[Comparative static biomechanical studies of tripod surface structures of cementless endoprostheses]

[On the history of cementless implants in extremity surgery]

The aim of implantation of cementless hip prostheses is vital ingrowth of bone into the structured metal surface of the implant. Since the 1960s several implants with surfaces made of cobalt-based alloys have been produced for this purpose. In the 1980s a novel hip endoprosthesis with a spongiosa-metal surface was introduced. The three-dimensional ingrowth of bone tissue into the structured surface of the implant could be demonstrated both histologically and using scanning electron microscopy (SEM). These implants made of cobalt-based alloys can also be used in endo-exo prostheses. Titanium implants with a microstructured surface have also been used and very good osseintegration of the surface was also demonstrated by histomorphology. The optimization of the surface and design of the prostheses plays an increasingly more important role in the field of revision endoprostheses.

[Endo-exo prostheses following limb-amputation]

BACKGROUND AND OBJECTIVE

Rehabilitation of patients having undergone limb amputation is difficult due to problems related to poor socket fit, which often deteriorates comfort, gait and the ability to take part in everyday life and work. The endo-exo prosthesis has been an alternative provision for people having undergone lower limb amputation for reasons other than diabetes or peripheral vascular disease for more than 10 years. The system consists of an intramedullar, osseointegrated and skin perforating prosthesis, which is implanted in the remaining bone and has an abutment to allow the attachment of the external prosthetic part including the knee joint in the case of a trans-femoral amputation. The idea originates in findings of modern tooth-implantology and involves a two-step operation. This study focuses on one centre's experience with the endo-exo prostheses in Lübeck, Germany, to describe and discuss the reliability of this alternative treatment method after lower limb amputation.

MATERIALS AND METHODS

This article presents the results of lower limb amputees operated on in Lübeck, Germany between 1999-2013. It focuses on theoretical aspects of osseointegration and different clinically-based findings using the endo-exo technique over the last decade.

RESULTS

74 lower-limb amputees were treated with an endo-exo prosthesis until December 2013. There were only 4 verified intramedullar infections, yet there were many unplanned surgical revisions secondary to soft-tissue infections in the beginning. They were successfully encountered via clinically-based changes that were made concerning implant design, wound treatment and operative technique.

CONCLUSIONS

Since 1990 a few groups have developed an innovative method that provides an alternative to traditional socket-type prostheses. This involves a skeletally anchored device that is inserted into the remaining stump and provides osseointegration into the bone. The distal part of the implant protrudes transcutaneously and allows attachment to a prosthetic limb. This creates a hard point where the forces are transmitted through the skeleton with a more physiological pathway because the bone becomes the force carrier again, closer in biomechanics to an able-bodied person. With long-term numbers that show successful osseointegration for more than 10 years it is evident that obligate bacterial colonization does not necessarily lead to an intramedullar infection. Especially short stumps that are difficult to treat with a socket can be successfully fitted with an endo-exo prosthesis. Amputees who would otherwise be bound to a wheelchair due to their challenging situation should specifically be regarded as potential profiteers of this novel treatment option.

[Implantation of the endo-exo femur prosthesis to improve the mobility of amputees]

OBJECTIVE

Improvement of function following above-knee amputation with an osseointegrated, transcutaneous femoral implant as a hard point for the exo prosthesis, the so-called endo-exo femur prosthesis (EEFP).

INDICATIONS

Above knee amputation following trauma, tumor, or infection.

CONTRAINDICATIONS

Diabetes, PAOD, psychiatric diseases, use of chemotherapeutic or corticosteroid medication, nonconcluded bone growth, lack of compliance, and florid infection at the time of implantation.

SURGICAL TECHNIQUE

Performed as a two-step procedure: Stage 1 (implantation): sharp dissection of the end of the residual bone, adequate access to the intramedullar canal, cortical reaming using curettes and a flexible drill followed by cement-free, press-fit implantation of the endoprosthesis itself, closing of the soft tissue coat of the femur stump to reduce the risk of infection, assurance of primary and secondary stability via the metal spongiosa-like surface of the implant (Spongiosa Metal 2®). Stage 2 (exteriorization): 6 weeks postoperatively, opening of the skin at the distal point of the femur stump, the soft tissue between the skin and endoprosthesis is then removed and the double conus and the connecting adapter for the exoprothesis is attached.

POSTOPERATIVE MANAGEMENT

Ascending weight bearing depending on bone quality. On average, full weight bearing can be achieved 8-10 weeks after stage 1 surgery.

RESULTS

The first endo-exo femur prosthesis (EEFP) was implanted in 1999. Through December 2009, 39 cases were operated in Lübeck, early serosanguinous drainage, soft tissue problems at the stoma, and ascending infections after mobilization of the patients could be minimized by further development of the design of the EEFP. Intramedullary infections were the exception (1 of 39 patients). A total of 4 explantations had to be performed (3 due to infection and 1 due to prosthetic failure). Two of those patients were again provided with an EEFP. Overall, the EEFP improved the gait pattern because of the bone-guided transmission of muscle power, increased osseoperception, and improved economical energy balance. Of the 39 patients, 37 said that they would again undergo operation.

Long-term results of the metal-cancellous cementless Lübeck total hip arthroplasty: a critical review at 12.8 years

INTRODUCTION

The influence of a spongy metal surface total hip arthroplasty (THA) (S&G, ESKA, Lübeck, Germany) on the clinical, psychometric, and radiograhic long-term results were examined.

MATERIAL AND METHODS

An amount of 137 THA with the cementless spongy metal Lübeck hip prosthesis were evaluated long-term, radiographically and clinically, with a mean follow-up time of 12.8 years (range 10.1-14.9 years). The MOS SF-36 was used to assess the health-related quality of life (HRQL).

RESULTS

Cumulative survival rates were 90% (+/-8%) for the cups and 86% (+/-5%) for the stems at 14.9 years. Four stems fractured at the middle part (3%) without major trauma. In the remaining patients the clinical results expressed as Harris Hip Score (HHS) averaged 88 (range 34-100). Patients above 60 years undergoing THA had no significant difference in HRQL (MOS SF-36) in comparison to the age-matched healthy population (P>0.05). Patients younger than 60 years had scores lower than normal in the physical function domains (P<0.01), but were comparable in the mental health domains (P>0.05). Radiolucent lines and bone atrophy related to stress shielding by distal fixation were found in the periprosthetic Gruen Zone I (19.8, 16.8%) and VII (10.3, 27.1%) of the proximal femur.

DISCUSSION

Whereas the rate of aseptic cup failures of the cementless spongy metal Lübeck hip prosthesis is among the best, the failure rate of the stems is attributable to osteolysis of the proximal femur. The fractures of the stem may be attributed to the combination of the lack of proximal support, the fully porous stem made of a cast cobalt-chrome-molybdenum alloy, and the narrow dimension of the stem core. The long-term results of the spongy metal cup are good, whereas the high loosening and fracture rate of fully coated stem are a source of concern especially with regard to the difficult revision scenario with frequent massive bone loss.