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Investigation of the Relationship Between Hip and Knee Osteoarthritis and Disordered Spinal and Pelvic Morphology

Introduction A critical question is the causal relationship between hip or knee osteoarthritis (OA) and disordered spinal and pelvic morphology. The aim of this study is to examine this correlation. Therefore, we studied the effect of total hip or knee arthroplasty (THA/TKA) on truncal parameters to determine the causal relationship between these two situations. Materials and methods This is a prospective study of the effect of THA or TKA in patients with hip or knee OA on truncal morphological parameters. Patients with one-sided hip or knee OA who chose to undergo THA or TKA were enrolled and surveyed. A control group (CG) was also surveyed for comparison with the patients. The patients were preoperatively examined for truncal parameters using the Diers Formetric four-D analysis system (surface topography technique) to calculate several truncal parameters in all planes at four months and 12 months postoperatively. Measurable examinations were performed using the Statistical Package for the Social Sciences (SPSS) version 17.00 (SPSS Inc., Chicago), and statistical significance was set at a p-value of <0.05. Results The study examined 34 patients who underwent THA, including 19 women and 15 men with a mean age of 67.62 ± 8.28 years. The study also examined 45 patients who underwent TKA, including 34 women and 11 men, with a mean age of 72.42 ± 7.0 years. These patients were also compared with a CG that consisted of 25 normal individuals, including 12 women and 13 men, with a mean age of 69.28 ± 10.11 years. The results of this study from four months after THA revealed that the lordotic angle, trunk torsion, pelvic inclination, pelvic obliquity, and pelvis rotation were improved to normal levels. At 12 months after THA, only the pelvic obliquity was improved to normal levels. At four months after TKA the lordotic angle, pelvic inclination, and pelvic obliquity were improved to normal levels. However, the fleche cervicale and vertebral rotation were worse. At 12 months after TKA, only the pelvic obliquity was improved to normal levels. Conclusions THA and TKA to correct hip and knee OA do not correct the disordered morphology of the trunk in the long term. Thus, hip or knee OA does not seem to be responsible for disordered trunk morphology. However, it cannot be ruled out whether the disturbed morphology is responsible for the appearance of the hip and knee OA.


Introduction
It is known from many studies that patients with hip and knee osteoarthritis (OA) have disordered spinal and pelvic morphology [1][2][3][4][5][6][7]. A critical question of concern in the orthopedic community is what the relationship is between hip and knee OA and disordered spinal and pelvic morphology. Specifically, it is unknown whether there is a causal relationship between them, which of the two situations precedes the other, and whether one causes the other. These questions have not been answered in recent studies [5,8,9].
The present study attempts to answer these questions by examining the impact of total hip or knee arthroplasty (THA/TKA) in patients with hip or knee OA on truncal morphological parameters. The same groups of patients with hip or knee OA have already been studied and compared with a control group (CG), and disturbed trunk morphologies have been found in both groups of patients preoperatively [1].
Thus, we assumed that if we have improvement of the truncal parameters after THA or TKA in the long term to correct hip or knee OA, then the hip and knee OA could be the cause of changes in the morphology of the spine and pelvis. In the opposite case, if the changes of the truncal parameters are still present after THA and TKA, then this could exclude that OA is responsible for the appearance of the disordered morphology of the trunk. However, it could not be determined whether the disturbed morphology of the trunk is responsible for OA.

Study design
This is a prospective study of the effect of THA or TKA in patients with hip or knee OA on truncal morphological parameters. Patients with one-sided hip or knee OA who chose to undergo THA or TKA at Tzaneio General Hospital of Piraeus were enrolled and surveyed. A CG was also surveyed for comparison with the patients. The study was approved by Attikon University General Hospital's Institutional Review Board (ΕΒΔ390/ 9-9-2014, date of approval 24-9-2014). The principles of the Declaration of Helsinki were applied throughout the study. Informed consent was obtained from all participants.

Inclusion and exclusion criteria
The following inclusion criteria of the CG were applied: (1) without OA in the joints of lower extremities, (2) without neurological deficits in lower extremities, (3) without a history of surgical intervention in the spine or lower extremities, and (4) without other diseases that would affect the alignment of the trunk. The following exclusion criteria of the patients were applied: (1) marked OA in other joints of lower extremities, (2) arthritis secondary to other diseases, e.g., ankylosing spondylitis, rheumatoid arthritis, developmental dysplasia, and trauma, (3) neurological deficits in lower extremities, (4) history of surgical intervention in the spine or lower extremities, and (5) other diseases that would affect the alignment of the trunk.

Data collection
The patients were preoperatively examined for truncal parameters using the Diers Formetric four-D analysis system (surface topography technique) to calculate several truncal parameters in all planes and at four months and 12 months postoperatively. All the calculations were performed using the Statistical Package for the Social Sciences (SPSS) version 17.00 (SPSS Inc., Chicago), and statistical significance was set at a p-value of <0.05.

Control group
The CG comprised of 25 normal individuals with 12 women, 13 men, with a mean age of 69.28 ± 10.11 years (range, 55-86 years). They had a mean weight of 79.40 ± 13.08 kg, a mean height of 165.04 ± 9.46 mm, and a mean body mass index (BMI) of 29.00 ± 3.00 kg/m 2

Patients with THA
A group of 34 patients with 19 women, 15 men, and a mean age of 67.62 ± 8.28 years (range, 47-84 years) was surveyed preoperatively. Of these patients, 15 were surveyed at four and 12 months postoperatively, 14 patients were surveyed only at four months postoperatively, and five patients were surveyed only at 12 months postoperatively. There were 20 patients who underwent an operation for the right hip, and 14 underwent one for the left hip. Four orthopedic surgeons carried out THA. Other characteristics of these patients include a mean weight of 82.32 ± 17.73 kg, a mean height of 165.79 ± 8.80 mm, and a mean BMI of 29.72 ± 4.31 kg/m 2 . Table 1 summarizes the homogeneity of the demographic characteristics between the CG and the patients with THA. No statistically significant differences were noted between the CG and patients with THA.

Discussion
We think that the relationships between the hip and knee OA and the disordered morphology of the spine and pelvis, as well as their possible causal relationship, are very interesting topics in orthopedics. We have tried to address this issue in two steps. The first step was to study the trunk morphology in two groups of patients with hip and knee OA and to compare them with a CG. The results of this study showed that the spine and pelvis morphology is actually disturbed in patients with hip and knee OA [1]. The same results were also mentioned in other studies [2][3][4][5][6][7]. The second step was to study the same groups of patients with hip or knee OA undergoing THA or TKA and to study the effect of these operations on the disturbed morphology of the spine and the pelvis.
Compared to the CG, the patients with hip OA had a greater forward inclination of the spine, increased scoliosis, more vertebral rotation and trunk torsion, and greater obliquity of the pelvis in the frontal plane [1]. The results of this study at four months after THA revealed that the lordotic angle, trunk torsion, pelvic inclination, pelvic obliquity, and pelvis rotation were improved to normal levels. In the long term, at 12 months after THA, only the pelvic obliquity was improved to normal levels.
Compared to the CG, the patients with knee OA had a greater forward inclination of the spine, increased scoliosis, apical deviation, more vertebral rotation and trunk torsion, and greater obliquity of the pelvis in the frontal plane [1]. The results of this study at four months after TKA revealed that the lordotic angle, pelvic inclination, and pelvic obliquity were improved to normal levels. However, the fleche cervicale and the vertebral rotation were worse. In the long term at 12 months after TKA, only the pelvic obliquity was improved to normal levels.
After THA there was a temporary improvement of the morphological parameters of the spine and pelvis at four months postoperatively. However, at 12 months after THA, these positive effects were eliminated, and the preoperative pathological morphology of the spine and pelvis returned. The only exception was the improved pelvic obliquity at the frontal level, which remained at 12 months.
In the case of TKA, it did not have an overall positive effect on the parameters of the spine. In the pelvis, despite the initial improvement of the sagittal inclination at four months, it was eventually eliminated at 12 months. Again, the only exception was the improved pelvic obliquity at the frontal level, which remained at 12 months. The improved pelvic obliquity at 12 months postoperatively in both groups of patients could be attributed to the fact that this parameter is largely determined by leg-length inequality. Therefore, the correction of this inequality after THA and TKA was enough to correct the pelvic obliquity at 12 months.
Thus, although THA and TKA operations repaired the hip and knee OA, they could not repair the disturbed morphology of the spine and pelvis in the long run. This means that the hip and knee OA could not be responsible for the disturbed morphology of the spine and the pelvis, but other causes and mechanisms should be responsible for this morphology. These mechanisms apparently persisted postoperatively, resulting in the recurrence of the same problems of trunk morphology at 12 months. A proposed etiological mechanism could be the asymmetric action of the trunk muscles in these patients, which pre-exist and persist postoperatively, resulting in the recurrence of disturbed morphology of the spine and pelvis in patients undergoing THA and TKA. In fact, a similar pathogenetic mechanism has been described in patients with scoliosis [10][11][12].
From the results of this study, it cannot be ruled out that the disturbed morphology of the spine and pelvis could be responsible for the appearance of hip and knee OA, but further studies are needed to determine if it is truly the cause. There may also be other factors than disordered trunk morphology that continue to exist after THA or TKA and could be responsible for the appearance of hip and knee OA.

Limitations
There were some limitations to this study. The first was that the number of patients was limited. The second was that not all the patients were examined at four and 12 months. The third was that the estimations using the Diers Formetric four-D system were done by only one examiner.

Conclusions
An interesting and unanswered issue in orthopedics is the relationship between the hip and knee OA and the occurrence of disturbed morphology of the trunk, as well as their possible etiological relationship. From this study, it appears that hip and knee OA is not responsible for the disturbed morphology of the trunk. On the other hand, it is still unclear whether the disturbed trunk morphology is responsible for causing the hip and knee OA. Other studies are necessary to provide an answer to this interesting question.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Attikon University General Hospital issued approval ΕΒΔ390/ 9-9-2014,. Attikon University General Hospital issued approval 24-09-2014. Consent was obtained by all participants in this study. The study was approved by the hospital's Institutional Review Board (ΕΒΔ390/ 9-9-2014, date of approval 24-9-2014). The principles of the Declaration of Helsinki were applied throughout the study. Informed consent was obtained from all participants. All patient data were coded and only the researchers had access to them. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.