Introduction

Sheep are gaining popularity as a large animal model for orthopaedic research because of their availability, docile nature and a musculoskeletal system that is closer in size to humans than many other typical laboratory animal species.

Osteoporosis

The aged ovariectomized (OVX) ewe as a model for postmenopausal osteoporosis has been useful to test newer drugs such as synthetic estrogens like raloxifene. Bone loss following OVX does not reach the severity of elderly women but this can be induced using a diet low in cation-anion balance. The docile nature of sheep is very convenient when the effect of mechanical stimulation at high frequencies on bone remodeling is evaluated.

Hot flashes

Hot flashes affect 50–80% of perimenopausal women and are the most characteristic symptom associated with the climacteric. We implanted computer chips to measure temperature every few minutes in OVX ewes and discovered that they indeed get hot flashes and sheep are protected somewhat by estrogen replacement therapy.

Spine fusion

100,000 lumbar spine fusion surgeries are performed annually in the U.S. in patients with lower back pain due to degenerative disc disease or spondylolisthesis. Sheep have been shown to be appropriate models for bone healing for both lumbar and cervical spine. Furthermore, studies of the quantitative biomechanical similarities of intact sheep and human spines has demonstrated that the animal spines were qualitatively similar and that they can serve as an alternative for the evaluation of spinal implants. At Colorado State University, we have been using sheep for the past 10 years to discover new methods of interbody fusion as a treatment people with low back and neck pain.

Rotator cuff repair

While primary repair of acute rotator cuff tendon tears may be possible, chronic injuries often result in tendon degeneration requiring extensive tendon mobilization. Using the infraspinatus tendon of the sheep shoulder, we have tested various biological scaffolds to promote a reconstructive healing response rather than formation non-specific scar tissue.

Meniscus

Traumatic tears of the menisci occur in active people participating in sports that require running and heavy physical contact. At the present time such tears are treated by arthroscopic resection. The growing interest in repair of the torn meniscus has prompted a search for suitable materials and techniques to suture the meniscal cartilage of the knee. We have used sheep to evaluate different meniscal suturing devices.

Compliant fixation for segmental bone replacement

Anchoring prosthetic devices following segmental tumor resections of the extremity has traditionally used a cemented intramedullary stem device. Loosening secondary to stress shielding and/or macrophage osteolysis has been a major late complication. A new bone-prosthetic fixation device utilizing high force compression loading spring washers to promote strong biologic fixation was tested in 17 sheep. This device has now been used successfully in over 100 people.

The following links access three PDF files submitted by Dr. Turner. Click on the links to open them in Adobe Acrobat Reader. The reader program is available online here. If you cannot open the files from within this proceedings program, start Acrobat Reader manually, then open the files from the Files directory on the CD.

Note: The .pdf files may be found on your CD

 The Sheep as a Model for Osteoporosis in Humans (turner1.pdf)

 Pattern of Focal g-bursts in Chess Players (turner2.pdf)

 Animal Models of Osteoporosis - Necessity and Limitations (turner3.pdf)