Surgical technique

 

 

OTNI  Surgical Technique

Introduction

OTNI Amputee osseointegration devices consist of intramedullary implants connected with a transcutaneous OTNI dual cone adapter for direct attachment of an external prosthetic leg to the skeleton in patients with extremity amputation. The OTNI devices enable in a natural fashion direct load transfer from the external prosthesis to the bone. Advantages of OTNI devices in comparison to conventional socket attachment of prosthetic limbs include proven significant increase in walking distance with low energy costs, increase in prosthesis wearing time and quality of life, osseoperception and better sitting comfort. The OTNI device is a press fit uncemented intramedullary implant made of titanium with titanium plasma sprayed or 3d printed mesh surface facilitating fast primary osseointegration.

Product specialists of OTNI are at your disposal for any further information and/or explanation about the contents of this Surgical Technique

 

Indications:

•               Lower limb amputation and gait restrictions with conventional socket prosthesis

 

Contra-indications

•               Inflammation (acute and chronical) of the stump.

•               Immune suppressive drugs or chemotherapy

•               Immature skeleton 

•               Severe diabetes with multi organ failure

•               Periferal vessel disease: occluded femoral arteria in TFA, occluded popliteal arteria in TTA 

•               Behavioural disorders that may result in low compliance to medical instructions

•               Inexplicable or disproportionate pain disorder  

 

Relative contra-indications

•               Smoking

•               Obesitas with large subcutaneous fat disposition in the proposed stoma area

 

 

Implantable components

1. OTNI OFP femoral stem

2. OTNICM 3 custom made femoral stem with skewed lag screw

3. OTNICM 4 custom made tibia stem with transverse locking screws

4. OTNI dual cone adapter

5. OTNI locking screw

 

Non-Implantable components

1. OTN canulated M14 self locking screw (to attach the OTN click safety adapter to the OTNI dual cone adapter)

2. OTN silicon cap for stoma gauze fixation (optional)

3. OTN click safety adapter (connects the OTNI dual cone adapter with the external prosthesis)

 

Pre-surgical planning

Calibrated AP X-rays and on indication CAT scans are used to: calculate the OTNI OFP implant diameter, design OTNICM3/4 implants and to calculate the exact level of the bone cut. In transfemoral amputees the knee joint space of the contra-lateral limb is used as reference to match the knee flexion axis of the external prosthesis exactly with the knee joint space of the sound limb. The size of the DC adapter is estimated based on the thickness of subcutaneous fat layer in the planned stoma area. Attention should be given to control for the height of femoral heads on the AP X-rays of both legs in standing position. The full range of OTNI femoral stem diameters has to be available at the time of surgery in case the pre-surgically estimated diameter does not provide the optimal press fit fixation. In cases with residual femur shorter than 140 mm between distal femur tip and mid line of the lesser trochanter, a custom made femoral stem with additional fixation of a gamma-type lag screw through the prosthesis into the femoral head, is to be considered. 

Osseointegration surgery is performed under general or spinal anesthesia including prophylactic intravenous antibiotics (e.g. vancomycin (1 g) or cephazolin (2 g) at induction of anesthesia. The patient is placed in supine position on a radiolucent surgery table. Draping and prepping is done in a fashion similar to that used for standard orthopedic surgery. The OTNI implants may be implanted in a single or two stage procedure.

 

Surgery

1. Open the skin and fascia to exposure of the distal bone tip

2. Release any tethering tissue, remove nearby nerves and neuroma

3. Shorten the bone with an oscillating saw according to pre-surgical plan and remove redundant skin and soft tissue

4. Ream the medullary canal with rigid drills for tibia and short femoral bones and use flexible reamers and OTNI curved rasps for OTNI OFP femoral implants under portable X-ray imaging. The curved OTNI rasps diameter correspond with the OTNI OFP diameter. Use lateral X-ray imaging to rasp exactly the curved anterior bow of the femur. Rasp diameter 17 mm matches an accurate press fitting of an OTNI OFP 17 mm implant. The rigid drills are used to place OTNICM 3 and OTNICM 4 for respectively short femora and tibia. The OTNICM 3/4 implants should always oversize the drill diameter with one mm. For example, a rigid drill diameter of 15 mm matches a custom made implant of 16 mm to achieve a 1 mm press fit.

5. Use the tip mill to create a distal bone cut plane exactly perpendicular to the longitudinal axis of the bone

6. Use the OTNI aiming device placed on the femur tip as reference to place the OTNI OFP curve exactly in correspondence with the femur anticurvation.

7. Make four 1.25 mm burr holes with K-wire in the distal femur tip to create a myodesis with four transosseal 4.0 sutures. For tibia osseointegration no myodesis is required. 

8. Tighten the screw at the proximal morse taper of the OTNI implant with screw driver hexa 4

9. Insert of the OTNI implants using the stem insertion tool and hammer. Use the surgical planning and OTNI femur aiming device with corresponding instructions for use for placement of the lag screw in OTNICM 3 implants. 

10. Perform a myodesis by suturing the muscular fascial layers to the bone with the previously applied transosseal sutures

11. Rinse the wound intensively

12. Remove subcutaneous fat nearby the tip of the implant

13. Close the wound in layers in standard fashion

(On indication; stage 2 surgery starts here)

14. Localize the implant by palpation and place a K-wire percutaneously in the thread of the implant

15. Create a stoma by cutting the skin and soft tissue with the 20 mm diameter corer knife guided over the K-wire 

16. Rinse the wound and the morse taper interior

17. Select the correct length of the OTNI DC adapter. The size of the DC adapter is related to the thickness of the soft tissue layer that covers the tip of the femur. At least 50 mm of the DC adapter length has to protrude through the skin.

18. Insert the correct OTNI DC adapter and tighten the OTNI locking screw with the retainer and the hexa 4 screw driver

19. Hammer the OTNI DC adapter into the morse taper of the implant using the punch and hammer and re-tighten the locking screw with the retainer and hexa 4 screw driver. 

20. Cover the stoma with wound gauzes and the place OTN silicon cap

21. Mount the OTN click safety adapter with the OTN canulated M14 self locking screw to the distal cone of the OTNI DC adapter with the hexa 6 T-wrench

22. The prosthetist may attach any available external prosthesis to the distal part of the OTN click safety adapter