Tobias E. Nowak

Modes of periacetabular load transfer to cortical and cancellous bone after cemented versus uncemented total hip arthroplasty: a prospective study using computed tomography-assisted osteodensitometry.

Stress‐shielding and periprosthetic bone loss after total hip arthroplasty (THA) may be clinically relevant for high‐demand patients. Analysis of cortical and cancellous bone density (BD) changes in vivo after THA is of interest to basic science researchers and joint reconstruction surgeons. An insufficient periprosthetic bone stock may predispose to migration, early mechanical failure, and major problems in revision surgery. We used computed tomography (CT)‐assisted osteodensitometry in two prospectively analyzed cohorts after cemented (n = 21) versus noncemented (n = 23) cup fixation. Periacetabular BD (mgCaHa/mL) was determined in five CT scans cranial and five CT scans at the level of the cup 10 days and 26 months postoperatively. For press‐fit cups BD decreased significantly in all CT cans except in four out of the five scans of cortical bone cranial to the cup. The decrease was highest for cancellous bone ventral to the cup (−45 to −53%). After cemented cup fixation, significant cortical BD decrease was seen ventral to the cup (−11 to −20%). Cancellous BD decrased only ventral (−21 to −31%) and in two scans cranial (−11 and −12%) to the cup. The modes of load transfer between cemented and uncemented cups differ fundamentally. Cemented cups especially prevent the loss of cancellous bone of the acetabulum while also cortical BD loss was significantly lower in most CT scans surrounding the cemented cup compared to the press‐fit component. Long‐term results are required to prove whether third‐generation cementing technique protects periprosthetic BD and thereby improve implant survival.

Intramedullary nailing vs. palmar locked plating for unstable dorsally comminuted distal radius fractures: A biomechanical study

BACKGROUND The purpose of this study was to compare the stability of a 2.4mm palmar locking compression plate and a new intramedullary nail-plate-hybrid Targon DR for dorsally comminuted distal radius fractures. METHODS An extraarticular 10mm dorsally open wedge osteotomy was created in 8 pairs of fresh frozen human radii to simulate an AO-A3-fracture. The fractures were stabilized using one of the fixation methods. The specimens were loaded axially with 200 N and dorsal-excentrically with 80 N. 2000cycles of dynamic loading and axial loading-to-failure were performed. FINDINGS Axial loading revealed that intramedullary osteosynthesis (Targon DR: 369 N/mm) was significantly (p=0.017) stiffer than plate osteosynthesis (Locking compression plate: 131 N/mm). With 214 N/mm the intramedullary nail also showed higher stability during dorsal excentric loading than the Locking compression plate with 51 N/mm (p=0.012). After 2000 cycles of axial loading with 80 N the Targon DR-group was significantly stiffer than the Locking compression plate-group under both loading patterns. Neither group showed significant changes in stiffness after 2000 cycles. Under dorsal excentric loading the Targon DR-group was still significantly stiffer with 212 N/mm than the Locking compression plate-group with 45 N/mm (p=0.012). The load to failure tests demonstrated higher stability of intramedullary nailing (625 N) when compared to plate osteosynthesis (403 N) (p<0.025). INTERPRETATION The study shows that intramedullary fixation of a distal AO-A3 radial fracture is biomechanically more stable than volar fixed-angle plating under axial and dorsal-excentric loading in an experimental setup.

Screw fixation of radial head fractures: Compression screw versus lag screw—A biomechanical comparison

INTRODUCTION Secondary loss of reduction and pseudarthrosis due to unstable fixation methods remain challenging problems of surgical stabilisation of radial head fractures. The purpose of our study was to determine whether the 3.0mm Headless Compression Screw (HCS) provides superior stability to the standard 2.0 mm cortical screw (COS). MATERIALS AND METHODS Eight pairs of fresh frozen human cadaveric proximal radii were used for this paired comparison. A standardised Mason II-Fracture was created with a fragment size of 1/3 of the radial heads articular surface that was then stabilised either with two 3.0 mm HCS (Synthes) or two 2.0 mm COS (Synthes) according to a randomisation protocol. The specimens were then loaded axially and transversely with 100 N each for 4 cycles. Cyclic loading with 1000 cycles as well as failure load tests were performed. The Wilcoxon test was used to assess statistically significant differences between the two groups. RESULTS No statistical differences could be detected between the two fixation methods. Under axial loads the COS showed a displacement of 0.32 mm vs. 0.49 mm for the HCS. Under transverse loads the displacement was 0.25 mm for the COS vs. 0.58 mm for the HCS group. After 1000 cycles of axial loading there were still no significant differences. The failure load for the COS group was 291 N and 282 N for the HCS group. CONCLUSION No significant differences concerning the stability achieved by 3.0 mm HCS and the 2.0 mm COS could be detected in the experimental setup presented.

Progressive femoral cortical and cancellous bone density loss after uncemented tapered-design stem fixation

Background Aseptic implant loosening and periprosthetic bone loss are major problems after total hip arthroplasty (THA). We present an in vivo method of computed tomography (CT) assisted osteodensitometry after THA that differentiates between cortical and cancellous bone density (BD) and area around the femoral component. Method Cortical and cancellous periprosthetic femoral BD (mg CaHA/mL), area (mm2) and contact area between the prothesis and cortical bone were determined prospectively in 31 patients 10 days, 1 year, and 6 years after uncemented THA (mean age at implantation: 55 years) using CT-osteodensitometry. Results 6 years postoperatively, cancellous BD had decreased by as much as 41% and cortical BD by up to 27% at the metaphyseal portion of the femur; this decrease was progressive between the 1-year and 6-year examinations. Mild cortical hypertrophy was observed along the entire length of the diaphysis. No statistically significant changes in cortical BD were observed along the diaphysis of the stem. Interpretation Periprosthetic CT-assisted osteodensitometry has the technical ability to discriminate between cortical and cancellous bone structures with respect to strain-adapted remodeling. Continuous loss of cortical and cancellous BD at the femoral metaphysis, a homeostatic cortical strain configuration, and mild cortical hypertrophy along the diaphysis suggest a diaphyseal fixation of the implanted stem. CT-assisted osteodensitometry has the potential to become an effective instrument for quality control in THA by means of in vivo determination of periprosthetic BD, which may be a causal factor in implant loosening after THA.

Quantitative Computed Tomography-Assisted Osteodensitometry of the Pelvis After Press-Fit Cup Fixation A Prospective Ten-Year Follow-up

BACKGROUND As a follow-up of a previously reported three-year study, we analyzed the periprosthetic acetabular cortical and cancellous bone density changes at ten years after implantation of a press-fit cup. METHODS Prospective clinical, radiographic, and quantitative computed tomography examinations were performed within ten days and at mean periods of one, three, and ten years after total hip arthroplasty with a press-fit cup, a femoral stem with a tapered design, and alumina-alumina pairing. Periacetabular cortical and cancellous bone density (mg CaHA/mL) in the cranial, ventral, and dorsal regions about the cup were measured for twenty-four hips in vivo. RESULTS All acetabular cups showed radiographic signs of stable ingrowth, and no acetabular component had to be revised. The loss of periacetabular cancellous bone density about the cup was as much as -37% cranially, -60% ventrally, and -71% dorsally; the decrease was progressive between the one-year and three-year examinations only. In contrast, cortical bone density above the dome of the acetabular cup remained constant throughout the ten-year follow-up. A moderate change in cortical bone density of -5% to -18% was seen at the level of the cup ten years postoperatively. CONCLUSIONS Both periacetabular cortical and cancellous bone density changes were nonprogressive between the three-year and ten-year examinations after press-fit cup fixation.

Fractures of the distal humerus in the elderly. Pros and cons of endoprosthetic replacement

The intraarticular fracture of the distal humerus in an elderly patient remains a challenge for trauma surgeons. In case of severe co-morbidities and/or osteoporosis stable fixation with screws and plates is difficult and in some cases can be impossible. Even if osteosynthesis is feasible the clinical outcome is still incalculable due to delayed or non-union of the fracture fragments. Endoprosthetic replacement of the elbow joint for comminuted distal humerus fractures has been used for almost 20 years. The clinical results are predominantly excellent or good and better predictable than those of osteosynthesis. There still is no guideline when a prosthesis for the elbow joint should be used. We reviewed the literature and outline the current recommendations for diagnostics and surgical therapy for distal humerus fractures in the elderly.

Frakturen des Ellenbogengelenkes

Fractures around the elbow joint comprise fractures of the distal humerus, the radial head, the olecranon and the coronoid process. Combined lesions are particularly demanding for the surgeon. Accurate knowledge of the anatomy and of the biomechanics is an essential requirement for a specific diagnosis and therapy. A stable and painless movable elbow joint is essential for most of the activities of daily living. Risk factors for the development of posttraumatic elbow joint arthrosis are non-anatomically reconstructed joint surfaces, axial malalignment of the joint axis and untreated concomitant injuries. Modern angular stable and anatomically preshaped implants facilitate a biomechanically adequate osteosynthesis and avoid or decrease functional impairment. In consideration of an increasing number of osteoporotic elbow joint fractures, endoprosthetic replacement has gained significance.ZusammenfassungZu den Frakturen des Ellenbogengelenkes zählen die Frakturen des distalen Humerus, des Olekranons, des Radiuskopfes und des Processus coronoideus. Insbesondere Kombinationsverletzungen stellen eine Herausforderung für den Operateur dar. Die genaue Kenntnis der Gelenkanatomie und der Biomechanik sind eine entscheidende Voraussetzung für eine gezielte Diagnostik und Therapie. Ein stabiles und schmerzfrei zu bewegendes Ellenbogengelenk ist essenziell für die meisten Alltagstätigkeiten. Risikofaktoren für die Entwicklung einer posttraumatischen Ellenbogengelenkarthrose sind nichtanatomisch rekonstruierte und ausgeheilte Gelenkflächen, Achsfehlstellungen und unbehandelte Begleitverletzungen. Moderne winkelstabile, anatomisch vorgeformte Implantate erleichtern eine biomechanisch adäquate Frakturstabilisierung und helfen, Funktionseinschränkungen des Ellenbogengelenkes zu verringern. In Anbetracht der steigenden Zahl an osteoporotischen Ellenbogengelenkfrakturen hat auch die endoprothetische Versorgung einen zunehmenden Stellenwert erlangt.AbstractFractures around the elbow joint comprise fractures of the distal humerus, the radial head, the olecranon and the coronoid process. Combined lesions are particularly demanding for the surgeon. Accurate knowledge of the anatomy and of the biomechanics is an essential requirement for a specific diagnosis and therapy. A stable and painless movable elbow joint is essential for most of the activities of daily living. Risk factors for the development of posttraumatic elbow joint arthrosis are non-anatomically reconstructed joint surfaces, axial malalignment of the joint axis and untreated concomitant injuries. Modern angular stable and anatomically preshaped implants facilitate a biomechanically adequate osteosynthesis and avoid or decrease functional impairment. In consideration of an increasing number of osteoporotic elbow joint fractures, endoprosthetic replacement has gained significance.

Distale Humerusfraktur beim älteren Menschen

The intraarticular fracture of the distal humerus in an elderly patient remains a challenge for trauma surgeons. In case of severe co-morbidities and/or osteoporosis stable fixation with screws and plates is difficult and in some cases can be impossible. Even if osteosynthesis is feasible the clinical outcome is still incalculable due to delayed or non-union of the fracture fragments. Endoprosthetic replacement of the elbow joint for comminuted distal humerus fractures has been used for almost 20 years. The clinical results are predominantly excellent or good and better predictable than those of osteosynthesis. There still is no guideline when a prosthesis for the elbow joint should be used. We reviewed the literature and outline the current recommendations for diagnostics and surgical therapy for distal humerus fractures in the elderly.

Retrograde nailing versus locking plate osteosynthesis of proximal humeral fractures: a biomechanical study

BACKGROUND In locking plate osteosynthesis of proximal humeral fractures, secondary varus malalignment is a specific complication. Retron nails (Tantum AG, Neumunster, Germany), among others, have been designed to improve medial support of the calcar humeri. The aim of our biomechanical study was to examine whether Retron nails provide increased stiffness for axial loads and adequate stiffness for torsional loads when compared with Philos plates (Synthes AG, Umkirch, Germany). MATERIALS AND METHODS Twenty-two fresh-frozen paired humeri were collected. After potting the specimens, intact bones were exposed to sinusoidal axial (10-120 N) and torsional (±2.5 Nm) loading for 8 cycles to calculate the initial stiffness and exclude pairs with differences. Afterward, an unstable proximal humeral fracture (AO 11-A3) was created by means of an oscillating saw, and the respective osteosynthesis devices were implanted. After another 4 cycles, initial changes in stiffness were measured. Subsequently, all specimens were tested for 1,000 cycles of loading before final stiffness was assessed. RESULTS We found no statistically significant differences between Retron and Philos specimens after 4 or 1,000 cycles of loading. CONCLUSION Our study suggests that retrograde nailing provides sufficient stability for axial and torsional loading in 2-part fractures of proximal humeri.

Periacetabular cortical and cancellous bone mineral density loss after press-fit cup fixation: a prospective 7-year follow-up.

The impact of total hip arthroplasty on strain adaptive bone remodeling has been extensively analyzed by dual-energy x-ray absorptiometry. In this study, we present a prospective computed tomography-assisted study of periacetabular cortical and cancellous bone mineral density (in milligrams of calcium hydroxyapatite [CaHA] per milliliter, or mgCaHA/mL) changes 10 days and 1, 3, and 7 years after press-fit cup implantation for 38 hips in vivo. Cancellous bone mineral density decreased by Ø -63% ventral and Ø -85% dorsal to the cup; cortical bone mineral density, by Ø -22% ventral and Ø -18% dorsal to the cup. The presented periacetabular strain adaptive bone mineral density data are the most extensive of the current literature. Even the measured extensive cancellous bone mineral density loss was thus far of no clinical relevance because all cups showed radiographic signs of stable ingrowth.