Spontaneous Fractures of a Modern Modular Uncemented Femoral Stem.

BACKGROUND: Femoral stem fracture following total hip arthroplasty is an uncommon event that requires immediate revision surgery. QUESTIONS/PURPOSES: We report on four patients who experienced stem fractures of one design and a review of the US Food and Drug Administration adverse event reports on this design. METHODS: Fracture surfaces of four EMPERION™ (Smith & Nephew, Memphis, TN) femoral stems were analyzed under optical and scanning electron microscopy. A search of the FDA's Manufacturer and User Facility Device Experience (MAUDE) that reports on all EMPERION™ adverse events was completed. RESULTS: Fracture surfaces exhibited characteristics consistent with a fatigue fracture mechanism. Sixteen MAUDE reports claimed stem fracture or breakage of EMPERION™ stems. CONCLUSION: The four cases of EMPERION™ stem fractures were likely driven by small stem diameter, high offset, and high patient weight. Modular stem-sleeve femoral systems are susceptible to fatigue failure under high stress and should only be used in appropriate patients, whom are not considered obese.

Kinematics of passive flexion following balanced and overstuffed fixed bearing unicondylar knee arthroplasty.

INTRODUCTION: Progression of osteoarthritis in the unreplaced compartment following unicondylar knee arthroplasty (UKA) may be hastened if kinematics is disturbed following UKA implantation. The purpose of this study was to analyze tibiofemoral kinematics of the balanced and overstuffed UKA in comparison with the native knee during passive flexion since this is a common clinical assessment. METHODS: Ten cadaveric knees were mounted to robotic manipulator and underwent passive flexion from 0 to 90°. The kinematic pathway was recorded in the native knee and in the balanced, fixed bearing UKA. The medial UKA was implanted using a measured resection technique. Additionally, a one millimeter thicker tibial insert was installed to simulate the effects of overstuffing. Tibial kinematics in relation to the femur was recorded. RESULTS: Following UKA the tibia was externally rotated, and in valgus relative to the native knee near extension. In flexion, installing the UKA caused the knee to be translated medially and anteriorly. The tibia was translated distally through the entire range of flexion after UKA. Compared to the balanced UKA, overstuffing further increased valgus at full extension and distal translation of the tibia from full extension to 45° flexion. CONCLUSIONS: UKA implantation altered tibiofemoral kinematics in all planes. Differences were small; nevertheless, they may affect tibiofemoral loading patterns. CLINICAL RELEVANCE: Alterations in tibiofemoral kinematics following UKA might have implications for prosthesis failure and progression of osteoarthritis in the remaining compartment. Overstuffing should be avoided as it further increased valgus and did not improve the remaining kinematics.

Effect of femoral offset on pain and function after total hip arthroplasty.

The effects of altering patients' femoral offset (FO) during total hip arthroplasty on postoperative pain and function have not been well described. This study compared clinical outcomes as assessed by the Short Form 12 Health Survey and Western Ontario and McMaster University Osteoarthritis Index between patients who had their FOs restored to varying degrees (compared to the contralateral normal hip [CL]). We retrospectively measured postoperative FOs on standard anteroposterior pelvis radiographs and compared to the CL. Patients were categorized into one of 3 groups: decreased offset (< -5 mm compared to CL), normal offset (between -5 and +5 mm), and increased offset (> +5 mm). The decreased offset group exhibited Western Ontario and McMaster University Osteoarthritis Index Physical Function scores that were less than those of the normal offset and increased offset groups (72.03, 82.23, and 79.51, respectively [P = .019]). In conclusion, reducing a patients' native FO led to inferior functional outcome scores.