Patient characteristics
Sixteen male and 7 female patients participated in the study. These 23 patients had 24 TPFs (1 male patient had bilateral simultaneous TPFs). Fourteen AO type B and 10 AO type C fractures were encountered. All patients underwent open reduction and internal fixation using the fork-shaped plate. No patient had an open fracture.
The median (minimum, lower quartile, upper quartile, maximum) age at injury was 40 years (18, 33, 46, 60 years). The follow-up period was 21 years (13, 15, 28, 33 years). The width of the tibial head was 105 % (99 %, 101 %, 109 %, 113 %) of the width of the femoral width. Postoperatively, this value improved to 102 % (94 %, 100 %, 103 %, 108 %); at follow-up, it changed to 100 % (94 %, 98 %, 102 %, 107 %). The injury produced an impression of 10.0 mm (0.0, 3.0, 12.0, 24.0 mm), which was surgically corrected to 0.0 mm (0.0, 0.0, 1.5, 3.0 mm). At follow-up, the impression was 0.0 mm (0.0, 0.0, 3.0, 14.0 mm); thus, some patients exhibited a settling of the lateral tibial condyle.
Osteoarthritis, Bone marrow edema and osteophytes
The KOOS was 418 points (127, 325, 471, 500 points), and the semiquantitative WORMS was 49 points (21, 31, 76, 96 points). Only a weak association was noted between the subjective complaints as measured by the KOOS and OA as measured by the WORMS: RS = −0.37 (95 % CI, −0.70 to −0.03). A moderate influence of age at the time of trauma on WORMS could be ascertained: RS = 0.57 (95 % CI, 0.25 to 0.88), whereas the duration of time from trauma to follow-up had no effect: RS = −0.01 (95 % CI, −0.40 to 0.38). This influence of age is illustrated in Fig. 4.
Twenty-three patients showed signs of fluid signal intensity in the bone marrow unrelated to MRI artifacts after metal removal (Fig. 5 b – arrow heads). A bone marrow edema pattern and bone marrow edema-like lesions are signs of OA and are not specific to TPF. The median WORMS subscore for bone marrow edema was 3 points (0, 2, 5, 9 points). There was no correlation with the KOOS: RS = −0.09 (95 % CI, −0.42 to 0.24).
Eight knees had no osteophytes. The WORMS subscore for osteophytes was 5 points (0, 2, 17, 33 points). It was weakly correlated with the KOOS: RS = −0.39 (95 % CI, −0.68 to −0.09).
Menisci
Twelve patients had lesions of the anterior (n = 9) and/or posterior (n = 7) root of the medial meniscus as shown by MRI. Two menisci exhibited no lesions; 9 degenerative lesions, 13 showed small ruptures (Fig. 4 b – Large arrows). Twenty-two patients had a lesion of the anterior (n = 19) and/or posterior (n = 16) root of the lateral meniscus. The external meniscus appeared normal by MRI in 2 patients, exhibited degeneration without rupture in 6, exhibited small ruptures in 12, and exhibited a rupture or subluxation in 4. The condition of the lateral meniscus at the long-term follow-up was dependent on widening of the TP at the time of the injury: RS = 0.56 (95 % CI, 0.27 to 0.85). This relationship was maintained when the analysis was restricted to patients in whom the widening of the TP was surgically corrected (i.e., widening of the TP ≤102 %): RS = 0.76 (95 % CI, 0.53–1.00) (Fig. 6). For comparison, the depth of the impression caused by the trauma exhibited no effect on the condition of the external meniscus at the time of follow-up: RS = 0.10 (95 % CI, −0.32 to 0.51). Notably, none of the patients underwent a meniscectomy at the initial operation. Furthermore, no meniscal injuries were documented in the operation reports.
Nineteen patients declared that their walking distance was not limited (24 knees). One patient was unable to walk more than a few steps, two were able to walk for up to 15 min, and two were able to walk for up to an hour. All five of these patients with restricted ambulatory ability had a lesion of the lateral meniscus: three had small tears and two had subluxations. All five patients exhibited a ≥105 % widening of the TP after the injury.
Collateral and anterior cruciate ligaments
Sixteen of 24 knees exhibited thickening of the medial collateral ligament on MRI (Fig. 4 b – Small arrows). Only six patients had a normal appearing anterior cruciate ligament (ACL) on MRI. Eight had some signs of degeneration, and the ACL was elongated in nine (Fig. 4 a). One ACL was ruptured and underwent a secondary operation for repair of subjective instability. This patient had no clinical instability in the clinical follow-up examination. The subjective feeling of instability was not associated with the ligamentous changes.