This is Part 3 of a series of articles on threats to a proper knee surgery recovery. In this installment we discuss achieving full knee extension after knee replacement. I encourage you to explore the other articles in the series which you can find by clicking on the link below.

• Deep Vein Thrombosis and Knee Replacement

• Infection and Knee Replacement

Getting to 0º: Achieving Full Extension

Physical therapists, surgeons, exercise physiologists, personal trainers all emphasize full terminal knee extension for their knee patients after surgery. Why?

Let’s start with defining our terms. Terminal Knee Extension is achieved when the angle of your leg is 0º when extending it out in front of you. 0º means it is perfectly straight. PTA Yvonne LaCrosse defines extension and flexion in this short video.

The Immediate Impact of Extension Loss

Lack of Full Knee Extension (1)

Here are five key results of the lack of proper knee straightening. Lack of a straight knee:

1. Leads to worse patient outcomes and statistical success scores
   • “The most statistically significant factor related to lower subjective scores was lack of normal knee extension. Normal knee straightening is considered to be within 2° of extension, including hyperextension.” (3)
2. Increases the risk for developing arthritis
   • Multiple studies have shown that people with limited knee extension have a higher prevalence of arthritis (even in as little as a 3° loss). For example:
     • “Less than normal knee extension ROM at discharge was a predictive factor for developing Osteoarthritis after ACL surgery” (3)
     • “Loss of normal knee ROM at final follow-up was associated with a higher prevalence of Osteoarthritis” (4)
3. Causes an abnormal walking pattern or gait
   • If you’re lacking knee extension motion, you can’t achieve TKE during terminal stance (fully straighten your leg, stand erect). Therefore this puts more strain/stress on other structures in the kinetic chain.
   • A slightly flexed position causes abnormal joint loading.
   • This abnormal joint loading makes it easier for you to fall by catching your foot as opposed to walking heel to toe
4. Higher demand on the patella tendon (what connects your kneecap to the tibia, the bone below your knee)
   • If your knee never gets fully straight (and into the closed-pack position) and is always slightly flexed, then it will put more strain and constant stress on the patella tendon
5. Limits the ability of the quad and other muscles to optimally function/produce force
   • A lack of full knee extension will impair the quad’s ability to generate proper force, leading to reduced knee extension torque (3)
     • There is evidence that there is a correlation between limited knee extension and quad weakness
   • Limited knee extension will also affect other joints, most notably the ankle and hip.  If the knee can’t fully extend, then the ankle and hip have to overcompensate and will have a hard time generating the appropriate force – leading to decreased performance and possible injury.

Click the play button below to listen to an interview with Dr. Carl Freeman. Dr. Freeman discusses the CPM machine, Traditional Physical Therapy and the X10.

We interview Dr. Carl Freeman one of the co-authors of the study who explains the findings of his study as well as explores the value of pre-hab based on a recently published look at pre-habilitation before surgery and how that compares to pre-hab on X10. Dr. Freeman also discusses why the X10 pre-hab program is so much more effective than traditional pre-hab programs.

Lack of Full Knee Extension (ACL Repair Cases)

There is a lot of published research regarding an extension deficit and ACL repair. I thought a few notable facts would be helpful which I share below:

“Knee extension deficit is frequently observed after anterior cruciate ligament reconstruction or rupture and other acute knee injuries. Loss of terminal extension often occurs because of hamstring contracture and quadriceps inactivation rather than mechanical intra-articular pathology. Failure to regain full extension in the first few weeks after anterior cruciate ligament reconstruction is a recognized risk factor for adverse long-term outcomes, and therefore, it is important to try to address it.” (2)

A Challenge to Full Recovery

A patient who presents with an extension deficit after an acute knee injury or surgery can be challenging to manage. The medical provider who first evaluates the patient must differentiate between two separate situations: In the “locked knee,” a displaced intra-articular structure mechanically prevents full extension, whereas the “pseudo-locked knee” occurs without the presence of any true mechanical block to motion.(1) Although frequently observed in clinical practice, the pathophysiology of the latter scenario had remained unclear for decades. In 1986 Allum and Jones 1 observed that spasms of the hamstrings were related to an extension deficit after knee injury, but no explanation was given. More recently, there has been increased interest in the subject, and multiple authors have postulated that the extension deficit, also observed after knee surgery, may be due to a process called “arthrogenic muscle inhibition” (AMI). (2, 3) AMI is believed to be responsible for the failure of quadriceps activation that is associated with hamstring contracture. (6)

In Plain English: Why We Care About Knee Extension

Extension can be a real issue for both Total Knee Replacement and ACL Repair patients. It can be hard to solve. And there is a condition where fluid (swelling) can play a negative role in recovering extension (called AMI above). This means that we want to eliminate all of the swelling in the joint to achieve full knee function and full extension.

Simply put:

1. We care about extension because our body will not work the way we want it to without it. This means we won’t walk right and our body will be slightly out of balance.
2. When part of a body is not working right other parts have to step up and help out. These parts take on a larger role and start to wear differently.
3. Poor extension can lead to a fall or accident: now you could be headed for more surgery, rehab and a downward health path.
4. For some, getting full extension can be a really big challenge. Be happy if you have it. Work hard on getting it back if you lose it.

As with infection, deep vein thrombosis, poor flexion, lack of strength, and other health complications, poor knee extension can be managed. This series of articles is all about knowing the facts, the obstacles to a great recovery, so we can avoid them completely. I welcome your thoughts in the comments section below.

References / Source Material

1. 5 Reasons Why You Need to Restore Terminal Knee Extension by Dennis Treubig

2. Shelbourn KD, Gray T.  Minimum 10-year results after ACL reconstruction - how the loss of normal knee motion compounds other factors related to the development of osteoarthritis after surgery. Am J Sports Med. 2017;3:471-480

3. Shelbourne KD, Benner RW, Gray T. Results of ACL reconstruction with patellar tendon autografts: objective factors associated with the development of osteoarthritis at 20 to 33 years after surgery. Am J Sports Med. 2017 Aug 1:363546517718827

4. Shelbourne KD, Urch SE, Gray T, Freeman H.  Loss of normal knee motion after ACL reconstruction is associated with radiographic arthritic changes after surgery. Am J Sports Med. 2012 Jan;40(2):108-113

5. What has the biggest impact on outcomes following acl reconstruction surgery by Mike Reinhold

6. How to Rapidly Abolish Knee Extension Deficit After Injury or Surgery: A Practice-Changing Video Pearl From the Scientific Anterior Cruciate Ligament Network International (SANTI) Study Group Jean-Romain Delaloye, M.D.,a Jozef Murar, M.D.,a Mauricio González Sánchez, M.D.,a Adnan Saithna, B.Med.Sci.(Hons), M.B.Ch.B., Dip.S.E.M., M.Sc., F.R.C.S.(Tr&Orth),b Hervé Ouanezar, M.D.,a Mathieu Thaunat, M.D.,aThais Dutra Vieira, M.D.,a and  Bertrand Sonnery-Cottet, M.D.a,∗