Editor: Charles Sorbie, MB, CHB, FRCS(E), FRCS(C)
Radiography is not a reliable method for determining whether a femoral prosthesis is loose. The reported accuracy rate can be as low as 50%. A.P. Georgiou and J.L. Cunningham (Clin Biochem. 2001; 16:315-323) have used a vibrator to detect loosening of components.
Engineers have long used vibration techniques to determine the integrity of laminated structures, eg, boat hulls. Excitation of a secure bone implant produces an output characteristic of a single unit having one resonant frequency and no harmonics, ie, the output wave is pure. After loosening or “delaminaton” of an implanted component, the separated elements respond to excitation differently. Appropriate instruments can demonstrate the differences.
The authors used the diagnostic vibration technique on 23 patients admitted for revision total hip arthroplasty surgery and on 10 patients with recent and presumably secure implants. The technique was 100% accurate in its findings of hip implant loosening.
Light at the End of the Tunnel
Intensive “keyboarding” by computer users is a controversial cause of carpal tunnel syndrome. Much work time is lost from symptoms that are labeled carpal tunnel syndrome. There is a considerable cost for confirmatory nerve conduction studies, keyboard ergonomics are expensively applied, and the carpal ligament may be unnecessarily incised.
The frequency of carpal tunnel syndrome among computer users at the Mayo Clinic in Scottsdale, Arizona was studied by J.C. Stevens et al (Neurology. 2001; 56:1568-1570). Questionnaires were sent to 257 employees identified as frequent computer users. The employees were asked if they experienced “pins and needles” or numbness in their hands. Although 29.6% of the employees reported hand paresthesias, only 10.5% met the clinical criteria for carpal tunnel syndrome, and 3.5% had the syndrome confirmed by nerve conduction studies. Affected and unaffected employees had similar occupations and years of using a computer. Working 6.5 hours a day using the computer did not increase the risk.
Preclinical Testing of Hip Implants
In vitro testing of implants before they are used in clinical practice would allow screening out implants that permit excessive slippage, before they are marked for clinical use. S.A. Maher et al (Clin Biomech. 2001; 16:307-314) have constructed an experimental device that may do just that.
Clinical studies using radiostereophotogrammetry have shown femoral implants that migrate rapidly in the first 2 postoperative years require early revision. A laboratory study devised to test various femoral implants by measuring migration when the implants are loaded would save time and avoid costly animal experiments.
The authors’ device uses a target of three spheres arranged in a cruciform structure. Six linear displacement transducers measured motion of the prostheses in relation to bone. During 2 million cycles, the pattern was recorded showing rapid initial followed by steady-state migration. The tested prostheses migrated distally, medially, and anteriorly.
The migration rate in the prostheses tested was however small, and the authors wondered if it was the result of not including posteriorly directed loading of the type experienced by patients during stair climbing. The absolute migration and its direction is similar to that observed in clinical studies, suggesting this in vitro preclinical test device is of value.
COX-2 Inhibitors Projected to Dominate Osteoarthritis Market in the Next Decade
In this, the Decade of the Bone and Joint, COX-2 inhibitors will take over part of the nonsteroidal anti-inflammatory medications market, according to a Decision Resources study.
COX-2 inhibitors were first approved by the Food and Drug Administration in December 1998. Since then, celecoxib and rofecoxib, the two currently available selective COX-2 inhibitors, accounted for $1.2 billion or 41% of the osteoarthritis market in 2000. The launches of valdecoxib, etoricoxib, and COX-189 are expected to spur the continuing growth of COX-2 inhibitors.
Iatrogenic Creutzfeldt-Jacob Disease From Surgical Instruments
North America has been spared the ominous threat of future, widespread Creutzfeldt-Jacob disease. Other regions, especially eastern Europe, where Creutzfeldt-Jacob disease has already caused many deaths, face the future with some trepidation. Health authorities in the United Kingdom are taking seriously the possibility of the disease being passed on via used, but sterilized surgical instruments (Frosh et al. BMJ. 2001; 7302:1558-1559.
The disease marker and likely transmissible agent (PPSc) has been identified in neural- and lymphoreticular tissues of the brain, tonsil, and spleen. The appendix, being lymphoreticular, is another possible repository. Prion diseases have been reported to be passed on by stainless steel surgical instruments. The infective agent has shown remarkable resistance to elimination by standard sterilization techniques.
Since the disease may take several decades to manifest itself, instruments used for pediatric surgery must be guaranteed free from contamination. The British government is not going to wait for indisputable evidence before acting. All blood and blood products are being leucodepleted. Every surgical instrument needs to have all traces of organic material removed and, when possible, instruments should be disposable. Authorities are considering making all tonsillectomy instruments disposable at present, in contrast to most neurosurgical ones.
But First, Catch a Tiger By the Tail
The Fauna Communications Research Institute at Hillsborough, North Carolina, is studying the purring of cats (Sci Am. June 2001:32). Some big cats such as cheetahs and lions may purr when stressed, wounded, or anxious. The frequency of the purr for house cats is between 27 and 40 Hz. It is the same frequency that affects bone growth and strengthening. Could application of this “comfort sound” heel our broken bones more quickly?
Comings and Goings
Orthopedics is pleased to welcome the following new members to the Board of Editors:
Michael Ain, MD, Baltimore, MD; Max Boehler, MD, Vienna, Austria; David Halsey, MD, Springfield, VT; Darren Johnson, MD, Lexington, KY; Robert Sellards, MD, Chicago, IL; James Wenz, Sr, MD, Baltimore, MD.
We also bid farewell to the Board of Editors members recently retired, and thank them for their generosity and dedication. (Length of tenure on the Board is noted in parentheses.)
Retiring Consulting Editors: Daniel Antonelli, PhD, Los Angeles, CA (15 years); W.P. Butt, MD, FRCR, FRCPC, Leeds, England (16 years); Michael Jabaley, MD, Jackson, MI (18 years); Robert Marier, MD, New Orleans, LA (18 years); Moshe Solomonow, PhD, New Orleans, LA (18 years); Donald Trunkey, MD, Portland, OR (18 years).