CT-based improved navigation system performance on the accuracy of implant placement in THA

ct-navigation-hip-cup-position

Effect of improved navigation performance on the accuracy of implant placement in total hip arthroplasty with a CT-based navigation system, Nakahara, I., Kyo, T., Kuroda, Y. et al. J Artif Organs (2018).

Abstract

A computed tomography (CT)-based navigation system is one of the support tools to place implant with appropriate alignment and position in total hip arthroplasty (THA). To determine whether the higher performance of the navigation would further improve the accuracy of implant placement in the clinical setting, we retrospectively compared the navigation accuracy of two different versions of a navigation system. The newer version of the navigation system had an upgraded optical sensor with superior positional accuracy. Navigation accuracy, defined as differences between postoperative measurements on CT images and intraoperative records on the navigation system, of 49 THAs performed with the newer version of the navigation system was compared with that of 49 THAs performed with the older version. With the newer version, the mean absolute accuracy (95% limits of agreement) of implant alignment was 1.2° (± 3.3°) for cup inclination, 1.0° (± 2.4°) for cup anteversion, 2.0° (± 4.9°) for stem anteversion, and 1.1° (± 2.4°) for stem valgus angle. The accuracy of the implant position was 1.5 mm (± 3.1 mm), 1.3 mm (± 3.0 mm), and 1.5 mm (± 3.1 mm) for cup x-, y-, and z-axes, respectively, 1.6 mm (± 3.2 mm), 1.4 mm (± 2.9 mm), and 1.5 mm (± 2.7 mm) for stem x-, y-, and z-axes, respectively, and 2.4 mm (± 4.5 mm) for leg length discrepancy. The values for the newer version were significantly more accurate with less variation compared to those of the older version. With upgraded navigation performance, more accurate implant placement was demonstrated in the clinical setting.

Extensile medial parapatellar approach to the distal femur and knee

The Extensile Medial Parapatellar Approach to the Distal Femur and Knee: Anatomic Landmarks and Surgical Technique, Stevens, Jarrad; Clement, Nicholas, D.; Patton, James, T. Techniques in Orthopaedics (2018) published ahead of print.

Abstract:

This paper describes an extensile surgical approach to the distal femur, which incorporates the medial parapatellar arthrotomy. This extensile exposure serves as an anterior utility approach to the knee, allowing the surgeon access to all aspects of the anterior knee and near circumferential access to the distal femur. Reported indications for access to this region include: tumor resection, difficult primary arthroplasty and revision arthroplasty of the knee, and intra-articular and extra-articular fractures of the distal femur. Despite adequate working knowledge of the standard medial parapatellar approach to the knee, the extensile approach is seldom required and, as a result, orthopedic trainees and practising orthopedic surgeons may not be familiar with the musculotendonous junctions that occur in the quadriceps tendon. This report describes a novel surgical approach and the relevant anatomy through a series of detailed clinical and fresh cadaveric dissections. A previously undescribed anatomic landmark is demonstrated through photographs and cadaveric variation studies, which may help guide the surgeon in defining crucial planes.

fat-stripe-junction-vastus-medialis
The fat stripe (arrow) identifying the non-adherent junction vastus medialis and rectus femoris. FS indicates fat stripe; M, medial; P, proximal.

Finite element method evaluates strain of spine metastasis

Chapter Effects Breast and Prostate Cancer Metastases on Lumbar Spine Biomechanics: Rapid In Silico Evaluation, Lorkowski J., Grzegorowska O., Kozień M., Kotela I.In: Advances in Experimental Medicine and Biology (2018). Springer, New York, NY.

Abstract:

Metastases to distant organs are a frequent occurrence in cancer diseases. The skeletal system, especially the spine, is one such organ. The objective of this study was to apply a numerical modeling, using a finite element method (FEM), for the evaluation of deformation and stress in lumbar spine in bone metastases to the spine. We investigated 20 patients (10 women and 10 men) aged 38–81 years. In women, osteolytic lesions in lumbar spine accompanied breast cancer, in men it was prostate cancer. Geometry of FEM models were built based on CT scans of metastatic lumbar spine. We made the models for osteolytic metastases, osteosclerotic metastases, and metastases after surgery. Images were compared. We found a considerable concentration of strain, especially located in the posterior part of the vertebral body. In osteolytic lesions, the strain was located below the vertebral body with metastases. In osteosclerotic lesions, the strain was located in the anterior and posterior parts in and below the vertebral body with metastases. Surgery abolished the pathological strain. We conclude that metastases to the lumbar spine introduce a pathological strain on the lumbar body. The immobilization of the vertebral body around fractures abolished the strain.

Increased torsional stability by a novel femoral neck locking plate

Increased torsional stability by a novel femoral neck locking plate. The role of plate design and pin configuration in a synthetic bone block model, Brattgjerd et al. Clin. Biomech (2018) in press, accepted manuscript.

Abstract:

Background
In undisplaced femoral neck fractures, internal fixation remains the main treatment, with mechanical failure as a frequent complication. As torsional stable fixation promotes femoral neck fracture healing, the Hansson Pinloc® System with a plate interlocking pins, was developed from the original hook pins. Since its effect on torsional stability is undocumented the novel implant was compared with the original configurations.

Methods
Forty-two proximal femur models custom made of two blocks of polyurethane foam were tested. The medial block simulated the cancellous head, while the lateral was laminated with a glass fiber filled epoxy sheet simulating trochanteric cortical bone. Two hollow metal cylinders with a circumferential ball bearing in between mimicked the neck, with a perpendicular fracture in the middle. Fractures were fixated by two or three independent pins or by five configurations involving the interlocking plate (two pins with an optional peg in a small plate, or three pins in a small, medium or large plate). Six torsional tests were performed on each configuration to calculate torsional stiffness, torque at failure and failure energy.

Findings
The novel configurations improved parameters up to an average of 12.0 (stiffness), 19.3 (torque) and 19.9 (energy) times higher than the original two pins (P < 0.001). The plate, its size and its triangular configuration improved all parameters (P = 0.03), the plate being most effective, also preventing permanent failure (P < 0.001). Interpretation The novel plate design with its pin configuration enhanced torsional stability. To reveal clinical relevance a clinical study is planned.

Highlights:

  • The Hansson Pinloc® system increased torsional parameters with a factor of up to 20.
  • The plate per se, its size and its triangular configuration improved all parameters.
  • The plate itself was the most effective novel component of the fixation.
  • Torsional failure by twisting of the pins was prevented by the plate itself.