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Papers by Andreas Loefler

Research paper thumbnail of Multiaxial Pedicle Screw Designs: Static and Dynamic Mechanical Testing

Spine, 2004

Randomized investigation of multiaxial pedicle screw mechanical properties. Measure static yield ... more Randomized investigation of multiaxial pedicle screw mechanical properties. Measure static yield and ultimate strengths, yield stiffness, and fatigue resistance according to an established model. Compare these measured properties with expected loads in vivo. Multiaxial pedicle screws provide surgical versatility, but the complexity of their design may reduce their strength and fatigue resistance. There is no published data on the mechanical properties of such screws. Screws were assembled according to a vertebrectomy model for destructive mechanical testing. Groups of five assemblies were tested in static tension and compression and subject to three cyclical loads. Modes of failure, yield, and ultimate strength, yield stiffness, and cycles to failure were determined for six designs of screw. Static compression yield loads ranged from 217.1 to 388.0 N and yield stiffness from 23.7 to 38.0 N/mm. Cycles to failure ranged from 42 x 10(3) to 4,719 x 10(3) at 75% of static ultimate load. There were significant differences between designs in all modes of testing. Failure occurred at the multiaxial link in static and cyclical compression. Bending yield strengths just exceeded loads expected in vivo. Multiaxial designs had lower static bending yield strength than fixed screw designs. Five out of six multiaxial screw designs achieved one million cycles at 200 N in compression bending. "Ball-in-cup" multiaxial locking mechanisms were vulnerable to fatigue failure. Smooth surfaces and thicker material appeared to be protective against fatigue failure.

Research paper thumbnail of Spinal fusion using an autologous growth factor gel and a porous resorbable ceramic

European Spine Journal, 2004

Research paper thumbnail of Mechanical and Histologic Evaluation of Collagraft?? in an Ovine Lumbar Fusion Model

Clinical Orthopaedics and Related Research, 2000

The purpose of this study was to determine the effectiveness of a composite material composed of ... more The purpose of this study was to determine the effectiveness of a composite material composed of Type I bovine dermal collagen, 65% hydroxyapatite, and 35% tricalcium phosphate ceramic (Collagraft Bone Graft Matrix Strip NeuColl Incorporated, Palo Alto, CA) as a bone graft substitute for spinal fusion with and without the use of autologous bone marrow in an ovine lumbar spine model with pedicle screw fixation. Twenty-four adult sheep underwent a single level posterolateral (intertransverse process) L3-L4 lumbar fusion with one of three graft materials combined with rigid pedicle screw fixation. The three graft materials were Collagraft, Collagraft with marrow, and autogenous corticocancellous bone graft. Animals were euthanized 6 months after surgery and evaluated using dual energy x-ray absorptiometry, radiographs, histologic analysis, and mechanical testing. Dual energy xray absorptiometry between the transverse processes revealed that the mineral densities for the two Collagraft groups were significantly higher than the autogenous bone graft group. Histologic analysis confirmed that Collagraft was highly compatible and was well incorporated into the fusion mass. Both Collagraft groups had thick trabeculae and a mixture of lamellar and plexiform bone. The autogenous bone graft group had a smaller fusion complex, composed primarily of lamellar bone with thinner and fewer trabeculae. All three groups had similar mechanical properties. These results support the use of Collagraft in spinal fusion with pedicle screw fixation.

Research paper thumbnail of Bridging osteophyte of the anterosuperior sacroiliac joint as a cause of lumbar back pain

British Journal of Sports Medicine, 2004

A case report is presented of a patient with an anterosuperior osteophytic bone bridge of the sac... more A case report is presented of a patient with an anterosuperior osteophytic bone bridge of the sacroiliac joint causing lumbar back pain. After prolonged physiotherapy, the bone bridge was excised, with complete resolution of the symptoms. Excision should only be considered in cases of symptomatic sacroiliac joint pain that does not respond to rehabilitation programmes and conservative treatment.

Research paper thumbnail of Short-term outcomes of local infiltration anaesthetic in total knee arthroplasty: a randomized controlled double-blinded controlled trial

ANZ journal of surgery, Jan 3, 2015

The primary objective of the study was to determine if local infiltration anaesthetic (LIA) reduc... more The primary objective of the study was to determine if local infiltration anaesthetic (LIA) reduced total length of hospital stay in total knee arthroplasty (TKA) patients. The study also examined whether LIA improves early pain management, patient satisfaction and range of motion in TKA patients. We conducted a randomized controlled double-blinded study. Fifty patients undergoing TKA were randomized to receive either placebo or LIA at the time of surgery and on the first day post-operatively. Pain scores, level of satisfaction and range of motion were recorded preoperatively and post-operatively. There was no statistical difference between the groups for length of stay, post-operative pain scores, satisfaction scores or range of motion 6 weeks post-operatively. This randomized double-blinded trial did not demonstrate a decrease in pain or reduction of length of stay due to local infiltration analgesia.

Research paper thumbnail of Multiaxial Pedicle Screw Designs: Static and Dynamic Mechanical Testing

Spine, 2004

Randomized investigation of multiaxial pedicle screw mechanical properties. Measure static yield ... more Randomized investigation of multiaxial pedicle screw mechanical properties. Measure static yield and ultimate strengths, yield stiffness, and fatigue resistance according to an established model. Compare these measured properties with expected loads in vivo. Multiaxial pedicle screws provide surgical versatility, but the complexity of their design may reduce their strength and fatigue resistance. There is no published data on the mechanical properties of such screws. Screws were assembled according to a vertebrectomy model for destructive mechanical testing. Groups of five assemblies were tested in static tension and compression and subject to three cyclical loads. Modes of failure, yield, and ultimate strength, yield stiffness, and cycles to failure were determined for six designs of screw. Static compression yield loads ranged from 217.1 to 388.0 N and yield stiffness from 23.7 to 38.0 N/mm. Cycles to failure ranged from 42 x 10(3) to 4,719 x 10(3) at 75% of static ultimate load. There were significant differences between designs in all modes of testing. Failure occurred at the multiaxial link in static and cyclical compression. Bending yield strengths just exceeded loads expected in vivo. Multiaxial designs had lower static bending yield strength than fixed screw designs. Five out of six multiaxial screw designs achieved one million cycles at 200 N in compression bending. "Ball-in-cup" multiaxial locking mechanisms were vulnerable to fatigue failure. Smooth surfaces and thicker material appeared to be protective against fatigue failure.

Research paper thumbnail of Spinal fusion using an autologous growth factor gel and a porous resorbable ceramic

European Spine Journal, 2004

Research paper thumbnail of Mechanical and Histologic Evaluation of Collagraft?? in an Ovine Lumbar Fusion Model

Clinical Orthopaedics and Related Research, 2000

The purpose of this study was to determine the effectiveness of a composite material composed of ... more The purpose of this study was to determine the effectiveness of a composite material composed of Type I bovine dermal collagen, 65% hydroxyapatite, and 35% tricalcium phosphate ceramic (Collagraft Bone Graft Matrix Strip NeuColl Incorporated, Palo Alto, CA) as a bone graft substitute for spinal fusion with and without the use of autologous bone marrow in an ovine lumbar spine model with pedicle screw fixation. Twenty-four adult sheep underwent a single level posterolateral (intertransverse process) L3-L4 lumbar fusion with one of three graft materials combined with rigid pedicle screw fixation. The three graft materials were Collagraft, Collagraft with marrow, and autogenous corticocancellous bone graft. Animals were euthanized 6 months after surgery and evaluated using dual energy x-ray absorptiometry, radiographs, histologic analysis, and mechanical testing. Dual energy xray absorptiometry between the transverse processes revealed that the mineral densities for the two Collagraft groups were significantly higher than the autogenous bone graft group. Histologic analysis confirmed that Collagraft was highly compatible and was well incorporated into the fusion mass. Both Collagraft groups had thick trabeculae and a mixture of lamellar and plexiform bone. The autogenous bone graft group had a smaller fusion complex, composed primarily of lamellar bone with thinner and fewer trabeculae. All three groups had similar mechanical properties. These results support the use of Collagraft in spinal fusion with pedicle screw fixation.

Research paper thumbnail of Bridging osteophyte of the anterosuperior sacroiliac joint as a cause of lumbar back pain

British Journal of Sports Medicine, 2004

A case report is presented of a patient with an anterosuperior osteophytic bone bridge of the sac... more A case report is presented of a patient with an anterosuperior osteophytic bone bridge of the sacroiliac joint causing lumbar back pain. After prolonged physiotherapy, the bone bridge was excised, with complete resolution of the symptoms. Excision should only be considered in cases of symptomatic sacroiliac joint pain that does not respond to rehabilitation programmes and conservative treatment.

Research paper thumbnail of Short-term outcomes of local infiltration anaesthetic in total knee arthroplasty: a randomized controlled double-blinded controlled trial

ANZ journal of surgery, Jan 3, 2015

The primary objective of the study was to determine if local infiltration anaesthetic (LIA) reduc... more The primary objective of the study was to determine if local infiltration anaesthetic (LIA) reduced total length of hospital stay in total knee arthroplasty (TKA) patients. The study also examined whether LIA improves early pain management, patient satisfaction and range of motion in TKA patients. We conducted a randomized controlled double-blinded study. Fifty patients undergoing TKA were randomized to receive either placebo or LIA at the time of surgery and on the first day post-operatively. Pain scores, level of satisfaction and range of motion were recorded preoperatively and post-operatively. There was no statistical difference between the groups for length of stay, post-operative pain scores, satisfaction scores or range of motion 6 weeks post-operatively. This randomized double-blinded trial did not demonstrate a decrease in pain or reduction of length of stay due to local infiltration analgesia.