Adapter Sleeve Research Articles

Influence of a Modified Procedure of Joining Ceramic Head and Adapter Sleeve on the Stem Taper in Revision: An Experimental Study.

In revision operations, ceramic heads of modular hip implants can be replaced. As the surface of the stem taper can be damaged, additional adapter sleeves are applied. The components are usually connected manually by the surgeon in a one-step procedure by hammer impacts. In this study, we investigated a two-step joining procedure with reproducible impaction force. First, the adapter sleeve and head were joined quasi-statically with a force of 2 kN using an assembly device. In the second step, these components were applied to the stem taper using a pulse-controlled instrument. For reference, the joints were assembled according to standard conditions using a tensile testing machine. An average pull-off force of 1309 ± 201 N was achieved for the components joined by the instrument, and the average measured values for the components joined by the testing machine were 1290 ± 140 N. All specimens achieved a force >350 N when released and therefore met the acceptance criterion defined for this study. This study showed that a modified procedure in two steps with a defined force has a positive effect on the reproducibility of the measured joining forces compared to previous studies.

Computer-based analysis of the taper connection strength of different revision head and adapter sleeve designs.

Ceramic revision heads, equipped with titanium adapter sleeves, are used in femoral head revision in total hip arthroplasty to avoid ceramic fracture due to the damaged taper. A finite element analysis of the taper connection strength of revision heads with varying head diameters combined with adapter sleeves of different lengths was conducted. The influence of various assembly forces, head diameter, and length of the adapter sleeves was evaluated. For two combinations, the pattern of contact pressure was evaluated when applying a simplified joint load (3 kN, 45° load angle). Experimental validation was conducted with 36 mm heads and adapter sleeves in size S, as well as 28 mm heads and adapter sleeves in size XL. The pull-off force increased with higher assembly forces. Using larger head diameters and adapter sleeves led to decreased pull-off forces, a reduced contact surface, and less contact pressure. The contact pressure showed significant peaks and a diagonal pattern under 45° angle loading when assembly forces were less than 4 kN, and larger adapter sleeves were utilized. A sufficient assembly force should be ensured intraoperatively, especially with an increasing head diameter and adapter sleeve size, as lower assembly forces might lead to reduced taper connection strength.

Taper connection strength of revision heads with adapter sleeves compared to standard heads made of ceramics

Abstract Revision ceramic heads with titanium adapter sleeves are used in case of a femoral head revision in total hip arthroplasty to avoid ceramic fracture due to damaged tapers. Objective of the present study was to evaluate the taper connection strength of revision ceramic heads. Therefore, revision ceramic heads (Ø36 mm; adapter sleeve S) and standard ceramic heads (Ø36 mm; neck length S) were assembled with an axial load (2 kN) to titanium tapers with various damage modes (undamaged, truncated, and elevated). Subsequently, the heads were either pulled-off directly after assembly or after dynamic loading over 2.5 million cycles (sinusoidal 0.3 kN–3.0 kN). Pull-off forces of the revision heads (1.24 kN–1.66 kN) were up to 43.7% higher compared to standard heads (1.02 kN–1.48 kN) in dependency of the taper damage. After dynamic loading, the pull-off forces did not change in case of standard heads. The pull-off forces of the revision heads decreased in combination with the undamaged and truncated tapers but increased in combination with the elevated tapers. In conclusion, revision heads with adapter sleeves (size S) showed higher taper connection strength than standard heads both on undamaged and damaged tapers.

Microstructure and Defect-Based Fatigue Mechanism Evaluation of Brazed Coaxial Ti/Al2O3 Joints for Enhanced Endoprosthesis Design.

Alumina-based ceramic hip endoprosthesis heads have excellent tribological properties, such as low wear rates. However, stress peaks can occur at the point of contact with the prosthesis stem, increasing the probability of fracture. This risk should be minimized, especially for younger and active patients. Metal elevations at the stem taper after revision surgery without removal of a well-fixed stem are also known to increase the risk of fracture. A solution that also eliminates the need for an adapter sleeve could be a fixed titanium insert in the ceramic ball head, which would be suitable as a damping element to reduce the occurrence of stress peaks. A viable method for producing such a permanent titanium–ceramic joint is brazing. Therefore, a brazing method was developed for coaxial samples, and two modifications were made to the ceramic surface to braze a joint that could withstand high cyclic loading. This cyclic loading was applied in multiple amplitude tests in a self-developed test setup, followed by fractographic studies. Computed tomography and microstructural analyses—such as energy dispersive X-ray spectroscopy—were also used to characterize the process–structure–property relationships. It was found that the cyclic loading capacity can be significantly increased by modification of the surface structure of the ceramic.

Incidence, Risk Factors, and Outcome of Ceramic-On-Ceramic Bearing Breakage in Total Hip Arthroplasty

BackgroundCeramic-on-ceramic bearing breakage is a rare but significant complication of total hip arthroplasty. This study aimed to identify risk factors for breakage and to determine the outcome of different revision options. MethodsAll ceramic-on-ceramic primary total hip arthroplasty procedures reported to the Australian Joint Replacement Registry from September 1999 to December 2019 were included. Procedures were subdivided into alumina or mixed ceramic (alumina/zirconia). All breakages were identified. The association between ceramic type and head size was assessed. Subsequent revision rates were compared and cause of revision assessed. ResultsThere were 23,534 alumina and 71,144 mixed ceramic procedures. Breakage was the reason for 1st revision in 84 alumina (5.27% of all revisions and 0.36% of procedures) and 56 mixed ceramic procedures (2.46% of all revisions; 0.08% of procedures). Alumina had a higher breakage rate than mixed ceramic (HR 2.50 (95% CI 1.75, 3.59), P < .001), and breakage was higher for 36-38mm head sizes using alumina (HR 2.84 (1.52, 5.31), P = .001). 17.8% of 2nd revisions occur by 3 years, due to dislocation, infection, metal-related pathology, and loosening. A neck adapter sleeve did not reduce 2nd revisions. Numbers were too low to compare revision bearing surface options. ConclusionCeramic breakage has reduced with mixed ceramics but has a 0.79/1000 incidence at 15-year follow-up. It is unclear what the risk factors are for modern ceramics with increasing head size a risk for alumina only. Risk of 2nd revision is high and occurs early. The optimal revision option is unknown.

Adapter sleeves are essential for ceramic heads in hip revision surgery

BackgroundRemoving a head during isolated acetabular revision surgery can cause damage to the stem taper surface from extraction tool contact. Implanting a ceramic head on the damaged stem taper might elevate the fracture risk, which can be mitigated with the use of titanium adapter sleeves. The aim of this study was to investigate whether the improved fracture strength of modern generation ceramic heads allows the direct implantation on damaged stem tapers without an adapter sleeve. MethodsFinite element models of taper junctions with and without adapter sleeve were generated. Different stem taper damages were modelled to investigate the influence on the ceramic head fracture load under axial compression. FindingsHeads without adapter sleeves exhibited slightly higher or equal fracture strengths compared with sleeved heads for most scenarios. However, a small metal elevation on the stem taper caused a drastic decrease of the fracture strength if no adapter sleeve was used (−96%). The sleeved head was not influenced by the metal elevation damage. InterpretationAdapter sleeves are essential to ensure patient safety and prosthesis longevity whenever implanting ceramic heads on used stem tapers.

Registry study on failure incidence in 1,127 revised hip implants with stem trunnion re-use after 10 years of follow-up: limited influence of an adapter sleeve

Background and purpose — Little is known about the role of retained trunnions in revision hip arthroplasties, i.e., when only the femoral head is substituted. Wear (fretting corrosion) and ceramic head fractures are 2 poorly understood concerns related to use, and the role of adapter sleeves has not been defined. In this registry study we assessed the influence of sleeve interposition on re-revision rates in revision hip arthroplasties with retained stems. Confounding factors (demographics, implant-related features) and failures were also analyzed.Patients and methods — We conducted a registry study on 1,127 revised implants (retained trunnion and head exchange). In 26% of implants an adapter sleeve was interposed; in 74% no adapter sleeve was implanted. Demographic and implant-related features were investigated including a descriptive analysis of failures.Results — The mean follow-up of revised implants with and without the use of an adapter sleeve was 3.3 and 5.1 years, respectively. The implant survival without an adapter sleeve was significantly higher, 98.4% (95% CI 96.9–99.8) vs. 95.2% (CI 93.2–96.6) with an adapter sleeve at 5 years. No re-revisions due to adverse local tissue reactions or ceramic head fractures were reported. In order to overcome the different distribution of head materials and head sizes in the two cohorts, only Delta balls were investigated.Interpretation — Adapter sleeve interposition had a minor influence on the revision rates. No adverse local tissue reactions or head fractures occurred.

Impact of stem taper damage on the fracture strength of ceramic heads with adapter sleeves

BackgroundUsing a new ceramic head with a titanium adapter sleeve offers the possibility of maintaining a well fixed stem when conducting cup revision of a total hip arthroplasty. The aim of this study is to test the impact of stem taper damage on the fracture strength of sleeved ceramic heads. MethodsPristine zirconia-toughened alumina heads with titanium adapter sleeves (BIOLOX®OPTION System) were tested on damaged Ti-4Al-6V stem tapers in accordance with ISO7206-10. Four distinctive damage types classified as intolerable by the manufacture were investigated, representing various reductions in contact area between the stem taper and sleeve taper as well as damage incurred from previous ceramic head fracture. FindingsThe largest reduction in fracture strength occurred for a loss of contact for the entire length of the stem taper. Nonetheless, the fracture strength in all investigated cases was several times higher than that defined by the FDA standards. InterpretationThe use of a titanium sleeve recreates a uniform contact situation between the ceramic head and the outer sleeve taper in situations of damaged stem tapers. For the investigated damage types a high fracture strength of the ceramic head was maintained. This study supports the clinical use for sleeved ceramic heads in instances of greater damages of stem tapers than previously defined in order to spare patients from stem removal.

Modular junction may be more problematic than bearing wear in metal-on-metal total hip arthroplasty.

In total hip arthroplasty (THA), local adverse reaction to metal debris (ARMD) may be caused by abnormal metal ion release from a metal-on-metal (MoM) bearing, or by wear and corrosion of the implant's modular junction. The aim of this study was to compare ion levels and rate of ARMD between patients sharing the same MoM bearing but 1 group having monoblock stems versus another having modular stems. Whole blood cobalt (Co) and chromium (Cr) ion concentrations, ARMD rate, revision rate, and function measured by UCLA and WOMAC scores were compared between groups. ARMD rate was significantly higher in the modular group (46%) compared with the monoblock group (16%, p = 0.031). Revision for ARMD was performed at 52.8 ± 8.1 months in the modular group versus 98.2 ± 15.5 months after primary THA in the monoblock group. ARMD originated from wear and corrosion of the junction between stem and femoral head adapter sleeve in all monoblock cases, and the junction between stem and modular neck in all the modular ones. Cr and Co ions levels were significantly higher in the modular stem group ( p < 0.001 for both). Although both groups had MoM bearings, corrosion at stem/neck or neck/head junctions combining dissimilar metal (Ti and Cr-Co) was seen as the source of excess metal ions release leading to ARMD. Poor performance of the modular junction may be more deleterious than wear of the bearing. To avoid such complications, THA femoral stem modular junctions should be eliminated (return to a full monoblock implant) or have improved junction design.

Device and method for measuring thickness variation of large roller element bearing rings

The thickness variation of a large bearing ring is an important measure effecting on the rotational accuracy and partly defining the dynamic properties of the bearing. For example, when a bearing inner ring is installed on a rotor shaft, the final roundness profile of the installed bearing inner ring is the sum of the roundness profile of the rotor shaft roundness and the thickness variations of the inner ring and the possible conical adapter sleeve. In the present study, a device and a method for measuring the thickness variation of large roller element bearing rings was presented. To enhance the measurement quality, each measurement consisted of 20 rounds of measurement data, which were averaged in the frequency domain after the Fast Fourier Transform. In addition, the quality of the measurement was analysed by comparisons with existing devices, coordinate measurement machine (CMM) and roundness measurement machine, and by repeatability measurements. In the analysis, both thickness variation profiles and their harmonic components were investigated. The results show, that the overall agreements with the CMM and the roundness measurement machine were satisfying and good respectively. The repeatability of the proposed device was similar to the roundness measurement machine. According to the results, the device and the method were considered to be valid and deserve further interest and investigation for the bearing ring measurements.

Adapter Sleeves Are Not Needed to Reduce the Risk of Fracture of a New Ceramic Head Implanted on a Well-Fixed Stem.

The purpose of this study was to assess (1) the prevalence of the fracture of ceramic heads implanted on used trunnions of well-fixed stems without using a titanium adapter sleeve; (2) the prevalence of trunnionosis secondary to fretting and/or corrosion at the trunnion of the well-fixed stem; and (3) clinical and radiographic results and the survival rate of the revised acetabular components. Eighty-eight patients (100 hips) underwent isolated revision of the acetabular components for polyethylene wear and osteolysis of the acetabulum. The study group consisted of 70 men and 18 women with a mean age of 52.8 years (range, 31-54 years) when the primary total hip arthroplasty was performed. Evidence of fretting and corrosion of the trunnion of all prostheses was examined macroscopically using a magnifying lens. Degree of fretting and corrosion of the trunnion was assessed using a 4-point scoring technique. A new 36-mm alumina delta ceramic head was implanted on the trunnion of a well-fixed stem without using a titanium adapter sleeve in all hips. The mean follow-up after revision of the acetabular component was 12.8 years (range, 10-14 years). Among the 100 new ceramic heads implanted on a well-fixed stem, no fracture of the ceramic head occurred at a mean follow-up of 12.8 years. The median fretting and corrosion scores for the trunnions were 1.5±1.1 and 1.3±0.9 points, respectively. The mean Harris hip score at the final follow-up was 89±15 points (range, 63-100 points). Survivorship of the revised acetabular components at 14 years was 95% (95% confidence interval, 87.6%-98.6%). [Orthopedics. 2018; 41(3):158-163.].

Ceramic Bearings with Titanium Adapter Sleeves Implanted During Revision Hip Arthroplasty Show Minimal Fretting or Corrosion: a Retrieval Analysis.

The BIOLOX® option system, consisting of a BIOLOX® delta ceramic femoral head with a titanium alloy adapter sleeve, is being increasingly utilized in revision hip arthroplasty. The sleeve protects the ceramic head from fracture and improper motion about the stem trunnion when a damaged trunnion is encountered at revision surgery. Corrosion and fretting due to metal-metal contact at the taper region of hip prosthesis create the potential of causing periprosthetic osteolysis and adverse local tissue reactions. The objective of this study was to identify the type and extent of damage to retrieved sleeves and ceramic heads to determine their in vivo performance. Twenty-four ceramic heads with titanium alloy sleeves were examined. The articular and taper surfaces for each ceramic head were assessed for metal transfer using a subjective grading system. All surfaces of the 24 titanium sleeves and stem trunnions (only available for 7 of 24 cases) were assessed for corrosion and fretting using an established grading system. Scanning electron microscopy and energy dispersive X-ray analysis were conducted on representative sample of sleeves. Fretting and corrosion were higher at the inner surface of the taper sleeve than the outer sleeve. Mean fretting scores at the inner taper and outer taper sleeve surfaces were 1.8 and 1.2, respectively. The mean corrosion score at the inner taper surface was 1.8; no corrosion was observed on the outer surface of any taper sleeve. SEM and EDS analyses provided further indications of low levels of damage. Fretting and corrosion were less severe than previously reported for conventional THA metal-metal taper connections, indicating that a ceramic head and titanium sleeve is a safe alternative in revision THA.

Mechanical Stability of the Taper Connection of Large Metal Femoral Heads With Adapter Sleeves in Total Hip Arthroplasty Analyzed Using Explicit Finite Element Simulations

BackgroundLarge diameter heads (LDHs) of metal-on-metal bearings in total hip arthroplasty provide increased range of motion and reduced dislocation rates. However, major concerns grew over high wear rates from the modular connection between femoral stem and head, especially in combination with adapter sleeves. MethodsA computational study on the taper connection stability of LDH (50 mm) with adapter sleeves of different lengths (S, M, L, and XL) compared with a standard femoral head (32 mm) without adapter sleeves was conducted using explicit finite element analyses. Four different impact configurations were considered resulting from varied mallet mass (0.5 vs 1.0 kg) and velocity (1.0 vs 2.0 m/s). The taper stability was evaluated by determination of the pull-off forces and micromotions due to simulated joint loads during walking (2 kN and 7.9 Nm, respectively). Moreover, the deformations of the adapter sleeves and the contact area in the taper connections were evaluated. ResultsAlthough the pull-off forces of the LDH with different-sized adapter sleeves were comparable, contact area decreased and adapter sleeve deformations increased (up to 283%) with an increasing adapter sleeve length. Moreover, the micromotions of LDH with adapter sleeves were up to 7-times higher, as compared with the standard femoral head without an adapter sleeve. ConclusionThe present numerical study confirms that the assembly technique of LDH with adapter sleeves reveals increased micromotions compared with standard femoral head sizes. We could demonstrate that deviations of the stem trunnion geometry and improper surgical instructions led to worse mechanical stability of the taper connection.

EXPERIMENTAL APPLICATIONS ON THE INFLUENCE OF INTERNAL OPERATION CLEARANCE OF THE FAULTY ROLLING BEARINGS UPON THEIR REMAINING LIFETIME

&lt;p&gt;In the calculation of the rolling bearings lifetime are taking in to consideration the distribution of the work load on each rolling elements, obliquity, internal operation clearance and pre-stressing. In the case of a rolling bearing with a defect, the internal operation clearance have an influence upon the evolution of its deterioration and remaining lifetime by: internal manufacturing clearance; the expansion of the inner ring when the rolling bearing is mounted on a adapter sleeve; the contraction of the outer ring when the rolling bearing is mounted in the housing; and the temperature difference between rolling bearing rings during operation. This paper presents an experimental study regarding to the influence of the internal operation clearance of the ZKL 1205K rolling bearing upon the remaining lifetime in same operating conditions. &lt;/p&gt;

“Trunionitis”: A Cause for Concern?

Large diameter heads (LDH) are connected to the stem by means of a Morse taper. An adapter sleeve may be also used to adjust the head offset intraoperatively and/or to change the bearing couple and size. This paper explains the effect of head diameter and friction coefficient on the frictional torque acting on the tapers. A greater frictional torque tends to increase the micromotion occurring with in the tapered junction. Other crucial parameters are those that determine the distance between the center of the head and the tapered junction engagement level (e.g. head offset, adapter sleeve). Caution must be paid in using LDH coupled to small tapered junction, with or without an adapter sleeve.

Fretting Corrosion and Trunnion Wear—Is it Also a Problem for Sleeved Ceramic Heads?

Some modular bearing systems with large diameter metal-on-metal articulation have exhibited higher than usual revisions due to corrosion and metal debris originating from modular metal connections. Large diameter ceramic-on-ceramic bearings exist, which use a titanium alloy adapter sleeve for fixing the ceramic ball head to the stem taper. This study addresses the issue of taper fretting and corrosion for large ceramic bearings with standard and a newly designed experimental setup. While large metal diameter heads have been shown to be a cause for failure of THA, our results demonstrate that large ceramic heads even with a metal adapter sleeve have no effect on corrosion of modular taper connections.

Comparison of Whole-Blood Metal Ion Levels in Four Types of Metal-on-Metal Large-Diameter Femoral Head Total Hip Arthroplasty: The Potential Influence of the Adapter Sleeve

Metal-on-metal bearings, as used in total hip arthroplasty prostheses that have a large-diameter femoral head, were proposed as an option for treating young and active patients with degenerative hip disorders. Despite the theoretical improved performance of large metal articulations with regard to wear, metal ion levels produced by total hip arthroplasty prostheses in which a large-diameter femoral head is used have not been thoroughly evaluated. From 173 eligible patients, 144 patients were allocated to undergo a unilateral total hip arthroplasty with use of metal-on-metal components and a large-diameter femoral head. The purpose of this study was to compare the amount of metal ion release (chromium, cobalt, and titanium) from four different types of prostheses from four different implant manufacturers (Biomet, DePuy, Smith & Nephew, and Zimmer). For cobalt ion levels, a significant difference was found between the different types of total hip arthroplasty prostheses with a large-diameter femoral head at three, six, twelve, and twenty-four months, but only in male patients or patients with a femoral head size of 50 mm or greater. The highest mean cobalt levels at all follow-up periods were observed with the Zimmer implant and the lowest with the Biomet implant. Titanium ion levels were highest in the Zimmer group at all follow-up periods, whereas no difference between groups was found for chromium. At the most recent follow-up, one hip was revised after the development of an adverse local tissue reaction. Of concern was the observation at the time of revision surgery of black metallic deposits inside the adapter sleeve and on the prosthetic femoral neck. This investigation revealed that metal ion release differs greatly between various total hip arthroplasty implants with a large-diameter femoral head. The sources of metal ion production are numerous, but it is hypothesized that wear and corrosion at the junction between the adapter sleeve and the femoral stem in some patients may be responsible for the elevated cobalt ion levels that were found in the Zimmer group. On the other hand, an adapter sleeve made of titanium, such as the one used with the Biomet large-diameter-head total hip arthroplasty, is an unlikely contributor to the release of cobalt ions. Current technology or design of some total hip arthroplasty systems that make use of a large-diameter femoral head may not yet allow the use of modular large heads with a metal-on-metal articulation, especially in young, active male patients whose activities generate high loads at the hip joint. Further research is needed to better understand the favorable design characteristics of modular junctions in metal-on-metal total hip arthroplasty implants that make use of large-diameter femoral heads.

A Tractor-Powered Method for Installing Earth Anchors during Fence Construction

Fencing is an important tool for managing rangelands. However, the cost of conventional fencing is often prohibitive for anything other than boundary or important cross fences (Moore et al. 1968). Suspension fences cost about half as much as conventional fences, and, under many conditions, will turn cattle equally well, last as long, and require less upkeep (McNamee and Kinne 1965). A suspension fence requires strong comer assemblies. A typical comer is double braced with the first brace post guyed to a ‘deadman” (a large object such as a rock or section of post) buried 60 cm deep midway between the corner and first brace post. Installing a deadman is hard, time-consuming work. Under most soil conditions it takes one man approximately 45 minutes per deadman if a power auger is used to dig the hole. This paper describes the adaptation of a tractor-powered post hole digger to screw earth anchors into the soil for use as a deadman, thus reducing the installation time per deadman from 45 to 10 minutes. It also reports on the suitability of earth anchors for holding fence-corner assemblies. The use of a tractor to install screw-in earth anchors requires an adapter to transmit the turning force of the auger power head to the earth anchor. The adapter (Fig. 1) fits on the power head in place of the auger and holds the eye of the earth anchor so that the power head can screw the anchor into the soil. The materials needed to construct the adapter are readily available ih most communities from some of the larger hardware stores (Fig. 1). The earth anchor used with the adapter shown in Figure 1 had an 1 1 / 16-inch (18 mm) rod, a 6-inch (15 cm) helix, and an overall length of 48 inches (122 cm). If an anchor with a different sized eye or rod were used, the dimensions of the adapter would need to be adjusted accordingly. Also, if the shaft of the power-head were different in size than the one used, a different sized adapter sleeve would be needed (Fig. 1). Earth anchors should be lined up and installed before the posts are set; this allows room to operate the tractor. The anchor is started perpendicularly to the ground and turned until the helix is covered by the soil surface. The anchor shaft is then angled towards

An Improved Propulsion System for Short-Range Projection of Immobilization Darts

An adapter and pipe were fitted onto the barrel of a .38 caliber revolver. Powered with a shotshell primer fitted into a modified cartridge case, the device was used to fire 2-cc darts to immobilize captive and trapped collared peccaries (Pecari tajacu). Performance and impact were uniform up to about 10 ft and there was no injury to the animals. The mechanism can be made by a machinist from materials easily available. The immobilization dart manufactured and sold by the Palmer Chemical Co.2 has become a useful and necessary piece of equipment in wildlife research. A lack of uniformity of performance and an unpredictable force of impact have been two serious shortcomings of the dart when fired from the gas-operated pistol or rifle. This has been especially true when captive or trapped animals have been immobilized. We have found that at close range the impact of the dart was difficult to adjust and damage to flesh often resulted. Darts have often bounced out of an animal unless barbed darts were used. To minimize these difficulties when working with captive and trapped animals, we have devised and successfully used a simple adaptation for firing immobilization darts with a uniform impact force up to about 10 ft. The new dart propulsion mechanism includes a metal sleeve adapter which fits over the muzzle of a .38 caliber revolver, a 6-inch length of %-inch galvanized pipe which has been reamed out to about /%inch diameter, and an empty .38 caliber pistol cartridge with a hole in the base into which is inserted a Winchester No. 209 shotshell primer to furnish the power charge. Fig. 1 shows the parts and their arrangement when the gun is ready for firing. The slotted metal sleeve slides back over the muzzle of the revolver. The forward end of the adapter is threaded inside so that the 3/s-inch galvanized pipe can be screwed into it. A turn of the adapter into a wider recess locks the adapter over the front sight of the revolver. The loaded 2-cc dart is then inserted into one end of the 3/8-inch pipe. The pipe is then screwed into the adapter so that the rear end of the dart is just ahead of the muzzle of the revolver. All of the parts necessary for this propulsion system are readily available or can be easily made by a machinist. Because individual revolvers vary in barrel taper, the adapter sleeve should be made by an experienced machinist to fit each gun. It can be made from round, cold finished screw stock or similar machine steel. The galvanized pipe can be reamed out by using any '/2-inch steel power drill. The cartridge case is prepared by first knocking out the spent primer and boring a 1/4-inch hole through the base of the cartridge case. This hole is then reamed out by lightly applying the tip of a '/2-inch high-speed steel countersink drill to the hole to obtain the proper smoothness and bevel. The 345 1 Contribution of the Arizona Cooperative Wildlife Research Unit: University of Arizona, Arizona Game and Fish Department, Wildlife Management Institute, and U. S. Bureau of Sport Fisheries and Wildlife, cooperating. 2 No endorsement of the Palmer Chemical Co. is being given by any of the cooperating agencies. This content downloaded from 157.55.39.144 on Mon, 25 Jul 2016 05:07:00 UTC All use subject to http://about.jstor.org/terms 346 Journal of Wildlife Management, Vol. 31, No. 2, April 1967