There has been a longstanding need for a structural biomaterial that can serve as a bone graft substitute or implant construct and is effective for fixation by bone ingrowth. A porous tantalum material was developed to address these issues. The purpose of this paper and presnetation is to describe the properties and 2 to 5 year clinical results of porous tantalum in various reconstructive orthopaedic procedures.

Porous tantalum has been used to manufacture primary and revision acetabular cups, acetabular augments, tibial and patella implants, patellar augments, structural devices for the treatment of osteonecrosis, and spinal fusion implants. Clinical follow-up includes: 2–5 year clinical and radiographic evaluation of: 414 monoblock cups in primary THA, 36 monoblock cups and 587 revision hemispheres used in revision THR, 16 hips revised with acetabular augments and revision hemispheres; 2 to 4 years for 101 tibial implants used in primary TKR and 69 patellas used in cementless TKR; 2–4 years for 11 patellar augments in salvage TKR, 1–5 years for 53 revision TKRs using knee spacers; 1–4 years for 91 osteone-crosis hip implants; and for 15 cervical fusion cases.

This innovative tantalum implant material with trabecular architecture possesses advantages in stiffness, friction coefficient, porosity, rate and extent of tissue ingrowth, and versatility in manufacturing of structural devices. It has been clinically validated in numerous and diverse reconstructive procedures.

Purpose: A porous tantalum cylindrical shaped implant (Osteonecrosis Intervention Implant, Zimmer, Warsaw, IN) has been designed to provide subchondral bony support of the subchondral plate, be osteoconductive and allow revascularization of an osteonecrotic femoral head. This study evaluates retrieved implants obtained at the time of conversion to total hip arthroplasty to determine the ability of this device to fulfill its objectives. |

Methods: Eighteen femoral heads with the tantalum implant still in situ were evaluated with contact radiographs and scanning electron microscopy to assess femoral head and bony anatomy, bone growth into the implant and femoral head revascularization. Retrievals from 12 males and 6 females with an average age of 46 years old (range, 31–61) and Stage I or II osteonecrosis were evaluated. |

Results: At a mean of 13.4 months (range, 3–36) postoperatively, all femoral heads demonstrated subchondral collapse. The bone surrounding the implant remained necrotic with no evidence of revascularization or healing. Ingrowth was marginal and averaged less than 5%.

Conclusions: This tantalum implant in its present design and surgical technique does not appear to uniformly provide structural support and promote healing of early osteonecrosis of the femoral head. This retrieval study suggests that successful results with this implant in certain cases of early osteonecrosis may be more attributable to the surgical technique requiring a core decompression, rather than the implant itself. |

Introduction: Proximal porous coating for cementless fixation of femoral stems enjoys increasing popularity. We report on the intermediate to long-term results with a circumferentially proximally coated stem with a non-porous cylindrical diaphyseal portion. The smooth stem provides temporary rotational stability so that proximal bony ingrowth can occur.

Materials and methods: Between 1991 and 1994, 124 Multilock stems were implanted in 101 patients. Patients were followed prospectively and re-evaluated at a minimum five years postop (range 60 to 117 months) by an author other than the surgeon. Four patients (5 hips) were lost to follow-up. Five patients (6 hips) had died. Twenty-six patients (30 hips) had phone interviews more than five years after surgery, but no radiographs as they refused to return for followup. None of these patients had required additional surgery and all were extremely satisfied with their outcomes. Sixty-six patients (83 hips) had clinical and radiographic followup at minimum five-years post-op. This report focuses upon this last group.

Results. The average age at surgery was 53.8 years (range, 27–75). The average follow-up was 78 months (range, 60–117). The average Harris Hip Score was 93 (range, 52–100). One stem had been revised for loosening (1%), and none were radiographically loose. Eight patients (9.6%) had minimal thigh pain related to excessive activity. These patients required mild analgesics only. Eighty-two stems (99%) achieved bony ingrowth. Twenty-nine stems (35%) had minimal osteolysis limited to Zones 1 and 7. There were no cases of diaphyseal lysis. Radiolucent lines adjacent to the porous coating were evident in 3 stems (3.6%), and along smooth portions in 20 stems (24%). No radiolucent lines were progressive or divergent. Some degree of stress shielding in the proximal metaphysis was evident in 52 hips (63%), but only 2 had cortical resorption.

Discussion and conclusion. Given the young age and high activity level of this cohort of patients, the Multilock stem has fared extremely well. Loosening and revision rates were very low, and distal osteolysis had not occurred. Bony fixation occurred reliably. Proximal stress shielding remains concerning and further follow-up will determine whether this becomes clinically significant. Lastly, patient function and satisfaction were high. In conclusion, the Multilock proximally porous-coated stem can be expected to perform well in the intermediate to long-term in young, active patients.

Threaded acetabular components are widely used in cementless total hip replacement, despite a poor understanding of the nature of the bone-implant interface. We have examined one case in which the threaded titanium ring appeared to be well incorporated with no discernible radiolucency. Microradiography and histology surprisingly showed that the threads were entirely encapsulated in fibrous tissue. This raises doubt about the relevance of plain radiography to the analysis of the acetabular interface.

Total hip replacement using porous-coated cobalt-chrome femoral implants designed for biological fixation has been evaluated in 307 patients after two years and in 89 patients after five years. Histological study of 11 retrieved specimens showed bone ingrowth in nine and fibrous tissue fixation in two. Fixation by bone ingrowth occurred in 93% of the cases in which a press fit of the stem at the isthmus was achieved, but in only 69% of those without a press fit. The clinical results at two years were excellent. The incidence of pain and limp was much lower when there was either a press fit of the stem or radiographic evidence of bone ingrowth. Factors such as age, sex, and the disease process did not influence the clinical results. Most cases showed only slight resorptive remodelling of the upper femur, but in a few cases with a larger, more rigid stem, more extensive bone loss occurred. The results after five years showed no deterioration with time. Fixation by the ingrowth of bone or of fibrous tissue both appeared to be stable, but bone ingrowth gave better clinical results.