Osseointegration

Definition

Osseointegration is the term used to define the direct structural and functional connection between living bone and the surface of a load-bearing (usually titanium-alloy based) artificial implant.  The term derived from the Latin ‘ossum’ or Greek ‘osteon’, meaning “bone”, and the Latin ‘integrare’, which means “to make whole”.  The laying down of new host bone on the implant surface creates mechanical stability, which resists destabilization by mechanical agitation or shear forces.

History of Osseointegration

The principles of osseointegration where initially noted between 1940 and 1952.  The researchers at that time where implanting titanium into animals and noted the tendency of the metal to fuse with the bone.  Professor Per-Ingvar Branemark of Sweden coined the term “osseointegration” following his studies of implanting titanium implant chambers into rabbit bone, and he postulated on the possibilities for human use.

The human implementation of osseointegration began in dental surgery.  In 1965, Branemark placed the first dental implants into a human patient.

The concepts of Branemark have been further developed and adapted to improve the quality of life for amputees.  In 1990, the first transcutaneous femoral intramedullary prosthesis was performed on an above knee amputee.  Since 1995, this technique has become more accepted for amputees, utilizing an integrated titanium alloy implant that is inserted into the residual bone, and is attached to a stem piece which protrudes through a permanent surgical opening (stoma) in the skin, which is then attached to the external prosthetic device.  A traditional suction socket prosthesis is no longer required.  Further, the new external prosthetic limb can be matched for length as well as having a torque controlled connector, which can be computer controlled and adjusted.  The more rigid construct with skeletal (bone) fixation allowed for much improved direct contact to the ground during walking, with better prosthetic control, and a reduction in overall energy expenditure.

In Australia, the first human osseointegration femoral transcutaneous procedure was performed by Associate Professor Ian Woodgate.  The initial case was undertaken for a patient who unfortunately had developed a deep periprosthetic infection following a total knee replacement.  The infection was unable to be successfully managed, and an above knee amputation had been required.  After 2 years of difficulty trying to fit a traditional suction socket device, she underwent a 2-stage osseointegration procedure, with the first stage insertion of the intramedullary component in March 2009, and the second stage creation of the stoma and attachment of the transcutaneous post in May 2009. 

Suitability for Osseointegration

Osseointegration is considered suitable for patients with above elbow (transhumeral) and above knee (transfemoral) amputations who have had reported difficulty with using a traditional suction socket (due to perspiration, skin problems, ulceration, pain), or when the prosthetic use and functionality is limited by pain, fatigue, or socket-fitting issues.

Patients with below knee (transtibial) or forearm (transradial) amputations are not routinely considered, unless there has been a clear history of socket and functional issues. 

Advantages of Osseointegration

There are a number of advantages that are reported for the use of an osseointegration prosthesis, including:

1.  No suction socket

1. The more natural transfer of loading forces to the femur and hip encourages and creates a more natural gait pattern, requiring less physical exertion, and possible maintenance of bone quality in the femur
2. Any fluctuation in fluid around the stump or variation in body weight will have no effect on the fit or functionality of the prosthesis
3. As there is no bulky suction socket, there is a more streamlined look when wearing clothes

2.  Ease of attachment

1. The knee prosthesis can be quickly attached or removed in a matter of seconds
2. No requirement for sleeves or silastic devices for attachment

3.  Freedom of Movement

1. Allows for full freedom of movement is most activities, including recreation and physical work
2. Adjacent joint (hip) range of motion is not restricted by the prominent edges of a traditional suction socket, which allows greater comfort and ease of walking, sitting and standing
3. The direct connection between host femoral bone, the intramedullary osseointegration implant, and the knee prosthesis enables more natural pivoting movement
4. Muscular strength in the thigh is more likely to be developed or maintained, which minimizes wasting of the stump

4.  Osseoperception

This term means that the prosthesis user regains a more accurate sense of how the prosthesis is interacting with the external environment.  It seems that mechanical events at the prosthesis (e.g. the foot component touching the ground) are transferred as vibrations through the bone-anchored intramedullary component, which may confer safer and more confident mobilization.

Disadvantages/Risks of Osseointegration

Apart from the routine risks of having to undergo a surgical procedure (usually 2 stages separated by about 6-12 weeks, and less commonly as a one stage procedure), other potential risks and disadvantages exist, including:

1. Infection

Deep or superficial infection is a potential risk of any surgical procedure.  Theoretically, this should be even higher with osseointegration procedures, due to the presence of the transcutaneous rod that traverses the skin stoma, and which connects the internal bone-anchored intramedullary osseointegration component to the removable external prosthetic device.  This creates by necessity a direct communication from the external environment to the implanted bone-anchored

Most patients will report small amounts of discharge around the skin stoma.  It is reported that the average patient will have at least one superficial infection every other year that requires antibiotic therapy.  Most are simply managed with adherence to more consistent local cleaning and dressing.

More significant deeper infections are less common, but can be much more significant as it may result in loss of mechanical fixation due to bone erosion, with loosening of the component.  This may require more significant surgical intervention, including the potential need to remove the osseointegration intramedullary rod.

Evolving technologies with regard to coatings that resist bacterial infection on the transcutaneous abutment rod are emerging, and will possibly lead to lower infection risk.

2. Bone-implant interface failure

This occurs when the osseointegration intramedullary device fails to obtain bone ingrowth with subsequent loss of mechanical stability.  The patient would perceive pain or discomfort with weight-bearing or torsional (rotating or pivoting) activities.  A stem fixation revision would be required.

3.Skeletal fracture (periprosthetic)

Fractures can occur either early (at the time of initial implantation) or late (usually following some form of trauma, such as a fall).  With the late fractures, if the bone-anchored component is still stable and well-fixed, the fracture can be managed on its merits with more traditional fixation techniques.  If the stem has become mechanically unstable (loosened), this will require revision of the bone-anchored component.

4. Delayed weight-bearing

Following stem insertion, there is a period of weight-bearing restriction where the external prosthesis cannot be utilized.  This is to allow for time for bone ingrowth into the stem, creating skeletal stability.  It is occasional possible to temporarily use a traditional suction socket device during this lag period.

Pre-Operative Patient Preparation for Osseointegration Surgery

Prior to osseointegration surgery, any patient will need to attend for an initial consultation with Associate Professor Ian Woodgate to determine suitability for the procedure.  This will of course include a full history and examination, and discussion about the treatment options and plans, including risk, benefits, and likely outcomes.  Appropriate further investigations, such as Xrays and scans, will be ordered as needed and subsequently reviewed.

Further preparation may also include pre-surgery physiotherapy and rehabilitation reviews, at which time use of crutches can be instructed (which can then be independently practiced at home), along with pre and post-operative exercises.  Those patients with pre-existing medical issues may require physician or anaesthetic reviews.

Other important pre-operative issues include:

1.  Education

Patients are encouraged to bring a list of questions for discussion to all consultations, as more clear and concise information will often allay fears (“information is power”).  The physiotherapists and prosthetists (patients are often familiar with the prosthetist who has been involved with the fitting of the more traditional suction socket devices) are also a good source of information.  On request, it is possible to arrange to meet or talk to previous patients who have undergone this surgery.

2.  Medications

Patients should provide a list of all current medications that they are taking, including any non-prescription herbal or naturopathic treatments, such as fish oil or turmeric/curcumin.  A/Prof Woodgate will advise which medications will need to be ceased and at what time prior to the surgery.

3.  Skin Preparation

In the two week period prior to osseointegration surgery, the patient should either eliminate the use or greatly limit the use of the previously worn traditional suction socket.  This will decrease the risk of infection from skin abrasions, rubbing with local contusions or bruising, or open wounds.

On the night prior to surgery, and on the actual morning of the procedure, the patient is required to shower and wash the leg with a Chlorhexidine-based antibacterial wash, such as Microshield 2%.  This is done to decrease the bacterial load on the skin.

4. Consent

Informed consent and all relevant pre-operative paperwork, including the Request for Admission should have been completed and forwarded to the Hospital.  Financial consent and costs for the procedure should be discussed with A/Prof Woodgate’s personal assistant.

5. Day of Surgery

The Hospital, or the attending anaesthetist, will have already notified you about fasting times for surgery.

It is most important that ALL Xrays/scans/investigations are brought with the patient to the Hospital, and MUST accompany the patient to the operating suite.

Osseointegration Surgical Technique

Surgery in usually performed over a two-stage procedure, though occasionally a single stage procedure can be utilized depending upon the patient’s existing conditions and suitability, as well as the type of implants matched for the patient.  In the more common transfemoral scenario, at least 160mm of proximal bone stump is required, though custom stems can be manufactured for unique anatomical situations.  No 2 patients or the problems are identical, and all matter need to be addressed on an individual basis.

There are a number of different osseointegration prostheses currently available for implantation.  A/Prof Woodgate is trained/utilized or is familiar with 3 current systems: 

1. The Eska Endo-Exo Integral Leg Prosthesis

2. The Compress (pre-stress) Device from Zimmer Biomet, and

3. The OGAP-OPL (Osseointegrated Prosthetic Limb).

First Stage Procedure    

• An incision is made on the distal end of the amputation stump incorporating the old wounds.
• Redundant skin and subcutaneous fat are removed to minimize the final implant/bone to skin distance, which reduces movement and irritation around the subsequently inserted transcutaneous abutment rod.
• Muscles and fascial coverings are mobilized for later transfer or repair with the goal of improving function.
• The residual bone stump is reshaped with removal of any spurs.
• The bone canal is opened and prepared with specialist reaming instruments to shape the intramedullary canal.
• The definitive internal osseointegration implant is then impacted (press-fitted) into the bone canal with firm interference fit to provide early stability that will enhance later bone ingrowth onto and into the component.
• Any neuroma (nerve swellings) on the ends of the previously cut nerves can be addressed at the same time, by removal of the painful neuroma, and then burying the freshened cut end of the nerve more proximally in either the deep thigh muscle or into a small window created on the surface of the bone.
• The stump wound is then closed in layers, with the intent of also creating a more pleasing cosmetic appearance due to the earlier reshaping.

Between 6 and 12 weeks is allowed between the first and second stages to allow for stable osseointegration.  At approximately 2-3 weeks, it is occasionally possible to wear a temporary suction socket if the wound has healed well, and provided weight-bearing restriction guidelines are followed.

Second Stage Procedure

• A stoma (circular skin opening) is fashioned at the base of the stump.  Through this opening, the transcutaneous adaptor rod in connected to the internal bone-anchored osseointegration prosthesis.
• The remaining external component of the prosthesis can be attached to the transcutaneous rod.

Post-Surgical Management After Osseointegration Surgery

Following the surgical procedures, you will be transferred to the Recovery Room initially where you will be closely monitored.  Once our condition is deemed stable, transfer to the Orthopaedic ward occurs.

Particular issues following the First Stage procedure include:

• Pain management -    Usually via a PCA machine (Patient Controlled Analgesia) which provides on demand pain relief intravenously.  Pain management is more significant in the First Stage due to the bone fixation required for the osseointegration internal component, as opposed to the Second Stage, which is minimally invasive soft tissue surgery.
• A drain will be required which removes excess blood from the operative site, and this is typically removed at 48-72 hours post-op.
• Intravenous antibiotics are utilized for 48 hours.
• Dressings are lightened on day 3, and at that stage you are permitted to sit out of bed.

Partial/protected weight bearing and final adjustments to the external limb prosthesis can take place within a few days after the second stage procedure.

This is done with the supervision of the combined surgical/physiotherapy/rehab team.

A specialized stump loader is fitted to the end of the transcutaneous implant to begin a controlled weight-loading programme, starting with five minutes of loading three a day, and this requires you to push and apply force through the loader to reach the pre-determined weight registered on a set of scales.  This time and level of loading programme is increased over a few days.

Once you can comfortably achieve weight loading at 50% of your body weight, as confirmed on the set of scales, a light leg will be fitted, and gait retraining will commence.  Some muscle discomfort is expected during this stage, as reactivation of disused or atrophied muscles occurs, and will take tale time to adjust to these changes and build up strength and endurance.

Partial weight-bearing is required for 12 weeks to ensure safe and stable bone osseointegration.  Practically, this usually requires use of one or two crutches throughout this period.

Patients often will try to push the boundaries during this very exciting early phase, and this temptation should be avoided.  Developing endurance, strength, and adaptation to the implant needs time and patience, and early control of these urges will lead to less risk of injuries or other complications.

Post-Op Care and Long Term Limitations

With an osseointegration prosthesis, patients can undertake all routine daily life activities including taking a bath, shower, walking, hiking, and cycling.  With the absence of a socket, the prosthesis always fits, always attaches correctly, and is always firmly held in place.

Post-op care of the stoma (skin opening) through which the transcutaneous external adaptor rod penetrates is important.  Washing daily in the shower, paying particular attention to the stump and stoma is routinely all that is required.

If increasing discharge, redness, or pain develops around the stump or stoma, A/Prof Woodgate should be notified as soon as possible.

Excessive rotational torque forces, such as twisting or pivoting movements under load, should be avoided or limited as a general rule.  However, if a high level strain episode should occur, the newer generation external implant attachment systems have safety shear pins that will break to afford some protection against the bone fracturing around the internal osseointegration implant.  These pins can be easily replaced/exchanged by the prosthetist.

Osseointegration Problems from Surgery Undertaken Elsewhere

Having first been exposed and utilized osseointegration in September 2007, and has familiarity with a number of different implants available, Associate Professor Woodgate recognizes that patients with transcutaneous implants present unique challenges and occasionally have unique complications.  He is happy to consult with any patient with concerns, and to provide measured, thoughtful and possibly innovation solutions.