Ninety-seven patients (98 acetabular fractures) were available for complete radiographic examination, with an average follow-up of 12.5 years (range, 9 to 20 years). The radiographs were evaluated for osteoarthritis as described by Letournel and Judet2. The initial fracture radiographs showed a mean step-off of 1.3 mm (range, 0 to 15 mm) in the anteroposterior radiograph, 0.8 mm (range, 0 to 12 mm) in the obturator oblique radiograph, and 1.0 mm (range, 0 to 15 mm) in the iliac oblique radiograph. The mean diastasis was 2.4 mm (range, 0 to 25 mm) in the anteroposterior radiograph, 1.9 mm (range, 0 to 25 mm) in the obturator oblique radiograph, and 2 mm (range, 0 to 16 mm) in the iliac oblique radiograph.
At the time of the latest follow-up evaluation, 53% of the patients had no osteoarthritis of the affected hip, 25% had Letournel grade 1, 7% had grade 2, 7% had grade 3, and 8% had grade 5. The development of osteoarthritis was analyzed with respect to intra-articular step-off and a diastasis of ≥2 mm. We found that an intra-articular step-off of ≥2 mm significantly increased the risk for developing osteoarthritis when measured in the obturator oblique (p = 0.001) and iliac oblique radiographs (p = 0.011). Furthermore, a fracture diastasis of ≥2 mm in the iliac oblique radiograph (p = 0.005) predicted secondary osteoarthritis development. No such correlation was found in the other projections. The presence of fracture lines in the upper 10 mm of the weight-bearing dome was not significantly associated with the development of osteoarthritis (p = 0.061).
In this prospective cohort study, our main aims were to determine the long-term survival of the native hip in patients who received conservative treatment for an acetabular fracture and to analyze influencing factors. The overall 10-year survival of the native hip was excellent, with a survival rate of 94% (95% CI, 89% to 97%).
Few studies have described long-term survival of the native hip after conservative acetabular fracture treatment. In a slightly younger group of 35 patients (mean age, 42 years), with substantially greater fracture displacement of a mean of 16 mm (range, 5 to 27 mm), Sen and Veerappa reported survival of 33 of 35 hips after a mean follow-up of 4.1 years (range, 2 to 12 years)6. Although the survival rate for the hips was good, the clinical results showed that only 18 patients (51%) had a good or excellent Merle d’Aubigné score.
In a cohort described by Rowe and Lowell, the survival rate was 85% (53 of 62 hips) at a mean follow-up of 6 years19. The full spectrum of comminuted, severely displaced, and nondisplaced fractures was included, and a close correlation was observed between displacement and later survival of the hip, with 100% survival in the group of 21 nondisplaced fractures. That series was published before CT scans were available.
In the present study, 50% of the failures occurred during the first 4 years, with an average time to total hip arthroplasty of 6.9 years. This is in contrast to the findings of Hesp and Goris, who reported that 51 of 55 native hips in their series survived, with all failures occurring in the first 2 years10.
The most significant factor in predicting a poor survival of hips in our series was a step-off of ≥2 mm in the obturator oblique radiograph. If one was present, the long-term survival decreased toward 60%. In a report on 72 patients who had an acetabular fracture, Dunet et al. noted that 42 patients were treated nonoperatively and had an average follow-up of 6.8 years20. Nine of the patients received a secondary total hip arthroplasty. Those authors also noted that a lack of joint congruency in the posterior part of the joint appeared to be a significant predictor of poor survival.
The development of osteoarthritis was strongly associated with a step-off of ≥2 mm as measured on the obturator oblique radiograph (p = 0.001). This association was also confirmed in the iliac oblique projection (p = 0.011), whereas no significant association was found for fracture step-offs in the anteroposterior radiograph. The clinical results were also significantly reduced for this group of patients with a greater fracture displacement. The mean group differences, however, were within what has generally been accepted as a minimal clinically important difference. This does not change the fact that there are large individual differences in the clinical scores, probably of considerable interest to the individual patient.
Sen and Veerappa reported results similar to ours after a medium-term follow-up interval in their study from 20096. They found that approximately 80% of the 18 patients with a fracture reduction of ≤3 mm had a good or excellent Merle d’Aubigné score at an average follow-up of 4.1 years. Only 14% of the 14 patients with a fracture displacement of >3 mm had good or excellent scores6. With even greater displacements, the clinical results seem to deteriorate further. In 21 nonoperatively treated patients with a minimum initial displacement of 5 mm, Matta et al. reported that only 24% had a good or excellent Merle d’Aubigné score after a mean follow-up of 3.7 years14. That study also confirmed a good correlation between clinical and radiographic outcome.
Tornetta, in his series of 41 posterior wall fractures, showed that good to excellent results could be achieved in >90% of the patients, providing that the hip and the fracture pattern were stable when tested with the patient under general anesthesia21. Similar results were obtained by McNamara et al.22. The series described by Tornetta had a mean follow-up period of only 2.7 years. The average time to failure in our study was 6.9 years, with only 50% of the failures occurring within the first 4 years. This fact should be remembered when interpreting reported short-term results for acetabular fractures.
Fracture involvement of the weight-bearing dome, described as the roof arc, has been used as a predictor for outcome and an indication for surgery by several authors14,21,23. In our series, we could only show a significantly reduced survival of the hip when the posterior roof arc was <45°. For fracture lines in the upper 10 mm of the weight-bearing dome, there was a nonsignificant trend (p = 0.086) toward reduced hip survival when the fracture lines were situated in the posterior part of the joint.
Long-term register studies have inherent weaknesses. When we started our database, the use of radiographs was still the gold standard in the evaluation of acetabular fractures, and to ensure comparable data, we continued their routine use. Furthermore, we found it easier to standardize the measurements on radiographs, even though the use of CT scans gradually has become the examination of choice and has since proven to be an accurate method24,25. Also, the intraobserver and interobserver reliability of our measurements have not been validated
The use of the Harris hip score and the modified Merle d’Aubigné score to evaluate clinical outcomes is not optimal26,27; however, on the basis of the fact that most of the investigators reporting on this patient group used them6,16,28,29, we chose them as the primary outcome measures when we started the register in 1994. With the development of newer and better validated scores for both hip function and general patient satisfaction, we now include the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Hip disability and Osteoarthritis Outcome Score (HOOS) as well as the EuroQol-5D (EQ-5D) in the follow-up of patients with an acetabular fracture.
The present study describes a cohort of patients with an acetabular fracture treated nonoperatively for various reasons, such as minimal joint displacement, secondary joint congruency, or medical contraindications to surgery. This creates a heterogeneous group of patients and fractures, and the results must be interpreted with this in mind. Even so, to our knowledge, the present study includes one of the largest cohorts of patients with nonoperatively treated acetabular fractures with long-term follow-up and provides useful insight regarding the outcome for this patient group over time.
Nonoperative treatment of acetabular fractures yields good to excellent long-term clinical and radiographic results for minimally displaced fractures. A loss of joint congruency with an intra-articular step-off of ≥2 mm leads to an increased rate of secondary osteoarthritis, a worsened functional outcome, and reduced survival of the native hip. The obturator oblique radiograph proved to be the most sensitive radiographic predictor.
For the acetabular fracture with a borderline surgical indication, the addition of oblique radiographic projections (Judet views) can be a useful tool in the decision-making process, as a fracture step-off of ≥2 mm has proven to be a strong predictor for an inferior long-term clinical and radiographic result. Acetabular fractures with a step-off of <2 mm can safely be treated nonoperatively. A greater step-off in the obturator oblique radiograph is prognostic of a poor clinical result for conservatively treated acetabular fractures.
Investigation performed at the Oslo University Hospital, Oslo, Norway
Disclosure: There was no external source of funding. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
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