Osseointegration and the O&P Practitioner

Osseointegration (OI) is a term that was more widely introduced by Per-Ingvar Branemark, MD, PhD, to explain the attachment of bone to the surface of metal implants.¹ His son, Rickard Branemark, MD, PhD, MS, furthered this work and extended the concept to patients with limb loss by using implants in the bone of residual limbs to allow direct skeletal attachment of a prosthesis, thereby eliminating the need for a socket and other suspension systems. While many patients and providers exalt the benefits of OI for individuals with limb loss, such that it improves comfort, fit, performance, sensory feedback (osseoperception), and quality of life,^2-4 the surgical and rehabilitative community should remain cautious.

It should be noted that the concept of direct skeletal attachment of prosthetic limbs is not new, as research dates back to the 1940s. The first surgery to give a patient a direct skeletal attachment implant in the United States was performed by Vert Mooney, MD, at Rancho Los Amigos Hospital in the early 1970s.^5-7 While enthusiasm about OI for the treatment of individuals with limb loss continues to grow across the United States, it must be emphasized that it is estimated that less than 1,000 patients have received this procedure worldwide, with the majority occurring in Europe and Australia. Furthermore, there remains considerable variability in the types of implants used across the globe, the different approaches to surgical placement (e.g. single versus two-stage), and pre/post implant rehabilitation strategies. OIs currently have over 15 years of clinical use and there is still much to be understood, including potential risks. Reports from clinical investigations that have studied 50 or more patients identified infection rates ranging from 35 to 55 percent.^8-10 Although most infections are superficial in nature and treatable with local skin care and oral antibiotics, more extensive complications, including the need for inpatient admission, intravenous antibiotics, surgical revision, and loss of OI implant have been reported.¹¹ Therefore, continued research in the field is likely to increase its efficacy and safety. As an example, a recent study by Juhnke et al. reported that the infection rate can be reduced if an approximate 1cm gap is maintained at the skin-implant interface, allowing the wound to stay open and drain.¹⁰ While these results remain promising, they have yet to be reproduced in the peer-reviewed literature and evaluated using different OI implant techniques.

Although infection remains a prominent concern for OI recipients, there are others worth noting. For example, bone and implant breakage have also been reported in the literature.¹² Unlike hip replacements, there exists no data thus far reporting the fatigue properties and strength of any of the OIs, such as the data that exists for the femoral stem in total hip replacements.^12-13 There is also little information on implant-bone interface mechanical failure other than a translational animal study.^14-15 Furthermore, there is a large gap in research discerning the optimal rehabilitative strategies following OI surgery, including the appropriate timing and selection of prosthetic components, ideal alignment based on patient anthropomorphics, and progression of weight bearing or other activities depending on the location of the OI (e.g. upper or lower limb). Moreover, when compared to traditional socket technology, data is lacking regarding which patients are the best candidates and information for clinicians to use when counseling their patients on the risks/benefits of the procedure. Are patients willing to accept the possibility that major fractures to the bone may require returning to the socket, previous suspension system, or a wheelchair? What are the indications for reimplantation or a return to socket technology if the bone has been compromised?

To advance the field of OI and ensure the best translation into clinical practice, rehabilitation professionals must be part of the research and discovery process. No doubt critical to this process will be the prosthetist, who is most likely to be on the front lines dealing with new OI recipients now requesting the most advanced exoprosthetic systems to achieve higher levels of function, but unsure of any potential risks. Moreover, what impact will OI surgery have on prosthetic component authorization and reimbursement? Traditionally, activity level has been classified by the Medicare K-level system; however, it is possible that after OI surgery, patients may be able to achieve higher K-levels. Likewise, the current system of L-Code reimbursement may also change significantly when providing services for OI recipients. Additionally, there are questions as to the liabilities patients, physicians, prosthetic manufacturers, prosthetists, and therapists might face as the OI field continues to grow. Optimally, patients should receive extensive education promoting realistic expectations and their ongoing care by the original surgeons and treatment teams. However, given geographical issues, seeking care with the original surgical and rehabilitation team may not always be feasible. We believe that with proper education, collaboration, and communication, additional healthcare providers should be able to provide care for individuals with OI implants.

The U. S. Food and Drug Administration (FDA) stance on providing care to individuals with OI implants is evolving, from the insertion of the implants, rehabilitation during and after the implant, and management of prosthetic components attached to the implant. Specific OI devices that are surgically implanted are FDA Class III devices. We believe that for optimum prosthetic care and rehabilitation, the prosthetic system attached externally to the OI implant should remain in their current FDA designation and should not be reclassified as Class III simply because they are attached to an OI implant. We believe that changing the classification of currently available prosthetic components and devices would be detrimental to the best interest of individuals with amputations and their medical care.

Complementary to the advancement of OI technology will be advances to create improved human-machine interface strategies. Existing advanced surgical techniques, such as targeted muscle reinnervation within a residual limb, coupled with implantable electrodes, have the potential to provide greater multi-degrees of freedom prosthetic control that is intuitive and much more reliable than existing superficial skin sensors, which often move within fixed sockets or stop working with excessive perspiration. In addition, proof-of-concept studies have already demonstrated the ability to pick up tactile stimuli from an exoprosthesis and transmit electrical stimulation to the residual nerves of patients with amputation to restore sensation.^16-19

In summary, OI technology has the potential to positively disrupt the O&P field and is likely to revolutionize the care of individuals with limb loss. Our initial experiences and observations at Walter Reed National Military Medical Center demonstrate that our patients with upper-limb OI are not only able to perform all the functions typically achieved with traditional socket technology, but have faster donning/doffing times, are able to perform more bimanual activities accurately, and are more likely to use both upper limbs when performing activities of daily living. They are more independent with overhead activities and other recreational activities, such as catching and throwing a ball, completing woodworking projects, and experience improved support when using firearms. We have had similar positive experiences with patients who have received lower-limb OI and are in the process of performing more formal gait kinematic and kinetic evaluations with different prosthetic components to help better inform the community.

We also provide the following guidelines for those engaged in the care of patients who have had OI surgery and are pursuing prosthetic devices.