Transcutaneous osseointegration for amputees with short residual bone: Is there increased risk for complications? – A pilot study

Jason Shih Hoellwarth; Adam Daniel Geffner; Taylor J Reif; S Robert Rozbruch

doi:10.4103/jllr.jllr_22_22

ORIGINAL ARTICLE

Year : 2022 | Volume : 8 | Issue : 2 | Page : 115-120

Transcutaneous osseointegration for amputees with short residual bone: Is there increased risk for complications? – A pilot study

Jason Shih Hoellwarth, Adam Daniel Geffner, Taylor J Reif, S Robert Rozbruch
Department of Orthopedic Surgery, Limb Lengthening and Complex Reconstruction Service, Hospital for Special Surgery, New York, NY, USA

Date of Submission	11-Jun-2022
Date of Decision	03-Oct-2022
Date of Acceptance	07-Oct-2022
Date of Web Publication	29-Dec-2022

Correspondence Address:
Adam Daniel Geffner
519 E 72^nd Street, New York, NY 10021
USA

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jllr.jllr_22_22

Abstract

Aims: Transcutaneous osseointegration for amputees (TOFA) provides improved mobility and quality of life for most patients versus a traditional socket prosthesis. One uncertainty regarding TOFA is whether a minimum residual bone length is necessary to achieve solid fixation. This study evaluated the relationship between residual bone length and occurrence of post-TOFA complications requiring operative intervention. Patients and Methods: A retrospective review of our osseointegration registry was performed. Inclusion criterion was index osseointegration at least 12 months prior. Chart review included demographics and whether additional surgery occurred to manage noninfected loosening, periprosthetic fracture, and infection. Occurrence rates were compared using binary logistic regression analysis and by stratifying implants as <140 versus ≥140 mm. Results: Sixty segments were included (58 patients and 2 bilateral femur amputees). The implant length averaged 129.4 ± 31.1 (48–200) mm. No noninfected loosening occurred. Six patients (10%) had infection-related post-TOFA operation, at lengths ranging from 130 to 160 mm (representing the central 60% of implant lengths): five were debridement with implant retention and one other was removed. No implants below 130 mm (n = 19, 32%) required debridement or removal. Three patients (5%) had periprosthetic fracture (all femurs), at lengths ranging from 140 to 160 mm (the central 55% of implant lengths); no implants below 140 mm (n = 22, 37%) had periprosthetic fracture. Regression identified no association between length and noninfected loosening (P = 1.000), periprosthetic fracture (P = 0.999), or infection (P = 0.124). Dichotomized <140 versus ≥140 mm rates of complication were as follows: noninfected loosening (0/22 = 0% vs. 0/38 = 0%, P = 1.000), fracture (3/38 = 7.9% vs. 0/22 = 0%, P = 0.292), and infection (5/38 = 13.2% vs. 1/22 = 4.5%, P = 0.400). Conclusion: Residual bone length does not appear to be associated with post-TOFA reoperation to address noninfected loosening, periprosthetic fracture, or infection. The "minimum necessary" length of bone to achieve stable transcutaneous osseointegration capable of supporting full body weight remains uncertain.

Keywords: Osseointegration, short amputation, short femur

How to cite this article:
Hoellwarth JS, Geffner AD, Reif TJ, Rozbruch S R. Transcutaneous osseointegration for amputees with short residual bone: Is there increased risk for complications? – A pilot study. J Limb Lengthen Reconstr 2022;8:115-20

How to cite this URL:
Hoellwarth JS, Geffner AD, Reif TJ, Rozbruch S R. Transcutaneous osseointegration for amputees with short residual bone: Is there increased risk for complications? – A pilot study. J Limb Lengthen Reconstr [serial online] 2022 [cited 2023 Mar 27];8:115-20. Available from: https://www.jlimblengthrecon.org/text.asp?2022/8/2/115/366302

Introduction

For patients with a limb amputation, the most common rehabilitation strategy is to provide a skin-suspended socket prosthesis (SP). Over the last 30 years, and particularly the last decade, there has been expanding evidence supportive that transcutaneous osseointegration for amputees (TOFA)^[1] confers superior mobility and quality of life.^[2],[3],[4] This reconstructive procedure directly anchors an intramedullary metal prosthesis into the residual skeleton such as a femur [Figure 1] or tibia [Figure 2], which is then passed through a permanent skin stoma to allow the attachment of a relatively standard external prosthetic limb. The implant remains stable over the long term through the biologic phenomenon of osseointegration, which is the growth of bone extremely close to the bioinert implant, so as to achieve a painless and effectively motionless construct between the implant and the bone.^[5] This interdigitation provides the strength to resist implant motion relative to the bone such as proximal migration, rotation, or pull-out. Accordingly, the strength of osseointegration is associated with the area and depth of the bone–implant interface.^[6],[7],[8]

Figure 1: Preoperative (a) and 2.5-year postoperative (b and c) clinical photographs, along with preoperative (d) and 10-month postoperative (e) AP radiographs of a 37-year-old female with a right transfemoral amputation due to a motor vehicle accident 3 years prior to osseointegration. She underwent lengthening and valgus correction on the residual limb 1 year prior to osseointegration at an outside institution in hopes of tolerating a SP but remained unable. She presented with an 81 mm residual femur and received a 25 mm × 80 mm OPL implant. The lateral plate and proximal screws from the valgus correction surgery were retained to protect the femoral neck from fracture. AP: Anterior-posterior, SP: Socket prosthesis, OPL: Osseointegrated prosthetic limb

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Figure 2: Preoperative (a) and 10-month postoperative (b and c) clinical photographs, as well as preoperative (d) and 1-month postoperative (e) AP radiographs of a 63-year-old male with a right transtibial amputation due to a crush injury 12 years prior to osseointegration. He presented with an 80 mm residual tibia and received a 28 mm × 70 mm OPL implant. AP: Anterior-posterior, OPL: Osseointegrated prosthetic limb

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The strength of pull-out resistance per unit area is not well determined. Therefore, there is no ability to quantify the amount of bone necessary for TOFA implants. The standard length of the textured stem of the original press-fit TOFA implant (integrated limb prosthesis; Orthodynamics, Lubeck, Germany) is 140 mm long. Our group uses the currently most common TOFA implant (osseointegrated prosthetic limb; Permedica Medical Manufacturing, Lecco, Italy), which is 160 mm. Most amputees have residual bones that are at least this long, but some have shorter residual bone, which requires a modification of the implant or of technique. Distraction osteogenesis can be performed prior to TOFA to try to increase the bone's length to that of the standard implant. Our strategy is to cut the implant shorter to fit the femur [Figure 1] or tibia [Figure 2] length. Studies of oral surgery have identified that a relatively short available alveolar height does not impair the stability and utility of osseointegrated dental implants.^[9],[10] However, for amputee osseointegration, there has never been an investigation into whether a shorter residual extremity bone length may be associated with adverse events such as infection, loosening, or periprosthetic fracture.

This study aims to address that knowledge gap by analyzing the rate of unplanned postosseointegration surgery for amputees with traditionally normal-length implants versus patients with implants modified to accommodate substantially shorter bone lengths.

Patients and Methods

Following institutional approval, a retrospective review of our osseointegration registry was performed. All patients whose index osseointegration was performed at least 12 months prior were included. Chart review included demographics and the primary outcome: whether additional surgery was required to address noninfectious loosening, periprosthetic fracture, or infection (debridement with implant retention, or implant removal). Antibiotic administration (oral or parenteral) without operative intervention was not counted because of the relatively low threshold to prescribe antibiotics (likely leading to a high rate of type 1 error, false positive). Indications for surgical intervention were based on individual surgeon discretion, not standardized a priori. The additional surgery rates were compared in two ways: first, using binary logistic regression analysis (XLMiner Analysis ToolPak for Google Sheets, Frontline Systems Inc., Incline Village, NV 89450, USA), and second, by stratifying implants as <140 mm (the length of the shorter traditional press-fit osseointegration implant stem, the Integral Limb Prosthesis) versus ≥140 mm and comparing complication frequency using Fisher's exact test (QuickCalcs, GraphPad Software, San Diego, CA, USA). Significance was set as P ≤ 0.05.

Results

[Table 1] summarizes the demographics and outcomes of all the patients as well as the dichotomized cohorts. Sixty osseointegrated segments were included (58 patients and 2 bilateral femur amputees): 34 femur, 2 humerus, 2 radius, and 22 tibia implants. The implant length averaged 129.4 ± 31.1 (48–200) mm. One patient, a 34-year-old female with a right transfemoral amputation, presented following unsuccessful attempted lengthening at another institution which was undertaken to facilitate SP use; she had osseointegration with an 80 mm implant without subsequent issues [Figure 1]. One case of implanting a grossly undersized femoral implant which fell out before loading was excluded (the patient's revision procedure was included, evaluated as a primary procedure).

Table 1: Demographics and outcomes

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[Table 2] and [Figure 3] detail the complications. Six patients (10%) had an operation to manage infection, at lengths ranging from 130 to 160 mm (representing the central 60% of implant lengths): five had debridement with implant retention and one had implant removal. No implants below 130 mm (n = 19, 32%) required debridement or removal. Three transfemoral amputees (5%) sustained periprosthetic fracture (detailed previously),^[11] at lengths ranging from 140 to 160 mm (the middle 55%); no implants below 140 mm (n = 22, 37%) had periprosthetic fracture. Regression identified no association between length and noninfected loosening (P = 1.000), periprosthetic fracture (P = 0.999), or infection (P = 0.124). Dichotomized <140 versus ≥140 mm rates of complication were as follows: noninfected loosening (0/22 = 0% vs. 0/38 = 0%, P = 1.000), fracture (3/38 = 7.9% vs. 0/22 = 0%, P = 0.292), and infection (5/38 = 13.2% vs. 1/22 = 4.5%, P = 0.400).

Figure 3: Visualization of the number of implants and complications, arranged by implant length. Each block represents one implant (amputated bone as identified). The complications are identified as color coded

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Table 2: Patients who had additional surgery following osseointegration

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Discussion

The most important finding of this study is that performing osseointegration on relatively short residual bone using implants shorter than standard length is not associated with an increased risk of subsequent surgery for noninfected loosening, periprosthetic fracture, or infection. In fact, a shorter bone was associated with a lower frequency of subsequent surgery, although this difference was not significant. Only one implant under 140 mm required subsequent surgery, and none under 130 mm. The shortest femur implant was 90 mm, and the shortest tibia implant was 60 mm.

Titanium-alloy and cobalt-alloy TOFA implants have consistently proven stable in human patients since 1990, both in screw-type and press-fit-type designs.^[1] However, the minimum amount of implant–bone contact to prevent pull-out has not been investigated. Accordingly, the topic of short residual bone has not been evaluated. Further, while there are some studies evaluating the pull-out strength in small animals such as mice^[12],[13] and rabbits,^[14] such data are not informative for human TOFA. There are few studies evaluating pull-out strength in large animals. One study using a screw-type implant in dogs found a maximal pull-out strength of 1.55 kN (approximately 350 pounds).^[15] A study of press-fit style implants reported 800–1200 N (180–270 pounds) with the resistance to pull-out increasing significantly through at least 24 weeks.^[16] Another canine femur study reported a pull-out force of 142 kgf (313 pounds, 1255 N) at 4–8 weeks.^[17] Bovine jaw osseointegration pull-out strength has been measured as 520 N (120 pounds) at 26 weeks but is not likely representative of human extremities given the substantial difference of implant size and bone tissue. No studies could be found regarding press-fit style implants in human-sized animal limbs. To our knowledge, there also have not been well-designed clinically applicable studies of pull-out strength of osseointegrated implants in human extremities.

The surgical options to improve the prosthesis experience for amputees with short residual bone remain controversial. Patients whose tibias are too short to wear socket prostheses may have improved prosthesis use facilitated by transfemoral amputation,^[18] but this eliminates an otherwise functional and rather beneficial knee joint. Conversely, lengthening an amputee's short bone using distraction osteogenesis before osseointegration could provide a long bone for an osseointegration implant. However, lengthening costs time and money, and bone lengthening has its own diverse set of associated complications.^{[19],[20],[21],[22]} Amputee lengthening is particularly difficult. Some complications may even require additional surgery to harvest bone from the patient's well leg,^[23] creating a potential for disability in a new extremity. Longer residual limbs provide better prosthesis control^[24] for amputees using SPs, but the osseoperception provided by TOFA^[25] may dominate the control-related benefits of lengthening. Since no evidence proves any particular length to be too short for extremity osseointegration stability, and the relatively high potential for lengthening complications, we believed that TOFA without lengthening could be a reasonable alternative to lengthening prior to TOFA. Thus far, that belief seems justified. The most frequent adverse events following TOFA are infection and periprosthetic fracture, with noninfected loosening being much less common. In our cohort, infection and fracture occurred less frequently in patients with shorter residual bone than those with "normal" or longer residual bone. The concern of inadequate fixation resulting in noninfected loosening or pull-out did not occur (one patient did have her prosthesis fall out several days following implantation, but that was due to a grossly undersized implant placed early in our experience; her revision osseointegration has been uneventful). TOFA without lengthening for patients with short residual femurs [Figure 1] and tibias [Figure 2] has avoided both the risks of lengthening and the concerns of insufficient fixation.

This study's limitations must be recognized. This was a retrospective observational study. The total cohort size (60 segments) was relatively small, and also of heterogeneous bones (humerus, forearm, femur, tibia). Patient demographics (age, sex, and weight) were diverse, and activity level was not evaluated. Comorbidities such as diabetes and smoking, while exceptionally infrequent, were not accounted for. Implant lengths were not planned in preparation for a comparison study and patients were not matched in any manner, limiting the comparison of "short" versus "long" cohorts. In addition, the total complication rate of all patients was low, further limiting this study's power to identify adverse events. Furthermore, the notion of a "short" residual bone was made arbitrary of a biologically supported definition, but given there is no known standard, it seemed reasonable to use the convenience standard of a typical implant length. Certainly, many aspects of selection bias (such as patients who present seeking TOFA and also patients who are considered appropriate) can also impact the findings. Notwithstanding these important limitations, we believe that the investigation is merited and meaningful. The total number of TOFA procedures in literature is not immense, but interest is rapidly growing. Whether amputees with relatively short residual bone should be directly osseointegrated, lengthened before osseointegration, or flatly contraindicated remains both unclear and not previously investigated. Further, truly understanding likely important factors such as patient activity level remains poorly evaluable, as observed walk tests are greatly influenced by patient culture, sex, height, and test experience.^[26],[27] In addition, the indications for post-TOFA operative intervention were not set a priori, so the results are subject to the surgeons' clinical judgment. The fundamental intent of this study was to identify any obvious safety concerns using short implants, in order to avoid patient harm. It is certainly acknowledged that a more robust study of large patient numbers, controlling for anticipated factors such as sex and weight and medical morbidities, is necessary to more definitively understand the extent to which bone length matters for TOFA.

The most notable strength of this is the lack of any patients being lost to follow-up; no complications were potentially undocumented. We also believe that given the dearth of data regarding pull-out strength of press-fit extremity osseointegration, this study provides important clinical insight regarding the topic of the ability of short bone to support full extremity loading via an osseointegrated implant.

Conclusion

Residual bone length does not appear to be associated with a risk for operative intervention for infection or for periprosthetic fracture following TOFA. Residual lower extremity limbs as short as 60 mm and upper extremity limbs as short as 48 mm appear to be capable of providing an uncomplicated experience following osseointegration. The "minimum necessary" length of bone to achieve stable transcutaneous osseointegration capable of supporting full body weight remains uncertain.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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