SUPPLEMENTAL INDENTURE

Exhibit 4.2

EXECUTION VERSION

SUPPLEMENTAL INDENTURE

SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as of April 3, 2012, among United Surgical Partners International, Inc., a Delaware corporation (the “Company”), each of the Guarantors listed on the signature pages hereto, (each a “Guaranteeing Subsidiary” and, collectively, the “Guaranteeing Subsidiaries”), and U.S. Bank National Association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, USPI Finance Corp. (“USPI Finance”) and the Trustee entered into that certain Indenture, dated as of April 3, 2012 (the “Indenture”), related to the 9.000% Senior Notes of USPI Finance due 2020 in original principal amount of $440,000,000 (the “Securities”);

WHEREAS, each Guaranteeing Subsidiary is to become a Guarantor under the Indenture and shall unconditionally guarantee all of the Issuer’s Obligations under the Notes and the Indenture on terms and conditions set forth herein;

WHEREAS, on the date hereof, USPI Finance is merging with and into the Company, with the Company being the surviving Person of such merger (the “Merger”); and

WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is authorized to execute and deliver this Supplemental Indenture.

NOW THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, each Guaranteeing Subsidiary and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders as follows:

1. CAPITALIZED TERMS. Capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture.

2. AGREEMENT TO GUARANTEE. Effective upon consummation of the Merger, each Guaranteeing Subsidiary shall be a Guarantor under the Indenture and be bound by the terms thereof applicable to Guarantors, including, but not limited to, Article 10 thereof.

3. ASSUMPTION OF OBLIGATIONS. Effective upon consummation of the Merger, the Company, pursuant to Section 5.01 of the Indenture, expressly assumes all of the Obligations of USPI Finance under the Indenture and the Securities.

4. EFFECT OF SUPPLEMENTAL INDENTURE. This Supplemental Indenture is an amendment supplement to the Indenture, and the Indenture and this Supplemental Indenture will henceforth be read together.

5. NEW YORK LAW TO GOVERN. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

6. COUNTERPARTS. The parties may sign any number of copies of this Supplemental Indenture. Each signed copy shall be an original, but all of them together represent the same agreement.

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7. EFFECT OF HEADINGS. The Section headings herein are for convenience only and shall not affect the construction hereof.

8. THE TRUSTEE. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by the Guaranteeing Subsidiary and the Issuer

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IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed and attested, all as of the date first above written.

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]