Assessing Taper Geometry, Head Size, Head Material, and Their Interactions in Taper Fretting Corrosion of Retrieved Total Hip Arthroplasty Implants.

BACKGROUND: Decreased fretting and corrosion damage at the taper interface of retrieved ceramic-on-polyethylene total hip arthroplasty (THA) implants has been consistently reported; however, resultant fretting corrosion as a function of femoral head size and taper geometry has not been definitively explained. METHODS: Eight cohorts were defined from 157 retrieved THA implants based on femoral head composition (n = 95, zirconia-toughened alumina, ZTA vs n = 62, cobalt-chromium alloy, CoCr), head size (n = 56, 32mm vs n = 101, 36mm), and taper geometry (n = 84, 12/14 vs n = 73, V40). THA implants were evaluated and graded for taper fretting and corrosion. Data were statistically analyzed, including via a 23 factorial modeling. RESULTS: Factorial-based analysis indicated the significant factors related to both resultant (summed) fretting and corrosion damage were head material and taper geometry; head material-taper geometry interaction was also a significant factor in resultant corrosion damage. Lower rates of moderate-to-severe fretting and corrosion damage were exhibited on ZTA heads (ZTA = 13%, CoCr = 38%), smaller heads (32mm = 18%, 36mm = 26%), and 12/14 tapers (12/14 = 13%, V40 = 35%). ZTA+32mm heads demonstrated the lowest rates of moderate-to-severe fretting and corrosion damage (12/14 = 2%, V40 = 7%), whereas CoCr heads with V40 tapers demonstrated the greatest rates of moderate-to-severe damage (32mm = 47%, 36mm = 59%). CONCLUSION: In this series, retrieved implants with ZTA, 32-mm heads paired with 12/14 tapers exhibited lower rates of moderate-to-severe damage. Factorial analysis showed head material, taper geometry, and their interactions were the most significant factors associated with resultant damage grades. Isolating implant features may provide additional information regarding factors leading to fretting and corrosion damage in THA. LEVEL OF EVIDENCE: IV (case series).

Biomechanical Comparison of Bicortical, Unicortical, and Unicortical Far-Cortex-Abutting Screw Fixations in Plated Comminuted Midshaft Clavicle Fractures.

PURPOSE: The objective of this study was to assess the biomechanical properties of bicortical locking screws, unicortical locking screws, and unicortical far-cortex-abutting locking screw fixation in a cadaver model of comminuted midshaft clavicle fractures stabilized with a locking plate placed on the superior surface of the clavicle. METHODS: Nine pairs of adult fresh-frozen cadaver clavicles were allocated into 3 groups for either bicortical, unicortical, or unicortical far-cortex-abutting locking plate fixation. After a 1-cm osteotomy to simulate a comminuted fracture and instrumentation with an 8-hole locking plate placed on the superior surface of the clavicle, the specimens were mounted in a custom dual-gimbal fixture in a materials-testing system and tested in axial compression, torsional, and torsional load to failure. RESULTS: Axial stiffness and axial osteotomy site stiffness did not demonstrate differences between constructs. In cyclical torsion, both the bicortical and the unicortical far-cortex-abutting constructs were significantly stiffer than the unicortical construct. For torsional failure stiffness, both the bicortical and the unicortical far-cortex-abutting constructs were significantly stiffer than the unicortical construct. There was no difference between bicortical and unicortical far-cortex-abutting for torsional failure stiffness. The bicortical construct exhibited significantly higher peak failure torque compared with the unicortical construct. CONCLUSIONS: Unicortical far-cortex-abutting locking screw fixation provides comparable mechanical properties under axial and torsional loads to bicortical fixation, without penetrating the far cortex. CLINICAL RELEVANCE: Unicortical far-cortex-abutting locking screw fixation obviates far cortex penetration, and thereby protects nearby anatomical structures, may ease symptomatic implant removal, alleviates refracture risk, and eases conversion to bicortical fixation in the case of revision surgery.