Aims. The risk of mechanical failure of modular revision hip stems is frequently mentioned in the literature, but little is currently known about the actual clinical failure rates of this type of prosthesis. The current retrospective long-term analysis examines the distal and modular failure patterns of the Prevision hip stem from 18 years of clinical use. A design improvement of the modular taper was introduced in 2008, and the data could also be used to compare the original and the current design of the modular connection. Methods. We performed an analysis of the Prevision modular hip stem using the manufacturer’s vigilance database and investigated different mechanical failure patterns of the hip stem from January 2004 to December 2022. Results. Two mechanical failure patterns were identified: fractures in the area of the distal fluted profile (distal stem fracture) and failure of the modular taper (modular fracture). A failure rate of 0.07% was observed for distal stem fracture, and modular fracture rates of 1.74% for the original and 0.013% for the current taper design. Conclusion. A low risk of mechanical failure for both fracture types was observed compared to other known complications in revision hip arthroplasty. In addition, the data show that a design change did significantly reduce the risk of a modular fracture. Cite this article: Bone Joint J 2024;106-B(2):151–157

250 words max Long polished cemented femoral stems, such as the Exeter Hip Revision stem, are one option available to the revision hip arthroplasty surgeon. When proximal bone stock is compromised, distal fixation is often relied upon for stability of the femoral component. In such circumstances, torsional forces can result in debonding and loosening. This study compared the torsional behaviour of a cemented polished and featureless (plain) stem with cemented, polished stems featuring fins or flutes. Nine torsional tests were carried out on each of these three different stem designs. The finned stem construct was significantly stiffer than the fluted stem (mean 24.5 Nm/deg v 17.5 Nm/deg). The plain stem mean stiffness was less than the featured stems (13 Nm/deg), but wide variability lead to no statistically significant difference. The maximum torque of the finned (30.5 Nm) and fluted stems (29 Nm) was significantly higher than the plain stem (10.5 Nm); with no significance to the difference between the finned and fluted stems. Distal stem features may provide a more reliable and greater resistance to torque in polished, cemented revision hip stems. Finned stem features may also increase the stiffness of the construct. Consideration should thus be given to the incorporation of distal stem features in the design of revision hip stems

Aims

When performing revision total hip arthroplasty using diaphyseal-engaging titanium tapered stems (TTS), the recommended 3 to 4 cm of stem-cortical diaphyseal contact may not be available. In challenging cases such as these with only 2 cm of contact, can sufficient axial stability be achieved and what is the benefit of a prophylactic cable? This study sought to determine, first, whether a prophylactic cable allows for sufficient axial stability when the contact length is 2 cm, and second, if differing TTS taper angles (2° vs 3.5°) impact these results.

Purpose: Massive endoprostheses have become the mainstay of treatment for reconstruction after resection of primary bone tumours. The Kotz Modular Femoral Tibial Replacement (KMFTR, Kotz prosthesis, Stryker Inc.) system has been one of the most widely utilized uncemented modular systems. Although this prosthesis has excellent bone ingrowth characteristics and a low aseptic loosening rate, we have identified a significant incidence of mechanical failure and breakage of the prosthesis. The purpose of this investigation is to review the outcomes after prosthetic revision for a broken Kotz prosthesis. Method: A retrospective review was undertaken of our institutional database from the years 1989, when we first utilized the Kotz prosthesis, until present. We identified all patients who had undergone a revision of the prosthesis for mechanical failure or prosthetic breakage. Periprosthetic fractures and revisions for polyethylene bushing wear were excluded. Results: 119 distal femoral, 55 proximal tibial and 47 proximal femoral Kotz endoprostheses (221 in total) have been implanted in our center since 1989. There were 21 revisions (9.5% of total prostheses) for mechanical failure. Of these, 16 were in the distal femur, four in the proximal tibia and one in the proximal femur. Mechanical failures occurred at a mean of 77 months (range 24–170). Of the 21 metal failures, 8 stems broke at the junction of the stem and body, 8 fractured through screw holes in the stem, 3 fractured the derotation lug, one fractured the tibial housing and one lateral side-plate failed. Of these failures only three implants had associated definite loosening and two of these three were cemented. Broken stems initially required extraction whilst preserving as much of the longitudinal and transverse bone stock as possible in order to facilitate osseo-mechanical integration of the revision prosthesis. This was accomplished using trephines to core the ingrown broken stem out of the bone. Over the last 20 years, the 16 broken stems have been revised in 5 patients to larger Kotz uncemented stems, 2 to cemented GMRS stems with an adaptor to the KMFTR system, 3 to Restoration uncemented revision hip stems with a custom adaptor to the KMFTR system, 2 to custom GMRS uncemented stems with an adaptor to the KMFTR system, and 4 to total femurs. All except one patient was alive with no evidence of disease. Post-revision, 14 patients had TESS, MSTS87, MSTS93 scores of 80.5, 25.5 and 70 respectively. Conclusion: Despite very low aseptic loosening rates, mechanical failure of the Kotz prosthesis continues to be a significant clinical problem even several years after implantation. Fatigue failure often leads to the difficult scenario of removing a well-ingrown uncemented stem. Our data illustrates that these prostheses can often be successfully revised by trephining out the broken stem and inserting new uncemented stems. Functional outcome continues to be good and is comparable to pre-revision levels