Clinical efficacy of extended modified posteromedial approach versus posterolateral approach for surgical treatment of posterior pilon fracture: a retrospective analysis CURRENT STATUS: POSTED

Background: Posterior pilon fracture is a type of ankle fracture associated with poorer treatment results compared to the conventional ankle fracture. This is partly related to the lack of consensus on the classification, approach selection, and internal fixation method for this type of fracture. This study aimed to investigate the clinical efficacy of posterolateral approach versus extended modified posteromedial approach for surgical treatment of posterior pilon fracture. Methods: Data of 67 patients with posterior pilon fracture who received fixation with a buttress plate between January 2015 and December 2018 were retrospectively reviewed. Patients received steel plate fixation through either the posterolateral approach (n = 35, group A) or the extended modified posteromedial approach (n = 32, group B). Operation time, intraoperative blood loss, excellent and good rate of reduction, fracture healing time, American Orthopaedic Foot & Ankle Society (AOFAS) Ankle-Hindfoot Scale score, and Visual Analogue Scale score were compared between groups A and B. Results: All patients were followed up for an average period of 15.4 months. No nonunion, failure of internal fixation, or anklebone stiffness occurred in either group during the follow-up period. However, the operation time was significantly shorter, intraoperative blood loss was significantly lower, AOFAS Ankle-Hindfoot Scale score was significantly higher, and Visual Analogue Scale score was significantly lower in group B than in group A (P < 0.05). Conclusion: Compared to the posterolateral approach, the extended modified posteromedial approach can provide a better surgical field for the treatment of posterior pilon fracture, which allows reduction and fixation of this type of fractures under direct vision and evaluation of reduction effects, and reduces operation time and intraoperative blood loss. Combining this approach with supporting steel plate fixation enables early functional rehabilitation of the ankle with more satisfactory clinical results.

can provide a better surgical field for the treatment of posterior pilon fracture, which allows reduction and fixation of this type of fractures under direct vision and evaluation of reduction effects, and reduces operation time and intraoperative blood loss. Combining this approach with supporting steel plate fixation enables early functional rehabilitation of the ankle with more satisfactory clinical results.

Background
The concept of posterior pilon fracture was first proposed by Hansen in 2000 [1]. Posterior pilon fracture is described as a posterior malleolar fracture extending into the posterior colliculus or even the anterior colliculus that is commonly complicated by posterior dislocation and cartilage injury of 3 the ankle. Previous research showed that this type of fracture accounts for 6-20% of all ankle fractures [2,3]. Moreover, its treatment results are poorer than those for the conventional ankle fracture [4]. The reason for the large statistical difference and poor therapeutic efficacy is the lack of understanding of the mechanisms of posterior pilon fracture, which is frequently misdiagnosed as a conventional trimalleolar fracture [5]. There is no current consensus on the classification, approach selection, and internal fixation method of the posterior pilon fracture due to short recognition time, low incidence, and small number of case reports [6].
Posterior pilon fracture is an intra-articular fracture. Its surgical treatment aims to achieve anatomical reduction of the articular surface and firm fixation of fractured fragments in order to reduce the incidence of traumatic ankle arthritis. This retrospective study investigated the clinical efficacy of reduction through the extended modified posteromedial approach versus posterolateral approach during the surgical treatment of posterior pilon fracture.

Study population
All cases of posterior pilon fracture treated by surgical reduction through the extended modified posteromedial approach or posterolateral approach in combination with fixation with a buttress plate at the Department of Orthopedic Trauma of Jining Medical College between January 2015 and December 2018 were reviewed. Patients aged ≥ 18 years, with good ankle movement prior to injury, and a new closed fracture corresponding to the imaging characteristics of posterior pilon fracture [7] (distal tibial fracture line extending along the coronal plane into the posterior colliculus or even the anterior colliculus, with or without the "double contour sign" of the proximal medial malleolus, the posterior malleolus displaced proximally, and the margin of the bone mass compressed and fragmented; Die-punch bone masses, with or without subluxation of the posterior talus, were also present) were included. Patients with pathological fractures, associated neurovascular injuries, a history of ankle disease or serious trauma prior to injury, and a follow-up < 12 months were excluded.
A total of 67 patients were included. Patients with dislocation were treated with plaster fixation and calcaneus traction. If blisters appeared, the fluid in the blisters was extracted and the epidermis was preserved and dried with infrared light. The affected limb was elevated, and detumescence and anticoagulant therapy were performed. Operations were carried out when the swelling subsided obviously, the skin folded, and blisters dried out [8]. bundles. The flexor longus muscle was pulled laterally and the posterolateral malleolus was exposed through the "lateral window." The posteromedial malleolus was exposed through the "medial window" created between the posterior tibial tendon and the flexor digitorum longus tendon.
In both surgical approaches, the fractures of the lateral malleolus or fibula were treated first. As for the common short oblique fractures of the lateral malleolus, tension screws were placed perpendicular to the fracture line and fixed with steel plates. Then, the posterior malleolus fracture 5 was treated, avoiding any damage to the posterior tibiofibular ligament. The broken ends of the fracture were opened using the book opening-like technique along the fracture line between the fractured posteromedial and posterolateral parts to expose the articular surface. The collapsed bone masses were reduced. If the fractured mass was ≤ 2 mm in diameter and dissociated, it was removed to avoid the entry of the dissociated bone mass into the articular cavity. The fractured posterior malleolus bone mass was reduced. Taking the continuity recovery of the proximal cortex of the fractured part as an anatomical sign, fluoroscopy was performed to ensure good fracture reduction and flat articular plane. Then, buttress plates were implanted. The fractured medial malleolus was exposed through the anterior side of the posterior tibial tendon and fixed with hollow screws or Kirschner wires after reduction. Then, cotton tests were performed. Lower tibiofibular screws were used to fix the unstable lower tibiofibular joint. After confirming that the supporting steel plate did not influence the tendon sliding, the incision was sutured.

Postoperative management
Antibiotics were used 24 hours after operation to prevent infection. Routine detumescence, analgesia, and anticoagulation therapy were performed. On day 1 after surgery, patients were instructed to perform isometric contraction of the quadriceps femoris, and active and passive flexion and extension of the toes and ankles. On day 2 after surgery, an anteroposterior radiograph of the ankle joint was obtained. At 2 months after surgery, partial weight-bearing exercise of the affected limb was initiated.
At 3 months after surgery, full weight-bearing exercise of the affected limb was started according to the results of imaging examination.

Efficacy evaluation and statistical analysis
The quality of fracture reduction, reduction loss, and fracture healing were evaluated according to Burwell-Charnley imaging criteria [9]. The Visual Analogue Scale (VAS) score (0-10) was used to evaluate the intensity of resting and movement-related pain during follow-up. At the last follow-up, patients were evaluated using the American Orthopaedic Foot & Ankle Society (AOFAS) Ankle-Hindfoot Scale score [10]. Operation time, intraoperative blood loss, fracture healing time, AOFAS Ankle-Hindfoot Scale score, and VAS score were compared between groups A and B. Statistical 6 analysis was performed using SPSS 19.0 software (SPSS Inc., Chicago, IL, USA). All measured data were expressed as mean ± SD. Wilcoxon's rank-sum test was used to compare non-normally distributed data, t-test was used to analyze normally distributed data, and chi-squared test was used to compare categorical data between the two groups. P values < 0.05 were considered statistically significant.  Table 2. Images of a typical posterior pilon fracture case are shown in Fig. 1. Table 1 Comparison of excellent and good rates of reduction between groups A and B

Discussion
The results of this study showed that for surgical treatment of posterior pilon fracture, the extended modified posteromedial approach outperforms posterolateral approach in terms of operation time, intraoperative blood loss, fracture healing time, AOFAS Ankle-Hindfoot Scale score, and VAS score.
This suggests that this approach may be more appropriate for routine surgical treatment of this type of fractures.
Klammer et al. [12] considered that the majority of posterior pilon fractures can be reduced by reduction sequence, and internal fixation [13]. The processing results of Die-punch bones are the key factors affecting the prognosis, and a wrong surgical approach may lead to difficulties in exposure and reduction of Die-punch bone, resulting in post-traumatic ankle arthritis [14].
Assal et al. [15] proposed a modified posteromedial approach for the treatment of complex pilon fractures, which includes a straight posteromedial incision of the lower leg that enters the space between the plantar flexor muscle and the posterior tibial blood vessels and nerve bundles. In this manner, posterolateral and posteromedial bone masses can be exposed through the lateral window and medial window, respectively. In the treatment of fracture of posterior distal tibia, the degree of soft tissue injury caused by steel plate implantation is likely to be higher than that caused by screw insertion, which may cause contracture of the posterior flexor tendon [16]. However, Viberg et al., in their multicenter study on the complications and efficacy of distal tibia fracture fixation with bone plate, reported that because there is a large amount of soft tissue covering the posterior part of the distal tibia, the phenomenon of soft tissue agitation rarely occurs when steel plate is inserted into the posterior distal tibia [17]. As for internal fixation for posterior pilon fracture, internal fixation with screws inserted neither anteriorly nor laterally can achieve enough fixation strength. Early weight-bearing functional exercises likely lead to relocation of fractured bone and internal fixation failure. In this study, posterior pilon fracture was fixed with steel plate in all included patients. Fifty-nine patients received internal fixation with a T-shaped locking plate at the distal radius and eight patients underwent fracture fixation with a 3.5 mm-sized locking plate at the distal tibia on the healthy side. After surgery, patients were encouraged to perform early functional exercises of the ankle joint. Fracture replacement, collapse of Die-punch bone mass, or internal fixation failure was not observed during the follow-up period.
Several limitations of this study should be considered when interpreting its results. First, the number of included patients was relatively small. Second, this was a retrospective, single center research.
Finally, the follow-up period was relatively short. Further larger-scale prospective studies are necessary to confirm obtained results.