Patterns of stress distribution at the proximal femur after implantation of a modular neck prosthesis. A biomechanical study

Locking compression plate fixation of femoral intertrochanteric fractures in patients with preexisting proximal femoral deformity: a retrospective study

Background

To investigate the clinical efficacy of locking compression plate fixation for the treatment of femoral intertrochanteric fractures in patients with preexisting proximal femoral deformity.

Methods

A retrospective analysis was conducted on 37 patients with femoral intertrochanteric fractures combined with preexisting proximal femoral deformity between January 2013 and July 2019. The patients included 24 males and 13 females aged from 23 to 69 years old, with an average age of 47.5 years. The preexisting proximal femoral deformities resulted from poliomyelitis sequela, proximal femoral fibrous dysplasia, malunion and implant failure combined with coxa vara after intramedullary nailing fixation. There were 6 cases of 31-A2.1, 6 cases of 31-A2.2, 20 cases of 31-A3.1, and 5 cases of 31-A3.2, determined based on the AO classification of intertrochanteric fractures. All fractures were managed through open reduction and locking plate fixation. The hip disability and osteoarthritis outcome score (HOOS) was used to assess hip function before injury and at the last postoperative follow-up. The short form 36 (SF-36) Health Survey Questionnaire was used to assess quality of life.

Results

Thirty-seven patients were followed up for 12 to 27 months (average, 20.7 months). All patients achieved bone healing within 5.1 months on average (range, 3 to 6 months). Postoperative complications included deep vein thrombosis in three patients, bedsores in one and delayed union in one patient. No other complications, such as surgical site infection, fat embolism, nonunion and re-fracture, were presented. There was no significant difference in the HOOS scores and the SF-36 Health Questionnaire outcomes at pre-injury and at the last postoperative follow-up (p > 0.05).

Conclusions

It is difficult to perform intramedullary fixation of femoral intertrochanteric fractures in patients with preexisting proximal femoral deformity, while locking compression plate fixation is a simple and effective method of treatment.

A biomechanical study of the effect of weight loading conditions on the mechanical environment of the hip joint endoprosthesis

BACKGROUND

Total hip arthroplasty is one of the most successful orthopedic surgical procedures aiming to eliminate pain related to several types of hip arthritis and restore mobility. Obesity has been associated with an increased risk of complications after a total hip arthroplasty such as poor wound healing, periprosthetic joint infection, instability, and aseptic loosening.

METHODS

This paper presents an in-vitro study on composite femoral models to investigate the impact of different weight loading conditions on the mechanical environment of the hip joint endoprosthesis considering normal-weight and overweight individuals from 70 to 110 kg. The micro strains on the femur during single-leg stance of gait were measured on critical stress points based on the Gruen femoral zones.

FINDINGS

The micro strains increase as the weight increases implying that the displacement in the hip joint endoprosthesis is higher for overweight subjects enhancing the risk of failure. The highest increase was measured in Gruen zone 1 by 5.60% indicating that the great trochanter is subjected to higher stress shielding with increasing the weight. Also, the statistically significant increase of the micro strain values with increasing the weight in Gruen Zones 3 (2.91%), 5 (1.56%), and 11 (1.75%) may enhance the risk for a periprosthetic fracture at the lower region of the prosthesis.

INTERPRETATION

This is the first biomechanical study which quantifies the effect of increasing weight loading conditions on the mechanical environment of the hip joint endoprosthesis considering different positions of evaluation.

The effect of the hip joint endoprosthesis length after a total hip arthroplasty: A biomechanical study

Background/purpose:

Total hip arthroplasty is a safe, cost-effective surgical intervention which restores mobility and alleviates pain from most kinds of hip arthritis. The proposed biomechanical study evaluates the effect of the stem size on the mechanical environment of the hip and its association with aseptic loosening.

Methods:

Medium left, fourth-generation, composite femoral models were used, and different prosthesis dimensions were examined. Fourteen strain gages were placed at specific positions on the femur. Load cycles were programmed to simulate single-leg stance of gait of a normal-weight subject.

Results:

Microstrains in the anterior and posterior region of the femur shaft were found to decrease with increasing the stem length, while no specific tendency was observed in the regions of the great and lesser trochanteric as well as in the medial and lateral femur.

Conclusion:

This study indicates that shorter implants are subjected to higher strains distally to the pertrochanteric area.

Custom-made femoral implants in total hip arthroplasty due to congenital disease of the hip: a review

Congenital disease of the hip (CDH) is a common reason for the development of secondary osteoarthritis at the hip joint and the need for total hip arthroplasty (THA). The distorted femoral anatomy in patients with CDH in combination with soft tissue considerations and leg length discrepancy complicate the procedure of THA and this sometimes precludes the implantation of classical industry designed femoral stems. In such cases a customised femoral implant must be used in order to optimise the fit of the stem to the femur, to improve strain distribution and to reconstruct hip biomechanics. The present study reviews the preoperative planning, the design and material selection of custom-made implants, the surgical techniques and the reported clinical results of the published literature on the use of custom-made femoral implants in patients with CDH.

Deformation pattern and load transfer of an uncemented femoral stem with modular necks. An experimental study in human cadaver femurs

BACKGROUND

Modular necks in hip arthroplasty allow variations in neck-shaft angles, neck version and neck lengths and have been introduced to improve accuracy when reconstructing the anatomy and hip joint biomechanics. Periprosthetic bone resorption may be a consequence of stress shielding in the proximal femur after implantation of a femoral stem. The purpose of this study was to investigate the deformation pattern and load transfer of an uncemented femoral stem coupled to different modular necks in human cadaver femurs.

METHODS

A cementless femoral stem was implanted in twelve human cadaver femurs and tested in a hip simulator corresponding to single leg stance and stair climbing activity with patient-specific loading. The stems were tested with four different modular necks; long, short, retro and varus. The long neck was used as reference in statistical comparisons, as it can be considered the "standard" neck. The deformation of bone during loading was measured by strain gauge rosettes at three levels of the proximal femur on the medial, lateral and anterior side.

FINDINGS

The cortical strains were overall reduced on the medial and lateral side of femur, for all implants tested, and in both loading conditions compared to the unoperated femur. Although there were statistical significant differences between the necks, the results did not show a consistent pattern considering which neck retained or lost most strain. In general the differences were small, with the highest significant difference between the necks of 3.23 percentage points.

INTERPRETATION

The small differences of strain between the modular necks tested in this study are not expected to influence bone remodeling in the proximal femur.

Adverse tissue reaction to corrosion at the neck-stem junction after modular primary total hip arthroplasty

Complications related to the neck-stem junction of modular stems used for total hip arthroplasty (THA) are generating increasing concern. A 74-year-old male had increasing pain and a cutaneous reaction around the scar 1 year after THA with a modular neck-stem. Imaging revealed osteolysis of the calcar and a pseudo-tumour adjacent to the neck-stem junction. Serum cobalt levels were elevated. Revision surgery to exchange the stem and liner and to resect the pseudo-tumour was performed. Analysis of the stem by scanning electron microscopy and by energy dispersive X-ray and white light interferometry showed fretting corrosion at the neck-stem junction contrasting with minimal changes at the head-neck junction. Thus, despite dry assembly of the neck and stem on the back table at primary THA, full neck-stem contact was not achieved, and the resulting micromotion at the interface led to fretting corrosion. This case highlights the mechanism of fretting corrosion at the neck-stem interface responsible for adverse local tissue reactions. Clinical and radiological follow-up is mandatory in patients with dual-modular stems.