The course of secondary fracture healing typically consists of four major phases including inflammation, soft and hard callus formation, and bone remodeling. Callus formation is promoted by mechanical stimulation, yet little is known about the healing tissue response to strain stimuli over shorter timeframes on hourly and daily basis. The aim of this study was to explore the hourly, daily and weekly variations in bone healing progression and to analyze the short-term response of the repair tissue to well-controlled mechanical stimulation.

A system for continuous monitoring of fracture healing was designed for implantation in sheep tibia. The experimental model was adapted from Tufekci et al. 2018 and consisted of 3 mm transverse osteotomy and 30 mm bone defect resulting in an intermediate mobile bone fragment in the tibial shaft. Whereas the distal and proximal parts of the tibia were fixed with external fixator, the mobile fragment was connected to the proximal part via a second, active fixator. A linear actuator embedded in the active fixator moved the mobile fragment axially, thus stimulating mechanically the tissue in the osteotomy gap via well-controlled displacement being independent from the sheep's functional weightbearing. A load sensor was integrated in the active fixation to measure the force acting in the osteotomy gap. During each stimulation cycle the displacement and force magnitudes were recorded to determine in vivo fracture stiffness. Following approval of the local ethics committee, experiments were conducted on four skeletally mature sheep. Starting from the first day after surgery, the daily stimulation protocols consisted of 1000 loading events equally distributed over 12 hours from 9:00 to 21:00 resulting in a single loading event every 44 seconds. No stimulation was performed overnight.

One animal had to be excluded due to inconsistencies in the load sensor data. The onset of tissue stiffening was detected around the eleventh day post-op. However, on a daily basis, the stiffness was not steadily increasing, but instead, an abrupt drop was observed in the beginning of the daily stimulations. Following this initial drop, the stiffness increased until the last stimulation cycle of the day.

The continuous measurements enabled resolving the tissue response to strain stimuli over hours and days. The presented data contributes to the understanding of the influence of patient activity on daily variations in tissue stiffness and can serve to optimize rehabilitation protocols post fractures.

In the course of uneventful secondary bone healing, a fracture gap is progressively overgrown by callus which subsequently calcifies and remodels into new bone. It is widely accepted that callus formation is promoted by mechanical stimulation of the tissue in the fracture gap. However, the optimal levels of the interfragmentary motion's amplitude, frequency and timing remain unknown. The aim of this study was to develop an active fixation system capable of installing a well-controlled mechanical environment in the fracture gap with continuous monitoring of the bone healing progression.

The experimental model was adapted from Tufekci et al. 2018 and required creation of a critical size defect and an osteotomy in a sheep tibia. They were separated by a mobile bone fragment. The distal and proximal parts of the tibia were fixed with an external fixator, whereas the mobile fragment was connected to the proximal part with an active fixator equipped with a linear actuator to move it axially for mechanical stimulation of the tissue in the fracture gap. This configuration installed well-controlled mechanical conditions in the osteotomy, dependent only on the motion of the active fixator and shielded from the influence of the sheep's functional weightbearing. A load sensor was integrated to measure the force acting in the fracture gap during mechanical stimulation. The motion of the bone fragment was controlled by means of a custom-made controller allowing to program stimulation protocols of various profiles, amplitudes and frequencies of loading events. Following in vitro testing, the system was tested in two Swiss White Alpine Sheep. It was configured to simulate immediate weightbearing for one of the animals and delayed weightbearing for the other. The applied loading protocol consisted of 1000 loading events evenly distributed over 12 hours resulting in in a single loading event every 44 seconds.

Bench testing confirmed the ability of the system to operate effectively with frequencies up to 1Hz over a range of stimulation amplitudes from 0.1 to 1.5 mm. Continuous measurements of in vivo callus stiffness revealed progressive fracture consolidation in the course of each experiment. A delayed onset of fracture healing was observed in the sheep with simulated delayed weightbearing.

The conducted preclinical experiments demonstrated its robustness and reliability. The system can be applied for further preclinical research and comprehensive in-depth investigation of fracture healing.

Aim: The purpose of this work is to report the early results from medial protrusio technique for placement of acetabular component without cement in patients who have acetabular dysplasia.

Material and Method: Thirty-two hip replacements were performed in thirty consecutive cases with dysplastic osteoarthritis between 2001 and 2003. In none of the patients an augmentation with bone or cement of the superolateral aspect of the acetabulum was made. Indication for operation was a painful hip joint that could not be alleviated by conservative treatment. According to Crowe’s criteria the dysplasia was evaluated as type I (19); type II (11); type III (3). The size and localization of the true acetabulum were evaluated using Ranawat’s triangle on a weigh-bearing preoperative X-ray. Clinical appraisal of the joint was done preoperatively, at the sixth, twelfth and thirty-six month postoperatively by the scheme of Merle dAubigne and Postel modified by Charnley. In 29 cases the surgery was performed via lateral transgluteal approach of Hardinge-Mulliken and in the rest of the cases through anterolateral approach of Watson-Jones. In all cases the medial wall was perforated with reaming and the medial periosteum was torn to visualize the illiacus muscle.

Results: One to three-year postoperatively clinical results showed significant improvement: in 28 joints 15–18 points (excellent and very good results); in 5 joints 14–16 points (good result). The medialization of the acetabular component is found to be 5.72.8 mm average values. X-ray evidences for medial migration of the acetabular component and early loosening were not found. Nerve palsy and intraoperative fracture of the femur did not occur, but one joint dislocated 24 days after the replacement despite the resection of anterior inferior iliac spine. Excessive medialization and impingement of the femur to the pelvic bone were the reasons for this complication.

Conclusion: When precisely planned the medial protrusion technique without cement fixation of the acetabu-lar component is a good alternative for arthroplasty in dysplastic hip joint. Particular attention must be paid in preserving enough thickness of the anterior and posterior acetabular walls during the reaming process. The perforation of the medial wall must not exceed 25–30% from the surface, because of plain risk of protrusion of the component beyond the teardrop figure of Kohler.