The most important finding of the present study was that MIPO led to a lower total complication rate when compared to ORIF in the surgical treatment of distal fibula fractures. Even though not statistically significant, surgery related complications such as skin necrosis, nonunion, infections and wound healing disorders as well as vascular-nerve injuries were found more frequently in the ORIF group. Lower postoperative pain scores were noted in the MIPO group. Operative time and length of stay were longer in the ORIF group. Postoperative radiographic measures, except the tibiofibular overlap, showed to be equivalent in both groups.
Since the introduction of minimally invasive plate osteosynthesis (MIPO) following a biological fixation principle by internal bridging of the fracture with preservation of soft tissue, this technique was successfully applied in the treatment of different long bone fractures (3, 4, 13, 14, 23–31).
In open techniques, wound complications remain among the biggest problems to overcome. Currently reported soft tissue complications range between 17,5–22% (4–6, 32). In elderly patients, complication rates concerning soft tissue might rise as high as 40% (7).
When taking into account concomitant systemic diseases, particularly diabetes and neuropathy, patients have even a 3.8 times increased risk of overall complications compared to healthy patients with ankle fractures (33).
MIPO seems to be a reasonable solution to solve the problem of soft tissue complications and an increasing number of publications about its use in the treatment of long bone fractures seem to underline this trend.
However, only few case series with limited number of patients have been done so far investigating MIPO in distal fibula fractures.
Krenk et al. (3) reported a series of 19 complex ankle injuries treated with MIPO that all healed without skin complications. Historically many patients complained of pain also due to retained hardware because of the subcutaneous plate placement. No such case was reported in their study and this may be secondary to the fact that in more than half of the cases a distal screw was not set in the plate.
Hess and Sommer could show the successful application of MIPO in 20 complex distal fibular fractures with critical soft tissue conditions. Of those 20 cases, seventeen fractures healed without complications at all. (8)
The only study done so far directly comparing ORIF and MIPO in the treatment of distal fibula fractures was the study done by Iacobelis et al. (4) They could show that none of the MIPO cases had any wound complications in comparison with 5 cases of wound complications in the ORIF group. With only 18 patients in each group this was nevertheless a rather small cohort study.
The present study consists of 35 complex fibular fractures treated with MIPO and 35 complex fibula fractures treated with ORIF in a single institution. Our rate of complications following the minimally invasive procedure is strongly comparable to the ones above. The rate of total complications in the MIPO group is statistically lower than in the ORIF group (14% vs. 37%, p = 0.029). Each complication rate, including infection, skin necrosis and nonunion showed to be lower in the MIPO group, even though not statistically significant.
To obtain correct joint congruency, prevent osteoarthritis and obtain satisfying clinical results after ankle fracture, proper anatomic alignment of the ankle mortise plays a key role (34–37).
In our study all postoperative radiographic values in both the MIPO and the ORIF group showed to be in the normal, widely accepted range. Nevertheless, those radiographic values have to be interpreted critically, because not only there is a substantial variability in normal anatomy between individuals, but also because of recent studies showing that two-dimensional radiographs are not reliable to rule out syndesmotic injury.
Hermans et al. showed that tibiofibular overlap did not correlate with syndesmotic injury, nor did a widened medial clear space correlate with deltoid ligament injury. But whenever measurements deviated, syndesmotic injury was always present, whereas normal measurements did not exclude syndesmotic injury (38). Those findings are supported by an MRI study showing that a normal tibiofibular radiographic relationship does not preclude syndesmosis disruption and resulting instability (39). In return stress radiographs are described to have good reliability (40, 41). So it was assumed that the majority of syndesmotic instabilities were recognised and adressed with a syndesmotic screw.
The observed statistically significant difference of the tibiofibular overlap between MIPO and ORIF might be accidental, with a large variety of this value described in the literature (42). In general the tibiofibular overlap should be greater than or equal to 10 mm (43). Measurements in both groups can therefore be considered normal.
The closer the postoperative angular and spatial values are to the contralateral healthy ankle the better. Unfortunatley our follow up protocol did not include a standard radiograph of the healty side. However, with five different measurements being in the normal range it could be expected that correct anatomic alignment was achieved in both groups.
The main limitation of this study is its retrospective design. It is also limited by a relatively small number of patients, even though it is the largest cohort published so far. The mix of different severity of malleolar fracture types included might be a possible confounding factor. However, different fracture types in our study were represented homogenously in both groups. Finally, lack of comparison of postoperative radiographic measurements with the contralateral side limits the interpretation of those values.