INTRODUCTION

Stimulation of angiogenesis via the delivery of growth factors (GFs) like vascular endothelial growth factor (VEGF) is a promising strategy for the treatment of avascular necrosis (AVN). Tyraminated poly-vinyl-alcohol hydrogels (PVA-Tyr), which have the ability to covalently incorporate GFs, were proposed as a platform for the controlled delivery of therapeutic levels VEGF to the necrotic areas[1]. Nevertheless, PVA hydrophilicity and bioinertness limits its integration with the host tissues. The aim of this study was to investigated the effectiveness of incorporating gelatin, an FDA-approved, non-immunogeneic biomaterial with biological recognition sites, as a strategy to facilitate blood vessels invasion of PVA-Tyr hydrogels and to restore the vascular supply to necrotic tissues.

The aim of this study was to compare the relative performance of total hip replacement constructs and discern if there is substantial variability in performance in currently commonly used prostheses.

All patients who underwent a primary total hip replacement (THR) registered in the NZJR between 1^st January 1999 to June 2020 were identified. Using a noninferiority analysis, the performance of hip prostheses were compared with the best performing contemporary construct. Construct failure was estimated using the 1-Kaplan Meier survival function method to estimate net failure. The difference in failure between the contemporary benchmark and other constructs was examined.

In total 135 432 THR were recorded comprising 1 035 different THR constructs. Notably 328 constructs were used just once. 48 constructs (62 251 THR) had >500 procedures at risk at 3 years post-primary of which 28 were inferior by at least 20% relative risk of which, 10 were inferior by at least 100% relative risk. 16 constructs were identified with >500 procedures at risk at 10 years with 9 inferior by at least 20%, of which one was inferior by >100% relative risk. There were fewer constructs noninferior to the best practice benchmark when we performed analysis by gender. In females at 10 years, from 5 constructs with >500 constructs at risk, 2 were inferior at the 20% margin. In males at 10 years, there were only 2 eligible constructs of which one was inferior at the 20% margin.

We discerned that there is substantial variability in construct performance and at most time points, just over half of constructs are inferior to the best performing construct by at least 20%. These results can facilitate informed decision-making when considering THR surgery.

Background

Reduced dislocation rates using lipped polyethylene (PE) liners in modular uncemented acetabular components has been shown, yet there may be increased wear because of impingement, which may lead to aseptic loosening. We used New Zealand Joint Registry (NZJR) data to compare survival rates, revision rates for dislocation and aseptic loosening between lipped and neutral liners.

When fixing a mid or distal periprosthetic femoral fracture with an existing hip replacement, creation of a stress-riser is a significant concern. Our aim was to identify the degree of overlap required to minimise the risk of future fracture between plate and stem.

Each fixation scenario was tested using 4th generation composite femoral Sawbones®. Each sawbone was implanted with a collarless polished cemented stem with polymethyl methacrylate bone cement and cement restrictor. 4.5mm broad Peri-loc™ plates were positioned at positions ½, 1 and 2 shaft diameters (SD) proximal and distal to the tip of the femoral stem. Uni-axial strain gauges (medial and lateral longitudinal gauges, anterior and posterior torsional gauges) measured microstrain at tip of the femoral stem with a standard load of 500N in axial, 3-point lateral and composite torsion/posterior loading using an Instron machine.

With axial loading fixation with 2SD proximal resulted in the least amount of strain, in both tension & compression, at the tip of the femoral stem. Fixation with 4 unicortical screws was significantly better than 2 alternating unicortical screws (mean microstrain difference 3.9 to 15.3, p<0.0001). With lateral 3-point loading fixation with 2SD proximal overlap and 2 alternating unicortical screws resulted in the least amount of strain, in both tension and compression, at the tip of the femoral stem (p<0.0001). With torsion & posterior displacement 2SD proximal fixation resulted in the least amount of rotational strain. There was no significant difference between 4 unicortical screws compared to 2 alternating unicortical screws (p>0.05 in 3 of 4 gauges).

Fixation of midshaft or distal femoral fractures with a well-fixed total hip arthroplasty should have at least 2 shaft diameters of proximal overlap with a 4.5mm broad plate. It is not clear if 4 unicortical screws or 2 alternating screws are optimal.

It has been proposed that the amount of energy transferred to the bone during a high velocity projectile injury determines the extent of bony injury. We studied the validity of this theory Fresh rear skeletally mature deer femurs were subjected to progressively increasing velocity projectile injuries within a pneumatic ballistic chamber with non-deforming steel spheres capturing the energy transferred. Analysis of fracture severity was performed including micro computer tomography analysis of micro-fractures. The effect of projectile caliber size was then analyzed.

Characteristic fractures patterns were observed with fracture lines extending radially from the impact site, often propagating longitudinally along the sample. It was found that a greater energy transfer resulted in more severe fracture for a given projectile. However, fractures of differing severity were produced by different projectiles for similar energy transfer. Neither specific energy transfer nor energy density could explain this phenomenon.

Although energy transfer plays a role in ballistic fracture, it is not the sole determinant. Other factors such as contact surface area, projectile mass and angle of impact may need to be considered.

Tibial eminence fractures were historically thought of as a condition of skeletal immaturity. Increasingly this injury has been recognized in adults.

The aim was to report on the demographics, mechanism, treatment and outcomes of this injury in adult and paediatric patients.

A retrospective review of all patients presenting to Dunedin Hospital, for management of a displaced tibial eminence fracture, between 1989 and 2009.

19 cases were identified, 10 skeletally mature and 9 skeletally immature. Alpine skiing with a forced flexion and rotation injury accounted for 7 cases, primarily adult females (5 cases). A hyper-extension and rotation injury accounted for 7 cases, primarily in skeletally immature males (4 cases), while direct trauma accounted for 5 cases, primarily males (4 cases).

Associated injuries were more commonly seen in adults and those with high energy trauma. Stiffness was the most common complication (10 cases). Tibial spine fractures are more common in adults than previously thought. Female skiers appear to be a group at particular risk. Our most common complication was stiffness. Early range of motion is essential to reduce the problem of stiffness and extension impingement. Laxity is an infrequent problem in adults and children.

Osteoporosis affects over 350,000 New Zealanders including 30% of women aged over 60 years and more than half aged over 80. Osteoporotic fractures are a significant cause of morbidity and mortality. From July 1999 to 30 June 2000, 3131 people aged over 65 sustained a fractured neck of femur. 27% died in the subsequent 12 months, equating to 17% of all cause mortality. Fractures are also a significant economic burden. In the period, July 2005 to June 2006, over $18 million was spent on hip fractures in those aged over 65 years. Bisphosphonates improve Bone Mineral Density and consequently reduce the incidence of fracture; however oral bisphosphonates are contraindicated in some patients. Zoledronate is an intravenous bisphosphonate that has recently been licensed for osteoporosis treatment.

We undertook a retrospective chart review and General Practitioner consultation of CMDHB patients who received zoledronate from June 2006 to June 2008. Assessment of clinician compliance with current safety protocols, patient outcomes and side effects were assessed. 78 patients received 101 doses of zoledronate, approximately double the preceding 2 year period (37 patients and 60 administrations). The most commonly indication was osteoporosis. 19% (19/101) administrations were organised through the geriatric clinic and 81% (82/101) were inpatients

Bone Mineral Densities within 2 years were available for 59% (48/82) of administrations. 80% (51/64) had previous osteoporotic fractures. 84% (54/64) of osteoporotic patients were utilising additional calcium and vitamin D therapy. Oral bisphosphonates were contraindicated in 94% (60/64) because of gastrointestinal upset, 3% (2/64) for headaches and 3% (2/64) for worsened BMD despite oral bisphosphonates. Following treatment 13% (8/64) of patients sustained further fractures. In inpatient administration 83% (21/82) pre-creatinine and 80% (66/82) post-creatinine measurements were appropriately assessed in comparison to 58% (11/19) and 79% (15/19) respectively for clinic patients. In inpatients administration 59% (48/82) pre-calcium and 63% (52/82) post-calcium measurements were appropriately assessed in comparison to 37% (7/19) and 68% (13/19) respectively for clinic patients. For GP follow-up of creatinine and calcium measurements, 90% had creatinine and 80% had calcium correctly assessed. Zoledronate was well tolerated with no jaw osteonecrosis in this cohort.

Zoledronate is a well tolerated treatment for osteoporosis in those patients intolerant of oral bisphosphonates. The use of zoledronate has more than doubled in the last 2 years. Stricter adherence to current guidelines is needed to prevent incipient adverse effects.

Revision arthroplasty for infected hip arthroplasty creates a challenging scenario to surgeons. Either a single stage or more traditionally a two-stage revision is performed. Most surgeons utilise an antibiotic loaded cement spacer, but the implant is often rotationally unstable predisposing to dislocation, acetabular bone loss and fracture of the spacer. Pain and discomfort on mobilisation also often occur. We would like to introduce an alternative approach to this challenging scenario with the use of a two-stage revision with an extended trochanteric osteotomy and loosely cemented hip arthroplasty as the first stage spacer.

Surgical Technique: The first stage involves removal of metal ware with all infected tissue and cement performed through an extended trochanteric osteotomy. Circlage wires reduce the osteotomy and a long stem femoral component is inserted with antibiotic infused cement limited to the calcar region. The acetabulum is similarly removed and replaced with a loosely cemented polyethylene liner. The second stage is delayed until the infection is settled and the osteotomy is healed. Removal of the metalware is performed with relative ease, without need for an osteotomy. Reinsertion of an uncemented femoral and acetabular component is then performed. However a second stage is not always required in some patients.

We report a single surgeon series comprising 10 patients from December 2003 to June 2007. The most common organism isolated was Staphylococci species. All operations were performed via a posterior approach. 9 patients were clinically assessed and the Harris hip score calculated. All patients were radiologically assessed. Osteotomies healed in all patients. Only 6 patients underwent a second stage and radiographs show good osseous integration of both components. Two patients are awaiting a second stage revision, while the other two are asymptomatic and not interested in undertaking the second stage.

No dislocations, bony erosions or reinfection was noted in our series.

We recommend this alternative approach to the conventional one or two staged revision arthroplasty. The extended trochanteric ostoetomy ensures rapid and complete removal of all foreign and infected material. The loosely cemented spacer effectively delivers local antibiotic and provides a stable, asymptomatic hip whilst awaiting the second stage, which may not be required.