INTRODUCTION

Component impingement in total hip arthroplasty (THA) can cause implant damage or dislocation. Dual mobility (DM) implants are thought to reduce dislocation risk, but impingement on metal acetabular bearings may cause femoral component notching. We studied the prevalence of (and risk factors for) femoral notching with DM across two institutions.

Introduction

The success of total knee arthroplasty (TKA) necessitates precise osteotomies and soft tissue balancing to realign the lower extremity to a neutral mechanical axis. While technological advances have facilitated precise osteotomies, soft tissue balancing has traditionally relied mostly on surgeons’ subjective and variable tactile feedback. As soft tissue imbalance accounts for 35% of early TKA revisions in North America, we aimed to compare outcomes when TKA was balanced free-hand versus a sensor-guided balancing device (VERASENSE, OrthoSensor, Inc (Dania, FL)).

Summary Statement

The modulation of both quantity and quality of peri-implant bone with either PTH or loading may be viable options to improve implant fixation and patient outcomes.

A strong bone-implant interface is essential for successful joint replacement surgery. This study investigated the differences in bone surrounding and within a porous titanium implant after single or combined treatment with two anabolic bone therapies: intermittent parathyroid hormone (teriparatide) and mechanical loading. Porous titanium implants were inserted bilaterally on the distal lateral femurs of rabbits. The right implant was loaded daily (1 MPa, 50 cycles/day) while the left implant was not. Rabbits received daily PTH injections (20 ug/kg) or saline vehicle. Periprosthetic cancellous bone 0.5, 1.0, and 2.0 mm below the implant surface, bone at the 0.25 mm bone-implant interface and total bone within each implant were examined using tissue-level analyses (quantitative backscattered electron microscopy), cellular analyses (immunohistochemistry staining of osteoblasts with procollagen-1 and TRAP staining of osteoclasts), and shear testing (implant-bone interface).

Statistical significance was determined using GEE models (p<0.05). For tissue located 0.5 mm below the implant, significant increases in bone area per total area (BA/TA) were observed with PTH treatment (56%) and with loading (27%). Further, an 18% increase in mineralization density with PTH treatment and a 20% increase in mineralization density with loading was found. Loading effects were not present beyond the 0.5 mm periprosthetic region, but PTH significantly increased BA/TA 2.0 mm below and mineralization density 1.0 mm below the implant. Tissue-level changes were supported by increases in osteoblast activity 0.5 mm below the implant with PTH (79%) and loading (34%), as well as by minimal osteoclast changes. At the 0.25 mm implant-bone interface PTH and loading increased BA/TA (16% and 23%, respectively), but only loading increased mineralization density (7%). Further, total integrated bone area was increased 35% with PTH.

Both PTH and loading enhanced the mechanical integrity of the implant-bone; shear strength increased 34% and 60%, respectively. Although combined treatment was not synergistic, both PTH and loading individually enhanced the amount and mineralization density of bone at the implant interface and immediately below the interface, thereby increasing the mechanical strength of the metal-bone interface. This research suggests that modulation of both quantity and quality of peri-implant bone may be viable options to improve implant fixation and patient outcomes.

Introduction

Traditional methods of component positioning in total hip replacement (THR) utilize mechanical alignment guides which estimate position relative to the plane of the operating room table. However, variations in pelvic tilt alter the relationship between the anatomic plane of the pelvis and that of the table such that components placed in optimal position relative the table may not land within the classic anatomic “safe zone” described by Lewinnek. It has been suggested that navigation software should incorporate adjustments for the degree of pelvic tilt. Current imageless navigation software has this capability, however there is a paucity of data regarding the accuracy of this technology.