CAUSES , FEATURES AND TREATMENT OF LOOSENING IN THR

LOOSENING SEPTIC ASEPTIC ACETABULAR FEMORAL CEMENTED CEMENTLESS

INTRODUCTION Is a radiographically demonstrable change in the mechanical integrity of the load-carrying cemented femoral component, specifically, fractured cement and an intersurface gap that produces a radiolucent zone in the cement-stem or cement-bone interface. Usually, loosening of a total hip prosthesis is accompanied by increasing pain, and by distinct radiological changes. Second most common indication for revision of total hip arthroplasty.

CAUSES Septic (Infections) Aseptic – Theories proposed Sensitivity to wear debris caused by motion of an improperly fixed implant. Improper techniques. Improper implants.

SYMPTOMS A painful hip that restricts the patient’s daily activities severely. “ Start up pain” Lasting and / or increasing pain in the hip. Stiffness (restriction of movements). NOTE: Patients with well functioning total hips may have  signs of loosening whereas there are patients with loose painful and stiff hip joints who do not have signs of loosening on plain radiographs.

DIAGNOSIS Periodic radiographic inspection of the implants, cement, bone and the interfaces. Special X-ray method called X-ray stereofotogrammetry . Zones as described by Gruen et al and DeLee and Charnley.

FEMORAL LOOSENING Standardized techniques and positioning of the limb to be used while taking radiograph. Cemented femoral components – list of radiographic changes diagnostic of loosening. 1. Radiolucency between the superolateral one third of the stem and the adjacent cement mantle, indicating debonding of the stem from the cement and possible early deformation of the stem.

FEMORAL LOOSENING(cntd..) 2. Radiolucency between the cement mantle and surrounding bone. 3. Subsidence of the entire cement mantle and stem or migration of the stem into the cement mantle, resulting in a more distal position of the collar or platform in relation to the proximal surface of the cement and the femoral neck. 4. Change of the femoral stem into a more varus position.

FEMORAL LOOSENING(cntd..) 5. Areas of rarefaction or fragmentation of the cement, especially between the superomedial aspect of the stem and the femoral neck or in areas of thin cement mantle. 6. Fracture of the cement mantle, most commonly near the tip of the stem. 7. Deformation of the stem in the anteroposterior or lateral radiographs. 8. Incomplete or complete failure (fracture) of the stem

FEMORAL LOOSENING

INNOCENT vs OMINOUS RADIOLUCENT LINES

FEATURES AND CAUSES OF INNOCENT RADIOLUCENT LINES Thin less than 2 millimeters thick Do not change on serial radiographs Can be due to cancellous bone that was not completely removed at surgery. Normal age related expansion of femoral canal and thinning of the femoral cortex.(0.33 mm/yr and 0.14 mm/yr)

MECHANISM Mechanical Debonding of the stem from the cement and cement fracture. Development of a fibrous membrane between the cement and the bone is a biological response to debris generated from the mechanical initiating factors.

MECHANISM

PISTONING

MEDIAL STEM PIVOT

CALCAR PIVOT

CANTILEVER BENDING

TECHNICAL PROBLEMS RELATED TO STEM LOOSENING    Failure to remove the soft cancellous bone from the medial surface of the femoral neck; consequently, the column of cement does not rest on dense cancellous or cortical bone and support the stem. The cement is subjected to greater tensile forces and fractures more easily.

PROBLEMS    Failure to provide a cement mantle of adequate thickness around the entire stem; a thin column cracks easily. The tip of the stem should be supported by a plug of cement because this part of the stem is subjected to axial loading.

PROBLEMS   Removal of all trabecular bone from the canal, leaving a smooth surface with no capacity for cement intrusion or failure to roughen areas of smooth neocortex that surrounded previous implants.   Inadequate quantity of cement and failure to keep the bolus of cement intact to avoid lamination.

PROBLEMS   Failure to pressurize the cement, resulting in inadequate flow of cement into the interstices of the bone.   Failure to prevent stem motion while the cement is hardening.   Failure to position the component in a neutral alignment or centralized within the femoral canal.

PROBLEMS The presence of voids in the cement as a result of poor mixing or injecting technique or allowing blood or fragments of bone to be mixed in the cement.

Grading system for the femoral component cement mantle Grade A - Complete filling of the medullary canal without radiolucencies (“white-out”)

Barrack , Mulroy and Harris Grading Grade B – Slight radiolucency at bone cement interface ( < 50%) Grade C – Radiolucency surrounding 50-90% or any cement mantle defect. Grade D - Complete lucency on any projection or a defect of the mantle at the tip of the stem

CEMENTLESS FEMORAL COMPONENTS Engh and Bobyn proposed a simple classification system for implant fixation. Classified as Bone ingrowth Stable fibrous fixation unstable

BONE INGROWTH Defined as an implant with no subsidence and minimal or no radiopaque line formation around the stem. Appears stable Cortical hypertrophy Stress shielding

STABLE FIBROUS FIXATION No progressive migration occurs but an extensive radiopaque line forms around the stem. Lines are parallel and space of upto 1 mm. No local hypertrophy.

UNSTABLE Progressive subsidence or migration within the canal and is at least partially surrounded by divergent radiopaque lines that are more widely separated from the stem at its extremities. Inc cortical density and thickenning.

ACETABULAR LOOSENING Cemented Acetabular components – List of radiologic findings suggesting loosening.   Absorption of bone from around part or all of the cement mantle and an increase in the width of the area of absorption, which is especially significant if more than 2 mm wide and progressive 6 months or more after surgery.

ACETABULAR LOOSENING   Superior or medial migration and protrusion of the cement mantle and cup into the pelvis; also, fracture of the medial cortex of the acetabulum.   Change in the angle of inclination or the degree of anteversion of the cup, indicating component migration.   Wear of the cup, as indicated by a decrease in the distance between the surface of the head and the periphery of the cup.

ACETABULAR LOOSENING Fracture of the cup and cement (both rare).    A radiolucency 2 mm wide with or without a surrounding fine line of density, which may develop in one or more of the three zones around the cement mass in the pelvis .

TECHNICAL PROBLEMS CAUSING CUP LOOSENING   Inadequate support of the cup by the surrounding bone and cement. Failure to remove all of the cartilage, loose bone fragments, fibrous tissue, and blood, and failure to make a sufficient number of holes in the acetabulum so that the surface will be irregular enough to secure a good cement-bone bond.

CUP LOOSENING Failure to pressurize the cement adequately to obtain an optimal cement-bone bond. Failure to distribute the cement about the entire outer surface of the cup. Movement of the cup or cement mantle while the cement is hardening. Movement of a relatively small cup while it is held in a large cement mantle in a large acetabulum.

CEMENTLESS ACETABULAR COMPONENTS Uncommon finding with follow-up of up to 10 years. It must be remembered that loosening of cemented acetabular components begins to escalate at approximately 10 years.

OSTEOLYSIS Particles of metal, cement, and polyethylene all can produce periprosthetic osteolysis. Mechanism of production of osteolysis – the generation of wear particles. the access of these particles to the periprosthetic bone. the cellular response to the particulate debris.

MECHANISM

HISTOLOGY OF OSTEOLYSIS A synovial-like membrane surrounding loose total hip components. Membrane contains macrophages and had the capacity to produce large amounts of collagenase and prostaglandin E2. High levels of IL-1, IL-6 AND TNF.

PATTERNS OF OSTEOLYSIS LINEAR – Expand around the periphery of the whole prosthesis. “loose prosthesis” Expansile – Begins at a small spot and expands into the bskeleton away from the prosthesis. ( not loose)

Mx OF SILENT OSTEOLYSIS ROUTINE CT SCAN FOR ALL AFTER 6-7 YRS negative positive Follow with regular xrays. Rpt CT in one yr. MODERATE EXTENSION THEN RPT CT IN ONE YR. AND START DRUGS . SEVERE EXTENSION THEN REVISION OPERATION

MATERIALS AND METHODS OF REVISION OPERATIONS. Shafts are longer and bulkier. Metal backed cups with plates and screws for better anchorage.

BONE TRANSPLANTAION IN REVISIONS. IMPACTION BONE GRAFTING

Wear- volumetric analysis

DECREASING THE GENERATION OF WEAR DEBRIS. Passivation One of the most imp ways of decreasing the chances of loosening. Methods include passivation and ion implantation of the implants. Corrosion resistant oxide layer formed over metal alloy in passivation.

ION IMPLANTATION Ion implantation is a process, performed in a vacuum, of hardening the surface that uses energized ions blasted into the surface of the metal alloy.

REFERENCES CAMPBELL’S OPERATIVE ORTHOPEDICS – 10TH AND 11TH EDITIONS. Sensitivity to metal as a possible cause of sterile loosening after cobalt-chromium total hip-replacement arthroplasty. - J Bone Joint Surg Am. 1977;59:164-168. Aseptic loosening in total hip arthroplasty secondary to osteolysis induced by wear debris from titanium-alloy modular femoral heads.- J Bone Joint Surg Am. 1989;71:1337-1342.