Patellafemoral Biomechanics

Last week Friday, I posted a infographic video that differentiated painful patterns seen in infrapatellar fat pad irritation vs patellafemoral joint syndrome. I wanted to dive a little deeper into this and explain the biomechanics behind this video.

As the knee flexes and extends through its arc of motion the patella accepts load in different locations and with different surface contact areas.

• With the knee in an extended position the patella loses its engagement within the femoral intercondylar groove.
  • With minimal joint reaction forces on the patella, the infrapattellar fat pad accepts more of the compressive load exerted by the quadriceps muscle.
• Conversely, as the knee begins to flex the patella engages within the intercondylar notch reaching maximum contact area between 60-90 degress
  • However, this surface area is approximately 1/3 of the total surface area of the patella and therefore large compressive force exerted by the quadriceps muscle can irritate the patellafemoral joint.

Clinical implications of treating patient’s with patella femoral pain:

• Closed kinetic chain exercises such as the squat should be performed between 0° and 45° of knee flexion
  • During CKCE, quadriceps activity increases as the knee reaches 90 degrees of flexion; therefore, they are limited in this initial range
  • This initial range also minimizes the enagement of the patella in the intercondyle groove
• If variable exeternal resistance is used during open kinetic chain exercises (OKCE), they should be performed between 45° and 90° of knee flexion
  • During CKCE, the quadriceps activity increases as the knee reaches 0 degrees due to increasing external flexion moment.
  • Due to greatest surface area, this compressive load is most effectivitly dispered in this range

 

 

Feedly Friday: 5 articles you should read this week

Feedly is a news aggregator app that offers a place to gather and read all the news from your favorite blogs, journal publications, podcasts, and Youtube channels.  This news is organized into various collections and you receive updates when new stories, videos, journal articles are published. It is basically a Facebook on steroids that gathers research for you in one place.

Here is what came across my Feedly that I thought was worth a read:

This weeks articles come from The Manual Therapist, Physiospot, Claire Patella, AJSM, and The PT Journal.

• In this blog post,  Dr. Esummarizes findings of EMG activation of the gluteal muscles and tensor fascia latae (TFL) during different rehabilitation exercises.
• In this blog post, they highlight study in that compares conservative and operative treatment for meniscal lesions. They conclude that there was no siginifcant difference between exercise therapy and meniscectomy for pain.
• In this infographic video,  Claire Patella depicts the differences between irritation to  patella femoral joint pain and infrapatellar fat pad

 

• In AJSM, authors Rathleff et al investigate the 2 year prognosis of knee pain among adolescents with and without diagnosis of patella femoral pain (PFP). They conclude PFP is not a self-limiting condition and greater focus on early detection and prevention is needed.
  • Rathleff MS, Rathleff CR, Olesen JL, Rasmussen S, Roos EM. Is Knee Pain During Adolescence a Self-limiting Condition? Prognosis of Patellofemoral Pain and Other Types of Knee Pain. Am J Sports Med. 2016;44(5):1165-71.
• In this study in the PT Journal, the authors investigated with chronic low back pain can identify those who respond better to MDT compared with back school. They had an interesting result finding that older people had 1.27 points more benefit I pain reduction from MDT than younger patients after 1 month of treatment. However, limitations in research design may limit this conclusion.
  • Garcia AN, Costa Lda C, Hancock M, Costa LO. Identifying Patients With Chronic Low Back Pain Who Respond Best to Mechanical Diagnosis and Therapy: Secondary Analysis of a Randomized Controlled Trial. Phys Ther. 2016;96(5):623-30.

Manual Monday: Nerve Mobilizations

Neurodynamic testing is part of a regular examination of a patient complaining of low back pain. The straight leg raise (SLR) is an easily performed test that objectifies lower extremity nerve mechanosensitivity. This assessment tool is very valuable as it can also be prescribed as an intervention.  Let’s look at the utilization of this test as both an assessment and intervention.

Neurodynamic tests are sequences of movements designed to assess both the mechanics and physiology of the nervous system. (1) The mechanical component includes the nerves ability to slide through its sheath as it courses from the spine distally into the extremity. The physiological component include irritates to the nerve itself such as “inflammation, ischaemia, and altered ion channel activity resulting in sites of abnormal impulse generation.” (1) If either of these components are impaired it will cause an increase in mechanosensitivity resulting in pain as the nerve attempts to accommodate the strain due to the movement of the lower extermity during the SLR.

The psychometric properties of the SLR as a neurodynamic test in the assessment of radiculopathy as a result of lumbar disc herniation was outlined in a cochrane systematic review. The authors found (2):

• the SLR showed high sensitivity (pooled estimate 0.92, 95% CI: 0.87 to 0.95) with widely varying specificity (0.10 to 1.00, pooled estimate 0.28, 95% CI: 0.18 to 0.40)
• The crossed SLR showed high specificity (pooled estimate 0.90, 95% CI: 0.85 to 0.94) with consistently low sensitivity (pooled estimate 0.28, 95% CI: 0.22 to 0.35).

Therefore, the SLR is a sensitive test in detecting impairments in LE neuodynamics, however, as indicated above it is not a specific test in determining why this impairment is occurring. An interesting side note: if the SLR is combined with crossed SLR there is more certainty that the nerve is being impaired by a lesion at the disc.

A positive assessment item, such as the SLR, can often result in one of the best patient-specific interventions. However, evidence-based dosage of this intervention is unknown. The authors of one recent article have suggested the following guidelines (1):

•  Some of the mechanisms associated with the benefits of joint mobilizations may be similar to those of neurodynamic treatment.
• If neurodynamic mobilizations exert their effects through a hypoalgesic or viscoelastic response, then using a longer treatment duration (3 x 2 minutes) is not different than using a shorter duration (3 x 1 minute)  if the desired outcome is to improve pain-restricted ROM. However, neurodynamic treatment, irrespective of treatment duration, may help to increase pain-restricted ROM.

Check out this article by Cleland, Childs, et al (3)  where they demonstrated significant improvement in reducing short-term disability and pain, and centralization of symptoms in patients with non-radicular low back pain when including nerve mobilizations.

In conclusion, the SLR is a very valuable assessment tool in the clinician’s arsenal that can be easily turned into an effective intervention. There is supporting evidence to suggest short treatment duration more efficient than longer treatment duration to improve pain-restricted movement. However, the subgroup of patient who may benefit the most from this intervention and by which mechanisms are still unknown and are a point or further research.

Work Citied

1. Neal hanney R, Ridehalgh C, Dawson A, Lewis D, Kenny D. The effects of neurodynamic straight leg raise treatment duration on range of hip flexion and protective muscle activity at P1. J Man Manip Ther. 2016;24(1):14-20.
2. Van der windt DA, Simons E, Riphagen II, et al. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane Database Syst Rev. 2010;(2):CD007431.
3. Cleland JA, Childs JD, Palmer JA, Eberhart S. Slump stretching in the management of non-radicular low back pain: a pilot clinical trial. Man Ther. 2006;11(4):279-86.