genourob - arthrometers

The first arthrometer

In 1978, K. Markolf published an article on the first arthrometer ; the optimal position is at 20° of flexion and the differential between the healthy knee and the knee suffering an ACL lesion is set at 3 mm (« the cut-off point »). This is the precursor of the arthrometers to come.

The KT-1000

This is the arthrometer that is used the most throughout the world and which appears the most frequently in the Anglo-Saxon literature. The cut-off point is set at 3 mm (Daniel D, 1985).

However :

1/ This test is difficult to reproduce between 2 inexperienced examiners,

2/ Reproducibility is good if the examiners are experienced,

2/ False negative diagnosis in 25 to 50% of all cases (Djian, Isberg),

3/ At best, the result is precise to 1 millimeter,

4/ What is the value of a differential between the two knees of 3 mm ?

The Rolimeter

Developed by par Roland Jacob.

A user-friendly, cost-effective system.

However :

1. the knee’s position is not verified,

2. the measurement is only taken under full traction,

3. Precise to 1 mm

4. Measurement taken directly by the examiner

The Telos

Developed by Hans Pässler in Germany in 1986, the Telos is a radiological system of comparative measurement performed at 150 N (cut-off at 8.5 mm) or 250 N (cut-off at 10 mm). The system is widely used in Europe but not in the USA (irradiation).

However :

1. What level of force should be used: 150 N, 250 N ?

2. How can we be sure that there is no contraction of the hamstring muscles?

3. How can the values be tracked on the X-Ray?

4. 28 % false negatives (Boyer T, RCO, 2004)

5. Precise at best to 0.5 mm,

6. This examination cannot be repeated at each visit due to the irradiation and the cost.

The radiographic Lachman developed by JL Lerat

Allows measurement of the differential translation of each compartment. (JBJS, 2000, 82-B).

However:

1. very much dependent upon the quality of the examiners ;

2. tracking the values is difficult.

Radiographic stereometry RSA

Allows measurement of femorotibial micro mobility in the laboratory after implantation of tantalum beads.

However:

1. This is an invasive technique,

2. Follow-up on the operated knee in post-op, without pre-op references or controlateral comparison

Electromagnetic systems

Sensors are attached to braces that encase the thigh and the proximal third of the leg. Precision is good (0.1 mm).

However:

1. There is a risk that the braces, and thus the sensors, might move.

2. Necessitates the presence of an engineer and of an environment free of all metallic objects.

Navigation

Peroperative 3-D measurement of translation of rigid bodies set into the tibia and femur.

However:

1. Measurements can only be taken peroperatively,

2. No measurement taken on the healthy knee.

The GNRB

See GNRB® video

The GNRB offers many advantages compared to other arthrometers:

1. A simple, non-invasive and painless system,

2. Precise to 0.1 mm,

3. Hamstring muscle activity is taken into account,

4. Reading and recording on a remote PC,

5. Sensitivity and specificity > 90 %,

6. Reproducibility.