Development of an optical measurement system for hip implant surgery to evaluate the leg length and the hip rotation center

The correct leg length and the position of the hip rotation center are the most important parameters for hip implant surgery. Until now there exist no suitable methods to measure it objectively. This paper describes an approach for determining leg length and hip rotation center with an optical measurement system for total hip replacement procedures. A software was programmed by the authors for this application implementing also commercial software solutions. The 3D models of the leg before and after the positioning of the hip implant were created with the Microsoft Kinect camera. Two scanned models of the leg were compared with each other. The difference between the point datasets on the screen is colored visualized and shall show the surgeon if the leg has the same length with the implant as before. During a feasibility study 30 leg models in different positions were compared to evaluate the accuracy, performance and usability of the software and the Kinect camera itself. The accuracy study shows that 96.4% of the 3D-model data points are within a range of 0-10mm. It can be recognized that the application of the Microsoft Kinect camera could be a suit-able approach for determining leg length and hip rotation center in a cost-efficient and patient-friendly way

Load and failure behavior of human muscle samples in the context of proximal femur replacement

Background: To ensure adequate function after orthopedic tumor reconstruction, it is important to reattach the remaining soft tissue to the implant. This study aimed at obtaining mechanical properties of textile muscle-implant and muscle-bone connections in a preliminary test. Methods: Two groups of soft-tissue attachment were mechanically tested and compared: Native bone-muscle samples obtained from human femora and muscles attached to a prosthetic implant by means of Trevira (R) attachment tubes. Additionally, muscle samples were tested with muscle fibers aligned parallel and perpendicular to the tension load. A uniaxial load was exerted upon all samples. Results: Failure loads of 26.7 +/- 8.8 N were observed for the native bone-muscle group and of 18.1 +/- 9.9 N for the Trevira (R) group. Elongations of 94.8 +/- 36.2 % were observed for the native bone-muscle group and 79.3 +/- 51.8 % for the Trevira (R) group. The location of failure was mainly observed in the central area of the muscle fibers. Muscle fibers with parallel fiber orientation (47.6 +/- 11.5 N) yielded higher tensile strength than those with perpendicular fiber orientation (14.8 +/- 4.1 N). Conclusions: Our experiments showed that higher forces were transmitted in the origin and insertion areas than in areas of flat soft tissue reconstruction using attachment tubes. The data indicate that the tested material allows reattaching muscles, but without reinforcing the insertion site. Therefore, attachment tubes with region-dependent and potentially anisotropic material behavior might be advantageous to optimize muscle-bone load transmission after surgery, which may allow lower complication rates and shorter physical recovery

Innervation of the hip joint capsular complex: A systematic review of histological and immunohistochemical studies and their clinical implications for contemporary treatment strategies in total hip arthroplasty.

The hip joint capsule contributes to the stability of the hip joint and lower extremity, yet this structure is incised and often removed during total hip arthroplasty (THA). Increasing incidence of osteoarthritis is accompanied by a dramatic rise in THAs over the last few decades. Consequently, to improve this treatment, THA with capsular repair has evolved. This partial restoration of physiological hip stability has resulted in a substantial reduction in post-operative dislocation rates compared to conventional THA without capsular repair. A further reason for the success of this procedure is thought to be the preservation of the innervation of the capsule. A systematic review of studies investigating the innervation of the hip joint capsular complex and pseudocapsule with histological techniques was performed, as this is not well established. The literature was sought from databases Amed, Embase and Medline via OVID, PubMed, ScienceDirect, Scopus and Web of Science; excluding articles without a histological component and those involving animals. A total of 21 articles on the topic were identified. The literature indicates two primary outcomes and potential clinical implications of the innervation of the capsule. Firstly, a role in the mechanics of the hip joint, as mechanoreceptors may be present in the capsule. However, the nomenclature used to describe the distribution of the innervation is inconsistent. Furthermore, the current literature is unable to reliably confirm the proprioceptive role of the capsule, as no immunohistochemical study to date has reported type I-III mechanoreceptors in the capsule. Secondly, the capsule may play a role in pain perception, as the density of innervation appears to be altered in painful individuals. Also, increasing age may indicate requirements for different strategies to surgically manage the hip capsule. However, this requires further study, as well as the role of innervation according to sex, specific pathology and other morphometric variables. Increased understanding may highlight the requirement for capsular repair following THA, how this technique may be developed and the contribution of the capsule to joint function and stability

Verification of a novel measuring method for determining pre- and postoperative leg length in the context of total hip arthroplasty: A technical feasibility study

Following total hip arthroplasty (THA), leg length can easily be modified, for example by different-sized endoprosthetic components. Currently, precise reconstruction depends mainly on the assessment of the surgeon. The aim of this study was to determine the accuracy of a new optical measuring system (OMS) using a novel measuring method capable of determining changes in leg length. Measurements with different investigators on an artificial leg and under clinical conditions were carried out. Measurements under clinical conditions were accomplished with a human body donor before and following prosthetic hip implantation. Furthermore, computed tomography (CT) was used to compare the function and the precision of the OMS relating to established measuring methods. The following results were achieved. The overall mean result of preoperative leg length determination by the OMS was 775.3 ± 5.8 mm (CT: 786.4 mm). The overall mean result of postoperative leg length determination by the OMS was 776.9 ± 10.8 mm (CT: 795.0mm). Measurements carried out showed that the novel measuring method works in principle. However, the viable prototype based on it has a lower accuracy compared to CT-based reference measurements, indicating the necessity of integrating more precise hardware

Modular systems and lightweight construction concepts - new possibilities for the defect-specific treatment of hip joint diseases

In tumor endoprosthetics, implants are applied to reconstruct the proximal femur. The main problems of these implants are often the high weight and the biomechanically not optimal attachment of soft tissue. The aim of this work is the development of a long-term stable biomechanically correct implant of a proximal femoral replacement. Based on lightweight construction concepts from vehicle construction, a topology optimization was performed with an existing modular implant basic body. The additive manufacturing process laser beam melting was applied to produce the implant with the material TiAl6V4. The individual modules were coupled by a specially designed polygon interface. To disconnect the interface, a joining instrument was used which applies a force at two defined points and thus elastically deforms the internal contour of the interface. This allows the reversible joining of the modular components. In order to fix the muscles anatomically correctly, textile attachment points made of multifilament polyester were produced by embroidery. A functional model of a modular implant was produced. On the basis of a topology optimization, the new implant has a mass reduction of 400 g compared to a proximal femoral set, which was assembled from the MML system. The greatest savings potential was found in the trochanter module (weight reduction by 55%). The load-bearing structures consisted of TiAl6V4, whereas the shell of the neck module was made of polyethylene. The reversible coupling was implemented by a polygonal interface. The force closure took place by switching off the external force effect and thus the deformation of the round bore hole into an elliptical geometry, which resulted in a "jamming" of the spigot. According to ISO 7206 the fatigue strength of the implant was determined. The test implantation at a body donor showed that the implant can be placed under realistic conditions