Introduction: Standard treatment for distal tibia fractures is the fixation with locking compression plates. Locking plate fixation has revolutionized fracture treatment in the last decade and may be ideally suited for a bridging plate osteosynthesis. This technique allows some controlled axial fracture motion, what essential for secondary bone healing is. A disadvantage of the locking plate technique seems to be an unsymmetrical micro motion along the fracture gap. The micromotion at the far cortex side is much larger than at the near cortex side (near the plate). It is supposed to be that the fracture movement on the near cortex is too small.

To increase the motion at the near cortex side a new kind of screws has been developed. In this study we examined the micromotion using normal locking head screws versus the new dynamic locking head screws.

Materials and Methods: A simplified fracture model was created by connecting 2 plastic cylinders (POM C, EModul: 3.1GPa) with a standard 11-holes Locking Compression Plate (Synthes). The fracturegap (between the two cylinders) amounted 3mm. Three kinds of fracture models were constructed: The model of a transverse fracture, an oblique fracture and a spiral fracture. An axial load from 0N up to 200N was applied with a testing machine (Zwick). The motion of the fracture model was measured in three dimensions using the optical measurement system PONTOS 5M (GOM, Braunschweig, Germany). The accuracy of the optical measurement system was about 5 micrometers.

Results: A total of 72 measurements were compared. Using the new screw, axial stiffness was decreased for 16% and micromotion was up to 200 μm higher in comparison to the old screw.

Discussion: Using the new dynamic locking head screw it’s possible to increase interfragmentary motion up to 200μm on the near cortex side (plate side).

In this retrospective study postoperative subscapularis (SSC) function was measured with an electronic force measurement plate (FMP) and clinical scores and correlated with SSC-muscle cross sectional area on defined MRI-sequences.

82 patients with subscapularis tears (34 isolated SSC tears and 48 combined SSC/SSP tears) were followed up at a mean of 38 (24–72) months after tendon reconstruction with the Constant score (CS) and clinical SSC-tests (Napoleon test, Lift off test). SSC-muscle function was assessed in the belly-press- and the lift off position using a custom made electronic FMP (force in Newton). SSC muscle strength values were compared with the contra-lateral side. SSC-muscle atrophy (muscle cross sectional area in mm²) was measured on standardised sagittal MRI-planes and compared with a healthy matched control group (CG) (Mann-Whitney-U-Test).

The mean CS improved from 51p to 81p in isolated tears (group 1) and from an average 47 p to 78 p in combined tears (group 2) (each p< 0.01). Overall 85% of the patients rated their result as good or excellent. Positive and intermediate postop. Napoleon tests were still present in 30% in group 1 and in 25% in group 2. Mean postoperative SSC-muscle strength in the belly-press position averaged 64 N (contralatera sidel-CL: 86 N) in group 1 and 81 N (CL: 91 N) in group 2. Lift-off test strength averaged 36 N (CL: 69 N) in group 1 and 50 N (CL: 63 N) in group 2 (each p< 0.05). Postoperative MRI revealed a significant reduced SSC muscle cross sectional area for the operated side compared with the CG (group 1: SSC: 1974 mm²; CG 2980 mm² p< 0,05; group 2: SSC: 1829 mm²; CG 2406 mm² − SSP: 570 mm²; CG 812 mm² each p< 0,05).

Despite good clinical results after reconstruction of isolated and combined subscapularis tears a marked subscapularis strength deficit remains that is not reflected in the Constant Score, but can be detected with the new measurement device. Additionally a subscapularis muscle atrophy remains in the postoperative course that cannot be reversed by surgery.