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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2022)

The soft fur of an animal, the pain that protects us from the burn of a hot mug, and the tender touch of a loved one, are sensations we often take for granted. Unfortunately, people with hand prostheses have only the ability to hold and move objects but they cannot “feel” the object. Providing sensation through a prosthetic device is a major unmet need. Current prostheses lack the sensory feedback mechanism to take in data from external environments and convert it into “natural” sensation for the user. The objective of this study is to find a functional solution for people with thumb amputations that restores embodiment of the prosthesis and sensation to the thumb.This thesis proposes a surgical and mechanical solution to transfer skin onto a novel implantable prosthetic thumb. Since current designs of prosthetic fingers do not allow for fixation to the bone and implantation under the skin, the first aim of this study is to design a prosthetic thumb that is implantable, allows for osseointegration with the residual phalanx, and restores grasp motion. To test the surgical solutions, the second aim of this study is to design a rat model that utilizes similar surgical techniques and allows for implantation of a prosthesis.

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Cover page: Design and Validation of a Skin-Covered, Linkage-Driven Implantable Prosthesis
  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2024)

The UCLA Anatomical Engineering Group has developed an innovative attachment method for prosthetic sockets using an implantable ferromagnetic element and an externally controlled electromagnet to connect the socket to the limb. As part of this project, it was crucial to construct sensorized silicone limb models to effectively compare the new attachment method with conventional ones. These limb models also serve to validate various socket types, such as ischial containment sockets or quadrilateral sockets.

To design the limb models, the team used a 3D scan of an actual patient's limb, provided by the Veterans Affairs (VA) Medical Center, ensuring anatomical accuracy. The bone model within the limb was precisely sized and positioned using X-ray data, which informed the design's structural elements. The limb models were embedded with piezoelectric (PZT) crystals to measure localized tissue deformation through sonomicrometry, a technique that uses acoustic signals to determine distances between crystals.

The construction phase involved 3D printing with advanced materials to create anatomically accurate limb models. The inclusion of pressure and temperature sensors allowed for comprehensive data collection on the limb's response during movement. An important aspect of the design was to account for volume changes, as an amputee’s limb volume can vary throughout the day due to factors such as diet, weather, and comorbidities. Different mold sizes were constructed to test the same limb geometry at different volumes, ensuring the attachment method’s effectiveness under varying conditions.

    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2024)

    Background

    The appropriate amount of cementation at the time of reverse total shoulder arthroplasty with significant proximal bone loss or resection is unknown. Extensive cementation of a humeral prosthesis makes eventual revision arthroplasty more challenging, increasing the risk of periprosthetic fracture. We analyzed the degree of subsidence and torque tolerance of humeral components undergoing standard cementation technique vs. our reduced polymethyl methacrylate (PMMA) protocol. Reduced cementation may provide sufficient biomechanical stability to resist physiologically relevant loads, while still permitting a clinically attainable torque for debonding the prosthesis.

    Methods

    A total of 12 cadaveric humeri (6 matched pairs) underwent resection of 5 cm of bone distal to the greater tuberosity. Each pair of humeri underwent standard humeral arthroplasty preparation followed by either cementation using a 1.5-cm PMMA sphere at a location 3 cm inferior to the porous coating or standard full stem cementation. A 6-degree-of-freedom robot was used to perform all testing. Each humeral sample underwent 200 cycles of abduction, adduction, and forward elevation while being subjected to a physiologic compression force. Next, the samples were fixed in place and subjected to an increasing torque until implant-cement separation or failure occurred. Paired t tests were used to compare mean implant subsidence vs. a predetermined 5-mm threshold, as well as removal torque in matched samples.

    Results

    Fully and partially cemented implants subsided 0.49 mm (95% CI 0.23-0.76 mm) and 1.85 mm (95% CI 0.41-3.29 mm), respectively, which were significantly less than the predetermined 5-mm threshold (P < .001 and P < .01, respectively). Removal torque between fully cemented stems was 45.22 Nm (95% CI 21.86-68.57 Nm), vs. 9.26 Nm (95% CI 2.59-15.93 Nm) for partially cemented samples (P = .021). Every fully cemented humerus fractured during implant removal vs. only 1 in the reduced-cementation group. The mean donor age in our study was 76 years (range, 65-80 years). Only 1 matched pair of humeri belonged to a female donor with comorbid osteoporosis. The fractured humerus in the partially cemented group belonged to that donor.

    Conclusion

    Partially and fully cemented humeral prostheses had subsidence that was significantly less than 5 mm. Partially cemented stems required less removal torque for debonding of the component from the cement mantle. In all cases, removal of fully cemented stems resulted in humeral fracture. Reduced cementation of humeral prostheses may provide both sufficient biomechanical stability and ease of future component removal.
      Cover page: Reverse total shoulder arthroplasty with proximal bone loss: a biomechanical comparison of partially vs. fully cemented humeral stems
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