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The Knee Post Injury: Scientific Outcomes

El Paso, TX. Chiropractor Dr. Alexander Jimenez looks at ways to test knee function after injury and rehab...

Functional Performance Testing (FPT) to measure functional outcome in the post- operative athletic knee has gained popularity in the past two decades following the arrival of aggressive accelerated rehabilitation programs for the postoperative long- term knee injuries such as anterior cruciate ligament reconstruction (ACL-R) and meniscal repairs.

The purpose of these functional performance evaluations is to acquire and compared to normal populations or the individual 'normal' knee. In the sports setting, these operational tests are utilized to recognize an athlete's ability to tolerate the physical demands involved in the selected sporting activity and give the clinician and athlete a positive indication as to when it is safe to return to play without danger of re-injury.

Examples of FPTs exist and they come under the headings of:

1. Hop tests

2. Jump/leap tests

3. Linear speed tests

4. Agility tests.

They need space and equipment, are quick to perform and staff is readily trained to administer the evaluations. It has been suggested that they measure the next such as dynamic equilibrium, neuromuscular management, muscle strength, pain tolerance chain control and physical confidence.

The tests' key features are:

1. Provides a measure -- time or space

2. Simulates the forces encountered during sport-specific activities

3. Indirectly measures how the operational Job is inhibited by pain

4. Quantifies muscle strength and power

5. Assesses ability of the limb

6. Feedback regarding progressions in rehab

7. Provides psychological assurance to the athlete.

Hop Tests

Hop tests are supposed to test for post-operative dysfunction than double leg hop tests as the tests are performed unilaterally and the leg acts as a control leg for measurement comparison. With two-legged jump evaluations, the uninvolved limb may mask deficits of the involved limb (Myer et al 2011)(1). The values on jump tests are measured as the Limb Symmetry Index (LSI) which is found by:

A. Distance hops. (Mean involved/mean uninvolved) x 100%

B. Timed hops. (Mean uninvolved/mean involved) x 100%

1. Single-leg hop tests
Standing on affected leg in semi-crouched position, arms may initiate the swing and the athlete hops as far as you can. The athlete is required to 'stick' the leap for it to be a trial. Can use functional outcome to be determined by the LSI.

2. Crossover hop tests
The athlete hops over a line as previously; however, and two forward-directed hops that are immediate follow this, crossing the midline with every jump.

3. Triple hop tests
Much like the jump, except three jumps are put into sequence. The athlete should 'stick' the hop to be successful.

4. 6m timed test
The athlete hops over a 6m track. This can be hand-timed or using timing gates.
Current hop tests provide scores for use with subjects' scores of greater than 90%. A minimum limb symmetry index of >90% percent is essential being deemed fit to perform their chosen sport.

Jump Tests

1. Vertical jumps
This can be measured using a vertical jump measurement apparatus (MX1 vertical jump trainer). A standing reach is measured first and this is compared to a vertical jump. As this is a double limb measure, the vertical jump can be used to compare to some predetermined values the athlete could have demonstrated pre-injury, to compare against other athletes of similar height and weight (that doesn't take into account individual variance in expressive power) or used as progress measures in the rehabilitation procedure.

2. Horizontal jumps
Standing with toes of both feet onto a line and use arm swing to leap as far as you can. Similar to the vertical jump, these scores can be measured against scores, against normative values or as progressions in rehabilitation.

Linear Speed Tests

1. 40m timed tests
If these have been recorded by strength and conditioning staff pre-injury measured with timing gates, the times are used as a measure against values. Straight line speed tests provide no idea whatsoever to the clinician about the ability to resist landing forces in jumping sports encountered or to change direction.

Agility Tests

1. Reactive agility tests
The athlete begins on the line shown. Timing gates are required and are put five meters to the two meters ahead of the start and right and left line. The tester starts on a timing mat. As the tester moves off the mat a beep is emitted and time starts. The player to run through the time beam and goes ahead and moves off the line. The timing stops when the beam breaks. The tester will select one of four scenarios that the participant must respond to:

A. Step forward and change direction

B. Step forward with left foot and change direction to correct;

C. Step forward with right foot and then change direction

D. Step forward with left foot, then right, and then change direction to left.

The good thing about this test is that cue recognition is required by it.

2. Agility T Test

This was developed as part of the NFL combine testing procedure. This test utilizes shuffling movements, forwards and backwards running. Set out four cones as shown below. The subject starts at cone A. On the control of this timer, the subject sprints to cone B and touches the bottom of the cone with their right hand. They then turn and shuffle to cone C, and touches its foundation, this time with their hand. They shuffle sideways to the right with the right hand to touch the base and cone D. Cone B touching with the left hand is then shuffled back to by them, and run backwards to cone A. As they pass cone A., the stopwatch is stopped


It's expected that people who suffer a knee injury or injury that needs an operative intervention will suffer some manner of leg asymmetry on that knee in aspects like strength, range of motion, balance, neuromuscular confidence and control. Functional Performance Tests may be used to measure this degree of asymmetry and help plan and progress the rehabilitation protocol. These tests should be easy to administer and require minimal equipment. Jump evaluations can be included by them, hops tests, speed tests and/or agility tests or a battery could be developed that incorporates each of these aspects. It has been shown that the single-limb jump tests identify residual deficits the finest in these individuals.

1. Myer et al (2011) Utilization of modified NFL combine testing to identify functional deficits in athletes following ACL reconstruction. J Orthop Phys Ther 41(6); 377-387.
2. Ross et al (2002) Test-retest reliability of 4 single leg horizontal hop tests. J Strength and Cond Research. 16(4); 617-622.
3. Sheppard et al (2006) An evaluation of a new test of reactive agility and its relationship to sprint speed and change of direction. Journal of Science and Medicine in Sport, 9; 342-349.

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