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. 2020 Sep 24;14:34–39. doi: 10.1016/j.jcot.2020.09.029

Short to long term outcomes of 154 cemented total hip arthroplasties in ankylosing spondylitis☆

Abhijeet Kumar a,∗, Hajime Nagai a, Jeremy Oakley a, Bianca Luu b, Mohamed Musheer Hussain a, Rishabh Gaba c
PMCID: PMC7920109  PMID: 33717894

Abstract

Background

Long-term outcome of Total Hip arthroplasty (THA) in Ankylosing Spondylitis (AS) remains unreported. Literature suggests a higher overall failure rate in ankylosing spondylitis as compared to osteoarthritis. Concern has been expressed regarding joint survival, given that recipients are generally young. The results of cemented THA in patients with ankylosing spondylitis were studied to determine the utility of THA for these patients.

Methods

Consecutive series of 96 patients (77 males (80%) and 19 females (20%)) with ankylosing spondylitis who underwent 154 cemented THAs at a tertiary referral orthopaedic centre between January 1990–September 2015 were retrospectively analyzed for clinical and radiological outcomes; 58 patients (60.4%) underwent bilateral surgery.

Results

Mean age at surgery was 48 years. Average follow up was 12.8 (2.1–24.8) years. 95% of the patients had a good or excellent post-operative outcome.

Out of the total 154 hips operated on, 11% (17 hips) developed post-operative complications. Overall, 15 hips (9.7%) required a revision of the procedure, with the most common indication being aseptic loosening of the acetabulum. Average time to revision was 8.5 years (2–15). Survivorship analysis revealed probability of survival of both components at the end of 10 years, with revision due to any reason as the end point to be 92% (with 95% confidence intervals).

21 hips (14%) developed heterotopic ossification post-operatively, of which 4 patients (2%) had clinically significant ossification (Brooker III or IV).

Conclusion

This is one of the largest series of patients with ankylosing spondylitis with long term follow up available. Cemented THA in patients with ankylosing spondylitis provided consistently good and predictable long term results, with low rate of complications and revisions.

Keywords: Hip, Ankylosing spondylitis, Total hip arthroplasty, Total hip replacement, Arthritis

Abbreviations: AS, Ankylosing spondylitis; THA, Total Hip Arthroplasty; THR, Total Hip Replacement; HO, Heterotopic Ossification; AVN, Avascular Necrosis; OA, Osteoarthritis; PPF, Peri-prosthetic Fracture; ROM, Range of Motion

1. Background

Ankylosing spondylitis (AS) is a chronic inflammatory disorder that is part of the seronegative spondyloarthritides group of disorders (rheumatoid factor negative). It is a progressive and irreversible disorder that affects the axial skeleton, entheses and less commonly the peripheral joints. The typical patient is a young male aged 20–30 presenting with chronic back pain and inflammatory changes at the sacroiliac joint and formation of syndesmophytes on x-rays. AS can also occur in the absence of x-ray changes and termed non-radiographic axial spondyloarthritis.

The incidence of the disease is 1% in the general population and the incidence of hip involvement in AS is 30–50%,1,2 and is bilateral in 47–90% of cases.2 A complication of this disorder that is often underappreciated is the associated decreased quality of life as a result of pain, stiffness and reduction in mobility and physical function.3 The patients with AS who undergo a total hip replacement are generally younger as compared to the patients undergoing the procedure for osteoarthritis. The common indications for arthroplasty procedures in these patients are refractory pain, stiffness, disability and radiologic evidence of damage to the hips, regardless of the age of the patients. In addition to hip involvement, spine stiffness and intra-thoracic problems can cause severe disability in AS patients.

Within current literature, there have been a limited number of studies that have analyzed the long-term outcomes of this cohort of patients following total hip arthroplasty. Among the evidence available, there is variation in the outcomes and also the follow-up of patients. Also, there are different schools of thought when it comes to choosing cemented or cementless hip arthroplasty in this group of patients.4 Overall, it is suggested that there is a higher failure rate of total hip arthroplasties in ankylosing spondylitis as compared to osteoarthritis.2

The aim of this study was to analyze the long-term clinical and radiological outcomes of cemented THA in patients with ankylosing spondylitis, and in addition to look at how advances in surgical practice may have an impact on post-op complications and survival rates. Also, as these groups of patients are generally young, another outcome we aimed to assess was joint survival.

2. Methodology

This was a retrospective study carried out at a tertiary referral orthopaedic centre after approval from the local research and ethics department. We analyzed patients with an established diagnosis of Ankylosing Spondylitis undergoing a cemented Total Hip Arthroplasty at our institution between January 1990 to September 2015. All the patients were operated by a single unit of hip surgeons at the hospital. The patients admitted in the trust were coded for demographics, diagnosis, and surgical management. Specific codes were applied by the coding department of the trust for characteristics such as ankylosing spondylitis, hip arthritis, surgical treatment with cemented total hip arthroplasty and date of admission. These patients were then analyzed for both clinical and radiological outcomes. Clinical and radiological data were collected until the latest follow-up, in the form of radiographs and clinic letters.

The following inclusion and exclusion criteria were applied:

Inclusion criteria:

  • •

    Cemented THA

  • •

    Hip involvement due to ankylosing spondylitis.

  • •

    Primary surgery

Exclusion criteria:

  • •

    Uncemented THA

  • •

    Follow up < 2 years

  • •

    Revisions

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    Previous surgery (arthroplasty, fusion, or osteotomy)

After applying the inclusion and exclusion criteria we identified a consecutive series of 96 patients with ankylosing spondylitis who underwent 154 primary cemented THAs. Out of the total 96, 58 patients (60.4%) underwent bilateral surgery. There were 77 males (80%) and 19 females (20%) among these 96 patients.

Common indications of performing hip arthroplasty in patients with AS were: severe pain, reduced function, stiffness/ankyloses and reduction in quality of life.

Clinical outcome scoring was performed using the modified Merle D’Aubigne and Postel scoring system.5 This scoring system makes use of pain, clinical function and passive range of movements. A score of 13–16 was considered a good outcome and a score of 17–18 was considered as an excellent outcome. These clinical outcomes were documented on the clinic letters at each follow-up visit either in the orthopaedic clinic or with the physiotherapists. This scoring was done both pre and post-operatively for all the patients.

Trust PACS system was accessed to evaluate patients’ radiology in the form of radiographs and CT scans. These radiological modalities were used to assess patients’ pre-operative condition of the hips and post-operative complications, if any.

Pre-operative radiographic assessment included assessment of the femur according to Dorr’s classification,6 protrusion of the acetabulum, heterotopic ossification/bony ankylosis, presence of osteoarthrosis, and any previous surgeries. Post-operatively, AP and lateral radiographs were taken for all the patients at each follow-up visit for evaluating the implant position, post-operative complications, signs of aseptic loosening and general condition of the hip joint. The patient radiographs were taken, pre-operatively, immediate post-operatively, 6 weeks post-operatively, 6 months post-operatively and yearly thereafter. The assessment of the femoral component was done with regards to cement-bone demarcation, cement-stem demarcation, cement fracture, and calcar loss. The areas in the femur where these abnormalities were identified were classified by the Gruen system.7 The acetabular demarcation was assessed in the zones described by DeLee and Charnley.8 The presence of any heterotopic ossification was classified by the Brooker system of classification.9 The acetabular inclination was measured using the inter-teardrop line as the reference.

The analysis of clinic letters and radiology was performed by orthopaedic surgeon (A.K) and a secondary review was done by orthopaedic surgeon (M.H). In case of any discrepancy in assessment where a consensus could not be reached between the two authors, a review was done by the consultant (J.O). The data then collected for each group was analyzed and compared using the appropriate statistical tests.

Pre-operatively, complete blood analysis including inflammatory markers were performed as a routine for all patients undergoing surgery. Spinal as well as pelvis radiographs were performed pre-operatively to help guide the surgical planning and anaesthesia. Antibiotics as per trust policy were administered 30 min before the surgery. All the replacement procedures were performed in clean air theatres with laminar air-flow and exhaust-suits. Exposure of the hip joint if found difficult due to fibrous/bony ankylosis, an in-situ osteotomy of the femoral neck was performed and the remaining femoral head was removed in a piece-meal fashion. All the patients received a cemented femoral stainless steel component in the form of C-Stem, C-Stem classic, or C-Stem AMT (manufactured by DePuy Synthes). The acetabular component was all-polyethylene (ultra high molecular weight, again by DePuy), and the femoral head used was 22.225 mm in 137 (89%) patients and 28 mm in 17 (11%) patients. Third generation cementing technique was used for all patients and no prophylaxis for HO was used. Two further doses of antibiotics were given post-operatively. Low molecular weight heparin prophylaxis was used post-operatively for 5 weeks and the patients were allowed full weight bearing from the first post-operative day.

Survivorship was calculated by performing the Kaplan-Meier analysis10 with 95% confidence intervals. Survivorship was constructed by using revision due to any reason as the end-point. For the purpose of the level of significance, a “p” value of 0.05 or less was considered to be statistically significant in this study as this would then mean that the difference in outcome could be due to factors other than by chance.11 Statistical analysis was performed using SPSS 19.0 software (IBM SPSS Statistics, USA, 2012).

3. Results

Out of the total 96 patients (154 hips) 58 patients (60.4%) underwent bilateral surgery. 8 patients (8.3%) were operated for a bilateral surgery in the same sitting and the remaining 50 had their bilateral surgery as a staged procedure (average time between the surgeries was 1.3 years). There were 77 males (80%) and 19 females (20%) included in the study. The average age at surgery was 48 (18–77) years with an average follow-up of 12.8 (2.1–24.8) years (because of the large range between the minimum and maximum, the average follow-up was calculated by using the median from the data set). At the latest follow-up, number patients between 2 and 10 years of follow-up from index surgery were 34, between 10 and 20 years were 51, and between 20 and 25 years were 11.

Of the 154 THAs, 81 (52.5%) were operated through a posterior approach, 59 (38.5%) via direct lateral approach with a trochanteric osteotomy and remaining 14 (9%) with a Hardinge approach.

When looking at the clinical function, at the final follow-up, all patients had a substantial improvement in terms of pain, function and ROM. 94% of the patients had a good or excellent outcome when evaluated with the Merle D’Aubigne and Postel score at their latest follow-up. The average score post-operative score was 14.7, as compared to 7.9 pre-operatively which is significantly better as compared to the pre-operative scoring. The use of some sort of walking aid or support was seen in 53 patients (55%) before surgery. Post-operatively only 9 patients (9%) required walking aids, which was mostly due to other contributing factors like associated spinal deformities and increasing age.

Pre-operatively, on radiographic evaluation, 33 hips showed bony ankylosis, 26 hips showed evidence of acetabular protrusion and 75 hips showed evidence of arthritis (either concentric or polar). Also, pre-operatively a discrepancy of leg length more than 2 cm was seen in 14 patients. Post-operatively, a leg length discrepancy of more than 2 cm was seen in 4 patients (not the same patients who had the discrepancy pre-operatively). None of the patients had to be re-operated due to this complication, and the symptomatic patients were managed with shoe raises.

Heterotopic ossification (HO) is the formation of bone in soft tissues and may be acquired following musculoskeletal trauma such as recent orthopaedic procedures.12 HO was graded in this study by the classification as described by Brooker et al.13 HO occurred in 21 hips (14%) post-operatively, but only four (2.5%) were considered clinically or radiologically significant (Fig. 1). All cases occurred within one year of surgery and considered radiologically significant if they met the criteria for Class III or IV of Brooker’s Classification. There were no cases of re-ankylosis and none of the hips had to be revised due to HO.

Fig. 1.

Fig. 1

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Post-operative heterotopic ossification- Class IV Brooker.

Out of the total 154 hips operated on, 11% (17 hips) developed post-operative complications (Fig. 2). Instability was the commonest, noted in 6 hips. Of the 6 hips with instability 3 of them had more than 2 episodes of dislocation and were noted to have major instability, thus, underwent revision surgery for re-alignment of the components. 4 patients had wound infections, and of those, 2 were superficial which settled with antibiotics and the remaining 2 were deep and had to undergo a two-stage revision. Two patients had a sciatic nerve palsy post-operatively, which had completely recovered by the last follow-up. One patient had a peri-prosthetic fracture of the femur 4 months post-operatively which had to be revised by doing an ORIF with plates and screws, keeping the original stem in situ. One patient had a fracture of the femoral stem 6 years post-operatively which again had to be revised. There were no cases of deep vein thrombosis or pulmonary embolism.

Fig. 2.

Fig. 2

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Post-operative complications.

Trochanteric nonunion (Fig. 3) due to failure tension band wiring (when operated with a trochanteric osteotomy) occurred in 3 hips, which resulted in abductor weakness, limp and pain. One patient had to undergo another operation for removal of wires and trochanteric re-attachment. In the other two patients, the symptoms were mild and were managed conservatively. Also, 11 patients had persistent trochanteric pain when operated using trochanteric osteotomy, but none had severe enough so as to undergo a revision. Thus, during the latter years of the study more surgeons preferred to use the posterior approach to the hip to prevent complications arising due to trochanteric-osteotomy.

Fig. 3.

Fig. 3

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Left Hip trochanteric non-union and broken wires.

While evaluating aseptic loosening of the acetabular component, this was seen in seen in 11 hips (7%). Out of the 11 acetabular components with bone-cement demarcation (Fig. 4), 3 hips had >2 mm demarcation in all the 3 zones, 2 hips had >2 mm demarcation in zone 1 and 2, and 6 hips had <2 mm demarcation in zone 1. The 5 hips (3%) with >2 mm demarcation had to be revised. Radiographic cement-bone interface demarcation was seen in 4 (2.5%) femoral components. This demarcation was seen commonly in zones 1, 3, and 5, and one stem had loosening in all the zones according to Gruen classification system. Two among these 4 had to be revised, and both of these femur components had subsidence >5 mm.

Fig. 4.

Fig. 4

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a and b- Figure a shows acetabular loosening in all the zones and dislocation of the right hip joint. Figure b is the post revision radiograph.

Out of the total 154 hips, 15 hips (9.7%) underwent a revision procedure. The average time to revision was 8.5 years (2–15 years). All the cases that underwent revision surgery have not required a further revision procedure so far. Reasons for revisions are included in the figure below (Fig. 5).

Fig. 5.

Fig. 5

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Reasons for revision.

Survivorship was calculated using the Kaplan-Meier analysis, and identified that the probability of survival of both components at 10 years was 92% with 95% confidence intervals, with revision due to any reason as the end point (Fig. 6).

Fig. 6.

Fig. 6

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Survivorship analysis.

4. Discussion

The most common indication of performing a hip arthroplasty in patients with AS is refractory and disabling pain. Ankylosis of the hip joint results in loss of ROM and quality of life but is generally painless.14 THA in AS is considered demanding and technically challenging due to a number of reasons. Firstly, it is a young cohort of patients with high functional demands, thus, likely to result in increased wear rates and loosening. Secondly, patients with AS are at an increased risk of post-operative HO resulting in reduction of ROM and decreased functional outcome.15 In addition, fixed spino-pelvic abnormalities and joint contractures may cause implant mal-positioning during surgery, and surgeons are prone to place the acetabular component more anteverted and vertical.4

This study is one of the largest single centre series with long-term follow-up in patients with ankylosing spondylitis that underwent cemented total hip arthroplasty. Looking at the available literature, there have been a few studies which have looked at the outcomes of hip arthroplasty (cemented and uncemented) in AS. Joshi et al., in 2002, looked at cemented hip arthroplasty in AS. In their study of 103 patients that underwent a total of 181 THAs with average follow-up 10.3 years, they reported a survivorship of 71% at 27 years, with a revision rate of 13.8%. Majority of the patients were significantly better in terms of pain and functional scores.16 Lehtimaki et al., in 2001 in their study of 76 hips that underwent cemented THA in AS and who were followed up from 8 to 28 years, had a survivorship of 80% at 10 years, 66% at 15 years and 62% at 20 years.17 In the study by Tang et al. in 2000, they had 95 cemented hips done for AS, with an average follow-up of more than 10 years. In their study they reported favourable outcomes in terms of pain and post-operative function and their revision rate was close to 20%.18 Sochart and Porter in 1997 in one of the largest series at the time looked at the long-term results of cemented THA in patients with AS over an average follow-up period of 22.7 years. The study included 43 TH A carried out between 1966 and 1978 in 24 patients with an average age of 28.8 years. They reported significant improvement in pain with 15 hips requiring revision with an average time of 13.3 years to revision. Survivorship analysis for both components at 10 years was 91%.19

There have been a few studies looking into the outcomes of uncemented THAs in AS. Those in favour of cementless arthroplasty believe that uncemented implants may have increased survival rates due to potential of bone ingrowth into the prosthesis.20 Bhan et al., in 2008 looked at primary cementless THA for bony ankylosis in patients with AS. Their study had 92 hips with an average follow-up 8.5 years and identified a survivorship of 85.8% at 8.5 years.4 In the study by Xu et al. they analyzed the outcomes of 81 uncemented hips performed for AS with an average follow-up of 3.6 years, and reported a complication rate of 11%.21 Ye at al., in 2014 studied 15 patients who underwent bilateral synchronous uncemented THA for AS. The total 30 hips had a mean follow-up of 2.5 years, and noted significant improvements in range of motion and improvement in the visual analogue scale.22

Goyal et al., in 2017 performed a systematic review looking at current literature regarding both cemented and cementless THR in patients with AS. They included 13 studies looking at a total of 917 arthroplasties that were carried out in a total of 585 patients. Significant improvement in hip function was seen across all studies. Failure rates as defined by need for revision THR was observed in 90 hips (11.9%).23 Also, HO as described by Brooker et al. was considered clinically significant (class III or IV) in only 40 cases, and suggested that HO after THA is not a common phenomenon and raising doubts about the use of routine prophylaxis in such patients. We did not use any prophylaxis in our study and the rate of radiologically significant HO was 2.5%

Thus in summary, cemented THA in patients with AS provide consistently good and predictable long term results with a low rate of complications and revisions. Our study had a complication rate of 11% and a re-operation rate of 9.7%, with an average time to revision being 8.5 years. Probability of survivorship of both implants at the end of 10 years was 92%. The rates in this study are comparable to those in Joshi et al. who analyzed the largest cohort of hips and had similar follow-up time. In this study, there’s lower re-operation rate of 9.7% compared to 13.8% (Joshi et al.) which may be due to advancement of the surgical technique over the years, combined with better implant quality and improved cementing techniques.

More studies prospectively comparing cemented and cementless hip arthroplasty in AS would be useful in the future. Also instability and acetabular cup loosening still remain major concerns in patients undergoing a hip arthroplasty in patients with AS.24 There have also been studies which have thrown light upon the fact that pre-operative spino-pelvic mobility assessment should guide the acetabular cup placement in terms inclination and version which may help reduce post-operative complications in these groups of patients.25

4.1. Limitations of the study

This study was a single centre retrospective system evaluation, unlike the prospective and randomized studies. Thus, further studies, which are multicentre, randomized and of prospective design and longer follow-up are required to address the issue in question.

5. Conclusion

In conclusion, this study is one of the largest single centre series with a long term follow-up of patients. Cemented THA in ankylosing spondylitis provided consistently good and predictable long term results, with low rate of complications and revisions. This study also suggested a good survivorship of implants when the technique of cemented total hip arthroplasty was used, which is comparable to hip arthroplasty performed for other indications. Our complication and re-operation rates were also comparable to hip arthroplasty carried out for other indications. However, hip arthroplasty in these patients is more challenging technically as well as with regards to surgical technique and post-operative rehabilitation as compared to other indications. A multicenter prospective RCT comparing the outcomes of cemented versus cementless hip arthroplasty in ankylosing spondylitis will be challenging but very useful.

Declaration of competing interest

  • •

    This is to declare that there were no conflicts of interests, and

  • •

    No funding or grants have been provided to carry out this research.

Footnotes

☆

This study was carried out at Wrightington, Wigan and Leigh NHS Foundation Trust.

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