Introduction

Short-segment posterior instrumentation for spine fractures is threatened by unacceptable failure rates. Two important design objectives of pedicle screws, bending and pullout strength, may conflict with each other.

Backgrounds

Hip fractures have significant excess mortality, but it is unknown how long excess mortality persists. Our study was to explore the short and long term excess mortality after hip fractures, assess the impact of hip fracture on excess mortality and estimate the population attributable risk proportion (PARP) of risk factors for excess mortality.

Objective: For humeral nonunions, plating is threatened by severe osteoporosis or comminution. Locked nailing alone is threatened residual fracture gap and motion. In the present study, interfragmentary wiring was added to locked nailing for fragment compression to reduce the fracture gap and increase the fixation stability.

Materials and Methods: Locked nailing was augmented with figure-of-eight interfragmentary wiring for 62 consecutive non-infected humeral nonunions with osteoporosis or comminution. The average age of patients was 58.6 (26–87) years with an average nonunion duration of 18.5 (6–36) months. Nonunions were located at the proximal third in 10, middle third in 37, and distal third in 15. Fifty-six patients had previous operations including 38 platings and 18 nailings. Antegrade nailing was used in 39 and retrograde in 23. Thirty-two nonunions were nailed with 8-mm nails and thirty with 7-mm nails. Iliac bone autografts were used in 26 nonunions and allografts in 36. The average follow-up time was 35.8 (18–48) months.

Results: With a single operation, 60 patients achieved eventual union with an average time of 19.6 weeks. One of them had second revisional nailing and wiring because of wire breakage. Two patients still had a thin visible radiolucent line on radiographs 2 and 2.5 years respectively after operation, but their arm functions were satisfactory. Five patients had transient radial nerve palsies and no patients had deep infection. At follow-up, except 3 patients with associated pre-existing diseases, the average eventual Neer score (90.2) was significantly better than the average preoperative score (54.3). Three patients with retrograde nailing had residual extension loss of elbow joints, 8° in 1 and 5° in two, but there was no elbow function impairment. Two patients with shortening > 3 cm still had satisfactory arm function with minimal cosmetic problems. There were no signifiant differences about the healing rate and functional recovery between allograft group and autograft group. The main complication of graft donar site was immediate post-op pain.

Conclusions: Humeral nonunions with osteoporosis or comminution could be successfully treated by locked nailing with interfragmentary wiring. Allografts were as effective as autografts in achieve eventual union

Objectives: The purpose of this biomechanical study was to compare the mechanical properties of locked nails and screws made from either stainless steel or titanium alloy.

Methods: The specially designed locked nails and screws with the same structures were made from either stainless steel or titanium alloy. The structural factors investigated included inner diameter and root radius for locking screws and outer diameter and nail hole size for locked nails. The mechanical properties investigated included bending stiffness, strength, and fatigue life. Finite element models were used to simulate the mechanical tests and compute the stress concentration factors.

Results: Increasing the root radius and the inner diameter could effectively increase the fatigue strength of the locking screws. Fatigue strength increased more in titanium than in stainless steel screws, especially when the inner diameter was increased. In contrast, the titanium locked nails were much weaker than their stainless steel counterparts. Finite element models could closely predict the results of the biomechanical tests with a correlation coefficient that ranged from −0.58 to −0.84 for screws and was −0.98 for nails. The stress concentration factors ranged from 1 to 1.81 for screws and from 3.06 to 4.17 for nails.

Conclusions: With larger root radius and inner diameter, titanium locking screws could provide much stronger fatigue strength than stainless steel counterparts. However, titanium locked nails might lose their advantages of superior mechanical strength because of high notch sensitivity and this limitation should be a critical concern clinically. Finite element analyses could be reliably used in research and development of locked nails and locking screws.