Microscopic Metallic Wear and Tissue Response in Failed Titanium Hallux Metatarsophalangeal Implants: Two Cases

INTRODUCTION

Various surgical treatment options for hallux rigidus have been described, including open or arthroscopic debridement, cheilectomy, resection arthroplasty, arthrodesis, and prosthetic replacement. ^{5,6,9,11,17 –19,25,27,28,38,40,42,43} First MP joint implant arthroplasty gained popularity after results with silicone rubber implants were reported. ⁴⁰ Subsequently, various implant designs have been developed, ^{1,3,5,9,17 –19,23,27,28,38} including the titanium hallux MP implant consisting of a tray replacing the joint space and a single stem in the proximal phalanx. ^3,23 Reported advantages of implant arthroplasty include pain relief and preservation of joint motion and length. ^{1,3,5,17,18,23,42} Complications of implant arthroplasty include joint stiffness, joint instability, transfer lesions, implant loosening and failure, silicone synovitis, soft tissue foreign body reaction, and progressive shortening of the hallux. ^{20,24,32,38,43}

The transformation of intact implant material into particulate debris, and the capacity to induce a foreign-body granulomatous membrane response, are important in the development of osteolysis leading to aseptic loosening of other orthopaedic implants such as total hip prostheses. ^{7,8,15,16,26,29,30,33,37,44} However, there is no available information about the synovial-like membrane at the implant-bone interface of failed titanium single stem hallux implants. In this study, we analyzed the membrane retrieved from two failed titanium single stem hallux implants to evaluate the hypothesis that metallic wear debris may cause a foreign-body reaction that may result in osteolysis and implant loosening.

CASE REPORTS

CASE 1

A 71-year-old woman with a history of gout, currently treated with colchicine, had had left first MP joint titanium single stem implant arthroplasty 2.6 years earlier at another institution. She had had open treatment of an ipsilateral left calcaneus fracture eight months ago. She currently developed acute pain at the left hallux with associated bruising, without recent trauma. The left hallux proximal phalanx was tender, and the hallux was in more valgus alignment than previously. Radiography showed that the MP joint implant was in dorsiflexion relative to the proximal phalanx, with the tip of the stem abutting against the thinned and expanded dorsal cortex of the proximal phalanx. There was a zone of radiolucency around the implant stem inside a surrounding sclerotic rim (Fig. 1).

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Fig. 1:

Preoperative radiographs of the left hallux in a 71-year-old woman, 2.6 years after titanium single stem first MP implant arthroplasty (case 1). (a) Anteroposterior view showing the zone of radiolucency around the implant stem inside a surrounding sclerotic rim.(b) Lateral view demonstrating that the MP joint implant is in dorsiflexion relative to the proximal phalanx. The tip of the implant stem abuts against the thinned and expanded dorsal cortex of the proximal phalanx.

Histology

Tissue specimens from the bone-implant interface of both patients were evaluated. The fibrous tissue membranes with attached bone fragments were excised from the proximal phalanx cavity after implant removal. The specimens were fixed in 4% paraformaldehyde (two days) and then decalcified in 14% EDTA (two weeks), washed in graded ethanol solutions, and stored overnight at 4°C in 100% ethanol. The specimens were then transferred to xylenes and embedded in paraffin. Tissue sections were cut, stained with hematoxylin and eosin, and examined under a microscope.

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Fig. 2:

Intraoperative appearance of failed titanium single stem first MP implant arthroplasty (case 1). (a) The implant is noted in situ, without any visible evidence of corrosion or discoloration of surrounding tissues. A dense, white, fibrous membrane is noted between the implant tray and the first metatarsal head (adjacent to the medial retractor). The dorsal cortex of the proximal phalanx is egg-shell thin and dorsally expanded, with evidence of microfracture and reactive bone formation. (b) The bony canal of the proximal phalanx is lined with a thick, white, fibrous membrane separating the implant stem (removed) from the bone. A fragment of the fibrous membrane is noted to the left of the curette tip as it is being removed.

Histologic analysis of the tissue from both patients revealed fibrous tissue stroma adjacent to the bone surface, which showed multiple regions of scalloping, covered by mononuclear cells (Fig. 3, 4). Fine metallic debris was seen throughout the fibrous tissue. A mild monocytic infiltrate was present, but polymorphonuclear leukocytes were absent. Multinucleated foreign-body giant cells were sparsely observed associated with fine metallic wear debris.

DISCUSSION

The histologic studies of the tissue membrane from the bone-implant interface of failed titanium hallux implants showed metallic debris and cellular reaction. These findings are similar to those observed in membranes retrieved from the implant-bone interface and the iliopsoas bursa of total hip arthroplasties complicated by aseptic loosening and osteolysis. ^{7,8,15,16,26,29,30,33,35,37,44,45} A similar reaction had also been observed in association with a loose custom total-knee titanium prosthesis. ³⁹ Information about the mechanism of failure and technique for salvage of failed titanium hallux implant arthroplasty should be useful because this procedure continues to be recommended by some practitioners ³⁶ and is currently used in approximately 1,500 joints annually in the United States. ¹⁴

Radiolucent lines may occur adjacent to well-fixed total hip prostheses without a fibrous layer as a result of peri-implant osteoporosis. ²¹ Furthermore, reaction to titanium may occur in a well-fixed total hip replacement as a result of wear debris from the prosthetic femoral head ^2,22 or screws ²² or cell-mediated immunity to titanium. ²² However, the hallux prostheses in the current study were noted at surgery to be grossly loose and were associated with a fibrous membrane. The macrophages and multinucleated giant cells observed (Fig. 3, 4) are characteristic of a foreign body granuloma caused by the metallic debris. Scalloping of the bone surface with mononuclear cells is consistent with osteolysis resulting from active bone resorption by inflammatory cells. Cell cultures of the retrieved membranes from hip implants have shown that this tissue may produce a variety of substances, including prostaglandin E2, collagenase, interleukin-1, and tumor necrosis factor, ^7,8,29 that may contribute to bone resorption and osteolysis. ^7,8,12,29 The absence of polyethylene from the hallux MP implants excludes this polymer—commonly used in total hip prostheses—as a potential source of inflammation in the current cases. Therefore, the histologic findings about the failed titanium hallux MP implants support the hypothesis that aseptic loosening of the implants, with osteolysis at the bone-implant interface, was caused by a foreign-body granulomatous inflammatory reaction associated with metallic debris, similar to that observed in aseptic failed total-hip arthroplasties.

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Fig. 3:

Microscopic appearance of the membrane-bone interface excised from the proximal phalanx canal (case 1). (a) Fibrous tissue (right) and scalloped bone edges (arrow) are noted suggestive of bone remodelling (low magnification).(b) Fine metallic wear debris (arrows) is noted within the fibrous tissue. A multinucleated giant cell is observed (arrowhead) (high magnification).

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Fig. 4:

Microscopic appearance of the membrane-bone interface excised from the proximal phalanx canal (case 2). (a) Fibrous tissue and scalloped bone edges (arrow) are noted suggestive of bone remodelling (low magnification). (b) Fine metallic wear debris (arrow) is noted within the fibrous tissue (high magnification).

Titanium has been used in joint arthroplasty because of favorable characteristics including low density, high tensile strength, excellent resistance to fatigue, superb ductility and formability, low modulus of elasticity, remarkable anticorrosive properties, and superior biocompatibility. ^13,35 In contrast, the known liabilities of titanium may include poor resistance to wear, notch sensitivity, and potential toxicity. ^33,41 The gross black staining previously observed in the membranes adjacent to failed total-hip implants had been attributed to metallic debris contained within histiocytes and giant cells. ^7,8,29,33 The absence of gross black staining of the tissues about the hallux implants is consistent with the histologic finding that the inflammatory cellular reaction was sparse, perhaps attributed to factors such as implant size, duration of implantation, and local tissue vascularity.