Will New Metal Heads Restore Mechanical Integrity of Corroded Trunnions?

BACKGROUND: Metal wear and corrosion from modular junctions in total hip arthroplasty can lead to further unwanted surgery. Trunnion tribocorrosion is recognized as an important contributor to failure. This study was performed to determine if new metal heads restore mechanical integrity of the original modular junction after impaction on corroded trunnions, and assess which variables affect stability of the new interface created at revision total hip arthroplasty. METHODS: Twenty-two trunnions, cobalt-chromium (CoCr) and titanium alloy (TiAIV), (CoCr, n = 12; TiAIV, n = 10) and new metal heads were used, 10 trunnions in pristine condition and 12 with corrosion damage. Test states were performed using an MTS Machine and included the following: 1, Assembly; 2, Disassembly; 3, Assembly; 4, Toggling; and 5, Disassembly. During loading, three-dimensional motion of the head-trunnion junction was measured using a custom jig. RESULTS: There were no statistical differences in the tested mechanical properties between corroded and pristine trunnions implanted with a new metal femoral head. Average micromotion of the head versus trunnion interface was greatest at the start of loading, stabilizing after approximately 50 loading cycles at an average of 30.6 ± 3.2 µm. CONCLUSION: Corrosion at the trunnion does not disrupt mechanical integrity of the junction when a CoCr head is replaced with a CoCr trunnion. However, increased interface motion of a new metal head on a corroded titanium trunnion requires additional study. The evaluation of ball head size on mechanical integrity of trunnions would also be a potential subject of future investigation, as increasing the ball head size at the time of revision is not uncommon in revisions today.

Q-angle and J-sign: indicative of maltracking subgroups in patellofemoral pain.

Mechanical factors related to patellofemoral pain syndrome and maltracking are poorly understood. Clinically, the Q-angle, J-sign, and lateral hypermobility commonly are used to evaluate patellar maltracking. However, these measures have yet to be correlated to specific three-dimensional patellofemoral displacements and rotations. Thus, we tested the hypotheses that increased Q-angle, lateral hypermobility, and J-sign correlate with three-dimensional patellofemoral displacements and rotations. We also determined whether multiple maltracking patterns can be discriminated, based on patellofemoral displacements and rotations. Three-dimensional patellofemoral motion data were acquired during active extension-flexion using dynamic MRI in 30 knees diagnosed with patellofemoral pain and at least one clinical sign of patellar maltracking (Q-angle, lateral hypermobility, or J-sign) and in 37 asymptomatic knees. Although the Q-angle is assumed to indicate lateral patellar subluxation, our data supported a correlation between the Q-angle and medial, not lateral, patellar displacement. We identified two distinct maltracking groups based on patellofemoral lateral-medial displacement, but the same groups could not be discriminated based on standard clinical measures (eg, Q-angle, lateral hypermobility, and J-sign). A more precise definition of abnormal three-dimensional patellofemoral motion, including identifying subgroups in the patellofemoral pain population, may allow more targeted and effective treatments.

McConnell taping shifts the patella inferiorly in patients with patellofemoral pain: a dynamic magnetic resonance imaging study.

BACKGROUND: Patellar taping is widely used clinically to treat patients with patellofemoral pain syndrome (PFPS). Although patellar taping has been demonstrated to reduce patellofemoral pain in patients with PFPS, the kinematic source for this pain reduction has not been identified. OBJECTIVE: The purpose of this study was to quantify the changes in the 6-degrees-of-freedom patellofemoral kinematics due to taping in patients with PFPS. DESIGN: A within-subject design and a sample of convenience were used. PARTICIPANTS: Fourteen volunteers (19 knees) who were diagnosed with patellofemoral pain that was present for a year or longer were included. Each knee had to meet at least 1 of the following inclusion criteria: Q-angle of > or =15 degrees, a positive apprehension test, patellar lateral hypermobility (> or =10 mm), or a positive "J sign." METHODS: Each knee underwent 2 randomly ordered testing conditions (untaped and taped). A full fast-phase contrast (PC) magnetic resonance image set was acquired for each condition while the participants volitionally extended and flexed their knee. Three-dimensional displacements and rotations were calculated through integration of the fast-PC velocity data. Statistical comparisons between baseline patellofemoral kinematics and the change in kinematics due to taping were performed using a 2-tailed paired Student t test. Correlations between baseline patellofemoral kinematics and the change in kinematics due to taping also were quantified. RESULTS: Patellar taping resulted in a significant patellofemoral inferior shift. The strongest correlation existed between the change in lateral-medial displacement with taping and baseline (r=-.60). CONCLUSIONS: The inferior shift in patellar displacement with taping partially explains the previously documented decrease in pain due to increases in contact area. The lack of alteration in 5 of the 6 kinematic variables with taping may have been due to the fact that post-taping kinematic alterations are sensitive to the baseline kinematic values.

Understanding patellofemoral pain with maltracking in the presence of joint laxity: complete 3D in vivo patellofemoral and tibiofemoral kinematics.

Patellofemoral pain is widely accepted as one of the most common pathologies involving the knee, yet the etiology of this pain is still an open debate. Generalized joint laxity has been associated with patellofemoral pain, but is not often discussed as a potential source of patellar maltracking. Thus, the objective of this study was to compare the complete 6 degree of freedom patellofemoral and tibiofemoral kinematics from a group of patients diagnosed with patellofemoral pain syndrome and maltracking to those from an asymptomatic population. The following null hypotheses were tested: kinematic alterations in patellofemoral maltracking are limited to the axial plane; knee joint kinematics are the same in maltrackers with and without generalized joint laxity (defined by a clinical diagnosis of Ehlers Danlos Syndrome); and no correlations exist between tibiofemoral and patellofemoral kinematics or within patellofemoral kinematics. This study demonstrated that alterations in patellofemoral kinematics, associated with patellofemoral pain, are not limited to the axial plane, minimal correlations exist between patellofemoral and tibiofemoral kinematics, and distinct subgroups likely exist within the general population of maltrackers. Being able to identify subgroups correctly within the omnibus diagnosis of patellar maltracking is a crucial step in correctly defining the pathophysiology and the eventual treatment of these patients.