Migration and wear of hydroxyapatite-coated press-fit cups in revision hip arthroplasty: A radiostereometric study

Screw-fixated and hydroxyapatite-coated press-fit cups were studied using radiostereometry in 29 revision and 14 primary arthroplasties. The acetabular defects in the revision cases varied from none to type 3 (wall defects) according to Gustilo—Pasternak. Morsellized allograft was used in 25 revisions. Nine of these cups rested on less than 50% living bone. After 2 years, the mean migration in the revised group reached 0.36, 0.21, and 0.49 mm in the horizontal, longitudinal, and anteroposterior (AP) directions. The mean rotations varied between 0.5° and 0.7° depending on direction. The primary implants displayed smaller mediolateral migration and AP tilt. The mean proximal wear rate for the whole group was 0.11 mm/y. A central gap on the postoperative AP view implied less migration. The size of the preoperative bone defects or amount of bone—graft used had no influence on the migration. Despite extensive use of morsellized allograft, this implant displayed the smallest migration so far reported in revision hip arthroplasty.     

Is There an Advantage to Repairing Infected Mitral Valves?

Background. The therapy for native mitral valve endocarditis is in evolution. Antibiotics have significantly improved survival rates, but patients with complications of endocarditis may require surgical treatment.

Methods. Between January 1985 and December 1995, 146 patients underwent surgical therapy (repair or replacement) for native mitral valve endocarditis. All patients had documented bacterial endocarditis. Univariate and multivariate analyses were performed to determine predictors of hospital death, long-term event-free survival, and probability of repair. Patients were evaluated in three groups: all patients, patients with acute endocarditis, and patients with chronic endocarditis.

Results. There were ten hospital deaths (6.8%). Patients undergoing repair had a lower hospital mortality rate (p = 0.008) then those having replacement. Event-free survival was improved after mitral valve repair in the overall group (p = 0.02) and in the group with healed (chronic) endocarditis (p = 0.05). Although the acute endocarditis group demonstrated an improved event-free survival rate after mitral valve repair versus replacement (74% versus 20% at 6 years), this did not reach statistical significance.

Conclusions. We conclude that mitral valve repair is preferable to mitral valve replacement when possible, in patients with complications of endocarditis, as repair results in a lower hospital mortality and an improved long-term survival.     

Silicone-Coated Polypropylene Hollow-Fiber Oxygenator: Experimental Evaluation and Preliminary Clinical Use

Background. A membrane oxygenator consisting of a microporous polypropylene hollow fiber with a 0.2-μm ultrathin silicone layer (cyclosiloxane) was developed. Animal experimental and preliminary clinical studies evaluated its reliability in bypass procedures.

Methods. Five 24-hour venoarterial bypass periods were conducted on dogs using the oxygenator (group A). In 5 controls, bypass periods were conducted using the same oxygenator without silicone coating (group B). As a preliminary clinical study, 14 patients underwent cardiopulmonary bypass with the silicone-coated oxygenator.

Results. Eight to 16 hours (mean, 12.2 hours) after initiation of bypass, plasma leakage occurred in all group B animals, but none in group A. The O₂ and CO₂ transfer rates after 24 hours in group A were significantly higher than at termination of bypass in group B (p < 0.005 and p < 0.03, respectively). Scanning electron microscopy of silicone-coated fibers after 24 hours of bypass revealed no damage to the silicone coating of the polypropylene hollow fibers. In the clinical study, the oxygenator showed good gas transfer, acceptable pressure loss, low hemolysis, and good durability.

Conclusions. This oxygenator is more durable and offers greater gas transfer capabilities than the previous generation of oxygenators.     

Can people hear the pitch change on a variable-pitch pulse oximeter?

The introduction of the variable-pitch feature on pulse oximeters in 1983 by the Nellcor Corporation (Hayward, CA) allowed users to rapidly detect changes in oxygen saturation by listening for changes in the pitch of the tones emitted by the pulse oximeter. A few individuals have reported that they have been unable to detect a change in pitch when oxygen saturation changes. To these individuals, the variable-pitch feature of these pulse oximeters has not been beneficial. Using the pitches from one manufacturer of oximeters, we created a computer program to simulate the pitches that accompanied various oxygen saturations. The pitches were recorded onto a tape player and played for 75 volunteer subjects unfamiliar with the pitches of a variable-pitch pulse oximeter. Of our sample, 67% were able to detect a single change in pitch corresponding to a 1% fall in oxygen saturation, and 11% of the population could not detect a change in pitch until there was a change in pitch with every beat. We suggested four alternative designs that may prove beneficial to this group of individuals.