Wesley P. Phipatanakul

The fallacy of evaluating biomaterial wear-rates with water as lubricant : A hip simulator study of alumina-PTFE and CoCr-PTFE combinations

Controversy surrounds wear data from hip-simulator studies, whether from the choice of lubricants or other parameters such as the particular biomaterial combinations used, and whether any such interactions could bias the resulting wear predictions. To investigate these phenomena, we studied the wear performance of CoCr and alumina femoral heads, in water and serum-based lubricants, using as our standard the polytetrafluoroethylene wear data derived clinically by Charnley. To model Charnleys clinical experience, PTFE acetabular cups were used in sets of three each with each size of femoral head for 22.25, 28, and 42-mm diameters in a nine-channel hip simulator. From the serum-based tests, the CoCr-PTFE wear data were consistently linear with duration of test, exhibited very large wear rates of 3,000-8,400 mm3/10(6), cycles had a precision within +/- 4% for each set of three cups, and copious amounts of small particulate were clearly seen circulating. The wear data clearly demonstrated Charnleys thesis that volume of wear increased with regard to size of femoral head. From the water-based tests, the CoCr-PTFE wear data were nonlinear with duration of test, had much reduced wear rates compared to the serum tests, lost the clinical relationship with ball size, and precision deteriorated to +/- 27% for each set. The wear debris appeared as 1-2 cm long ribbons which floated to the surface. For the alumina-PTFE combination in serum, the wear data appeared identical in performance to the CoCr-PTFE data in serum. Thus, the PTFE wear rates were not sensitive to the choice of femoral-head material. The most surprising outcome in this study was the zero-wear performance of the ceramic-PTFE combination in water. This contrasted remarkably with the large wear rates established for the same combinations run in serum. The zero-wear performance of the ceramic-PTFE combination in water was unexpected, but a similar phenomenon was noted in published simulator tests of ceramic-UHMWPE run in water. It now seems likely that such data may reflect the capricious behavior of water lubrication rather than any other variables under evaluation. The water-based experiments clearly favored the ceramics superior tribological performance and placed metal bearings at a decided disadvantage. Therefore, for an in vitro simulation of materials wear-ranking of clinical relevance, it may be advisable to use a serum-based lubricant.

Failure of a new intramedullary device in fixation of clavicle fractures: a report of two cases and review of the literature

Operative fixation is gaining popularity in the treatment of displaced midshaft clavicle fractures. Plates have traditionally been used in the surgical stabilization of these fractures. External fixators are rarely used, mainly being used in cases of open clavicular fracture or septic nonunion. Intramedullary devices behave as internal splints that maintain alignment of the fracture without rigid fixation. They are theoretically advantageous when compared with plate/screw devices because they entail minimal soft-tissue dissection and periosteal stripping, shorter hospital stays, cosmetic surgical exposure, and no skin prominence at the fracture site, and they avoid stress shielding. Intramedullary devices are now becoming streamlined to the anatomic specificities of the clavicle. The sigmoid shape of the clavicle dictates that intramedullary clavicle pins must be narrow and flexible enough to be installed through the curved medullary canal. The Sonoma CRx intramedullary clavicular pin (Sonoma Orthopedic Products, Santa Rosa, CA) is a new clavicle fixation pin that addresses the challenges of intramedullary fixation with a flexible head, grippers, and a buttressing screw. The flexible head contains grippers that extend within the medial fragment once the device is in place. Activation of the grippers transforms the flexible head into a rigid structure shaped according to the anatomic contours of the medullary canal. The locking screw is

Evaluation of the learning curve for reverse shoulder arthroplasty.

This purpose of this study was to quantify the surgical learning curve and provide guidelines to surgeons interested in teaching and performing reverse shoulder replacement. Sixty-two consecutive primary reverse shoulder replacements performed by a single surgeon were retrospectively reviewed. Using data from consecutive cases, surgical time was plotted against patient case order, and the linear regression slope was calculated. Case length slope analysis demonstrated a significantly negative slope with the first 18 cases, which subsequently leveled thereafter. The number of cases needed to arrive at this flat slope was defined as the proficiency point.The proficiency point was then verified using the measurable variables of baseplate screw number and glenosphere overhang by dividing the series into 2 groups: Group A included patients who had surgery prior to the proficiency point, and group B included patients who had surgery after the proficiency point. In group A, only 33% (6/18) had all 4 glenoid baseplate screws placed as compared to 66% (29/44) in group B (P=.02). Glenosphere overhang increased from a mean of 1.02 mm (+/-1.29 mm) in group A to 2.58 mm (+/-1.89 mm) in group B (P=.003).A learning curve of approximately 18 cases was found in this series based on the technical aspects of performing reverse shoulder replacement. This curve is likely even longer for lower volume shoulder surgeons. We recommend specialized training prior to performing this procedure.

Removal of well-fixed flanged humeral prostheses may require humeral expansion

BACKGROUND A flanged humeral stem design can be advantageous in achieving an interlock between the prosthetic and bone interface leading to a long-term stable loading pattern. The purpose of this study is to report a short case series involving revision of a flanged humeral prosthesis. Our hypothesis was that a greater percentage of the flanged prostheses undergoing revision would require some form of bone expansion to achieve stem removal compared to the nonflanged. METHODS AND RESULTS In the period from October 2004 to July 2008, 43 patients underwent revision of a humeral prosthetic stem by a single surgeon. Of these, 6 prostheses were of a triflanged design. Of these six, five (83%) could not be removed with longitudinal force and required some expansion of the bone in order to achieve stem extraction. Of the nonflanged humeral stems, 3/37 (8%) required bone expansion to achieve extraction. Analysis of the 2 groups showed a statistical difference in the need for humeral expansion (P < .000001). CONCLUSIONS Surgeons preparing to revise a flanged humeral stem should include expansion of the humeral shaft, by episiotomy or windowing, as part of their preoperative planning and informed consent of the patient.

Cyanoacrylate Microbial Sealant May Reduce the Prevalence of Positive Cultures in Revision Shoulder Arthroplasty

BackgroundCyanoacrylate-based, microbial sealant is an adhesive skin barrier designed to prevent bacterial contamination in surgical wounds. This type of adhesive barrier could have use in decreasing the incidence of positive cultures and subsequent infection in shoulder arthroplasty.Questions/purposesWe therefore evaluated whether cyanoacrylate microbial sealant reduced the positive intraoperative culture rates in revision shoulder arthroplasty.MethodsWe retrospectively reviewed 55 patients who underwent revision shoulder arthroplasties. Intraoperative aerobic and anaerobic deep tissue culture results taken during the revisions were compared. Cultures were taken of the deep synovial tissue lining the prosthesis. Patients were divided into two groups: those who underwent standard preparations with adhesive, iodine-barrier drapes (Group SP) and those who had placement of cyanoacrylate microbial sealant in addition to the standard prep (Group MS).ResultsThe prevalence of cases with positive cultures was 18% (seven of 40) in Group SP compared with 7% (one of 15) in Group MS. The prevalence of positive, anaerobic Propionibacterium acnes cultures was 13% in Group SP compared with 7% in Group MS. The prevalence of infections confirmed at revision surgery was 8% in Group SP versus 0% in Group MS.ConclusionsOur observations suggest application of a cyanoacrylate microbial sealant may reduce the prevalence of positive cultures and thereby subsequent infections in revision shoulder arthroplasties.Level of EvidenceLevel III, retrospective cohort study. See Guidelines for Authors for a complete description of levels of evidence.

2017@@@Insurance-Mandated Stay Prolongs Hospitalization Following Total Shoulder Arthroplasty@@@81: 85

Medicare currently requires a 3-night hospitalization for a patient to be considered for skilled nursing facility (SNF) placement. The purpose of this study was to analyze the relationship between length of stay and (a) insurance status and (b) readmission rates in Medicare-age patients undergoing primary total shoulder arthroplasty. A retrospective review of 251 primary consecutive total shoulder arthroplasty cases was performed. In patients discharged to SNF, Medicare insurance was associated with a significantly longer hospital stay (p < .001) compared with patients with private insurance. Readmission rates for Medicare and private insurance patients were similar at 30 and 90 days after surgery (p = 1.000). Ninety-five percent of Medicare patients discharged to SNF had a prolonged hospital stay primarily to fulfill the 3-night requirement. These findings call into question the necessity of the current 3-night inpatient hospitalization requirement for facility placement following total shoulder arthroplasty.