Out of 132 patients deemed eligible by chart review, 105 were successfully contacted and invited to provide data for this retrospective analysis. However, only 58 (27 males) of these patients returned the KOOS questionnaire and consented to participate in the clinical examination. Patients presented with a median age of 58.5 [26.0–86.0] years and a BMI of 25.9 [17.1–37.8] kg/m2, respectively. Tibial fractures were due to high- and low-energy accidents in 42 and 16 cases. Patients with a high-energy accident were slightly younger compared to those with a low-energy trauma (52.5 [23–80] years vs. 59.0 [35–75] years; p = 0.043). The median time to follow-up was 3.05 [0.96–6.11] years and 2.56 [1.00–6.041] years in patients with a high- and low-energy accident, respectively. The classification of the fractures according to AO/OTA and Luo is presented in Table 1. In about half of the patients, either a single or a combined surgical and/or arthroscopically guided approach was used, while a solely arthroscopically guided treatment of the fracture was possible in only 2 patients. Regardless of the surgical approach, ligament refixation was performed as appropriate. During the post-operative period, complications (compartment syndrome (n = 5), prolonged healing (n = 5), bleeding (n = 4), superficial infections (n = 3), and thrombosis (n = 1)) were observed in 11 patients and in 8 of those TPF was due to a high-energy accident. Regardless of this, all complications were successfully treated in all of them. 8 and 3 patients experiencing high-and low -energy accidents, respectively.

Five patients (3 males) aged 63, 77, 65, 86, and 75 years of age and presenting for the study examinations 2–6 years after fracture used crutches (n = 2) or wheeled walkers (n = 3). Two patients out of this 5 experienced a low-energy fracture.

All patients answered the questions referring to the subcategories “symptoms”, “pain”, “activities of daily live”, and “quality of life”. Data on sports was not provided by 3 patients (1 male) aged 61, 63 and 86 years and being examined 4 to 6 years after fracture. All of them experienced a high-energy trauma and two of them used walking aids. Results of the KOOS are summarized in Fig. 1. While the majority of our patients was fairly satisfied with the outcome in terms of “symptoms”, “pain” and “activities”, this was not the case in the dimensions “sport” and “quality of live”. Scoring of the outcome was neither related to the time of follow-up nor to the type of injury, i.e., a high- or low-energy trauma.

Distribution of KOOS results for the subcategories symptoms (A), pain (B), activity (C), sport (D), and quality of life (E). The frequency of scores per quartile is presented with “100” representing the best and “0” representing a worst outcome, respectively. Open bars: data from patients with a low-energy injury (n = 16); filled bars: data from patients with a high-energy injury (A–C and E: n = 42; D: n = 39)

The findings from the clinical examination of the knee are summarized in Table 2. The TUG revealed severely (48.7 s) and moderately (23.0 s) impaired mobility in two patients (two males, 58 and 62 years of age at time of TPF, five and three years after three-column TPF; AO/OTA C3.1 and C1.3) and both experienced a high-energy accident. Mobility was mildly impaired (11–19 s) and without any impairments (≤ 10 s) in 29 and 27 patients, respectively. Categorization of the patients according to preserved (TUG ≤ 10 s; n = 27) and impaired (TUG > 10 s; n = 31) mobility revealed C-type fractures in 6 and 13 patients, respectively. Considering the classification of Luo, we noted 4 and 9 three-column fractures in both groups. Results of the TUG were neither related to the type of fracture, the cause of the fracture, nor the time to follow-up. However, we noted a fairly strong association between the TUG and the patient reported outcome (Fig. 2, Supplemental Table 1).

Rating of the outcome in the perception of the patient (KOOS) regarding the subcategories symptoms (A), pain (B), activity (C), sport (D), and quality of life (E), and mobility in terms of the TUG. Data from patients depending on walking aids are excluded. The vertical line indicates the upper limit for diagnosis of a preserved mobility and the horizontal line represent a score of 50. Open circle: data from patients with a low-energy injury (n = 14), filled circle: data from patients with a high-energy injury (n = 55)

While all patients were capable of level walking in-house, three patients out of five patients using crutches or wheeled walkers were unable to climb stairs and refused outdoor walking with the loadsol®-system. For each participant and condition, we averaged the mean contact time and mean ground reaction force per leg from 90 ± 14, 26 ± 5, and 46 ± 5 steps, respectively.

Although limping was hardly visible even in patients using walking aids, discrepancies between the median step averaged ground reaction forces and contact times per leg were noted. In particular, the step averaged contact time during stair climbing as well as the averaged ground reaction forces recorded for the previously fractured leg were significantly lower than for the unaffected one under all conditions (Fig. 3). Next, we considered the FOIB as an individual measure of the walking abilities and evaluated the putative relation to both, the patient’s perception of outcome and the TUG. While the FOIB recorded during indoor level walking was not related to the KOOS, a moderate but significant inverse correlation with either dimension of the KOOS (Spearman rank correlation coefficients of − 0.40 (symptoms, pain, activities), − 0.39 (sport), and − 0.46 (quality of life); each p ≤ 0.005) and the FOIB during stair climbing was detected. Except for the category “symptoms”, this holds true for the FOIB recorded during outdoor level walking, as well (Spearman rank correlation coefficients of − 0.38 (pain, quality of life; each p < 0.005), − 0.33 (activities; p < 0.05), and − 0.29 (sport; p < 0.05)). Leaving out the data from patients depending on walking aids and thus looking at patients with preserved or mildly impaired mobility only, revealed a good correlation between TUG and the FOIB during outdoor level walking, while only moderate correlations of the TUG with the FOIB recorded either during in-house level walking or during stair climbing were noted (supplemental Table 1, Fig. 4).

The mean averaged contact time per step (A) and the mean averaged ground reaction forces (B) for the previously fractured (open symbols) and unaffected leg (filled symbols) during in-house level walking, stair climbing, and outdoor level walking. Open circles and triangles represent data obtained from the leg experiencing a low- and high-energy trauma, respectively. Filled symbols refer to data from the unaffected leg. Median averaged contact time and ground reaction forces for the affected and unaffected legs as well as significant differences are indicated (*p < 0.05; **p < 0.005)

Scatter plot for visualization of the FOIB during indoor level walking (A), stair climbing (B), and outdoor level walking (C) relative to the results of the TUG. Data from patients depending on walking aids are excluded. The vertical line indicates the upper limit for diagnosis of a preserved mobility and the horizontal line represent a FOIB of 0.05. Open circle: data from patients with a low-energy injury (n = 14), filled circle: data from patients with a high-energy injury (n = 55)

The FOIB was neither related to the type of fracture nor to the time to follow-up. However, the FOIB during outdoor level walking tended to be higher in patients with a low-energy injury compared to those with a high-energy injury (0.06 [0.01–0.38] vs 0.04 [0.00–0.30]; p = 0.05).