ORIGINAL RESEARCH


https://doi.org/10.5005/jojs-10079-1118
Journal of Orthopedics and Joint Surgery
Volume 5 | Issue 2 | Year 2023

Functional and Radiological Outcome of Protrusio Acetabuli Managed with Total Hip Arthroplasty


R Raj Kishore1, R Arokia Amalan2, EMV Muthu Subash3

1-3Department of Orthopaedics, Tirunelveli Medical College, Tirunelveli, Tamil Nadu, India

Corresponding Author: R Arokia Amalan, Department of Orthopaedics, Tirunelveli Medical College, Tirunelveli, Tamil Nadu, India, Phone: +91 9442182087, e-mail: ramalan76@gmail.com

Received on: 24 May 2023; Accepted on: 15 June 2023; Published on: 07 July 2023

ABSTRACT

Background: Primary migration of the femoral head into the acetabulum (Protrusio) is something not seen very often. It is seen in hip arthritis secondary to ankylosing spondylitis, rheumatoid arthritis (RA), Paget’s disease and previous trauma. Primary total hip replacement (THR) can be demanding technically as there is significant proximal and medial migration of the joint center and reduced bony support to the acetabular component placed at the rim.

Aim and objective: To analyze the functional and radiological outcome of Protrusio acetabuli managed with total hip arthroplasty (THA).

Materials and methods: This study has been conducted in the Department of Orthopaedics, Medical College Hospital, Tirunelveli, Tamil Nadu, India, during the period of December–November 2022 and is a prospective study. The morselized femoral head, antiprotrusio cage, and multihole cup were used in this study. Clinical outcome was determined by using Harris hip score.

Results: Patients were followed up every month for a period of 2 years. X-rays were taken during each follow-up to assess the graft incorporation and cup position, and patients are examined clinically by assessing a range of movements, and pain during movements. In our study, most of our patients have a moderate (5–15 mm) grade of protrusion. In our study group, we’ve encountered about 10% of complications including distal femur fracture and nerve injury. The preoperative (pre-op) mean Harris hip score of 48 has been increased to 78.4 in our study.

Conclusion: Total hip arthroplasty (THA) overseen utilizing impacted morselized bone graft along with cementless metal modular cups with trabecular lining was powerful in managing people with various grades of protrusion. The impacted graft is used in acetabular reconstruction for restoring the medial wall, providing a buttress for the acetabular implant to be seated, and lateralizing the implant to restore the center of the hip. However, structural issues with the acetabulum should be carefully considered and potential defects include problems with the weak acetabulum and a thin acetabular wall.

How to cite this article: Raj Kishore R, Arokia Amalan R, Muthu Subash EMV. Functional and Radiological Outcome of Protrusio Acetabuli Managed with Total Hip Arthroplasty. J Orth Joint Surg 2023;5(2):66-70.

Source of support: Nil

Conflict of interest: None

Keywords: Antiprotrusio cage, Medial wall defect, Morselized, Protrusio.

INTRODUCTION

Medial migration of the head of the femur happening primarily into the acetabulum (primary protrusion) is something that doesn’t occur in all arthritic hips. It is seen in hip arthritis secondary to ankylosing spondylitis, rheumatoid arthritis (RA), Paget’s disease, and previous trauma.1,2 Total hip arthroplasty (THA) in protrusio requires surgical expertise as there is a significant migration of the center of the hip joint both proximally and medially, absence of a bony base to the acetabular cup at the rim (Fig. 1).

Fig. 1: Protrusio grading using Kohler’s line

Previously several techniques were described in the management of medial protrusion of the acetabulum. These include using acetabular components with an impacted morselized bone to reconstruct the acetabulum or using cemented acetabular cup.3 But cement had a high-risk of loosening and migration which have been reported in the medium term for bone grafts used along with cement. Cemented acetabular components usage in younger patients results in early loosening and high revision rates during the first decade after implantation.4 Other methods for acetabulum reconstruction includes block bone grafts, metal cages, and reinforcement rings Figures 2 to 4.5

Fig. 2: Antiprotrusio cage

Fig. 3: Burch-Schneider’s ring

Fig. 4: Muller’s ring

Using an impacted morselized bone graft along with a cementless acetabular component provides restoration of native biomechanics of the hip, ensures a long-term fixation without loosening or migration, and provides a biological solution to medial bone deficiency.6

MATERIALS AND METHODS

Our study is a case series study on the functional and radiological outcome of Protrusio acetabuli managed with THA Department of Orthopaedics, Tirunelveli medical college from December 2020 to December 2022.

After institutional board approval, the patients were enrolled prospectively. We recorded patient demography, type, grade of progression of the disease, and operative findings. All cases were assessed preoperative (pre-op) by X-ray radiographs, computed tomography scans, and three-dimensional reconstructions.

Inclusion criteria Exclusion criteria
  • Age > 18 years

  • Patient with acetabular protrusion (pelvis AP showing evidence of medial acetabulum moved over Kohler’s line)

  • Secondary ankylosing spondylitis and RA with end-stage arthritis

  • Age < 18 years

  • Ipsilateral knee involvement

  • Medically unfit for surgery

  • Clinically detectable active foci of infection

SURGICAL APPROACH

The hip joint was exposed using the Southern Moore approach for all cases.7 Osteotomy of the neck was done before dislocating in almost all cases Figure 5.

Fig. 5: Position and approach

Femoral head dislocation after exposing the hip joint was challenging as it had protruded medially. The head of the femur along with the neck was stuck within the acetabular cavity in patients with significant protrusions, making it challenging to execute a routine femoral neck osteotomy. In these individuals, a bone knife or drill bit was used to initially remove a portion of the edge of the femoral head along with a portion of the neck that was concealed in the acetabulum.8 In order to assist osteotomy, the neck was partially uncovered by using traction given to the leg followed by abduction.9

The medial floor was prepared first followed by periphery of acetabulum (Fig. 6). Initially the peripheral cavity was reamed up to a size of about one or two lower than the initial templated cup, while still protecting the subchondral bone with larger reamers. Numerous tiny holes are then made on the acetabular wall with a Kirschner wire (Fig. 6) to expose the bleeding subchondral bone, depending on how sclerotic the medial wall appeared to be.10 Atleast 50% acetabulum of good quality must be in contact with the cup in order for it to be stable enough to support the underlying graft and encourage bone ingrowth into the shell. In preparation for bone grafts, the resected femoral head (Fig. 7) was fined into fine morsels of about 5 mm in diameter (Fig. 8).

Fig. 6: Medial wall defect

Fig. 7: Extracted femoral head

Fig. 8: Morselized femoral head

Following the impaction technique, screws are used to fix the acetabular cup (Figs 9 and 10). On the first postoperative (post-op) day, all patients were permitted to transfer from their beds to wheelchairs.

Fig. 9: Acetabulum packed with graft

Fig. 10: Lateralized cup after

In some cases of protrusion in a revision scenario, we used a femoral head allograft which was demineralized and freeze-dried as there were not any femoral head autografts available (Figure 11).

Fig. 11: Femoral head chips allograft

OBSERVATIONS

The observation and results from the study are as follows:

Table 1: Age distribution
Age (years) <35 36–45 46–55 56–65 >66
No. of patients 2 1 5 9 3
Percent (%) 10 5 25 45 15
Table 2: Etiology
Etiology Primary RA Ankylosing spondylitis Tuberculosis Post-THR
No. of patients 7 3 3 5 2
Percent (%) 35 15 15 25 10
Table 3: Grade of the protrusion (Sotelo-Garza and Charnley classification)
Mild <5 mm Moderate 5–15 mm Severe >15 mm
No. of patients 7 11 2
Percentage(%) 35 55 10
Table 4: Augmentations
Femoral head autograft Multihole cup + autograft Femoral head allograft
No. of patients 15 3 2
Percentage (%) 75 15 10
Table 5: Complications
Infection Nerve injury Distal femur fracture Nil
No. of patients 0 1 1 18
Percentage (%) 0 5 5 90
Table 6: Harris hip score: preoperative
Score <65 66–70 76–85 >86
No. of patients 4 6 6 4
Percentage (%) 20 30 30 20
Table 7: Harris hip score: postoperative
Score <35 36–50 51–65 >66
No. of patients 2 10 7 1
Percentage (%) 10 50 35 5

Fig. 12: Preoperative (pre-op) vs postop Harris hip score

DISCUSSION

Medial femoral head migration (Protrusio acetabuli) could be either the primary or due to secondary cause. The secondary protrusion is usually due to conditions such as RA, tuberculosis, Paget’s disease, and posttraumatic. Acetabular protrusion is also seen in patients with steroid abuse. Hip joints with RA exhibit congestion of the synovium, edema, and articular cartilage erosion. In many RA cases, the head usually gets destroyed or disappears. During the movement of the hip joint and weight bearing, there is a constant abrasion of the destroyed head of the femur into the acetabular cavity.10

Acetabular protrusion secondary RA accounts for about 5% and progresses at a rate of about 2 mm per year.11 The acetabular protrusion does not stop in some cases and may progress until the proximal aspect of the greater trochanter or femoral neck is hindered by the acetabular margin, which prevents further protrusion. In acetabular protrusion the center of rotation of the hip displaces inwardly, leading to shortening of the limb, reduced tension of gluteal muscle, and severe pain in the hip. Total hip replacement (THR) is advised if there is a significant compromise in activities of daily living.

In patients with protrusion secondary to RA, THA is technically demanding as a severe alteration in the acetabular cavity increases the complexity of the surgery and affects the fit of the component.12 The weak osteoporotic acetabulum and thin acetabular wall cannot deliver the acetabular cup with sufficient support. Range of motion of hip restricted in all planes. Femoral head dislocation is cumbersome during surgery. Forceful manipulation leads to iatrogenic acetabular wall fracture or femoral shaft fracture.13

Usually, excision of the head is done in a retrograde manner only following the femoral neck osteotomy due to added difficulty in dislocating the hip. In cases of severe secondary Protrusio acetabuli due to RA, osteotomy would not be feasible as the femoral neck and head lie well within the acetabular cavity. The protruded neck is exposed by removing the outer parts of the head which increases the hip abduction permitting osteotomy at the neck. Additional osteotomy of the greater trochanter can be done if femoral neck osteotomy is difficult which would increase the exposure of the femoral neck.14

The impacted graft is used in acetabular reconstruction for restoring the medial wall, providing a buttress for the acetabular implant to be seated, and lateralizing the implant to restore the center of the hip. An acetabular rim creates a hoop that provides support for the acetabular component. Care should be taken to preserve the rim of the acetabulum as its thin in RA patients.

In cases of severe acetabular rim erosion an antiprotrusio cage or cup-reinforcing ring, which offers additional mechanical support, is indicated. The acetabular wall is hardened with weak bottom. Hence small bone holes till the subchondral layer are made after removing the residual cartilage using curettes or gouges over the thinned medial wall. This allows the flow of blood from the pelvis enhancing incorporation of bone graft and remodeling of bone. The acetabular medial wall is filled with bone graft and impacted. Bone defect in the acetabulum is managed by an iliac graft or head of the femur resected to a suitable shape. There is an unacceptably high recurrence rate following the usage of cemented acetabular cup for the reconstruction of the medial wall in protrusion of acetabulum leading to migration of implant into the acetabulum.

Poor outcomes have been linked to thermal necrosis brought on by the heat of cement polymerization over the medial wall which is thin already, particularly in RA patients. Cemented cups show a high failure rate. The majority of people with RA-related Protrusio acetabuli are young, so the cementless acetabular cup is recommended as it has better hip survival rates compared to cemented acetabular cups.

Bone graft alone is many times not adequate in situations where the femoral head has vanished or is seriously damaged or in revision cases along with extreme acetabular protrusion. Extra mechanical support such as a cage or shell could be added by the surgeon when there is evidence of a huge cavity but needs surgical expertise with the added risk of cup malposition happening inside the cage which is anticipated. Also, we had a relatively small sample size and the need for cages or shells were not needed.

CONCLUSION

Total hip arthroplasty (THA) oversaw utilizing morselized bone graft along with cementless metal cups with trabecular lining was powerful in managing people with various grades of protrusion. The impacted graft is used in acetabular reconstruction for restoring the medial wall, providing a buttress for the acetabular implant to be seated, and lateralizing the implant to restore the center of the hip. However, structural issues with the acetabulum should be carefully considered and potential defects include problems with the weak acetabulum and a thin acetabular wall. Although we have accomplished good results in the short term, the long-term stability of the acetabular component and possible invagination of bone graft following graft incorporation require longer follow-up.

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