Abstract
Purpose
The purpose of this study was to determine the functional outcome, imaging and complications of conversion of hip fusion to uncemented total hip replacement.
Method
The study group comprised eighteen patients who had undergone conversion of unilateral hip fusion to total hip replacement between 1996 and 2007. There were five men and 13 women. The diagnosis prior to fusion was traumatic injury in eight patients, developmental dysplasia in three patients, and septic arthritis in seven patients. Four of the patient who had septic arthritis in childhood had spontaneous hips fusion while the other underwent surgical arthrodesis.
The mean age at the time of conversion was 53 years (range, 21–77) and the mean time between fusion and conversion to hip replacement was 33 years (range, 11–60). Mean follow up was five years (range 2–15 years).
Data was collected by retrospective review of a prospective database. Uncemented acetabular components were used in all cases and uncemented femoral components were used in all but two patients. In three patients with abductor and soft tissue deficiency an intraoperative decision was made to use a constrained acetabular liner.
Results
The Harris hip score increased from a mean of 49 pre operatively to 75 at a mean of five years p<0.001. There was poor correlation between patient age, duration of hip fusion and hip scores at six months, 12 months and at final follow-up at a mean of five years.
Heterotopic ossification developed in seven of the 18 (39%) patients. It was grade one in four patients, grade two in one patient, grade three in one patient and grade four in one patient.
Four complications occurred in four of the 18 (22%) patients. Two patients (11%) had neurological injury in the common peroneal nerve distribution. In one patient heterotopic ossification resulted in joint ankylosis. This patient underwent reoperation to excise the heterotopic ossification 16 months after the initial hip replacement procedure. One patient developed a deep venous thrombosis. There were no hip dislocations. One acetabular component was loose and had migrated at 15 years follow up.
Conclusion
Conversion of hip fusion to hip replacement carries an increased risk of heterotopic ossification and neurological injury. We advise prophylaxis against heterotopic ossification. When there is concern about hip stability we suggest that the use of a constrained acetabular liner is considered. Despite the potential for complications, this procedure had a high success rate and was effective in restoring hip function.
