Being commonly missed in the clinical practice, Lisfranc injuries can lead to arthritis and long-term complications. There are controversial opinions about the contribution of the main stabilizers of the joint. Moreover, the role of the ligament that connects the medial cuneiform (MC) and the third metatarsal (MT3) is not well investigated. The aim of this study was to investigate the influence of different Lisfranc ligament injuries on CT findings under two specified loads.

Sixteen fresh-frozen human cadaveric lower limbs were embedded in PMMA at mid-shaft of the tibia and placed in a weight-bearing radiolucent frame for CT scanning. All intact specimens were initially scanned under 7.5 kg and 70 kg loads in neutral foot position. A dorsal approach was then used for sequential ligaments cutting: first – the dorsal and the (Lisfranc) interosseous ligaments; second – the plantar ligament between the MC and MT3; third – the plantar Lisfranc ligament between the MC and the MT2. All feet were rescanned after each cutting step under the two loads.

The average distances between MT1 and MT2 in the intact feet under 7.5 kg and 70 kg loads were 0.77 mm and 0.82 mm, whereas between MC and MT2 they were 0.61 mm and 0.80 mm, without any signs of misalignment or dorsal displacement of MT2. A slight increase in the distances MT1-MT2 (0.89 mm; 0.97 mm) and MC-MT2 (0.97 mm; 1.13 mm) was observed after the first disruption of the dorsal and the interosseous ligaments under 7.5 kg and 70 kg loads. A further increase in MT1-MT2 and MC-MT2 distances was registered after the second disruption of the ligament between MC and MT3. The largest distances MT1-MT2 (1.5 mm; 1.95 mm) and MC-MT2 (1.74 mm; 2.35 mm) were measured after the final plantar Lisfranc ligament cut under the two loads. In contrast to the previous two the previous two cuts, misalignment and dorsal displacement of 1.25 mm were seen at this final disrupted stage.

The minimal pathological increase in the distances MT1-MT2 and MC-MT2 is an important indicator for ligamentous Lisfranc injury. Dorsal displacement and misalignment of the second metatarsal in the CT scans identify severe ligamentous Lisfranc injury. The plantar Lisfranc ligament between the medial cuneiform and the second metatarsal seems to be the strongest stabilizer of the Lisfranc joint. Partial lesion of the Lisfranc ligaments requires high clinical suspicion as it can be easily missed.

Displaced intraarticular calcaneal fractures are debilitating injuries with significant socioeconomic and psychological effects primarily affecting patients in active age between 30 and 50 years. Recently, minimally and less invasive screw fixation techniques have become popular as alternative to locked plating. The aim of this study was to analyze biomechanically in direct comparison the primary stability of 3 different cannulated screw configurations for fixation of Sanders type II-B intraarticular calcaneal fractures.

Fifteen fresh-frozen human cadaveric lower limbs were amputated mid-calf and through the Chopart joint. Following, soft tissues at the lateral foot side were removed, whereas the medial side and Achilles tendon were preserved. Reproducible Sanders type II-B intraarticular fracture patterns were created by means of osteotomies. The proximal tibia end and the anterior-inferior aspect of the calcaneus were then embedded in polymethylmethacrylate. Based on bone mineral density measurements, the specimens were randomized to 3 groups for fixation with 3 different screw configurations using two 6.5 mm and two 4.5 mm cannulated screws. In Group 1, two parallel longitudinal screws entered the tuber calcanei above the Achilles tendon insertion and proceeded to the anterior process, and two transverse screws fixed the posterior facet perpendicular to the fracture line. In Group 2, two parallel screws entered the tuber calcanei below the Achilles tendon insertion, aiming at the anterior process, and two transverse screws fixed the posterior facet. In Group 3, two screws were inserted along the bone axis, entering the tuber calcanei above the Achilles tendon insertion and proceeding to the central-inferior part of the anterior process. In addition, one transverse screw was inserted from lateral to medial for fixation of the posterior facet and one oblique screw – inserted from the posterior-plantar part of the tuber calcanei – supported the posterolateral part of the posterior facet. All specimens were tested in simulated midstance position under progressively increasing cyclic loading at 2 Hz. Starting from 200N, the peak load of each cycle increased at a rate of 0.1 N/cycle. Interfragmentary movements were captured by means of optical motion tracking and triggered mediolateral x-rays.

Plantar movement, defined as displacement between the anterior process and the tuber calcanei at the most inferior side was biggest in Group 2 and increased significantly over test cycles in all groups (P = 0.001). Cycles to 2 mm plantar movement were significantly higher in both Group 1 (15847 ± 5250) and Group 3 (13323 ± 4363) compared to Group 2 (4875 ± 3480), P = 0.048. Medial gapping after 2500 cycles was significantly bigger in Group 2 versus Group 3, P = 0.024. No intraarticular displacement was observed in any group during testing.

From biomechanical perspective, screw configuration implementing one oblique screw seems to provide sufficient hindfoot stability in Sanders Type II-B intraarticular calcaneal fractures under dynamic loading. Posterior facet support by means of buttress or superiorly inserted longitudinal screws results in less plantar movement between the tuber calcanei and anterior fragments. On the other hand, inferiorly inserted longitudinal screws seem to be associated with bigger interfragmentary movements.