The lateral wall thickness (LWT) in trochanteric femoral fractures is a known predictive factor for postoperative fracture stability. Currently, the AO/OTA classification uses a patient non-specific measure to assess the absolute LWT (aLWT) and distinguish stable A1.3 from unstable A2.1 fractures based on a threshold of 20.5 mm. This approach potentially results in interpatient deviations due to different bone morphologies and consequently variations in fracture stability. Therefore, the aim of this study was to explore whether a patient-specific measure for assessment of the relative LWT (rLWT) results in a more precise threshold for prediction of unstable fractures.

Part 1 of the study evaluated 146 pelvic radiographs to assess left-right symmetry with regard to caput-collum-angle (CCD) and total trochanteric thickness (TTT), and used the results to establish the rLWT measurement technique. Part 2 reevaluated 202 patients from a previous study cohort to analyze their rLWT versus aLWT for optimization purposes.

Findings in Part 1 demonstrated a bilateral symmetry of the femur regarding both CCD and TTT (p ≥ 0.827) allowing to mirror bone's morphology and geometry from the contralateral intact to the fractured femur. Outcomes in Part 2 resulted in an increased accuracy for the new determined rLWT threshold (50.5%) versus the standard 20.5 mm aLWT threshold, with sensitivity of 83.7% versus 82.7% and specificity 81.3% versus 77.8%, respectively.

The novel patient-specific rLWT measure can be based on the contralateral femur anatomy and is a more accurate predictor of a secondary lateral wall fracture in comparison to the conventional aLWT. This study established the threshold of 50.5% rLWT as a reference value for prediction of fracture stability and selection of an appropriate implant for fixation of trochanteric femoral fractures.

Proximal humeral shaft fractures are commonly treated with long straight locking plates endangering the radial nerve distally. The aim of this study was to investigate the biomechanical competence in a human cadaveric bone model of 90°-helical PHILOS plates versus conventional straight PHILOS plates in proximal third comminuted humeral shaft fractures.

Eight pairs of humeral cadaveric humeri were instrumented using either a long 90°-helical plate (group1) or a straight long PHILOS plate (group2). An unstable proximal humeral shaft fracture was simulated by means of an osteotomy maintaining a gap of 5cm. All specimens were tested under quasi-static loading in axial compression, internal and external rotation as well as bending in 4 directions. Subsequently, progressively increasing internal rotational loading until failure was applied and interfragmentary movements were monitored by means of optical motion tracking.

Flexion/extension deformation (°) in group1 was (2.00±1.77) and (0.88±1.12) in group2, p=0.003. Varus/valgus deformation (°) was (6.14±1.58) in group1 and (6.16±0.73) in group2, p=0.976. Shear (mm) and displacement (°) under torsional load were (1.40±0.63 and 8.96±0.46) in group1 and (1.12±0.61 and 9.02±0.48) in group2, p≥0.390. However, during cyclic testing shear and torsional displacements and torsion were both significantly higher in group 1, p≤0.038. Cycles to catastrophic failure were (9960±1967) in group1 and (9234±1566) in group2, p=0.24.

Although 90°-helical plating was associated with improved resistance against varus/valgus deformation, it demonstrated lower resistance to flexion/extension and internal rotation as well as higher flexion/extension, torsional and shear movements compared to straight plates. From a biomechanical perspective, 90°-helical plates performed inferior compared to straight plates and alternative helical plate designs with lower twist should be investigated in future paired cadaveric studies.

Introduction and objective: Infection is one of the greatest threats in hip surgery. It is agreed that the implant should be removed. The debate remains open if one or two stage surgery is perferable. This study evaluates the two stage septic hip revison arthroplasty and compares our results with the literature.

Materials and Methods: A retrospective clinical and radiological study was performed on patients that had a two stage septic revision hip surgery. The Harris Hip Score (HHS) and the Mayo Hip Score (MHS) were applied. The ASA-Score for evaluation of preoperative morbidity was introduced. Statistical evaluation included the t–test.

Results: 40 patients with 41 primary total hip replacements underwent septic revision. 17 patients with 18 hip prostheses (8 male, 9 female) could be evaluated. 14 patients were deceased, the rest was unable to participate due to severe health problems.12 patientswith 13 hips had a primary reimplantation, 5 patients had to be left with a Girdlestone situation. The mean follow up was 52 months (4.3 years, standard error +/−28). The average age was 68 years. The mean preoperative ASA-Score was 3.24 (+/−0,75). Staph. aureus was the most common infectious agent (35%) followed by Staph epidermidis (24%) and E. coli (12%). The mean time between removal and re-implantation was 158 days. The most frequent primary preoperative indication for hip arthroplasty was osteoarthritis (62%) followed by trauma (24%) and avascular necorsis of the femoral head (14%). In 42%, the onset of ionfection was early (under 12 months after implantation), 58%% of the patients had a late onset infection. The MHS in the group who had a reimplantation was an average of 66/standard error +/−21). The patients with a Girdlestone situation had a HHS that was not significantly lower than the rest (58 in Girdlestone patients, 61 in patients with re-implantation).

Discussion: The study demonstrated that our results compare well to those of other studies. It supports the conclusion that two stage septic hip arthroplasty is still an excellent option in septic revision arthroplasty. The preoperative ASA-Score which is not routinely mentioned in other studies showed that many of our patients were critically ill. This may explain the long interval between removal and reimplantation, and it may also be of value to determine wether to re-implant at all costs. This study remarkably demonstrated that patients with resection arthroplasty did not have a significantly lower HHS than those with performed re-implantation. The resection arthroplasty may be considered a valuable solution in clinically very ill patients according to our results. If a second operation considering the ASA -score would be too risky it should be discussed if reimplantation must be achieved.