Correlation between changes in spinal pelvic parameters and lower back pain in patients with hip spinal syndrome after total hip arthroplasty: A short-term follow-up study

Abstract

Backgroud

A number of patients with hip osteoarthritis (HOA) have lower back pain (LBP) and hip joint pain, a symptom named hip spine syndrome (HSS). The purpose of this study is to analyze the efficacy of total hip arthroplasty (THA) in treating HSS using spinal pelvic parameters and multiple clinical scoring systems.

Methods

We prospectively collected HOA patients who underwent THA by surgeons from the same medical research center. 52 patients were included in the study according to the inclusion and exclusion criteria. Analyze patient baseline information, take full-length lateral radiographs of the spine before and 6 months after surgery, measure PI, PT, LL, SS, and SVA. Calculate the Oswestry Disability Index score (ODI), Visual Analog Scale score (VAS), and Hip Harris score (HHS) before and 6 months after surgery.

Results

A total of 52 patients with hip spine syndrome were included for follow - up and were divided into two groups based on whether postoperative back pain was relieved: the group with continued in back pain and the group with improvement in back pain. Among them, 33 people (63 %) achieved relief in back pain. There were significant differences (p < 0.05) in postoperative LL, SVA, and PI-LL between the two groups. There were significant differences in spinal parameter changes among patients with improved LBP after THA, with increased LL, decreased SVA, and matched PI-LL. The postoperative clinical scoring scale showed that the HHS score of the group without improvement in LBP was significantly lower than that of the group with improvement in LBP, and all clinical scores of the group without improvement in LBP were poor after surgery.

Conclusion

There was a significant difference in the changes of spinal pelvic parameters in patients with improved LBP after THA, i.e., LL was elevated and SVA were decreased, PI-LL maintains matching. These spinal pelvic parameters may be key factors in the mechanism of low back pain improvement after THA surgery.

1. Introduction

Restricted functional hip motion due to a variety of end-stage hip disorders, resulting in a wobbly gait and further symptoms of low back pain (LBP), known as Hip Spine Syndrome (HSS), was originally introduced by Offierski and Macnab.¹ in 1983. With the increasing aging population, the prevalence of coexisting LBP and hip joint diseases is increasing annually. Reports indicate that approximately 28 % adults in the United States suffer from LBP each year,² Causes serious socio-economic burdens. There are numerous etiologic factors that cause low back pain in patients with HSS, but the reasons for their occurrence are unknown.

The treatment modalities for HSS include pharmacological, physical, and surgical interventions.³ THA is an effective and widely adopted surgical procedure for end-stage hip joint diseases, especially those accompanied by femoral head collapse and secondary acetabular changes.⁴ By 2030, the projected annual number of THA procedures in the United States alone will increase by 174 %, reaching 572,000 cases.⁵ In recent years, studies have shown that a portion of HSS patients have significantly relieved their low back pain after THA,⁶ but the mechanisms by which patients recover from postoperative low back pain have not been determined. some scholars have begun to focus on sagittal spinal pelvic parameters, whose parametric changes have been studied after total hip arthroplasty (THA).

Some scholars believe that patients with HSS have a smaller lumbar lordosis (LL) or sacral tilt(SS) angle compared to normal people, which will lead to the spine being in compensation for a long time and cause low back pain7. Other studies suggest that the relief of low back pain after THA in HSS patients may be related to the sagittal vertical axis.⁸ As an orthopedic clinician, it is important to determine the reasons for the onset of low back pain as well as the mechanism of postoperative low back pain relief. Changes in spine-pelvic parameters have been reported in patients with HSS who underwent THA, but not all patients with HSS had relief of low back pain after THA, and the prognosis for patients with unrelieved low back pain is clearly poorer. Therefore, we aimed to investigate spinal parameter changes in patients who had LBP improvement after THA to elucidate the mechanism of LBP improvement.

2. Patients and MethodsStudy

2.1. Study design

Following institutional review board approval,161 consecutive patients receiving THA for osteoarthritis of the hip were recruited from January 2023 through April 2024, during the initial visit, patients were asked if they suffered from low back pain, which was recorded, wherein a lumbar VAS score of ≥3 would be included in the study. Exclusion criteria included no preoperative or postoperative spinal X-ray, incomplete clinical scoring, failure of follow-up, femoral neck fracture, death within 1 year of surgery, spinal or lower extremity surgery within 1 year of surgery, history of severe lower extremity trauma, polio hemiplegia, inability to stand before surgery, unmeasurable spinal X-ray, or history of inflammatory arthropathies involving the hip.

Basic demographic data including age, gender and body mass index (BMI) were collected. Among the patients we recruited, 72 had a lumbar VAS score of ≥3. After screening based on the exclusion criteria, a total of 52 patients were finally included (postoperative follow-up was ≥6 months postoperatively in all cases), and they were categorized into a persistent lumbar pain group (group A) and a relieved lumbar pain group (group B) based on the presence or absence of lumbar pain at the time of the last follow-up visit, out of which a total of 19 patients, 10 males and 9 females were enrolled in Group A. A total of 33 patients, 21 males and 12 females were enrolled in Group B. Baseline data such as age and body mass index (BMI) were collected from both groups and statistically analyzed to compare any significant differences between the two groups. Study design process can be found in Fig. 1.

Fig. 1.

Flowchart of patient inclusion and classification.

Fig. 1. VAS, Visual Analog Scale; ODI, Oswestry Disability Index; HHS, Harris Hip Score.

2.2. Surgical methods

All patients underwent THA, performed by orthopaedic surgeons from the same medical centre. After anaesthesia induction, the patients were positioned on the unaffected side, and the surgical approach was posterolateral. Briefly, after preoperative fixation of the pubic symphysis and sacrum, an incision extending 10–15 cm downwards from the apex of the greater trochanter was made. The skin, subcutaneous tissue, and fascia lata were sequentially incised, and the gluteus maximus muscle was bluntly separated. The hip joint was adducted and internally rotated, and the external rotator muscles were severed at their femoral attachments. The gluteus minimus muscle and the superior joint capsule were bluntly dissected to expose the joint capsule, which was then incised to reveal the femoral head and acetabulum. The femoral head and part of the femoral neck were resected 1 cm above the lesser trochanter. Acetabular retractors were used to expose the acetabulum, and the labral and pathological tissues were removed. The acetabulum was reamed at an abduction angle of 40°–45° and an anteversion angle of 10°–15° until point bleeding at the acetabular floor was achieved, after which trial prostheses were fitted. The trial prosthesis was placed into the acetabulum, adjusted to the optimal position, and secured after confirming that there was no abnormal movement or loosening. The acetabular cup and liner were then positioned and fixed. The lower limb was placed in external rotation, extension, and adduction. The femur was broached and reamed, and a trial stem was inserted to test the stability of the prosthesis. Intraoperative C-arm fluoroscopy was used to check the size and position of the prosthesis; if found satisfactory, the femoral head and stem prosthesis were implanted. The incision was irrigated with saline, a drainage tube was placed, and the wound was closed in layers.

2.3. Postoperative management

Postoperative management included muscle strengthening exercises during the hospital stay, such as ankle pump exercises and isometric contractions of the lower limb muscles, along with gait training. Patients began bed-based functional exercises within 24 h post-surgery, were mobilised out of bed after the drainage tube was removed, and gradually progressed to weight-bearing. NSAIDs were considered for pain control postoperatively.

2.4. Radiographic observational indices

All patients underwent preoperative and postoperative the whole spine in the coronal and sagittal planes in the standing position radiographs, with all images accessible and measurable within the PACS system at this medical research centre. Radiographic imaging was performed preoperatively and 6 months postoperatively. The following parameters were measured: Lumbar Lordosis (LL): the angle between the upper endplates of L1 and S1. Pelvic Incidence (PI): the angle between a line perpendicular to the midpoint of the sacral endplate and a line from this point to the midpoint of the femoral heads. Pelvic Tilt (PT): the angle between a line from the midpoint of the sacral endplate to the midpoint of the femoral heads and a vertical line from the sacral endplate. Sacral Slope (SS): the angle between the sacral endplate and the horizontal line. Sagittal Plane Vertical Axis (SVA): the distance from the plumb line dropped from the centre of the C7 vertebra to the posterior edge of the sacral endplate.

All data measurements were independently carried out by two orthopaedic surgeons from this medical research centre, with each surgeon unaware of the other's measurements, the final statistical analysis used the average values from both surgeons. Imaging images and measurement methods can be found in Fig. 2.

Fig. 2.

Imaging images and measurement methods.

Fig. 2. SS, Sacral Slope: the angle between the sacral endplate and the horizontal line; LL, Lumbar Lordosis: the angle between the upper endplates of L1 and S1; PT, Pelvic Tilt: the angle between a line from the midpoint of the sacral endplate to the midpoint of the femoral heads and a vertical line from the sacral endplate; PI, Pelvic Incidence: the angle between a line perpendicular to the midpoint of the sacral endplate and a line from this point to the midpoint of the femoral heads; SVA, Sagittal Plane Vertical Axis: the distance from the plumb line dropped from the centre of the C7 vertebra to the posterior edge of the sacral endplate.

2.5. Pain and functional evaluation metrics

Hip joint function was assessed using Harris hip score(HHS), the LBP and hip pain were evaluated using a visual analog scale (VAS), with scores ranging from 0 to 10 (0, no pain; 10, maximum pain),while lumbar function was evaluated using the ODI, The ODI has previously been validated as a condition-specific patient-reported outcome tool used to assess patient-perceived levels of disability in 10 everyday daily activities of living, which are then assigned a subjective score of degree of function. The Oswestry Disability Index (ODI) score of level of function relates to a percentage of subjective disability: Scored as 0%–20 % = minimal disability, 21%–40 % = moderate disability, 41%–60 % = severe disability, 61%–80 % = crippling disability and 81%–100 % = bed bound/non-ambulatory. Evaluations were conducted preoperatively and 6 months postoperatively.

2.6. Statistical methods

Data analysis was performed using SPSS Statistics version 26.0 (IBM Corporation, Armonk, NY, USA). Measurement data were expressed as mean ± standard deviation ($\bar{\mathrm{X}}$ ±s). For normally distributed data, comparisons between two groups were made using the independent samples t-test, for non-normally distributed data, the Mann-Whitney U tests was used. P < 0.05 was considered statistically significant.

3. Results

3.1. Preoperative baseline data of patients

This study included 52 patients with hip joint pathology. In the A group, there were 10 men and 9 women (mean age: 62.8 ± 13.5 years). In the B group, there were 21 men and 12 women (mean age: 56.9 ± 10.40 years). Among the included patients, there were no statistically significant differences in sex, age, and BMI between the two groups (P > 0.05). Patient demographics in this study can be found in Table 1.

Table 1.

Patient demographics in the LBP continued group (A group) and LBP improved group (B group).

	A group	B group	P value
Number of patients (n)	19	33	–
Sex (Men/Women)	10/9	21/12	0.44
Body mass index	25.5 ± 3.0	26.1 ± 3.2	0.31
Age in y	62.8 ± 13.5	56.9 ± 10.40	0.09

The symbol '∗' indicates a significant difference (P < 0.05).

3.2. Preoperative and postoperative spinal alignment and changes of patients

There was no statistically significant preoperative spine and pelvic parameters in the two groups. There were significant differences (p < 0.05) in LL, SVA, and PI-LL between the two groups after surgery. The result can be found in Table 2.

Table 2.

Preoperative and postoperative spinal alignment and changes in the LBP continued group (A group) and LBP improved group (B group).

	A group	B group	P value
Preoperative parameters
SS(°)	33.7 (±5.5)	36.1 (±7.1)	0.06
LL (°)	41.5 (±13.3)	46.9 (±3.7)	0.03∗
PT (°)	16.7 (±8.1)	14.8 (±6.0)	0.04∗
PI (°)	50.5 (±10.8)	50.9 (±12.8)	0.84
SVA (mm)	50.3 (±44.1)	31.6 (±48.0)	0.03∗
PI-LL (°)	9.7 (±16.7)	4.9 (±12.5)	0.02∗
Postoperative parameters
SS (°)	30.1 (±9.5)	33.8 (±10.6)	0.07
LL (°)	39.8 (±14.3)	44.6 (±12.7)	0.01∗
PT (°)	19.4 (±12.55)	17.8 (±9.1)	0.07
PI (°)	49.8 (±13.7)	50.2 (±12.6)	0.86
SVA (mm)	46.6 (±51.2)	31.4 (±41.7)	0.01∗
PI-LL (°)	13.3 (±18.6)	6.0 (±12.5)	0.01∗
Changes of parameters
△SS (°)	−3 (±4.3)	−2.3 (±5.5)	0.84
△LL (°)	−1.7 (±6.7)	−2.3 (±5.6)	0.08
△PT (°)	2.7 (±3.5)	3.0 (±4.7)	0.56
△PI (°)	−0.5 (±3.2)	−0.7 (±3.9)	0.69
△SVA (mm)	−3.7 (±24.9)	−0.2 (±26.8)	0.05
△PI-LL (°)	3.6 (±5.5)	1.1 (±4.2)	0.02∗

The symbol '∗' indicates a significant difference (P < 0.05).

3.3. Preoperative and postoperative clinical score scale of patients

There was no significant preoperative clinical score scale between the two groups(P > 0.05). The postoperative clinical score scale showed that the postoperative HHS score of the LBP unimproved group was significantly lower than that of the LBP improvement group, and all clinical scores of the LBP unimproved group were worse after surgery. The result can be found in Table 3.

Table 3.

Preoperative and postoperative clinical score scale in the LBP improved group (A group) and LBP continued group (B group).

	A group	B group	P value
Preoperative scores
HHS	47.5 (±14.8)	51.8 (±13.7)	0.05
Hip VAS	5.4 (±3.0)	4.80 (±3.3)	0.30
Lumbar VAS	4.6 (±2.7)	4.9 (±2.4)	0.38
ODI	39.8 (±14.5)	40.6 (±13.2)	0.40
Postoperative scores
HHS	87.4 (±9.7)	94.1 (±4.7)	0.02∗
Hip VAS	1.2 (±1.4)	0.6 (±0.9)	0.26
Lumbar VAS	3.5 (±2.6)	0.8 (±1.2)	0.03∗
ODI	28.5 (±15.8)	14.3 (±14.1)	0.00∗

The symbol '∗' indicates a significant difference (P < 0.05).

4. Discussion

With the extension of the average life expectancy in society, the incidence of LBP has been increasing year by year, the symptoms of LBP have also received more attention from joint surgeons. Among patients with HOA, the incidence of LBP is 21.2 %–49.4 %,⁹ our research shows that 72 out of 161 patients (44 %) suffer from LBP, which is consistent with current literature. There is no clear conclusion on the causes of LBP in HOA patients. Several possible reasons have been proposed by scholars, such as abnormal LL angle, limited hip joint range of motion, and weakened muscle strength around the lumbar spine. However, there is no clear evidence to support these reasons, and there are few literature related to effective treatment of low back pain in HOA patients.

Staibano et al.¹⁰ pointed out that among 82 THA patients, 44 patients showed significant improvement in moderate to severe LBP after 1 year of follow-up Jia et al.¹¹ conducted a follow-up study on 306 patients with developmental dysplasia of the hip (DDH) and preoperative LBP who underwent THA, showing that over time, patients with Crowe type III and IV DDH experienced more significant relief from LBP postoperatively.Zhang et al.¹² emphasized that 43 patients with bilateral Crowe IV type DDH recovered to normal approximately 12 months after THA surgery. Of note, compared to other similar studies, our study analyzed the changes in spinal pelvic alignment in patients through impressionistic imaging and evaluated postoperative lumbar spine function and quality of life using ODI scores, resulting in a more comprehensive assessment. However, our cohort study was a short-term follow-up study. Parvizi et al.⁹ reported that 49.4 % of patients reported LBP before THA, compared to 44 % in our cohort. Similarly, among 170 patients who underwent THA surgery, 113 cases of LBP were relieved, with a relief rate of 66.4 %. Our results were 63 %, which is consistent with the research findings. Compared to Parvizi's results, the remission rate of LBP was reduced in our study, as our study was limited to patients who had not undergone spinal surgery or had no structural spinal diseases in the past 2 years. Other studies included patients who had undergone back surgery or were currently undergoing back surgery.

The mechanism of LBP in HOA patients is not fully understood. In recent years, with the increasing attention of surgeons to spinal pelvic alignment, the relationship between hip joint and spinal pelvic parameters has been considered an important factor leading to LBP. HOA patients in the late stage may exhibit limited hip joint movement function.¹³ In order to maintain trunk balance and complete daily functional joint activities, the lumbar spine needs to compensate for the insufficient hip joint movement, which increases the risk of spinal pelvic imbalance. Therefore, reduced hip joint range of motion is considered an important factor leading to lower back pain in patients with hip osteoarthritis. Buckland et al.¹⁴ conducted a retrospective study to explore the spinal pelvic compensation mechanism in patients with hip osteoarthritis and reduced hip joint range of motion. They found that patients had reduced hip joint range of motion when standing, insufficient pelvic back pressure, and tended to rank behind smaller LL and larger PT when sitting. In the long run, this can lead to inadequate lumbar compensation, ultimately resulting in LBP.

The purpose of this study is to investigate the relationship between spinal pelvic parameters and LBP relief after THA, and to find clinical evidence for the reasons for LBP relief in patients after surgery. Our study showed that 63 % (33/52) of patients had improved LBP 6 months after THA. The significant differences in spinal parameter changes in group A were a decrease in LL, an increase in SVA, and a mismatch in PI-LL. In group B, SVA improved and PI-LL remained unchanged. In addition, all postoperative clinical scores were significantly worse in group B. Another study reported the changes in spinal pelvic parameters in patients with low back pain after THA and showed that the changes in spinal pelvic parameters did not significantly correlate with the improvement in low back pain, thus suggesting that the causes of low back pain in patients with hip OA may be multifactorial.¹⁵ Only 52 patients with low back pain before THA were included in this study, and therefore, its statistical validity may be insufficient in this study.

Our study showed that the lumbar spine always plays some kind of compensatory role in patients with hip osteoarthritis. Dubousset and Cotrel¹⁶ first introduced the ‘economic cone’ theory, which posits that when the human body is standing or walking, coordination among the spine, hip joints, and knee joints, along with the support of muscles, ligaments, and other soft tissues, allows the body to maintain balance with minimal energy expenditure. During this state, the SVA should ideally be within the range of 0–5 cm.^17,18 The pelvis acts as a link, connecting the spine and hip joints into a single unit, a structure often referred to as the closed kinetic chain 19. When hip joint pathology alters the structure of the hip joint, the body compensates through other mechanisms, typically by adjusting the movement range of adjacent structures such as the lumbar spine to compensate for the hip joint's reduced motion. When the lumbar spine loses its compensatory ability, structural abnormalities may arise, leading to LBP.

Weng et al. examined 69 patients with hip OA and abnormal sagittal spinal-pelvicleg alignment who underwent unilateral, primary THA, of which 39 patients reports LBP preoperatively.²⁰ They demonstrated a significant correction in abnormal alignment, with significant relief in those patients with back pain at 1 year. In our all study cohort, LL and SS were changed by both groups after performing THA, in which LL enlargement was significantly greater in the low back pain relieved group (group B) than in the persistent low back pain group (group A), and the improvement of ODI scores in the low back pain relieved group was significantly greater than in the persistent low back pain group, and the lumbar spine enlargement of the patients who had relieved their low back pain was positively correlated with the improvement of lumbar spine function scores in the postoperative period. We believe that patients with hip OA have reduced muscle function around the hip joint, which can be characterized by claudication, contracture, disuse atrophy, limitation of hip range of motion, and unfavorable muscle tone due to hip pain, which may lead to abnormal mechanical loading of the lumbar spine-pelvis, an associated adjacent structure; THA may ameliorate the above problems and reduce compensatory loading of the lumbar spine thereby relieving some degree of low back pain21.

This study had several potential limitations. We currently focused only on sagittal spinal pelvic parameters, and other spinal factors associated with low back pain were not evaluated, including spinal coronal parameters, spinal degeneration, sacroiliac joint pain 22 and paraspinal muscle volume size, etc. However, our experimental design and findings are reasonable and help surgeons understand the causes of low back pain in patients with hip OA as well as the mechanisms of low back pain relief in THA. In addition, all of our data comes from a single medical research center, so external validity may be reduced. In the future, we hope to conduct similar studies in multiple medical research centers. Finally, psychological factors, insurance, education, annual household income, and the presence of comorbidities were not assessed.²³ In addition, we excluded patients without preoperative LBP. Although the changes in spinal pelvic parameters in patients without LBP are important, the aim of this study was to study the changes in spinal pelvic parameters in patients with LBP after THA in order to elucidate the mechanism of LBP improvement. Therefore, we decided to collect spinal pelvic parameters from patients with preoperative LBP. Finally, the observation period for patients after THA is only 6 months, and longer-term studies are needed to elucidate the relationship between spinal lesions and THA. We focused on changes in spinal pelvic parameters to determine the mechanism of back pain improvement after THA. Therefore, follow-up studies beyond 6 months may be sufficient because aging pathology of the musculoskeletal system may occur in long-term studies.

5. Conclusion

Our results show that 63 % showed improvement in LBP 6 months after THA. There was a significant difference in the changes of spinal pelvic parameters in patients with improved LBP after THA, i.e., LL was elevated and SVA was decreased, PI-LL maintains matching. in contrast to those with unimproved LBP who had elevated SVA and decreased LL. These spinal pelvic parameters may be key factors in the mechanism of low back pain improvement after THA surgery.

CRediT authorship contribution statement

Jiawei Liu: Data curation, Writing – review & editing. Shuai Yu: Supervision. Di Jia: Writing – review & editing. Guangfeng Sun: Software, Validation. Ya Ding: Visualization, Investigation. Hongliang Wang: Conceptualization, Methodology, Software.

Patient consent for publication

A written informed consent was obtained from each patient.

Data sharing statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Ethical statement

The study protocol was approved by the Fuyang People's Hospital Medical Ethics Committee (Permit No. 2023103), all patients were registered in our database, and data were collected prospectively. The study was conducted in accordance with the principles of the Declaration of Helsinki.

Funding statement

This work was supported by the Fuyang Municipal Health Commission (FY2021-009); "Medical Innovation Fund" Project of Anhui Spinal Malformation Clinical Medical Research Center in 2022 (AHJZJX-GG2022-003); Anhui Medical University Research Fund project in 2022 (2022xkj084).

Conflict of interest

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.