Functional and Radiological Outcome Analysis of Bipolar Prosthesis Used in Femur Neck Fracture through Inter-Prosthetic Joint Movement: A Study Protocol

Background: Fracture neck of femur is the commonest fracture in old aged individuals because of osteoporosis and advancing age causing more brittleness of bone. Blood to neck and head of femur is rich and complicated. A hip operation is successful only when it provide a stable hip which is pain free and has a good range of movement. The Austin – Moore and Thompson prostheses have been used successfully for treating fracture NOF. Excruciating pain and erosion of acetabulum are very common complications after the use of the AustinMoore prosthesis. The bipolar prosthesis was developed by James E Bateman in 1974, which had the great advantage of second joint, below the acetabulum. So hip motion is to occur at two surfaces thus reducing the articular erosion. Studies have shown that over an increasing period of time the bipolar prosthesis will become more of a unipolar prosthesis functionally due to stiffening up of the inter-prosthetic joint. By this study we will be able to assess whether bipolar prosthesis really functions as it’s name suggests or vice versa. Objectives: 1. Analysis of Inter – prosthetic joint movement in Bipolar prosthesis by radiological means. Study Protocol Upadhyay and Ambade; JPRI, 33(64A): 462-470, 2021; Article no.JPRI.80858 463 2. Co-relating the inter-prosthetic joint motion with functional outcome of Bipolar prosthesis using Oxford hip score. Methodology: By appropriate and easy sampling method, the patients undergoing Bipolar hemiarthroplasty for NOF fracture will be assessed radiologically for amount of inter-prosthetic joint motion during post-operative period. Results: Results would be assessed on basis of clinical evaluation, functional evaluation and radiological evaluation and statistical analysis would be done to conclude the findings. Conclusion: That over an increasing period of time the bipolar prosthesis will become more of a unipolar prosthesis functionally due to stiffening up of the inter-prosthetic joint.


INTRODUCTION
Fracture neck of femur is a common orthopaedic problem in old age and they have a tremendous impact on both the health care system and society in general [1]. The NOF fracture remains an unsolved fracture in terms of treatment inspite of better implant design, surgical technique and patient care [2]. NOF fractures are on the rise, which is not surprising given that overall life expectancy has increased significantly over the last few decades. These fractures may double in the next 20 years, and the fracture rate has increased to twice for each decade of life after the fifth [3]. Because of osteoporosis and advancing age, which causes bone brittleness, this is the most common fracture in the elderly. As a result, prolonged immobilisation during such fractures in the elderly will jeopardise the patients' lives. The blood flow to the neck and head of the femur is rich and complicated. A good blood supply is vital for better healing process [4]. The main consequences of this fracture include non-union, avascular necrosis of the femoral head, and secondary degenerative arthritis. Non-union may be under the surgeon's control, while avascular necrosis and arthritis may be beyond his control. This complicates the management of these fractures because the healing process is never certain. It's also common knowledge that the hip is a weightbearing joint that is responsible for a variety of performance-related functions. A good hip joint procedure should result in a pain-free, stable hip with a wide range of motion.
Since the early 1950s, prosthetic replacement has been used to solve problems such as femoral neck fracture necks and vitallium intramedullary prosthesis, which has helped to prevent non-union and avascular necrosis. This prosthesis was proven to be extremely useful, with promising results. The Austin -Moore and Thompson prostheses have been used successfully for treating fracture NOF. Excruciating pain and erosion of acetabulum are very common complications after the use of the Austin-Moore prosthesis [5,6]. The bipolar prosthesis was developed by James E Bateman in 1974, which had the great advantage of second joint, below the acetabulum. So hip motion is to occur at two surfaces thus reducing the articular erosion [7]. However, studies that attempted to demonstrate the relative movements at the interfaces produced contradictory results. It is well known that friction generates particulate debris from the polyethylene liner, which was thought to be the cause of foreign body reaction, resulting in stiffening of the interprosthetic joint as well as osteolysis and aseptic loosening of the implant [8]. According to studies, the stiffening of the inter-prosthetic joint causes the bipolar prosthesis to function more like a unipolar prosthesis over time [9]. This research presents the assessment of the IPJ movement in bipolar prosthesis done for fracture NOF at 6 months and mid-term follow-up by radiological means [10]. By this study we will be able to assess whether bipolar prosthesis really functions as it's name suggests or vice versa as the literature suggests.

Aim:
Analysis of the inter-prosthetic joint movement in bipolar hemi-arthroplasty done for NOF fracture patient through X-rays.

Objectives:
1. Analysis of Interprosthetic joint movement in Bipolar prosthesis by radiological means. 2. Co-relating the inter-prosthetic joint motion with functional outcome of Bipolar prosthesis using Oxford hip score Consist of 2 parts.

MATERIALS AND METHODS
Part I is a (prospective study) in which Patient's who would undergo Bipolar hemiarthroplasty for NOF fracture at AVBRH will be included in the study after obtaining their consent during the period of May 2019 to April 2021. Study will be done on a total of 50 patients.
Part II will be a retrospective study where we take a data of patients who were operated earlier in our institute and had completed at least 2 years of follow-up.

Methodology:
By appropriate and easy sampling method, the patients undergoing Bipolar hemiarthroplasty for NOF fracture will be assessed radiologically for amount of inter-prosthetic joint motion during post-operative period.

Inclusion Criteria:
Patients who underwent bipolar hemiarthroplasty for NOF fracture would be included from 2016 onwards.

Exclusion Criteria:
 Bedridden patients  Patients who have had post-operative infection,  Patients who have developed myositis following bipolar hemiarthroplasty and  Patients who have had Peri-prosthetic fractures

Implant used:
For all patients Life ortho care Bipolar prosthesis will be used (ISO -13485 certified company). The implant is constructed of stainless steel 316. The femoral stem measures 150 mm in length and 8 mm in diameter. The diameter of the outer head ranges from 37 to 53 mm, with 2 mm increments. The inner diameter of the prosthetic femoral head was 26 mm, and the lining between the outer and inner heads was constructed of UHMWPE (Ultra High molecular Weight Polyethtylene). The angle of the neck shaft is 130 degrees. There are two forms of prosthesis (Fixed solely with collar, Modular with or without collar, and Extraextended stem).

Part 1 -(Prospective study):
Pre-operative management: All patients who are undergoing bipolar hemiarthroplasty for fracture neck of femur will be considered for the study after getting a written consent from them.
All Patients will be adequately worked up before surgery. A detailed history about the mode of injury and type of fracture will be noted.
Surgical Procedure: Surgeries would be elective and done with all the aseptic precautions, Surgery will be performed under spinal anaesthesia or GA. Patient would be positioned laterally lying on the unaffected side. For all the patients Modified posterolateral approach will be used in our series.
Post-operative protocol: Abduction and external rotation of the limb would be avoided as much as possible throughout the post-operative period. During the immediate post-operative phase, all patients will receive Quads strengthening exercises as well as mechanical DVT prophylaxis. All patients will begin full weight bearing ambulation as soon as they are able. Specific X-rays would be taken after the initial pain subsided to assess the inter-prosthetic joint (IPJ) and outer bearing movement during the immediate post-op period (24 to 48 hours), at 6 weeks, and after 6 months with the operated hip in neutral and maximum abducted positions.

X-ray Technique:
Two A.P X-rays of pelvis will be taken.

Limbs in neutral position and neutral
rotation X-ray with affected limb in Maximum abduction will be taken.

Radiological Assessment:
We follow the method of plain radiographs, as described by Bochner.
On the X-ray in the neutral position, 3 lines are drawn as follows: Line 1: A tangent is drawn through the inferior aspects of bith the ischial tuberosities which is used as a reference line.
Line 2: A tangent drawn along the Inferior aspect of acetabular part of the prosthesis.
Line 3: Line along the centre of femoral stem's long axis.

Fig. 1. X-ray image
Angle A is defined as the intersection of the line 1 and line 2 Angle B is formed by the intersection of the line 2 and line 3 The same process will be repeated on the maximum abduction AP X-ray also and angles are marked as A1 and B1.

Fig. 2. X-ray of pelvis
Now, B2 is the difference b/w angle B and B1 which represents total amount of abduction of the hip in the operated limb.
A2 is the difference b/w angle A and A1 which represents the extent of motion taking place between the acetabular part and the acetabulum (Outer bearing interface).
As we have 2 variables ie. (B2total amount of abduction, A2motion at the outer bearing interface),the difference between B2 and A2 represents the extent of abduction happening at the Inter-Prosthetic joint.
Thus the sum of abduction, movement at outer bearing interface and Movement at inter-prosthetic joint will be calculated and tabulated for each patient at each follow-up. After the half yearly follow-up, in addition to Radiological assessment Functional outcome will also be assessed with Oxford hip score.

Part -2 (Retrospective study):
Patients in this group who have already undergone Bipolar H.A and completed 2 years follow-up will be received. The x-rays will be taken in the similar fashion as described above.
Functional outcome assessment will be done using Oxford hip score. The retrospective study helps us to assess Inter prosthetic joint movement at 6 months follow-up.

Oxford Hip Score (OHS):
• It's useful to Analyse the results post surgical procedures by measuring patient's perceptions in relation to surgery. OHS assesses pain (6 items) and function (6 items Statistical Analysis -Appropriate statistical test would be applied to analyze data.

Follow-up:
Follow-up of all patients at 2 weeks, 6 weeks, 3 months and 6 months.

RESULTS
Results would be assessed on basis of clinical evaluation, functional evaluation and radiological evaluation and statistical analysis would be done to conclude the findings.

DISCUSSION AND CONCLUSION
The primary benefit of the Bipolar prosthesis over a conventional unipolar prosthesis is mobility at the two interfaces, namely between the prosthetic inner femoral head and the polyethylene liner and between the acetabulum and the outer head. This study hypothesised that by minimising wear caused by sliding motion in the acetabular socket, issues such as acetabular erosions could be delayed or averted. The prosthesis has been scanned in various nonweight-bearing and static weight-bearing positions to quantify the fraction of movement that occurs at the inter-prosthetic joint in a bipolar prosthesis in several radiography examinations. According to Drinker and Murray, while some inner motion occurred in most implants, it was less than predicted. Philips TW (1987) had done a study on Fluroscopic movement in 100 patients who had undergone Bateman Bipolar arthroplasty. Out of these 100 patients Group I had 76 patients with arthritis of hip and Group II had 24 patients with neck of femur fractures. In 80% of group I patients, the prosthesis retained Bipolar function at the end of 4 years follow-up study as compared to only 25% of group II patients retained the bipolar functioning of the prosthesis.
Verbene G.H.M (1983), did a radiological study of movements of two components in Variokopf prosthesis in 20 patients with fracture neck of femur during Immediate, 1 month and 3 months post-operative period. He observed that the IPJ lost mobility and at 3 months it became almost completely stiff with inter-prosthetic joint motion of only 16.9% being retained.

CONSENT
As per international standard or university standard, patients' written consent will be collected and preserved by the author(s).

ETHICAL APPROVAL
As per international standard or university standard written ethical approval will be collected and preserved by the author(s).

COMPETING INTERESTS
Authors have declared that no competing interests exist.