In this article we present the surgical technique of our anterior minimally invasive approach to the hip joint. This is aligned along an interneural plane and makes the approach truly minimally invasive. This technique is performed in a lateral decubitus position on a normal operating table; there is not a need for a specific orthopaedic or fracture table. As leg traction is not necessary, this enables the approach to be used routinely. Most of the instruments used for this procedure are standard instruments, only the acetabular reamers and positioners are angulated and specifically designed. The angled instruments (MI -minimally invasive) are especially useful when performing hip replacement in obese patients.An excellent view of both the acetabulum and the proximal femur can be obtained through an incision of only 6-8 cm, using this MI approach. The approach follows the interval between the tensor fascia lata muscle and the sartorius muscle using a section of the anterior iliofemoral approach described by Smith-Peterson. No tendon or muscle is cut or detached. The joint capsule is split and preserved in toto. The hip joint is not dislocated and we perform the osteotomy of the femoral neck in-situ.To date we have performed over 500 MicroHip ™ operations. We have not observed any nerve lesions or fractures of the trochanter. Our experience to date shows that the method we have developed allows us to operate reliably on virtually any patient. Preliminary results also show that important factors like length of stay, pain, blood loss and return to work can be reduced significantly. The MicroHip ™ technique is being used by more and more different clinics all over the world and can be applied with success after suitable training.

Acute and chronic osteomyelitis can be difficult to treat by conventional means. Current methods of treatment involve the use of systemic antibiotics, the local implantation of non-degradable drug carriers, and surgical débridement. Each method has specific drawbacks. We report on the use of a new controlled release system utilizing gentamicin and bioerodible, biocompatible polymers (polyanhydrides) designed for drug delivery applications for the treatment of clinical osteomyelitis. We compared this system's ability to reduce bacterial levels in infected bone with that of conventional non-degradable delivery systems based on polymethylmethacrylate (PMMA) and gentamicin. Polyanhydride copolymers of bis-carboxyphenoxypropane and sebacic acid P loaded with gentamicin sulfate and PMMA/gentamicin matrices were implanted in the long bones of Sprague-Dawley rats infected with a strain of Staphylococcus aureus. After 3 weeks of implantation, the polymeric delivery devices were removed and quantitative cultures were used to determine bacterial levels in bone. The polyanhydride/gentamicin matrices demonstrated significant degradation over the 3 week implantation period. Levels of bacteria, measured in colony forming units, were significantly lower in bone implanted with the polyanhydride/gentamicin release system than in long bones of control animals without an implant (p < 0.01), of animals with a polyanhydride polymer implant alone (p < 0.01), and of animals with a PMMA/gentamicin implant (p = 0.03). Bioerodible polyanhydrides show promise as a new treatment modality for infections in bone.

A series of 216 biomechanical tests with 36 calf spines were performed to evaluate the rigidity of three newly developed prototypes of transpedicular fixation systems (Spine Fix, AO/ASIF prototype 1, AO/ASIF prototype 2) as compared to the already established Cotrel-Dubousset (CD) system. The Spine Fix system follows the same principle of spinal fixation as the CD system, while the two prototypes of the AO/ASIF group introduce a new concept of spinal reduction and fixation technique, using a three-dimensional adjustable fastening system of transpedicular screws to a longitudinal rod. This allows for correction and fixation of the instrumented vertebra segments in any position. During the tests the main point of interest was whether the newly gained degrees of freedom are associated with a loss of stiffness in the construct. Furthermore, the study evaluated whether transpedicular systems should be optimized from the technological point of view, or whether the stability and rigidity of these systems is determined mainly by the quality of pedicular anchorage. Load displacement was measured using a calf spine model with a precisely defined three-column lesion. Each implant was loaded up to 15 Nm in flexion, extension, lateral bending, and axial rotation. In all tests, the construct behaved in a highly linear fashion (r2> 0.94). By continously measuring the forces and moments at the cranial end of the spine specimen high accuracy of the tests was achieved (standard deviation: x-axis, 1.74%; y-axis, 1.36%; z-axis, 1.21%). In general, the stifness was found to be highest in lateral bending, followed by flexion/extension and axial rotation. Spine Fix was the stiffest implant in flexion/extension, AO/ASIF prototype 1 in lateral bending, and AO/ ASIF prototype 2 in rotation. In comparison to the CD system (stiffness of CD = 100%), differences in stiffness ranged from 77.3% prototype 1 to 140.8% Spine Fix in flexion, from 78.2% prototype 2b to 134.7% Spine Fix in extension, from 108.1% prototype 2b to 213.5% prototype 1 in lateral bending, and from 80.3% prototype 1 to 110.6% prototype 2 in axial rotation. The Spine Fix and prototype 2 systems showed equal or higher stiffness coefficients compared to the CD system. Prototype 1 is significantly more flexible, except in lateral bending, than the CD. From the technical point of view, the two AO/ ASIF prototypes allow the correction and fixation of an instrumented vertebra in any position. Prototype 2, despite the additional joint between transpedicular screws and longitudinal rods, shows stiffness comparable to that of the CD system.

Internal fixation of comminuted unstable fractures of the severely osteoporotic proximal femur is sometimes supplemented with polymethyl-methacrylate (PMMA). We here report an in vitro biomechanical evaluation of a biodegradable particulate composite that might be used for similar purposes. The composite includes a matrix phase consisting of a hydrolyzable prepolymer [polypropylene fumarate (PPF)] cross-linked with methacrylate monomer, and a particulate phase consisting of tricalcium phosphate and calcium carbonate. We implanted dynamic hip screws in 22 cadaveric proximal femora and measured the yield load for an oblique force applied to the femoral head. The hip screws were then reinforced with either PMMA or the PPF composite and tested again. On the basis of analysis of variance, the average increases in yield load for PMMA and PPF reinforcement of 1,750 and 1,130 N were statistically significant (p less than 0.00005), suggesting that both materials enhance congruence between implant and bone and thereby increase the projected load-bearing area of the implant. The increase in yield force with PMMA was slightly higher than the increase with PPF (p less than 0.05), but both values after reinforcement were close (3,790 +/- 561 N for PMMA vs. 3,240 +/- 669 N for PPF). If we can demonstrate that appropriate rates of degradation, bony ingrowth, and static and fatigue properties can be achieved in vivo with this system, our data suggest that this PPF composite may have potential as an adjunct to the internal fixation of unstable fractures of the osteoporotic hip.