Semiprone Position for Posterior Approaches to Acetabular fractures Allows Intuitive Radiographic Acquisition and Versatility for Surgical Hip Dislocation: A Technical Note and Preliminary Report

position is semiprone alternative.


Abstract Background
Although the pros and cons of prone and decubitus positioning methods, for posterior approaches to acetabular fractures, have been widely discussed, it remains inconclusive whether a particular patient position is superior to the other. Here we present our preliminary experience with placing the patient in the semiprone position for posterior approaches to the acetabulum as a potentially advantageous alternative.

Methods
Technical notes were provided as well as the preoperative, intraoperative and postoperative images of the demonstrative cases. From July 2018 to April 2020, eight selected patients with complex acetabular fractures were surgically treated through posterior approaches in semiprone position. Patient demographics, fracture pattern, poor prognostic factors and associated conditions were recorded. The quality of fracture reduction was assessed by Modi ed Matta's criteria. The operative hip's function was evaluated by the Modi ed Merle d'Aubigné-Postel score if follow-up was more than 3 months.

Result:
The Median age of our cohort was 48.55 years (24. 3-70.6). The median body mass index was 23.90 kg/ m 2 (17. 6-26.4). Satisfactory reduction was achieved in 6 of the 8 patients. Intraoperative radiographs obtained by the standard vertical and horizontal projection of the C-arm machine resembled the classic Judet views. Trochanteric ip osteotomy and surgical hip dislocation were feasible. One hip was converted to total hip replacement 5 months after primary fracture surgery due to femoral head osteonecrosis.

Conclusion:
The preliminary radiographic and reduction quality of our cohort were comparable to those reported in the literature. The advantages of semiprone position include intuitive intraoperative radiographic acquisition, making gravity as a aid for reduction and feasibility of surgical hip dislocation. Long-term follow-up and further case-controlled or randomized controlled studies are necessary to uphold its value.

Background
Surgical treatment for certain types of acetabular fractures warrants posterior approaches, such as Kocher-Langenbeck approach or modi ed Gibson approach [1,2]. There are pros and cons for each positioning method [3]. For lateral position, most surgeons are familiar with it and surgical hip dislocation is readily applicable. Reduction against gravity and maintenance of the reduction quality are the issues since gravity tends to cause medialization of the medial acetabular wall, or the quadrilateral plate [3,4]. For prone position, gravity may act as an aid, instead of an obstacle, for reduction. But hip manipulation is relatively limited and surgical hip dislocation may not be feasible. It remains inconclusive whether a particular patient position is superior to the other. The choice of the patient positioning method depends mainly on the surgeon's decision.
A well-trained technician is paramount for good intraoperative radiographic acquisition in both traditional positioning method., especially when Judet views are required. The advantage of intuitive radiographic acquisition on semiprone position was rst noted by our orthopedic oncology team during surgeries involving the pelvis or acetabulum. Selected cases were put in semiprone position to facility the excision and reconstruction surgery. The intraoperative radiographs acquired from standard vertical and horizontal projections were similar to the classic Judet views [5]. We started to apply this positioning method to selected acetabular fractures from July 2018. Here we share our preliminary experiences of 4. Vertical projection of the radiation beam from C-arm machine ( gure 3a) will produce iliac oblique view of Jude on the image intensi er. Figure 3b and 3c show the radiographs acquired intraoperatively during reduction process of posterior column.
5. Horizontal projection of the radiation beam will produce obturator view of Judet ( gure 4a). Reduction process of the posterior wall is shown in gure 4b and 4c.
6. The nal construct is shown in gure 5a-d.
B. For surgical hip dislocation 1. During positioning, a space should be left between the lower back and the posterior posts ( Fig. 1b) to allow position switching between lateral decubitus and semiprone position. It should be checked before disinfection and must be interchangeable smoothly.
2. If hip reduction via surgical hip dislocation approach is planned to be done rst, as in the situation of irreducible femoral head fracture-dislocation or incarcerated fragments in the hip joint, the patient is put in semiprone position rst during preparation.
3. After surgical eld disinfection, the posterior aspect from the back to the buttock was draped aseptically. A non-scrubbed-in assistant help to push the upper trunk and shoulder backward in cooperation with the anesthesiology team, while the scrubbed-in change the patient position to lateral decubitus. The scrubbed-in must then exchange gloves. Disinfection was applied again to previously nonsterile part and the whole surgical eld. Then we continue to nish the draping. Doing it in the opposite manner, decubitus position rst, is also possible and may be applied according to the surgical planning.
4. After dealing with intraarticular conditions via surgical hip dislocation, we may change the patient position to semiprone position to treat the acetabular fracture.

5.
Here we show case number 7, a case of femoral head fracture and associated T-shaped acetabular fracture with irreducible hip dislocation in closed manner, for example ( Fig. 6). After disinfection and draping as described, surgical hip dislocation was done rst in lateral decubitus position to reduce the hip and treat the femoral head fracture. The femoral head bone loss was inevitable due to multiple comminuted non-xable fracture fragments. We managed to reduce the fracture and shape the femoral head as spherical as possible. After completion of femoral head xation, we change the patient position to be semiprone by pushing the back, again, in cooperation with the anesthesiology team. The T-shaped acetabular fracture was then reduced and xed.   Table 1. Matta's criteriae were applied with modi cation to evaluate the standard postoperative plain lms for evaluation of reduction quality [6]. That is, residual gap ≤ 1 mm for anatomical reduction, 1-3 mm for imperfect reduction and > 3mm for inadequate reduction on standard AP and the Judet views [7,8]. Poor prognostic factors, associated conditions and hip survival were recorded [7]. Modi ed Merle d'Aubigné-Postel score during the last follow-up was also recorded if it was more than 3 months [9].

Preliminary Results
Good intraoperative Judet views could be acquired by simple vertical and horizontal projections as demonstrated. Five out of eight patients had anatomical reduction (< 1 mm). One had imperfect (1-3mm). Two had inadequate reduction, that is, gap or step-off > 3mm according to Matta's criteria. Six of the eight cases achieved "satisfactory reduction", including the anatomical and the imperfect reduction [6,7]. The result regarding fracture reduction is comparable to the reported literatures [7]. Three of the eight patients were treated with anterior intrapelvic approach rst, which determined the major part of fracture reduction. Subsequently we put the patients in semiprone position to address the signi cant posterior wall fragments. Anatomical reduction was achieved in two. The other was inadequate, mainly due to the special condition of high bone mass osteogenesis imperfect and mélange of troublesome fracture patterns as listed in table 1.
Patient number 2 had intraoperative anatomical reduction, including the reduced and grafted marginal impaction by direct vision and intraoperative images. But the postoperative plain lms showed suspicious re-collapsed marginal impaction, about 2 mm step-off, con rmed by follow-up computed tomography (CT). Later the patient had ipsilateral femoral head osteonecrosis and received total hip replacement 5 months after the primary fracture surgery. Patient number 5 was bedridden due to brain injury caused by the motor-vehicle accident. The follow-up for Patient number 7 and 8 was shorter than 3 months. After patient number 3, 7 and 8 were excluded, good-to-excellent outcome was achieved in 4 of 5 hips, and in 3 of 4 survived hips.

Discussion
The fracture personalities of these selected patients were knotty, while the reduction quality in our small cohort was still comparable to the reported literatures [4,6,7]. For surgical treatment of acetabular fractures, the quality of reduction is directly related to the outcome [7]. For certain acetabular fractures, gravity acts to medialize the medial wall of the acetabulum in decubitus position, which may cause problems during reduction [4]. If at the same time surgical hip dislocation is favored, surgeons would face a dilemma. The semiprone positioning method offers some bene ts of prone position and provides the versatility for surgical hip dislocation.
There are three scenarios that we will consider putting the patient in semiprone position. First, when posterior wall fracture extends superiorly with hip subluxation, gravity will keep the femoral head anterior in the acetabular socket. Gibson approach or trochanteric ip osteotomy may be done with uncompromised anterior access. Second, when a markedly medialized quadrilateral plate warrants posterior approach for reduction, gravity will not be so much an obstacle as in decubitus position. Again, anterior access is preserved for insertion anterior column screw or interfragmentary screws. Surgical hip dislocation may also be performed if intraarticular inspection is necessary [1]. Third, when there are intraarticular acetabular fragments or Pipkin IV fractures, surgical hip dislocation in combination with Kocher-Langenbeck or Gibson approach may be done to treat both intraarticular conditions and the acetabular fracture.
Good intraoperative radiograph acquisition may further help the surgeons strive to get anatomical or satisfactory reduction. Experienced technicians or assistants are helpful in getting the Judet views when patients are put in prone or lateral position. When patients are put in semiprone position, it become intuitive to acquire intraoperative Judet views as demonstrated.
Postoperative computed tomography (CT) may be more accurate in evaluating the quality of reduction than traditional radiographs, and is associated with hip survivorship [10][11][12]. Verbeek et al. identi ed residual gap of 5 mm and step-off of 1 mm as critical cut-off, measured at the high weight bearing dome on computed tomographic images [11]. The clinical utility of postoperative CT is not yet determined and its routine use has not been justi ed [8,10]. However, we do observe an increase in frequency of ordering postoperative CT in our daily practice and in the reported literatures [7,8,10,12]. Only small portion of the patient will be treated differently by routine postoperative CT. Careful selection may add its value [13].
This is a small numbered retrospective study without long-term outcome. But we consider semiprone positioning method potentially advantageous and worth spreading. Long-term follow-up, as in all outcome studies for acetabular fracture surgery, is necessary. Further large scale, case-controlled or randomized controlled studies may be necessary to prove its value.

Conclusions
Semiprone position may be a viable alternative positioning method for posterior approaches to acetabular fractures. It is advantageous for intuitive intraoperative radiographic acquisition, preservation of anterior access, making gravity as an aid for fracture reduction and being versatile for surgical hip dislocation. Further studies are necessary to uphold its value.

Declarations
Ethics approval and consent to participate The study was approved by National Taiwan University Hospital Research Ethics Committee. The study has been conducted under the Declaration of Helsinki.

Consent for Publication
Written informed consents were acquired prior to publication.

Competing Interests
The authors declare no competing interests.   Intraoperative Iliac Oblique View Fig. 3a: We used a 3D-printed pelvic fracture model for demonstration of semiprone position. The white arrow represents the vertical projection of radiation beams from C-arm machine, centered on the acetabulum. Fig. 3b & c: The intraoperative images acquired on image intensi er resemble iliac oblique views of Judet. The images show the process of reduction and preliminary xation with lag screws and a position screw. Besides direct vision and nger palpation, the reduction quality of posterior column can be further evaluated by these images.

Figure 4
Intraoperative Obturator Oblique View Fig. 4a: The white arrow represents the horizontal projection of radiation beams from C-arm machine, centered on the acetabulum. Fig. 4b-d: The reduction process was recorded by the intraoperative images, resembling obturator oblique views of Judet. The posterior wall fragment was reduced and the reduction was maintained by ball spike pusher with a disc. Preliminary xation was done via a lag screws and a position screw. Two neutralizing plates were then applied in standard manner.