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Musculoskeletal > Surgical management of hip dysplasia > Flashcards

Surgical management of hip dysplasia Flashcards

1
Q

What are prophylactic surgical options for hip dysplasia?

A

Pubic symphysiodesis, TPO, DPO

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2
Q

At what age does complete ossification of the pubic symphysis occur?

A

2-6 years

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3
Q

What is pubic symphysiodesis?

A

The application of electrosurgery to the hyaline cartilage of the pubic symphysis resulting in heat-induced necrosis of the germinal chrondrocytes.

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4
Q

What is the result of pubic symphysiodesis?

A

Closure of the pubic symphysis with shortening of the pubic ramus and unrestrained dorsal growth. Result is external rotation of the acetabulae in a ventrolateral axial direction.

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5
Q

At what age should pubic symphysiodesis be performed?

A

12-20 weeks of age. Unlikely to be effective in very severely affected dogs as determined by excessive distraction index.

The younger the puppy the greater the change in femoral head angle.

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6
Q

What is the surgical approach for pubic symphysiodesis?

A

Ventral approach. The origins of the adductor and gracilis muscles are elevated from the symphysis. A small incision is made in the cranial aspect of the pubic symphyseal brim, allowing introduction of a finer or sterile wood spatula to protect the urethra.

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7
Q

How much of the pubic symphysis is cauterized in pubic symphysiodesis?

A

The cranial 1/3 to 1/2

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8
Q

What radiographic changes are expected after successful pubic symphysiodesis?

A

Note: procedure does not result in reduction of pelvic canal width.

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9
Q

What are the most common complications associated with pubic symphysiodesis?

A

Lack of efficacy most common. Theoretical risk of thermal damage to the rectum or urethra, but not reported.

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10
Q

What is the goal of pelvic osteotomy procedures (TPO/DPO)?

A

Axial rotation and lateralization of the acetabulum to provide greater dorsal coverage of the femoral head and improved joint congruence.

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11
Q

What is the difference between TPO and DPO?

A

TPO includes osteotomy of the ilium, pubis and ischium, whereas DPO only includes osteotomy of the ilium and pubis.

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12
Q

What is the recommended age for patients undergoing TPO or DPO?

A

Less than 10 months to 1 year. Should have no evidence of osteoarthritis or hip luxation.

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13
Q

What is the surgical approach to DPO/TPO?

A

Lateral recumbency.

Pubic osteotomy performed first at the level of the tendon of origin of the pectineus at the iliopectineal eminence. Dissection of the cranial abdominal muscle cranially should be limited to prevent caudal abdominal hernia.

Ischial osteotomy performed second (TPO) via elevation of the internal obturator muscle dorsally, and the semimembranosus, semitendinosus, and external obturator ventrally.

The ilial osteotomy is performed last via lateral gluteal roll-up, just caudal to the sacroiliac joint.

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14
Q

What instrument is depicted?

A

A rotation bar for rotation of the caudal ilial segment during TPO/DPO.

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15
Q

What angles of TPO and DPO plate are commonly available?

A

TPO: 20, 30, 40 degrees
DPO: 25 and 30 degrees

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16
Q

Should the DPO be rotated slightly more or less than the TPO?

A

Slightly more (by 5 degrees) due to the intact ischium that may limit rotation

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17
Q

How is the ideal angle of rotation for the DPO or TPO determined?

A

Ideally 5 degrees more than the angle of subluxation as determined by Ortolani testing. There is no benefit to rotating more than 40 degrees (may increase risk of complications including narrowing of pelvic canal, impingement of the dorsal acetabular rim on the femoral neck)

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18
Q

What can be transected to improve rotation of the caudal segment in DPO?

A

Sacrotuberous ligament.

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19
Q

What are the most common complications associated with DPO and TPO?

A

Screw loosening and pelvic canal narrowing (more likely in TPO than DPO). Bilateral TPO can result in severe pelvic canal narrowing.

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20
Q

What can be used to reduce the risk of screw loosening/pull-out in TPO/DPO procedures?

A

Use of locking implants, increased penetration of the sacrum with the cranial screw holes (although reports are mixed), addition of a ventral plate.

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21
Q

What implants are shown?

A

DPO plates

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22
Q

What materials are most commonly used for total hip replacement components?

A
  1. 316L stainless steel (molybdenum, iron, nickel and chromium, low carbon): rarely used.
  2. Cobalt chromium (chromium, molybdenum and nickel): very hard and excellent wear resistance, hard to machine. [Biomedtrix BFX and CFX implants].
  3. Titanium: inadequate strength for load bearing. Can be used as an alloy but prone to wear debris. [Zurich cementless implants].
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23
Q

What is the impact of material elastic modulus on stress shielding or wear debris?

A

The greater the difference between the elastic modulus of the material and the bone or bone cement the greater the propensity for stress shielding or wear debris.

Stainless steel and cobalt chromium prostheses (200 GPa) have a much higher elastic modulus than titanium (100 GPa).

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24
Q

What is stress shielding?

A

When the difference in elastic modulus between the bone and implant is too great, the bone is protected from stress. It consequently undergoes disuse atrophy which may result in implant loosening.

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25
Q

What are the types of wear debris?

A
  1. Abrasion: irregularities on a hard surface damage the opposing surface.
  2. Adhesion: material from the softer bearing surface is transferred to the opposing surface.
  3. Fatigue: consequence of cyclic loading.
  4. Erosion:
    a - impingement: implant to implant contact or implant to bone contact.
    b - solid particle: impact of suspended particles on a surface.
  5. Corrosion
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26
Q

What are the consequences of wear debris?

A

Osteolysis and aseptic loosening

27
Q

What is the most common type of material articulation used in veterinary total hip implants?

A

UHMW polyethylene is most commonly used for the acetabular cup components.

Femoral heads are predominantly composed of cobalt chromium or titanium with a coating. Cobalt chromium generates less wear debris than titanium but it is more inflammatory.

Ceramic-on-ceramic implants are very hard and may produce less wear debris, but are not currently commercially available. Squeaking may occur.

28
Q

What are the main classifications of total hip prostheses based on immediate fixation technique?

A

Cementless, cemented (PMMA), hybrid.

In cemented implants the cement must withstand shear stresses, whereas with a press-fit implant compressive forces at the interface must be greater than shear stresses.

29
Q

What are the two types of osseointegration?

A

Bone ingrowth (porous surface) and bone ongrowth (roughened surface texture).

30
Q

What are some third generation cementing techniques used to improve the cement-bone interface?

A

Pulsatile lavage, centrifugation, pressurization

31
Q

What are the ideal qualities of a material to allow bony ingrowth?

A

Porosity of 30-40%, pore sizes between 50-400um, micromotion at the bone interface of less than 20um (greater than 150 um results in fibrous interface). This is commonly achieved using a sintered bead surface.

32
Q

What is the surface coating on the fifth generation Zurich cementless acetabular cup and stem components?

A

Hydroxyapatite. Enhances bone ingrowth and prevents the migration of wear debris.

33
Q

What is femoral offset?

A

The distance between the center of rotation of the femoral head and the anatomic axis of the femur.

Decreased angle of inclination (varus neck) increases femoral offset.

The greater the femoral offset the less risk of impingement.

34
Q

What is the normal range of motion of the hip?

A

148 degrees of extension, and 118 degrees of flexion.

35
Q

What is the effect of increased anteversion of a total hip implant?

A

Increase range of motion but increased risk of craniodorsal luxation during external rotation (may also increase the risk of lateral patellar luxation).

36
Q

What is the effect of longer femoral neck on hip joint kinematics?

A

Increased range of motion but longer lever arm that makes luxation easier.

37
Q

What is the femoral head to neck ratio?

A

Difference in circumference of the femoral head and neck. A larger ratio leads to more wear debris but greater range of motion and less risk of luxation.

38
Q

What is the jumping distance?

A

Increased jumping distance reduces risk of luxation but increases wear debris.

39
Q

What factors might contribute to risk of luxation of a total hip prosthesis?

A
  1. Femoral offset (length of the femoral neck and angle of inclination).
  2. Angle of anteversion.
  3. Femoral head:neck ratio.
  4. Jumping distance.
40
Q

Are total hip implants constrained or semiconstrained?

A

Semi-constrained. Allow movement in flexion, extension and rotation, but do not permit translation.

The degree of constraint is primarily determined by femoral head coverage.

41
Q

How is acetabular implant positioning described?

A

Angle of inclination (when using a truncated cup), angle of version, and lateral opening.

42
Q

What is the ideal version and lateral opening angle of an acetabular cup?

A

15-20 degrees of retroversion, 45 degrees lateral opening

43
Q

Is an open trochanteric apophysis a contraindication for THR?

A

No. Neither is an open capital physis. Although an open acetabular growth plate is a contraindication.

Concurrent orthopedic or neurologic disease is also a relative contraindications.

44
Q

What are the challenges of performing THR in a dog with chronic hip luxation?

A

Overcoming muscle contracture and loss of surgical landmarks due to anatomic deformation.

45
Q

What are the two common anatomic variations of femur conformation relevant to THR implantation?

A

Stovepipe (need to use cemented implant), champagne flute (press-fit)

46
Q

What radiographic view should be included when measuring for THR to prevent femoral foreshortening?

A

Cross-table.

47
Q

What is the ideal angle of anteversion of the femoral stem component in a THR?

A

15-25 degrees of anteversion

48
Q

What is primarily responsible for the stability of a press-fit acetabular cup?

A

The cranial and caudal bone columns. Dorsal rim augmentation has been suggested in instances of greater than 50% dorsal rim bone loss. Medialization of the cup or undersizing of the cup might also be required to ensure secure press-fit in instances of inadequate bone stock for reaming.

Identification of the location of the acetabulum may be challenging in cases of advanced hip dysplasia. Use of the transverse ligament of the acetabulum as a landmark may be useful.

49
Q

What are some mechanical failures that can be seen with THR?

A

Luxation, femur fracture, subsidence, fractured acetabulum, cup avulsion, implant failure.

50
Q

What can predispose to femoral head luxation following THR?

A

Excessive (craniodorsal) or inadequate (caudoventral) anteversion and lateral opening angles (<25, >60), pre-existing hip joint laxity, periarticular osteophytosis.

51
Q

What are the classifications of femur fracture following THR?

A

Vancouver classification system:
AL and AG: fractures of the lesser or greater trochanters of the femur.
B1: fracture with stable prosthesis (implants with screw fixation).
B2 and B3: fractures with unstable prosthesis (press-fit implants).
C: fracture distal to prosthesis (cemented implants)

52
Q

When is prophylactic use of cerclage wire recommended by some surgeons performing THR?

A

When performing cementless THR in stovepipe femur, or patients at high risk for femur fracture (thin cortices).

53
Q

What are the mechanical causes of cement failure following THR?

A

Debonding (residual fat or particulate bone debris present at the time of stem implantation) or cement fracture (improper cement preparation techniques).

54
Q

What degree of total hip implant subsidence is normally of clinical significance?

A

> 4-5 mm. Can result in retroversion, luxation, or femur fracture.

55
Q

What are some biologic causes of THR failure?

A

Aseptic loosening (due to wear debris, or stress shielding), septic loosening, femoral medullary infarction (clinical significance unknown), pulmonary embolism, sciatic neuropraxia

56
Q

What percentage of patients undergoing THR have pulmonary emboli?

A

82%, although a very small percentage of those are clinically affected. Canal pressurization may be associated with increased risk.

57
Q

What can cause sciatic neuropraxia in dogs undergoing THR?

A

Retraction of the femur during acetabular preparation, or leakage of PMMA caudal to the acetabulum.

58
Q

What surgical procedure is indicated?

A
59
Q

What muscle flaps have been described for use in conjunction with FHO?

A

Deep gluteal, biceps femoris. Generally have fallen out of favour. Interposition of the joint capsule preferred.

60
Q

What are the main complications associated with FHO?

A

Sciatic nerve injury, fracture of the femur, inadequate resection of the femoral neck.

61
Q

What are examples of salvage procedures of the hip joint?

A

THR, FHO

62
Q

What are examples of palliative procedures of the hip joint?

A

Hip denervation, pectineus myectomy (largely fallen out of favor).

63
Q

What nerves supply the sensory innervation to the hip joint?

A

Cranial gluteal, obturator, sciatic, femoral. Enter at the dorsal aspect of the acetabulum.

64
Q

In a study by Monotti 2020 in VCOT, what was the predominant type of vancouver fracture configuration seen in femoral fracture following THR with cementless implants? What was the major complication following surgical revision with a lateral plate +/- cerclage?

A

Type B fractures predominated (specifically B1).

The major complication following surgical revision was deep infection. Mechanical failure also occurred in some cases.

Musculoskeletal (36 decks)

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