Minimally invasive osteosynthesis

Question 1

What are the tenets of biological osteosynthesis?

Answer 1

1. Minimal use of hardware and interfragmentary screws or cerclage wires.
2. Gentle manipulation of the bone with indirect reduction.
3. No use of bone graft.
4. No attempt at anatomic reconstruction.

Question 2

What are the three different surgical approaches to fracture fixation based on their biologic footprint?

Answer 2

Question 3

What device is depicted?

Answer 3

Question 4

Why is imaging of the contralateral limb recommended for minimally invasive osteosynthesis?

Answer 4

1. Optimizes preoperative implant selection.
2. Allows comparison with the fractured segment for identification of normal v. abnormal.
3. Allows accurate evaluation of post-operative alignment.

Question 5

Should the C-arm generator be placed under or over the table for use during minimally invasive procedures?

Answer 5

Under the table to prevent backscatter to operating personnel.

Question 6

What are methods of fracture reduction during minimally invasive osteosynthesis?

Answer 6

1. Distraction and /or ligamentotaxis of the segments adjacent to the bone. Distraction relies on concentric pressure applied on the shaft of the bone by the surrounding musculature, easing fragments into place. Ligamentotaxis is more commonly used to refer to juxta- or articular fractures, with use of the surrounding joint capsule and ligaments to achieve fracture reduction.
2. Direct manipulation of the metaphyseal or epiphyseal fragments of the bone with the use of surgical instruments.

Question 7

What are some instruments that can be used during fracture reduction in minimally invasive osteosynthesis?

Answer 7

1) Toothed reduction forceps (or ‘joysticks’).
2) Custom made distraction frame using circular ESF rings.
3) Purpose designed distractors that allow for both multiplanar manipulation and self-retaining distraction ability (Foot and Ankle distractor).

Question 8

What are methods to reduce radiation exposure from c-arm units during minimally invasive osteosynthesis?

Answer 8

1) use the lowest amount of radiation possible to achieve diagnostic images, 2) use proper shielding gear, 3) increase the distance between the personnel and radiation source.

Additionally proper operating room set-up, selecting a mini c-arm, laser guidance and collimation, and positioning of the x-ray source under the table can also aid in reducing exposure.

Question 9

Radiation exposure decreases by what factor with increasing distance from the radiation source?

Answer 9

Square of the distance (inverse square distance law).

Question 10

Backscatter toward the generator can represent what percentage of the primary beam?

Answer 10

25-40%

Question 11

What are the downsides of positioning the fluorscopic x-ray generator under the operating table for reduced backscatter radiation?

Answer 11

1) lower image quality.
2) excessive magnification.
3) low clearance between the cumbersome detector and the patient.

Question 12

What instrument is shown?

Answer 12

Question 13

Is creation of the epiperiosteal tunnel typically performed in a proximal to distal to distal to proximal direction during minimally invasive osteosynthesis?

Answer 13

Depends on the offset of the fracture fragments, location of the fracture, and the proximity of neurovascular bundles and tendons.

Question 14

How can the stiffness of an ESF structure be augmented when used for minimally invasive fracture repair?

Answer 14

Adjusting (1) the frame type; (2) the number, diameter, and material of the connecting bar(s); and (3) the diameter, number, distribution, and working length of the fixation pins.

Question 15

How can the pin-bone interface of an ESF be preserved when used for minimally invasive fracture repair?

Answer 15

Short fixation pin working lengths, increased number of fixation pins (at the cost of increased morbidity), large threaded fixation pins (up to 25% of the bone diameter), and full pins instead of half pins, predrilling, optimal pin location within the bone cross-section, hydroxyapatite coating, the use of pins with tapered run-out junction (Duraface, IMEX), and optimal postoperative activity restriction.

Question 16

What plate-to-bone offset distance may have a deleterious effect on the biomechanical properties of a LCP when used during MIPO?

Answer 16

> 5mm offset results in an increased risk of plate failure (<2mm was shown to have little effect on 4.5mm LCP construct strength).

Question 17

Does off axis screw application in a LCP affect construct biomechanics?

Answer 17

Yes, 10 degree off axis screw insertion results in a 77% reduction in push-out force and 69% reduction in bending load to failure.

Question 18

Does use of monocortical locking screws in a locking system affect the working length of the construct?

Answer 18

Only in torsion, where the working length of the screw is relative to the thickness of the cortex.

Question 19

What are the main advantages/disadvantages associated with minimally invasive osteosynthesis?

Answer 19

Advantages: reduced infection, delayed union, and non-union.

Disadvantages: increased prevalence of malalignment.

Question 20

Limb malalignment in which plane is fairly well tolerated?

Answer 20

In the saggital plane (recurvatrum, procurvatum). Loss of length is also well tolerated.

Malalignment in the frontal (varus/valgus) and rotational malalignment are poorly tolerated.

Question 21

How can a tendency toward hyperanteversion of the femoral neck be avoided during minimally invasive osteosynthesis procedures?

Answer 21

Visualization of the arciform crest (that extends from the greater trochanter to the third trochanter and serves as part of the origin of the vastus lateralis) should remain lateral during reduction (with the femoral trochlea as the distal landmark).

Question 22

What are four strategies that may help prevent intra-articular screw penetration?

Answer 22

1) Use a non-locking screw distally, directed away from the joint.
2) Use a short locking screw distally.
3) Shorten the plate.
4) Contour the distal plate to angle away from the joint surface.

Question 23

During MIPO of the humerus what neurovascular structures must be avoided?

Answer 23

Lateral: radial nerve (best avoided by ensuring tunnelling deep to the brachialis muscle).

Medial: musculocutaneous, median, ulna nerves (central and distal thirds of the diaphysis of the humerus).

Question 24

What are common reasons for delayed union/non-union in minimally invasive osteosynthesis repairs?

Answer 24

1) Malalignment or poor fragment approximation resulting in large bone defects.
2) Periosteal stripping during tunneling.
3) Excessive external manipulation of the fragment.

Question 25

What is the most likely type of implant failure with MIPO techniques?

Answer 25

Failure at the plate screw interface. Risk can be minimized by maintaining a plate-to-bone offset <2mm.