Clemens Hengg

The relevance of neutral arm positioning for true ap-view X-ray to provide true projection of the humeral head shaft angle

IntroductionTextbooks commonly recommend using the true anterior–posterior (ap)-view with the patient’s arm in a sling and therefore in internal rotation (IR) for radiologic diagnostic assessment of the proximal humerus after trauma. However, IR or external rotation (ER) may affect the projection of the head shaft angle (HSA) and therefore bias the diagnostic conclusion significantly. We hypothesized that neutral rotation (NR) of the arm is mandatory for true ap-view to provide true projection of the HSA.Materials and methodsA simplified geometrical model of the proximal humerus was used to examine the influence of different arm positions and angulations of the central ray in relation to the projection of the HSA.ResultsBoth ER and IR misleadingly suggested an increased valgus angle. Simulating the true ap-view with the central ray in cranio-caudal direction, IR changed the projection of the HSA substantially.ConclusionIn conclusion, standard fixation of the patient’s arm in a shoulder sling in IR for true ap-view may result in an oblique projection, potentially leading to incorrect surgical implications. To prevent misdiagnosed valgus or varus angulation, NR of the arm should be obeyed when performing true ap-view X-ray. We, therefore, highly recommend to overcome the traditionally arm position, ensuring the true amount of dislocation to assure correct surgical implications and comparable follow-up examinations.

Mechanical torque measurement for in vivo quantification of bone strength in the proximal femur.

INTRODUCTION Bone strength determines fracture risk and fixation strength of osteosynthesis implants. In vivo, bone strength is currently measured indirectly by quantifying bone mineral density (BMD) which is however only one determinant of the bones biomechanical competence besides the bones macro- and micro-architecture and tissue related parameters. We have developed a measurement principle (DensiProbe™ Hip) for direct, mechanical quantification of bone strength within the proximal femur upon hip fracture fixation. Previous cadaver tests indicated a close correlation between DensiProbe™ Hip measurements, 3D micro-CT analysis and biomechanical indicators of bone strength. The goal of this study was to correlate DensiProbe™ Hip measurements with areal bone mineral density (BMD). METHODS Forty-three hip fracture patients were included in this study. Intraoperatively, DensiProbe™ Hip was inserted to the subsequent hip screw tip position within the femoral head. Peak torque to breakaway of local cancellous bone was registered. Thirty-seven patients underwent areal BMD measurements of the contralateral proximal femur. Failure of fixation was assessed radio graphically 6 and 12 weeks postoperatively. RESULTS Peak torque and femoral neck BMD showed significant correlations (R=0.60, P=0.0001). In regression analysis, areal BMD explained 46% of femoral neck BMD variance in a quadratic relationship. Throughout the 12-week follow-up period, no failure of fixation was observed. CONCLUSIONS DensiProbe™ Hip may capture variations of bone strength beyond areal BMD which are currently difficult to measure in vivo. A multicenter study will clarify if peak torque predicts fixation failure.

Trabecular bone strength is not an independent predictive factor for dynamic hip screw migration—A prospective multicenter cohort study

This study assessed whether mechanically measured trabecular bone strength is an independent predictor of dynamic hip screw (DHS) stability, i.e., DHS migration (DHSM) after the fixation of proximal femoral fractures. One‐hundred and seven patients older than 50 years with proximal femoral fractures were included. During fracture fixation, a mechanical probe (DensiProbe™ Hip) was inserted at the site where the DHS tip would ultimately be positioned. Peak torque to breakaway the trabecular bone was measured. Fracture reduction, primary implant position and postoperative DHSM were assessed by radiographs taken postoperatively, at 6 and 12 weeks after surgery. Univariate regression analysis revealed no association between peak torque and DHSM (R2 = 0.025, p = 0.135). DHSM correlated with the primary DHS position, i.e., the distance between the DHS and (i) the central femoral neck axis (CNFAD, R2 = 0.230; p < 0.0001) and (ii) the apex of the femoral head (R2 = 0.110; p = 0.001). DHSM did not correlate with areal BMD of the contralateral proximal femur. Multivariable regression modeling revealed the CFNAD as predictive factor for screw migration. The primary implant position measured by the CFNAD, rather than DensiProbe™ Hip measured bone strength, is an independent predictor of DHSM.

Biomechanical evaluation of cable and suture cerclages for tuberosity reattachment in a 4-part proximal humeral fracture model treated with reverse shoulder arthroplasty

BACKGROUND Sufficient tuberosity fixation in proximal humeral fractures treated with shoulder arthroplasty is essential to gain a good clinical outcome. This biomechanical study evaluated the strength of the reattached tuberosities in reverse total shoulder arthroplasty fixed with cables or with sutures in a cerclage-like technique. Considering the mechanical advantages of flexible titanium alloy cables compared with conventional sutures for cerclage-like fixations, we hypothesized that titanium alloy cables would achieve higher fixation strengths of the tuberosities compared with heavy nonabsorbable sutures. METHODS A 4-part fracture was created on 8-paired proximal human humeri. The tuberosities were reduced anatomically and fixed by 2 heavy nonabsorbable sutures (suture group) or by two 1-mm titanium alloy cables (cable group) in a cerclage-like technique around the neck of the prosthesis. The humeri were placed in a custom-made test setup enabling internal and external rotation. Cyclic loading with a stepwise increasing load magnitude was applied with a material testing machine, starting with 1 Nm and increasing the load by 0.25 Nm after each 100th cycle until failure of the fixation occurred (>15° rotation of the tuberosities). Any motion of the tuberosities was measured with a 3-dimensional ultrasound motion analysis system. RESULTS Overall, the cable group reached 1414 ± 372 cycles, and the suture group reached 1257 ± 230 cycles until the fixations failed (P = .313). The suture group showed a significantly higher rotation of the lesser tuberosity relative to the humerus shaft axis after 200, 400, and 600 cycles compared with the cable group (P = .018-.043). CONCLUSIONS Tuberosities reattached with cable cerclages showed higher fixation strength and therefore less rotation compared with suture cerclages in a 4-part proximal humeral fracture model treated with reverse total shoulder arthroplasty. Whether this higher fixation strength results in higher bony ingrowth rates of the tuberosities and thus leads to a better clinical outcome needs to be investigated in further clinical studies.

A Simple Method for Measurement of Femoral Anteversion-Validation and Assessment of Reproducibility.

Objectives: To propose a simple method for measurement of femoral anteversion (AV) with a conventional fluoroscope, to evaluate the interobserver and intraobserver reliability of this method on the basis of human cadaver femurs, and to validate such method on the basis of computed tomography (CT). Methods: Fourteen human cadavers with 28 intact femurs were included in the study. Three blinded observers measured femoral AV of the specimen with a fluoroscope. The session was repeated 8 weeks later and CT of the femurs were performed. Mean AV values and the difference between single and mean AV values were calculated. Interobserver/intraobserver reliability of the proposed method was assessed. Correlation between AV values measured with fluoroscope and CT was calculated. Results: Mean AV was 18.1° when measured with fluoroscope and 19.2° when measured with CT. Mean differences between single AV values were 2.2° with fluoroscope and 2.5° with CT. The mean maximum observer variation per specimen was 8.8°. Interobserver reliability was excellent (intraclass correlation coefficient: 0.853) and intraobserver reliability was good (intraclass correlation coefficient: 0.682). A high correlation was found between AV values measured with fluoroscope and CT (rho = 0.739, P < 0.01). Conclusion: The presented technique allows reliable and simple measurement of femoral AV with a conventional fluoroscope. The mean interobserver variation is comparable to what has been reported for CT. Maximum interobserver variation was <15° in all specimens. A clinical study will be necessary to prove the value of this technique for intraoperative adjustment of femoral AV according to the intact contralateral side.

Area-based determination of bone loss using the glenoid arc angle.

To the Editor: Concerning the article by Dumont et al., “Area-Based Determination of Bone Loss Using the Glenoid Arc Angle,” published in the July 2012 issue of Arthroscopy, we appreciate the mathematical-geometrical approach to determine glenoid bone loss and hope that it becomes morepopularas itwaspublished in thishigh-level journal. Dumont et al. state that a bilateral CT scan for comparison has the inherent disadvantage of added radiation exposure for the patient. This is not correct because recording axial scans of one shoulder with spiral CT automatically causes radiation exposure to both shoulders, because the scanner has to radiograph the entire transversal section. Therefore, recording axial scans of both shoulders has no additional radiation exposure. The radiologist may reconstruct both sides out of the same data set as long as the surgeon requests primary axial scans of both shoulders. Jeske et al. confirmed that the healthy inferior glenoid has the shape of a circle, and they described a perfect side-to-side correlation of the glenoid surface area. This correlation can be applied to improve measurement of bony glenoid defects by using the diameter of the ROI of the nonaffected glenoid as a reference. According to our institutional experience, especially large glenoid defect sizes tend to be underestimated, without taking the contralateral healthy glenoid into account. The glenoid arc angle method with bilateral testing may hold the potential for higher reproducibility and practicability, but this has not been proven yet. An exact consistent measurement standard will allow recommendations on treatment of shoulder instability combined with glenoid bone loss and may be the precondition to define the critical size of glenoid bone loss.