The Company has two reporting segments, which consist of Global Spine and Global Extremities. Within the Global Spine reporting segment there are three product categories: Bone Growth Therapies, Spinal Implants and Biologics.

The tables below present net sales by major product category by reporting segment:

	Three Months Ended March 31,
(U.S. Dollars, in thousands)	2019		2018		Change
Bone Growth Therapies	$	47,283	$	46,163		2.4	%
Spinal Implants		22,903		20,707		10.6	%
Biologics		15,732		14,335		9.7	%
Global Spine		85,918		81,205		5.8	%
Global Extremities		23,194		27,504		-15.7	%
Net sales	$	109,112	$	108,709		0.4	%

The table below presents net sales, which includes product sales and marketing service fees, for the three months ended March 31, 2019 and 2018.

	Three Months Ended March 31,
(U.S. Dollars, in thousands)	2019		2018
Product sales	$	93,934	$	94,889
Marketing service fees		15,178		13,820
Net sales	$	109,112	$	108,709

Product sales primarily consist of the sale of bone growth therapy devices and internal and external fixation products. Marketing service fees are received from MTF Biologics based on total sales of biologics tissues and relate solely to the Global Spine reporting segment. Revenues exclude any value added or other local taxes, intercompany sales and trade discounts. Shipping and handling costs for products shipped to customers are included in cost of sales.

The Company’s contract assets, excluding trade accounts receivable (“other contract assets”), largely consist of payments made to certain distributors to obtain contracts, gain access to customers in certain territories, and to provide the benefit of the exclusive distribution of Orthofix products. Other contract assets are included in other long-term assets or other current assets, dependent upon the original term of the related agreement, and totaled $2.7 million and $1.9 million as of March 31, 2019, and December 31, 2018, respectively.