Impact of periprosthetic femoral fracture fixation plating constructs on local stiffness, load transfer, and bone strains

Therapy aspects of peri-implant femoral fractures-a retrospective analysis of 64 patients

PURPOSE

The incidence of peri-implant femoral fractures (PIFF) is increasing. Information regarding outcomes, timing of surgery, risk factors, and a clinically applicable treatment algorithm are lacking. The aim of this study was to identify outcome-related risk factors and to derive a treatment algorithm.

METHODS

Sixty-four PIFFs treated between 01.01.2006 and 31.12.2020 in a level I trauma centre were evaluated retrospectively for fracture pattern, surgical technique, risk factors, complications, and 1-year mortality. The study was approved by the ethics committee (No. 21-2714-104).

RESULTS

One-year mortality was 24.1%. Surgical complications occurred in 4.7%, and general complications in 15.6% of the patients. General complications, low haemoglobin level at admission, elevated CHA2DS2-VASc, and Charlson score resulted in increased 1-year mortality. Time to surgery > 24 h did not increase complication or mortality rates. The three predominant fracture patterns were fractures close or distal to cephalomedullary nails, close or proximal to distal lateral plates, and close or distal to sliding hip screws. Recommendations for surgical treatment were derived: Osteosynthesis should enable as much weight-bearing as possible; the initial implant should only be removed, if this is essential for the new osteosynthesis; lateral locking plates should span the whole femur; antegrade nails should have a cephalomedullary component to avoid consecutive femoral neck fractures; implants should overlap to reduce the risk of consecutive inter-implant fractures.

CONCLUSION

Risk factors for 1-year mortality in patients with PIFFs were identified. A treatment algorithm and general principles for surgery of PIFFs were developed.

Impact of bone health on the mechanics of plate fixation for Vancouver B1 periprosthetic femoral fractures

BACKGROUND

Condyle-spanning plate-screw constructs have shown potential to lower the risks of femoral refractures after the healing of a primary Vancouver type B1 periprosthetic femoral fracture. Limited information exists to show how osteoporosis (a risk factor for periprosthetic femoral fractures) may affect the plate fixation during activities of daily living.

METHODS

Using total hip arthroplasty and plate-implanted finite element models of three osteoporotic femurs, this study simulated physiological loads of three activities of daily living, as well as osteoporosis associated muscle weakening, and compared the calculated stress/strain, load transfer and local stiffness with experimentally validated models of three healthy femurs. Two plating systems and two construct lengths (a diaphyseal construct and a condyle-spanning construct) were modeled.

FINDINGS

Osteoporotic femurs showed higher bone strain (21.9%) and higher peak plate stress (144.3%) as compared with healthy femurs. Compared with shorter diaphyseal constructs, condyle-spanning constructs of two plating systems reduced bone strains in both healthy and osteoporotic femurs (both applying 'the normal' and 'the weakened muscle forces') around the most distal diaphyseal screw and in the distal metaphysis, both locations where secondary fractures are typically reported. The lowered resultant compressive force and the increased local compressive stiffness in the distal diaphysis and metaphysis may be associated with strain reductions via condyle-spanning constructs.

INTERPRETATION

Strain reductions in condyle-spanning constructs agreed with the clinically reported lowered risks of femoral refractures in the distal diaphysis and metaphysis. Multiple condylar screws may mitigate the concentrated strains in the lateral condyle, especially in osteoporotic femurs.