Document:

<PAGE>

                                                                    Exhibit 4.17

                               AMENDMENT NO. 3 TO
                          REGISTRATION RIGHTS AGREEMENT

     AMENDMENT NO. 3 TO REGISTRATION RIGHTS AGREEMENT (this "Amendment") dated
as of November 20, 2002 by and among Concentra Inc., a Delaware corporation
formerly known as Concentra Managed Care, Inc. (the "Company"), the several
persons signatory hereto and named on Schedule I hereto under the heading
"Schedule I Purchasers" and the several persons signatory hereto and named on
Schedule II hereto under the heading "FFC Purchasers". Capitalized terms used in
this Amendment which are not otherwise defined herein shall have the meanings
ascribed to them in the Registration Rights Agreement referred to below.

                              W I T N E S S E T H:

     WHEREAS, the Company, the several persons named on Schedule I hereto under
the heading "Schedule I Purchasers" (the "Schedule I Purchasers") and the
several persons named on Schedule II hereto under the heading "FFC Purchasers"
(the "FFC Purchasers" and, together with the Schedule I Purchasers,
collectively, the "Purchasers") are parties to a Registration Rights Agreement
dated as of August 17, 1999 (the "Registration Rights Agreement");

     WHEREAS, on November 1, 2001, the Company issued to certain of its existing
shareholders an aggregate 2,266,546 shares of Company Common Stock and warrants
to acquire an aggregate 771,277 additional shares of Company Common Stock and,
in connection therewith, the Registration Rights Agreement was amended by
Amendment No. 1 thereto dated as of November 1, 2001 to provide for certain
registration matters relating to such 2,266,546 shares of Company Common Stock
and the 771,277 shares of Company Common Stock issuable upon exercise of such
warrants;

     WHEREAS, in connection with the Company's November 2001 acquisition of
National Health Resources, Inc. (the "NHR Merger"), the Registration Rights
Agreement was further amended by Amendment No. 2 thereto dated as of November 5,
2001 to permit the Company to grant certain registration rights with respect to
shares of Company Common Stock issued by the Company in the NHR Merger;

     WHEREAS, the Company proposes to issue an aggregate 1,515,152 shares of
Company Common Stock (the "New Common Shares") pursuant to the terms and
conditions of a Stock Purchase Agreement (the "Stock Purchase Agreement") dated
as of the date hereof among the Company and the purchasers named therein (the
"Purchasing Stockholders");

     WHEREAS, upon the issuance of the New Common Shares, each Purchaser will
own the number of shares of Company Common Stock, Company Class A Common Stock
and/or New Warrants, as the case may be, appearing opposite the name of such
Purchaser on Schedule I or Schedule II hereto, as the case may be;

                                        1

<PAGE>

     WHEREAS, it is a condition to the respective obligations of the Company and
the Purchasing Stockholders under the Stock Purchase Agreement that this
Amendment be executed and delivered by the Company and each of the Purchasing
Stockholders, including (i) the holders of a majority in interest of the
Restricted Stock currently held by the Schedule I Purchasers and (ii) the
holders of a majority in interest of the Restricted Stock currently held by the
FFC Purchasers;

     WHEREAS, the parties hereto desire to execute and deliver this Amendment in
order to fulfill such condition and to provide for certain registration matters
relating to the New Common Shares;

     NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements herein contained, the parties hereto hereby agree as
follows:

     SECTION 1. Amendments to Registration Rights Agreement. The Registration
Rights Agreement is amended as follows:

          (a)  Section 1 of the Registration Rights Agreement is amended by
deleting the definition of New Common Shares appearing therein and inserting in
the appropriate alphabetical order the following new definition:

               "'New Common Shares' shall mean the `New Common Shares' referred
          to in Amendment No. 1 to this Agreement dated as of November 1, 2001
          and the `New Common Shares' referred to in Amendment No. 3 to this
          Agreement dated as of November 20, 2002."

          (b)  Schedule I to the Registration Rights Agreement is deleted in its
entirety and replaced by Schedule I to this Amendment.

          (c)  Schedule II to the Registration Rights Agreement is deleted in
its entirety and replaced by Schedule II to this Amendment.

          (d)  All references to "FFT" or to the "FFT Purchasers" contained in
the Registration Rights Agreement shall be deleted and replaced by references to
"FFC" or to the "FFC Purchasers", as applicable.

     SECTION 2. Miscellaneous.

          (a)  This Amendment shall be governed by and construed in accordance
with the laws of the State of New York.

          (b)  This Amendment may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

          (c)  Headings and section reference numbers in this Amendment are for
reference purposes only and shall not in any way affect the meaning or
interpretation of this Amendment.

                                       2

<PAGE>

          (d)  This Amendment is limited precisely as written and shall not be
deemed to be a modification, acceptance or waiver of any other term, condition
or provision of the Registration Rights Agreement.

     IN WITNESS WHEREOF, each of the parties hereto has executed this Amendment
No. 3 to Registration Rights Agreement, all as of the day and year first above
written.

                                            CONCENTRA INC.

                                            By:  /s/ Richard A. Parr II
                                                 -----------------------
                                                 Richard A. Parr II
                                                 Executive Vice President,
                                                 General Counsel and Secretary

                       [PURCHASER SIGNATURE PAGES FOLLOW]

                                        3

<PAGE>

Address for Notices:                    The Purchasers:

c/o Welsh, Carson, Anderson & Stowe     WELSH, CARSON, ANDERSON & STOWE VIII,
                                        L.P.
320 Park Avenue                         By:  WCAS VIII Associates, L.L.C.,
Suite 2500                                    General Partner
New York, NY 10022
Attention: Jonathan Rather              By:    /s/ Jonathan M. Rather
Facsimile: (212) 893-9548                  -------------------------------------
                                             Managing Member

                                        WELSH, CARSON, ANDERSON & STOWE VI, L.P.
                                        By:  WCAS VI ASSOCIATES, L.L.C.
                                             General Partner

                                        By:  /s/ Jonathan M. Rather
                                           -------------------------------------
                                             Jonathan M. Rather
                                             Attorney-in-Fact

                                        WCAS MANAGEMENT CORP.

                                        By:  /s/ Jonathan M. Rather
                                           -------------------------------------
                                             Jonathan M. Rather
                                             Treasurer

                                        John Almeida, Jr.
                                        Bruce K. Anderson
                                        David F. Bellet
                                        Russell L. Carson
                                        Anthony J. deNicola
                                        James B. Hoover
                                        D. Scott Mackesy
                                        Thomas E. McInerney
                                        Robert A. Minicucci
                                        Priscilla A. Newman
                                        Andrew M. Paul
                                        Paul B. Queally
                                        Jonathan M. Rather
                                        Richard H. Stowe
                                        Sean M. Traynor
                                        Laura M. VanBuren
                                        Patrick J. Welsh

                                        By:  /s/ Jonathan M. Rather
                                           -------------------------------------
                                             Jonathan M. Rather, Individually
                                             and as Attorney- in-Fact

<PAGE>

                                              /s/ James D. Hann
                                        ----------------------------------------
                                            James D. Hann

                                              /s/ William G. Payne
                                        ----------------------------------------
                                            William G. Payne

                                              /s/ Kurt Anderson
                                        ----------------------------------------
                                            Kurt Anderson

                                              /s/ Arthur Canario, M.D.
                                        ----------------------------------------
                                            Arthur Canario, M.D.

                                              /s/ David Cardelle
                                        ----------------------------------------
                                            David Cardelle

                                              /s/ James Doody
                                        ----------------------------------------
                                            James Doody

                                              /s/ Steven E. Nelson
                                        ----------------------------------------
                                            Steven E. Nelson

                                              /s/ Robert Seeds
                                        ----------------------------------------
                                            Robert Seeds

                                              /s/ Timothy Smith
                                        ----------------------------------------
                                            Timothy Smith

<PAGE>

c/o Leeway & Co. (AT&T)                     J.P. MORGAN DIRECT CORPORATE FINANCE
J.P. Morgan Investment Management           INSTITUTIONAL INVESTORS LLC
522 5/th/ Avenue, 13/th/ Floor
New York, NY 10036
Attention: Robert Kiss                      By:  /s/ Robert E. Kiss
Facsimile: 212-837-1301                        ---------------------------------
                                                 Name:  Robert E. Kiss
                                                 Title: Portfolio Manager

                                            J.P. MORGAN DIRECT CORPORATE FINANCE
                                            PRIVATE INVESTORS LLC

                                            By:  /s/ Robert E. Kiss
                                               ---------------------------------
                                                 Name:  Robert E. Kiss
                                                 Title: Portfolio Manager

                                            522 FIFTH AVENUE FUND, L.P.

                                            By:  /s/ Robert E. Kiss
                                               ---------------------------------
                                                 Name:  Robert E. Kiss
                                                 Title: Portfolio Manager

<PAGE>

c/o CMS Companies                   CMS PEP XIV CO-INVESTMENT SUBPARTNERSHIP
1926 Arch Street
Philadelphia, PA 19103
Attention: Rick Mitchell
Facsimile: (215) 246-3083

                                    By:    /s/ Richard A. Mitchell
                                      ---------------------------------------
                                           Richard A. Mitchell
                                           Authorized Representative

                                    CMS CO-INVESTMENT SUBPARTNERSHIP II

                                    By:    /s/ Richard A. Mitchell
                                      ---------------------------------------
                                           Richard A. Mitchell
                                           Authorized Representative

                                    CMS DIVERSIFIED PARTNERS, L.P.

                                    By:    /s/ Richard A. Mitchell
                                      ---------------------------------------
                                           Richard A. Mitchell
                                           Authorized Representative

<PAGE>

c/o Hamilton Lane                 HAMILTON LANE PRIVATE EQUITY PARTNERS, L.P.
GSB Building
One Belmont Avenue, 9/th/ Floor   By:  HLSP Investment Management, LLC,
Bala Cynwyd, PA 19042                  its General Partner
Attention: Bradley Atkins
Facsimile: (610) 617-9853         By:  Hamilton Lane Investment Holdings, L.L.C.

                                  By:  Hamilton Lane Advisors, L.L.C.

                                  By:      /s/ Mario L. Giannini
                                       -------------------------------------
                                           Mario L. Giannini
                                           CEO

                                  HAMILTON LANE PRIVATE EQUITY FUND, PLC

                                  By:      /s/ Mario L. Giannini
                                       -------------------------------------
                                           Mario L. Giannini
                                           Director

                                  By:      /s/ Leslie A. Brun
                                       -------------------------------------
                                           Leslie A. Brun
                                           Director

<PAGE>

c/o Nassau Capital Funds, L.P.      NASSAU CAPITAL PARTNERS III L.P.
22 Chambers Street, 2/nd/ Floor
Princeton, NJ 08542
Attention: Jeffrey Tuder            By:        /s/ Robert Honstein
Facsimile: (609) 924-8887              -----------------------------------------
                                             Name: Robert Honstein
                                             Title:

                                    NASSAU CAPITAL PARTNERS IV, L.P.

                                    By:        /s/ Robert Honstein
                                       -----------------------------------------
                                             Name: Robert Honstein
                                             Title:

                                    NAS PARTNERS LLC

                                    By:        /s/ Robert Honstein
                                       -----------------------------------------
                                             Name: Robert Honstein
                                             Title:

<PAGE>

c/o Portfolio Advisors, LLC         A.S.F. CO-INVESTMENT PARTNERS, L.P.
9 Old Kings Highway South           By:  PAF 10/98, LLC
Darien, CT 06820                    By:  Old Kings I, LLC, as Managing Member
Attention: Jonathan Murphy
Facsimile: (203) 662-0013
                                    By:  /s/  Jonathan F. Murphy
                                       -----------------------------------------
                                         Name: Jonathan F. Murphy
                                         Title: Managing Member

<PAGE>

51 Madison Avenue, Suite 3009     NEW YORK LIFE CAPITAL PARTNERS, L.P.
New York, NY 10010                By: NYLCAP Manager LLC, its Investment Manager
Attention: Steven Benevento
Facsimile: (212) 576-5591
                                  By:      /s/ Steven Benevento
                                     -----------------------------------------
                                       Name: Steven Benevento
                                       Title:

<PAGE>

                                    FERRER FREEMAN & COMPANY, LLC

                                    on behalf of FFC PARTNERS I, L.P.
                                    and as its General Partner

                                    By:    /s/ Carlos A. Ferrer
                                       -----------------------------------------
                                           Carlos A. Ferrer
                                           Manager

                                       and

                                    on behalf of FFC EXECUTIVE PARTNERS I,
                                    L.P. and as its General Partner

                                    By:    /s/ Carlos A. Ferrer
                                       -----------------------------------------
                                           Carlos A. Ferrer
                                           Manager

                                       and

                                    on behalf of FFC PARTNERS II, L.P.
                                    and as its General Partner

                                    By:    /s/ Carlos A. Ferrer
                                       -----------------------------------------
                                           Carlos A. Ferrer
                                           Manager

<PAGE>

                                                                      SCHEDULE I

                              Schedule I Purchasers

                                  See attached.

Address for Schedule I Purchasers:

c/o  Welsh, Carson, Anderson & Stowe
     320 Park Avenue, Suite 2500
     New York, New York 10022
     Attention: Paul B. Queally
     Telecopy: (212) 893-9566

<PAGE>

                                                                     SCHEDULE II

                                 FFC Purchasers

                                  See attached.

Address for FFC Purchasers:

c/o   Ferrer Freeman & Co.
        The Mill
        10 Glenville Street
        Greenwich, Connecticut 06831
        Attention: Carlos Ferrer
        Telecopy: (203) 532-8016<PAGE>

                                                                    Exhibit 4.18

                AMENDMENT NO. 4 TO REGISTRATION RIGHTS AGREEMENT

     This Amendment No. 4 to Registration Rights Agreement (this "Amendment"),
dated as of December 1, 2002, by Concentra Inc., a Delaware corporation formerly
known as Concentra Managed Care, Inc. (the "Company"), and a majority in
interest of each of the Schedule I Purchasers and FFC Purchasers (each as
hereinafter defined). Capitalized terms used in this Amendment which are not
otherwise defined herein shall have the respective meanings assigned to them in
the Registration Rights Agreement referred to below.

                                   WITNESSETH:

     WHEREAS, the Company is party to a certain Registration Rights Agreement
dated as of August 17, 1999 (as amended, the "Registration Rights Agreement"),
together with the several persons named on Schedule I thereto under the heading
"Schedule I Purchasers" (the "Schedule I Purchasers"), and the several persons
named on Schedule II thereto under the heading "FFC Purchasers" (the "FFC
Purchasers" and, together with the Schedule I Purchasers, collectively, the
"Purchasers"); and

     WHEREAS, on November 1, 2001, the Company issued to certain of its existing
shareholders an aggregate 2,266,546 shares of Company Common Stock and warrants
to acquire an aggregate 771,277 additional shares of Company Common Stock and,
in connection therewith, the Registration Rights Agreement was amended by
Amendment No. 1 thereto dated as of November 1, 2001, to provide for certain
registration matters relating to such 2,266,546 shares of Company Common Stock
and the 771,277 shares of Company Common Stock issuable upon exercise of such
warrants; and

     WHEREAS, in connection with the Company's November 2001 acquisition of
National Healthcare Resources, Inc. (the "NHR Merger"), the Registration Rights
Agreement was further amended by Amendment No. 2 thereto dated as of November 5,
2001, to permit the Company to grant certain registration rights with respect to
shares of Company Common Stock issued by the Company in the NHR Merger; and

     WHEREAS, on November 20, 2002, the Company issued to certain of its
existing shareholders an aggregate 1,515,152 shares of Company Common Stock and,
in connection therewith, the Registration Rights Agreement was amended by
Amendment No. 3 thereto dated as of November 20, 2002, to provide for certain
registration matters relating to such 1,515,152 shares of Company Common Stock;
and

     WHEREAS, in connection with the Company's December 1, 2002, acquisition of
Em3 Corporation ("Em3"), the Company issued an aggregate 1,826,956 shares of
Company Common Stock to certain of its existing shareholders and to certain
former shareholders of Em3 who were not already shareholders of the Company, and
the Company wishes to afford to such new shareholders the opportunity to become
parties to the Registration Rights Agreement as set forth herein; and

                                       1

<PAGE>

     WHEREAS, pursuant to Section 13(d) thereof, the Registration Rights
Agreement can be amended as set forth in this Amendment by approval of the
Company and affirmative vote of a majority in interest of each of the Schedule I
Purchasers and FFC Purchasers;

     NOW, THEREFORE, in consideration of the foregoing and the mutual agreements
and covenants set forth herein and other good and valuable consideration, the
parties hereto agree as follows:

     1.   Amendment to Registration Rights Agreement. Schedule I to the
Registration Rights Agreement is hereby amended to include each of the persons
set forth in Exhibit A hereto "Joining Persons"), upon such Joining Persons'
execution and delivery of a Joinder Agreement substantially in the form attached
hereto as Exhibit B.

     2.   Miscellaneous.

          (a)  This Amendment shall be governed by and construed in accordance
with the laws of the State of New York.

          (b)  This Amendment may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

          (c)  Headings and section reference numbers in this Amendment are for
reference purposes only and shall not in any way affect the meaning or
interpretation of this Amendment.

          (d)  This Amendment is limited precisely as written and shall not be
deemed to be a modification, acceptance or waiver of any other term, condition
or provision of the Registration Rights Agreement.

     IN WITNESS WHEREOF, the parties hereto have executed this Amendment as of
the date first above written.

                                 CONCENTRA INC.

                                 By:   /s/ Richard A. Parr II
                                    ---------------------------------
                                       Richard A. Parr II
                                       Executive Vice President

         [Schedule I Purchaser and FFC Purchaser Signature Page Follows]

                                        2

<PAGE>

Schedule I Purchasers:               WELSH, CARSON, ANDERSON & STOWE VIII, L.P.
                                     By:  WCAS VIII Associates, L.L.C.,
                                          General Partner

                                     By:  /s/ Jonathan M. Rather
                                       ----------------------------------------
                                          Managing Member

                                     WELSH, CARSON, ANDERSON & STOWE VI, L.P.
                                     By:  WCAS VI ASSOCIATES, L.L.C.
                                          General Partner

                                     By:  /s/ Jonathan M. Rather
                                        ---------------------------------------
                                          Jonathan M. Rather
                                          Attorney-in-Fact

FFC Purchasers:                      FERRER FREEMAN & COMPANY, LLC
                                     on behalf of FFC PARTNERS I, L.P.
                                     and as its General Partner

                                     By:  /s/ Carlos A. Ferrer
                                        ---------------------------------------
                                          Carlos A. Ferrer
                                          Manager

                                                    and

                                     on behalf of FFC EXECUTIVE PARTNERS I, L.P.
                                     and as its General Partner

                                     By:  /s/ Carlos A. Ferrer
                                        ----------------------------------------
                                          Carlos A. Ferrer
                                          Manager

                                                     and

                                     on behalf of FFC PARTNERS II, L.P.
                                     and as its General Partner

                                     By:  /s/ Carlos A. Ferrer
                                        ---------------------------------------
                                          Carlos A. Ferrer
                                          Manager

                                        3

<PAGE>

                                    EXHIBIT A

                                 Joining Parties

Michael Correia

Gary Zigenfus

William R. Winton

Eric Lee

Curtis J. Hoffman

Trudy Rios

Elijah C. Marentette

John K. Carlyle

Ken Wilkinson

Michael T. Fricke

Michael S. McCord

Kristan A. Covey

Ben Morgan

Geneva M. Giang

Mary P. Nixon

                                      A-1

<PAGE>

                                    EXHIBIT B

                            Form of Joinder Agreement

                                JOINDER AGREEMENT

     This Joinder Agreement (the "Joinder") to the Amendment No. 4 to
Registration Rights Agreement, dated as of August 17, 1999 (as amended, the
"Registration Rights Agreement"), among Concentra Inc. (f/k/a Concentra Managed
Care, Inc.), a Delaware corporation ("Concentra"), and the several persons named
in Schedules I and II thereto, is executed and delivered by ________________
(the "Joining Party") as of December 1, 2002. Each capitalized term used but not
otherwise defined herein shall have the meaning set forth in the Registration
Rights Agreement.

     1. Agreement to be Bound. The Joining Party hereby agrees to be bound by
all of the terms of the Registration Rights Agreement, attached to this Joinder
as Exhibit A (as the same may be hereafter amended, restated, or otherwise
modified from time to time). The Joining Party shall hereafter be deemed to be a
"Schedule I Purchaser" and a "Purchaser" for all purposes under the Registration
Rights Agreement.

     2. Concentra Representations and Warranties. Each of the representations
and warranties of Concentra set forth in the Registration Rights Agreement is
true and correct in all material respects as of the date hereof with the same
effect as though such representation and warranty had been made on and as of
this date.

     3. Notices. For purposes of notices and other communications to be
delivered to the Joining Party, the addresses and facsimile numbers set forth
below shall be deemed an amendment to Schedule I of the Registration Rights
Agreement with respect to the Joining Party.

     4. Governing Law. This Joinder Agreement shall be governed by and construed
in accordance with the laws of the State of New York.

AGREED AND ACCEPTED:                  __________________________________________
                                             Signature of Joining Party

CONCENTRA  INC.
                                      Print Name:_______________________________

By:_________________________          Address:__________________________________
     Richard A. Parr II
     Executive Vice President                 __________________________________

                                      Facsimile No:_____________________________

                                       B-1

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