**4.1 Long bone fractures**

The most common fractures are long bone fractures. In the treatment of long bone fractures by osteosynthesis, the most commonly used manipulation is bicortical drilling.

The main problem during bicortical bone drilling is the second cortex breakthrough detection and drill bit penetration value. The average soft tissue penetration in bi-cortical drilling manipulations is 6.31 mm when drilling is executed manually [20]. Furthermore, there is a significant difference in plunging (soft tissue penetration) depth when sharp or blunt drill bit was being used. Surgeons, regardless of their experience level, when used blunt drill bit, penetrate over 20 mm in normal bone and over 10 mm in osteoporotic bone [21]. This means that there is a risk of tendon or blood vessel rupture and protection of the posterior bone wall is required (leading to additional tissue excision).

When performing the drilling by the orthopedic bone drilling robot ODRO, the manipulation can be conditionally described by several stages: searching the

**143**

**Figure 11.**

*21.016 s, 1561 AU.*

**Figure 10.**

*time 21.016 s, 1561 AU.*

*Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications*

contact with the first cortex; its drilling; automatic stop; searching the contact with the second cortex; its drilling; automatic stop; going to reference position after the

In **Figures 10** and **11** experimental results are presented for the current position and the feed rate consequently during a bicortical mid-diaphyseal pork femur bone

**Figures 12** and **13** present experimental data for thrust force variation during bicortical pig femur bone drilling when using a new drill bit (**Figure 12**) and a drill

The time is expressed in arbitrary units (AU) of measurement where 1 unit is defined as the scoring time, i.e. the interval of time between two measurements. During bicortical bone drilling process the feed rate takes various values in any stage in the range 0.5-6 mm/s. These values depend on drill bit position and real

The first drilling stage is illustrated in **Figure 11** (search of contact with first cortex). Its parameters are feed rate 6 mm/s and drill speed 0 rpm. When the contact is realized, the feed rate stops (at 145 AU in **Figure 11**) and the drill speed is switched on. As the tubular bones generally have not flat shape the drill bit may slip from the needed point of drilling start. That can be notices and corrected by the surgeon

*Actual position [mm] versus time during drilling. Maximal drilling feed rate 2 mm/s; drill bit 2.8 mm; total* 

*Feed rate [mm/s] versus time during drilling. Maximal drilling feed rate 2 mm/s; drill bit 2.8 mm; total time* 

*DOI: http://dx.doi.org/10.5772/intechopen.96768*

drilling end.

drilling procedure.

time force sensor data.

bit after 35 drillings (**Figure 13**).

*Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications DOI: http://dx.doi.org/10.5772/intechopen.96768*

contact with the first cortex; its drilling; automatic stop; searching the contact with the second cortex; its drilling; automatic stop; going to reference position after the drilling end.

In **Figures 10** and **11** experimental results are presented for the current position and the feed rate consequently during a bicortical mid-diaphyseal pork femur bone drilling procedure.

**Figures 12** and **13** present experimental data for thrust force variation during bicortical pig femur bone drilling when using a new drill bit (**Figure 12**) and a drill bit after 35 drillings (**Figure 13**).

The time is expressed in arbitrary units (AU) of measurement where 1 unit is defined as the scoring time, i.e. the interval of time between two measurements.

During bicortical bone drilling process the feed rate takes various values in any stage in the range 0.5-6 mm/s. These values depend on drill bit position and real time force sensor data.

The first drilling stage is illustrated in **Figure 11** (search of contact with first cortex). Its parameters are feed rate 6 mm/s and drill speed 0 rpm. When the contact is realized, the feed rate stops (at 145 AU in **Figure 11**) and the drill speed is switched on. As the tubular bones generally have not flat shape the drill bit may slip from the needed point of drilling start. That can be notices and corrected by the surgeon

#### **Figure 10.**

*Latest Developments in Medical Robotics Systems*

the zone drilled just before.

**Figure 9.**

*Bone drilling process.*

low density area.

**4.1 Long bone fractures**

bicortical drilling.

number of subtractions ( *<sup>k</sup>*

ε

the "not typical force sensor data" in the drilling area.

the result of the operation is presented on the display.

**4. Areas of application and experimental results**

required (leading to additional tissue excision).

The parameter *ds* ∆*I* is formed as a difference between two consecutive values. It gives information for tissue density deviation in current drilling area. The higher the *ds* ∆*I* the bigger is bone density deviation in the current zone in comparison with

Next, the comparison of the value *ds* ∆*I* with some appropriately chosen reference value allows taking a decision for the breakthrough detection of second cortex as well as the far cortex registration. The dimension of *ds I* from view point of

dency of increasing or decreasing the bone density and in the same time minimizes

The dimension of *ds I* from view point of number of samples of discretization is in connection with the extent of the drill bit penetration when it starts moving in

Once the drilling process is completed according to the selected operating mode,

The most common fractures are long bone fractures. In the treatment of long bone fractures by osteosynthesis, the most commonly used manipulation is

The main problem during bicortical bone drilling is the second cortex breakthrough detection and drill bit penetration value. The average soft tissue penetration in bi-cortical drilling manipulations is 6.31 mm when drilling is executed manually [20]. Furthermore, there is a significant difference in plunging (soft tissue penetration) depth when sharp or blunt drill bit was being used. Surgeons, regardless of their experience level, when used blunt drill bit, penetrate over 20 mm in normal bone and over 10 mm in osteoporotic bone [21]. This means that there is a risk of tendon or blood vessel rupture and protection of the posterior bone wall is

When performing the drilling by the orthopedic bone drilling robot ODRO, the manipulation can be conditionally described by several stages: searching the

*k r act* = − *F F* ) assures the accurate monitoring the ten-

**142**

*Actual position [mm] versus time during drilling. Maximal drilling feed rate 2 mm/s; drill bit 2.8 mm; total time 21.016 s, 1561 AU.*

#### **Figure 11.**

*Feed rate [mm/s] versus time during drilling. Maximal drilling feed rate 2 mm/s; drill bit 2.8 mm; total time 21.016 s, 1561 AU.*

#### **Figure 12.**

*Thrust force [N] versus time during drilling maximal drilling feed rate 2 mm/s; new drill bit 2.8 mm; total time 18.297 s, 919 AU. Drilling time (101–796 AU) – 13.85 s.*

#### **Figure 13.**

*Thrust force [N] versus time during drilling. Maximal drilling feed rate 2 mm/s; hole-used 35 times drill bit 2.8 mm; total time 24.828 s, 1,239 AU. Drilling time (128–1,097 AU) – 19.42 s.*

in the case of first cortex but for drilling the second cortex such a slippage (which starts from inside the bone) cannot be avoided. It results to drill bit bending which reflects to hole inaccuracy, bigger friction and heat generation [1].

The second drilling stage (drilling start) begins after the contact is established. In order to eliminate the case of drill bit bending at the first cortex entrance site the drilling is executed with a feed rate 0.5 mm/s (from 148 to 288 AU in **Figure 11**). During this time interval the thrust force is identified for the first cortex (thrust force = 40 N, **Figure 12**). So that a thrust forces reference value is set to 50 N (**Figure 12**) for the first cortex wall for further drilling.

At the third drilling stage the feed rate has maximal value 2 mm/s. The fourth drilling stage indicates the end of the first cortex drilling at 509 AU in **Figure 11** and the drilling automatically stops; drill speed and feed rate become equal to 0 (the fifth drilling stage) according to the auto-stop criterion [22].

The registration of the inner (or outer) wall of the near (or far) cortex and the decision to stop the drilling process depends on the bone density evaluation in the current drilling zone (thrust force = 40 N, **Figure 12**) [22]. After pressing the start button again the drilling process starts at 817 AU in **Figure 11**. The drill speed is 1000 rpm and the drill bit movement is executed with feed rate of 2 mm/s (along 2 mm distance - from 818 to 892 AU in **Figure 11**).

**145**

**Figure 14.**

*The result of the drilling process; new drill bit 2.8 mm.*

room is 54.50

*Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications*

The drill bit does not penetrate through the bone wall entirely when the first cortex wall drilling is finished from the "robot viewpoint" (the penetration is less than 1 mm but the stop decision works out successfully). This way, delamination of bone layers at the exit of the drill bit at the second wall of the first cortex is eliminated. Then the process continues with feed rate 6 mm/s until the second cortex contact is reached (in the same style like the first drilling stage but now for the second cortex) – feed rate 6 mm/s (893–1046 AU in **Figure 11**). When the second cortex contact is registered (1047 AU in **Figure 11**) the drilling process continues according to the algorithm steps already described up to now for the first cortex drilling until an automatic stop is realized when the second cortex drilling is finished. Then the drill bit was extracted back to the reference position (after 1400 AU in **Figure 11**) with negative value (6 mm/s) of the feed rate (the fifth drilling stage for the second cortex).

The drilling of the first or second cortex, which is in the interval of 299–509 AU in **Figure 11**, is executed with feed rate not greater than 2 mm/s. This value changes

When the resistant force values become less than the reference force, drilling is executed with feed rate 2 mm/s, for example in the intervals 320–351 AU and 438– 497 AU in **Figure 11**. Feed rate values less than 2 mm/s correspond to slower translation motion (the resistant force values are higher than the reference value) and also correspond to application of a smaller thrust force (352–399 AU in **Figure 11**). Thus, the negative feed rate values correspond to drill bit back-motion while a recurring overshoot of the reference value occurs (for example 400–431 AU in **Figure 11**). That is in agreement with the scientific reports of ultrasonically-assisted drilling method (UAD) [23–27]. This is a concept of minimizing the thrust force during drilling. The original idea of this approach is a module coupled with the drill bit, realizing the micro back translation motions with 5-25 μm amplitude and 10–30 kHz frequency. The advantages of UAD in comparison with conventional drilling reflect in a decrease of force from 60–65 N to 35–38 N (for UAD) [23, 25]. When the drill position becomes close to the second cortex outer surface (which

can be recognized by additional criteria) then the feed rate decreases to 1 mm/s (498–508 AU in **Figure 11**). The reduction of the feed rate aims to guarantee a minimal penetration (maximum 1 mm) in the tissue outside the bone. Additionally, reduction the speed to 1 mm/s (respectively the thrust force) at the end of drilling

The feed rate control has important role from viewpoint of usage of spoiled drill bits which occurs very often in orthopedic practice. It is confirmed by a report where about 600 and more drillings are executed [28]. The dulled drill bits cause higher temperature in the drilling area. The maximal temperature reached by a bit taken from the operation

of wear and the temperature increase and the same can be said for cutting forces [29]. After the end of every concrete drilling, the result is shown on the display. In **Figures 14** and **15** results of the drilling in both cases concerning the new and the used drill bits (see **Figures 12** and **13**) are shown on the display. The thickness of the

C [28, 29]. A proportional relationship is observed between the intensity

allows forming accurately the breakthrough itself, i.e. without bone debris.

during the drilling process in dependence on the force sensor data.

*DOI: http://dx.doi.org/10.5772/intechopen.96768*

### *Orthopedic Bone Drilling Robot ODRO: Basic Characteristics and Areas of Applications DOI: http://dx.doi.org/10.5772/intechopen.96768*

The drill bit does not penetrate through the bone wall entirely when the first cortex wall drilling is finished from the "robot viewpoint" (the penetration is less than 1 mm but the stop decision works out successfully). This way, delamination of bone layers at the exit of the drill bit at the second wall of the first cortex is eliminated. Then the process continues with feed rate 6 mm/s until the second cortex contact is reached (in the same style like the first drilling stage but now for the second cortex) – feed rate 6 mm/s (893–1046 AU in **Figure 11**). When the second cortex contact is registered (1047 AU in **Figure 11**) the drilling process continues according to the algorithm steps already described up to now for the first cortex drilling until an automatic stop is realized when the second cortex drilling is finished. Then the drill bit was extracted back to the reference position (after 1400 AU in **Figure 11**) with negative value (6 mm/s) of the feed rate (the fifth drilling stage for the second cortex).

The drilling of the first or second cortex, which is in the interval of 299–509 AU in **Figure 11**, is executed with feed rate not greater than 2 mm/s. This value changes during the drilling process in dependence on the force sensor data.

When the resistant force values become less than the reference force, drilling is executed with feed rate 2 mm/s, for example in the intervals 320–351 AU and 438– 497 AU in **Figure 11**. Feed rate values less than 2 mm/s correspond to slower translation motion (the resistant force values are higher than the reference value) and also correspond to application of a smaller thrust force (352–399 AU in **Figure 11**).

Thus, the negative feed rate values correspond to drill bit back-motion while a recurring overshoot of the reference value occurs (for example 400–431 AU in **Figure 11**). That is in agreement with the scientific reports of ultrasonically-assisted drilling method (UAD) [23–27]. This is a concept of minimizing the thrust force during drilling. The original idea of this approach is a module coupled with the drill bit, realizing the micro back translation motions with 5-25 μm amplitude and 10–30 kHz frequency. The advantages of UAD in comparison with conventional drilling reflect in a decrease of force from 60–65 N to 35–38 N (for UAD) [23, 25].

When the drill position becomes close to the second cortex outer surface (which can be recognized by additional criteria) then the feed rate decreases to 1 mm/s (498–508 AU in **Figure 11**). The reduction of the feed rate aims to guarantee a minimal penetration (maximum 1 mm) in the tissue outside the bone. Additionally, reduction the speed to 1 mm/s (respectively the thrust force) at the end of drilling allows forming accurately the breakthrough itself, i.e. without bone debris.

The feed rate control has important role from viewpoint of usage of spoiled drill bits which occurs very often in orthopedic practice. It is confirmed by a report where about 600 and more drillings are executed [28]. The dulled drill bits cause higher temperature in the drilling area. The maximal temperature reached by a bit taken from the operation room is 54.50 C [28, 29]. A proportional relationship is observed between the intensity of wear and the temperature increase and the same can be said for cutting forces [29].

After the end of every concrete drilling, the result is shown on the display. In **Figures 14** and **15** results of the drilling in both cases concerning the new and the used drill bits (see **Figures 12** and **13**) are shown on the display. The thickness of the

**Figure 14.** *The result of the drilling process; new drill bit 2.8 mm.*

*Latest Developments in Medical Robotics Systems*

*time 18.297 s, 919 AU. Drilling time (101–796 AU) – 13.85 s.*

in the case of first cortex but for drilling the second cortex such a slippage (which starts from inside the bone) cannot be avoided. It results to drill bit bending which

*Thrust force [N] versus time during drilling. Maximal drilling feed rate 2 mm/s; hole-used 35 times drill bit* 

*Thrust force [N] versus time during drilling maximal drilling feed rate 2 mm/s; new drill bit 2.8 mm; total* 

The second drilling stage (drilling start) begins after the contact is established. In order to eliminate the case of drill bit bending at the first cortex entrance site the drilling is executed with a feed rate 0.5 mm/s (from 148 to 288 AU in **Figure 11**). During this time interval the thrust force is identified for the first cortex (thrust force = 40 N, **Figure 12**). So that a thrust forces reference value is set to 50 N

At the third drilling stage the feed rate has maximal value 2 mm/s. The fourth drilling stage indicates the end of the first cortex drilling at 509 AU in **Figure 11** and the drilling automatically stops; drill speed and feed rate become equal to 0 (the

The registration of the inner (or outer) wall of the near (or far) cortex and the decision to stop the drilling process depends on the bone density evaluation in the current drilling zone (thrust force = 40 N, **Figure 12**) [22]. After pressing the start button again the drilling process starts at 817 AU in **Figure 11**. The drill speed is 1000 rpm and the drill bit movement is executed with feed rate of 2 mm/s (along

reflects to hole inaccuracy, bigger friction and heat generation [1].

*2.8 mm; total time 24.828 s, 1,239 AU. Drilling time (128–1,097 AU) – 19.42 s.*

(**Figure 12**) for the first cortex wall for further drilling.

2 mm distance - from 818 to 892 AU in **Figure 11**).

fifth drilling stage) according to the auto-stop criterion [22].

**144**

**Figure 12.**

**Figure 13.**

#### **Figure 15.**

*The result of the drilling process; hole-used 35 times drill bit 2.8 mm.*

near cortex (Cortex I), the thickness of the far cortex (Cortex II) and the depth of the hole are shown in the second row on the display.

At equal drilling conditions – drilling process control algorithm, drill bit diameter, bone specimen, drilling area – the following can be seen in **Figures 12** and **13**: for new drill bit max thrust force is 55 N; for used drill bit max thrust force is 80 N; for new drill bit the hole depth is 23 mm for 13.85 s duration and for used drill bit the hole depth is 26.3 mm for 19.42 s respectively.

At automatic drilling the reasons for the negative final result caused by dulled drill bits should be minimized by feed rate control [30]. Also, it successfully solves the problem of higher drill bit penetration after the end of second cortex. It is realized by feed rate reduction to 1 mm/s just before the breakthrough.
