What does Mid-Level Practitioner mean?

When you first visit our offices, you will be seen by an Attending Physician (the supervising faculty member), a Resident (a doctor who has completed medical school and now is in specialty training for orthopaedics), a Nurse Practitioner (NP), a Physician Assistant (PA), or a Registered Nurse (RN). One of these professionals will talk to you and conduct your initial physical exam.

NPs and PAs are clinical professionals with advanced degrees (Masters Degree) who are licensed to practice medical care, and who work in collaboration with physicians. NPs and PAs are collectively referred to as Mid-Level Providers or Practitioners. They can diagnose, plan treatment, and prescribe medication and therapies (physical therapy, occupational therapy). RNs are responsible for caring for and educating patients and implementing orders written by physicians, PAs or NPs, but are not licensed to make official diagnoses or to prescribe medication or therapies.

If you are being seen by a Nurse Practitioner or Physician Assistant they will evaluate and treat the orthopaedic condition. If a surgical consultation is needed, your NP or PA will then leave the room and will discuss your concerns and their findings from the physical exam with the attending surgeon. Then both of them will return to your exam room for further assessment and to discuss your treatment plan with you.

Please meet our NPs, PAs and RNs below. Our attending physicians can be found on the Faculty pages, and our Residents can be found on the Residents page.

Everyone on our team is committed to providing you with the best orthopaedic care possible.



Advanced Degree



Pediatric Orthopaedic Mid-Level Practitioners


Karen Kracker, PA-C

Towson University

Fractures, Bowlegs,
In-toeing, and
Pediatric Surgery

Dr. Tis

JH Outpatient Ctr

Prior to earning my Master’s Degree and Certification to become a Physician Assistant, I taught high school science for five years.  I have always wanted to work with children and adolescents and now that has become a reality working as a PA in Pediatrics.

I began working at Johns Hopkins Hospital in the Department of Orthopedic Pediatric Surgery in November, 2012. I assist in the care of patients seen by Dr. John Tis, which includes pre- and post- surgical care as well as assisting in the Operating Room.

I also see patients in my own clinics that focus on Fractures, Bowlegs, In-toeing, and Out-toeing.

I have participated in medical outreach, both locally and abroad. Most recently, I was part of a Medical Mission Trip to the Dominican Republic where I was part of a team that provided medical care and supplies to impoverished communities.


Colleen Lenz, CRNP

New York University

Pediatric Rehabilitation, Pediatric Intensive Care,  Pediatric Orthopaedic Surgery

Dr. Sponseller

JH Outpatient Ctr

Kennedy Krieger

I am a certified pediatric nurse practitioner with eight years combined registered nursing and nurse practitioner experience in various pediatric settings. Work environments include Pediatric Rehabilitation, Pediatric Intensive Care, and Pediatric Orthopaedic Surgery.

Over the last three years I have been specializing in the care of children with special needs requiring outpatient orthopaedic care at both Johns Hopkins Hospital and Kennedy Krieger Institute.

I am also clinically trained and certified to complete intrathecal baclofen pump medication refills and dose management in children with spasticity.

My most recent research activity includes a publication on the relation of obesity in fracture healing of children. I am interested in becoming certified to complete intramuscular Botox injections under ultrasound guidance to children with spasticity.


Kristen Venuti, CRNP

Johns Hopkins University

Non-operative Management of Pediatric Spine and Leg Conditions

Dr. Sponseller

JH Outpatient Ctr

Kennedy Krieger

I developed a special interest in pediatric orthopaedics after working as a Hopkins bedside nurse on the adolescent medical-surgical inpatient unit. I completed my undergraduate and graduate nursing studies at Johns Hopkins University, becoming a Certified Registered Nurse Practitioner in 2003.

I have been working full-time as a CRNP in the Department of Orthopaedic Surgery since 2003. My role as an NP includes assessment, diagnosis, and management of children presenting with acute and chronic musculoskeletal concerns.

My areas of special interest include the non-operative management of scoliosis, kyphosis, clubfeet, and hip dysplasia, as well as fracture care. I also enjoy providing consultation for children with gait or walking concerns. I am involved in the multidisciplinary care of children with spina bifida.

I practice autonomously as well as in collaboration with pediatric orthopaedic surgeon Paul Sponseller. My practice locations include The Johns Hopkins Outpatient Center and The Kennedy Krieger Institute.

Outside of work, I enjoy running, vegetable gardening, and playing in the parks of Baltimore with my husband and 3 year old son Will.


Mary Teresa (Tresie) Yost, FNP-C

Johns Hopkins

Skeletal Dysplasia

Dr. Ain

JH Outpatient Ctr

I have worked at Johns Hopkins Hospital for 34 years. I developed a love for orthopaedics in 1991, when I began working in the orthopaedic clinic, assisting in the management of patients seeing a multitude of bone specialists. For the past 12 years, I have been directly helping Dr. Ain in his practice.

Dr. Ain specializes in pediatric orthopaedics, spine surgery, and skeletal dysplasias (dwarfism or little people).  Currently, I am practicing as a Family Nurse Practitioner after receiving a Masters in Nursing from Johns Hopkins University in 2011.

I continue to work in the office of Dr. Ain, in a collaborative effort caring for his patients.

I have an independent clinic on Thursday afternoons at the Johns Hopkins Outpatient Center.

My special interests include any type of pediatric orthopaedic condition, scoliosis and skeletal dysplasia’s.

Outside of work, I enjoy the eastern shore of Maryland, spending time with my family, cooking, gardening, and traveling.

Johns Hopkins Department of Orthopaedic Surgery
601 N. Caroline Street
5th Floor, JH Outpatient Center (JHOC)
Baltimore, MD 21287
(443) 997-2663

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Link to Johns Hopkins Patient Privacy Practices

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