Total hip arthroplasty is effective in relieving pain and improving function in ankylosing spondylitis. Five percent of AS patients have been reported to need hip replacement surgery and the overall rate of joint replacement surgery in AS has increased by 40% .Previous studies have shown and established that this disease has a higher male to female ratio of about 2:1 to 3:1 and it was evident in our study also as 90% of our patients were males.
The most known indication of THA is stiffness and pain. Patients with stiff hips or bony ankylosis have significant, functional disabilities. THA brings about dramatic changes in function and quality of life in these young patients. The increased hip ROM and subsequent functional improvement in these individuals support THA in this condition.
Malory modification of the Harding approach is used routinely for THA in our unit. Lateral approach with trochanteric osteotomy has been described.There is lack of data regarding functional outcome following THA in AS with fused hips with this approach. There has been some concern regarding the approach in fused hips with AS with concern regarding the risk of damage to the weakened abductor and hence the posterior approach has been advocated. The modified lateral approach preserves the posterior 2/3 rd of the abductor and is useful especially in the stiff hips with the flexion deformity as the anterior capsular release is facilitated by the approach itself. Flexion deformity in the 45 hips were successfully corrected with the extensive soft tissue release with the lateral approach. The insitu neck resection in 26 fused hips was done with particular attention to prevent damage to the posterior acetabular wall during osteotomy. Femoral neck osteotomy could be challenging with the posterior approach especially in fused hips external rotation deformity. The choice of implant for the acetabulum was based on the bone quality at the time of preparation. Gradual sequential reaming with information obtained from preoperative templating aided in cementless fixation with optimum fit and bone stock utilisation in all 69 hips with additional screws when necessary.
Cemented femur was used in 8 Dorr C femurs and cementless components achieved stable fixation in the remaining 61 hips. Increased risk of of intra operative femur fracture would be high if uncemented fixation is attempted with larger sizes to achieve stable fixation in the larger canal with thin cortices.
The proximal femur required wiring in 2 hips for medial femur calcar split seen at preparation. Cementless implants in AS have found favour with long term survivorship in recent series as opposed to cemented fixation which was advocated earlier.
The average follow up of patients in our series was 38.33 months with no evidence of clinical or radiological signs of implant loosening at last review. There were 21 hips with HO seen at review with no functional limitations. Our protocol was to use copious lavage before closure to remove bone debris and active mobilisation. The patients were re started on their DMARDS post operatively.
The mean flexion in 69 hips changed from 29.35 (SD 31.38) to 102.17 degrees (SD 10.48) indicating a mean improvement of 72.82. The ROM in 43 hips had flexion less than 30 degrees with 23 fused hips also recorded significant improvement in their flexion at follow up which was comparable to patients who had preoperative ROM more than 90 degrees. This significant improvement in ROM in the 69 hips resulted in considerable improvement on the hip function at follow up.
Modified HHS improved from 17.03(SD 6.02) to 90.66 (SD7.23) which was statistically significant (p < 0.001) as 30/40 patients had a modified HHS > 90 at review. This improvement in HHS is due to the significant increase in the activity levels achieved in these stiff hips.
92% of our patients in this series in this study have no pain or ignorable pain that did not compromise any activity. 8% had moderate pain with unusual activity rarely that required occasional analgesics for pain relief.
31 out of 40 patients showed excellent or good scores in SF-36 and SF 12 physical and mental components analysis. This was comparable with other quality of life analysis done in spondyloarthropathy. The improvement in ROM with the HHS and SF 36 indicates and overall improvement in the hip joint function as well as quality of life. Data regarding functional outcome and health related QOL after THA in AS has been limited[4, 15].
The functional scores along with quality of life assessment has been reported in patients with AS. The mental component did not show a significant change and mean physical component score was significantly lower in the study group[10, 16]. The SF 36 scores in this series did not have a preoperative value for comparison.
Reports suggest that quality of life in AS patients have significantly impaired quality of life with most of the domains affected in the SF 36 assessment.
SF 36 in our series done at the time of follow up and this indicated a significant improvement in the quality of life after total hip arthroplasty in this group of patients with AS. The general quality of life was seen in all the domains assessed indicating an overall although researching the short-and mid-term effects of THA in AS patients is acceptable; the number of cases may have been too small (69 THAs), good score in the physical and emotional quotient(Table 3)
The SF 36 scores which evaluates 8 domains used as a functional outcome measure has added value when used with the modified HHS and the ROM improvement in these stiff hips. SF 12 has a physical and mental component assessment and has lesser detail when compared to the SF 36. The SF 36 used to assess functional outcome in THA and TKA was found to have significant improvement following THA. Our series took into consideration the improvement in ROM along with the modified HHS. The modified HHS allows for evaluation of the hip joints studied as the HHS allows for evaluation of the whole patient. The evaluation of the individual joint deformity, ROM especially in the bilateral THAs is possible with the modified HHS. These scores along with the SF 36 showed a significant overall improvement in these patients with stiff hips in AS.(Table 4)
The limitations in this study include relatively short duration of follow up and small number of patients that could be included in this series. The retrospective nature of this study is one of the main limitations. Five year follow up with radiological and clinical outcomes would have been ideal to study the various outcomes while our study’s average follow up was 38.33 months (range 6–83 months). We will continue to follow up on these patients to study the clinical, radiological and overall outcome. The risk of complications in THA with AS is associated with stiffness of the spine. The possibility of fractures, component loosening are few complications that could be seen on longer follow up.