| Abstract|| |
Background: Bipolar hip arthroplasty was devised for fracture neck femur in elderly patients. Subsequently, indications have been expanded to include conditions affecting acetabulum like rheumatoid arthritis, osteoarthritis and avascular necrosis of femoral head.
Materials and methods: We have studied the results of bipolar hip arthroplasty in 38 such patients, with severely involved acetabulum due to rheumatoid arthritis, avascular necrosis of femoral head and primary osteoarthritis. Acetabulum was reamed to get a tight 'equatorial' or 'rim' fit of the prosthesis. Prosthesis selected was 1 mm bigger than the maximum size of reamer used. Cement was used in femur whenever there was marked osteoporosis or wide medullary canal. Post operatively all patients were regularly screened for pain, range of movement, protrusio acetabuli, loosening / sinking of prosthesis and radiographic assessment of movement in the two bearings of prosthesis.
Results: Overall results achieved were good to excellent in 80% of patients.
Conclusions: The ultimate outcome is comparable to total hip arthroplasty. The added advantage is of low cost, simplicity of procedure and easy future revision.
Keywords: Bipolar hip arthroplasty; Rheumatoid arthritis; Osteoarthritis; Avascular necrosis femoral head.
|How to cite this article:|
Dudani BG, Thawrani D, Chikale S. Outcome measures of bipolar hip arthroplasty for atraumatic hip disorders - A preliminary report. Indian J Orthop 2005;39:212-7
|How to cite this URL:|
Dudani BG, Thawrani D, Chikale S. Outcome measures of bipolar hip arthroplasty for atraumatic hip disorders - A preliminary report. Indian J Orthop [serial online] 2005 [cited 2020 Jan 21];39:212-7. Available from: http://www.ijoonline.com/text.asp?2005/39/4/212/36571
| Introduction|| |
In 1974, Bateman  presented the use of a bipolar implant for hip reconstruction, used principally in fresh fractures in the aged, aseptic necrosis and non-unions of the femoral neck. A number of further contributions have been made based chiefly on the use of the implant in post-traumatic conditions and aseptic necrosis of the femoral head.
Success with the bipolar prosthesis in femoral neck fractures led to expansion of its indications to include some hip pathologies which were commonly treated with total hip arthroplasty  . These included patients with advanced osteoarthritis of hip, either primary or secondary to conditions like rheumatoid arthritis, avascular necrosis of femoral head or even cases with acetabular dysplasia.
The bipolar hip prosthesis was designed to reduce the shear stresses and decrease the incidence of protrusio acetabuli and stem loosening ,. The impact loads are better absorbed by the bipolar prosthesis, thus providing further protection for the acetabulum  Added advantage of the bipolar design is greater stability and reduced likelihood of dislocation as a result of an increased range of motion ,
| Material and methods|| |
Thirty eight patients, having rheumatoid arthritis (16), avascular necrosis of femoral head (14) and primary osteoarthritis (8), were included in study. Mean age at which surgery was performed was 56.39 years. All patients were assessed pre operatively with X-rays of pelvis with both hips -antero-posterior view in internal rotation, lateral view of the affected hip and clinical assessment by Harris hip score.
We used articulated (fixed) bipolar prosthesis for patients more than 65 yrs of age, while in younger patients (less than 65 yrs) modular prosthesis was used [Figure - 1]. As the young patients are more active compared to elderly, it is mandatory that the fill of medullary canal is maximum with femoral stem. Fixation was further enhanced with bone cement in most of the patients as there was associated osteoporosis or the femoral canal was wide, while in those who had good bone stock and narrow femoral canal, uncemented prosthesis was used.
The hip joint was approached through postero-lateral incision. After incising the joint capsule along the base of neck, the hip was dislocated. Then, the neck of the femur was osteotomised at the pre-determined level (as per the pre operative assessment over the templates)  . The head size was measured and appropriate size of the bipolar prosthesis was determined - - for a "tight-fit". Acetabulum was reamed gently when there was a gross acetabular irregularity, to get a tight 'equatorial' or 'rim' fit of the prosthesis. Reaming was done mainly to remove loose cartilage and make the acetabulum concentric. The size of outer head of the chosen prosthesis was 1mm bigger than the acetabular reamer last used so as to get a tight fit. Prosthesis head was reduced in hip in the usual manner and the stability of reduction was assessed by checking hip movements in all directions.
In rheumatoid cases, we excised the posterior capsule while only pyriformis and gluteus maximus tendons were secured back to original position.
Post operative care: The position and reduction of the prosthesis was confirmed radiologically. A triangular pillow was kept in between the legs to maintain abduction while shifting the patient to ward. This was then replaced by a long knee brace which was used for a period of 10 days to 3 weeks.
Patients were mobilized in the bed after 2 days and active and active assisted physiotherapy was started from day 5. On the 5th day, wound was dressed and the patients were made to walk with partial weight bearing with the help of walker. On the 10 th post-operative day all sutures were removed, full weight bearing was allowed with walker and patients were discharged on the 11 th or 12 th day with advice that they were not supposed to squat or sit cross-legged and had to use a chair commode for toilet. Walker was gradually withdrawn over a period of 4 - 6 weeks and patients were advised to use a cane on the opposite side to increase the longevity of the prosthesis.
Patients were then called for regular follow ups -fortnightly for 1 month, monthly for next 3 months and then every 3 monthly. Mean period of follow up was 6.84 years (range 6 to 8.5 years). Harris hip score was calculated for all patients at each follow up visit. Any evidence of protrusio acetabuli and stem loosening / sinking and leg length discrepancy was looked for. Also the movement of inner head versus outer cup of the prosthesis was checked radiologically.
| Results|| |
There was a significant improvement in the Harris hip score (p< 0.01) post operatively as compared to the pre operative values [Table - 1]. Bipolar head motion (inner bearing v/s outer bearing) was assessed radiologically , with three reference lines on AP view X-rays in full abduction and in full adduction. Patients with primary osteoarthritis and rheumatoid arthritis showed around 75% and 82.18% of motion in the inner bearing respectively [Table - 2].
Post-operative assessment was done by Harris hip score and graded as excellent, good, fair and poor. Overall 30 out of 38 patients had good to excellent results after bipolar hip arthroplasty [Table - 3]. There was no evidence of protrusio acetabuli in any of the cases [Figure - 2]. In two osteoarthritis patients, there was evidence of sub-chondral bony reinforcement of acetabulum [Figure - 3]. Prosthesis subsidence up to 2 to 4 mm was seen in 5 cases of rheumatoid arthritis, where bone cement was not used. But it did not affect the hip function clinically.
There was no incidence of dislocation or infection. Heterotrophic ossification was seen in one patient with primary osteoarthritis. There were 2 poor results in rheumatoid series where uncemented prosthesis had loosened in femoral canal (more than 2mm). Patients have been advised revision surgery.
| Discussion|| |
Total hip arthroplasty is an established modality of treatment for severe cases of rheumatoid arthritis, avascular necrosis of femoral head and osteoarthritis of the hip. The procedure has been very successful and complications were few in the early years. With longer follow-up the problems of loosening, especially of the acetabular component, malalignment leading to instability, dislocation and difficulty in revision are of a prime concern. Other simpler and gratifying approach has been the use and assessment of bipolar hip arthroplasty in osteoarthritis and till now enough data has become available to evaluate this procedure which has yielded good results in both aged and younger patient population.
Bateman  , in his series of 760 degenerative hips followed for 15 years after bipolar hip arthroplasty has shown good results wherein preoperative Harris hip score improved from 51 to 87. They have shown healthy acetabular bone preservation and gradual acetabular floor reinforcement. McConville et al  , in their 100 consecutive patients of degenerative arthritis treated with bipolar hip arthroplasty, found it to be a viable alternative to total hip arthroplasty especially with respect to absence of most complications related to acetabulum. Ninety three to 96% good to excellent results have been reported in osteoarthritis in other series,. .
Bipolar hip arthroplasty has been used in avascular necrosis of femoral head (Ficat stage III) for a number of years ,,, . Chan et al  , in their article on bipolar hip arthroplasty versus total hip arthroplasty for hip osteonecrosis in the same patient observed that after a follow-up of more than 6 years, there was no stastical difference in both groups in terms of clinical result, thigh pain, groin pain, osteolysis, dislocation and revision rate. Hiroshi et al  in their study of bipolar hip arthroplasty for osteonecrosis of femoral head had 42% radiographic failure and 25% hips were revised. Harris hip score increased from 46 to 86. Groin symptoms were present in 42% hips. Their results were inferior to those previously reported for total hip arthroplasty. They no longer use bipolar hip arthroplasty for avascular necrosis. Mess and Barmada  in their series of 47 hips with avascular necrosis femoral head had Harris hip score increased from 24 to 84. They also had 14 hips where multiple level motion was seen as long as 7 years post operation.
Patients with severe rheumatoid arthritis affecting multiple joints are generally physically weak and cannot tolerate multiple soft tissue and total joint replacement operations in quick succession. In this situation, bipolar hip arthroplasty is an operation of considerably smaller magnitude (as compared to any of total hip arthroplasties).
Bateman in his series of 82 rheumatoid arthritis hips did not find any acetabular protrusion and noticed subchondral line of ossification in most of his patients. Harris hip score increased from 39 preoperatively to 82. Vazquez-vela et al (1990) in a study of 114 rheumatoid hips followed for 3-14 years, got almost 88-90% excellent to good results. In 50% of their 11 patients with protrusio and thin medial wall, significant thickening of the medial acetabular wall took place. No bone grafts were used. In the remaining half, there was no increase in protrusio. This reflects the better biomechanical tolerance of the bipolar prosthesis by the acetabulum. Bhan et al in their 7 cases of rheumatoid hips with protrusio also noticed that there was no further progression in protrusio. Mechanical tolerance and biomechanical equilibrium seem to be so good that even subchondral cysts (which reflect the continued damage in rheumatoid arthritis) gradually disappear in spite of generalized osteoporosis.
In our series, 2 of the rheumatoid hips showed loosening of femoral stems at 5 year follow-up. In these two cases monoblock prosthesis was used and the stems were uncemented. There have been divergent views as to whether to use cement or not in bipolar hip arthroplasty. We had used cement wherever the femoral canal was wide and or osteoporotic irrespective of whether the patient was young or old. Whenever there was a good bone stock, we performed uncemented fixation of the prosthesis. We had also considered calcar to canal isthmus (CC) ratio as described by Dorr  for deciding whether to use cement or not. A CC ratio greater than 75% has been recommended to be a relative contraindication to non cemented arthroplasty. 
There was no dislocation of prosthesis in our study. Incidence of dislocation with bipolar prosthesis is much lower (1-3%) as compare to total hip arthroplasty (more than 3%). Bipolar prosthesis has a self-aligning acetabular component, which finds a correct orientation on its own, and the problem of subluxation and dislocation is taken care of while in case of total hip arthroplasty, if the dislocation becomes recurrent, it requires a major revision procedure. A number of articles have come up where bipolar hip arthroplasty has been done for such revision  .
Ectopic para-articular bone formation following total hip arthroplasty in osteoarthritic hips is fairly common i.e. 6080% ,, . Functional impairment due to this occurs in 3 to 10% cases of total hip arthroplasty , . Incidence of this complication is minimal after bipolar hip arthroplasty and this is due to a simple operative technique where acetabular preparation is either not required or is minimum. Also minimal capsular exposure is needed. We had only one case of heterotropic ossification in our study.
As compared to total hip arthroplasty, bipolar hip arthroplasty has been blamed for incidence of groin pain and thigh pain  . This has been variably attributed to preservation of joint capsule, to irritation of the subcondral nerve endings of the acetabulum or to acetabular erosion. Sometimes groin pain can be as high as 42% as reported by Hiroshi et al  . Pandit et al  1996 reported transient start-up soreness in 34 of 100 osteoarthritic hips at 5 years. It is generally believed by most of the surgeons doing regular bipolar hip arthroplasty that poor fitting bipolar prostheses can lead to cartilage necrosis and degeneration  . Reaming creates a better fit which will affect the frictional conditions, movements and result in reduced pain and damage to acetabular bone stock. It is when a good fit is not achieved that problem of erosion can occur  .
Fantasia  presented results of 926 bipolar prostheses in a range of indications over 10 years. His experience suggested that, it is better to limit outer head motion which may be responsible for a 'rising from chair' pain. Eccentricity of inner and outer head centres and congruency is important and he advised to use bipolar cup 1mm larger than the acetabulum. In our study, we have excised the diseased capsule and have done gentle acetabular reaming to make the acetabulum concentric and have used 1 mm larger cup as advocated by Fantasia et al  . Also as nerve endings in the posterior capsule supply the acetabulum, excising it blocks the nerve supply to the acetabulum and thus helps in relieving the pain. We had no case of acetabular erosion or protrusion even at the end of 8.5 years. On the contrary, we noticed that there was a subchondral bony reinforcement in two of our osteoarthritic hips 3 years after the surgery. This finding supports the view of Bateman  that acetabular floor retains a regenerative property, which regenerates bone in the subchondral region if stimulation in the form of weight bearing is given through an accurately fitted bipolar cup. Some authors  have studied acetabular cartilage histologically at revision surgery and found that there was evidence of fibro-cartilage formation at head and acetabular interface. According to Egan  , with fibrocartilage, outer bearing motion will be favored in prostheses smaller than 50 mm where as bone contact will always favour inner bearing motion. We have seen good inner bearing motion in all our patients. In avascular necrosis head femur, the acetabulum is less affected as compared to rheumatoid arthritis and osteoarthritis. Hence the movement occurred somewhat equally at both inner bearing and the outer bearing [Table - 2]. While in rheumatoid arthritis and osteoarthritis, the acetabulum was more affected. Here outer cup motion was grossly hindered by the uneven surface of the acetabulum. Thus, more movement at the inner bearing was observed as compared to the outer bearing, resulting in less wear of the acetabular surface, which is helpful if revision surgery is planned at a later date. In effect, with increased movements at inner bearing, it worked like low friction arthroplasty. These findings are similar to those of Bateman's series where cases were followed for 15 years.
In conclusion, bipolar hip arthroplasty is a viable alternative to total hip arthroplasty in cases of osteoarthritis and avascular necrosis head femur, while in rheumatoid arthritis long term results need evaluation. It is a simpler and cost effective operation compared to total hip arthroplasty and can be performed by all orthopaedic surgeons. Technically, it is less demanding and has a rapid learning curve as compared to total hip arthroplasty. Blood loss and operating time in bipolar hip arthroplasty is less and have low infection rate. In bipolar hip arthroplasty, there are no complications with the acetabular component (outer head) since it is free while in total hip arthroplasty acetabular component is fixed and there are complications related to cementing, mal-alignment, instability, loosening, dislocation etc. One should take care in selecting a proper bipolar implant and should ensure that the bipolar outer head gets a concentric tight fit in acetabulum and select a stem which achieves the most complete "fill" of the medullary cavity of the femur. Lastly revision of bipolar arthroplasty is easy compared to the revision of total hip arthroplasty.
We believe bipolar hip arthroplasty is the procedure which every orthopaedic surgeon can master with proper training and there are no complications related to cup placement which is one of the major problems seen in total hip replacement.
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Baldev G Dudani
Department of Orthopaedics, Inlaks and Budhrani Hospital, 7-9, Koregaon Park, Pune
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3]
[Table - 1], [Table - 2], [Table - 3]