Hounsfield unit values are useful for predicting early outcomes after acetabular fractures: a retrospective study.

Background: Acetabular fractures are among the most challenging orthopaedic fractures, and a high total hip arthroplasty (THA) conversion rate has been reported in older patients with acetabular fractures. Bone quality is a poor prognostic factor after acetabular fracture fixation and has been assessed using computed tomography (CT). However, the relationship between Hounsfield unit (HU) values measured using CT and early acetabular fracture outcomes remains unknown. This study aimed to elucidate the effect of HUs on early acetabular fracture outcomes.

Methods: 50 consecutive patients who underwent open reduction and internal fixation for acetabular fractures were included. The mean follow-up duration was 24 months. 27 hips had elementary fractures and 23 had associated fractures. The reduction quality assessed using CT was as follows: anatomical, 13 hips; imperfect, 10 hips; and poor, 27 hips. Secondary hip osteoarthritis was observed in 5 patients (10%), and the surgery was converted to THA in 1 patient (2%). The HU values of the fifth vertebral body and the unaffected side of the femoral head were measured. The fracture type, radiological secondary hip osteoarthritis, conversion to THA, and postoperative displacement gap were recorded.

Results: The unaffected femoral head HU values in elementary fractures (250.5 ± 50.5) were significantly higher than those in associated fractures (221.5 ± 48) (  0.047). The HU values of the fifth vertebral body and the unaffected femoral head were significantly correlated with the postoperative residual displacement gap and were significantly lower in those with secondary osteoarthritis than in those without it. The cut-off value for predicting early osteoarthritic change after an acetabular fracture was approximately 180.

Conclusions: The HU values were correlated with the fracture type, postoperative displacement gap, and early osteoarthritic change after acetabular fractures and are clinically useful prognostic factors for early acetabular fracture outcomes.