Thanks, Mark.
Total revenue for the fourth quarter 2017 was $11.7 million, up 24% when compared to $9.4 million for the same period in 2016. U.S. revenue in the fourth quarter 2017 increased 21%, to $8.8 million, when compared to $7.3 million in the same period last year, representing 75% of our total revenue. International revenue in the fourth quarter 2017 was $2.9 million, a 33% increase compared to $2.1 million in the same period last year, representing 25% of our total revenue.
Total revenue in 2017 was $45.6 million, a 22% increase compared to $37.3 million for 2016. U.S. revenue in 2017 was $34.9 million, a 21% increase compared to $28.8 million for 2016, representing 77% of our total revenue. International revenue in 2017 was $10.7 million, a 27% increase compared to $8.5 million for 2016, representing 23% of our total revenue.
Our fourth quarter and full year 2017 revenue breakdown by product category was as follows.
Trauma and deformity revenue in the fourth quarter 2017 was $8.5 million, a 27% increase compared to $6.7 million in the same period last year and $32.8 million in 2017, a 22% increase compared to $26.8 million in 2016. This was driven by double-digit growth across the majority of our product line.
Scoliosis revenue in the fourth quarter 2017 was $2.9 million, a 22% increase compared to $2.4 million in the same period last year and $11.6 million in 2017, a 24% increase compared to $9.3 million in 2016. This was driven by strong product acceptance and customer adoption, supplemented with growing sales competency in the U.S., partially offset by a slight reduction in international scoliosis sales due to the timing of cash collections.
Lastly, sports medicine and other revenue in the fourth quarter of 2017 was $286,000, representing an 18% decrease when compared to $348,000 in the same period last year, primarily due to lower set sales to our international distributors. Sports medicine/other revenue in 2017 was $1.2 million, an increase of 12% compared to $1.1 million in 2016. Nearly all of our revenue growth was driven by increased unit volumes.
Moving down the income statement, gross profit for the fourth quarter 2017 was $8.8 million, a 38% increase compared to $6.4 million in the same period last year. Gross margin in the fourth quarter of 2017 was 76%, compared to 68% in the fourth quarter of 2016. Gross profit in 2017 was $34.5 million, an increase of 31% compared to $26.4 million in 2016. Gross margin in 2017 was 76%, compared to 71% in 2016. As previously discussed, we have multiple factors driving the improvement in our gross margin, but the primary benefit comes from transitioning four countries from stocking distributors to an agency model.
Sales and marketing expense in the fourth quarter 2017 increased 27%, to $5.4 million, when compared to $4.3 million in the same period last year, and full year sales and marketing expense increased 23%, to $20.5 million, when compared to $16.7 million in 2016. This was driven by an increase in unit volumes sold and associated commissions in the U.S., the addition of commissions being paid in the four international markets that we have transitioned to an agency model, and ongoing marketing expenses.
General and administrative expenses in the fourth quarter 2017 were $6.7 million, an increase of 140% when compared to $2.8 million in the fourth quarter 2016. Fourth quarter 2017 included $2.1 million for accelerated noncash stock compensation as a result of our October 2017 IPO and $500,000 for new public company expenses. Total year 2017 G&A expenses were $17 million, an increase of 46% when compared to $11.6 million in the prior period. The full year results were also impacted by the unusual items reported in the fourth quarter. Excluding the previously mentioned unusual items, the fourth quarter and total year G&A expense increased as a result of additional personnel and resources to support the growth of our business as well as higher external professional fees.
Research and development expenses increased 51%, to $900,000, in the fourth quarter of 2017, when compared to $600,000 in the same period last year, and increased 54% to $3.4 million, compared to $2.2 million in 2016. The increase was due to the addition of experienced engineer personnel, significant product launches, as well as incremental project to accelerate our product development and future pipeline.
Total operating expenses in the fourth quarter 2017 were $13 million, an increase of 35% compared to $9.7 million in the fourth quarter of 2016, and total operating expenses in 2017 were $40.9 million, an increase of 26% compared to $32.5 million in 2016. Operating loss in the fourth quarter 2017 was $4.2 million, as compared to a loss of $3.3 million in the fourth quarter of 2016, and full year 2017 was a loss of $6.5 million, up from a loss of $6.1 million in 2016.
Adjusted EBITDA for the fourth quarter of 2017 was negative $612,000, compared to negative $473,000 for the fourth quarter of 2016, and adjusted EBITDA for the full year of 2017 increased approximately $937,000, or 94%, to a negative $58,000 compared to negative $995,000 for the full year of 2016.
Interest expense in the fourth quarter 2017 was $600,000, a 51% increase to $400,000 in the same period last year, and was $2.5 million for 2017, a 69% increase compared to $1.5 million for 2016. The increase in interest expense was due to the use of incremental debt to support the growth of the company and the transition of the four international countries to agency model.
Net loss in the fourth quarter 2017 was $4.8 million, compared to a net loss of $3.6 million in the same period last year. Net loss per share attributable to common stockholders in the fourth quarter of 2017 was $4.35 per basic and diluted share, or $3.03 per basic and diluted share in the same period last year.
Net loss in 2017 was $8.9 million, compared to $6.6 million in 2016. Net loss per share attributable to common stockholders in 2017 was $6.12 per basic and diluted share, compared to a loss of $7.14 per basic and diluted share in 2016.
Turning to our balance sheet, as of December 31, 2017, our cash balance was $42.6 million, compared to $1.6 million as of December 31, 2016.
As a reminder, in October we raised $46.9 million in net proceeds from our IPO after deducting underwriting expenses, commissions, offering expenses and payment of Series B dividends.
Net purchases of property and equipment during the fourth quarter 2017 were $1.3 million, a 27% decrease compared to $1.7 million during the same period last year, and were $5.2 million in 2017, a 20% increase compared to $4.3 million in 2016. The primary driver of an increase in purchase of property and equipment was the deployment of consigned sets, which include product-specific instruments as well as cases and trays. As Mark noted before, the consignment of additional sets in the future should drive future growth for the company.
As of December 31, 2017, total net debt was $25.5 million, up from $17.5 million as of December 31, 2016. The increase was primarily driven by the conversion of our four international countries to our agency model and additional consigned sets. During the fourth quarter we signed an amendment to our current debt agreement with Squadron Capital, our largest shareholder, to modify and extend the terms of our term notes and revolving credit facility. We were able to consolidate a majority of the term note amounts into a $20 million term loan and reestablish a $15 million revolver. We have used $3.9 million of the revolver credit facility.
In terms of guidance, we anticipate 22% annual sales growth for total year 2018. We plan to increase our annual investment in consigned sets from an average of $3.5 million historically to approximately $10 million for the full year of 2018.
Let me now turn the call back over to Mark for closing remarks.