As a sedentary lifestyle is increasing in the 21st sanctuary, obesity is becoming worldwide endemic. A large number of patients with obesity are undergoing hip and knee arthroplasty ^[1]. As per WHO definition, BMI of 20–30 is defined as normal. BMI of 30–40 is considered obese, and BMI of >= 40 is considered morbidly obese. In the United States, >34 million people are obese, and >13 million people are morbidly obese ^[2]. Morbid obese patients are often considered unfit for replacement surgeries because they are likely to develop complications such as dislocation, wound problems, cardiac complications and many other complications when undergoing major orthopaedic surgeries. In hip and knee arthroplasty surgeries, outcomes are inferior in obese patients compare to non-obese patient ^[2]. Morbid obesity is associated with an increased rate of dislocation after total hip replacement (THR), and one of the biomechanical proposition is to increase thigh girth causing soft tissue impingement and low muscular support, leading to instability of the joint ^[3]. There is a high chance of dislocation risk using standard liners in obese patients, while THR with dual mobile liner can significantly reduce the risk postoperatively ^[4].

A 69-year-old female with a weight of 140 kg and BMI of 62.2 presented to us after twist and fall bathroom associated with left hip pain and inability to bear weight without any neurological deficit. She was operated on 1 year back for total hip arthroplasty (THA) for fracture neck of femur in the same hip (Fig. 1a, b).
X-ray pelvis with both hips was done, showing left prosthetic hip dislocation (Fig. 2a, b). CT scan was done to confirm the posterior dislocation of the hip (Fig. 3a, b, c, d). The version acetabular side and femoral side were found to be 15.6° and 17.8°, respectively. The anteversion of the acetabular cup was found to be 56°. The hip reduction was done under GA (Fig. 2a, b). The patient presented again 1 month later with the same dislocation. The patient was planned for implant exit from the acetabular side and revision dual mobile cup prosthesis implantation. On further investigation, we found the presence of deep vein thrombosis (DVT) in the patient. Preoperative DVT prophylaxis was taken as per cardiology consultation, and inferior vena cava filter was used.

The standard OT table was insufficient for the patient, and two OT tables are joined together to provide a safe positioning of the patient (Fig. 4a). Before starting the procedure, an attempt was taken to reduce the hip joint. The joint was found to get reduced but was unstable and can be dislocated with minimal internal rotation. In lateral decubitus position through the posterior approach, a 10–15 cm curved incision was given posterior to greater trochanter over old scar mark. Superficial dissection was done by incising fascia lata and gluteus maximus. Deep dissection was done by detaching short external rotators and opening the capsule and fibrous tissue. The prosthesis was dislocated, and the head was detached from the femoral stem. The poly liner was removed. The acetabular shell was found to have a solid fixation, and we could not extract it using the standard attachment. The cup extractor system was used to cut the bone prosthesis interface with ease (Fig. 4b). The extracted cup size was 46 mm. further reaming was done up to 48 mm, and an acetabular cup of 48 mm was implanted after the trial implant ^[5] (Fig. 4c). Efforts were made to achieve an approximate 45° inclination and 15° anteversion. The acetabular shell was stabilized with three 6.5 mm cancellous screws to the ilium. The femoral head components were assembled with a 22 mm head size (Fig. 5a, b, c, d, e) Intra-operatively the joint was found to be stable. The wound was closed in layers keeping a negative suction drain.
The drain was kept for 48 h post-surgery and was removed with a minimal collection. But there was continuous soakage from the surgical wound site and was continue up to post-operative day 6. It was managed with a single-use negative pressure wound therapy device (Fig. 6). The soakage was controlled, and the patient was discharged on post-operative day 15. The patient was mobilized with assistance from post-operative day 1 with the walker (Fig. 7, 8) Patient can move independently with a walker after 1 month from the date of surgery. She could able to walk unassisted after 3 months from the date of surgery. The patient was followed up for 1 year, and there were no reported complications (Fig. 9).

According to recent studies, more than 1.9 billion adults are overweight, while 650 million people are obese. It is estimated that more than 135 million people are affected by obesity in India. The prevalence is higher in the urban population and high socioeconomic status ^[6].
BMI is the most commonly used measurement in classifying obesity ^[7] (Table 1).
Bourne et al. have reported from a large cohort study done on 54,406 subjects that BMI >40 kg/m2 is associated with a 8.56 fold higher risk of undergoing hip arthroplasty due to hip arthritis ^[8]. Venous thromboembolism and pulmonary embolism are severe complications after total joint arthroplasty. Although the literature suggests a higher chance of complications with obesity, there is no significant difference in obese patients compared to non-obese patients ^[9]. Hip dislocation after THR is one of the earliest complications. With every ten-point increase in BMI, the risk of dislocation increases by 113.9%. The postulated cause of the dislocation is that BMI more than 40 kg/m2, the circumference of the thigh is increased, which puts lateral force on the prosthesis and causes the dislocation. This complication can be reduced by decreasing the abduction angle and high offset neck. Increasing head size has shown not to be helpful in these cases ^[9]. Elkins et al. did a biomechanical study and showed no benefit in using a 36 mm head compared to a 28 mm head. 28 mm head provides full 180° head coverage compared to 36 mm, which is 163 degree. It is easier for a 36 mm head to slide out due to the rounded chamfer. 8 mm neck offset has also shown to increase stability by increasing periarticular soft tissue tension and ROM before implanting the implant. They have suggested that dislocation depends on the cup shape and geometry rather than size ^[3].
Revision surgery in a morbidly obese patient after THA is higher. As the BMI of the patient increases, there is associated higher wear, lesser survivorship and increased implant failure due to aseptic loosening. BMI higher than 30, aseptic failure for revision is higher, around 56% in obese compare to 12% in non-obese. In super obese patient, a BMI of more than 50 is associated with poor survivorship of the implant ^[9]. In a systemic review of 66000 THA in morbidly obese patient and 700,000 non-obese patients, the revision rate was around 8% in the morbidly obese group compared to 2.75% in non-obese patients ^[10]. Prosthetic joint infection is one of the worrisome complications in the morbidly obese patient after THR surgery. BMI >40 is a significant risk factor for deep prosthetic infection, and the incidence is lower than total knee arthroplasty ^[9].
Various factors to be considered preoperatively in a morbidly obese patient. They often have multiple medical comorbidities, which has a significant impact on the outcome of the surgery. Furthermore, there are anesthetic risk factors associated. Diabetes mellitus, obstructive sleep apnea and cardiopulmonary diseases are usually associated with obesity and can significantly increase the overall complication rate ^[11]. Bariatric surgery is one of the popular treatments of choice for decreasing obesity in a patient undergoing THR. It has shown to be a decrease rate of dislocation compare to continue with the same weight. However, higher rate of dislocation was observed if a standard cup with a simple liner was used without bariatric surgery before THR [4, 5].
Dual mobile and constrained implants are helpful to prevent dislocation and to treat repeated dislocation. The shape and functionality of the dual mobile liner creates a large diameter articulation and covers the femoral head when the thigh comes in contact. Constraint liner prevents dislocation by retention mechanism, which prevents translation of femoral head with thigh impingement ^[4]. Hernigou et al. studied revision THR in 32 obese patients using standard cups with 32 mm head and 35 obese patients with dual mobile with 28 mm head. They reported dislocation in five patients in standard cups and 0 patient to compare to dual mobile cup on 1 year follow-up, seven patients in the standard group and one patient in the dual mobile group on 5 years follow-up. Hence, dual mobility liners are an efficient technique to prevent post-operative dislocation in the morbidly obese patient ^[12].
Various post-operative complications are associated with THA in super obese (BMI>50) patient. The most common complication associated is superficial wound infection, prolonged wound drainage or erythema. Other associated complications are aseptic loosening, sciatic nerve injury, dislocation, deep surgical infection, and periprosthetic fractures. Super obese patients are associated with a six-fold increase in complications and a threefold increase in severe complications ^[13]. Our patient developed post-operative wound discharge and was managed with a single-use negative pressure wound therapy device. The device aims to reduce the post-operative infection, the opportunity for the patient to be managed at home, and decreased hospital cost with improved recovery. The PICO NPWT system is a portable, ultra-lightweight, very practical option for ambulatory patients ^[14].
Revision THR compares to primary THR is associated with more soft tissue damage, increases operating time, and risks the incidence of superficial and deep infection. There is a higher dislocation rate after revision due to a greater extent of soft tissue damage and further muscle weakness ^[15]. Morbid obesity is associated with a 38% increase in the 10-year mortality rate compare to non-obese after undergoing primary THA ^[16]. They present various challenges starting from medical comorbidities, anesthesia fitness and implant of choice to post-operative complications. The case was presented to us with a dislocated THR, a known complication in the morbidly obese patient after THR. She would have been managed with dual mobile THR prosthesis and constrained implants. It is difficult to re-operate in such cases due to morbidities, surgical and anesthetic challenges. Our case report will guide physicians to plan and manage morbidly obese patients by choosing the right implants and achieving good outcomes with fewer complications.

Morbid obesity is increasing worldwide with increasing sedentary lifestyle and increased urbanization. Obesity itself is associated with many morbidities and medical complications. When it presents with a need for arthroplasty, it becomes more challenging. Arthroplasty surgery in obese patients needs proper planning, thorough preoperative preparation, proper intraoperative care and identification with adequate post-operative complications management. Options of preoperative bariatric surgery, dual mobile prosthesis and constrained implants can help in decreasing the risk of hip dislocation in the early post-operative period. One can achieve good surgical and functional outcomes in such morbid obese patients by taking appropriate measures.

Dual mobile total hip replacement should be considered in morbid obese patient as primary implant choice for primary hip arthroplasty.