Stricter correction of lower extremity length is required during total hip arthroplasty in patients with ankylosing spondylitis

doi:10.21203/rs.3.rs-2466020/v1

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Research Article

Stricter correction of lower extremity length is required during total hip arthroplasty in patients with ankylosing spondylitis

https://doi.org/10.21203/rs.3.rs-2466020/v1

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published 03 Oct, 2023

Read the published version in BMC Musculoskeletal Disorders →

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Background: Patients with ankylosing spondylitis often have fusions in the spine and sacroiliac joints, such that it is difficult to compensate for the difference in length of the lower extremities.

Methods: We retrospectively measured the difference in lower extremity length after total hip arthroplasty(THA) in 89 patients with ankylosing spondylitis from June 2004 to February 2021 at Our institute. Patients were divided into two groups based on a difference in lower extremity length of 5 mm or 10 mm. Clinical outcomes were investigated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Harris Hip Score (HHS). In addition, these points are investigated : patient satisfaction with the operation; whether there was a current difference in leg length; and whether there was a limping gait.

Results: The group with a leg length difference of 5–10 mm rather than <5 mm had significantly worse WOMAC pain and stiffness. The survey revealed statistically significant differences in patient satisfaction with the operation, limping gait, and whether back pain had improved.

Conclusion: For patients with ankylosing spondylitis, reducing the difference in length of the lower extremities to <5 mm, which is more accurate than the current standard of <10 mm, may produce greater improvement in clinical outcomes after hip arthroplasty.

Ankylosing spondylitis

coronal balance

leg length inequality

total hip arthroplasty

Ankylosing spondylitis (AS) is a chronic inflammatory disease that causes inflammation in multiple joints, more frequently in the spine and sacroiliac joints. Spinal fusion often occurs in patients with advanced AS, and patients with AS have reduced flexibility in their vertebral joints [1]. Inflammation in the hip joint occurs in about 24–36% of cases, and total hip arthroplasty (THA) is the preferred surgical treatment for moderate-to-severe hip arthritis [2]. AS has a higher incidence of various complications after THA than in patients undergoing THA for other diseases [3]. A difference in lower extremity length is recognized in about 30% of patients after THA [4]. The degree of discomfort has been reported to vary with differences of 5–10 mm in lower extremity length after THA [5, 6]. Many patients with AS experience discomfort due to an imbalance of the lower extremities during walking, or an imbalance of the whole body when standing, after THA. There has been no study on the extent to which the difference in length of the lower extremities due to THA causes discomfort in patients with AS. The purpose of this study was to compare the difference in functional indicators after surgery in patients with ankylosing spondylitis by dividing the patients into groups based on differences in the length of their lower extremities observed at follow-up after THA.

This study was approved by the Institutional Review Board of Chonnam national university hwasun hospital. All procedures of this study were carried out in accordance with relevant guidelines and regulation. The need for informed consent was waived by the Institutional Review Board of Chonnam national university hwasun hospital, because of the retrospective nature of the study. A retrospective study was conducted on a group of 89 patients diagnosed with ankylosing spondylitis from June 2004 to February 2021 at our institute. Among the 89 patients, 13 who were not followed-up with an imaging examination after ≥ 6 weeks were excluded. One patient with a fused hip on preoperative imaging was excluded from the study, as we were unable to determine the difference in length of the lower extremities (Fig. 1). Patients’ demographic information was collected retrospectively through the hospital’s medical information system (Table 1).

Table 1

**Patient Demographics**
	LLD < 5mm	5mm ≤ LLD < 10mm	Total	P-value
	(N = 50)	(N = 25)	(N = 75)
Age at surgery (year)	42.32 (22 ~ 59)	46.20 (26 ~ 59)	43.61 (22–59)	0.122
Sex				0.597
Female	2	2	4
Male	48	23	71
BMI (kg/m²)	23.80	26.46	24.67	0.019
Follow up duration (year)	10.08 (1 ~ 18)	8.60 (1 ~ 18)	9.59 (1 ~ 18)	0.237
Side				0.870
Left	25	12	37	\({{\chi }}^{2}=0.027\)
Right	25	13	38
Approach				0.066
MIS-2	43	17	60	\({{\chi }}^{2}=3.375\)
Posterolateral	7	8	15
Lumbar spine fusion	19	20	39	0.157

The difference in lower extremity length was measured through imaging tests after at least 6 weeks had elapsed after the operation, when the difference in lower extremity length had stabilized [7]. Three orthopedic surgeons not related to this study repeatedly measured the lower extremity lengths through pre- and postop pelvic X-ray. A questionnaire was used to ask patients whether they currently felt a difference in length of their lower extremities, and to ask patients about their satisfaction with THA. The survey items were determined by selecting relevant items from those previously used in studies on the difference in lower extremity length [8] (Table 2). Two orthopedic surgeons not related to this study conducted the surveys.

Table 2

Group Differences in Survey Responses
Question / Score	Response	LLD < 5mm (N = 42)	5mm ≤ LLD < 10mm (N = 23)	P-Value
Q1. Do you notice LLD?				0.258
	Yes, all the time	7	3	\({{\chi }}^{2}=2.706\)
	Sometimes	10	10
	No, never	25	10
Q2. Does it bother you?				0.723
	Yes, all the time	3	1	\({{\chi }}^{2}=0.648\)
	Sometimes	9	8
	No, never	5	4
Q3. Did you notice LLD before THA?				0.460
	Yes, all the time	15	5	\({{\chi }}^{2}=1.555\)
	Sometimes	2	2
	No, never	25	16
Q4. Was your operation worthwhile?				0.017
	Yes, all the time	42	20	\({{\chi }}^{2}=5.743\)
	Sometimes	0	0
	No, never	0	3
Q5. Do you walk with a limp?				0.010
	Yes, all the time	0	4	\({{\chi }}^{2}=9.217\)
	Sometimes	13	9
	No, never	29	10
Q6. Do you have low back pain?				0.848
	Yes, all the time	7	5	\({{\chi }}^{2}=0.\)
	Sometimes	15	7
	No, never	20	11
Q7. Did your low back pain worsen or improve after THA?				0.005 \({{\chi }}^{2}=7.783\)
	Improved	42	19
	Worsen	0	4

The survey response rate was 87%, with 65 of 75 patients responding. Among the 65 responders, 50 patients had a difference in lower extremity length of < 5 mm, and 25 patients had a difference of 5mm ≤ LLD < 10mm after surgery. As the primary outcome, discomfort according to the length of the lower extremities and satisfaction with the operation were confirmed. Secondary outcomes were patients’ subjective pain reduction and functional improvement, as determined by Harris Hip Score (HHS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

All patients were operated on by two high-volume arthroplasty surgeons using one of two approaches. The modified minimally invasive two-incision approach was used in 60 cases (80%), and the posterolateral approach was used in 15 cases (20%) in the lateral decubitus position [9, 10]. For patients with large differences in lower extremity length, for patients with a prior surgical history, the posterolateral approach was used. An cementless stem and an cementless acetabular component with ceramic on ceramic bearing were used in all patients. For the intraoperative identification of leg-length discrepancies (LLDs), bilateral lesser trochanter position through the C-arm were compared. In addition, LLD was checked through the difference in length of both heels in the state of full extension of both lower extremities. Restoration of the difference in length of the lower extremities during surgery was considered important, but the operation was performed with the more important goal of maintaining implant stability.

Radiographic measurements

Radiographic examination was performed within 1 week before surgery and > 6 weeks after surgery. The reason for limiting the examination to > 6 weeks was to provide an accurate measurement of lower extremity length [7]. The imaging test performed at the last outpatient follow-up was used as the standard. The interval between the questionnaire survey and the last x-ray follow-up date did not exceed 1 year. The imaging test was based on anteroposterior radiographic images of the pelvis, and the lower extremities were rotated internally by 15 degrees to adjust for size of the lesser trochanter and the obturator foramen on both sides.

To measure the difference in length of the lower extremities, the tip of the lesser trochanter was compared, based on the line connecting the lower ends of the teardrops on both sides [11][. This measurement was done by three reviewers, who were orthopedic surgeons not related to this study. Measurements were made twice for each case separated by an interval of 2 weeks. The average measured correlation coefficient for absolute agreement was calculated using a 2-way random-effects model, which had good intra-observer reliability (intraclass correlation coefficient [ICC] 0.996, 95% confidence interval [CI]: 0.993–0.997) and inter-observer reliability (ICC 0.875, 95% CI: 0.821–0.915).

Statistical analyses

For each survey item, a Chi-squared test was performed to compare differences between groups. An independent t-test was used to evaluate differences between the HHS and WOMAC scores in each group. A Chi-squared test or independent t-test, or a Fisher’s exact test, evaluated ifferences in demographic data between the groups. An alpha-level of P < 0.05 was considered statistically significant. IBM SPSS Statistics 28.0.1.1 (SPSS Inc., Chicago, IL, USA) was used for analysis.

The mean follow-up period for 75 patients was 9.59 (range 1–18) years, and the mean age at the time of surgery was 43.61 (range 22–59) years. There were 71 males, accounting for 94.6% of patients. The mean body mass index was 24.67 (range 18.59–42.44) kg/m². Postoperative complications occurred in six patients: acetabular cup aseptic loosening (n = 1), stem aseptic loosening (n = 2), wound dehiscence (n = 2), and discomfort due to LLD (n = 1). Table 1 presents demographic data for groups divide by LLD. Among 65 patients who responded to the survey, there was no significant difference in the rate of subjective LLD after surgery between the group with a difference of < 5 mm and the group with a difference of ≥ 5 mm. There were significant differences in patient satisfaction with the THA surgery, and in limping gait during walking. Additionally, back pain after arthroplasty was significantly improved in the patient group with an LLD of < 5 mm (Table 2). The average HHS after surgery in the group with a difference of < 5 mm was 97.88, and in the group with a difference of ≥ 5 mm, it was 87.87, showing a significant difference. In addition, average WOMAC pain, WOMAC stiffness, and WOMAC physical function were 0.33, 0.10, and 1.74 in the group with a difference of < 5 mm, and 2.48, 0.96, and 10.70 in in the group with a difference of ≥ 5 mm. Statistically significant differences were also confirmed in HHS and WOMAC pain, stiffness, and physical function scores (Table 3).

Table 3

**Group Differences in Score**
	LLD < 5mm (N = 42)	5mm ≤ LLD < 10mm (N = 23)	P-Value
Mean HHS	97.88	87.87	< 0.001
Mean WOMAC
Pain	0.33	2.48	< 0.001
Stiffness	0.10	0.96	< 0.001
Physical function	1.74	10.70	< 0.001

When patients were divided according to LLD of 5 mm after THA, statistically significant differences were evident in the incidence of limping gait and patient-reported satisfaction with the operation. In addition, patients with a leg length difference of < 5 mm after THA reported a significant improvement in back pain compared with the group with an LLD of ≥ 5 mm. Röder et al. reported that leg length inequality > 10mm after THA significantly affected postoperative limping gait, back pain, and surgical satisfaction [7]. Alice et al. also reported that patients can recognize an LLD of ≥ 5 mm after THA [2].

In patients with remaining spine facet joint movement, trunk imbalance can be resolved with a compensatory action due to the movement of each spine facet joint. However, since patients with ankylosing spondylitis have partial or complete fusion of the spine, trunk balance is not compensated. Therefore, a difference in lower limb length of ≥ 5 mm may cause patient dissatisfaction with the operation. A difference in lower extremity length of ≥ 5 mm can also cause a functional limping gait. In addition, the statistically significant improvement in lower back pain in patients whose LLD was corrected to < 5 mm suggests that the imbalance caused by LLD is related to low back pain in patients with ankylosing spondylitis and a fused spine. Even when there was a difference of ≥ 5 mm in length of the lower extremities on radiologic examination, many patients answered in the survey that they did not feel the difference. However, eight patients reported that they felt a difference in leg length, even though the difference was < 5 mm on radiologic examination. A characteristic of these eight patients was that they had pelvic obliquity, and correct correction of the LLD caused more inconvenience (Fig. 2). This suggests that surgery that considers only the difference in lower extremity length may cause more discomfort in patients with ankylosing spondylitis with pelvic obliquity rather than without pelvic obliquity. For these patients, the goal is not to correct the length difference of the lower extremities accurately after surgery, but to make a difference in leg length to maintain the body balance after surgery is thought to be helpful in improving the postoperative result.

Although this study has limitations as a retrospective study, it was impossible to conduct a prospective study due to the patient group and research topic. Although there are many cases of hip arthritis in patients with ankylosing spondylitis, the number of cases requiring surgical treatment is limited; thus, the number of patients in each group was small. For patients’ evaluation, only a simple radiographic examination was performed to measure patients’ postoperative lower extremity length. In patients with ankylosing spondylitis, where the spine and sacroiliac joints are fused and the vertebral joints have less compensatory function, a more accurate difference could be determined if balance was measured through a whole-body spinal radiograph or gait test that considered whole-body balance, and not just the difference in length of the lower extremities. All patients reported that they did not wear insoles, even though insoles can improve a limping gait and discomfort; however, recommendations or guidance from doctors about insole use may have been insufficient.

Previous studies have emphasized the importance of the difference in lower extremity length after THA, but there has been no study on the extent of LLD after THA in patients with ankylosing spondylitis. When performing THA for patients with ankylosing spondylitis, it is necessary to perform surgery to a stricter LLD standard of < 5 mm, compared to patients with general arthritis, as spinal compensation is insufficient in patients with ankylosing spondylitis, who may feel severe discomfort and dissatisfaction with THA.

Acknowledgements

We thank all patients included in this study.

Authors' contributions

Im wrote the main manuscript text. Park designed and directed this study. Beom prepared figures 1 and 2. Kim and Yoon pointed out the shortcomings of this study and gave advice on areas to be corrected. All authors reviewed the manuscript.

Funding

This study did not receive any funding support.

Availability of data and materials

The datasets generated and/or analysed during the current study are available from the corresponding authors upon reasonable request.

Ethics approval and consent to participate

This study was approved by the Institutional Review Board of Chonnam national university hwasun hospital (CNUHH-2022-119) in July 2022. The need for informed consent was waived by the Institutional Review Board of Chonnam national university hwasun hospital, because of the retrospective nature of the study. All methods were performed in accordance with the relevant guidelines and regulations.

Consent for publication

The X-ray images included in this paper were used with the consent of the patient.

Competing interests

All the authors declare that they have no competing interests.

Authors information

¹ Department of Orthopaedic Surgery, Chonnam National University Medical School and Hospital, Hwasun, Republic of Korea

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No competing interests reported.

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Journal Publication

published 03 Oct, 2023

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Editorial decision: Major revision
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You are reading this latest preprint version

Stricter correction of lower extremity length is required during total hip arthroplasty in patients with ankylosing spondylitis

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Abstract

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Introduction

Material And Methods

Radiographic measurements

Statistical analyses

Results

Discussion

Conclusions

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References

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