20 Primary Total Hip Arthroplasty
I. Typical patient complaints:
Pain located in the groin, anterior thigh, lateral thigh, and sometimes buttocks.
Limitations in activities of daily living, such as ambulating longer distances, walking up and down the stairs, putting on socks and shoes, getting up from a sitting position, and getting in and out of a car.
Limp sometimes necessitating assistive devices for ambulation.
In later stages of degenerative joint disease of the hip, patients will awaken at night from pain.
Presentation and duration of symptoms may vary somewhat based on the disease process leading to surgery.
I. Significant limitations in activities of daily living secondary to hip pain and dysfunction.
II. Failure of nonsurgical treatments: activity modification, weight loss, nonsteroidal anti-inflammatory drugs (NSAIDs), physical therapy, and use of assistive devices.
III. Typical disorders presenting for primary total hip arthroplasty (THA) include the following (expand as needed):
Inflammatory arthritides (rheumatoid arthritis, psoriatic arthritis, lupus, etc.).
Posttraumatic degenerative joint disease.
Displaced subcapital femoral neck fracture in active and independent individuals.
Acute THA for acetabular fractures with preexisting arthritis (evolving).
IV. Radiographic changes consistent with end-stage hip degenerative joint disease.
V. Medical optimization and complete preoperative risk assessment has been performed:
All modifiable risk factors (BMI [body mass index], smoking cessation, diabetes, chronic opioid dependence, etc.) need to be optimized.
Expectations, anticipated restrictions, and outcomes discussed preoperatively.
I. Radiographic examination:
Low anteroposterior (AP) pelvis: assess leg lengths, offset, and compare with the other side.
AP of affected hip: typically obtained with a marker for digital templating or to calibrate for acetate templating/planning.
Lateral of affected hip: frog-leg lateral and shoot thru: can assess acetabular version, columns, and femoral deformities.
CT scan: rarely necessary unless there is the need to assess an acute fracture or acetabular anteversion.
MRI: rarely necessary to plan for THA.
II. Degenerative joint disease:
Osteoarthritis: joint space narrowing, subchondral sclerosis, subchondral cysts, osteophyte formation ( Fig. 20.1a).
III. Inflammatory arthropathy:
Rheumatoid and general inflammatory arthritis: symmetric joint space narrowing, periarticular osteopenia, bony erosions, periarticular cysts, and coxa profunda/protrusio acetabuli ( Fig. 20.1b).
Ankylosis spondylitis: symmetric joint space narrowing, protrusio acetabuli, and bony ankylosis.
Interval: sartorius/tensor fascia latae, rectus femoris/gluteus medius.
Dangers: lateral femoral cutaneous nerve, ascending branch of the lateral femoral circumflex artery.
Advantages: extensile to anterior column of the pelvis and true internervous plane.
Disadvantages: difficult femoral exposure, technically demanding, specialized equipment needed, heterotopic ossification, periprosthetic femoral fractures, learning curve.
Can be performed supine on regular table (radiolucent) or on traction/fracture table.
Outcomes: no long-term differences in clinical outcome between direct anterior and posterior approaches 3 , 4 or direct anterior and the direct lateral approaches. 5 , 6 No statistical difference has been described in dislocation rates in direct anterior versus posterior approach (0.84 vs. 0.79%, respectively). 7
II. Anterolateral (Watson–Jones) approach:
Interval: tensor fascia latae/gluteus medius.
Dangers: femoral nerve, branch of superior gluteal nerve, superior gluteal artery.
Advantages: lower dislocation rates, good acetabular and femoral exposure.
Disadvantages: abductor damage—postoperative limp, difficult femoral exposure, technically demanding.
Positioning can be lateral decubitus or supine.
Outcomes: no differences in clinical outcome between anterolateral, direct lateral, and posterior approaches. 8 Dislocation rates have been described as similar rates between anterolateral (3%) and posterior (4%) approaches. Rates of aseptic loosening are reported to be higher in the anterolateral approach (24%) compared to the posterior approach (20%). 9
III. Lateral (Hardinge) approach:
Interval: none. Modified Hardige approach divides the anterior one-third from the posterior two-thirds of the gluteus medius: the split through the gluteus medius can be in line with its fibers straight superiorly, or may involve the anterior one-third of the gluteus medius to minimize muscle damage.
Dangers: femoral nerve, branch of superior gluteal nerve and artery.
Advantages: lowest dislocation rate out of all approaches, good exposure to acetabulum and femur.
Disadvantages: postoperative abductor weakness (Trendelenburg gait, up to 18%), high rate of heterotopic ossification (up to 47%).
Positioning can be lateral decubitus or supine.
Outcomes: no differences in clinical outcome between direct anterior, anterolateral, direct lateral, and posterior approaches. 6 – 8 No significant difference between dislocation rates between posterior (1.3%) and direct lateral surgical (4.2%) approaches has been describeD. The risk of nerve palsy appears to be significantly higher among the direct lateral approaches (20 vs. 2% for the posterior approach). 10
Interval: none: gluteus maximus split.
Dangers: sciatic nerve.
Advantages: abductor preservation, good exposure, easy to extend exposure, low overall complication rates, “workhorse approach.”
Disadvantages: leg length discrepancy (to minimize dislocation risk), risk of foot drop and dislocation.
Outcomes: no differences in clinical outcome between the anterolateral, direct lateral, and posterior approaches. With the advent of a posterior capsular repair, dislocation rates of the posterior approach have been described as 0.79% (vs. 0.84% for direct anterior, vs. 4.2% for direct lateral vs. 3% for anterolateral approaches). 7 – 10
I. Goal: restore native hip biomechanics—offset, leg length, center of femoral head rotation.
Choose appropriate implants—Assess Dorr’s classification 12 :
Dorr’s classification forms the ratio of the inner canal diameter at midportion of the lesser trochanter divided by the diameter 10 cm distal to it.
Dorr A: ratio less than 0.5—consider uncemented stem, with a narrow distal geometry.
Dorr B: ratio 0.5 to 0.75—consider uncemented stem.
Dorr C: ratio greater than 0.75—consider cemented stem.
Determine component positioning:
Acetabulum usually set for 45 degrees of abduction and at the level of the inferior teardrop. Medialize to or near the teardrop.
Femoral neck cut length is measured, assure implant will wedge where coating exits, and assess the need for adjunct reamers.
Restore leg length, femoral offset—use other side if normal.
Assess for limb length and need for shortening osteotomy.
Evaluate any proximal femoral deformities that may need to be addressed.
I. Cemented THA 13 :
Utilizes polymethyl methacrylate (PMMA):
PMMA components 14 :
Liquid MMA monomer.
Powered MMA–styrene copolymer.
Stabilizer/inhibitor: hydroquinone (prevents premature polymerization).
Initiator: dibenzoyl peroxide.
Accelerator: N, N-dimethyl-p-toluidine (encourages polymer and monomer to polymerize at room temperature).
Opacifying agents: zirconium dioxide (ZrO2) or barium sulfate (BaSO4).
Mixing of liquid MMA monomer and a powered MMA-styrene copolymer results in exothermic polymerization around the prepolymerized powder particles, generating a “PMMA grout.”
Stronger in compression than tension.
Produces interlocking between surfaces (“grout”).
First described by Gluck in 1891 and popularized by Charnley in the 1950s.
Dorr’s type C femur ( Fig. 20.3 ).
Elderly patients with osteoporotic bone.
Controversial for acetabular component fixation due to higher rate of loosening at 9 to 12 years (31% cemented vs. 0% cementless). 15
First: hand mixed and finger packed.
Second: cement restrictor, cement gun, and canal preparation.
Third: vacuum mixing and cement pressurization.
Fourth: heating the stem—greater interface shear strength of stem–cement interface, improvement of fatigue lifetimes, and decrease in interface porosity. 16
Avoid varus positioning of the stem.
Increased rate of fracture with mantle less than 2 mm.
Radiographic grading of the femoral cement technique 17 :
i. Grade A: complete filling of medullary canal (“white out”).
ii. Grade B: minimal radiolucency at the bone–cement interface.
iii. Grade C:
C1: radiolucency greater than 50% at the bone–cement interface.
C2: mantle less than 1 mm thick or stem touches bone.
iv. Grade D: major defects in the mantle, or multiple large voids in the mantle, no cement distal to the stem tip.
i. Polished: Ra less than 1 µm, minimal abrasion, allows for stem subsidence and compressive loading of the cement mantle.
ii. Matte: Ra less than 2 µm, no excessive abrasion unless micromotion, mechanical interlocking with cement.
iii. Rough: Ra greater than 2 µm, excessive abrasion.
iv. Outcomes: increased aseptic loosening with matte finish (10% at 10 years vs. 4% at 20 years with polished stem). 20
i. Smooth surfaces without sharp edges to avoid stress concentration on implant–cement interface.
ii. Wider laterally than medially to diffuse the compressive loads medially and tapered from proximal to distal to allow for subsidence within the cement mantle (“triple taper concept”).
iii. Mostly cobalt–chromium alloy stems → stiffer, generate less particulate debris than titanium implants (compared with mostly titanium implants in uncemented femoral stems).
II. Cementless THA stems and cups:
Biologic fixation in which bone formation secures the implant:
Bone ingrowth: bone grows into the porous coating.
Bone ongrowth: bone grows onto the roughened surface (grit blasting vs. plasma spraying):
Grit blasting: abrasive particles (aluminum oxide or corundum) create a textured surface.
Plasma spraying: molten material is sprayed onto an implant to create a more textured surface.
Hydroxyapatite (calcium phosphate compound): osteoconductive surface sprayed onto implant enhances bone growth.
First FDA (Food and Drug Administration) approved implant in 1983 (anatomic medullary locking [AML] stem).
In 2012, over 90% of THA in the United States were cementless.
Press-fit: implant slightly larger than prepared surface (0.5–1 mm):
Increased risk of fracture.
Line-to-line: implant size equal to prepared surface.
Biologic fixation and optimization (latest data show, for new implants is 60 to 70% porosity, interconnecting pores and pore sizes approximately 200 to 400 µm):
Pore size: 50 to 150 µm.
Porosity: 40 to 50%.
Gaps: less than 50 µm.
Micromotion: less than 150 µm.
Coefficient of friction: would like to be close to 1; it is ideal for the early fixation to have a coefficient of friction that will aid in limiting early micromotion.
Historically all-polyethylene cemented acetabular components were used.
It transitioned to noncemented acetabular components in the 1980s and has shown greater than 90% survivorship.
Contemporary components utilize a titanium porous coating:
i. Screw fixation is optional depending on stability.
ii. Hydroxyapatite coating may enhance bone ongrowth but use has been limited by cost.
Names of sections of a femoral stem include:
i. Head, neck, trunnion, body.
Standard/primary femoral components:
i. Neck sparing stems: preserve bone and may limit stress shielding.
ii. Single taper stems (blade type): metaphyseal fixation.
iii. Double taper stems: metaphyseal fixation.
iv. Extensively porous-coated stems: metaphyseal/diaphyseal fixation:
May increase stress shielding.
Often laterality specific with anteversion built in to the prosthesis.
v. Anatomic stems: metaphyseal/diaphyseal fixation.
vi. Excellent clinical results with each subtype of noncemented femoral stems.
i. In addition to modular heads, these implants incorporate at least one additional modular interface: may include stem, body, neck, and head.
ii. Allow for adjustment of femoral version, offset, length.
iii. Disadvantage: increased potential for motion, corrosion, and failure at additional interfaces, and price.