ORT Hip Week
Hips are made of:
-Cobalt Chrome (more common in knee) -Titanium Alloy (more common in hips) - made for press fit
Results of increase in Anatomic Offset:
-Extensor, Adductor, and Abductor Tension -May increase wear characteristics -Adduction and/or Extension Contracture
Femoral Neck Angle
-Formed by the intersection of the Femoral Axis and the Femoral Neck Axis -Neck shaft angle average is about 124.7 deg. (Range 105 to 155 deg) -Change in Neck Angle causes the Leg Length and Offset to change
Porous Coating Examples
-Sintered Beads -Plasma Spray
Results of reduction in Anatomic Offset:
-acetabular/femoral head joint instability can lead to dislocation and ultimately a Revision -Extensor, Adductor and Abductor Laxity which can lead imbalance of a JRF
Reasons Hips Fail
-aseptic loosening (26.5%) -infection of the joint (17.7%) -fracture of the bone (19.5%) -unstable joint/dislocations (21.6%) -wear of one or more of the implants -breakage of the implant *** -pain
2 Types of Ceramic
1) Biolox Delta (pinky) 2) Biolox Forte (peachy)
3 Neck Angles
1) Coxa Vera (< 120 degrees) 2) Normal (120-135 degrees) 3) Coxa Valga (>135 degrees)
3 Types of Acetabulum Implants
1) solid 2) cluster 3) multi hole all are sized from 46-64 degrees with increase in 2mm incrimints
3 Approaches to enter Hip Joint
1) straight anterior approach 2)
Avascular Necrosis
AVN - when not enough blood gets to the femoral head. When that happens, the femoral head may die.
ARMD
Adverse Reaction to Metal Debris Tissue reacting to metal wear (Metal on Metal - MOM)
Joint Reaction Force
Balance of forces across the hip joint.
Size and shape of native canal:
Chili Pepper (metaphyseal fit) Taper Wedge (proximal fit) AML (proximal & distal fit)
Sir John Charnley
Combination of 3 components: • Metal hip stem • Polyethylene acetabular component • Bone cement Promoted low friction approach. The use of a small femoral head reduces wear due to its' smaller surface area Father of Modern Joint Arthroplasty
Greater Trochertaric Plate
Designed to fixate the greater troc back onto the femur
Who pioneered what we call today Total Hip Arthroplasty (THA)?
Dr. Charnley
T/F: 12/14 tapers are all the same and any manufacture's head with a 12/14 ID taper can be used on any company's stem.
False
T/F: Every company has an anatomical dual mobility cup for the left and right.
False, only Stryker does. As opposed to a 1 piece cup it is a two piece cup.
12/14 Tapers
Head to trunnion tapers have settled on 12/14, however there is a significant design in each companies 12/14 taper and head swapping is NOT recommended in the industry. Poor contact with the taper and trunnion will cause fretting and can lead to osteolysis
Femoral Offset
Horizontal distance between the femoral head center and the femoral axis (anatomic axis). • Average offset is about 43.9mm (27 to 57mm) -if offset is incorrect, muscles will be too loose and create chance of dislocation or muscles will be too tight and cause wear/pain
Extensor, Adductor and Abductor Laxity which can lead imbalance of _________________.
Joint Reaction Force (JFR)
Femoral Acetabular Impingement (FAI)
Labral tear of the femur 1) Examiner instructs patient to flex the knee and hip 90 degrees 2) Examiner adducts and internally rotates femoral head. Positive - patient complains of pain radiating to groin of affected side. Indicates impingement of femoral head into the acetabulum (OA, osteophytes, congenital irregular of femoral head or acetabulum).
Larger head size
Larger heads provide greater stability Larger surface area of contact For any given size, a larger head reduces poly thickness
Femoral Neck Length
Measured from level of neck resection to Femoral head center, along femoral neck axis.
Femoral Leg Length
Measured vertically, from the level of the medial neck resection, often referred to as the Calcar, to the femoral head center.
ingrowth vs ongrowth
Ongrowth: 2D like plasma spray (think stucco)
Cup Position Anteversion
Recommended 20 - 25 degrees
Cup Position Abduction
Recommended 40 - 45 degrees
Themistocles Gluck
Replaced fractured hips with Ivory prostheses in the 1880s
Acetabular - Femoral head joint instability can lead to dislocation and ultimately _______________.
Revision
Companies with Dual Mobility Acetabular:
Smith&Nephew Zimmer DePuysynthes Stryker
Most popular size/shape of canal:
Taper Wedge (proximal fit)
Osteolysis
The destruction of bone due to a biologic reaction to wear debris (such as cement mantle breaking down). Only possible if poly is present.
T/F: Leg length increase when offset increases.
True
T/F: The greater the neck angle, the stronger the implant.
True
T/F: The lower the neck angle, the offset increases.
True
What is the standard type of plastic used in THA (before cross linking or Vitamin A)?
UHMWPE (poly)
Peri-Prosthetic Fractures
a broken bone that occurs around the implants of a total hip replacement. It is a serious complication that most often requires surgery.
Legg-Perthes Disease
a childhood condition that occurs when blood supply to the ball part (femoral head) of the hip joint is temporarily interrupted and the bone begins to die. This weakened bone gradually breaks apart and can lose its round shape.
Leg Length Discrepancy
a source of patient dissatisfaction • One of the most common reasons for litigation • Impacts function and pain
Average Offset
about 43.9mm (27 to 57mm)
Protrusio
an uncommon defect of the acetabulum. When the acetabulum begin to wear at the bone and enter the "pooper" region.
Cemented stems are typically made of ___________ while cement-less stems are usually made of _______.
cobalt chrome, titanium
Jump Distance
distance the femoral head has to travel to dislocate
Iliotibial Band (IT Band)
if too tight, can cause hip and/or knee problems muscle from lateral hip to knee
Aplasia of the Acetabulum
inadequate development of the acetabulum which is "shallow" and "dish shaped" rather than cup shaped
Most common cause of revision THA was ____________.
instability / dislocation (22.5%), followed by mechanical loosening (19.7%), and infection (14.8%).
Rheumatoid Arthritiis
most common in knee and hip
Osteoarthritis
most common in knees and hips
Retroversion
movement of hip inward - internal rotation A decrease in the angle between the femoral neck and posterior condyles (Head twisted backward )
Anteversion
movement of hip outward - external rotation Femoral anteversion of 10°-20° along with acetabular anteversion provides inherent stability to the hip joint An increase in the angle between the femoral neck and posterior condyles (Head twisted forward )
Leg length is synonymous with ____________ ___________.
neck angle
Neck angle changes the ________
offset.
Most likely technique for THA:
pressfit acetabulum pressfit femur metal head crosslink poly
Broaching
shaping femur to match hip implant
Modular Dual Mobility
the acetabulum cup has a liner (modular second piece - metal back piece of liner as opposed to a piece of poly). the ball and liner articulate. primary articulation is the ball. secondary articulation is the liner within the initial cup.
Bipolar Movement of the Implant
the acetabulum cup is articulating in the acetabulum and the ball is also articulating in the poly of the acetabulum cup
Indo Movement of the Implant
the acetabulum cup is articulating in the acetabulum, but the ball does not move within the acetabulum cup
Head Center (aka Pivot Point)
the goal of surgery is to duplicate this point as closely as possible. Is the center of the universe in Hip Biomechanics
Stress shielding
the phenomenon where an implanted device shields the bone from exposure to normal physiological loads, typically leading to bone resorption/disappearance.
Closed Reduction
when the hip implant is dislocated, so is relocated (reduced) without opening the patient
Calcar
where the femoral head meets the femur neck/femur made of very thick and hard cortical bone - it is very hard because it is weight bearing due to Wolfe's Law the start of the mechanical axis
Dr. Engh
• "Press-Fit" or "Porous Coating" • Designed Depuy AML • First Porous Coated Cementless Hip Stem • Designed for "Standard of Care" • Can accommodate most patients • Several design philosophies • Can be modular
Technical Challenges in Revisions of THA
• Elderly & Debilitated Patients • Compromise Soft Tissues • Inadequate Metabolic Reserves • Poor Bone Stock
Objectives of THA:
• Increase stability • Reduce wear • Increase ROM • Help make surgical experience simpler
Neck Resection Level
• Set according to pre-operative templating • Many surgeons will use "one finger proximal (above) to Lesser Troch" to determine neck resection, intraoperatively
Acetabular Shells
• Solid • Cluster Hole • Multi hole • Spiked
Dorr Classification
• Type A: narrow canal with thick cortical walls (champagne flute canal) •Type B: moderate cortical walls •Type C: wide canal with thin cortical walls (stove-pipe canal) - most problematic
Factors of success in a THA:
•Leg length •Offset •Version of femur & cup •Center of rotation
