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Conversion of Fused Hip to THR

- Discussion:
    - can reduce back and knee pain;
    - improved ability to sit for longer periods of time;
    - increased incidence of dislocation;
    - indications for conversion:
          - painful pseudarthrosis
                - pseudorthrosis rates are 0-10% using modern techniques for fusion;
                - be sure to rule out infection;
          - mechanical low back pain - most frequent complaint of patients with fused hips;
                - multi-level arthritic changes seen in LS spine 32.9 years following fusion (Amstutz et al, (1975));
                - malposition (especially increased abduction) is a major cause;
                - excessive leg length inequality also causes LBP over time;
                - Total joint replacement for ankylosed hips. Indications , technique, and preliminary results.
          - knee pain/instability - ipsilateral pain if the hip is fused with increased adduction;
                - contralateral pain more likely with increased hip abduction;
          - contralateral hip pain - rarely on isolated problem;
    - preoperative evaluation:
          - ensure that patient has a good indication for conversion
          - exam to check skin incisions, leg lengths, nerve function;
          - AP pelvis and cross table lateral to identify bone stock, hardware;
          - Judet views are helpful to identify anterior or posterior column deficiencies;
          - these plain films also help assess the status of the greater trochanter;
          - it will sometimes be insufficient due to prior surgery or insufficient growth secondary to pediatric pyarthrosis;
          - CT scan can sometimes be helpful for identifying bone stock, the proximity of heterotopic bone to neurovascular structures and 
                 abductor muscle mass;
    - surgical approach:
          - we prefer a standard posterior approach though others report success with a direct lateral or a trans-trochanteric approach;
          - we have 3 indications for an trochanteric osteotomy:
                 - exposure;
                 - to decrease injury to atrophied/weakened abductors during the case;
                 - advancement at the end of the case to improve stability
          - existing hardware should be removed if it limits exposure or if it is in the way of component placement;
          - heterotopic bone should be removed as is possible.
          - old hardware can often guide one to the correct plane for bone removal;
          - neck cut in situ:
                 - care must be taken since Amstutz has described 2 eases where cuts were too proximal resulting in fractures of the pubis and the 
                 - if in doubt, place guide pins and obtain a radiograph;
                 - soft tissue releases (ilio psoas, adductors, etc.) are frequently required;
    - acetabular component:
          - structural grafting is sometimes required;
          - one should be prepared to cement the socket if the shell has <50 % contact with native bone;
          - a constrained liner is frequently required because of insufficient soft tissue tension post-op (esp. abductors);
    - femoral component:
          - we recommend modular femoral components in order to restore hip mechanics and improve hip stability;
          - uncemented stems are sometimes useful if screw holes are present in the proximal femur;
          - if cement is used, unicortical screws can be placed in the femur to keep cement in the canal;
          - if the trochanter is bald and there are no abductors, the proximal femur can be sewn to the tensor fascia lata anteriorly and te gluteus 
                 maximus and ITB posteriorly;
    - results:
          - relief of low back pain occurs 70-95% of the time
          - leg lengths can usually be improved
          - ipsilateral knee pain typically improves but it persists in at least 1/3 (especiailly if instability was a problem pre-op)
          - a trendelenberg gait typically persists though abductor function improves for 2-5 years;
          - results from conversion of spontaneous fusions are typically better than results of conversion of surgical fusions;
    - complications:
          - deep infection 1.9-15.3% (higher in conversion of surgical fusion)
          - dislocation 1.7 - 6.25%
          - sciatic nerve palsy 1.8-13.4%
          - femoral nerve palsy 3.6%

The treatment of the painful hip in cerebral palsy by total hip replacement or hip arthrodesis.

Hip arthrodesis in young patients. A long-term follow-up study.

Thompson arthrodesis of the hip in children.

Hip arthrodesis. A long-term follow-up

Contralateral Total Hip Arthroplasty or Ipsilateral Total Knee Arthroplasty in Patients Who Have a Long-Standing Fusion of the Hip.

Hip fusion in young adults. Using a medial displacement osteotomy and cobra plate.

Walking patterns of men with unilateral surgical hip fusion.

Joint replacement for ankylosed hips.

Total knee arthroplasty in patients with prior ipsilateral hip fusion.

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