Anatomical reduction of marginal impaction in posterior wall acetabular fractures ensures mid-term satisfactory outcomes

Abstract

This study aimed to compare the postoperative radiological and functional outcomes of posterior wall acetabular fractures with and without marginal impaction. Patients who underwent surgical treatments for posterior wall acetabular fractures at a single level I trauma center between January 2013 and June 2022 were enrolled. Seventeen patients with marginal impaction were classified into group I, and the remaining 24 were classified into group II. Immediate postoperative reduction quality was confirmed using computed tomography (CT), final follow-up results were evaluated using simple x-ray. Heterotopic ossification (HO), post-traumatic osteonecrosis of femoral head (ONFH), rate of conversion to total hip arthroplasty (THA), and Harris Hip Score (HHS) also compared between the two groups. Marginal impaction occurred in 41.5% of acetabular fractures involving the posterior wall. Posterior dislocation at initial trauma was significantly lower in group I than in group II. There were no significant differences in the postoperative quality of reduction between the two groups. HO in five patients in each group, but there was no significant difference. There was no post-traumatic ONFH and conversion to THA in total population at a minimum 2-year follow up. There was no significant difference in term of HHS. It is important to carefully interpret the preoperative CT images to identify the marginal impaction and to achieve anatomical reduction and satisfactory surgical outcomes.

Introduction

Acetabular fractures are among the most challenging injuries to be treated by orthopedic trauma surgeons¹. The complex shape of the acetabulum and its deep anatomical position surrounded by major neurovascular structures and large muscles make surgical exposure and reconstruction demanding^2,3. Involvement of the posterior wall occurs in approximately 20–30% of acetabular fractures, and it increases to 75% in more complex fracture patterns^4,5.

The type of acetabular fracture is classified as elementary in the Letournel and the Judet system⁶; however, the prognosis may be critically influenced by certain features of acetabular fractures^5–10. These features have been included in the comprehensive classification proposed by the Arbeitsgemeinschaft für Osteosynthesefragen (Association for the Study of Internal Fixation [AO group])^11,12.

The terms “marginal impaction and depression fracture” were introduced to describe a rotated, impacted, single, or multi-fragmented fracture with depression of the osteochondral fragments in the underlying cancellous bone^6,8,11. This specific pattern occurs in approximately 30% of fractures that involve the posterior wall^5,6,8. Marginal impaction is a known risk factor, resulting in poor results; hence, before definitive reconstruction of the cortical wall fragments, marginal impaction must be identified and stabilized appropriately^{4–6,13–20}. However, there are no studies comparing whether there is differences in surgical results of posterior wall acetabular fractures, especially radiological results, depending on the presence or absence of marginal impaction.

We hypothesized that anatomically reduced marginal impaction would not affect radiological and functional outcomes in posterior wall acetabular fractures. This study aimed to compare the mid-term radiological and functional outcomes of posterior wall acetabular fractures with and without marginal impaction.

Materials and methods

Ethics

This retrospective cohort study was conducted with the approval of the Institutional Review Board (IRB) of Ulsan University Hospital (IRB No. 2023-02-006). All methods were performed in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants.

Participants

This study included patients who underwent open reduction and internal fixation of posterior wall acetabular fractures between January 2013 and June 2022 at single Level I trauma center. Inclusion criteria were (1) patients with traumatic, unilateral, simple, or multi-fragmentary posterior wall acetabular fractures with or without hip joint dislocation, and (2) patients were followed up for at least two years to evaluate mid-term outcomes^8,21–23. Exclusion criteria were patients with (1) ipsilateral combined acetabular injury, (2) combined pelvic ring injury, (3) contralateral pelvic and acetabular injury, 3) fragility fracture, or (4) a history of pelvic trauma.

Of a total of 90 patients, 49 were excluded, and 41 were finally included in this study. The patients were grouped according to the presence or absence of marginal impaction (Fig. 1). Of the 41 patients, 17 had a marginal impaction. Patients with marginal impaction were classified into group I (n = 17), and the remaining (n = 24) were classified into group II. Medical records were reviewed for age, sex, body mass index, mechanism of injury, associated injuries, periods from injury to surgery, and follow-up duration.

Fig. 1.

Flow chart.

Surgical procedures and postoperative protocol

Surgical treatments were performed by a senior orthopedic surgeon (KH Jung) when the patients’ general medical condition was considered favorable. All patients underwent surgery under general anesthesia in the lateral position using the Kocher-Langenbeck approach. In seven cases, trochanteric flip osteotomy was conducted when needed to enhance the visibility of the high posterior wall and improve the evaluation of joint reduction (Table 1)^4,20,24. The decision to perform digastric osteotomy was made intraoperatively. This procedure was carried out in situations where the greater trochanter obstructed the view of the posterior wall, making it poorly visible, or when bone fragments were not detectable²⁵. When marginal impaction of a fragment was present, the impacted articular cartilage was elevated and rotated to reduce its anatomic position over the femoral head as template (Fig. 2)^8,9,26. The resulting defect was filled with cancellous autografts harvested from the greater trochanter^19,26. Either 2.0 or 2.4 mm screws were used for fixation of the impacted articular fragment^20,26. When satisfactory reduction of the posterior wall of the acetabulum was achieved, definitive fixation of the fracture was performed using one or two 3.5 mm cortical inter-fragmentary screws and reconstruction plates (Fig. 3). The postoperative rehabilitation protocol was initiated when the patients’ medical condition was found to be favorable. In all patients, protective weight-bearing was applied for up to 12 weeks after surgery.

Table 1.

Demographic data between the two Groups.

Variables	Group I (n = 17)	Group II (n = 24)	P-value
Age (years)	50.7 ± 12.1	44.3 ± 16.2	0.17
Sex			0.06
Male	14 (82.4)	24 (100)
Female	3 (17.6)	0
Body mass index (kg/m2)	25.3 ± 4.6	24.2 ± 3.3	0.36
Injury mechanism			0.40
Dashboard injury	9 (52.9)	15 (62.5)
Motorcycle traffic accident	3 (17.6)	6 (25.0)
Fall from > 2 m	3 (17.6)	2 (8.3)
Pedestrian traffic accident	2 (11.8)	0
Sports activity	0	1 (4.2)
Associated injury*			–
None	8 (47.5)	13 (54.2)
Head	1 (5.9)	5 (20.8)
Thoracic	4 (23.5)	4 (16.7)
Abdominal	1 (5.9)	0
Combined	3 (17.6)	2 (8.3)
Period from injury to surgery (days)	8.3 ± 4.8	4.3 ± 2.0	0.004
Digastric osteotomy	4 (23.5)	3 (12.5)	0.37
Follow-up duration (months)	31.2 ± 15.7	30.8 ± 19.5	0.94

Data were presented as n (%) or mean ± standard deviation.

*Multiple answer.

Fig. 2.

A, Intraoperative view of multi-fragmentary posterior wall acetabular fracture through the Kocher-Langenbeck approach. The white arrow identifies the impacted fragment. B, Intraoperative view after elevation and rotation of the impacted articular cartilage to reduce its anatomic position over the femoral head (*) as template.

Fig. 3.

A and B, Anteroposterior and obturator oblique view of pelvic radiographs of a 59-year-old man with minimally displaced posterior wall acetabular fracture. C, Iliac oblique view demonstrating an intact posterior column. D, E,and F, Postoperative pelvic radiographs.

Radiological evaluations

Radiological evaluations were performed by two orthopedic surgeons (SM Jang and HJ Lee) and in case of disagreement, a consensus was reached after discussion with one additional orthopedic surgeon (KB Park).

Preoperative radiographic evaluations included an anteroposterior and two Judet 45° oblique radiographs of the pelvis⁶. In all patients, a computed tomography (CT) scan of the pelvis with three-dimensional (3D) reconstruction was also performed in the initial imaging evaluation phase to obtain a more accurate morphology of the fracture^19,27. The acetabulum was categorized as illustrated in Fig. 4. Moreover, we divided the impaction fracture sites into two groups: high posterior wall (occurring between 12 o’clock and 2 o’clock) and non-high posterior wall (occurring between 2 o’clock and 6 o’clock)²⁵. We also evaluated the presence of multi-fragmentary fractures, femoral head fractures, dislocations, and bone-free fragments within the joint space that required surgical extraction^25,28. In patients with hip dislocation, follow-up CT scan was performed after closed reduction of the dislocation to assess the adequacy of reduction.

Fig. 4.

A, Preoperative coronal computed tomography (CT) image demonstrating impaction fracture (white arrow) located between 12 o’clock and 2 o’clock (high posterior wall). B, Sagittal CT image demonstrating impaction fracture (white arrow) located between 2 and 6 o’clock (non-high posterior wall).

Postoperatively, CT scans of the pelvis were obtained and evaluated the degree of displacement by the Matta’s reduction criteria (Fig. 5)²⁹: anatomical (displacement ≤ 1 mm), imperfect (2–3 mm displacement), and poor (> 3 mm displacement). And postoperative intra-articular screw penetration was also analyzed.

Fig. 5.

A, Preoperative axial computed tomography (CT) image demonstrating posterior wall acetabular fracture with a marginal impacted fragment (white arrow). B, Sagittal CT image demonstrating multi-fragmentary fragments (*). These are not easily visualized on plain radiographs. C and D, Postoperative axial and sagittal images which same plane with preoperative images demonstrating elevation of the marginal impaction.

The radiological outcome, obtained at the most recent follow-up, was graded using Matta’s radiographic grade criteria previously described^8,29 based on plain radiographs. Patients with normal appearance of the hip joint were evaluated as “excellent”, those with mild arthritic changes such as small osteophytes, 1 mm narrowing of the joint space, and minimal subchondral sclerosis were evaluated as “good”, those with intermediate changes such as moderate-sized osteophytes, < 50% narrowing of the joint space, and moderate subchondral sclerosis were evaluated as “fair”, and those with advanced arthritic changes such as large osteophytes, > 50% narrowing of the joint space, and collapse of the femoral head and acetabulum were evaluated as “poor”.

And heterotopic ossification (HO), post-traumatic osteonecrosis of the femoral head (ONFH), and rate of conversion to total hip arthroplasty (THA) were analyzed at final follow-up. The diagnosis of ONFH was determined using the 2019 revised Association Research Circulation Osseous (ARCO) staging criteria³⁰. In group I, a sub-analysis was performed to determine whether Matta’s radiographic grade varied depending on the location of the impaction fracture: high posterior wall or non-high posterior wall.

Functional evaluations

Functional evaluations were performed by one specialized nurse (JS Choi) at the most recent follow-up and used Harris Hip Score (HSS)³¹.

Statistical analysis

Categorical variables were expressed as frequencies with percentages, and continuous variables were expressed as the mean ± standard deviation. Comparisons between the two groups were performed using the Fisher’s exact test for categorical variables and Student’s t-test for continuous variables, as appropriate. Data manipulation and statistical analyses were performed using the SPSS software version 24 (IBM Corp., Armonk, NY, USA). The threshold for statistical significance was set at P < 0.05.

Results

Demographics of the participants

The baseline characteristics of the patients are summarized in Table 1. There were no statistically significant differences between the two groups in terms of demographic data such as age and sex (P > 0.05). The mean follow-up period was 29.2 ± 1.7 months. The dashboard injury was the most common mechanism of injury in 24 patients. The time interval from injury to surgery was significantly longer in group I than in group II (P = 0.94).

Features of acetabular fracture and combined injuries

Table 2 shows proportion of patients with multi-fragmentary fracture, femoral head fracture, posterior dislocation at initial trauma, and free bone fragments in the joint. According to the AO classification^11,12 80.5% (33/41) of total population were multi-fragmentary fractures, and only 8 cases (19.5%) were simple cases. However, there was no statistically significant difference in the proportion of multi-fragmentary fractures and simple fractures between the two groups (P = 0.70). The percentage of patients with femoral head fracture was 64.7% and 41.7% in groups I and II, respectively, with no significant difference (P = 0.15). Posterior dislocation at initial trauma was significantly lower in group I (70.6%) than in group II (100%, P = 0.005). The percentage of patients with bone free fragments inside the joint space requiring surgical removal was 52.9% and 66.7% in groups I and II, respectively, with no significant difference (P = 0.38).

Table 2.

Radiological characteristics between the two Groups.

Variables	Group I	Group II	Pearson Chi-Squre	P-value
Multi-fragmentary fracture	13 (76.5)	20 (83.3)	0.30	0.59
Femoral head fracture	11 (64.7)	10 (41.7)	2.11	0.15
Dislocation	12 (70.6)	24 (100)	8.04	0.005
Free bone fragments in the joint	9 (52.9)	16 (66.7)	0.79	0.38

Data were presented as n (%).

Radiological evaluation of the hip joint according location of impaction fractures in group I

In 14 (82.4%) of the 17 patients in group I with impaction fracture, the location of impaction fracture was the high posterior wall, and in the remaining 3 patients, it was between 2 and 6 o’clock. There was no significant difference in the final radiological evaluation of the hip joint according to the location of impaction fracture (P = 0.501).

Postoperative quality of reduction on CT scan

Table 3 shows the postoperative radiological results. The postoperative quality of reduction according to Matta’s criteria²⁹ was as follows: anatomic reduction was found in 22 cases, imperfect reduction was found in 17 cases, and poor reduction was found in 2 cases. There were no significant differences in postoperative quality of reduction. At the immediately postoperative CT scans, there were no cases of postoperative intra-articular screw penetration.

Table 3.

Radiological outcomes between the two Groups.

Variables	Group I (n = 17)	Group II (n = 24)	P-value
Postoperative quality of reduction			0.66
Anatomical	10 (58.8)	12 (50.0)
Imperfect	7 (41.2)	10 (41.7)
Poor	0	2 (8.3)
Screw penetration	0	0	–
Final evaluation of the hip joint			1.000
Excellent	15 (88.2)	22 (91.7)
Good	–	–
Fair	–	–
Poor	2 (11.8)	2 (8.3)
Heterotopic ossification (+)	5 (29.4)	5 (20.8)	0.71
Osteonecrosis of femoral head (+)	0	0	–
Conversion to total hip arthroplasty	0	0	–

Data were presented as n (%).

Final radiologic grade on plain radiograph

The final radiological evaluation of the hip joint according to Matta’s criteria^8,29 was excellent in 37 patients (90.2%), and poor in 4 patients (9.8%). There were no significant differences in the final radiological evaluation of the hip joint between the two groups. HO in five patients in each group, but there was no significant difference. There were no cases with post-traumatic ONFH or conversion to THA at final follow-up.

Functional outcomes

The HHS was 93.6 points (range, 73–100) in group I and 94.2 points (range, 81–100) in group II, with no significant differences between the two groups (P = 0.77).

Discussion

This study compared the radiological and functional outcomes of posterior wall acetabular fractures according to with and without marginal impaction. The most important findings of this study were that marginal impaction was common enough to be identified 4 out of 10 patients, and that radiological and functional outcomes were satisfactory even in posterior wall acetabular fractures accompanied by marginal impaction if anatomical reduction was performed.

Letournel et al.⁶ reported that marginal impaction occurred in approximately 30% of fractures involving the posterior wall. Further, Kreder et al.⁵ reported that the proportion of this pattern in isolated posterior wall fractures was approximately 22.7%. In the present study, the incidence was 41.5%, which was higher than that reported in the previous studies. In this regard, we believe that as 3D-CT became popular, more patients were tested to obtain accurate characteristics, including the presence of marginal impaction of the fracture^19,27 to establish appropriate preoperative planning and ensure good results. Therefore, considering the utility of 3D-CT scans, we recommend examining 3D-CT images thoroughly before surgery due to the possibility of a much higher rate of marginal impaction than previously reported.

Posterior wall acetabular fractures can occur in isolation, but are often seen in conjunction with other fracture types¹⁴. In a study by Kreder et al.⁵128 patients who underwent surgery for fractures involving the posterior wall of the acetabulum were analyzed. The study revealed that 65.6% of these cases were complex fractures, with 51 patients experiencing transverse fractures, 22 with fractures involving the posterior column, and 11 presenting T-shaped acetabular fractures. The research highlighted that fracture pattern, marginal impaction, and residual displacement exceeding 2 mm were linked to the onset of arthritis, which in turn was associated with diminished function and the requirement for hip replacement. Although we suggested that anatomical reduction of marginal impaction led to positive radiological outcomes, it is limited by the fact that the absence of arthritis development and conversion to hip replacement in both groups could be attributed to the exclusion of complex fractures, such as ipsilateral combined acetabular injuries.

Previous studies have shown that accurate and anatomic reduction of the posterior wall is associated with improved radiological and functional results^{17,19–21,32,33}. Mitsionis et al.¹⁵ showed that the adequacy of reduction determines long-term results. Letournel et al.⁶ reported that 19 (16%) of 119 posterior wall fractures that were perfectly reduced developed notable post-traumatic osteoarthritis during follow-up. The rate of post-traumatic osteoarthritis is higher than 10% of all acetabular fracture types with anatomic reduction⁴. We assumed that anatomical reduction would be more difficult in patients with posterior wall acetabular fractures with marginal impaction resulting in worse results. However, in this study, there were no statistically significant differences in the final radiological results, regardless of marginal impaction. We assumed this is because all patients were inspected using preoperative 3D-CT to identify marginal impaction and accurate fracture morphology for appropriate preoperative planning, resulting in anatomically optimal intraoperative fracture reduction and fixation.

The size of posterior wall acetabular fractures, the presence of marginal impaction, or column fractures of the acetabulum are related to the degree of hip flexion³⁴. And the posterior wall fragment may either remain attached to the joint capsule or an additional rupture of the capsule may occur³⁵. In the presence of an intact capsule, the femoral head is directed to the remaining posterior osseous structures by ligamentotaxis and may cause marginal impaction there. In this study, the authors were unable to evaluate the degree of hip flexion at the time of impact or the presence of additional rupture of the capsule, interestingly, patients without an initial posterior hip dislocation were more likely to have marginal impaction. The influence of various factors mentioned above must be considered, however, in light of the pathophysiology of marginal impaction described above^6,8,11 we assumed that if the external force applied to the posterior wall of the acetabulum is enough to cause posterior hip dislocation, fracture-dislocation of the poster cortical bone will occur before the osteochondral fragment is depressed into the cancellous bone, resulting in a multi-fragmentary fracture pattern. Conversely, if there is no posterior dislocation, the posterior wall receives the entire external force, resulting in osteochondral depression. Further research with cadaveric studies is required to verify our hypothesis.

Generally, HO occurs most frequently in patients requiring surgical dissection of the gluteal muscles for surgical approaches like Kocher-Langenbeck^4,36. For prophylaxis against HO, devitalized gluteal muscle tissue debridement was performed during surgery. Although HO was the most frequent late complication at follow-up, the overall frequency of this complication (20%) in this study was similar to or slightly lower than that observed in previous studies on posterior wall fractures (20–40%)^{10,15,37–39}. Among the patients in whom HO was observed during outpatient department follow-up, none had symptoms that required additional treatment.

The ARCO classification system³⁰ was described as follows: Stage I showed osteosclerosis, localized osteoporosis, or cystic changes in the femoral head, visible on plain radiographs or CT scans. Stage II was characterized by subchondral fracture, fracture within the necrotic area, and/or flattening of the femoral head. Stage III was identified by specific findings on plain radiography or CT, while Stage IV was marked by hip joint osteoarthritis, including joint space narrowing, acetabular changes, and destruction evident on plain radiographs. Additionally, magnetic resonance imaging (MRI) could reveal a low-signal-intensity band lesion surrounding the necrotic region, or bone scan might display a cold spot, both indicative of Stage I. However, since this study participants did not undergo postoperative MRI or bone scans, it was difficult to identify Stage I ONFH that would typically be diagnosed using these imaging techniques.

Previous retrospective cohort study evaluating 685 operative acetabular fractures reported that 108 patients (16%) underwent conversion to THA, with 52% of conversions occurring within 1 year, an additional 27% within 2 years, and the remaining 21% within 6 years of the index acetabular open reduction and internal fixation⁴⁰. Other retrospective cohort study evaluating conversion to THA in patients with posterior wall acetabular fractures reported that the overall rate of conversion to THA was 5% at 2 years, 14% at 5 years, and 17% at 9 years and there were no THA conversions among patients with less than 1 mm of diastasis/step-off on postoperative CT scan³³. In this study with a minimum 2-year follow up, there was no conversion to THA after index acetabular open reduction and internal fixation, regardless of the presence or absence of marginal impaction. Because preoperative CT scans were carefully analyzed for marginal impaction, fragmentation, etc. and near-anatomic reduction was performed, we determined that there was no THA conversion in patients included in this study.

Research by Kreder et al.⁵ demonstrated that merely achieving anatomical reduction was insufficient to restore function in patients with posterior wall acetabular fractures. The presence of marginal impaction was correlated with the onset of arthritis, which subsequently led to compromised functioning. Giannoudis et al.⁸ noted that advanced age and inferior location of impaction were linked to more severe pain. Despite these findings, Perumal et al.²¹ utilized anatomical reduction and cancellous allograft to address complex posterior wall acetabular fractures with marginal impaction, achieving excellent or good functional outcomes in 6 out of 10 cases. Additionally, Khira and El-Aidy²⁶ proposed a technique involving the elevation and grafting of marginal impaction fragments in posterior wall acetabular fractures, reporting clinical outcomes that were 20% excellent, 80% good, and 15% fair.

The strength of this study stems from its comparative nature, assessing the radiological and functional outcomes based on the presence or absence of marginal impaction in posterior wall acetabular fractures. The study highlights the higher incidence of marginal impaction than previously reported. Some limitations of the study include the retrospective nature of the study and the probable selection bias as all surgeries were performed by a single senior surgeon at a single institute. Second, this study was conducted on patients with posterior wall acetabular fractures who were consecutively treated during the study period; therefore, the sample size was small. For the same reason, power analysis could not be performed and a descriptive study design was used. And readers should be aware that the sample size was too small, which may result in Type II error. Although the number of samples was small, the surgery and postoperative care were performed by a single surgeon at a single institution, so there was an advantage in being compared in a group of patients who received the same level of treatment. Finally, this study excluded patients with combined pelvic ring injuries as part of its criteria. This may limit the generalizability of the findings, as posterior wall acetabular fractures often occur in conjunction with other pelvic injuries. Nevertheless, by focusing solely on posterior wall acetabular fractures and eliminating combined pelvic ring injuries, the researchers were able to standardize preoperative conditions that could influence functional outcomes including pain levels, reliance on support devices, walking capacity, presence of a limp, ability to navigate stairs, and sitting comfort.

Conclusion

There were no significant differences in radiological and functional outcomes of posterior wall acetabular fractures, regardless of marginal impaction. For better surgical outcomes, it is important to carefully interpret the preoperative 3D-CT results to identify the presence of marginal impaction and to achieve maximum possible anatomical reduction.

Abbreviations

AO

Arbeitsgemeinschaft für Osteosynthesefragen

IRB

Institutional review board

CT

Computed tomography

3D

Three-dimensional

HO

Heterotopic ossification

ONFH

Osteonecrosis of the femoral head

THA

Total hip arthroplasty

ARCO

Association Research Circulation Osseous

MRI

Magnetic resonance imaging

HSS

Harris hip score

Author contributions

The following authors have made substantial contributions to the following: (1) the conception and design of the study (K. H. J., S. M. J., and K. B. P.), (2) provision of study materials or patients (S. M. J. and J. W. A.), (3) acquisition of data (H.J.L., J. W. A., S. H. O.), (4) analysis and interpretation of data (K. H. J., S. M. J., H.J.L., and K. B. P.), (5) drafting the article (K. H. J., S. M. J., K. B. P., and S. H. O.), (6) revision of the articles (K. H. J.,S. M. J, H.J.L., K. B. P, and J. W. A.), and (7) final approval of the version to be submitted (K. H. J., S. M. J., H.J.L., K. B. P., J. W. A., and S. H. O.).

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Competing interests

The authors declare no competing interests.