SUPPLEMENTAL INDENTURE

Exhibit 4.3

Execution Version

SUPPLEMENTAL INDENTURE

Supplemental Indenture (this “Supplemental Indenture”), dated as of January 14, 2011, among SCA Surgery Holdings, LLC (the “Guaranteeing Subsidiary”), a subsidiary of Surgical Care Affiliates, LLC, a Delaware limited liability company (the “Company”), Surgical Holdings, Inc. (the “Co-Issuer” and, together with the Company, the “Issuers”) and Wells Fargo Bank, National Association, as trustee (the “Trustee”).

W I T N E S S E T H

WHEREAS, each of Surgical Care Affiliates, LLC, Surgical Holdings, Inc. and the Guarantors (as defined in the Indenture referred to below) has heretofore executed and delivered to the Trustee a Senior Subordinated Notes Indenture (the “Indenture”), dated as of June 29, 2007, providing for the issuance of an unlimited aggregate principal amount of 10.0% Senior Subordinated Notes due 2017 (the “Notes”);

WHEREAS, the Indenture provides that under certain circumstances the Guaranteeing Subsidiary shall execute and deliver to the Trustee a supplemental indenture pursuant to which the Guaranteeing Subsidiary shall unconditionally guarantee all of the Issuers’ Obligations under the Notes and the Indenture on the terms and conditions set forth herein and under the Indenture (the “Guarantee”); and

WHEREAS, pursuant to Section 9.01(8) 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, the parties mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes 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. The Guaranteeing Subsidiary hereby agrees as follows:

(a) Along with all other Guarantors named in the Indenture (including pursuant to any supplemental indentures), to jointly and severally unconditionally guarantee to each Holder of a Note authenticated and delivered by the Trustee and to the Trustee and its successors and assigns, irrespective of the validity and enforceability of the Indenture, the Notes or the obligations of the Issuers hereunder or thereunder, that:

(i) the principal of and interest and premium, if any, on the Notes shall be promptly paid in full when due, whether at maturity, by acceleration, redemption or otherwise, and interest on the overdue principal of and interest on the Notes, if any, if lawful, and all other obligations of the Issuers to the Holders or the Trustee thereunder shall be promptly paid in full, all in accordance with the terms thereof; and

(ii) in case of any extension of time of payment or renewal of any Notes or any of such other obligations, that same shall be promptly paid in full when due in accordance with the terms of the extension or renewal, whether at stated maturity, by acceleration or otherwise. Failing payment when due of any amount so guaranteed for whatever reason, the Guarantors and the Guaranteeing Subsidiary shall be jointly and severally obligated to pay the same immediately. This is a guarantee of payment and not a guarantee of collection.

(b) The obligations hereunder shall be unconditional, irrespective of the validity, regularity or enforceability of the Notes or the Indenture, the absence of any action to enforce the same, any waiver or consent by any Holder of the Notes with respect to any provisions hereof or thereof, the recovery of any judgment against the Issuers or any other Guarantor, any action to enforce the same or any other circumstance which might otherwise constitute a legal or equitable discharge or defense of a guarantor.

(c) The Guaranteeing Subsidiary hereby waives: diligence, presentment, demand of payment, filing of claims with a court in the event of insolvency or bankruptcy of the Issuers, any right to require a proceeding first against the Issuers, protest, notice and all demands whatsoever.

(d) This Guarantee shall not be discharged except by full payment of the obligations contained in the Notes, the Indenture and this Supplemental Indenture. The Guaranteeing Subsidiary accepts all obligations applicable to a Guarantor under the Indenture, including Articles XI and XII of the Indenture. The Guaranteeing Subsidiary acknowledges that by executing this Supplemental Indenture, it will become a Guarantor under the Indenture and subject to all the terms and conditions applicable to Guarantors contained therein.

(e) If any Holder or the Trustee is required by any court or otherwise to return to the Issuers, the Guarantors (including the Guaranteeing Subsidiary), or any custodian, trustee, liquidator or other similar official acting in relation to either the Issuers or the Guarantors, any amount paid either to the Trustee or such Holder, this Guarantee, to the extent theretofore discharged, shall be reinstated in full force and effect.

(f) The Guaranteeing Subsidiary shall not be entitled to any right of subrogation in relation to the Holders in respect of any obligations guaranteed hereby until payment in full of all obligations guaranteed hereby.

(g) As between the Guaranteeing Subsidiary, on the one hand, and the Holders and the Trustee, on the other hand, (x) the maturity of the obligations guaranteed hereby may be accelerated as provided in Article VI of the Indenture for the purposes of this Guarantee, notwithstanding any stay, injunction or other prohibition preventing such acceleration in respect of the obligations guaranteed hereby, and (y) in the event of any declaration of acceleration of such obligations as provided in Article VI of the Indenture, such obligations (whether or not due and payable) shall forthwith become due and payable by the Guaranteeing Subsidiary for the purpose of this Guarantee.

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(h) The Guaranteeing Subsidiary shall have the right to seek contribution from any non-paying Guarantor so long as the exercise of such right does not impair the rights of the Holders under this Guarantee.

(i) Pursuant to Section 11.02 of the Indenture, after giving effect to all other contingent and fixed liabilities that are relevant under any applicable Bankruptcy or fraudulent conveyance laws, and after giving effect to any collections from, rights to receive contribution from or payments made by or on behalf of any other Guarantor in respect of the obligations of such other Guarantor under Article XI of the Indenture, this new Guarantee shall be limited to the maximum amount permissible such that the obligations of such Guarantor under this Guarantee will not constitute a fraudulent transfer or conveyance.

(j) This Guarantee shall remain in full force and effect and continue to be effective should any petition be filed by or against the Issuers for liquidation, reorganization, should the Issuers become insolvent or make an assignment for the benefit of creditors or should a receiver or trustee be appointed for all or any significant part of the Issuers’ assets, and shall, to the fullest extent permitted by law, continue to be effective or be reinstated, as the case may be, if at any time payment and performance of the Notes are, pursuant to applicable law, rescinded or reduced in amount, or must otherwise be restored or returned by any obligee on the Notes and Guarantee, whether as a “voidable preference”, “fraudulent transfer” or otherwise, all as though such payment or performance had not been made. In the event that any payment or any part thereof, is rescinded, reduced, restored or returned, the Note shall, to the fullest extent permitted by law, be reinstated and deemed reduced only by such amount paid and not so rescinded, reduced, restored or returned.

(k) In case any provision of this Guarantee shall be invalid, illegal or unenforceable, the validity, legality, and enforceability of the remaining provisions shall not in any way be affected or impaired thereby.

(l) The obligations of the Guaranteeing Subsidiary under this Guarantee are subordinated in right of payment, to the extent and in the manner provided in Article XII of the Indenture, to the prior payment in full of all existing and future Senior Indebtedness of the Guaranteeing Subsidiary.

(m) Each payment to be made by the Guaranteeing Subsidiary in respect of this Guarantee shall be made without set-off, counterclaim, reduction or diminution of any kind or nature.

(3) Execution and Delivery. The Guaranteeing Subsidiary agrees that the Guarantee shall remain in full force and effect notwithstanding the absence of the endorsement of any notation of such Guarantee on the Notes.

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(4) Merger, Consolidation or Sale of All or Substantially All Assets.

(a) Except as otherwise provided in Section 5.01(c) of the Indenture, the Guaranteeing Subsidiary may not consolidate or merge with or into or wind up into (whether or not Guaranteeing Subsidiary is the surviving Person), or sell, assign, transfer, lease, convey or otherwise dispose of all or substantially all of its properties or assets, in one or more related transactions, to any Person unless:

(i)    (A) such Guaranteeing Subsidiary is the surviving Person or the Person formed by or surviving any such consolidation or merger (if other than such Guaranteeing Subsidiary) or to which such sale, assignment, transfer, lease, conveyance or other disposition will have been made is a Person organized or existing under the laws of the jurisdiction of organization of the Guaranteeing Subsidiary, as applicable, or the laws of the United States, any state thereof, the District of Columbia, or any territory thereof (the Guaranteeing Subsidiary or such Person, as the case may be, being herein called the “Successor Person”);

(B) the Successor Person, if other than such Guaranteeing Subsidiary, expressly assumes all the obligations of the Guaranteeing Subsidiary under the Indenture and the Guaranteeing Subsidiary’s related Guarantee pursuant to supplemental indentures or other documents or instruments in form reasonably satisfactory to the Trustee;

(C) immediately after such transaction, no Default exists; and

(D) the Company shall have delivered to the Trustee an Officer’s Certificate and an Opinion of Counsel, each stating that such consolidation, merger or transfer and such supplemental indentures, if any, comply with the Indenture; or

(ii) the transaction is made in compliance with Section 4.10 of the Indenture;

(b) Subject to certain limitations described in the Indenture, the Successor Person will succeed to, and be substituted for, such Guaranteeing Subsidiary under the Indenture and the Guaranteeing Subsidiary’s Guarantee. Notwithstanding the foregoing, such Guaranteeing Subsidiary may merge into or transfer all or part of its properties and assets to another Guarantor, the Company or the Co-Issuer.

(5) Releases. The Guarantee of the Guaranteeing Subsidiary shall be automatically and unconditionally released and discharged, and no further action by the Guaranteeing Subsidiary, the Issuers or the Trustee is required for the release of the Guaranteeing Subsidiary’s Guarantee, upon:

(1)    (A) any sale, exchange or transfer (by merger or otherwise) of the Capital Stock of the Guaranteeing Subsidiary, after which the Guaranteeing Subsidiary is no longer a Restricted Subsidiary or all or substantially all the assets of the Guaranteeing Subsidiary, in each case if such sale, exchange or transfer is made in compliance with the applicable provisions of the Indenture and the Guaranteeing Subsidiary is released from the guarantee, if any, of, and all pledges and security, if any, granted in connection with, the Senior Credit Facilities;

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(B) the release or discharge of the guarantee by the Guaranteeing Subsidiary of the Senior Credit Facilities or the release or discharge of the guarantee which resulted in the creation of the Guarantee, except a discharge or release by or as a result of payment under such guarantee;

(C) the designation of the Guaranteeing Subsidiary as an Unrestricted Subsidiary in compliance with the applicable provisions of the Indenture; or

(D) the Issuers exercising their Legal Defeasance option or Covenant Defeasance option in accordance with Article VIII of the Indenture or the Issuers’ obligations under the Indenture being discharged in accordance with the terms of the Indenture; and

(2) the Guaranteeing Subsidiary delivering to the Trustee an Officer’s Certificate and an Opinion of Counsel, each stating that all conditions precedent provided for in the Indenture relating to such transaction have been complied with.

(6) No Recourse Against Others. No director, officer, employee, incorporator or stockholder of the Guaranteeing Subsidiary shall have any liability for any obligations of the Issuers or the Guarantors under the Notes, any Guarantees, the Indenture or this Supplemental Indenture or for any claim based on, in respect of, or by reason of, such obligations or their creation. Each Holder by accepting Notes waives and releases all such liability. The waiver and release are part of the consideration for issuance of the Notes.

(7) Governing Law. THIS SUPPLEMENTAL INDENTURE WILL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

(8) 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.

(9) Effect of Headings. The Section headings herein are for convenience only and shall not affect the construction hereof.

(10) 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.

(11) Subrogation. The Guaranteeing Subsidiary shall be subrogated to all rights of Holders of Notes against the Issuers in respect of any amounts paid by the Guaranteeing Subsidiary pursuant to the provisions of Section 2 hereof and Section 11.01 of the Indenture; provided that, if an Event of Default has occurred and is continuing, the Guaranteeing Subsidiary shall not be entitled to enforce or receive any payments arising out of, or based upon, such right of subrogation until all amounts then due and payable by the Issuers under the Indenture or the Notes shall have been paid in full.

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(12) Benefits Acknowledged. The Guaranteeing Subsidiary’s Guarantee is subject to the terms and conditions set forth in the Indenture. The Guaranteeing Subsidiary acknowledges that it will receive direct and indirect benefits from the financing arrangements contemplated by the Indenture and this Supplemental Indenture and that the guarantee and waivers made by it pursuant to this Guarantee are knowingly made in contemplation of such benefits.

(13) Successors. All agreements of the Guaranteeing Subsidiary in this Supplemental Indenture shall bind its Successors, except as otherwise provided in this Supplemental Indenture. All agreements of the Trustee in this Supplemental Indenture shall bind its successors.

[Signatures on following page]

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

Signature Page to Supplemental Indenture (Senior Subordinated Notes) – SCA Surgery Holdings, LLC