Biomechanics of periprosthetic femur fractures and early weightbearing

Periprosthetic Fractures around Total Hip Replacement-Is There a Rush to Fix?

BACKGROUND

Periprosthetic fractures now account for 14.1% of all hip revisions. Surgery is often highly specialised and can involve the revision of implants, fixation of fractures, or a combination of both. Delays to surgery are frequent as specialist equipment and surgeons are often required. UK guidelines are currently moving in favour of early surgery in a similar way to the neck of femur fractures, despite a lack of evidential consensus.

METHODS

A retrospective review of all patients who underwent surgery for periprosthetic fractures around a total hip replacement (THR) at a single unit between 2012 and 2019 was performed. Risk factors for complications, length of stay (LOS), and time to surgery data were collected and analysed using regression analysis.

RESULTS

A total of 88 patients met the inclusion criteria: 63 (72%) were treated with open reduction internal fixation (ORIF) and 25 (28%) underwent revision THR. Baseline characteristics were similar in both the ORIF and revision groups. Revision surgery was more likely to be delayed than ORIF owing to the need for specialist equipment and personnel (median 143 h vs. 120 h, p = 0.04). Median LOS was 17 days if operated within 72 h and 27 days if delayed beyond this (p < 0.0001), but there was no increase in 90-day mortality (p = 0.66), HDU admission (p = 0.33), or perioperative complications (p = 0.27) with delay beyond 72 h.

CONCLUSION

Periprosthetic fractures are complex and require a highly specialised approach. Delaying surgery does not result in increased mortality or complications but does increase length of stay. Further multicentre research into this area is required.

Biomechanical analysis of different fixation methods for Rorabeck II supracondylar femoral fractures after total knee arthroplasty

BACKGROUND

Locking plate (LP) and retrograde intramedullary nailing (RIMN) are widely used to fix Rorabeck II supracondylar femoral fractures after total knee arthroplasty (TKA). The biomechanical properties of the implant used for treatment influence its longevity. Therefore, we aimed to evaluate the biomechanical stability of different fixations using finite element analysis.

METHODS

Seven finite element models (FEMs) were established, including LP groups (short LP, long LP, and double LP), RIMN groups (short RIMN and long RIMN), and mixed groups (long LP with short RIMN and long LP with long RIMN). The stress of the implants around the fracture area was calculated to evaluate the biomechanical stability under loads.

RESULTS

Stress was mainly distributed around the fracture area in all models. The stress-shielding phenomenon was most evident in the short LP. The trend in maximum equivalent stress values of implants around the fracture area for the seven internal fixations was: short LP (324.63 MPa) > short RIMN (306.37 MPa) > long LP (275.06 MPa) > long RIMN (262.74 MPa) > double LP (203.19 MPa) > long LP with short RIMN (124.42 MPa) > long LP with long RIMN (112.41 MPa). We found that the double LP can better disperse the stress than a single LP, and a long LP with long RIMN can prevent stress concentration and make the stress distribution more uniform.

CONCLUSION

From the perspective of biomechanics, long LP with long RIMN can stabilize fractures and avoid stress concentration in Rorabeck II supracondylar femoral fractures after TKA.

LOQTEQ® VA Periprosthetic Plate-A New Concept for Bicortical Screw Fixation in Periprosthetic Fractures: A Technical Note

Internal fixation using angle stable plates is the treatment standard in periprosthetic fractures around stable implants. To provide instant postoperative full weight-bearing, bicortical screw fixation is advisable but often surgically demanding. This work presents the first clinical results of the LOQTEQ^® VA Periprosthetic Plate (aap Implantate AG, Berlin, Germany), a new plate system to simplify screw placement around implants. This plate system uses insertable hinges that allow for variable angle screw anchorage. Data of 26 patients with a mean age of 80 years and a mean follow-up of 13.9 months were retrospectively collected. Patients were clinically and radiologically examined. Bony union was achieved in 14 out of 15 patients with no signs of non-union or implant loosening. One patient, however, presented with implant failure. Clinical scores demonstrated acceptable results. Since the hinge plates are easy to apply, the first results are promising.