Clinical History, Examination and Blood Test Results

  • Acetabular step 7 case 9 presents a 49-year old female with mild left hip pain and raised cobalt and chromium levels (Co = 146ppb and Cr = 120ppb). 17 years previously she had undergo a left Birmingham MoM hip resurfacing. The original indication for this was unilateral hip dysplasia (DDH).

  • She had an excessively anteverted femur at the time of the resurfacing, leading to dislocation in the follow up phase. For this she received a sub trochanteric de-rotational osteotomy using a lateral plate.

  • Bloods taken at her first encounter with our service suggested her metal ion levels were rising with a cobalt of 188ppb and a chromium of 126ppb. She had no known systematic problems (heart, endocrine and brain etc.)

  • Examination revealed the left leg was slightly shorter than the right. There was a good range of movement throughout on both sides. There was some clunking with rotation of the left leg.

  • At the time of referral, she was still able to ski, do her gardening and walk a few miles.


Imaging Results

PRE-OP RADIOGRAPHS

Scroll through the images

 

PRE-OP MRI

Scroll through the images

These anterior posterior and lateral radiographs show radiographic features of osteolysis around the acetabular and femoral components. The patient remained asymptomatic at presentation.

The MRI of her hip revealed left sided gluteal muscle wasting but no signs of loosening. There were no other abnormalities.

 

PRE-OP EOS

Scroll through the images 

 
 

Pre-operative EOS scanning was used to assess leg length discrepancy in a functional position.

 

Diagnosis

  • A multi-disciplinary team (MDT) meeting concluded that revision was required due to very raised blood metal ion levels (MHRA suggest levels above 7ppb are of concern) and imminent risk of peri-prosthetic acetabular fracture.

  • They suggested a further CT scan to assess the remaining bone stock.


Treatment

PRE-OP CT SCAN

Scroll through the images

 

HEMIPELVIC DEFECT

Scroll through the images

This is used by the surgeon and the biomedical engineer to design the custom implant specifically to the patient’s acetabular bone stock. This CT demonstrates significant loss of bone stock relating to the left hip resurfacing.

This series of four images demonstrates the hemipelvic defect reconstructed from the CT scan.

 

IMPLANT DESIGN

Scroll through the images

TRABECULAR TITANIUM

Click on the image for a closer look

This series of images demonstrates the custom acetabular implant designed around this patients bony anatomy. The blue areas highlight regions of trabecular titanium.

This image shows the trabecular titanium metallic structure. This is manufactured using 3D printing methods to produce a continuous porous structure to encourage bony osseointegration

 

Key surgical steps

  • Use old incision

  • Lateral plate removed

  • Femur prepared for modular-taper fluted stem

  • Cup X used to remove cup

  • Minimal bone removed

  • Reamed to 60mm

  • Promade fitted well with all screws achieving good fixation and the planned length

  • Dual mobility liner with ceramic head

  • Leg length good and joint stable

  • Wash, ethibond, vicryl then clips to close


Imaging Outcomes

POST-OP RADIOGRAPH

Click on the image for a closer look

 

POST-OP CT SCAN

Scroll through the images

Square post-op march AP.png

Post-operative AP radiograph demonstrating the implant in situ with the surgical clips and a urinary catheter.

The post-operative CT scan shows that the large acetabular component has sat down into the bony cavity.

 

POST-OP RADIOGRAPHS (6-WEEKS)

Scroll through the images

POST-OP RADIOGRAPHS (6-MONTHS)

Scroll through the images

There is no evidence of implant migration at 6-weeks.

The acetabular implant is stable at 6-months post-op. There is no evidence of any migration or broken screws. The femoral component is also stable.

 

POST-OP EOS (4-MONTHS)

Scroll through the images

 
 

The post-operative EOS at 4-months shows no leg length discrepancy with a level pelvis on standing.

 

Clinical Outcomes

  • 6-weeks post-op - She was able to partially weight bear with two crutches. The wound had healed well and she was able to straight leg raise.

  • 3-months post-op - She was able to fully weight bear, was trendelenburg negative and the EOS revealed no leg length discrepancy. She had no pain in the joint. She was using an exercise bike and swimming for rehabilitation.

  • 6-months post-op - She was walking without support, had a good range of movement and was pain free. Her metal ion levels were a cobalt level of 11.3ppb and a chromium level of 21.0ppb, a huge reduction.


Learning Points

  • The key to this case was the careful removal of the socket. There was a high risk of fracture during removal which would have resulted in a very difficult fitting of the tailor made implant.