Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-07-22
2004-01-20
Jackson, Gary (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
C606S060000, C606S062000, C606S092000
Reexamination Certificate
active
06679890
ABSTRACT:
BACKGROUND OF THE INVENTION
Femoral neck fractures are a major source of morbidity and mortality in the elderly population. Ninety-eight percent of all hip fractures occur in people over the age of fifty, with the average age being seventy-nine for females and seventy-four for males. By age ninety, thirty-two percent of all females and seventeen percent of all males in the United States will have sustained a hip fracture. Hip fractures occur at a frequency of 9.6/1000 people—translating into 240,000 hip fractures per year in the U.S. alone. Due to the increase of the elderly population, the projected conservative estimates predict that by the year 2040, there will be 520,000 hip fractures per year. The risk of sustaining a second hip fracture is increased nine fold (from 1.6/1000 to 15/1000), and six fold in females (from 3.6/1000 to 22/1000).
Hip fractures are the number one cause of accidental death in the U.S. in the age group over 75. There is a twelve percent decrease in a person's life expectancy after sustaining a hip fracture with the greatest mortality occurring in the first four to six months. Between fourteen to thirty-six percent of all hip fracture patients die in the first year post injury. Only sixty-four percent of the patients return to the community and twenty percent will not regain the ability to ambulate without assistance.
Medical cost from hip fractures are a significant strain on our already over-taxed healthcare system.
The femoral neck poses a difficult problem to the elderly patient and the treating orthopedic surgeon. During the aging process, in general, endosteal and outer periosteal diameters increase as a protective mechanism. As the bone mass shifts further from the epicenter, skeletal strength is maximized despite a decrease in bone mass. However, similar protective mechanisms do not occur in areas of cancellous bone (i.e., the femoral neck). In addition, the femoral neck is deficient in periosteum and is, therefore, unable to compensate for loss of endosteal bone by periosteal bone formation. When an elderly patient falls, it is estimated that approximately 3700 kg-cm of energy must be dissipated. The femoral neck can only absorb approximately 60 kg-cm of energy prior to fracture. Most of the energy in a fall is absorbed by active muscle contractions. In an elderly patient, the neuromuscular response cannot act quickly enough to dissipate the kinetic energy. Consequently, when the level of stored energy in the neck exceeds its threshold, a fracture develops.
Treatment of femoral neck fractures is a challenge for orthopedists despite progress in practice and technology, particularly with osteoporotic bone. Femoral neck fractures are usually repaired using hip screws or an angled blade plate, both techniques requiring a metallic plate fixed to the lateral femur through cortical screws. Substantial surgery is associated with lateral places. The surgery usually stiffens the femur laterally but risks overloading the lateral femur. Either procedure may not provide enough stability at the fracture site in osteoporotic bone. These treatments are only used as post-fracture curatives. No standard procedure is performed to prevent femoral neck fractures, although Crockett in 1960 proposed pinning the femoral neck for prophylactic use.
A limited number of reports investigated prophylactic strengthening of an intact femoral neck. Beside medical measures, Crockett (1960) suggested pinning, using a pin of 4 mm, the femoral neck of high-risk patients. Pinning the femoral neck along the neck axis strengthens most effectively against shear stresses. Crockett supported his contention that pinning intact femora can effectively strengthen the femoral neck through experiments. In addition to the risk of shear fracture of the femoral neck, delamination between cortical (cortex of the bone) and cancellous bone remarkably reduces mechanical strength of the femoral neck composites (cortical and cancellous bone). The risk of delamination is highest at the interface of cancellous to cortical bone. Delamination risk can therefore be reduced if the interface and the supporting cancellous bone are strengthened.
Franz, et al. (February 2001) presented at the 47
th
meeting of the Orthopaedic Research Society a study investigating the feasibility of injecting low-viscosity bone cement into the proximal femur and determining the corresponding augmentation effect. In their study, Franz, et al. drilled a 3.5 mm canal along the femoral neck axis. Bone cement was injected using a 4 mm biopsy needle. Although this study showed improved capacity of injected femora to withstand larger forces prior to fracture if compared to contra-lateral femora, there was a rise in temperature due to curing cement, and unpredictable long-term behavior of cements. These factors prevented current use of this technique as prophylactic measures for reducing fracture risk of the femoral neck. Although filling the proximal femur with bone cement can effectively reduce delamination fracture of the femoral neck, limited shear capacity of bone cement remains unpredictable for long-term use. Although the cement injection was monitored, there was no mechanism to control injection.
The above data clearly shows that a new effective and widely applicable strategy to prevent hip fracture is urgently needed. Medical treatment to prevent femoral neck fractures, as well as other fractures in the elderly have been geared with guarded effectivity to decreasing the rate of bone mass loss by either hormonal therapy (i.e., estrogen), by calcium supplementation, and by weight bearing exercises. Surgical treatment has been used solely as a post-fracture modality in the treatment of femoral neck fractures. To date, no surgical technique has been developed to prevent femoral neck fractures from developing.
References
1. Crockett, GS (1960).
Osteoporosis in the Elderly. Clinical Practice.
2. Franz, T; Heini, PF; Frankhauser, C; Gasser, B (February, 2001).
Reinforcement of the Osteoporotic Proximal Femur Using PMMA Bone Cement—An In Vitro Study.
47
th
Orthopaedic Research Society.
P. 0989, San Francisco, Calif.
SUMMARY OF THE INVENTION
An objective of this invention is to develop a method and apparatus of a femoral neck augmentation technique. The goal is to strengthen the femoral neck sufficiently to withstand a larger amount of force prior to fracture, utilizing a minimal invasion procedure. Traditional methods of surgical instrumentation are being used to fix the femoral neck fracture. Most of these methods require substantial surgical and anesthetic procedure. None of these methods can be used as a prophylactic method to augment the bone and prevent an impending fracture.
The proposed invention provides a new method of surgical prevention, by performing a minimal novel surgical procedure before a fracture occurs. Thereby, a bigger and more complicated procedure may be prevented.
The method includes percutaneous injection of uncured plastic material into the weakened femoral neck, before a fracture occurs. First, a hole is drilled into the femoral neck. The hole is filled with an uncured filler cement after loose materials have been removed from the hole. Then, an open-ended tube, an implant, having openings through its walls is inserted into the hole and attached to the bone. Finally, additional filler cement is provided under pressure to the inside of the tubular implant. The filler cement flows into spaces in the bone structure via the tube wall openings. Pressure is maintained until the filler cement has hardened.
Materials, which are currently used in surgery in the body, are used as the implant and cement for femoral neck augmentation. The filler cement has a degree of resilience and the capability of adhering to bone and the implant. The tubular implant and filler cement are less rigid than pins and screws, allowing the bone-cement construction to absorb energy prior to fracture.
The present invention relates to a cannulated implant that prophylactically strengthens an intact osteoporotic femoral neck whi
Aebi Max
Baroud Gamal
Margulies Joseph Y.
Steffen Thomas
Cooper Leonard
Jackson Gary
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