Impaction Grafting for Repair of Proximal Humeral Fractures

with Hemiarthroplasty: Thermal and Biomechanical Implications1Timothy M. Hoggard, B.S.; 1Jeremy Miles, M.D.; 1Chris R. James, M.D.; 2Ben Cottrell, B.S.;

1Leon Anijar, B.S.; 2Brandon G. Santoni, Ph.D.; 3Mark A. Mighell, M.D.1 University of South Florida, Morsani College of Medicine, Tampa, FL

2Phillip Spiegel Orthopaedic Research Laboratory, Foundation for Orthopaedic Research and Education, Tampa, FL3 Shoulder and Elbow Service, Florida Orthopaedic Institute, Tampa, FL

Proximal humeral fractures are common osteoporosis

related fractures, with most occurring in patient

populations greater than 60 years of age. Greater

tuberosity malunion subsequent to hemiarthroplasty is

often met with poor clinical results, including decreased

functionality and patient dissatisfaction. While

tuberosity failure involves several factors, it is known

that thermal injury to bone occurs with the curing of

methylmethacrylate cement used for implant fixation.

Prior studies have shown thermal injury to bone is

initiated at 47°C. This complication may be avoided

using an impaction grafting technique, consisting of

cementing the implant stem distally and the use of

impacted bone graft proximally. To date, neither the

thermal consequence nor the biomechanical stability of

this construct has been validated in a controlled

laboratory setting.

Thermal data demonstrated no significant difference in mean baseline temperature at any

position between the groups (Table 1). A significant decrease in the maximum-recorded

temperature at the surgical neck was observed in Group 2 (39.7 +/- 4.1°C) when

compared to Group 1 (55.7 +/- 9.1°C, p=0.005), with no difference between maximum-

recorded temperatures at the cement mantle between the groups (p=0.451).

Biomechanical data demonstrated increased relative micromotion at baseline (2.5 N-m) in

Group 2 (1.4 +/- 0.6°) compared to Group 1 (0.3 +/- 0.1°, p=0.002). Relative

micromotion was also significantly increased at maximal torsion (10 N-m) in Group 2

(5.8 +/- 2.0°) compared to Group 1 (1.7 +/- 0.6°, p=0.002).

The exposure of bone to elevated temperature produces

well-known detrimental effects and may contribute to

tuberosity malunion following proximal humeral

fracture repair with hemiarthroplasty. This study offers

significant laboratory-based evidence indicating

impaction grafting of hemiarthroplasty stems may aid in

avoiding tuberosity thermal damage elicited by the use

of methylmethacrylate bone cement. However, this

potential benefit may come at the expense of acute

construct stability, thus adding further insight for the

clinical and surgical management of these fractures.

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Surgical neck fractures were created in matched pairs of

cadaveric humeri (n=7). Each was instrumented with a

hemiarthroplasty stem and randomized to: (1) a cement

group receiving full cementation or (2) an impaction

grafting group receiving only cement distally and bone

graft proximally. During instrumentation,

thermocouples measured cortical temperature at the

stem tip (representing the cement mantle), 2.5 cm distal

to the surgical neck (representing the cement-graft

interface in Group 2) and at the surgical neck

(tuberosity interface). Torsional loading was applied in

2.5 N-m increments up to 10 N-m to evaluate relative

micromotion between the implant stem and humeral

shaft.

Table 1. T0 and TMAX Values in the Control and Experimental Group.

Distal (°C) Middle (°C) Proximal (°C)

Group Temp. Mean SD Mean SD Mean SD

Cement T0 37.0 0.6 36.7 1.0 36.4 1.5

Graft T0 36.4 1.5 35.2 3.0 34.9 2.9

p-value 0.230 0.156 0.118

Cement TMAX 53.6 7.2 49.4 6.4 55.7 9.1

Graft TMAX 53.1 5.4 44.6 5.2 39.7 4.1

p-value 0.451 0.096 0.005

37.0

47.0

57.0

67.0

77.0

Dist Mid Prox

TM

AX

(°C

)

CEMENT

GRAFT

47°C – injury

onset

p=0.005

52°C

Irreversible

Damage

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Baseline 2.5 N-m 2.5 N-m 5 N-m 7.5 N-m 10 N-m

Ro

tati

on

[d

egr

ee

s]

Relative Rotation [degrees]

IMPACTION GRAFT TREATMENT

CEMENTED CONTROL

A B

Acknowledgements: The authors would like to acknowledge Jacob Cox, M.D., and Aniruddh

Nayak for assistance in data collection and experimental execution

Research Supported By: This research was supported by a summer scholarly award from the

Scholarly Concentrations Program at USF Health, Morsani College of Medicine and implant

stems were provided by DJO Global.