Aseptic Loosening of the Glenoid Component of Anatomic Shoulder Arthroplasty

Cyclic off-center loading of the humeral head on the glenoid component of anatomic total shoulder replacements, known as rocking-horse motion, is associated with early fixation failure and loosening of the glenoid implant.  We have a developed a biomechanical test system (Modified from ASTM F 2028-08) that includes continuous real-time tracking of genoid component micromotion and subsidence throughout the entire rocking-horse test and correlation of those displacements to the humeral head component position. Utilizing this test system, we evaluate the effects test substrates, implant design, and implant fixation techniques on the  stability of glenoid components subjected to rocking-horse loading.  

Related Reports:

  • Reed K, Bisogno M, Sreniawski K, Paterson P, Howard CS, Ehrensberger MT.  “A Comparison of Rocking Horse Loosening of Metal-Backed Versus All Polyethylene Glenoid Components” 62nd Annual Meeting of the Orthopedic Research Society 2016

  • Sreniawski K, Reed KB, Howard CS, Ehrensberger MT. “Rocking-Horse Loosening of Glenoid Components Cemented in Cadaver Bone and Bone Foam” 60th Annual Meeting of the Orthopedic Research Society 2014

  • Reed KB, Rotella NA, Buran JR, Howard CS, Stegemann PM, Ehrensberger MT. “Comparision of Two Glenoid Component Cementing Techniques Using Real-time Tracking of Rocking-Horse Loosening” 59th Annual Meeting of the Orthopedic Research Society 2013

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Reverse Shoulder Arthroplasty Glenoid Baseplate Stability with Superior Bone Loss

Reverse total shoulder arthroplasty has been shown to be an effective treatment for patients with rotator cuff tears and deficiencies. With the loss of rotator cuff strength, superior subluxation of the humeral head becomes a problem leading to excessive wear and superior glenoid bone deficiency. The presence of this superior defect can lead to complications when performing reverse total shoulder arthroplasty largely due to glenoid baseplate loosening. This laboratory based biomechanics study utilizes custom test systems to quantify the effect of different levels of superior bone defect on initial stability of the baseplate.

Related Reports:

  • Martin EJ, Duquin TD, Ehrensberger MT. “Measurement of Reverse Total Shoulder Glenoid Baseplate Stability with Superior Glenoid Bone Loss” Orthopedic Research Society 2017 Annual Meeting. Poster Presentation

Mechanics of Orthopedic Reaming

Rotational cutting tools, known as reamers, are used in a variety of orthopaedic surgeries ranging from intramedullary nailing of long bone fractures to total joint arthroplasty. Clinical concerns with reaming include thermal necrosis of the bone tissue and pressure-generated emboli, both of which are related to the reaming mechanics.  We have developed an instrumented reamer system with a wirelessly powered load/torque/rpm sensor combined with a infrared motion tracking system that can be utilized by surgeons in an unconstrained fashion to provide direct mechanical performance data during real or simulated reaming procedures. This system is also currently being modified to incorporate an instrumented reaming guide wire for temperature and pressure measurements.

Related Reports:

  • Puma KA, Phillips P, Ehrensberger MT. “Mechanical Profile of Intramedullary Reaming in the Tibia” Orthopedic Research Society 2017 Annual Meeting.

  • Yerrabolu SR, Mollendorf JC, Baier RE, Ehrensberger MT. “Examination of Factors Influencing Intramedullary Reaming Into Femurs” ASME International Design & Engineering Technical Conference 2014.

  • Puma KL and Ehrensberger MT. “Mechanical Comparison of Traditional & Minimally Invasive Acetabular Reamers for Total Hip Arthroplasty” ASME International Design & Engineering Technical Conference 2014.

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Validation of Image-Based Joint Contact Area and Pressure Measurements

Accurate and non-invasive measurement of the contact area between articulating surfaces of a load-bearing joint has a broad range of orthopaedic applications. A new cone beam CT system has been developed for imaging of extremities under load bearing conditions. This system also has novel analytical tools that include measurement of joint contact area and joint contact pressure distribution.  The purpose of this cadaveric study is to compare the image-based measurements of joint contact area and pressure obtained with the CT system to direct sensor-based measurements acquired with a Tekscan thin film sensor system that is directly inserted into the joint space. By validating the ability this cone beam CT system to measure joint contact area and pressure, it would allow for a non-invasive, rapid, in vivo method of assessing the biomechanical properties of joints.   This method could then be applied to areas of orthopedics such as the impact of joint diseases, the effects of corrective surgery, and orthopedic implant design.