femoral fractures. Palmu et al11 reported long-term follow-up of children who had sustained femur fractures. In total, 52 patients were reviewed at a mean of 21 years after injury. Knee arthritis was detected in the injured limb of 6 patients and noninjured in 1 at a mean age of 34 years. They noted increased deformity in the sagittal and coronal plane in individuals with arthritis than in those without. Interestingly, sagittal plan deformity was more strongly associated with arthritis than was coronal deformity; this may be due to a high magnitude of sagittal deformites in their cohort. The authors concluded that acceptable angulation in individuals over 11 years of age is 10 degrees of sagittal deformity and 5 degrees of coronal deformity. The level of deformity relative to the knee was not correlated with arthritic change in their study.11
A second study evaluating slightly longer term outcomes of malunited femoral fractures drew a similar conclusion. Kettelkamp and colleagues evaluated 14 patients with 15 limbs with 31 year follow-up (range, 10 to 60). Nine femoral fractures had residual varus from 3 to 25 degrees, and all patients developed arthritis at an average age of 28 years. The authors noted that the arthritic compartment was universally the one overloaded by deformity, and that varus produced earlier arthritic changes than valgus.12 However, the authors did not stratify outcomes according the level of deformity or the overall MAD.
Dietz and Merchant evaluated the long-term outcome of malunited tibial fractures in 37 children at an average of 29-year follow-up. They reported a nonsignificant increase in radiographic arthritic grade of the fractured limb compared with the nonfractured limb. Although they were unable to define a clear upper limit based on alignment and degenerative changes where outcome was unacceptable, the authors concluded that deformity of <10 degrees in the sagittal plane and 5 degrees in the coronal plane were acceptable for tibial fractures.13
Tibial malunion has also been evaluated in the adult setting by several authors. Two studies demonstrated correlation with malunion and arthritis at follow-up of 8 to 24 years. Degenerative disease was more common with varus than valgus malalignment. Both authors concluded that anatomic alignment was ideal, with statistically increased risk of arthritis after malunion >5 degrees.14,15 In contrast, another study found minimal to no increased risk of arthritic change at 28 years follow-up of tibial malunions. However, the group was highly selected and only 5 of 88 patients had proximal 1 of 3 fractures, which would have higher risk of degeneration based on extrapolation from biomechanical data. Only 2 patients had higher than 15 degrees of angular deformity.3,16
Clinical Follow-up Data: Correction of Malalignment
The long-term outcome of children who have undergone limb realignment for deformity has not been reported in the literature. A wealth of data are available with regard to the treatment of adults with established arthritis using joint realignment procedures; however detailed review of this literature is beyond the intended scope of this review. A meta-analysis of high tibial valgus osteotomy versus unicompartmental arthroplasty demonstrated mean survival time to total knee arthroplasty of 9.7 years, with 90% survival at to 5 to 8 years of follow-up.17 It has been demonstrated that joint realignment for less severely affected knees has improved outcome compared with more severe disease.18 Extrapolation of these data to the pediatric population and preventative surgical intervention is difficult, although it stands to reason that prevention would have a longer lasting effect than delayed treatment.
As regards, the natural history of a joint that has been surgically realigned, relatively few studies are available to give guidance. A study of high tibial osteotomy with second look arthrotomy demonstrated the presence of “regenerated” cartilage in the site of previous overload and cartilage defect.19 It is unclear what the durability of this regenerated tissue is, but it may indicate improved joint health after relief of pathologic loading. In animal models, it has been shown that the duration of pathologic loading is critical to the development of arthritis.20 It is reasonable to anticipate that earlier relief of the abnormal loading would correlate with better cartilage health in the long term, though this remains unproven.
Gait Laboratory Data
When using standing images, we assume a static representation of a dynamic problem. The correlation between lower extremity angular deformity and joint overload during gait is not necessarily 1:1.21 Alterations in gait parameters to compensate for lower extremity deformity and to possibly decrease joint overload have been observed.22 Further study may eventually help elucidate why some patients progress to osteoarthritis and some do not, despite similar static images.
Wang and colleagues evaluated the long-term outcome of proximal tibial osteotomy for medial arthritis interpreted through the lens of the gait laboratory. Internal tibial rotation can increase the adductor moment. Dividing patients with similar static alignment into high and low knee adduction moment groups based on preoperative gait analysis generated a large discrepancy of outcomes, with reduction from 100% good to excellent results in the low adduction moment group to 64% in the high adduction moment group. An increased rate of deformity recurrence was also noted in the high moment group.23
A recent study reviewed gait laboratory evaluation of patients before and after growth modulation for coronal deformity. Eight patients were treated with growth modulation for idiopathic genu varum or valgum. The authors found that changes in static alignment measurements correlated well with changes in the gait laboratory between preoperative and postoperative analysis. However, both in the preoperative and postoperative settings there was little correlation between abnormal static alignment and dynamic loading abnormalities. The authors noted that abnormal parameters were generated in 2 patients who had previously normal analysis before growth modulation.24 As a result, they argued that preoperative normal gait analysis in the setting of static deformity should generate careful review of surgical indications.
In contrast, a previous and larger study of 16 patients with idiopathic genu valgum treated by growth modulation demonstrated normalization of gait parameters and static measurements through guided growth. Generation of pathologic gait parameters was not noted in their study. No patient was noted to have normal gait analysis before implantation however, indicating that further study of this concern is needed.25
Patellofemoral (PF) Joint Considerations
The PF joint is known to undergo arthritic changes at a high rate.26,27 The role of mechanical alignment in PF degenerative changes has been evaluated in several clinical studies. Weinberg and colleagues reviewed anatomic and demographic factors associated with PF arthritis in a sample of 71 human skeletons. Valgus alignment was noted to have a modest effect on development of PF arthritis, as was a lateral tibial tubercle and shallow trochlear groove.28
Teichtahl and colleagues reviewed initial and follow-up radiographs and magnetic resonance imaging studies in patients with symptomatic osteoarthritis of the knee. Specific attention was paid to mechanical alignment and PF cartilage volume. They noted decreasing lateral patellar cartilage volume in subjects with increasing valgus alignment. The authors posited that this is due to increasing lateral loads in the PF joint.29 Two large studies of patients with known PF osteoarthritis demonstrated increasing rates of lateral PF arthritis with valgus alignment and medial PF arthritis with varus alignment.30,31 Three-dimensional analysis of patellar spin during resisted knee extension exercises demonstrated internal spin with varus knees, and external spin with valgus knees, indicating a complex relationship between patellar mechanics and coronal alignment.32 Further study is needed to elucidate the contribution of mechanical alignment to PF disease.
Correlating Deformity Angles With MAD
Many surgeons measure lower extremity deformity using the concept of mechanical axis deviation, with subsequent description of zones of the knee through which this axis may pass.33 The correlation of this with tibiofemoral angles is not necessarily direct. Depending on segmental lengths, femoral neck orientation and length, different angles may manifest variably when measuring MAD. The use of MAD for deformity measurement is more sound from a strict mechanical standpoint, as the force experienced at the fulcrum is strongly related to the length of the lever arm. Therefore, direct correlation of MAD with the angles measured in many older papers is difficult. On the basis of the authors experience, 5 degrees correlates well with zones 1 to 2, and 10 degrees correlates well with zone 3 (Figs. 2–5). A study to confirm this is currently underway.
To summarize available biomechanical, experimental, and clinical data, it is clear that deformity generates abnormal joint forces, which in animal models creates early degeneration and arthritic change. Clinical data supports the concept that this is a relevant concern in the human knee. The long-term effects of malalignment correction remains unclear, but based on extrapolation of data from joint salvage procedures and experimental studies, early realignment of symptomatic individuals can be expected to be helpful.
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Keywords:Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.
lower extremity malalignment; degenerative arthritis; genu varum; genu valgum